-------
SECTION VI
SELECTION OF POLLUTANT PARAMETERS
Introduction
This section of the report reviews the waste character-
ization detailed in Section V and identifies in terms of
chemical and physical constituents that which constitutes
pollutants as defined in the act. Rationales for the
selection and, more particularly g the rejection of waste-
water constituents as pollutants are presented.
First, consideration was given to the broad range of
chemicals used in the metal finishing industry. Those
considered to be amenable to treatment are identified.
A larqe variety of chemicals that become waste water
constituents are used in the metal finishing. The important
ones were identified in Section V. Not all of these
constituents will be found In the i*&ste waters from every
facility, since the number of processes in a single facility
varies as well as the nurses: of b&sic materials pretreated
and types of posttre&tntent operations. When present, metal
ions are usually coprecipitated with copper, nickel,
chromium, and/or zinc. The nonmetallic cations and anions
(hydrogen, ammonium, sulfate^ phosphate, chloride, etc.)
from electroplating copper ? nickel, chromium, and zinc can
be considered typical of the metal finishing industry.
waste Water Constituents ami p&raaiatera of Pollutftonal
Significance
The waste water constituents of pollutional significance are
total suspended solids, phosphate^ oxidizable cyanide, total
cyanide, fluoride, aluminum, cadmium^ hexavalent chromium,
total chromium, copper, iron, nickel, tin, zinc, and pH.
These constituents are the subject of effluent limitations
and standards of performance regardless of the physical form
(soluble or insoluble metal) or chemical form (valence state
of a metal and whether or not it is complexed) .
The pH is subject to effluent limitations because it affects
the solubility of metallic compounds such as zinc hydroxide
and the soluble metal content of the treated effluent.
71
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Thus, the major chemical, physical, and biological waste
water constituents and parameters of pollutional
significance are as follows
Total suspended solids
Phosphate
Oxidizable cyanide
Total cyanide
Fluoride
Aluminum
Cadmium
Hexavalent chromium
Total Chromium
Copper
Iron
Nickel
Tin
Zinc
pH.
Other waste water constituents of secondary importance that
are not the subject of effluent limitations or standards of
performance are as follows
Total dissolved solids
Chemical oxygen demand
Oil and grease
Turbidity
Color
Temperature
72
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Nitrate
Ammonia
gaiiorjale £QT the Select log £f HMtS $£&££ G9niSfc4tVtaOtP ABd
Parameters.,.
suspended solids . Suspended solids was selected as a
parameter to further assure that efficient clarification is
practiced. control of total wsat-al discharged, i.e.f lead,
also assures that clarification td.il be efficient. However,
control of suspended solids i.lso assures that excess solids
will not be unnecessarily discr* surged. Furthermore, in spite
of extensive review of bot:h compositions and a listing of
waste water constituents there may be waste water
constituents In individual plants not covered by the
listings and not selected as polliixarit parameters. If such
constituents are also precipitated, by the chemical treatment
methods employed to remove 'psllutants that have been
selected as pollutant pa r& meters, they will be removed
providing there is a limltstcion en auipssnded Bolide. Metals
such an arsenic,, beyllitsmw, co-UKbioif, g&llium, germanium,
hafnium, manganese, molybdenum, titanium, tungsten, uranium,
vanadium^, and zirconium would be- irsmov«d to some extent by
neutralization and
Phosphorous. Phosphate is prvsse.^v. ira significant amounts in
cleaners, acia dips, a ad processing baths in Subcategory (1)
processes and can ba rencvsii by reaction with lime to form
insoluble caxciuEi phoapLtt'te^ Liuie is a suitable
neutralizing agenc and t'na piioaphate may therefore be
coprecipitated ivi-cn the hesvy aeiiils.
Cyanide, Amenable to Qxid£.-cl.:tg| bv Chlorine. Oxidizable
cyanide may be present in significant amounts in the waste
water from this segment, of the eLaetroplatiag industry and
is amenable -co oxidation by chlorine under alkaline
conditions.
Cyanide.^ Total, some forms of cyanide are not amenable to
chlorine oxidation and can appear in the waste water in
significant amounts which era w.iafc be removed. Cyanide is
present in waste waters c.s the free cyanide ion (CN-) or
complexed with metals such a.s copper* zinc, cadmium, and
silver. The free cyanide and the cyanide in the metal
complexes mentioned are destroyed by chlorine. However,
more stable cyanide complexes such as those with nickel,
cobalt, and iron are not effectively oxidised by chlorine,
although may be by ozone fsee Section VII) . Since iron,
cobalt,, and nickel are not plated from cyanide solutions
73
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their source, if present, is not from electroplating baths.
However, some cleaners and stripping solutions contain
cyanide and the dumps and rinses from these are normally
combined with rinses from nickel, cobalt, and iron baths to
constitute the acid-alkali waste water stream. There are
alternatives to use of cyanide in stripping solutions and it
is believed that the cyanide in cleaners can be minimized or
eliminated. Thus, it is practicable to limit the amount of
cyanide that is not amenable to oxidation and this may be
considered a pollutant parameter. Total cyanide is more
easily determined than difficult-to-oxidize cyanide. Since
it is made up of oxidizable cyanide which is a pollutant
parameter and difficult-to-oxidize cyanide, which could be
regarded as a pollutant parameter, the total cyanide is also
a pollutant parameter.
Fj-uogj-deg
As the most reactive non-metal, fluorine is never found free
In nature but as a constituent of fluorite or fluorspar,
calcium fluoride, in sedimentary rocks and also of cryolite,
sodium aluminum fluoride, in igneous rocks. Owing to their
origin only in certain types of rocks and only in a few
regions, fluorides in high concentrations are not a common
constituent of natural surface waters, but they may occur in
detrimental concentrations in ground waters.
Fluorides are used as insecticides, for disinfecting brewery
apparatus, as a flux in the manufacture of steel, for
preserving wood and mucilages, for the manufacture of glass
and enamels, in chemical industries, for water treatment,
and for other uses.
Fluorides in sufficient quantity are toxic to humans, with
doses of 250 to U50 mg giving severe symptoms or causing
death.
There are numerous articles describing the effects of
fluoride-bearing waters on dental enamel of children; these
studies lead to the generalization that water containing
less than 0.9 to 1.0 mg/1 of fluoride will seldom cause
mottled enamel in children, and for adults, concentrations
less than 3 or 4 mg/1 are not likely to cause endemic
cumulative fluorosis and skeletal effects. Abundant
literature is also available describing the advantages of
maintaining 0.8 to 1.5 mg/1 of fluoride ion in drinking
water to aid in the reduction of dental decay, especially
among children.
74
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Chronic fluoride poisoning of livestock has been observed in
areas where water contained 10 to 15 mg/1 fluoride.
Concentrations of 30 - 50 mg/1 of fluoride in the total
ration of dairy cows is considered the upper safe limit.
Fluoride from waters apparently does not accumulate in soft
tissue to a significant degree and it is transferred to a
very small extent into the milk and to a somewhat greater
degree into eggs. Data for freah water indicate that
fluorides are toxic to fish at concentrations higher than
1.5 mg/1.
Cadmium in drinking water supplies la extremely hazardous to
humans, and conventional treatment, as practiced in the
United states, does not remove ita Cadmium is cumulative in
the liver, kidney, pancreas, and thyroid of humans and other
animals. A severe bone and kidney syndrosne in Japan has
been associated with the ingsstion of as little as 600
ug/day of cadmium.
Cadmium is an extremely dangerous cumulative toxicant,
causing insidious progressive chronic poisoning in mammals,
fish, and probably other animals because the metal is not
excreted. Cadmium could form organic compounds which might
lead to mutagertic or teratogenic effects. Cadmium is known
to have .marked acute and chronic effects on aquatic
organisms also.
Cadmium acts synergisticaily with other metals. Copper and
zinc substantially increase its toxicity. Cadmium is
concentrated by marine organisms, particularly molluscs,
which accumulate cadmium in calc&raous tissues and in the
viscera, h concentration factor of 1000 for cadmium in fish
muscle has been reported? as have concentration factors of
3000 in marine plants, and up to 29,600 in certain marine
animals. The eggs and larvae of fish are apparently more
sensitive than adult fish to poisoning by cadmium, and
crustaceans appear to be more sensitive than fish eggs and
larvae.
Chromium
Chromium, in its various valence states, is hazardous to
man. It can produce lung tumors when inhaled and induces
skin sensitizations. Large doses of chromates have
corrosive effects on the intestinal tract and can cause
inflammation of the kidneys. Levels of chromate ions that
have no effect on man appear to be so low as to prohibit
determination to date.
75
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The toxicity of chromium salts toward aquatic life varies
widely with the species, temperature, pE, valence of the
chromium, and synergistic or antagonistic effects,
especially that of hardness. Fish are relatively tolerant
of chromium salts, but fish food organisms and other lower
forms of aquatic life are extremely sensitive. Chromium
also inhibits the growth of algae.
In some agricultural crops, chromium can cause reduced
qrowth or death of the crop. Adverse effects of low
concentrations of chromium on corn, tobacco and sugar beets
have been documented.
Lead
Lead is a cumulative poison to the human system and
concentrates itself primarily in bones. Symptoms of
advanced lead poisoning are anemia, abdominal pain, and
qradual paralysis. Immunity to lead does not develop but
reaction grows more acute. It is not an elemental essential
to the metabolism of animals.
Lead poisoning has been reported in humans drinking water
with a concentration as small as 0.042 mg/1. However,
concentrations of 0.16 mg/1 seem to have had no effect over
Long periods. It is generally felt that 0.1 mg/1 can cause
poisoning if ingisted regularly.
Chronic Lead poisoning among animals h&s been caused by
concentrations less than 0.18 mg/1. changes have been noted
in nervous systems of laboratory rats after ingistion of
0.005 mq/ per kg of body weight.
Lead concentrations of approximately of 0.5 mg/1 appear to
be the maximum safe limit.
studies on the effect of lead on fishes indicate that lead
reacts with an organic constituent causing a mucus to
obstruct the gills and body. The fish ultimately dies of
suffocation. Concentrations between 0.1 mg/1 and O.U1 mg/1
have resulted in a TL 50 within 48 hours to sticklebacks,
guppies,, minnous, brown trouts and coho salmon.
Iron
Iron in small amounts is an essential constituent to animal
diets. Th<» daily nutritional requirement is 1-2 mg and most
people intake an average of 16 nig. However, drinking water
becomes umpalatable at approximately 1.0 mg/1. Ferrous iron
imparts as taste at 0.1 mg/1 and ferric Iron at 0.2 mg/1.
76
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It also tends to precipitate causing stains and
discoloration of water. For these reasons drinking water
limitations have been recommended at 0.1 mg/1.
Very high concentrations of iron have been toxic to fish.
Iron hydroxides have been known to precipitate on the gills
of fish causing obstruction. Also heavy precipitation may
smother eggs.
Tin
Tin is not a nutritional requisite but neither does it
appear harmufl to human or animal life. The average diet
contains 17.14 mg/day. Very large doses of 30-50 mg/kg of
body weight caused much loss of weight in cats. Trace
amounts of tin appear beneficial to some fish.
BMr Acidity ajQg AlkaUnto
Acidity and alkalinity are reciprocal terms. Acidity is
produced by substances that yield hydrogen ions upon
hydrolysis and alkalinity is produced by substances that
yield hydroxyl ions. The terma "total acidity" and "total
alkalinity" are often used to express the buffering capacity
of a solution. Acidity in natur&l waters is caused by
carbon dioxide, ndner&l &ei
-------
33HK -
&£
aj £hg ssissiiaa a« satai mai aa 4
clarification prior to discharge of the effluent t«
naviqable waters is assumed. einuent to
than £nm°^ii °f -t0^} suspended solids to levels of
than 50 mg/1, significant removal of metal hvdroviri««
suspen
water.
78
-------
content (dissolved metal plus any metal in suspended solids
left from clarification) . For the purpose of establishing
effluent limitations and standards of performance it is
herein specified, in the absence of any qualifying
statement, that the concentration of metals in mg/liter
means total metal, aa analytically determined by acid
digestion prior to filtering,
Rationale for Rejection of other Waste Water Constituents as
Pollutants for Subcategory (1) Processes
Metals. The rationale for rejection of any metal other than
those described as a pollutant above is based on one or more
of the following reasons:
(1) They are not present In the processing
solutions used In the metal finishing
industry. It would be redundant to
make a long Hat of materials that
can be controlled but that are not
present,
(2) Insufficient data exiat upon which
to base effluent limitations and
s-canfiards of performance. Waste-
water constituents such as sodium,
potassium, nitrate and ammonia are
present in many prooassing solutions
and waste waters, bvit there is no
practicable Method s/c prssent of
removing them fro.r. solution.
Dissolved Solids. Dissolved solids is not a significant
pollution parameter la -en is industry. Although the
concentration of total dissolved solids will become higher
as efforts are directed to reducing fc*ater use and volume of
effluent discharged, the total quantity of dissolved solids
will remain unchanged*
chemical Oxygen,.. Sem&Dd. The chemical oxygen demand can be
significant in some cases because of the oil and grease
removed from the work in the cleaning operation, which then
constitutes a part of the cleaner when it is dumped. It is
possible to minimize chemical oxygen demand in some cases by
use of organic vapor degreasers prior to alkaline cleaning.
However, if there is a high chemical oxygen demand
practicable technology to lower it has not been demonstrated
in the electroplating industry.
79
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Biochemical oxygen Demand. Biochemical oxygen demand is
usually not an important pollution parameter in the
Subcategory (1) processes. An electroplating plant in a
suburban location not discharging to a publicly owned system
must treat its own sanitary sewage in a separate treatment
facility. if the plant chooses to mix the treated sanitary
effluent with process wastes prior to treatment BOD would be
considered a major parameter.
Turbj.di.ty. Turbidity is indirectly measured and controlled
independently by the limitation on suspended solids.
Temperaturg. Temperature is not considered a significant
pollution parameter in the Subcategory (1) processes.
However, cooling water used to cool process tanks and/or
evaporative recovery systems that are not subsequently used
for rinsing could contain pollutants from leaks in the
system.
Aluminum
Aluminum may be present in significant amounts in the waste
water stream. Limits are not placed on aluminum at this
time due to insufficient data. However,, it is believed that
significant removal will result when conventional chemical
treatment techniques are employed.
80
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SECTION VII
CQNTRQLAND TREATMENT TECHNQLOQY
Introduction
The control and treatment technology for reducing the
discharge of pollutants from metal finishing operations is
discussed in this section.
The control of metal finishing waste waters includes process
modifications, material substitutions, good housekeeping
practices, and water conservation techniques. The in-plant
control techniques discussed are generally considered to be
normal practice in these industries.
The treatment of metal finishing waste water includes
techniques for the removal of pollutants and techniques for
the concentration of pollutants in the waste waters for
subsequent removal by treatment or recovery of chemicals.
Although all of the treatment technologies discussed have
been applied to waste waters from metal finishing
operations, some may not be considered normal practice in
this industry.
Chemical treatment technology is discussed first in this
section because some treatment of this type is required of
many waste waters generated by metal finishing operations
before discharge into navigable streams. After chemical
treatment the amount of pollutants discharged to navigable
waters is roughly proportional to the volume of water
discharged.
The proper design, operation,, and maintenance of all waste
water control and treatment systems are considered essential
to an effective waste management program. The choice of an
optimum waste water control &n& treatment strategy for a
particular metal finishing facility requires an awareness of
numerous factors affecting both the quantity of waste water
produced and its amenability to treatment.
Chemical Treatment Technology
Applicability
Chemical treatment processes for waste water from metal
finishing operations are based upon chemical reactions many
of which go back to the beginning of modern chemistry over
200 years ago. These reactions have been used as the basis
81
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for the design and engineering of systems capable of
treating waste water containing a large variety of
pollutants and reducing the concentration of metal below 1
mq/1. Control procedures have been devised to assure the
effectiveness of the processes,
Processes
2f Stress. Waste Waters from different
operations in a metal finishing process may be combined in
some cases and kept separate in other cases prior to
chemical treatment. The nature of the waste waters and the
pollutants present will determine where segregation is
desirable and where combination is practical. Some
pollutants cannot be properly removed in the presence of
others, while some are better removed when combined with
others. Combination of some streams will result in a
reaction to form additional pollutants and ones that can be
of immediate danger to personnel involved in the metal
finishing operations, e.g., a cyanide containing stream
combined with an acid stream may caus® evolution of gaseous
hydrogen cyanide. In general,, waste waters containing
cyanide are segregated aacl treated separately, waste waters
containing hexavalent chromium are segregated and treated
separately. After treatment the cyanide^ chrome, and metal
ion streams are combined for further treatment to
precipitate metal hydroxides which are settled out,
sometimes filtered, and disposed of on land. The treatment
facilities may be engineered for batch* continuous, or
integrated operations. However , the treatment methods for
several pollutants can deviate considerably from this
general jlan. The design of a suitable procedure and system
to treat a specific pollutant mix requires considerable care
and experience.
h. Treatment. The batch method is generally used for
small or nedium-sized plants. Batch treatment is useful not
only for rinse waters but for expendable process solutions
containing high concentrations ol chemicals or spills,
leaks, or other accidental discharge of process solutions.
Holding tanks collect the waste water and are large enough
to provide ample time to treat* test, and drain a tank while
another is being filled. Analytical tests are made before
treatment to determine the amount of reagent to add and
after treatment to establish that the desired effluent
concentrations have been obtained.
S2fi£«fiiioy_§ Treatment. ™he chemical treatment process may be
made continuous by
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SECTION VII
JWP TRMTMSNT TECHNOLOGY
Introduction
The control and treatment technology for reducing the
discharge of pollutants from metal finishing operations is
discussed in this section.
The control of metal finishing waste waters includes process
modifications, material substitutions, good housekeeping
practices, and water conservation techniques. The in-plant
control techniques discussed are generally considered to be
normal practice in these industries.
The treatment of metal finishing waste water includes
techniques for the removal of pollutants and techniques for
the concentration of pollutants in the waste waters for
subsequent removal by treatment or recovery of chemicals.
Although all of the treatment technologies discussed have
been applied to waste Tatars from metal finishing
operations, some may not toe considered normal practice in
this industry.
Chemical treatment technology is discussed first in this
section because some treatment of this type is required of
many waste waters generated by metal finishing operations
before discharge into navigable streams. After chemical
treatment the amount of pollutants discharged to navigable
waters is roughly proportional to the volume of water
discharged.
The proper design, operation^ and maintenance of all waste
water control and treatment systems are considered essential
to an effective waste management program. The choice of an
optimum waste water control and treatment strategy for a
particular metal finishing facility requires an awareness of
numerous factors affecting both the quantity of waste water
produced and its amenability to treatment.
chemfcal Treatment
Applicability
Chemical treatment processes for waste water from metal
finishing operations are based upon chemical reactions many
of which go back to the beginning of modern chemistry over
200 years ago. These reactions have been used as the basis
81
-------
for the design and engineering of systems capable of
treating waste water containing a large variety of
pollutants and reducing the concentration of metal below 1
mq/l. Control procedures have been devised to assure the
effectiveness of the processes.,
ProceaseR
of Streajns. Waste Waters from different
operations in a metal finishing process may be combined in
some cases and kept separate in other cases prior to
chemical treatment. The nature of the waste waters and the
pollutants present will determine where segregation is
desirable and where combination is practical. Some
pollutants cannot be properly removed in the presence of
others, while some are better removed when combined with
others. Combination of some streams will result in a
reacticn to form additional pollutants and ones that can be
of immediate danger to personnal involved in the metal
finishing operations, e.g., a cyanide containing stream
combined with an acid stream may causa evolution of gaseous
hydrogen cyanide. in general , vast® waters containing
cyanide are segregated and treated separately, waste waters
containing hexavalent chromium are segregated and treated
separately. After treatment the cyanide^ chrome, and metal
ion streams are combined for further treatment to
precipitate metal hydroxides which are settled out,
sometimes filtered, and disposed of on land. The treatment
facilities may foe engineered for batch* continuous, or
integrated operations. However^, the treatment methods for
several pollutants can deviate considerably from this
general flan. The design of a suitable procedure and system
t,o treat a specific pollutant mix requires considerable care
and experience.
. Treatment. The batch method is generally used for
small or medium-sized plants. Batch treatment is useful not
only for rinse waters but for expendable process solutions
containing high concentrations of chemicals or spills,
leaks, or other accidental discharge of process solutions.
Holding tanks collect the waste water &n& are large enough
to provide ample tima to treat* test, and drain a tank while
another is being filled, Analytical tests are made before
treatment to determine the amount of reagent to add and
after treatment to establish that the desired effluent
concentrations have been obtained.
. Tgeatmept. ?he chemical treatment process may be
made continuous by
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reactions; (2} providing continuous monitoring of pH and
oxidation/reduction potentials and controls for regulating
reagent additions by means of these monitors; and (3)
providing a continuousoverflow settling tank that allows
sludge to be pumped off periodically through the bottom.
A flow diagram for a large continuous-treatment plant is
shown in Figure 5. The dilute acid-alkali stream originates
from rinses associated with alkaline cleaners, acid dips,
and baths containing metal ions*, but no cyanide or
hexavalent chromium. When concentrated acid and alkali
baths are to be discarded cney ara transferred to a holding
tank and added slowly -co the dilate stream. In this
manner, sudden demands* ca the reagent additions and
upsetting of the treatment: conditions are avoided. The
dilute acid-alkali stre&ir. i'ire/t enters a surge tank to
neutralize the waste water s.r»d equalize the composition
entering the precipitation tank. Kse hex&valent chromium is
reduced at. a pH of £,0 tc 2*5, and the addition of the SO^
and HC1 are controlled by suitable monitors immersed in the
well-agitated reduction t&ftk* Cy&nide is destroyed in a
large tank with coBipartments tc sliow & two-stage reduction.
Reaction time Is about 3 hours™
The treated chrome,, cyanide, ar^d neutralized acid-alkali
streams are run into a common u^k where pH is automatically
adjusted to optimise the precipitation of metal hydroxides.
The stream then enters a solide contact and settling unit
where mixing? coagulated 4 f Peculation r re circulation,
solids concentration, sludcjo collection,? and sludge removal
are accomplished. Flocculates ar^s usually added to this
tank. The overflow from the settling unit constitutes the
discharge froifi trie plant. i?h'«s kludge may be dewatered by
filtering and the filtrate x
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strong
00
*».
1.8 gpm
sludge
FIGURE 5 DIAGRAM OF A TYPICAL CONTINUOUS-TREATMENT PLANT
-------
Because metals are precipitated separately at a relatively
high concentration? the metal hydroxide settled in the
reservoir may be recovered* dissolved, and returned to the
plating bath from which it originated. In contrast to batch
and continuous treatments, which are generally carried out
in a separate facility, th« reservoir in the integrated
system is in proximity to the plating room because of the
necessity for circulation. The layout of an integrated
system for treating rinse water wast® from a cyanide plating
solution and & chromium plating bath in shown in Figure 6«
Unit Operations
^j.gR. The effluent levels of metal attainable by
chemical treatment depend upon the insolubility of metal
hydrolysis products in the created water and upon their
settling and filtering characteristics which affect the
degree to which they can be separated. The solubilities of
the hydrolysis products are dependent upon many conditions
during precipitations such as pEs presence of other cations
and aniors, vime allowed oefor* separating out the solids,
the precipitation agent used,,, the degree of agitation, etc.
Schlegel and Hartinger have studied precipitation reactions
extensively and have bean sblfi to obtain low concentrations
of metal IOAS in solution iu a seasonable time, i.e., 2
hours,
When metal loris are preeipitamsd separately the pH may have
to be adjusted differently for euch ion. This immediately
raises the question of whet ha;: t^ metals can be efficiently
precipitated together et a coaiason §>H. This is possible as
shown in Table 23
It is apparent tnat It is dif .cic^It to predict in detail the
conditions -chat will give th,e beat precipitation results in
a practical situation. However,, just as several parameters
can be adjusted In the labor&tory to obtain optimum results,
suitable eon<5itj.cm8 may be rfouinfi la the field. Flocculating
agents, o'ddad »co aid in set-cling th«i precipitate, play a
significa-AT rol<< i- r-ediscing concentration of suspended
solids.
When soliabilizimg cowplftxing agents are present , the
equilibrium constant of the completing reaction has to be
taken into account in determining theoretical solubility
with the result that the solubility of the metal is
generally increased. Cyanide iorsa .-roast be destroyed not
only because they are toscic but alao because they prevent
effective precipitation of copper and sine as hydroxides.
85
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Reuse woler
oo
Sodium
hypochlorite
L
Chromic
acid wcsfe
treotment
Cyonioc
woste
freotment
To pH control
clcrifier
Water reuse pump
Water slow down
to sewer
Feed
pump
Cyonide waste
treatment reservoir
r>
5
U
-d
3-
g
J
Chromium waste
treotment reservoir
g
Feed
pump
Sodium carbonate
Sodium hydro-
sulfite
To sludge bed
FIGURE 6 INTEGRATED TREATMENT SYSTEM
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TABLE 23 COMPARISON OF PRECIPITATION OF METAL
HYDROXIDES SEPARATELY AND IN COMPARISON
Initial
Metal Ions
Cu:Ni
Cu:Cr
Cu:Ni:Cr
Ratio of
in Solution
2:1
1:1
1:2
1:1
1:1:1
Soluble
Metal Two Hour*
after Neutralization,
Cu-H-
0.76
0.6
0.32
<0.2
0.25
Ni-"-
12
15
28
—
0.25
ms/1
Cr*H-
—
0.74
0.19
Initial PH 8.5
87
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IF cyanide is replaced in a plating bath by a nontoxic
complexing agent such as EDTA (ethylenedlaminetetraacetic
acid), the new complexing agent could have serious
consequences as far as the removal of metal ions by
precipitation. Ammonium ion* present in many metal
finishing baths, will complex copper, zinc, and other heavy
metal ions and interfere with their precipitation as
hydroxides.
Theory and experimental results confirm that it is not
possible to achieve complete removal of metal ions from
waste water by precipitation as hydroxides even if
separation of precipitate were 100 percent effective. Thus,
a finite concentration of pollutant will remain in the
etfluent. The best indication of what can be achieved in
reducing metal concentration is the results of daily
operation in exemplary plants rather than theory or
laboratory experiments. Clarification efficiency is an
important factor in determining the total metal content of
tho effluent. it is safe to say that the soluble metal
content will be no greater than the total content achieved
in practice and may be less,
s2iM§__ Separation. The first step in separating the pre-
cipitated metals is settling, which is very slow for gellike
zinc hydroxide, but is accelerated by coprecipitation with
the hydroxides of copper and chromium. Coagulation can also
be aided by adding metal ions such as ferric iron which
forms ferric hydroxide and absorbs some of the other
hydroxide, forming a floe that will settle. Ferric iron has
been used for this purpose in sewage treatment for many
years as has aluminum sulfate. Ferric chloride is
frequently added to the clarifier of chemical wastetreatment
plants in plating installations. Plocculation and settling
ar*> further improved by use of polyelectrolytee, which are
hlqh molecular weight polymers containing several ionizable
ions. Due to their ionic character they are capable of
-swelling in water and adsorbing the metal hydroxide which
they carry down during settling.
Settling is accomplished in the batch process in a stagnant
tank, and after a time the sludge may be emptied through the
bottom and the clear effluent drawn off through the side or
top. The continuous system uses a baffled tank such that
the stream flows first to the bottom but rises with a
decreasing vertical velocity until the floe can settle in a
practically stagnant fluid.
Although the design of the clarifiera has been improved
through many years of experience, no settling techniques or
88
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clarifier will completely remove solids from the effluent
which contains typically 5 to 20 mg/1 of suspended solids.
This floe contains some metal.
3J.pdge Dj,3po§ajL. Clarifier underflow or "sludge" contains
typically 1 to 2 percent solids and can be pumped to a
lagoon.
Metal ions in the liquid associated with the sludge can
percolate through porous soil and become a. potential source
of groundwater contamination. Impervious lagoons require
evaporation into the atmosphere. However, in many parts of
the U.S., the average annual rainfall equals or exceeds the
atmospheric evaporation. Additionally, heavy rainfalls can
fill and overflow lagoons. Metal ions may be leached from
metal hydroxides and the surface run-off to adjacent streams
or lakes may be in sufficient quantity to be detrimental.
A case in point is contamination of groundwater by plating
wastes held in lagoons in Nassau County, New York. Plating
wastes have seeped down from the lagoons into the aquifier
intermittently since 19«1«, This seepage has resulted in a
plume of contaminated water some
-------
Centrifuges will also thicken sludges to the above range of
consistency and have the advantage of using less floor
space. The effluent contains excessive suspended solids and
is returned to the clarifier.
Pressure filters may be used, In contrast, to rotary filters
and centrifuges, pressure filters will produce a filtrate
with less <;han 3 ing/1 of suspended solida ao that return to
the clarifier is not needed. The filter cake contains
approximately 20 to 25 percent solids. Pressure filters are
usually designed for a filtration rate of 2.01 to 2.W
liters/min/sq m (0.05 to 0.06 gprn/aq ft) of clarifier
sludge.
Solids contents from 25 to 35 percent in filter cakes can be
achieved with semicontinuous tank filters rated at 10.19 to
13.4«t liters/min/sq m (0.25 to 0«33 gpm/sq ft) surface. A
solide content of less than 3 mg/1 Is normally accepted for
direct effluent discharge. The units require minimum floor
space,,
Plate and frame presses produce filter cakes of 1*0 to 50
percent dry solids and a filtrate with less than 5 mg/1
total smspencled solids. Because automation of these presses
is difficult, labor costs tend to be high. The operating
costs are partially offset by low capital equipment costs.
Automated tank type pressure filters are just now finding
application. The solids content of the cake can reach as
high as 60 percent while the filtrate may have up to 5 mg/1
of tot.il suspended solids. The filtration rate is
approximately 2.0^1 liters/min/aq m (0.05 gpm/eq ft) filter
surface area. Pressure filters containing from 300 to 500
mg/1 tmspended solids at design of 1.88 to 6.52
liters/min/sq m {0.12 to 0.16 gpm/aq fit) and still maintain
a low scllds content in the filtrate.
Filter cakes can easily be collected in solid waste
containers and hauled away to landfills. There may be
situations, however, where the metal in the filter cake
could be redissolved if it came into contact with acidic
water. Careful consideration should be given to where such
a materiel is dumped.
A proprietary process is available for solidifying sludge by
addition of chemical fixing agents. Relative to filtration,
the amount of dried sludge to be hauled away is increased.
The fixing process appears to insolublize the heavy metal
ions so t.hat in leaching tests only a fraction of a part per
90
-------
million is found in solution. A fill is produced that is
similar to dried clay.
The possibility of recovering metal values from sludges
containing copper, nickel, chromium, and zinc have been
considered but such a system appears to be uneconomic under
present circumstances. It may be profitable to recover metal
values if 900 to 2300 kg ?2POGO to 5,000 pounds) of dried
sludge solids can be processed per day with a thoroughly
developed process. To attain this capacity would almost
certainly require that sludge from a large number of plants
be brought to a central processing station. The recovery
would be simpler if the metallic precipitates were
segregated, but segregation would require extensive
modification, investment, and increased operating expense
for precipitation and clarification. Laboratory experiments
showed that zinc could be leached from sludge with caustic
after which copper, nickel, and chromium were effectively
dissolved with mineral acids. Ammonium carbonate dissolved
copper and nickel but not trivalent chromium, thus giving a
method of separation. Electrowinning of the nickel and
copper appeared to be a feasible method of recovering these
metals.
Cyanide Oxidation. Cyanide in waste waters is commonly
destroyed by oxidation with chlorine or hypochlorite prior
to precipitation of the metal hydroxides. The method is
simple, effective, and economically feasible for most waste
waters, even for small volume installations. A factor in
how rapidly cyanide is destroyed, if at all, is how strongly
the cyanide is complexed to metal iona and how rapidly the
complex can be broken. Therefore, some waste waters present
special problems. A comprehensive study of the method was
made by Dodge and Zabban the results of which have been used
to work out the practical processes* The following are
proposed reactions for chlorine oxidation.
(1) NaCn + C12 - CNCi •» NaCl
(2) CNCI + 2NaOH « NaCNO * NaCi * H20
(3) 2NaCNO + 3C12 + <4NaOH = N^ * 2CO£ * 6NaCl + 2H2O.
Reaction (2) goes rapidly at pH 11.5, under which conditions
build up of the toxic gas CNCI by Reaction (1) is avoided.
Treatment of dilute rather than concentrated solutions also
minimizes its formulation. Oxidation to cyanate (NaCNO) is
completed in 5 minutes or less. Reaction (3) goes more
slowlyr requiring an hour in the preferred pH range of 7.5
to 9.0, and a longer time at higher pH. After the
91
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conversion to nitrogen and carbon dioxide, excess chlorine
is Destroyed with sulfite or thiosulfate.
Sodium hypochlorlte may be usad In place of chlorine.
Recent technical innovations in electrochemical hypocblorit*
generators for on-t«ite use raise tha poesibility of
controlling the addition of hypochiorit® to tha cyanide
solution by controlling the current to the electrochemical
generator, using sodium chloride as the feed material.
Concentrated solutions, such as contaminated or spent baths,
cyanide dips, stripping solutions, and highly concentrated
rinses, are normally fed at a slow rate into a dilute
cyanide stream and treated with chlorine. However,
concentrated solutions may also be destroyed by electrolysis
with conventional equipment available in the plating shop.
In normal industrial practice the process is operated
batchwise, whereas the optimum system, from an operating
standpoint, would be a cascaded one in which successively
larger tanks are operated at successively lower current
densities. This is the more efficient system. In addition
to the oxidat.ion of cyanide at the anodaff valuable metal can
b® recovered at the cathode. The process becomes very
inefficient when the cyanide concentration reaches 10 ppm,
but at this point tha solution can bj fed into the process
stream for chemical destruction of cyanide 'to bring the
concentration to the desired level. The addition of
chloride ions to the concentrated solutions, followed by
electrolysis, produces chlorine or hypochlorite in solution,
which can then destroy Uie cyanide to the sarna low levels as
obtained by direct chlorination. With the provision that
chlorine or hypochlorite be formed at, a rate equal to the
concentration of cyanide passing through the system, the
process can be operated continuously:
2NaCN -1 2NaOCl •- 2FaCNO * 2NaCl
2NaCNO_ *_3JJ3QC1_+__.B2Q...* 2C02 * N2 * 2MaOH * 3NaCl
2NaCN + 5 NaOCl * H2O 2C02 * N2 * 2S&OH * SNaCl.
The Cynox process, based on the above principles,, produces 1
kg of active chlorine per 5.5 Kwh. Equipment needs are the
same with the exception that the tanks must be lined, and
graphite or platinized anodes must be used.
Poiysulfide-cyanide strip solutions containing copper and
nickel do not decompose as readily and as completely as do
plating solutions. Although the cyanide content can be
reduced from 75,000 to 1000 mg/1 during two weeks of
92
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electrolysis anode scaling prevents further cyanide
decomposition unless anodes are replaced or freed from
scale. Minimum cyanide concentration attainable is about 10
mg/1 after which the solution can be treated chemically.
The electrolysis of dilute cyanide solutions can be improved
by increasing the electrode area. Area can be increased by
filling the space between flat electrodes with carbonaceous
particles. The carbon particles accelerate the destruction
process 1000 times, but flow rate through the unit must be
carefully adjusted, if used on a continuous basis to achieve
complete destruction (Plant 30-1).
Although cyanide can be destroyed by oxygen or air under
suitable conditions, cyanide concentrations in the effluent
are reported to be 1.3 to 2.2 mg/1, which is high for
discharge to sewers or streams. A catalytic oxidation unit
using copper cyanide as a catalyst and activated carbon as
the reactive surface has been described for oxidizing
cyanide with air or oxygen and at least two units were put
in operation. Performance data is not available. Catalytic
oxidation units must be custom designed for each
installation for maximum effectiveness.
Ozone will oxidize cyanide (to cyanatef to below detectable
limits independent of the starting concentration or of the
complex form of the cyanide. Decomposition can be achieved
with cyanides such as those of nickel and iron that are not
readily oxidized by chlorine. Systems that will oxidize the
cyanides that are usually treated, i.e., copper and zinc
compounds have been installed in production units and
demonstrated. Development work is continuing to enhance the
efficiency and reliability of modern ozone generators and to
decompose the more stable cyanides with the help of
ultraviolet radiation and heat.
A method employing thermal decomposition for cyanide
destruction has been recently announced. Cyanide solutions
are heated to 160 to 200 C under pressure for 5 to 10
minutes. Ammonia and formate salts are formed. No
information is given on the final cyanide concentration.
One process destroys cyanides of sodium, potassium, zinc,
and cadmium and also precipitates zinc and cadmium. The
process xs discussed later in this section.
Precipitation of cyanide as ferrocyanide is restricted to
concentrated wastes. Ferrocyanide is lees toxic than
cyanide, but Is converted back to cyanide in sunlight.
Treatment is accomplished by adding an amount in excess of
93
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amonnf kg °f PeS°4 *** kg of cyanid«| . Large
amounts of sludge are produced which add to the pollution
load. Complex cyanides do not break down readily and the
™SiSn StMPS xhe"*a °°nc«»*»tion °f 10 mg/i of cyanide is
reached. No benefits can be foreseen in terms of reducing
waste volume and concentration. uu^xng
Cyanide is also destroyed by reaction with polysulf ides.
« K "?^6 r?action rates arc obtained only if the solution
is boiled. Since the reaction does not destroy all of the
cyanide further treatment is necessary.
7P^H?£ 3* flMHXalfflp Chromium. Hexavalent chromium
(crvi) is usually reduced to trivalent chromium at a pH of 2
to 3 with sulfur dioxide (SO2) , sodium bisulfite, other
sulfite-containing compounds, or ferrous sulfate. The
reduction makes possible the removal of chromium as the
ooid?M«n h*dr.oxi?e wh*ch Precipitates under alkaline
conditions. Typical reactions for SO£ reduction are as
follows:
S02 + H2O =H2_S03
2H2CrOU + 3H2SQ3 =Cr2 (SO 4) 3 + SH^O.
Representative reactions for reduction of hexavalent
chromium under acid conditions using sulfite chemicals
instead of S0.2. are shown below:
(a) Using sodium metabisulf ite with sulfuric acid:
* 3Na.|S.205 + 3H2SO4 -
(b) Using sodium bisulfite with sulfuric acid:
4H2Cr04 * 6NaHSO3_ + 3H^SO1 - 3Na^S04
(c) using sodium sulfite with sulfuric acid:
2H2Cr04 + 3Na2S03 + 3H2SOJi = SNa^SOji
+ 5H20.
Reduction using sulfur dioxide is the most widely used
method, especially with larger installations. The overall
reduction is readily controlled by automatic pH and ORP
(Oxidation-Reduction Potential) instruments. Treatment can
be carried out on either a continuous or batch basis.
94
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Hexavalent chromium can also be reduced to trivalent
chromium in an alkaline environment using sodium hydro-
aulfite as follows:
2H2CrOf« * 3Na 282.04 + 6N»OH fiNa^iC^ * 2Cr(OH)£ * 2HJO.
As indicated in the above equation, the chromium is both
reduced and precipitated in this one- step operation.
Results similar to those obtained with sodium hydrosulfite
can be achieved using hydrazine under alkaline conditions.
= 4Cr(OH)3 + 3N2 + i»H2O.
Sodium hydrosulfite or hydrazine are frequently employed in
the precipitation step of the integrated system to insure
the complete reduction of any hexavalent chromium that might
have been brought over from the prior reduction step
employing sulfur dioxide or sodium bisulfite, where ferrous
sulfate is readily available (e.g., from steel pickling
operations) , it can be used for reduction of hexavalent
chromium; the reaction is as follows:
2Cr01 + 6FeSOtJ.7H20 + 6H2S04 = 3Fe^(SO]i)i * Crg (SO4 ) 3_
* 48H2.0.
Cr*» may be reduced at a pH as high as 8.5 with a
proprietary compound. It is not necessary to segregate
chroma te- containing waste waters from the acid-alkali
stream, and the use of acid to lower pH is eliminated in
this case. Precipitation of chromic hydroxide occurs
simultaneously in this case with the reduction.
Cr*« ions may be reduced electrochemically. A concentration
of 100 mg/1 was reduced to less than 1 mg/1 with a power
consumption of 1.2 kwh/1000 liters. The carbon bed
electrolytic process previously described for cyanide may
also be used for chromate reduction in acid solution and
Plant 30-1 has achieved a Cr+* concentration of .01 mg/1
using this method. Electrolysis may also be used to
regenerate a reducing agent. A process has been described
involving the reduction of Fe (III) to Fe (II)
electrochemically and the reduction of Cr (VT) by Fe (II) .
The method should be capable of achieving low Cr (VI)"
levels. '
95
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The siaailataneous reduction of Cr*a and oxidative
destruction of cyanide finds limited application in waste
treatment practice. The reaction requires mixing of Cr+*
and cit- in ratios between 2 and 3 using Cu** as a catalyst
in concentrations of 50 to 100 mg/1. The catalyst
introduces additional pollutant into the ^aste stream.
Reaction rates are generally slow, requiring from 6 to 2U
hours for cyanide concentrations? ranging from 2,000 to less
than 50 mg/1 at a solution pH of 5. The slowness of the
reaction and the high Initial concentrations of reactants
required make the method unsuitable for treating rinse
waters. Its use is limited to batch treatment of
concentrated solutions, No benefits are obtained in terms
of wa-cer volume and pollution reduction. Destruction is not
as complete as obtained by the wore common chemical methods.
Practical Operating Systems
Chemical treatment was used by every plant contacted during
the effluent guidelines study with the exception of those
that are allowed to discharge plating waste effluents into
sewers or streams without treatment.
In Plait 33-2 the discharge of eyanida is eliminated by
electrochemical decomposition in & t&nk held at uufficiently
high temperature to evaporate th® wdBtawator as rapidly as
it is introduced. Therefore, no liquid stream leaves the
tank. Fluorides and fluoborate containing waste waters in
Plant 31-15 are collected separately and treated with lime.
Plant 3')-8 disposes of sludge in a pit lined with special
concrete blocks that filter out solids and allow liquid to
permeate into the surroundings. Relatively few finishing
plants have installed filters,, although the problem of
disposing of unflitered sludge in many cases should provide
an impetus for the use of one or more filters in the future.
Plants 12-8 and 31-16 yuse large rotary filters to
concentrate sludge fori?: a clarifies:. Plant 33-30 is able to
filter the solution from the neutralizer directly, without a
preceding clarification step,, A settling tank centrifuge
combination is in use in over 200 waste treatment
installations, including those in metal finishing plants.
The Chen.fix system for solidifying sludge is in use at
several plants.
Demonstrati90 status. The us Bureau of Mines has done some
development on a process in which the acid wastes and
alkaline cyanide wastas neutralise each other. The acid
wastes ere slowly added to the alkaline wastes in a closed
reactor <;o i7orm easily filtered metal cyanide precipitates.
96
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The precipitates are heated in air to form stable metal
oxides.
'J -ftf _^Jl*!3Jj4ca 1 T^^^rl1^ Techniques
The ef ff;<:l ivoriess of chemiea L treatment techniques depend-;
on the nature of the pollutant, the nature and concentration
of interfering ions, the procedure of adding the appropriate
amount of chemicals (or adjusting pH) , the reaction time and
temperature and the achievement of effective separation of
precipitated solids. Effective removal of heavy metal
pollutants is inhibited by some types of chelating ions such
as tartrate or ethylene diamine tetracetate ions.
The concentrations of metals and cyanide achievable by the
chemical techniques employed for treating waste from copper,
nickel, chromium, and zinc electroplating and zinc
chromating processes are summarized in Table 24.
Concentrations lower than those listed as maximum in Table
24 were reported by companies using all three (continuous,
batch, and integrated) treating systems,
Higher-than-normal concentrations of metals, when they
occur, are usually caused by: (1) inaccurate pH adjustment
(sometimes due to faulty instrument calibration) ; (2)
insufficient reaction time; or (3) excessive concentrations
of chelating agents that complex the metal ions and prevent
their reaction with hydroxyl ions to form the insoluble
metal hydroxides; (4) lack of suitable coprecipitating
agents. The causes for higher-than-normal concentrations of
cyanide are similar, but another important factor must be
added to the list of potential causes for incomplete cyanide
destruction. In this case, sodium hydroxide and chlorine
must be added continuously during the reaction to maintain
the optimum pH and provide sufficient reagent to complete
the reaction, which is normally monitored by an Oxidation-
Reduction-Potential (ORP) recorder^controller. The
maintenance of this system is a critical factor affecting
the effectiveness of chemical oxidation.
Suspended Solids. The suspended solids discharged after
treatment and clarification sometimes contribute more heavy
metal than the dissolved metal. The concentration of total
suspended solids in the end-of-pipe discharge from typical
chemical treatment operations sampled during this study
ranged from 20 to 21 mg/1. Lower values are reported for
some facilities. Maintaining conditions so as not to exceed
these amounts requires (1) a properly designed settling
and/or clarifying facility, (2) effective use of
flocculating agents, (3) rate of removal of settled solids,
-------
VO
00
TABLE 24 CONCENTRATIONS OF HEAVY METALS AND CYANIDE ACHIEVABLE BY
CHEMICAL TREATING OF WASTE CREATED BY COPPER, NICKEL,
CHROMIUM AND ZINC PLATING AND ZINC CHROMATING OPERATIONS
Soluble Concentration Contribution From
After Chemical Treating Suspended Solids (2)
Pollutant
Cyanide, oxidizable(^)
Cyanide , total
Phosphorus
Chromium6"1"
Chromium, total
Copper
Nickel
Zinc
Total suspended solids' '
Minimum, mg/£
< 0.01
0.1
0.007
< 0.01
0.05
< 0.01
< 0.01
0.05
20
Maximum, mg/£W Minimum, mg/£ Maximum, mg/ 1
0.03 —
0.2
0.6 — —
0.05
0.25 0.02 0.30
0.2 0.02 0.76
0.5 0.02 0.15
0.5 0.04 0.80
24
(1) Values below these limits have been reported by plants utilizing continuous (Plants 40-6, 8-4,
33-6, and 11-8), batch (Plants 36-1, 21-3, 33-8), and integrated (Plants 36-2 and 20-13) treat-
ment techniques. Others (Plants 3-3 and 33-3) utilize a combination of integrated and batch or
continuous treatments to achieve these or lower limits.
(2) Data for Plants 33-1, 12-8, 36-1 and 11-8.
(3) Oxidizable by chlorine.
-------
and (4) sufficient retention time for settling, and (5) rate
of overflow of clarified effluent. Of course, minimum
retention time depends on the facility -size and design aiul
the rate of solution flow through the facility. In
practice, thi;j time ranges from about 2 to H hours tot
plants that are able to reduce suspended solids to about />•>
mq/1 or less.
Precipitation of Metal Sulfides
Applicability. The sulfides of metals are much less soluble
than their corresponding hydroxides. However, direct
precipitation of metal ions with hydrogen sulfide or sodium
sulfide involves the problem of excess sulfide ion which can
then become an additional pollutant parameter. A sulfide
precipitation system has recently been developed that avoids
the possibility of excess sulfide ion being present in
treated effluent. Iron sulfide, which itself has a very
small solubility, is used as the reagent to precipitate
copper, zinc, and nickel sulfides of even lower solubility.
Experimental results are shown in Table 25 indicating that
low concentrations can be achieved with sulfide
precipitation even when metals are complexed with ammonia.
The disposal of sulfide solid wastes is a serious and
unsolved problem. Unlike the metal oxides, metal sulfides,
in the presence of air, decompose to sulfates and the metal
ions can thereby be solublized. This commonly happens to
ferrous sulfide as a result of coal mining operations and
contamination of streams with acid and iron is a result.
However, there is insufficient information available to
determine whether any significant oxidation will occur with
mixed metal sulfide sludges disposed of properly on
landsites. The lower solubility of metal sulfides should
reduce the amount leached directly into rainwater.
Therefore, if significant oxidation is found to occur, means
will have to be found to contain the sulfide precipitates or
insolublize them by some system such as the Chemfix Process.
Practical Operating Systems. Plant 9-2 is precipitating
cadmium as the sulfide.
Demonstration Status. The process described is still being
developed, and it is anticipated that a demonstration plant
will be built and operating in the near future.
Combined Metal Precipitation and Cyanide
Destruction-Proprietary Process A
99
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TABLE 25 COMPARISON OF SOLUBLE POLLUTANT
PARAMETERS AFTER PRECIPITATION
BY IRON SULFIDE OR BY HYDROLYSIS
Waste
compo-
sition
in ppm
Unknown
Cu} 100
Ni, 7.7
NH3, 475
NH3, 475
Cr(VI), 4.8
Zn, 3.5
Pollutant residues
Sulfide
precipi-
tation
in ppm
Cu, 0.1
Zn, negligible
Cu, 1.8
Cu, 0.4
Ni, 2.0
Cr(VI), negligible
Zn, 0.03
from--
Hydroxide
precipi-
tation
in ppm
0.8
2.0
95.8
5.9
1.0
2.0
0.05
2.0
100
-------
Applicability. This process is applicable to zinc and
^^ide solutions. The metal hy< iroxlde is
s
lome states. A modified Kastone Process may be App
to copper cyanide.
Process Principles and Equipment. Cyanide in zinc and
fadmiSm -pnti^Tbaths is destroyed by a nuxture of formalin
and hydrogen according to the formula:
3CN- + 2H202 + HCOH + 2H2O = CNO~ + OR- * NH3
+ H2C (OH) CONH2) (glycolic acid amidej .
The metal hydroxide is also precipitated. The hydrogen
peroxide is contained in the reagent (41%) which contains
Stabilizers and additives to promote the reactions and help
in settling the metal hydroxide precipitate. The process
may ^carried out on a batch or continuous basis, and is
particularly convenient for the small shop. However, the
Slycolic acid generated is not a desirable constituent for
discharge to streams and the use of the Kastone Process
should be restricted to plants discharging to sewers.
Figure 7 shows the apparatus for batch treatment. To be
economical the rinse water should contain at least 55 ppm of
cyanide, and sufficient counter-flow rinses are normally
iSSlled to assure a sufficient cyanide concentration. The
typical treated effluent contains 0.1 mg/1 of cyanide and 1
to 2 mg/1 of zinc. Table 26 shows an analysis of the
products for decomposing 79U ppm of cyanide.
is being used in approximately 30 installations.
chemical Treatinent_gf_Ef fluents From Specific
Process Operations
Constituents
iron. Iron baths have relatively simple compositions and
nasalization of waste water constituents "ill reduce the
soluble iron concentration well below 1 JJ'J- '""^
chloride is a common constituent in such baths and "used
as a flocculating agent in clarification systems for Phase I
101
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Air -*-
Woler from first
rinse tank
Air (for mixing)
s-J;(&y$$£tiWv$M
^Fp^p^'.Tp filter v;.1;
'.•^'.Measurement
'
To sewer
FIGURE 7 - BATCH TREATMENT OF CYANIDE RINSE WATERS BY THE KASTONE PROCESS
102
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TABLE 26 DECOMPOSITION PRODUCTS OF CYANIDE IN
RINSE WATER(I) FROM A CYANIDE ZINC
ELECTROPLATING OPERATION AFTER TREATMENT
WITH "KASTONE"^2) PEROXYGEN COMPOUND
Products Formed
by Treatment
Cyanate 351
Ammonia (free-
Diesolved 57
Volatilized O) 32
Combined Ammonia
Calc'd as NH3 95
Calc'd as glycolic
acid amide 419
Amount Formed
Actual Cyanide Equivalent
ppm ppm percent
265
164
91
274
33
21
11
35
794
100
(1) Analysis of water before treatment:
Cyanide* 794 ppm
Cyanate* 336 ppra
Ammonia * 41 ppm
* Cyanide calculated as NaCN, cyanate as NaOCN, and
ammonia as NH~.
(2) Hu Pont trademark.
(3) Not determined; estimated by difference.
103
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«f,^ihi f°^low^q neutralization, to give an effluent
suitable for discharge. The waste waters (dilute acid) and
the concentrated plating baths (cono«ntrat«d but weakly
acidic) enter the waate treatment ayntftm via the* "diluto
acid- strong acid" streams of Figure 2. aumo
After oxidation of cyanide or in noncyanide waste
water, cadmium can be precipitated as the hydroxide by
adjustment of PH. The waste water and strong solution
discharge streams are shown as "weak cyanide" and "strong
oHi^M ^/iqfe l\ Alkalinity has a significant effect
on solubility of cadmium. The theoretical solubility values
according to Pourbaix are approximately values
Solubility
8 3000
9 30
1° 0.03
11 0.003 (minimum)
Therefore, soluble cadmium might not be reduced to a low
level by coprecipitation with Cr, Ni, Cr, 2n at pH 8 to 9.
Should a pH of 11 be used, there is danger that the *ini
concentration in the effluent will be too hioh
Consideration of the above theoretical data suggests that
cadmium might not be reduced to a low level wh*n
coprecipitated with cu. Mi, Cr, Zn at pH 8 to 9. The
insolubility of cadmium carbonate suggests that
precipitations with soda ash may reduce soluble cadmium to
very low levels in effluent. since many combined waste
waters contain some carbonate it is very possible that
cadmium carbonate rather than cadmium hydroxide is
precipitated when waste waters are neutralized with caustic
or lime, some reported values that seem unrealistically low
for hydroxide precipitation may be achieved by this
mechanism. Cadmium sulfide is very insoluble (solubility
product K« 10-* •), yo that a precipitation system based
upon sulfides, combined with efficient removal of dissolved
solids, may provide acceptable effluent. A schematic of the
treatment scheme is shown in Figure 8. In this figure, the
cadmium sulfide sludge is recovered. If segregated
treatment of a cadmium stream is required, the best way of
holding the sludge may be to ship it to a metal recovery
unit, or convert it to a form suitable for return to the
plating bath.
Alternative to recovering sulfide precipitate, an evaporator
can be installed to recover plating bath and reusable water.
104
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Water
Cadmium
Cyanide
Bath
Cone.
Soln.
I
\
Rinse
1
1
I
Evaporate
to
Concentrate
Evaporate
to
Dryness
I *
2
Water
j—
Dry Sludge
to Recovery
FIGURE 8 SCHEMATIC OF CADMIUM WASTEWATER
TREATMENT WITH MINIMUM SOLID
DISPOSAL
105
-------
omitted, nuoborate containing waataa cane from
'
adjustment. However, operating data sho» that
Solubility
si
6
8 500
6
3
a
The chloride and aulfate are too soluble to achieve
sufficiently low lead concentration, but sulfide
precipitation should reduce the concentration adequately
Lead carbonates and basic carbonates have low solubUitie^
™,«- ^er«fore carbonate present incidentally in the
neutralization process or deliberately added may reduce lead
to low .levels in effluent. The problem of suspended so Ud"s
remains. Sludge would most appropriately be sen? to a Seta?
to^S^ ^ K^ convftrted ^ • form suitable for returi
to the plating bath. Waste treatment operations are similar
to those shown for cadnium in Figures 8^nd 9° omittina the
cyanide oxidation. Lead plating wastes contain^ fluSboratJ
which 13 covered in a subsequent section. ^Auwoorare
Tin. The tin concentration can be reduced to low levels
in Utj;i"5?i0? betW?Sn PH 8 and 9 whether the tS irpresent
in the diyaient form from acid baths or the quadrivalent
form from alkaline baths. Therefore, chemical treatment is
adequate for this constituent, m principle, thTsulf ide
S S Sn?*' ^ diSCU88ed for cedmi«m «- lead, is
°?Pper all°y Plati«9 contributes copper,
to I*8t water' a11 of which
*.»» ,*.K.«.».in i M. , r "•-"• ""*• »>«*.v»ii cut« amenaoj
to chemica.1 treatment, as discussed for these metals alone.
Processes
106
-------
Water
Cadmium
Cyanide
Bath
Rinso
1
1
1
1
| ^
Rinse
2
Oxidizo
Cyanide
Adjust
pH
Sulfida
Precipitate
#— Liquid of fluent
Metal
Recovery
FIGURE 9 SCHEMATIC FOR SULFIDE PRECIPITATION
OF CADMIUM IN WASTEWATERS
107
-------
Fluoborate. Since several of the plating baths (those for
lead, tlr>7 and their alloys) contain the fluoborate ion, the
applicability of chemical treatment to remove this ion from
liquid effluent is of. interest. Upon dilution the
fluoborate hydrolyzes:
BF4™ * EgO - HF + BFJ + OH
The 3F^ is very stable.
Thus, the problem is to reduce the concentration of HF in
the waste water. The fluoride may be precipitated with
lime, but the concentration can be reduced only to
approximately 15 mg/1. This suggests that fluoborate
plating baths be operated as closed-loop systems with
recovery by evaporation, and that spills and leaks be
segregated so that they can be treated separately. In this
way, the fluoride discharged In liquid effluent can be held
to a very small amount.
Wire 4pd Strip. Effluent constituents from cepper, nickel,
chromium, zinc, and tin plating of wire and strip are
amenable to the same chemical treatment methods as discussed
previously.
Activation and catalvzj.tiq» Chemical precipitation is the
method generally used for treating wastes from these
operations for preparing pl&stics and nonconductors for
plating. Rinse waters contain tin for activating and palla-
dium from catalyzing operations. Waste Waters are
•segregated and treated separately by neutralization and
precipitation, The tin is precipitated at pH 8 and removed
by settling or filtration. The palladium is precipitated at
pH 8 to 9 and recovered by settling or filtration.
Platipq. The waste wa'eer constituents in rinses
.t..
from immersion plating are essentially the same as the
constituents from electroplating wastes for the same metals
plated. Waste Water treatment may be either batch or
continuous, precipitated solids being removed by settling or
filtration. Acids are neutralised to pH 6-9 when heavy
metals e*re precipitated as hydroxides. The sludge is
disposed of in the same way as is sludge from treatment of
waste water from electroplating the same metal. Cyanide is
destroyed by chlorine oxidation in alkaline solutions.
Anodising. Rinse waters &re neutralized with lime to
precipitate aluminum, zinc, copper, chromium as Cr*3 after
Cr+* is reduced, phosphate? and fluoride^ as shown in the
schematic in Figure 10. A ferric iron salt is added to
108
-------
A'l
Anodi.zc
Mg
Anodize
Water
I
Rinse
Rinse
I
Water
Lime pp t
pH 7 to 8
Sludge
Holding
Basin
Liquid
Waste
Stream
FTGURF 10 SCHEMATIC FOR CHEMICAL TREATMENT OF WASTEWATERS
FIGURE 10 o ANODIZING OPERATION
109
-------
flocculate the precipitated Hydroxides of the metals
Klumxnum phosphate precipitates when these two ions are in
the same neutral solution. Clarification by settling of
suidge and liquid overflow is both batch and continuous,
depending on effluent water volume. Aluminum concentration
is reported to be reduced to 2 mg/1 or less by chemical
treatment (Edwards and Burreli, p 17ft) with 0.5 mg/1 being
reported. Reduction of magnesium concentration to 2 mo/1
levei would probably require a pK in excess of 10.
orthophosphate ia reported ae a trace ar*d fluoride as 1.5 to
2«0 mg/1 in effluent.
Effluents from chromating operations
are amenable to chemical treatment to reduce the hexavalent
chromium and precipitate triv&lent hydroxide as done in
treating waste water from chromium plating- Phosphates from
phosphatlng operations can be reduced to the 1 mg/1 level by
addition of aluminum ions. Removal of phosphate can occur
when aluminum sulfate ia added to the elarifier as a
flocculating agent. Heavy metals, auch ad iron and zinc,
oerived from the basis metals and solution formulations, are
removed by neutralization and precipitation.
Both alkaline and acid waste waters are
involved and contain metals depending on the basis materials
be^ng processed. Aluminum is milled in concentrated caustic
solution containir.c? proprietary additives that are not
disclose*, water remaining after neutralization of aluminum
chemical milling wastes is beneficial to municipal sewage
treatments plants that remove phosphates by precipitation.
Steel and other alloys (nonaluminuw) are milled in acidic
solutions. The acidic waste waters are neutralized and
heavy metals are precipitated by the same techniques as for
analogoue waste water in other metal finishing operations.
Neutralization and chemical precipitation are used
to remove metals as for the same metals in other metal
finishing operations. If the waste water contains chromium
r-rosr. evening of stainless steel) , reduction is not
necessary because fche chromium is present in the trivalent
form. Because the etching solutions become depleted with
use,, they are regenerated. Regeneration is most/ effective
in decreasing copper waste from etching or printed circuits
The cupric chloride solutions are electrolysed in a closed-
loop scheme to -aiectrodepcsit the excess copper and
reoxidize the solutions. Copper ©tenants containing
chromate, WHftOH to pH 9 to 11, chloride and acetates are
used for etching printed circuits. These are now being
nandled by metal recovery plants. Ammonium persulfate
110
-------
etchants and peroxide-sulfuric acid etchants are also common
and copper can be recovered from them.
eyr cpngervation TUygugh Control ,
The volume of effluent is reduced if water is conserved
during rinsing operations. The solubility limit of effluent
constituents is essentially constant, so that a reduction in
the effluent volume accomplishes a reduction in the amount
of effluent constituents discharged. Water conservation can
be accomplished by in-plant process modifications requiring
little capital or new equipment, materials substitutions,
and good housekeeping practice. Further water conservation
is obtained by installing counterf low rinse tanks and ion-
exchange, evaporative recovery, or reverse osmosis systems.
Other systems that may accomplish water conservation are
freezing, electrodia lysis, electrolytic stripping, carbon
adsorption, and liquid-liquid extraction.
Process Modifications
Substitution of low-concentration metal finishing solutions
for high-concentration baths has been adopted in recent
years, principally for reducing the cost of chemicals used
for cyanide destruction. The dilute solutions require less
water for rinsing when electroplating parts are transferred
to rinse tanks. Assuming a 50 percent reduction in total
dissolved solids in the plating solution and two rinse tanks
in series, a 30 percent redoc^ion in rinse water
requirements is achieved. U-^ce Water constituents
requiring treatment are reduced by the same amount. Adverse
effects in terms of lower efficiency and reduced
productivity per unit facility may be encountered when
dilution is adopted to conserve rinse water and reduce waste
water constituents requiring treatment, unless other factors
affecting plating rate are modified to adjust for the
effects of dilution. Thus, dilution should not be adopted
before a complete analysis is made of all pertinent factors.
The advent of effluent limitations is expected to encourage
research and development on other processes that will
eliminate or reduce water waste. A dry process for applying
chromate coatings, which is currently being developed, may
prove useful for such a purpose, for example. Chemical
vapor deposition processes partially developed a few years
ago may be revived for plating hard chromium.
Material Substitutions
111
-------
Woncyanide solutions, which have been developed for metal
finishing operations in place of cyanide solutions, reduce
the costs of treatment by eliminating cyanide destruction,
but do not eliminate treatment to precipitate and separate
the metals. The chelating agents employed in some non--
cyanide baths to keep the metal in soluble form are
precipitated when rinse water waste is treated with lime to
precipitate the metals, but other agents such as ethylene
diamine tetraacetic acid inhibit the precipitation of zinc
and contribute organic matter to the treated water waste.
Thus, the applicability of the noncyanide solutions as
replacements for cyanide baths must be considered carefully
in the light of the effluent limitation guidelines
recommended in this document.
Trivalent chromium baths have recently been introduced to
the electroplating industry. They eliminate the need for
sulfur dioxide reduction of waste water associated with
chromium plating. The trivalent chromium baths appear to
have other advantages for decorative plating such as better
throwing power, current efficiency and plating rate. The
dark color of the deposits is cited as a disadvantage by
some purchasers, however. Nevertheless 8, this process
modification may ultimately prove to be significant for
reducinr waste treatment costs. No details have been
released! on the treatment required for minimising the
aoiuble chromium concentration in treated effluent, however.
Good Housekeeping Practices
Good housekeeping practices that reduce the waste generated
in metal finishing facilities include the following:
(1) Maintain racks and rack coatings to prevent
the transfer of chemicals from one operation
to another. (Loose rack coatings are
noteworthy as an example of poor practice.)
(2) Avoid overcrowding parts on a rack, which
inhibits drainage when parts are removed
from a process solutions.
(3) Plug all floor exits to the sewer and con-
tain spills in segregated curbed areas or
trenches, which can be drained to direct
the spills to rinse water effluent with the
same chemicals.
Wash all filters, pumps and other auxiliary
equipment in curbed areas or trenches.
.12
-------
which can be drained co direct the wash
water to a compatible holding tank or
rinse water stream,
(5) Install anti-syphon devices on all inlet
water lines to process tanks,
(6) Inspect and maintain heating and cooling coils*
to avoid leaks.
(7) Inspect, and maintain all piping installed for
waste water flow, including piping from fume
scrubbers.
Water Conservation by reducing Dragout
Draaout. Dragout is defined as solution on the workplace
carried beyond the edge of the processing tank. The dragout
of concentrated solution from the processing tank can vary
over a wide range depending on the shape *»<*<» °* th%SfrJl
A value of 16-3 liters/1000 sq m (0.4 gal/1000 sq ft) is
considered a minimum for vertical parts that are well
drained. The practical range for parts ot various shapes
that are well drained is about 40 to 400 liters/1000 sq m (1
to 10 gal/1000 sq ft).
Reduction of dragout with the above methods is not without
problems. By returning chemicals to the processing t*nk,
impurities tend to build up in the processing solution-
Therefore, purification systems, such as ion exchange,
batch-chemical treatments, and/or electrolytic purification
are required to control impurities. The purification
systems create some effluents which must be treated prior to
end-of-pipe discharge.
Water Conservation During Rinsing
Water conservation procedures that are used after processed
work is transferred fco a rinse tank include fl) adding a
wetting agent to the rinse water, (2) installing air or
ultrasonic agitation and (3) installing countarfiow rinses
whereby water exiting the last tank in the rinsing operation
becomes feed water for the preceding rinse. With two
counterflow rinses, water consumption is reduced 96 percent
in comparison with a single rinse, assuming that the aragout
solution mixes immediately with the rinse water. *nis
assumption is incorrect. While a part of the dragout
solution mixes rapidly with the rinse water, particularly if
agitation is used, the remaining film on the work comes off
rather slowly by a diffusion process. A more typical value
113
-------
5?' ,the W?*?r. reducti<™ might be 85%, cor respon ding to a
tinsing efficiency of approximately 9055. Use of
conductivity meters in the final rinse provides automatic
control of water use according to need. Rinse water flow is
shut off automatically when no work is being processed
Excessive use of water can also be avoided by use of flow
restrictors in the water feed lines.
Although multitank, counterflow rinsing imposes capital
investment costs for tanks, pumps, and floor space, these
costs are compensated for by a savings In water (and sewer)
charges. Further incentive is provided when regulatory
agencies require pollutional control. when end-of^process
ch«j»icax treatment is used, design of wastetreatment
facilities usually indicates the economic advantage of
r-aucing rinse-water flow by installing two or more
counterMow rinses.
Because waste treatment facilities are usually overdesigned
to handle future expansion in production, there is a
tendency to use the water flow capacity of the treatment
facility whether or not it is needed for effective rinsing.
Furthermore, rinse water flows set by an orifice are not
always -turned off when plating production is shut down. It
is probanly more economical to reduce rinse water usage bv
use of good rinsing practice than to increase water-
trodScticn facilitiea in the event of an increase in
Ringing can foe carried out beyond the point consistent with
good practice, even though there is an economic incentive to
save water. The result is unnecessary pollution. Typical
concentration levels permitted in the rinses followino
various process tanks, should not be decreased unless
quality problems can be associated with the dis-
-
solids concentrations Hated below for representative
rinsing systems;
Max Dissolved Solids
Alkaline cleaners 750
Acid cleaners* dips 750
Cyanide plating 37
Copper plating 37
Chromi am plating 15
Nickel plating 37
Chromi am bright dip 15
Chromate passivating 350-750
114
-------
A problem not considered in proposing a maximum dissolved
solids in the final rinse, is the dragin of these rinses
into a subsequent processing operation. If the dragin
attained from the concentration proposed is deleterious to
the following processing operation, the dissolved solids in
the final rinse would have to be decreased or means for
purification provided.
The following is an example, using various rinse
combinations, of the reduction In water volume that can be
obtained for rinsing assuming that the dragout and the rinse
water mix immediately. A Watts-type plating bath typically
contains 270,000 mg/1 of total dissolved solids. Obtaining
37 mg/1 in the final rinse requires 27,600 (7300 gallons) of
rinse water if a single rinse tank is used, in" order to
dilute 3.78 liters (1 gallon) of a Watts-type plating
solution containing 270 g/1 of dissolved solids. The same
degree of dilution in a final rinse tank may be obtained
with less water by use of series and counterflow arrangement
of two or more rinse tanks. If the tanks are arranged in
series and fresh water is fed in parallel to each tank in
equal volume, the ratio, r of rinse water to dragout is:
i
n
Co
T * n CF ,
where Co = concentration in the process solution
CF = concentration in last rinse tank and
n = number of rinse tanks.
If the tanks are arranged in the same way, but flow proceeds
from the last rinse tank to the first rinse tank
(counterflow) ,
n
£2
r = CF
By feeding water to counterflow tanks instead of in series,
the reduction in water varies n-fold. Values of n
calculated for several rinsing combinations, using the Co
and CP values given above for a nickel bath are as follows:
- ,- Rinse Combj.natj.gn __ Rinse Ratio, r
Single rinse 7300
115
-------
Two rinses„ parallel feed 171
Three rinses, parallel feed 58.3
Two rinses, counterflow feed 85.5
Three rinses,, counter flow feed 19.5
There is a significant reduction in water use by addition of
a second rinse tank, and at least two rinse tanks can be
considered normal practice. These should best be fed in
countarflow. Counterflow rinse tanks increase the
concentration of a metal or other constituent in the first
rinse tank following the plating or process bath. The water
in the first rinse tank can be used to supply makeup water
for the plating bath. As the concentration in the first
rinse tank increases„ more of the dragout from the plating
bath can be returned to the bath in the makeup water, and
less will require treatment and/or disposal. Therefore, the
addition of countercurrent rinse tanks can decrease both the
volume of water to be treated and the amount of dissolved
metal that must be removed, at least in some cases. A
problerr not. considered in using counterflow rinses is that
the concentration in the first rinse tank can become so high
that the diffusion of the dragout from the film on the
workpiese can be slowed considerably and, therefore, the
rinsing efficiency decreased substantially. Therefore, the
more cotintercurrent rinse tanks that are used, the less
accurate Is the calculation assuming that the dragout and
rinse welter mix immediately*
The rate of evaporation from the plating bath is a factor in
determining how much makeup water must be added. Operating
a bath at a higher temperature will allow more of the
dragout to be returned to the bath because of the higher
rate of evaporation. However, the temperature at which a
bath may foe operated is sometimes limited because of the
decomposition of bath components. Progress has been made in
developing bath components that allow higher bath
temperatures to be used. For example, brighteners for zinc
cyanide baths have been developed ^hich allow bath operation
at 50 C (120 F) as compared to 32 C (90 P) . The new
brightene rs permit the return of more of the dragout to the
plating bath and a lessened load on the waste treatment
system,, in addition to what other processing advantages they
may offer,
Advanced Treatment Technologies
116
-------
Ion Exchange
ADDlicability. Ion exchange is currently a practical com-
Sercially accepted method for the in-procesa treatment of
m raw water, (2) proceatlnq bath*, (3) rlnte wtert. Raw
water is treated to provide deioni*«d water for both makeup
and critical final rinsing operations. Plating baths are
treated to remove impurities, i.e., removal of nickel ions
from a chromic acid bath with a cation exchange resin.
Rinse waters are treated to provide water that can be
returned to the process solution. The concentrated
regenerant can be chemically treated more easily than the
original volume of rinse water and in some cases the
chemicals can be recovered and returned to the bath. The
in- process treatment of chromium and nickel plating
effluents by ion-exchange techniques are the more econom-
ically attractive treatment operations currently being
carried out. Ion exchange also is beginning to find
increased use in combination with evaporative and reverse
osmosis systems for the processing of metal finishing rinse
waters.
Advantages an^Ufflitatiaiia. 3om€ ^vantages of ion exchange
for treatment of plating effluents are as follows:
(1) Ion exchange is an economically attractive
method for the removal of small amounts
of metallic impurities from rinse waters
and/or the concentration for recovery
of expensive processing chemicals.
(2) Ion exchange permits the recalculation
of a high-quality water for reuse in the
rinsing operations, thus saving on water
consumption.
(3) Ion exchange concentrates processing bath
chemicals for easier handling, treatment,
subsequent recovery, or disposal operations.
Some limitations or disadvantages of ion exchange for
treatment of process effluents follow:
(1) The limited capacity of parallel bed ion
exchange systems means that relatively
large installations are necessary to provide
the exchange capability needed between
regeneration cycles. Continuous ion exchange
units reduce the size compared to dual-bed
units.
117
-------
(2) Parallel-bed ion exchange systems require
periodic regeneration with expenditures
for regenerant chemicals. Unless regeneration
is carried out systematically or continuous
ion exchange units are used, leakage of
undesirable components through the resin
bed may occur,: In addition, the tssual
treatment methods must be employed to
dispose of the regenerated materials.
(3) Cyanide generally tends to adversely affect
the resin performance because of tightly
held metal cyanide co&iplexes on strongly
basic anion resins r so that processing of
cyanide effluents fexcept for very dilute
solutions) does not appear practical at
the present time.
Resins, which are not highly cross-linked
(or macroreticu lar| , slowly deteriorate with
use under oxidizing conditions.
-^, ...„ on exchange involves a
reversible interchange of ions between a solid phase and a
liquid phase. There is no permanent or substantial change
in the structure of the solid resin particles. The capacity
of an ion exchange material is equal to the number of fixed
ionic sites that can enter into an ion exchange reaction,
and is usually expressed as milliequivalents per gram of
substance. Ion exchange resins can perform several
different operations in the processing of waste water,
including:
(1) Transformation of ionic species
(2) Removal of ions
(3) Concentration of Ions*
The performance of some of these functions is illustrated in
Figure I'.:., which is a generalized schematic presentation of
the application of ion exchange to treatment of electro-
plating effluents. In practice, the solutions to be treated
by ion exchange are generally filtered to remove solids such
as precipitated metals, soaps, etc., which could
mechanically clog the resin bed. Oils, organic wetting
agents, brighteners, etc,, which might foul the resins, are
removed ty passage through carbon filters.
During processing, the granular ion exchange resin in the
column exchanges one of its ions for one of those in the
118
-------
Waste from
contaminated
rinse overflow
Waste-water
reservoir
To clean water
reservoir and
process rinse tanks
Caustic -Hydrochloric
soda ' acid
rtx
_D
n
To recovery
or waste
treatment
FIGURE 11 SCHEMATIC PRESENTATION OF ION-EXCHANGE APPLICATION -
FOR PLATING-EFFLUENT TREATMENT(7,25)
-------
rinse water or other solution being treated. This process
continues until the solution being treated exhausts the
resin. When this happens, solution flow is transferred to
another column with fresh resin. Meanwhile,, the exhausted
resin is regenerated by another chemical which replaces the
ions given up in the ion exchange operation, thus converting
the resin back to its original composition, with a four-
column installation consisting of two parallel dual-bed
units, as shown in Figure m, the ion exchange process can
be applied continuously by utilizing the regenerated units
while -he exhausted units are being regenerated.
Most ion exchange systems depend upon regenerating with acid
and base t.o form the acid and base forms of "the resin.
These ace capable of exchanging with and thereby removing
from solution both heavy metals and dissolved salts such as
sodium chloride. However, resins can be regenerated with
salts, i»e.f sodium chloride to form sodium and chloride
forms of the resin, These will exchange with heavy metals
but not the soluble salts. Since exchange capacity is
reserved for heavy metals only, the frequency of
regeneration is decreased as is the cost of heavy metal
removed,
EEaSti£S]v»afigiaiiaa_SistgiEs. The Phase 1 report described
systems in use to remove nickel ions and trivalent chromium
ion from chromium plating baths. The more dilute baths for
producing chromium conversion coating are treated in a
similar manner to remove,, zinc ions. Aluminum is removed
from chromic acid anodizing baths, and from phosphoric acid
baths used for bright dipping. Cyanides may also be
removed, in a 3-bed system, consisting of strongly acidic,
weakly baiiic, and strongly basic ion exchangers. The system
provides ease of regeneration and little chance of cyanide
leaking through. The three-bed system has been in
Commercial operation in Europe aid only recently introduced
in the US. Sevaral of the systems are being installed one
of which will be supported to a limited extent under an EPA
grant to obtain performance and economic information.
Pemonstratj on ^Status. An ion exchange system using a short
30-minute cycle, Including a 3 to H-minute back wash to
recover chromic acid from rinse waters has been in operation
for over a year, The resin undergoes very little
performance deterioration since the chromic acid is not
deeply absorbed into the resin during such a short cycle.
Another system under development uses an ion exchange column
to achieve separation of components in much the same manner
that chrome tographic columns are used* For example, a
120
-------
solution for biio!
phosphoric acid and a.
basic ion exchange co
the ion exchange sit.?-,
retarded in comply,
flow unimpeded thrui.g:
considered a very
the ion exchange i. e^I.
much of the alwmiuv
returned to tbe bricu
Evaporative Recovery-
.luauiu
'j a no-.
is.;; c
s -:he
Th-.-
t "•<./.
cr ;.
; aluminumt containing
l rv^ through a strongly
.; JA ;*.;-•.- ions interact with
-,,>.. phosphoric acid is
trie aluminum ions, which
which may be
for regenerating
ii phosphoric acid with
he phosphoric acid is
v'J;;".-: ,
distilled ir- ;;?< c
returned to the -•'.ft
res pond i n g j: i n r f c -;-
on a ai.nffl*? pi«x
distillation, irou
operating costs ivfpo
distillation ev^j! pino-.rc. ?a:
of 300 gph are m>c~ d .*;-« pi^ci
tinse water is achieved In, i,,
the use of <^-. leo^t vruwe
itself reduces trie waste c*.t
for all of the •.-ir.se eye
tanks following j:.-ic.'r.iu9 ?H; .„>;«.
chemicals and retaoi tli^sm x.o u.i'.v;
plating costs, ""n^ >.u;lts "ru-v.5: :
or acid dip II ".e& Lacuuse v-
aufficienc i,> saxe ">_.c,,i
contatninantatf !««*„ oil &i-,ci 91
system di f f ic^J t.,
Kvapora-cior? Irs A fis-^^v oatt;-.,',,'„;:•
recovering pi a tin*? ch^st.icals a;"s-,"-
ef f I ue nt s,. C online 2 < • .1 A t « a' t»
nickel, chromium, an?1 ox-nar XL-*.,,
operating aucceeofH.l,. y &r,J; e*;.'O
to 10 years or io:-.q**,, ^'^0..^
treatment of pl^t .,ug V^SV.«;A
manufacturers,
At least 100 ev.^pur. ,ts v<-j :^i•',•;.-. h
means that t.heir a.:•<-. ;; ^
percentage of the shops*
installations and aaviiig
and evaporative
grow in use« fiovve-v^i:'; ..i
»
-------
strictly on the basis of savings in chemicals such factors
as value of the chemicals, their concentration in the
process bath, and the dragout rate are important in
determining whether a savings is possible
Advantages and frj-roitangos. The following are some of the
advantages of using evaporation for handling plating waste
effluents:
(1) Recovers expensive plating chemicals, which
were either lost by discharge to a sewer or
effluent which would have to be treated or
destroyed prior to disposal; chemicals
concentrated to plating strength can be
returned to the plating tank.
(2) Recovers distilled water for reuse in the rinse
operations, thus lowering water and sewer
disposal.
(3) Eliminates or greatly minimizes the amount of
sludge formed during chemical treatment and
eliminates or reduces the amount requiring
disposal by hauling or lagooning.
(<*) The use of vacuum allows evaporation to accur
at relatively low temperatures (e.g., 110°F)
so that destruction of cyanides or other heat-
sensitive materials is lessened.
(5) The technology of evaporators (conventional and
vapor recompression units) is firmly established,
so their capabilities are well known and their
performance should be readily predictable and
adaptable to plating effluent handling.
Some of the limitations or disadvantages of evaporative
recovery systems are given below:
(1) The rinse water saving (e.g., 1100 1/hr (300 gph))
is rather small, and by itself does not signifi-
cantly lighten the rinse water load on the final
chemical treatment plant.
(2) Evaporative units have relatively high capital
and operating costs, especially for the vacuum
units, steam and coolant water are required.
(3) The evaporative units are fairly complex and
require highly trained personnel to operate
122
-------
and maintain them.
W separate units are required if or handling the
waste effluent from each line, since various
solutions, such as zinc, nickel, copper,
chromium, cannot be mixed for chemical
recovery.
i*>\ As with all closed- loop systems, evaporation
( } in most cases results in a build-up of impurities
which must be taken care of by a bleed stream
or directly in the closed- loop system.
The advantages offered by evaporative recovery o^ten
outweigh ?he disadvantages. Evaporative recov**y *%*
nromisinq and economical method currently available for
KndlinS plying waste effluents and limiting treatment
SlSnt 2i£e Where existing chemical treatment cyanide
destruction; chromate reduction, and chemical precipitation)
-
chemicals plays the significant role in judging the overall
meri« of the evaporative system for a specific operation.
Process Principles_and Equipment. A representative closed
^himicals and water from a
ve o
ola?inq line with a single-effect evaporator is shown in
?iqure 12 A single-effect evaporator concentrates flow from
the rinse wlte? holding tank. The Concentrated rinse
solution is returned to the final rinse tank. With the
closed^loop system, no external rinse water is added except
fo? Sakeup of atmospheric evaporation losses. The system is
designed for recovering 100 percent of the chemicals,
normally lost in dragout! for reuse in the plating process.
Sinqle-, double-, and multiple-effect evaporators, and
vapo^recompression evaporator units are ^^°* *a*}dl *ng
plating effluent. Open-loop and combined evaporation (i.e. ,
evaporation combined with ion exchange, reverse osmosis or
other systems) are also employed for Handling plating
effluent.
A single-effect evaporator is preferred, if relatively
untrained operating personnel are involved, or low initial
SSpiSl outlSy is desired. It's the simplest in design and
?£ererore the easiest to operate. However, it is less
123
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Concentrotc hold tonk
Distillote hold tank
tasssaaK^i
Plating work travel •
Plotingbath. Rinse
inse tanks ( to 5} | r
-i-i.^r ' _j |T!r^r^l-~ —JL~
4 Rinse water
I holding tank
Condenser ^Vacuum jet
•C.VV. out
Reboiler
Recirculation concentrate pump
Steam
Distillate pump
Condensote
FIGURE 12 REPRESENTATIVE CLOSED-LOOP SYSTEM FOR
RECOVERY OF CHEMICALS AND WATER WITH
A SINGLE-EFFECT EVAPORATOR
124
-------
economical than a double-effect. »>r \?a ;.-.-.-* ^compression unit
with regard to utility casts,, « tfou me- effect evaporator
should be considered when lower opsrati.^ cost is desired
with a modest increase in capital
& vapor-' re compress ion evaporator should foa considered if no
steam or cooling water Is avai'lA&ie. Where utilities for a
conventional steam evaporator &rs available* the high
initial cost of the vapor r^c OKI press! on unit is not
economically justified. Its ope/raxing cost is the lowest of
the three systems. I -is despondence on an expensive and
complex mechanical compressor is th<& Kiai/i disadvantage.
Some sources report considerable Rifii.vi^iiance and down time
and have dispensed with use of evaporator units. Other
sources report little or no trouble sand are very satisfied
with the opera.tior?.. It appears; tnai iihe units can perform
very satisfactorily If tha installation is properly
engineered, and if preventive maintenance and trouble-
shooting are carried oat by fcnowic-dg^fcible personnel.
In some instances, evaporation procedures snaet be used in
combination with chemical or other methods in order to
handle small amounts of impurity build-up (e.g.,
brighteners,, carbonates v. ext.r&neaus metal ions, etc. , in
closed loop operation) or for t nsa tsnerst of minor bleed-off
streams (open-loop^ „
Atmospheric evaporation,, whieii a»es air flow through packing
media in an evaporator, can concentrate plating solution
such as chromic acid tsp -co siSQ g/1 {"4 Ib/galJ .
The corning Glass Company Siss jifstro»5i/:.'e<5 a new concept for
evaporative recovery, h glass shell tiad tv.be heat exchanger
is motanted vertically &n>. -;.r»fese processes. Small
-------
amounts of spxlls, leaks, if segregated, are evaporated to
dryness, and the solid waste sent to a metal recovery unit.
Failing film atmospheric evaporators have been installed in
a tew plants.
, - Status. The "rising film" units are
undergoing pilot and plant test.
Reverse Osmosis
AEElisabjLlity.. Reverse Osmosis uses a pressure differential
across a membrane to separate a solution into a concentrate
and a more dilute solution that may approach the purity of
the solvent. It therefore accomplishes the same type of
fnSJftn1?? a84 di?tlllati°n and has been applied in plating
installations in the same manner. Small units under 300 gph
have been installed to recover plating baths chemicals and
make closed- loop operation of a line possible.
There are limitations on the acidity and alkalinity of
solutions suitable for treatment by reverse osmosis that
eliminate some alkaline baths and chromic acid baths from
consideration unless modifications are made to the solutions
prior to treatment. Another use of reverse osmosis is for
end~of-process water recovery following chemical treatment.
A recently designed system for Plant 11-22 offers promise
that large capacity reverse osmosis systems are possible and
therefore not subject to the size constraints of evaporative
systems. If so, they should play a key role in the design
of plants that will have no liquid effluent.
Most of the development work and commercial utilization of
the reverse osmosis process, especially for desalination and
water treatment and recovery, has occurred during the past
10 years. There is a steadily growing number of commercial
installations in plants for concentration and recovery of
plating chemicals along with recovery of water under
essentially closed-loop conditions. Most of the existing
commercial installations are for treatment of nickel plating
solutions, since reverse osmosis is especially suited for
handling nickel solutions and also because of the favorable
economics associated with recovery and reuse of expensive
nickel chemicals. Commercial reverse osmosis units for
handling acid zinc and acid copper processes also have been
installed, however. Laboratory pilot plant and full-scale
in- plant studies directed at handling cyanide and chromium-
type effluents are under way.
Reverse osmosis is especially useful for treating rinse
water containing costly metals and other plating salts or
126
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materials. Generally, the purified water is recycled to the
rinse, and the concentrated salts to the plating bath. In
instances where the concentrated salts cannot be recycled to
the plating tank, considerable savings will be achieved
because of the reduced amount of waste-containing water to
be treated.
Advantages jgnj ]^i!Ei£ja£i£a§. Some advantages of reverse
osmosis for handling process effluents are as follows:
(1) Ability to concentrate dilute solutions
for recovery of salts and chemicals
(2) Ability to recovery purified water for
reuse
(3) Ability to operate under low power require-
ments (no latent heat or vaporization or
fusion is required for effecting separa-
tions; the main energy requirement is for
a high- pressure
(U) Operation at ambient temperatures (e.g.,
about 60 to 90 F)
(5) Relatively small floor space requirement
for compact high-capacity units.
Some limitations or disadvantages of the reverse osmosis
process for treatment of process effluents are listed below:
(1) Limited temperature range for satisfactory
operation,, (For cellulose acetate systems
the preferred limits are 65 to 85 F;
higher temperatures will increase the rate
of membrane hydrolysis, while lower temper-
ature will result in decreased fluxes but
not damage the membrane) .
(2) Inability to handle certain solutions
(strong oxidizing agents, solvents and
other organic compounds can cause dissolu-
tion of the membrane) .
(3) Poor rejection of some compounds (some
compounds euch as berates and organics of
low molecular weight exhibit poor rejection) .
Fouling of membranes by slightly soluble
components in solution.
127
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(5) Fouling of membranes by feeds high in sus-
pended solids (such feeds must be amenable
to solids separation before treatment by
reverse osmosis).
(6) Inability to treat highly concentrated
solutions (some concentrated solutions may
have initial osmotic pressures which are so
high that they either exceed available
operating pressures or are uneconomical to
treat).
Process Principles and Eouip|jfient. Water transport in
reverse osmosis (RO) is opposite to the water transport that
occurs in normal osmosis, where water flows from a less
concentrated solution to a more concentrated solution. In
reverse osmosis, the more concentrated solution is put under
pressure considerably greater than the osmotic pressure to
drive water across the membrane to the dilute stream while
leaving behind most of the dissolved salts. Salts in
plating baths such as nickel sulfate or copper sulfate can
be concentrated to solutions containing up to 15 percent of
the salt, by weight.
Membrane materials for reverse osmosis are fairly limited
and the bulk of the development work has been with specially
prepared cellulose acetate membranes, which can operate in a
pH range of 3 to 8 and are therefore useful for solutions
that are not strongly acid or alkaline, i.e., rinses from
Watts nickel baths. More recently, polyamide membranes have
been developed that will operate up to a pH of 12, and
several of these units are operating in plants for the
treatment of cyanide rinse waters.
Figure 13 is a schematic presentation of the reverse osmosis
process for treating plating-line effluent. The rinse
solution from a countercurrent rinse line is pumped through
a filter, where any suspended solids that could damage or
foul the membrane are removed. The rinse solution is then
raised to the operating pressure by a highpressure pump and
introduced into the reverse osmosis unit. The concentrated
salt stream is returned to the plating tank, while the
dilute permeate stream is returned to the second rinse tank.
Currently, several different configurations of membrane
support systems are in use in commercial reverse osmosis
units. These include plate and frame, tubular, spiral
wound, and hollow fine fiber designs.
128
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to
Rinse
1
Low-pressure
pump
Concentrate
R everse-osmosis
unit
Permeate
Parts
Makeup
water
FIGURE 13 SCHEMATIC DIAGRAM OF THE REVERSEOSMOSIS PROCESS
FOR TREATING PLATING EFFLUENTS
-------
§y§tejj8. Reverse osmosis units are in
._^ __
operation for recovering nickel from rinse waters. The
concentrate is returned to the plating bath.
Demonstration Status. The reverse osmosis units installed
at the Rock Island Arsenal as part of an en d~of- process
water recovery system, remains fco be demonstrated as a part
of a total successful system, A project sponsored by the
American Electroplating Society ha® demonstrated that
cellulose acetate membranes can operate successfully on
nickel and copper sulfate rinse waters and that spiral wound
and hollow fiber polyamide membranes can be used to treat
copper, zinc, and cadmium cyanide baths. A second phase of
this study is a demonstration in a plating shop of a full
scale reverse osmosis system on copper cyanide rinse water.
The freezing process would be capable of
recovering metal and water values from plating rinae water
to permit essentially closed- loop type operation if fully
developed. The feasibility of using freezing for treatment
of plating rinse waters was demonstrated on a laboratory
scale using a mixed synthetic solution containing about 100
mg/1 each of nickel, cadmium,, chromium,, and sine, along with
30,000 mg/1 of sodium chloride. Greater than 99.5 percent
removal of the metallic ions was achieved in the
experiments, with the purified water product containing less
than 0.5 mg/1 each of the individual plating metals. The
separation tests were carried out using the 9500 1/hr (2500-
gpd) pilot plant unit at Avco Systems Division, Wilmington,
Massachusetts .
Process Princip_les_and_^guigment.- The basic freezing pro-
cess for concentration ana recovery of water from plating
effluents is similar to that used for recovery of fresh
water from the sea. A schematic diagram of the treatment of
plating rinses by the freezing process is shown in Figure
1U. The contaminated reuse water is pumped through a heat
exchanger (where it is cooled by melted product water) and
into a freezer. An immiscible refrigerant {e.g., Freon) is
mixed with the reuse water. As the refrigerant evaporates,
a slurry of ice and concentrated solution is formed. The
refrigerant vapor is pumped out of the freeser with a
compressor. The slurry is pumped from the freezer to a
counterwasher , where the concentrated solution adhering to
the ice crystals is washed off.
The counterwasher is a vertical vessel with a screened
outlet located midway between top and bottom. Upon entering
130
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Pump
Cooling
water
To rinse
Uuuc
Heat exchanger
Metter/
condenser
Counter
washer
1 Concentrate
Refrigerant
(Freon)
f\ Compressor
Refrigerant
vapor
Freezer
FIGURE 14 SCHEMATIC DIAGRAM OF FREEZING PROCESS FOR RECOVERY
FIGURE S CHEMICALS FROM PLATING RINSES (37.38)
-------
the bottom, the slurry forms a porous plug. The solution
flows upward through the plug and leaves the counterwasher
through the screen. A small fraction of the purified
product water (less than 5 percent) flows countercurrently
to the ice plug to wash off concentrated solution adhering
to the ice. The ice is pumped to a condenser and melted by
the release of heat from the refrigerant vapor which had
been originally evaporated to produce the ice, and which had
been heated by compression to a saturation temperature
higher then the melting point of the ice«
Because of the pump work, compressor %»ork, and incomplete
heat exchange, a greater amount of refrigerant is vaporized
than can be condensed by the melting ice. Consequently,, a
heat removal system is needed to maintain thermal
equilibrium. This system consists of a compressor which
raises the temperature and pressure of toe excess vapor to a
point where it will condense on contact: with ambient cooling
water.
The freezing process offers several advantages over some
other techniques. Because concentration takes place by
freezing of the water in direct contact with the
refrigerant, there is no heat-transfer surface (as in
evaporation) or membrane (as in reverse osmosis) to be
fouled by the concentrate or other contaminants. Suspended
solids do not affect the freezing process and are removed
only as required by the end use to be made of the recovered
products.
The heat of crystallization is about 1/7 the heat of
vaporization, so that considerably less energy is
transferred for freezing than for a comparable evaporation
operation. Because freezing is a low-temperature process,
there will be less of a corrosion problem than with
evaporation, and less expensive materials of construction
can be employed. The freezing process requires only
electrical power, as opposed to the evaporation process
which also requires steam generating equipment. The cost of
the freezing method may be only 1/3 that for evaporative
recovery.
A method of freeze drying metal finishing solutions has been
demonstrated in the laboratory. Droplets of the solutions
are injected into cold liquid-hexan* where they are
immediately frozen. The droplets were separated out and the
water removed at subfreezing temperature. The method leaves
a dry chemical residue, and the pure vaporized water could
be recycled to process. The economics of the process on a
practical scale are unknown.
132
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Practical Operating Systems . No commercial utilization of
freezing~f or treatment of waste water from metal finishing
is known.
Demonstration Status. No demonstrations are in progress in
metal finishing plants. However, a 9500 liters/day (2500
gpd) unit is in operation to demonstrate desalination of
water.
Electrodialys is
Applicability. Electrodialys is removes both cations and
anions from solution and is most effective with mult i-va lent,
ions. It is capable of reducing the concentration of heavy
metal ions from solutions whether they are complex or not.
Chromate and cyanide ions may also be removed.
Process Principles aM Equipment. The simplest
electrodialysis system consists of an insoluble anode and an
insoluble cathode separated by an anion permeable membrane
near the anode and a cation permeable membrane near the
cathode. An anode chamber, cathode chamber, and middle
chamber are thereby formed. Upon electrolysis anions pass
from the middle chamber to the anode compartment and cations
pass from the middle chamber to the cathode compartment.
The concentration of salt in the central compartment is
thereby decreased. By employing several anion and cation
permeable membranes between the electrodes several chambers
are created. A stream may then be run through several of
these chambers in which the concentration is successively
increased. The net effect is similar to that of a
continuous moving bed ion exchange column with electrical
energy used for regeneration rather than chemicals.
- practical operating systems
have been reported. However, development has resulted in
several demonstrations, discussed below.
Deroonstira.fciQIi--J&a&*§« Several demonstrations have shown
that electrodialysis is a promising method. Further
development and use of the method may be expected. Copper
cyanide rinse water may be concentrated sufficiently to be
returned to the bath by using two units on a double
counterflow rinse system, i.e., between the first and second
rinse tank and between the bath and first rinse tank.
Copper may be recovered and chromic acid regenerated in a
spent etching solution for printed circuits. The Metal
Finishers Foundation has put priority on a future project on
cyanide removal by electrodialysis^
133
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Ion-Flotation Techniques
Ion- Flotation techniques have not been
developed for application to process rinse water effluents.
If successfully developed into a practical method for
effluent treatment, ion flotation offers possibilities of
reducing the amount of water discharged by 60-90 percent for
some operations. These savings are based on results of
small-scale laboratory studies on solutions containing
cyanides or hexavalent chromium.
Process.^ Principles _and .Bgii^gment, Separation of ions from
aqueous solutions by a flotation principle is a concept
first recognized about 25 to 30 years ago. In the ion-
flotation operation a surface active ion with charge
opposite to that of the ion to be concentrated is added to
the solution and bubbles of air or other gas are introduced
into the solution to form a froth of the surface-active
materials. The foam is separated and collapses to form a
scum containing an ion concentrate. Ion flotation combines
the technologies of mineral flotation and ion exchange. A
schematic diagram of an ion-flotation cell is shown in
Figure 15.
Experimental results indicate that 90 percent of the
hexavalent chromium in a 10 to 100 ppm solution can be
removed with primary amine surface-active agents. However,
the amine suffered deterioration when regenerated for reuse,
since the removal efficiency dropped to 60 percent after two
regenerations of the amine.
Grieves,, et al. , have demonstrated the feasibility of using
ion flotation on dichromatc solutions with a cationic
surfactant (ethylhexadecyldimethylaroonium bromide) . A
continuous operation with a retention time of 150 minutes
was devised. The feed stream contained 50 mg/1 of
dichromate. Approximately 10 percent of the feed stream was
foamed off to produce a solution containing 150 mg/1 of
dichromate, while the stripped solution contained 15 mg/1.
Cyanides have been removed from dilute solutions with mixed
results. The extraction efficiency from a cadmium cyanide
solution containing 10 ppm of cyanide was 57 percent, using
primary,; tertiary, and quaternary ammonium compounds as
collectors. Extraction efficiencies for nickel and iron
cyanide solutions were approximately 90 percent, but these
systems are of relatively little interest.
Practical. _ Operating Systems. There are no practical
operating systems.
134
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Air in
(
lMg
Foam concentrate
lake -off
Purified
solution — «
removal
^njcction port .. -
for collector »*•
ogent
-t-^j-V^J-u-t,
-"-**-"-—
»* »
% 1
0 b
V
•i!
6 0
'U,
i
0
«;
/.
* ft
/ Oi
/
40
'
# ^
• ',
»«
»'
);';
i
»
^*^
Air out
— Foam level
_ . .. . .
boiution level
•"" Solution sunipliny
_______ r>r.«t
poit
FIGURE 15 SCHEMATIC DIAGRAM OF ION-FLOTATION CELL
FOR TREATMENT OF PLATING EFFLUENT
135
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Demonstration fftatus. The process has not been demonstrated
in an operating plant.
Electrolytic Stripping
Applicability. Electrolytic stripping is not in general use
for removing heavy metals although some procedures have been
employed for recovering precious metals.
Process Principles and Equipment. In order to strip a solu-
tion by electrodeposition it is necessary that the metallic
ions in a dilute solution reach the cathode surface at a
sufficient rate so that essentially all of the ions can be
deposited in a reasonable time. 3isrfleet and Crowle have
discussed several methods of accomplishing this. One method
called the "integrated" system uses baffles in a tank to
create a very long path through which the water may be
recirculated at a high velocity. The method is suitable
only for metals having a relatively high limiting current
density for dilute solutions, such aa gold, silver, and tin.
The fluidized bed electrode is a bed of metal spheres or
metal-coated glass spheres that is fluidiaed by pumping the
dilute solution through it and causing aa expansion of 5 to
10 percent, With spheres of 100 to 300 ailerons in diameter,
a total geometric area of 75 cm'/cm3 Is obtained. Thus, the
current density is very low aad the flow of electrolyte
through the bed provides the forced convection to support
high currents. Another system employs electrodes made of
expanded metal and the turbulence arowxd this structure
enhances the rate of deposition of metal when solution is
pumped past it. Turbulence and an increase in the rate of
deposition at a plane electrode may also be promoted by
filling the space between electrodes with a woven plastic
screen, glass beads, etc.
In another system the electrode is introduced into a narrow
gap between two porous carbon electrodes. The bulk of the
solution (99%) is forced through the cathode where copper is
deposited out. Predeposited copper on the anodic electrode
is dissolved into the 1 percent of the electrolyte that
permeates through this electrode and a copper concentrate is
produced. The two electrodes are periodically reversed so
that copper deposited from a large volume of solution is
dissolved into a small volume of electrolyte. Copper in
solution has been reduced from 670 mg/1 to 0.55 mg/1 in the
cathode stream and concentrated to 4ft g/1 in the anode
stream. A similar system has been used for depositing
metallic impurities from strong caustic solutions.
136
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Practical Operating Systems, There are many systems in
operation for the recovery of precious metals.
Demonstration Status. The porous electrode system is still
under development at the University of California and has
been scaled up to handle 250 gpd of copper sulfate solution.
Metal Finishers Foundation has established priority for a
future project to remove zinc from effluent by
electrodeposition.
Carbon Adsorption
Applicability. Activated carbon has been used for the
adsorption of various materials from solution, including
metal ions. Experimental data show that up to 98 percent ot
the chromium can be removed from waste water. The treated
water can be recycled to the rinse tanks.
£rocessi Pr|.nct6lg§ and gguipment. The process relies upon
the adsorption of metal ions on specific types of activated
carbon. In the case of Chromium VI, a partial regeneration
of the carbon can be accomplished with caustic solution
followed by an acid wash treatment to remove residual
caustic and condition and carbon bed for subsequent
adsorption cycles. The equipment consists of holding tanks
for the raw waste, pumps and piping to circulate the waste
through adsorption columns similar to those used for ion
exchange.
Practical Operating Systems. Systems based on adsorption
and desorption are still under laboratory development and no
practical operating systems are known.
Demonstration Status. Pilot p?,.ant equipment has been
operated successfully in an electroplating plant treating
chromium rinses at a flow rate of 19 liters/min (5 gpm) at
concentrations from 100 to 820 mg/1 hexavalent chromium.
Adsorption was continued until the effluent reached
concentrations of 10 ppm of Chromium VI.
Water Conservation by Liquid-Liquid Extraction
Applicability. Liquid-liquid extraction has been used on an
experimental basis only for the extraction of hexavalent
chromium from waste waters. The effect is to concentrate
impurities in a smaller volume,, which in turn will have to
be treated by other means or suitably disposed of. The
fully extracted aqueous phase may be recycled to the rinse
tanks, water savings from 50 to 73 percent appear to be
possible.
137
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—Principj.es—and Equipment. The metal-ion pollutant
is reacted with an organic phase in acid solution, which
separates readily from the aqueous phase. Metal is subse-
quently stripped from the organic phase with an alkaline
solution. Hexavalent chromium, for example, has been
extracted from waste water at pH 2 with tertiary and
secondary amines dissolved in kerosene. After the reaction
of the chromium with the amine and phase separation* the
chromium is stripped with alkaline solution from the organic
phase restoring the amine to its original composition. For
liquid-liquid extraction to be feasible the following
conditions would have to be met:
(1) The extraction of chromium should be virtually
complete
(2) Reagent recovery by stripping would be efficient
(3) The stripping operation should produce a
greatly concentrated solution
(4) The treated effluent solution should be
essentially free from organic solvents
(5) capital and operating costs should be
reasonable.
The equipment required consists basically of mechanically
agitated mixing and settling tanks, in which the phases are
intimately dispersed in one vessel by agitation and then
permitted to flow by gravity to a settling vessel for
separation. Holding tanks for extractant and stripper and
circulating pumps for these solutions, as well as the
purified waste water, are necessary. Equipment for liquid-
liquid extraction would also include horizontal and vertical
columns, pulsed columns and centrifuges.
Practical Operating Systems. Liquid-liquid extraction
systems are not known to be operating for treatment of metal
finishing wastes.
Demonstration status. Experimental evidence exists indi-
cating that up to 99 percent of chromium can be successfully
extracted from rinse waters containing 10 to 1000 mg/1 of
Cr*+. With 10 ppm of Cr«+ in the rinse water, the treated
effluent contained as little as 0.1 mg/1 of the ion; with
100 ppm in rinse water concentration was reduced to 0.4
mg/1. Stripping was effective as long as the amines were
not allowed in contact with the chromium for a prolonged
period of time which would allow oxidation by Cr*+ ions.
138
-------
The effluent, however, contained from 200 to 500 mg/1 of
kerosene, which is undersirabie.
NfPthods of Achieving No Dj,sch.arae of gollutants
Although chemical methods of treating waste waters are
achieving the low effluent discharges recorded in this
report, they are not improvable to the point of achieving
zero discharge of pollutants. Also the problem of
recycling sludges or solid wastes remains. It is easy to
design systems that will in principle close the process loop
and prevent discharge. In practice, however, this can only
be done with considerable forethought and experience, since
closed systems are in general subject to impurity buildup.
Progress in achieving no-discharge systems is likely to take
place in a series of steps in which the amount of discharge
is consistently reduced until it is negligable.
A major problem with a series of metal finishing processes
in a closed cycle is that of dragin. After a closed cycle
has been run long enough any stagnant tank,, i.e.., a plating
solution that is normally not discarded,, will contain the
same concentration of contaminant as the preceding tank in
the cycle, the assumption being that the volume of dragin
and dragout are equal. Therefore* if the final rinse
following nickel plating contains 12 ppm of nickel and
chromium plating follows, the chromium bath will ultimately
contain 12 ppm of nickel. Nickel is frequently removed from
chromium plating baths by ion exchange* but since the ion
exchanger requires periodic regeneration^ the regenerant
must somehow be returned to the system if it is to be
considered a closed one. The nickel in the regenerant might
be recovered and returned to the nickel bath, but the
dissolved solids, i.e., sodium sulfate? and sodium chloride
are really excess products that cannot be completely
returned to the process, while the main process loop may be
closed, the secondary purification loops may be more
difficult to close. With some process baths, it may not be
possible to find a method for purification that is as
adaptable as is ion exchange to the removal of nickel from a
chromium bath. Alternatives then are to (1) develop
processing baths that can tolerate the impurity buildup or
(2) to design rinse systems in which the concentration of
impurity in the final rinse tank is reduced to a tolerable
level.
Some systems, designed to remove a specific impurity, are
found to remove other components as well, which may require
further treatment. An example of such a system is that used
for removing carbonates from cyanide baths. Whether
139
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freezing or precipitation with calcium is used, the
carbonates occlude and adsorb significant quantities of
cyanide that must then be further treated, with the result
that cyanide is not maintained in a closed system.
Therefore, with present technology, it is likely that there
will be some discharge from a process loop in spite of the
best efforts that are made to close it. Some waste water
effluent will be produced and the next consideration is how
well a waste treatment system can be closed.
The effluent will contain heavy metals, cyanide, and
chrornate all of which can be treated to relatively low
levels to give (1) liquid containing small amounts of heavy
metals, cyanide and chromate and larger amounts of soluble
salts such as sulfate and chlorides, and (2) sludge
containing heavy metals, phosphate, carbonates, flocculating
agents, etc. The liquid, if large in volume may be
concentrated further by evaporation, reverse osmosis, ion
exchange, or some other process followed by a further
purification to reduce the heavy metal effluent to a
negligable value. The liquid may alternatively be passed
through a salt loaded ion-exchange column to remove all
traces of heavy metals and yield an effluent containing
essentially soluble salts that may be discharged to the
ocean if not to a stream or sewage facility. Alternatively,
solutions of soluble salts may be evaporated to dryness and
the solid salt contained or fixed in cement, etc.
Sludge, obtained either directly from waste water or from
ion-exchange regenerants, cleaning and pickling baths, etc.,
would need to be reclaimed for metal values or the metal
salts separated out for return to process tanks in order to
provide a closed or recycle system.
Thus, to attain the ideal of providing a system where input
is energy and materials and output is solely a finished
product will require further research and development,
considerable ingenuity, and expert engineering and design.
However, the capability for progressing towards this goal is
available.
140
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SECTION VTII
NONWATER QUALITY ASPECTS
Introduction
In this section, costs associated with the degree of
effluent reduction that can be achieved by exemplary
treatment methods are discussed. The nonwater qualzty
aspects concerning disposal of solid waste and the energy
impact of the waste treatment technologies also are
discussed.
Treatment and Control Costs
Chemical Treatment to Achieve Low Levels of Pollutants
BPCTCA LimitatiQns_JTable_ll. Costs associated with control
technology consistent with the exemplary practice of
chemical treatment in 26 plants avera9ed a1;?^™0 ^"
treated with a standard deviation of $1.91/1000 liters
(Table 27) . Operating costs include a cost of capital equal
to 8 percent of the investment and depreciation equal to 10
percent of the investment.
The operating cost of waste treatment as a percent of cost
of metal finishing for 13 companies is 7.4 percent with a
standard deviation of 5.4 percent. The figures were arrived
at from estimates by the plants themselves concerning the
relative cost of waste treatment.
The plot in Figure 16 shows the large variation in
investment costs for individual plants and reflects the
large deviations reported above. Thus, there are no typical
plants. Rather, costs are highly dependent upon local
conditions. Costs were calculated in terms of volume of
waste water treated rather than surface area finished
because costs are believed to be more closely related to the
volume treated. Water use is highly variable and relating
waste treatment costs to area finished would have provided
even more variable results. For a nominal water use of 80
liters/sq m (2 g/sq ft) the cost of $1.06/1000 liters is
equivalent to $0.085/sq m ($.0079/sq ft).
In addition to the cost data collected from plants with
waste treatment facilities, costs were also estimated by
modeling metal finishing facilities together with waste
treatment facilities providing effluent that would meet
141
-------
TABLE 27 COSTS FOR WASTE TREATMENT FACILITIES
Plant
No.
20-24
33-24
33-25
36-12
33-2
33-4
8-5
6-37
19-11
15-3
9-7
4-9
3J-19
8-8
33-22
33-23
20-22
20-20
33-35
20-23
4-8
5-35
9-2
23-7
30-13
?3-30
19-24
6-35
31-16
46-4
33-29
Investment
Processes (1971)
Plating Cortmon Metals
Plating Cocoon Metals
Plating Coanon Metals
Plating Con. , Prec. Ketals
Placing Free. Metal*
Fiatir.g Free. Metals
Plating Prec. Metals
Plating Prec. Metals
Plating Prec. Xetals
Plating Prec. Metals
Electropainting, Anodizing
Electroless Plating
Electroless Plating
Electroless Plating
Electroless Plating
Anodizing
Anodizing
Anodizing
Anodizing
Anodizing
Ar.ecizing
Chemical Milling
Chemical Milling
Chemical Milling
Chemical : Li 11 ing
Ciienical Milling
Phosp'-iatiny
Etching
Inversion
Printed Circuits
Elect ropolishing
Elect roaachinlng
34,000
172,000
27,932
200,000
25,000
66,000
300,000
400,000
110,000
66,113
100,000
45,325
23,292
217,725
51,679
193,846
167,575
130,902
155,300
125,000
123,414
17,45?
300,000
'',208/100
1^2 /'06
2y',A?>2
9-'t,500
295,615
5b,°s3
1,05 0,0 00
', 1 , 9.1 '->
Operating
Cost/Year
(1971)
14,195
80,430
10,694
72,809
14,968
18,205
115,995
121,905
49,985
25,552
32,249
45,312
9,746
168,312
13,430
51,515
Ay, 658
113,3-0
/ ' '^
2S^2U
41,855
16,675
33,753
685, 847
3'13 .?!•'>
11,'jl?
19,726
1?G,211
ij,7i -1
23V ,611
:4.">6C
Hours
Operated
Per Year
4,800
4,000
7,200
7,520
1,025
1,800
2,400
2,250
2,000
2,000
4,000
4,000
4 , 000
8,400
4,000*
4,000
6,000
6,oeo
7,200
7,200
6,000
4, BOO
2 , 000
6,000
S.OQO
3,'JjO
3,600
2,000
2,250
4,000
4,170
4 , 000
Volume to
Treatment
Plant, 1/hr
26,497
15,897
4,163
6,813
12,615
24,224
34,065
113,562
45,424
57,727
30,851
1,741
3 , 985
104,087
36,794
9,000
13,925
79,485
129,447
3,028
22,712
7,570
7,570
i89,250
159. OCC
6,813
54,509
6,813
11,356
90,849
30,659
22,710
Volume to
Treatment
Plant, 1/yr
1.271 x 108
6.359 x 107
2.997 x 107
•7
5.123 x 107
1.293 x 107
4.366 x 107
8.176 x 107
2.555 x 108
9.08 x 107
1.154 x 108
1.234 x 108
6.964 x 10t>
1.594 x 107
8.743 x 108
1.471 x 108
3.600 x 10'"
Q
1.135 x 10-
4.769 x 108
Q
9.320 x 10a
2.180 x 10'"
1.362 x 108
-7
3.634 x 107
~J
1.514 x 1C'
1.136 x 109
Q
9.540 x 1U8
2.6?!'. x 107
_.^o^ ,-. .,w
1.362 x 107
2.555 x 10 7
3.633 x 10 ^
1.278 x 103
7
9-Ot'4 x 10'
Invest-
ment/
1/hr
$ 1.28
10.82
6.71
29.36
1.98
2.72
8.81
3.52
2.42
1.15
3.24
26.03
5.84
2.09
1.40
21.54
8.85
2.: 8
1.20
41.28
5.43
2.31
3S.63
15.36
3.66
4.^
i. n
43.39
5.19
11.56
L.37
Operating
Cost/
1000 liters
$ 0.30
1.26
0.36
1.42
1.15
0.42
1.42
0.48
0.55
0.22
0.26
6.51
0.61
0.19
0.09
1.43
0.44
0.24
0.09
1.30
0,31
0.46
5.53
0.60
1'. 'ij
0.43
0.30
8.83
O.b2
0.65
0,1.1
Treating
Cost/
Processing
Cost
14
3
0
5
0.65
7
7.5
33
, 7
• A
'•'<
7 .1,
1.0
18
- - "•
•'< •*
hours jer
-------
I07
1 r
10"
o
•o
o
o
cE
0>
«»
v
>
c
10=
10"
i 1 1
I0a
Capacity Liters.hr
FIGURE 16
INVESTMENT COSTS OP WASTE TREATMENT PLANTS
WITH VARYING VOLUME CAPACITY
-------
BPCTCA standards. By modeling plants it was possible to
derive selfconsistent costs for various degrees of treatment
and for various plant sizes. Plants were sized according to
the number of employees, which is desirable if data are to
be used for cost impact studies. Table 28 and 29 summarize
the results of one cost estimate.
The lowest investment cost of $22,980 is for a 5-employee
urban plant that precipitates heavy metals, does not treat
cyanide or hexavalent chromium, and does not clarify. This
plant also has the lowest operating cost of $12,294/yr. The
highest investment cost of $378,455 is for a plant with HI
employees carrying out complete waste water treatment
including clarification and filtering of sludge. This plant
also has the highest operating cost of $157,894/yr. The
operating cost probably could be reduced somewhat by using a
filter press directly on the neutralized waste water.
However, this technology is not as well established as that
using a clarifier.
Costs per area are $1.02/1000 liters for the 5-man plant
neutralizing only and $1.09/1000 liters for the U7~man plant
doing complete waste treatment. These figures compare
favorably with the $1.06/1000 liters average value for the
plants listed in Table 28.
The operating costs as a function of plant size have been
plotted in Figure 17 and show that in the size range studied
costs are roughly linear with the number of employees. The
makeup of the production processes varies somewhat, both
with the extent of treatment and with plant size. Processes
using cyanide or chromate were not included where treatment
for cyanide and/or chromate was omitted. The smaller plants
were assumed to be concerned with electroplating only while
processes such as anodizing and electroless plating were
confined to the largest plant. Even among the smaller
plants there are some variations in plating processes. Some
of the 5-man plants included cadmium plating as a specialty
while the 10-man plant omitted cadmium but concentrated more
on tin plating. The product mixes listed are only one of
many sets that might have been chosen but reflect in general
the amount of finishing that can be accomplished in the
various sized plants with diverse operations. The amount of
waste water to be treated, and the amount of waste produced
are thus typical of the various size plants.
The productivity of a plant, measured in area processed/
hour will vary with the process mix even though the number
of employees is not changed. Thus, in Table 29 the 5-man
plants that require only coprecipitation (A) or cyanide
144
-------
TABLE 28
TtCATMBTT BQUVMENT COSTS. VALUES IN O. S. DOUAM. 1*74
A.
*.
C.
D.
t.
T.
C.
Item
Concrete Holding Pin
Valves. Cootrob. Monitor] * tecotden
Sturert
Pnmpj
Tan to
Clariflen
Lagoons (Soil)
Pointing Fillers
Evaporator
Ion-exchanger
Sulfonatoc
Chlorinaror
Subtotal A
Treatment Building
Land COM. Urban
Rural
LaoJ Cost. Pin & Lagoon). OlbU
•and
Subtotal B
Urban
Rural
Total A&8
Urban
Rural
Equipment InaaUatton
Tout C4D Urban
Rural
C*D. Urn Cluifttt. Urbn
Sludge Filler (Option)
Urban
Rural
Total E4F
Urban
Rural
A
4»
2,600
1.100
3.140
2.945
12.550
100
2.600
—
—
—
—
26.045
1.990
345
SO
40
10
4.215
4.050
so.s*
10.095
5.210
54.51*
M.3D*
•*•*•
3.868
S.»90
19,390
39.195
SEnp
»
420
4. 850
1.10»
4.TW
3.550
12.559
130
2. TOO
--
—
—
1.550
33.629
5.910
365
75
30
10
C,30S
5.995
39.925
19. CIS
C.72S
4«.*S»
4*.M*
M.KO
4.59*
4.CS9
51.24*
50.9SO
BOIpCCS W ElHplOTCd *vB EMpWl'V
c
sso
S.08*
1.100
4.S4S
4.939
14. 900
230
2. "TOO
—
--
1.550
—
11.8*5
8.160
500
100
30
H
•.•98
•,370
4C.S75
4C.15S
7.5*0
54, IS*
M.73*
30. t*»
4.8SO
4. MO
S9.005
St. CIS
D
60S .
7.215
1.100
8,300
5.300
14.900
230
3,300
—
—
3.550
3.550
46.050
9.960
610
125
45
10
a*. CIS
10.095
S4.66S
56. 145
9.310
«.«5
**.*S*
M.91S
4.300
4.330
70.175
89.685
A
950
2.945
1.100
4.940
3,7*0
19,100
100
S.1SO
—
—
—
—
35.065
9.660
595
120
225
45
__
10.480
9.825
45.545
44.898
7.01S
•2.660
51.905
11.460
7,750
7.880
60.310
59.185
»
945
5.080
1.100
6.330
3.700
19.000
130
3.200
—
--
—
3. SSO
43.095
11.160
720
145
185
40
».«8S
11.91$
SS.780
55.040
•.(20
64. HO
83.660
4.538
7.720
7.850
71.100
71.51*
C
1.335
5.310
1.100
6.800
4.605
23.400
230
5.100
--
—
3.550
--
50.430
15.060
925
185
2*5
CO
M.tT*
15.105
•6.700
CS.7*
10.090
76.798
75.815
•4.190
7.745
7. MB
•4.535
«1.7*»
D
1,350
7,445
1.100
1.490
5, MS)
22.490
230
5. WO
—
—
3.550
3.550
51.T3*
16.7M
1.025
3X5
215
55
M.CH
16.970
75.73*
74.C**
11.545
•7.215
M.S3S
M.CT*
7.14»
7.M8
*5.M*
•4.115
A
1.S4S
3.945
1.100
5.650
l.*95
35.400
ICO
5. 600
—
—
—
—
46.295
13,020
795
160
340
45
M.*35
11. 325
«t.32*
M.sn
•.2*0
CS.SM
M.7M
44.1*8
11. 380
11.510
•0.980
•0.290
»
1.S2S
5.310
1.100
1.110
3,440
25.400
160
6.500
--
--
—
3.550
54.095
11.540
1.135
230
310
IS
». 045
W.84S
74". 14*
73.940
10.820
•4.960
•3.760
**.*•*
I1.S40
11.490
98,200
95.250
C
1.725
5.310
1.100
1.880
S.11S
28.000
230
6,500
--
--
3.SSO
—
60,010
19.050
1.110
235
300
60
20.520
19.345
•0.530
19.355
12.005
•3.535
91.360
«4.*3*
11. MO
12.580
104.915
103.940
D
1.740
7.445
1.100
12.340
7.200
28,000
230
6.500
—
—
3.550
3.550
71.665
21.180
1.300
260
310
65
33.791
31.505
•4.455
93.170
14. IK
1*8.7**
KM. SOS
80.180
12.380
. 12.580
121.17*
120. OK
A
2.490
1.185
2.200
9.300
8.355
41,100
410
14.000
146.000
550
--
--
343.200
29.520
1.810
365
475
95
11. MS
39.9*0
MS. 005
373.180
48.640
123. 64S
321,820
31«,S4»
13. MO
13.220
136. SIS
338.040
41CmplorM*
I
2.S3S
10.610
2,200
11.610
13.95S
41.100
410
14,000
146.000
550
--
3. SSO
252. SSO
33.150
2.0 JO
410
520
105
35,100
33.6SS
2M.280
2M.HS
50,520
138,800
MC. 165
tfl.100
12.938
13.220
3S1.130
S49.98*
C
2.890
9.690
2.200
11. U9
12.230
49.630
600
15.600
144.000
--
3.550
--
254.240
44.310
2.720
545
765
155
41.855
45.010
302.095
299.310
SO. SSO
3*2.945
350.160
10. IK
12. SSO
13.050
365.495
36X21*
D
3.9*3
14.485
2.500
12.140
11.130
50.600
110
IS. COO
146.000
—
1,550
3.550
264.130
45.360
2.180
560
805
160
48.9*5
4*. 010
313. r>*
3tt. 31*
52. (5*
IS*. 901
363.040
31*. 30*
11. SM
11. M*
378.4**
31 6. 898
A-Neutrallunon.
• -Cyanide oxidation pan Mntulizatloo,
C-Chramaie reduction pka noilralltatkio.
D- Cyanide oxidation chromate redcctlon.
-------
TABiuE 29
ANNUAL OPDUTING COSTS, WASTt TMATMENT, U. S. DOUARS, 1ft4
Proceo
«.'•. of Pate.
t~flr,t*l mTj
» 75
-5
Kt
10 17i
171
zy»
» 2»
•>»
tv» cu
1VS
ITS
riant Size
Vic. Treatment
t/hr Type
«.v/>
t.'/'/O
S.O'/O
11. COT
n.c/ii
18.4W
21.200
10.440
M.feW
SC.400
51.'/.)
«5 200
A
B
r
D
A
t
C
D
A
B
D
A
1
of
Capital'"
2.843
3.1T2
4 111
5.270
4. 2-.S
5.151
6.144
8.8«1
6 137
7 403
8.104
25.832
21. 104
28.236
23.213
Chemical
Depreciation^' Uw
3.553
4. CCS
S.41«
6,588
5.2SG
6.438
1,619
8.728
6.958
8.496
9 254
10.879
32.3C5
33.880
38.295
36.591
481
3.300
2.741
4.589
1.5)2
8,919
4.655
10.789
1.793
11,831
5,592
15,413
4,990
15,829
10,110
24,132
Electric
Labor"1 Maintenance**' Power'5'
4.000
4,000
4.000
4.000
12.000
12,000
12,000
12.000
24,000
24,000
24,000
24,000
32.000
32.000
32.000
32.000
711
933
1,084
1.318
1.052
1,288
1,536
1.146
1,392
1,100
1.851
2.116
(.500
8.776
7.059
7.J19
1,440
1,440
1,826
1.82C
2.217
2.217
2,409
2.409
3,036
3,036
3,198
3.195
11,603
11,803
11.288
13.899
Water
ft
SewcrW
240
240
306
306
380
380
402
402
506
sog
634
634
1.918
1.918
2,258
2,228
evaporator
Stodge Ion
RennvaK1" Exchanged) Treatment?*)
1.536
864
3,012
2,016
2.208
2.592
8,184
8.184
3.456
3,456
5,184
S.184
10,464 ' 650
10,464 880
8.619
18,60*
"*
-•
--
--
—
—
8.080
(.080
8.080
a.o«o
Credit
Save<10' Balance
:: ::
••
„
.. -.
..
« ~.
11,828 3.148
11.828 3,748
11.82* a. 14*
11.S28 3. 748
Urban
14,004
19.040
22,178
•28. 913
C8.95!!
39. 10$
40,009
46.708
59.8.V
87.113
10.185
121.434
136,716
131.114
151.894
Total*1"
Rural
1-I.OS4
19. ICO
M.655
85, 7W
23.709
38. 915
39.608
48.040
46.458
57. 396
70.468
1-V.41S
135. 311
130.048
156.180
Total' 5I1 (Vf.tK filter PicaK
No. Clitltler
16. 7.V
19.198
:;.93J
C5. 139
35.305
33.010
43.7iil
41.613
51.513
65. i:5
IK. 014
126. SSS
121.284
141.174
rrfcan
U.-'oi
I5.JT6
19.706
.3.sr
36.513
34. J-'S
4J.OS7
43. :s:
*- •*-*
65.601
110. »Ti<
IS:. 436
fciral
U. Iti
\?.:a
19.851
•'• **
:*..«*!
34.3:3
J4.c:4
4:. ??»
5r.lU
5...1-
6S..S4
121. m
141. It)
ID ! ?ercen of H!««ment
«•» It.V.'bf ,
it, I jtnes of u:\tvrxn
ri, :. JS - '/. i-5 !/l>•-/ lalloni of »«ef added wlib treatment diemlcab
Ci r-.l"'i Cvual n UkcnneL! com
»7) D«u fr>n ?fa«dl« for •>>'> jal/Sr e»r»ralar
fl':, !**jl on a dra?-»i! rate •sf 2 ?ai/IT<)0 iq ft plated and a w!ulU» con of 2.80/gallon
(llj DLfcreoce between »rban and rural li the eon of aewage charge only
(U, <.KtJ*4 for tic COM of ilutje .etro.al, UK I* conjunction Mlth C<|UlBffleK Con Oau,
-------
• l£l^i*il*'*l \ '<:-l'\
^ti* M-£-|.*\\' \\
^~i\\\\l\ ill 1
|£ ifSi? |j: '}
-**sill-l 2 £ a S*
•S t a B ! .ff.fr r '53 S &
a :n
•s t>i 5
3. ^ S S * E
H
»»
-5
is
It
'
a
i
1 M1 i !
11 !
! hi n tl
•i!.1
s
!
M
Ih
U
P $
l\ if
!l H'
t s jf
15 ti
*•*
SI
1
-
pl
u
l!
•:»
p «i
r<
R S
*4f U; |i IT" 14
u s ! h ni *«.
£
t's H fuj
>.i j H s g"S. g
is. •• tl s i- i:
S s
i i
tt
I
H
1
8
i
S
§
*
8
§
i
ii
i, :• £ a ^ a ft
1
J*
•
I I i
S §
i i
g s s
'§ § i
* M W
*- S £
§ § i
ft 5 3
S i §
.* .3 .3
I § S
P S »
1 i i
P ^ «
5 £ S
! ! i 1 1 1
8 S
il
i*
ctual
KNtoeiM
nr-/ht
mi
fill
sif
ill
si
***>.
dollan
II
|Sflf
r*Mi
pH|5
I. «i L^ S &
fH«i
f
W
OJ
o
w
^s
< o
O W
M H
M
3*
O
0 C3
DC C/)
M HJ
O J5
*^ Hg
w w
PI Cfl
-------
160,000
140,000
120,000
100,000
to
Vt
0)
o
•Q
m
o
o
00
a
J-l
a>
a.
o
80,000
60,000
40,000
20,000
Coprecipitatlon only
D Oxidation of cyanide +
coprecipitation
Reduction of chromate +
coprecipitation
X Oxidation of cyanide, reduction
of chromate, coprecipitation
10
20 30
No. of Employees
40
50
FIGURE 17 OPERATING COSTS RELATED TO PLANT SIZE AND
EXTENT OF WASTE TREATMENT
148
-------
oxidation plus coprecipitation for treatment of wastes can
process 75 sq m/hr, while 5-man plants that include chromium
plating and chromating (C,D) can process 100 sq m/hr.
It was concluded that costs for a captive or independent
shop would be similar if the waste treatment plant was sized
for the metal finishing operation only. Captive metal
finishing operations may discharge waste waters into large
systems that handle other plant wastes, but it would be
difficult to estimate what volume percent of waste water
typically came from the metal finishing operations and what
portion of total waste treatment costs should be allocated
to them. Flow sheets of the waste treatment plants that
were costed are shown in Figures 18, 19, 20 and 21.
Another plant was modeled to ascertain investment and
operating costs of a medium large plant employing (1)
segregated chemical treatment of waste waters containing
individual metals, and (2) no discharge of pollutants.
Costs for waste treatment employing destruction of cyanide,
reduction of chromate wastewaters and coprecipitation of all
metals were also developed as a basis of comparison. Table
30 summarizes both investment and operating costs of the
waste treatment plants. Investment and operating costs
increase in the order
(1) Combined chemical treatment and
coprecipitation
(2) Segregated chemical treatment and
coprecipitation
(3) Combined chemical treatment plus
end-of-pipe treatment to eliminate
discharge of pollutants.
The operating cost for combined chemical treatment and
coprecipitation is equivalent to $1.41/1000 liters, which is
approximately 30 percent higher than the $1.09/1000 liter
figure for a similar model in the previous discussion.
While the two models are slightly different the difference
is mainly due to the fact that the two cost values were
arrived at by two cost analysts, each of whom assumed what
he considered were the most realistic costs. Such a
discrepancy is not surprising and indicates the necessity
for making analysis self-consistent. Thus, the results in
Table 28 and 29 were made by one analyst and are set of cost
factors and the cases (1) through (3) above by another
analyst with a different set of cost factors. The
149
-------
High-ond low-level control
ff
Acid-alkali
holding and
mixing
Sump
High-and low-level control
Pressure pumpf I ,. -
Stream
FIGURE 18,.TYPICAL PLANT OPERATION
COPRECIPITATION ONLY
CHEMICAL TREATMENT (A);
150
-------
Acid-alkali
holding and
mixing
Cyanide
holding and
mixing
Cyanide
oxidation
Optional
Filter
Stream
FIGURE 19 .TYPICAL PLANT OPERATION - CHEMICAL TREATMEI^ (*}•
CYANIDE OXIDATION AND coPRECIPITATION "
151
-------
HondL
Acid-alkali
holding and
mixing
Plating
Non-CN/Non-Cr
M
J>H
Neutralization
and
precipitation
Hand L
Chromium
holding and
mixing
->QSufnp
D3
HandL
•W
*-o^
HgSO^T
Chromium
reduction
fro1"*' rv
¥^~J \ ^Circ.
$
Flocculant
To stream
FIGURE 20, TYPICAL PLANT OPERATION - CHEMICAL TREATMENT (C);
CHROMIUM REDUCTION AND CO PRECIPITATION
152
-------
Cr- cont'q
rinses
r
CN- cont'q
rinses
H and L
H and L |T
Acid-alkali
holding and
mixing
3
} Sump
i
1
CN-holdmg
and .
mixing
-c
j Sump
Ha
rr
Cr-holding
and
mixing
I Sump
Neutralization
and
precipitation
jin, „„ ^B «M M. A. «•• •— *^
Filter Pump
HandL1
Tl '
I I I
i
Lagoon
H and L
Cr-reduction
Pump
0
M HzS04 Circ.
OH
S02
Pump
Sump
Settling
Pump
Flocculont
Overflow
H and L
Pump
Filter
Filter
o
Backwosh
To stream
FIGURE 21 .TYPICAL PLANT OPERATION - CHEMICAL TREATMENT (D);
CYANIDE OXIDATION, CHROMIUM REDUCTION, AND
COPRECIPITATION
153
-------
difference is actually much smaller than that of actual
costs reported in Table 27.
The use o!: a system to eliminate pollutant discharge
requires approximately twice the investment and operating
cost as a system for combined chemical treatment. The costs
can be reduced in :~ome situations by in-process recovery
systems where the savings in chemicals more than compensate
for the costs of operating the recovery system. Evaporative
recovery systems were not economical to use in the plants
assumed since the value,, bath concentration, and dragout of
chemicals were not sufficient, to make their in-process
recovery worthwhile., ihe costs of installing more counter-
current rinse tanks, evaporative equipment, and steam more
than offset the savings in
In- process reverse osmosis systems may have lower operating
costs than evaporative systems, bat are still in a
demonstration stage for baths other than nickel. Use of
reverse osmosis systems on the nickel lines in the plant
model would not be expected to reduce overall in operating
costs by more than 5 percent „
Figure 22 shows the operations in the plant and a schematic
iiagram of a segregated waste treatment system. Figure 23
shows a coprecinjtation system and Figure 24 the
modifications made at the end of trie coprecipitation system
with a reverse osmosis unit and. salt evaporator to eliminate
the discharge of pollutants.
Preliminary calculations indicated that use of evaporators
in- process and a'-, the end -of -pipe t.c eliminate pollution
would be more expensive than use of reverse osmosis at end-
of-pipe for the particular metal finishing lines considered.
With the installation, of a reverse osmosis system the
neutralizing agent was sodium hydroxide rather than the lime
used with the coprecipitation and segregated precipitation
systems. Lime was used to precipitate phosphate as well as
heavy metalsf but precipitatS.on products with lime are
likely to foul the reverse osmosis membranes. These
membranes remove phosphate directly and lime is not needed.
The cost of a minimum batch treatment system was also
estimated. The layout is shown in the schematic diagram of
Figure 25. The system was sized to handle tl50Q 1/hr of
waste water, which is less than produced by the 5-man plant
discussed above. For calculating operating costs an 8-hour
day and 5- day week were assumed.,
Small Platers
154
-------
U1
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C":r.m»i£
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>4-. n>f - AI :» tph
An.^. - AI i.v. crd
Xl Acrt. - AI UlScf*
.» -* WOcph
tiae 3
A^tJ. ^urvl
• i ' .-rhji.
li.-e -•
rk.ll. k-
Sl. .(1
Z o F*o*phaie 130 ept)
A A lu. cph
Elt.-t. N! M ppli
A 'A 1igpl>
C*mMK*ClCN
!»* . 65 - US flfc
CM
c«rrr.
OxrWa
Onhtoedm
rrotao-uogd- *~
r
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darifier
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. M* SMp w Lapaa snap
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1M t lie « 4» • 260 gpk "
f
Ckraa
Iteductla
C*. Z». *
Ci Mett
4ITT
CUrtflcr
AcM/Aft Streams 1080 gpk
me . MS » ioso »I»M '
« 400 » ago » MO * 100 • sn
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^rttclafeate
r
i
• f
/d^\
- — «J rmt< 1 •"•
Efn«« nlaan • Iran
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MO » 210 » MS = US mil
z> rk«r. uo uph 1
Elect. Nl M Rpd
Mmft
ITT
Rate pll 10
U.Ola
< fMnpIci
' •
CtortAa
-/T"^
FIGURE 22 PHASE I, IA, AND II MASTER FLOW PATTERN
-------
MrfM
C*nM!K4 Cnmiit Sotimi
C» • Zi » Cd
CSS • TIO » 115 » UW tpb
'> » Chroraacc Stfcaa
. . 14,1 . 7« . 710 - 113 ' 4^ * -~> gpk
TotjJ ;»-,l ,3*
I Ai.v!i^u>c 1 in
:f.' - C3. • 345 - SSi cpfc
tUct. Xi 15^ _jfh
XI rur.n.-i Atul .«r« Sm>m«
»*>.-:.»» ipk
FIGURE 23 COMBINED CHEMICAL TREATMENT AND NEUTRALIZATION-PRECIPITATION
-------
HaC«
Cn
C. . Z. . O)
n: ««i . MC « 75 < 710 fph
110 . 110 . Jtt = "60 jpd
Tcul 970 gjh
iiif; tad Zn Phosplutlng Smuu
• 530 . MS - Si g|*
£• nvnprjtinc 130 cpb
W nana; * Caoiblac* Ackl/AH Sliunu
Ccrabuc4 Acrt Alk 7MO gfk
Total 7410 |f*
to Hnd Axaj Dlipnal
FIGURE 24 COMBINED CHEMICAL TREATMENT AND PRECIPITATION FOLLOWED BY END-OF-LINE
REVERSE OSMOSIS TREATMENT FOR ZERO LIQUID EFFLUENT DISCHARGE
-------
L-_^~Ss_| ?unp
' ??h 1
Cvanice , „
TinrgpH—[ Pu:np
00
Neutralization
Sludge
FIGURE 25- BATCH TREATMENT SYSTEM FOR SMALL PLANT
-------
Costs have been estimated for the 1-4 man shop and 5-9 man
shop and may be found with accompanying assumptions in the
following tables:
Sizing Assumptions
. 1-4 employee shop (3 employees)
. 30 sq m plated per hour
. 80 1/sq m per hour
. 1/4 of the flow is cyanide bearing (and can be
segregated)
. The cyanide concentration is 20 ppm
The concentrations in the rest of the flow are equivalent
to 100 ppm of Fs++*
Engineering Assumptions
. Complete manual operation utilizing minimal equipment
. store 1 day of cyanide containing waste and treat overnight
. Equalize flow in a tanJc corresponding to 1/2 of the
daily output. Operate in backmix with adjustment every
two hours.
. All adjustment from carboys or drums.
Of Chemicals Verfication
Cyanide Total waste flow 2100 1/hr
Cyanide flow 600 1/hr
Total cyanide waste 4800 I/day
Total cyanide in waste 98 gm per day
Chlorine requirement approximately 700 gm per
day or 1.5 Ib
Using hypochlorite (1 Ib Cl£ 1 gal hypochlorite)
1.5 gallons per day.
Using caustic 1 lb/1 Ib of chlorine - say,
1. 5 Ibs/day
Neutralization (Assume that the caustic from cyanide treat-
~ ment is used in the first 1/2 day)
Total caustic required - about 2 gm per gm of iron (120/56)
(120/56) 1/2 day flow 9600 1 960 gm of iron
Caustic required - 2800 gm/or 4.5 Ib.
Additional - 4.5 - 1,5 * 3 Ibs.
Rest of day - 4.5 Ibs.
Total per day - 7.5 Ibs
159
-------
O.K. to add by hand (drum of caustic - approximately
400 Ibs)
O.K. to use a small bucket (8 gals, approximately or
80 Ibs)
Residence time - 4 hours (nominal or actual) for equalization
Equipment List
Equalization tank - 2500 gals.
Agitator - 5 HP
Chlorination tanks - 2 x 800 gals.
2 Agitators - 1 HP
1 Transfer pump
High level alarm - 3
Valves - 5
Other piping and supplies
Installation - 25%
$2500
1000
1500
800
150
400
300
—HP.
$6800
1700
$8500
Instrument
pH meter
colorimeter
400
1PJ2
Total $9100
Area required - 400-500 square feet (assumed available)
Assume that there is room for equipment, e.g. a 2500 gal.
tank of normal configuration is 6.5* in diameter and
101 in height (without legs).
Sizing Assumptions
5-9 employee shop (7 employees)
70 sq m plated per hour
80 1/sq m 5600 1/hr of flow
1/4 flow is cyanide bearing (and can be segregated)
Cyanide concentration » 20 ppm
The concentrations in rest of waste flow are equivalent
to 100 ppm FS++ +
Engineering Assumptions
. Cyanide flow - 1400 1/hr - say, 350 gals/hr.
. Assume that a hand operation once a day is used for
cyanide (Automatic continuous unit would cost about
$18,000-22,000).
. Equalize daily flow in a 1/2 day tank.
. Check for hand addition - or cheapest equivalent.
160
-------
Cyanide . Cyanide total - 11,200 I/day 2800
„ . , .„ gals. (3000)
. Total cyanide in wash - 224 am/day
. Chlorine required - 1500 gm/day say 3 5 ibs
. Hypochlorite - 1 gal/lb of chlorine 3.5
gallons (can be added out of a plastic lined
55 gallon drum with a hand pump)
. Caustic - 3>5 lbg>
Out of a 55 gallon drum ( 500 lb) with a
scoop, (a big scoop is about 5 lb)
pJL.AdJust 2 gm per gm of iron
1/2 day flow (total) 22,400 1. (say 6000 gals)
Ir°« 2,240 gm
Caustic 4,500 gm 10 Ibs.
2 to 3 scoops.
Manual addition from a drum appears feasible.
Material handling equipment - 1 chlorine resistant
hand pump - say $200
Eguipment List
1 Equalization tank - carbon steel 6000 gals. $ 4,100
%S« ^reat tankS ~ carbon steel, epoxy lined* 7,200
(3000 gal)
(35°0) <2 * 10°°>
High level alarms ™
valves (5) *JJ
Other piping and supplies 300
installation - 25%
instruments T°tal $22'900
Hand pump
PH meter
Colorimeter 200
$23,700
*Add 20^ for epoxy lining.
If a 2 hour equalization is required
use a 3000 gal tank «• 5 HP agitator (3000 + 1000) 4,000
instead of 4100 + 3500 (7600)
thus, 18300 - 3600 1a 700
3*700
161
-------
18,400
Save ft ,500
19. OO
The total capital investment and operating and maintenance
costs for both size plants are as follows:
No. of Capital Investment ($1000) Annual OSM Costs ($1000)
employees 80 1/sq m 160 1/sq m 80 1/sq m 160 1/sq m
tnln max min max min max min max
1-4 9.1 13.7 13.7 20.5 3.9 6.5 3.9 6.5
5-9 23.7 35.6 35.6 53.3 4.3 7.1 4.3 7.1
New Source Performance Standards (NSPS1 . New sources that
are required to meet the recommended standards of
performance have the opportunity of designing and building
plants that reduce water flow. Such systems as counterflow,
spray, and fog rinses, interlocks to provide water flow only
during processing sequences, drip tanks, etc., can be
provided. The capital investment for installing an extra 31
x 3' tank in each rinsing sequence of a plating line to
reduce further the water use in counterflow rinsing is of
the order of $3,000. The plant modeled in Figure 22 has 27
rinses so adding one more tank for each rinse would increase
capital investment $81,000 for a total of $300,200 for
combined chemical treatment and precipitation in an urban
plant. It is probable that water use can be reduced 100
percent by installing only half this number of tanks at a
cost of $40,000 or an increase in capital investment of 18
percent over a plant meeting BPCTCA standards. Operating
costs would increase $7200/yr minus a credit of $520 for
water and sewer charges or $6680/yr« The increase in
operating cost is 6 percent as compared to those for a plant
meeting BPCTCA standards.
No Discharge of Pollutants
The elimination of liquid discharge from metal finishing
processes has not been demonstrated with present technology.
Anticipating that future development will make this
elimination possible, it is desirable to have a rough
estimate of the cost impact of doing this. Technically,
evaporative recovery, reverse osmosis, and ion exchange can
concentrate wastes after which the concentrate can be
evaporated essentially to dryness. Purified water can be
returned to process. Approximate cost analysis have been
made for a medium large plant 240 sq m (2600 sq ft) per hour
assuming use of 80 liters/sq m of water. The effects of
closing the liquid loop without a purge on the buildup of
impurities are not known and the cost of solving problems
162
-------
connected with impurity buildup will depend greatly upon how
much impurity must be removed, the development of efficient
systems for their removal, and how many of the components
that are recovered can be recycled rather than discarded.
To determine the cost effectiveness of various control and
treatment alternatives much of the data developed for Plant
33-1 in Phase I was used. For those examples involving
evaporative recovery, an additional investment of $150,000
was allowed for a unit to evaporate concentrate to dryness.
Results of the calculations are shown in Table 31. A
finishing cost of $2.70/sq m ($0.25/sq ft} is equivalent to
$644/hr, and all of the projected costs for waste treatment
are less than 10 percent of this figure. Of course, the
$2.70/sq m figure is too high for soine processes, but
provides a basis for at least a rough estimate of the cost
impact of waste treatment.
Nonwater Quality Aspects
Energy Requirements
Introduction. Energy requirements will be discussed for
chemical treatment, evaporative recovery, ion-exchange, and
reverse osmosis.
Chemical Treatment. Energy requirements for chemical
treatment are low,~"the main item being electrical energy for
pumps, mixers, and control instruments. Electrical costs
have been tabulated for several plants in Table 32. Data
for Plants 33-1 through 33-6 were obtained from the Phase I
study. Results indicate that approximately 5 percent of the
waste treatment cost is for electric power.
It is estimated in the Phase I study that electrical energy
for treating 2.271 x 10* liters per hour by a reverse
osmosis unit for a000 hours per year would cost $6,400. The
electrical energy cost is therefore 7.0*5 x 10-«. The
liters per year processed by all plants listed in Table 32
add up to 3.964 x 10« liters and the cost of electricity for
processing this water by reverse osmosis is $279,200. The
total electrical cost for chemical treatment for the plants
listed in Table 32 is $75,330. These figures can be used to
roughly estimate the increases in electrical power
requirements in going to a system with no liquid effluent.
For best practical control technology currently available
the electrical cost would be essentially that of current
estimates or $75,330. For the best available technology
economically achievable the combination of chemical
treatment and reverse osmosis plus evaporation of the
163
-------
TABLE 31 COST EFFECTIVENESS OF
CONTROL ALTERNATIVES
(247 Sq M/Hr)
Type of Control
Plant 33-1
Rinse System -
Chemical treatment
Three countercurrent
Investment
Cost
$264,274
330,000
Operating
Cost/Year
$112,361
121,387
Water
Treated
1/Hr
25,210
9,766
Operating
Cost per
100 Sq M
$17,30
18.68
rinses - chemical
treatment
Single stage evapor- 890,000
ators (21 units)
Dry evaporator
Five single stage 400,000
evaporative units
and one vapor com-
pression unit - dry
evaporator
Chemical treatment 560,000
plus reverse osmosis
Sludge drier and dry
evaporator for
concentrate
327,895
109,913
161,328
50.47
16.92
24.83
16-4
-------
TABLE
32
COST OF POWER RELATIVE TO TOTAL OPERATING
COST FOR CHEMICAL TREATMENT
Plant
No.
33-1
11-8
36-1
20-14
20-17
3-4
33-3
33-6
33-22
20-20
20-22
33-24
36-12
33-2
33-4
8-5
6-35
30-19
Processes
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr , Zn
Plating Cu, Ni, Cr, Zn
Plating Cu, Ni, Cr, Zn
Anodizing
Anodizing
Anodizing
Plating Common Metals
Plating Precious Metals
Plating Precious Metals
Plating Precious Metals
Plating Precious Metals
Chemical Milling
Chemical Milling
Electric
Cost/Year
$ 4,100
668
5,220
6,000
8,940
600
240
1,460
1,948
4,763
12,623
1,212
1,894
1,082
120
16,239
3,897
4,330
x = 4,185
o = 4,454
Waste
Treatment
Operating
Cost/Year
$112,361
391,406
221,009
93,240
798,840
4,064
18,019
77,460
51,515
83,481
113,370
80,430
72,809
14,968
18,205
115,995
83,758
168,312
x = 139,957
a = 187,688
Electric
Cost x
100 /Waste
Treatment
Cost
$ 3.65
0.17
2.36
6.44
1.12
14.76
1.33
1.88
3.78
5.71
11.13
1.51
2.60
7.23
0.66
14.00
4.65
2.57
x = 4.75
a = 4.44
165
-------
concentrate (that would require little electrical energy)
the electrical cost would be $75,330 plus $279,200 or
$354,530. The ratio of $354,530/75,330 is 4.70. On this
basis going to a system without discharge of liquid effluent
will increase the use and cost of electrical energy 5-fold.
fiYfl PgEfrU YSJS.SSO.YAEY.' From the Phase I report the cost of
steam for operating a 300 gph single-stage evaporator is
approximately $2100/yr corresponding to approximately
1,900,000 Ib of steam. The single-effect evaporators
require considerable energy. This requirement can be
diminished by use of multiple stage or vapor-compression
evaporators.
Ion Exchange. The few pumps required for ion-exchange
systems should consume very little power.
Reverse osmosis. The energy requirement for reverse osmosis
systems is the electricity for operating the high pressure
across the membrane and for operating low pressure transfer
pumps. The estimate is $6400/yr for a 6000 gph facility
operating 4000 hours/yr.
Impact of Power Requirements for Waste
Treatment. Domestic production of electrical energy in 1971
was 1.717 x 10»« kwh. For the plating industry the
electrical energy requirement is estimated to be 9.75 x 10»
kwh. The metal finishing industry as a whole is estimated
to consume no more than twice this value, which would be
1.950 x 10« kwh. The percentage of annual power that is
used for metal finishing operations should be no more than:
1.950 x 10it/1.717 x 10»2 = 0.114 percent.
Power for pumps, lights, fans, etc. , and waste treatment
should not more than double this figure to 0.228 percent.
Cost of Recovery of Metal Values from Sludge
Tribler et. al. is a report on the feasibility of recovering
metal values from sludge b digesting the sludge with acid to
dissolve it followed by electrolysis and neutralization
procedures to recover metal values. The case considered was
a sludge containing primarily copper, nickel, chromium, and
zinc values. A cost estimate was included for a small plant
that would treat 45 kg of dry sludge during a 12 hour day to
yield 2.27 kg of copper, 0.09 kg of nickel* and 4.54 kg of
chromium. However, the chromium was obtained as an oxide
mixed with some iron. The investment for a small plant was
166
-------
estimated to be $15,130. Operating cost per day was
estimated to be $85.30. This did not include a cost of
capital, which if assumed to be eight percent of the
investment per year, would raise the daily operating cost to
$91.35. The total weight of metal recovered per day is 6.90
kg so that the cost is estimated to be $13.23 kg. The cost
is obviously very high compared to market prices so that the
small operation would be far from economic. Undoubtedly,
the cost of processing would be less with a larger
installation, but if more than one metal finishing
installation were served there would be an additional cost
for transporting sludge to the recovery operation.
167
-------
SECTION IX
BffST PRACTICABLE CONTROL TECHNOLOGY Cl
AVAILABLE. GyIpELlNES* ANQ LIMITA!
Introduction
The effluent limitations which must be achieved by July 1,
1977, are to specify the degree of effluent reduction
attainable through the application of the best practicable
control technology currently available. Best practicable
control technology currently available is generally based
upon the average of the best existing performance by plants
of various sizes, ages, and unit processes within the
industrial category and/ or subcategory.
Consideration must also be given to:
(a) the total cost of application of technology
in relation to the effluent reduction benefits
to be achieved from such application
(b) the size and age of equipment and facilities
involved
(c) the processes employed
(d) the engineering aspects of the application of
various types of control techniques
(e) process changes
(f) nonwater quality environmental impact
(including energy requirements).
The best practicable control technology currently available
emphasizes treatment facilities at the end of a
manufacturing process but includes the control technologies
within the process itself when the latter are considered to
be normal practice within an industry.
A further consideration is the degree of economic and
engineering reliability which must be established for the
technology to be "currently available". As a result of
demonstration projects, pilot plants and general use, there
must exist a high degree of confidence in the engineering
and economic practicability of the technology at the time of
commencement of construction or installation of the control
facilities.
169
-------
industry Category and Subcategory Covered
The effluent limitations recommended herein cover the
following metal finishing processes: anodizing, chemical
milling and etching, immersion plating, chemical conversion
coating. These processes have been divided into three
categories: Subcategory (1) consists of anodizing,
Subcategory (2) consists of coatings, and Subcategory (3)
consists of chemical etching and milling,
I<3ejltification of Best .Practicable, contffsj,
Technology Currently Ava4J.abj1g
Best practicable control technology currently available for
Subcategories (1) , (2) and (3) is the use of chemical
methods of treatment of waste water at the end of the
process combined with the best practical in-process control
technology to conserve rinse water and reduce the amount of
treated waste water discharged.
Chemical treatment methods are exemplified by destruction of
cyanide by oxidation, reduction of hexavalent chromium to
the trivalent form, neutralization and coprecipitation of
heavy metals as hydroxides or hydrated oxides with settling
and clarification to remove suspended solids prior to dis-
charge or prior to dilution with other nonelectroplating
process water before discharge. The above technology has
been widely practiced by many plants for over 25 years.
However the above technology cannot achieve zero discharge
of heavy metals because of finite solubility of the metals.
In addition, it is not practicable to achieve 100 percent
clarification and some small amount of metal is contained in
the suspended solids. By optimum choice of pH and efficient
clarification it is possible to achieve a significant re-
duction in the heavy metal pcllutional load.
Zero discharge of heavy metals in effluent may be achieved
only by eliminating the effluent itself by such techniques
as reverse osmosis and evaporation, which offer the
possibility of p\irifying all waste water to a sufficient
degree to be recycled to process or by evaporating to
dryness so that waste water constituents are disposed of as
solid waste.
No generalization regarding the degree of metal pollution
reduction is possible because of the mij£ of finishing
processes possible in a single plant and the variety of
metals in the raw waste of most plants. Because of this
fact and the high cost of inplant segregation of all waste
170
-------
streams according to metal» coprecipitation of metals is the
general practice. Thera is an optician pH for precipitating
each metal that results in the greatest removal by
clarification. The optimum pH for removing all metals
cannot be utilized for coprecipitaticn so the pH selected
for a mixture of metals is a compromise. However,
coprecipitation can result in lower discharge of metals than
if each is precipitated separately at its optimum pH value
if synergistic effects of the type shown in Table 26 are
operating. For copreeipitatlost to provide lower discharge
than segregated precipitation in-process dilution must be
minimal.
There are several advanced recovery methods available for
closing up the rinse water cycle on individual metal
finishing operations. These methods ^evaporation, ion
exchange, reverse osmosis, conntarcurrent rinsing) have not
yet been applied to rinse watars from pretreatment and
posttreatment operations. The corresponding rinse waters
plus concentrated solution draps and floor spills may
contain one or all of the pertinent metals (copper, nickel,
chromium, and zinc) in significant amounts requiring
chemical treatment. Thus? chemical treatment of at least
the typical acid/ alkali stream from pretreatment and
posttreatment operations represents the best practicable
control technology currently Available to achieve the
effluent limitations recomroeadaat
Having identified the technology for end-of-process
treatment and recognizing the technical and practical
limitations on removal of heavy metals by this technology
(metal solubility and clarification efficiency), further
reduction in the quantity of matal pollutants discharged
must be achieved by reduction in the volume of treated water
discharged. There are many in-process controls designed to
reduce the volume of waste water which is principally that
resulting from rinsing. Some of these controls, designed to
minimize dragout of concentrated solutions or to reclaim as
much dragout as practical can be considered normal practice
within the industry. It can be assumed according to good
practice that reclaim tanks and/or still rinses are being
used and that all evaporation losses are made up with the
reclaimed solution. Dragout reclaimed does not contribute
to the raw waste load normally discharged from remaining
rinses. There is economic incentive to reduce the chemicals
purchased for bath makeup and the added economic incentive
to reduce the cost of treatment chemicals required for end-
of- process treatment. Reduction of dragout leads to
reduction in water requirements for rinsing.
171
-------
Further reduction in rinse water use can be achieved by use
of a stagnant rinse for recovery or by multiple-tank
countercurrent rinsing. Counteracting the cost of
installing multiple rinse tanks are the savings in treatment
chemicals, water costs, and sewer charges. Further, the use
of advanced recovery techniques (evaporation, ion exchange,
and reverse osmosis) which concentrate the rinse water
sufficiently to allow reclaim of the valuable metal
finishing solution can often provide the economic incentive
to use this technology and justify the cost of recovery
equipment plus the cost of installing multitank
countercurrent rinsing. However, it should be recognized
that the major water reduction occurs because of the
installation and use of multitank countercurrent rinsing.
In the past there has been little economic incentive to
reduce water use for rinsing after preparatory and
posttreatment operations. The cost of the chemicals has not
made their recovery from rinse waters worthwhile. High
dragout from preparatory cleaning solutions has not been
considered an unfavorable factor since the dragout of
impurities along with bath chemicals has prolonged the life
of the bath in some cases. The disadvantage of high dragout
is that more water must be used for rinsing to prevent
significant concentrations of impurities, i.e., grease, from
contaminating the processing solutions.
Best practicable control technology currently available also
includes water conservation through rinsing. A water use of
160 1/sq m/operatlon (4 gal/sq m/operation) has been
estimated as that achievable by the industry. This figure
precludes the use of countercurrent or series rinses.
Exclusive use of single stage rinsing will not meet this
water use. It has been calculated that for 186 sg m/hr
(2000 sq ft/hr) proudction the rinse water need for various
rinsing techniques are:
1 - single rinse 1/hr 499,620 (132,000 gal/lir)
2 - tank countercurrent 2800 1/hr (1HO gal/hr)
3 - tank countercurrent 477 1/hr (126 gal/hr)
4 - tank countercurrent 201 1/hr (53 gal/hr)
5 - tank countercurrent 121 1/hr (32 gal/hr)
This corresponds to a water use of:
1 - single rinse 2686 1/sq m (66 gal/sq ft)
2 - tank countercurrent 15 1/sq m (.37 gal/sq ft)
3 - tank countercurrent 2.56 1/sq m (.06 gal/sq ft)
4 - tank countercurrent 1.2 1/sq m (.026 ga/sq ft)
5 - tank countercurrent .65 1/sq m (.016 gal/sq ft)
172
-------
A 3 - stage series rinse consumes approximately the same
quantity of water as a 2 - stage countercurrent*
The 160 l^q m (U gal/sq ft) takes into account the
contributions made by the pretreatmcnt steps of alkaline
cleaning and acid pickling and allows some use of single
rinses.
An alternative mode of operation to the above is to dump
cleaning baths frequently so that dr&gout of impurities is
minimized. Then the amount of rinae water can be reduced
and can be even further reduced by use of multiple
countercurrent rinsing technique®,, The increased cost of
chemicals from more frequent dumping and the cost of
multiple rinse tanks is counteracted by savings in water and
sewer charges. Water use can therefore be greatly minimized
since preparatory solutions, i.e*? alkaline cleaners and
acid dips contain chemicals that can be tolerated in fairly
high concentrations in subsequent processing solutions,
i.e., plating baths. In general, the amount of rinse water
required should be substantially less for rinsing following
alkaline cleaning and pickling than for ringing following
typical metal finishing operations aueh as electroplating.
While sufficient economic incentive may not be present to
achieve reduction in the volume of the rinse water from pre-
and posttreatment operations, there is an opportunity for
significant reduction in pollution. The above factors are
taken into account in recommending the effluent limitations.
Even in plants currently achieving good waste treatment
results, there are further opportunities for reduction in
volume of effluent discharge.
Rationale fqr Selecting ^he Best practicable
Control— Technology Currently Available
General Approach
In determining what constitutes the best practicable control
technology currently available, it was necessary to
establish the waste management techniques that can be
considered normal practice within the metal finishing
industry. Then, waste-management techniques based on
advanced technology currently available for in-process
control and end-of -process treatment were evaluated to
determine what further reduction in pollution might be
achieved considering all the important factors that would
173
-------
influence the determination of best practicable control
technology currently available.
Management Techniques Considered!
Practice jn the Metal Iloighina Industry
For that portion of the metal finishing industry that
discharges to navigable waters, many are currently using
chemical treatment for end-of-process pollution reduction.
Some of these waste- treatment facilities have been in
operation for over 25 years with a continual upgrading of
performance to achieve greater pollution abatement. Because
of the potentially toxic nature of the chemicals used in the
metal finishing industry, there is a relatively high degree
of sophistication in its water pollution abatement
practices. For example, the accidental release of
concentrated solutions without treatment to navigable waters
is believed to be a rare occurrence today. This is because
adequate safety features are incorporated in the design of
end-of-process waste treatment facilities in conjunction
with good housekeeping within the electroplating facility.
This example and other waste management techniques were con-
sidered as examples of normal practice within the metal
finishing industry in determining the best practicable
control technology currently available. Other examples of
normal practice include:
(1) Manufacturing process controls to minimize
dragout from concentrated solutions such as
(a) proper racking of parts for easy
drainage
(b) slow withdrawal of parts from the
solution
(c) adequate drip time or dwell time
over the tank
(d) use of drip collection devices.
(2) Effective use of water to reduce the
volume of effluents such as
(a) use of rinse water for makeup of
evaporation losses from solutions
(b) use of cooling water for noncritical
rinses after cleaning
174
-------
(c) use of treated waste water for
preparing solutions for waste-
treatment chemicals.
(3) Recovery and/or reuse of waste water
constituents such as
(a) use of reclaim tanks after metal
finishing operations to recover
concentrated solutions for return
to the plating tank to make up
evaporation losses
(b) reduction in waste water volume by the
use of at least two series flow rinse
tanks after each finishing operation
with return of as much rinse water as
possible to the finishing tank.
Other waste-management techniques not considered normal
practice, but currently in use in one or more plants, were
evaluated on the basis of reduction in the quantity of
pollutants in the effluent discharged.
Degree of Pollution Reduction
*>v_ pianos
- _
Aaes. and Processes Using
Treatment Technology
Identification of Best Waste Treatment Facilities
The initial effort was directed toward identifying those
companies that had well engineered and operated metal
finishing process and waste treatment methods. Such
companies were identified on the basis of personal
knowledge, and referrals by people well acquainted with the
industry (EPA regional representatives, state pollution
control authorities, trade associations, equipment
suppliers, consultants) . Representatives of approximately
75 companies returned questionnaires mailed to them and
these representatives were further contacted by telephone or
further correspondence in many cases to clarify the
information in the questionnaires and obtain further data.
Furthermore, visits were made to 11 plants for development
of detailed data on several of the processes. Effluent
samples were collected at five plants and analyzed at
Battelle-Columbus Laboratories. The above constitutes the
data based for the Phase II study.
175
-------
Waste Treatment Results
Volume Capacity of Treatment Plant^sfnigigri- Figure 26 shows
the volume capacity of the waste treatment plants for which
data were received, as measured by the amount, of waste water
treated per hour. The rang© of capacities
approximately two orders o£ magnitude.
covers
The plot ie a cumtnulative on® indicating how snany plants
have a water use leas than r.he voitsrwa corresponding to the
cummulative number. Thu«?, r.S plants have a volume of
100,000 liters/hour or less and 4 plants have a greater
volume.
ConsentratJiop ,.o. £.
-------
100,000 —
.c
^
tO
o>
a
to
o
a»
a
10,000 •-
1000
10 ?-0 30
Cumulative Number of Plants
FIGURE 26. DISTRIBUTION OF WASTEVVIER VOLUME TREATED
177
-------
TABLE 3 3 CGSOSatBATIOa OF BH&DBR COBStlTOSHTS
-J
CO
Plant
So. Processes Ag Al
20-24 1'iating Conon Metals
33-24 Plating Casaaoa Metals
33-26 Plating Coanon Hetals
31-1 Plating CosHBoa Metals
3&-12 Platiag Com, .Free. Metala <0,01
33-2 Plating Precious Metals traces
33-4 Plating Precious Metals
8-5 Plating Precious Hetals
6-37 Plating Precious Metals <5
19- LI Platiag Precious Metals (0)
15-3 Plating Precious Metals
9-7 Electropainting, Amodizing 6.5
9-6 Electropainting
33-34 Electropainting
4-5 Electroless Plating
8-8 Electroless Plating
30-19 Electroless Plating
33-22 Anodizing <0.05
33-23 Anodizing 0.91
20-22 Anodizing 1.0
20-20 Anodizing 3.7
33-35 Anodizing l.OS
20-23 Anodizing 8. IS
47-9 Anodizing
6-35 Chemical Milling <1
9-2 Chemical Milling 0.25
23-7 Chemical Milling 0.5E
33-30 Phosphating
19-24 Etching - 0.5
31-16 Printed Circuits
6-36 Immersion Plating
46-4 Electropolishing
E - estimated
S - soluble
Concentration | mg/1
Total ,
Au Cd CH~ CR Cr Cu F~ Fe RL
0.02 0.54 0,17 11 i.S
<0.025 <1 <0.05 <1 <1
0.05 0.3 7
j __ ]_§
<0, 1
traces 0.1
(0)
<1 <5 <5
(0) (0) <0.5S <1§
0.02 0.04 0.08 0.06 0.03 0.03
'!•
7.7
<0.02
<0.03 0.2 <0.05 20 1.0
0,40 0.37 0.24
0.13 0.05
<0.18
oa (o) i.o
-------
TABLE 33 COHCEMTRATION OF EFFLUENT COMSTITOEKTS (Continued}
v»
Plant
Mo,
20-24
33-24
33-26
31-1
36-12
33-2
33-4
8-5
6-37
19-11
15-3
9-7
9-6
33-34
4-5
§-<
30-19
33-22
33-23
20-22
20-20
33-35
2tt~23
4J-f
*-.15
9-2
23-7
33-30
19-24
31-16
6-36
46-4
Concentration, «g/l
Processes Pb
Plating Common Metals 0.6
Plating Common Metals
Plating Coraaon Metals 0.3
Plating Common Metals
Plating Com. ,Prec. Metals
Plating Precious Metals
Plating Precious Metals
Plating Precious Metals
Plating Precious Metals
Plating Precious Metals
Plating Precious Metals
Electropainting
Electropaiating
Elect repainting
Electroless Plating
Electroless Plating
Electroless Plating 0.5
Anodizing
Anodizing
Anodizing
Anodizing
Anodizing
Anodizing
Anodizing
Chemical Milling
Chemical Milling
Chemical Mining
Phosphating
Etching
Printed Circuits <0.2
IsMzcioa Platiaf
ElMtropel 1 ••*•«,
Pt
H>4~3 Metal
<,0
traces
(0)
<0.4
8.1
50
13
180
0.3
0.8
0.17
trace
2
0.15
70-85
Susp.
Sn Zn Solids
<2 0.25 4
<1.0 <25
Mil 78
0.2S
0.5S <10
6
6.9
<20
0.5
10
40
130
<0.02 22.7
100
<10
. 25-60
10
5
16
29
<0.1 <5
(0)
0.1 5
2.2 11
0.1
1-34
Dis.
Solids
676
1400
1250
1642
200
640
2760
250
400
204
500
>10
3600
1500
993
708
300
1690
927
506
220
1200
PH
8.5-9.5
7-9
8.0
7.0-8.0
8.0
5-10
7.5-8.5
7.5-8.0
7-10.5
7-8
7.0
6.2
8.4
7
7
6.5-10
6.5-9.0
6.5-9.0
7.5
6.8-9.2
6.5-9.5
8
8.0
8.6
8.0
S.7
2.6-5.*
Other
BF~ - 75
/COD - 34
ICobalt -
COD = 320
(Barium -
ICOD = 624
Ammonia -
Anemia -
Hitrate -
Hltrate -
mg/1
mg/1
<0.03 •»/:
mg/.i
1.0 mg/1
mg/1
6.8 Bf/1
10 mg/1
50 Bg/1
18 mg/1
-------
TABLE 34 WATER USE IN METAL-FINISH ING PROCESSES
Plant
36-12
30-2
33-30
20-3
33-24
33-5
15-3
9-7
33-34
6-36
31-16
30-19
33-27
33-23
33-22
9-2
20-20
33-35
20-22
20-23
41-2
6-35
47-9
4-8
Line
Sn
Cu-Sn
Rack Cd-Zn
Rack Cd
Barrel Cd
Rack alkaline Sn
Rack acid Sn
Rack Ni, CuPbSn, Sn
Rack zincate dip, Cu,
CuPbSn, Sn
Rack Cu-Sn
Basket Sn
Rack Ni, CuPbSn, PbSn
Rack Cd, manual
Barrel Cd, manual
Barrel Sn, manual
Ditto
Electropaint
Immersion
Electroless Cu
Ditto
"
Electroless Sn
Electroless Ni
Ditto
"
Anodizing Al
Ditto
"
Anodizing Mg
Anodizing Al
Ditto
"
"
"
"
"
Chemical Milling
Ditto
-
Production,
sq m/hr
42.8
122.8
171.5
123.4
45.8
46.5
46.5
9.3
9.3
92.90
21.1
25.1
1.86
11.15
18.58
1.39
139.4
529.5
48.8
23.23
25.08
23.23
13.94
1.39
10.03
11.71
297.4
148.7
83.6
4.65
269.5
55.8
3.253
102.2
16.73
9.29
13.94
37. IT
9.29
9.29
Water Use,
1/hr
454
908
5,995
18,160
11,355
9,463
3.936
6,188
12,737
7,040
3,407
2,725
2,161
220
1,553
2,120
8,395
4,315
1,022
12,491
5,678
5,678
76
1,590
1,590
2,271
18.927
27 , 254
44.895
7,382
79,494
2,082
87 , 064
18 , 927
5,678
2,271
1,930
3,785
1,893
1,893
Number of
Operations
1
2
2
1
1
1
1
3
4
2
1
3
1
1
1
1
1
1
1
5
3
3
1
7
5
10
4
3
4
1
3
6
4
4
4
2
1
2
2
2
Liters/
Sq m/
Operation
10.61
7.39
17.49
147.2
247
203.7
84.7
222
343
37.9
161.5
36.2
1,162
19.7
83.6
1,525
60.22
8.15
20.94
107.5
75.5
81.48
5.45
163
31.7
19.4
15.9
61.09
134.3
1,558.9
98.3
6.2
6.7
46.3
84.9
122.2
138.5
50.9
101.9
101.9
180
-------
TABLE 3 4 (Continued)
Plant
30-9
6-36
33-20
23-7
6-37
30-21
31-16
8-5
15-3
33-4
33-2
36-12
30-19
31-16
Line
Chemical Milling
Ditto
„
-
•>
"
Auto rack silver
Ditto
Man rack silver
Ditto
Auto rack silver
Ditto
,i
.,
Man rack silver
ii
Cont strip silver
Auto rack silver
Stripping silver
Man rack gold
Ditto
Auto rack gold
Man rack silver
Man rack gold
Man rack silver
Ditto
Man barrel silver
Auto rack gold
Man rack gold-silver
Man rack silver-rhodium
Cont strip silver
Chemical etching
Ditto
„
„
n
..
Production,
sq m/hr
92.9
9.29
B9.fi
13.4
24.6
27.9
74.33
293
59.5
11.61
35.3
11.61
22.22
4.65
6.50
6.50
4.65
0.84
1.12
1.39
0.74
8.55
0.093
0.093
0.047
1.86
5.57
1.21
2.79
2.79
31.6
92.9
8.36
16.73
18.6
18.6
11.15
Water Use,
1/hr
6,814
2,725
3, 785
3,028
6,613
15, 141
13, 967
20,363
9,084
8,365
8,270
5,602
9,311
8,316
908
908
5,942
(0)
757
8,138
1,817
1,590
3,028
379
460
462
462
4,637
5,678
1,703
454
13,248
2,271
2,725
3,785
6,624
7,570
Liters/
Number of Sq m/
Operations Operation
2
2
2
3
2
2
4
4
3
4
4
4
4
4
3
2
4
1
1
4
3
2
2
1
2
2
2
3
3
3
2
2
2
2
2
2
2
36.7
146.7
31,8
'16.3
134.4
271.3
46.98
17.40
50.92
180.1
58.57
120.6
100.2
447.6
46.54
65.32
319.8
(0)
658
1,460
815
93
16,280
4,080
4,952
124
41.43
1,281
679
204
7.18
71.3
135.7
81.5
101.9
178.3
340.2
181
-------
TABLE 3 4 (Continued)
Plant
4-9
36-16
33-30
20-25
23-8
46-1
33-29
33-29
4-4
Production,
Line sq m/hr
Chemical etching
Ditto
"
"
Chemical Machining
Ditto
Zn phosphating steel
Ditto
Fe phosphating steel
Electropolishing
Electrochemical machining
(Neutral Salt Electrolyte)
Electrochemical machining
(Acid Electrolyte)
Electrochemical machining
(Neutral Salt Electrolyte)
18.6
13.94
13.94
4.65
6.51
3.12
66.91
464.7
153.4
10.59
0.53
0.37
0.19
Water Use, Number of
1/hr Operations
4,088
1,362
1,362
1,362
5,299
1,514
11,356
11,356
946
1,817
7.6
22,700
7.6
2
2
2
2
2
2
2
2
1
2
1
1
1
Liters/
Sq m/
Operation
110.0
48.9
48.9
146.7
407
203.5
84.9
12.2
6.17
185.8
14.3
61,400
•
40.0
182
-------
The flrsst method of expressing water use requires choosing
what operations in the overall process will be included in
calculating water use «nd what operations will not be
included. "This method was followed in the Phase I guide-
lines, where all operations involving electrodeposition and
posttreatment were included but cleaning and pickling were
omitted. The water use has been calculated in terms of
llters/sq in/operation where the square meters refer to the
finished worK and the operations exclude cleaning and
pickling,
This method of expressing water use allows one to consider
its variation in terms of those operations that are
different from process to process* on the other hand, those
operations that, are common to moat processes, i.e., cleaning
and pickling, and involve about, the aame water use
regardless of'the process in which they occur, can be
eliminated from consideration as a cause of variations in
water use. Calculations for Phase II processes have been
made using the above formula, omitting the initial cleaning
and pickling operations^ but counting all subsequent
operations in. a process.
A.S mentioned previously, lss>8 water is required for rinsing
following alkaline cleaning and pickling than for rinsing
following most other operations.
Data provided by the companies on area processed and water
use ia given in Table 3UM From this data, frequency
distributions for water use Cl/sq m operation) for processes
in subeategories (I) , {2} ©nd (3) were derived. These are
given in Figures 7, 3 and «*. ?he median water use for each
subcategory' %*as used as a basis for the guidelines. It was
felt that the plants identified by the contractor were well
designed and well-operated and therefore the median value
was a good approximation of the ''average of the best
"criteria specified for BPCTC& treatment.
Determination of Effluent Limitationa
Effluent limitations were established from three parameters:
(1) constituent concentration in the effluent* (2) water
use, enfi (3) area processed or plated. Sosie dependence
among these parameters is known* i»e., coagulation of
precipitates out. of dilute eolation is wore difficult than
out of more concentrated solutions and area processed in a
giver, line increases with couples shapes that give higher
dragout awd require more watar for rinsing* Th© plant data
obtain.ec show no evident correlation betw®«n the three
183
-------
factors probably because variations in water use and
concentration due to other factors mask out the relationship
between the three factors mentioned. Within the accuracy of
the information available the three factors will be
considered independent, that is, the concentration
achievable in the effluent by exemplary chemical treatment
is not related to the amount of water used for processing.
The best water use is not necessarily found in a plant
operating an exemplary waste treatment facility and vice
versa. However, once exemplary values for both water use
and concentrations have been established the product of the
two represents an overall figure of merit that takes into
account both parameters. Therefore, the guidelines can be
expressed in terms of the product of the two parameters:
(mg/1) x (1/sq m) « mg/sq m. More water may be used if
lower concentrations are achieved and vice versa.
Concentrations of Effluent Constituents and pH. Table 35
lists the concentrationbasisForeachconstituent, The
values given are for the total amount of constituent,
dissolved and suspended. Therefore, both proper
precipitation and efficient clarification and/or filtration
are required to meet the concentrations considered
achievable.
Water Use. The values of water use for each type of process
cover a wide range. Variations in dragout, the
concentration of dragout, and the degree of rinsing required
vary and are in part responsible for the range of values.
However, inefficiencies in reducing dragout to a minimum,
rinsing beyond requirements, and poor design of rinsing
facilities and waste of water are also responsible for
making in making a wide range of water use . It is
necessary, then, to estimate the minimum water use that can
be achieved by essentially all of the lines of a given type
of process.
Subcategory (1)
The process covered in this subcategory is anodizing.
Data on water use for anodizing operations from ten plants
on eleven different lines are given in Table 34.
Supplemental information and configuration data was obtained
from two of these plants by plant visits.
184
-------
TABLE 35. CONCENTRATION VALUUS FOR WASTBWATBR
CONST ITUL7NTS FOR BPCTCA
Present Phase II
Constituent Proposal, mg/1
TSS 20
Cyanide (oxidizable) .05
Cyanide (total) 0.5
Fluoride 20.0
Cd 0.3
Cr+0 0.05
Cr (total) 0.5
Cu 0.5
Fc 1.0
Pb 0.5
Ni 0.5
Sn 1.0
Zn 0.5
Phosphorus I.Q
PH 6-9
185
-------
Plant 33-23 is an aluminum anodissing plant which has a large
automatic rack line for anodizing aluminum alloy parts.
Figure 27 is a schematic of this facility. The waste
treatment plant for treating the spent processing solutions
and the rinse water effluents from this operation is shown
in Figure 28. Data taken during the plant visit for
treated effluent pollutant concentration are shown in Table
36.
Plant 6-35 is a large chemical anodizing and milling
facility. Although the anodizing line was not operating
during the time of the plant visit. Information on the
sequence of operating steps and analyses of the waste
treatment plant effluent was obtained and is given in Figure
29. Addi tonal data on rinse water flows and production
rates were provided by the plant at a later date. The 65th
percentile water use was found to be 90 i/sq m-operation
(2.2 gal/sq f t-operation) .
Subcater 2
Subcategory (2) covers coatings - phosphating, chromating
and immersion plating.
One immersion plating plant was visited in this study.
Plant 6-36 has an immersion tin plating facility consisting
of one barrel plating line. Treatment of the wastes from
this plant is done in an integrated waste treatment plant
which was installed in 1972. The sludge from the treatment
reservoirs is collected in storage tanks and hauled away by
truck to a landfill several times a year.
Three chemical conversion coating plants were covered in
this study. Two were zinc phosphating on steel and the
other was iron phosphating on steel. The data on water use
for these operations is listed in Table 34. The 65th
percentile was found to be 17 1/sq m-operation (.42 gal/sq
ft-operation) . since there was no apparent reason for this
much smaller water compared to other subcategories, the
largest value reported of 80 1/sq m-operation (2 gal/sq ft-
operation) was chosen as the water use factor.
Subcateaorv (3)
Subcategory 3 covers chemical milling and etching.
Data on nine chemical milling lines in six plants are given
in Tables 33 and 34. Supplemental data on two of these
plants was obtained on visits to these plants.
186
-------
Water •*>-
Batch Treat
Then Sent .
To Tank 1
City and
Used Cooling Water •
Workplaces go
into one of the
threo anodizing
tanks; after
anodizing work
goes to Station II,
and then Stations
15 and 16.
22.
PI Water
Rinse
21.
Dl Water
Rinse
-*r
0.
Diehromata
Sea!
1/10 to 1/2 g/l K2Cr207)
19.
Dl Water
Rinse
«q
KBM
8> Nickel
Acetate Soal
(1/2 g/l Nickel Acetate)
17.
Dl Water
Rinse
-------
Anodizing
Waste Effluents
.Waste
Effluent
Collecting and
Mixing Sump
PH-Controlled
Automatic
Lime Addition
Neutralization
Vessel
Clarified Effluent to Stream
oo
CO
Sludge to
Storage and
Then Hauled
Away to Landfffl
FIGURE 28, SCHEMATIC REPRESENTATION OF WASTE TREATMENT SYSTEM
FOR HANDLING ANODIZING EFFLUENTS AT PLANT 33-23
-------
PUMP
rn
VO
CHROMATE
WASTES
li
71
II
HOLDING
TANK 5
EQUALIZAT!
TANK 1
^-
1
1
j
ON
1
1
1
1
..
/
1
1
I
"\- _ L
r. _=r-riJ- I
...J7] i£..
"
i
V^i
REACTION
TANK 2A
FirjiiR
)H
c
- i
1
',
i
i
I
]
O
......
I *
""•*
~" "™ £1
1 |
_ OPB,-Jrli P
1 V V 2
; L' ^
r7
\^
REACTION
TANK 2B
CPU! PM ATtr QCDDI~C
H
C
— =
-l\l-
-^
1
"^
r f\
LEGEND
[¥] SULFONATOR
O PUMP
O ALARM
I VALVE
C pH & ORP RECORDER -CONTROL
CHEM CAL rEED
NON-CHRQMATE CONTROL SIGNAL
WASTES
" ' A
>.,/-.
r"/w<— f—i
:..<. ..; Q. (LACIrlED)
j pH EFFLUENT
"1 • : (Hb) ID HIVtri
>
>J-tJ APH ,O POINT
?<6S1 rnil 1;
* ** ! ivii ii / \
1 ^ ' v
^ SUMP /' X,
<\X^^
^ ci I-J-R/^I |7ATInl\l
TANK 3 CLARIFIER j
TANK 4 y
SLUDGE TO
DRYING LAGCCM
FC* i-u.\JOLING CHEMICAL MILLING A\D OTHER METAL FINISHING
EFFLL'E ' 73 -T p^ , .- g_35
-------
TABLE 36 COMPARISON OF BCL ANALYTICAL RESULTS WITH TYPICAL ANALYTICAL
RESULTS REPORTED BY PLANT 33-23 FOR TREATED EFFLUENT
Constituent
AT
+ 6
Cr
tot
Cr
PC
4
SS
IDS
pli
Total Concentrat1onB mp/1
Typical Plant 33-23
[ffluent Analysis
0.1
0.30
0.32
9.1
23
3600
7.0
Contractor
Sampled Effluent
0.2
0.10
0.28
10.5
22
3500
8.0
190
-------
Plant 30-9 is a large aluminum and titanium chemical milling
installation. Chemical milling of the two metals is carried
out in the same area and some of the tanks are used
interchangably, since some of the operating steps are
similar.
The spent chemcial milling etchants a d other processing
solution frcm this plant are haule.^ away by a licensed
scavenger, and the rinse waters are it to large Bettl'.r-j
ooiids on company property.
Data on ten etching lines is given in Tables 33 and 34.
Plant 31-16 was visited during this study and data t-°cen
during the plant visit is covered under subcategory <*)
processes.
The 65th percentile water use for this eubcategory is 120
1/sq m-operation (3.0 gal/sq ft-operationj.
Thirty Day Average Vs One D*.y Maximum
Five months of daily data were obtained from plant 15-1.
This data appears in Table 35. ' In this time period the 30-
day average value of 80 mg/sq m-operation for Zn was
exceeded on two occasions, December *&, 1974 and December 10,
1974. The thirty day average of 80 mg/sq m-operation for
CNT was never exceeded. The one-day maximum of 160 mg/sq m-«
operation was never exceeded by Zn or CN.
One month's effluent data was chosen at random from plant
12-6. It appears in Table 36. Ni, TSS, Cu, Zn, CNT are not
out of compliance with the thirty day average or one-day
maximum. cr+* is not out of compliance with the 30-day
average but is out on the one-day maximum three times during
the month.
Five months of twice weekly sampling TSS, for plant 33-15 is
shown in Table 39. CrT. Ni, Cu never exceed the 30-day
average or one-day maximum. Cr^« is not in compliance for
30-day average or one-day maximum.
Plants Meeting the Guideline^
The effluent concentrations and water use factors have been
collected for 21 plants in Table 40. Except as indicated on
the table, all values are in tota*. solids. Plants 36-1, 36-
12, 15-3, 15-1, 12-6, 33-15 and 12-8 meet the 1977
standards. Plants 36-1 and 36-12 meet the new source
performance standards. Plants 11-8 and 33-: were out of
compliance on only one or two parameters.
191
-------
TABLE 37
PLANT 1$ - 1
mgAn2-Operation
DATE
PH
CN CH-6
CrT
Cu
6-01-74
6-02-74
6-03-74
6-04-74
6-05-74
6-06-74
6-07-74
6-08-74
6-09-74
6-10-74
6-11-74
6-12-74
6-13-74
6-14-74
6-15-74
6-16-74
6-17-74
6-18-74
6-19-74
6-20-74
6-21-74
6-22-74
6-23-74
6-24-74
6-25-74
6-26-74
6-27-74
6-28-74
6-29-74
6-20-74
HI
9.3
8.6
8.4
8.6
8.1
8.1
8.7
9.5
8.2
9.0
7.9
8.0
8.6
8.9
9.0
8.6
8.1
8.2
8.5
9.1
8.3
9.5
7.9
8.9
8.8
8.9
9.6
9.8
9.5
8.1
Lo
7.5
6.9
6.9
6.3
6.6
6.8
7.8
8.0 •
6.8
7.1
6.6
6.4
7.4
6.4
7.5
7.2
6.9
6.6
7.3
7.3
7.5
8.3
6.6
7.3
7.2
7.6
7.8
8.0
8.3
7.0
5.7
7.4
5.3
6.2
6.6
7.2
10.6
16.6
35.3
22.3
19.2
7.0
6.6
10.1
6.2
7.0
5.7
5.7
6.2
5-7
6.6
8.4
7.4
5.7
6.2
6.2
6.2
5.7
5.7
3^1
•
.52
5.4
.48
2.2
1.8
1.3
4.8
.52
4.2
.62
.60
1.3
.60
.92
.56
1.3
1.0
1.0
2.8
8.3
8.4
40.3
46.2
.52
5.6
2.2
1.7
7.6
78.0
.28
5.2
6.8
4.8
5.6
6.0
6.5
9.6
5.2
6.0
.72
6.0
6.4
6.0
9.2
5.6
6.4
5.2
5.2
5.6
10.4
30.0
15.2
170.
10.4
16.8
5.6
5.6
6.8
130.
22.4
5.2
12.6
19.2
11.2
12.0
19.5
28.8
5.2
12.0
7.2
12.0
19.2
24.0
36.8
16.8
12.8
5.2
10.4
11.2
20.8
12.0
15.0
20.4
10.4
5.6
16.8
11.2
15.6
15.6
11.2
5.2
20.4
48
44.8
48.0
58.5
67.2
31.2
42.0
50.4
^8.0
57.6
60
73.0
39.2
38.0
41.0
36.4
44.8
41.6
42.0
22.8
61.2
52.
50.4
50.4
33.6
52.0
57.2
19.6
•".•II !•!• IJ
15.6
13.6
*^W " "
38.4
56.0
60.0
84.5
96.0
20.8
42.0
21.6
36.0
57.6
66.0
110.4
56,0
25.6
46.8
36.4
67.2
31.2
66.0
30.4
61.2
41.6
56.0
44.8
39.2
31.2
20.8
8.4
TSS
1508
408
696
476
930
813
3984
2392
690
806
360
536
1560
3588
1736
832
416
806
308
3196
810
2546
1156
1378
1316
980
644
Average 8.7 7.2
8.6
8.0
22.4 16.2
46.0
1950
194
1170
192
-------
TABLE 38
PLANT 12-6
mg/m2-0peratlon
DATE J)H Zn CNT
11-13-74 8 1.3 27-7
11-14-74 7 11.9' 14.5
11-18-74 6 15.8 18.5
11-19-74 7 13.2 22.4
11-20-74 7 48.8 14.5
11-25-74 8 15.8 29.0
11-26-74 10 6.6 31.7
Average 7.6 17.4 23-3
12-02-74 8 10.6 30.4
12-03-74 7 14.5 46.2
12-04-74 7 12.1 29.0
12-05-74 6 55.4 17.2
12-06-74 6 17.2 21.1
12-09-74 ' 9 15.8 31.7
12-10-74 9 92.4 23.8
12-11-74 7 29.0 21.1
12-12-74 10 5.3 23.8
12-13-74 8 37.0 37.0
12-16-74 8 ^7.7 22.4
12-18-74 7 9-2 19.8
12-19-74 7 25.1 17.2
Average 7.6 38.4 26.2
1-03-75 6 10.6 23.£
1-06-75 9 11.9 15.8
1-07-75 7 6.6 19.8
1-08-75 7 7-9 13-5
1-09-75 7 33.0 15.3
1-10-75 8 66.0 18.5
1-13-75 8 13.2 29.0
1-14-75 10 11.9 52.8
1-15-75 8 15.8 27.7
1-16-75 7 13.2 111.5
1-17-75 7 48.8 13.2
1-20-75 6 15.8 18.5
1-22-75 8 6.6 15.8
1-23-75 7 *.6 15.8
1-24-75 8 3^.3 22.4
1-27-75 8 9.2 17.2
1-28-75 6 7-9 18.5
1-29-75 7 1.3 14.5
1-30-75 7 26.4 29.0
1-31-75 7 21. j. 26.'
7.4 18.6 20 9
193
-------
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TABLE 4il
.'U-NT l/m2-op (qal/ft2-or>) Cu Ki • r-i-T ^,+6
2 w — '. **
1--36-1
J. '•36-12
33-5
«5-3
2C-i»
33-2 J.
33-2
S15-1
S12-6
J33-15
*11-8
6-37
43-1
S-7
19-24
2U-17
23-7
30-21
12t (3.0)
...'I (4.4)
29 (.733)
i: (.329)
232 (5.8;
184 (4.6)
232 (5.8)
128 (3-21
4440 (111)
132 (3.3)
60 (1.5)
211 (5.3)
50 (2.0)
52 (1.3)
-
- —
-
-
-
-
.12 .60 .045 .03 .53
1-S* -09 .20 .10 .43
•H -08 .06 .36 .34
.7: - - .S.i
.330 5.7
•2« --4 .07 .023 .1;
.17 I.S .54 . -25
<1-0 - <1.0 -
-------
The plated area is the primary unit of production on which
the effluent limitations in Table 1 «re based. Plated area
in defined with reference to Faraday 2 Law of electrolysis
by the following equation:
JBU
100 kt ^uation 2
whcve s = arec., sq m (sq ft)
v. - cathode current efficiency.,, pcrc
I ~ current used, amperes
T = time,? hours
t = average thickness of deposit ff r,ra
k = a constant for each metal pla-ced baaed on the electro-
chemical equivalent for metal deposition, amp-hr/mm-sq m
(amp-hr/mil-sci ft) ,
The numerical product of current ar»d time (IT) is the value
that would be measured by an ampere-hour meter. Values of
the constant k based on equivalent i/«iffiht ssad the valance of
the metal deposited are shown in Table 41.
Average thickness can be approximated by averaging thickness
measurements at several points on a single plated part, to
establish the ratio of average to minimum thickness.
Minimum thickness is customarily monitored to meet the
specifications of purchasers of electroplated parts, based
on service requirements.
This equation was used in this study to determine the plated
areas per unit cime in each plating oparation when the only
available information was the current used and the average
thickness of deposit. This equation was also used as a
check on estimates of surface area plated provided by the
plants contacted.
To calculate the total plated &sr©£ on which the effluent
limitations are based for a specific plsnt? it was necessary
to sum up the area for each electroplating process line
using Equation (2) . For process lines containing two or
more electroplating operations (such &3 in copper-nickel-
chromium decorative plating^ the plated area is calculated
by Equation (2) for each plating oper&ticn in the process.
The results should be the same, since the same parts are
processed through each operation. However, if the
calculated plated area differed r^..' sach plating operation
in a single process line, the average of the calculated
plated areas for the operations was used. Th? sum of the
plated area for each process line le the total ated area
for the plant.
197
-------
Process Chanqor?
Process changes are not currently available for the metal
finishing industry that would lead -to greater pollution
reduction than can be achieved by the recommended effluent
limitations. Some possible process changes such as use of
noncyanide plating baths may eliminate one pollution
parameter, but do not eiirnineite all and Bi&y causi. ot-iiar
problems. They may be useful i;i some facilities for
reducing the cost of meeting the effluent limitations
recommended in this document.
Nonwater Quality Environmental Impact
As discussed in Section VIII of this report^ the principal
nonwater quality aspect of metal finishing waste treatment
is in the area of solid waste disposal. Disposal of sludges
resulting from metal removal by chemical treatment is a
current problem in many states that have a high
concentration of facilities. The problem might be partially
alleviated by disposal of drier sludge. Such added costs
for removal of water from sludge would be imposed by the
requirements for solid waste disposal and does not directly
result from the requirement for water pollution reduction.
The use of advanced technology to recover metal plating
chemicals from rinse water rather than chemical treatment
which adds to the sludge is being applied in areas where the
sludge-disposal problem is greatest. Further impetus in the
direction of recovery rather than disposal is expected to be
provided by authorities responsible for solid waste
disposal. This will have an overall beneficial effect on
water pollution because of the concurrent requirements for
water conservation for economic application of recovery
techniques.
It is estimated that many of the existing sources dis-
charging to navigable waters are already using chemical
treatment methods with a high percentage removal of metals.
This is particularly true in geographic areas where water
pollution reduction has been emphasized and the sludge-
disposal problem is most evident.
There will be no direct effect on air quality as a result of
the application of recommended technology for water
pollution reduction. Indirect effects related to increased
energy use are estimated to be modest.
Plated Area Unit of Production
198
-------
Sma.ll discrepencies in the above calculation for two or more
plating operations in the same process line might be related
to a difference in the actual current efficiencies from
those in Table 37 which are to be us«d for the calculation.
However, experience with data from several plants indicated
that the more lively cause of the diicrepancy is the
accuracy of the reported values of &va^fe,g plate thickness.
ThM use of ampere-hour on rectifiers - ..ght have value fo:
monitoring or record keeping for scsva plants In lieu of
measu
-------
TABtK 4 1 jLECTOtiCKEMICAI. EQUIVALENTS AHO tiE'-ATES
(All n»ur«> In this t»'»;« «<• b*«« hf M »-,- !>? ll
dijWUil 9.891 ^.ifedl it to. . ,! *
ld./M| tk iietocnt Htf'-» * iff
It. 05 *J
17.4 ft
10,*
24,1 An
14.3
14.S 11
S.93
9.73 C4 «,.«• , ,fr.lC«
Si.8 Cr 21 » 13
23.1
1».0 Co t,®S li»
17.7 Cu 7.30 100
8.W 3.5* 39-108
14.0 Oa
• is. 6 e«
U.6 Au
12.4
t.t ?,£3 100
U.I Xc. S.1J 56 :«»
29.4 IK
12.1
17. » I* 7.38 tvi
*.91 n I.J3 100
16.3 Ha
8.55 K«
4.27
19.0 »1 8.05 180
28.6 N 12.12
- 21.4 ».07
14.2 6.02
27.6 ?S 11. »? *0
13.85 *•*!» *0
.„».» »0
30. g KB li.OS
23.1 ».?•» *0
15,3? *.:.
»a S K.
13.4 1*
6.14 *t *•«*• i"9
12.4 T*
(.19
3.12 n ,
13,63 IB 6.62 «
7.12 3.31 I''*
13.7 lu 3.80 1UO (ACID)
••* i'J
-------
be defined as any step followed by
a rinse in the electroplating process
in which a metal is «electrodeposited
on a basis material. Electroless
plating on non-metallic materials
for the purpose of providing a
conductive surface on tha basis
material and preceding tJ 3 actual
electroplating stepp and the past
treatment steps of chroirating,
phosphating and coloring uhere an
integral part of tr,3 plating line
and stripping whers DQ^chicted in
conjunction with el a .strop I at, ing for
the purpose of stlvagirscf improperly
plated parts na^ "o
-------
in the effluent da*; to
processes before dilution by
from other processes favarag® fv?,, ?C
sequential daysj .
Determination of Finished Area/Hr/Qperation
•*•"'"• ..... "" m*'**"-*™"-™*-*-****"*** immi IB«^»^»»— •» J»«KII'I IM;I i na^n»»K*^«» 1,1 1. ili*limB.HTH^i»-»iift nslr. i ~- ja» JflBm»B«j j»
The area for each line will be determined ttom
on the (1) average amperes used,, (2) th^ sequence of plating
operations, and (3) the average tMcicn^s in mil o'~ ,-*< h
type of plate. If complete datd on thickness is? la.-kii-g,
the following value will be usedi
Copper 0,,3 ,'RlI
Nickel 0.3 mil
Zinc Q»3 mil
Chromium 0.015 ri'i 1
Where chroma ting follows plating, the area will be the same
an that of tho primary plating operation. The equation:
S = El T/ 100 kt
is then used to calculate plated area.'\ir/cper«<-io»« In a
line with several sequential operations, it is likely that
the calculated plated areas i',v e^ch :\I ;-.ting operation will
vary from each other although the act u '. snea plated should
be the same. The difference in calculatec- areas may vary by
a factor of two or three. When applying t.'bs qt^idelines, the
figure used for area plated should be th ,: at3 bhmetic average
of the calculated pi'\' -^ areas.
Where actual amperes **.& not knowny ,.,' ,-, ., c- equal to 2/3
the installed capacity for the line s-* .-'Jd be u&ed, »-'
information on amperes is completely lackincf for a li>e
water use is available,, i.be sq m/hr may be ileteiisstned by
Sq m/hr -- t£..hr.,jised__?u
(?00 1 /?<--. rn) (no. of
Sq ft/ht - S^lifli, .,!«§S3_2D_£iJS
(5 gal/or) (no. of opera "icr'«^
Once the plated area h--^ ' •:•,.•;* measured tiie t^f'.cJ'- lines can be
used to det^ttfurva tr*e total -v. lowable disr.hara-*: of waste
water constituents fzor? i.he plant Every time the surface
is rinsed, following SOTO ^v>aratLot! in the process; line, it
is assumed that more waste water ia produced, and a greater
quantity of -,'aste wait..-: constit.ueuto may be disefa
-------
therefore incorporated into the rinse following the first
plating operation for purposes of calculating the allowable
amount of waste water constituents discharged. The total
allowable discharge in g/day will b«:
(lO*) (sq m plated/hr) (effluent ilmitatior in mg/sq m)
(No. of oper.) (hr/day)
The total allowable discharge in ib/dey It s
(sq ft plated/hr)(effluent limitation
in Ib/million sq ft (No. of oper.J fhr/day)
These relations hold for each effluent limitations guideline
value listed in Table 1. The relations apply to each
process line or part of a process line if the area plated/hr
changes in the line.
The actual discharge from the plant is the product of the
volume of effluent/hr and the concentration of waste water
constituent in the effluent.
Thus,
q/day » (liters/hr) (mg/1) (10-«J Chr/dayJ
Ib/day = (8.33 x 10-*) (gal/hr) (ng/1) (hr/day)
Figure 30 represents such a situation The line processes
15 sq m/hr. The volume of effluent is 3,000 1/hr. The
plant operates 10 hr/day. There are three operations in
this line, chromium electroplating* etching, and anodizing.
The discharger is allowed: (10-*) (sq m/hr) Jeffluent
limitation in mg/sq m-operation)(number of operation)
(hr/day) = kg/day pollutant
The actual discharge is the product of the volume of efflu-
ent/hr and the concentration of waste water constituent.
Kg/day = (liters/hr) (mg/1) (10-»J ^hr/dayj
Thus, in this example the dischargai .s allowed to discharge
the following amount of chromium fox chromium electroplate
(10-*) (15 sq m/hr) (80 mg/sq m-operation) {1 operatl ,n)
(10 hr/day) = 1.2 x 10-* kg/day
203
-------
for anodizing
(10-6) (15) (t»5) (1) (10) = 6.75 x 10-' kg/day
for etching
(10-») (15) (60) (1) (10) = 9.0 x 10-3 kg/day
In total he may discharge the sum of the three:
2.78 x 10~z kg/day of chromium total.
He may discharge one-tenth of that or
2.78 x 10~1 kg/day of Cr+6
If the final effluent concentration is equal to 0.56 rn.g/1
for CrT and 0.06 mg/1 for Cr+6, the actual discharge will be
(3000 l/hr)(.56 mg/1)(10~6)
(10 hr/day) = 1.68 x 10~2) kg/day of CrT
and
(3000 l/hr)(.06 mg/1)(10-6)
(10 hr/day) = 1.8 x 10-1 kg/day of Cr+6
Thus, the plant is meeting the guidelines.
204
-------
Alkaline
Clean
Rin&e
Acid
Pickling
I
Rinse
f
Chromium.
Plate
Rinse
Etch
Rinse
Anodi ze
Rinse
Dry
205
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BEST AVAILABLE TECHNOLOGY BCCaOMICALLY
ACHIEVABLE.... Q^lpB^Sf *~_AJfo._.LXMI5?ATIOHS
limitations
„ are o specify r,i;e
attainable through
ch ecoomic
j&troductloja
The effluent
1983 „ are to
attainable through the applies .^
technology economic-"" * i r:hlav&lJ
based on the very !.:-ast convr^s"..
employed by a specific point ^ , r.
category and/or suhrav sgcry cr !".
transferable from one lr,5r:<5-ir" •;
specific finding must be r.ad
control measures and prec-dces t%, ^
pollutants, taking into acr.ou:" w,~
tion.
Consideration must also tj-s given to
(a) the age of the
involved
:•*,< achieved July 1,
'f fluent reduction
of -cLe
best available
*is technology can be
d treatment technology
uilthin the industry
:iology that is readily
,; &£3 tc another. A
r.o the availability of
the discharge of
of such elimina-
facilities
(b)
(c)
(d)
(e)
the process
the ens neevring aep«£Ct & cC ria application
of var* ous types of
process changes
.';v.
Oi
cost of achieving -che
resulting from -the t
reduction
(f) non water qua lit./ etWirc.'^
(including enerc,y requi.'.'.e-
The best available tecL^olog:/ ^.,o:.;
assesses the availaoilicy .In .^ll
controls as well as tirae concrol
techniques employed ar the enfi cf e
A further consideration is the dv&iLl.
control technoloqy at tha pilot plar
levels, which have fieKori^trtt*
performances and economic viability ,•-
reasonably justify
lnve&tir.g
Impact
^wlly achievable also
cases of in-process
.r aa
-------
available technology economically achievable is the hiyLast
degree of control technology that has been achieved or has
been demonstrated to be capable of being designed for plant
scale operation up to and including no discharge of
pollutants. Although economic factors are considered, 1.he
co.ts for this level of control are intended to be top-of-
the-lirsc of current technology siibject to limitations
imposed by economic and engineering feasibility. However,
best available technology economically achievable may be
characterized by some technical risk with respect to
performance and with respect to certainty of costs and thus
may necessitate some industrially sponsored work prior to
its application.
Industry category and Subcat^orx Cgve^ejl
The pertinent industry category is the metal finishing
segment of the electroplating industry divided into
Subcategories (1) and (2) as previously discussed in Section
IV,
Identification,of Best Available Economically Achievable
Subcategory (1)
The best available technology economically achievable is the
use of in-process and end-of-process control and treatment
to achieve no discharge of pollutants. By the use of in-
process controls to reduce the volume of waste water, it
becomes economical to use end-of-process treatment designed
to recover water and reuse the water within the plant thus
avoiding any discharge of effluent :-.o navigable w#Aers.
Solid constituents in the wastewa*. Jt, are disposed of to
landfill or otherwise. A line in Plant J.u-21 plating Oliver
has eliminated liquid effluent discharge for several mcmtha,
and continued demonstration of this operation will support
the fact that technology is available to achieve this.
Plant 11-22, a chromium electroplater studied in £hase I, Is
using a system designed to eliminate liquid effluent by
subjecting effluent from the clarjfier of the chemical
treatment plant to reverse osmosis and recycJ ing water to
process. The concentrate from the reverse osmosis unxt i&
evaporated to dryness. It is expected that other methods
will be developed dux ,.ag the next five years to avoid
discharge of effluent to navigable waters and thus achieve
no discharge of pollutants in an economical manner. While
the above examples of zero discharge are being achieved in
conjunction with electroplating operations, the similarity
of operations in processes in Subcategory (I) to those in
the electroplating processes, and the similarity of the
208
-------
was.-e waters, suggests that techniques of obtaining zero
discharge for electroplatiaq processes are equally
applicable to the other processes in Suboategory (1) .
Subcategory (2) and
The best available technology economically achievable is the
use of in-process and end- of -process contr© and treatment
to achieve no discharge of pollutants Processes in
Subc<.teqory (2) are distinguished from fchoae in Subcategory
(1) only by water use. The operations in the two
subcategorlos are very similar, the types of waste waters
obtained are essentially the same, and the types of waste
treatments that are applicable are the same. The evidence
that zero discharge is being and will be attained for
processes in Subcategory (1) is equally applicable to
processes in Sutcategory (2) .
Rationale for Selegt^op of Best Aval lab. 1 8
Technology Economically Achievable
Age of Equipment and Facilities
Replacement of older equipment and facilities will permit
i-he installation of modern multitank countercurrent rinsing
systems after each operation in each process line with
conservation of water use for rinaing. The use of reclaim
and recovery systems after each finishing operation should
be possible. Use of inprocess controls to the maximum
extent will reduc< the volume of effluent -co the point that
recovery and reuse of water is economically feasible.
Process Employed
The application of the technology for end-of -process
recovery and reuse of water to the maximum extent possible
is not dependent on any significant change in the processes
now used. Most water recovery technology can produce a
higher quality of water than normally available from public
or private water supplies. High purity water for the final
rinse after metal finishing operations is desirable to
improve the quality of the product.
Engineering Aspects of the Application of Various Types of
Control ^echniques
Many slants are successfully using evaporative recovery
systems after one or more plating operations with a net
savings compared to chemical treatment. Evaporative systems
are in current use after copper, nickel, chromi* n, zinc,
209
-------
brass, tin, lead, and gold plating operations. Some pie fits
have succeeded in using recovery systems after all plating
operations in their facility. The engineering feasibility
of in-process controls for recovery of chemicals and reusfe
of water are sufficiently well established. Sufficient
operational use has been accumulated to reduce the technical
risk w*th regard to performance arid any uncertainty with
respect to costs.
The technical feasibility of end-of-process water recovery
systems has been established by extensive development of tint
recovery of pure water in many related Industrial processes.
Although some uncertainty may remain concerning the overall
costs when applied to metal finishing wast* waters, such
uncertainty primarily relates to the volume of water that
must be processed for recycling and reuse. Th© fact th&t
the technology as applied to the electroplating industry has
progressed beyond the pilot plant stage and has been
designed and is being built for fullscale operational use
indicates that the technology is available and probably
economical. These systems are equally applicable to
processes other than electroplating due to the similarity in
the waste water produced.
Process Changes
Application of the technology is net dependent on any
process changes. However, process changes and improvements
are anticipated to be a natural conscience of meeting the
effluent limitations in the most economic mannei1*
Nonwater Quality Environmental Impact
Application of technology to achle^ j no diacterg-e of
pollutants to navigable waters by July 1, 1983, will have
little impact on the solid waste disposal problem with
regard to metal removal as sludge beyoad that envisioned to
meet effluent limitations recommended for July 1;, 1977. The
volume of soluble salts will be substantially increased.
In general, it is anticipated that the technology will be
applied in a manner such that no discharge of effluent to
surface waters occurs. Thus, metal oxide sludges would be
disposed of on land with suitable precautions. The soluble
salts which are largely innocuous should be suitable for
disposal in salt water. Because these salts are not large
in amount and can be dewatered to dry solids (by
incineration if necessary) very little additional impact, on
the solid waste disposal problem is anticipated.
210
-------
No impact on air pollution is expected as the result of
achieving no discharge of pollutants to surface water. The
available technology creates no air pollutants.
B *6 fflLdMLABSiSffcffl of
The recommended effluent limitations to I a achieved by July
1, ,983, for existing sources based on -c '•*« application of
Best Available Technology Economically Achievable is no
dis^harq*.' of pollutants to navigable waters for
Subca -egories (1) r (2) and (3).
Achieving the effluent limitations of no discharge of
pollutants by achieving no discharge of effluent to surfaje
waters is the most direct method that eliminates the need
for sampling and analysis. If th@re is other effluent
discharge to surface waters from the plant not associated
with metal finishing, a determination is required that no
waste waters originating from met&I finishing processes are
admixed with this other plant effluent.
211
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SECTION XI
SOURCE PERFORMANCE STANDARDS
Introduction
The standards of performance which nmat be achieved by new
sources are to correspond to the degree of effluent
reduction attainable through the application of higher
levels of pollution control than those identified as best
avc,:.A.able -sctoG.,ogy economically achievable for existing
sources.. .'he added consideration for new sources is the
degree c/; ' •-:fl;eat redaction attainable through the use of
improver production processes and/or treatment techniques.
The term "new sources" Is defined by the Act to mean "any
source, the construction of ^hich is commenced after
publication of proposed regulations prescribing a standard
of performance."
New source performance stane^rda ar« based on the best in-
plant and end—of-process technology identified as best
available technology economically achievable for existing
sources. Additionel considerations applicable to new source
performance standards take into account techniques for
reducing the level of effluent by changing the production
process itself or adopting alternative processes, operating
methods, or other alternatives. The end result will be the
identification of effluent standards which reflect levels of
control achievable through the use of improved production
processes (as w.-ll as control technology), rather than
prescribing a pa~-.icular type of process or technology which
must be employed,, A further determination must be made as
to whether a standard permitting no discharge of pollutants
is practicable.
Consideration must also be given tos
(a) The type of process employed and process
changes
fb) operating methods
(c) batch as opposed to continuous operations
"-•u uge of alternative raw materials and mixes
of raw materials
(e) use of dry rather than wet processes
(including substitution of recoverable
solvents for
213
-------
(f) r covery of pollutants as by-products.
Standards of performance for new sources are based on
applicable technology and related effluent limitations
coveri'.q discharges directly into waterways.
consideration iust also be given to the fact that Standards
of Performer - for Net-- Sources could require compliance
about three ?^ra sooner than the effluent limitations to be
achieved by eAi.itinq sources by July 1, 1977. However, new
sources should achieve the same effluent limitations as
existir-a sources by July 1, 1983 .
Industry Category and Subcategory Covered
The pertinent industry category is the metal finishing
industry divided into Subcategories (1) and (2) , as
previously discussed in Section IV.
Identification Qf control and Treatment
Ifichnology Applisablg to,
.
Standards and Pretreatment 3tan.da.rde of
New Soytrcei-t
Subcategory (1)
The technology previously identified in Section IX under
Subcategory (1) as best practicable control technology
currently available is al 30 applicable to new source
performance standards. IN addition, a new source can
utilize the best practice in multitank rinsing after each
operation in the process as required to meet the effluent
limitations at the time of construction. Thus, with no
practical restrictions on rinse water conservation after
each operation by multitask rinsing, there are fewer
restrictions on the use of advanced techniques for recovery
of bath chemicals and reduction of wastewater from rinsing
after pretreatment and post treatment. Maximum use of
combinations of evaporative, reverse osmosis, and ion
exchange systems for in-process control currently available
should be investigated. A small end~of-pipe chemical
treatment system can be used to treat spills, concentrated
solution dumps,, and any other water flows not economically
amenable to in-process water and chemical recovery.
The net res a of the improvements cited should be a
reduction in Baiter use as compared to that considered
achievable for best practicable control technology currently
available. This reduction should result in a lowe^
214
-------
discharge of waste water constituents. Although methods are
beinq developed that may make possible a further reduction
in the concentration of constituents and a reduction in the
discharge of waste water constituents in chemically treated
effluents, present technology Is capaiale only of achieving
the concentrations listed in Table 39 by exemplary chemical
treatment. It would be anticipated that some plants now
operating, due to having been designed recently to minimize
water use or because of other favorable circumstances such
as adequate space to make modifications«. are attaining a
water use well below 120 1/sq la/operation. Table 37 shows
12 lines involving processes in Subca^agory fl) that achieve
a water use of less than H5 1/sq m/op©ration. These are
found in Plants 33-23, 33-35, 20-22, 20-23. It is estimated
that a new source can achieve a water use of U5 1/sq
m/operation for processes in Subcategory (1) by use of the
technology described above for reducing water use,
Subcategory (2)
The technology previously identified in Section IX as best
practicable control technology currently available for
processes in Subcategory (2) Is also applicable to new
sources. In addition, a new source can «aa best rinsing
practice and advanced techniques for recovery of bath
chemicals and reduction of rinse water a*3 described under
Subcategory (1) above. The similarity of operations in
processes of Subcategory (2) to the operations of processes
in Subcategory (1) , and the similarity in waste water
compositions and treatment methods can be cited to indicate
that the same methods of reducing water use are applicable
to Subcategory (2) as are applicable to Subcategory (1) .
The application of the same techniques to the two
Subcategories should reduce the waiter proportionately so
that if a reduction of 90 1/sq m/optration to U5 1/sq
m/operation can be achieved by a new source with a
Subcategory (1) process, a reduction from 80 1/sq
m/operation for a Subcategory C2J process in a present
source to 40 1/sq m/operation for the aam© process in a new
source should be achievable. Th«r^fosr«s it is estimated
that new sources can achieve a w&fcer use of HO 1/sq
m/operation for Subcategory {2} processes. Two lines in
Table 34 involving Subcategory (2f processes have a water
use of less than MO 1/sq m/operatioru These lines are in
Plants 6-3&, 20-25, 23-8.
Subcategory (3)
The technology previously identified in Section IX as best
practicable control technology currently avaf .able for
215
-------
processes in Subcategory $2) ia also applicable to new
sources. In addition, a new source can use best rinsing
practice and advanced techniques for recoverv of bath
chemicals and reduction of rinse water as described under
Subcategory (1) above. The similarity of operations in
processes of Subcategory (2) to the operations of processes
in Subcategory (1), and the similarity in waste water
compositions ai-d treatment methods can be cited to indicate
that the same methods of reducing water uss are : [-r »,icafole
to Subcategorv (2) as are applicable to St^ntegorv (1).
The application of the same technique-*- to t! a two
Subcategories should reduce the water proportionately so
that if a reduction of 90 1/sq m/operation to 45 1/sq
m/operation can be achieved by a new source with a
Subcategory (1) process, a reduction from 120 1/sq
m/operation for a Subcategory (2) process in a present
source to 60 1/sq m/operation for the same process in a new
source should be achievable. Therefore, it is estimated
that new sources can achieve a water ue@ of 60 1/sq
m/operation for Subcategory (2) procaaees. Two lines in
Table 34 involving Subcategory (2) processes have a water
use of less than 60 1/sq m/operation. These lines are in
Plants 4-8, 30-9, 9-2, 4-9.
Rationale for Selection of Control and
Treatment Technology Applicable to New
Source Performance Standards
The rationale for the selection of the above technology is
applicable to new sources discharging to navigable waters is
as follows:
(1) In contrast to an existing source, a new
source has complete freedom to choose the
most advantageous equipment and facility
design to maximize water conservation by
use of as many multitank rinsing operations
as necessary. This, in turn, allows for
economic use of in-process controls for
chemical and water recovery and reuse.
(2) in contrast to an existing source which may
have 2c present a large capital investment
in was'-e treatment facilities to meet
effluent limitations by July 1, 1977, * new
source has complete freedom in the selection
the design of new waste treatment facilities.
(3) In contrast to an existing source, a new
216
-------
source has freedom of choice with regard to
geographic location*
Standards of Performance Apg^JLca|?l^ .to
The recommended St s.ndards of Perfosrffl&nc® t- b® achieved by
new sources discharging to navig*bl« .atera waa shown
previously in Tc.ble 2 of Section II,
The quantitative values for the SO-da^ .average standard for
eaeli p^'-weter in mg/sq K -J'.b*-.. 5o 0*3 ft) is based on a
nomin- 1 water use one-half as l&/gc && tlrioae used to develop
1977 guidelines combined with tits concestrrations achievable
by chemir.al tre&w.-inc as previously shown in Table 39 of
Section IX. For examp^, G.5 asg/* for copper,, nickel, total
chromium, zinc, and total cyanide? 0,05 Rig /I for hexavalent
chromium and .,075 mg/l for oscidlsable cyant'ie, 20 mg/1 fjr
suspended solids, when combined with &$i effluent factor of
45 1/sq m are the basis for the 30*»d&y 8V
-------
Guidelines for the Application of
New Source Performance Standards
The recommended guidelines tor the application of standards
of performance for new sources discharging to navigable
waters are the same as those in Section IX relating to
existing sources based on use of the best practicable
control technology currently available and those in Section
X based on use of best available technology economically
achievable.
218
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SECTION XII
ACKNOWLEDGEMENTS
The Environmental Protection Agency was aided in the
preparation of this Development Document by Battelle
Columbus Laboratories under the direction of William H.
Safranek, Luther Vaaler, John Gurklis and Carl Layer on
Battelle*s staff made significant eontributions.
Kit R. Krickenberger served as project officer on this
study. Allen Cywin^ Director, Effluent Guidelines Division,
Ernst P. Hall, Deputy Director, Effluent Guidelines Division
and Walter J. Hunt, Chief, Effluent Guidelines Development
Branch, offered guidance and suggestions during this
program.
The members of the working group/steering committee who
coordinated the internal EPA review are:
Walter J. Hunt, Effluent Guidelines Division
Kit R. Krickenberger, Effluent Guidelines Division
Devereaux Barnes, Effluent Guidelines Division
Murray Strier, Office of Permit Programs
John Ciancia, NERC, Cincinnati, (Edison)
Alan Eckert, office of General Counsel
James Kamihachi, Office of Planning and Evaluation
Acknowledgement and appreciation is also given to Nancy
Zrubek, Kaye Starr, and Alice Thompson of the Effluent
Guidelines Division for their effort in the typing of drafts
and necessary revisions, and the final preparation of this
document.
Appreciation is extended to the following organizations
associated with the electroplating industry:
American Electroplaters0 Society, East Orange,
New Jersey
Aqua-Chem, Milwaukee, Wisconsin
Artisan Industries, Inc., Waltham, Massachusetts
E.I. duPont de Nemours and Co.g Wilmington,
Delaware
Heil Process Equipment Corporation, Cleveland,
Ohio
Haviland Products company, Grand Rapids, Michigan
Industrial Filter and Pump Manufacturing Co ,
Cicero, Illinois
219
-------
Institute of Printed Circuits, Chicago, Illinois
Ionic International, Incorporated, Detroit,
Michigan
Lancy Laboratories, Zelienople, Pennsylvania
M & T Chemicals, Incorporated, Matawan, New Jersey
Electroplating Suppliers* Association, Incorporated,
Birmingham, Michigan
National Association of Metal Finishers, Upper
Montclair, New Jersey
Osmonics, Incorporated, Minneapolis, Minnesota
Oxy Electroplating Corporation, Warren, Michigan
The Permutit Company, Paramus, New Jersey
Pfaudler Sybron Corporation, Rochester, New York
220
-------
SECTION XIII
References
(1) Table 3, pg 36, "1967 Census of Manufacturers",
U.S. Bureau of Commerce.
m "Where to Buy Metal Finishing Services", Modern
Metals, 28 (6), p. 71 (July, 1972).
(3) Institute of Printed Circuits* Chicago, Illinois.
(4) jjgfrfl Finishing, p. 42, March 1972.
(5) Sidney B. Levinson, J. Paint Technology, 44 (569) 49.
(6) J. Schrantz, industrial Finishing, 20-29, October, 1972.
(7) Table 3, p. 7-45, "1967 Census of Manufacturers",
U.S. Bureau of commerce.
(8) Modern Electroplating, Edited by P. A. Lowenheim,
2nd Ed., John Wiley ind Sons (1963), Chap. 7,
pp 154-205.
(9) M»+*l FMpfghincr Guidebook and Directory, Metals
Pstics Publications, Inc., 1973.
(10)
and Plastics Publications, Inc
Metals
i i.
and Plastics Publications, Xnc. 1972.
(11) Modern fi jflcfrr opiating— * P 69
(12) Mo^£D_£l££^rQplflUngy P 708.
^^ Q
Ed. , Van Nostrand Rheinhold, 3rd Ed., 1971, p
(1«») schrantz, J. Industrial Finishing, April, 1973,
pp 37-40.
(15) Stiller, Frank P.., Metals Finishing guidebook and
Directory, Metals and Plastics Publications, Inc.,
pp 548-553, 1972.
(16) George, D.J., Walton, C.J., and Zelly, W.G.,
pahr|c3tion and Finishing. Vol 3, Am Soc for Metals,
1967, pp 387-622.
221
-------
(17J Innesf W.P. , Metal Finisaing Gu4debook and Directory,
1972, p 554. ~~~
(^8) Pocock, Walter, E. Metal Finishing Guidebook and
A£
-------
(33) Environmental Sciences. Inc., "Ultimate Disposal
of Liquid Wastes by Chemical Fixation".
(34) Dodge, B.F., and Zabban. W. , "Disposal of *ljtinj
* ' Room wastes. III. cyanide Wastes" Treatment with
Hypochlorites and Removal of Cyanates", Plating
18 (6), 561-586 (June, 1951).
(35) Dodge, B.F., and Zabban, W. , "Disposal of
( } Room wastes. III. Cyanide wastes: Treatment
Hvoochlorites and Removal of Cyanates. Addendum ,
Plating, 39 (4) , 385 (April, 1952) .
(36) Dodge, B.F., and Zabban. W. . "Disposal of Plating
C ' Room wastes. IV. Batch Volatilization of Hydrogen
Cyanide From Aqueous Solutions of Cyanides",
Plating, 12 (10), 1133-1139 (October, 1952).
(37) Dodge, B.F., and Zabban, W. , "Disposal of Plating
( ' Room Wastes. IV. Batch Volatilization of Hydrogen
Cvanide From Aqueous Solutions of Cyanides.
continuation", Plating, 32 (11). 1235-1244 (November,
1952).
(38) "Overflow", Chemical Week, HI (24), 47 (December,
1972),
(391 ovler, R.W. , Disposal of Waste Cyanides by Electro-
( * ?yt!c Oxidation"? Plating, 16 (4), 341-342 (April,
1949) .
(UO) Kurz, H. , and Weber, W. , "Electrolytic Cyanide
Dedication by the CYNOX Process" , Galvanotechnik
and Oberflaechenschutz, 3, 92-97 (1962).
(41) "Electrolysis speeds Up Waste Treatment", Environmental
Science and Technology", 4 (3), 201 (March, 1970).
(42) Thiele, H., "Detoxification of cyanide-Containing
waste Water by Catalytic oxidation and Adsorption
Process", Fortschritte wasserchemie Ihrer
Grenzgebiete, 9, 109-120 (1968): CA, 70, 4054
(1969) .
rim Bucksteeq, W. , "Decomposition of Cyanide Wastes by
( } Se?hods of Catalytic 6xidation Absorption", Proceedings
of the 21st Industrial Waste Conference, P«rdue
University Engineering Extension series, 688-59b
(1966) .
223
-------
(44) "Destroy Free Cyanide in Compact, Continuous Unit",
Calgon Corporation Advertisemente Finisher's
Management, 19 (2), 14 (February,, 1973),
(45) sondak, N. E., and Dodge, 3. F., W1h« QKidation
of Cyanide Bearing Plating Pastes by Ozone.
Part I", Plating, US (2) 173-180 (February,
1961).
(46) Sondak, N.E., and Dodge, B.F., "The Oxidation
of Cyanide Bearing Plating Wastes by Ozone.
Part II", Plating, J8 (3), 280-284 (March,
1961) .
(47) Rice, Rip G., letter from Effluent Discharge
Effects Committae to Mr. Alien Cvwin? Effluent
Guidelines civiaion, July 9, 1973.
(48) "Cyanide Wastes Might Be Destroyed at One-Tenth
the Conventional Cost", Chemical Engineering,
79 (29), 20 (December 25, 1972).
(49) Manufacturers' Literature, DMP Corporation,
Charlotte, North Carolina (1973*.
(50) Ible, N., and Frei, A.M., "Electrolytic Reduction
of Chrome in Waste water", Galvanotechnik and
Oberflaechenschutz, 5 (6), 117-122 (1964).
(51) schulze, G., "Electrochemical Reduction of
Chromic Acid-Containing Wast® Water*1, Galvanotechnik,
58 (7), 475-480 (1967): CA, 6jfr 15876t C1968).
(52) Anderson, J.P., and Weiss, Charles c%, "Methods
for Precipitation of Heavy Metal 3«lfid
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-------
(68) Campbell, R.J., and Eimnerman, O.K. r "Freezing and
Recycling of Plating Rinse Water", Industrial water
Engineering, 9 (4), 38-39 (June/July, 1972).
(69) A.J. Avila, H.A., Sauer, T.J. Miller, and R.E.
Jaeger, Plating, 60 239 (1973).
(70) Dvorin, R., "Dialysis for Solution Treatment in
the Metal Finishing Industry", Metal Finishing,
57 (4), 52-54 4 62 (April, 1959).
(71) Ciancia, John, Plating 60, 1037 (1973).
(72) communication with P. Peter Kovatia, Executive
Director, National Association of Metal Finishers.
(73) "An Investigation of Techniques for Removal of
Chromium From Electroplating Wastes", Battelle,
Columbus Laboratories Report on Program No.
12010 EIE to the Environmental Protection Agency
and Metal Finishers1 Foundation (March, 1971) .
(74) Grieves, R., et al., "Dissolved-Air Ion Flotation
of Industrial Wastes. Hexavalent Chromium",
Proc. 23rd Industrial Waste Conference, Purdue,
University, 1968, p 154.
(75) Surfleet, B., and crowle, V.A., "Quantitative
Recovery of Metals from Dilure Solutions",
Transactions of the Institute of Metal Finishing,
50, 227 (1972).
(76) Bennion, Douglas N., and Newman, John, "Electro-
chemical Removal of Copper Ions from Very Dilute
Solutions", Journal of Applied Electrochemistry,
2, 113-122 (1972).
(77) Carlson, G.A., and Estep, E.E., "Porous Cathode
Cell for Metals Removal from Aqueous Solutions",
from Electrochemical Contributions to Environmental
Protection, a symposium volume published by the
Electrochemical Society, Princeton, New Jersey,
p 159.
(78) "Water Quality Criteria 1972," National Academy of
Sciences and National Academy of Engineering for the
Environmental Protection Agency, Washington, D.C.
1972 (U.S. Govt. Printing Office Stock No. 5501-00520)
226
-------
SECTION XIV
GLOSSARY
Acid Dip
An acidic solution for activating the workpiece surface
prior to electroplating in an acidic solution, especially
after the workpiece has been processed in an alkaline
solution.
Alkaline Cleaning
Removal of grease or other foreign material from a surface
by means of alkaline solutions.
Anodizing
The production of a protective oxide film on aluminum or
other light metals by passing a high voltage electric
current through a bath in which the metal is suspended. The
metal serves as the anode. The bath usually contains
sulfuric, chromic, or oxalic acid.
Automatic Plating
(1) full - plating in which the cathodes are automatically
conveyed through successive cleaning and plating tanks. (2)
semi - plating in which the cathodes are conveyed
automatically through only one plating tank.
garrel Plating
Electroplating of workpieces in barrels (bulk).
Basis Metal or Material
That substance of which the workpieces are made and that
receives the electroplate and the treatments in preparation
for plating.
Batch Treatment
227
-------
Treatment of electroplating rinse waters collected in
adjacent tanks. Water is not allowed to leave the tank till
treatment is completed.
Best Available TechnQloqY_gconomicallv Achievable
Level of technology applicable to effluent limitations to be
achieved by July I, 1983, for industrial discharges to
surface waters as defined by Section 301 (b) (2) (A) of the
Act.
Level of technology applicable to effluent limitations to be
achieved by July 1, 1977, for industrial discharges to
surface waters as defined by Section 301 (b) (1) (A) of the
Act.
Bright Qj.g
A solution used to produce a bright surface on a metal.
Captive Operation
Electroplating facility owned and operated by the same
organization that manufacturers the workplaces.
Process utilizing an addition agent that leads to the
formation of a bright plate, or that improves the brightness
of the deposit.
Chemical Etch ^ng
To dissolve a part of the surface of a metal or all of the
metal laminated to a base.
Chemical Metal Coloring
The production of desired colors on metal surfaces by
appropriate chemical or electrochemical action.
228
-------
The improvement in surface smoothness of a metal by simple
immersion in a suitable solution.
Chromati^jng
To treat or impregnate with a chromate or dichromate
especially with potassium dichromate.
Chrome-Pickle Process
Forming a corrosion^resistant oxide film on the surface of
magnesium-base metals by immersion in a bath of an alkali
bichromate.
cosed-Loop Evaporation
A system used for the recovery of chemicals and water from a
plating line. An evaporator concentrates flow from the
rinse water holding tank. The concentrated rinse solution
is returned to the plating bath, and distilled water is
returned to the final rinse tank. The system is designed
for recovering 100 percent of the chemicals, normally lost
in d ragout, for reuse in the plating process.
Continuous Treatment
Chemical waste treatment operating uninterruptedly as
opposed to bath treatment; sometimes referred to as flow
through treatment.
Conversion Coatipq
A coating produced by chemical or electrochemical treatment
of a metallic surface that gives a superficial layer
containing a compound of the metal, for example, chromate
coatings on zinc and cadmium, oxide coatings on steel.
Deoxidizing
The removal of an oxide film from an alloy such as aluminum
oxide.
Descaling
229
-------
The process of removing scale or metallic oxide from
metallic surfaces.
De s mutt ing
The removal of smut, generally by chemical action,
Draqin
The water or solution that adheres to the objects removed
from a bath,
Draqout
The solution that adheres to the objects removed from a
bath, more preciously defined as that solution which is
carried past the edge of the tank,
Abbreviation for ethylfnediamine-tetr$*cetic acid,,
Effluent
The waste water discharged from a point source to navigable
waters.
Electrobrighten^ng
Electrolytic brightening (electropolishing) produces smooth
and bright surfaces by electrochemical action similar to
those that result from chemical brightening.
Electrochemical Mach|,nin^ (ff9M|
A machining process whereby the part to be machined is made
the anode and a shaped cathode is maintained in elope
proximity to the work. Electrolyte is pumped between the
electrodes and a potential applied with the result that
metal is rapidly dissolved from the work in a selective
manner and the shape produced on the work complements that
of the cathode,
230
-------
Electrodialvsis
Membrane dialysis under the influence of direct current
electricity.
Electroless Plating
Deposition of a metallic coating by a controlled chemical
reduction that is catalyzed by the metal or alloy being
deposited.
fflectropainting
A coating process in which the coating is formed on the
workpiece by making it anodic or cathodic in a bath that is
generally an aqueous emulsion of the coating material.
The electrodeposition of an adherent metallic coating upon
the basis metal or material for the purpose of securing a
surface with properties or dimensions different from those
of the basis metal or material.
Electroplating Process
An electroplating process includes a succession of
operations starting with cleaning in alkaline solutions,
acid dipping to neutralize or acidify the wet surface of the
parts, followed by electroplating, rinsing to remove the
processing solution from the workpiece, and drying.
Electrolytic corrosion process that increases the percentage
of specular reflectance from a metallic surface.
Electrostatic Precipitation
Use of an electrostatic field for precipitating or rapidly
removing solid or liquid particles from a gas in which the
particles are carried in suspension.
Heavy Metals
231
-------
Metals which can be precipitated by hydrogen sulfide in acid
solution, e.g., lead, silver, gold, mercury, bismuth,
copper, nickel, iron, chromium, sine, cadmium, and tin.
Hot Dipping
A method of coating one metal with another to provide a
protective film.
Hydrogen, Embr|,ttleme nt
Embrittlement of a metal or alloy caused by absorption of
hydrogen during a pickling, cleaning, or plating process.
Immersion Plate
A metallic deposit produced by a displacement reaction in
which one metal displaces another from solution, for
example:
Fe + Cu++ Cu * Fe++
Independent
Job shop or contract shop in which electroplating is done on
workpieces owned by the customer.
Integrated chemiqal Treatment
A waste treatment method in which a chemical rinse tank is
inserted in the plating line between the process tank and
the water rinse tank. The chemical rinse solution is
continuously circulated through the tank and removes the
dragout while reacting chemicals with it.
Ion-Flotation Technique
Treatment for electroplating rinse waters (containing
chromium and cyanide) in which ions are separated from
solutions by flotation.
Iridite Dip Process
232
-------
Dipping process for zinc or zinc coated objects that
deposits an adherent protective film that is a chrome gel,
chrome oxide or hydrated chrome oxide compound.
Phosphatizing
Process of forming rust- resistant coating on iron or steel
by immersing in a hot solution of acid manganese, iron, or
zinc phosphate.
An acid solution us«d to r«mov« oxides or other compounds
related to the basis metal from its surface of • metal by
chemical or electrochemical action.
Pickling
The removal of oxides or other compounds related to the
basis metal from its surface by immersion in a pickle.
Point Source
A single source of water discharge such as an individual
plant.
precious petals
Gold, Silver, Platinum, etc.
Electroplating of workpieces on racks.
Reverse osmosis
A recovery process in which the more concentrated solution
is put under a pressure greater than the osmotic pressure to
drive water across the membrane to the dilute stream while
leaving behind the dissolved salts.
Rochell salt
233
-------
Sodium potassium tartrate: KNaCUH4O6 . 4H20.
Shot Peening
Dry abrasive cleaning of metal surfaces by impacting the
surfaces with high velocity steel shot.
Sludgy
Residue in the clarifier of a chemical waste treatment
process.
Strike
nnAAi 7 a thin coafcing of metal (usually less than
0.0001 inch in thickness) to be followed by other coatings.
(2) noun - a solution used to deposit a strike. (3) verb
- a plate for a short time, usually at a high initial
current density.
Stripping
Removal of an electrodeposit by a chemical agent or reversed
electrodeposition.
Workpiece
The item to be electroplated.
234
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to
en
MULTIPLY (ENGLISH UNITS)
English Unit
Abbreviation
Conversion Table
by
Conversion
TO OBTAIN (METRIC UNITS)
Abbreviation Metric Unit
acre
acre - feet
British Thermal Unit
British Thermal Unit/pound
cubic feet/minute
cubic feet/second
cubic feet
cubic feet
cubic inches
degree Fahrenheit
feet
gallon
ga 1 Ion/minute
horsepower
inches
inches of mercury
pounds
million gallons/day
mile
pound/square inch (gauge)
square feet
square inches
tons (short)
yard
ac
ac ft
BTU
BTU/lb
cfm
cfs
cu ft
cu ft
cu in
op
ft
gal
gpm
hp
in
in Hg
Ib
mgd
mi
psig
sq ft
sq in
ton
yd
0.405
1233.5
0.252
0.555
0.028
1.7
0.028
28.32
16.39
0.555(°F-32)*
0.3048
3.785
0.0631
0.7457
2.54
0.03342
0.454
3785
1.609
(0.06805 psig+1)*
0.0929
6.452
0.907
0.9144
ha
cu m
kg cal
kg cal/kg
cu m/rein
cu m/min
CU Bt
1
CU On
°c
m
1
I/sec
kv
cm
atir.
kg
cu m/day
kra
atm
sq n>
sq cm
kkg
n>
hectares
cubic meters
kilogram - calories
kilogram calories/kilogram
cubic meters/minute
cubic meters/minute
cubic meters
liters
cubic centimeters
degree Centigrade
meters
liters
liters/second
kilowatts
centimeters
atmospheres
kilograms
cubic meters/day
kilometer
atmospheres (absolute)
square meters
square centimeters
metric tons (1000 kilograms)
meters
Actual conversion, not a multiplier
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