United States Patent [19]
Reynolds et at
[11]
[45]
4,244,735
Jan. 13, 1981
[54] CHLORIDE LEACH PROCESS FOR
RECOVERING METAL VALUES IN THE
PRESENCE OF ARSENIC
[75] Inventors: James E. Reynolds; Enzo L.
Coltrinari, both of Golden, Colo.
[73] Assignee: Hazen Research, Inc., Denver, Colo.
[21] Appl. No.: 61,411
[22] Filed: Jut 27, 1979
[51] Int. CI.J C22B 13/04; C22B 11/04;
C22B 15/08; C22B 19/22
[52] U.S. CI. 75/101 R; 75/104;
75/114; 75/115; 75/117; 75/118 R; 75/120;
75/121; 423/39; 423/87
[58] Field of Search 75/101 R, 117, 118 R,
75/120, 121, 104, 115, 114; 423/39, 87
[56] References Cited
U.S. PATENT DOCUMENTS
13 Claims, No Drawings
Primary Examiner-G. Ozaki
Attorney, Agent, or Firm-Sheridan, Ross, Field &
McIntosh
An improvement in the hydrometallurgical recovery of
metals, such as, lead, silver, gold, antimony, and bismuth
from materials such as flue dust in the presence of
arsenic, comprising precipitating arsenic as an insoluble
ferric-arsenic compound in the first processing step,
carrying the insoluble arsenic compound through a
chloride leach step, in which it is insoluble, to recover
the metals, and disposing of the residue in which the
arsenic has been fixed with ferric ions to render it nonpolluting,
or alternatively, recovering the arsenic by
caustic leach and crystallization.
Reynaud et al. 75/114 X
Carpenter et al. 75/120 X
Dorenfeld et al. 75/120 X
Gandon et al. 75/120 X
Kupfer 75/120 X
Peters 75/120 X
Langhorst et al. 75/117 X
Prater et al. 75/117 X
Demarthe et al. 75/104
ABSTRACT
5/1958
8/1972
9/1972
12/1976
4/1977
12/1977
9/1978
4/1979
9/1979
2,835,569
3,687,828
3,689,253
3,998,628
4,018,680
4,063,933
4,113,471
4,149,880
4,166,737
[57]
Cunnington 75/120 X
Field 75/120 X
Parsons et al. 423/87
Kuss 75/120 X
Fink et al. 75/118 R X
McGan1ey et al. 75/117 X
10/1905
2/1920
9/1924
111939
5/1942
8/1954
803,472
1,331,334
1,509,688
2,142,274
2,283,198
2,686,114
Values Leached
Cu, Zn, Cd, Ge,
Pb, Ag, Bi, Au, Sb
As
Unreacted sulfides of
Cu, Zn and Fe; sulfur.
gold, tin, gypsum, and
unreacted ferric oxides
Hot H2S04
Hot chloride
Hot caustic
(As (fixation)
Types
BEST MODE FOR CARRYING OUT THE
INVENTION
Leach Stage
IZ
3
Tails
The process is effective with a wide range of arsenic
bearing materials including flue dusts containing in
excess of 10% arsenic and less than 6% iron.
In the first leach of the preferred embodiment, copper,
zinc, cadmium, and germanium are solubilized by a
sulfuric acid leach, which also solubilizes the arsenic.
To avoid carrying the arsenic over into the further
2
ing subsequent copper cementation with iron powder,
and finally oxidizing the solution with blowing air to
form a stable iron arsenate. This process does not overcome
the necessity for handling arsenic in its dangerous
5 soluble forms during metal recovery steps, as does the
present invention, nor does it immobilize arsenic in an
insoluble state early enough so that substantially complete
copper recovery is possible (HzS precipitation
must be halted at 2-3 grams of copper per liter of
solution to avoid precipitating arsenic with the copper
in this process). Neither does it provide for the recovery
of arsenic in saleable form as sodium arsenate. The
present process overcomes these problems and allows
for substantially complete recovery of copper, zinc,
cadmium, lead, and other metals, as well as sodium
arsenate.
U.S. Pat. No. 4,149,880 to Prater, et aI., discloses a
copper cementation process following an oxygen pressure
leach of the ore wherein some arsenic is insolubilized
and about 0.5 to 2.0 grams per liter arsenic remain
in solution. In this process, no attempt is made to insolubilize
essentially all the arsenic value as is done in the
present process.
U.S. Pat. No. 2,686,114 to McGauley, et aI., discloses
the insolubilization of arsenic values in a high pressure,
high temperature ore oxidation leach using air. Arsenic
is precipitated with iron in the ore and with alkaline
earth metals as arsenates of these metals. The advantages
of total insolubilization of arsenic with ferric ions
apparently are not known to these inventors.
In accordance with the objective of recovering the
most valuable metal products first, and processing the
arsenic with the least possibility of contamination of
recovered products and danger to the environment and
to workers handling the materials, copper smelters flue
40 dust is first leached under oxygen pressure with acid,
preferably hot sulfuric acid, containing ferric ions to
recover one or more of the following: copper, zinc,
cadmium, and germanium and to precipitate arsenic as
an extremely insoluble ferric-arsenic compound. Next,
the residue is leached with hot chloride solution to
extract anyone or more of the metal values lead, silver,
gold, bismuth, and antimony, without solubilizing the
arsenic. Finally, the residue is leached with hot caustic
to recover arsenic as a saleable product, and the tails,
after final arsenic fixation, are safely disposed to the
environment. The sequential leaching process is summarized
as follows:
4,244,735
1
BACKGROUND ART
DISCLOSURE OF THE INVENTION
TECHNICAL FIELD
The invention lies in the field of hydrometallurgical
recovery of metals from materials containing contaminating
substances such as arsenic.
CHLORIDE LEACH PROCESS FOR RECOVERING
METAL VALUES IN THE PRESENCE OF ARSENIC
A process is provided for recovering from a material
containing arsenic at least one of the metals, lead, silver,
gold, antimony, and bismuth which comprises precipitating
arsenic in a first stage as a compound insoluble by
subsequent processing, and carrying the insoluble ar- 10
senic compound through the metal recovery stage with
the result that it is isolated as a final insoluble residue
which can be disposed of within environmental requirements
or processed to produce an arsenic compound
which is saleable. 15
A first selective metal recovery stage may be performed
via an acid-oxygen pressure leach in which
copper, cadmium and other metals are solubilized in a
filtrate from which they are readily recoverable by
conventional techniques, enough ferric iron being pres- 20
ent in the leach to precipitate substantially all of the
arsenic as a ferric-arsenic compound. This compound is
insoluble in a chloride leach under oxidizing conditions.
The chloride leach solubilizes lead, silver, gold, antimony
and bismuth. Lead is recovered by pelletization 25
with coke or other carbonaceous material and lime or
other alkaline material such as calcium oxide, using the
alkaline material as a fluxing agent for the lead reduction,
and recycling the chloride generated during the
reaction to the chloride leach. Other metals are ce- 30
mented out of solution with elemental lead. The ferricarsenic
compound remains in the final residue. Because
of its high insolubility it can be disposed of in compliance
with the environmental requirements. Alternatively,
the ferric-arsenic compound may be converted 35
to a soluble arsenic salt in a final caustic leach. This
compound can be recovered as a saleable product by
crystallization.
45
A paper, entitled "Hydrometallurgical Recovery or
Removal of Arsenic From Copper Smelter By-products"
by K. Togawa, Y. Umetsu and T. Nishimura,
presented at the 107th A.I.M.E. annual meeting at Denver,
Colorado on Feb. 27-Mar. 2, 1978, discusses the 50
problems involved in recovering valuable metals from
copper ore refining flue dust, as well as the removal of
arsenic as insoluble arsenates and as arsenic sulfide from
aqueous solutions, and the hydrometallurgical recovery
of arsenic trioxide from arsenic sulfide. The paper re- 55
covery from the flue dust of metals uncontaminated
with arsenic, or the recovery of arsenic as a saleable
product, nor does it disclose the other advantages or
objectives of the present process.
An earlier article entitled "Recovery of Metals from 60
the Dusts of Flash Smelting Furnace" by Eikichi Mohri
and Minoru Yamada presented at the World Mining and
Metals Technology Proceedings of the Denver Joint
MMIJ-AIME meeting in 1976 discloses a hydrometallurgical
process for treating copper smelter dusts by 65
leaching, precipitating some (but not all) copper with
hydrogen sulfide, neutralizing to pH2 with calcium
carbonate to prevent precipitation of iron arsenate dur4,244,735
4
fate pressure leach. Cadmium and germanium may be
recovered by cementation with zinc, and zinc sulfate
recovered by evaporation. Because the arsenic has been
removed, the filtrate may also be recycled without
metal recovery therefrom, to enrich the feed of conventional
metallurgical recovery processes for copper and
zinc.
Filtered and washed residue from the oxidizing acid
leach is advanced to a chloride leach to solubilize lead,
silver, gold, bismuth and antimony. A hot chloride
solution with an oxidizing agent in the presence of ferric
ions extracts the metal values while leaving the arsenic
compound undissolved.
Calcium chloride extracts lead as its chloride, which
is highly soluble in the chloride solution, from its insoluble
sulfate, precipitating gypsum. The chloride solution
contains calcium chloride if extraction of lead is desired,
and may also contain sodium chloride, hydrogen chloride,
magnesium chloride, barium chloride, and/or seawater
as the source of the chloride ions necessary to
solubilize the desired metal values.
The oxidizing agent may be sodium chlorate, manganese
dioxide, ozone, chlorine, hydrogen peroxide or
others, and preferably is sodium chlorate or manganese
25 dioxide.
The oxidizing agent, added in amounts required to
adjust the emf to at least about -700 mv, solubilizes the
gold while preventing re-leaching of the arsenic. If gold
recovery is not desired, only slight oxidizing conditions
need be maintained. A preferred emf in this case is at
least about -450.
If there is insufficient lead in the oxidizing acid leach
residue to merit recovery or lead recovery is otherwise
not required, the chloride leach may be adjusted by
reduction of the calcium chloride and the temperature
in order that the lead sulfate will not be solubilized
while silver, gold and bismuth values are leached. The
chloride level must be sufficient so as to maintain the
silver in solution.
The temperature of between about 80° C. and about
boiling temperature, preferably between about 80° C.
and about lOY C., and more preferably approximately
95° C.-100° c., and the pH, adjusted at between about
0.1 and 1.0 and preferably between about 0.4 and 0.6
with sulfuric acid, allow for maximum solubilization of
the metal values with minimum arsenic extraction.
The leach materials are allowed to remain in contact
for between about one-half and two hours and preferably
about one hour to insure complete dissolution of the
lead, in the presence of ferric ions in a concentration of
about 2 to about 4 gil, and preferably about 3 gil, added
if necessary as FeCI3. These additional ferric ions, in the
oxidizing conditions of the leach, insure that the ferric
to ferrous ratio will be high enough to prevent formation
of gold and prevent re-Ieaching of the ferric-arsenic
compound.
A liquid-solid separation is performed, and the lead
crystallized as high purity lead chloride, after which it
may be reduced to elemental lead by pelletization with
a carbonaceous material such as coke and an alkaline
material such as calcium carbonate or calcium oxide at
between about 800° C. and about 1000° C. producing a
CaCh flux which may be recycled to regenerate the
chloride leach and return chloride to the system. Silver,
gold, bismuth, and antimony may be cemented out of
the solution with elemental lead.
Alternatively, the arsenic-free filtrate may be used to
enrich feed material for processing of lead ores.
3
processing of the liquor to redeem the metal values, the
arsenic is oxidized under oxygen pressure and precipitated
out as an extremely insoluble ferric-arsenic compound.
The preferred method for supplying the extra ferric 5
ions when necessary for the stoichiometry of completely
insolubilizing all the arsenic present is the addition
of ferrous sulfate, preferably in excess of the
amounts necessary for combination with all the arsenic.
The leach system is maintained in an oxidizing mode. 10
The excess ferric ion generated insures precipitation of
virtually all of the arsenic.
Although ferric iron may be present in the system in
the form of hematite, the solubility of hematite is not
high enough to efficiently produce the required excess 15
of ferric ions.
The metal values to be leached are solubilized within
a very short time, but because the arsenic present in the
flue dust is also extremely soluble, being 50% soluble in
water alone, the materials in the system must be allowed 20
to remain in contact for over an hour: depending on
temperature and pressure as well as economic requirements,
from 1 to 8 hours, and more preferably from 2 to
3 hours. This extended period of time allows for the
formation of the insoluble ferric arsenic compound.
An oxidizing mode is maintained at approximately
-400 to approximately -500 mv (satuarated calomel/platinum
electrodes) with oxygen at a pressure of approximately
25 to approximately 75 psi, and more preferably,
about 45 to about 55 psi, in order to oxidize the 30
ferrous ions to their ferric state, the arsenic to its pentavalent
state, and the sulfides to their more soluble sulfates.
The reaction is conducted at a temperature of between
about 90° C. and about 130° C., and more prefera- 35
bly between about 105° C. and about 115° C.
The pH is maintained from about 0.1 to about 1.5,
preferably with sulfuric acid, to solubilize as much of
the metal values as possible without dissolving the ferric-
arsenic compound. 40
As an optical step, in order to increase the filtration
rate of the leach slurry, gypsum may be generated as a
filter aid in situ by partially neutralizing the slurry (from
100 to 50 gil sulfuric acid) with calcium carbonate. This
partial neutralization was shown to increase the filter 45
rate in gpm/ft2 by a factor of approximately 10. This
step should be omitted iflater arsenic recovery from the
residue is desired, as the excess sulfate in the residue
lowers arsenic recovery.
A liquid-solid separation is performed and the leach 50
filtrate is then neutralized to pH approximately 2 to 4 by
the gradual addition, with agitation, of calcium carbonate.
During neutralization, the arsenic is precipitated to
less than 100 parts per million, and preferably less than
10 parts per million. This arsenic appears in the gypsum 55
cake formed during neutralization. The ferric-arsenic
compound solubility product is nearly constant at this
pH, and thus arsenic precipitation increases with increased
ferric ion concentration in solution.
During neutralization, the temperature is permitted 60
to reduce to between about 50° C. and about 60° c., to
decrease arsenic solubility, and the materials are allowed
to remain in contact for about ! hour to allow
time to aid the precipitation.
Copper, zinc, cadmium, and germanium are recov- 65
ered from the filtrate by conventional methods, including
electro winning of the copper, with sulfuric acid
produced in the copper cells being recycled to the sulEXAMPLES
6
might result in contamination of the product with crystallized
sodium hyroxide.
Due to the high solubility of sodium arsenate in water,
the crystals are not washed, but are dried at approx5
imately 80° C.
The excess sodium hydroxide filtrate is recycled to
the caustic leach. The caustic leach residue may be
treated with additional ferric ions to fix the small
amount of remaining arsenic and allow for safe disposal
10 to the environment.
From the foregoing, it may be seen that an integrated
process has been provided comprising the inventive
steps of (1) a first oxidizing acid leach during which
arsenic is precipitated as a highly insoluble ferricarsenic
compound, to be carried inertly through, (2) a
second chloride leach, and recovered in, (3) a third
caustic leach. No more than 100 parts per million arsenic
reports to the neutralized liquor and less than 0.5
percent reports to the leach liquor in the brine leach.
The results show that the process recovers essentially
all of the arsenic in the feed and that the precipitation of
arsenic as a ferric-arsenic compound in the first leach
prevents any contamination of the recovered metals
with arsenic. All of the metals that are being removed in
each leach are removed in one pass.
The chloride leach might also be applied separately
to various feed materials bearing lead, silver, gold, bismuth
or antimony after arsenic fixation.
The caustic leach with subsequent arsenic fixation
may be used to recover saleable arsenic from any feed
materials comprised predominantly of ferric-arsenic
compounds, at the same time allowing for safe disposal
of the tails.
4,244,735
5
Excess sodium hydroxide is used. In addition to the 15
stoichiometric amount required for the above reaction,
an excess of sodium hydroxide improves the performance
of the circuit, and provides for better crystallization
of the sodium arsenate.
The caustic leach is conducted for one-half to two 20
hours, and preferably about one hour to insure maximum
arsenate solubilization.
It is noteworthy that where the oxidizing acid leach
slurry was partially neutralized with calcium carbonate
prior to filtration, arsenic recovery during the caustic 25
leach is somewhat reduced, and thus, when arsenic
recovery is to be performed on the residue, calcium
carbonate neutralization should be performed on the
original leach liquor after it has been separated from the
arsenic-containing residue so as not to add large quanti- 30
ties of gypsum to the residue.
The caustic leach is performed at least 40° C. in order
to solubilize the arsenate. Upper temperature limits are
determined by the needs of the crystallizatin step.
After a liquid-solid separation, sodium arsenate of 35
high purity is crystallized from the liquid by vacuum The following examples are descriptive, but not limitevaporation
and cooling to approximately 25° c., while ing of the invention.
stirring, which concentrates the sodium hydroxide from 1. Sulfate pressure leach
about 58-79 gil NaOH to about 154-160 gil NaOH. Five-hundred (500) gram samples of copper smelter
The crystals are then filtered, and dried. 40 flue dust were leached in a 2-liter Parr autoclave having
The excess sodium hydroxide in the liquid insures an impellor speed of 1550 rpm at 100° C. under an oxythat
substantially all the arsenic will be crystallized gen pressure of 50 psig with an oxygen bleed of 300 cc
when concentrated to about 154-160 gil NaOH at room per minute (except for Test 5 where no oxygen bleed
temperature. Further concentration is unnecessary and was used). The dust contained 13.9% copper, 2.05%
45 zinc, 9.51% arsenic and 5.60% iron. Test results are
summarized in Table 1.
The chloride leach residue, like the oxidizing acid
leach residue, bearing the fixed arsenic, is safe for disposal
to the environment. If necessary, additional arsenic
fixation with ferric ions can be effected prior to
disposal.
If arsenic is to be recovered in saleable form, the brine
leach residue is leached in a caustic leach of heated,
strong, basic solution, preferably a solution of approximately
50% sodium hydroxide, to extract arsenic as
sodium arsenate, according to the generalized reaction-
TABLE I
SULFATE PRESSURE LEACH
TEST NO. 2 4 5 6
LEACH TIME 2 2 2 2
(hr.)
emf (mv) 4.10 430 450 460 435 460 460
pH 0.35 0.1 0.0
LEACH
SOLUTION
gil H2SO4 100 114 50 98 100 100
gil iron 5Fe+3 16.4Fe+3 15.7Fe+3 19.8Fe+ 2 20Fe+2 34.3Fe203Reagent
RESIDUE
ASSAY(%)
Cll 1.30 1.79 1.36 1.30 1.48 1.24 1.33
Zn 0.25 12.8 0.23 0.20 0.27 0.24 0.23
As 11.2 12.8 12.9 13.8 13.4 13.2 12.8
LIQUOR
ASSAY (gil)
Cll 51.8 59.2 56.6 56.6 56.8 52.5 52.0 54.7
Zn 7.40 8.65 8.08 8.08 8.16 7.80 7.76 7.68
ASro1 13.3 5.58 4.57 5.46 3.65 2.98 5.37 3.47 2.40 18.6
Fe 1.0 3.10 0.56 4.55 3.84 3.80 4.65 3.81 3.92 0.70
%EXTRACTED
Cll 94.7 92.5 93.8 94.1 93.8 94.4 94.6
TEST NO.
Zn
As
4,244,735
7
TABLE I-continued
SULFATE PRESSURE LEACH
I 2 4 5 6
93.1 92.6 92.9 94.4 92.4 92.8 92.8
34 14 II 13 8.9 7.3 14 9.5 6.7 45
2. Neutralization
The autoclave slurry of Example 1 is filtered and the
liquor neutralized with calcium carbonate. In Test 1, 10
prior to filtration, partial neutralization (from 100 gil
H2S04 to 50 gil H2S04) is effected with calcium carbonate
and in Test 2, this partial neutralization is omitted.
The patial neutralization of Test 1 precipitates gyp- 15
sum which increases the filtration rate for the leach
slurry from 0.013 gpm/ft2 to 0.17 gpm/ft2• After filtration
of the slurry, the liquor is cooled to 50° to 60° C.
and vigorously agitated while calcium carbonate is
added in order to neutralize the solution to a pH of 20
about 3. After one-half hour, the material is again filtered.
The results of these tests are summarized in Table
2.
The residue from the brine leach described in Example
3 was leached in sodium hydroxide at 40° C. to
extract arsenic as sodium arsenate. 3 grams of sodium
hydroxide were used for each gram of arsenic dissolved
plus an excess of 70 gil. Test 1 residue was the result of
the partially neutralized autoclave slurry described in
Example 2. Test 2 was as described in Example 2. The
leach slurry was then filtered and the liquid evaporated
under vacuum to alter the sodium hydroxide concentration
from 58-79 to 154-160 gil NaOH, and cooled to
25° C. while stirring to crystallize sodium arsenate from
the liquid. The crystals were then dried on a Buchner
funnel without washing, and further dried at 80° C. Test
2 residue was derived from non-neutralized autoclave
slurry residue. Test residues are summarized in Table 4.
The values for "Liquor" and "Residue" resulted from
TABLE 2
NEUTRALIZAnON WITH CALCIUM CARBONATE
DISTRIBUTION %
TEST I TEST 2
PRODUCT Cu Zn Cd Ge As Cu Zn Cd Ge As
LIQUOR 94.0 92.7 72.4 82 6.2 94.0 93.2 76.9 82 6.7
RESIDUE 6.0 7.3 27.6 18 93.8 6.0 6.8 23.1 18 93.3
NEUTRAliZED
LIQUOR 93.2 92.7 71.0 53 <0.03 92.9 93.1 72.5 42 <0.03
CaS04CAKE 0.8 <0.1 1.4 29 6.2 1.1 0.1 4.4 40 6.7
CaCO 3
CONSUMPTION
Ib/ton DUST 282 514
3. Brine Leach
250 grams of autoclave residue was leached with 250
gil NaCl, 25 gil CaCh and 3 gil ferric ion as FeC13. 40
6H20, at a temperature of 95° C. to 100° C. and a pH of
0.5, adjusted with HCl in an oxidizing mode using NaCI03
to achieve an emf of -690 to -700 mv. Test 1
residues were those in which the autoclave leach slurry
was partially neutralized before filtration with CaC03, 45
as described in Example 2, and Test 2 residues were not
previously treated with CaC03. Test results are summarized
in Table 3.
TABLE 3
the caustic leach. The values for "Mother Liquor" and
"Crystals" resulted from the sodium arsenate crystallization.
A further test was performed on non-neutralized
residue using a leach time of 4~ hours and an excess
sodium hydroxide of 80 gil, and resulting in 88.3%
arsenic extraction.
Sodium arsenate crystals from all tests were of good
purity, with only minor amounts of entrained sodium
sulfate and co-crystallized tin as impurities. Bismuth and
germanium, which tended to report in varying degrees
BRINE LEACH
(DISTRIBUTION AS A PERCENTAGE OF TOTAL FLUE DUST FEED
MATERIAL)
TEST I TEST 2
PRODUCT As Pb Ag Au Bi As Pb Ag Au Bi
LIQUOR <0.5 99.5 83.6 89 77.7 <0.5 99.2 85.8 89 77.8
RESIDUE 93.8 0.4 16.0 II 21.0 93.3 0.8 13.8 II 21.8
4. Caustic leach and sodium arsenate crystallization to all prior leach liquors and residues, were substantially
not present in the sodium arsenate crystals.
TABLE 4
CAUSTIC LEACH AND SODIUM ARSENATE CRYSTALLIZATION
DISTRIBUTION AS A PERCENTAGE OF THE FLUE DUST FEED MATERIAL
TEST I TEST 2
PRODUCT As Bi Sn Ge As Bi Sn Ge
LIQUOR 80.9 0.1 1.9 <5 87.0 0.1 3.0 <5
RESIDUE 12.9 20.9 94.6 8-18 6.3 21.7 92.6 8-18
MOTHER LIQUOR 8.4 0.1 4.9 0.1
9
4,244,735
10
TABLE 4-continued
CAUSTIC LEACH AND SODIUM ARSENATE CRYSTALLIZATION
DISTRIBUTION AS A PERCENTAGE OF THE FLUE DUST FEED MATERIAL
TEST I TEST 2
PRODUCT As Bi Sn Ge As Bi Sn Ge
CRYSTALS 72.5 1.8 82.1 2.9
caustic to recover arsenic as an arsenic salt crystallized
from the caustic leach liquor.
6. The process of claim 1 wherein gold is one of the
metals to be recovered and the oxidation potential of
the leach is maintained at an emf of at least about - 700
35
mv.
7. In a process for recovering at least one of the metals
lead, silver, gold, bismuth and antimony from a material
containing ferric-arsenic compounds, the improvemet
comprising:
(a) performing a chloride leach on the material
wherein the chloride solution is selected from the
group consisting of calcium chloride, sodium chloride,
magnesium chloride, barium chloride, hydrogen
chloride and sea water to bring the chloride
ion concentration of the leach to a value sufficient
to solubilize at least one of the metals lead, silver,
gold, bismuth and antimony, in the presence of
ferric ions in an amount of 2-4 gpl and an oxidizing
agent at a pH of between about 0.1 and 1.0;
(b) performing a liquid-solid separation on the material
of step (a); and
(c) recovering at least one of the metals lead, silver,
gold, bismuth and antimony from the liquids of step
(b).
8. The process of claim 7 wherein lead is one of the
metals to be extracted in step (a), and the chloride solution
contains sufficient calcium chloride to extract lead
from lead sulfate and precipitate calcium sulfate.
9. The process of claim 7 wherein the pH of the leach
40 is adjusted to between about 0.4 and about 0.6 with
sulfuric acid.
10. The process of claim 7 wherein the leach is maintained
at a potential of at least about - 700 mv.
11. In a process for recovering at least one of the
45 metals copper, cadmium, zinc and germanium from
arsenic-containing flue dust resulting from the pyrometallurgical
processing of copper ores, wherein during
leaching of said metal values, arsenic is precipitated as
an extremely insoluble ferric-arsenic compound, a liq-
50 uid-solids separation is performed, and the liquid further
processed for recovery of the metal values, and wherein
the solid residue contains, in addition to ferric-arsenic
compounds, lead and at least one of the metals silver,
gold, bismuth and antimony, the improvement compris-
55 ing:
(a) leaching the solid residue with a chloride solution
in the presence of ferric ions at a concentration of
approximately between about 2 and about 4 grams
per liter ferric at a pH of between about 0.4 and 0.6
adjusted with sulfuric acid at a temperature of
between about 95° C. and about 100° C. in the
presence of an oxidizing agent selected from the
group consisting of sodium chlorate, manganese
dioxide, ozone, chlorine and hydrogen peroxide to
maintain the emfat between about - 450 and - 700
mv; in order to solubilize at least one of the metals
lead, silver, gold bismuth and antimony and leave
the ferric-arsenic compound unsolubilized;
60
SOLUBILITY 30
pH ppm/As
TABLE 5
ARSENIC FIXATION
BRINE RESIDUE (neutralized)
Days: ° 4.0 <0.3
1 3.4 <0.4
4 3.4 <0.3
5 3.5 <0.3
BRINE RESIDUE (not neutralized)
Days: ° 4.0 <0.3
1 3.5 <0.3
4 3.5 <0.3
CAUSTIC RESIDUE (neutralized)
Days: ° 4.0 <0.3
3 3.6 <0.3
4 3.7 <0.3
5 3.8 <0.3
CAUSTIC RESIDUE (not neutralized)
Days: ° 4.0 <0.3
3 3.6 <0.3
4 3.8 <0.3
5 3.8 <0.3
We claim:
1. In a hydrometalurgical process for recovering
metal values selected from the group consisting of lead,
silver, gold, antimony and bismuth from a material containing
arsenates wherein substantially all of the arsenic
is present in its pentavalent state, the improvement comprising
leaching said metal values with a solution containing
sufficient chloride ion concentration, in an
amount of 2-4 gpl ferric ions and an oxidizing agent at
a pH of at most about 1.0 in order to solubilize a substantial
portion of the desired metal values to the exclusion
of the arsenates.
2. The process of claim 1 wherein the emf is adjusted
to at least about - 700 mv.
3. The process of claim 1 wherein the emf is adjusted
to at least about -450 mv.
4. The process of claim 1 wherein the pH is adjusted 65
to at between about 0.4 and 0.6.
5. The process of claim 1 wherein the solid residue
from the leach is further processed by leaching with hot
5. Arsenic fixation 10
Arsenic solubility in the brine and caustic leach residues,
for residues initially partially neutralized before
filtration of the sulfate pressure leach as described in
Example 2 and for non-neutralized residues, was determined
after fixing the arsenic by the addition of2 mllOO 15
gil Fe+3 in the form of Fe2(S04» to 10 grams ofresidue
slurried with 75 ml H20, the emf being adjusted to
-500 mv, and the pH being adjusted to approximately
2.0 with sulfuric acid. Calcium carbonate was then
added to adjust the pH to 4.0 and the mixture stirred for 20
one hour at 25° C. The solubility of the fixed arsenic
was then tested by contacting with demineralized water
for up to 5 days. Test results are summarized in Table 5.
These results show extremely low arsenic solubility,
even at fairly low pH, thus confirming that the brine 25
and caustic leach residues are environmentally safe for
disposal.
4,244,735
11
(b) performing a liquid-solid separation on the leach
materials of step (a); and
(c) recovering at least one of the metal values from
the liquid of step (b).
12. The process of claim 11 wherein the chloride
solution comprises brine and calcium chloride.
13. The process of claim 11 wherein the leach of step
12
(a) is performed at a temperature of less than about 800
C., and with sodium chloride and calcium chloride
present at a weight ratio to each other of greater than
10:1, in amounts sufficient to solubilize the other metal
5 values, but insufficient to solubilize the lead present in
the said solid residue.
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