United States Patent [19]
Reynolds et al.
[11]
[45]
4,244,734
Jan. 13, 1981
[54] PROCESS FOR RECOVERING METAL
VALVES FROM MATERIALS CONTAINING
ARSENIC
[75] Inventors: James E. Reynolds; Enzo L.
Coltrinari, both of Golden, Colo.
[73] Assignee: Hazen Research, Inc., Denver, Colo.
[21] Appl. No.: 58,868
[22] Filed: Jul. 19, 1979
[51] Int. CI,3 C22B 13/04; C22B 11104;
C22B 15/08; C22B 19/22
[52] V.S. Cl. 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, 121,
75/118 R, 120, 104, 115, 114; 423/39, 87
[56] References Cited
U.S. PATENT DOCUMENTS
18 Claims, 1 Drawing Figure
Primary Examiner-G. Ozaki
Attorney, Agent, or Firm-Sheridan, Ross, Fields &
McIntosh
Carpenter et at. 75/120 X
Gandon et at. 75/104
Peters 75/101 R
Prater et at. 75/117
Demarthe et at. 75/104
ABSTRACf
8/1972
12/1976
12/1977
4/1979
9/1979
3,687,828
3,998,628
4,063,933
4,149,880
4,166,737
An improvement in hydrometallurgical recovery of
metals, i.e. copper, zinc, cadmium, germanium, indium,
lead, silver, gold, antimony and bismuth from materials
such as flue dust containing arsenic in which the metals
are selectively separated in successive process steps for
final recovery, the improvement comprising precipitating
arsenic as an insoluble ferric-arsenic compound in
the first processing step, carrying the insoluble arsenic
compound through subsequent processing steps in
which it is insoluble until the other metals have been
recovered leaving the ferric-arsenic compound as the
final residue which can be disposed of without violating
pollution requirements or converted to soluble sodium
arsenate and recovered from solution by crystallization.
[57]
Cunnington 75/120 X
Field 75/120 X
Parsons 423/87
Kuss 75/120
McGauley et at. 75/117 X
Reynaud et at. 75/114 X
10/1905
2/1920
1/1924
1/1939
8/1954
5/1958
803,472
1,331,334
1,509,688
2,142,274
2,686,114
2,835,569
COPPER SMELTER
DUST
RECYC LE Cu
ANOLYTE
SOLUTION Cu [ELECTROLYSIS]
FI LTE R ';;;;';;::~~:':'2>2. Cd ~EMENTATION WITH
Zn]
3. ZnS04 [fVAPORATION]
~
SULFATE
PRESSURE
LEACH
NEUTRALI ZATION
I I.
CaC0.3
BRINE
LEACH
CAUSTIC
LEACH
NaOH
RECYCLE BRINE
SOLUTION
SOLUTION I. Pb IPbClz CRYSTALLlZFILTER
":::':':':":::~~I!> ATiONAND PYRO-REDUCTION]
2. Ag,Au, Bi [CEMENTAllON
WITH Pb]'
RECYCLE CAUSTIC
SOLUTION
FILTER SOLUTION!> Naj As04 [EVAPORATIVE/
COOLING CRYSTALLIZATION]
ARSENIC
FI XATION
TAl LS
u.s. Patent Jan. 13, 1981 4,244,734
COPPER SME LTER
DUST
RECYC LE Cu
ANOLYTE
. Cu [ELECTROLYSIS]
FILTER SOLUT/ON~2.Cd~EMENTATIONWITH
Zn]
3. ZnS04 ~VAPORATIONJ
- SPRUELSFSA•UTREE -
LEACH
I
- NEUTRALl ZATION ~
I I
CaC03
NaCI03 BRINE
LEACH RECYCLE BRINE
H2 SO4
SOLUTION
I. Pb [Pb02 CRYSTALLlZFI
LTER SOLUTION. ATION;;ND PYRO-REDUCT/
ON]
2. Ag,Au, Bi [CEMENTACAUSTIC
11ON WITH Pb]
NaOH LEACH RECYCLE CAUSTIC
SOLUTION
FILTER
SOLUTION Na,3As04 [EVAPORA-
.. TIVE/ COOLING CRYSTALLIZATION]
Fe+3 ARSEN I C
FI XATION
TAILS
1
4,244,734
2
I Hot H2S04 Cu, Zn, Cd, Ge, In
2 Hot brine Pb, Ag, Bi, Au, Sb
3 Hot caustic As
Tails (As fixation) Unreacted sulfides of
Cu, Zn and Fe; sulfur,
gold, tin, gypsum, and
unreacted ferric oxides
DESCRIPTION OF THE DRAWING
The single drawing is a generalized flow sheet showing
one embodiment of the process of this invention.
BEST MODE FOR CARRYING OUT THE
INVENTION
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 smelter flue
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, germanium, and indium, and to precipitate
arsenic as an extremely insoluble ferric-arsenic compound.
Next, the residue is leached with hot brine 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:
carbonate to prevent precipitation of iron arsenate during
subsequent copper cementation with iron powder,
and finally oxidizing the solution with blowing air to
form a stable iron arsenate. This process does not over-
5 come the necessity for handling arsenic in its dangerous
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 (H2S precipitation
must be halted at 2-3 grams of copper per liter of solution
to avoid precipitating arsenic with the copper in
this process). Niether 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 al., 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 al., 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.
60 -------------------
Leach Stage Types Values Leached
TECHNICAL FIELD
BACKGROUND ART
DISCLOSURE OF THE INVENTION
PROCESS FOR RECOVERING METAL VALUES
FROM MATERIALS CONTAINING ARSENIC
40
The invention lies in the field of hydrometallurgical
recovery of metals from materials containing contaminating
substances such as arsenic.
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 does 55
not disclose an integrated process for the successful
recovery 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
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-AIMT meeting in 1976 discloses a hydrometal- 65
lurgical process for treating copper smelter dusts by
leaching, precipitating some (but not all) copper with
hydrogen sulfide, neutralizing to pH2 with calcium
A process is provided for recovering from a material
containing arsenic at least one of the metals copper,
zinc, cadmium, germanium, indium, lead, silver, gold,
antimony and bismuth which comprises insolubilizing
the arsenic as a ferric-arsenic compound and selectively 10
leaching the metals for recovery. The process may be
conducted in successive leach stages with arsenic being
precipitated in the first stage and remaining insoluble
during subsequent processing. The insoluble arsenic
compound is carried throughout the successive metal 15
recovery stages, with the result that it is isolated as a
final insoluble residue which can be disposed of within
environmental requirements or processed to produce a
saleable arsenic compound.
The first selective metal recovery stage is an oxygen 20
pressure leach in which copper, cadmium, zinc, germanium
and indium are solubilized in a filtrate from which
they are readily recoverable by conventional techniques,
enough ferric ions being present in the leach to
precipitate substantially all of the arsenic as a ferric- 25
arsenic compound, and enough time being allowed to
complete the precipitation. This compound is insoluble
in the first and subsequent metal recovery leaches. The
second leach is a brine leach which selectively solubilizes
lead, silver, gold, antimony and bismuth in a solu- 30
tion from which these metals can be recovered. The
ferric-arsenic compound is insoluble in the brine leach
and remains in the final residue. Because of its high
insolubility it can be disposed of in compliance with
environmental requirements. Alternatively, the ferric- 35
arsenic compound may be converted to soluble sodium
arsenate in a final caustic leach. This compound can be
recovered as a saleable product by crystallization.
4,244,734
3 4
The process is effective with a wide range of arsenic During neutralization, the temperature is permitted
bearing materials including flue dusts containing in to reduce to between about 50° C. and about 60° C, tL
excess of 10% arsenic and less than 6% iron. decrease arsenic solubility, and the materials are al·
In the first leach of the preferred embodiment, cop- lowed to remain in contact for about ~ hour to allow
per, zinc, cadmium, germanium and indium are solubi- 5 time to aid the precipitation.
lized by a sulfuric acid leach, which also solubilizes the Copper, zinc, cadmium, germanium and indium are
arsenic. To avoid carrying the arsenic over into the recovered from the filtrate by conventional methods,
further processing of the liquor to redeem the metal including e1ectrowinning of the copper, with sulfuric
values, the arsenic is oxidized under oxygen pressure acid produced in the copper cells being recycled to the
and precipitated out as an extremely insoluble ferric- IO sulfate pressure leach. Cadmium and germanium may
arsenic compound. be recovered by cementation with zinc, and zinc sulfate
The preferred method for supplying the extra ferric recovered by evaporation. Because the arsenic has been
ions when necessary for the stoichiometry of com- removed, the filtrate may also be recycled without
pletely insolubilizing all the arsenic present is the addi- metal recovery therefrom, to enrich the feed of convention
of ferrous sulfate, preferably in excess of the 15 tional metallurgical recovery processes for copper and
amounts necessary for combination with all the arsenic. zinc.
The leach system is maintained in an oxidizing mode. The residue from the sulfate pressure leach, and the
The excess ferric ion generated insures precipitation of gypsum cake from the neutralization of the leach liquor
virtually all of the arsenic. containing fixed arsenic, may be safely disposed of in
Although ferric iron may be present in the system in 20 compliance with environmental regulations. Additional
the form of hematite, the solubility of hematite is not arsenic fixation with ferric ions may be preferred.
Alternatively, filtered and washed residue from the
high enough to efficiently produce the required excess oxidizing acid leach is advanced to a brine leach to
of ferric ions.
solubilize lead, silver, gold, bismuth and antimony. A
The metal values to be leached are solubilized within 25 hot mixed brine (CaCh+NaCI) with an oxidizing agent
a very short time, but because the arsenic present in the
such as sodium chlorate, manganese dioxide, ozone or
flue dust is also extremely soluble, being 50% soluble in chlorine, and in the presence of ferric ions, extracts the
water alone, the materials in the system must be allowed metal values while leaving the arsenic compound undisto
remain in contact for over an hour: depending on solved.
temperature and pressure as well as economic require- 30 Calcium chloride extracts lead as its chloride, which
ments, from 1 to 8 hours, and more preferably from 2 to is highly soluble in the brine, from its insoluble sulfate,
3 hours. This extended period of time allows for the precipitating gypsum. The sodium chlorate or mangaformation
of the insoluble ferric arsenic compound. nese dioxide (added in amounts required to adjust the
An oxidizing mode is maintained at approximately emf to approximately _ 700 mv) solubilizes the gold
-400 to approximately -500 mv (saturated calomel!- 35 while preventing re-leaching of the arsenic. If gold
platinum electrodes) with oxygen at a pressure of ap- recovery is not desired, only slight oxidizing conditions
proximately 25 to approximately 75 psi, and more pref- need be maintained.
erably, about 45 to about 55 psi, in order to oxidize the If there is insufficient lead in the oxidizing acid leach
ferrous ions to their ferric state, the .arsenic to its penta- residue to merit recovery, the brine leach may be advalent
state, and the sulfides to theIr more soluble sul- 40 justed by reduction of the calcium chloride and the
fates. .. temperature in order that the lead sulfate will not be
The reactIOn IS conducted at a temperature of be- solubilized while silver, gold and bismuth values are
tween about 90° C. and about 130° C., and more prefera- leached. The chloride level must be sufficient so as to
bly between about 105° C. and about 115° C. maintain the silver in solution.
The pH is maintained from about 0.1 to about 1.5, and 45 The temperature of between about 80° C. and about
preferably about 0.1 to about 1.0, preferably with sulfu- 105° C., and preferably approximately 95° C.-100° C.,
ric acid, to solubilize as much of the metal values as and the pH, adjusted at approximately 0.5 with sulfuric
possible without dissolving the ferric-arsenic com- acid, allow fot maximum solubilization of the metal
pound. values with minimum arsenic extraction.
As an optional step, in order to increase the filtration 50 The leach materials are allowed to remain in contact
rate of the leach slurry, gypsum may be generated as a for between about one-half and two hours and preferafilter
aid in situ by partially neutralizing the slurry (from bly about one hour to insure complete dissolution of the
100 to 50 gil sulfuric acid) with calcium carbonate. This lead, in the presence of ferric ions in a concentration of
partial neutralization was shown to increase the filter about 3 gil, added if necessary as FeCI3. These addirate
in gpm/ft2 by a factor of approximately 10. This 55 tional ferric ions, in the oxidizing conditions of the
step should be omitted iflater arsenic recovery from the leach, insure that the ferric to ferrous ratio will be high
residue is desired, as the excess sulfate in the residue enough to prevent formation of gold and prevent relowers
arsenic recovery. leaching of the ferric-arsenic compound.
A liquid-solid separation is performed and the leach A liquid-solid separation is preformed, and the lead
filtrate is then neutralized to pH approximately 3 by the 60 crystallized as high purity lead chloride, after which it
gradual addition, with agitation, of calcium carbonate. may be reduced to elemental lead by pelletization with
During neutralization, the arsenic is precipitated to less coke and lime at about 900° C. producing a CaCh flux
than 100 parts per million, and preferably less than 10 which may be recycled to regenerate the brine leach
parts per million. This arsenic appears in the gypsum and return chloride to the system. Silver, gold, bismuth,
cake formed during neutralization. The ferric-arsenic 65 and antimony may be cemented out of the solution with
compound solubility product is nearly constant at this elemental lead.
pH, and thus arsenic precipitation increases with in- Alternatively, the arsenic-free filtrate may be used to
creased ferric ion concentration in solution. enrich feed material for processing of lead ores.
4,244,734
EXAMPLES
The following examples are descriptive, but not limiting
of the invention.
1. Sulfate pressure leach:
Five-hundred (500) gram samples of copper smelter
flue dust were leached in a 2-liter Parr autoclave having
an impellor speed of 1550 rpm at 100° C. under an oxygen
pressure of 50 psig with an oxygen bleed of 300 cc
per minute (except for Test 5 where no oxygen bleed
was used). The dust contained 13.9% copper, 2.05%
zinc, 9.51% arsenic and 5.60% iron. Test results are
summarized in Table 1.
6
treated with additional ferric ions to fix the small
amount of remaining arsenic and allow for safe disposal
to the environment.
From the forgoing, it may be seen that an integrated
5 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 brine leach, and recovered in, (3) a third caustic
10 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 residue from the sulfate
and brine leaches could be disposed ofat the end ofeach
20 leach without further leaching. For example, if economic
considerations did not dictate recovery of the
metals recovered in the second leach, the process could
be stopped after the pressure leach and the residue from
this leach disposed of without violating environmental
requirements because of the high insolubility of the
ferric-arsenic compound.
The brine 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.
FeAs04+3NaOH~Na3As04+Fe(OH)J.
5
The brine 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
Excess sodium hydroxide is used. In addition to the
stoichiometric amount required for the above reaction,
an excess of sodium hydroxide improves the perfor- 15
mance of the circuit, and provides for better crystallization
of the sodium arsenate.
The caustic leach is conducted for one-half to two
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
leach is somewhat reduced, and thus, when arsenic
recovery is to be performed on the residue, calcium 25
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 quantities
of gypsum to the residue.
The caustic leach is performed at least 40° C. in order 30
to solubilize the arsenate. Upper temperature limits are
determined by the needs of the crystallization step.
After a liquid-solid separation, sodium arsenate of
high purity is crystallized from the liquid by vacuum
evaporation and cooling to approximately 25° C., while 35
stirring, which concentrates the sodium hydroxide from
about 58-79 gil NaOH to about 154-160 gil NaOH.
The crystals are then filtered, and dried.
The excess sodium hydroxide in the liquid insures
that substantially all the arsenic will be crystallized 40
when concentrated to about 154-160 gil NaOH at room
temperature. Further concentration is unnecessary and
might result in contamination of the product with crystallized
sodium hydroxide.
Due to the high solubility of sodium arsenate in wa- 45
ter, the crystals are not washed, but are dried at approximately
80° C.
The excess sodium hydroxide filtrate is recycled to
the caustic leach. The caustic leach residue may be
TABLE I
SULFATE PRESSURE LEACH
TEST NO. 2 3 4 5 6
LEACH TIME 2 2 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 15.7 19.8Fe+ 2 20Fe+ 2 34.3Fe203Reagent
Fe+3
RESIDUE
ASSAY(%)
Cu 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)
eu 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
As 13.3 5.58 4.57 5.46 3.65 2.98 5.37 3.47 2.40 18.6
Fetor .73 2.55 .33 3.54 3.28 3.24
4,244,734
7
TABLE I-continued
SULFATE PRESSURE LEACH
TEST NO. 2 3 4 6
% EXTRACTED
Cu 94.7 92.5 93.8 94.1 93.8 94.4 94.6
Zn 93.1 92.6 92.9 94.4 92.4 92.8 92.8
As 34 14 11 13 8.9 7.3 14 9.5 6.7 45
2. Neutralization:
The autoclave slurry of Example 1 is filtered and the 10
liquor neutralized with calcium carbonate. In Test 1,
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.
15
The partial neutralization of Test 1 precipitates gypsum
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 20
added in order to neutralize the solution to a pH of
about 3. After one-half hour, the material is again filtered.
The results of these tests are summarized in Table
2.
tion 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 Buckner
funnel without washing, and further dried at 80· C. Test
2 residue was derived from non-neutralized autoclave
slurry residue. Test results are summarized in Table 4.
The values fOf "Liquor" and "Residue" resulted from
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
TABLE 2
NEUTRALIZATION WITH CALCIUM CARBONATE
DISTRIBUTION %
TEST I TEST 2
Cu Zn Cd Ge As Cu Zn Cd Ge As
94.0 92.7 72.4 82 6.2 94.0 93.2 76.9 82 6.7
6.0 7.3 27.6 18 93.8 6.0 6.8 23.1 18 93.3
93.2 92.7 71.0 53 <0.03 92.9 93.1 72.5 42 <0.03
0.8 <0.1 1.4 29 6.2 1.1 0.1 4.4 40 6.7
PRODUCT
LIQUOR
RESIDUE
NEUTRALIZED
LIQUOR
CaS04 CAKE
CaC03
CONSUMPTION
Ib/ton DUST 282 514
3. Brine Leach:
250 grams of autoclave residue was leached with 250 40
gil NaCl, 25 gil CaCh and 3 gil ferric ion as FeCI3.6H20,
at a temperature of 95· C. to 100· C. and a pH of
0.5, adjusted with HCI 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 45
was partially neutralized before filtration with CaC03,
as described in Example 2, and Test 2 residues were not
previously treated with CaC03. Test results are summarized
in Table 3.
TABLE 3
sulfate and co-crystallized tin as impurities. Bismuth and
germainium, which tended to report in varying degrees
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
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 11 21.0 93.3 0.8 13.8 11 21.8
4. Caustic leach and sodium arsenate crystallization:
The residue from the brine leach described in Exam- 60
pIe 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 65
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 concentra-
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 8.4 0.1 4.9 0.1
LIQUOR
CRYSTALS 72.5 1.8 82.1 2.9
5. Arsenic fixation:
10
stantially all of the arsenic to pentavalent arsenic
while contacting the leach solution with ferric ions
in an amount to precipitate substantially all of the
arsenic as a ferric-arsenic compound and to solubilize
metals selected from the group consisting of
copper, zinc, cadmium, indium and germanium;
(b) performing a liquids-solids separation on the
slurry of step (a) to separate the solids from the
. solution;
(c) adjusting the pH of the solution of step (b) to a pH
of at least 3 to precipitate the remainder of the
arsenic as ferric arsenate and reduce the arsenic
content of the solution to no more than about 100
ppm;
(d) removing the arsenic precipitate from the solution
of step (c);
(e) recovering the metals solubilized in step (a) from
the solution of step (d) in substantially arsenic-free
form;
(f) leaching the residue of step (b) with a brine leach
in the presence of the ferric-arsenic precipitate to
solubilize metals selected from the group consisting
of antimony, bismuth, lead, silver and gold;
(g) performing a liquid-solids separation on the slurry
of step (f) to separate the solids from the solution,
and
(h) recovering the metals solubilized in step (f) from
the solution of step (g) in substantially arsenic-free
form.
5. The process of claim 4 wherein the ferric ions of
step (a) are generated during the leach from ferrous
ions.
6. The process of claim 5 wherein the leach of step (a)
35 is performed under an oxygen pressure of between
about 25 and about 75 psi.
7. The process of claim 5 wherein the leach of step (a)
is performed under an oxygen pressure of between
about 45 and 55 psi.
8. The process of claim 4 wherein the leach of step (a)
is performed at a temperature of between about 90° C.
and about 130° C.
9. The process of claim 4 wherein the leach of step (a)
is performed at a temperature of between about 105° C.
and about 115° C.
10. The process of claim 4 wherein arsenic is recovered
from the residue of step (b) by means of a hot
caustic leach with subsequent crystallization of a soluble
arsenic salt from the leach liquor.
11. The process of claim 4 wherein the ferric ion is
oxidized in situ from ferrous sulfate added to produce
ferric ion in solution in excess of stoichiometric amounts
to precipitate the arsenic as a ferric-arsenic compound.
12. The process ofclaim 4 wherein the emfis adjusted
to between about -400 and about -500 mv in the
leach.
13. The process of claim 4 wherein the solids of step
(b) are further processed to recover arsenic in soluble
form.
14. The process of claim 13 wherein arsenic is recovered
by means of the following steps:
(a) leaching the solids of step (d) with a strong, basic
solution in excess of stoichiometric amounts to
solubilize the arsenic;
(b) performing a liquid-solid separation on the material
of step (a); and
(c) crystallizing sodium arsenate from the liquid of
step (b).
30
25
4,244,734
SOLUBILITY 20
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. A process for separating arsenic from a material 40
containing arsenic and one or more metal values selected
from the group consisting of copper, cadmium,
zinc and germanium, comprising:
(a) leaching the material to solubilize arsenic and the
other metal values; 45
(b) contacting the leach solution with ferric ions to
precipitate arsenic as a ferric-arsenic compound;
(c) retaining the leach solution in contact with the
ferric ions for a sufficient period of time to precipitate
substantially all the arsenic present in solution; 50
(d) performing a liquid-solid separation; and
(e) neutralizing the liquid of step (d) to a pH of about
3 to precipitate a substantial portion of the remaining
arsenic.
2. The process of claim 1 wherein the retention time 55
of step (c) is at least one hour.
3. The process of claim 1 wherein the leach solution
contains sulfate, the liquid-solid separation of step (d) is
accomplished by filtration, and between steps (c) and
(d) the leach materials are partially neutralized with 60
calcium carbonate to generate gypsum.
4. A process for recovering metals selected from the
group consisting of copper, cadmium, zinc, germanium,
indium, antimony, bismuth, lead, silver and gold from a
copper smelter flue dust containing arsenic which com- 65
prises:
(a) leaching the flue dust with sulfuric acid at a pH of
0.1-1.5 under oxidizing conditions to convert sub-
9
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 ml100 5
gil Fe+3in the form of Fe2(S04)3 to 10 grams of residue
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 10
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 15
and caustic leach residues are environmentally safe for
disposal.
12
germanium from a copper smelter flue dust containing
arsenic which comprises:
(a) leaching the flue dust with sulfuric acid at a pH of
0.1-'1.5 under oxidizing conditions to convert substantially
all of the arsenic to pentavalent arsenic
while contacting the leach solution with ferric ions
in an amount to precipitate substantially all of the
arsenic as a ferric-arsenic compound, and to solubilize
said metals;
(b) performing a liquid-solids separation on the slurry
of step (a) to separate the solids from the solution;
(c) adjusting the pH of the solution of step (b) to a pH
of at least 3 to precipitate the remainder of the
arsenic as a ferric-arsenic compound and reduce
the arsenic content of the solution to no more than
about 100 ppm;
(d) removing the arsenic precipitate from the solution
of step (c); and
(d) recovering the metals solubilized in step (a) from
the solution of step (b) in substantially arsenic-free
form.
18. A process for recovering metals selected from the
group consisting of antimony, bismuth, lead, silver and
gold from a copper smelter flue dust containing arsenic
which comprises:
(a) leaching the flue dust with sulfuric acid at a pH of
0.1-1.5 under oxidizing conditions to convert substantially
all of the arsenic to pentavalent arsenic
while contacting the leach solution with ferric ions
in an amount to precipitate substantially all of the
arsenic as a ferric-arsenic compound, and to solubilize
said metals;
(b) performing a liquid-solids separation on the slurry
of step (a) to separate the solids from the solution;
(c) leaching the residue of step (b) with a brine leach
in the presence of a ferric-arsenic precipitate to
solubilize metals selected from the group consisting
of antimony, bismuth, lead, silver and gold;
(d) performing a liquid-solids separation on the slurry
of step (c) to separate to solids from the liquids; and
(e) recovering the metals solubilized in step (c) from
the solution of step (d) in substantially arsenic-free
form.
4,244,734
11
15. A process for recovering at least one of the metals
copper, cadmium, zinc, indium and germanium from
arsenic-containing flue dust resulting from the pyrometallurgical
processing of copper ores comprising:
(a) leaching the feed material with sulfuric acid at a 5
pH approximately 0.5, at a temperature between
about 90· C. and about 130· C. to dissolve the
aforesaid metal values, in the presence of oxygen
under pressure of between about 25 and about 75
psi to adjust the emfof the system to between about 10
-400 and about -500 mv and sufficient ferric ions
to insolubilize all the arsenic as a ferric-arsenic
compound;
(b) allowing the leach materials of step (b) to remain
in contact for a period of about 1 to about 3 hours 15
to allow precipitation of arsenic as a ferric arsenic
compound;
(c) filtering the leach materials of step (b);
(d) neutralizing the liquid of step (c) with calcium
carbonate to pH at least about 3.0 and cooling for 20
about one-half hour to precipitate out additional
arsenates;
(e) recovering a metal value or values selected from
the group comprising copper, germanium, cadmium,
zinc, and indium from the liquid of step (d). 25
16. The process of claim 15 wherein valuable metals
are recovered by means of the following additional
steps:
(f) leaching the solid residue of step (c) with a mixture
of sodium chloride and calcium chloride, in the 30
presence of ferric ions at a concentration of approximately
3 gil ferric for about an hour at a pH
of about 0.5 adjusted with sulfuric acid at a temperature
of between about 95· C. and about 100· C. in
the presence of an oxidizing agent to maintain the 35
emf at up to about - 700 mv, in order to solubilize
at least one of the metals lead, silver, gold, bismuth
and antimony, and leave the ferric-arsenic compound
undissolved;
(g) performing a liquid-solid separation on the leach 40
materials of step (f); and
(h) recovering at least one of the metal values from
the liquid of step (g).
17. A process for recovering metals selected from the
group consisting of copper, zinc, cadmium, indium and 45 * * * * *
50
55
60
65