111111111111111111111111111111111111111111111111111111111111111111111111111
US007128767B2
(12) United States Patent
French et al.
(10) Patent No.:
(45) Date of Patent:
US 7,128,767 B2
Oct. 31, 2006
(73) Assignee: GTL Energy, Wellington, CO (US)
(54) METHOD TO UPGRADE LOW RANK COAL
STOCKS
(75) Inventors: Robert R French, Wellington, CO
(US); Robert A. Reeves, Arvada, CO
(US)
7/1980 Krorruey 44/6
5/1982 Burns 44/6
5/1982 Draper et al. 44/24
6/1983 Pike 44/6
11/1983 Yaghmaie et al. 44/51
6/1987 Mark 106/283
1111988 Hueschen 44/51
2/1990 Najjar et al. 44/51
7/1991 Kennepohl et al. 44/502
12/1991 Koppelman 44/621
6/1994 Child 44/608
10/1998 Dean........................... 34/340
5/2000 Benham et al. 208/950
1112001 Waycuilis 585/314
3/2003 Shah 210/765
12/2003 French et al. 518/700
4,214,875 A
4,331,445 A
4,331,446 A
4,389,218 A
4,417,902 A
4,670,058 A
4,783,198 A
4,904,277 A
5,033,230 A
5,071,447 A
5,324,336 A
5,815,946 A
6,068,760 A
6,313,361 Bl
6,533,945 Bl *
6,664,302 Bl
Jul. 1, 2004
( *) Notice:
(22) Filed:
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 0 days.
(21) Appl. No.: 10/884,393
(65) Prior Publication Data
Related U.S. Application Data
(60) Provisional application No. 60/484,564, filed on luI.
1,2003.
(51) Int. CI.
CIOL 9/00 (2006.01)
CIOL 9/02 (2006.01)
(52) U.S. CI. 44/620; 44/280; 44/281;
44/282; 48/202
(58) Field of Classification Search 44/620,
44/280,281,282; 48/202
See application file for complete search history.
(56) References Cited
U.S. PATENT DOCUMENTS
* cited by examiner
Primary Examiner---Cephia D. Toomer
(74) Attorney, Agent, or Firm-Sheridan Ross, Pc.
The ash content of raw coals, lignite, and other carbonaceous
materials is reduced by leaching the high-ash material
with an aqueous acidic waste product produced by a
Fischer-Tropsch reaction. The acidic aqueous waste is
mixed with coal and process conditions are described. The
claim takes advantage of using otherwise uneconomic coal,
lignite or other carbonaceous material by upgrading the
material to a suitable feedstock for combustion in a power
plant or gasifier.
US 2005/0039386 Al Feb. 24, 2005
(57) ABSTRACT
3,996,026 A 12/1976 Cole 48/197 21 Claims, 1 Drawing Sheet
25
Raw ~1
:~hcoal 3
Crush~
~4 5 ~~v,~r. ~ '" ~'
7 ".-v Solid-liqUid Separatio Precipitation-ClarificationLSludge to Disposal ,,:.:t. ~'~M.k>'Jp FffimW_
19 ~ 20 16 17 (J
t ~ Sl t ~22 18
Gasifier~ . ag 0
~ -, Disposal
23 t 21
'-----'- Fischer-Tropsch
Reactor ~24
26~
Naphtha
27 ~Distillate Fuel
Wax Products
u.s. Patent Oct. 31, 2006 US 7,128,767 B2
25
1
Raw ~ ::::reoa
, 3
Crush~ f--4 5
,------.. Agitated vessr 9
6~ 8 ~ 10 ~1
7 ,r./ Solid-Liquid Separatio Precipitation-ClarificationL Sludge to Disposal
14 ~Jse .. 15 ~3~Make-Up Fresh Water
19 ~ 20 16 17 (J
+~ 51 t ~22 18
Gasifier..---... . ag 0
~ "Disposal
23 + 21
L------'-___ Fischer-Tropsch
Reactor ~24
26~
Naphtha
27 ~Distillate Fuel
Wax Products
Figure 1
US 7,128,767 B2
FIG. 1 is a schematic diagram of one embodiment of the
50 present invention.
2
SUMMARY OF THE INVENTION
DETAILED DESCRIPTION OF THE
INVENTION
BRIEF DESCRIPTION OF THE DRAWING
The methods of the present invention leach a significant
portion of the ash constituents of coal or lignite with
Fischer-Tropsch (FT) waste water. The process can be
conducted continuously or in batches. The process is amenable
to the use of any carbonaceous material commonly
used as a feed to a gasification facility. This feed includes,
but is not limited to, anthracite, low rank coals, bituminous
coals, subbituminous coals, brown coal, cannel coal and
lignite. For the purposes of this disclosure and the appended
claims, the term "coal" is used to encompass each of these
carbonaceous natural fuels.
All coals contains various concentrations of noncombustible
materials called ash. The constituents that form ash
The present invention utilizes an inexpensive source of
aqueous acidic reagent to upgrade coal for certain gasification
applications. Coal gasification plants produce a syngas
consisting principally of carbon monoxide and hydrogen.
When fed to a Fischer-Tropsch (FT) reactor, this syngas
produces both salable liquid products and an acidic waste
water. Operators of FT plants must incur costs to dispose of
this waste water which consists of acetic acid, alcohols, and
other light molecular weight organic compounds. This material,
because of its acidic nature, is a potent leaching reagent
for removing ash from coal feedstock. Thus, the methods of
the present invention treat coal with an aqueous waste
product, namely an aqueous acidic waste liquor produced by
the Fischer-Tropsch process. The treatment includes contacting
coal with FT waste water to remove ash, thereby
upgrading the quality ofthe coal. The mixture of coal and FT
waste water is preferably agitated in a vessel for sufficient
time to dissolve materials contained in the coal including
sodium, potassium, calcium and magnesium.
ity coal reserves, especially those found in abundance in the
western United States in abandoned coal waste piles in
Appalachia, and in many other areas in the world, could be
economically useful if a practical method were available to
enhance the quality of the coal. Upgrading low-rank coals
and lignite by reducing the amount of sodium present would
greatly improve the utilization value ofthe fuel. A significant
amount of sodium in the coal is associated with basic
compounds that dissolve in acids and other chemicals.
10 Unfortunately, the high cost ofthese acids and other reagents
make the upgrading process economically unattractive to
both coal producers and users. The cost of the feedstock
(coal, natural gas or petroleum) constitutes the majority of
the overall cost of gasification and conversion. The cost of
15 coals increases with the quality and therefore an inexpensive
process that would upgrade coal, particularly poor-quality
coal, prior to gasification is needed to enhance the overall
economics of gasification and conversion. In particular, the
process would be beneficial if it reduced ash minerals such
20 as those containing sodium, potassium, calcium and magnesium,
elements that often create difficulty with gasification
and combustion, to levels that make the use of low rank
coals economically feasible.
FIELD OF THE INVENTION
CROSS REACTION TO RELATED
APPLICATION
BACKGROUND OF THE INVENTION
1
METHOD TO UPGRADE LOW RANK COAL
STOCKS
The invention provides methods of treating coal with a
liquid waste product to up-grade the quality of the coal.
Because the United States has become increasingly
dependent on foreign sources of natural gas and petroleum,
recent focus has shifted to the abundant domestic sources of
coal to replace a portion ofthe foreign sources of natural gas
and petroleum. Switching from foreign energy sources to
domestic coal will lead to price stability and increased
national security.
Coal remains an important source of fuel for electricity 25
generation and a feedstock for coke making and chemical
production. Coal is preferred to natural gas and petroleum
because of its secure domestic supply and relatively low,
stable price. However, using coal requires more extensive
processing than natural gas and petroleum to mitigate dust 30
and gas emissions and other environmental concerns. Many
investigations have been undertaken to mitigate dust, nitrous
oxide, and sulfur dioxide emissions from coal-fired power
plants and other sources that use coal. Additionally, other
pollutants such as mercury have recently come under scru- 35
tiny by governments and health organizations. As a result,
future regulations may force coal users to significantly
reduce mercury and other heavy metal emissions at great
cost.
Coal gasification offers favorable environmental benefits 40
and high energy conversion efficiencies relative to traditional
combustion methods used by pulverized, coal-fired
power plants. Gasification occurs when coal is placed in a
vessel under high temperature and pressure and mixed with
steam and oxygen. The organic materials contained in coal 45
are converted into carbon monoxide, carbon dioxide, hydrogen,
and other compounds. The combustible components
carbon monoxide and hydrogen are typically separated from
non-combustible water vapor, carbon dioxide and other
gases. The mixture of combustibles, often referred to as
synthesis gas or "syngas," provides a feedstock for combustion
turbines and gas-to-liquid processes such as the FischerTropsch
process. The Fischer-Tropsch process converts syngas
into valuable salable organic chemicals such as distillate
fuels, naphtha, and wax. Combustion turbines are typically 55
arranged in a combined-cycle configuration to produce more
electricity from a given amount of syngas.
The efficiency of gasification, and subsequent gas-toliquid
reactions in a Fischer-Tropsch process, largely
depends upon the quality and specific energy content of the 60
coal feedstock. High-quality feedstocks provide better conversion
efficiencies than low quality materials resulting in
reduced carbon dioxide emissions from high-quality feedstocks.
Countries with few natural gas or petroleum reserves, 65
such as Germany and South Africa, rely on coal and the
Fischer-Tropsch process to produce liquid fuels. Low qual-
This application claims priority to U.S. Provisional Patent
Application Ser. No. 60/484,564, filed luI. I, 2003, incorporated
here, in its entirety, by this reference.
US 7,128,767 B2
3 4
2H2+CO~H20+CH2 Reaction (3)
If the gas mixture is passed over a catalyst under high
temperature and pressure, longer-chain hydrocarbons and
water are produced:
Other oxygenated species are also produced in Reaction
(3) including, primarily, acetic acid and ethanol. These and
other acids and alcohols are dissolved in the water that is
produced in the FT process. When iron-based catalysts are
used, the weight of oxygenates dissolved in the water is
between about 7% and about 10%. Of these oxygenates,
about two-thirds is acetic acid, giving a concentration of
between about 47 g and about 67 g of acetic acid per liter of
the aqueous products. The amount of aqueous phase containing
acetic acid produced in the FT reaction using an
iron-based catalyst and lignite feed is about 8wt %. Conversely,
when cobalt-based catalysts are used, a larger
amount of water is produced because the water gas shift
activity is generally very low. Additionally, the ratio of
alcohols to acids in the aqueous waste products is generally
higher when using cobalt-based catalysts.
The methods of the present invention utilize acidic aqueous
FT waste to extract ash from high-ash coal to produce
a coal product with improved value as a fuel. The raw,
high-ash coal is preferably crushed to a specified topsize.
The topsize may be selected to balance the cost of leaching
with the cost to separate leach liquors from the solids. Small
particles often leach faster than larger particles, but are more
difficult to separate from the leach liquor. The desired
particle size is selected after measuring leaching rates and
liquid-solid separation characteristics. Preferably, the coal is
crushed to a particle size between about 0.5 mm and about
15 mm in the longest dimension. More preferably, the coal
is crushed to a particle size between about 1 mm and about
2 mm in the longest dimension.
The crushed coal is contacted with acidic FT waste water
to leach ash from the coal. Preferably, the FT waste water is
wanned to a temperature between about 20° C. and about
70° c., more preferably, the FT waste water is warmed to a
temperature between about 40° C. and about 65° c., even
more preferably, the FT waste water is wanned to a temperature
between about 50° C. and about 60° C. While the
FT waste water can be poured over the coal as a stream to
remove ash, the best leaching of the ash from the coal is
accomplished by mixing the coal in the FT waste water. A
slurry is created with crushed coal and Aqueous FT waste.
The slurry mixture is agitated in the vessel for a period of
time that is sufficient to allow the desired reduction in ash to
occur. The time is chosen as a function of mixing efficiency,
temperature, particle size, ratio between the quantity of FT
waste water and coal solids present in the agitated vessel,
and the leaching rate of the coal. Economics and the desired
coal quality are taken into consideration when specifYing the
retention time. To thoroughly mix the coal and the Aqueous
FT waste, crushed coal is typically agitated in a suitable
vessel with the FT waste water for a period ofbetween about
1 minute and about 30 minutes. Preferably, the coal and the
FT waste water are mixed together for a period of between
about 3 minutes and about 15 minutes. More preferably, the
60 coal and the FT waste water are mixed together for a period
of about 10 minutes.
This mixing process is best accomplished by feeding the
coal and the FT waste water into an agitated vessel at a
controlled rate. The ratio of coal to FT waste water is chosen
65 to ensure that adequate leaching occurs without excessive
use of FT waste water. The specific characteristics of the
Reaction (2) coal feed are monitored to match the appropriate amount of
Reaction (1)
In 1923, Gennan scientists Fischer and Tropsch developed
a method of producing synthetic hydrocarbons by
passing steam over hot coke to fonn carbon monoxide and
hydrogen, the water gas reaction:
include silicon, aluminum, iron, titanium, calcium, sodium,
potassium, magnesium and minor concentrations of other
elements. The depositional environment and method of
mining and preparation determine which of these constituents
of ash are present in the coal. The ash materials are
deleterious to combustion and gasification because they
dilute the valuable organic compounds that provide carbon
and hydrogen. Ash is typically heated to melting temperatures
in the combustion and gasification process to fonn a
liquid slag that is ejected from the boiler or gasification 10
vessel. A portion ofthe feedstock is consumed to provide the
heat contained in the molten slag, resulting in an energy loss.
Therefore, it is preferable to use low-ash feedstock to
minimize the amount of fuel required to melt ash and fonn 15
slag.
The composition of the ash predicts how the ash will
behave during combustion or gasification. The melting temperature,
slag viscosity, and tendency to adhere to refractory
and tube surfaces in a boiler or gasification vessel are 20
influenced by the relative concentrations of the elements that
compose the ash. Some coals are unacceptable for combustion
or gasification because they exhibit adverse behavior.
These adverse ash properties have created enormous economic
losses for coal producers and users. For example, coal 25
and lignite from the northern Powder River Basin and North
Dakota are otherwise valuable coal reserves that have
greatly limited application due to unfavorably high levels of
undesirable constituents in the ash, such as sodium.
30
Mining companies, utilities, and governmental agencies
have worked to identifY the ash constituents that lead to
unacceptable behavior during combustion and gasification.
Potential methods to reduce the total ash content and specific
ash constituents have been identified. But many of the 35
proposed processes have proven to be too costly or are
incompatible with commercial gasification practices. As a
result, enormous reserves of domestic coal and lignite
remain underutilized.
Certain ash constituents are amenable to leaching by 40
acids. Typically, the basic constituents of sodium, calcium,
potassium and magnesium can be leached with acids and
separated from the coal by traditional liquid-solid separation
and rinsing methods improving the ash characteristics and
making a suitable fuel for combustion or feedstock for 45
gasification.
Many low-rank coals and lignite contain sufficient concentrations
of sodium that may affect their utilization characteristics.
Sodium reduces the melting temperature of the
ash formed during combustion when the partially melted ash 50
particles can stick to heat transfer surfaces and reduce the
amount of heat available to generate steam. Ash deposits
also restrict the passages that pass flue gas through the
boiler, thus reducing efficiency. In gasification applications,
sodium can adversely affect ash handling and conversion 55
reactions.
When an iron-based FT catalyst is used to convert water
and carbon monoxide into hydrogen and carbon dioxide, the
water gas shift reaction occurs:
US 7,128,767 B2
20 0 C. Leach Temperature 65 0 C. Leach Temperature
15- 15-
60 Coal 3-min Leach min Leach 3-min Leach min Leach
Powder River 13 41 58 78
Basin
Subbituminous
Texas Lignite 28 68 60 72
North Dakota 35 58 53 67
65 Lignite
Morwell 35 66 67 82
Percent Reduction in Untreated Coal Sodium Content
TABLE 2
TABLE 1
83
79
47
29
Reduction in
Concentration, %
of Initial Value
Example 2
Ash
Constituent
This example demonstrates that sodium is substantially
reduced for the tested coals under moderate process conditions
using FT waste water as the leaching reagent. A series
oftrials was conducted with FT waste water to measure how
much sodium could be leached from various low-rank coals
and lignite.
FT Waste Water Leaching Conditions and Results-14 mesh Solids,
9 Wt % Solids Mixture, Atmospheric Pressure
Changes in Specific Ash Constituents by
Leaching with Agueous FT Waste
This example demonstrates the percent reduction in ash
using the methods of the present invention. In this example,
a low rank coal was leached with acidic Fischer-Tropsch
waste water. The total ash content (the non-combustible
fraction of the coal) was reduced by 30%. The corresponding
higher heating value was increased by almost 100 Btu/lb.
Specific ash minerals were reduced by the values listed in
Table 1.
Example 1
levels of ash to minimize the use of fresh water. In this
embodiment, the coal is crushed and mixed with warm FT
waste water for use with slurry-fed gasifier applications. In
these cases, the feed must be crushed to slurry size regardless
of subsequent treatment, so the cost of crushing is not
credited to the leaching application. Cost savings occur
because waste water disposal costs are minimized, and the
crushed coal does not have to be dewatered prior to making
slurry as the ash content is already at acceptable level. Thus,
the circuit established in this embodiment of the present
invention represents a means of recycling waste water and
decreasing fresh water consumption in the use of high
quality, low-ash content coals in slurry-fed gasifier applications.
6
EXAMPLES
5
FT waste water to achieve an acceptably high level of ash
removal without excessive FT waste water use. Important
factors to monitor in adjusting the coal to waste water ratio
include the quantity of leachable ash minerals present in the
coal and the strength ofacid contained in the FT waste water.
For example, when FT waste water containing 0.9 N acid
(acetic acid) was mixed with a subbituminous coal containing
4.81% ash (dry basis), approximately 0.3-gram equivalents,
or 0.4 liters of FT waste water per kilogram of coal
were required to completely leach the calcium, magnesium, 10
sodium, and potassium minerals. In commercial practice
however, a reduction in ash between about 50% to about
80% is typically sufficient to achieve the economically
desired increase in fuel value. Typically, the ratio of coal to
FT waste water is between about 1:1 and about 1:50 on a 15
wt/wt basis. More typically, the ratio of coal to FT waste
water is between about 1:5 and about 1:20 on a wt/wt basis.
Preferably, the ratio of coal to FT waste water is about 1: 10
on a wt/wt basis. The actual consumption ofFT waste water
and the time and temperature of agitation are then adjusted 20
accordingly.
Leached solids exit the vessel and are screened at a fine
aperture size to separate the leachate from the solids. Various
liquid-solid separation methods, such as filtering and settling,
and separation devices, such as thickeners and clari- 25
fiers, may be used to recover the finely sized solids. The
screened solids may be washed with fresh water to reduce
the concentration of leached materials. The drained and
rinsed solids are dried and stockpiled as fuel for a power
plant or feedstock for a gasifier. 30
Leachate, containing the dissolved ash minerals, is processed
by conventional water treatment processes to precipitate
and concentrate the dissolved minerals for disposal.
The clarified water, substantially free of dissolved materials,
is recycled to the process to further minimize the overall 35
water consumption.
In one embodiment of the present invention, a low rank
coal is prepared as feedstock for a gasifier using the aqueous
acidic waste water from a Fischer-Tropsch reactor which is,
in turn, fed the syngas from the gasifier to complete a circuit 40
with the water while utilizing a high-ash coal. Referring to
FIG. 1, raw high-ash coal (1) obtained from is received (2)
and crushed (3) to a particle size amenable for leaching. The
crushed product (4) is feed at a controlled rate to an agitated
vessel (5) where it is mixed with warm aqueous acidic waste 45
material (25) produced by the Fischer-Tropsch reactor (24).
The leached slurry (6) reports to liquid-solid separation (7)
where the leachate (8) is partitioned from the leached solids
(12). The drained leached solids (12) are rinsed (14) with
clarified water (13) and makeup fresh water (17) is obtained 50
from a source of fresh water (18) to further remove residual
leachate.
The leachate (8) and rinse liquor (15) are combined and
precipitated and clarified (9) to produce a mineral-rich
sludge (10) for disposal (11). Clarified process water (13) 55
produced by the precipitation and clarification step (9) is
combined (16) with make-up fresh water (17) to rinse (14)
the leached solids (12).
Drained and rinsed low-ash solids (19) are fed to the
gasifier (20) producing slag (21) for disposal (22). Syngas
(23) containing principally hydrogen and carbon monoxide
feeds the Fischer-Tropsch reactor (24) producing salable
products (26) naphtha, distillate fuel, and wax (27). Aqueous
acidic waste (25) produced by the Fischer-Tropsch reactor
(24) reports to the agitated vessel (5) completing the circuit.
In another embodiment of the present invention, the
circuit described above is used with coals having acceptable
US 7,128,767 B2
7 8
* * * * *
9. The method of claim 5, wherein contents of the vessel
are maintained at a temperature ranging from about 20° C.
to about 70° C.
10. The method of claim 5, wherein contents ofthe vessel
are maintained at a temperature ranging from about 40° C.
to about 65° C.
11. The method of claim 5, wherein contents of the vessel
are maintained at a temperature ranging from about 50° C.
to about 60° C.
12. The method of claim 1, wherein the separating comprises
filtering the coal from the aqueous Fischer-Tropsch
waste.
13. The method of claim 1, wherein the separating comprises
settling the coal in the aqueous Fischer-Tropsch
15 waste.
14. The method ofclaim 1, wherein the ratio ofthe weight
of the coal to the weight of the aqueous Fischer-Tropsch
waste is between about 1: 1 and about 1:50.
15. The method ofclaim 1, wherein the ratio ofthe weight
20 of the coal to the weight of the aqueous Fischer-Tropsch
waste is between about 1:5 and about 1:20.
16. The method ofclaim 1, wherein the ratio ofthe weight
of the coal to the weight of the aqueous Fischer-Tropsch
waste is about 1: 10.
17. A method of leaching soluble ash from a coal comprising:
a. crushing a raw coal to form a crushed coal having a
particle size between about 0.5 mm and about 15 mm
in the longest dimension;
b. agitating the crushed coal in the presence of an aqueous
Fischer-Tropsch waste to promote contact of the aqueous
Fischer-Tropsch waste with the crushed coal and to
leach ash present in the coal into the aqueous Fischer-
Tropsch waste; and,
c. separating the crushed coal from the aqueous FischerTropsch
waste to isolate a coal having a sodium content
lower than the sodium content of the raw coal.
18. The method of claim 17, comprising the additional
step of suspending the coal having a lower sodium content
40 than the sodium content of the raw coal in an aqueous
solution to prepare a slurry feed for gasification.
19. The method of claim 18, wherein the aqueous solution
is an aqueous Fischer-Tropsch waste.
20. A method of leaching soluble ash from a coal com45
prising:
a. contacting a coal with a liquid consisting of an aqueous
Fischer-Tropsch waste; and,
b. separating the coal from at least a portion of the liquid,
wherein ash present in the coal is dissolved in the liquid
and removed from the coal in the liquid.
21. A method of leaching soluble ash from a coal comprising:
c. contacting a coal with a liquid consisting essentially of
an aqueous Fischer-Tropsch waste; and,
d. separating the coal from at least a portion of the liquid,
wherein ash present in the coal is dissolved in the
liquid, and removed from the coal in the liquid.
55
10
35
30
15min
Leach
65 0 C. Leach Temperature
3-min Leach
15min
Leach
TABLE 2-continued
Percent Reduction in Untreated Coal Sodium Content
20 0 C. Leach Temperature
3-min Leach
FT Waste Water Leaching Conditions and Results-14 mesh Solids,
9 Wt % Solids Mixture, Atmospheric Pressure
Lignite
Coal
The foregoing description of the present invention has
been presented for purposes of illustration and description.
Furthermore, the description is not intended to limit the
invention to the form disclosed herein. Consequently, variations
and modifications commensurate with the above teachings,
and the skill or knowledge of the relevant art, are
within the scope of the present invention. The embodiment
described hereinabove is further intended to explain the best
mode known for practicing the invention and to enable
others skilled in the art to utilize the invention in such, or 25
other, embodiments and with various modifications required
by the particular applications or uses of the present invention.
It is intended that the appended claims be construed to
include alternative embodiments to the extent permitted by
the prior art.
What is claimed is:
1. A method of leaching soluble ash from a coal comprising:
a. contacting a coal with an aqueous Fischer-Tropsch
waste; and,
b. separating the coal from at least a portion of the
aqueous Fischer-Tropsch waste, wherein ash present in
the coal is dissolved in the aqueous fischer-Tropsch
waste and removed from the coal in the aqueous
Fischer-Tropsch waste.
2. The method of claim 1, wherein the coal is selected
from the group consisting of lignite, bituminous coal and
subbituminous coal.
3. The method of claim 1, wherein the coal has a particle
size between about 0.5 mm and about 15 mm in the longest
dimension.
4. The method of claim 1, wherein the coal has a particle
size between about 1 mm and about 2 mm in the longest
dimension.
5. The method of claim 1, wherein the contacting com- 50
prises agitating the coal and the aqueous Fischer-Tropsch
waste in a vessel.
6. The method of claim 5, wherein the agitating is
conducted for a period of time between about 1 minute and
about 30 minutes.
7. The method of claim 5, wherein the agitating is
conducted for a period of time between about 3 minutes and
about 15 minutes.
8. The method of claim 5, wherein the agitating is
conducted for a time of about 10 minutes.
�/Xve'�^D��ttom:0in;margin-bottom:.0001pt;line-height: normal;mso-pagination:none;mso-layout-grid-align:none;text-autospace:none'>the slurry was contained in a non-adhesive liner. The reaction
temperature was varied as shown in Table I. In each
instance, the reaction was permitted to operate for one hour.
Fifty grams of sulfur with 100 psi oxygen overpressure were
provided.
Yields were obtained by observing the amount of acid
produced as compared to the amount of elemental sulfur
provided (a theoretical yield of 100% was calculated to
represent 3.06 grams H2S04 /g sulfur).
As can be seen from the results shown in Table I,
enhanced acid yields were obtainable with enhanced temperature
and the utilization of a dispersant, such as ground
sand, mineral processing tailings, or other suitable material.
TABLE I
O2 Usage
g °ig % of H2 SO4
Temp. Time % reacted theoretical Strength Yield
Test (0 C) (min.) % SO Sand SO 1.5 gig So (giL) gig So %
A 160 65 15 5.08 339 1.6 0.02 0.7
B 220 60 0 1.88 126 69 1.55 50.8
C 220 60 5 1.78 nla 84 1.75 57.1
D 235 55 0 1.88 126 114 2.38 77.4
E 235 60 5 1.82 122 121 2.63 86.0
F 250 60 0 1.92 128 129 2.70 88.4
G 250 60 5 2.08 139 134 2.83 92.4
40 Referring now to FIG. 2, residue 18 from liquid-solid
phase separation step 106 (FIG. 1) may be subjected to
various further processing to recover metals contained
therein, particularly precious metals, such as gold and silver,
which may exist in the residue. Depending on the charac- 45
teristics of residue 18, it may be advantageous to subject it
to neutralization and/or pH adjustment, such as is illustrated
in step 202. The residue once so treated may then be
subjected to further processing or otherwise utilized. Such
processing may include, with continued reference to FIG. 2, 50
an optional hot lime boil (step 204) followed by precious
metal recovery (step 208), such as through the use of
conventional cyanide leaching (step 206) followed by liquid-
solid phase separation (step 210). If cyanide leaching is
used, the resultant tailings may be recycled and utilized 55
elsewhere in connection with a hydrometallurgical process,
for example as a sulfur dispersant, (not shown), typically
after the cyanide is destroyed (step 212). Alternatively, the
tailings may be disposed (step 214). As those skilled in the
art will recognize, any number of precious metal or other 60
metal recovery methods may be suitable to achieve the
objective ofrecovering metals, such as precious metals (e.g.,
silver and gold) from residue stream 18, and therefore
alternative processing routes may be successfully utilized.
The Examples set forth hereinbelow are illustrative of 65
various aspects of certain preferred embodiments of the
present invention. The process conditions and parameters
EXAMPLE 2
A medium temperature pressure leaching residue containing
23.8 wt % elemental sulfur was prepared for pressure
leaching by making a feed slurry having lOA wt % solids
with synthetic raffinate and water. The feed was provided to
a stirred 2.0 liter Parr pressure leaching vessel at 225° C.
with 50 psi oxygen overpressure for 60 minutes. The resulting
solution contained 55.9 giL free acid and a bulk residue
(containing 2.9% elemental sulfur and 5.1% sulfate). Precious
metals were recovered from the residue in acceptable
quantities (i.e., 88% gold and 99% silver extraction).
The graphical profile of FIG. 3 further illustrates the
benefits on sulfuric acid yield as a function of temperature
and dispersant addition in accordance with various embodiments
of the present invention. These results generally
indicate that sulfuric acid production increases with increasing
temperature. Moreover, the comparison of Curve 32
versus Curve 34 illustrates sulfuric acid yield can be
enhanced, on the order of between about 5 and about 10%,
with the addition of a suitable dispersant, for example,
ground sand.
An effective and efficient method of producing sulfuric
acid from an elemental sulfur-bearing material has been
presented herein. The use of a dispersing agent as well as
elevated temperatures during pressure leaching may aid in
alleviating processing problems caused by the high viscosity
of elemental sulfur. Further, the present inventors have
US 7,041,152 B2
9 10
* * * * *
cess carried out at a temperature in the range of about 1400
C. to about 1800 C. the process comprising the steps of:
a) comminuting the elemental sulfur-bearing solid residue
from the pressure leaching process carried out at a
temperature in the range ofabout 1400 C. to about 1800
C. to produce a feed material;
b) forming a feed slurry by combining said feed material
with a dispersant wherein said dispersant comprises at
least one of a surfactant, ground sand, mineral processing
tailings, or combination thereof, and a sufficient
amount of fluid medium;
c) pressure leaching at least a portion of said feed slurry
at a temperature in the range of about 2200 C. to about
275 0 C. in an oxygen-containing atmosphere to yield a
pressure leach product slurry comprising a sulfuric acid
solution;
d) reducing the temperature and pressure of said product
slurry;
e) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a solid
residue;
f) recovering at least one metal value from said solid
residue.
7. The process of claim 6 wherein said step of recovering
at least one metal value from said solid residue comprises
recovering one or more precious metals contained in said
residue.
8. The process of claim 6 wherein said step of reducing
the temperature and pressure of said product slurry comprises
flashing said product slurry.
9. The process of claim 6, said process further comprising
the step of utilizing at least a portion of said sulfuric acid
solution in connection with other processing operations.
10. The process of claim 6 wherein said step of pressure
leaching at least a portion of said feed slurry is conducted at
a temperature in the range in excess of about 2350 C.
11. A process for the production of sulfuric acid and
recovery of precious metals from an elemental sulfur-bearing
material comprising the steps of:
a) providing an elemental sulfur-bearing material wherein
said elemental sulfur-bearing material comprises an
elemental sulfur-containing residue from a pressure
leaching operation;
b) pressure leaching said elemental sulfur-bearing material
at a temperature in the range of about 2200 C. to
about 275 0 C. in an oxygen-containing atmosphere in
an agitated multiple-compartment pressure leaching
vessel to form a product slurry comprising a sulfuric
acid solution;
c) adding a dispersant during said pressure leaching step
wherein said dispersant comprises at least one of a
surfactant, ground sand, mineral processing tailings, or
combination thereof;
d) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a solid
residue;
e) recovering at least one precious metal value from said
solid residue.
12. The process ofclaim 11 wherein said step of providing
an elemental sulfur-bearing material comprises providing an
elemental sulfur-containing residue from a pressure leaching
60 operation carried out at a temperature in the range of about
1400 C. to about 1800 C.
13. The process of claim 11 wherein said step of pressure
leaching comprises pressure leaching at a temperature of
about 2350 C.
40
20
advanced the art of copper hydrometallurgy by recognizing
the advantages of not only producing sulfuric acid solution
from sulfur-bearing materials, such as by-products of
medium temperature pressure leaching of copper sulfide
minerals, but also enabling the recovery of metals, such as
precious metals, entrained therein, which otherwise may
have been lost.
The present invention has been described above with
reference to a number of exemplary embodiments and
examples. It should be appreciated that the particular 10
embodiments shown and described herein are illustrative of
the invention and its best mode and are not intended to limit
in any way the scope of the invention as set forth in the
claims. Those skilled in the art having read this disclosure
will recognize that changes and modifications may be made
to the exemplary embodiments without departing from the 15
scope of the present invention. These and other changes or
modifications are intended to be included within the scope of
the present invention, as expressed in the following claims.
What is claimed is:
1. A treatment process comprising the steps of:
a) providing a feed stream comprising an elemental
sulfur-bearing material and a dispersant wherein said
dispersant comprises at least one of a surfactant,
ground sand, mineral processing tailings, or combination
thereof, and wherein said elemental sulfur-bearing 25
material comprises an elemental sulfur-containing residue
from a pressure leaching operation carried out at a
temperature in the range of about 1400 C. to about 1800
c.;
b) pressure leaching at least a portion of said feed stream 30
at a temperature in the range of about 2200 C. to about
275 0 C. in an oxygen-containing atmosphere in an
agitated multiple-compartment pressure leaching vessel
to form a product slurry comprising a sulfuric acid
solution;
c) separating at least a portion of said sulfuric acid 35
solution from said product slurry to yield a residue;
d) recovering at least one metal value from said residue.
2. The process of claim 1 wherein said step of recovering
at least one metal value from said residue comprises recovering
at least one precious metal from said residue.
3. The process of claim 1 wherein said step of pressure
leaching at least a portion of said feed stream comprises
pressure leaching at temperatures above about 2350 C.
4. A treatment process comprising the steps of:
a) providing a feed stream comprising an elemental 45
sulfur-bearing material-wherein said elemental sulfurbearing
material comprises an elemental sulfur-containing
residue from a pressure leaching operation
carried out at a temperature in the range of about 1400
C. to about 1800 c.; 50
b) pressure leaching at least a portion of said feed stream
in the presence of a dispersant wherein said dispersant
comprises at least one of a surfactant, ground sand,
mineral processing tailings, or combination thereof, at
a temperature in the range of about 2200 C. to about
275 0 C. in an oxygen-containing atmosphere in an 55
agitated multiple-compartment pressure leaching vessel
to form a product slurry comprising a sulfuric acid
solution;
c) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a residue;
d) recovering at least one metal value from said residue.
5. The process of claim 4 wherein said step of recovering
at least one metal value from said residue comprises recovering
at least one precious metal from said residue.
6. A process for recovering metal values from an elemental
sulfur-bearing solid residue of a pressure leaching pro
='fo�`�ie�^D��nt-family:"Times New Roman","serif";mso-fareast-font-family: HiddenHorzOCR'>at a temperature in the range of about 220° C. to
about 275° C. in an oxygen-containing atmosphere in
an, agitated multiple-compartment pressure leaching
vessel to form a product slurry comprising a sulfuric
acid solution;
c) adding a dispersant during said pressure leaching step;
d) separating at least a portion of said sulfuric acid
solution from said product slurry to yield a solid
residue;
e) recovering at least one precious metal value from said
solid residue.
17. The process of claim 16 wherein said step of providing
an elemental sulfur-bearing material comprises providing an
5 elemental sulfur-containing residue from a pressure leaching
operation carried out at a temperature in the range of about
140° C. to about 180° C.
18. The process of claim 16 wherein said step of pressure
10 leaching comprises pressure leaching at a temperature of
about 235° C.
* * * * *