Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25C—PROCESSES FOR THE ELECTROLYTIC PRODUCTION, RECOVERY OR REFINING OF METALS; APPARATUS THEREFOR
  • C25C1/00—Electrolytic production, recovery or refining of metals by electrolysis of solutions

Definitions

• ABSTRACT Assignee: Cyprus Metallurgical Processes Corpora- "on, Los Angela Calm A pollution-free process for the electrolytic dissolution of sulfide ores of the metals of Groups lB, ll B, V A, VI A, of the 1 Flledl 1971 Periodic Table and lead in aqueous acidic media with the formation of metal ions and elemental sulfur followed by Appl' recovery of the metal ions from solution in the electrolyte media, the process characterized by certain critical process [52] [1.8. CI. ..204/105 R, 204/107, 204/ l l 1, conditions, these being the use of:
• U.S. Pat. No. 2,331,395 discloses the electrolytic recovery from sulfides of certain metals utilizing an alkaline electrolyte
• U.S. Bureau of Mines Technical Progress Report 26, June 1970, entitled Electrolytic Recovery of Metals teaches the recovery by electrolysis of mercury from cinnabar in an alkaline electrolyte.
• antimony experimentation has shown that the metals of Groups I B, II B, V A, VI A of the Periodic Table and lead cannot be economically recovered by electrolytic processes in an alkaline media. While antimony can be so economically recovered it is more economic to recover it from acidic media. This is supported by theoretical considerations.
• the limit of efficiency in the electrolytic dissolution of metal ions is the electric current required to oxidize the sulfur present from sulfide ion (-2) to sulfate ion (+6).
• the electric current required to ionize a given quantity of the desired element is readily calculated.
• the ampere hours/pound of metal ionized varies from 452 for argentite to 3,240 for chalcopyrite.
• U.S. Pat. No. 2,839,461 discloses an electrolytic process for the recovery of nickel from nickel sulfide utilizing an acid sulfate-chloride electrolyte and which is dependent upon a highly conductive nickel sulfide anode, the anode current being passed through a nickel matte anode. It has been found that the metals of Groups I B, II B, V A, VI A of the Periodic Table and lead cannot be economically recovered by electrolysis from their sulfides in an electrolyte containing substantial sulfate ions or by a process in which sulfate ions are produced in appreciable amounts.
• 2,839,461 teaches the addition of sulfur to chalcocite to 'convert it to covellite which has about 100 times lower resistivity, thus making a product which is amenable to the process.
• the process of the referenced patent cannot be applied to base metal sulfides because of their high resistivities.
• U.S. Pat. No. 2,761,829 discloses the electrolytic recovery of copper from sulfide ores containing iron sulfides in an acid media in which current densities said to be applicable to in situ mining are so low that the process is economically prohibitive when applied to mined and concentrated ore.
• metal sulfide as contained 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 recovery of the metals of Groups I B, II B, V A, VI A of the Periodic Table and lead from their sulfide and mixed sulfide ores 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 I) an alkali metal and/or alkaline earth metal chloride electrolyte, (2) a sulfide feed particle size smaller than 60 mesh U.S.
• the process parameters which have been found to control the current requirements for the process are electrolyte composition, feed particle size, operating pH range, operating temperature, and anode current density. As the examples which follow show, these factors are mutually interacting and dependent as respects their effect on current requirements.
• the sulfide ores of metals of Groups I B, II B, V A, VI A of the Periodic Table and lead are characterized by certain similar properties related to the electrolytic dissociation to elemental sulfur and metal ions therefrom, not possessed by other metal sulfides, which support group classification.
• these sulfides all have relatively low conductivities
• the metal ions are most favorably produced by electrolysis in aqueous alkali metal and/or alkaline earth metal chloride electrolytes at a pH range from about 0.01 to 3.9 using anode current densities above about 12 amperes/ft at a temperature between about 60-l05 C with the sulfide particle feed size being smaller than about 60 mesh US. Standard.
• 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 metals which can be recovered from their sulfide and mixed sulfide ores by the process of the invention are those of Groups I B, 11 B, V A, V] A of the Periodic Table and lead. Although antimony, bismuth, cadmium and selenium were recovered in Example 7 which follows as trace metals, the process is operative for recovering them regardless of the amounts existing in the ores or minerals. The minerals to which the process is applicable often contain the metals in the form of complex or mixed sulfides.
• the electrolyte media for the process must be acidic as an alkaline electrolyte has proven unsatisfactory for recovery 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 in this media through thiosulfate, hydrosulfite, sulfite 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 efficiency. Further, it was found that at high current densities in the presence of sulfate, graphite anodes were appreciably attacked.
• the preferred electrolyte media is an aqueous acidic solution of alkali metal chloride or alkaline earth metal chloride, or mixtures thereof.
• the chlorides of sodium, potassium, barium and calcium, or mixtures thereof have been found suitable. Concentrations within the range of 0.5-4N or saturation may be used. Voltage across the cell is lower at higher salt concentrations so that the latter are preferred except where low grade feeds are used and where salt losses would therefore become significant.
• the particle size of the feed material is critical as it directly affects the conversion 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 consequently lower current consumption, as explained above.
• An average grain size range for the feed sulfide smaller than about 60 mesh US. Standard is the operable range and is compatible with other critical parameters.
• a pH range for the electrolyte media between about 0.01 and 3.9 is preferred. Current efficiency is reduced at pHs above 3.9, and at very high acidities (low pH values) in the absence of substantial concentrations of alkali or alkaline earth, metal chlorides.
• the preferred pH range for lead, silver and zinc sulfides is about 2.0 3.0, the most preferred pH being about 2.5.
• the preferred range for copper sulfides is 0.5 1.5 with about l.0 being most preferred.
• reaction temperature of the electrolyte is critical and high process efiiciency is not obtained at low temperature.
• a temperature range of about 60-l05 C is the operable range when used in conjunction with the other critical factors. A temperature of C is most preferred.
• the current density is also critical as used with the other critical parameters with a preferred range being above about 12 ampereslft
• a preferred current density range is about 200-480 amperes/ft with the most preferred value being about 300 amperes/ft.
• iron sulfide predominates current densities between 50-120 amperes/ft are preferred.
• diaphragm cell consists of two anodes made of graphite or other suitable corrosion resisting material each on one side of a cathode made of stainless steel.
• the anodes are separated from the cathode by a space and by a cloth (filter cloth of suitable plastic) which then forms a cathode compartment and an anode compartment.
• a pump circulates the catholyte past the cathode.
• this type of cell is well known in the art and may be provided with a multiplicity of anodes and cathodes.
• Examples 2, 3, 5-9, 13 and 14 were run using diaphragm type cells, with non-diaphragm type cells being used in the remaining examples.
• Grain size is given in US. Standard mesh size, current density is given in amperes/ft", current requirement is reported in terms of ampere hours/pound of metal dissociated, and recovered sulfur is based on grams of elemental sulfur dissociated/gram of non-ferrous metal dissociated.
• the feed material was a commercial chalcopyrite copper concentrate assaying 26.6 percent copper, .l.63 percent zinc, 0.24 percent lead, 0.048 percent antimony, 0.11 percent selenium and by mineral examination consisting of about percent chalcopyrite and 6 percent pyrite and about 4 percent other metals.
• EXAMPLE 1 A series of tests were run to demonstrate the effect of the composition of the electrolyte upon the efficiency of dissolving copper from chalcopyrite. In each case a slurry of grams of feed in 1,800 milliliters of electrolyte was made and subjected to 60 ampere hours of current.
• alkali chlorides and alkaline earth metal chlorides are very effective as electrolytes.
• Sodium chloridesodium sulfate electrolyte as taught in US Pat. No. 2,893,461 proved unsatisfactory and a substantial evolution of oxygen at the anode was noted.
• the efficiency of this electrolyte was about a factor of four poorer than those tests where sulfate concentration was low.
• EXAMPLE 3 A series of tests were run to demonstrate the effect of temperature upon the efficiency of dissolving copper from a chalcopyrite concentrate. in each case a slurry of 200 grams of feed in 1,800 milliliters of electrolyte was used and subjected to 30 ampere hours of current.
• Example 6 illustrates the operability of the process at a chloride salt electrolyte concentration as low as 1N Feed was 200 grams of the chalcopyrite concentrate previously used and dispersed in two liters of electrolyte and subjected to 30 ampere hours of current.
• EXAMPLE 7 A test was run to demonstrate that trace metal values can be recovered in the process along'with copper.
• the feed was two kilograms of the chalcopyrite concentrate. it was dispersed in 27 liters of electrolyte and subjected to 400 ampere hours of current.
• EXAMPLE 9 A test using a different cupreous pyrite concentrate containing 2.0 percent copper was run. A feed of 200 grams was slurried with 2,400 milliliters of electrolyte and subjected to ampere hours of current.
• EXAMPLE 12 A test was run on a mixed zinc-lead-silver concentrate. The feed analyzed 35.4% Zn, 22.0% Pb, 0.021% Ag. A feed of 100 grams was slurried in 1,700 milliliters of electrolyte and sub jected to 60 amperes hours of current.
• This example demonstrates the effectiveness of the process on mixed lead, zinc and silver ores.
• the example further illustrates the equivalency of these metals and their sulfides in the process.
• EXAMPLE 13 A low grade zinc-copper concentrate containing substantial pyrite impurity was tested. The concentrate assayed 5.9 percent copper, 25.4 percent zinc, and 20.2 percent iron. The copper was chiefly in the form of chalcopyrite. A feed of 200 grams was slurried in 3,800 milliliters of electrolyte and subjected to 30 amperes hours of current.
• Examples 12 and 13 demonstrate the effectiveness of the process for mixtures of sulfides of the metals on which the process is effective. Along with other examples they show the effectiveness of the process for these metals.
• EXAMPLE 14 A feed of 200 grams of a low grade gold ore which assayed 0.5 oz. of gold per ton and 2.7 percent arsenic was slurried with L600 milliliters of electrolyte and subjected to 15 ampere hours of current.
• the power 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. 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.
• a process for the recovery of metals of Groups I B, I] B, V A, VI A of the Periodic Table and lead from their sulfides and mixed sulfides, and mixtures thereof, by electrolysis with the formation of elemental sulfur-and, metal ions which process comprises:
• 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 alkali metal chlorides and alkaline earth metalchlorides, the solution having a concentration from about IN to saturation;
• metals are selected from the group consisting of antimony, arsenic, bismuth, cadmium, copper, gold, lead, selenium, silver and zinc.
• an electrolyte media comprising an acidic aqueous solution of at least one chloride salt selected from the group consisting of alkali metal chlorides and alkaline earth metal chlorides, the solution having a concentration from about IN to saturation;
• a process for the dissociation of metals from their sulfides, mixed sulfides, and mixtures thereof, by electrolysis with the formation of elemental sulfur which process comprises:
• 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 alkali metal chlorides and alkaline earth metal chlorides, the solution having a concentration from about IN to saturation;

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• Chemical Kinetics & Catalysis (AREA)
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• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)
• Manufacture And Refinement Of Metals (AREA)

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Cited By (25)

Citations (4)

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• 1971
  • 1971-02-08 US US113751A patent/US3673061A/en not_active Expired - Lifetime
• 1972
  • 1972-01-27 GB GB379172A patent/GB1345102A/en not_active Expired
  • 1972-01-31 IE IE128/72A patent/IE36195B1/xx unknown
  • 1972-02-01 FR FR7203920A patent/FR2124519B1/fr not_active Expired
  • 1972-02-01 ZA ZA720641A patent/ZA72641B/xx unknown
  • 1972-02-01 CA CA133,677A patent/CA975712A/en not_active Expired
  • 1972-02-01 DE DE19722204724 patent/DE2204724A1/de active Pending
  • 1972-02-02 SE SE7201180A patent/SE374566C/xx unknown
  • 1972-02-03 JP JP47012535A patent/JPS5133483B1/ja active Pending
  • 1972-02-04 PH PH13251*A patent/PH10022A/en unknown
  • 1972-02-04 NL NL7201463A patent/NL7201463A/xx unknown
  • 1972-02-04 ES ES399486A patent/ES399486A1/es not_active Expired
  • 1972-02-07 ZM ZM21/72A patent/ZM2172A1/xx unknown
  • 1972-02-07 NO NO321/72*[A patent/NO133903C/no unknown
  • 1972-02-07 IT IT9338/72A patent/IT949343B/it active
  • 1972-02-07 BE BE779036A patent/BE779036A/xx unknown
  • 1972-02-08 LU LU64751D patent/LU64751A1/xx unknown

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