SOLID
WASTE
PROCESSING
state-of-the-art
report on unit
operations and
processes
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SOLID WASTE PROCESSING
state-of-the-art report
on unit operations and processes
This report (SW-4c) was prepared for the Bureau of Solid Waste Management
by RICHARD B. ENGDAHL
and staff of the Battelle Memorial Institute, Columbus Laboratories
under Contract No. PH 86-66-160
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Consumer Protection and Environmental Health Service
ENVIRONMENTAL CONTROL ADMINISTRATION
Bureau of Solid Waste Management
1969
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2d Printing
1971
ENVIRONMENTAL PROTECTION AGENCY
Public Health Service Publication No. 1856
LIBRARY OF CONGRESS CATALOG NO. 70-602720
For sale by the Superintendent of Documents, U.S. Government Printing Office
Washington, D.C. 20402 - Price 75 cents (paper cover)
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Foreword
UNDER authority of the Solid Waste Disposal Act (Public
Law 89-272) the Department of Health, Education,
and Welfare has assumed major responsibilities for improving
solid waste management practices in the United States. These
responsibilities include conduct of research and demonstra-
tions for developing or improving solid waste handling and
disposal methods.
The Bureau of Solid Waste Management has sponsored
the present study to provide a comprehensive reference to
currently available solid waste unit operations and processes.
Information is offered on the reliability of processes, perform-
ance data, economic factors, and range of commercially
available equipment as an aid to researchers and those now
engaged in solid waste management.
—RICHARD D. VAUGHAN, Director,
Bureau of Solid Waste Management.
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Contents
PAGE
INTRODUCTION 1
Unit Operations and Processes
DENSIFICATION AND SIZE REDUCTION 3
Preparation for sanitary landfill 4
Densification
Size reduction
Preparation for incineration 8
Densiflcatian
Size reduction
Preparation for composting 9
Hammermills
Flail mills
Vertical-axis rasps
Drum rasps
Roller crushers
Pulpers
Preparation for salvage 10
SEPARATION 11
Processes incidental to separation 11
Size reduction
Sizing
Fluid-solid separation
Sorting 13
Hand sorting
Mechanical sorting
Washing and scrubbing 13
Gravity separation 13
Heavy-media separation
Jigging
Table separation
Spiral separation
Magnetic separation 14
Electrostatic separation 15
Flotation 15
SANITARY LANDFILL AND OPEN DUMPING 15
Types of solid wastes dumped 16
INCINERATION 16
General characteristics of the incineration process 16
Kinds of furnaces 17
Industrial incineration 17
Capital costs 18
Operating costs 19
Waste-heat recovery 21
Heat available
Methods of heat recovery
Applications for recovered heat
Performance of heat-recovery systems
Economic incentive for heat recovery
CHEMICAL PROCESSING 22
Hydrolysis 22
Combustion (.incineration) 23
Extraction 23
Pyrolysis 23
Carbonisation 23
Oxidation (chemical) 23
Sintering 23
Precipitation, gelling, and crystallization 23
iv
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Page
Calcination 23
Melting 23
Electrolysis and electrodialysis 24
Combination and addition 24
Evaporation 24
Ion exchange 24
Miscellaneous processes 24
RECOVERY AND UTILIZATION 24
The scrap metals industry 24
Quantities of scrap returned to industry
Kinds of nonferrous scrap metals and materials
Prices of scrap metals
Sources of scrap metals
Marketing scrap metals
Preparation of scrap metals 28
Production of marketable metals from scrap materials 29
Melting
Melting and refining
Smelting and refining
Distillation
Hydrometallurgical processes
Regulations Concerning Solid Waste Dis-
posal Based on August 1966 Survey 31
Major Waste Categories 33
Bibliography 59
Figures
1 Densification data, refuse at Chandler, Arizona, test station (1954) _ 5
2 Compaction data, treatment of British refuse (.1963) 6
3 Compaction ratio versus percent reduction in volume 7
4 Typical size-reduction flow sheet 12
5 The reclamation of municipal refuse by the SACS process 26
6 Depithing of bagasse 37
7 Processing of U.S. Steel basic open-hearth slag at Wylam,
Alabama 50
8 The deinking of secondary paper fiber by screening 54
Tables
1 Classes of chemicals used in flotation 15
2 Principal components of a municipal incinerator and costs 18
3 First cost distribution for parts of an incinerator installation 18
4 Capital investment in equipment for fly-ash collection at the
South Charleston, West Virginia, powerplant 19
5 Comparative costs of two types of incinerators in New York City __ 19
6 Operating costs for municipal incinerators in six U.S. cities 20
7 Annual costs of operating electrostatic precipitators at the South
Charleston, West Virginia, powerplant 20
8 The commercial treatment of industrial and municipal solid
wastes 25
9 Nonferrous scrap recovered in the United States in 1964 27
10 Partial list of precious metal scrap 27
11 Scrap metal quotations for August 16, 1966 28
12 The production and utilisation of blast-furnace slag in 1957 49
13 Typical formulations used with flotation machines 53
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SOLID WASTE PROCESSING
A state-of-the-art
report on unit
operations and
processes
MANY KINDS of solid wastes
from a wide variety of sources
must be processed daily for disposal
in the United States. The great
diversity in physical form and chem-
ical content of the thousands of tons
of solid wastes produced makes it
extremely difficult to obtain an over-
all view of the disposal problem. Add-
ing to the complexity of the situation,
various industries and municipalities,
influenced by a wide range of geo-
graphical, technical, and historical
considerations, employ many different
methods of treatment and combina-
tions of equipment. Intimately asso-
ciated with the disposal of wastes,
moreover, is a problem of equal sig-
nificance: the conservation of the
nation's natural resources.
The importance and intricacy of
the solid wastes disposal problem and
the need to deal with it effectively
and economically led to the state-of-
the-art survey covered by this report.
The material presented here was com-
piled to be used by those in govern-
ment and private industry who must
make or implement decisions con-
cerning the processing of solid wastes
and the recovery and utilization of
the wastes that are salvageable. The
survey involved a detailed review of
the pertinent technical and trade
literature, personal interviews with
individuals knowledgeable in appro-
priate fields, and questionnaires sent
to the State health departments.
For convenience, the report is
divided into two major parts: Unit
Operations and Processes and Major
Waste Categories. Because overlap is
considerable, cross-referencing is ex-
tensive to eliminate repetition. The
first part of the report is divided into
six sections: Densification and Size
Reduction, Separation, Sanitary
Landfill and Open Dumping, Incin-
eration, Chemical Processing, and
Recovery and Utilisation. This first
part of the report also includes var-
ious regulations concerning solid
waste disposal, discussion being based
on responses to the questionnaires
sent to the State health departments.
The second part of the report, ar-
ranged alphabetically, covers all the
major waste categories considered.
The report concludes with a bibliog-
raphy, which relates to both parts of
the report.
ACKNOWLEDGMENTS
Many people in government and in-
dustry cooperated with the Battelle
survey team and contributed valuable
information from their varied experi-
ences for this compilation. Their as-
sistance is gratefully acknowledged.
The survey team, whose activities were
coordinated by Richard B. Engdahi,
included the following: David E. Bear-
int and Hobart A. Cress—densification
and size reduction; Edward A. Beidler,
Mary R. Fulmer, and George F. Sach-
sel—incineration, sanitary landfill,
and open dumping, and chemical re-
duction processes; John R. Burke and
Raymond W. Schatz—physical sepa-
ration; and Howard C. Renken, John
R. Burke, and Raymond W. Schatz—
recovery and utilization. Editing and
review were provided by Dolores
Landreman.
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Unit operations and processes
WHETHER one or a sequence of unit
operations is required for solid waste
processing depends on many factors,
chief of which is the nature of the
solid waste. In this survey, considera-
tion of metallic wastes was limited
primarily to nonferrous materials, be-
cause iron and steel scrap processing
is already receiving considerable
attention from both industrial and
government organizations; automo-
bile salvaging therefore, is not cov-
ered in the section on densiflcation
and size reduction. There are, how-
ever, many other waste disposal proc-
esses that require densiflcation and
size reduction. Consequently, this sub-
ject is discussed first.
DENSIFICATION AND SIZE
REDUCTION*
Densification and size reduction are
two unit processes employing equip-
ment widely different in function, per-
formance, and character.
Densification equipment signifi-
cantly increases the weight of ma-
terial occupying a given volume. A
scrap-metal baling press is an excel-
lent example. Densification or com-
pacting equipment is not to be con-
fused with pelletizing, or briquetting,
types of equipment. Pelletizing equip-
ment functions in a particle-size-
enlargment capacity by agglomerating
material and usually does not produce
a significant reduction of the bulk
volume.
"The highly developed secondary-
materials industry is not discussed, nor
is equipment to provide densification and
size reduction of waterborne solid wastes.
Size-reduction equipment divides
materials and reduces their individual
or particle sizes. "Comminution" is
a general term often applied to size-
reduction processes. Some of the
more familiar examples of size-reduc-
tion equipment are rock crushers,
flour mills, and domestic sink-
mounted garbage grinders.
Densification and size-reduction
equipment is readily available in a
wide range of types and capacities
from many manufacturers. While
much of this equipment was designed
to handle materials other than solid
wastes, most manufacturers are ready
to modify existing equipment or to
aid in the design and development of
new equipment for solid waste
disposal.
Densification 'and size-reduction
equipment has been applied to most
methods of solid waste disposal.
Sanitary landfill operations employ
various machines to increase the
compaction and reduce the bulk vol-
ume of the refuse. Size-reduction
equipment has been used in France
on sanitary landfills for years and
has recently been tried in North
America. Size-reduction equipment
has been used to reduce oversize and
bulky wastes for incinerators. Shred-
ding the entire feed to the conven-
tional incinerator has been tried, but
apparently with little success. Com-
posting operations make extensive
use of size-reduction equipment;
however, most United States com-
posting plants have been of the pilot
or demonstration type; hence, full-
scale and long-term operating experi-
ence with such equipment has been
lacking. Disposal by salvage has ac-
338-244—70-
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4 SOLID WASTE PROCESSING
counted for an extremely small
percentage of solid wastes. While
densiflcation and size-reduction
equipment has been employed in
salvage, applications have been few.
An exception to this is found in
England and Scotland, where direct
salvage of solid wastes has been
intensively practiced.
In general, details on equipment
were not found in the literature. Per-
formance data, if mentioned, were
usually limited to the horsepower rat-
ing of the driving motor, a rotor speed,
or perhaps the average size of the
comminuted material. Reliability was
rarely mentioned. Economic factors
were usually limited to estimated
operating or maintenance costs. Capi-
tal costs were not discussed to any
great extent in the literature surveyed.
If more details are required, it will be
necessary to initiate a more extensive
program of correspondence and visits
to manufacturers, operating sites, and
consulting firms.
Pertinent information on manufac-
turers of densiflcation equipment can
be found in Thomas Register of Amer-
ican Manufacturers7 under the head-
ings "Presses" and "Balers." Another
source is The Waste Trade Directory.3
Size-reduction equipment is widely
used and is particularly important in
the mineral and chemical process in-
dustries. Because of this broad inter-
est, many articles were found dealing
with the various aspects of size reduc-
tion. Various types of size-reduction
equipment are reviewed in the Chem-
ical Engineers Handbook1 and The
Encylopedia of Chemical Process
Equipment? A review article by Stem
also contains a list of manufacturers
and the types of equipment each sup-
plies.432 Other sources for manufac-
turers of size-reduction equipment are
Thomas Register and the Mechanical
Engineers' Catalog? None of the
equipment mentioned in these refer-
ences was designed specifically for
solid waste disposal.
PREPARATION FOR SANITARY
LANDFILL
Most solid wastes have been dis-
posed of in landfills. In fact, other
disposal methods produce their own
solid wastes that ultimately must find
their way to a landfill of one type
or another. Landfills have always been
required and from all indications this
will not change in the near future.
Following is a discussion covering
the types of densification and size-re-
duction equipment that have been
used when disposal is to a sanitary
landfill. Some of the types to be dis-
cussed, such as packer-type collection
trucks, could also be discussed in con-
nection with incineration or other
methods of disposal. However, since
landfill is the most common method
of disposal, they are included here.
Densification. As human popula-
tions grow, suitable sanitary landfill
areas become more difficult to locate
and more expensive. One obvious al-
ternative is to make maximum use of
available areas by reducing the bulk
of the solid wastes. In most sanitary
landfills, crawler or rubber-tired bull-
dozers have been used to work the
fills. Depending on the character of
the refuse, these machines can ef-
fect a compaction ratio of about 3 to
1. A machine designed specifically for
sanitary landfill work has become
available.25 This is a 25-ton com-
pactor-dozer employing lugged or
gear-tooth-like wheels. The claim has
been made that it quickly reduces
packing crates and other large debris.
It was reported that twice as much
refuse can be placed in a given area
without increasing the depth of fill as
was formerly possible when a crawler
tractor was used for compaction.
Another landfill-compaction de-
vice is a ballasted-drum type with
lugs; it is pulled behind a dozer.35
It also vibrates to improve compac-
tion. A gasoline engine carried on the
frame of the compactor supplies the
energy of vibration.
Few references were found in the
literature relative to compaction de-
vices at sites of solid waste genera-
tion. A British publication mentioned
a lever-operated unit intended to
crush empty food, oil, or paint cans.530
A somewhat different unit, apparently
of United States manufacture, was
said to crush tin cans, glass bottles,
and plastic bottles and jugs.645 The
crushing occurred between continu-
ous belts running at 100 feet per
minute.
Vacuum-type leaf collectors seem
to be increasingly common. The high
velocities at which the leaves enter
the collection box result in a signifi-
cant amount of compaction. An article
in Public Works described a 30-horse-
power "Giant Vac" leaf loader that
uses a 14-cubic-yard plywood collec-
tion box fitted to a 13-foot-long
dump-body chassis.91 The cost was
given at $2,800, which included $300
for labor.
Compacting of solid wastes at the
point of collection has been practiced
in the United States since 1950 when
packer-type refuse trucks were intro-
duced. A review of some of the vari-
ous types available from United States
manufacturers can be found in Ref-
use Collection Practice.*3 A more re-
cent review appears in Machine De-
sign.2" These trucks normally carry
10- to 30-cubic-yard bodies on a
standard heavy-duty truck chassis.
An exception to the practice of using
a standard heavy-duty truck chassis
is the Wesco Jet, a packer truck de-
signed specifically for refuse collec-
tion. Depending on the character of
the refuse, packer-type trucks can re-
duce the material to as little as one-
third its original loose volume.8* Prices
for complete packer-type trucks
ranged from $18,000 to over $30,000.se
Kuropean collection vehicles were
reviewed by Rogus in Part II of an
article in Public Works."'"' Four com-
paction systems are shown and de-
scribed. One system employs two-
stage compaction with a reciprocating
ram followed by a swiveled compres-
sion plate that moves the refuse into
the truck body. Two of the systems
use helical screws to compact and
move the refuse into the truck body.
The fourth system is quite unique in
that the truck body is a cylindrical
drum fitted with an internal two-lead
worm welded to the inner walls. The
drum rotates at 3 to 4 rpm, crushing,
compressing, and advancing the ref-
use toward the front of the drum.
As landfills are moved to more
distant sites, it becomes more eco-
nomical to employ central collection
stations. At these stations, local col-
lection trucks dump the refuse into
large-capacity transfer semitrailers
for hauling to the landfill site.30 Local
trucks dump the refuse into a hopper,
where it is hydraulically compacted
and pushed into the transfer trailer.
Rogus mentioned a similar type of
centralized collection station used in
Europe.370 This appears to be the same
system described in somewhat more
detail in an English article.563 This
system is based on a 7-foot-diameter
by 21-foot-long compaction cylinder
fitted with a hydraulic ram. A 75-
horsepower electric motor powers the
hydraulic system. Refuse is loaded
from the top through a hatch closed
by a sliding door. When the compac-
tor cylinder is full, the end is opened
and the refuse is pushed into a
matching circular container mounted
on a transfer truck.
A recent development in solid waste
compaction is a unique machine de-
signed by the D and J Press Com-
pany.
The machine is 60 feet
long by 23 feet wide and it weighs
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Preparation for sanitary landfill 5
1500
1000
500
400
350
250
20 40 60 80
Applied Lood.psi
FIGURE 1. Densification data. Refuse at Chandler, Arizona, test station, 1954.
75 tons. Mounted on the machine are
a wheel trencher and conveyor sys-
tem, a tamper, a dozer blade, and a
four-stage hydraulic press. Refuse is
dumped onto a side apron, which
transfers it to the compaction presses.
The refuse is extruded from the ma-
chine via a 36- x 36-inch chute into
a self-dug trench that can be up to
8 Va feet deep. Pill dirt is placed over
the compressed refuse and tamped.
It was reported that the machine can
handle large items such as old re-
frigerators and furniture. Compaction
ratio was reported to vary between
10 to 1 and 20 to 1. Two 450-horse-
power diesel engines supply the power
under the control of two operators.
Cost effectiveness and reliability ap-
parently remain to be determined.
In a refuse compaction project at
the King County Sanitary Operations,
Seattle, Washington, the objective
was to produce a solid that would
neither decay nor emit harmful gases
when used in a landfill. A proposed
high-pressure (200-psi) compaction
process was expected to reduce solid
wastes to one-tenth of the original
volume.
A glass-wool and shingle manufac-
turer in the United States was re-
ported as using a transfer station
compactor.*39 With use of the compac-
tor, trailer runs from the plant to the
disposal site were reported to have
been reduced from 105 per week to
only 10 per week.
An unsuccessful attempt at com-
pacting refuse was made in Los An-
geles County, California, where com-
pacting and baling of municipal
refuse was tried.469'4™ Compressors
and balers used were not entirely
satisfactory and the bulldozers at the
landfill sites had difficulty moving the
bales around. Some work has also
been done at the United States Pub-
lic Health Service Test Station at
Chandler, Arizona, on compression
and baling of municipal refuse. The
only published information found on
this latter operation is a density-
versus-applied-load curve (Figure
I).84
This curve appears to be in con-
flict with British data in a report de-
scribing a machine for compacting
refuse in barges.620 For hundreds of
years London has been reclaiming
areas by disposing of refuse in low-
lying wastelands along the lower
reaches of the Thames. Barges have
been used to transport refuse from
London wharves and to disposal sites.
The low density of the refuse reach-
ing the barges made for uneconomi-
cal light loads. To improve the
situation, an overhead foot-type
compacting machine was developed
and installed at Walbrook Wharf.
The British report describes this
unique machine in some detail.
An interesting feature of the Brit-
ish report is a plot of percent reduc-
tion in volume versus compressive
pressure for refuse of three initial
densities. These data are referenced
to the Institute of Public Cleansing
and the work of W. A. Lewis.259 When
the Chandler, Arizona, data are re-
plotted to a percent reduction in vol-
ume basis, rather than density, they
differ from the British data (Figure
2). The curves for the 170- and 243-
pounds-per-cubic-yard British refuse
begins to flatten out with approxi-
mately a 70 percent reduction in vol-
ume at pressure of 6 to 8 pounds per
square inch. The comparable 250-
pounds-per-cubic-yard Chandler ref-
use curve has a very different shape
and a 70 percent reduction in volume
is not achieved until the pressures are
3 to 4 times those required with the
British refuse. No doubt differences
in refuse composition caused this
variance.
The curves charted from the Brit-
ish data indicate where the point of
diminishing returns is located with
respect to the applied pressure. The
British article concludes that pres-
sures much over 6 to 8 pounds per
square inch would be wasteful and
uneconomical, since higher compres-
sion pressures would result in only
small increase; in the percent reduc-
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6 SOLID WASTE PROCESSING
170 Ib/yd
Chandler, Arizona
Data,250 Ib/yd3
j 5 10 15
Compressive Force, psi
FIGURE 2. Compaction data. Treatment of British refuse, 1963.
20
25
tion In volume. While this analysis
applies to barges where total weight
that can be carried by a barge is lim-
ited, it does not hold for landfills,
where a much greater unit loading
can be supported. For example, when
compaction ratio is plotted against
percent reduction in volume (Figure
3), this is not a straight-line func-
tion. Most important is the increase
in the slope of the curve with increase
in the percent reduction in volume.
Thus, at the higher values of percent
reduction in volume, small increases
result in very large gains in the com-
paction ratio. For example, if col-
lected refuse receives a 70 percent
reduction in volume, the compaction
ratio is 3.33. Gaining another 10 per-
cent in the percent reduction in vol-
ume raises compaction to 5.0, a
50 percent gain over a compaction
ratio of 3.33. Another 10 percent gain
to 90 percent reduction in volume
puts the compaction ratio at 10, or
300 percent above that obtainable
with a 70 percent reduction in volume.
If the objective, then, is a reason-
able tradeoff between compaction
ratio and overall compactor costs, it
might be approached on the basis of
a plot of compaction ratio versus ap-
plied compressive pressure. The point
of diminishing returns will then be
where the slope of this curve "knees
over" and becomes very nearly paral-
lel to the pressure axis.
Since extensive compaction-ratio
versus applied-pressure data did not
appear to exist, it is recommended
that they be accumulated. Such data
would be of great value to users and
designers of refuse compaction equip-
ment. It would also be interesting to
know how refuse might respond when
the applied load is released.
Size reduction. Few published ac-
counts were available on the size re-
duction of solid wastes for disposal
by sanitary landfill. Some applications
are rather unusual, at least compared
with ordinary United States practice.
The more unusual methods will be
discussed first.
Upon first consideration, grinding
municipal refuse before it is disposed
of to a landfill might seem a needless
and expensive proposition. It is not an
unknown practice, however. A short
article by Meyer briefly outlines the
Heil-Gondard solid wastes reduction
system based on a grinder developed
in France.295 The unique claim for
this hammermili type grinder is that
it will reject items that cannot be
easily reduced. This is achieved first
by hammer rotation that is opposite
in direction to that in conventional
hammermills and second by a rather
tall vertical discharge chute built over
the top of the mill. Ungrindable mat-
ter is said to be batted up into the
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Preparation for sanitary landfill 7
20
15
(T
o
or
J
"o
o
Q.
J
10
j = Initial volume
= Final volume
20
40
60
Percent Reduction in Volume(PRV),
80
Vj-Vf
V;
100
MOO
PRV = I -
V;
CR
CR =
PRV
100
PRV
CR
0%
10
20
30
40
50
6O
70
80
90
95
100%
1.00
l.ll
1.25
1.43
1.67
2.00
2.50
3.33
5.0
10.0
20.0
00
FIGURE 3. Compaction ratio versus percent redaction in volume.
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8 SOLID WASTE PROCESSING
chute, where it is collected. Grinding
and sorting would therefore be ac-
complished in one operation. Milled
refuse with an original density of 375
pounds per cubic yard has had its
density increased to about 1,050
pounds per cubic yard, for a compac-
tion ratio of about 2.8 to 1. The milled
refuse was claimed to be less attrac-
tive to pests.
This system was reported in use at
a number of French landfills and at a
large landfill at Montreal. The city of
Madison, Wisconsin, recently received
a demonstration grant to test the
Gondard process. Bogus mentions that
some French farmers have been ap-
plying screened, shredded, and pul-
verized refuse to their farmlands for
many years.379
Another rather unusual size-re-
duction process was described in Engi-
neering.,MS Relatively simple, it consists
of a large rotating pulverizer drum
into which refuse and water are intro-
duced. On the drum inside wall are
fixed plates that elevate the refuse
through a fixed crushing cone as it is
forced farther along the drum. The
addition of water (up to 40 percent)
helps fibrous materials, like paper, to
break down. The resulting product
has a peat-like appearance and is
no longer dusty or offensive. Density
increase is about 2.8 to 1, working with
a feed density of about 286 pounds
per cubic yard. Process time in the
drum is about 1 hour.
The pulverizer described above is
made by Vickers Seerdrum Limited,
Surrey, England, and a plant is in
operation at Wheatley, Oxfordshire,
England. This particular drum is 8
feet in diameter by 29 feet in length
and rotates at 11.5 rpm. Nominal ca-
pacity rating is 45 tons per day (TPD),
although a continuous IVz tons per
hour (TPH) throughput is possible.
It is housed in a temporary 18- by
30-foot building, has a 50-kw power
requirement, and is operated by two
men. The plant is designed to be
moveatale to a new site. The British
article quoted present "all-up costs"
at $1.40 per long ton, which they said
could conceivably drop to $0.84 per
long ton with further development.
A slurry-type waste disposal system
using size reduction has been de-
scribed that combines a grinder, a
slurry-transfer system, and a water
extractor .""•63-M7'E" Paper and food
wastes are wet-ground to a pulp and
the resulting slurry is pumped to an
extractor where the water is removed
and recirculated to the grinder. The
semidry pulp is discharged to a can
for final disposal. An 80-percent re-
duction in volume, or 5 to 1 compac-
tion ratio, was reported as typical.
Grinders were available from 18 to
72 inches in diameter with screen
openings from %Q to % inch in di-
ameter. Separators are available to
remove metal, wood, plastics, glass,
and other nonpulpable materials.53
Where feed material was uncontami-
nated paper, the resulting uniform
pulp was being reused by some paper
mills, by manufacturers of roofing
paper, and as paper mache for packing
and decorative items.
Two applications of the system
have been described in the literature,
one in a new bank building,5" where
the system handles dining-room
wastes, and the other at the Anaheim
(California) Stadium.543 The latter
application is a $50,000 installation
designed to reduce the 13,000 pounds
of trash that accumulate during a
typical ball game. Nominal capacity
of this unit is 2,000 pounds per hour.
Brush chippers represent another
type of on-site solid waste size-reduc-
tion equipment that has been coming
into wider use. These brush chippers
are smaller versions of large wood
hogs, which are simply hammermills
with knife-like hammers. They were
available from many manufacturers.
Reduction in volume is about 80 per-
cent. Chippers can be unit-towed be-
hind a truck51S or mounted with a
packer on a truck chassis."2
Paperboard-box shredders are yet
another method for reducing bulk
volume at the site of solid waste gen-
eration. Although box shredders have
been rather common and the equip-
ment has been readily available, no
technical literature was found on the
subject, although general advertising
pamphlets were available.
PREPARATION FOR INCINERATION
The literature describes appli-
cations of both densification and
size-reduction equipment to incinera-
tors although the majority of these
applications involve size-reduction
equipment.
Densification. Densification equip-
ment is not normally associated with
the incineration of solid wastes. The
only description approaching a densi-
fication process was found in Rogus'
review on Western European practice,
in which the making of briquettes
from refuse was mentioned.3'9 Experi-
mental work has been done in Eng-
land and Switzerland, and more was
being planned. The process involved
sorting the refuse to remove noncom-
bustibles, grinding for greater uni-
formity, drying to bring moisture
content below 10 percent, and, finally,
extruding a 2- to 3-inch-diameter bri-
quette. Calorific value was reported to
be in the range of 8,000 to 10,000 Btu
per pound. One drawback seemed to
be that 6 tons of normal domestic
refuse produce 1 ton briquettes and
the remaining 5 tons had to be dis-
posed of by other means.
Metal recovery from incinerator
residue is a common practice. In
Europe, some plants bale this for sub-
sequent sale. In the U.S. literature this
aspect of densification was barely
mentioned.
Size reduction. With a few excep-
tions, the present application of size-
reduction equipment to municipal
incinerators has been limited to the
reduction of bulky or oversized items
in the United States as well as in Eu-
rope. Shredding of the entire feed has
been tried and was apparently in very
limited use recently. Its use has been
advocated for future incinerator ap-
plications by Meyer.295
Bulky or oversized refuse is the com-
bustible solid waste that cannot, for
several practical reasons, be directly
charged to conventional municipal in-
cinerators. This waste may be too
large for direct charging, it may burn
too slowly, or it may contain noncom-
bustible portions that interfere with
the incinerator grates or residue-dis-
charge system. Typical examples are
construction and demolition wastes,
furniture, mattresses, and tree stumps.
A hammermiU installation at the
Gansvoort Street Incinerator in New
York City was described in 1961.633
A test run indicated that it would re-
duce demolition wastes (primarily
wooden beams). Nothing further was
found in the literature, however, and
it was learned from other sources that
the mill was soon taken out of service.
A more recent news item indicates
that the problem of satisfactorily re-
ducing bulky solid wastes still remains
to be solved.10 The news item also men-
tioned that the New York City Sani-
tation and Air Pollution Control De-
partments were working together to
evaluate the use of shredders for re-
ducing oversize burnable wastes.
Rogus, in articles on European in-
cinerators, stated that most of the
incinerators investigated also handled
large, oversize materials.3"' ™ These
materials were segregated and moved
by crane to specially designed impact
crushers or multiple-type shears.
After being reduced, the material was
chuted to the common receiving pit
-------
for processing with the normal refuse.
Fichtner, Maurer, and Muller re-
ported that a Hazemag impact crusher
was in use at the Stuttgart incinera-
tion plant to reduce bulky incoming
refuse.134 The article did not discuss
the crusher further.
Kaiser proposed the burning of bulky
items on a refractory floor in a special
bulk-refuse furnace, thus eliminating
the need for hammermills, which have
sometimes operated with only indif-
ferent results.219' Ma
A wood chipper in use at a Pitch-
burg, Massachusetts, incinerator in
1955 5" was used to reduce Christmas
trees, banana stalks, and demolition
wood wastes. Prior to use of the chip-
per, tree sap had caused grate prob-
lems by sticking and jamming the me-
chanical components.
Although shredding of the entire
refuse feed to an incinerator has not
been common practice, it was tried in
the early 1950's at the Betts Avenue
Incinerator in New York City.262' m-648
Four hammermills, each having a 30-
TPH nominal capacity, were designed
into the plant. The shredding opera-
tion was admittedly experimental.
The objective was to provide operat-
ing data and experience that would
determine whether a more homogen-
eous feed justified the additional
operating, maintenance, and capital
costs associated with the shredding
equipment. It is interesting to note
that shredders were not incorporated
in subsequent New York City incin-
erator plants for treating the entire
feed to the incinerator.
Meyer, describing the Heil-Gon-
dard hammermill, mentioned the first
commercial installation of this mill in
an incinerator would be made by a
French firm in St. Quentin.295 A Swiss
incinerator was also described in
which the refuse was milled, sewage
sludges were added, and the wet mix-
ture dried and then burned. The heat
for drying was derived from the pre-
viously dried refuse-sludge fuel mix-
ture.
Meyer and Leibman each claimed
greatly improved incinerator opera-
tion and savings on cost and size of
other components from the use of
shredders.295'2M Explosive hazards
from containers of volatile liquids and
aerosal cans were eliminated. Also,
feed rates to the incinerator could be
more uniform and easier to control,
but no published data were found on
these effects.
The use of size-reduction equip-
ment in shredding the entire feed for
an incinerator has not been a great
success in the past. On the basis of
the two articles referenced above, it
appears that hammermills have been
unable to handle unsegregated refuse
at an acceptable level of reliability
and maintenance.295'258
PREPARATION FOR COMPOSTING
Densification equipment is not nor-
mally associated with composting.
There is mention in the literature of
pelletizing compost; however, this ac-
tually functions as a particle-size-en-
largement process. Baling of salvage
materials, such as paper, cardboard,
and metals, has been practiced at
some compost plants.
With respect to size-reduction
equipment, composting operations
have represented what is perhaps the
most extensive application of such
equipment in the field of solid waste
disposal. A size-reduction operation is
required at one point or another in
virtually all of the many types of
composting processes.
The amount of size reduction prac-
ticed during composting operations
can vary, depending on the type of
composting process and the intended
use of the resulting product. A few
operations compost the refuse in the
"as-collected" condition, with no size
reduction at all. Other processes re-
quire some size reduction of the in-
coming material, sometimes in a slow-
moving rasping machine. Still other
composting processes require average
particle sizes below an inch. This re-
quirement has often been met by two-
stage grinding in hammermills. If the
final product is to be acceptable for
home gardening and horticultural
purposes, it must be of uniform char-
acter and free of rocks, glass shards,
large metal fragments, and other un-
desirable, potentially injurious com-
ponents. Screening, ballistic separa-
tion, and final reduction in a roll
crusher or hammermill usually ac-
complish this before the compost is
bagged for distribution and sale.
Other uses for compost usually do not
require such stringent control on the
character of the product, so that a re-
duced degree of size reduction or none
at all, is employed.
As far as the size-reduction process
is concerned, all composting plants in
the United States appear to differ
from each other, even others of the
same type, possibly because most
plants are demonstration or pilot
projects. Barely do two plants use the
same size-reduction equipment, in the
same manner, and on the same type of
solid waste. In view of this, size-
Preparation for composting 9
reduction equipment for composting
will be discussed in six broad cate-
gories: hammermills, flail mills, ver-
tical-axis rasps, drum rasps, roll
crushers, and pulpers.
Hammermills. Hammermills repre-
sent the broadest category and cover
all types of high-speed crushers,
grinders, chippers, or shredders that
employ pivoted or fixed hammers or
cutters. These machines usually have
a simple horizontal rotor, but twin
rotors and a vertical rotor orientation
were also available. However, the
literature provided very few details.
Part of the United States Public
Health Service research project ini-
tiated in 1953 at Chandler, Arizona,
was the development, construction,
and operation of a 70-tons-per-week
(TPW) experimental composting
plant.8* During the operation of this
pilot facility, substantial information
was reportedly gathered on the cost
of refuse grinding, but further details
were not given in the project report,
and attempts to obtain more informa-
tion were unsuccessful.
A 1956 report of the American So-
ciety of Civil Engineers presents cost
information on 12 different compost
methods.39* The pilot-plant operation
at San Diego which is described was
on a rather small scale, initial pile
weights running between 5,340 and
8,340 pounds. According to the report,
the cost figures do not include the ex-
pense of supervision, plant invest-
ment, and other overhead, but do
reflect the expense of grinding, clean-
up, power, turning, wetting, fly con-
trol, additive materials, and screen-
ing when utilized. Operating costs
ranged from $1.56 per ton for an
unground, no-additive, compost to a
high of $20.48 per ton for a coarse
grind with a straw additive. The aver-
age cost was $12.79 per ton. When
grinding was employed, its costs ac-
counted for 30 to over 60 percent of
the total cost per ton. The size-reduc-
tion unit was simply identified as a
garbage grinder and no further in-
formation was supplied.
A full-scale operation involving the
Dano process was initiated in 1956 at
Sacramento.169 The picked refuse, be-
fore entering the Dano biostabilizer
drum, was ground in a 25-ton Penn-
sylvania hammermill. The mill was
considered oversized for the job, and
breakdowns were reported as being
infrequent. Major maintenance con-
sisted of removing, resurfacing, and
replacing the hammers. This took 3
to 4 hours to accomplish and was done
every 3 months. Another hammermill
-------
10 SOLID WASTE PROCESSING
reduced the compost leaving the bio-
stabilizer. This plant was shut down in
1963.
A 1963 review of European com-
posting equipment mentions hammer-
mills and rasping machines as the two
types of refuse grinders used in Eu-
rope.485 Most of the hammermills
were of the single-rotor, swing-ham-
mer, high-speed type. Some recent
hammermills, however, have employed
two rotors running at different
speeds—for example 1,500 and 3,000
rpm.98
Another 1963 review covers a verti-
cal-shaft hammermill developed by
Tollemache Composting Systems,
Limited, London, England.™ While
any size is possible, the one described
is a 150-horsepower unit rated at 12
TPH. The unit features mobility and
ballistic separation of ungrindables.
Maintenance was reported to be less
than $0.25 per ton of refuse processed.
The van Maanen system of com-
posting makes no attempt at size re-
duction until decomposition is com-
plete.*47 Raw, incoming refuse is
sprinkled with water and placed in
windrows. In 2 or 3 months, the wind-
rows are turned, and in 4 to 8 months
the compost is mature. It is then
screened, sorted, and finally passed
through a hammermill. This economi-
cal system of composting was in use
in The Netherlands, where the com-
post was applied to arable farmland
to maintain and improve the physical
characteristics of the soil. The article
mentions hammermills but does not
go into any further details.
The Heil-Gondard hammermill
mentioned previously has also been
applied to composting. In Haarlam,
Holland, a plant used such a mill,203
as did several in Spain.88 The Span-
ish installations were at Pamplona
(60 TPD), Zaragoza (120 TPD),
Cadiz (40 to 50 TPD), and Madrid
(200 TPD). Several others were being
built or were being planned. The
Gondard hammermills are rated in
the 10- to 14-TPH range and reduce
the refuse to a nominal size of about
an inch.
See also: Zircaloy.
Flail mills. A composting system.
under development for a number of
years in the United States makes use
of flail-type size-reduction equip-
ment.85' ""• **•288' M1 This is a horizon-
tal, single-rotor unit with a studded
shell -and hammers attached to the
rotor by means of chains. Replace-
ments of hammers and chains were
reported to be relatively easy, while
new shell studs, due to the unique
design, were moved into position by
simple rotation. This unit was de-
signed specifically for the reduction
of municipal solid wastes when shock
loads and abrasion predominate. The
flail reducer was used at two points in
the composting process—on the in-
coming refuse and during a regrind
midway through the digestion phase.
Vertical-axis rasps. Another ap-
proach to reducing operation and
maintenance costs of solid waste size
reduction is to use the rasping ma-
chine. The vertical-axis rasp was de-
veloped in The Netherlands.87'ltL- ** It
consists of a vertical axle carrying
eight horizontal arms hinged to ro-
tate upward. The axle rotates at
about 15 to 25 rpm, sweeping the arms
over the upper bottom, or grinding
floor, of the unit. The grinding floor
is made up of alternate plate sections
containing either perforations or
welded extensions. The material to
be reduced is dropped into the unit
where the rotating arms move it into
contact with the protruding rasping
pins. The material that is sufficiently
reduced then drops through the holes
in the following plate.
Rasping units are about 16 feet in
diameter by about 7 feet in height.
Capacities are in the 5- to 15-TPH
range, depending primarily on the
size of the holes in the perforated
plates. Compared to a hammermill,
a rasping unit has a higher first cost
and is larger. The advantages of a
rasp are in reduced power require-
ments and much less maintenance.
Drum rasps. Another type of rasp-
ing unit is the drum type. In the
United States, this has been devel-
oped in the form of a unit known as
a pulverator.149'28T' **• K1 This is a 6-
foot-diameter by 16-foot-long in-
clined drum covered on the inside
wall with triangular steel plates. This
unit has been used to tear open bags,
break up large agglomerations, and
mix the incoming refuse before it is
sent to the flail-type hammermills.
The Dano grinder, Egsetor unit, is
a drum-type rasp.1" In addition to in-
ternal rasping bars, this unit has a
screen within the outer drum. Mate-
rial falling through the screen is
passed to the grinders or directly to
compost piles. It rotates at 12 rpm
and was reported to require about 6
kw per ton of refuse. The Dano bio-
stabilizer also has a mechanical rasp-
ing action on material moving
through the rotating drum.
Roll crushers. A crusher that seemed
to have had limited application to
composting operations is the roller
type. Only one reference to its use
was found in the literature.483 This
article briefly describes a smooth,
double-roll crusher in use at Almelo,
in The Netherlands. It was reported
that this crusher was used to reduce
glass shards and other brittle mate-
rials in mature compost before it
leaves the plant.
Pulpers. A final type of size-reduc-
tion unit employed with composting
operations is the unique pulper in use
at Altoona, Pennsylvania.389 This wet
pulper consists of a 6-foot-diameter
steel bowl with a rotatable steel plate
mounted in the bottom. During opera-
tion, the bowl is first partially filled
with water, which is followed by the
solid material to be composted. The
steel plate rotates at 650 rpm and in 5
minutes produces a slurry containing
about 5 percent solids. The slurry is
then discharged through a screen to
a screw-type dewatering press where
the moisture content is reduced to 75
to 80 percent. A second press follows,
which reduces the moisture content
to 50 to 60 percent. The pulp is then
discharged to the digester.
PREPARATION FOR SALVAGE
The last method of solid waste dis-
posal to be considered in this section
of the report is disposal by salvage.
For the purposes of this study, salvage
is intended to cover the applications
of densification and size-reduction
equipment to the direct recovery,
processing, and use of materials taken
from nonferrous, mixed solid wastes,
such as those collected by municipali-
ties. This discussion does not cover the
wide range of equipment in everyday
use in the existing and already highly
developed automobile scrap and sec-
ondary-materials industries.
The literature survey indicated that
disposal of solid wastes by salvage was
limited. This was particularly true in
North America, and, with two excep-
tions, it seemed as limited in Western.
Europe. Only three articles were found
with more than passing mention to
salvage as a means of solid waste dis-
posal. Several of the articles found on
composting do mention that salvage
operations were being, or could be,
applied to the system. None, however,
offered details describing existing or
proposed densification or size-reduc-
tion equipment.
In the United States, large-scale
disposal of municipal-type solid wastes
by salvage seemed to be limited to the
unique system existing in Los Angeles,
California. An article on this subject
appeared in a 1963 issue of Compost
-------
Processes incidental to separation 11
Science.™ Prior to 1957, residents of
Los Angeles separated their solid
wastes into garbage, combustible re-
fuse, and noncombustible refuse. The
garbage was fed to swine and the com-
bustibles were burned in backyard
incinerators. The resulting incinerator
residue was mixed in with the non-
combustibles, which were collected
and disposed of through the salvage
industry. Since 1957 and the passing
of air pollution laws, Los Angeles no
longer permits backyard incineration.
Garbage not ground and flushed to
sewers was being put in with com-
bustibles and disposed of to municipal
incinerators or landfills. Noncom-
bustibles were still being separated
and disposed of by a contractor.
The prime material salvaged from
Los Angeles' noncombustible refuse
was tin cans, although scrap iron, cast
iron, and nonferrous metals were also
removed. The cans were being used
in a process that precipitated copper
from leaching solutions at cooper-
refining operations. After magnetic
separation and processing to remove
extraneous materials (food wastes,
labels, paint, etc.), the tin cans were
shredded into "premt". The can
shredder was described as a special
one developed to provide an ideal
product for the precipitation of
copper. Further details on the
shredder were not given.
Apparently, the only other large-
scale direct salvaging operation in
North America was an installation
outside Montreal, Canada.654 The
prime purpose of this plant was act-
ually bulk reduction of municipal
solid wastes, not salvage. The refuse
moved from the receiving pits to hop-
pers and from there to conveyor belts,
where it passed through a sorting
room. Apparently, all sorting was done
by hand labor, the workers dropping
the salvageable material into collec-
tion boxes via chutes. Salable material
was taken to one of two baling presses.
It was reported that when salvag-
ing was in operation, bulk was reduced
by 40 percent and weight by 25 per-
cent, based on the incoming refuse.
All material not salvaged passed to
one of two Gondard hammermills.28'
Prom the mills, the refuse went to a
stationary packer which loaded 35-
cubic-yard containers. These were, in
turn, picked up by a special truck and
hauled to a landfill. Maintenance costs
on the hammermills were estimated to
be less than $0.57 per ton, with ham-
mers being replaced every 1,000 tons.
Salvage as a disposal method in
European countries was discussed in
Rogus' series of articles on Western
European practices. Rogus stated
that, with the exceptions of England
and Scotland, direct salvaging was
not practiced extensively in Western
Europe. He went on to point out that
English salvage plants did employ
highly developed and efficient ma-
chinery, including presses and baling
machines. More extensive informa-
tion was not given. Rogus concluded
that the trend was away from sal-
vaging because of the effects of high
labor costs, modern technology, and
development of synthetic materials.
He further reasoned that new end
uses would have to be found for
salvageable material before this
method of disposal could be con-
sidered competitive.379
See also: Recovery and Utilization;
Individual Waste Types.
SEPARATION
Physical methods of separation
may be applied to solid wastes by
utilizing existing or induced differ-
ences in the physical properties of the
materials being separated. The sepa-
ration may result in the production
of a useful product or in easier dis-
posal of one or more fractions of the
waste.
The materials defined as solid
waste, "garbage, refuse, and other
discarded solid materials", have not
been subject to separation treatment
other than the simplest type such as
handsorting, because until recently
there has been no need for separation
to permit easier disposal. It is quite
probable that with increased empha-
sis on this subject, more of the avail-
able techniques will find application.
A few cost data are presented here,
but they should be used only as a
guide because costs may vary mark-
edly in different applications of the
same process. In addition, available
cost data are at least several years
old, and with the changing economic
picture can no longer be considered
firm.
A large number of companies man-
ufacture various designs of the equip-
ment described. A typical reference
source to manufacturers is the Mining
Guidebook, which is published yearly.6
Similar guidebooks are published by
the trade journals that serve the vari-
ous industries.
The major differences in physical
properties by which solid wastes may
be separated are as follows: color,
luster; size; shape; tenacity, brittle-
ness, or friability; structure and frac-
ture, texture; surface characteristics;
specific gravity; magnetic susceptibil-
ity; electrical conductivity; radio-
activity; and decrepitation.
In many instances it is possible to
change physical properties by such
means as chemical alteration of sur-
face characteristics, drying to im-
prove electrical conductivity, oxida-
tion to affect magnetic properties, and
application of vacuum to porous ma-
terials to change specific gravity. The
unit processes that are described in
the following paragraphs are: (1)
Processes incidental to separation, in-
cluding size reduction (crushing and
grinding), sizing (screening and clas-
sification) , and fluid-solid separation
(thickening, filtration, dust collec-
tion) ; (2) sorting; (3) washing and
scrubbing; (4) gravity concentration;
(5) magnetic separation; (6) electri-
cal separation; (7) flotation.
See also: Diamond Grinding Wheel
Dust; Refractory; Wastepaper.
PROCESSES INCIDENTAL TO SEP-
ARATION
Size reduction. Before separation
can be accomplished, the materials to
be separated must be liberated and
sufficiently reduced in size for appli-
cation of separation techniques. Size
reduction and sizing, consequently,
may play an important part in most
separation processes. Because the ma-
terials that constitute solid wastes
may range from the hard-rock types
to vegetable, fibrous, and even fleshy
types, a wide range of crushing and
grinding equipment is required. In
one instance, equipment peculiar to
the mineral industry may be quite
satisfactory, yet in another instance
the same machinery might be un-
usable. For treating some materials,
new equipment might have to be de-
signed, as has recently been the case
for the processing of automobile
bodies. In general, it might be con-
cluded that with the various types of
crushing and grinding equipment
available, units can be procured for
almost any type of size-reduction
operation.
If the material to be treated is hard
and abrasive yet will fracture under
impact or can be abraded, equipment
used in the mineral industry, such
as jaw and gyratory crushers, rolls,
ball and rod mills, and hammermills,
is applicable. For materials that de-
form under pressure, knife-blade or
cutting-type hammermills, shredders,
chippers, etc., are applicable.
If extremely fine grinding is re-
quired, particularly for materials uti-
lization rather than liberation, sucb
338-244-
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12 SOLID WASTE PROCESSING
Feed
Size Reduction
I
Sizing Oversize
1
Finished Product
FIGURE 4. Typical size-reduction flow sheet.
devices as vibratory ball mills and
fluid-energy mills are available.
High-speed agitators or macerators
may be utilized in some operations.
In the utilization of waste paper, for
example, liberation of ink from news-
print is done in a Hydrapulper, a
high-speed agitator manufactured by
the Black Clawson Company. A sim-
ilar machine is the Wet Pulper man-
ufactured by The French Oil Mill
Company.
The use of several different types of
crushing and grinding equipment is
quite common. This has led to the
development of such terms as primary
or coarse crushing, secondary or in-
termediate crushing, fine crushing,
and grinding, the distinctions between
the operations being purely arbitrary.
What may be a fine-crushing unit in
one treatment may be a coarse-
crushing unit in another.
Size-reduction equipment is usually
quite massive. It is generally avail-
able in unit sizes varying from lab-
oratory devices to mammoth units
that require several-thousand-horse-
power motors to operate.
The crushing surfaces are usually
replaceable, thus, the life of the
equipment is long. A 30- or 40-year
life for well-designed and well-con-
structed units is not unusual.
The cost of size reduction in the
coarse sizes is low—a few cents per
ton, whereas in fine grinding it may
run from $0.50 to $1.00 per ton. The
primary cost item is power, mainte-
nance being next. Labor cost is usual-
ly low unless the operation requires
attendance to permit uniform feeding.
Sizing. In many operations sizing
is concurrent with size reduction.
The function of sizing is to limit the
size of materials going to the next
unit process—either further crushing
or separation—as may be seen from
a typical size-reduction-sizing flow
sheet (Figure 4).
A combination of size reduction and
sizing may also constitute a unit sep-
aration process when one or more of
the constituents grinds more easily
than another, thus producing a fin-
ished coarse fraction and a finished
fine fraction. The treatment of alu-
minum dross is an example of this.
The slag component breaks up
readily, whereas the malleable alu-
minum does not. After crushing and
screening, a coarse oversize, high in
aluminum, and a fine undersize,
high in slag, are produced.
Sizing may be done either wet or
dry with screens or classifiers. Screens
may be either stationary or moving,
flat or inclined. Screen movement
may be brought about by shaking, ro-
tation, or vibration. Screen openings
may vary from several inches or more
in the coarse grizzly screens, the screen
being constructed of railroad rails, to
fine screens with openings 0.0015 inch
in diameter (400 mesh), or bolting
cloths with even finer openings. The
openings may be round, square, rec-
tangular, or slotted. Bound, flat, and
wedge-shaped wires may be used.
Classification generally takes the
place of screening in the fine-size
ranges. Wet classifiers of the helical-
spiral type, the rake type, or the cy-
clone type are very common. Air
classification likewise employs cy-
clones or mechanically driven cen-
trifugal separators
The mechanism of sizing by screens
is dependent simply on particle size
versus size of opening, whereas in
classification, settling rates determine
the size of the separation. Settling
rates are a function of size, shape, and
specific gravity. Of two particles of the
same size and shape, the one with the
higher specific gravity will settle first.
Consequently, in a classifier closed-
circuit grinding operation, it is not
unusual to find a concentration of
higher specific-gravity material in the
finer size fractions of the classifier
product.
Particle shape affects sizing. Acicu-
lar (needle-like) and platy materials
are much more difficult to size than
equidimensional particles.
Probably one of the most significant
advances in screening has been the in-
troduction of the sieve bend. This is a
stationary, concave screen made up
of wedge wire bar screen at right
angles to the material flow. Because
of the angle at which the material
contacts the screen, a wider screen
opening can be used for a given size
of separation. This increases the com-
mercial field of application down to as
fine as 100 mesh for high capacity
per unit of screen area and minimizes
blinding, the filling of screen openings
by particles of the same size.
The greatest improvement in classi-
fication has probably been the intro-
duction of the cyclone, both wet and
dry.
Sizing is a relatively simple and in-
expensive operation. Horsepower re-
quirements have been low. Screen
cloth replacement has been the major
maintenance item in screening,
whereas in classification wear of
flights or spirals has been the major
cost item. Rubber, ceramic, or other
linings keep maintenance low in cy-
clones or centrifugal separators.
See also: Bagasse; Brewing, Dis-
tilling, Fermenting Wastes;
Wastepaper; Wood Wastes; Zir-
caloy.
Fluid-solid separation. In most
processes of physical separation of
materials, some method must be em-
ployed for the removal of a solid frac-
tion from a fluid medium.
-------
For liquid-solid separation, such
devices as thickeners, niters, centri-
fuges, cyclones, classifiers, and even
screens have commonly been used for
this purpose. Crude liquid-solid sepa-
ration can be effected by stationary
drainage on a sloping floor or in tanks
or bins with provision for liquid re-
moval at the bottom.
G-aseous-solid separations (dust
collection) may be accomplished in
settling chambers, baffle-type collec-
tors, centrifugal collectors (cyclones),
mechanical-type collectors, gas niters,
bag houses, spray washers, and elec-
trical precipitators.
In many of these devices, separa-
tion of the fluid and solid is simply
a matter of settling by means of
thickeners, settling chambers, bag
houses, etc. In other devices, such as
filters, the fluid of the fluid-solid
stream is forced through a membrane
(filter cloth) that retains the solids
on its surface.
Thickening followed by filtration
has probably been the most common
procedure used in liquid-solid sepa-
ration. With solids that filter reason-
ably well, vacuum filters of either the
drum or the leaf type can be used.
For more difficult filtration problems,
pressure filtration in plate and frame
or pressure-tank-type units can be
employed. In vacuum filtration, the
pressure differential has been limited
to atmospheric pressure (14.5 psi at
sea level), whereas with pressure fil-
ters, pressures of 50 to 60 psi have not
been unusual.
The cost of vacuum filtration has
varied widely, $0.10 to $0.20 per ton
being the average. Thickening costs
have been very low, as in the cost of
dewatering by screening, cycloning,
and similar methods.
The cost of electrostatic precipita-
tion may vary from as little as $0.02
to as much as $0.30 per 100,000 cubic
feet of gas treated, depending on the
solids content, the solids size, and the
efficiency of removal required.
Drying may be required in some in-
stances to reduce the moisture con-
tent to an acceptable figure. Rotary
kilns and spray driers have been two
commonly used types. Heated floors
and vertical towers have also been
employed. The primary cost in drying
has been that of fuel, and the fuel
requirements are virtually a direct
function of the moisture content.
SORTING
Both hand sorting and mechanical
sorting have been employed, with
much of the mechanical sorting
equipment being associated with the
waste-paper-salvage industry.
Hand sorting. Hand sorting of ma-
terial is probably the oldest unit proc-
ess of physical separation. To a de-
gree, sorting operations are performed
in virtually every manufacturing in-
dustry, if for no other reason than to
reject imperfect items.
The material to be sorted must have
a readily distinguishable property
such as color, luster, shape, size, gen-
eral appearance, or radioactivity. It
should be the minor constituent and
of such size and weight that it can
readily be moved.
In some basic industries such as
mining, hand sorting has been elim-
inated because of the increasing cost
of labor, and, to a lesser degree, the
development of mechanical methods.
Much of the solid waste generated
by an urban population could be hand
sorted at its source to minimize subse-
quent disposal problems. (This has
been done in Los Angeles for many
years.) Separation of household and
similar waste into such categories as
paper, glass, metal (cans, etc.), and
garbage, would impose no particular
problem on the individual household
and would be done at no cost to the
overall waste-disposal program. The
sorted items could then be channelled
to their proper disposal point (e.g.,
reuse, incineration).
Hand sorting of contractors' con-
struction waste into its various com-
ponents should facilitate waste dis-
posal without adding a significant
cost to construction.
A very effective method of hand
sorting is to use a picking belt about
24 inches wide if there are sorters
only on one side, or 36 to 48 inches
wide if there are sorters on both sides.
Sorters are usually about 5 feet apart.
A belt speed of 30 to 40 feet per min-
ute has been the average. Chutes or
belts below the picking belt are pro-
vided to handle the picked fraction.
The material on the belt should be
clean, not more than one unit deep,
and well illuminated. Benches or
tables can also be used, particularly
where deposition of a uniform layer
on a belt is not feasible, as in the case
of wastepaper-type materials. Pick-
ing rates vary widely from several
hundred pounds per hour for light,
bulky material to as much as 10 tons
for dense rock types. At a labor cost
of $1.00 per hour, this corresponds to
a cost range from $0.10 to $7.00 per
ton.
See also: Refractory; Tin; Waste-
paper.
Gravity separation 13
Mechanical sorting. Mechanical
sorters utilizing color or radioactivity
have recently been introduced. Color
difference or radioactivity is detected
by a sensing device, which in turn
triggers an air blast that blows the
sensed particle out of the mainstream
of fall. At Eldorado, Canada, uranium
ore larger than 3 inches is sorted. A
demonstration run in South Africa
treated between 25 and 50 tons per
hour.
See also: Wastepaper.
WASHING AND SCRUBBING
Washing and scrubbing techniques
have been employed to remove minor,
fine constituents from, the main
coarse bulk of a material. If hand
sorting is to be employed, removal of
these fines may be advantageous in
removing surface dirt. Washing and
scrubbing can be used if a fine frac-
tion is worthless or if it would create
a problem in subsequent separation
processes. Clay, for example, is read-
ily removed by washing. Clay left with
an ore is troublesome in crushing and
grinding, screening, and various sepa-
ration processes, particularly flota-
tion. A trommel screen equipped with
spray nozzles is a good washing device.
The tumbling of the material as the
screen rotates exerts a scrubbing ef-
fect. For heavy-duty work where
more scrubbing is required, the log-
washer type of equipment is employed.
See also: Pickle liquor.
GRAVITY SEPARATION
Gravity separation or concentration
is based on differences in specific
gravity and sizes of materials. In-
cluded are jigging, tabling, spiraling,
and heavy-media separation. Two
particles of the same size but of dif-
ferent specific gravity can be sepa-
rated, as can two particles of the
same specific gravity but of different
size. Inasmuch as proper combina-
tions of specific gravity and size will
result in a large particle of low spe-
cific gravity that reacts to applied
forces in the same fashion as a small
particle of high specific gravity, sizing
prior to separation is desirable for
maximum effectiveness. Heavy-media
separation is an exception to the fore-
going statement in that, regardless of
size, specific gravity is the only prop-
erty that has an effect.
See also: Animal-Product Residues;
Wood Wastes; Zinc.
Heavy-media separation. Various
solutions or pulps with different spe-
cific gravities are available. If a ma-
terial is immersed in one of these
-------
14 SOLID WASTE PROCESSING
solutions or pulps, it will float or sink,
depending on its own specific gravity
and the specific gravity of the solution
or pulp. Thus, if a mixture of sand of
sp gr 2.65 and hematite (Fe2O3) of sp
gr 5.0 is immersed in a pulp composed
of ferro-silicon and water (sp gr 3.0),
the sand will float and the hematite
will sink, thus effecting a separation.
Although various heavy liquids such
as carbon tetrachloride (sp gr 1.67),
acetylene tetrabromide (sp gr 2.95).
and thallous formate-nialonate (sp
gr 4.2) among others, have been avail-
able, their costs and the problems of
recovering them have limited their use
to laboratory experimentation. In op-
erating plants, heavy media have
found rather wide application. The
pulp or heavy medium consists of a
mixture of water and fine solids, usu-
ally sand, galena, magnetite, or fer-
rosilicon. Choice of the solid and the
ratio of solids to water in the pulp
determines the specific gravity of the
heavy media. Sand has normally been
used for low-specific-gravity media,
magnetite and galena for intermedi-
ate-specific-gravity media and ferro-
silicon for high-specific-gravity me-
dia. Maximum specific gravities ob-
tainable have been about 3.2 to 3.4
with ferrosilicon. Use of sand media
would normally be restricted to the
treatment of coarse, low-specific-
gravity materials, the sand being re-
covered from the separated fractions
by washing and screening. When ga-
lena is used, the galena is recovered by
flotation. Magnetite and ferrosilicon
can be recovered by magnetic meth-
ods. The upper size limit of material
treatable by heavy-media procedures
has been about 2 inches, the lower
limit about 65 mesh.
Various types of vessels have been
used in heavy-media separation, the
most popular being cones, classifiers,
and drums for particle sizes coarser
than about % inch, and cyclones for
deslimed feed V* inch x 65 mesh.
Capacities of heavy-media units
have varied widely, depending on the
size of the material, specific gravities,
and the closeness of the cut desired.
A 4-foot-diameter cone processing 1 yz
x %-inch iron ore has treated 40 tons
per hour.
Treatment cost probably would not
exceed $0.50 per ton on coarser ma-
terials. Loss of the flotation media
and labor, together with the media-
recovery system, would account for
most of this cost.
Jigging. If a mixture of materials
of different specific gravities is placed
in a wire-mesh basket and the basket
is moved up and down in a container
of water, it will be found that after
sufficient movement the higher-
specific-gravity materials will be
concentrated at the bottom of the
basket. This is jigging. In commercial
practice, a water-solid mixture is
passed through a trough or box hav-
ing a perforated bottom. Water is
alternately forced up through the
bed and then drawn back down by
means of a plunger. This action
opens up the bed of material, moving
the lower specific-gravity particles
farther than the higher. Since the
bed compacts on the reverse stroke,
the heavier particles move farther
than the light particles. As the mate-
rial passes through the trough or box,
this action is repeated a number of
times at a rate of several hundred
strokes per minute, thus stratifying
the material so that it can be sepa-
rated as it leaves the jigs. The pul-
sating movement can be obtained by
mechanical plunger action or by air,
the latter having been the one most
used.
Material as coarse as several inches
down to about 10 mesh can usually be
successfully treated on jigs. Generally
speaking, water requirements are
high for jigging operations. Skilled
labor and close attention has been
called for in good jigging operations.
Table separation. Tables are bed-
type gravity-separation machines
used in the treatment of sand-size
materials. The more common tables
have been rectangular, the feed being
introduced as a slurry at one end of
the narrow side of the table. A re-
ciprocating motion is imparted to the
table. This motion is normally a slow
forward stroke followed by a quick re-
turn. Under this action, heavier par-
ticles move forward a greater distance
than light particles. At the same time
wash water is applied across the ta-
ble at right angles to the direction
of movement. The wash water exerts
a greater influence on the lighter par-
ticles, causing them to move across
the table at a greater rate than the
heavier ones. The combination of
stroke and water results in a partially
diagonal particle movement, with the
heavier particles discharging at the
end of the table and the lighter ones
over the side. The deck may be riffled
to aid in the separation. The riffles
provide a place for the fine, heavy ma-
terial to avoid the action of the wash
water coming across the table. Space
requirements are high, and the shak-
ing action requires substantial foun-
dations. To a considerable extent, ta-
bles have been replaced by spirals.
For low-specific-gravity materials,
tables with porous decks have been
available. Air blown through the deck
acts as the fluid medium for separa-
tion.
The standard Wilfley table is about
17 V2 feet long and 6 feet wide, requires
iVz to 2 horsepower, and has a ca-
pacity of 15 to 150 tons of material per
24 hours.
Spiral separation. The Humphreys
Spiral is a gravity concentrating de-
vice for the treatment of sand-size
material. It consists of a cast-iron
trough of curved cross section wound
in a spiral with 2-foot outside diam-
eter. The trough contains five or six
complete turns, depending on use.
The feed in the form of pulp is intro-
duced at the head of the spiral. The
heavy material remains in the bottom
of the trough and is discharged
through ports spaced along the bot-
tom. The lighter material rides up on
the side of the trough and is dis-
charged at the end of the spiral. Wash
water may be added along the spiral
to assist in the separation.
Spirals take up little space, have no
moving parts, and are extremely easy
to operate. Capacities with ores have
ranged from about 1.0 to 0.5 tons per
hour.
MAGNETIC SEPARATION
If a mixture contains some parts
that are affected by a magnetic field,
magnetic separation may be possible.
Probably the simplest illustration of
magnetic separation is the common
use of a magnet head pulley on a belt
to remove cans or tramp iron. The
nonmagnetic fraction falls vertically,
whereas the magnetic material clings
to the belt under the influence of the
magnet and drops from the belt at a
different location.
Magnetic separations can be made
dry or wet and with either low or high
magnetic intensity. The majority of
magnetic separation have used low-
intensity separators (5,000 gauss) in
removing most ferrous alloys. High-
intensity separators (20,000 gauss)
may be employed in the treatment of
weakly magnetic materials such as
hematite and manganese ores.
There are a variety of different types
of separators, the belt, induced-roll,
and drum being the most common.
The magnetic field may be produced
by electromagnets or permanent mag-
nets. The latter are becoming more
popular because they require no elec-
trical equipment.
Pretreatment may be employed to
-------
Sanitary landfill and open dumping 15
TABLE 1
CLASSES OF CHEMICALS USED IK FLOTATION
Classification
Function
Typical chemicals
Frothers._.
Collectors-
Depressors. _.
pH modifiers.
Stabilize froth Pine oil, cresylic acid,
alcohol.
Make particles hydrophobia Xanthates, dithiophos-
phates, soaps, fuel oil,
amines.
Make particles hydrophilic_. NaCN, various inorganic
salts.
Change pH to intensify ef- Acids and alkalies.
feet of other reagents.
convert a nonmagnetic material to a
magnetic one. Hematite, which is non-
magnetic, can toe converted to mag-
netic artificial magnetite by a reduc-
tion roast.
See also: Aluminum; Refractory;
Slag; Zircaloy.
ELECTROSTATIC SEPARATION
Some materials are conductors of
electricity, others are not. If a mix-
ture of conductors and nonconduc-
tors is fed onto a grounded, moving
roll and charged by means of an elec-
trode, the nonconductors acquire a
charge and are pinned to the roll,
which they adhere to until brushed
off. The conductors, on the other
hand, do not acquire a charge and
thus discharge from the roll in ac-
cordance with their normal trajectory
as determined by their mass and the
speed of the roll. This method of sepa-
ration makes use of the so-called
pinning effect. A lifting effect can
also be obtained, thus altering the
discharge paths of the particles.
The same separation effect can be
obtained by dropping the material
between oppositely charged plates.
The path of fall is affected in accord-
ance with the electrical conductivity
of the materials.
The application of electrostatic
separation has been limited to the
range of about 20 to 100 mesh. For
maximum effectiveness, the particle
bed on the drum or in free fall can
be a single layer thick. This naturally
limits capacity. Equipment cost has
been relatively high because of the
auxiliary power facilities required.
FLOTATION
Flotation may be defined as a
physiochemical method of concen-
trating finely divided material. Specif-
ically, the process involves chemical
treatment of surfaces in a pulp to
create conditions favorable for the
attachment of air bubbles to selected
particles. The air bubbles carry the
particles to the surface and form a
stabilized foam that can be scraped
off. The unwanted minerals remain
in the pulp. In addition to altering
surface properties to make certain
substances more floatable, it is pos-
sible to use various chemicals to
reduce floatability.
The surface characteristics of ma-
terials can be classified as either hy-
drophobic or hydrophilic. In flotation,
these properties can be altered as de-
sired. The hydrophobic particles at-
tach themselves to the air bubbles
and float, while the hydrophilic par-
ticles remain in the pulp. Alteration
of a surface may result from the re-
action or adsorption of flotation-
reagent molecules. Flotation reagents
that produce hydrophobic surfaces
are composed of long-chain molecules
that resemble matches, the heads of
which represent the end that reacts
with the particle. The other end is
hydrophobic.
The chemicals that have been used
in flotation may be grouped into sev-
eral classes according to their pri-
mary function. Some of the more im-
portant are shown in Table 1.
The process is carried out in a flo-
tation machine or cell, which is sim-
ply a box that contains an agitator
for keeping the solids in suspension.
An agitator may provide the air for
the air bubbles by aspiration, or air
may be added under low pressure di-
rectly beneath the agitator. Pulp flows
by gravity from one cell to the next.
Cells vary from 16 by 16 inches in
cross section by 18 inches in depth
(2% cubic feet) to 56 x 56 x 56 inches
(100 cubic feet). The smaller cell
would require approximately % horse-
power; the larger 10 horsepower.
In addition to the individual cell-
type construction, other flotation ma-
chines are like long, deep troughs with
a number of agitators positioned uni-
formly throughout their lengths.
The number of cells required for
any particular operation is a function
of the quantity of materials to be
processed, the percent solids of the
pulp, and the length of flotation time.
The cost of flotation has varied
from $0.50 to several dollars per ton,
depending on reagent consumption
and the complexity of the treatment
process. Skilled operators have usu-
ally been required, but one operator
can ordinarily look after a number of
banks of cells.
Flotation has been one of the most
efficient and widely applicable sepa-
ration processes hi use. Theoretically,
it can be applied to any mixture of
particles that are essentially liberated
and small enough to be lifted by air
or gas bubbles. Particles ranging in
size from 20 mesh down to about 5
microns are responsive to flotation
separation techniques.
See also: Wastepaper.
SANITARY LANDFILL AND
OPEN DUMPING
Probably the most widely used
methods for final disposition of solid
wastes have been sanitary landfill and
open dumping. These have generally
cost less than other disposal methods
while not creating the acute pollution
problem that has often occurred
when solids have been discharged di-
rectly to waterways or to the atmos-
phere. However, interest has been
growing in methods of disposal other
than on the land for several reasons:
(1) Land disposal requires large tracts
of land. Many communities and in-
dustries can no longer obtain the
large areas needed. The ever-increas-
ing quantity of waste makes this an
urgent problem in some areas; (2)
water pollution may result when sur-
face or groundwater leaches the
wastes dumped on spoil areas. Even
waste materials that are innocuous in
themselves often form injurious prod-
-------
16 SOLID WASTE PROCESSING
ucts upon degradation; (3) air pollu-
tion may result from degradation of
dumped and improperly covered
wastes, either when particles of waste
become airborne or when combustible
wastes ignite to produce mixtures of
particulate and gaseous matter; (4)
increased industrial activity results
not only in the generation of a greater
quantity of wastes, but also in a
greater variety of wastes. Thus, the
burden imposed on the land, air, and
water resources is increasing in mag-
nitude and complexity; (5) certain
resources, such as copper, zinc, and
lead, are nonrenewable. These mate-
rials are squandered when wastes
containing them are indiscriminately
dumped in spoil areas; and (6) open
dump areas are scenic blights and
have an adverse effect on land values.
While a properly operated sanitary
landfill can greatly limit these ad-
verse effects, especially (2), (3), and
(6), development of alternative dis-
posal methods or salvage techniques
is a desired goal, because in densely
populated areas, space for sanitary
landfills is decreasing.
As a consequence of these trends
the United States Congress enacted
Public Law 89-272, which authorized
research and development into im-
proved methods for solid waste
disposal.
TYPES OF SOLID WASTES DUMPED
OR BURIED
In the questionnaire sent to the
State health departments as part of
this survey, information was re-
quested concerning the kinds and ex-
tent of disposal problems created by
solid industrial wastes generated
within the State. In the case of 10
States, the reply was that no inven-
tory is made of solid wastes. The re-
maining 19 States were in a position
to give some information as to types
of industrial solid wastes disposed of
by dumping or burial. No State (ex-
cept Rhode Island) kept quantitative
records, although two States (Geor-
gia and Montana) estimated that the
waste from mining was about several
thousand tons per day.
Examples of industrial solid wastes
disposed of on or in the ground are:
papermill residues from waste treat-
ment (Alabama, Georgia, Minnesota,
Ohio, Pennsylvania); radioactive
wastes (Alaska, South Dakota); heavy
machinery (Alaska); mining wastes
(Alaska, Arizona, Georgia, Idaho,
Minnesota, Montana, Nevada); sea-
food processing wastes (Alaska);
metal refining wastes (Arizona, Min-
nesota, Nevada, Ohio); quarrying
wastes (Georgia, Minnesota); ba-
gasse (Hawaii); potato-processing
wastes (Idaho); canning wastes
(Idaho); meat-processing and
slaughterhouse wastes (Idaho, Min-
nesota, Nebraska); lumbering wastes
(Idaho, Minnesota); rubber wastes
(Rhode Island); plastics wastes
(Rhode Island); textile wastes
(Rhode Island); chemical wastes
(Minnesota, Rhode Island); oils
(Rhode Island); buffing wastes and
leather scraps from tanneries (New
Hampshire); sawdust and shavings
from sawmills and woodworking
plants (Minnesota, New Hampshire,
North Carolina); scrap from shoe fac-
tories (New Hampshire); brickyard
wastes (New Hampshire); wastes
from the investment casting process
(New Hampshire); coal-washing fines
(Ohio); fly ash from power plants
and ashes from various other indus-
tries (Minnesota, Ohio); precipitates
from treatment of metal-finishing
wastes (Minnesota, Ohio, Pennsyl-
vania) ; coal refuse (Pennsylvania);
and lime sludge from beet-sugar
processing (Minnesota).
A report from Rhode Island titled,
Refuse Disposal in Rhode Island,
probably the best source of informa-
tion on disposal of industrial solid
wastes, stated that: "Officially or re-
liably, there is little known about the
disposal of industrial wastes. Cer-
tain general information is available
that may give some ideas on the quan-
tities, types, and expected problems
involved in this aspect of solid wastes
disposal." Data on the quantities of
solid wastes produced by industries in
Rhode Island were presented, but
since the units were not clear, the
data are omitted from the present re-
port. Knowing the number of manu-
facturing employees in each of these
industries, and assuming that costs of
disposal average $8.00 a ton, it was
calculated "that Rhode Island indus-
try may expend $750,000 to $1,000,000
per year for solid waste disposal." m
In a report of a study made in the
San Francisco Bay area, it is recom-
mended that there be detailed report-
ing of solid waste production by in-
dustries.20
In addition to describing kinds of
wastes, some States also responded
with information on the methods of
solids disposal. It was reported that
in Georgia sludges and muds from
mining, quarrying, metal finishing,
and papermaking are normally im-
pounded in low areas for sedimenta-
tion with the sedimentation basins
being abandoned when they are filled.
In Nebraska, slaughterhouse wastes
are spread in open fields where they
are later disked in. Meat-processing
plants in Nebraska dump grease slur-
ries in open pits.
INCINERATION
The incineration of municipal ref-
use has been treated in detail in
Municipal Refuse Disposal but a brief
review of some of that information is
given here so that an integrated dis-
cussion can be presented. For details,
the original work should be con-
sulted.84 Part of the experience mu-
nicipalities have had with waste in-
cineration can be applied to incinera-
tion of some industrial wastes.
GENERAL CHARACTERISTICS OF
THE INCINERATION PROCESS
The complexity of an incineration
plant increases with its capacity and
the existing air-pollution standards.
Some general characteristics of the
incineration process are: (1) when
well operated it disposes of the health
problems associated with refuse ac-
cumulation and reduces waste volume
at least 60 percent (more frequently
80 to 85 percent) in a central plant
with minimum nuisance; (2) it is
adaptable over a wide range of equip-
ment capacities, such as from small
domestic incinerators to large central-
ized municipal incinerators with ca-
pacity of 1,000 tons per day or more;
(3) it can handle the mixture of gar-
bage and rubbish which results from
the currently favored single-collection
method; and (4) the passive charac-
ter of the clinker produced in prop-
erly operated furnaces considerably
aids its ultimate disposal.
Incineration costs reported by Ro-
gus in 1955 showed a decline of from
$4.78 per ton in older New York City
plants to $2.50 per ton in a new plant,
and $2.39 per ton cost for a new Ro-
chester, New York, plant.381
Gilbertson and Black quoted a
charge to homeowners in the Wash-
ington suburban sanitary district of
$36 per year for refuse service, and
state that at least 85 percent of the
total cost of providing refuse service
is spent on collection.154 Assuming an
annual load of 2.5 tons of refuse per
household and an incineration cost
of about $3.00 per ton, the incineration
process might cost an average of $7.50
per household. Making some allowance
for present cost of landfill (assumed
at $1.00 per ton), complete conver-
sion to incineration might raise the
Gilbertson and Black figure by ap-
proximately 15 percent.
The furnace, as either a single or
-------
Industrial incineration 17
a multiple unit, is essential to all in-
cineration plants. A secondary cham-
ber provides space for the complete
combustion of unburned furnace gas
and elimination of odors from stack
gas and for the destruction of the
organic content of any solids carried
by it. This secondary chamber may
be integral with the furnace.
A gas cooler usually precedes the
solids separator, since available sepa-
rators have not operated at tempera-
tures usual for exit gases from the
secondary chamber.
It was reported that Dorr-Oliver
supplied a system using high-speed
centrifugal dewatering teamed with
thermal oxidation in a fluidized
(sand) bed reactor to incinerate
sludge.520
Fly-ash emission is determined by
plant design and operating conditions.
Schwarz described measures to be
taken by incineration plants to con-
trol air pollution. Fly ash increases
with burning rate, air rate, or agita-
tion.400 Some idea of particle size and
analysis was given in Municipal Ref-
use Disposal."* The fallout that oc-
curred in an area around an incinera-
tion plant in Paris, France, was
reported by Chovin.76
Dry collection of fly ash includes the
use of refractor baffles, low-velocity
subsidence chambers, and multicy-
clone centrifugal separators. But such
methods have been hardly adequate to
meet the fly-ash limitations recom-
mended by the American Society of
Mechanical Engineers (see comments
of Ellsworth and Engdahl)."" Electro-
static dust precipitators, as have been
used in Europe, have been discussed
by Bump.03
Wet collection employs either water
sprays or impingement on a wet sur-
face. Results by various methods have
been reported by Fife and Boyer136 and
by Vickerson.487
The nature of incinerator slags has
been discussed by Herbert18* and
Regis.-18'
KINDS OF FURNACES
Michaels listed three types of refuse
furnaces287: (1) The single-chamber,
cylindrical, batch-feed type. This is a
refractory-lined furnace charged
through a door in the upper part of
the furnace. Refuse is dropped into
the furnace periodically and stoked to
the periphery manually or mechan-
ically by a rotating cone with ex-
tended rabble arms. The dumping
grates are located around the periph-
ery and are operated whenever the ac-
cumulation, of ash warrants rcni- v.ii.
(2) the single- or multiple-cell, rec-
tangular, batch-feed type. This may
be a refractory-lined or water-cooled
furnace with a charging door in the
middle or near the back of the ceiling
of each cell. It is equipped with either
fixed or moving grates set level or in-
clined; and (3) the continuous-feed
type. The major mechanical differ-
ence between this and the batch-feed
types is obvious from the names: ref-
use is fed into one in batches; into the
other continuously. Ashes are also re-
moved continuously, and an air seal
is maintained with the furnace con-
tinuously. The inclined, rotating-kiln
type is essentially the same as the con-
tinuous-feed type, except that it has
a refractory-lined, slowly revolving
cylindrical kiln that is used in the
final burning stage.
In the continuous-feed types of
furnaces, the grates are the traveling
type, inclined, flat, or a combination;
the furnaces require a minimum of
manual stoking.
Usually, all three types of furnaces
are lined with refractories and insu-
lating brick.
Various designs are shown in the
literature. These include cross-section
drawings M of the furnaces of the Cal-
umet incineration plant in Chicago,
the Northwest plant in Philadelphia,
a modern continuous-feed-type in-
cineration plant, the Volund rotat-
ing-kiln incinerator, a continuous-
feed grate, the Saint-Ouen (France)
plant,482 and the Fort Lauderdale in-
cinerator.31
INDUSTRIAL INCINERATION
The use of incinerators for disposal
of solid industrial wastes appeared to
be very limited. Fourteen States re-
sponding to the survey questionnaire
reported that the kind and amount of
industrial solid wastes incinerated
were unknown.* California reported
that there was little incineration be-
cause of air-pollution regulations and
economics. The only industry in that
State which carried on extensive
burning was agriculture, which was
exempt from air-pollution laws. Idaho
reported that although no industries
incinerated wastes, many of them did
burn wastes prior to dumping.
Solid industrial wastes reported as
being incinerated were sawmill and
lumber-industry wastes, corncobs,
bagasses, packing material, and textile
rejects. "Tepee" type burners were
often used to burn sawdust and corn-
cobs in four States, f Bagasse was
Inrinerat^d for fuel in Hawaiian sugar
.i'iL.s. ', --raft PU!T; '"il! '•• <>n«" ;-,U»,e
•Arizona, Arkansas, Colorado, Kansas,
Kentucky, Maine, Missouri, Montana,
New York, North Carolina, Pennsylvania,
Texas, Washington, Wyoming.
tNebraska, New Hampshire, South Da-
kota. Utah.
-------
18 SOLID WASTE PROCESSING
dried and burned its sludge in bark-
burning boilers. Georgia's mills were
also considering this method of dis-
posal. In that State, most industries
maintained burning areas where dry,
combustible solids such as packing
material and textile rejects were in-
cinerated, and some industries main-
tained regular incinerators for this
purpose. A chemical industry had
adopted incineration on an experi-
mental basis in Minnesota.
Only Tennessee reported that many
industries in the State incinerated
solid wastes. Incineration of wood
wastes was reported to be fairly
common in the lumber industry in
Minnesota.
The general overall approach to
industrial incineration is presented
in two papers,™' ** and design cri-
teria are reviewed in several.84'2eS| 3oe'
467,6w Thermodynamic calculations re-
quire specific information on the
amounts of combustibles, their den-
sity, moisture, and calorific values,
availability of carbon, hydrogen, oxy-
gen, etc. Their abrasive and corrosive
action on grates, refractories, and
other materials must be considered.
Practically no information of this sort
was available for some of the newer
special wastes, for example, various
synthetics and chemicals.380 The
heating values of various fuel
materials together with the heating
values of various wastes have been
reported.127' m
Incineration provides an effective
method to remove combustible mate-
rials from scrap metals. It has been
widely used to bum the insulation
from copper wire and cable. The prac-
tice of burning piles of insulated
wire in open fields formerly was wide-
spread, but has become rather lim-
ited. According to Lipsett the adop-
tion of plastic for insulation and
stringent pollution regulations have
introduced serious difficulties in re-
moving insulation from wire.264 He
stated in 1963 that fortunes have been
spent on facilities to remove the new
insulating compounds from the wire,
but that most of the installations were
not entirely satisfactory in the abate-
ment of the smoke nuisance.
See also: Chemical Wastes; Paint;
Petroleum Residues; Pulp and
Paper.
CAPITAL COSTS
Michaels noted that municipalities
tend to have a different view of capi-
tal costs than private enterprises.297
A municipality attempts to keep capi-
tal charges low to minimize the fi-
nancing required—usually a bond is-
sue—particularly since the adminis-
tration that builds the plant may not
have to operate it. This explanation
accounts in part for the wide range
in capital costs of various plants as
from $1,000 to $5,000 per ton of ca-
pacity. This approach tends to reduce
the premium on good operability and
design.
Construction costs were described
in Municipal Refuse Disposals: "Most
incinerator plants cost from $3,000 to
$4,000 per ton of rated 24-hour ca-
pacity to build and equip. Buildings
account for from 40 to 76 per cent of
total costs (an average of 58 per cent
furnaces and appurtenances account
for from 18 to 24 [sic] per cent of the
total (the average 35 per cent); and
the chimney accounts for from 4.5 to
11 per cent (the average 7 per cent).
"Construction costs adjusted to 1957
levels reported for 21 incinerators
built since 1949 (16 since 1954) had
a median of $3,650 per ton of capacity.
This compares to a median cost for
1946 of $2,000 a ton, or an increase
of approximately 82 per cent in 11
years. General construction costs for
the same period increased approxi-
mately 100 per cent."84
Construction costs for New York
incinerators have been separated by
the following functions: architectural
and structural; mechanical; electri-
cal; heating; ventilating; plumbing;
and miscellaneous (Table 2).
Greeley estimated that about 40 per
cent of the cost of an incinerator was
for furnaces and appurtenances, and
above 60 percent for building, chim-
ney, approaches, and storage bin1"
(Table 2). Greeley also estimated the
relative costs for parts of the instal-
lation (Table 3).
Michaels tabulated incinerator con-
struction costs for 25 incinerators.3"
Data were given on the location; ca-
pacity; year completed; material
burned; type of grate; number of fur-
naces; capacity of each furnace; com-
bustion chamber volume; type of
dust-collection system; number.
height, and diameter of stacks; type
of wall construction in furnace,
chamber, and flue; waste-heat utili-
zation; plant operation; and cost of
plant.
Coal-fired powerplant experience
provides a guide to possible first costs
of incinerator collection. The capital
investment in equipment installed at
the South Charleston, West Virginia,
powerplant of the Union Carbide Cor-
poration for the collection of fly ash,
has been given by Magnus.272 Costs
were given for both electrostatic and
TABLE 2
PRINCIPAI COMPONENTS OF A MUNICIPAL
INCINERATOR AND COSTS m
Item
Illustrative
unit
cost/ton
of rated
capacity
(dollars)
Scales, scale house, entrances
and exits, maneuvering
yard, dumping rail, and
enclosing wall
Storage bin
Cranes
Outsides flues and fly-ash-
removal facilities
Chimneys
Miscellaneous items, such as
drains, piling, and wood-
hogs
Furnaces
Inside flues
Building and enclosures
$100
200
825
400
300
75
1,200
85
1,415
Total 4,000
TABLE 3
FIRST COST DISTRIBUTION FOR PARTS OF AKT
INCINERATOR INSTAIIATION "»
Appro IE-
Part imate
percent of
total cost
Scales, yard, storage bin,
and outside appurtenances. 11.0
Building and cranes 37.0
Furnaces, combustion cham-
bers, flues, and appur-
tenances 35.0
Eelatively simple fly-ash-
removal facilities 7.0
Chimney 10.0
TotaL
100.0
-------
Operating costs 19
baffle-type collectors as well as the
1963 costs for replacing this equip-
ment, the steam-generating rates of
the equipment, and the costs of the
equipment on a cost-per-pound-of-
steam basis (Table 4). Magnus states
that the cost of mechanical collectors
and electrostatic precipibators is
roughly $0.15 and $0.55 per pound of
powerhouse steam-generating capac-
ity, respectively.
OPERATING COSTS
Michaels noted difficulties in com-
paring operating costs between vari-
ous plants. "Determining typical op-
erating costs is rather difficult because
some municipalities include the cost
of removing residue; others exclude
maintenance costs, etc. However, a
plant containing an average amount
of mechanization, operating on a 24
hr a day basis, and having a mini-
mum capacity of 300 tons/day, if effi-
ciently run, should cost between l/z
and 1 man-hour/ton to operate. Ob-
viously, the type of material handled,
i.e., mixed refuse, garbage, rubbish,
etc., the degree of mechanization, the
air pollution and other health stand-
ards to be met, and the housekeeping
standards all have a bearing upon the
ultimate operating costs. The cus-
tomer should be aware of these fac-
tors and should be able to advise the
consulting engineer of the standards
he requires." *"
Rogus reported overall operating
costs. "In 1953, landfill cost was $2.26/
ton while the average incineration
cost of 12 plants was $4.78. However,
the new Gansevoort Incinerator has
averaged only $2.50/ton. A new plant
at Rochester, New York, is reported to
have a basic operating cost of only
$2.39/ton including the cost of operat-
ing a stack-gas washer. The initial
cost of the plant was $1,373,726.
Hence, it appears that incinerator op-
erating costs are becoming competi-
tive with landfill costs and the
principal remaining problem is to
assure their clean operation." **•
A higher plant cost can provide a
lower operating cost81 (Table 5).
Providing for 24-hour furnace op-
eration has been shown to be desir-
able by comparison of the daily aver-
age operational costs, in dollars per
ton of furnace, for 1-, 2-, and 3-shift
operations.84 But collection on an 8-
hour-per-day basis necessitates buffer
storage capacity the size of which
should provide for variations in the
foreseeable future in amount and
character of the incoming refuse.
338-244—70 4
TABIE 4
CAPITAL INVESTMENT IN EQUIPMENT FOR FLY-ASH COLLECTION AT THE
SOUTH CHARLESTON, WEST VIRGINIA, POWERPLANT*"
Collection equipment
Total
installed
cost ($)
Replacement
cost ($) »
Steam
generating
rate (Ib/hr)
Capital
cost
per
pound
of
steam
per
hour
($)
(1)
(2)
(3)
(4)
(5)
(6)
(7)
Precipitators (Boilers 9 through 13)
(1947)
Mechanical separators (Boilers 9
through 13) (1937)
Precipitators (Boilers
(1942)
14 and
15)
Precipitator (Boiler 16) (1945)
Precipitators (Boilers
(1944)
17 and
18)
270,
fi9
79,
35,
74,
711
346
084
236
974
528,
174,
205,
81,
178,
000
000
000
800
000
Precipitator and mechanical separator
(Boiler 25) (1954). .
Mechanical separators
31) (1961-64)
(Boilers 30
and
104,
804
43,646
135,
43,
500
646
410,
300,
150,
300,
289,
300,
000
000
000
000
000
000
1.
0.
0.
0.
0.
0.
29
68
55
59
47
14
Total 667,853 1,345,946
» 1963 equipment and labor cost index=l,0.
TABIE 5
COMPARATIVE COSTS OF TWO TYPES OF INCINERATORS IN NEW YORK CITY (195 COSTS) «<
Cost item
Total construction costs per ton per day of capacity
(including engineering but exclusive of land)
Total operating costs per ton of refuse destroyed
Operating less residue disposal
Maintenance and repair
Administrating and supervision
Pension., _ _ __ _ ___
Fuel and utilities _
Amortization
Cost
Mechanized
continuous type
(average for 3)
$5,500. 00 »
5. 55
2. 40
1. 05
0. 50
0. 60
0. 05
0 95
Manually
stoked
hatch type
(average
for 4)
83,750. 00
7. 50
4. 20
1. 05
0. 65
0. 90
0. 05
0. 95
* Two plants have since "been constructed elsewhere for $3,600 per ton per day.
-------
20 SOLID WASTE PROCESSING
Recommended storage capacity ranges
were between 12 and 36 hours of
plant capacity.84 A 1000-TPD New
York City plant design provided I ton
of liquid-level pit capacity per ton
per day of plant capacity. One ton of
liquid-level pit capacity was consid-
ered equivalent to 6 cubic yards of
truck-compacted refuse.
Storage and handling facilities
should provide for handling objects at
least 80 inches square according to
Wiehrmann.482
It was pointed out that operating
costs also varied widely, depending on
the type of refuse burned and the
thoroughness of the burning, the de-
gree of sanitation controls exercised,
the type of incinerator plant and the
extent of its mechanization, the wage
scale and amount of fringe benefits,
and the productivity of labor and ef-
ficiency of management.84 Operating
costs for six cities were compared
(Table 6).
Maintenance and repairs were
commented on. "The modern incin-
eration plant is dirty, dusty, odor
producing, and requires more than
normal routine care to even approach
a power plant in spit-and-polish ap-
pearance and trouble-free operation.
"An annual budget for maintenance
and repairs approximating 5 percent
of the total capital costs of the plant
usually is adequate, particularly if
the plant is well designed and con-
structed; if it was properly tested,
adjusted, and broken in; and if it is
always kept in good condition. Main-
tenance and repairs can be expected
to cost between 10 percent and 15
percent of the total cost of operation,
depending on the size and type of
plant. Approximately half the cost
will be for labor and the other half
for materials.
"Routine maintenance is preven-
tive. Weekly inspections, cleaning,
and greasing, removal of clinkers and
slag, minor repairs to easily accessible
parts of the plant and machinery,
and less frequent inspections and re-
pairs to hard-to-get-at parts of the
plant will help prevent major dam-
age and emergencies.
"In addition to routine maintenance
and repairs, major repairs are needed
occasionally; reconstruction and mod-
ernization of furnaces, cranes, and
other parts of the plant are needed
less frequently; and a complete over-
haul and modernization of the plant
is necessary perhaps every 25 years
or so." **
Refuse storage to afford 24-hour
operation minimizes the installation
size and its operating cost. Grab-
bucket crane material handling
equipment is more suitable for bulky
objects than a conveyor system ac-
cording to Wiehrmann.482
Some indication of operating costs
of electrostatic precipitators is pro-
vided from power plants. The total
cost of collecting fly ash at the South
Charleston Union Carbide coal-fired
plant with eight electrostatic precipi-
tators was reported as $31,500 per
year with a breakdown of this cost
and operating costs on a unit basis
(Table 7). Seven of the precipitators
were equipped with 25-kva double-
halfwave mechanical rectification
units, while the precipitator of Boiler
25 was supplied with a vacuum-tube
rectifier (a 75-kv 25-kva full-wave
Kenotron unit).
The costs of constructing and op-
erating air pollution control equip-
ment as required to meet various
municipal incinerator stack emission
limits were reviewed by Fife and
Boyer.135 Rogus has reported foreign
costs for Western Europe.37' The total
costs of on-site domestic incineration
have been estimated by Engdahl and
Hein to be higher than for municipal
disposal.128
Certain economy in plant cost re-
sults from the use of a dust separator,
since higher gas velocities then be-
come permissible in the preceding
TABIE 6
OPERATING COSTS FOR MUNICIPAL INCIN-
ERATORS IN SIX U.S. CITIES «
Cost per ton
City of refuse
processed
Philadelphia $4. 24
Washington, D.C.h 2.28
Detroit 4. 30
Milwaukee 6.49
New York City 5.55
los Angeles 3.13
a Costs are for one plant in each city in 1959, except
for New York, where the cost is the 1958 average for
three plants.
b Does not include amortization ccsts.
c Cost computed on basis of tons burned (amount
charged minus residue).
TABLE 7
ANNUAL COSTS OF OPERATING ELECTROSTATIC PRECIPITATORS AT THE SOUTH CHARLESTON,
WEST VIRGINIA, POWER PLANT m
Total annual Annual cost of Annual cost of
Cost item cost of all mechanical vacuum
units rectification tube (unit
(unit basis) basis)
Operating labor
Electric power
Water
Repair labor .
Repair material.
$12,460
7,875
1,002
9,027
1,136
$1,558
1,680
127
"723
M25
116
$1,558
895
127
•134
>>855
210
Total 31,500
4,629
3,779
Factors:
Number of units: 7 with mechanical rectification, 1 with vacuum-tube recti-
fication.
Labor, $4.45 per hr (hourly rate plus fringe benefits).
Power, $6.00 per mkwh.
Water, $160 per mmg.
• Daily maintenance.
b Semiannual overhaul
-------
parts of the plant which operate at
high temperatures and therefore are
of more costly construction. Usually
an efficient collection device is needed
to reduce the amount of suspended
particulate solids in the stack gas to
the desired air pollution limit.
Several references concerning the
use of afterburners to combat the
smoke from incinerators appear in the
literature.1"638 Houston stated that
burning was the best method for re-
moving insulation from copper wire,
but that this required incineration
with proper smoke controls. He added
that probably the cheapest way to
control smoke would be by burning
the insulation with an afterburner, a
secondary combustion chamber main-
tained at 1,800° to 2,200° P. by burn-
ing oil or gas.
Houston also claimed that if after-
burners were well designed and were
operated properly, the matter released
to the atmosphere would be reduced
to a light haze. He estimated that the
bare, direct cost of the smallest prac-
tical incinerator unit and the cheapest
method of smoke control would be be-
tween $11,000 and $14,500. That esti-
mate was published in May 1957.197
Salvage and sorting have not been
considered rewarding beyond the im-
provement they have afforded in han-
dling and in the uniformity of feed
and the combustibility of the refuse.
Similar benefits result from grinding,
but some sorting is usually required to
protect the grinders.
While it may be advantageous to
remove metal, large objects, and non-
combustibles from refuse in prepara-
tion for charging it into the
incinerator, experience in the United
States has indicated that salvage
operations and reduction processes
have generally not been profitable.
The appearance of new products
such as plastic packaging materials in
refuse, and therefore in the furnace
feed, can produce certain gaseous de-
composition products necessitating
stack-gas treatment. The require-
ments for such treatment would be
difficult to predict.
Designs and performance of equip-
ment for the control of air pollution
from municipal incinerators have
been discussed in detail by Jens and
Rehm.215
WASTE-HEAT RECOVERY
A few combustible industrial wastes
generated in manufacturing proc-
esses have normally been used as fuel
by the organizations that generate
them. Useful heat is required for gen-
eration of process steam or electric
power.127 Usually, this has been done
in conventionally designed boilers and
furnaces, with perhaps specialized
equipment installed only for conveying
and feeding the combustible material
into the combustion chamber.271
-------
22 SOLID WASTE PROCESSING
sidered important, has been the vol-
ume effect of the extraction of heat
from exhaust gases in the furnace
and the use of less excess air because
of the completely water-cooled fur-
nace. Both of these factors have
greatly reduced the volume of dusty
gases to be cleaned, and hence have
reduced first costs, operating costs,
and maintenance costs of suitable
dust-collecting equipment.
CHEMICAL PROCESSING
Chemical processing of solid wastes
for recovery of usable materials and
energy is inherently one of the most
appealing approaches to the disposal
problem. In practice, however, such
processing has often proved costly. In
addition to the many articles cited,
this survey of published information
on chemical processing covered
Chemical Abstracts, Engineering In-
dex, and Industrial Arts Index for the
period 1950 to 1966. Public Health
Service Publication No. 91, Bibliog-
raphy Series No. 4, Supplement E, en-
titled Refuse Collection and Disposal
1960-1961, was reviewed also.
Twenty-nine processes of interest
were identified. The list includes some
processes that are physical rather
than chemical to insure that this sec-
tion of the report covers all "non-
mechanical" processes: acidification;
alcoholysis; calcination; carboniza-
tion; chlorination; combination and
addition; combustion (incineration);
condensation; dehydration, dewa-
tering, and drying, dilution; dis-
placement; dissolution; distillation;
electrolysis and electrodialysis; evap-
oration; extraction; hydrogenation;
hydrolysis; ion exchange; melting;
neutralization; nitrogenation; nitra-
tion, and ammoniation; oxidation
(chemical); polymerization; precipi-
tation, crystallization, and gelling;
pyrolysis; reduction; sintering; va-
porization and gasification.
Two main groups of chemical proc-
esses can be distinguished, the deter-
mination depending upon whether
entirely new products are obtained in
the course of treatment or whether
only a recovery of existing raw ma-
terials takes place. The classification
differentiates between the manufac-
ture of new products and reclamation
processes. The latter are cyclic proc-
esses. Waste products in the true sense
do not occur. The term is commonly
used, and is used in this study even
though at the present time many ma-
terials are or could be recycled in-
stead of simply being processed as
wastes.
Ideally, the techniques used for dis-
posal of solid wastes should: (1) Pro-
duce a revenue or at least cost the
producer little or nothing; (2) con-
sume most of the material; (3) be of
a nonseasonal nature; (4) produce an
end product that contributes some
beneficial results to the economy of
the country; (5) not result in pollu-
tion of the environment.
Selection of techniques for inclu-
sion in this study, however, was not
ordinarily limited by these criteria.
Processes that consume very small
amounts of waste—10 percent or less
—were excluded, on the other hand,
as offering no appreciable reduction of
the solid-wastes problem.
Although this has been essentially
a study of the waste problem in the
United States, techniques for chemi-
cal reduction of solid wastes described
in the foreign literature are covered
even though it is recognized that one
of the basic problems of effective dis-
posal is economics and that economics
are different for every area of the
world. A number of articles and pat-
ents are considered, although evidence
of industrial practice was lacking, be-
cause air, land, and water pollution
control and conservation of resources
are becoming more urgent all the time.
In the future these may alter the
economics of some solid waste dis-
posal processes. In some cases, the
processes decribed in the literature
may not have survived because of eco-
nomic or other conditions. Neverthe-
less, knowledge of their temporary
demonstration or use may be helpful
in similar circumstances.
The literature reviewed showed that
although chemical processing of some
solid wastes for salvage and recovery
is technically feasible, there has been
limited interest in these processes not
only because of problems of economics
and marketing, but also because of
impurities and nonuniformity of
quantity and composition of the waste
material.
It was apparent from the literature
and from correspondence with State
health departments that there have
not been many commercial applica-
tions of chemical processes for treat-
ing solid industrial wastes. A few in-
dustries have incinerated solids.
Many more have burned wastes in
open dumps. The most common
method of disposal has been to ac-
cumulate solid wastes in spoil areas.
This choice has toeen dictated by eco-
nomics. Land disposal has nearly al-
ways been selected as the cheapest
method. Most chemical processes re-
quire a substantial capital investment,
and the cost of operation has also
been significant. As long as justifica-
tion for chemical processing of waste
is based solely on the ability to sell
the products above fixed and operat-
ing costs, there is little chance that
these processes will be adopted. If
poor public relations are engendered
by pollution or unsightly conditions,
chemical recovery processes may
nevertheless become necessary.
The chemical processes described in
the literature are reviewed here briefly
in the order of the frequency of their
appearance in the literature. The lit-
erature on acidification, chlorination,
condensation, dehydration, dilution,
displacement, dissolution, hydrogena-
tion, neutralization, nitrogenation,
polymerization, reduction, and vapor-
ization of solid industrial wastes was
found to be very scanty. No reference
to commercial applications of any of
these processes was found. More de-
tailed discussions will be found in the
"Major Waste Categories" section of
this report.
HYDROLYSIS
Hydrolysis provides a means for
utilizing agricultural residues and
wood wastes. Its potential application
is worldwide. Glucose is obtained by
hydrolysis of the cellulose portion of
plants. Hydrolysis of the hemicellu-
loses in plants yields pentoses, which
upon dehydration form furfural, an
important raw material for plastics.
The lignin remaining after recovery
of these hydrolysis products is a po-
tentially valuable chemical raw ma-
terial. Lignin can also be hydrolyzed.
When plant residues are used for
manufacture of paper, board, and
rayon, it is the lignin that is hydro-
lyzed to alcohols and acids in order
to recover cellulose fibers from the
waste. At least one plant in the United
States has hydrolyzed lumber and
pulp-mill leftovers to obtain glucose.
A number of sulfite mills have pro-
duced alcohol with yeast from the
glucose formed in pulping process.
This is justifiable as a means of re-
ducing stream pollution. A review of
hydrolysis equipment has been made
by Taubin."6
See also: Agricultural Wastes; Ani-
mal-Product Residues; Bagasse;
Brewing, Distilling Fermenting
Wastes; Food-Processing Wastes;
Fruit Wastes; Germanium;
Leather Fabricating and Tannery
Wastes; Plastic; Pulp and Paper
Wastes; Textiles; Vegetable
Wastes; Wood Wastes.
-------
Melting 23
COMBUSTION (INCINERATION)
Combustion or incineration has ap-
peared to offer the most hope for
implementation in the near future.
It has the advantage of providing the
"ultimate in volume reduction, and
frequently it is the most practical way
to treat toxic substances. Although
chemical recovery is possible in some
cases (e.g., recovery of chemicals
from black liquor for sulfate pulping),
heat is generally the only salvageable
by-product. Air pollution control
measures may limit this practice in
some areas or call for advanced de-
sign and process control.
See also: Animal-Product Residues;
Asbestos; Ash, Cinders, Flue Dust,
Ply Ash; Bagasse; Brewing, Dis-
tilling, Fermenting Wastes; Brick
Plant Wastes; Chemical Wastes;
Coal Refuse; Electroplating Resi-
dues; Gypsum; Molasses; Organic
Wastes; Paint; Pulp and Paper;
Petroleum Residues; Photograph-
ic Paper; Plastic; Rubber; Sulfur;
Wood Wastes; Yttrium.
EXTRACTION
Extraction of constituents from
waste solids by means of solvents has
been an important means of obtaining
salable chemicals and metals. How-
ever, the high cost of most solvents has
limited the commercial value of many
of these recovery processes.
See also: Agricultural Wastes; Alu-
mium; Animal-Product Residues;
Brewing, Distilling, Fermenting
Wastes; Coffee; Fish; Fruit
Wastes; Glass; Manganese; Nuts;
Pickle Liquor; Plastic; Poppy;
Pulp and Paper; Sisal; Titanium;
Vanadium; Vegetable Wastes;
Zinc.
PYROLYSIS*
Pyrolysis of carbonaceous waste
materials leads to recovery of a num-
ber of by-products, the most impor-
tant of which is charcoal. Pyrolysis
has been practiced on a commercial
scale in the United States. The atom-
ized-suspension technique is useful
for pyrolyzing sludges.
See also: Animal-Product Residues;
Fruit Wastes; Leather Fabricat-
ing and Tannery Wastes; Petro-
leum Residues; Plastic; Pulp
and Paper; Rubber; Vegetable
Wastes; Wood Wastes.
CARBONIZATION*
Carbonization of carbonaceous
wastes has been practiced to obtain
activated carbon. It has been carried
out on a commercial scale.
See also: Brewing, Distilling, Fer-
menting Wastes; Food-Processing
Wastes; Petroleum Residues;
Rice; Textiles; Wood Wastes.
OXIDATION (CHEMICAL) t
Chemical oxidation of organic waste
materials yields a variety of products,
but there has not been much com-
mercial application of this process.
Some use has been made of bagasse
and sawdust as reducing materials in
metallurgical operations.
See also: Bagasse; Carbides; Chem-
ical Wastes; Food-Processing
Wastes; Inorganic Wastes; Pulp
and Paper; Rubber; Wood
Wastes.
SINTERING
Sintering has been practiced for re-
covery of metals and for converting
wastes to a form usable in building
materials, particularly for utilization
of slag and fly ash.
See also: Aluminum; Ash, Cinders,
Flue Dust, Fly Ash; Bauxite Resi-
due; Coal Refuse; Cobalt; Inor-
ganic Residues.
PRECIPITATION, GELLING, AND
CRYSTALLIZATION
Precipitation, gelling, and crystalli-
zation have limited application for
processing solids industrial wastes.
Some metals (e.g., silver) have been
recovered by precipitation.
See also: Animal-Product Residues;
Copper; Fish; Fruit Wastes; Gyp-
sum; Leather Fabricating and
Tannery Wastes; Pickle Liquor;
Pulp and Paper; Titanium.
CALCINATION
Calcination has had fairly wide-
spread application for the recovery of
calcium compounds, such as lime and
gypsum, from sludges. A continuous
calciner which reduces aqueous waste
concentrates to anhydrous melts has
been described by Hittman.188
See also: Acetylene Wastes; Asbes-
tos; Calcium; Coal; Pickle Liq-
uor; Pulp and Paper; Slag; Ti-
tanium.
MELTING
Melting residues to recover metals
such as copper, iron, zinc, and lead
has been practiced. Silicon-containing
wastes have also been melted for by-
product recovery.
See also: Animal-Product Residues;
Ash, Cinders, Flue Dust Fly Ash;
Brick Plant Waste; Copper;
Glass: Lead; Pulp and Paper;
Plastic; Titanium.
*The terms pyrolysis and carbonization
are not entirely Interchangeable, al-
though carbonization may be considered
as a special case of pyrolysis in
which volatiles are cooled sufficiently
rapidly to prevent further decomposition
(cracking).
fThis term refers to oxidation by
chemically combined oxygen, such as
contained in HNO3, PejO3, etc. It thus
differs from combustion, which involves
oxidation with free oxygen.
-------
24 SOLID WASTE PROCESSING
ELECTROLYSIS AND ELECTRO-
DIALYSIS
Electrolysis and electrodialysis can
be used to recover iron and acid from
spent pickling solutions and to recover
chemicals from spent sulflte pulping
liquor. A pilot plant has been in oper-
ation for treating sulflte waste in this
manner.
See also: Beryllium; Manganese;
Pickle Liquor; Pulp and Paper;
Titanium.
COMBINATION AND ADDITION
Combination and addition reactions
are steps in the production of di-
methyl sulflde and sulfoxide from the
lignin in kraft black liquor. This has
been used on a commercial basis.
See also: Calcium; Pulp and Paper.
EVAPORATION
Evaporation has been used to re-
cover salable solids from waste
liquors. Steep water, whey, and beet
pulp have been evaporated and used
for feed. Copperas has been recovered
from pickle liquor by evaporation.
Lignosulfonates have been produced
by evaporation of sulflte liquors.
See also: Brewing, Distilling, Fer-
menting Wastes; Pickle Liquor;
Pulp and Paper; Starch.
ION EXCHANGE
Ion exchange can be used for the
recovery of chemicals from the solu-
ble-base (sodium, magnesium, am-
monium) pulping liquors.
See also: Ash, Cinders, Flue Dust,
Fly Ash; Pulp and Paper.
MISCELLANEOUS PROCESSES
Acidification
See: Ash, Cinders, Flue Dust, Fly
Ash; Wood Wastes.
Alcoholysis
See: Plastic.
Chlorination
See: Carbonaceous Shales; Fruit
Wastes.
Condensation
See: Plastic; Wood Wastes.
Dehydration, dewatering, and drying
See: Coal; Food-Processing Wastes;
Pulp and Paper; Wood Wastes.
Dilution
See: Chemical Wastes.
Displacement
See: Calcium; Pickle Liquor.
Dissolution
See: Leather Fabricating and Tan-
nery Wastes; Plastic; Pulp and
Paper.
Distillation
See: Chemical Wastes; Food-Proc-
essing Wastes; Fruit Wastes, Pe-
troleum Residues; Plastic; Pulp
and Paper.
Hydrogenation
See: Pulp and Paper.
Neutralization
See: Chemical Wastes; Pickle Liq-
uor.
Nitrogenation, nitration, and ammo-
niation
See: Bagasse; Carbonaceous Shales;
Plastic.
Polymerisation
See: Bagasse; Paint; Plastic.
Reduction
See: Copper; Lead.
Vaporization and Gasification
See: Ash, Cinders, Flue Dust, Fly
Ash.
RECOVERY AND UTILIZATION
The disposal of solid waste mate-
rials frequently involves their direct
ultimate disposal. However, some
types of solid wastes have been proc-
essed for the recovery of valuable
constituents prior to the ultimate dis-
posal of the remaining material. Such
wastes have usually been processed to
recover or produce any one or more
of the following types of products:
(1) Products that are recycled to the
operation from which the waste ma-
terial originated; (2) Products that
serve as raw materials for manufac-
turing operations; and (3) Products
that are utilized directly.
The scope of the commercial appli-
cation of physical beneficiation unit
processes to the treatment of such
wastes is indicated in Table 8.
Furlow and Zollinger have described
a proposed system for the disposal of
municipal garbage and refuse that
features the recovery of nonferrous
scrap, ferrous scrap, aluminum scrap,
glass, plastics, rubber, rags, and paper
by hand sorting and magnetic sepa-
ration.148 A diagram of the plant is
shown in Figure 5.
Roughly 20 percent of the waste
tonnage processed would be removed
in the salvage section by hand sorting.
Four successive selection conveyors
-------
The scrap metals industry 25
would be employed in this section lor
the salvage of various solid materials.
Cardboard, newsprint, kraft paper,
and mixed paper would be shredded
and baled after being hand sorted
from the first selection conveyor.
Bags, glass, plastics, miscellaneous
nonferrous metals, and rubber would
be hand sorted from the second selec-
tion conveyor into large salvage con-
tainers located on both sides of the
conveyor. Light ferrous metals and
tin cans would be removed from the
delivery end of the second selection
conveyor and from, the third selection
conveyor by magnetic belt separators.
The separator of each of these selec-
tion conveyors would be equipped with
a strong electromagnet and a belt
oriented at right angles to the direc-
tion of refuse movement. Heavy fer-
rous metals would be removed from
the refuse stream by a magnetic head
pully located at the discharge end of
the third selection conveyor. The final
step in the reclamation of solids from
the waste stream would involve the
hand sorting of aluminum cans and
containers from the fourth selection
conveyor. The remaining waste would
then be processed through the prepa-
ration, digestion, and finishing steps,
which are in experimental stages.
THE SCRAP METALS INDUSTRY
The reclamation and utilization of
nonferrous scrap metals is an old and
well established industry engaged in
a multimillion-dollar business annu-
ally. Thousands of dealers, smelters,
and refiners have been strategically
located throughout the United States
to collect and process scrap metals
and metal-bearing products. A partial
list of such companies is presented in
the 1966 edition of Metal Statistics.' It
illustrates the geographical distribu-
tion of firms and the kinds of scrap
materials with which those firms deal.
Several of the companies listed also
operated mines, smelters, and refin-
eries internationally, and some had
more than one plant in the United
States for the treatment of nonfer-
rous scrap metals. A number of for-
eign buyers are included in the list.
The Waste Trade Directory contains
a complete list of scrap-metal proces-
sors arranged geographically and ac-
cording to kinds of metals processed."
The major conclusions drawn from
the study of nonferrous scrap are:
(1) The large number of dealers
and processors for gathering, prepar-
ing, smelting, refining, and market-
ing scrap metals assures much com-
petition and consequently promotes
TABLE 8
THE COMMERCIAL TREATMENT OF INDUSTRIAL AND MUNICIPAL SOLID WASTES
Solid waste
Waste-producing industry
Waste-processing industry Waste-separation process
Recovered useful products
Garbage and refuse
Residential, commercial,
and industrial
assemblages.
Municipalities-
Waste wood Pulp.
Bark
Bagasse
Wastepaper.
Pulp
Sugar
Residential, commercial,
and industrial
assemblages.
Grinding wastes Tool-
Fly ash
Slag
Foundry wastes-
Electric power-
Steel
Foundry
Nonferrous metal
scrap.
Nonferrous metal
residues.
Atomic power, electric
power, automobile.
Smelting
Hand sorting, magnetic
separation.
Paper Gravity separation (by
heavy media).
Fertilizer Screening
Paper Screening
Paper Hand sorting, gravity
separation (by
cyclones), mechanical
sorting, screening,
magnetic separation,
flotation.
Gravity separation (by
heavy liquids),
flotation.
Electric power Magnetic separation, air
classification, screening.
Steel Magnetic separation,
screening.
Foundry Magnetic separation,
screening, gravity
separation (by shaking
tables), air classifi-
cation.
Atomic power, Magnetic separation,
electric power, screening.
automobile.
Smelting Screening, gravity sepa-
ration (by jigs and
shaking tables), air
classification, heavy-
media separation.
Nonferrous scrap,
ferrous scrap,
glass, plastics,
rubber, rags, paper.
Wood, bark.
Sized bark.
Bagasse fiber, pith.
Paper fiber.
Diamonds.
Ferropozzolan, puri-
fied pozzolan.
Sized slag.
Molding sand, metals,
alloys.
Alloys, metals.
Metals.
-------
26 SOLID WASTE PROCESSING
Landfill^
Disposal
Garbage
and refuse
Tin cans and light ferrous
metals
» Baled
paper/
Water, liquid
organic wastes,
or sewage sludge
Coarse compost and
reject items
Crude compost
JL
compost
FIGURE 5. The reclamation of municipal refuse by the SACS process.
-------
The scrap metals industry 27
efficiency in reclamation and utiliza-
tion.
(2) Because of the efficiency of the
industry, large tonnages of new scrap
metals generated in manufacturing
operations by major companies are
transferred to secondary processors to
produce marketable metals.
(3) The operations to produce mar-
ketable metals are complex, and they
require special skills, expensive fa-
cilities, and knowledge of metal
marketing. They must be conducted
in reasonably large scale to be
competitive.
(4) The recovery and refining op-
erations are much simpler and hence
less expensive when different types of
materials are treated separately in-
stead of as mixtures.
Quantities of scrap returned to in-
dustry. The United States Bureau of
Mines compiles and publishes statis-
tics regarding the recovery in the
United States of the major nonfer-
rous scrap metals. These data 'nay
be found in Minerals Yearbook? The
Bureau of Mines, as well as the indus-
try in general, has differentiated be-
tween "primary" and "secondary"
production of metals. "Primary" pro-
duction derives metals from ores and
concentrates, while "secondary" pro-
duction derives them from scrap met-
als and industrial by-products. The
term "new scrap" has been used to
designate cuttings, turnings, and
other waste materials generated dur-
ing the fabrication of equipment and
merchandise. "Old scrap" refers to
parts of obsolete equipment and to
piping, wire, and other materials re-
claimed in dismantling buildings,
ships, and the like.
The Minerals Yearbook for 1964,
Volume 1, contains information re-
garding the activities of secondary
producers of metals and the tonnages
of products. The data in Table 9 were
abstracted from that publication to
show the magnitude of the second-
ary-metals industry.
Kinds of nonferrous scrap metals
and materials. The referenced data
on the quantities of industrial scrap
metals showed a number of classifica-
tions for the materials processed and
the products obtained. Actually, there
are many more classifications of non-
ferrous scrap metals. The National
Association of Secondary Material In-
dustries, Inc., has issued Circular NF-
66, "Standard Classification lor Non-
Ferrous Scrap Metals", which con-
tains standard classifications for 119
types of nonferrous scrap metals.318
Precious metals have been recov-
ered from a variety of materials, in-
cluding photographic film and solu-
tions. Parry presented the list of such
materials in an article published in
1962 (Table 10) .34°
Recovery of the less common
meta's has also been important in-
dustrially as evidenced by literature
describing plants and operations.
See also: Nonferrous Scrap; Pre-
cious Metals.
Prices of scrap metals. Four cate-
gories of nonferrous scrap materials
have been particularly important be-
cause of the large tonnages involved.
Scrap aluminum, copper, lead, and
zinc have been sufficiently important
industrially to warrant dally publi-
cation of prices for the more common
types of scrap containing those met-
als. Table 11 lists the scrap-metal
prices for August 16, 1966, given in
American Metal Market. It illustrates
the price differentials for the various
types of copper, lead, zinc, and alu-
minum scrap.
Sources of scrap metals. Most of
the nonferrous scrap metals returned
to industry have been obtained from
industrial plants that generally have
not processed their scrap metals for
reuse. Plants that generate large
amounts of scrap metals may have
contracts with wholesale dealers for
the collection of those metals. The re-
mainder of scrap metals has been
brought to dealers by collectors from
sources such as small shops and mu-
nicipal refuse collection. The dis-
mantling of obsolete machinery and
buildings has also provided a source.
Examples of the reclamation of
scrap metals on a large scale by a
major manufacturer and on a modest
scale by a municipality have been de-
scribed in recent publications. An
article of January 1966 described
equipment used to collect 150,000
pounds daily of aluminum chips from
profiling operations.516 Problems re-
sulting from the accumulation of
scrap aluminum at the source were
eliminated by installing at each pro-
filer a Torbit separator to gather the
continual flow of metal particles. The
publication stated that the sale value
of the scrap aluminum was increased
noticeably by the chip-collecting sys-
tem because contamination of the
product was prevented by continuous
removal of the chips from the pro-
filers.
Sanders has furnished information
TABLE 9
NONFIREOUS SCEAP RECOVEBED IN THE
UNITED STATES IN 19645
Weight
Type o£ scrap recovered,
thousands
of tons
Aluminum 552.0
Antimony:
Antimonial lead 22.3
Secondary smelters 20.8
Primary smelters 0.3
Copper, alloyed and unalloyed
(73 to 90% as much as
domestic mine output,
1955-64) 1093.0
Secondary lead 541. 6
Magnesium alloys 10. 0
Mercury (76-lb flasks) 0.9
Nickel 23.0
Tin . 23.5
TABLE 10
PARTIAL LIST OF PRECIOUS METAL SCRAP «
Type of scrap
Turnings, chips, shavings.
Silver on steel bearings.
Silver steel turnings.
Grindings.
Blanking scrap, stampings, strip, and
wire.
Powder mixtures.
Screen scrap.
Solder scrap.
Brazing alloy scrap.
Contact alloy scrap.
Silver on steel, tungsten, and molyb-
denum scrap.
Bimetal scrap.
Silver-paint waste, wipe rags, paper,
and cans.
Old batteries.
Plating solutions.
Precipitates, sludges and sediments.
Coated copper wire and racks.
Filter pads.
Anode ends.
Tank scrapings.
Electrolytic silver.
Hypo solutions.
X-ray film.
Coated plastics, ceramics, glass, mica,
quartz, etc.
Chemicals.
Mirror solutions(NaN03).
Platinum-bearing material.
Gold on molybdenum or tungsten wire.
338-244—70
-------
28 SOLID WASTE PROCESSING
TABLE 11
SCRAP METAI QUOTATIONS FOB AUGUST 18, 1966—CARLOAD LOTS DELIVERED TO BUYER'S WORKS •>
Type of scrap metal
Wholesale
buying price,
cents (or
dollars, where
indicated)
REFINERS' COPPER SCRAP b
Copper:
No. 1 _ _
No. 2 _
light .
Refinery brass °_
44.00
39.00
35.50
32.00
BRASS-INGOT MAKERS' SCRAP "
Copper:
No. 1
No. 2
light .
No. 1 composition solids 37
Composition borings, turnings 36
Radiators 26
Yellow brass :
Solids
Turnings
SMELTERS' SCRAP
Battery plates: Smelting charge per
(East)
Clean, heavy soft lead
Cable lead :
Lead content e
Copper content e
East
44. 00
39. 00
35.50
00-37. 50
00-36. 50
00-26. 50
25. 00
21.00
LEAD
ton
dollars
cents- .
do
.do
Midwest
44.00
39. 00
36. 00
36. 00-36. 50
35. 00-35. 50
26. 00
24. 00
21. 00
i 70.00-75.00
12. 75-13. 00
12. 75-13. 00
» 38. 50
Type of scrap metal
Wholesale
tuymg price,
cents (or
dollars, where
indicated)
SMELTERS' SCRAP ZINC
New zinc clippings
Old zinc (clean)
Old die cast (clean basis)
Die-cast slab (92% minimum)
Dross galvanizing-
Zinc skimmings '
10. 50-11. 00
8. 00-8. 75
7. 50-8. 00
10. 15-11. 20
10. 75-12. 00
9. 80-11. 00
Up to 3. 75
SMELTERS' SCRAP ALUMINUM
Aluminum clippings:
3003 3s
6151 515
110025 _____ __ __
5052525
2014 i«
2017"5
2024 2«
7075 «5
Old aluminum cast, including clean crankcases,
Aluminum borings and turnings, clean dry
basis, less than 1% zinc, 1% iron content
16. 00-16. 50
16. 00-16. 50
16. 00-16. 50
16. 00-16. 50
15. 00-15. 50
15. 00-15. 50
15. 00-15. 50
13. 00-13. 50
14. 50-15. 50
12. 00-13. 00
12. 50-13. 50
* Source:"American Metal Market," August 17, 1966.
i> Nominal.
« For dry copper content guaranteed in excess of 60%.
d S60.00-S62.50 in Chicago, based on 14.80 cents in St. Louis.
• Less S30.00 handling charge.
f Basis sample.
concerning the collection of scrap by
the Light, Gas, and Water Division of
the City of Memphis.382 He emphasized
the importance to profitable salvage
operations of the conversion of scrap
into forms that bring the highest
prices. In 1963, scrap brass from light
bulbs and other sources were sold to
dealers for $3,500. Coils of insulated
copper wire, lengths of lead-covered
cable, and leaded copper connectors
were heated to destroy the insulation
and to separate lead from copper by
melting the lead below the melting
point of copper. About 87,000 pounds
of lead and 262,000 pounds of copper
were salvaged in 1963 by the utility
division of the City of Memphis.
See also: Slag.
Marketing scrap metals. Scrap met-
als have been sold by dealers to whole-
salers and to smelters. The value of
the scrap and whether a specific kind
of scrap will be sent to a primary or a
secondary smelter depend on the
proximity of the smelters, together
with other considerations. The most
important factor is the composition
of the scrap in desirable metals and
undesirable metals or foreign mate-
rials. The composition influences the
expenses for transporting, sorting,
sampling, preliminary treating, smelt-
ing, and refining.
PREPARATION OF SCRAP METALS
Nonferrous scrap materials fre-
quently require treatments to prepare
them for melting, smelting, and refin-
ing operations. Turnings, borings, and
punchings of new metals may be sub-
jected to magnetic separation to re-
move iron or steel fragments. In some
instances, degreasing has been prac-
ticed to overcome the adherence of the
ferrous contaminants to the turnings
and borings. Stripping machines or
manual methods have been used to
remove lead sheathing and insulation
from electrical cables. Materials that
are not entirely metallic, such as
sweepings, drosses, ashes, and slags.
-------
Production of marketable metals from scrap materials 29
may be ground to liberate metallic
prills, drippings, and grindings. The
liberated metallic particles can then
be recovered by physical methods of
separation based on differences in
specific gravity or other physical
properties.
If the source of a particular lot of
scrap metal is known, the lot can oe
sold without analysis. Mixed materials
of uncertain origin must be sampled
and analyzed to provide a basis for
payment. These operations add to the
expense of the transactions, but they
can be minimized or avoided by care-
ful segregation or sorting of scrap
metals.
Scrap metals acquired by dealers
have been sorted piece by piece by
workmen who have attained great
skill irr identifying-the many-types'of
metals and alloys encountered. The
sorting process has frequently been
repeated at the smelting plant. The
surest and simplest means for fden-
tifying scrap is by knowledge of its
use or origin. Thus, plumbing fixtures,
copper wire, automobile radiators, and
lead battery plates are easily distin-
guished, even by only slightly expe-
rienced ipeople.
Less obvious metallic articles may
be subjected to tests depending on
specific physical and chemical prop-
erties of metals and alloys. Pieces may
be tested with a magnet to help
identify steel with nonferrous coat-
ings and certain bronze and nickel
alloys. Filing and drilling are used to
determine the relative hardness of
pieces, and the freshly exposed sur-
faces of metals may be noted for color
and texture as an aid in classification.
A number of spot tests with chemicals
have been developed for rapidly iden-
tifying metals or alloys. These tests
make use of characteristic colors,
gassing, or formation of precipitates
when reagents are dropped on metallic
surfaces. Well-equipped laboratories
for chemical analyses are adjuncts to
some scrap-handling plants. They are
used to identify and analyze scrap for
purposes of classification as well as
for the control of smelting and alloy-
ing processes.
Kobrin has discussed the influence
of identifying and segregating types
of scrap on the profitability of sec-
ondary-metals recovery.238 He claimed
that dealers were being confronted
with greater amounts of such ma-
terials as beryllium-copper, Inconel,
titanium, and precious metals. When
scrap is properly segregated, it can
be directed back to specific mills.
Therefore, developing special tech-
niques and equipment to identify, sort,
process, and package scrap is a vital
phase of the business, according to
Kobrin. One sorting technique he de-
scribed was based on the marked ef-
fect of certain impurities on the hard-
ness of titanium. Hence, Kobrin
stated, Brinell hardness tests can be
used to segregate various grades of
titanium scrap.
An example of the use of grinding
to free scrap metal from glass is given
in another article by Sanders on the
salvage shop of the Light, Gas, and
Water Division of the City of Mem-
phis.383 He described the use of a ro-
tary druta crusher, which treated
89,000 light bulbs in 1 year. The grind-
ing drum was filled with light bulbs
and several chunks of scrap iron. Ro-
tation of the drum ground the glass
free from the metallic ends.
Bulky materials (e.g., wire, turn-
ings, thin plates, sheets, and radi-
ators) have been baled by compression
in hydraulic presses to facilitate han-
dling and charging the materials to
furnaces. Compaction of small pieces
also promotes heat transfer in the
furnaces and minimizes losses of
metals by oxidation and by entrain-
ment of metal particles in slags. In
contrast to the requirements for mas-
sive charge materials in furnacing
processes, chemical methods require
the large surface areas of particulate
materials for the most efficient reac-
tion. Therefore, in contrast to baling
or briquetting of fine particles, it may
be advantageous to grind or shred ma-
terials when chemical processes are
employed.
It frequently is necessary to expel
moisture from scrap metals simply to
guard against explosions upon contact
with hot materials in the furnaces.
Conventional dryers, fired directly
with the most readily available fuel,
have been used.
PRODUCTION OF MARKETABLE
METALS FROM SCRAP MATE-
RIALS
The production of metals as mar-
ketable ingots, bars, pellets, or other
shapes and forms from scrap mate-
rials is discussed here according to
the major unit operations employed.
The operations vary from simply
melting scrap metal in a heated vessel
preparatory to pouring the molten
product into molds to form appropri-
ate solid shapes, to complex combi-
nations of hydrometallurgical and
pyrometallurgical procedures.
Melting. The simplest operation for
bringing scrap metals into salable
forms has been to melt them and then
cast them into convenient shapes for
handling industrially. This can be
done with metallic scrap that has been
sorted and otherwise prepared so that
the metal or alloy will be of a market-
able composition.
The terms "melting" and "smelt-
ing" are frequently used interchange-
ably. However, simple alteration from
a solid to a liquid, usually by heating,
is considered "melting". "Smelting"
refers to melting or fusing, and is
usually applied to ores, with accom-
panying chemical changes to sepa-
rate metals or compounds of metals
from other constituents of the ores
or charge materials. In general, how-
ever, plants that produce secondary
metals by furnacing operations are
called smelters. The nonferrous-scrap
industry employs various kinds of
conventional equipment for melting,
depending on the properties and the
quantities of the materials to be
melted.
Indirectly Fired Kettles and Cruci-
bles. Heated kettles or pots can be
used to melt magnesium, zinc, and the
so-called white metals (alloys of tin
or of lead), because these materials
melt at relatively low temperatures.
Kettles for this purpose have been
made in essentially hemispherical
shapes from cast iron or welded steel.
They are mounted in refractory fur-
naces in such a manner that their
contents are exposed to view and so
that fuel oil or gas can be burned in
the space under the kettles. Kettles
have been available in sizes to hold
any desired tonnage up to 100 tons or
more.
The same method of indirect heat-
ing has also been employed on a much
smaller scale to melt gold, silver, or
alloys of the precious metals. For this
purpose, a ceramic crucible of per-
haps 25-pound capacity is used in-
stead of a metallic kettle because the
temperature required to melt the pre-
cious metals is too high for use of iron
or steel vessels. Crucibles of larger
sizes are used widely in the scrap-
metal industry to melt alloys of cop-
per, lead, zinc, aluminum, and other
metals.
Equipment to melt metals in cruci-
bles has been manufactured by a
number of companies. The heat may
be supplied by burning fuels or by the
consumption of electrical energy.
Some of this equipment has been de-
signed to permit tilting of the crucible
or the entire furnace to pour the
molten metal. High-frequency indue-
-------
30 SOLID WASTE PROCESSING
tion furnaces belong in this category.
They have been used extensively for
melting precious metals that are
treated in relatively small amounts.
Ordinarily, little or no obnoxious
smoke or fume is produced from the
kinds of melting equipment described
above. The reason for this—in the case
of melting kettles—is that the melting
is conducted at temperatures too low
to volatilize metals or their compounds
and that the gaseous products of com-
bustion do not come in contact with
the charge material. The usual small
scale of operation with indirectly
heated crucibles generally does not
produce much fume or smoke.
Melting and refining. In the ma-
jority of cases, scrap metals require
some refining after melting, even
though the scrap was carefully sorted
and prepared for melting. The refining
treatment may consist of simply skim-
ming dross and slag from the surface
of the molten bath, or it may involve
successive treatments with reagents
to remove one contaminant after an-
other. Several types of internally
fired furnaces have customarily been
applied for the melting and refining of
scrap metals.
The reverberatory types of furnace,
stationary and rotary, produce the
major portions of secondary metals.
It has been estimated that most of the
brass and bronze ingots consumed by
industry originated from the treat-
ment of scrap materials in reverbera-
tory-type furnaces. Large amounts of
aluminum, lead, and zinc metals and
alloys have also been produced with
such furnaces.
Reverberatory Furnaces. A rever-
beratory furnace is a rectangular en-
closure, usually lined with magnesite
brick, with openings in the sides or
the roof for receiving charge mate-
rials. Skimming doors are installed in
the side walls of the furnace to remove
slag or dross, and tap-holes extend
through the refractories at several
levels above the furnace bottom for
skimming slag and for draining the
molten metal product. Burners for the
combustion of oil or gas are inserted
through one end of the furnace and
a flue for exhausting the products of
combustion is provided at the oppo-
site end. The heat from the combus-
tion is transferred directly to the
charge by radiation and conduction.
"Reverberatory" refers to the rever-
beration or radiation of heat from the
roof of the furnace onto the charge
or bath in the furnace. The rever-
beratory type of furnace which has
probably been the one most commonly
used in the secondary-metal indus-
try has been used almost exclusively
for the primary smelting of copper,
and the open-hearth furnaces used
for steelmaking can be classified as
reverberatory furnaces. Reverberatory
furnaces can be designed and erected,
in sizes to suit various needs, by a
large number of engineering and con-
struction firms. The capacities of
furnaces used in the secondary-met-
als industry have ranged from as lit-
tle as 1 ton to about 150 tons.
See also: Aluminum; Copper; Lead.
Rotary Furnaces. A rotary furnace
consists of a refractory lining in a steel
shell that resembles a cylindrical ro-
tary kiln. Magnesite brick is the usual
refractory lining material. The steel
cylinder is surrounded by riding rings,
which run on steel rollers mounted on
piers. Burners are attached at the end
of the furnace, and an opening is pro-
vided in the side of the cylinder.
Charge materials are introduced
through the opening. Slag and metal
are skimmed or drained by rotating
the furnace to bring the opening to
any desired level. Rotary furnaces are
commonly supplied by companies en-
gaged in the erection of smelting
equipment. The capacities of single
units may be from about 1 to 50 tons.
Rotary furnaces operate in the same
manner as reverberatory furnaces,
that is, by internal combustion of fuel
in the space above the charge mate-
rial. Some metallurgists favor rotary
furnaces over stationary reverberatory
furnaces because heat transfer and
coalescense of prills of metal are pro-
moted by the ability to mix the charge
by rotating the furnace. Rotation of
the furnace also enables the opera-
tor to pour the molten contents
conveniently.
Smelting and refining. Smelting in-
volves chemical changes in conjunc-
tion with melting or fusing of mate-
rials. The chemical changes generally
consist of reduction or dissociation of
oxides or other compounds to form
metals, and the formation of slags.
Ordinarily, it has not been possible to
make the chemical reactions so selec-
tive that only one metal is produced in
smelting. Consequently, it has gen-
erally been necessary to refine the
metallic products from smelting op-
erations to obtain separate marketable
metals.
Schedules for purchasing ores and
concentrates have been developed and
are widely used, especially by the com-
panies engaged in the primary smelt-
ing of copper, lead, and zinc. Although
such schedules are intended for ores
and concentrates, they may be in-
formative to producers of nonmetallic
products that require smelting and
refining. Salsbury et al. presented data
that can be used to survey available
markets and to make preliminary esti-
mates of the return to be expected
from an ore.391
Reverberatory types of furnaces
may be used for smelting and refining.
Blast furnaces also are employed for
smelting nonferrous scrap materials.
See also: Aluminum.
Blast Furnaces. Blast furnaces con-
sist of vertical shafts. They are
charged at the top with a mixture of
metal-bearing materials, fluxes, and
coke. The coke is burned in air sup-
plied through tuyeres placed near the
bottom of the shaft. A crucible and
tap holes are positioned below the
tuyeres. The crucible serves as a reser-
voir for the molten materials, which
descend through the incandescent
coke at the tuyere level. The molten
products are removed periodically
through the tap holes.
Oxygen enrichment of the air sup-
plied in blast-furnace smelting of
scrap materials has been adopted and
substantial benefits have been claimed
from this practice when applied to
charges of battery plates and lead
drosses.
Blast furnaces can be erected in a
variety of sizes, and the smaller sizes
can be obtained as complete units
ready to install on foundations. A
somewhat typical furnace, which has
been described in the literature, meas-
ures 6 feet by 3 feet by 10 feet deep.
That furnace is water jacketed and
has six tuyeres on each long side of
the furnace. The water-jacketed type
of construction has been most com-
mon. It has the advantage that a shell
of solidified slag forms on the water-
jacketed walls of the shaft to take the
place of refractories. The crucibles of
blast furnaces have ordinarily been
formed of basic refractories.
An article published in the Engi-
neering and Mining Journal describes
advantages for an unusual method of
constructing a blast furnace for
smelting copper scrap.536 It states that
the capacity for smelting a copper
scrap was increased from 35 to 100
TPD of charge material. At the same
time, coke consumption dropped from
25 to 10 percent of the charge. These
benefits resulted from inverting the
bosh of a blast furnace; that is, from
increasing rather than decreasing the
cross-sectional area of the furnace
shaft at the tuyere line. The lowest
grades of scrap, consisting of irony
brass, sweepings, ashes, skimmings,
residues, radiators, wire, grindings,
-------
Regulations concerning solid waste disposal 31
powders, cuttings, chips, and clad ma-
terials, were smelted in this furnace.
Blowers to supply the air blast and
pumps to furnish the cooling water
may be of the positive-displacement
or the centrifugal types. Ladles and
slag pots are needed to receive and to
convey the molten slag and metal
products. The gaseous products from
the tops of blast furnaces have con-
tained too much fume to be expelled
directly to the atmosphere; hence, the
top gas has been passed through bag
houses or scrubbing plants.
The use of blast furnances for sec-
ondary smelting has been confined
mostly to the treatment of materials
containing lead or copper. The rela-
tionship between reverberatory fur-
naces and blast furnaces in the smelt-
ing of battery plates and lead drosses
were discussed in connection with the
uses of reverberatory furnaces. Blast
furnaces have generally been em-
ployed for smelting the poorer grades
of copper-bearing scrap because the
process can reduce copper from its
oxides and it can produce copper
relatively free from contaminants.
The product from a copper blast
furnace, called black copper, how-
ever, contains small but objectionable
amounts of antimony, bismuth, tin,
lead, zinc, and nickel. Such material
requires electrolytic refining.
See also: Copper; Slag.
Distillation. Distillation has been
employed to reclaim metals having low
boiling points from scrap materials.
Several types of furnace have been in
general use, but their essential fea-
tures are similar. The larger furnaces,
for the distillation of scrap zinc, have
been refractory-lined chambers sur-
rounding bottle-shaped retorts made
of molded refractory materials.
Either gas or oil has been burned in
the furnaces to supply heat through
the walls of the retorts. Retorts usu-
ally hold about 4,000 pounds of scrap
which may be charged as solid or
molten metal.
Distilled zinc may be condensed to
a molten form or to zinc dust. A con-
denser consisting of a steel shell lined
with refractory has been used for pro-
ducing molten zinc. It is attached to
the retort and protrudes from the
furnace. The usual dimensions of a
condenser are about 8-foot length
and 3-foot diameter. The product is
withdrawn through a tap hole in the
condenser and cast into slabs for
marketing.
Unlined steel condensers have been
used to produce zinc dust. They may
be 8 feet long, 7 feet wide, and 14 feet
tall. The product from such condens-
ers has been screened to yield dust
containing 96 percent metallic zinc
with 96 percent of it as minus 325-
mesh particles.
Retort Furnaces. Retort furnaces
have been used to produce zinc metal
from zinc dross, zinc die castings, new
and old zinc scrap, and similar types
of scrap that contain mostly zinc.
Lower grades of materials and non-
metallic materials are preferably
processed at primary smelters. Re-
tort furnaces have been employed to
separate the more valuable metals
such as zinc, cadmium, and mercury,
from silver.
Slag Fuming. The process known as
"slag fuming" is a form of distilla-
tion because it utilizes the high vapor
pressure of metallic zinc at elevated
temperature. Initially, it was applied
to recover zinc as zinc oxide from
molten slag while slags were being
produced. The process was also used
to reclaim zinc from slags rejected to
waste dumps before the fuming proc-
ess was invented. It depends on the
reduction of the zinc compounds in
slag by reaction, either directly or in-
directly, with carbon injected into the
molten slag.
Pulverized coal suspended in air is
blown into the molten slag contained
in a rectangular furnace of water-
jacketed construction. The mixture of
coal and air is introduced through
tuyeres placed near the bottom of the
furnace. The method causes violent
turbulence of the slag bath. The coal
not only provides for reduction of the
zinc, but also for generation of heat.
The coal requirement has been about
20 percent of the weight of the slag;
about 2 hours of blowing time has
been required to eliminate the zinc
from a batch of slag. Slag quarried
from old dumps can be charged with
molten slag from smelting furnaces.
The ratio of cold slag to molten slag
and the ratio of coal to air has been
controlled to maintain the tempera-
ture in the furnace at about 2,200° F.
The mixture of zinc vapor and car-
bide monoxide expelled from the slag
bath is oxidized in the space above.
Then the gaseous mixture containing
zinc oxide passes through coolers and
bag filters. The product from the bag
filters has normally contained about
70 percent of zinc and about 8 percent
of lead. It is densified, and most of the
lead is expelled by heating in rotary
kilns at about 2,300° F. with additions
of about 2 percent of fine coke. This
treatment increases the density of the
zinc oxide from about 40 to 185 pounds
per cubic foot and provides a product
containing about 1 percent of lead.
Most of the zinc oxide produced by
slag fuming plants has been trans-
ported to electrolytic zinc plants for
recovery of the zinc as metallic zinc.
Hydrometallurgical processes. A
number of hydrometallurgical proc-
esses involving operations such as dis-
solution, precipitation, cementation,
filtration, and electrodeposition have
been employed in the recovery and
utilization of metals from scrap ma-
terials. In many cases the methods
are combinations of familiar steps
commonly used in separations for
chemical analysis. The combinations,
however, may be very complex, and
they must be varied to suit the specific
properties of the materials to be
treated and the types of products de-
sired. And in turn, the equipment for
conducting the operations must be
suited to those needs and to the re-
agents and other conditions of the
operations.
See also: Copper; Germanium; Pre-
cious Metals; Pyrite Cinder;
Uranium; Yttrium; Zinc.
REGULATIONS CONCERNING
SOLID WASTE DISPOSAL
(Based on August 1966 Survey)
In the August 1966 survey of the
State health departments, informa-
tion was requested concerning regu-
lations covering the disposal of solid
wastes. Information contained in the
following paragraphs was supplied.
In most States, the municipalities
or counties have the authority to op-
erate and control solid-waste activi-
ties. Ten* States did not have any
legal authority in the matter of solid
waste disposal, private or municipal.
The legal authority reported by 13t
States was based on general health or
nuisance laws and on water and air
pollution control laws. In Minnesota
and Texas permits must be obtained
from the water pollution control board
when areas adjacent to waters of the
state are used as waste disposal areas.
It was pointed out that in Montana
muds and sludges from mining are not
'Arizona, Colorado, Georgia, Hawaii,
Kansas, Maine, Missouri, Nevada, Wash-
ington, Wyoming.
t Alabama, Alaska, Arkansas, California,
Idaho, Minnesota, New Hampshire, North
Carolina, Ohio, Pennsylvania, Tennessee,
Texas, Utah.
-------
32 SOLID WASTE PROCESSING
a health hazard, so industries are left
to themselves to work out disposal
methods.
Depending on the situation, these
safeguards may be required in order
to obtain a permit in Minnesota: (1)
Diking around the site (assuming the
dike is sound); (2) diversion or con-
tainment of surface drainage; (3)
sealing of previous soil or rock forma-
tions; (4) covering- of dumped or
stored material to minimize erosion
and control drainage and storm-water
percolation; (5) regular supervision
and control of operations; and (6)
provision of an alternate site disposal.
The following were listed as being
subject to regulation because they are
potentially deleterious or detrimental
to public health: slaughterhouses,
rendering works, glue works, deposi-
tories of dead animals, tanneries,
wool-washing establishments, paper
mills, by-product coke ovens, dye
works, oil refineries, dairies, cream-
eries, cheese factories, milk stations
(Pennsylvania, Montana) and the
burning of cotton-gin wastes (Texas).
Only six States had specific legis-
lation providing authority for the
State health departments to conduct
a program for the control of the stor-
age, collection, and disposal of solid
wastes (Montana, Nebraska, New
York, Oregon, South Dakota, Texas).
In Texas this authority is specific for
refuse deposited within 300 yards of
a public highway. In Idaho legislation
of this type has been proposed.
No routine testing was reported by
any State for the detection of con-
tamination of water by solid wastes
deposited in spoil areas. It was indi-
cated that normally routine stream
surveys show whether pollution is oc-
curring. If problems develop, the tests
in Minnesota were generally highly
specialized, as required by the nature
of the problem. One State reported
that tests were run in the vicinity of
a spoil area used by an industry man-
ufacturing insecticides. Samples were
collected in test wells adjacent to the
burial area (Tennessee). Observa-
tional wells have also been required
before a permit was issued for an in-
dustrial waste disposal area (Texas).
Tests have also been made for radio-
active contamination of a wel> (Utah).
Water contamination, of course, is
of special interest. The survey of State
health departments revealed that a
number of solid industrial wastes have
contaminated State waters: (1) For-
est industry and lumbering wastes,
such as sawdust, bark, drainage from
log ponds, and slabs (Alaska, Idaho,
Minnesota, South Dakota); (2) runoff
from mining wastes subsequent to
leaching (Arizona, Nevada); (3)
mining wastes (Georgia, Idaho, Min-
nesota, South Dakota, Texas); (4)
pulp and paper sludge (Georgia,
Pennsylvania); (5) sulfur from
stockpiles (Minnesota); (6) calcium
hydroxide from the manufacture of
acetylene gas (Georgia); (7) potato-
processing wastes, such as culls, and
other potato wastes (Idaho); (8) ani-
mal carcasses (Idaho); (9) Meat-
packing and rendering wastes
(Texas); (10) metal refining wastes
(Nevada); (11) metal finishing
waste sludges (Pennsylvania); and
(12) feed lot wastes (Texas).
In Texas, to prevent water contami-
nation by feed lot wastes, facilities
were required that would retain all
runoff generated by a 2-inch rain from
a waste disposal area.
In response to a question concern-
ing the tests made to determine the
stability of solid industrial wastes
deposited in a spoil area it was re-
vealed that generally the tests used
to determine whether surface water or
groundwater is being contaminated by
solid industrial waste deposited in
spoil areas depend upon the nature
of the material deposited. Tests used
in Texas include color, turbidity, dis-
solved oxygen, biochemical oxygen
demand (BOD) , and both ammoniacal
and nitrate nitrogen. In addition,
samples were analyzed for organic
content by chromatography.
Current activities reported by stater
responding to the questionnaire in-
cluded the following:
The Arkansas State Pollution Con-
trol Commission was designated the
State agency for reviewing solid waste
grant applications. No staff had as
yet been obtained.
In California a statewide inventory
was being made of sources, quantities,
methods of disposal, etc., of all types
of solid wastes.
In Idaho a planning grant had been
obtained to study the solid waste prob-
lem, including solid industrial wastes.
Also in Idaho, a regulation providing
for State authority for control of ref-
use disposal had been proposed.
In Rhode Island in July 1966 a solid
waste disposal program was estab-
lished in the Division of Environ-
mental Health. One of the main ob-
jectives of the new program was to
determine the adequacy or inadequacy
of existing solid waste disposal prac-
tices and the need for additional regu-
lations for the enforcement of an
acceptable statewide solids disposal
program. No full-time personnel were
working with industries or munici-
palities to help them with solid waste
problems.
In Maine, the Division of Sanitary
Engineering was gathering data with
which to develop a statewide compre-
hensive plan for solid waste disposal.
Municipal solid waste disposal was
being studied. Solid industrial wastes
might be studied at a later date.
A bill to give the Ohio State Health
Department authority to regulate
solid wastes was scheduled for intro-
duction into the next session of the
legislature. Ohio had obtained a grant
under the Solid Waste Act (P.L. 89-
272) for a survey of and statewide
planning for solid waste disposal.
-------
Major Waste Categories
Acetylene Wastes
Agricultural Wastes
Aluminum
Animal-Product Residues
Antimony
Asbestos
Ash, Cinders, Flue Dust, Fly Ash
Asphalt
Bagasse
Bauxite Residue
Beryllium
Bismuth
Brass
Brewing, Distilling, Fermenting
Wastes
Brick Plant Waste
Bronze
Cadmium
Calcium
Carbides
Carbonaceous Shales
Chemical Wastes
Chromium
Cinders
Coal
Cobalt
Coffee
Coke-Oven Gas
Copper
Cotton
Dairy Wastes
Diamond Grinding Wheel Dust
Distilling Wastes
Electroplating Residues
Fermenting Wastes
Fish
Flue Dust
Fluorine
Fly Ash
Food-Processing Wastes
Foundry Wastes
Fruit Wastes
Furniture
Germanium
Glass
Glass Wool
Gypsum
Hemp
Hydrogen Fluoride
Inorganic Residues
Iron
Lead
Leather Fabricating and Tannery
Wastes
Leaves
Lime
Magnesium
Manganese
Mica
Mineral Wool
Molasses
Molybdenum
Municipal Wastes
Nonferrous Scrap
Nuts
Nylon
Organic Wastes
Paint
Paper
Petroleum Residues
Photographic Paper
Pickle Liquor
Plastic
Poppy
Pottery Wastes
Precious Metals
Pulp and Paper
Pyrite Cinders and Tailings
Refractory
Refrigerators
Rice
Rubber
Sal Skimmings
Sand
Seafood
Shingles
Sisal
Slag
Sodium
Starch
Stone Spalls
Sugar Beets
Sugar Cane
Sulfur
Tantalum
Tetraethyllead
Textiles
Tin
Titanium
Tobacco
Tungsten
Uranium
Vanadium
Vegetable Wastes
Wastepaper
Wood Wastes
Wool
Yttrium
Zinc
Zircaloy
Zirconium
33
-------
34 SOLID WASTE PROCESSING
ACETYLENE WASTES
Acetylene wastes have been cal-
cined and carbide made from the re-
covered lime. One plant was reported
as having a capacity of 330 TPD.180
AGRICULTURAL WASTES
See also: Animal-Product Resi-
dues; Bagasse; Pood-Processing
Wastes; Fruit Wastes; Nuts;
Slag; Sugar Beets; Vegetable
Wastes; Wood Wastes; Refer-
ences 18, 21, 46, 47, 103, 156, 252,
279, 285, 300, 308, 315, 331, 341,
367, 395, 406, 437, 460, 473, 486,
490.
EXTRACTION
Carotene has been extracted from
certain leaf meals for use as a feed
supplement.513
HYDROLYSIS
The Soviet Union hydrolytic indus-
try has produced large quantities of
ethyl alcohol, 2-furaldehyde, carbon
dioxide, acetic acid, activated char-
coal coal, vanillin, trioxyglutaric acid
and glucose from, wood and agricul-
tural residues.240 The products and by-
products of agrarian residues were
surveyed in 1956 by Wilder and Hir-
zel"4 and in 1952 by Goethals.166 A
continuous process for hydrolysis of
wood and agricultural wastes was de-
scribed by Desforges in 1952.104
The nature of reaction products
from hydrolysis of cellulosic wastes
was described by Heinemann.183 The
waste materials from hydrolysis can
be used as a humectant in agricul-
ture w and as f ertilizer.197 '
The hemicelluloses that occur in as-
sociation with cellulose have been
used for large-scale production of fur-
fural. They are hydrolyzed by sulfuric
acid, which then dehydrates the liber-
ated pentoses to form furfural. Corn
stalks, flax wastes, sunflower stalks,
fruit seeds or pits, bagasse, peach gum,
nut shells, reeds, olive husks, and
corn cobs are examples of residues
that can be hydrolyzed to produce
furfural44< 71> 78> 79r 313' 155> M7> 158> 212> 223> 270'
271, 339, 344, 385, 488
The swelling rate of plant waste and
its influence on the yield of furfural
has been reported.405 Acetic acid as a
by-product of furfural production has
been reported.3" The residue from fur-
fural production from sal bark, areca
(palm) nut husks, and coconut shells,
has been used as a filler for phenolic
plastics.316 Furfural can be readily con-
verted to furan, tetrahydrofuran, hex-
amethylenediamine, and adipic acid
for the synthesis of nylon; or to di-
chlorobutane, adiponitrile, E-amino
capronitrile, and caprolactam for the
synthesis of Perlon. Furan as the
starting material for polyamide, poly-
urethane, alkyd and Buna-type resins,
and rubber has been discussed.96 Steps
for the preparation of nylon from fur-
fural are given by Voss.m Use of plant
residues in the manufacture of plas-
tics has been reviewed.961'436
Alkaline digestion of the stems of
rye and reed softens tissues to improve
assimilability by ruminant animals.
ALUMINUM
See also: Recovery and Utilization;
Reference 148.
SMELTER RESIDUES
Residues from aluminum smelting
operations (drosses) are treated by
a crushing-grinding-screening-classi-
flcation operation for the recovery of
the contained metallic aluminum.
This aluminum is in the form of prills,
shot, large spill splatters, etc., and is
intimately mixed with or coated by
slag. The aluminum metal, being mal-
leable, resists crushing or grinding,
whereas the slag is very fragile and
breaks up easily. Consequently, this
waste material is amenable to a dif-
ferential crushing-grinding operation
using screens or air classification
equipment to effect the separation.
Hammermills are normally used for
disintegration. Ball mills have been
employed, but they tend to beat small
particles of slag into the malleable
aluminum. Any of the usual vibrating
or shaking-type screens are suitable,
as well as the normal type of air
classifiers. The waste or dross treated
will contain some 20 to 30 percent
metallic aluminum. The product for
return to furnaces should contain
from 60 to 70 percent aluminum.
Dusting is a problem in that up to
10 percent of the feed may eventually
be dust. In addition, because of the
friable nature of the slag, about 50
percent of the feed may finally be a
relatively fine-size fraction (minus 20
mesh), which is not considered treat-
able because of the fine dissemination
of the aluminum in the slag.
The beneficiation process is simple
and reliable. It is relatively inexpen-
sive, but no specific cost data were
available. The recovered aluminum is
generally melted in reverberatory-
type furnaces, cast into pigs, and sold
to consumers of metallic aluminum.
It has not been feasible to remove
metallic contaminants, except magne-
sium, from molten aluminum scrap
materials. Therefore, the producers of
aluminum ingots from scrap have had
to make salable products without
benefit of refining. This has meant
that the scrap could not contain ex-
cessive contaminants. Alloying metals
may be added, however, to bring the
composition of the product to specifi-
cations, or the contaminants may be
diluted to acceptable levels by addi-
tions of purer metals or alloys.
See also: Recovery and Utilization;
Reference 233.
ALUMINUM TURNINGS
Morken presented a comprehensive
discussion of problems connected with
the preliminary treatment of oily
aluminum turnings.3" The turnings or
chips considered were produced at the
rate of about 20,000 pounds per day by
machining operations in an automo-
bile plant. They contained about 21
percent of liquids present as oil and
water. About 0.30 percent of uncom-
bihed iron, evidently abraded from
cutting tools, was present as very fine
particles adhering to the oily alumi-
num chips. It was imperative to re-
move the iron because the reclaimed
aluminum was to be used for pistons.
Morken wrote that magnetic sepa-
ration appeared to be the best method
for removing the iron, but that this
would require dried chips. The most
economical and satisfactory procedure
for drying oily chips appeared to be
by use of a rotary kiln, directly fired
with gas. The method in which heat
input was controlled to vaporize rather
than burn the oil minimized oxidation
of the aluminum but caused much
smoke. It was believed that, in addi-
tion to the smoke nuisance, the
method of heating presented a severe
explosion hazard. A number of experi-
ments were conducted to remove oil by
means other than heating. None of
the experiments was satisfactory, ac-
cording to Morken.
Eventually, Morken and his asso-
ciates returned to thermal removal
of the oil. It was learned that the
drum-type dryer could be used without
nuisance or hazard, provided the
amount of oil on the chips was held
reasonably constant. A process was
developed in which centrifugal sepa-
rators were used to remove oil to a
content of 2.1 to 2.3 percent. This was
done by flushing the chips in a
centrifuging basket with cold water
and then admitting 90-psi steam for
about 2 minutes.
The flow of aluminum chips
through the reclaiming facilities was
described by Morken as follows. The
incoming oily chips were received in
skid boxes, which were dumped into
a conveyor system containing mag-
netic separators to remove tramp
-------
iron. The conveyor deposited the
chips in a surge hopper, which fed
two centrifugal separators. After cen-
trifuging, the chips were conveyed
pneumatically to the drum dryer.
The dryer discharged into a bucket
conveyor, which fed a double-deck
vibrating screen. This screen removed
particles less than 30 mesh in size
because it was considered uneconomi-
cal to recover this fine material. The
screen oversize was discharged onto
a magnetic separator from whence
the cleaned chips were conveyed to
melting furnaces.
Evidently, considerable thought and
experimentation was required to de-
vise the successful process for the
preparation of aluminum scrap out-
lined in the foregoing paragraph. It
is interesting that the solution came
from the judicious selection of a
proper combination of well-known
types of equipment and machinery.
See also: Separation.
REVERBERATORY FURNACES
Reverberatory furnaces have been
preferred for melting aluminum
scrap. Ordinarily a layer of flux has
been used to protect the surface of
the molten aluminum from oxidation.
The flux may consist of sodium chlo-
ride, potassium chloride, and cryolite.
Calcium chloride and sodium fluoride
also might be used. Chlorine gas may
be bubbled through the molten bath
to combine with magnesium if it is
necessary to eliminate that element.
Nitrogen is introduced as a refining
agent to expel dross and oxides from
the metallic baths of aluminum.
See also: Recovery and Utilization.
DRYING
A rather common preparatory
treatment is simple drying. It fre-
quently is necessary to expel moisture
from scrap metals to guard against
explosions from contact with hot ma-
terials in furnaces. Conventional dry-
ers, which are fired directly with the
most available fuel, are used for dry-
ing scrap materials.
EXTRACTION
Furnace wastes from the manufac-
ture of aluminum are extracted to re-
cover fluorine, sodium, and aluminum
compounds.123' "°
MAGNETIC SEPARATION
Morken also described how the
piston foundry of the Chrysler Cor-
poration recovered aluminum metal
from oily aluminum turnings by mag-
netic separation and screening.310 The
aluminum recovered was eventually
melted, cast into ingots, and recycled
to the foundry. The quantity of alu-
minum recycled was sufficient to pro-
vide about 60 percent of the metal re-
quired by the foundry for piston
manufacture.
Chapman has described how the
Duke Power Company of Charlotte,
North Carolina, employed magnetic
separation to recover aluminum metal
from strands of steel and aluminum
wire.70
See also: Separation.
SINTERING
Fe-Si-Al-Ti alloys were produced
from red mud from aluminum oxide
preparation in an arc furnace.179
ANIMAL-PRODUCT RESIDUES
Several industries including soap,
leather, glue, gelatin, and animal
feed manufacture, have been based
on meatpacking waste products. Bio-
chemicals have also been produced
from packinghouse residues. Freezing
these wastes has largely overcome
shipping and storage problems.
EXTRACTION
Biochemicals extracted from pack-
ing house materials include hor-
mones, vitamins, enzymes, liver prod-
ucts, bile acids, sterols, feed supple-
ments, and glandular products.
Glands and organs have been col-
lected and preserved by freezing until
shipment lots accumulated.623 Curing,
evaporation, and extraction are in-
volved in coverting the collagen in
hide trimmings, tannery fleshings,
etc., to gelatin and glue. Tallow has
been produced by extraction of tank-
age.263
HYDROLYSIS
Hydrolyzates of materials of ani-
mal origin such as feathers, fish meal,
meat, and fish residue can be used
as animal feed ingredients.187 The
Twitchell method has commonly been
used to obtain fatty acids and glycer-
ine from fats by hydrolysis. A plant
near Chicago has been reported to
process 100 million pounds of fats and
oils per year by this method.2"
MECHANICAL SEPARATION
Inedible slaughterhouse materials
have been passed through a grinding
machine to a heating device, a cook-
ing vessel, and a centrifuge to recover
fat, meat, and bone scrap.2*1
MELTING
Bones have been auitoclaved and
Ash, cinders, flue dust, fly ash 35
treated with steam in the absence of
oxygen. The proteins and fats ob-
tained were separated and the
purification completed by vacuum
distillation.178
PYROLYSIS
Fuels and solvents can be manufac-
tured by pyrolysis of waste products
from the fat and vegetable-oil in-
dustries.595
ANTIMONY
See: Lead.
ASBESTOS
See: Plastic; Reference 284.
CALCINATION
Silica refractories are obtained by
calcining asbestos waste and raw
magnesite.433
INCINERATION
Asbestos wastes plus clay and bind-
ers are cast in plastic and fired to
produce porous ceramics.-86
ASH, CINDERS, FLUE DUST,
FLY ASH
Fly ash has been described as a
finely divided, powdery, man-made
pozzolan composed of spheres of
amorphous silica and alumina.631 Ac-
cording to Russel, 8.25 million tons of
it were produced in the United States
in 1956 by pulverized-coal-fired boil-
ers.387 He further indicated that the
annual domestic production of fly ash
has been increasing since 1953 and
could go as high as 16.8 million tons
per year. Chemicals contained in coal
ash include: cobalt, nickel, molybde-
num, chromium, vanadium, tin, zinc,
lead, arsenic, gold, platinum, pal-
ladium, silver, beryllium, gallium, lan-
thanum, silicon, aluminum, iron,
manganese, magnesium, calcium,
phosphorus, sodium, and potassium.
Approximately 1 gram of gold per
ton is found in coal ash, but this is
not an economic source because the
chemical processing problems involved
in recovery are extremely complex.
The problems of enrichment and iso-
lation of the separate chemicals have
not been solved successfully.
Dumping is the easiest and most
economical way of disposing of fly
ash, but even dumping costs $1.00 per
ton or $16 million per year, most of
this to the utility companies.
Industry has found that not only is
the disposal of fly ash expensive, but
the areas available for its disposal are
becoming scarce. Fly-ash disposal is
a particularly annoying problem of
major importance to the electric
power plants that burn pulverized
-------
36 SOLID WASTE PROCESSING
coal, since it is not uncommon for a
single utility system to produce as
much as a million tons of fly ash per
year. The electric-power industry
realizes that the solution to this prob-
lem lies in the large-scale utilization
of the ash.
Most of the fly ash not disposed of
by landfllling has been utilized di-
rectly without being processed. The
following are some of the ways In
which fly ash has been utilized: (1) In
Portland cement; (2) in mass struc-
tural concrete; (3) in masonry cinder
and concrete building blocks; (4) in
lightweight aggregate; (5) as a road-
base choking material for highway
construction; (6) as a filler for bitu-
minous mix; (7) as a filler material in
roofing and putty; (8) as a soil con-
ditioner; (9) as a soil stabilizer; (10)
in oil-well grouting; (11) as a sand
substitute in sand blasting; (12) as a
metal-polishing agent and mild abra-
sive; and (13) as a filtering medium.
Recent research to improve knowl-
edge of the characteristics and prop-
erties of fly ash has been described by
Snyder.419' "»
See also: Incineration; Inorganic
Residues; Reference 506.
COLLECTION
Katz stated that the various types of
cyclone collectors are suitable for the
collection of particles that are usually
larger than from 5 to 10 microns in
projected-area diameter.227 Such col-
lectors have been applied in series with
the electrostatic precipitator, especial-
ly where large particles of carbon or
grit predominate in the effluent gases.
The installation of a cyclone im-
mediately following the electrostatic
precipitator would improve the over-
all collection efficiency of a system
troubled by the severe reentrainment
of highly conductive ash that agglom-
erates upon passing through the
precipitator.
Katz indicated that the effective
collection of fly ash by electrostatic
precipitation depends primarily upon
the electrical power input to the pre-
cipitator. The optimum power char-
acteristics of the precipitator are
determined by the electrical resistiv-
ity of the fly ash. This in turn is de-
pendent upon the sulfur content of the
coal burned in the plant, the tempera-
ture of the effluent gas, and the car-
bonaceous content of the fly ash. He
stated that, "it is conceivable that by
altering the coal burned, flue gas tem-
perature, or the particle size distribu-
tion of the pulverizers, the plant op-
erator could correct a sub-normal
collector performance".
Magnus described the collection of
fly ash at the South Charleston, West
Virginia, power plant of the Chemicals
Division of the Union Carbide Cor-
poration.272 The fly ash produced by
the coal-fired boilers of this plant was
collected by electrostatic precipitators
at the rate of 328,000 pounds per day.
About 36,850 pounds of fly ash were
released daily to the atmosphere by
the precipitators.
The problem of maintaining high
collection efficiencies developed soon
after the precipitators had been in-
stalled at the plant. The gas flow rate
eventually proved to be the critical
factor that had affected the achieve-
ment of the desired collection effi-
ciency. It was also found that changes
in the characteristics of the coal
burned by the plant had a direct effect
upon the operation of the precipita-
tors. The plant has, however, been able
to achieve precipitator collection ef-
ficiencies ranging from 93.2 to 95.7
percent.
TREATMENT
A process for the recovery of ferro-
pozzolan and a fine purified pozzolan
from fly ash by magnetic separation,
air classification, and screening has
been described in Power.531 Fly ash
was treated in a Roto-Plux magnetic
separator by sieves, air separators, a
battery of magnetized coils, and a
conveyor belt to produce magnetic
ferropozzolan, coarse purified poz-
zolan, and fine purified pozzolan. The
separator could process 10 tons of fly
ash per hour to produce a ferropoz-
zolan containing from 50 to 70 per-
cent of the iron oxide content of the
original ash. Ferropozzolan has been
employed as a heavy-medium ma-
terial in heavy-medium separations
and as a constituent of ferral cement
for the manufacture of special dense
mortars and concretes. The chief
product of the separation is purified
pozzolan, a high-strength product
that is offered on the market on a
certified quality-controlled basis. The
Roto-Flux separator requires little
space and costs about $15,000.
DISPOSAL WITH SEWAGE SLUDGE
Investigation of the possibility of
disposing of fly ash with sewage
sludge has shown that the material
will dry to a nondusting mass requir-
ing less disposal space than when the
two are disposed of separately. Fly
ash can also enhance the filtration of
sludge.
ACIDIFICATION
The adsorption capacity of fly
ash3" and brown coal ashira is in-
creased by treating these ashes with
hydrochloric acid.
INCINERATION
By burning a mixture of coal ash
with lime and sand, a binding ma-
terial can be obtained that is similar
to Portland cement.372
ION EXCHANGE
Of three media—ion-exchange res-
ins, cinders, and light ashes—light
ashes are reported as giving the best
removal of phenol from phenolic
wastes. They decolorize the wastes as
well.320
MELTING
Coal ashes, limestone, coal, and
Fe2O3 have been melted to form
2Fe*SiC>2. The calcium aluminate slag
has then been leached. The residue,
after the addition of limestone, can
be used in the manufacture of iron
cement.234
SINTERING
Fly ash from a Long Island power
station has been sintered and used as
lightweight aggregate in cement.476 M2
Germany also had a plant for mak-
ing products from fly ash.203 Blast fur-
nace flue dust has been sintered and
returned to the blast furnaces for
smelting.181
VAPORIZATION
Flue dusts from the production of
copper, zinc, and manganese have
been processed for the recovery of
arsenic and bismuth. In this process
the dust is roasted, and the arsenic
given off as a fume is condensed.85
ASPHALT
See: Reference 308.
BAGASSE
Bagasse is the fibrous residue that
remains after the sugar juice has been
pressed from sugar cane. It consists
of about 30 percent pith, 10 percent
water-soluble materials, and 60 per-
cent good-quality fibers that range
in length from 1.5 to 1.7 mm. These
fibers are normally pulped following
their separation from the nonfibrous
pith cells, dirt, finely divided bagasse
fibers, and weeds.
Bagasse is separated into fractions
for applications that range from use
as feedstuff to use as a raw material
for high - grade - paper processing.
When utilization schemes are not
feasible, residues can often be burned
-------
Bauxite residue 37
Sugar mill bagasse
To pulp
mill
Tramp iron
Pith to sugar mill
boilers
Baled bagasse
to storage
FIGURE 6. Depithing of bagasse.
to recover their fuel value. Charcoal
and activated carbon can also be ob-
tained from many of these materials.
Bagasse has frequently been burned
as a fuel to produce steam required by
the sugar mill for both power and
processing. However, the pulp and pa-
per industry has found that bagasse
fibers are quite suitable for the pro-
duction of insulation board, particle
board, and almost any type of paper,
ranging from bleached fine-quality
writing and printing papers to un-
bleached wrapping papers and news-
print. The first pulp and paper mill
to utilize bagasse as a raw material
has been in operation for over 20
years. The construction of other mills
was impeded for a time, however, by
various technical difficulties. The de-
velopment of new techniques about 10
years ago was soon followed by the
construction of over 30 bagasse pulp
mills throughout the world.
An annotated bibliography prepared
by West describes the utilization of
bagasse for paper, board, plastics, and
chemicals.480 Bagasse utilization has
been summarized in three papers.64'2S1'
484
See also: References 18, 22, 24, 42,
55, 78, 88, 92, 107, 155, 198-201,
212, 214, 253, 254, 266, 271, 283,
290, 299, 301, 302, 325, 401, 411,
443, 486, 488, 539.
DEPITHING
Bagasse fiber is usually prepared
for paper pulping in a depithing sta-
tion (Figure 6). Tramp iron entering
the depithing station with the bagasse
is first removed by a magnetic separa-
tor. Most of the pith is then sepa-
rated from the bagasse fiber in a
Horkel depithing mill. In this mill, the
bagasse is first shredded by hammer-
mills and then screened into separate
fractions of pith and fiber. The sepa-
ration is not a clean one, for the fiber
still contains about one-third of the
pith initially charged to the mill. A
portion of the depithed fiber is
shipped directly to the pulp mill for
subsequent wet depithing and pulping
with dilute caustic soda, while the re-
maining fiber is usually baled and
stored for future use. The pith sepa-
rated by the Horkel mill is returned
to the sugar mill, where it is burned
in the boilers as fuel. It is either trans-
ferred to the boilers by conveyors and
bucket elevators or by blowers and
cyclones. The bagasse and the de-
pithed fiber are removed through the
depithing station with conveyors.
HYDROLYSIS
Pulp for viscose rayon is produced
by hydrolysis of bagasse.
See also: Agricultural Wastes;
Vegetable Wastes; Reference 275.
INCINERATION
Whole bagasse is normally burned
at 45 to 50 percent moisture in boilers
having special furnaces. Steam is
generated at between 100 and 150 psi.
Oven-dry bagasse has a calorific value
of about 8,200 Btu per pound. Bagasse
with 50 percent moisture has a gross
heating value of about 4,400 Btu per
pound. An average of 1.2 tons of ba-
gasse (moisture-free basis) is pro-
duced for each ton of cane sugar
output.100' *"• *87
NITRATION
Nitrolignin is obtained from bagasse
by nitration and digestion of the
product.2"
OXIDATION
A mixture of bagasse and coke is
used in the reduction of nickelif erous
serpentine.32
POLYMERIZATION
A plastic molding material called
Valite has been produced by polymer-
izing aldehyde and ketone products of
bagasse with phenol.84
SCREENING
The recovery of fiber from bagasse
by screening has been mentioned by
Martinez in connection with the utili-
zation of bagasse for the manufac-
ture of paper by the pulp and paper
industry.283
BAUXITE RESIDUE
A mixture of bauxite residue and
fuel that has been pelletized and sin-
tered has been used as lightweight
aggregate.322
-------
38 SOLID WASTE PROCESSING
BERYLLIUM
An electrolytic refining process is
used to produce beryllium from scrap
at Beryllium Metals & Chemical
Corporation.508
BISMUTH
See: Lead.
BRASS
See: Copper; Foundry Wastes; Ref-
erence 390.
BREWING, DISTILLING, PER-
MENTING WASTES
The brewing, distilling, and fermen-
tation industries are concerned with
the production of alcoholic beverages,
Pharmaceuticals, and a limited num-
ber of organic chemicals. The princi-
pal solid waste from distilleries is
stillage, the residual grain mash from
distillation columns. In 1964, 630,000
tons were utilized. This material is re-
covered almost completely by the in-
dustry for animal feed or for conver-
sion to chemical products. It has been
reported that 85 percent of the stil-
lage is recovered as dried feeds, 14
percent as wet feed, and only 1 per-
cent is lost.
Some chemicals have been recov-
ered from fermentation broths.
Among them are d-lactone and 1-lac-
tone following calcium pantothenate
production, vitamins and amino acids
from fermentation wastes, bacitracin
and amino acids from distillers' solu-
bles, tartaric acid from wine residues,
nicotinic acid from vitamin wastes,
and glycerol from alcohol stillage.
See also: Food-Processing Wastes;
Molasses.
CARBONIZATION
The ash of distillers' dried solubles
has growth-stimulation properties ac-
cording to Dannenburg.93
EVAPORATION
Brewery wastes have been eva-
porated and the residue used as feed.312
EXTRACTION
Tartrates, tannins, vitamin P-like
compounds, potash, acetic acid, and
other compounds have been produced
from winery wastes.484 Proteins are
extracted from brewery residues and
converted to plastics.*18
HYDROLYSIS
Hydrolyzates from distillery sludge
are sources of edible protein, deficient
only in tryptophan and methionine.366
INCINERATION
Potash has been recovered by in-
cineration of fermentation wastes.3'3
SCREENING
Spent grains after fermentation are
almost universally removed on fine
screens and are processed for use as
cattle food. Eight to 10 pounds of this
material can be recovered per bushel
of grain processed. This by-product is
an essential part of the industry's
overall economy.
BRICK PLANT WASTE
INCINERATION
Brick-plant waste has been burned
and exploded and used as building
material.337
MELTING
Scrap brick, slag, and other indus-
trial wastes can be melted and used
to produce mineral wool.348 403
BRONZE
See: Copper.
CADMIUM
See: Reference 249.
CALCIUM
See also: Lead.
COMBINATION AND ADDITION
Calcium sulfate sludge formed, in
the course of various manufacturing
processes (e.g., from the working of
potash salts, from the neutralization
with lime of the sulfuric acid spin-
ning solutions of the rayon industry,
and in the manufacture of phosphoric
acid from phosphates) can be simul-
taneously utilized with the ammonia-
cal liquors of cokeries and carbon di-
oxide to produce ammonium sul-
fate.203
CALCINATION
Modern (1949) methods for recal-
cining waste calcium carbonate have
been surveyed by Knibbs and Gee.234
DISPLACEMENT
Silicon carbide has been prepared
by extracting the calcium hydroxide
from the furnace sediment formed
during the manufacture of calcium
carbide, mixing the remainder with
carbon, and heating the mixture in an
electric furnace.220
CARBIDES
Tungsten and cobalt have been re-
covered from scrap sintered carbides.
The metals are oxidized with sodium
nitrite as the first step in the recovery
process.61
See also: Lead.
CARBONACEOUS SHALES
Humic fertilizer has been obtained
from carbonaceous shales by nitra-
tion and chlorination.229
CHEMICAL WASTES
Chemical manufacturing plants
produce solid wastes that are extreme-
ly varied in nature. Many toxic chem-
icals (e.g., phenol) can be destroyed
by incineration. Occasionally, solid
wastes from chemical plants can be
utilized in some fashion, e.g., use of
waste tar from alcohol preparation for
a bitumen-type binder.
See also: Inorganic Residues.
CHEMICAL OXIDATION
A bitumen-type binder has been
produced by oxidation of the waste
tar from the preparation of synthetic
alcohol.124
DILUTION
Effluent residues from conversion
of paraffins into fatty acids can be
diluted and used as a base for foundry
binder.37
DISTILLATION
Most solvents can be reclaimed by
distillation.50'm Light oil and solvent
can be obtained by distillation of spent
straw oil from coke production.60
INCINERATION
Poisonous sediments and solutions
containing phenols, waste oils, and
the like can be destroyed by oil-
gasification burners with special
injectors, even when the moisture con-
tent is high or fluctuating.481 Solid
cyanide has been incinerated using
waste solvent as fuel.172 The incinera-
tion of solid wastes from tank-car
cleaning has been described.173
Dow has a $2.25 million incineration
plant that handles 81 million Btu/hr
of liquid wastes and 60 million Btu per
hour of solid wastes. Materials dis-
posed of include 400,000 gallons per
month of liquid still residues, washes,
slurries, and other contaminated
liquid products, 1700 drums and other
containers of semiliquid and solid
wastes per month; 17,000 cubic yards
per month of other refuse, including
large amounts of plastics.637
Lederle has incinerated rubbish,
garbage, and valueless by-products
from plant operations and sludges
from sewage and waste-treatment op-
erations. Iron, glass, and other non-
combustibles have been removed by
hand sorting.171
Industrial wastes have been incin-
erated at the Badische Anilin-Soda
Fabrik plant.144
At Kodak Park, trash, waste sol-
-------
vents, oils, and various solid and liquid
chemicals have been burned in an in-
cinerator.283
Three wastes that have been in-
cinerated even though auxiliary fuel
is required for their combustion are a
carbon waste slurry, a highly colored
TNT waste, and a gas containing hy-
drogen sulfide.69
NEUTRALIZATION
Tailings in the production of hy-
drofluoric acid can be dry neutralized
with calcium carbonate and used as
an additive to control the setting of
cements.72
CHROMIUM
Heating sludges containing chro-
mium above 200° C. causes the chro-
mium to convert to the poisonous
chromate form.370
CINDERS
See: Ash, Cinders, Flue Dust and
Ply Ash; Pyrite Cinders and
Tailings.
COAL
See also: Lime; Reference 331.
CALCINATION
The carbonaceous pyrite in the resi-
due from calcining wastes from grad-
ing of coal can be used to produce sul-
furic acid.472 Calcined wastes from, coal
mines can be used in the preparation
of cement.321
DEHYDRATION
Charcoal of high discoloration
power can be obtained from lignite
by dehydration with sulfuric acid.73
INCINERATION
Coal washery refuse has been
burned and used in the manufacture
of concrete.119'*»•213 Carbon sludge
from partial oxidation of fuel is dis-
posed of by spraying it into a furnace
for burning.88
MECHANICAL SEPARATION
There has been increased interest
in reclaiming fine coals from coal
processing waste waters. Both flota-
tion techniques and use of cyclones
and centrifuges appear to have merit
for this purpose.
SINTERING
Disposal of tailings from coal proc-
essing is made easier by installing
shaft furnaces in which dewatered
material is dried and partially sin-
tered.141 The sinter can be crushed,
mixed with Portland cement, and used
as a building material.106'2M The manu-
facture of light concrete aggregate by
the suction sintering process has been
described.538 Bubble, slag sand, boiler
ash, coal dump heat, fly ash, and clay
can be utilized in this manner.298 Sin-
tered coal refuse can also be reworked
to fibers, yam, or wool.105 The indus-
trial significance of the elements in
coal ash have been described by
Headlee.181
COBALT
Wastes of cobalt xanthate contain-
ing cobalt, copper, and zinc have been
sintered to recover these metals.265
See also: Lead; Pyrite Cinders and
Tailings; Zinc; Reference 61.
COFFEE
Coffee grounds have been extract-
ed to obtain oils, fats, waxes, and
resins.33
COKE-OVEN GAS
See: Pickle Liquor.
COPPER
See also: Recovery and Utilization;
Cobalt; Inorganic Residues;
Lead; Pyrite Cinders and Tail-
ings; Zinc; References 32, 66, 426.
BLAST FURNACES
The blast furnace has been used
for melting copper scrap, the copper
afterwards being refined in adjacent
reverberatory furnaces.509' 51°
CHEMICAL REDUCTION
Slags from copper smelters have
been reprocessed into building ma-
terials by blowing air and carbon
dioxide through the slag in the elec-
tric furnace and feeding lime and a
solid reducing agent onto the surface
of the slag.111
HYDROMETALLURGICAL PROCESS-
ING
A process for producing copper tub-
ing from scrap copper by a three-step
procedure is described in Iron Age.'™
The copper scrap is leached in am-
monium carbonate with aeration.
After purification, the solution is
treated at 325 P with hydrogen in
an autoclave to precipitate copper
powder. The powder is filtered from
the solution and dried in an inert
atmosphere, after which it is screened
to yield closely controlled particle
sizes for extrusion into copper tubing.
Similar techniques for dissolution in
ammonium salts have been employed
to reclaim copper from copper-clad
steel and items such as small motors
Reverberatory furnaces 39
and generators. The residual iron can
then be consumed in iron or steel
making.
MELTING
A process has been developed to
produce steel from copper slag. The
slag piles at Anaconda, Montana, and
Clarkdale, Arizona, have amounted to
40 and 30 million tons, respectively.
About 3 tons of slag are required to
produce 1 ton of steel.140 Three plants
were being erected to recover iron
from copper slag. It was also planned
to recover copper from the slag.4™'5el
PRECIPITATION
Copper has been recovered from
copper-bearing waste solutions by
precipitation on iron.305
REVERBERATORY FURNACES
Reverberatory furnaces are used for
melting, refining, and alloying cop-
per, brass, and bronze scrap metals.
The intent in processing these types
of scrap is to sort the types so that
marketable copper or alloys of cop-
per can be produced with a minimum
of refining, a minimum loss of alloy-
ing metals, and a maximum utiliza-
tion of alloying metals from scrap
sources. Preparatory operations, such
as magnetic separation, drying, and
baling frequently are required prior
to furnace treatments.
A charge of copper-bearing scrap is
first melted and then stirred and sam-
pled for chemical analysis. The chem-
ical analysis dictates the refining
steps, which normally consist of flux-
ing, oxidation, and slagging. Suitable
mixtures of limestone, silica, and iron
oxides are added as fluxes to combine
with oxides of metals so that those
oxides may be removed from the fur-
nace. In fact, oxidation of contami-
nating metals is induced by blowing
air through iron pipes into the melt.
It is frequently necessary to sample
and analyze the metal again after the
fluxing and refining operations. And
finally, if the product is brass or
bronze, additions of zinc, tin, or other
alloying metals may be made to bring
the product to specifications.
The slag from an operation of this
kind is skimmed into pots and allowed
to solidify. The slag generally contains
enough copper to warrant reworking.
This might be done by smelting it in a
blast furnace. Alternatively, the slag
from a reverberatory furnace might
be crushed to liberate shots of metal
from the mass of earthy material. The
shots may be recovered by screening
or by other physical methods. The
final residual slag may or may not
contain sufficient copper or other
-------
40 SOLID WASTE PROCESSING
metal compounds to justify smelting
to reduce those compounds to metals
incident to their recovery.
SMELTING
Some copper and copper-base scrap
has been smelted in primary smelters
for the purpose of reclaiming only
the copper. With this type of smelt-
ing, most or all of the alloying metals
such as zinc and tin, are wasted. On
the contrary, the brass and bronze
ingot makers who treat scrap ma-
terials have endeavored to retain all
of the valuable alloying metals, as well
as the copper, from the scrap because
bronze scrap ordinarily is purchased
on the basis of the copper and tin
contents of the scrap.
Reclamation of all of the metals in
copper-base alloys is an apparent ad-
vantage in favor of secondary smelt-
ers. That advantage can be realized
best if the scrap materials are sorted
into types that can be made directly
into saleable grades of ingots. If the
scrap material contains undesirable
contaminants, expensive refining op-
erations are required, or the contami-
nants must be diluted to tolerable
limits by blending with purer alloys
or metals. In cases in which the con-
taminants are large or difficult to re-
move, it might be most economical
to treat the scrap in a primary smelt-
er, where copper can be traced from
large proportions of iron, sulfur, and
many other metals or compounds.
A means for reclaiming metals from
starters and generators from obsolete
automobiles is to charge the parts to
steel-making furnaces to obtain cop-
per-bearing steel. Starters and gen-
erators have also been treated in cop-
per smelters to remove the iron as
slag while the copper is collected as
molten metal.
COTTON
Citric and malic acids are extracted
from cotton-production wastes.245
See also: Reference 73.
DAIRY WASTES
See: Food-Processing Wastes.
DIAMOND GRINDING WHEEL
DUST
Many grinding wastes contain fine
industrial diamonds used iu grinding
operations. Although diamonds can
be recovered by several methods, in-
cluding acid leaching, separation in
heavy liquids, and flotation, the pro-
cedures which have been used art
proprietary and closely guarded
The collection of diamond grinding-
wheel dust from the tool-grinding op-
erations of the Tungsten Carbide Tool,
Incorporated, of Detroit, Michigan,
has been briefly described in Steel.™
Diamond dust has been collected at
this plant in compact, fllterless cen-
trifugal collectors that weigh only 65
pounds each. These units were mount-
ed on the walls of the plant, but they
can also be installed on machinery,
suspended from the ceiling, or placed
on tables that occupy little more than
2 square feet of floor space. Each unit
is priced under $200—no more than
the cost of the average diamond
grinding wheel. Almost one-fifth of
the cost of a grinding wheel can be
saved by the recovery of diamonds
from the grinding dust.
DISTILLING WASTES
See: Brewing, Distilling, Ferment-
ing Wastes; Molasses.
ELECTROPLATING RESIDUES
Metals are recoverable from some
electroplating residues, but recovery
processes have rarely been applied un-
less the waste contained precious met-
als. Metal sludge from the treatment
of electroplating' wastes has been
combined with a variety of combus-
tible wastes (fly ash, coal dust, paint
sludge, oil, and grease) and burned
in an incinerator on conical inclined,
rotating grate containing perfora-
tions for the passage of ashes and
clinker.345' "*
FERMENTING WASTES
See: Brewing, Distilling, Ferment-
ing Wastes.
FISH
Gelatin is prepared from fish
wastes.38 Fish wastes are hydrolyzed
and the product is used in the manu-
facture of cosmetic ointments.423
Prawn-shell wastes have been ex-
tracted with acetone, decalcified, and
refluxed with caustic to produce
chitin.224
See also: Animal-Product Residues.
FLUE DUST
See: Ash, Cinders, Flue Dust, Fly
Ash.
FLUORINE
See: Reference 123.
FLY ASH
See: Ash, Cinders, Flue Dust, Fly
Ash.
FOOD-PROCESSING WASTES
The annual production of agricul-
tural residues in the United States is
something like three times the coun-
try's annual consumption of food.
Agriculture residues are generated in
large amounts throughout the world
(e.g., the quantity of only one waste—
bagasse—produced in the world each
year amounts to about 300 million
tons). Many of these wastes can be
utilized as raw materials for produc-
tion of chemicals and plastics, as cat-
tle feed and mulch, and lor manu-
facture of paper, board, and rayon.
The Bureau of Agriculture and In-
dustrial Chemistry of the Department
of Agriculture has been investigating
methods for utilizing these residues
since 1936. A majoi? deterrent- to the
construction of processing plants is
the fact that much of this industry is
seasonal. Installations designed on
the basis of peak loads would remain
idle much of the year.
See also: Animal-Product Residues;
Bagasse; Fruit Wastes; Rice;
Vegetable Wastes; Sanitary
Landfill and Open Dumping;
References 112,292.
CARBONIZATION
Many carbonaceous waste materials
have been used for the manufacture
of activated carbon. The properties of
the finished product depend on the
waste carbonized. Decolorizing acti-
vated carbons have usually been em-
ployed as powders. Sawdust and lignin
produce carbons of this kind. Vapor
adsorbent carbons are usually in the
form of hard granules and are gen-
erally produced from coconut shells
and fruit pits (e.g., plum and apricot
kernels). Carbonization proceeds at
temperatures that are high enough to
remove most of the volatile constitu-
ents but not high enough to crack the
evolved gases.413 Use of chemical im-
pregnating agents causes carboniza-
tion to proceed under conditions that
prevent the deposition of hydrocar-
bons on the carbon surface.413
Carbonization of residues from alco-
hol, beer, and sugar factories and of
acorn husks is carried out to obtain
activated carbon.' Sawdusts from var-
ious woods and peanut, cottonseed,
and rice hulls are impregnated with
ZnCl3 or CaO and carbonized. The
product is used for bleaching cotton-
seed oil."41
DEHYDRATION, DEW^T BRING,
DRYING
Charcoal of high discoloration
power can be obtained irmn various-
-------
wastes (cottonseed and sunflower-
seed hulls, corn husks, straw, sawdust,
and lignite) by dehydration with sul-
furic acid." Pear, apple, potato, beet,
whey, and other food-processing
wastes have been dried and used for
stock feed.58'423' ** The high water con-
tent has restricted the use of food-
processing wastes for many uses. Im-
proved dehydration techniques are
needed. Industries most likely to be
customers for dehydrated food wastes
that can be transported at low cost
are the animal feed, chemical, and
fertilizer industries.69' M
DISTILLATION
Furfural has been obtained from
various food processing residues by
distillation with hydrochloric acid.
Methods of improving the yield have
been described.108
HYDROLYSIS
The cellulose in plant residues is
readily saccharified and fermented.
Sugars obtained in this manner have
been used as feed to fermentation
plants producing ethanol, methanol,
acetone, butanol, and fusel oil, as well
as protein, and yeast for cattle feed.
The residue is a reasonably pure lig-
nosulfonic acid solution. However,
starch has generally been a cheaper
raw material for glucose than cellu-
lose.
OXIDATION
The Zimmerman process, which in-
volves wet oxidation of wastes under
pressure with partial recovery of fuel
value, is applicable to some food-
processing wastes.64
FOUNDRY WASTES
Foundry wastes have often been
treated for the recovery of materials
that can be recycled to the foundry
operation. Foundry sand, metals, and
alloys have commonly been recovered
from various types of foundry wastes
by means of magnetic separation,
screening, gravity separation, and air
classification. Recovered metals and
alloys not recycled within the foundry
can be sold as scrap.
St. John has described the general
application of magnetic separation,
screening, and gravity separation to
the recovery of brass, foundry mould-
ing sand, and metals from those
wastes commonly generated in brass
foundries.390 These wastes include
brass turnings, wet foundry sand, and
metal-bearing nonmetallic material
such as skimmings, skulls, slags, ashes,
and refractories. Brass is usually re-
covered with a centrifuge and a mag-
netic pulley. It is usually recycled to
the foundry, while tramp iron is sold
as scrap. Vibrating screens are fre-
quently employed for the recovery of
molding sand from metal-sand mix-
tures. The cleaned sand is reused on
the foundry molding floor, while the
separated metallic pieces and core
butts are subsequently treated for the
recovery of the various metals they
contain. Metals and alloys are often
recovered from these and the non-
metallic waste materials by means of
screens, shaking tables, ball mills, jaw
crushers, and magnetic pulleys. The
metal concentrate produced from the
beneficiation of these wastes is either
recycled to the foundry for melting or
shipped to a secondary smelter.
The recovery of clean foundry sand
from waste-containing, burned clay,
carbonaceous material, and silica
flour by means of magnetic separa-
tion, screening, and air classification
has been described by Zimnawoda.503
After the waste molding sand has been
prepared by magnetic separation and
screening, it is pneumatically scrubbed
against the cone-shaped target of
a dry pneumatic scrubber. Coatings of
dehydrated clay and burned carbon
are removed from the sand grains by
attrition and separated from them by
means of air entrainment and subse-
quent dust collection.
The application of this same dry
pneumatic scrubber to the reclama-
tion of foundry sand at the Superior
Foundry, Incorporated, of Cleveland,
Ohio, has been described by
Barczak.34
Puryear and Wile have mentioned
the use of magnetic separation and
screening in their description of a
thermal process employed by the
Lynchburg Foundry Company of
Lynchburg, Virginia, for the recovery
of molding sand from waste con-
taining a resin binder and a carbon
residue.380
Herrmann has described the appli-
cation of magnetic separation and
screening to the preparation of a simi-
lar waste prior to the reclamation of
sand by another thermal process em-
ployed at the Dearborn, Michigan,
specialty foundry of the Ford Motor
Company.187
See also: Inorganic Residues; Sep-
aration; Recovery and Utiliza-
tion; Slag; Specific metals.
FRUIT WASTES
See also: Food-Processing Wastes;
References 58, 437.
AMMONIATION
Dried, limed citrus pulp when am-
moniated and treated with acid can
Glass 41
be used as food for ruminants and fer-
tilizer for plants.05
CHLORINATION
Chlorination of the terpene frac-
tion of orange oil from orange peel
produces a material useful as an in-
secticide.1^
DISTILLATION
Products of the distillation of apri-
cot kernels are benzaldehyde, benzole
acid, and hydrogen cyanide. The resi-
due is fed to animals.160
EXTRACTION
Various by-products such as pectin,
seed oils, limonene, peel oils, glyco-
sides and vitamin P (citrin) are ex-
tracted from citrus wastes.137-424 Pectin
and malic acid are extracted from ap-
ple wastes. A plasticizer has been
made from the refuse from production
of Chinese citron.19
GELLING
A process for producing dried pulp
for cattle feed from peelings, cores,
and trimmings wasted in canning of
pears involves treatment of the waste
to form a calcium pectate gel. The
sediment from this treatment is
pressed and dried and sold as cattle
feed.162' 32°
HYDROLYSIS
Pectin is produced by hydrolysis of
dried peel of citrus fruits.28 The prod-
ucts of hydrolyzing the protein in ap-
ple seeds have been described.409 Grape
wastes can be hydrolyzed to recover
sugars and other chemicals.97
PYROLYSIS
Peach pits are charred and made
into charcoal briquets.292
FURNITURE
See: Sanitary Landfill and Open
Dumping; References 35, 530, 555.
GERMANIUM
An automated process for reclaim-
ing high-grade germanium from scrap
has been described.532 Germanium
chloride has been isolated by hydroly-
sis from wastes from the manufacture
of diodes and transistors.210
See also: Lead; Nonferrous Scrap;
Zinc.
GLASS
The Bassichis Company in Cleve-
land has since 1900 been processing
and marketing powdered glass in var-
ious mesh sizes and types and is the
largest in its field. Conventional proc-
essing machinery, adapted to this par-
ticular material and need has been
used. Sources of scrap glass for proc-
essing have been altered drastically by
-------
42 SOLID WASTE PROCESSING
many factors including two major
trends, one technologic, the other eco-
nomic: (a) the trend from bottles to
cans and paper cartons, (b) the elim-
ination by higher labor costs of the
practice of salvaging broken glass
from general refuse. As a result, some
industries that could use cracked bot-
tles as a raw material have had to
turn to other materials because the
supply of scrap bottles is too small and
undependable. Thus, an economic
method for segregating scrap bottles
from municipal refuse would find a
ready market. Dark glasses have been
manufactured from industrial polish-
ing waste and construction glass.489
See also: Recovery and Utilization;
Reference 148.
EXTRACTION
Rare-earth elements in wastes from
grinding optical glasses can be almost
completely extracted by complex
chemical procedures for experimental
use.11
MELTING
Most glass manufacturers remelt
for reuse the scrap glass resulting
from their own processes if the scrap
has not become contaminated with
other materials along the way.
GLASS WOOL
See: Sanitary Landfill and Open
Dumping; Reference 439.
GYPSUM
See also: References 189, 190, 209,
356.
CRYSTALLIZATION
When powdered waste gypsum
from the pottery industry is heated
with aluminum sulfate solution,
large crystals of gypsum are obtained.
The properties of the calcined crystals
have been given."6
DEHYDRATION
Gypsum plaster has been manufac-
tured from waste-gypsum molds by
autoclaving.
HEMP
See: Reference 14.
HYDROGEN FLUORIDE
Slag from the manufacture of hy-
drogen fluoride has been washed,
elutriated, crushed, and stirred with
sulfates or chlorides to form pure
crystals of calcium sulfate.209
INORGANIC RESIDUES
See also: Ash, Cinders, Flue Dust,
Fly Ash; Foundry Wastes; Pickle
Liquor; Slag; Specific inorganic
residues; Reference 403.
In the mining and mineral indus-
tries, recovery of materials is rarely
feasible.
All pyrometallurgical processes
produce slags. Blast-furnace slag is
produced in greatest quantity. The
amount of slag is about equal to the
amount of pig iron produced. All slags
contain a certain proportion of the
metal produced or refined, but re-
covery is not practiced to any extent.
There are several mechanical uses for
slags. They are used as aggregates,
rail ballast, housing-project founda-
tions, and gravel for roadmaking and
railway building, and in practically
all circumstances where gravel or
crushed stone could be used. A serious
drawback to many slags is their tend-
ency to dust or disintegrate during
the course of time. Chemical uses of
slags include their use as cement, fer-
tilizer, and slag wool.
Three kinds of sludge are produced
in the steel industry: flue dust, mill
scale, and neutralized pickle liquor.
About 1 billion gallons of pickle liquor
are generated in the United States
each year. This amount of pickle liq-
uor contains 250,000 tons of iron. The
total amount of solids in spent, neu-
tralized pickle liquor amounts to
about 2 million tons each year. The
neutralized slurry remains plastic for
an almost infinite time. Pickle liquor
can be processed for recovery of iron
and iron compounds and acid. These
processes are becoming more wide-
spread as time goes on. The neutral-
ized sludge can be used as a construc-
tion material. Flue-dust sludge is
generally filtered, sintered, and re-
turned to the blast furnace. The
average furnace produces about 1,000
tons of dust a day. The scale re-
moved in rolling mills is deposited in
a scale pit and is usually charged to
the furnace. It amounts to about 60
tons per day for a rolling operation.
IRON
See: Copper; Foundry Wastes; In-
organic Residues, Pickle Liquor;
Pyrite Cinders and Tailings.
LEAD
See also: Tetraethyllead; Waste Re-
covery and Utilization.
Lead scrap can be made into the
various grades of pure lead or into
lead alloys by secondary smelters. This
is possible because the usual impuri-
ties in lead scrap can be removed
readily. Hence, lead battery plates
may be smelted to produce antimoni-
cal lead for the manufacture of new
batteries, or the lead may be refined
to produce pure lead and pure anti-
mony as separate products. In either
case, the antimony as well as the lead
is returned to industry. This is im-
portant because both the antimony
and the lead content generally are
paid for in purchasing scrap battery
lead.
CHEMICAL REDUCTION
Lead waste from electrodes of
storage batteries containing lead sul-
fide has been molded with carbide
sludge and water and chemically
reduced.492
MELTING
Lead has also been reclaimed from
various solid wastes by melting.122'136
REVERBERATORY FURNACES
Lead is recovered from a variety of
materials by use. of- reverberatary
furnaces. Battery plates, which con-
stitute the largest source of scrap lead,
usually are smelted in blast furnaces
to produce antimonial lead. That
product may be made into soft lead
(free from antimony) in a reverbera-
tory furnace or in a kettle. Battery
plates also are melted in a reverbera-
tory furnaces directly to produce
antimonial lead. A variety of lead al-
loys from scrap pipe, coffins, bear-
ings, and roofing also are melted in
kettles or reverberatory furnaces. The
lead from most of its scrap materials
can be refined to products equal to
the refined lead from primary smelt-
ers. In fact, the refining steps, soften-
ing (removing antimony), decopper-
izing, dezincing, and debismuthizing
may be the same in secondary plants
as in primary smelters.
Reverberatory furnaces also are
employed to smelt various lead
drosses, especially those obtained
from the refining of scrap lead in ket-
tles. And reverberatory furnaces in
turn produce slags and drosses that
are smelted best in blast furnaces. A
rather complex relationship exists be-
tween the melting, smelting, and re-
fining of the many types of lead scrap
and the equipement used for the
operations.
LEATHER FABRICATING AND
TANNERY WASTES
Leather wastes have been processed
to manufacture glue, carburizing
agents, and fertilizer. Tannery wastes
have been used to produce feed. Fer-
tilizers have been produce from waste
leather.421
DISSOLUTION
Constituents of glue have been re-
-------
covered from leather wastes by vari-
ous dissolution processes.41' '"•m
HYDROLYSIS
Collagen-containing wastes of the
leather industry have been treated by
hydrolysis to produce an artificial
leather.450 Albuminoid hydrolyzates
prepared from leather wastes can be
used in cosmetic preparations.298 Pro-
tein-containing skin, bones, and other
tannery refuse can be hydrolyzed to
produce a food product.
PRECIPITATION
Chromates can be recovered from
tanning wastes by precipitation.373
PYROLYSIS
Waste leather or wool can be auto-
claved and the residue used as fer-
tilizer.421 Leather trimmings can be
converted into a carburizing agent by
heating in a muffle furnace and then
mixing with calcium carbonate.225
LEAVES
See: Sanitary Landfill and Open
Dumping; Reference 91.
LIME
Waste from lime works has been
mixed with coal wastes, formed into
shapes, combined with solid fuel, and
burned to a clinker.230 Various lime
wastes are used in the liming of pod-
zolic soils.237 Some lime sludge is also
dried and used for acid-waste
neutration.
See also: Stone Spalls; Sugar
Beets; References 57, 234.
MAGNESIUM
Hydrochloric acid has been used to
leach iron and aluminum from, the
solid wastes from magnesium pro-
duction.121
See also: Aluminum.
MANGANESE
Metallic manganese has been ob-
tained by electrolysis of a solution of
manganese obtained by extracting a
mixture of manganese containing
slags and pyrolusite.
MICA
Mica has been recovered in sheets
after chemical processing of wastes
from mica mines.
MINERAL WOOL
See: References 105, 346.
MOLASSES
Potassium salts have been recov-
ered by incineration of wastes from
molasses."
See also: Brewing, Distilling, Fer-
menting Wastes.
MOLYBDENUM
See: Reference 145.
MUNICIPAL WASTES
Only one chemical method, incin-
eration, has been practiced for the
disposal of municipal wastes. It em-
ploys oxidation of the waste with
free air at elevated temperatures. A
variant of this process, so-called "wet
oxidation," has been practiced to a
limited extent in recent years, with
at least one application to sewage
sludge.501 In the process, the sludge is
oxidized to destruction by pumping a
water suspension of it and air into
a pressure vessel; both are maintained
for some time at elevated pressure
and temperature.
See also: Incineration; Reference
163.
NONFERROUS SCRAP
Precious metals are recovered from
a great variety of industrial waste
materials. Examples of annual recov-
eries of nonferrous metals during 1964
are: over one-half million tons of
aluminum, slightly more than one
million tons of copper, and 120,000
ounces of platinum-group metals. The
less common metals, such as germa-
nium, zirconium, and yttrium are also
reclaimed from scrap metals.
The term "secondary", when used
in connection with metals, does not
refer to quality. It refers to metals
produced from scrap or waste ma-
terials to distinguish them from "pri-
mary" metals, which are produced
from ores and concentrates of ores.
Two other designations are used in
the secondary-metal industry; name-
ly, "new scrap" and "old scrap". The
scrap generated as turnings, punch-
ings, trimmings, damaged parts, and
the like, by fabricators of machinery
and equipment is called new scrap.
Metals salvaged from obsolete ma-
chinery, buildings, or ships is termed
old scrap.
Most manufacturers prefer to send
their scrap metals to plants estab-
lished for the processing of such ma-
terials. Consequently, the source of
much of the secondary metals is man-
ufacturing plants. The other sources
are the scrap metals brought to deal-
ers by collectors from small shops,
municipal refuse, obsolete machinery,
and dismantled buildings.
A great deal of sorting and proc-
essing of scrap materials may be re-
quired preparatory to the production
of marketable metals. The smelting
and refining of metals is much sim-
pler and less expensive if relatively
pure types of metals are treated sep-
Nylon 43
arately. This makes careful sorting
advantageous. Various operations, in-
cluding sorting, drying, degreasing, in-
cinerating, and baling, are used in the
preparation of scrap metals for smelt-
ing and refining.
The actual production of market-
able metals from scrap materials in-
volves five major processes: melting,
melting and refining, smelting and re-
fining, distillation, and hydrometal-
lurgical processes.
Ample facilities and processes exist
for producing useful metals from
metallic scrap. This makes it possible
for small amounts of scrap from scat-
tered sources to be brought to strate-
gically located centers. The scrap can
be processed economically at those
centers because the volume of ma-
terial can be sufficiently large for the
purpose.
See also: Recovery and Utilization;
Foundry Wastes; Inorganic Resi-
dues; Precious Metals; Pyrite
Cinders and Tailings; Specific
nonferrous metals; Reference
148.
NUTS
Extraction of cashew-kernel rejec-
tions gives a bland yellow oil. The
residue can be used in the manufac-
ture of chocolate or as feed.402
Destructive distillation of the hulls
of groundnuts yields gas, acetic acid,
methanol, and charcoal.483
See also: Agricultural Wastes;
Food-Processing Wastes; Ref-
erence 463.
NYLON
Nylon fibers can be recovered from
waste nylon by destroying the non-
nylon portion of the waste with
acid.333 Waste nylon has good ion-ex-
change properties.26 Chemical treat-
ment of Nylon-6 waste has been re-
viewed by Diba and Varacek.10"
Nylon-6 wastes have been depolymer-
ized to 6-caprolactam by alkaline de-
polymerization at elevated tempera-
tures or by hydrolysis.108 Nylon-6
waste can be dissolved under pressure
in alcohol, particularly ethyl alcohol;
the polymer will precipitate in the
form of fine particles when the solu-
tion is cooled.109 It can be dried and
reused. Polyamide (nylon) wastes can
be dissolved and reprecipitated; the
precipitate can be reused to produce
nylon.247-Ka Waste nylon-6 can be
treated with an alkaline solution to
precipitate impurities. After the rub-
bery precipitate is filtered off, capro-
lactam can be isolated from the so-
lution.352
-------
44 SOLID WASTE PROCESSING
See also: Agricultural Wastes;
Plastic; References 304, 307, 371,
414.
ORGANIC WASTES
Many organic industrial waste
sludges can be burned with little or
no auxiliary fuel after they have been
partially dewatered by filtration, cen-
trifugation, or screening. By use of
multiple hearth incinceration (where
heat economy is relatively high) even
liquid sludges can be burned. An ap-
paratus for purifying industrial efflu-
ents and utilizing organic matter for
fuel is described.500 Carbonaceous
waste materials can be destructively
distilled in a retort. Condensible ma-
terials are removed from the vapor,
and the remainder is returned to the
retort. The solid can be used for
charcoal.383 The simultaneous carboni-
zation and sulfonation of organic
wastes produces a granular carbon
possessing ion-exchange properties.3"5
See also: Agricultural Wastes; Ani-
mal-Product Residues; Pood-
Processing Wastes; Fruit Wastes;
Vegetable Wastes; Specific or-
ganic wastes; References 395,
396.
PAINT
The solid material demanding ulti-
mate disposal by paint users is the
paint-waste sludge removed from
holding pits in spray booths. This
waste is in the form of a sticky mass
with the consistency of modelling
clay.
INCINERATION
Paint sludge has been burned in pit
incinerators.24'aHI Air pollution from
these installations may be a problem
if the solids content of the sludge is
high.
POLYMERIZATION
A method which has been consid-
ered for disposal of paint waste is
polymerization by heating to a tem-
perature and for a time equivalent to
practice in curing paint.28
PAPER
See: Photographic Paper; Pulp and
Paper; Wastepaper.
PETROLEUM RESIDUES
Petroleum residues include tank
bottom sludges from storage tanks
and cracking, polymerization, and
similar processes; coke from equip-
ment tubes and towers; oil emulsions
and oily waste waters from cracking
and distillation and similar processes;
and acid sludges, caustic sludges, and
emulsions from the chemical treat-
ment of oil. Petroleum residues are
usually disposed of by incineration
after removal of most of the oil and
water from these residues.
CARBONIZATION
Activated carbon has been produced
by burning the sludges from oil
refineries.*0
DISTILLATION
Distillation of petroleum residues
yields a material that is a plasticizer
and agglutinant.303
INCINERATION
Petroleum sludges are usually dis-
posed of by incineration after as much
of the oil is recovered as possible.
These sludges may be viscous liquids
or semisolids containing water, free
acid or alkali, and other chemicals.
The calorific value on a dry basis is
10,000 to 15,000 Btu per pound. Effi-
cient heat recovery is not possible
without carefully designed equip-
ment."7 Thermal disposal methods are
recommended for disposal of sludge
from leaded-gasoline tanks.30
The coke residue from petroleum
refining has generally been burned
with coal for heat recovery, but it can
be burned alone in a specially de-
signed furnace. The sulfur content
may introduce corrosion or sulfur di-
oxide problems. The high vanadium
content of the ash can also cause cor-
rosion.177 The economics of using this
coke as fuel have been reported.308
The oily sludges from treatment of
waste emulsions have been incinerated
by flame incinerators and fluidized-
bed techniques.29
PHOTOGRAPHIC PAPER
Silver and gelatin-free paper can
be recovered when photographic
paper wastes are treated with cal-
cium oxide and alum in a beater.291
Silver can also be recovered from
photographic wastes by burning the
wastes under controlled conditions
and recovering the silver from the ash
by smelting.13"' *»• <81
See also: Chemical Wastes; Plastic;
References 293, 362.
PICKLE LIQUOR
See also: Inorganic Residues.
CALCINATION
The ferrous sulfate by-product of
pickle-liquor regenerative processes
can be roasted to produce sulfur diox-
ide suitable for sulfuric acid.18"
CRYSTALLIZATION
Waste pickle liquor has been regen-
erated using high-acid (18%) baths.
The spent bath is evaporated, seeded,
and acidified and the ferrous sulfate
removed by crystallization. The acid
supernatant can be reused.280
DISPLACEMENT
In the Ruthner process, sulfuric
acid and iron oxide are recovered
from spent pickling liquor by convert-
ing ferrous sulfate to ferrous chloride
and sulfuric acid by reacting it with
hydrochloric acid. The ferrous chlo-
ride precipitate is roasted to reclaim
hydrochloric acid, and the ferrous
oxide is returned to the blast fur-
nace. A demonstration recovery plant
based on this process was operated at
the Niles, Ohio, plant of Republic
Steel Corporation. Seven major steel
companies shared the cost of the
$400,000 program.2'7'BS1
ELECTROLYSIS AND ELECTRO-
DIALYSIS
Iron and sulfuric acid can be re-
covered from pickle liquor by electrol-
ysis.132280 Iron is deposited on the
cathode and sulfuric acid is recovered
in the anode solution by electrodial-
ysis of spent pickling solutions. The
capital cost of a plant treating 1,720
gallons per hour of pickle liquor (10
TPD iron) was reported as about $2.5
million. Operating cost was reported
as $3,070 per day, and credits came
to $1,593 per day.2"
EVAPORATION
Ferrous sulfate can be recovered
from pickle liquor by evaporation.280
Sodium sulfate can also be recovered
by evaporation.615
EXTRACTION
Iron in spent pickle liquor can be
complexed and extracted. The iron is
recovered by adding lime to the ex-
tract. Acid can also be reclaimed in
the process.663
NEUTRALIZATION
Metallurgical sludge containing
calcium oxide and magnesium oxide
can be used to neutralize spent pickle
liquor.328
SCRUBBING
Iron oxide and ammonium sulfate
are produced when coke-oven gas is
scrubbed with spent pickle liquor.373
PLASTIC
Many waste plastics can be proc-
essed for reuse. Most thermosetting
-------
plastics, however, defeat attempts at
large-scale utilization and are not
even suitable as fuel because the de-
composition (ignition) temperature
is high and the flame is not self-
sustaining. One or two varieties have
been used as fertilizer and some, when
ground fine, may be useful as filters.
Preliminary experiments have been
made to obtain usable materials from
bakelite scrap by means of acetyla-
tion, methylation, halogenation, sul-
fation, or nitration.*05
See also: Recovery and Utilization;
Agricultural Wastes; Nylon; Ref-
erences 148, 331.
ALCOHOLYSIS
Lacquer resins can be prepared
from the waste products of poly-
ethylene terephthalate by their alco-
holysis with glycerol.404 Cellulose film
wastes can be treated by transesteri-
fication. The products can be used
in the preparation of thermoplastic
materials.382
CONDENSATION
Waste polyethylene glycol has been
heated with ethylene glycol and the
mixture polycondensed. The product
can be molded.168 Spinnable polyethyl-
ene terephthalate can be obtained
from fiber waste by a condensation
process."3
DISSOLUTION
Cellulose-ester film scrap has been
treated with caustic and ferrous sul-
fate, dissolved in dichloromethane
and methanol, and centrifuged to
produce a clear solution that can be
reused." Waste synthetic polymers
which have been recovered by dissolu-
tion processes include acrylic, vinyl,
and polyester resins.62
DISTILLATION
Polymethacrylic resin waste prod-
ucts can be chemically treated and
distilled to recover methyl meth-
acrylate.81
EXTRACTION
Polyurethane scrap can be ex-
tracted with an alkaline solvent to
remove a portion of the waste poly-
urethane, which, after chemical proc-
essing, can be reused.86 Several waste
synthetic polymers can be dissolved
without apparent chemical change
and then reused after the solvent and
impurities are distilled off .*•• "4 Capro-
lactam can be recovered from super-
polyamide wastes by heating, dissolv-
ing, treating with activated carbon,
and filtering.882 Several solvents can
be used in the recovery of polymer
from waste nylon-6, including 6-
caprolactam: sulfuric acid, hydro-
chloric acid, formic acid, calcium
chloride and methyl alcohol, water
under pressure, and alcohols under
pressure. After extraction, the poly-
mer is recovered by precipitation.871
Extraction of organic components to
regenerate asbestos from plastic prod-
ucts was not successful.284
HYDROLYSIS
Polyethylene terephthalate waste
has been subjected to complete alka-
line destruction, aqueous hydrolysis,
and methanolysis before reuse.438
Waste nylon has been hydrolyzed to
recover raw materials.304' 3°7 Polyester
urethane can be treated by hydrolysis
with steam and the recovered mate-
rial blended with new material.348
Cellulose acetate wastes or cellulose
2,5-diacetate obtained by hydrolysis
of photographic film can be treated
with epoxy resins, the resultant mix-
ture being crushed, ground, and
granulated before reuse.117 Recovery
of the polymer in waste Nylon-6 can
ba accomplished by hydrolysis.109 Syn-
thetic resins that contaminate waste-
papers can be removed by
hydrolysis.235
INCINERATION
For a very large number of chemi-
cal and plastic wastes the degree of
burnability, decomposability, corro-
siveness, and hazard is unknown.380
The liquid residue from burning scrap
polyurethane can be returned to the
normal foaming process without de-
creasing the quality of the final prod-
uct.1*3 a86 Rigid polyurethane-foam
particles have been heated to give
rigid products useful in place of wood
panels and tile.15 Polyesters have been
recovered from scrap polyurethane by
burning in air.12 The pit incinerator
has been used to incinerate nylon
wastes.29 Excess activated sludge from
treatment of nylon-plant wastes has
been mixed with equal parts of com-
bustible waste and incinerated.255 As-
bestos in waste plastics has been re-
generated by burning away the or-
ganic matter.284
MELTING
Polyethylene terephthalate in waste
fibers has been melted, and the melt
condensed and extracted to recover
spinnable polyethylene terephthal-
ate.464 Polymer of nylon-6 waste has
recovered by melting.811
POLYMERIZATION
Methods for processing plastic
wastes for repolymerization have been
Precious metals 45
described by Tobola.451 Polyamide
wastes have been mixed with mono-
mers and autoclaved to produce a
copolymer.412
PYROLYSIS
Synthetic resins can be cracked in
vacuo by direct contact with melted
metals.2"
POPPY
Morpnine is extracted from poppy
wastes.207
POTTERY WASTES
See: Gypsum.
PRECIOUS METALS
Scrap that contains precious metals
may be worth processing. A checklist
of precious-metal scrap has been pre-
sented by Perry.340
Gold, silver, and the platinum-
group metals have been reclaimed
from a great variety of industrial
waste materials. Combinations of
melting and chemical treatments have
been applied to separate and to refine
the metals. Dissolution and precipi-
tation have been practiced to separate
the previous metals from base metals
or from catalyst carriers and to con-
centrate the precious metals into
small bulk. The great value of the
metals permits the use of very cor-
rosive reagents because small units of
expensive equipment can be em-
ployed. Glass-lined vessels, glass pipe-
lines, and glandless pumps have been
used extensively. Earthenware, rub-
ber-lined steel, and stainless steel
have also been used for digesters,
filter presses, and cementation vessels.
Some typical methods are decribed
briefly in the following paragraph.
Nitric acid or sulfuric acid can be
used to "part", that is, to selectively
dissolve, silver from gold in alloys that
are preponderantly silver. The silver
can be recovered from solution by
cementation with copper. Finally, the
separated gold and silver can be re-
fined by electrolysis or other means
and cast into bars lor delivery.
In the treatment of the platinum
group of metals, solutions containing
the major portion of the gold, plati-
num, and palladium as chlorides can
be prepared by digestion with aqua
regia. This treatment leaves a residue
of the less soluble metals, iridium,
rhodium, ruthenium, and osmium.
Gold can be recovered from the solu-
tion by reduction with ferrous chloride
and filtration. Ammonium chloride
can be added to the filtrate to precipi-
tate ammonium chloroplatinate. The
precipitate can be filtered and calcined
-------
46 SOLID WASTE PROCESSING
to produce platinum sponge. Palla-
dium can be precipitated as dichloro-
diamminepalladium; palladium
sponge can be obtained by calcination
of the filtered precipitate.
The original residue of iridium,
rhodium, ruthenium, and osmium
can be fused with alkaline and oxi-
dizing fluxes. The fused mass can be
dissolved in water and distilled to
separate ruthenium and osmium as
volatile oxides. These metals can be
precipitated as complex salts in the
manner described for platinum and
the precipitates calcined to metallic
sponges. The residue from the distil-
lation would contain iridium and rho-
dium. It can be treated to precipitate
complex ammonium compounds sepa-
rately, and those precipitates can
also be calcined to yield metallic
sponges of the iridium and rhodium.
The separate sponge metals can be
converted to solid ingots or other suit-
able shapes by melting and casting
or by sintering, forging, and rolling.
See also: Recovery and Utilization;
Ash, Cinders, Flue Dust, Ash Fly;
Electroplating Residues; Nonfer-
rous Scrap; Photographic Paper;
Specific metals; References 389,
391.
PULP AM) PAPER
The solid wastes generated by pulp
and paper mills are mostly in the form
of sludges. The amount of solids dis-
charged from a mill varies from about
20 to 160 pounds of solids per ton of
paper produced. About 70 million tons
of pulp are produced in the world per
year. Waste solids from this industry
amount to something like 3.5 million
tons per year. The solids content of
the sludges may be as low as 0.75 per-
cent or as high as 10 percent. The
sludges from pulp-mill effluents are
composed primarily of cellulose and
inert filler materials. They also can
contain starch, rosin, casein, inks, and
other organics together with grit,
wood, wire, rags, and other miscel-
laneous trash. The sludge from a
white-water recovery system is almost
entirely cellulose fibers.
Final disposal of sludge has usually
been on the land. It has generally been
disposed of in the liquid state, but
more and more plants are using some
form of dewatering equipment so it
can be handled in the semisolid form.
Sludge-burning methods such as the
Zimmerman and Atomized Suspen-
sion techniques have seemed to be
promising methods for further de-
creasing the sludge volume.
A number of paper companies in
the United States have concentrated
sulfite waste liquor to 50 percent sol-
ids and sold it as such or as a powder
produced by spray drying. The prod-
uct modified for particular applica-
tions can be sold as a binder or a
dispersing agent. A small amount has
been sold in the form of metal com-
plexes for agricultural applications.
Chemicals have been recovered
from the sludges at some plants. The
Ontario Paper Company has proc-
essed sludge for recovery of 4,800
pounds per day of vanillin, 2,400
pounds per day of calcium oxalate,
2,400 pounds per day of lignin, and
120,000 pounds per day of sodium sul-
fate.
See also: Recovery and Utilization;
Wastepaper; References 68, 148.
CALCINATION
A fluidized-bed reactor can be used
to calcine lime mud from recaustizing
operations at paper mills. The lime
can be reused. The reactor capacity
of a mill using this process was re-
ported as 45 TPD.19e'2'9 Calcined
deinking mill sludge can be used for
filler and in the manufacture of build-
ing materials.324
COMBINATION AND ADDITION
Dimethyl sulfide can be produced
from kraft liquor. The process consists
of adding sulfur to the liquor, heat-
ing, and flashing off crude dimethyl
sulfide, which is then condensed and
purified by extraction and distillation.
About 60 pounds of dimethyl sulfide
have been produced per ton of kraft
pulp. A smaller amount of methyl
mercaptan can be produced and iso-
lated. Several plants have been in op-
eration. One produced 5 million
pounds per year of dimethyl sul-
fide.182' 370' ™> Pressure heating kraft li-
quor with additional sodium sulfide
and sodium hydroxide yields ether-
soluble degradation products (up to
50 percent or more of the organic sub-
stances) plus methyl sulfide, acetic
and formic acids, and a reactive de-
methylated lignin (yielding pyrocate-
chol and its homologues, usable in
plastics of the bakelite type).130 The
cellulose in paper wastes reacts with
methanolic hydrogen chloride to pro-
duce methyl glucoside, which can be
used to make polyethers for urethane
foam. Starch can be used as a raw
material for polyethers.182
DEWATERING
The problems of dewatering paper-
mill sludges have been described.
DISSOLUTION
Wastepaper ingredients (e.g., ink)
are dissolved by cooking the paper in
a mixture of chemicals, principally
caustic soda; the fiber residue is suit-
able for reuse.325
DISTILLATION
Tall oil from black liquor can be
redistilled and sold as such or sent
to a fractionation operation where
rosin and fatty acids are recovered.™
Methanol is recovered fcy distillation
of evaporated black-liquur solids fol-
lowing treatment with barium hy-
droxide.™ Pine oil is separated from
sulfate turpentine by fractional dis-
tillation. Between 0.2 and 2 gallons
of pine oil are produced per ton of
pulp. The turpentine is recovered by
decantation from the condensed re-
lief gases from kraft digestion at the
rate of 1 to 6 gal/ton of pulp.373 Tur-
pentine and rosin are distilled from
pine gum and stumps.182
ELECTROLYSIS AND ELECTRO-
DIALYSIS
Spent sulfite liquor is being treated
on a pilot-plant scale by electrodialy-
sis to recover pulping liquor, produce
lignosulfonic acids, and separate
lower molecular-weight organics. The
plant is being operated by the Sulfite
Pulp Manufacturers' Research League
in Appleton, Wisconsin.527
By electrolyzing fibrous waste sus-
pended in a sodium chloride solution,
the fibrous material is simultaneously
digested and bleached.350
EVAPORATION
Lignosulfonates are produced by
evaporation of sulfite liquors to 50 per-
cent solids in a self-descaling evapo-
rator. It is an advantage to convert
the calcium lignosulfonates to the
soluble sodium form by ion exchange
prior to evaporation.373
EXTRACTION
Acetic and formic acids have been
recovered from the waste liquors
from neutral sulfite semichemical
pulping by an extraction process.
8381475 Tannins have been extracted
from the bark of trees including the
two principal pulp trees in the Pacific
Northwest, Douglas fir and western
hemlock. In addition, hemlock bark
has been extracted for phenolic acids.
Arabogalactan has been extracted
from western larch by the lumber di-
vision of one of the large paper com-
panies. Several other complex wood
extractives can be produced from
wastes. The possible isolation of wax
from Douglas fir bark has been in-
-------
vestigated. Methods have been found
for extracting xylose from hard-
woods.182 The sludge precipitated by
treating an alcohol plant effluent with
lime has been leached with soda ash.
The calcium carbonate residue has
been reused in the process. Vanillin,
lignin, calcium, oxalate, and sodium
sulfate have been recovered from the
leaching solution. The raw material
for an alcohol plant was the effluent
from the pulp mill.812
Asphalt-coated paper, when treated
with certain solvents, has been
claimed upon solvent evaporation to
contain the asphalt in microscopic
particulate form, permitting its use as
an ingredient in pulping operations."
Bitumen-containing wastepapers can
be utilized in the papermaking proc-
ess after extraction with acid.397
The ash from the incineration of
spent cooking liquor from the kraft
process can be leached and the ex-
tract causticized to recover caustic
and sulflde chemicals used in the
process."1
HYDROGENATION
Phenolic materials can be produced
by hydrogenation of lignin in paper-
mill wastes.373 Sugars in sulfite-waste
liquors can be hydrogenated to alco-
hols. There has, however, been no eco-
nomical means of separating the
sugars from the other waste solids.182
HYDROLYSIS
Many attempts have been made to
profitably utilize the vast quantities
of waste lignin from pulping proc-
esses and wood hydrolysis. Recovered
lignin can be used in the preparation
of synthetic resins.'*5 The character-
istics of lignin have been described.
338,3<2,373 -pj^ sugars produced by hy-
drolysis in the sulflte-pulping process
are converted to alcohol and yeast.182
A kraft mill with a capacity of more
than 1,400 TPD uses shavings and
sawdust to produce pulp.542
INCINERATION
The burning of papermill sludge
(solids obtained from the so-called
white water from paper machines)
has been limited in the United States.
The economics of the process is de-
pendent on the moisture content and
the Btu content of the sludge. The
Btu content per pound of sludge
volatiles is on the order of 8,000.
The heat needed to volatilize a pound
of water ranges from 1,900 to 3,500
Btu. Data on the degree of dewater-
ing required of sludges of various vol-
atile contents to support their own
combustion has been presented in
graph form by Blosser.49
The Zimmerman process, which em-
ploys the principle of wet combus-
tion, has been used for combustion of
paperbill sludges and liquid dis-
posal.89' 329' *»• m Wet-combustion eco-
nomics are almost independent of the
dry-solids content of the waste. This
process is installed at the A/S Bore-
gaard mill at Sarpborg, Norway. In-
stallation costs for a unit to burn 200
tons per day of dry solids have been
reported to be in excess of $11
million.82
The atomized-suspension technique
was developed by the Pulp and Paper
Research Institute of Canada for
burning sludges. In this process, after
some heating and thickening by ex-
haust gases, sludge is injected through
nozzles or other atomizing devices
into a heated chamber, where it is
burned at atmospheric pressure.46' **'•
263, 551
Burned sludges have been used as
filter material for rubber and asphalt
tile.49 Pelletized sludge subjected to
high temperatures has been used as a
lightweight concrete. It might also be
used to manufacture lightweight
brick.49 A mixture of sugar-factory
muds, papermill sludge, and clay yields
Portland cement when it is burned.458
Experimental incineration of paper-
mill sludges has been described.48'529
Black liquor from sulfate pulping
has nearly always been evaporated
and incinerated. The liquor is brought
to 50 percent solids in multiple-ef-
fect evaporators and is further evap-
orated to 65 percent solids in direct-
contact evaporators. This is then fed
to the recovery furnace where the
organics decompose, carbon is burned
away, and the inorganics melt and
are reduced. Caustic soda, sodium sul-
flde, and soda ash are recovered from
the smelt.373 481
Acid calcium sulfite liquor has
often been evaporated and inciner-
ated as an antipollution measure.
Steam is produced as a by-product.
Scaling is a particular problem in
these evaporators. The capital in-
vestment for evaporation and incin-
eration for a 200-TPD plant has been
reported to be $1.5 million, with a
negative return on investment.373
In the case of magnesium-based
cooking liquors, the evaporated liq-
uor is burned in a recovery furnace.
Sulfur dioxide is then recovered by
wet scrubbing, and magnesium oxide
by dry scrubbing, for recycle. Both
ammonium- and sodium-based liq-
uors may be treated in this fashion. A
Pyrolysis 47
recently proposed approach has been
the use of atomized-suspension
radiant pyrolysis for the incineration
of sulfite liquors. The capital invest-
ment for evaporation and incinera-
tion for a 250-TPD plant has been
reported as $5.2 million and rate of re-
turn as 16 percent.373 Sulfur has been
recovered from the gas during com-
bustion and reused.180'483 A fluidized-
bed system has been used to recover
chemicals, such as sodium sulfite and
soda ash, in the Container-Copeland
process."
ION EXCHANGE
The Pritchard-Praxon and Abiperm
processes are examples of ion-ex-
change recovery systems for sodium-,
magnesium-, calcium-, or ammon-
ium-based liquors.272 The capital in-
vestments for ion-exchange systems
for 100-, 200-, and 300-TPD plants
have been reported as $767,000,
$1,163,000, and $1,511,000, respect-
ively. Rates of return have been re-
ported at 9.0, 12.4, 14.7, in the same
order.373
OXIDATION
Meso-tartaric acid can be obtained
by oxidizing cellulose with nitrogen
tetroxide and then hydrolyzing with
hydrochloric acid.182 Materials con-
taining lignosulfonic acid can be oxi-
dized in alkaline medium to obtain
vanillin, acetovanillin, lignin, and cal-
cium oxalate.334
PRECIPITATION
In the Howard process, various por-
tions of the sulfite pulp wastes are
separated by fractional precipitation.
One portion is burned to provide heat,
and the residue is processed to re-
cover chemicals. Other fractions con-
tain materials useful as raw materials
for the manufacture of plastics and
vanillin.171 Lignin can be recovered
from kraft liquor by precipitation of
the lignin with acid. The lignin so ob-
tained can be processed into useful
chemicals.182
PYROLYSIS
Practically all vanillin has been
produced by the alkaline pyrolysis of
lignin sulfonic acid from sulfite-waste
liquor. The yields are low, between 6.0
and 12.0 percent based on the lignin
sulf onic acid, and an elaborate extrac-
tion and purification process is re-
quired to produce a pure product. In
North America, about 1.5 million
pounds of vanillin are produced per
year and sold at about $3.00 per
pound. Most of the vanillin has been
used for flavoring, a small amount be-
-------
48 SOLID WASTE PROCESSING
ing converted to other flavoring
agents and medicinal derivatives.182'442
The cracking of lignin gives a
source of chemical raw material com-
parable to coal-tar production."3 Cel-
lulose heated in a vacuum to relatively
high temperatures produces 1,6-anhy-
droglucose, which can in turn be
polymerized. Its trimethyl ether, when
treated with sodium in liquid
ammonia, produces phenol in yields
that have been reported at over 50
percent.183 Activated charcoal is pro-
duced by pyrolysis of black-liquor
effluents.183
SMELTING
There are several processes for re-
covering heat and chemicals from
sulflte wastes by evaporation followed
by smelting. Among these are the In-
stitute process, the Mead process, the
Sivola process, the Stora Kopparberg
process, the Western Precipitation
(Bradley) process, the Sulfox process
and the A. D. Little process. The
capital investment for smelting for a
200-pound-per-day plant ranges from
$2.45 million to $3.32 million, depend-
ing on the process used.873
PYRJTE CINDERS AND TAIL-
INGS
A number of nonferrous metals can
be recovered from cinder, which is the
residue, essentially iron oxide, from
burning pyrite for the manufacture of
sulfuric acid. Cinders, in some circum-
stances, are valuable as sources of iron
for making iron and steel. In many
cases, however, cinders contain small
but objectionable amounts of nonfer-
rous metals. Hence cinders can be
processed to recover nonferrous metals
while beneflciating the iron product.
The kinds and amounts of recoverable
nonferrous metals in cinder depend
on the composition of the pyrite that
is burned in forming the product. One
author has stated that a mixture of
residues from pyrite produced in
European countries contained over 50
elements. Most of those elements were
present in such minute amounts that
recovery was not feasible.
Copper, cobalt, and zinc have been
recovered from cinders containing less
than 1 or 2 percent of any one of these
elements. The usual procedure is to
roast the cinder, mixed with about 10
percent of common salt, at about
1,100 P in multiple-hearth furnaces.
The gas from the roasting furnaces is
scrubbed with water, and the resultant
liquor is used to leach the calcine
produced. The roasting operation ren-
ders the desired metals soluable in the
weak acid effluent from the gas
scrubber.
Copper is removed from the leach
liquor by cementation with scrap iron.
The product is sent to a copper smel-
ter for refining and marketing. If
cadmium, thallium, and indium are
present in the decopperized liquor,
they are precipitated by cementation
with zinc dust. Cobalt is removed by
oxidizing with chlorine and precipita-
ting with zinc hydroxide. The filtered
precipitate is calcined to produce
cobalt oxide for sales. Zinc is precipi-
tated as zinc hydroxide by use of lime.
The precipitate is thickened, filtered,
dried, and finally calcined to produce
material suitable for reduction by the
electrolytic process.
Iron oxide can be recovered from
pyrite tailing by heating the tailings
to 2,000 F. The liquid ferrous sulfide
can be granulated and roasted to give
iron oxide and sulfur dioxide. Sub-
limed lead, zinc, and sulfur vapor can
be condensed and separated.585 Pyrite
wastes can be purified by extraction
and reused.126
See also: Coal Refuse.
REFRACTORY
The W. E. Plechaty Company of
Cleveland has developed a nearly
automated process for reclaiming re-
fractory material from nearby steel
mills. In steel manufacture, refractory
linings in furnaces and ladles are
eroded by the process so that at least
50 percent of the refractory is lost in
the slag. When the remaining refrac-
tory is too thin for proper contain-
ment, the furnace or vessel is shut
down, and the deteriorated refractory
is removed and replaced by the new
refractory. The discarded material is
removed from the mill and is proc-
essed in the following manner: (1)
magnetic removal of all irons; (2)
screening of all fine particles either
good or bad; (3) hand sorting to type
and quality; and (4) crushing and
screening for a marketable refractory
product.
The high costs of automation, the
industry's label of "salvage or used",
and the lack of trained supervision in
this field have combined to place a
tremendous limitation on expansion
of this reclaming system into other
areas.
See also: Foundry Wastes; Refer-
ence 116.
REFRIGERATORS
See: Sanitary Landfill and Open
Dumping; References 35,530,555.
RICE
The adsorption properties of car-
bonized rice hulls and rice stalks have
been evaluated.867
See also: Pood-Processing Wastes.
RUBBER
See also: Reference 303.
INCINERATION
Use of a two-combustion-chamber
incinerator incorporating burners in
both chambers to insure complete
combustion reportedly solves the odor
and smoke problem of incinerating
rubber wastes.228 A packaged unit
complete with afterburner is mar-
keted and used for incineration of
rubber waste.560
OXIDATION
Ozonization treatment of rubber
waste with hydrogen peroxide yields
a material useful in polymerization.170
PYROLYSIS
Under proper conditions of pyrol-
ysis, waste rubber yields materials
that are useful as solvents, plasti-
cizers, and surface-active agents.
Thermal cracking of waste rubber
yields a mixture of maleic acid and
oil which is useful as a plasticizer.129
Pyrolysis of waste rubber yields a
fraction that can be used in the pro-
duction of surface active agents.355
Scrap rubber can be destructively dis-
tilled leaving an ash residue.81' "8 Dis-
tillation of scrap rubber results in a
light fraction suitable for a varnish
solvent and a residue that can be
used as a filler.108
SAL SKIMMINGS
Sal skimming are spent flux re-
moved from the surface of galvanizing
baths on which fluxes are used. They
are a mixture of metallic zinc, zinc
oxide, and some of the zinc ammoni-
um chloride of the original flux. Sal
skimmings are the least desirable and
hence the least valuable of the wastes
from galvanizing operations. They are
poorly suited to the distillation and
electrolytic processes for reclaiming
zinc because of their chloride content.
For that reason, most of the sal skim-
mings produced in the United States
(over 25,000 tons annually) are treat-
ed chemically.
One method is to leach the sal
skimmings with muriatic acid and to
remove the insolubles, which include
heavy metals formed by cementation
with the metallic zinc. A liquor con-
sisting of about 46 percent zinc chlor-
-------
Magnetic separation, screening grinding 49
TABLE 12
THE PRODUCTION AND UTIIIZATION OF BLAST-FURNACE SIAG IN 1957 (HO
Slag type
Slag processed
(short tons)
Utilization
Screened 25,414, 327 82% used as railroad ballast, aggregate in
air-cooled portland-cement concrete construction, all
types of bituminous construction, and mis-
cellaneous highway and airport construction.
Unscreened 2, 166, 678 61% used as aggregate in highway and airport
air-cooled construction.
Granulated 4, 318, 485 43% used as raw material in manufacture of
hydraulic cement; 45% used in constructing
base and insulating courses for highways and
also as road fill; and 12% used in concrete-
block manufacture and in agricultural and
miscellaneous uses.
Expanded 2, 941, 650 Bulk used in manufacture of lightweight con-
crete blocks.
ide and 4 percent ammonium chloride
is produced. Ammonia is added and
zinc ammonium chloride is crystal-
lized from the resulting solution. That
product is sold for galvanizing flux.
SAND
See: References 34, 187, 360, 503.
SEAFOOD
See: Fish.
SHINGLES
See: Sanitary Landfill and Open
Dumping.
SISAL
Wax is extracted from sisal
wastes.89
SLAG
Large quantities of various types of
slags have been processed and mar-
keted by industry for a variety of uses.
According to Chemical and Engineer-
ing News in 1959, from 30 to 35
million short tons of ferrous blast-
furnace slag were being produced
annually by the steel industry for
eventual reuse.559 Pit and Quarry
stated that 35 million tons of blast-
furnace slag valued at $52 million
were produced in 1957.5U Approxi-
mately 72 percent of this slag was
processed by methods involving the
separation of solid particles. Accord-
ing to Blast Furnace and Steel Plant,
slag processors recovered 409,259
short tons of iron from blast-furnace
slag in igse.249 In 1961 a British blast-
furnace slag plant was turning out
products for varied uses.166
Open-hearth slag has not been
utilized as extensively as blast-fur-
nace slag; its use has been largely ex-
perimental in nature. Chemical and
Engineering News stated in 1959 that
from 18 to 20 million short tons of
open-hearth slag were being produced
annually by the steel industry.650 Of
this amount, United States Steel alone
produced 6 million short tons, but
processed less than half of it for
marketing.
Most of the blast-furnace slag pro-
duced has been utilized in the manner
indicated in Table 12. It has also been
employed: (1) in glass for the manu-
facture of amber bottles; (2) In fiber-
glass manufacture; (3) As a condi-
tioner for oyster beds; and (4) As a
conditioner for cranberry bogs.
Open-hearth slag has not been
utilized as extensively as blast-furnace
slag, but it has been used: (1) As an
agricultural liming material and fer-
tilizer; (2) as a soil supplement and
conditioner; (3) as railroad ballast;
(4) as highway chips; (5) as a sealing
for highway surfaces; (6) as highway
fill; (7) as an aggregate for the manu-
facture of bituminous concrete; (8)
as a sand-blasting grit; and (9) as
a source of trace elements.
The slag produced during the manu-
facture of elemental phosphorus has
been utilized: (1) As a road-base ma-
terial; (2) in septic-tank drain fields;
(3) as a drainage stone in sewer lines;
and (4) as a roofing aggregate.
See also: Recovery and Utilization;
Foundry Wastes; Inorganic Resi-
dues; References 184, 403, 550.
CALCINATION
Slags have been calcined to produce
cement, three types being produced.
In 1939 there were 600,000 tons of
blast-furnace slag alone used for this
purpose.54'16S| 3U
INCINERATION
Refractory ceramics have been
made by burning slag.116
MAGNETIC SEPARATION, SCREEN-
ING, GRINDING
Open-hearth and blast-furnace
slags have commonly been prepared
for various markets by magnetic sepa-
ration and screening. Magnetic sep-
aration has usually been employed for
the recovery of tramp-iron, scrap and
primary ferrous metal. Screening has
often been used to size the slag itself
into fractions suitable for various uses.
Trauffer has described the process
employed at one Detroit plant for
treating 110 tons per hour of blast-
furnace slag by means of magnetic
separation and screening to produce
eight fractions of sized slag.455 And
Peck has described a similar but
smaller operation which produces six
sizes of screened blast-furnace slag
at a rate that varies from 300 to 350
tons per hour.343 The sizing of both
blast-furnace and open-hearth slag at
a single plant has been described by
Utley.459 Rock Products briefly men-
tioned how one plant sized phorphorus
slag at the rate of 700 tons per day.86*
Trauffer45* has also described the
production of sized agricultural slag
from basic open-hearth slag by means
of magnetic separation and screening.
The Birmingham Slag Division of
the Vulcan Materials Company at
Wylam, Alabama, has processed basic
open-hearth slag produced at Bir-
mingham and stockpiled at Wylam
-------
50 SOLID WASTE PROCESSING
Basic open -hearth slag
75-Ton Hopper I
i
12" x 14" Bar
Grizzly
1
24" x 40" Syntron
Vibrating Feeder
*
30" x 60' Belt
Conveyor
*
4' x 8' Tyler Single-Deck ,
2" Scalping Screen '
+2" -2"
t
:o" x 40"
Good Roads
Jaw Crusher
With 1 3/4" Set
24" x 15'
Belt Conveyor
1
Dings Magnetic
Head Pulley """
*
Conveyor
*
Link-Belt Bucket Elevator
»
Pust -j otaiy Cooler (u x 40 )
' t
Dusuactor Dusuactor Link-Belt Bucket Elevator
Multicyclone -" « — Muiucyclone ^
Dust Collector Dust Collector 4' Symons Short Head Cone
A- A,r Crusher With 3/8" Set
f i _ 1
Whirlex Whirlex Bucket Elevator
Wet separator Wet separator # Iroi
1 1 | steel Bin J
L i — .J I
\ \ 1
Jj ^ 20" x 30" Syntron
Sl^ge to Gardner- vwnng ••«.«
settling P»nv?r t
pond Blower | 24" Belt Conveyor
1 \
Two 10* x 12' Mine & Smelter Marcy
800-Ton Ball Mill With 3/4" Discharge Grate
Storage •< ,
Silos
7570 -100 mesh
1
Bucket Elevator 10" Link-Belt Elevator
*
stock
' i
iron
pile
Dings
— Magnetic
Head
Pulley
"Rabbit ear"
Belt Conveyor
Alhs-Chalmers Aerovibe +20-
^. , Single-Deck 20-mesh mt,.h ^
'^ — — mesh mesn ~~
slcg Screen (5' x 10') slag
FIGURE 7. Processing of U.S. Steel basic open-hearth slag at Wylam, Alabama.
-------
by the United States Steel Corpora-
tion. Slag ranging in size up to 12-
to 15-inch chunks has been treated
in this plant at the rate of 60 tons
per hour by the process illustrated in
Figure 7. Large pieces of slag held
up by the bar grizzly are sledged
through it to the vibrating feeder.
Kach of the Dustractor dust-collect-
ing systems employed has a capacity
of 28,000 cubic feet per minute. The
Marcy ball-mill grinds an average of
60 tons of slag per hour to at least 75
percent minus 100 mesh. It has a 4-
inch manganese steel lining and is
charged with 60 tons of United States
Steel high-carbon-steel grinding balls
ranging in diameter from 1 to 4
inches. The belt conveyor employed
to recycle the plus 20-mesh slag is
equipped with a Dings magnetic head
pulley, which removes any remaining
iron and any undersize grinding balls
that may pass through the mill grate.
The entire mill circuit is connected to
a 10,000-cubic-foot-per-minute Pang-
born bag-type dust collection, which
discharges to the screw conveyor that
reclaims processed slag from the stor-
age silos. This processed slag has been
sold at USS Basic Slag for use as a
soil conditioner.
SODIUM
See: Reference 123.
STARCH
Gluten, the principal by-product of
the starch industry, can be obtained
by evaporating steep water. It is used
for f eed.*84
STONE SPALLS
Boynton has pointed out that in
most limestone-processing operations
there are large tonnages of stone sizes
that cannot be used or sold, at least
without further processing and classi-
fication." These "spalls" may accumu-
late to the extent that they consti-
tute a storage problem. Since the cost
of producing such waste stone has
already been absorbed, the waste may
have no value, or even a negative
value. Through research and re-
processing, it is often possible to
obtain salable products from such
wastes by grinding and screening at
low cost, often at costs appreciably
lower than costs of other producers
manufacturing the same gradation as
a prime product. The market may
then become sated, and prices badly
depressed, and the prime producer
may lose both volume and profit. Such
by-product-stone sources may be only
temporary, disappearing in a year or
two after the spalls are exhausted.
But the unpredictable availability of
such byproducts and the sporadic
losses it causes is a serious problem
to the prime manufacturer. The con-
stant threat of such competition
serves as a depressant on stone prices.
Similarly, a large captive stone pro-
ducer, typified by the lime, steel,
alumina, alkali, and other industries,
processes stone primarily for its own
use as kiln feed, flux stone, raw ma-
terial, etc. The cost of producing this
stone is absorbed by the end product.
Therefore, the sizes that cannot be
consumed are regarded as waste. Any
monetary return from the sale of such
stone is applied to reducing the over-
all cost of the end product. Convert-
ing such stone to marketable products
enables the captive plant to sell at a
lower price than the prime stone pro-
ducer can. Often such stone is not
merchandised, but is sold or "dumped"
at unreasonably low prices. Subse-
quently, prices of such by-products
may be raised to a reasonable level,
but meanwhile, dumping has a dam-
aging effect upon competition. In
many areas, by-product stone deter-
mines the price for all similar prime
stone.
SUGAR BEETS
Lime sludge from beet sugar mills
has been reburned in a fluidized-bed
reactor and recycled to the process.269
Lime sludges from beet-sugar mills
can be used as fertilizer for low-pH
soils.873
SUGAR CANE
See .'Bagasse.
SULFUR
Sulfur-refining wastes have been
burned in a fluidized bed.77
TANTALUM
See: Reference 145.
TETRAETHYLLEAD
Sludges resulting from the manu-
facture of tetraethyllead are prepared
for recovery of lead in the furnace by
compressing and pelletizing them un-
der pressure.162
TEXTILES
The major categories of solid textile
wastes have included cotton and cot-
ton linters, woolen scrap and rags,
woolen noils, scraps from silk, hemp,
flax, rayon, and other synthetic ma-
terials. These are recovered and re-
processed to yield lanolin, sugar,
paper, furfural, fiberboard, and ad-
hesives.
Titanium 51
See also: Recovery and Utilization;
Cotton; Reference 333.
CARBONIZATION
The vegetable-fiber content of
woolen rags has been treated with
gaseous HCI and the carbonized fibers
are removed, after which the material
is reused.203
EXTRACTION
Wool and linen waste, jute waste,
and rayon waste have been extracted
with an organic solvent to recover
wool grease.61
HYDROLYSIS
Hydrolysis with hydrochloric acid of
cotton linters yields sugar.248 Cotton
linters mixed with sulfuric acid make
an adhesive paste.493 Carding wastes
have been processed by hydrolysis to
produce cigarette paper.248 Furfural
has been obtained by hydrolysis of
linen and flax wastes.223'35°'416 Rayon-
pulp-mill rejects have been digested
and heated and formed into flber-
board.403
TIN
During World War II tin cans were
collected for the purpose of recover-
ing the tin. Collection of the cans was
costly, and processes for tin recovery
were not successful. However, this in
no way detracted from the success of
the initial hand-sorting operations
performed at the source.
See also: Recovery and Utilization.
TITANIUM
A processing method employed to
prepare titanium chips for marketing
has been described in an article ap-
pearing in Steel.™ The article states
that turnings of titanium that arrive
at the plant, in lots ranging from a
few hundred pounds to many tons,
are usually contaminated with other
alloys and with cutting oils. Each lot
must be identified and crushed.
Trained workers hand-sort the pieces
and use a series of chemical and elec-
trothermal tests to determine alloy
types and metal contents. After the
chips are identified and crushed, they
are thoroughly cleaned in a vibrating
degreaser to remove all traces of cut-
ting oil, greases, and fines. Other con-
taminating metal particles, such as
tool bits, are removed by special mag-
netic equipment as the chips are con-
veyed to an electronic checker, where
they are visually inspected before
packaging. The production of zirco-
nium, tungsten alloys, molybdenum,
columbium and tantalum from scrap
is covered in the Steel article.
In Iron Age a new furnace that per-
-------
52 SOLID WASTE PROCESSING
mits recovery of titanium scrap is
described.5"
CALCINATION
Pure gypsum can be obtained by
calcining waste sludge from TiOz
manufacture.™
ELECTROLYSIS
The production of high-purity ti-
tanium by electrolysis from scrap has
been discussed.557
EXTRACTION
Titanium oxide can be recovered
from solid wastes from titanium pro-
duction by leaching and chlorinating
to oxidize iron.121
MELTING
Waste sand from titanium mineral
processing can be made into a re-
fractory by melting it with bauxite in
a resistance-arc furnace.457
RECRYSTALLIZATION
The gypsum obtaned by neutraliz-
ing the waste acid from TiO2 manu-
factured with limestone can be cal-
cined and then recrystallized. The
properties of recrystallized gypsum
have been given.358
TOBACCO
See: Reference 230.
TUNGSTEN
See: References 61, 145.
URANIUM
Jasmy reported on a process for re-
covering uranium from unirradiated
fuel-element scrap.213 Techniques were
described for dissolving uranium-
stainless steel in nitric acid, uranium-
zirconium alloy in hydrofluoric and
nitric acids, and uranium-aluminum
alloy in sodium hydroxide and sodium
nitrate. The scrap is received as bil-
lets, turnings, strips, and fines. Ura-
nium has been recovered from the so-
lutions of dibutyl carbitol extraction,
with 99.9 percent overall efficiency.
The uranium can be stripped from
the carbitol with nitric acid to yield
pure uranyl nitrate.
See also: Separation.
VANADIUM
Vanadium is recovered from the
production of aluminum oxide by ex-
traction.463
VEGETABLE WASTES
See also: Agricultural Wastes; Ba-
gasse; Food-Processing Wastes;
References 103, 331, 513.
EXTRACTION
Pectin can be extracted from potato
pulp.498 Hemicellulose esters have been
extracted from lima-bean pods and
corn cobs.481 Protoplasts can be ex-
tracted from leafy wastes as chloro-
phyll derivatives for industrial and
pharmaceutical use.484
HYDROLYSIS
The sugar in green-pea hulls can
be hydrolyzed under pressure in sul-
furic acid and Torula utilis grown on
the sugars produced.444 Torula utilis
can also be grown on hydrolyzates of
reed grass refuse.460 Butanol and ace-
tone are produced from sugars from
corn cobs and other vegetable waste
products.315 The hydrolyzates of saw-
dust, sunflower wastes, cereal straw,
and the hulls, grits, and other wastes
of barley and millet milling have been
fermented to produce yeast."'U2' 1M
Plant residues have been subjected to
hydrolysis to obtain cellulose for use
in the manufacture of paper and
board. Agricultural residues,23'46' K°- 49°
tobacco wastes,114- 23° banana stems,
areca stalks,437 corn stalks,285 jute
sticks,169'299 the woody part of hemp,14
esparto grass,270 straw,368 and ba-
rt-Qop£>38. 21, 22, 2i. 42, 55, 75, 88-90, 10T, 146, 171, 102-
gctoot;,
201, 226, 252, 253, 263, 281, 290, 301, 325, 401, 411, 486, 528,
539 have all been used for this purpose.
A continuous process has been devel-
oped to prepare pulp from plant resi-
dues.298 Plastic can be obtained from
plant wastes by hydrolysis.331
PYROLYSIS
Fuels and solvents have been manu-
factured by pyrolysis of waste prod-
ucts from the fat and vegetable-oil
industries.395
WASTEPAPER
The reuse of wastepaper products is
a growing industry. Much effort is cur-
rently devoted to improving practices
and cutting costs not only by the vari-
ous individual companies, but also by
the research activities of the organiza-
tions to which the companies belong,
among which are the Boxboard Re-
search and Developments Association,
the Waste Paper Institute, and the
Technical Association of the Pulp and
Paper Industry.
Wastepaper that can be reused en-
compasses almost every type of paper
manufactured. According to the Waste
Paper Institute, some 40 grades are
recognized. Most of these grades refer,
however, to paper types that can be
classified as: (1) mixed paper, kraft
wrapping, old corrugated containers,
etc., from industrial concerns, depart-
ment stores, etc., (2) old newspapers
and magazines collected from private
homes or over-issues from publishers,
(3) waste from printers, envelope
manufacturers, etc., and (4) cuttings
from box and bag manufacturers.
The contamination of such paper
with polystyrenes and polyethylenes,
asphalt papers, carbon paper, and
plastic-coated paper has presented
difficulties and no means were found
reported for their economic separa-
tion. However, Kobor has described
a means of removing synthetic resin
contaminants by hydrolysis.235
Since the market value of waste-
paper products has varied widely, the
collection and treatment of it has been
somewhat risky. The approproximate
prices paid per ton in November 1966
for various types of reusable waste-
paper products were as follows: over-
issue news, $25; No. 1 news, $18; old
corrugated, $22; white ledger, $50;
books, $20; and manila tab cards, $85.
Sorting increases the value of waste-
paper products, but it is expensive.
From one half to 7 man-hours are
required to sort a ton of such material.
Considerable quantities of wastepa-
per have been collected by charitable
organizations and fed back into the
paper industry; this paper is hand
sorted at the home level. However,
when this material has been mixed
with other trash and hauled to a cen-
tral disposal point, its segregation and
reuse has been virtually impossible.
Charitable groups utilizing volun-
teer labor have been about the only
organizations that can afford to col-
lect newspapers, magazines, etc., from
private homes. Wastepaper dealers,
on the other hand, have been able to
profitably handle overissue news, con-
tainers, cuttings, etc. from manufac-
turers, since the cost incurred in their
disposal is often included in that of
their production. Contaminants must
first be sorted from any waste ground-
wood or pulp paper products destined
for use in the manufacture of the best
quality paper. The reuse of wastepa-
per has been comparatively common
in Europe where pulp wood has been
in short supply and where paper prod-
ucts of a relatively low grade are
utilized.
It is probable that almost every box-
board plant (2,300 in the United
States) uses waste in one form or an-
other, the majority employing only
mechanical disintegration. It has been
estimated that more than 30 plants
employ deinking operations with an
annual capacity over 500,000 tons.
See also: References 16, 397.
JUNK REMOVAL
Since few paper mills sort their
wastepaper before it is deinked, the
-------
Screening 53
stock that many of them treat for
fiber reclamation is often contami-
nated with waste materials other than
ink. The removal of these contami-
nants frequently involves the removal
of miscellaneous waste materials such
as dirt, cellophane, wet-strength pa-
per, adhesive tape, binding cement,
heat-seal label scraps, rubber bands,
paper clips, staples, plastics, baling
wire, rags, string, gummed tapes, and
pins. Material such as this must be
eliminated from the pulped paper fiber
before deinking to protect the paper-
making equipment and to insure the
proper quality and uniformity of the
finished paper product.
Junk removal is often achieved
by screening, centrifugal separation,
magnetic separation, or mechanical
sorting. The junk encountered in most
wastepaper is of such a variety that
both screening and cycloning are re-
quired to remove it. While the removal
of junk from pulped paper is fre-
quently employed in conjunction with
deinking operations, it is not consid-
ered an inherent part of the deink-
ing process itself.
Brown refers to the removal of for-
eign matter from pulped fiber by
means of screening, magnetic separa-
tion, and centrifugal separation.00
Large pieces of such material can be
removed by perforated plates if they
are not broken up during the pulping
of the fiber. Metallic objects of iron
such as paper clips and staples are
frequently removed by magnetic
separators.
McKela has described several pieces
of equipment that are utilized in the
removal of junk from pulped waste-
paper.289 The ragger and bucket ele-
vator or junk remover are commonly
employed to clean the pulped fiber
produced by the Hydrapulper. These
devices operate efficiently with mini-
mum fiber loss when treating Hydra-
pulper consistencies that range from
1.5 to 2.5 percent. In this consistency
range, the ragger and junk remover
are most efficient in the removal of
baling wire, rags, string, gummed
tapes, wet-strength papers, etc., and
bottle caps, wood, beer cans, glass,
nuts and bolts, etc., respectively. The
ragger consists of a double-serrated
sheave with an adjustable, weighted
wheel that holds the rag or rope in
place. Power is supplied to the device
by a small, variable-speed motor that
governs the rate at which the rope is
withdrawn from the Hydrapulper tub.
The action involved in the separation
of materials by the ragger can be de-
TABLE 13
TYPICAL FOKMUIATIONS USED WITH FLOTATION MACHINES
II
0.8% triton X-100 1.5% Na202.
2.0% tripolyphosphate.^ ... __ 3.75% Na2Si03.
1.7% soft soap _ 3.0% soap.
1.3% CaCla CaCl2 to produce equivalent CaC03-
hardness of 215 ppm.
Cook in Hydrapulper 30 min at 120 F Cook in Hydrapulper 30 min at 120 F.
Float 3-5 min at 0.8% consistency Float 3-5 min at 0.8% consistency.
scribed as a form of mechanical
sorting.
See also: Separation.
DEINKING
If separation of ink and dirt from
paper is required, screening or flota-
tion is usually done after the waste has
been mechanically hydrapulped with
chemicals to free contaminants from
the fibers. Chemicals commonly used
to loosen ink are sodium silicate, so-
dium peroxide, soda ash, soap, deter-
gents, and phosphates. Hydrapulping
is normally done at 120° to 160° F. for
an hour or more. Consistencies may be
as low as 4 percent or as high as 25
percent, depending upon the system
employed.
After hydrapulping and cooking,
the pulp, at less than 1 percent con-
sistency, is passed over various types
of screens to remove coarse impuri-
ties, and probably through cyclone-
type devices for removal of heavy dirt
and metallics. The pulp is then ready
for deinking by either flotation or
screening (washing).
In the screening-washing type of
cleaning, the operation is performed
on multistage washing cylinders cov-
ered with wire of about 65 mesh. Cop-
ious amounts of wash water are re-
quired to remove the carbon, fillers,
etc. Fiber recovery of 85 percent may
be anticipated with a chemical cost of
$10 to $15 per ton. Generally speaking,
the higher the chemical consumption,
the brighter the recovered stock.
See also: Reference 324.
FLOTATION
Flotation may also be used to re-
move the contaminants from waste-
paper treated in secondary reclama-
tion systems. After proper preparation
with chemicals the pulp is treated in
flotation machines, and the contam-
inants removed as a froth or scum.
Two typical formulations are shown
in Table 13.
Recent developments have indicated
that polystyrene and polyethylene
materials may also be removed by
flotation.
The cost for flotation machines for
a 50- to 100-ton-per-day plant would
be approximately $50,000 to $75,000,
depending on the time of float. Only
one operator would be required per
shift. The primary cost item in proc-
essing is that of chemicals and may
be from $10 to $15 per ton of paper.
Labor, maintenance, and power should
not exceed $1.00 per ton. A fiber re-
covery of 90 percent may be expected.
After the impurities are separated,
bleaching may be used to whiten the
stock before it is prepared for use by
further washing and thickening.
See also: Separation.
MECHANICAL DISINTEGRATION
Another method of wastepaper proc-
essing is simple mechanical disinte-
gration in an agitator, such as the
Hydrapulper manufactured by the
Black Clawson Company, until the
fiber has been beaten up to the de-
sired fineness. A similar machine is
the Wet Pulper, manufactured by the
French Oil Mill Company. Material
so processed can be utilized as a filler
in the manufacture of boxboard,
matches, and other low-grade prod-
ucts where color and/or specks are
not objectionable and where bulk is
the primary requirement.
See also: Separation.
SCREENING
Kleinau has described the process
utilized by the Bergstrom Paper Com-
pany of Neenah, Wisconsin, for the
-------
54 SOLID WASTE PROCESSING
Wastepaper
Rejects to sewer
Fiber
Fiber to washing system
FIGURE 8. The deiriking of secondary paper fiber by screening.
deinking of secondary paper fiber by
screening.232 The process, illustrated
in Figure 8, has been employed pri-
marily for deinking pulped secondary
paper fiber, but contaminants such
as plastic and rubber can also be
eliminated. The entire stock of pulped
paper is first passed over only two
Jonsson screens at a flow rate above
that of their normal screening capac-
ity. This is done to assure a high rate
of reject flow to the subsequent de-
fibering operation. The fiber bundles
and ink of the reject pulp are then
broken up in a defibering machine
known as a Supraton fiberizer. A
third Jonsson screen is finally em-
ployed to separate the reject mate-
rial from the clean paper fiber of the
defiberized pulp. The cleaned stock
produced by the three screens is sub-
sequently transferred to the pulp-
washing system, while the reject
material is discharged to sewers.
In this operation, the fiberizer
treats a pulp consistency of slightly
under 3 percent at a throughput of
12 tons per day of stock, a flow rate
equivalent to about 7 percent of the
total. The fiberizer utilized has been
supplied with a 75-horsepower motor,
but used only 25 horsepower at a rate
of 2.1 horsepower-day per ton. This
fiberizer was unique in that it facili-
tates the screening of extraneous
material, such as rubber and plastic,
from the paper fiber by permitting
them to pass unchanged through the
defibering operation.
Lehman has considered the general
application of various types of
screens to the cleaning of waste
paper in deinking systems.267 Screens
have been employed in these systems
primarily to remove nonferrous ma-
terials of low specific gravity.
Multistage screening systems have
been employed by many mills in an
effort to derive the maximum benefit
from their fine screens. The coarse
screens utilized in these systems must
have large holes and a high capacity
per unit to remove large particles.
The vibrating-deck screen has been
most commonly used for this pur-
pose, but flat screens, rotary-type
screens, and pressure screens can be
employed as well.
Most of the fine screens in use have
been designed to use fine-slotted
-------
plates. The types most frequently en-
countered are the flat screen and the
rotary-vibratory screen. Fine screens
with round holes have, however,
proved to be much better. Pressure
screens and centrifugal screens are
types of round-holed screens that
should be strongly considered in any
new or revised screen layout. Vertical
pressure screens have come close to
being the ideal fine screens, as they
operate in a closed system that is both
clean and quiet.
Reject or tailing screens have been
employed in the multistage systems
because fine screens do not function
efficiently without rejecting good fiber
with waste material. Flat and vibrat-
ing-deck screens are the only types
of screens capable of achieving the
clean separation of fiber and fiber-
free waste.
See also: Separation.
CYGLONES
The general application of cyclones
to systems involved in the deinking
of secondary paper fiber has been re-
viewed by Fahlgren.131 Cyclones em-
ployed in the pulp and paper industry
have ranged in size from 3 to 48
inches in diameter, and in throughput
from less than 20 to as much as 6,000
gallons per minute respectively.
Large-volume cyclones have largely
replaced the space-consuming riffler
for the removal of dirt from pulped
paper fiber. Separations achieved
with them have been far superior to
that achieved by the riffler, at both
high and low stock consistencies.
Large cyclones are usually em-
ployed after pulping and prior to
screening for the removal of junk such
as bottle caps, paper clips, tramp iron,
rocks, and coarse sand. The following
types of cyclones are suitable for the
removal of such material: (1) large-
volume cyclones operating at rela-
tively low consistencies, (2) large-
volume cyclones capable of handling
high-consistency stocks, and (3) rel-
atively low-volume cyclones capable
of operating at consistencies as high
as 61/2 percent air dry.
The smaller cyclones, ranging in
diameter from 3 to 12 inches, have
been widely employed for the removal
of shives and specks from low-density
stocks. Installations of these cyclones
have been either single or multistage,
the primary units often being
equipped with a secondary unit. These
units are efficient dirt removers and
operate with a minimum loss of fiber.
The maximum cleaning efficiency has
been provided, however, by a multi-
stage installation involving the dilu-
tion and recirculation of fiber pulp
between stages. The rejects from the
primary cyclones usually contain
good, usable fibers that can subse-
quently be recovered in second, third,
or fourth stages. Small cyclones op-
erate according to the following prin-
ciples as given by Fahlgren151: (1)
The smaller the cyclone diameter, the
more efficient the removal of specks
and fine dirt particles; (2) the larger
the diameter, the longer the shive
that can be removed; (3) the higher
the efficiency of speck removal, the
higher the concentration of short fi-
bers; (4) for the smaller diameter
units, consistency of 0.5 percent is
most effective; lor larger diameter
units, 0.7 percent is considered eco-
nomical and efficient; (5) secondary
and following stages should operate
at lower consistencies than the pri-
mary stage; (6) reject rate is con-
trolled by the back pressure and the
size of the reject opening; and (7)
the back pressure should be kept con-
the back pressure should be kept
constant for maximum cleaning
efficiency.
The size and number of cyclones
required for a given operation may be
determined by the character of the
furnish, the character and amount ol
foreign particles to be removed, and
the volume of the stock to be handled.
A high-capacity, high-efficiency, pri-
mary cyclone can be used for the re-
moval of low- and medium-specific-
gravity materials (such as glass and
sand), which often pass through the
perforations of the Hydrapulper with
the stock flow. This device is equipped
with conical ceramic inserts that have
proven to last longer than those of
alloy steel.
See also: Separation.
WOOD WASTES
Wood wastes start in the forest
where only about 81 percent of the
tree is removed as sawlog, in the
lumber mills where 16 percent is
wasted as sawdust and 34 percent as
slabs and edging, and in the paper
mills where about 50 percent of the
log is discharged in waste effluents or
is disposed of by burning. Wood
wastes can be processed to recover a
variety of by-products, but these
processes have been applied to only
a small extent.
Lignin, the main noncellulosic con-
stituent of wood, can be processed to
obtain valuable chemicals, such as
pure lignin and dimethyl sulfide. It
can also be utilized without processing
Condensation 55
as a binder, a dispersant, an emulsion
stabilizer, and a sequestrant.
The hemicellulose or polysaccharide
portion of the wood is readily hydro-
lyzed into simple sugars. In the sulfite
process, about 300 to 400 pounds of
hemicellulose have been converted into
sugar for each ton of sulfite pulp pro-
duced. Although processes for utilizing
these sugars are technically feasible,
the economics have been unfavorable.
Studies in Canada have shown that
the minimum economical size for a
plant to produce alcohol would pro-
duce 1 l/z tomes the national consump-
tion of alcohol. Fodder yeasts and or-
ganic chemicals such as furfural are
important products of sugars from
hemicelluloses, and the market for
these materials could grow.
Sawmill waste® can be utilized by
the pulp industry to a large extent.
Several mills in Canada have formed
cooperatives and purchased the equip-
ment needed to bark and chip wood
wastes to make them suitable for pulp-
ing. Waste bark and mill waste have
also been sent to companies that make
wallboard and roofing felts.
The proximity of a healthy petro-
chemical industry on this continent
has kept the pace of chemical utiliza-
tion of forest products considerably
behind that of the Scandinavian
countries, since many wood chemicals
are competitive with petroleum chem-
icals. Experimental work is being done
in this country to make a lignin-type
plastic from wood waste.
See also: References 202, 436, 442,
456.
ACIDIFICATION
A pasty coal igniter has been pre-
pared by treating a mixture of peat,
sawdust, and cellulose wastes with
acid and wetting the product with
sulfur in gasoline.434 Cellulose, oxalic
acid, acetic acid, vanillin, tannin, etc.,
are recovered from wood and vegetable
waste in an apparatus specially de-
signed for continuous recirculation of
nitric acid through the waste.103
CARBONIZATION
The activity of carbons from saw-
dust in relation to the activation proc-
ess has been described.231 "* Dry distil-
lation of sawdust was reported to yield
activated carbon of high grade.260
CONDENSATION
Lignocellulosic wastes have been
condensed with sulfur compounds and
digested with water at high tempera-
ture to produce plastic material suita-
ble for pressing into boards.317
-------
56 SOLID WASTE PROCESSING
DEHYDRATION
Charcoal of high discoloration
power can be obtained from sawdust
by dehydration with, sulfuric acid.73
EXTRACTION
Extractives, the noncellulosic por-
tion of wood extractable by neutral
solvents, include a number of poten-
tially valuable organic chemicals. An
adhesive that is cold-setting and
waterproof has been called one of the
most promising extract products.
Wood wastes can be extracted with
gasoline15i and methyl alcohol2K to ob-
tain rosin.
GRAVITY SEPARATION
The application of gravity separa-
tion to the recovery of waste wood
produced in the pulp and paper indus-
try has been described by Wesner.478' 47°
HYDROLYSIS
The conversion of wood cellulose to
fermentable sugars has been the sub-
ject of numerous investigations.52'90> 12°
158, 211, 221, 238-240, 246, 275, 282, 302, 327, 341, 416, 416
504 Yeast containing 25 percent fat
has been grown in these sugars.428 Al-
cohol has been distilled from the fer-
mented wood sugars.185' ** White wine
can be obtained by refluxing sawdust
with sulfuric acid.685 The glucose ob-
tained from lumber and pulp-mill
leftovers can be concerted to levulinic
acid and formic acid.182 Wood as a
chemical raw material has been dis-
cussed by Wenzel."7 Furfural is an im-
portant product of wood hydrolysis.
2W, Sltt, 223, 327, 350, 408 Many autn(jrs repOrt
on the use of wood wastes in the man-
ufacture of paper board.160' ""• m- m' ™
«0, 440, «1, 494, 542, 566 The influenCe Qf fearfc
on the properties of pulp has been de-
scribed.353' 3M
See also: References 104, 328.
INCINERATION
Wood residue has been incinerated
in tepee waste burners with some de-
gree of air pollution—low enough to
be acceptable in some areas.56 Wood
waste has been used for fuel in a large
water tube boiler.398 The products of
combustion of wood wastes can be
used to produce ammonia.376
See also: References 354, 533.
OXIDATION
Oxidation and hydrolysis under
pressure followed by hydrogenation
has appeared to be a possibility for the
preparation of various petroleum
chemicals from wood wastes and agri-
cultural residues.477
Fertilizer can be prepared from saw-
dust or wood chips by first oxidizing
the material with nitrogen dioxide
and then adding ammonia to increase
the nitrogen content.142 Mellitic acid
and other polycarboxylic acids can bs
obtained by nitric acid oxidation of
sawdust.147 Sawdust has been added to
kilns to reduce iron in the production
of ferronickel from nickel ores.80 Oxi-
dation of lignin waste and sawdust
with either phenol nitrate or copper
oxide yields vanillin.184'10E
SCREENING
The application of screening to the
sizing of bark was mentioned by Pierce
and Sproull in their description of a
process involving the conversion of
bark to plant food.349 The production
of plant food and soil-amendment
products from southern pine bark by
the Greenlife Products Division of The
Chesapeake Corporation of Virginia
was the first commercial application
of this process (United States Patent
2, 881,066). In the process, bark is
first ground and then screened into
various size fractions. Selected size
fractions are subsequently steamed at
a temperature above 170° F. and im-
pregnated while hot with solutions of
various nutrients. After the bark has
been impregnated, it is dried and
bagged. Information concerning proc-
ess costs and equipment has not been
available.
See also: Separation.
PYROLYSIS
Dry distillation of sawdust and wood
wastes yields activated carbon of high
grade together with methanol, acetic
acid, acetone and wood tar as by-
products.200' *" high temperature and
catalytic cracking during pyrolysis of
sawdust produces an equimolar mix-
ture of hydrogen and carbon mon-
oxide.433 The heat values of the fuel
gas obtained have been given.115 Saw-
dust can be decomposed in a fluidized
bed.115'242-495 Thermal decomposition of
wood in aqueous medium under pres-
sure resulted in larger amounts of
chemicals than destructive distilla-
tion.241 After recovery of products ob-
tained by heating sawdust soaked in
kerosene at temperatures below 275°
P., the temperature is raised, the kero-
sene is distilled, and the residue is
used as a fuel.417 While the pyrolysis
of wood to produce acetic acid and
methanol was in past years a substan-
tial industry, it has largely been sup-
planted by synthetic methods. How-
ever, recently about 20 million pounds
of acetic acid a year and 14 million
pounds of methanol a year was being
produced by the old process.182
VAC-SINK PROCESS
The Vac-Sink Process was developed
for recovery of the wood fraction from
waste products.478'4T9 The separation is
based upon the inducement of a grav-
ity differential between the wood and
the bark. After the bark has been
freed from the wood with a chipper,
the mixture is immersed in water and
a vacuum is applied. Entrained air is
easily withdrawn from the continuous
and interconnected passages of the
wood but not from the collapsed pas-
sages of the bark. The release of the
vacuum causes water to enter the vas-
cular passages of the wood formerly
occupied by air. The heavy combina-
tion of wood and water quickly sinks
away from the lighter combination of
bark and air that remains at the water
surface. Wood recoveries of over 90
percent are usually achieved in wood-
bark separations such as this.
The Vac-Sink process was first em-
ployed on a commercial scale at the
Savannah, Georgia, mill of the Union
Bag-Camp Paper Corporation. This
plant can process waste wood at a ca-
pacity equivalent to 100,000 cords of
wood per year. The wood recovered by
the plant can subsequently be proc-
essed to make paper, the bark being
utilized as a fuel. Cost data and infor-
mation concerning the equipment em-
ployed in the plant have not been
available.
See also: Agricultural Wastes; Pulp
and Paper; Sanitary Landfill and
Open Dumping.
WOOL
See: Textiles; Reference 421.
YTTRIUM
Provow and Fisher published a pa-
per describing a process for reclaim-
ing yttrium scrap by chemical pro-
cedures.357 According to these authors,
yttrium can be recovered from wastes
by burning the wastes and dissolving
the residue in nitric acid. The impu-
rities can be removed by precipitation,
the yttrium then being precipitated
with oxalic acid.
Provow and Fisher have also de-
scribed a low-cost process that uses
readily available chemical reagents
and equipment to reclaim yttrium
from scrap in the form of small pieces,
turnings, and saw filings.357 The scrap
is converted to crude oxide by ignition.
One-hundred-pound batches of the
minus 80-mesh oxide are dissolved in
50 percent nitric acid. The resulting
solution is purified by hydrolysis of
zirconium, iron, aluminum, and tita-
nium. Then potassium ferrocyanide is
added to precipitate copper and nickel.
The yttrium is precipitated as oxa-
late with oxalic acid, after which the
-------
Zirconium 57
filtered and washed precipitate is ig-
nited to produce the oxide. The chem-
ical costs of a large-scale operation
were reported as $0.67 per pound of
yttrium oxide.
See also: Nonferrous Scrap.
ZINC
See also: Lead; Pyrite Cinders and
Tailings; Sal Skimmings.
EXTRACTION
Weak hydrochloric acid has been
used to leach zinc from waste mate-
rials.313 Cadmium is extracted from
the residue of zinc refining with sul-
furic acid. The acid solution is elec-
trolyzed to recover cadmium.249
GRAVITY SEPARATION
Phillips briefly mentioned the ap-
plication of gravity separation to the
recovery of zinc from contaminated
crusts of zinc and zinc oxide in zinc-
smelting operations.347 These crusts
form on the fireclay condensers
utilized in the reduction of zinc in
horizontal retorts. The spent con-
densers have usually been crushed to
produce metal-bearing refractory
particles which have subsequently
been treated in jigs and on shaking
tables to produce a concentrate con-
taining from 60 to 70 percent zinc
and from 60 to 80 percent of the con-
denser zinc. This concentrate can
eventually be recycled to the retorts.
Heavy-medium separation has been
applied in one plant to recover me-
tallic zinc from electrothermic zinc
residues.
See also: Separation.
HYDROMETALLURGICAL
PROCESSING
Zinc metal has been produced from
zinc oxide in retort or electrolytic re-
duction plants operated mainly for
the production of primary zinc. The
preferred method for reduction of
zinc oxide has been the electroly-
tic process. The procedure in one
plant treating zinc oxide fume alone
has been as described below.
The fume contained about 77 per-
cent zinc, about 1 percent each of lead
and iron, and less than 0.1 percent
each of germanium, cobalt, and cop-
per. It was ground in airswept ball
mills to about 70 percent minus 325
mesh and leached batchwise with the
sulfuric acid in spent electrolyte from
the deposition process. The resulting
neutral liquor of zinc sulfate was
filtered to remove iron and lead, and
the filtrate purified. Purification was
accomplished by stirring copper sul-
fate, arsenious oxide, and zinc dust
into the liquor. That treatment re-
moved and reclaimed germanium,
copper, and cobalt.
The purified zinc sulfate liquor was
electrolyzed in the conventional man-
ner with anodes of lead alloy and
aluminum cathodes. The deposition
of zinc was accompanied by the for-
mation of sulfuric acid in the
so-called "spent electrolyte". That
acid liquor was used to leach more
fume. The zinc sheets deposited by
electrolysis were stripped from the
cathodes, washed and melted. The
molten zinc was cast into slabs of
"Special High Grade" quality.
ZIRCALOY
Rubin and Gessner have described
the use of magnetic separation and
screening in the recovery of Zircaloy
scrap at atomic-power facilities.384
Chips produced during the machin-
ing of hot-rolled Zircaloy strip are
first crushed in a hammermill. The
crushed material is then conveyed
over strong magnets to remove mag-
netic contaminants and is finally
sized on a 20-mesh screen to elimi-
nate fine particles. The cleaned
Zircaloy is subsequently melted into
ingots for later reuse.
ZIRCONIUM
See: Nonferrous Scrap; Reference
145.
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-------
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U S GOVERNMENT PRINTING OFFICE 1970
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