3,736,238 Process for the recovery of metals from sulfide ores through electrolytic dissociation of the sulfides

Patent Number/Link:

United States Patent Office 3,736,238

Patented May 29, 1973

1 2

The term metal sulfide as used herein is inclusive of

the complex as well as the simple sulfide minerals which

contain economically recoverable quantities of the specified

metals.

The invention is a pollution-free process for the recovery

of the metals of Groups I-B, II-B, IV-A, V-A, VI-A

and VIII of the Periodic Table, from their sulfide and

mixed sulfide ores or concentrates in which the sulfide is

electrolytically dissociated in an acid aqueous media into

elemental sulfur and metal ions which are then recovered

from solution in the electrolyte media by conventional

pollution-free techniques.

The electrolysis process is characterized by certain critical

process conditions which render it economically feasible,

these being the use of:

(l) An electrolyte comprising: a soluble metal chloride

selected from the group consisting of soluble chlorides

of aluminum, chromium, copper, iron, manganese, nickel,

zinc and rare earth metal chlorides either alone or mixed

in combination with alkali metal and/or alkaline earth

metal chlorides, said electrolyte being at least .5 normal

in chloride ion,

and have created demands for pollution-free processes.

An electrolytic process requiring only economic quantities

of power, in which substantially all the sulfur in the above

metal sulfides related to this invention is converted to ele-

5 mental sulfur is an answer to the pollution problem.

The high degree of concentration required for economic

pyrometallurgical processing results in losses in concentration

and in the loss of potentially valuable co-product

values which are not readily recovered. The presence of colO

product values in the main metal product often results in

economic penalties being assessed against the concentrates.

Thus low grade concentrates which are not amenable to

physical segregation techniques are often considered valueless

or of low value because they cannot be processed

economically by conventional pyrometallurgical processes.

In co-pending application of Ser. No. 113,751, filed

Feb. 8, 1971, by Paul R. Kruesi, now U.S. Pat. No. 3,673,061,

it is disclosed that the use of a basic electrolyte media

for electrolytic dissociation of sulfide ores results in the

sulfide sulfur being converted into sulfate with high current

consumption while the use of an acidic electrolyte

media comprised of alkali metal and/or alkaline

earth metal chlorides under specified conditions results

in the sulfide sulfur being converted to elemental sulfur

with a substantial reduction in required current.

While the use of alkali and alkaline earth metal chlorides

as electrolytes as disclosed in the above cited application

Ser. No. 113,751 results in an economic pollutionfree

process for the processing of sulfide ores and concentrates,

it has been found that certain other metal chlorides

under the conditions herein specified are equally

effective as electrolytes for the same purpose and in certain

cases have unexpected advantages.

Many commercial sulfide concentrates contain substan-

35 tial quantities of iron either as a part of the mineral as

in the case of chalcopyrite or mannatite, or as an impurity

as is the case with pyrrhotite. In the process of this

invention the conversion of this iron to chloride results

in a convenient electrolyte media.

In the past it has been difficult to process galena in a

chloride media because of the limited solubility of lead

chloride. Particularly, it was generally believed that this

low solubility would mitigate against economic plating at

the cathode. It has been found that the solubility of lead

chloride is surprisingly high in aluminum chloride and

that aluminum chloride is a suitable electrolyte media for

the efficient electrolytic dissociation of lead sulfide and

subsequently plating of lead at the cathode. This is clearly

shown in Example 6 below.

STATEMENT OF THE INVENTION

BACKGROUND OF THE INVENTION

There are disclosures in the prior art of processes for the

electrolytic recovery of certain metals from their sulfide

ores under various conditions. These processes cannot be 40

used for the economic recovery of metals of Groups I-B,

II-B, IV-A, V-A, VI-A and VIII of the Pe~iodic Table

from their sulfide and mixed sulfide ores, partlcularly low

"rade ores, for various reasons.

b U.S. Pat. No. 2,839,461 discloses an electrolytic process

for the recovery of nickel from nickel sulfide but it 45

is dependent upon the formation of a highly conductive

nickel sulfide matte anode and is not applicable to low

grade concentrates. Such common sulfide minerals as

galena, sphalerite, chalcopyrite, and chalcocite have resistivities

many times that of the anode used in the proc- 50

esses of Pat. No. 2,839,461 and, therefore, that process

cannot be used with these minerals.

U.S. Pat. No. 3,464,904 relating to the electrolytic recovery

of copper and zinc from their sulfide ores discloses

the use of a hydrochloric acid electrolyte having a con- 55

centration of 5-10%. In the absence of the metal chlorides

used in the electrolytes of co-pending application SeI. No.

113,751 and in the electrolytes of this application, this high

acidity does not lead to economic recovery from their

sulfides of the metals to which the present invention ap- 60

plies as demonstrated in Example 8 which follows.

Prior to the present time there has been little incentive

for the development to commercial application of electrolytic

or other pollution-free processes for the recovery

of metals from sulfide ores. Metals are conventionally re- 65

covered from their sulfide ores by pyrometallurgical processes

in which sulfur contained in the ores or concentrates

is oxidized to sulfur dioxide, of which a substantial portion

is released to the atmosphere with consequent damage

to the environment and loss of sulfur values. Recently 70

promulgated pollution standards have made the pyrometallurgical

processes, as presently applied, prohibitive

ABSTRACT OF THE DISCLOSURE

A pollution-free process for the electrolytic dissociation

of sulfide ores of the metals of Groups I-B, IT-B, IV-A, 15

V-A VI-A and VIII of the Periodic Table in aqueous

acidi~ media with the formation of metal ions and elemental

sulfur followed by recovery of the metal ions from

solution in the electrolyte media, the process characterized

by certain process conditions, these being the use ?f: 20

(1) An electrolyte comprising a soluble metal chlo;lde

selected from the group consisting of soluble chlondes

of aluminum, chromium, copper, iron, manganese, nickel,

zinc and rare earth metals alone or mixed or in combination

with alkali metal and/or alkaline earth f!1etal ch.lo- 25

rides, the electrolyte being at least .5 normal III chlonde

ion,

(2) A sulfide feed of average particle size smaller than

about 60 mesh U.S. Standard,

(3) A pH range of up to about 3.9, 30

(4) An electrolyte temperature range between about

50° C.-105° C., and

(5) An anode current density above about 12 ampere/

ft.2•

3,736,238

PROCESS FOR THE RECOVERY OF METALS FROM

SULFIDE ORES THROUGH ELECTROLYTIC DiS·

SOCIATION OF THE SULFIDES

Paul R. Kruesi, Wheatridge, and Duane N. Goens,

Golden Colo., assignors to Cyprus Metallurgical Processes

C~rporation, Los Angeles, Calif.

No Drawing. Filed Apr. 21, 1972, Ser. No. 246,435

Int. Cl. C22d 1/10,1/14,1/16

U.S. Cl. 204-105 R 37 Claims

3,736,238

efficiency. Further, it was found that at high current densities

in the presence of sulfate graphite anodes were appreciably

attacked and this type anode is the most satisfactory.

5 The preferred electrolyte media has been set forth

above. Ferrous chloride is particularly effective as an

electrolyte for dissociation of chalcopyrite as this compound

is produced in quantity by the electrolytic dissociation

of chalcopyrite in an acid medium. Aluminum

10 chloride is particularly suited as an electrolyte for the

dissociation of lead sulfide ores and concentrates, leadzinc

and lead-silver concentrates, because of the high

solubilities of lead and silver chloride in aluminum chloride.

This discovery is highly unexpected in view of the

15 insolubility of lead and silver chlorides in most solvents.

Zinc chloride is preferred with zinc ores essentially free

of lead.

Concentrations of chloride ion in excess of .5 normal

to saturation may be used for the process. Voltage across

20 the cell is lower at higher salt concentrations and the

latter are preferred except where low grade feeds are used

and where salt losses would therefore become significant.

It is highly important that a high percentage of the

sulfur in the metal sulfide be recovered as elemental sulfur

both from the standpoint of pollution control and the

electrical efficiency of the process. If sulfur is converted

to sulfate, high current consumption results and the disposal

of the sulfate may create a pollution problem. Every

mole of sulfur which is oxidized beyond the elemental

state requires six Faradays which is equivalent to 2275

ampere hours per pound of sulfur. As chalcopyrite, for

example, contains approximately one pound of sulfur per

pound of copper, any sulfur oxidation of the sulfate represents

a substantial loss of efficiency. As shown by the

examples below, an average of at least 90% of the sulfur

in the sulfides is converted to elemental sulfur in the process

of the invention. The elemental sulfur does not result

in any polarization problems at the reaction temperatures

of the electrolyte media.

The particle size of the feed material is critical as it

directly affects the conversion of 'sulfide sulfur to elemental

sulfur. The elemental sulfur produced is extremely

fine. The anode current attacks the metal sulfide preferentially

to sulfur provided the sulfide has sufficient activity

near the anode. The activity of the sulfide is a

function of its concentration and its exposed surface

area. Therefore, the presence of a high concentration

of fine sulfide near the anode prevents the continuing

oxidation of sulfur and results in higher efficiency and

conseqeuntly lower current consumption. An average

grain size for the feed sulfide smaller than about 60

mesh U.S. Standard is the operable range and is compatible

with other critical parameters.

A pH range for the electrolytic media up to about 3.9

is prderred. Current efficiency is reduced at pH's above

3.9 and at very high acidities (low pH values) in the

absence of substantial concentrations of the specified

metal chlorides. In certain cases such as that of aluminum

chloride which hydrolyzes at about pH 2.0, chromic

chloride which hydrolyzes at about pH 3.0, and rare

earth metal chlorides which hydrolyze at about pH 4.0,

the acidity must be strong enough to prevent this hydlOlysis.

The preferred pH range is 0.3-0.8. The pH of

the electrolyte is conveniently adjusted with hydrochloric

acid.

The reaction temperature of the electrolyte is critical

and high process efficiency is not obtainable at low temperature.

The preferential attack on the sulfide over elemental

sulfur is accentuated at high temperatures and,

indeed, at temperatures below 50° C. a substantial portion

of the sulfide is converted to undesirable sulfate. The

operable range is about 50° C.-105° C. when used in

conjunction with the other critical factors. A temperature

of 80° C. is most preferred.

(2) A sulfide feed of average particle size smalIer than

about 60 mesh U.S. Standard,

(3) A pH range up to about 3.9,

(4) An electrolyte temperature range between about

50° C.-105° C., and

(5) An anode current density of above about 12 amperes/

ft.2• The temperature and pH ranges are the most

critical of the above parameters. Within the above process

parameters the chloride electrolytes of this invention

are substantial equivalents for electrolytic dissociation of

the metal sulfides of metals of Groups I-B, II-B, IV-A,

V-A, VI-A and VIII of the Periodic Table.

The other soluble halide salts, including the bromides,

iodides and fluorides, of aluminum, chromium, copper,

iron, manganese, nickel, zinc, and rare earth metals, are

operative for the purpose of the invention; however, they

are not as economically attractive as the chlorides of these

metals. Soluble halide metal salts in general are operative

as electrolytes for recovering metals from their sulfides

in accordance with the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The economic feasibility of the process is dependent

upon the current required to produce a given quantity of

metal. It is expressed herein as the ampere hours of cur- 25

rent required to release a pound of metal. The current

requirement will vary for each metal and economic viability

will depend somewhat on the cost per pound at

which that metal can be produced by present processes.

This statement does not take into consideration recently 30

promulgated air pollution standards which may completely

eliminate or drastically limit the economic competition

of present air polluting processes.

The process parameters which have been found to control

the current requirements for the process are elec- 35

trolyte composition, feed particle size, operating pH range,

operation temperature, and anode current density. As the

examples which follow show, these factors are mutually

interactin¥ and dependent as respects their effect on cur- 40

rent reqUIrements.

It has been found that sulfide ores and concentrates

of metals of Groups I-B, II-B,IV-A, V-A, VI-A and

VIII of the Periodic Table are characterized by certain

similar properties related to the electrolytic dissociation

to elemental sulfur and metal ions therefrom by the proc- 45

ess of this invention. For example, their sulfides all have

relatively low conductivities. While certain nickel sulfides

are relatively good conductors, others are not. Further,

the metal ions of these sulfides are most favorably produced

by electrolysis in aqueous acidic electrolytes of 50

soluble chlorides of aluminum, chromium, copper, iron,

manganese, nickel, zinc, rare earth metals, alkali metals,

and alkaline earth metals, and mixtures thereof, at a pH

range of up to about 3.9 using anode current densities

above about 12 amperes/ft.2 with a sulfide feed particle 55

size smaller than about 60 mesh U.S. Standard, and a

temperature range between about 60° C.-105° C. for the

alkali and alkaline earth metal chlorides and between

about 50° C.-lOS ° C. for the other electrolytes. The examples

which follow illustrate that the power require- 60

ments for the process applied to recover the stated metals

from their sulfides are well within the limits of commercial

feasibility.

The minerals containing the metals which can be recovered

by the process often contain the metals in the 65

form of complex or mixed sulfides.

The electrolytic media for the process must be acidic

as an alkaline electrolyte has proven unsatisfactory for

recovery from their sulfides of the defined metals to which

the invention is related. Elemental sulfur is not stable 70

in an alkaline media because oxidation of the sulfur proceeds

rapidly through thiosulfate, hydrosulfite, sulfide to

sulfate. The presence of sulfate ions is undesirable because

at high sulfate concentrations oxygen is rapidly

evolved at the anode resulting in a decrease in current 75

3,736,238

The anode current density is also critical as used with

the other critical parameters with a preferred range being

above about 12 amperes/ft.2 anode current density. In

contrast to the earlier prior art teaching (U.S. Pat. No.

2,761,829) it was found that high copper dissociation in

copper sulfide concentrate in the presence of iron sulfide

(pyrite) was attained at current densities of 240 .amperes/

ft.2• For the mixture of chalcopyrite and pyrite

where chalocpyrite is the predominant mineral, a preferred

current density range is 120--240 amperes/ft.2•

Where pyrite predominates current densities of between

60-120 "amperes/ft.2 are preferred.

Within a fairly broad range current anode density may

in the process of the invention as operated within the

critical parameter ranges of temperature, current density,

pH and particle size.

For each test 400 grams of comemrcial copper sulfide

5 concentrate having a particle size of -60 mesh analyzing

by weight 27.7% copper and 28.4% iron was slurried

in 2 liters of electrolyte and subjected to 30 amps./hr.

of current under the conditions shown. For the mixed

electrolytes approximately equal volumes of each were

10 used. Other alkali metal chlorides may be added to the

electrolyte, such as, potassium and lithium cWorides.

Alkaline earth metal chlorides, such as, calcium and

barium chlorides may be added.

Test No 1 2 3 4 5 6

Electrolyte •• • __ ._ 2 M AICh 1 M AI0I3 2 M NaCI; 0.5 M FeCh__ • 2M NaCI; 3 M FeCh.

1 M AlCh. 1M FeCI,.

Temperature (0 C.)---------------------- ••• ---------- 78 • 74 0_ 75 75__; cc 75__•• _•• _. __ ._ 75.

Anode current density (ACD) (amps/ft.')------------- 120 120 •__ 120 • __ • __ 120. ••__ 120._••••• _._._ 120.

pH ••• 004 • __ 0.5 ._ 0.6 •••__• 0.6__ ._•• __ • 0.5_. ._._. __ 0.5.

~~~~nil~·e?~e~r~e§~~~~========================== §g~===========~ ~=~=========~= g8=~==~==~=~~=~ ~~~~=~~~===~~~ ~~~==~~=~==~==~ ~~~.

be adjusted to the situation so long as it is above about

12 amperes/ft.2. With low grade feeds an anode current

density between 40-120 amperes/ft.2 may be used. Often

when metal is being plated at the cathode the necessities 25

of cell geometry will dictate the anode current density.

Thus with copper if copper powder is desired current densities

of 100-200 amperes/ft.2are preferred at the cathode

and this range of current density is suitable for high

grade copper concentrates. When plating lead or zinc at 30

the cathode a current density range of 20--30 amperes/ft.2

is preferred at the cathode and is suitable for the anode.

The following examples with results are illustrative of

the process of the invention but not limiting thereof. The

process is not limited to a specific electrolytic cell design 35

or type of cell. The cells used in the examples, well

known in the art, comprised an anode section containing

a suitable anode such as graphite or coated titanium, provided

with means for agitation and heating, and separated

from the cathode section by a diaphragm. The cathode 40

section consisted of a suitable cathode of stainless steel,

copper, lead or aluminum depending upon the metal being

plated or the cathode reaction desired and was provided

with means for liquid circulation and heating.

In the examples, average grain size is given in U.S. 45

Standard mesh size, anode current density designated as

The high conversion of sulfide sulfur to elemental sulfur

and low current consumption prove the effectiveness

of the electrolytes within the parameter ranges of the

process. As in the examples which follow in which it is

reported the high conversion of sulfide sulfur to elemental

sulfur in the acid electrolyte and low current consumption

is in marked contrast to prior art processes

using basic electrolytes resulting in conversion of the

sulfide sulfur to sulfates with consequent high current

consumption.

EXAMPLE 2

Selection of the following tests was made to demonstrate

the equivalence for the purposes of the invention

of the electrolytes of Example 1 and the electrolytes

nickelous chloride, cupric chloride, chromic chloride,

managanous chloride, and rare earth metal chlorides.

For each test 400 grams of -60 mesh particle size

copper sulfide concentrate analyzing by weight 27.7%

copper and 28.4% iron were slurried in 2 liters of electrolyte

and subjected to 30 ampere hours of current under

the conditions shown. Analysis by weight of the rare earth

metal chloride mixture as oxides was as follows:

La20a-78.7%, Ce20a-11.2%, Pr20a-3.8%, Nd20 a-l%,

Sm20a-2%.

Test No 1 2 3 4 5

Electrolyte • 1 M NiCh 1 M CUCh. 1 M CrCh 1 M MuCh 1 M (rare earth) 013'

Ibr:P(~~/fr,)~~~~================ i~iC=======~=== i~o============== ik============= ik============= i~. pH 0.6 ._ 0.5 •• _ 0.5 • 0.5 0.5.

Amp-hrs./lb Cn recovered 586 745_. 799 601. __ • 565.

Percent S as elemental S • 87 • __ 85. 94 • • 85.

EXAMPLE 3

In order to define the critical temperature range for the

process utilizing other conditions within the process

parameter ranges the following tests were performed.

For each test 400 grams of -60 mesh particle size com.

mercial copper sulfide concentrate analyzing by weight

The results of the example in terms of large conversion

of sulfide sulfur to elemental sulfur with low current consumption

demonstrates the effectiveness of the electrolytes

under the conditions for a representative metal sulfide. In

the case of all the electrolytes used in the tests except

60 cupric chloride and chromic chloride the copper was recovered

essentially as cuprous copper resulting in very

high electrical efficiency. The copper recovered using

cupric cWoride and chromic chloride electrolytes was essentially

cupric copper, this accounting for the somewhat

65 higher current consumptions. The higher valent forms of

copper and chromium are preferred because the lower

valent forms have limited solubility. However, cuprous

chloride may be used as the electrolyte instead of cupric

chloride.

EXAMPLE 1

The following tests were selected to illustrate the operativeness

of aluminum chloride and ferrous chloride

alone and with an alkali metal chloride as electrolytes 75

ACD is given in amperes/ft.2, current requirement is 55

reported in terms of ampere hours/pound of metal dissociated,

and recovered. The percent sulfur converted to

elemental sulfur is computed by dividing the amount converted

to elemental sulfur by the total amount of sulfur

converted from sulfide sulfur and is expressed in percent.

The metal dissolved in the electrolyte can be finally

recovered by conventional methods such as, electrolysis,

precipitation, cementation, etc., depending on the metal

being recovered. In certain cases the metal can be plated

out on the cathode during the dissociation process and

recovered in this manner.

Elemental sulfur is readily recovered from the electrolyte

media by the process disclosed in co-pending application

Ser. No. 233,352, filed in the U.S. Patent Office on

Mar. 9, 1972, William G. Kazel, entitled "Sulfur Re· 70

covery Process."

3,736,238

27.7% copper and 28.49% iron were slurried in 2 liters

of electrolyte and subjected to 30 ampere hours of current

under the conditions recorded.

lyte were separated to enhance plating of lead and zinc of

high purity. The electrolyte media was subjected to 38.3

ampere hours of current before analysis for results at an

Test No 1 2 3 4 5 6

Electrolyte 2 M AlCh 2 M AICh 2 M AlCla 3 M FeCb 3 M FeCb 3 M FeCI,.

~~~l~~~~:~mm:m~~~~~im~:::~:~~:-~~~:~:m:~~~~~:~:~~~~:~~:~~~j:::~::~:~m::~:m~~:mm~~~.

The results show striking increase in current consumption

and decrease in cOIiversion of sulfide sulfur to elemental

sulfur at temperatures below about 50° C. with

current consumption as high as 2193 amp./lb. Cu recovered

and sulfur conversion as low as 54%. The results

illustrate that the lower limit of the critical temperature

range is somewhere between about 44-50° C.

EXAMPLE 4

The following tests are incuded to demonstrate the operativeness

of the process at high acidities.

For each test 400 grams of-60 mesh commercial

copper sulfide concentrate assaying by weight 27.7% copper

and 28.4% iron were slurried in 2 liters of electrolyte

and subjected to 30 ampere hours of current under the

conditions indicated with the following results.

anolyte pH of 0.5, a temperature of 80° C., and a cur15

rent density of 30 amps/f1.2 on both the anode and cathode.

The following results were obtained.

MetaL__________________________________ Lead Zinc Iron Silver

Dissolved metal (gms.) _________________ 76.0 33.8 10.3 .044

Pereentage recovery ofmetals___________ 97.7 27.3 31. 9 69.8

133 grams of lead were plated at the cathode indicating

90% cathode current efficiency.

The electrolysis was continued for an additional 65.6

25 ampere hours with the same anolyte pH and temperature

using anode and cathode current densities of 30-60 amps!

f1.2 • Zinc chloride dissolved in aluminum chloride was

used as the catholyte. The following results were obtained.

Test No .!,, 1 2 3 4 5 6 7

.059

93.7

Silve·r

17.1

52.8

Iron

98.4

79.5

Zinc

79. 2 126.7 . 09 39.5 .07

9696..28 93.2 95.7 74.7 82.0_

95 _

Dissolved metal (gms.) _

Percentage recovery of metal _

Sulfur reeovered, gms _

Pereent S as elemental S _

The high percentage recovery of lead, zinc, silver and

cadmium demonstrates the suitability of ferrous chloride

as an electrolyte for recovery of the metals from their

MetaL__________________________ Pb

70 grams of zinc were plated at the cathode indicating

a cathode current efficiency of 91 %.

The example illustrates that lead, zinc, and silver can

be recovered from their sulfides by the process of the

invention using a representative chloride electrolyte for

the process of this invention and that the process is particularly

effective for these metals with an aluminum

chloride electrolyte.

The process is equally effective for the recovery of O'old

germanium and tin from their sulfides. 0 ,

EXAMPLE 7

Dissolved metal (gms.) 77.5

Percentage reeovery of metals________ 99.6

MetaL________ Lead

The following test is included to show the suitability of

ferrous chloride electrolyte for recovering lead, zinc,

silver and cadmium from their sulfides.

470 grams of -60 mesh particle size sulfide ore concentrate

assaying by weight 31.9% zinc, 17.1% lead,

12.6% iron, .0219% silver, and .018% cadmium were

slurried in 2 liters of electrolyte and fed to the anode

side of a diaphragm cell. The anolyte, 2 molar ferrous

chloride, was subjected to 157.5 ampere hours of current

65 at 80° c., pH 0.5 at an anode current density of 60 amps!

£t.2• The results obtained are shown below.

Cn-2.0

41.5 , " _

5429.85 ------------------------------_ 60

The low current consumption and high sulfur conversion

obtained illustrate the effectiveness of the process for

the recovery of nickel and cobalt from their sulfides.

EXAMPLE 6

The following example is included to show the effectiveness

of the process for the recovery in chloride electrolyte

of additional metals from their sulfides, particularly lead.

500 grams of a -60 mesh particle size commercial sul- 70

fide ore concentrate assaying by weight 25.6% lead,

24.8% zinc, and .013% silver were processed in a diaphragm

cell. The concentrate was slurried in 2 liters of 2

M AICla which served as anolyte. Lead chloride dissolved

in 2 M AlCla served as catholyte. The anolyte and catho- 75

Wt. of metal dissolved (gms.) Fe-46 Ni-1.7 Co--O.2

Gms. snlfur recovered _

Amp-hrs./lb. of combined

metals reeovered _

Percent S as elemental S .i

The results demonstrate the effectiveness of the process

at acidities as high as pH 0.01. The economically feasible 40

maximum pH is about 3.9.

EXAMPLE 5

The following test is included to show the effectiveness

of the process utilizing a representative electrolyte on the 45

sulfides of nickel and cobalt.

For each test 400 grams of a -60 mesh particle size

low grade sulfide ore concentrate assaying by weight

8.33% nickel, 0.337% colbalt, 5.16% copper and 37.8%

iron were slurried in 2 liters of electrolyte and subjected 50

to 60 ampere hours of current under the conditions shown.

Using a 4 M FeC12 electrolyte at a temperature of 80°

C., pH of 0.5 and an anode current density of 120 amps!

ft.2 the following results were obtained from analysis of

the electrolyte media at the end of the test. 55

3,736,238

sulfides by the process. Commercially feasible current

consumptions were noted.

EXAMPLE 8

The following tests were run to compare the efficiency

of aluminum chloride and ferrous chloride electrolytes

with that of hydrochloric acid electrolyte.

For each of the tests a commercial -60 mesh particle

size copper sulfide concentrate assaying by weight 27.7%

copper and 28.4% iron was used. 100 grams were used

for Test No. 1 and 400 grams were used for Tests No. 2

and No.3. The concentrate was slurried in 2 liters of

electrolyte and subjected to 30 ampere hours current

under the conditions shown in a diaphragm cell with the

following results.

HCI (5%) 2 M AlCb 3 M FeCI,.

80 78 75.

0.01 (5% HCI)_ 0.01 (5% HCl)_ 0.01 (5%

HCl);

120 ;'c 120"_~_"_;_"_C_ 120.

1,566 "_ 463 558.

73 c =-.' 95 c_"_._C" 88.

Test No "_~_" • 1

Electrolyte • _

pTHemperature (0 C.) __

ACD (amps/it.') "_" __

Amp-hrs./lb. Cn recovered.

Percent S as elemental S_

2 3

EXAMPLE 11

The following tests were performed to determine the

effectiveness of the process of the invention in recovering

arsenic, cadmium, antimony and selenium from their

5 sulfides.

232 grams of a -60 mesh grain size commercial low

grade chalcopyrite concentrate analyzing by weight 4.0%

lead, 9.2% zinc, 24.0% copper, 25.5% iron, 0.5% arsenic,

0.018% cadmium, 0.025% antimony and 0.36% selenium

10 wertl slurried in 2 liters of 3 M ferrous chloride electrolyte

and subjected to 30 ampere hours of current at 75° C.,

pH 1.5, and an anode current density of ,60 amps/ft.2

with the following results.

Percent metal

15 Metal: dissolved

Copper ' ----------- 9.4

Zinc 36.4

Lead 87.4

Arsenic 97.0

20 Cadmium ------ 42.9

Antimony 52.0

Selenium 28.9

As demonstrated with a representative electrolyte the

25 process is effective for the electrolyte recovery of the

metals arsenic, cadmium, antimony and selenium from

their sulfide ores. The process is equally effective for the

recovery of bismuth and tellurium from their sulfides.

The current requirements set forth in the examples are

30 well within commercial feasibility ranges for large scale

production of the metals from their sulfide and mixed sulfide

ores. The cost of the recovery of the metals from

the electrolyte after electrolysis by conventional techniques

is comparatively small. The process permits the

35 recovery in significant yields of metals present in trace

quantities. The high percentage recovery of sulfur from

the sulfides as elemental sulfur substantially reduces the

pollution problems associated with prior art processes

and enhances the economic attractiveness of the process.

Accordingly, the invention provides a process for recovery

of the metals from their sulfide and mixed sulfide

ores which has the advantages of being commercially

feasible and pollution free.

What is claimed is:

1. A process for the recovery of metals of Groups I-B,

II-B, IV-A, V-A, VI-A and VTII of the Periodic Table

from their sulfides and mixed sulfides, and mixtures thereof,

by electrolysis with the formation of elemental sulfur

and metal ions, which process comprises:

(a) providing an electrolyte in an electrolytic cell including

at least an anode and a cathode, the electrolyte

comprising an acidic aqueous solution of at

least one chloride salt selected from the group consisting

of chlorides of aluminum, chromium, cop·

per, iron, manganese, nickel, zinc, and rare earth

metals, and mixtures thereof, the solution having a

concentration from about .5 N to saturation;

EXAMPLE 10

Test No • 1

The example shows that, somewhat contrary to the 45

teaching of U.S. Pat. 2,761,829', copper dissolves readily

at the high current densities shown under the process

conditions of the invention.

The following tests were performed to demonstrate

the effectiveness of zinc chloride as an electrolyte.

For each test 400 grams of a -60 mesh grain size commercial

zinc sulfide concentrate assaying by weight 57.2%

zinc was slurried in 2 liters of electrolyte and subjected 55

to 30 ampere hours of current under the conditions indicated

with the following results.

Electrolyte 3 M FeCb 3 M FeCb

Temperature (0 C.) " 75 75.

pH " 0.5 ~ 0.5.

ACD (amps/it.') C " ;'_ 120 240.

Amp-hrs./lb. Cu recovered 558 617.

Percent S as elemental S c_ 88 86.

The results demonstrate the superiority of aluminum

chloride and ferrous chloride acidified with hydrochloric

acid over hydrochloric acid alone as electrolytes.

EXAMPLE 9

The test 'below is included to demonstrate the effectiveness

of the process at high current densities.

400 grams of a-60 mesh gram size chalcopyrite concentrate

assaying by weight 27.7% copper and 28.4%

iron (mineralogical examination showed the sample material

to be about 80% chalcopyrite and 8% pyrite) was

slurried in 2 liters of electrolyte and subjected to 30

ampere hours of current under the conditions shown with

the following results.

Test No 1 2 3 4

Electrolyte c_ 3 M ZnCb 1.5 M ZuCh 3 M ZnCb 3 M ZnCh.

r~~-:::s~i~;)~=~====================:==~~~::=::::=:::::~:~~:::::::::::::~:E:::=:::=::::~l. Amp-hrs./lb. Zn recovered 386 313 372 381.

Sulfur recovered (gms.) 13.2 16.8 12.7 9.7.

Percent S as elemental S.. "" 85 89 83 71.

The tests illustrate that zinc chloride is as effective as

an electrolyte as the other chloride electrolytes of the

invention. Test No.4 was performed at a 3.5 pH which

is near the top of the critical pH range of 3.9 and this

test shows the adverse effect of low acidity on conversion

of sulfide sulfur to elemental sulfur. 75

(b) mixing with the electrolyte a solid feed sulfide of

the metal having an average particle size smaller

than about 60 mesh U.S. Standard;

media at about 50° C. to 105° C., and the pH of

the electrolyte media below about 3.9 while intro3,736,238

3,673,061

3,464,909

27. The process of claim 24 in which the metal is

copper.

28. The process of claim. 23 in which the metal is

copper.

29. The process of claim 22 in which the metal is

copper.

30. The process of claim 31 in which the metal is

copper.

31. The process of claim 21 in which the metal is selected

from the group consisting of antimony, arsenic,

cadmium, cobalt, copper, iron, lead, nickel, selenium, and

zinc.

32. The process of claim 20 in which the metal is

copper.

33. The process of claim 19 in which the metal is

copper.

34. The process of claim 35 in which the metal is

selected from the group consisting of lead, silver and

zinc.

35. The process of claim 18 in which the metal is selected

from the group consisting of silver, copper, iron,

lead and zinc.

_ 36. The process of claim 2 in which the alkali metal

chloride is sodium chloride.

37. A process for the recovery of metals of Groups I-B,

II-B, IV-A, V-A, VI-A and VIII of the Periodic Ta:ble

from their sulfides: and mixed sulfides, and mixtures thereof,

by electrolysis with the formation of elemental sulfur

and metal ions, which process comprises:

(a) providing an electrolyte in an electrolytic cell including

at least an anode and a cathode, the electrolyte

comprising an acidic aqueous solution of at

least one soluble halide salt selected from the group

consisting of soluble halide salts of aluminum, chromium,

copper, iron, manganese, nickel, zinc, and

rare earth metals, and mixtures thereof, the solution

having a concentration from about .5 N to saturation;

(b) mixing with the electrolyte a solid feed sulfide of

the metal having an average particle size smaller

than about 60 mesh U.S. Standard;

media at about 50· C. to 105· C., and the pH of

the electrolyte media below about 3.9 while introducing

electric current into the electrolytic cell to

provide an anode current density above about 12

amperes per square foot to dissociate the metal sulfide

into metal ions and elemental sulfur; and

(d) recovering metal from the electrolyte.

References Cited

UNITED STATES PATENTS

6/1972 KIue~ 204--107

9/1969 Brace 204--114

U.s. Cl. X.R.

60 204--106, 107, 111, 113, 117, 118, 123,293

55 JOHN H. MACK, Primary Examiner

R. L. ANDREWS, Assistant Examiner

ducing electric curemt into the electrolytic cell to

provide an anode current density above about 12

amperes per square foot to dissociate the metal sulfide

into metal ions and elemental sulfur; and

(d) recovering metal from the electrolyte. 5

2. The process of claim 1 in which at least one chloride

salt selected from the group consisting of alkali metal

chlorides and alkaline earth metal chlorides is added to

the electrolyte.

3. The process of claim 1 in which the metal is recov- 10

ered from the sulfide and mixed sulfide in the presence

of iron sulfides.

4. The process of claim 1 including the step of recovering

the metal from solution in the electrolyte by electrodeposition

on the cathode. _

5. The process of claim 1 including the step of recovering

elemental sulfur from the electrolyte.

6. The process of claim 1 in which the metal recovered

is copper.

7. The process of claim 1 in which the metal recov- 20

ered is lead.

8. The process of claim 1 in which the metal recovered

is silver.

9. The process of claim 1 in which the metal recovered

is zinc. 25

10. The process of claim 1 in which the metal recovered

is antimony.

11. The process of claim 1 in which the metal recovered

is arsenic.

12. The process of claim 1 in which the metal recov- 30

ered is cadmium.

13. The process of claim 1 in which the metal recovered

is selenium.

14. The process of claim 1 in which the metal recovered

is nickel.

15. The process of claim 1 in which the metal recovered

is cobalt.

16. The process of claim 1 in which the metal recovered

is iron.

17. The process of claim 1 in which the metals are 40

selected from the group consisting of antimony, arsenic,

cadmium, copper, cobalt, iron, lead, nickel, selenium,

silver and zinc.

18. The process of claim 1 in which the electrolyte is

aluminum chloride.

19. The process of claim 1 in which the electrolyte is

copper chloride.

20. The process of claim 1 in which the electrolyte is

chromium chloride.

21. The process of claim 1 in which the electrolyte is 50

ferrous ch10ride.

22. The process of claim 1 in which the electrolyte is

manganous chloride.

23. The process of claim 1 in which the electrolyte is

nickelous chloride.

24. The process of claim 1 in which the electrolyte

comprises at least one rare earth metal chloride.

25. The process of claim 1 in which the electrolyte is

zinc chloride.

26. The process of claim 25 in which the metal is zinc.