US3736238A - Process for the recovery of metals from sulfide ores through electrolytic dissociation of the sulfides - Google Patents

Abstract

A POLLUTION-FREE PROCESS FOR THE ELECTROLYTIC DISSOCIATION OF SULFIDE ORES OF THE METALS OF GROUPS I-B, II-B, IV-A, V-A, VI-A AND VIII OF THE PERIODIC TABLE IN AQUEOUS ACIDIC 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 OF: (1) 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 METALS ALONE OR MIXED OR IN COMBINATION WITH ALKALI METAL AND/OR ALKALINE EARTH METAL CHLORIDES, THE ELECTROLYTE BEING AT LEAST .5 MORMAL IN CHLORIDE ION, (2) A SULFIDE FEED OF AVERAGE PARTICLES SIZE SMALLER THAN ABOUT 60 MESH U.S. STANDARD, (3) A PH RANGE OF UP TO ABOUT 3.9, 74) AN ELECTROLYTE TEMPERATURE RANGE BETWEEN ABOUT 50*C.-105*C., AND (5) AN ANODE CURRENT DENSITY ABOVE ABOUT 12 AMPERE/ FT.2.

Description

United States Patent US. Cl. 204-105 R 37 Claims ABSTRACT OF THE DISCLOSURE A pollution-free process for the electrolytic dissociation of sulfide ores of the metals of Groups I-B, II-B, IVA, V-A, VI-A and VIII of the Periodic Table in aqueous acidic 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 of:

(1) 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 metals alone or mixed or in combina tion with alkali metal and/or alkaline earth metal chlorides, the electrolyte being at least .5 normal in chloride (2) A sulfide feed of average particle size smaller than about 60 mesh US. Standard,

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

(4) An electrolyte temperature range between about 50 C.-l05 C., and

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

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 used for the economic recovery of 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, particularly low grade ores, for various reasons.

U.S. Pat. No. 2,839,461 discloses an electrolytic process for the recovery of nickel from nickel sulfide but it 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 processes of Pat. No. 2,839,461 and, therefore, that process cannot be used with these minerals.

US. 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 concentration of 510%. In the absence of the metal chlorides used in the electrolytes of co-pending application Ser. 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 applies 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 recovered 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 promulgated pollution standards have made the pyrometallurgical processes, as presently applied, prohibitive 3,736,238 Patented May 29, 1973 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 elemental 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 coproduct 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 substantial quantities of iron either as a part of the mineral as in the case of chalcopyrite or marmatite, 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 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 IB, IIB, IVA, 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:

(1) 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,

(2) A sulfide feed of average particle size smaller than about 60 mesh US. 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/ftfi. 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, IVA, 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 current 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 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 electrolyte composition, feed particle size, operating pH range, operation temperature, and anode current density. As the examples which follow show, these factors are mutually interacting and dependent as respects their effect on cur rent requirements.

It has been found that sulfide ores and concentrates of metals of Groups I-B, II-B, IV-A, V-A, VIA 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 process 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 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. with a sulfide feed particle size smaller than about 60 mesh US. Standard, and a temperature range between about 60 C.-l05 C. for the alkali and alkaline earth metal chlorides and between about 50 C.-l05 C. for the other electrolytes. The examples which follow illustrate that the power requirements 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 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 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 4 efiiciency. 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.

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 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 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 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 efiiciency 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 efiiciency. 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 sutficient 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 preferred. Current efiiciency is reduced at pHs 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 hydiolysis. 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.l05 C. when used in conjunction with the other critical factors. A temperature of C. is most preferred.

The anode current density is also critical as used with the other critical parameters with a preferred range being above about 12 amperes/ft. 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. For the mixture of chalcopyrite and pyrite where chalocpyrite is the predominant mineral, a preferred current density range is 120-240 amperes/ft. Where pyrite predominates current densities of between 60-120 'amperes/ft? are preferred.

Within a fairly broad range current anode density may 6 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 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 used. Other alkali metal chlorides may be added to the electrolyte, such as, potassium and lithium chlorides. Alkaline earth metal chlorides, such as, calcium and barium chlorides may be added.

Test No 1 2 3 4 5 6 Electrolyte 2 M A1013..." 1 M A1013... 2 M NaCl; 0.5 M FeOlz--- 2 M NaCl; 3 M FeCli.

1 M A1013. 1 M FeClz. Temperature 0.)- 78 74 75 75 75 75. Anode current density (ACD) (amps/ft!) 1 120 120 12 120 120. pH-.. 0.4-. 0.5.... 0.6.- 0.6- 0.5.. 0.6. Amp-hrsJlb. Cu recovered 488 561 581 613 654 558, Percent S as elemental S. 93 88---" 90 88 87 88.

be adjusted to the situation so long as it is above about 12 amperes/ft. With low grade feeds an anode current density between 40-120 amperes/ft. may be used. Often when metal is being plated at the cathode the necessities of cell geometry will dictate the anode current density. Thus with copper if copper powder is desired current densities of 100-200 amperes/ft. are preferred at the cathode and this range of current density is suitable for high grade copper concentrates. When plating lead or zinc at the cathode a current density range of 20-30 amperes/ft. 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 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 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. 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.

l 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 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: La O -78.7%, Ce O -l1.2%, PI203'3.8%, Nd2031%, Sm203-2%.

Test No 1 2 3 4 5 Electrolyte 1 M NiClz 1 M 011012 1 M CrCla 1 M M11012 1 M (rare earth) (31 Temperature 0.)- 74 7 75-.. 75 75. ACD (amps/ft?) 120 120 120. 120 120, pH-- 0.6 0.5- 0.5. 0.5- 0.5. Amp-hrsJlb Cu recovered-- 586 745 799.. 601 565 Percent S as elemental S. 87 85 94 85.

ACD is given in amperes/ft. current requirement is 55 The results of the example in terms of large conversion 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 Recovery Process.

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 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 cupric chloride and chromic chloride the copper was recovered essentially as cuprous copper resulting in very high electrical efliciency. The copper recovered using cupric chloride and chromic chloride electrolytes was essentially cupric copper, this accounting for the somewhat 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 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 commercial copper sulfide concentrate analyzing by weight 27.7% copper and 28.49% iron were slurried in 2 liters lyte were separated to enhance plating of lead and zinc of of electrolyte and subjected to 30 ampere hours of current high purity. The electrolyte media was sub ected to 38.3 under the conditions recorded. ampere hours of current before analysis for results at an Test No 2 3 4 5 6 2M AlCl 2 M A101 2 M A101 a u FeGl a M FeCl a M neon.

''llllf" 7R 3 so a 44 .1 75 -5 so .f so. AIgD (amps/it.- (1)22.--" imp-braille. 3n recovered 488:- Percent S as elemental S 93..-

The results show striking increase in current consumpanolyte pH of 0.5, a temperature of 80 C., and a curtion and decrease in conversion of sulfide sulfur to ele- 1 mental sulfur at temperatures below about 50 C. with current consumption as high as 2193 amp/lb. Cu rerent density of 30 amps/ft. on both the anode and cathode. The following results were obtained.

covered and sulfur conversion as low as 54%. The r sults t l Lead Zine Iron Silver illustrate that the lower limit o the Critical temperature Dissolved metal (gms.) 76.0 33.8 10.3 .044 range is somewhere between about 44-50 C. Percentage r v y of metals 97.7 27.3 31.9 69.8 EXAMPLE 4 133 grams of lead were plated at the cathode indicating The following tests are incuded to demonstrate the 0p- 90% cathode current efficiency. erativeness of the process at high acidities. The electrolysis was continued for an additional 65.6 For each test 400 grams of 60 mesh commercial ampere hours with the same anolyte pH and temperature copper sulfide concentrate assaying by weight 27.7% copusing anode and cathode current densities of -60 amps/ per and 28.4% iron were slurried in 2 liters of electrolyte ft. Zinc chloride dissolved in aluminum chloride was and subjected to 30 ampere hours of current under the used as the catholyte. The following results were obconditions indicated with the following results. tamed.

Test No no--. 1 2 3 4 5 6 7 Electrolyte 3 M Fe C12. Temperature C 75. ACD (amps/m 120-" 1 0. 0 120-.. 120. pH 0.01 (5%HC1)- 0.4 1.0 2.0.-. 0.01 (5%}101 l.4 2. lAmp-hrsJlb. Cu recovered 463 483 9 488 582-.- 6,486 Percent S as elemental S 95.- 3 93 0 88 92.

The results demonstrate the effectiveness of the process at acidities as high as pH 0.01. The economically feasible Metal Lead Zinc Iron Silver maximum PH is about llgissolvted metal (gmsf) E 1 77, 5 93 4 17 1 05g EXAMPLE 5 ercen g l ve y 0 me a s 99. 6 79.5 52, s 93.

The following test is included to show the eifectiveness 70 grams of zinc were plated at the cathode indicating of the process utilizing a representative electrolyte on the a cathode current efficiency of 91%. sulfides of nickel and cobalt. The example illustrates that lead, zinc, and silver can For each test 400 grams of a 60 mesh particle size be recovered from their sulfides by the process of the low grade sulfide ore concentrate assaying by weight invention using a representative chloride electrolyte for 8.33% nickel, 0.337% colbalt, 5.16% copper and 37.8% the process of this invention and that the process is pariron were slurried in 2 liters of electrolyte and subjected ticularly effective for these metals with an aluminum to 60 amp'ere hours of current under the conditions shown. chloride electrolyte.

Using a 4 M FeCl electrolyte at a temperature of 80 The process is equally effective for the recovery of gold, C., pH of 0.5 and an anode current density of 120 amps/ germanium and tin from their sulfides. ft. the following results were obtained from analysis of the electrolyte media at the end of the test. EXAMPLE 7 The following test is included to show the suitability of Wt. of metal dissolved (gins) Fe-46 Ni1.7 Co-0.2 Oil-2.0 ferrous chloride electrolyte for recovering lead, zinc, Gum Sulfur recovered 5 ilv r n Cadmium from their sulfides.

Amp-hrsJlb. of combined 470 grams of mesh particle size sulfide ore conmetals recovered 5425 centrate assaying by weight 31 9% zinc 17 1% lead 5 l tal s 9s Percent age men 12.6% lI'Ol'l, .02 19% silver, and .018% cadmium were The low current consumption and high Sulfur conver slurried in liters of electrolyte and fed to the anode sion obtained illustrate the effectiveness of the process for slde f 3 dla'phrajgm cell- The 2 molar ferrous the recovery of nickel and cobalt from their sulfides chloride, was sub ected to 157.5 ampere hours of current at 80 0, pH 0.5 at an anode current density of 60 amps/ EXAMPLE 5 ft. The results obtained are shown below.

The following example is included to show the effectiveness of the process for the recovery in chloride electrolyte Metal Pb Zn Ag Fe Cd of additional metals from their sulfides, particularly lead. l ussolv stl metal (gmsf) 132.; 03 39. .07 500 grams of a -60 mesh particle size commercial sul- 7O iff age g 0 me a fide ore concentrate assaying by weight 25.6% lead, percht t iesfitii s13: I:::::::::::::::::::::::::::::::

24.8% zinc, and 013% silver were processed in a diaphragm cell. The concentrate was slurried in 2 liters of 2 The high percentage recovery of lead, zinc, silver and M AlCl which served as anolyte. Lead chloride dissolved cadmium demonstrates the suitability of ferrous chloride in 2 M AlCl served as catholyte. The anolyte and cathoas an electrolyte for recovery of the metals from their sulfides by the process. Commercially feasible current consumptions were noted.

EXAMPLE 8 Test N 1 2 3 Electrolyte HCl (5%) 2 M A1013.-- 3 M FeClz.

Temperature C.) 80

pH 0.01 (5% H01)- 0.01 (5% H01). 0%

ACD (amps/ft!) 12o 12o- 12 Amp-hrs/lb. Cu re- 1,566 463 558.

covered.

Percent S as elemental S. 73 r.' 95 88.

The results demonstrate the superiority of aluminum chloride and ferrous chloride acidified with hydrochloric acid over hydrochloric acid alone as electrolytes.

EXAMPLE 9 Test No 1 2 Electrolyte 3 M FeClz 3 M FeClz. Temperature C.)- 75 75. pH 0.5- 0.5. ACD (amps/ft?) 120 240. Amp-hrsJlb. Cu recovered 558 617. Percent S as elemental S. 88 86.

The example shows that, somewhat contrary to the teaching of US. Pat. 2,761,829; copper dissolves readily at the high current densities shown under the process conditions of the invention.

EXAMPLE 10 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%

10 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 sulfides.

232 grams of a mesh grain size commercial low grade chalcopyrite concentrate analyzing by weight 4.0% lead, 9.2% zinc, 24.0% pper, 25.5% iron, 0.5% arsenic, 0.018% cadmium, 0.025% antimony and 0.36% selenium were slurried in 2 liters of 3 M ferrous chloride electrolyte and subjected to 30 ampere hours of current at 0., pH 1.5, and an anode current density of 60 amps/ft. with the following results.

Percent metal Metal: dissolved Copper 9.4 Zinc 36.4 Lead 87.4 Arsenic 97.0 Cadmium 42.9 Antimony 52.0 Selenium 28.9

As demonstrated with a representative electrolyte the 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 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 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, IIB, IV-A, V-A, VI-A and VIII 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, copzinc was slurried in 2 liters of electrolyte and subjected 55 P iron, malfgamse, nickel, Zinc, f rare ear h to 30 ampere hours of current under the conditions indimetals, and mlXfllres thereof, he SOIHUOH havlng a cated with the following results. concentration from about .5 N to saturation;

Test No 1 2 3 4 Electrolyte 3 M ZnCl 1.5 M ZnClr 3 M ZnCh 3 M ZnOlz.

Temperature 0.)- 75 75 75 75.

pH 0.8... o.&.. 0.3.. 3.5.

ACD (amps/IL) 120 120 120 120.

Amp-hrs/lb. Zn recovered 386 an 372 381.

Sulfur recovered (gms.) 13.2--- 16.8 12.7.-- 9.7.

Percent S as elemental S 89 83 71.

The tests illustrate that zinc chloride is as effective as (b) mixing with the electrolyte a solid feed sulfide of an electrolyte as the other chloride electrolytes of the the metal having an average particle size smaller invention. Test No. 4 was performed at a 3.5 pH which than about 60 mesh US. Standard; is near the top of the critical pH range of 3.9 and this (0) maintaining the temperature of the electrolyte test shows the adverse efiect of low acidity on conversion media at about 50 C. to C., and the pH of of sulfide sulfur to elemental sulfur. 75 the electrolyte media below about 3.9 while intro- 1 1 ducing electric curernt 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.

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 recovered 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 recovered 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.

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 recovered 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 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 ferrous chloride.

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.

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 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 VHI 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 elect-rolyte 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;

(c) maintaining the temperature of the electrolyte media at about 50 C. to 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.

U.S. Cl. X.R. 204106, 107, 111, 113, 117, 118, 123, 293