f/EPA
United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Research Triangle Park NC 27711
EPA-600/7-79-025b
January 1979
Fuel Contaminants:
Volume 4.
Application of Oil
Agglomeration to Coal
Wastes
Interagency
Energy/Environment
R&D Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
RESEARCH AND DEVELOPMENT series. Reports in this series result from the
effort funded under the 17-agency Federal Energy/Environment Research and
Development Program. These studies relate to EPA's mission to protect the public
health and welfare from adverse effects of pollutants associated with energy sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses of the transport of energy-related pollutants and their health and ecological
effects; assessments of, and development of, control technologies for energy
systems; and integrated assessments of a wide-range of energy-related environ-
mental issues. . .
EPA REVIEW NOTICE
This report has been reviewed by the participating Federal Agencies, and approved
for publication. Approval does not signify that .the contents necessarily reflect
the views and policies of the Government, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161. .
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EPA-600/7-79-025b
January 1979
Fuel Contaminants:
Volume 4.
Application of Oil Agglomeration
to Coal Wastes
by
E.J. Mezey, Seongwoo Min, and Dale Folsom
Battelle-Columbus Laboratories
505 King Avenue
Columbus, Ohio 43201
Contract No. 68-02-2112
Program Element No. EHE623
EPA Project Officer: Lewis D. Tamny
Industrial Environmental Research Laboratory
Office of Energy, Minerals, and Industry
Research Triangle Park, NC 27711
Prepared for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Washington, DC 20460
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DISCLAIMER
This report has been reviewed by the Industrial Environmental
Research Laboratory, U.S. Environmental Protection Agency and approved
for publication. Approval does not signify that the contents necessarily
reflects the views and policy of the Agency, nor does mention of trade
names or commercial products constitute endorsement or recommendations for
use.
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ABSTRACTS
In the first phase of this program, the utility and limitations
of the oil agglomeration technique for removing sulfur and trace element
contaminants in coal were identified from the literature. Although the
technique was found to be effective for the separation of much of the ash
forming mineral matter from finely ground fresh coal, it was found to be
almost ineffective for the separation of the liberated pyrite. No report
could be found of the use of this technique for the recovery of coal
values from coal cleaning plant wastes or for the control of effluents
from such cleaning plants.
This program was undertaken to investigate the feasibility of
the oil agglomeration technique for the recovery of coal values from
preparation plant wastes and thereby possibly reducing the environmental
consequences of coal cleaning plant effluents. The program also found
several approaches for the enhancement of pyrite removal during oil
agglomeration of freshly ground coal.
The following environmentally significant accomplishments and
extension of the state of the art resulted from this study:
• Coal recoveries of 90 percent or greater were
realized from sediments from fresh, aged and weathered
cleaning plant (i.e., slurry pond) wastes.
• The total sulfur and ash concentrations of the coal
recovered from wastes were lower than the coal being
shipped from the cleaning plant.
• The rejected mineral matter was essentially free of
coal, exhibits improved settling characteristics and
appears to be suitable for land disposal and may
have potential as a raw material.
iii
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• Recovered coal costs based on hypothetical flow
diagram based on results from the study were estimated
at $14 per ton.
o Various oils were found to be effective including
coal derived liquids.
• - For the first time using the oil agglomeration
technique, pyrite removal from freshly ground coal
was enhanced by mild chemical treatment and the use
of a dispersing agent to levels attainable by float
sink analysis.
Benefits that might be realized by the adaptation of the oil
agglomeration technique by the coal industry include the following:
• Reduces the hazards and environmental impact of exist-
ing coal slurry ponds.
• Recovers valuable resources from wastes.
• Allows environmental control of effluents from coal
preparation plants faced with increased throughput
to meet energy needs and environmental constraints.
• Applicable to coal preparation plants used to
prepare feed for coal conversion plants.
• Dewaters wet coal fines. /
• Permits direct application of technology developed •
for clay stabilization to residues.
• In principle, may reduce risks of catastrophic
dam failure when used as a replacement for raw wastes.
IV
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CONTENTS
Abstracts
Figures vi
Tables vii
1. Introduction 1
Objective 2
Background 2
Coal Slurry Ponds ' 4
2. Conclusions 8
3. Recommendations 10
4. Experimental Procedures j.1
Sample Acquisition, Handling and Characterization .... 12
General Oil Agglomeration Procedure 19
5. Results 21
Coal Recovery from Sediments 21
Residue Characterization 47
Enhancement of Pyrite Removal 56
6. Discussion 75
Coal Recovery from Waste Streams 75
Preparation of Coal Feed to Liqeufaction Plants .78
Enhancement of Pyrite Removal 79
Estimation of Product Cost 79
References 84
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FIGURES
Number Page
1 Flow diagram of the NACCO Mining Company coal preparation
plant, Alledoma, Ohio 14
2 Influence of aged slurry sediment concentration and kerosene
concentration on (a) material recovery, (b) ash in recovered
coal and (c) percentage of coal recovered 25
3 Influence of aged sediment slurry concentration and tetralin
concentration on (a) material recovery, (b) ash in
recovered coal and (c) percentage coal recovered 26
4 Influence of aged .coal sediment slurry concentration and oil
concentration on (a,d) material recovered, (b,e) ash in
recovered coal and, (c,f) percentage coal recovered 30
5 Influence of fresh black water sediment slurry concentration
and No. 6 fuel oil-kerosene mixture (12:88 volume ratio) on
(a) material recovery, (b) ash recovered coal and (c) per-
centage coal recovered 38
6 Settling rates for 10 percent slurry of aged sediments and
the residue after removal of coal values by agglomeration
(20 percent kerosene concentration) 49
7 Settling rates for 10 percent slurry of fresh black water
sediment and the residue after removal of coal values by
agglomeration (20 percent kerosene concentration) bulk
density after 3 day = 1.14 g/cc 50
8 Calibration curve for determination of oil content by
CC14—extraction 52
9 Equipment for chemical pretreatment of a coal slurry .... 62
10 Equipment for electrolytic pretreatment of coal slurry ... 67
11 Flow diagram of oil agglomeration process - . . 81
VI
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TABLES
Number ' Page
1 Analysis of Sludges from Drill Holes Taken by Bureau of
Mines at Inactive Coal Slurry Ponds in West Virginia .... 6
2 Sieve Analysis of Illinois No. 6 Coal Samples
After Grinding 12
3 Analysis of Illinois No. 6 Coal Samples 13
4 Characteristics of Aged and Fresh Sediments from Jig
Washing Operation of Ohio Pittsburgh Seam No. 8 (Deep
Mined) 16
5 Characteristics of Partially Dried Old Coal Sediments
from Southwestern Ohio 17
6 Analysis of Coal Samples from Coal Cleaning Plant
Pittsburgh Seam No. 8 Ohio, Belmont County 18
7 Experimental Results of Coal Recovery from Aged Sediments
Using Kerosene 23
8 Experimental Results of Coal Recovery from Aged Sediments
Using Tetralin 24
9 Experimental Results of Coal Recovery from Aged Slurry Pond
Sediment Using a Mixture of No. 6 Fuel Oil and Kerosene
(12:88 Volume Ratio) 28
10 Experimental Results of Coal Recovery from Aged Slurry Pond
Sediment Using No. 2 Fuel Oil 29
11 Effect of Oil Concentration on Ash and Sulfur Content of Coal
Recovered from Aged Sediment (All 10 Percent Slurry Concen-
trations) 31
12 Ash and Sulfur Content of Coal Recovered from Aged Slurry.
Pond Sediment 33
13 Effect of Agitating Speed and Retention Time on Agglomera-
tion of Aged Slurry Pond Sediment with Emulsified Kerosene . 34
vn
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TABLES - (Continued)
Number Page
14 Effect of Flocculation Agent on Agglomeration of Aged
Slurry Sediments (10 Percent Slurry) 35
15 Experimental Results of Coal Recovery from Fresh Black Water
Sediment Using No. 6 Fuel Oil and Kerosene Mixture (12:88
Volume Ratio) 36
16 Experimental Results of Coal Recovery from Fresh Black Water
Sediment Using Various Oils . . 40
17 tAsh and Sulfur Content of Coal Recovered from Black Water
Sediments 41
18 Effect of Agitating Speed and Retention Time on Agglomera-
tion of the Fresh Black Water Sediment with Kerosene .... 41
•19 Effect of Successive Washing on Agglomeration of Partially
Dried Old Coal Sediment 43
20 Effect of Dispersing Agent on Agglomeration of Unwashed
Partially Dried Old Coal Sediment 43
21 Effect of Single Wash of Sediments, pH Adjustment and Low
Level Sodium Silicate Additions Before Agglomeration on Coal
Recovery from Partially Dried Old Sediments 45
22 Comparison of Agglomeration Behavior of Segregated Lumps of
Loose Material Found in Partially Dried Old Coal Sediment . . 46
23 Analysis of Residues from Agglomeration 51
24 Amount of Oil Lost to the Residue Slurry During Agglomeration
of the Aged Slurry Sediment 54
25 Effect of Secondary Washing of Coal Recovered by
Agglomeration 55
26 Results of Chemical Pretreatment at 25 C on Pyrite Separation
from Illinois No. 6 Coal During Agglomeration (25 Grams
Coal in 225 Grams Water 58
27 Effectiveness of Depressants for Removal of Pyrite from
Illinois No. 6 Coal During Agglomeration Compared to Results
from Float-Sink Analysis 59
28 Effect of Aqueous Oxidation Pretreatment on Pyrite Removal
During Oil Agglomeration of Illinois No. 6 Coal 63
Vlll
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TABLES - (Continued)
Number Page
29 Effect of Aqueous Oxidation Pretreatment on Pyrite Removal
During Oil Agglomeration of Ohio Pittsburgh Seam No. 8 Coal . 64
30 Effect of Electrolysis on the Pyrite Removal During Oil
Agglomeration of Ohio Pittsburgh Seam No. 8 Coal (Without
Thimble)- 68
31 Effect of Electrolysis on Pyrite Removal During Oil Agglomer-
ation of Ohio Pittsburgh Seam No. 8 Coal (With Thimble) ... 69
32 Effect of Microwave Treatment on Pyrite Removal During Oil
Agglomeration of Ohio Pittsburgh Seam No. 8 Coal 71
33 Effect of Chemical Reagent on Pyrite Removal During Oil
Agglomeration of Ohio Pittsburgh Seam No. 8 Coal 73
34 Effect of Combined Treatment on Oil Agglomeration of Ohio
Pittsburgh Seam No. 8 Coal 74
35 Comparison of Quality of Coal Recovered from Sediments to
Cleaned Coal 77
36 Material Costs for Oil Agglomeration Process 82
ix
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SECTION 1
INTRODUCTION
In the first phase of the program on fuel contaminants a review
was made of the utility and limitations of several technologies reported
in the literature for the removal, before combustion, of contaminants in
coal that produce pollutants when coal is utilized as a fuel. The oil
agglomeration technique was one of those that appeared to have the potential
for the removal of trace elements and under special conditions the physical
removal of pyritic sulfur liberated from coal during grinding. The results
of the review also suggested that the technique might be used to clean up
coal slurry pond sediments accumulated during coal cleaning plant operations
by removing the coal values they contain. The two areas are related in that
pyrite removal from old coal slurry pond sediments is enhanced by the auto-
trophic bacterial actions on the surface of pyrite that are supported in
these sediments. Understanding the cause of these effects could be
useful for developing a technique for removing pyrites from freshly ground
fine coal slurries by oil agglomeration. Conversely, any technique developed
to enhance pyrite removal from fresh coal could in effect be used to speed
up natures process and the recovery of low pyrite coal from coal waste
streams, both fresh and aged.
This report presents the experimental results which extend the
state of the art of oil agglomeration to the recovery of coal from coal
cleaning plant wastes and the removal of pyrite from freshly ground coal to
V
the extent that they can be removed during float-sink analysis. In this
program, both an Illinois No. 6 coal and an Ohio Pittsburgh Seam Number 8
coal were investigated.
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OBJECTIVE
The objectives of this study were to determine the feasibility of
coal recovery from coal cleaning plant wastes by immiscible fluid agglomera-
tion technique and to evaluate the effects of physical and chemical treat-
ments on enhancement of pyrite removal during agglomeration of these wastes
and fresh coal.
BACKGROUND
Water immiscible liquids, usually hydrocarbons, have been used to
separate coal from its impurities. In principle it is an extension of
principles of froth flotation where the hydrocarbons wet the hydrophobic sur-
face of coal and the mineral impurities which are mostly hydrophilic remain
in aqueous suspension. Separation of the two phases takes place after
agglomeration or coalescence occurs and produces agglomerates of clean coal
containing the oil and an aqueous suspension of the mineral matter nearly
free of combustible material. Effective separation can be made with coal
with a size of minus 28 mesh (0.590 mm) and often with sizes too small for
any other recovery scheme. Hydrocarbon fluids such as kerosens and fuel
oils have been found very effective for the separation of the mineral
matter from finely divided coal suspended in an aqueous slurry (i.e., reduce
ash). The selective agglomeration process is attractive because the coal
does not have to be dried after wet face mining, wet size reduction and
conventional coal preparation operations. In addition the agglomerated
coal can be readily dewatered by mechanical action providing energy trade-
offs between oil use and drying.
The major limitation of the process as it was used in the past is
that removal of pyrite is poor due to the similarity of its surfacial
properties to those of coal and the fact that in some coals pyritic sulfur
is uniformly disseminated in the coal and is present in the size range of
0.5 to 20 micrometers. Extensive size reduction, use of known pyrite
depressants, bacterial action etc. have found only limited success in
reducing the pyritic sulfur content. Nonetheless the process has the
potential of removing the trace elements commonly associated with the mineral
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matter in coal in a form that they exist in nature and rendering these
species amenable'for safe disposal.
The amount of mineral matter removed can be increased with size
reduction. In general, pyrites are also released from the coal during size
reduction but they are not readily removed by the agglomeration process.
To reject them from the oil phase into the aqueous phase, their surface
properties or composition must be altered to make them hydrophilic. The
common pyrite depressant reagents developed for metallurgical froth
flotation separations were founcl to be only partially successful for enhanc-
ing pyrite removal during agglomeration.'^>^) Recent studies on Iowa coals
by Min' ' suggested approaches that might be used to alter the pyrite in
other coals. He found that chemically pretreating pulverized coal in a
manner designed to oxidize the surface of the pyrite (to render it hydro-
philic) was more effective than the application of pyrite depressants. The
pretreatment involved sparging a slightly alkaline aqueous slurry of
a coal with air at 80 C. (The best pretreatment was the use of 0.5 g
each of Na?CO^ and Ca(OH)2 with 100 g of coal in 500 ml ^0 for 30 minutes
which resulted in about a 42 percent reduction in total sulfur.) Min also
reported on other physical treatment sequences for the desulfurization
of coal.^ ^ The most effective treatment sequence involved chemical comminu-
tion, float and sink separations at a specific gravity of 1.6, pulverizing
and grinding the float fraction -and recovery of the fine-size coal by
agglomeration. Coal recovery was 82-84 weight percent with a reduction in
pyritic sulfur of 85 to 86 percent. Optimum conditions identified for Iowa
coals in the study might not be applicable to coals from other regions such
as Appalachian coals.
Other studies on the theoretical aspects of coal cleaning by oil
agglomeration and laboratory, bench and pilot scale studies on ash removal
(4-6) (4)
and dewatering have been recently reported. Capes, et al. pointed
out that the utility of oil agglomeration of coal fines will increase as more
mechanized mining of progressively poorer grades of coal develop. Increased
percentages of fines will end up in the waste streams from the coal prepara-
tion plants (black water). Usually these wastes are impounded for long term
settling before the water is discharged.
Several research organizations have become involved in developing
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oil agglomeration methods. The U.S. Bureau of Mines, Pittsburgh Energy
Research Center (PERC) concluded that excellent recoveries of low ash coal
were possible both in a laboratory unit and a 500 pound-per-hour pilot plant
(7)
but that sulfur reduction was negligible. PERC is presently not active
in the further demonstration of the use of agglomeration although a joint
/ Q \
effort with Jones and Laughlin Steel Co. had been attempted in 1977 .J
Bergbau-Forshung, GMBH, of West Germany, has developed the OLIFLOC
process for recovery of ultra-fine coal (minus 230 mesh) in a 3- ton-per-hour
pilot plant. ' Two, 30 ton-per-hour plants were installed during 1977.
The Central Fuel Research Institute of India has also investigated oil
agglomeration of a 25 percent ash coal in order to optimize processing con-
ditions. This fine coal, which was not amenable to economical cyclone
washing or froth flotation, could be upgraded by oil agglomeration. A
2 ton-per-hour agglomeration unit has been installed for upgrading a coal
slurry from the Lodna washery of the Bharat Coking Coal, Ltd. in India.*- '
In Australia, the Broken Hill Proprietary Company, Ltd. have published the
results of their studies on the process parameters controlling selective
agglomeration of raw coal slurry in their pilot facility. They found
that agglomerates produced in a continuous process are considerably larger
than those obtained from batch experiments.
Of these reports only a small amount of work was reported on
improving pyrite removal during agglomeration and only one suggested the
potential of the process to recover coal from fresh, aged or weathered sedi-
ments from coal slurry ponds.
COAL SLURRY PONDS
On February 26, 1972 a coal waste embankment failed near Saunders,
West Virginia. The resulting flooding of the Buffalo Creek Valley took the
lives of 125 people and destroyed over 500 homes in addition to extensive
damage to other properties in the valley. Immediately after this disaster
a special U.S. Department o'f Interior Task force began investigations into
the coal waste hazards problem. Its objectives were to determine modes of
failure of such embankments and to develop means for safe disposal of coal
waste materials. The coal was.te materials originated from preparation plants
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at the mine sites. In early findings published by the Bureau of Mines,
Busch reported that the preparation plants that fed the refuse piles studied
ranged from being relatively simple to extremely complex.
Since the early 1960's, the coal industry has been under constant
pressure by environmental legislation to clean up liquid discharges into
streams. Consequently, rather large sludge (slurry) ponds have been
developed which consist of fine coal, fine soil and water. These ponds are
usually formed behind large piles of coarse coal waste which together make
up the often criticized coal waste impoundments. The Bureau of Mines has
reported on the physical and chemical properties of fine coal wastes in two
(I7)
of these ponds. The ponds selected for their study were inactive and
partially drained. Core samples were taken from regions in the slurry ponds
where saturated fine sludge accumulated at the points farthest from the
discharge lines. The analysis of 'the sediments from the different areas in
West Virginia Are given in Table 1.
The amount of coal in the slurry pond sediments varies depending
on the effectivenss of the coal cleaning operation. The Bureau of Mines
study concluded that the extremely fine size (50 percent by weight less than
2-10 micrometers) plus rather well graded grain sizes make permeability low
and the sediments extremely difficult to drain. They suggested that the ash
and Btu per pound of the dried sediment make it equivalent to the sub-
bituminous coal range (9,000 Btu/lb) and the hazards of waste embankments
may be resolved by utilization of the waste as a fuel. Direct recovery of
the sludge without beneficiation is currently being practiced. Certainly
recovery of the material becomes more attractive as coal costs rise. The
high ash content is not attractive to most users, however, upgrading the
waste could open new markets. If the beneficiation removes pyritic sulfur
as well, the product would be even more attractive. The immiscible fluid
agglomeration technique has the potential of removing most of the ash
values. If pretreatment is used to enhance pyrite separation during
agglomeration, a fuel with reduced sulfur (and ash) might be realized.
Other physical separation techniques (e.g., Humphreys Spiral)
have been investigated as a means reducing the ash content at the Mine
Resources Institute and Experiment Station at the University of Alabama.
In waste streams from the simpler coal preparation plants employing
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TABLE 1. ANALYSIS OF SLUDGES FROM DRILL HOLES TAKEN BY
BUREAU OF MINES C.12) AT INACTIVE COAL SLURRY
PONDS IN WEST VIRGINIA
Analysis, percent BDH-1 WDH-1
Moisture 35.0 55.4
Moisture Free:
Ash 25.5 32.3
Moisture and Ash Free:
Hydrogen 4.9 4.8
Carbon 83.6 82.8
Nitrogen 1.3 1.2
Oxygen 9.2 10.5
Sulfur 1.0 0.7
Heat content, moisture free Btu/lb 10,690 9,600
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screening, jigging and tabling (no flotation) the undersize fraction, often
finer than 0.25 inch, is rejected resulting in 10 to 15 percent loss of the
coal processed. The author of the report estimated that an aggregate of
1 million tons of coal is wasted annually in fines impounded near" coal washing
plants located at strip mines in Alabama. Typically the ash values for the
samples of the waste which ranged between 9 and 50 percent were reduced to 5 to
12 percent ash product with about a 90 percent coal recovery. In this
process, however, only the plus 200 mesh material was treated and the minus
200 mesh was discarded.
In an assessment of the feasibility of returning underground coal
mine wastes to mined-out areas, a National Science Foundation report
estimates "the total number and volume of sizable active and abandoned waste
piles and impoundments in the eastern coal fields alone is at 3000-5000 cum-
mulatively containing 3 billion tons of refuse " (not all of which are coal
(14)
slurry pond sediments). In effect the impoundments containing coal fines
are a ready reserve of mined fuel wherein the mining costs have already been
factored in, which can be utilized in times of shortages. In addition the
reduction of the size and number of the slurry ponds would reduce the
hazards and the potential for environment encroachments bv these slurry
ponds. As energy goals of the Nation are met by increased mining, and
greater volumes of coal passing through preparation plants to meet
established emission standards, methodology to recover the coal values
preparation plant tailings and slimes would appear to be an essential part
of the overall program to increase the availability of the Nation's coal.
Most approaches to clean fuels from coal appear to be directed
toward conversion processes (gasification and liquefaction), which requires
the preparation of a finely ground coal feed stock (-200 mesh). It
appears that oil agglomeration processes could contribute significantly to
the removal of contaminants before the conversion process is undertaken. In
addition to this, the ability of agglomeration technique to dewater finely
ground wet coal suggests further incorporation of this process in any
environmentally sound preparation plant supplying these conversion plants.
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SECTION 2
CONCLUSIONS
This study has demonstrated that coal recoveries of 90 percent or
greater are attainable from fine coal slurry wastes using the oil agglomera-
tion technique. These high levels of recovery are attainable from fresh
black water sediments generated during coal cleaning, aged sediments
accumulated in slurry ponds and excavated, weathered, and partially dried
slurry pond sediments. The quality of the coal was good and had lower ash
and sulfur content than the coal shipped from the mine.
The residue from the agglomeration process contained between 2 to
5 percent of the oil used in agglomeration and very little coal, i.e.,
90 percent ash or greater. The residue suspension obtained after agglomera-
tion settled more rapidly than the original slurry. The residue material
appears to be well suited for land disposal.
The experimental results suggest the following environmental and
conservation advantages of the agglomeration process based on these current
results and on understanding of the relationships between various contami-
nants, mineral matter and organic matter.
• Recovered coal contains lower ash and reduced sulfur
(and trace heavy metals) than the parent coal.
• Recovered coal is easily dewatered and the product
remains dust free.
o Volumes of waste from coal cleaning facilities can be
significantly reduced resulting in less impoundment and
thus less land utilization.
• Waste characteristics are improved since they are faster
settling, more compatible with soil since they are not
altered, and less prone to support bacterial activity
that cause acid drainage.
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• Rather than disposal of the concentrated mineral
matter it may be amenable as a raw material for
ceramics, cement and other construction purposes or
for the recovery of useful mineral values such as
alumina.
Coal derived liquids such as the distillate) recovered from SRC
dissolver product is able to yield 90 percent or greater coal recoveries.
Its behavior is not any different than that of the petroleum derived liquids
such as No. 2 fuel oil, No. 6 fuel oil-kerosene mixture and kerosene alone.
With regard to the enhancement of pyrite removal during agglomer-
ation, use of sodium metaphosphate will remove 42 percent of the pyritic
sulfur from freshly ground minus 48 mesh coal. This is the same as that
obtained by float-sink analysis suggesting removal of all" the liberated
pyrite in the ground coal. Equally good results were obtained when a coal
slurry was treated with oxygen in the presence of sodium carbonate at 25 C.
These same treatments could be applied to black water and slurry pond
sediments to enhance pyrite removal during coal recovery.
An estimation of the product cost recovered from agglomeration
step as an add-on to an existing coal cleaning plant or as a portable
facility is about $14/ton.
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SECTION 3
RECOMMENDATIONS
Based on results of this study, it is recommended that the oil
agglomeration technique be further developed as a method to control effluents
from coal cleaning plants in^order to reduce the hazards and environmental
impact of increased quantities of wastes that would result as the Nation
shifts its energy dependence to coal and strives for the production of clean
fuels in an environmentally sound manner. Further work is needed to
demonstrate the applicability of the process to various origins of coal.
•wastes and the effluents from coal cleaning plants with varying degrees of
complexity. The development of a bench scale process suitable for the
treatment of- both sediments and black water effluent should also be under-
taken.
10
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SECTION 4
EXPERIMENTAL PROCEDURES
SAMPLE ACQUISITION, HANDLING
AND CHARACTERIZATION
For Studies on Enhancement of Pyrite Removal
Two samples of a drift mined Illinois No. 6 coal (Seam No. 6,
Mine No. 10) and on Ohio deep mined Pittsburgh Seam No. 8 coal were used in
the study. The Pittsburgh Seam No. 8 coal is characterized later.
The samples of Illinois coal had been jig washed at the mine and
'part was ground to pass through a 14 mesh (1.19 mm) screen (Tyler). The
other part was used to prepare a minus 48 mesh (0.297 mm) coal. The sieve
analysis of both sized coals are given in Table 2. The analysis for the
two coal sizes and the analysis of a second sample of Illinois No. 6 coal
also used in this study are given in Table 3. Included in the table are the
analyses of the products from the float-sink analysis at 1.9 specific
gravity. The values are given on a moisture free (MF) and moisture and ash
free (MAF) basis.
For Studies on Coal Recovery from
Slurry Pond Sediments
The coal and coal slurry pond sediments were obtained from the
North American Coal Company preparation plants in Belmont County, Ohio. The
coal being processed at the site is deep mined from Pittsburgh Seam No. 8
using room and pillar techniques. The plant is rated at 600 TPH and cleans
run-of-the-mine coal (minus 8 inch) using primarily jig washing, classifying
cyclones, spiral classifiers and filters. , A block diagram of the operation
is given in Figure 1. Waste process water is settled in a large, static
thickener and the underflow is discharged into & slurry pond. A new pond
was started in 1976 and the old one was used from 1972 to 1976.
11
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TABLE 2. SIEVE ANALYSIS OF ILLINOIS NO. 6 COAL SAMPLES
AFTER GRINDING
Sieve Mesh
Range (Tyler)
Minus 14
(~67 percent minus
+14
-14 +28
-28 +48
-48 +65
-65 +80
-80 +100
-100
Minus 48
(~60 percent minus
+48
-48 +65
-65 +80
-80 +100
-100 +150
-150 +200
-200
Percent
Mesh Coal
28 mesh [0.
0.05
33.55
26.43
8.94
3.39
3.49
24.15
Mesh Coal
100 mesh [0
0.24
8.71
8.48
9.26
14.29
11.38
47.65
Cumulative
Percent
595mm])
0.05
33.60
60.03
68.97
72.36
75.85
100.00
.149 mm])
0.24
8.95
17.43
26.69
40.97
52.35
100.00
12
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TABLE 3. ANALYSIS OF ILLINOIS NO. 6 COAL SAMPLES (Weight Percent)
Coal Sample
Minus 14 Mesh
Fraction at
Float (94.
Sink (5.9
U)
Minus 48 Mesh
Fraction at
Float (93.
Sink (6.7
Minus 48 Mesh
(1.19 mm)
1.9 Sp. gr.
1 percent)
percent)
(0.297 mm)
1.9 Sp. gr.
3 percent)
percent)
(0.297 mm)(c)
MAF
-------
Co«r«« Cl««n Co«l (1-1/4" » 0)
l*v Co.l
(6" ..0)
• Staple •!!••
FIGURE 1. FLOW DIAGRAM OF THE NACCO MINING COMPANY COAL PREPARATION PLANT, ALLEDOMA, OHIO
-------
Coal Slurry Sediments—
Five-gallon samples representative of the thickener underflow were
taken in the plant. A sample of sediments was taken from the inactive pond
in a region exposed to air near where water was draining into rivulets
passing over the settled coal. The sample was taken to the depth of about
18 inches (0.5 meter) of an estimated depth of 3 feet (1 meter) using a
conically shaped sludge dipper. Water from the inactive pond near the
sampling point was added to the solids for bacterial culture development.
A third sample of coal slurry pond sediment was obtained from a 5 year old
pile from the excavation of an inactive slurry pond at the site of NACCO
No. 5 mine. Samples of the cleaned coal being shipped from the No. 6 mine
and the fine coal from the thermal drier before it is mixed with coarser
clean coal were obtained and analyzed.
The wet slurry samples were stored in polyethylene lined 5-gallon
buckets under a nitrogen atmosphere. After a 7-day period of settling, the
/
solids and liquids levels were measured to estimate the sediment and
supernatant volumes. After .the supernatant water was removed the sediment
was weighed to determine its specific gravity. The solids content of the
slurries are given in Table 4 along with the moisture-free ash content. The
results of analyses for total sulfur, pyritic sulfur and sulfate sulfur are
also given on a moisture and ash free (MAP) basis. The supernatant water
from the inactive pond had a pH of 7.3 while the supernatant water from the
fresh sediment (black water) had a pH of 7.0.
A wet screen analysis of each of the sediments was made. The
aged sediment was 77. percent minus 100 Tyler mesh (0.149 mm) while the
fresh sediment was 89 percent minus 100 mesh. (NACCO attributed the differ-
ence in the size to the use of new hydroclones which have enabled the plant
to improve separation of the coal fines from fresh sediments of the thickener
underflow.) The consist of both sediments make it attractive for coal recov-
ery by agglomeration techniques since the size appears to be too small for
effective froth flotation recovery. Of equal significance is that the coal
content of the sediments were 50 percent or greater based on the ash values.
The partially dried aged sediments from No. 5 mine were charac-
terized in a similar manner in Table 5. ..It is richer in coal and total
and pyritic sulfur than the sediments from No. 6 mine. The slurry of the
15
-------
TABLE 4. CHARACTERISTICS OF AGED AND FRESH SEDIMENTS
FROM JIG WASHING OPERATION OF OHIO PITTSBURGH
SEAM NO. 8 (DEEP MINED)
Aged Sediment (Slurry Pond)
Composite: Sediment = 91.0 volume percent
Clear Water - 9.0 volume percent
(after seven days)
pH = 7.3
Sediment:
it: . Density -v. 1.3 g/cc
Solids = 64.1 percent
Ash =45.2 percent (MF)
Percent
Percent (MAF)
STOT
, 2.90
5.35
SPYR
1.52
2.81
fso,
0.04
0.07
Concist:
Direct Data, %
Tyler Mesh
+ 28
28 x 35
35 x 48
48 x 65
65 x 100
100 x 200
200 x 325
Weight
7.6
3.2
4.1
4.2
3.7
10.2
7.6
MF Ash
1-5.59
14.33
17.67
18 . 73
19.82
15.81
15.48
Weight
7.6
10.8
14.9
19.1
22.8
33.0 '
40.6
MF'-Ash
15.59
15.22
, 16.01
16.61
17.13
16.72
16.49
- 325 59.4 60.60 100.0 42.70
(77 percent minus 100 mesh)
Fresh Sediment (Black Water)
Composite: Sediment = 64.6 volume percent
Clear Water = 35.4 volume percent
pH = 7.0
Sediment: Density ^1.2 g/cc
Solids =41.7 percent
Ash = 50.8 percent (MF)
Concist:
Tyler Mesh
+ 28
28 x 35
35 x 48
48 x 65
65 x 100
100 x 200
200 x 325
-325
STOT SPYR SSO/.
2.30 1.27
4.73 2.61
Direct
Weight
3.3
1.5
1.7
1.8
2.4
5.3
5.0
79.0
Data, %
MF Ash
,8.55
17.74
20.36
18.28
18.97
13.87
10.72
53.30
0.09
0.18
Cumulative Data, %
Weight
3.3
4.8
6.5
8.3
10.7
16.0,
21.0
100.0
MF Ash
8.55
11.42
13.75
14.74
15 . 68
15.08
14.04
49.78
(89 percent minus 100 mesh)
16
-------
TABLE 5. CHARACTERISTICS OF PARTIALLY DRIED OLD COAL
SEDIMENTS FROM SOUTHWESTERN OHIO
Moisture
Ash
STot
SPyr
SSO;
Percent
17.4
26.6
3.76
1.61
1.18
Percent
32.2 (MF)
6.71 (MAF)
2.88 (MAF)
2.11 (MAF)
Sieve Analysis
Tyler Mesh
+28
28x35
35x48
48x65
65x100
100x200
-200
Direct
Weieht
3.32
4.46
7.14
6.49
9.02
14.01
55.56
Data, %
MF Ash
6.71
8.79
10.95
13.51
15.51
16.01
44.09
Cumulative
Weight
3.32
7.78
14.92
21.41
30.43
44.44
100.00
Data, %
MF Ash
6.71
7.90
9.36
10.62
12.07
13.31
30.41
(69 percent minus 100 mesh)
17
-------
aged sediment had a pH of 2.9. The size of the material as determined by
wet sieve analysis was 69 percent minus 100 mesh. The ash contained in each
fraction was also determined. It was the waste from a preparation plant
that used only a double cell jig operating at a water slurry specific-
gravity of 1.6. The slurry was accumulated in the pond for a period of
6 to 9 months and allowed to settle for 3 months. The sediment was then
excavated and stacked in piles for drainage. This sample was taken from a
pile that was about 5 years old and exposed to air for the period. The
concists of the sediments reflect the simpler coal cleaning operation and
reduced fine coal recovery.
Coal Samples—
Samples of coal were obtained that are representative of the
coarse coal shipped from the coal cleaning plant and also a sample of the
thermally dried fine coal that is added back to the coarse coal before ship-
ment (see Figure 1). A I/64th cut of the coals were submitted for analysis
and the results are given in Table 6. The 1/2 cut was ground in a hammer-
mill to a size to pass through Tyler 48 mesh (minus 0.215 mm). The ground
sample was stored under nitrogen until it was used.
TABLE 6. ANALYSIS OF COAL SAMPLES FROM COAL CLEANING PLANT
PITTSBURGH SEAM NO. 8 OHIO, BELMONT COUNTY^
Analysis, percent
Moisture
As Shipped 3.91
—
Dried Fines 1.67
Ash S Total S Pyritic
8.88 4.26 1.78
9.24 (MF) 4.88 (MAF) 2.04 (MAF)
4.68 4.41 1.57
9.84 (MF) 4.97 (MAF) 1.77 (MAF)
(a) North American Coal Co. Mine No. 6, Belmont County.
18
-------
GENERAL OIL AGGLOMERATION PROCEDURE
The laboratory method for performing oil agglomeration experiments
have been described by Capes et al. and Min. The procedures used in
this study are very similar to theirs and are common to all experiments per-
formed in this study. A single speed laboratory Waring blender operating
at 15,000 RPM with water was used. The procedure consists of the following
steps.
1. A weighed sample of the dry fine coal (usually 25 g) is
mixed with enough water to give the selected slurry con-
centration and then agitated in the blender for a short
interval to give a slurry. When a wet sediment was used,
the water present in the sediment was considered when
preparing the slurry concentration desired.
2. An amount of oil was weighed out in a syringe to
give the oil concentration desired based on the dry
solids present and then added to the water coal slurry.
3. The mixture was blended for a period of time, usually
2.5 minutes.
4. After blending the mixture was allowed to stand for
about 15 to 30 seconds and then the mixture was poured
onto a 48 mesh screen to separate the agglomerated coal
from the suspended mineral matter. The separation was
aided by washing the agglomerated coal with a stream
of water from a wash bottle. The agglomerated coal was
transferred to a weighed Buchner funnel to remove
excess water. The mineral suspension passing through
the screen was collected in weighed dishes.
5. The agglomerated coal was dried at 60 C in a vacuum
oven and the water was evaporated from the mineral
slurry in air in an oven set at 110 C. The recovered
coal and mineral residue were weighed and analyzed,
usually for ash and the sulfur types.
Modifications of this procedure were incorporated into the study
and are identified in the discussions of the experiments where they were
made. For example, when the effect of pH was examined, the pH of the coal
19
-------
slurry was changed from the slurry pH by adding hydrochloric acid or sodium
hydroxide. The pH measured before the addition of the oil was taken as the
pH of the agglomeration. Chemical pretreatment of coal especially as it
relates to pyrite removal was done with enough coal to prepare three batches
for agglomeration treatment.
The experimental results that follow are divided into two major
areas. The first deals with the recovery of coal from sediments and the
second describes the results from experiments in which enhancement of pyrite
removal from fresh coal of the same source were investigated. Techniques
developed in this area could be applied to coal cleaning slurry pond sedi-
ments.
20
-------
SECTION 5
RESULTS
COAL RECOVERY FROM SEDIMENTS
This part of the study was undertaken to determine the applica-
bility of the oil agglomeration technique for the recovery of coal from fine
coal cleaning or coal preparation plant wastes. Wastes of three ages
were used in the study. The oldest was the sediment excavated from a slurry
pond about 5 years ago and had been partially dried (drained) in a heap as
part of an o.ngoing slurry pond reuse program. The youngest sediment inves-
tigated was the coal slurry waste stream from a thickener underflow which
was being discharged to a new pond. Finally, an intermediate age sediment
was typical of an inactive pond that had been in use for four years but
which still had not been excavated.
The objective of the study was to determine the optimum slurry
concentration, oil concentration and the oils suitable for the maximum recov-
ery of low-ash coal from the waste streams described above. In the case of
aged partially dried sediments, the study was to determine the most suitable
treatment needed to recover the maximum coal values. In addition, the effect
of processing variables such as the agitation speed of the blender, use of
flocculating or dispersing agents and added washing stages on coal recovery
were investigated. Finally the study was to characterize the residue after
agglomeration including some estimation of the oil carried with the residue.
Aged Slurry Pond Sediments
The wet aged slurry pond sediments were adjusted to slurry con-
centrations of 5, 10 and 15 percent. The oils used in the agglomerating
study were used at levels equal to 1.5, 3, 5, 10 and 20 weight percent of
the dried sediment. The oils used at these levels were'kerosene and
21
-------
tetralin and the results of the experiments undertaken to establish mixing
parameters are given in Tables 7 and 8. The mixing procedure described
earlier was used. As shown in Figure 2a and 3a, a 10 percent slurry concen-
tration when agglomerated with kerosene or tetralin at 3, 5 and 10 percent
oil concentration appears to give the best recovery of agglomerated material.
The recovery with kerosene was about 58 percent while with tetralin was
about 53 percent. These values are not exceeded during agglomeration using
an oil concentration of 20 percent. The ash in the coals recovered from 5
and 10 percent slurries (see Figure 2b) using 5, 10 and 20 percent oil con-
centrations were the lowest. The ash content of the coal ranged between
8.2 and 9.2 percent. The use of 1.5, 3 and 5 percent kerosene concentra-
tions gave coals with erratic ash content. The ash contents of the coals
recovered using tetralin were less erratic at the lower oil concentrations
(see Figure 3b). With 1.5 percent tetralin, the ash in the coal recovered
from the 5 and 10 percent slurry was between 6.5 and 7.2 percent. With 5
and 10 percent tetralin concentrations the ash content of the coal recovered
was between ..9.5 and 10.5 percent which is about 1 percent higher than that
obtained with kerosene.
The percentage of the coal recovered from the aged sediments was
estimated by the following:
n (100 - % Ash) , x (% of Feed) ,
Percentage _ product product
Coal Recovery ~ (100 - % Ash)feed
Using this estimation, kerosene at 10 and 20 percent oil concentrations gave
greater than 90 percent coal recovery for all three slurry concentrations
(Figure 2c). The coal at these recovery levels contained between 8.2 and
9.2 percent ash from an aged sediment that contained about 45.6 percent ash.
Tetralin at oil concentrations between 3 and 20 percent gave 80 to 96 per-
cent recovery. The ash content of these coals recovered using tetralin from
the same aged sediment as those recovered using kerosene, was between 9.5
and 10.5 percent. Coal recovery falls off for both kerosene and tetralin
at oil concentrations lower than 5 percent.
The results of these experiments indicated that the experiments
could be limited to the 3, 5 and 10 percent oil concentrations because of
the marginal results at 1.5 percent and the small incremental gains at
22
-------
TABLE 7. EXPERIMENTAL RESULTS OF COAL RECOVERY FROM AGED SEDIMENTS USING KEROSENE
ho
U)
Run
51-1
51-2
51-3
51-4
51-5
51-6
51-7
51-8
51-9
51-10
51-11
51-12
51-13
51-14
51-15
(a) Oil
th} Tnal
Agglomerating Conditions
Slurry Cone. ,
petcent
15
10
5
15
10
5
15
10
5
15
10
5
15
10
5
concentration
Coal Product
Oil Cone.. Percentage HF Ash, Coal Recovered,
percent'3' of Feed percent percent''')
20
20
20
10
10
10
5
5
5
3
3
3
1.5
1.5
1.5
based on weight
54.1
56.2
60.1
56.6
58.3
57.2
52.6
53.6
45.4
54.5
56.3
44.3
32.7
40.9
34.6
8.57
8.97
8.64
9.31
9.11
8.02
8.21
10.01
9.51
12.80
12.46
8.13
7.99
8.78
14,74
90.9
94.0
100. 9
94.4
97.4
96.. 7
88.8
88.7
75.5
87.4
92.7
74.8
55.3
68.6
54.2
Percentage
of Feed
45.9
.43.8
39.9
43.4
41.7
42.8
47.4
46.4
54.6
45.5
43.7
55.7
67.3
59.1
65.4
Residue
MF Ash,
percent
85.40
88.18
90.75
86.06
90.20
90.59
80.64
80.21
85.33
74.47
81.75
72.85
61.62
69.70
64.83
Ash Removed ,
percent
86.0
84'. 7
79.4
81.9
82.5
85.0
83.8
81.6
]02
74.3
78.3
89.0
90.9
90.3
92.8
of moisture free sediment.
(100 -
% ash) x %
product
of feed
(100 - % ash)
feed
(c) Value greater than 100 percent due to residual kerosene retained after drying.
-------
TABLE 8. EXPERIMENTAL RESULTS OF COAL RECOVERY FROM AGED SEDIMENT USING TETRALIN
Run
46-1
46-2
46-3
46-4
46-5
46-6
46-7
46-8
46-9
46-10
46-11
46-12
46-13
46-14
46-15
(a) Oil
(b) Coal
Agglomerating Conditions - -
Slurry Cone. ,
percent
15
10
5
15
10
5
15
10
5
15
1.0
5
15
10
5
concentration
1 rppnv*»r*»H vnl
Coal
Product
Oil Cone.. Percentage MF.Ash, ' Coal Recovered, Percentage
percent ^a' of Feed percent percent '*'' of Feed
20
20
20
10
10
10
5
5
5
3
3
3
1.5
1.5
1.5
based on weight
56.6
54.4
53.2
53.8
51.9
52.5
48.9
53.8
54.2
52.0
\
55.1
43.3
34.0
29.5
27.1
9.
9.
7.
9.
10.
10.
9.
9.
9.
10.
9.
8.
10.
7.
6.
42
15
86
54
23
11
68
37
38
43
54
92
87
27
59
of moisture free sediment
(100 - % ash) . . x (%
product
94.
90.
90.
89.
85.
86.
81.
89.
90.
85.
91.
72.
55.
50.
46.
2
8
1
1
6
7
2
6
3
6
6
5
7
3
4
43.5
45.6
46.8
46.2
48.1
47.5
51.1
46.2
45.8
48.0
44.9
56.7
66.0
70.5
72.5
Residue
MF Ash , Ash Removed ,
percent percent
90.42
90.63
90.42
87.98
86.37
83.34
78.85
82.47
80.55
78.95
79.40
65.20
60.57
58.63
57.11
86.
90.
92.
89.
91.
86.
88.
83.
80.
83.
78.
81.
87.
90.
90.
3
6
8
1
1
8
4
6
9
I
2
1
7
6
8
used.
of feed 'product
(100 - % ash)
feed
-------
(a)
(b)
(c)
5 6 73 9 10 11 12 15
Keroaene Conc»ntratior. (percent)
15 16 17 IS 19
FIGURE 2. INFLUENCE OF AGED SLURRY SEDIMENT CONCENTRATION AND KEROSENE
CONCENTRATION ON (a) MATERIAL RECOVERY, (b) ASH IN RECOVERED
COAL AND (c) PERCENTAGE OF COAL RECOVERED
25
-------
(a)
(b)
(c)
Slurry Conccnitdcipa
v IS pcicent
• 10 percent
«* 5 percent
012 34! 6 7 8 9 10 11 1! 13 14 15 16 17 18 19 20
.90
So
60
Slurry Concentration
fl _15 percent
• 10 percent
A S percent
I | t . I I 1 L L 1 1
1234507
8 9 10 11 12 13 1' 15 16 17' 13' .19 :0
Slurry Cuncencr.itlm
V «S percc:ic
• 10 percent '.^
A S percent
|}1 2 3 "P 5 « 7 8 9 10 11 12 13 I* 15 16 17 18 19 »
T«trbltn Conci.ntrotlor. '.p-rccut)
FIGURE 3. INFLUENCE OF AGED SEDIMENT SLURRY CONCENTRATION AND
TETRALIN CONCENTRATION'ON (a) MATERIAL RECOVERY,
(b) .ASH IN, RECOVERED COAL .AND (c) PERCENTAGE COAL RECOVERED
26
-------
20 percent over that attainable at 10 percent.
The amount of coal recovered from aged slurry pond sediments and
its ash content using a mixture of 12 volume percent No. 6 fuel oil and
88 percent kerosene, and No. 2 fuel oil at 3, 5 and 10. percent oil concen-
tration are given in Tables 9 and 10 respectively. The results given
graphically in Figure 4 suggests less scatter exists in the data for the
material recovered, its ash content, and coal recovery than were observed
wi-th kerosene alone and tetralin.,
The 45 to 55 percent material recovered from aged sediments with
the No. 6 fuel oil-kerosene mixture is about the equal to the recoveries
obtained with No. 2 fuel oil although there is slightly greater scatter in
the latter data. The performance of the two oils differs in their ability
to reduce the ash in the coal recovered from 10 and 15 percent slurries "
using a 3 percent oil concentration. For the coal recovered from the
15 percent slurry, an ash value of 9.2 percent was produced using No. 2
fuel oil while with the No. 6 fuel oil-kerosene mixture the ash content was
about 7.5 percent. At all other oil and slurry concentrations the ash
values are comparable with the No. 6 fuel oil-kerosene mixture producing a
product with a slightly lower overall ash content. Highest apparent coal
recovery, 98 percent, occurred using a No. 2 fuel oil concentration of
5 percent and a 10 percent sediment slurry. However this coal had about an
8.4 percent ash. The fuel oil-kerosene mixture appears to yield higher coal
recoveries for all three slurry concentrations at the 5 and 10 percent oil
concentrations while the No. 2 fuel oil gives a greater scatter of coal
recoveries. At the 5 and 10 percent oil concentrations both give coal
recoveries greater than 90 percent.
Sulfur Values of Coals Recovered
from Aged Sediments—
Coal recovered from 10 percent slurries using the 1.5 to 20 percent
range of oil concentrations were analyzed for pyritic and total sulfur and the
results are shown on Table 11. There is a reasonable correlation of the
sulfur values with ash values, i.e., the lower the ash values the lower sulfur
values for the coal recovered using tetralin. Although coal recovery is
lowest for the 1.5 percent oil for both tetralin and kerosene the coal still
27
-------
TABLE 9. EXPERIMENTAL RESULTS OF COAL RECOVERY FROM AGED
SLURRY POND SEDIMENT USING A MIXTURE OF NO. 6
FUEL OIL AND KEROSENE (12:88 VOLUME"RATIO)
Agglomerating
Conditions .
Run
62-1
62-2
62-3
62-4
62-5
62-6
62-7
62-8
62-9
Slurry
Cone ..
15
10
5
15
10
5
15
10
5
Oil
JConc.
10
10
10
5
5
5
3
3
" 3
Coal Product
% of
_Feed
54.9
55.4
56.0
57.0
56.4
56.2
50.0
52.3
54.3
MF
7
7
8
8
8
8
7
7
7
Ash,
%
.76
.18
.12
.42
.27
.12
.71
.42
.16
Coal
Recovered,
%
93
94
94
95
95
94
84
89
92
.1
.5
.6
.9
.1
.9
.8
.0
.7
Residue
Ash
% of MF Ash, Removed,
Feed % %.
45.1
44.6
44.0
43.0
43.6
43.8
50.0
47.7
45.7
89
89
88
87
88
87
79
82
86
.51
.89
.01
.61
.91
.95
.85
.86
.74
88.5
87.9
84.9
82.6
85.0
84.5
87.6
86.7
86.9
28
-------
TABLE 10. EXPERIMENTAL RESULTS OF COAL RECOVERY FROM AGED
SLURRY POND SEDIMENT USING NO. 2 FUEL OIL
Agglomerating
Conditions
Run
59-1
59-2
59-3
59-4
59-5
59-6
59-7
59-8
59-9
Slurry
Cone.
15
10
5
15
10
5
15
10
5
Oil
Cone.
10
10
10
5
5
5
3
3
3
Coal Product
% of
Feed
54.8
57.0
57.8
53.0
58.1
53.5
49.6
52.2
43.8
MF
7.
8.
7.
8.
8.
8.
•9.
8.
7.
Ash,
85
17
31
26
38
36
13
17
17
Coal
Recovered ,
92
96
98
89
97
90
82
88
74
.8
.2
.5
.4
.9
.1
.8
.1
.7
% of
Feed
45.2
43.0
42.2
47.0
41.9
46.5
50.4
47.8
56.2
Residue •
MF
85
89
90
81
87
83
76
76
75
Ash,
.53
.94
.82
.67
.59
.48
.86
.54
.57
Ash
Removed ,
84.8
84.8
84.0
84.2
80.5
85.1
85.0
80.2
93.1
29
-------
(a)
(b)
(c)
100
90
30
70
•JO
, 5°
w
30
20
' 10
* 0
13.0
. 9
8
7
«
5
4
3
2
1
0
100
90
- 80
(70
60
50
0
•
•
-
-
-
-
-
1 --1 1 I • -
312 3 4 5. 6 7 '8 9 10
' — —^- "
- x^"^"^^
-
!
-
-,
_
-
i i ( i i i i - 1 i i
12J11567S910
Hu. t, Fufl Oil .inrunene Mixturt
-•^""= =~~ -==*
^
:
123'«5678910
No. 6 rual Oil and Karoaene Kizture
100
. 90
80
70
60
50
1,0
30
20
' 10
10
9
8
6
5
-
J
2
1
(
100
90
80
70
60
50
0
-
-
-
-
-
/^^•*'
/
-
~" 1^,15' rere*nt
• 10 percent
.. A 5 r«r«nt
' 1 1 t i i i i i i
2123456789 10
ho. ?. Fuel Oil
\
\
- ^/>~===^^i
- 0 15 p
-------
TABLE 11. EFFECT OF OIL CONCENTRATION ON ASH AND SULFUR
CONTENT OF COAL RECOVERED FROM AGED SEDIMENT
(ALL 10 PERCENT SLURRY CONCENTRATIONS)
Oil
Concentration, %
20
10
5
3
1.5
20
10
5
3
1.5
Coal
Recovered, %
Tetralin
90.8
85.6
89.6
91.6
50.3
Kerosene
94.0
97.4
88.7
92.7
68.6
MF Ash,
%
9.15
10.23
9.37
9.54
' 7.27
8.97
9.11
10.01
12.46
8.78
MAF Sulfur, %
Pyr
1.86
1.96
1.84
1.89
.1.48
' 2.28
1.98
1.79
1.65
1.56
Total
3.97
4.14
3.87
3.86
3; 27
3.99
4.10
3.70
3.57
3.23
31
-------
contains a significant quantity of ash especially with kerosene. There is
however a drop in the amount of pyritic (and total) sulfur contained in the
coal recovered at 1.5 percent oil concentration.
Samples of coal recovered using kerosene and tetralin which had
the following characteristics were selected for sulfur analysis:
e High coal recovery and low ash
9 High coal recovery and high ash
a Low coal recovery and low ash
9 Low coal recovery and high ash.
The results of the analyses of these samples for-pyritic and total sulfur
given in Table 12 suggest that only low coal recoveries produce the
coal with the lowest sulfur. Of these coals the ones with the lowest ash
content had the lowest percentage of sulfur. Conversely excellent coal
recovery seems to keep sulfur values high and appears to be independent of
ash content. This behavior suggests that the pyrites and coal are moving
together either as separate particles or as finely disseminated material
held in the coal. Again the tendency of tetralin to recover a lower-ash and
sulfur coal than kerosene is observed.
Other Processing Variables—
The effect of the use of slower agitating speeds (as rpm of
impeller) and residence times less than 2.5 minutes during agglomeration are
summarized in Table 13. In these experiments the kerosene was emulsified
before use to provide uniform dispersion of the agglomerating oil regardless
of blender speed. . At the slow rpm and short residence times it appears that
the ash and the coal do not have enough time to separate into the two phases
necessary for good ash removal. Although the amount of material recovered
is usually about 60 .percent of the feed, it has an ash content about one-half
that of the feed material (45.6 percent ash).
In any attempt at reducing the oil concentrations to levels less
than 10 percent (for economic and environmental reasons), one of the
difficult steps in the recovery of coal by agglomeration will be the
dewatering of the agglomerated coal. At oil levels less than 10 percent
dewatering becomes slow and separation of the agglomerated coal from the
residue slurry is incomplete. In order to improve the dewatering
32
-------
TABLE 12. ASH AND SULFUR CONTENT OF COAL RECOVERED
FROM AGED SLURRY POND SEDIMENT
Coal
Recovered, !
MF Ash,
1 %
With
' 90
89
50
55
.1
.1
.3
.7
/ TT \ \ ^.
\ **/
(H)
(L)
(L)
} 7
9
7
10
AVG 8
.86
.54
.27
.87
.89
With
100
97
55
54
.9
.4
.3
.2
(H)
(H)
(L)
(L)
8
9
7
14
AVG 10
.64
.11
.99
.74
.12
Tetralin
a)(b)
(H)
(L)
(H)
Kerosene
(L)
(H)
(L)
(H)
MAF Sulfur, %
Pyr
1
1
1
1
1
2
1
1
1
1
.88
.87
.48
.55
.70
.28
.98
.35
.89
.88
Total
3
3
3
3
3
3
4
3
3
3
.80
.82
.28
.68
.40
.99
.10
.56
.81
.87
(a) H = relative high value.
(b) L = relative low value.
33
-------
TABLE 13. EFFECT OF AGITATING SPEED AND RETENTION TIME ON AGGLOMERATION
OF AGED SLURRY POND SEDIMENT WITH EMULSIFIED KEROSENE1
Run
No.
84-1
84-2
84-3
84-4
84-5
84-6
84-7 .
84-8
Agitating Speed
rpm
3,500
3,500
3500
5,300
5,300
5,300
10,000
10,000
Retention Time
sec
10
30
60
10
30
60
10
30
Product,
Of Feed
50.2
63.7
59.3
54.9
60.7
59.9
64'. 2
61.1
percent
MF Ash
20.5
23.2
22.6
22.5
21.6
20.2
23.6
16.4
(a) Slurry concentration, 10 percent; kerosene concentration, 10 percent
and emulsified in water ultrasonically before agglomeration.
34
-------
characteristics, the addition of a flocculating agent was added before, during
and after adding the oil and agglomerating was studied. The flocculating
agent used was Percol 728 cationic flocculant manufactured by Allied Colloids
Inc. A concentration of 10 ppm was used. A 10 percent slurry concentration
was treated using kerosene at the 10 and 5 percent levels and the results of
these experiments are given in Table 14. The results show that the addition
of flocculant before, during and after the oil addition at the 10 percent
level improved the quality of the coal (lower ash) from that obtained with
out the flocculant with some loss in the coal recovery (84 to 90 percent
versus 97 percent coal recovery). At the 5 percent oil leve, the quality
of the coal was also improved (due to the low ash values in the coal) but
only at the cost of sacrificing significant amounts of coal loss (48 to
58 percent versus 89 percent coal recovery).
Fresh Black Water Sediments
The consist of fresh black water sediments in effluents from
modern coal cleaning plants suggest that this material would be more
amenable to the agglomeration techniques for coal recovery than are the
aged sediments. The fact that 89 percent of the material is finer than
100 mesh (0.11 mm) and that there has been little or no weathering of the
coal support this hypothesis. The results of the experiments in which 5,
10 and 15 percent slurries were treated with No. 6 fuel oil-kerosene mix-
ture (12:88 volume ratio to give a specific gravity of 0.83 at 27 C) are
given in Table 15. These results are summarized in Figure 5 where the
material recovered, ash in the recovered coal and the percentage coal
recovery are presented as a function of the slurry and oil concentration.
The results show very little dependence on slurry concentration
since there is very little scatter of points. (Similar behavior was noted
when the fuel oil-kerosene mixture was used on the aged sediment slurries
but for only 3, 5 and 10 percent oil concentrations). In Figure 5a, it can
be seen that for all oil concentrations except 1.5 percent, the material
recovery was between 45 and 52 percent regardless of the slurry concentra-
tion. As shown in Figure 5b, the amount of ash in the recovered coal did
not vary greatly and fell between 6 and 7.5 percent, except when a
35
-------
TABLE 14. EFFECT OF FLOCCULATION AGENTON AGGLOMERATION
OF AGED SLURRY SEDIMENTS (10 PERCENT SLURRY)
Run No .
37-1
37-2
.37-3
'51-5 "
37-4
37-5
37-6
51-8
Kerosene Cone. ,
percent
10
10
10
10
5
5
•5
5-
Flocculant
Addition
Before
During
After
None
Before .
During
After •
None
.Product, percent
Of Feed
48.8
' 51.2
51.9
58.3
27.8
32.2
33.1
53.6
Coal
MF Ash Recovery-, %
6.05 '
7.28
6.07
9.11
5.35
4.98
5.05.
10. Ol"
84
'87
90
97
48
56'
58
89
(a) Percol 728 cationic flocculant manufactured by Allied Colloids, Inc.,
at the concentration of 10 ppm.
36
-------
TABLE 15. EXPERIMENTAL RESULTS OF COAL RECOVERY FROM FRESH
BLACK WATER SEDIMENT USING MO. 6 FUEL OIL AND
KEROSENE MIXTURE (12:88 VOLUME RATIO)
Agglomerating
Conditions
Slurry
Run Cone.
65-1
65-2
65-3
65-4
65-5
65--G
65-7
65-8
65-9
65-10
65-11
65-12
65-13
65-14
65-15
15
10
5
15
10
5
15
10
5
15
10
5
15
10
5
Oil
Cone .
20
20
20
10
10
10
5
5
5
3
3
3
1.5
1.5
1.5
Coal Product
I of
Feed
50.9
50.5
51.7
50.2
51.6
49.5
48.0
49,5
48.9
46.1
47.9
44.7
27.8
16.0
21.1
MF Ash,
%
6.31
6.43
5.90
6.82
6.75
6.54
7.03
7.56
7.27
6.71
6.88
6.64
6.46
6.61
5.70
Coal
Recovered,
%
96.8
96.0
98.2
95.0
97.7
93,9
90.7
92.9
92.2
87.4
90.6
84.9
52.9
30.4
40.6
Residue
Ash
% of MF Ash, Removed,
Feed % %
49.1
49.5
48.3
49.8
48.4
50.5
52.0
50.5
51.1
53.9
52.1
55.3
72.2
84.0
78.9
90.77
90.70
91.06
90.13
91.45 '
89.72
86.91
87.84
89.11
85.55
88.85
84.66
63.66
57.42
62.53
87.7
88.4
86.6
88.4
87.1
89.2
89.0
89.3
89.6
90.8
90.8
92.2
90.5
95.0
97.1
37
-------
(a)
(b)
(c)
Slurrv Concentration
• 15 percent
. 1C' rfcr.1t
A 5 percent
>• 5 6 7 3 9 10 11 12 1} H 15 16 17 18 19 20
No. d Fuel Oil aoc Kerosene Mixture Corcrntration (percer.t)
5 •
Slurry
• 1" pt
A 5 r-:-
01 2 3 't 5 67 f 9 10 11 12 i; li 13 16 17 13 19 ,10
00
90
80
70
£0
50
"
-
/
-1
1
1
1
— r— — *
/ * ^-^^ *
/ '"^/^
If/
u
* 15 percent
• 10 -.•crc*.-:t
A '• percent
9. f
2 3 it 5 6 ? 8 9 10 11 12 13 1'. 15 16 17 IS 19 20
FIGURE 5. INFLUENCE OF FRESH SLACK WATER SEDIMENT SLURRY CONCENTRATION AND
NO. 6 FUEL OIL-KZROSENZ MIXTURE (12:88 VOLUME RATIO) ON (a) MATERIAL
RECOVERY, (b) ASH RECOVERED COAL AND (c) PERCENTAGE COAL RECOVERED
38
-------
1.5 percent oil level with the 5 percent slurry was used. The percentage of
coal recovered was a maximum 98 percent when a 10 percent oil-kerosene level
was used to agglomerate the coal in a 10 percent slurry (see Figure 5c).
A 95 percent coal recovery was obtained using the same oil concentration
on a 15 percent slurry.
The results of experiments in which other oils were used in the
agglomerations of coal values from fresh black water sediments are given
in Table 16. Tetralin, kerosene and No. 2 fuel oil were used under condi-
tions found most effective for coal recovery from the aged sediments. At
the 20 percent oil concentration levels each oil produced an apparent coal
\
recovery of greater than 94 percent. At the 10 percent level, the amount
of coal recovered from 5 percent slurries was lowest with kerosene
(80.5 percent) and highest with No. 2 fuel oil (99.1 percent). Use of
No. 2 fuel oil produced apparent coal recoveries near or in excess of
100 percent due to the retention of the oil after drying at 100 torr at
60 C overnight.
Since the experiments with tetralin, which is one of the hydrogen
transfer agents in coal liquefaction process employing hydrogenation, were
successful, the concept of using a coal derived liquid directly as an
agglomerating oil were investigated and the results are given in Table 16.
Unfiltered solvent refined coal (SRC) dissolver product did not give good
coal recovery when used at 20, 10 and 5 percent oil concentrations. The
best result was about 61 percent recovery of coal that contained 16 percent
ash. Use of the distillate collected below 315 C from the SRC dissolver
product gave coal recoveries of about 90 percent from 5 and 10 percent
slurries using 10 and 20 percent oil concentrations. The ash in the
recovered coal was between 7.5 and 8 percent which is about 1 percent higher
than the coals recovered using tetralin or kerosene.
Sulfur Values of Coals Recovered from
Black Water Sediments—
The sulfur content determined for the coals recovered from the
black water sediments using the No. 6 fuel oil-kerosene mixture are given in
Table 17. The results show the same trend as observed for the coals recovered
from aged slurry pond sediment, i.e., the pyrite levels seem to follow coal
39
-------
TABLE 16. EXPERIMENT RESULTS OF COAL RECOVERY FROM FRESH BLACK WATER SEDIMENT USING VARIOUS OILS
Coal Product
Agglomerating Conditions
Run
76-1
76-2
76-3
76-4
76-5
76-6
80-1
80-2
80-3
80-4
80-5
80-6-
Slurry
Cone.
5
10
5
5
5
5
5
5
10
5
10
10
Oil
Type
Tetralin
Tetralin
Kerosene
Kerosene
//2 Fuel Oil
If 2 Fuel Oil
SRC u(b)
SRC u
SRC u
SRC d(c)
SRC d
SRC d
Oil
Cone.
20
5
20
10
20
10
20
10
5
20
10
5
% of
Feed
49.8
47.3
52.0
42.1
55.2
52.2
35.5
20.7
17.5
48.1
46.3
33.2
MF Ash,
6.88
6.98
6.45
5.94
6.20
6.51
15.66
9.04
7.80
8.00
7.49
6.89
Coal
Recovered,
94
89
98
80
105
99
60
38
32
89
87
62
.2
.4
.9
.5
.l
.1
.9
.3
.8
.9
.0
.8
% of
Feed
50.2
52.7
48.0
57.9
44.8
47.8
64.5
79.3
82.5
51.9
53.7
66.8
Residue
MF Ash,
92.1
86.0
92.0
79.1
91.9
91.3
63.2
47.9
57.4
85.4
82.7
68.4
Ash
Removed ,
91
90
88
91
82
86
81
75
94
88
88
91
.0
.3
.0
.1
.0
.9
. 2
.7
.3
.3
.6
.02
(a) Value greater than 100 percent due to residual fuel oil retained after drying.
(b) Unfiltered solvent refined coal dissolves product.
(c) Distillate from solvent refined coal dissolver product, 315 C cut.
-------
TABLE 17. ASH AND SULFUR CONTENT OF COAL RECOVERED
FROM BLACK WATER SEDIMENTS(a)
Coal
Recovered, %
98.2
97.7
40.6
AVG
MF
Ash,
MAF Sulfur,
%
% Pyr Total
5
6
5
6
.87
.83
.68
.13
1.42 3
1.65 3
1.16 3
1.41 3
.61
.90
.48
.66
(a) Using a No. 6 fuel oil and kerosene mixture (12:88 volume ratio)
TABLE 18. EFFECT OF AGITATING SPEED AND RETENTION TIME ON AGGLOMERATION
OF THE FRESH BLACK WATER SEDIMENT WITH KEROSENE(a)
Run No.
1-1
1-2
1-3
1-4
1-5
.1-6
1-7
1-8
1-9
Agitating
Speed, rpm
3500
3500
3500
5300
5300
5300
10000
10000
10000
Retention
Time, sec
10
30
60
10
30
60
10
30
60
Product,
Of Feed
12.5
12.6
23.7
28.8
52.6
44.4
42.8
48.7
47.3
percent
MF Ash
9.07
11.02
9.01
16.91
18.24
6.33
11.20
8.86
6.32
Coal Recovery,
percent
23
23
44
49
87
85
77
90
91
(a) Slurry concentration, 10 percent; kerosene concentration, 10 percent,
41
-------
recovery more closely than they do ash values. Samples of coal from a high
recovery experiment containing high ash (6;83 percent) had a higher sulfur
value than did those from high recovery and low ash (5.87 percent). However
when the recovery is low and the ash is low (5.68 percent) the amount of
pyritic sulfur in the coal is the lowest.
Other Process Variables—
Experiments were carried out with fresh black water sediments to
study the effect of agitating speed (blender rpm) and retention time on
agglomeration. The results of these experiments given in Table 18. The
results suggest that higher agitating speeds and longer retention time gave
higher coal recovery. It appears that an agitation speed of at least 5300 rpm
and a retention time of 30 sec or more are necessary to achieve good recovery
of a coal with the lowest ash values.
Partially Dried Old Sediments
The sample of a partially dried, old coal slurry pond sediments
had a moisture free (MF) ash content value of 32.2 percent and sulfate sulfur
concentration of 2.11 percent on a moisture and ash free basis (MAF). The
pH of a 10 percent slurry was 2.2 and the supernatent had a yellow color.
Agglomeration of this slurry with kerosene gave very poor coal recoveries
even with the high oil concentrations and at high pH values (adjusted by
the addition of NaOH). It appeared that during exposure to'air during
drying the coal particles lost their hydrophobia surfacial characteristics
perhaps by adsorption of ferric ions. In an attempt to restore the hydro-
phobicity, the sediment was washed several times by reslurrying with fresh
water after filtration of the previous wash. After each washing at approxi-
mately the same sediment to water ratio, a portion of the slurry was taken
for agglomeration. Table 19 summarizes the effect of successive washing on
the agglomeration characteristics of the sediment. The results indicate
that repeated washings improved coal recovery and decreased the ash content
of the coal recovered.
In the experiments in which chemical treatment of unwashed old
slurry pond sediments was used to reduce the ferric and sulfate ions, the
-------
TABLE 19. EFFECT OF SUCCESSIVE WASHING ON AGGLOMERATION
OF PARTIALLY DRIED OLD COAL SEDIMENT
No. of
Washing
1
2
3
4
7
pH
After
Washing
3.1
3.6
3.9
4.0
4.0
PH
-------
slurry was adjusted to a pH greater than 7 with NaOH to precipitate iron
hydroxide and then was treated with CaCl^ solution to a pH of about 7 to
precipitate calcium sulfate. Recovery experiments with these treated
slurries using kerosene and fuel oil-kerosene mixtures indicated that the
coal particles had agglomerated well. However the separation of the
agglomerated coal from the residue suspension was extremely difficult due
to plugging of the sieve openings by the precipitated residue. In order to
control this effect, several dispersing agents were tried. The results of
their use on the agglomeration of coal slurries neutralized with NaOH (no
CaCl~ addition) are given in Table 20. The dispersing agents improved the
separation of the agglomerated coal from the residue suspension, but the
coal recovery and quality were not satisfactory. Sodium metaphosphate
appeared to be most promising.
The data given in Table 21 are the results of experiments in which
a sequence of treatments were tried. The treatment consisted of a combina-
tion of a single stage washing with water followed by adjustment of the pH
either to about 6 or 5 with sodium hydroxide which was followed by addition
of sufficient sodium silicate solution to raise the pH to either about 9
or 8. The results indicate coal recovery is greater when coal is washed
and sodium silicate is used. Washing the slurry before addition of sodium
hydroxide and sodium silicate reduces the ash in the recovered coal. The
lowest ash in the recovered coal occurred when the pH was adjusted to
about 5 with sodium hydroxide alone.
This behavior was attributed to differences in the
composition of the partially dried old slurry pond sediment that became
segregated during use of the material. The major portion of the sediment
was a loose material which had mixed with it firm lumps ranging in various
sizes up to 3 inches in diameter. Towards the end of these studies, the
larger lumps were used as part of the feed material.
The behavior of these two types of materials during slurry
preparation and agglomeration were compared. As shown in Table 22,
the aqueous slurry made from the aggregated sediment had a pH of about 6.5
while the slurry made from the loose sediment had a pH of 2.9. When the pH
2.9-slurry was adjusted to a pH of 6.5 to match that of the aggregate
slurry and then agglomerated using a 10 percent concentration of No. 2 fuel
-------
TABLE 21. EFFECT OF SINGLE WASH OF SEDIMENTS, pH ADJUSTMENT AND LOW LEVEL
SODIUM SILICATE ADDITIONS BEFORE AGGLOMERATION ON COAL
RECOVERY FROM PARTIALLY DRIED OLD SEDIMENTS(a)
Slurry pH
Initial
Unwashed
Washed
Washed
Unwashed
Washed
3.
3.
3.
3.
3.
2
3
3
1
3
Adjusted
NaOH
5
5
5
5
5
.8
.8
.0
.1
.3
After Sodium^ Product,
Silicate Of Feed
9.2 64.
9.6 66.
8.2 66.
— (°) 62.
65.
8
7
7
3
0
percent
MF
7
6
6
5
5
Ash
.43
.13
.64
.40
.36
Coal
Recovered
percent
88
92
92
87
91
(a) Slurry concentration, 10 percent; No. 2 fuel oil concentration, 10 percent,
(b) pH values after adding sodium silicate solution (8.9% Na~0 + 24% Si00) .
(c) No sodium silicate added.
45
-------
-P-
O\
TABLE 22. COMPARISON OF AGGLOMERATION BEHAVIOR OF SEGREGATED LUMPS
OF LOOSE MATERIAL FOUND IN PARTIALLY DRIED OLD COAL SEDIMENT
Loose Sediments
Aggregated Sediment
Original
Slurry
2.6
6.4
Slurry pH
Diluted for
Agglomeration
2.9
6.5
At
Agglomera tion (a )
6,
6,
,5(b)
.5(C)
Produc t ,
Of Feed
8.47
60.4
percent
MF Ash
8.19
5.02
(a) Slurry concentration, 10 percent; No. 2 fuel oil concentration, 10 percent.
(b) pll adjusted with NaOH.
(c) No adjustment required.
-------
oil, only 8.5 percent of the material was separated. In contrast,
agglomeration of the slurry of the aggregate yielded 60 percent of the feed
and the recovered coal had lower ash content. This may have been due to the
reduced exposure to weathering that these aggregates had compared to the loose
materials. It could also be due to a higher coal concentration in the aggregate.
RESIDUE CHARACTERIZATION
Once coal values have been removed, the residue material is
relatively free of combustible material. For example, the solids recovered
from the aqueous residue suspension after agglomerating with a mixture of
No. 6 fuel oil and kerosene contain about 90 percent moisture free ash
while the residue solids from the aged slurry pond sediments contained
about 89 percent moisture free ash. Part of the weight loss during ash
determination could have been due to the loss of water so in effect the
quantity of coal present is very small. As reported by Capes et al. many
of the trace elements in coal considered to be hazardous are removed with the
mineral matter during agglomeration.
Any process designed to use the agglomeration technique for
recovery of fine coal from coal slurry waste streams or to reduce the
environmental threat of slurry ponds will be concerned with the disposal
of the residues from the operation. To this end studies were initiated to
measure the settling characteristics of the residue suspensions and the
concentration of the agglomerating oil they may retain.
Settling Rates
The settling rates of the original coal slurry and of the residue
suspension were obtained by preparing sufficient 10 percent slurry to make
up 1700 ml and shaking the suspension thoroughly in a 2000 ml graduated
cylinder for several minutes. The settling rate was measured by following
the level of the clear interface with time. After completion of this cycle,
the slurry was agglomerated using a 20 percent kerosene concentration in a
one-gallon blender. After the usual coal recovery technique (including
washing on the screen), the residue suspension was now contained in
2000 ml. The settling rate was measured again.
47
-------
The settling rates for the aged slurry pond sediment and the
resulting residue suspension are given in Figure 6. Settling rates for the
fresh black water sediments and the resulting residue suspension are shown
in Figure 7. The settling rates of both residue suspensions are faster
than the parent sediment slurries containing the coal. Removal of the
coal from the residues which appear to be mostly fine clays probably
increases settling in part due to the decreased slurry concentration. This
is a very desirable result. In addition, specific agents.known to improve
clay flocculation can now be applied more specifically.
The pulp density of the residues (1.09 and 1.14 g/ml) at the end
of the 3-day settling period suggest that they remain pumpable. The
residues recovered after settling were dried at 110 C and then analyzed (see
Table 23). As expected the results for the two materials from the same
mine are similar and the composition is characteristic of clays with SiCL
to A^O., ratio of about 4 (perhaps illites since iron, calcium and
potassium are present).
Oil in Residue
An estimate of the amount of agglomerating oil that is lost to
the residue suspension after agglomeration was made. The procedures used
for determining the oil content in the residue slurry were as follows:
1. The residue water suspension from the oil agglomeration
(mostly mineral matter) was mixed well with 50 ml of
carbon tetrachloride in a 1000 ml separating funnel.
2. The mixture was allowed to separate into two phases
and the heavier CC1/ phase was drained off.
3. These extraction steps were repeated five times.
4. A 24 ml aliquot of the CC1, extract (250 ml) was placed
in a weighed dish and evaporated in a constant tempera-
ture bath at 80 C for 20 min.
5. The weight of remaining oil was measured and multiplied
by 10 to calculate the total amount of oil in the
residue slurry.
48
-------
2000k-
1800
1600
1400
1200
•o
a
1000
800
600
Residue
Suspension
400
200
Final Pulp Density of
Residue = 1.09 g/ml
30
60
90 120
Time, min
150
180
210
FIGURE 6. SETTLING RATES FOR 10 PERCENT SLURRY-OF AGED SEDIMENTS AND
THE RESIDUE AFTER REMOVAL OF COAL VALUES BY AGGLOMERATION
(20 PERCENT KEROSENE CONCENTRATION)
49
-------
2000
1800
1600
1400
1200
1000
c
0)
800
,•'1600
400
Residue
Suspension
460 at
1125 min
390 at
1335 min
200
Final Pulp Density of
Residue =1.14 g/nl
J \ 1 L
_I__J II II
30
60
90
120
Time, min
150
.180
210
FIGURE 7. SETTLING RATES FOR 10 PERCENT SLURRY OF FRESH BLACK WATER
SEDIMENT AND THE RESIDUE AFTER REMOVAL OF COAL VALUES BY
AGGLOMERATION (20 PERCENT KEROSENE CONCENTRATION)
BULK DENSITY AFTER 3 day = 1.14 g/cc
50
-------
TABLE 23. ANALYSIS OF RESIDUES FROM AGGLOMERATION
Source
of Residue SiO« ^-9^7
Ag'ed Sediment 54.4 21.5
Fresh Sediment 55.6 24.8
Composition, percent
Na20
0.77
0.71
CaO MgO
6.07 0.32
4.05 0.33'
K20 Fe203
].31 3.49
2.55 3.30
The above method, however, suffers from the following uncertainties:
• The CC1, does not appear to extract all of the oil
present in the residue slurry.
9 Some of the.oil evaporates together with CC1, .
o The original sediments may contain oily substances
which can be extracted by CC1,.
Base-line experiments were conducted to determine the amount of
No. 2 fuel oil evaporated with CC1, at several known oil concentrations.
The results indicated that the amount of oil lost during evaporation varied
with the oil content. Figure 8 is the calibration curve which shows the
relationship between the actual oil content and that measured by the
evaporation technique." In order to find the amount of oily substances in
the original samples, the CC1,-extraction was conducted with the aged
4 i 5
slurry sediment. It was found that essentially no oil could be found in
the sediment with this technique. Another base-line experiment was carried
out to determine the amount of oil which could not be extracted by the
CCl^-extraction. The extraction experiments on the aged slurry sediment
mixed with the known amount of No. 2 fuel oil indicated that about 10 percent
of the oil could not be extracted by this technique.
* More precise measurements using infrared spectral analysis of the CC1/
oil solutions are available, but were not applied to these preliminary
evaluations.
51
-------
3.0
0.5 1.0 1.5 ' 2.0 2.5, r 3.0
Oil Content (Measured), g of No. 2 fuel oil/100 ml of CC14
FIGURE 8. CALIBRATION CURVE FOR DETERMINATION OF
OIL CONTENT BY CCl^-EXlRACTION•
52
-------
This modified CC1,-extraction technique was applied to determine
the amount of oil loss to the residue suspension during agglomeration of the
aged slurry sediment with No. 2 fuel oil. The results are summarized in
Table 24. It is shown that the amount of oil loss in the residue varied
depending upon the amount of oil used. The smallest oil loss was 2.24 per-
cent at 10 percent oil concentration. The 20 percent oil concentration
resulted in larger oil loss due to the "free" oil unattached to coal
particles. At the 5 percent oil concentration, the sizes of agglomerated
coal were so small that some of the coal was lost into the residue and oil
was carried with it.
Staged Washing of Agglomerated Coal
(3)
Min suggested that resuspension of the recovered agglomerated
coals in water can be effective in further reducing the ash content of
the recovered coal as well as producing large size, strong agglomerates of
the coal. The washing technique consisted of performing an agglomera-
tion of a 10 percent slurry using a 10 percent oil concentration and
then placing the entire mixture into an air-float cell (60 mm ID x
300 mm tube fitted with a fritted glass disc at the bottom). A very
slow flow of air bubbles lifted the agglomerated coal to the top of
the cell where it was removed with a screen. Once all of the coal
fraction had been collected it was either dried and analyzed or it was
resuspended in clean water and air floated a second time and
recovered.
The results of these air float washings are given in Table 25.
The single stage washing gave only a minor improvement in the ash content
(8.90 vs. 9.11 percent) of the coal recovered from the aged sediment and
the 85 percent coal recovery was significantly lower than the 97 percent
recovery obtained by the usual procedure. A significant improvement
in ash in the recovered coal was obtained in the two stage washing (5.66
vs. 8.90 percent) at only a slightly lower coal recovery than in the single
stage washing (80 vs. 85 percent). (No. 2 fuel oil and kerosene containing
1 percent palmitic acid did not offer any improvement in the two stage
washings.) The pyritic sulfur in the recovered coal after the second
53
-------
-P-
TABLE 24. AMOUNT OF OIL LOST TO THE RESIDUE SLURRY DURING AGGLOMERATION
OF THE AGED SLURRY SEDIMENT
(a)
Oil
g
1.25
2.5
5.0
Used
Cone. ,
%
5
10
20
I
Oil Content
(experimental) ,
g Oil/100 ml C04
0.0332
0.0156
0.0590
Oil Content^
(corrected) ,
g Oil/ 100 ml C04
0.05
0.02
0.10
Oil Extracted,
8
0.125
0.05
0.25
Total Oil(c)
in Residue,
g
0.139
0.056
0.278
Oil Loss
in Residue,
%
11.12
2.24
5.56
(a) 250 g of-'Slurry (10% slurry concentration) was agglomerated with No. 2 fuel oil
(b) Oil content is corrected according to the calibration curve (Figure 9).
(c) Total amount of oil in the residue is estimated as
oil extracted (g)
0.9
-------
TABLE 25. EFFECT OF SECONDARY WASHING OF COAL RECOVERED BY AGGLOMERATION
(a)
Ui
Oi
Single Stage Wash
, . Product, percent Coal Recovery,
Oil Used^d' Of Feed MF Ash percent
Aged Sediment
Kerosene 50.8 8.90 85
No. 2 fuel oil^
„ Kerosene — — —
Black Water Sediment
Kerosene 50. 4 8.15 94
Product
Of Feed
46.2
41.0
45.8
48.1-
Two Stage
, percent
MF Ash
5.66
5.22
5.40(C)
5.78
Wash
Coal Recovery,
percent
80
71
80
92
(a) Slurry concen tra t.i.on, 10 percent; oil concentration, 10 percent.
(b) Oils contain 1 percent palmitic acid.
(c) For coal recovered $t , = 3.38 percent, S = 1.05 percent (MAF).
-------
washing was about one-half of that ob.tained in coal recovered by the conven-
tional method (1.05 vs. 1.98 percent).
The results from the experiment using fresh black water sediments
were better. Coal recovery after two stage air float washing was 92 percent
and the ash content of the recovered coal was 5.78 percent which is
significantly lower than the 8.16 percent ash for a coal recovery of 94 per-
cent using the usual agglomeration technique.
ENHANCEMENT OF PYRITE REMOVAL
Because of similarity in the surface characteristics of coal and
pyrite (i.e., both are hydrophobic), oil agglomeration faces difficulty
in removing pyritic sulfur from coal. The earlier study by Sun and
(16)
McMorris showed that the oil agglomeration process was very effective for
recovery of low ash coal but the reduction in sulfur content, was negligible.
The Bureau of Mines recent study also confirmed .that the agglomeration
process provided only limited sulfur reduction. Thus, in order to enhance
pyrite removal during oil agglomeration, it is necessary to modify the sur-
face characteristics of pyrite to become hydrophilic.
There are many chemicals which are considered to be good pyrite
depressants in the flotation practice of sulfide minerals. They include lime,
cyanides, permanganates, sodium sulfite or sulfide, etc. The effectiveness
of these chemicals during agglomeration of coal had .been tested by Cape
et al. and Min. The results showed that these chemicals provided only
limited success on depressing pyrite. The preliminary work in earlier phases
(2)
of this program also confirmed that the pyrite depressants tried did not
improve the separation of pyrite from coal significantly. This ineffective-
ness may be due to the highly porous structure of coal. The coal particles
may adsorb the 'depressing agents rapidly before they can alter the surface
property of pyrite particles. Hence, an excessive amount of depressing
agents may be needed to affect the pyrite. In general, however, the use of
excessive agents deteriorates coal recovery.
Instead of using the conventional pyrite depressants, other
approaches have been studied to alter the surfacial characteristics of the
pyrite. Capes, et al. showed that the surface of the pyrite could become
56
-------
hydrophilic during grinding in a slurry containing iron-oxidizing bacteria,
Ferrobacillus-Thiobacillus group. More than 90 percent of the pyritic sulfur
could be removed after such a treatment. It was postulated that the surface
of the pyrite particles were oxidized by bacterial action rendering hydro-
philic surfaces. On the other hand, Min reported that the surface of the
pyrite could also be altered by mild chemical treatments in an aqueous
alkaline solution with air at elevated temperature. Presumably the surface
oxidation of pyrite in water led to the formation of a film of hydrated
ferric oxide which reduced the floatability of the pyrite.
During this screening study, the following alternative approaches
were tried to find an effective method which could selectively alter the
pyrite surface to become hydrophilic:
• Aqueous oxidation treatment
« Electrolytic treatment
• Microwave treatment
9 Wetting-agent treatment
The approaches and results are described in the subsequent sections.
Aqueous Oxidation Treatment
Unheated Treatments—
Pretreatment of the coal with a pyrite depressant at 25 C was done
before any attempt at agglomeration. Known pyrite depressants were used at
-4
concentrations of 5 x 10 g per g of coal (or one Ib per ton of coal) or
less. An attempt was also made to pretreat coal with ferric sulfate solution
under conditions more mild than the TRW-Meyers process which is known to
react with pyrites. When this was done, the coal was separated by
filtration before agglomeration was attempted. The slurry pH was adjusted to
a specied value before agglomeration with dilute sodium hydroxide or sulfuric
acid solutions. Studies on the use of depressants to improve pyrite removal
were done using kerosene with a loading of 20 percent of the dry coal weight
and a blending time of 2.5 minutes to accomplish the agglomeration. The
results of the experiments on the effect of chemical treatment at 25 C on
pyrite removal during agglomeration are given in Table 26.
In Table 27, the reduction of pyritic sulfur of untreated and
57
-------
TABLE 26. RESULTS OF CHEMICAL PRETREATMENT AT 25 C 'ON PYRITE SEPARATION FROM ILLINOIS
NO. 6 COAL DURING AGGLOMERATION (25 Grams Coal in 225 Grams Water)
Pretreatment of Coal
Experiment
No.
Feed Coal
60
62
65
66
67 .
70
71
72
U1
CO 75
76
77
78
79
80
1
Feed Coal
2
3
4
5
6
8
Mesh
Size
-14
-14
-14
-14
-14
-14
-14
-14
-14
-14
-14
-14
-14
-14
-14
-14
-14
-48
-48
-48
-48
-48
-48
-48
Amount Time,
Agent ml/25 g Coal mln
NaOCl Solution
NaOCl Solution
2N Fe2(S04>3
2N Fe2(S04)3
2N Fe2(S04)3
.IN Fe2(S04>3
.IN Fe2 (804)5
.IN Fe2(S04>3
.IN Fe2(S04^3
.IN Fe2(S04>3
.IN Fe2(S04)3
.IN Fe2(S04>3
NaOII
0.1M K4Fe(CN)6
0.1M K3Fe(CN)6
.IN Fe2(S04>3
.IN Fe2(S04)3
.IN Fe2(S04>3
0.1M l<4Fe(CN)6
0.1M K3Fe(CN)6
0.1M K4Fe(CN)0
NaOII
4.0
0.4
150
150
150^
2.0
2.0
150
2.0
2.0
2.0
2.0
150
3.0
4.0
150
150
2
3
4
3
150
0.5
10.7
15
60
15
0.5
2.5
15
15
15
15
15
15
15
15
15
15
15
15
15
15
15
Temp. ,
C
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
Agglomeration Conditions
Type(a)
A
A
A
A -
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
A
C
Oil
Charge, f
7.5
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
Time,
5 mln
0.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5"
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
PH
10.8
10.7
2.3
• 2.3
11.0
4.0
4.0
2.3
4.5
10.9
7.4
4.4 to 8.0
8.0 to 6.2
10.7
4.6
4.4
2.1
2.3
5.2
5.3
5.2
5.2
5.4
Product, percent
Feed
10.8
58.4
2.0
1.6
3.2
63.6
56.4
24.8
44.0
0.4
23.6
9.2
72.0
68.8
61.6
2.0
0.4
85.6
83.5
94.0
94.8
86.4
MF
Ash(b)
14.0
9.47
7.92
6.51
)
8.34
8.82
8:15
7.42
8.06
--
7.59
--
8.24
7.93
8.27
--
12.9
--
7.47
8.08
7.81
7.81
8.62
Residue, percent
MAF(c)
STOT
5.93
4.64
4.38
3.75
--
4.10
4.23
4.62
4.68
4.21
4.52.
--
3.78
--
4.51
4.39
4.37
--
5.75
--
4.59
4.54
4.43
4.52
5.01
SPYR
3.12
2.33
1.67
2.02
--
1.51
1.50
1.80
1.83
1.62
1.79
--
1.44
--
1.80
1.52
1.65
--
2.89
--
1.99
1.89
1.81
1.87
2.11
Feed
84.8
39.2
96.0
93.2
52.0
32.4
39.2
70.4
53.2
101.6
72.8
87.6
26.8
29.2
36.8
97.6
94.8
9.6
12.8
7.6
7.6
7: 6
MF
Ash(b)
12.7
15.0
11.7
--
14.0
16.6
17.4
12.6
14.7
--
13.1
--
20.96
19.2
16.6
--
--
40.5
33^9
53.6
53.7
41.3
MAF(c)
STOT
5.20
5.45
4.84
--
5.09
5.60
6.00
5.07
5.48
--
4.76
--
6.91
6.24
6.09
--
--
11.06
9.64
20.3
19.9
8.93
SPYR
2.41
2.73
2.32
--
2.42
2.82
3.19
2.49
2.81
--
2.60
--
3.94
3.44
3.01
--
--
8.53
7.38
17.0
17.2
6.39
(a) Oil types: A = Kerosene; B - No. 2 Fuel Oil; C = Tetralln
(b) MF = Moisture-Free basis
(c) MAF - Moisture- and Ash-Free basis
(d) Pretreatment of coal In separate vessel and filtered before: use In,agglomeration
(e) Separation on 28 meah sieve
(f) Separation on 48 mesh sieve.
-------
TABLE 27. EFFECTIVENESS OF DEPRESSANTS FOR REMOVAL OF PYRITE FROM ILLINOIS NO. 6 COAL
DURING AGGLOMERATION COMPARED TO RESULTS FROM FLOAT-SINK ANALYSIS
Product (Float)
Feed Coal
Agglom.
Agglom.
Agglom.
Agglom.
41(c)
61
70
79
Float-Sink
Analysis
Feed Coal
Agglom.
Agglom.
Agglom.
50
3
6
Float-Sink
Analysis
Mesh
Size
-14
-14
-14
-14
-14
-14
-48
-48
-48
-48
-48
Residue (Sink)
Pretreatment Z Re- MF(«) Ash, MAF,(b) 70 % Re_ MF Ash, MAF, %
of Coal covered
None 43.6
pH 10.7 64.8
2 ml, 0.1N
Fe2(S04>3 63.6
30 seconds
3 ml, 0.1M
K4Fe(CN)6 68.8
15 rain
1.9 specific 94.1
gravity
None 84.4
2 ml, 0.1N
Fe2(S04)3 85.6
15 min
3 ml, 0.1M 94.8
KAFe(CN)6 15 min
1.9 specific 93.3
gravity
14
9
7
8
7
9
12
7
7
7
9
%
.0
.18
.97
.82
.93
.77
.9
.83
.47
.81
.32
S
5
4
4
4
4
3
5
4
4
4
3
TOT
.93
.43
.18
.62
.39
.89
.75
.15
.59
.53
.87
Pyritic
Sulfur
J>PYR covered % ^fQf ^PYR Reduction, %
3.12
1.56 49.2 13.8 5.52 2.70
1.62 32.8 21.1 6.48 3.56
1.80 32.4 16.6 5.60 2.82
1.52 29.2 19.2 6.24 3.44
1.28 5.9 51.3 37.5 25.9
2.89
1.53 10.0 42.3 17.4 14.4
1.99 9.6 40.5 11.1 8.53
1.87 7.6 53.7 19.9 17.2
1.09 6.7 49.7 40.10 34.5
50
48
42
51
59
47
31
35
62
(a) MF = Moisture Free basis
(b) MAF = Moisture and Ash Free basis
(c) All agglomerations were performed with kerosene using 20 percent of the weight of the coal
feed.
-------
pretreated coal are compared to the reduction attainable from float sink
analysis for the two coal sizes studied. These data suggest that of the
reagents tried with the coarser coal, only potassium ferrocyanide seemed to
give good coal recovery and pyrite separation. However, it does not attain
the performance of float-sink separation. The next best system appears to be
the adjustment of the pH of 10 to 11. Potassium ferrocyanide exhibited
similar improvements in coal recovery and pyrite removal for the minus
48 mesh coal. Although these improvements with the finer coal are signifi-
cant, they do not match the separation possible at a specific gravity of 1.9.
This is especially true for pyrite in the residue. It should be noted that
ash remaining with coal after agglomeration treatment is less than that
obtained by the float-sink separation. In all but the experiment in which
potassium ferrocyanide was used, the amount of misplaced coal may account
for this effect.
Solutions with concentrations typical of that used by the TRW-
Meyers process (i.e., 2 Normal) were used to treat the coal for period of
15 and 60 minutes but with no heating. The intent of these experiments was
to attack the surface of the pyrites through the same reaction that consumes
them during the TRW-Meyers process. It was found that the hydrophobic
character of the coal was destroyed, essentially no agglomeration occured
under conditions known to be successful, and more than 90 percent of the coal
passed through the screen (Experiments 65, 66, and 67, Table 26). Even
solutions of 0.IN Fe9(SO,)» caused the coal to be wetted by water. By
decreasing the dosage to only 2 ml of 0.1N Fe^SO per 25 g of coal (0.6 g
Fe«(SO,)~/100 g) only slight improvements were noted. Adjustment of the pH
to 10.9 compounded the hydrophylic effect probably because the absorbed
ferric ion on the coal surface formed the hydroxide. (The effect of acid was
not investigated.)
!
In those experiments where agglomeration gave 80 percent coal
recovery or better, the water occluded in the coal-kerosene agglomerate was
about 46 percent of the wet cake. This amount was reduced to 24 by only
mechanical action (kneading on the screen).
Heated Treatments—
The jib-washed coal samples from Illinois No. 6 described earlier
60
-------
were ground to minus 48 mesh and pretreated in an aqueous slurry before oil
agglomeration. Figure 9 shows the apparatus used for this treatment step.
One hundred grams of ground coal was mixed with 400 ml of distilled water in
a 500 ml gas washing bottle and a small amount of chemical was added. The
slurry was agitated with a magnetic stirrer and heated by an electrical heat-
ing tape. After the temperature reached above 90 C, air bubbles were intro-
duced through a porous glass plate at about 400 cc/min for 30 minutes. The
reaction temperature was maintained about 90 C and a condenser was mounted
above the reactor to prevent loss of water by evaporation.
After the pretreatment, the slurry was diluted to 10 percent
slurry concentration by adding distilled water and cooled to room tempera-
ture. One-quarter of the slurry was taken and agglomerated with 5 g of
kerosene. With each pretreated slurry, three agglomeration runs were made
at acid, neutral and basic pH values by adjusting with either hydrochloric
acid or sodium hydroxide solution. The experimental results are summarized
in Table 28. The data.show that the aqueous oxidation treatments signifi-
cantly improved pyrite removal during agglomeration as compared with the
untreated coal samples (Run #24). However, the observed differences in
sulfur reduction among the different chemical conditions are too small to
choose which condition is the best for treating the pyrite. It appears that
the adjustment of pH after the chemical treatment did not have any marked
effect on the agglomeration results.
Another series of aqueous oxidation treatments were carried out
with the jig-washed coal sample from Ohio Pittsburgh Seam No. 8 coal to
examine the effects of wider variety of chemical conditions. The apparatus
and experimental procedures were the same as the previous runs except that
the treated slurry was agglomerated with 2'. 5 g of No. 2 fuel oil. Table 29
summarizes the pretreatment conditions and the agglomeration results. For
the sake of comparison, a float-sink analysis of the same coal (minus
48 mesh) at 1.59 specific gravity is also shown in the table. Since the
specific gravity of pyrite is about 5.0, the float fraction at the specific
gravity 1.59 is supposed to be free from liberated pyrite and the remaining
pyrite represents that locked in the coal matrix. Hence, the pyritic
sulfur reduction obtained by the 1.59 specific gravity float was set as the
attainable goal by the oil agglomeration technique.
61
-------
Thermometer
Rota-
Meter
Air
Reflux Condenser
«-Cooling Water
Electrical Heating Tape
Porous Glass
Magnetic
Stirrer
FIGURE 9. EQUIPMENT FOR CHEMICAL PRETREATMENT OF
A COAL SLURRY
62
-------
TABLE 28. EFFECT OF AQUEOUS OXIDATION PRETREATMENT ON PYRITE REMOVAL DURING
OIL AGGLOMERATION OF ILLINOIS NO. 6 COAL (FRESH GROUND)
ON
U)
Run No.
Chemical Agent
0.5 g/100 g coal
PH
Of
Feed
Feed coal
24-1
-2
-3
7-1
-2
-3
12-1
-2
-3
14-1
-2
-3
16-1
-2
-3
22-1
-2
-3
27-1
-2
-3
None
None
None
Air
Air
Air
Na -S+Air
2
Na S+Air
Na 2 S+Air
Fe7(SO K+Air
Fe"(SO K+Air
Fe0(SO,K+Air
z 43
NaHCO +Air
NaHCO^+Air
3
NaHCO +Air
(NH ) CO +Air
(NlO^COil+Air
(Nil ) CO +Air
Na 02+Air
Na 02+Air
Na 0 +Air
4.3
7.4
9.0
5.3
7.2
8.9
7.2
5.0
8.9
3.1
5.1
6.9
7.0
5.1
9.1
7.8
5.2
8.8
8.3
5.1
6.9
98.0
94.0
97.7
94.0
90.9
87.8
92.1
91.6
83.9
93.7
91.3
94.3
87.1
93.1
92.4
95.4
86.6
92.6
90.5
92.3
91.2
Product ,
percent
MAP
MF Ash
11.3
8.70
9.02
9.15
7.64
7.78
7.82
7.50
7.30
7.32
8.05
8.20
8.41
7.63
7.70
8.04
8.03
7.62
7.78
7.72
7.77
7.78
STot
4.07
3.79
—
3.53
3.56
3.61
3.74
—
—
3.58
—
—
3.51
—
—
3.76
—
—
,3.70
--
—
SPyr
1.36
1.27
--
1.00
1.00
1.15
1.01
--
—
1 . 08
—
—
1.03
—
—
1.06
—
—
0.98
—
—
Reduction, percent
Ash
23.0
—
32.4
31.2
30.8
33.6
35.4
35.2
28.8
27.4
25.6
32.5
31.9
28.8
28.9
32.6
31.2
31.7
31 . 2
31.2
STot
6.9
--
13.3
12.5
11.3
8.1
—
—
12.0
—
—
13.8
—
—
7.6
—
—
9.1
—
—
SPyr
6.6
—
26.5
26.5
15.4
25.7
—
—
20.6
—
—
24.3
—
—
22.1
—
—
27.9
—
—
-------
TABLE 29. EFFECT OF AQUEOUS OXIDATION PRETREATMENT ON PYRITE REMOVAL
DURING OIL AGGLOMERATION OF OHIO PITTSBURGH SEAM NO. 8 COAL
Product ,
Run No .
Feed Coal
Float at
1.59 Sp.
44-1
46-1
41-1
89-1
91-1
97-1
7-1
52-1
48-1
93-1
99-1
9-1
95-1
65-1
74-1
Chemical ,
g/100 g coal
Cr.
None
Air
Air
°2
°2
Na S (0.1)
Na^S (0.1)
Air +'"Na2S (1.0)
Air + Na?S (1.0)
07 + Na2S (0.1)
Na2CO3 (0.1)
Na2C03 (0.1)
02 + Na2C03 (0.1)
Sediment wash
water (a)
Sediment wash
water 'a/'
Na202 (1.0) + Air
Temp . ,
C
RT
96
RT
92
RT
95
RT
96
RT
RT
99
RT
RT
RT
96
Time,
min
900
30
30
30
30
30
900
30
30
30
30
30
240
5280
30
PH
6.7
7.2
8.3
3.7
2.9
4.7
4.0
9.7
10.9
4.7
4.5
3.7
4.5
3.8
2.7
11.5
Of
Feed
95.4
97.2
96.5
95.1
96.4
96.5
96.8
95.8
95.6
94.1
96.0
96.0
95.6
96.4
96.0
90.5
79.6
percent
MAF
MF Ash
10.50
8.69
7.44
6.50
6.16
6.98
6.91
6.68
6.62
6.03
5.84
6.67
7.13
6.53
6.86
6.96
6.54
6.79
STot
5.25
4.22
4.89
4.19
4.18
4.20
4.19
4.22
4.15
4.17
4.09
4.12
3.95
4.04
4.2,4
4.17
4.18
SPyr
2.24
1.30
2.32
1.65
1.57
1.63
1.54
1.58
1.51
1.49
1.48
1.93
1.39
1.35
1.82
1.57
1.65
Ash
17.2
29.1
38.1
41.0
33.5
34.2
36.3
36.9
42.5
44.3
36.4
32.1
37.8
34.6
33.7
37.7
26.5
Reduction ,
percent
STot
19.6
6.9
20.2
20.4
20.0
20.2
19.6
21.0
20.6
22.1
21.5
24.8
23.0
19.2
20.6
20.6
sPyr
42.0
(-3.6)
26.3
29.9
27.2
31.3
29.5
32.6
33.5
33.9
• 13.8
37.9
39.7
18.8
29.9
29.9
(a) The sediment wash water was filtrate of the slurry containing 100 g partially dried old coal
sediment and 500 ml distilled water.
-------
With reference to Table 29, the following qualitative observations
can be made:
1. As compared with the float-sink values, the oil
agglomeration products were lower in ash content but
higher in pyritic sulfur content. However, the total
sulfur contents of the pretreated samples were as low
as or lower than that of the float-sink value.
2. All of the pretreatments provided a cleaner product
than could be obtained by direct oil agglomeration
(Run 44-1). '
3. In general, the pyritic sulfur reductions were higher
with oxygen treatments than those with air treatments,
while the ash reductions were reversed.
4. A comparison of Runs 89-1 and 91-1 indicates that
the low temperature provided a higher pyrite reduction
than the high temperature. This may be due to the
lower solubility of oxygen at higher temperature.
5. In the sodium sulfide treatments (Runs 97-1 and 7-1),
a higher pyritic sulfur reduction was obtained at
lower temperature. This may indicate that the
depressing action of sodium sulfide was caused by
adsorption rather than by chemical reaction.
6. The results of Runs 89-1, 97-1 and 93-1 show that the
treatment with sodium sulfide and oxygen together pro-
vided a higher pyritic sulfur reduction than could be
obtained by either one alone. The results of Runs
89-1, 99-1 and 95-1 also show the similar synergetic
effect.
7. In the sodium carbonate treatments (Runs 99-1 and 9-1),
a higher temperature provided significantly cleaner
product. This suggests that the depressing effect of
sodium carbonate was apparently caused by chemical
reaction.
65
-------
8. The treatments with sediment wash water, which may
contain some iron-oxidizing bacteria, show that pro-
longed reaction was needed to depress the pyrite.
Electrolytic Treatment
Another approach was the electrolytic pretreatment of a coal slurry
prior to oil agglomeration. It was hoped that electrolytic reaction might
offer a selective means of modifying the surface characteristics of pyrite
particles. The apparatus used for the electrolysis is shown in Figure 10.
A stainless steel rod (3/4 in. dia. x 4 in.) was used as a rotating '
cathode and a sheet of brass or steel (4 x 8-1/2 in.) rolled into a cylinder
was used as an anode. The cathode chamber was kept separated from the anode
chamber by a porous alundum thimble (1-3/4 in. dia. x 5 in.). A 400 ml
beaker was used in all experiments. Coal slurry containing 25 g of the
ground Ohio Pittsburgh Seam No. 8 .(minus 48 mesh) was electrolyzed for
30 minutes at 10 volt potential and 0.5 ampere limiting current. Elec-
trolysis was carried out in two different configurations: one with the
porous thimble in place and the other without the thimble. The treated
, coal slurry was then agglomerated with 2.5 g of No. 2 fuel oil at 10 percent
slurry concentration. Tables 30 and 31 summarize the experimental conditions
and agglomeration results. In general, the electrolytic treatments were hot
as effective as the aqueous oxidation treatments on the pyrite removal
during agglomeration. This might be due to the poor reactor configuration
in which the oxygen bubbles generated from the . anode surface failed to make
good contact with the pyrite particles. The best pyrite removal was
obtained when sodium carbonate was used as an electrolyte (Run 42-1),
but the amount of coal recovery was very low.
Microwave Treatment
Another approach employed was the use of 2450 MHz microwave
energy. It was hoped that pyrite particles might be preferentially heated
by the microwave energy, thereby modifying their surface characteristics.
The ground Ohio Pittsburgh Seam No. 8 coal (minus, 48 mesh)' in either dry
or wet state was exposed to microwave energy under a nitrogen- atmosphere in a
66
-------
DC Power ©
Source ©
Ammeter
Variable Speed
Electric Motor
c
Magnetic Stirrer
— Rotating Cathode.
•Stationary Anode
""Porous Alumdum Thimble
FIGURE 10. EQUIPMENT FOR ELECTROLYTIC PRETREATMENT OF COAL SLURRY
-------
TABLE 30. EFFECT OF ELECTROLYSIS ON THE PYRITE REMOVAL DURING OIL AGGLOMERATION
OF OHIO PITTSBURGH SEAM NO. 8 COAL (WITHOUT THIMBLE)
00
Eroduct
PH
Run No .
Anode Electrolyte
Before
After
, percent
Of
Feed
'Feed Coal
Float at
1.59 Sp
44-1
19-1
19-3
19-4
34-1
34-2
34-3
42-r
. Gr.
No Pretreatment
Brass None
Brass .NaOH'- '
Brass NaOH^a^
Steel 0.5% NH^OH
Steel 0.1% Fe2(SO^)3
Steel 0.1% Na2"S
Steel 0.03% Na2C03
6.
3.
10.
7.
10.
2.
8.
5.
7
5
0
0
8
7
4
4
6.
5.
10.
10.
10.
2.
8.
6.
7
3
3
0
5 .
6
2
5
95
97
92
95
96
89
9.3
94
84
.4
.2
.3"
.6
.6
.2
.7
.6
.3
MF Ash
10
8
7
7
10
10
7
7
8
7
.50
.69
.44
.86
.21
.39
.73
.78
.66
.99
5
4
4
4
4
4
4
4
4
MAF
STot
.25
.22
.89
.31
—
.62
.38
.73
.92
.25
S
2.
1.
2.
1.
-
2.
'I.
2.
2.
1;
Reduction,
Pyr
24
30
32
90
-
33
86
13
17
48
Ash
17,2
29.1
25.1
2.8
1.0
26.4
25.9
17 .5
23.9
STot
19
6
17
-
12
16
9
6
19
.6
.9
.9
-
.0
.6
.9
.3
.0
percent
SPyr
42.0
(-3.6)
15.2
—
(-4.0)
17.0
4.9
3.1
33.9
(a) One molar sodium hydroxide solution w.as added to adjust the pH.
-------
TABLE 31. EFFECT OF ELECTROLYSIS ON PYRITE REMOVAL DURING OIL AGGLOMERATION
OF OHIO PITTSBURGH SEAM NO. 8 COAL (WITH THIMBLE)
PH
Run No.
Feed Coal
Float at
1.59 Sp.
44-1
19-11
19-10
32-1
32-2
19-7
19-5
Cr.
Anode (brass)
Cathode
Anode (brass)
Cathode
Anode (steel)
Cathode
Anode (steel)
Cathode
Anode (brass)
Cathode
Anode (brass)
Cathode
Coal
1 wt
1 wt
Coal
Coal
1 wt
Coal
1 wt
Coal
Old
Old
Coal
Content
slurry
. % CaCl2
. % CaCl2
slurry
slurry
. % NaOll ..
slurry
• % Na2S
slurry
coal sediment
coal sediment
slurry
Before
6
3
7
7
3
3
11
3
11
3
2
2
3
.7
.5
.7
.7
.5
.3
.9
.3
.8
.3
.5
.5
.5
After
6.7
5.2
12.0
5.9
11.8
2.6
11.8
2.3
11.8
4.0
3.3
3.8
10.8
Of
Feed
95.
97.
95.
87.
91.
87.
93.
53.
60.
91.
4
2
3
9
7
3
8
5
8
9
Product, percent
MAF Reduction, percent
MF
10
8.
7.
7.
8.
7.
7.
7.
27.
20.
9.
Ash STot Spyr Ash STot
.5 5.25 2.24
69 4.22 1.30 17.2 19.6
44 4.89 2.32 29.1 6.9
57 4.53 2.08 27.9 13.7
48 — — 19.2
44 4.26 1.94 29.1 18.9
86 4.42 2.01 25.1 15.8
14 4.16 1.92 32.0 20.8
67
32
23 -- — 12.1
sPyr
42.0
(-3.6)
7.1
—
13.4
30.27
14.3
—
-------
Varian Industrial Microwave Systems Model EW3-DPM35. After treatment, 25 g
of coal was taken and agglomerated with 2.5 g of No. 2 fuel oil at 10 per^
cent slurry concentration. Table 32 summarizes the treatment conditions and
agglomeration results.
Improvement in pyrite reduction could be noticed when the wet
coal impregnated with sodium hydroxide (Run 29-3) was heated by the micro-
wave. One advantage of the microwave treatment is short reaction time, i.e.,
seconds vs. minutes, and hence this treatment may be suited for continuous
pretreatment^before oil agglomeration
Wetting-Agent Treatment
Another approach was addition of chemical reagent from the known
classes of either wetting or dispersing agents. In the; pretreatment step,
100 g of ground coal (minus 48 me'sh) was mixed with 400 ml of distilled water
and a small amount of reagent. The slurry was agitated with a magnetic
stirrer at the room temperature for a specified time. After the pretreatment,
one quarter of the slurry was taken and agglomerated with 2.5 g of No. 2
fuel oil at 10 percent slurry concentration.
The specific- chemical reagents were chosen for the following
reasons:
a Sodium-di-octyl sulfosuccinate and sodium dodecyl sulfate
are commonly known as wetting agents. In a U.S. patent
/ 1 Q \
by Chia, these agents are. claimed to be effective f:or
desulfurizing high sulfur low grade coal.
9 Phytic acid and myo-inositol-2-monophosphate are chosen
because of their structural similarity with phosph'atidal-
inositol which is identified as the. wetting agent
secreted by bacteria during their oxidation of sulfide
minerals.
« Sodium metaphosphate, sodium carboxy methyl cellulose
and sodium tripolyphosphate are dispersing agents. A
(20)
U.S. Bureau of Mines study shows that they are
effective in dispersing mineral particles during selec-
tive flocculation of coal slimes.
70
-------
TABLE 32. EFFECT OF MICROWAVE TREATMENT ON PYR1TE REMOVAL DURING OIL
AGGLOMERATION OF OHIO PITTSBURGH SEAM NO. 8 COAL
Product,
Microwave
Run No. Coal Sample Energy, watt
Feed Coal
Float at
1.59 Sp. Cr.
16-1 Dry
29-1 Coal
powder 500
1000
+ 1% NaOH 500
Overdrled
29-3 Coal
Wet
+ 1% NaOH 500
paste
Exposure Temp., Of
Time, mln C pll Feed
95
3
2 238 4.7 96
3 120 10.4 96
5.9(a) 96
3 98 H-4, , 8*
6.9CdJ 92
.4
.6
.8
.9
.5
.5
percent
MAP Reduction, percent
MF
10.
8.
9.
8.
8.
7.
8.
Ash
50
69
10
18
12
31
21
STot SPyr Ash
5.25 2.24
4.22 1.30 17
4.77 2.22
13
4.27 2.14 22
22
4.14 1.69 30
21
.2
.3
.2
.7
.4
.8
STot SPyr
19.6 42.0
9.1 0.9
18.7 4.5
—
21.1 24.6
(a) pH was adjusted with HC1 solution before agglomeration.
-------
Table 33 summarizes the experimental results. The data show that
the reagents generally provided cleaner product than could be obtained
without the reagent. In particular, the results obtained with sodium
metaphosphate are surprisingly good and the product was cleaner than that
of 1.59 Sp. Gr. float. Although more work is needed to verify this
exceptionally good result, it appears that sodium metaphosphate disperses
the liberated, pyritic particles to prevent them from being -entrapped in the
agglomerated coal.
Combined Treatment
An exploratory experiment was conducted to examine the added
effectiveness of successive pretreatment steps. One hundred grams of the
ground Ohio Pittsburgh Seam No. 8 coal was mixed with 0.1 g sodium
carbonate in 300 ml distilled water and electrolyzed without the thimble as
described previously. After the electrolysis,' the treated slurry was
''divided into four parts and each part was agglomerated with 2.5 g of No. 2
fuel oil at the following conditions:
1. Agglomeration without further treatment.
2. Agglomeration after mixing with 0.25 ml of 5 percent
sodium metaphosphate solution.
3. Same as (-2) except after agglomeration, 0.25 ml of
0.1 percent Percol 728 cationic flocculant was added
before screening.
4. Same as (3) except sodium metaphosphate solution
was added.
The experimental results are shown in Table 34. Except Run 42-4,
the data indicate that the agglomerated product became cleaner as more
steps were added. The product of Run 42-3 was much cleaner than that of
1.59 Sp. Gr. float.
72
-------
TABLE 33. EFFECT OF CHEMICAL REAGENT ON PYRITE REMOVAL DURING OIL
AGGLOMERATION OF OHIO PITTSBURGH SEAM NO. 8 COAL
Product, percent " Reduction,
Reagent, Time, Of MAF percent
Run No .
Feed Coal
Float
1.59 Sp.
44-1
56-1
58-1
62-1
60-1
1-1
3-1
g/100 g coal min pH Feed MF Ash STot Spyr Ash STot
10.50 5.25 2.24
Cr. 95.41 8.69 4.22 1.30 17.2 19.6
None 6.7 97.2 7.44 4.89 2.32 19.5 6.9
Sodium-dioc tyl
sulfosuccinate (0.2) 100 7.3 96.6 6.98 4.20 1.61 24.5 20.0
Sodium dodecyl
sulfate (0.2) 100 7.3 96.0 8T05 4.37 1.77 12.9 16.8
Phytic acid
calcium salt (0.2) 100 6.8 96.2 6.37 4.37 1.73 31.1 16.8
Myo-inositol-2-
monophosphate (0.0004) 3900 4.8 92.5 6.61 4.44 1.77 28.5 15.4
Sodium metaphosphate (0.5) 30 4.2 94.0 6.39 4.10 1.29 30.8 21.9
Sodium carboxy methyl
SPyr
42
(-3
28
22
22
22
42
.0
.6)
.1
.0
.8
.0
.4
5-1
cellulose (0.1)
Sodium tripolyphosphate
(0.5)
30 4.1 95.2 7.85 4.23 1.60 15.0 19.4 28.6
30 5.1 97 6.96 4.31 1.68 24.7 17.9 25.0
-------
TABLE 34. EFFECT OF COMBINED TREATMENT ON OIL AGGLOMERATION
OF OHIO PITTSBURGH SEAM NO. 8 COAL
Run No.
Product, percent
Of MAP Reduction, percent
Treatment Feed MF Ash Sfot spyr Ash STot SPyr
Feed . 10.50 5.25 2.24
Float at
1.59 Sp. Gr. 95.4 8.69 4.22 1.30 17.2 19.6 42.0
42-1 Electrolysis 84.3 7.99 4.25 1.48 23.9 19.0 33.9
42-2 Electrolysis + sodium metaphosphate 86.1 7.21 4.12 1.38 31.3 21.5 38.4
42-3 Electrolysis + sodium metaphosphate
+ Percol 728 85.0 6.55 3.99 1.26 37.6 24.0 43.8
42-4 Electrolysis + Percol 728 86.5 10.19 — — 3.0
-------
SECTION 6
DISCUSSION
COAL RECOVERY FROM WASTE STREAMS
The coal mining industry is under constant pressure to limit the
effluents from coal mining and preparation operations and coal refuse
handling and water management are two areas of immediate concern for the
industry. Laws regulating pollution control and tailing water runoff exist.
The ultimate goal is to produce clear water for reuse in the preparation
plant, while the undesirable solids end up as a dry manageable solid that
can be disposed of as a landfill or as mine backfill to reduce acid mine
drainage. The less coal present in this solid, the more attractive it is
with respect to minimizing environmental impact and land requirements for
disposal while maximizing the recovery of a valuable fuel from what usually
is considered a waste.
As mentioned at the beginning of this report the present strategy
is to impound fine coal cleaning wastes in slurry ponds to permit sufficient
residence time for settling to occur before the water is discharged to
natural waterways or reused. This approach has resulted the accumulation of
billions of tons of refuse in active and abandoned waste piles and impound-
ments. A greater accumulation is anticipated as mining and coal cleaning
activity increase to meet the Nation's increasing dependence on coal.
The results from this study on the recovery of coal from fine
(minus 28 to 0 mesh) coal cleaning wastes suggest that good coal recovery
from sediments by the oil agglomeration technique is technically feasible.
The technique can be applied to black water and aged slurry pond sediments
directly, but partially dried and weathered sediments excavated from slurry
ponds require modest treatment before coal recovery is attempted. This
study has identified what appears to be the conditions to recover 90 percent
75
-------
or more of the coal value from wastes containing about 50 percent coal for
one small region in southeastern Ohio. Even within this region it was found
that conditions for recovery of coal values from black water sediments are
slightly different from those used for recovery of aged sediments. This was
due in part to recent changes in the coal cleaning plant unit operations
which produced a much finer suspension making the waste stream more responsive
to coal recovery by the oil agglomeration technique. What is even more
significant is that the technique can be modified slightly and applied to aged
sediments as well for recovery of a quality fuel without the associated mining
costs.
The quality of the coal recovered* from aged slurry pond
sediments and black .water sediments compared to that presently being
shipped from the mine (after jig washing), is given in Table 35.
The quality of the dryer product is also included to give .a com-
parison to fine coal. It can be seen that the recovered coals are lower in
ash and sulfur and generally of better quality than the coal shipped from
the mine. In addition the recovered coal can be dewatered easily. The
residues from the operations retain only about 2 to 5 percent of the
agglomerating oil used and consist of about 92 percent ash. Their mineral
composition probably consists of the unaltered major minerals normally
associated with coal (i.e., illites, kaolinite, montmorillonite, quartz,
gypsum, .pyrite, calcite, dolomite, siderite) and possibly many of the minor
minerals (and the trace elements commonly associated with them). Indica-
tions are that some of the pyrites liberated from the coal in the wastes
are removed in the process. Chemical treatment of the slurry by techniques
i
developed for reducing the pyrites in the coal (discussed later) could be
used to further reduce the pyritic sulfur in the recovered coal.
Since the residues from the coal recovery operation consist mostly
of unaltered mineral matter taken from the earth, they would be compatible
with any landfill disposal method. The residue slurry settles rapidly and
can be concentrated by settling. Since it now consists mostly of clays,
technology developed to improve settling of such materials could be applied
Using agglomeration technique without chemical treatment for enhanced
pyrite removal.
76
-------
TABLE 35. COMPARISON OF QUALITY OF COAL RECOVERED
FROM SEDIMENTS TO CLEANED COAL
Shipped
• Coal
Product
Clean Coal(a)
Dryer Product
MF
9
9
Ash,
%
.24
.84
MAF
Pyr
2.04
1.71
Sulfur, %
Total
4.88
4.97
Recovered from Sediment, .
from Slurry Pond (Avg)(C) 8.89 1.70 3.40
Recovered from Sediment/ v
from Black Water (Avg)U; 6.13 1.41 3.66
(a) Jig cleaned. '
(b) Fines before mixing for shipping.
(c) Average of values for high coal recovery-high ash, high recovery-
low ash, and low recovery-low ash.
77
-------
more specifically through the use of flocculants and/or coagulants. The
material also may be used as raw material directly (e.g., for ceramic
products) or as a source of mineral for metal recovery (e.g., alumina).
In addition to the coal recovery from the slurry wastes, the oil
agglomeration technique can be utilized for cleaning and dewatering of fine
coal. For example, oil agglomeration can provide more effective means
of cleaning ultrafine coal than the froth flotation. It was demonstrated
in Germany that the use of the oil agglomeration process for the minus 250
mesh coal improved the capacity and selectivity of fine coal cleaning cir-
(9)
cuit, and the product was easy to filter, rendering low moisture content.
If the coal cleaning industry adopts new desulfurization techniques such as
high-gradient magnetic separation, chemical treatments and bacterial treat-
ments in which the coal sizes are required to be very small for effective
treatment, the oil agglomeration technique will be a viable means of
isolating and dewatering of the desulfurized product. Furthermore, if the
use of coal-oil mixture becomes widely -accepted in commercial boilers, the
oil agglomeration technique will be an ideal method of coal cleaning
because the oil used for agglomeration will not represent any additional
cost and the agglomerated product can be readily dispersed in the oil.
PREPARATION OF COAL FEED TO LIQUEFACTION PLANTS
Reports about facilities proposed to prepare clean fuels by
liquefaction of coal often skim over the critical aspects of the coal
preparation plant operation that prepares the fine coal to be fed into the
oil slurry preparation prior to entering the liquefaction process. The
coal must be ground to a fine size usually 70 percent minus 200 mesh
(0.05 mm) and then mixed with recycle oil to prepare a slurry. Grinding
the coal to this size is an extremely dusty operation when done dry but
wet grinding is usually ruled out because of the energy required for drying
before the coal can be utilized. However, wet grinding would be advan-
tageous for environmental and health reasons.
This study demonstrated that coal can be recovered from fine coal
slurries with coal liquid distillates as well as with hydrocarbons derived
from petroleum. These agglomerates could be dewatered to levels of
73
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^ 15 percent. In addition when a coal is ground to minus 200 mesh, signif-
icant amount of mineral matter is liberated and can be removed during
agglomeration. Thus a process is envisioned where wet grinding can be
utilized to remove significant ash from the coal feed before entering the
liquefaction step. The feed would be agglomerated with an oil used to
prepare the oil slurry feed to the liquefaction process preheater or
dissolver. The reduced ash loading would significantly reduce filtration
and/or catalyst life problems and reduce trace element emissions in the
subsequent gasification of the char or liquefaction residues.
ENHANCEMENT OF PYRITE REMOVAL
These studies have shown that chemical treatment specifically
directed at making the surface of pyrite hydrophylic have improved the
removal of pyrite liberated from the coal. Pyrite removal of 42 percent
has been reached and is equal to that obtained by float-sink separation at
a specific gravity.of 1.59. This is especially significant for the fine
size of the fresh coal evaluated (minus 48 mesh Tyler). The two chemical
treatments capable of producing this level of removal are (1) the treatment
with oxygen at room temperature of a slurry of coal containing 0.1 g of
N32COT/100 g of coal and (2) the treatment of a coal slurry with 0.5 g of
sodium metaphosphate/100 g of coal. In Treatment 1, it is believed that
the pyrite surface was oxidized to produce a hydrated ferric oxide layer
which renders the surface hydrophylic. When Treatment 2 is used, it is
believed that the pyrite surface adsorbed phosphate ion to make them
wettable. When the treatment with sodium metaphosphate was preceeded by
electrolysis and then followed by the addition of a flocculant, further
reductions in pyritic sulfur were realized but in general did not exceed
that attainable in laboratory float-sink separations.
ESTIMATION OF PRODUCT COST
The experimental data have shown that the oil agglomeration
technique can recover low ash coal from the coal preparation plant wastes.
Furthermore, the sulfur content of the agglomerated product can be
79
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significantly reduced through suitable treatments. For the purpose of
preliminary estimation of product cost, a conceptual design of an oil
agglomeration plant was made. Figure 11 shows a hypothetical flowsheet of
the oil agglomeration unit which can be either an add-on unit to an existing
coal cleaning plant for the purpose of recovering coal fines from the
thickener underflow or a portable plant for reclaiming coal values from the
coal waste .pond sediments.
The thickener underflow or waste pond sediment containing 35 wt.
percent solids is fed to the pretreatment tank where sodium carbonate and
air bubbles are introduced to oxidize the slurry. The pretreated slurry is
then sent to the conditioning tank where the slurry is diluted to 10 wt.
percent solid and sodium metaphosphate is added to provide good dispersion.
The conditioned slurry is pumped to the oil agglomeration tank
where oil is added and agglomeration is carried out with a high-shear
agitation. After agglomeration is completed, the slurry is transferred to
the flqcculation tank where flocculating agent is added to facilitate
settling of reject materials. The slurry is then sent to a vibrating screen
where agglomerated coal is separated from residue slurry. The recovered
coal is fed into a dewatering centrifuge to reduce the moisture content.
The residue slurry is pumped to a static thickener where reject materials'
are settled, and water and some oil are recovered for recycling.
The material balances shown in Figure 11 are chosen based on the
information obtained from this experimental work. From an economic point
of view, one of the most important variables in the process is the amount
of oil used. The experimental data have shown that a 5 percent oil concen-
tration will give adequate recovery of coal when the No. 6 fuel oil-kerosene
mixture.'was used (Figure 5). With these values, material costs for the
agglomeration process are estimated and summarized in Table 3.6.
The results show that the total material cost is $11.48/ton of
product, of,which about 97 percent represents the cost of oil. In addition,
cost of power requirement will range from 20 to 30c/ton of .product (@ 2.5c/
kWh). The total capital and fixed costs are approximately $2.00/ton of
(21)
product. With these economic estimates, the product cost will be about
$14/ton. Considering the current market price of coal at $20/ton, it
appears that the oil agglomeration process is economically viable in the
80
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Thickener Underflow
or
Waste Pond Sediment
35 TPHS
265 GPMW
Soda Ash
Air
70 Ib/hr
Pretreatment
Tank
Sodium
Metaphosphate
7 Ib/hr
Conditioning
Tank
Oil
505 gal/hr
Oil Agglomeration
Tank
Flocculant
0.35 Ib/hr
Flocculation
Tank
Recovery Screen
995 GPMW Water
Recycle
Water
Refuse
Coal
18 TPHS
72 GPMW
17 TPHS'
1188
GPMW
Dewatering
Centrifuge
Static Thickener
0.5 TPHS
60 GPMW
Product
17.5 TPHS
12 GPMW (15% Moisture)
FIGURE 11. FLOW DIAGRAM OF OIL AGGLOMERATION PROCESS
81
Refuse
17.5 TPHS
253 GPMW
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TABLE 36. MATERIAL COSTS FOR OIL AGGLOMERATION PROCESS
Item
Soda ash
Sodium metaphosphate
Flocculant
Kerosene
No. 6 fuel oil
Total
Feed Rate
70 Ib/hr
7 Ib/hr
. 0.35 Ib/hr
444 gal/hr
61 gal/hr
Unit Pric.e
$91/ton
$33/100 Ib
$1.77/lb
$0.40/gal
$0.28/gal
Costs
$/Tdn of Clean Coal
0.18 '
0.13
0.04
10.15
0.98
11.48
82
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case of coal recovery from wastes that have essentially no value.
As discussed above, the major cost determinant of the oil
agglomeration product is the cost of the oil used. The oil used, however,
will contribute to the overall heating value of. the product. The heating
value of agglomerated product using 5 percent oil can be estimated as:
Heating value of marketed coal - 11,000 Btu/lb
Heating value of oil - 140,000 Btu/gal
Heating value of agglomerated coal - 11,484 Btu/lb
Hence, the product cost based on .the heating value will be 61C/MM Btu
compared to the market price of coal at 91C/MM Btu.
In addition to the profitability, oil agglomeration provides a
number of additional possible advantages. In particular, the oil agglomer-
ation process will significantly reduce the waste volume which will not
only save handling and disposal costs but also reduce environmental
problems from its disposal.
83
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REFERENCES
1. Mezey, E. J., S. Singh and D. W. Hissong. Fuel Contaminants: Volume 2,
Removal Technology Evaluation, EPA 600/2-76-177b, U.S. Environmental
Protection Agency, Research Triagnle Park, N.C., 1976, 316 pp.
2. Mezey, E. J. and S. Singh. Fuel Contaminants: Volume 3, Removal
Feasibility Studies, Draft Report prepared by Battelle's Columbus
Laboratories for EPA, Industrial Environmental Research Laboratories
at Research Triangle Park, N.C.. , 1977.
3. Min, S. Physical Desulfurization of Iowa Coal, Energy and Mineral
Resources Inst. Publication IS-1CP-35, Iowa State University, Ames,
Iowa, March 1977.
4. Capes, E. C., A. E. Mcllkinney and A. F. Sirianni. Agglomeration from
Liquid Suspensions—Research and Applications. In: Agglomeration 77
(Proc. of the 2nd Int. Symp. on Agglomeration) Vol. 2, Am. Inst.
Min. Met. and Pet. Eng., New York, N.Y.,'l977.
5. " Bhattachayya, R. N., A. K. Moza and G. E. Sarkar. Role of Operating
Variables in Oil Agglomeration of Coal, Ibid.
6. Swanson, A. R.., C. Bensley and S. K. Nical. Some Fundamental Aspects
of the Selective Agglomeration of Fine Coal, Ibid.
7. Hoffman, L., J. B. Truett, and S. J. Aresco. An Interpretative
Compilation of EPA Studies Related to Coal Quality and Cleanability,
MITRE Technical Report, MTR-6648, March 1974, pp. 107-112.
8. Deurbrouck, A. W. Personal Communication, October' 1977.
9. Bogenschneider, B. and H. Kubitza. The Olifloc Process for the
Dewatering and ^Cleaning of Ultras-Fine Coal Slurries. Paper presented
a;t the 15th Biennial Conference of the Institute for Briquetting and
Agglomeration, August 22-25, 1977, Montreal, Quebec, Canada.
10. Fisher, R. W. and T. D. Wheelock. Advanced Development of Fine Coal
Desulfurization and Recovery Technology. Fossil Energy Division
Quarterly Techincal Progress Report, Oct. 1, 1976-Dec. 31, 1976.
Ames Laboratory, ERDA, Ames, Iowa.
11. Busch, R. A., R. -R. Backer and L. A. Atkins. Physical Property Data on
Coal Waste Embankment Material. U.S. Bur. of Mines- RI-7964, 1974.
84
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12. Busch, R. A., R. R. Backer, L. A. Atkins. Physical Property Data on
Fine Coal. Refuse. U.S. Bur. of Mines RI-8062, 1975.
13. Browning, J. S. Recovering Fine-Size Coal from Alabama Surface Mine
Washer Wastes Using the Humphreys Spriral. MRI Technical Series
IR No. 2, Mine Resources Institute and Experiment Station, University
of Alabama, 1977.
14. Anon. Underground Disposal of Coal Mine Wastes. Report to the
National Science Foundation by the Study Committee to Assess the
Feasibility of Returning Underground Coal Mine Wastes to Mined-Out
Areas, Environmental Studies Board, Board on Energy Studies, National
Academy of Science, Washington, D.C., 1975.
15. Capes, C. E. et al. Rejection of Trace Metals from Coal During
Beneficiation by Agglomeration. Env. Sci. and Tech. 8(1), 35, 1974.
16. Sun, S. C. and W. L. McMorris, Factors Affecting the Cleaning of Fine
Coals by the Convertol Process. Mining Eng. 11(11), 1151 (1959).
17. Capes, C. E., A. E. Mcllhinney, A. F. Sirianni, and I. E. Puddington.
Bacterial Oxidation in Upgrading Pyritic Coals. Canadian Mining and
Metallurgical (CIM) Bulletin 66, 88 (1973).
18. Chia, T. Y. Method of Desulfurizing Coal, U.S. Patent 3,988,120,
Oct. 26, 1976.
19. Zabic, J. E. Microbial Biogeochemistry, Academic Press, New York
(1969), p. 133.
20. Hucko, R. E. Beneficiation of Coal by Selective Flocculation - A
Laboratory Study. U.S. Bureau of Mines, RI-8234 (1977).
21. Capes, E. C., A. E. Smith and I. E. Puddington. Economic Assessment
of the Application of Oil Agglomeration to Coal Preparation.
Canadian Mining and Metallurgical (CIM) Bulletin 67, 115 (1974).
85
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TECHNICAL REPORT DATA
(Please read faarucrions on the reverse before completing]
1. REPORT NO.
EPA-600/7-79-025b
2.
3. RECIPIENT'S ACCESSION*-NO.
4. TITLE AND SUBTITLE
Fuel Contaminants: Volume 4. Application of Oil
Agglomeration to Coal Wastes
5. REPORT DATE
January 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOH(S)
E.J.Mezey, Seongwoo Min, and Dale Folsom
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Batte lie-Columbus Laboratories
505 King Avenue
Columbus , Ohio 43201
10. PROGRAM ELEMENT NO.
EHE623
11. CONTRACT/GRANT NO.
68-02-2112
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Industrial Environmental Research Laboratory
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final: 8/77 - 4/78
14. SPONSORING AGENCY CODE
EPA/600/13
is. SUPPLEMENTARY NOTES ffiRL-RTP project officer is Lewis D. Tamny, Mail Drop 61, 919/
541-2709. EPA-600/2-76-177a and -177b are earlier reports in this series.
is. ABSTRACT
rep0rt gives results of a study of the application of oil agglomeration
to coal wastes. There are an estimated 3000-5000 sizeable active and abandoned
coal waste piles and impoundments in the eastern U.S. coal fields alone, containing
3 billion tons of refuse, part of which are slurry ponds. The impoundments, contain-
ing coal fines from coal preparation/cleaning plants, are a ready reserve of mined
fuel for use in times of shortages. It appears that oil agglomeration could contribute
significantly to the removal of contaminants before the conversion process is under-
taken. The ability of agglomeration to dewater finely ground wet coal also suggests
further incorporation of the process in any environmentally sound preparation plant
supplying these conversion plants. Early studies indicated that, although agglomer-""
ation can effectively remove much of the ash forming minerals . it was unable to
separate the liberated pyrite from coal. This program was undertaken to investigate
several approaches, identified during the first phase, to enhance pyrite removal du-
ring agglomeration and to demonstrate the utility of the technology to reduce the
environmental impact of increased quantities of coal cleaning refuse. Study results
show that the coal recovered is of better quality than the coal now being shipped from
the mine, in that sulfur and ash values are lower. Coal value recoveries were >90%.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Croup
Pollution
Coal
Wastes
Agglomeration
Dewatering
Coal Preparation
Liquefaction
Tailings
Slime
Pyrite
Desulfurization
Pollution Control.
Stationary Sources
Coal Waste Piles
Oil Agglomeration
13B 07D
21D,08G
08H
13H,07A
081
13. (DISTRIBUTION STATEMENT
Unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
95
20. SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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