4,244,734 Process for recovering metal values from materials containing arsenic

Patent Number/Link:

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

- 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

4,244,734

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

The invention lies in the field of hydrometallurgical

recovery of metals from materials containing contaminating

substances such as arsenic.

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.

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.

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

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.

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

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:

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;

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

step (b).

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;

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-

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.

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;

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;

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

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;

(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 * * * * *