EP0652979A1 - Compositions de perbromure inorganique et procedes d'utilisation - Google Patents

Compositions de perbromure inorganique et procedes d'utilisation

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Publication number
EP0652979A1
EP0652979A1 EP93918586A EP93918586A EP0652979A1 EP 0652979 A1 EP0652979 A1 EP 0652979A1 EP 93918586 A EP93918586 A EP 93918586A EP 93918586 A EP93918586 A EP 93918586A EP 0652979 A1 EP0652979 A1 EP 0652979A1
Authority
EP
European Patent Office
Prior art keywords
solution
set forth
bromide
bromine
weight
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93918586A
Other languages
German (de)
English (en)
Other versions
EP0652979A4 (fr
Inventor
Ahmad Dadgar
Jonathan N. Howarth
Rodney H. Sergent
Nicolai A. Favstritsky
Julie A. Mckeown
Dennis W. Borden
Brent M. Sanders
L. Jane Likens
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Great Lakes Chemical Corp
Original Assignee
Great Lakes Chemical Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Great Lakes Chemical Corp filed Critical Great Lakes Chemical Corp
Publication of EP0652979A1 publication Critical patent/EP0652979A1/fr
Publication of EP0652979A4 publication Critical patent/EP0652979A4/fr
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B11/00—Obtaining noble metals
    • C22B11/04—Obtaining noble metals by wet processes
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/20—Treatment or purification of solutions, e.g. obtained by leaching
    • C22B3/42—Treatment or purification of solutions, e.g. obtained by leaching by ion-exchange extraction
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
    • C22B3/00—Extraction of metal compounds from ores or concentrates by wet processes
    • C22B3/04—Extraction of metal compounds from ores or concentrates by wet processes by leaching
    • C22B3/06—Extraction of metal compounds from ores or concentrates by wet processes by leaching in inorganic acid solutions, e.g. with acids generated in situ; in inorganic salt solutions other than ammonium salt solutions
    • C22B3/10—Hydrochloric acid, other halogenated acids or salts thereof
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/20—Recycling

Definitions

  • This invention relates to compositions containing inorganic perbromides and having desirable physical characteristics such as high bromine levels and low bromine vapor pressures.
  • the invention further relates to the use of such compositions for the recovery of precious metals, including platinum and palladium, from a variety of sources thereof.
  • the invention further relates to a method for the electrolytic production of bromine solutions, and to the use of electrolytically produced from mixed halide bromine solutions in applications including precious metal recovery and water treatment.
  • bromine solutions have been used for the recovery of certain precious metals. Prior art recovery processes using molecular bromine have been effective, but pure bromine is a corrosive, fuming liquid which generates a suffocating vapor and must be subjected to special handling. Bromine can be dissolved in water to a certain extent, but the resulting solutions exhibit a substantial bromine vapor pressure.
  • Molecular bromine can be generated from the acidification of alkali metal bromates, but by themselves bromates provide only a limited source of molecular bromine, and bromate salt solutions have a high crystallization temperature which makes them inconvenient to use as leaching agents for precious metals.
  • Fig. 1 is a schematic illustrating the electrogeneration process of the invention
  • Fig. 2 is an illustration of a cell assembly that is 5 especially preferred for use in the practice of the process of the invention
  • Fig. 3 is a general schematic showing the application of electrogeneration of bromine to the recovery of gold from a source material; 10 Fig. 4 is a more detailed schematic showing the application of the electrogeneration process of the invention to recovery of gold from ore;
  • Fig. 5 is a schematic flow sheet of an alternative embodiment of the rocess for recovery of gold 15 in which an aqueous bromine leaching solution is circulated between a leaching tank and an electrogeneration system;
  • Fig. 6 is a schematic flow sheet showing the application of the principles of the process of Fig. 11 to a 20 continuous cascade leaching reactor system
  • Fig. 7 is an Eh/pH diagram for the system H 2 O-10 "4 M Pd-O.IM Br " .
  • Fig. 8 is an Eh/pH diagram for the system H 2 O-10" 4 M Pt-O.IM Br " . 25
  • Fig. 9 illustrates an especially preferred embodiment of the invention in which an aqueous leaching solution containing bromine is produced at the anode of a divided electrolytic cell and gold is recovered from a pregnant leach solution by electrowinning at the cathode of 30 the same cell.
  • inorganic perbromide concentrates have been discovered which may be used advantageously in a variety of applications.
  • these concentrates may be diluted with water to provide aqueous working solutions that are used in practicing the method.
  • the concentrates generally contain a substantial percentage of equivalent molecular bromine, they exhibit remarkably low vapor pressures.
  • concentrates of high equivalent bromine content exhibit remarkably low vapor pressure not only in those embodiments in which the pH is in the range of 6.5 to 7.5 but also in those concentrates of the invention which are quite acidic (as low as zero or less) .
  • compositions are advantageously adapted for shipping, storage and/or use in harsh climates.
  • Various of these concentrates exhibit favorable freeze/thaw stability, and certain of them exhibit exceptionally low thermodynamic crystallization temperatures.
  • compositions are inorganic perbromides which have been discovered to exhibit exceptionally low vapor pressures at, alternatively, pH below 1.0 or pH in the range of 6.5 to 7.5.
  • the inorganic perbromide concentrates with acidic pH ranges include a hydrogen halide acid component, while those stable within a pH range of 6.5 to 7.5 include a bromate salt component.
  • the latter concentrates containing bromate may optionally be converted to acidic concentrates by addition of an acid to the concentrate.
  • compositions of the invention are formulated from a metal bromide, a hydrogen halide acid, molecular bromine, and a protic solvent.
  • the protic solvent may be water, alcohol or an organic acid, or a mixture thereof.
  • Compositions of the invention may contain 10-40% by weight equivalent molecular bromine, defined in molar terms as the sum of the actual molar concentration of molecular bromine, the molar concentration of perbromide ion, the molar concentration of hypobromous acid, and the molar concentration of hypobromite ion. Hypobromous acid and hypobromite are produced in the equilibrium reaction:
  • the molecular bromine concentration of the acidic concentrates is between about 30% and about 36% by weight.
  • Each of these acidic compositions is prepared by mixing a source of halide ion with molecular bromine in such proportions that the halide ion is in excess.
  • Halide sources generally include both a metal halide salt and a hydrogen halide.
  • the halide ion is bromide and the molar ratio of bromide ion to molecular bromine in the formulation is between about 1.2:1 and about 2.0:1, most preferably between about 1.4:1 and about 1.8:1.
  • the molecular bromine combines with bromide ion to form perbromide or a mixed perhalide ion in accordance with the equations:
  • the metal bromides which can be incorporated in the composition of the invention are alkali metal salts such as sodium bromide, potassium bromide, and lithium bromide, and alkaline earth metal salts such as calcium bromide.
  • Hydrogen halides used in preparing the composition include HC1, HI and, preferably, HBr.
  • the acidic concentrates of the invention further contain an alcohol or a low molecular weight organic acid. Alcohols and organic acids have a lower dielectric constant than water. Because the equilibrium constant for the above reactions increases with the reciprocal of the dielectric constant, the inclusion of an organic solvent in the composition also conduces to maintaining a low bromine vapor pressure at a high molecular bromine concentration.
  • Useful organic acids include acetic, propionic, succinic, adipic and the like.
  • Useful alcohols include methanol, butanol, and the like.
  • compositions containing alcohol and bromine can be unstable, under certain circumstances explosive, due to reaction of alcohol with bromine.
  • organic solvents other than alcohols be used.
  • Br 2 /alcohol compositions can be stable, and used safely, if the alcohol content is sufficiently low.
  • Bowman, et al. report that methanol/Br 2 compositions are essentially nonreactive, provided that the alcohol content is less than 10% by volume on an alcohol + Br 2 basis.
  • compositions used in the invention which contain hydrobromic acid and an organic protic solvent are generally formulated from: Br 2 10-40% by wt.
  • compositions are formulated from:
  • compositions exhibit a bromine partial vapor pressure not greater than about 40 mm Hg at 25% bromine and 20°C, and a bromine vapor pressure not greater than about 50 mm Hg at 34% bromine and 20°C
  • Thermodynamic crystallization temperatures are in the range of between about -30°C to about -50°C at 34% Br 2 for compositions in which water is the solvent, and between about -55°C and about -68°C for compositions in which the solvent comprises an organic solvent.
  • The— H is less than 1.0 and generally less than 0.20.
  • Preferred compositions have a pH ⁇ 0. Regardless of whether the solvent comprises 25 water, an organic acid, or a mixture thereof, it is especially preferred that the Br 2 concentration be greater than 25%.
  • Such compositions are formulated from:
  • compositions are formulated from:
  • compositions in which HC1 is substituted for HBr are preferably formulated from:
  • the sodium ion content of the formulation be in the range of between about 1% and about 3% by weight, and that the molar ratio of Na + to equivalent Br 2 be no greater than about 0.8. It has been found that such relatively low proportions of Na + conduct to a relatively low thermodynamic crystallization temperature, and to excellent freeze/thaw stability of the concentrate.
  • a preferred formulation for a freeze/thaw stable NaBr 3 concentrate is: NaBr 5-15%
  • An especially preferred low Na + acidic composition comprises:
  • Calcium bromide compositions exhibit exceptionally low vapor pressure at high equivalent molecular bromine concentrations and low pH. This is believed to be attributable to the greater ionic strength of calcium bromide as compared to alkali metal bromides. Greater ionic strength tends to increase the equilibrium constant for the reactions:
  • the Ca(Br 3 ) 2 acidic concentrates have a bromine partial vapor pressure of less than about 40 mm Hg at 20°C, while at 34% equivalent molecular bromine, they have a bromine partial vapor pressure of less than about 50 mm Hg at such temperature.
  • calcium perbromide compositions provide especially low thermodynamic crystallization temperatures (TCTs), e.g., in the range of between about -50°C and about -60°C where water only is the solvent, and below -60°C where the solvent comprises an organic solvent. Such TCTs are also believed to be attributable to the greater ionic strength of these formulations as compared to alkali metal perbromides.
  • TCTs thermodynamic crystallization temperatures
  • Calcium perbromide compositions preferably are formulated from:
  • the acidic concentrates described above are preferably prepared by adding the bromide or other halide salt and hydrogen halide to a protic solvent, and then adding liquid bromine to the acidic bromide salt solution. This sequence insures the presence of an excess of bromide ion for reaction with the liquid bromine to form perbromide or XBr 2 " ion (where X is halide) during bromine addition.
  • saturated or nearly saturated premix solutions are prepared for both the bromide salt and hydrogen halide, and these premix solutions are added to water to produce a precursor solution to which the liquid bromine is added.
  • a solution containing an organic protic solvent may be prepared by mixing in the following sequence:
  • an NaBr 3 concentrate is preferably prepared by mixing: 6 to 40 wt.% water
  • liquid bromine Further included in the compositions of the invention are hydrogen perbromide concentrates formulated from:
  • composition preferably contains:
  • these HBr 3 compositions exhibit a bromine partial vapor pressure of less than about 40mm Hg.
  • compositions of the acidic concentrates of the invention are formulations, i.e., summaries of the components " from which the concentrates are formed in the relative proportions used in forming the concentrates. As indicated, these formulations _ equilibrate to convert Br 2 and Br " to Br 3 " . Additionally, some of the Br 2 reacts with water to produce hypobromous acid, which in turn dissociates to a limited degree:
  • inorganic perbromide concentrates which have a relatively high pH (about 6.5 to about 7.5), and include a bromate ion component.
  • These compositions may be prepared by mixing a perbromide salt component solution and a bromate component solution.
  • the concentrates of this embodiment are particularly suited for dilution with water to produce a leaching solution for recovery of platinum and palladium.
  • the remarkably low vapor pressure of the alkaline concentrates facilitates their handling and minimizes hazards of using molecular bromine for such purposes.
  • dilution of the alkaline concentrate to produce the leaching solution can be carried out without any serious problem of containment of bromine vapor.
  • a leaching solution precursor concentrate containing perbromide and bromate salts is initially produced.
  • this concentrate is diluted to provide the leaching solution.
  • the pH may be adjusted either before or after dilution by addition of an acid such as HBr, HC1, H 2 S0 4 , or Cl 2 , or a base, such as NaOH, KOH or Ca(0H) 2 .
  • a component solution of an alkali metal or alkaline earth metal perbromide is mixed with a component solution of alkali metal or alkaline earth metal bromate.
  • the perbromide solution is prepared by addition of bromine to an aqueous solution of a bromide ion as discussed above regarding the preparation of the acidic perbromide concentrates.
  • sodium perbromide and calcium perbromide are prepared by saturating the Br 2 content of the respective aqueous NaBr or CaBr 2 5 solution with molecular bromine:
  • the metal bromide solution initially has a concentration of at least about 25% by weight, preferably essentially saturated to its solubility limit, i.e., 45-50% by
  • liquid or vapor Br 2 is added to the solution to the extent of saturating the bromide ion therein, i.e. in full stoichiometric equivalence with the Br " content.
  • the Br 2 is added to a NaBr solution that is initially at its solubility limit, the amount of bromine introduced, as may be determined by iodometric titration, is equivalent to a weight concentration in the resulting perbromide solution of about 40-50% Br 2 . Because of the reversibility of the reactions of
  • the alkali metal or alkaline earth metal bromate component solution is prepared by addition of liquid bromine or bromine vapor to an aqueous solution of metal hydroxide, most preferably an alkali metal hydroxide. Hydroxyl ions and
  • this reaction proceeds essentially quantitatively to the right.
  • the strength of the initial caustic (or other alkaline) solution and the amount of molecular bromine added thereto are controlled so that, when the bromate solution is mixed with the solution of alkali metal or alkaline earth metal perbromide in predetermined relative proportions, the resulting mixture has a pH of between about 6.5 and about 7.5.
  • the strength of the initial caustic solution and the degree of bromination are selected so that the bromate solution contains at least about 15% by weight equivalent molecular bromine, i.e., at least about 4% by weight bromate ion.
  • the bromate solution component of the concentrate contains between about 5% and about 8% by weight bromate ion, roughly equivalent to between about 20% and about 30% by weight molecular bromine.
  • the initial concentration of the caustic solution is preferably in the range of 10-20% by weight in the case of sodium hydroxide. Equivalent molar proportions may be computed for other alkalis.
  • the bromate component solution may be prepared by dissolving an alkali metal bromate or alkaline earth metal bromate salt in water.
  • This in fact is the preferred method for preparing a component solution comprising an alkaline earth metal bromate, since difficulty may be encountered in the preparation of such solution by addition of molecular bromine to a lime or magnesia solution or slurry.
  • an alkali metal or alkaline earth metal bromide is also incorporated so as to produce an overall composition essentially equivalent to that obtained by dissolving Br 2 in a caustic solution.
  • the perbromide solution and bromate solution are mixed in proportions of between about 4 parts by weight perbromide solution per part by weight bromate solution and about 4 parts by weight bromate solution per part by weight perbromide solution.
  • approximately equal portions of the two component solutions are mixed.
  • the pH of the resultant composition should be between about 6.5 and about 7.5, and the ratio of the molar concentration of bromate ion to the sum of the molar concentrations of molecular bromine and perbromide ion in the composition is between about 0.05 and about 0.8.
  • the molar concentration of bromide ion in the alkaline concentrate of the invention is equal to the sum of the molar concentration of molecular bromine and five times the molar concentration of bromate ion.
  • the bromate ion concentration is at least about 2%, typically ranging from about 2% to about 6% by weight
  • the equivalent perbromide content is preferably at least about 10%, ranging from about 55% to about 10% by weight
  • the concentration of bromide ion (as computed on the basis of no dissociation of perbromide ion) generally ranges from about 3% to about 19%, the preferred compositions thereof typically containing bromide ion weight concentrations in the range of about 6% to about 17%.
  • the equivalent molecular bromine content of the concentrate is between about 10% and about 40%, preferably between about 20% and about 40%, by weight. More preferably, the equivalent Br 2 content is at least about 25% by weight.
  • a concentrate can be prepared containing 34% by weight or more equivalent molecular bromine. JLo
  • the molecular bromine content of the concentrate is generally not converted to bromate and bromide, i.e., equation 7 does not proceed appreciably to the right.
  • equation 7 there is a stable equilibrium between perbromide ion and Br 2 , and the composition of the concentrate is stable within the ranges discussed above.
  • 20 recovery of precious metals may be prepared by dilution of the alkaline or acidic concentrate of the invention. Prior to or after dilution, the pH may be adjusted by addition of an acid such as H2S04, HBr, HC1, or C12, or a base, such as NaOH or KOH. Where the concentrate is acidified, HBr is preferred
  • H2S04 is the preferred acid for use in connection with palladium and platinum recovery.
  • the leaching solution is effective over a wide range of pH, but operation is preferably carried out at a pH of less than about 6.
  • an acidic pH is generally preferred to promote the conversion of bromate ion to molecular bromine.
  • Compositions used for dissolution of Pd and/or Pt preferably 5 contain between about 1 and about 8 equivalents acid per liter of solution.
  • Sul uric acid is preferred. Where sulfuric acid is the acid used to provide the desired acidity, it is preferably present in a proportion of between about 5% and about 40% by weight, more preferably between about 5% and about 30% by weight, most preferably between about 10% and about 20% by weight.
  • bromate/bromide concentrate of alkaline or neutral pH acidification is preferably carried out prior to dilution, thus producing an acidic concentrate having a pH of less than about 2.5, and an equivalent molecular bromine concentration in the range of between about 28% and about 40% by weight.
  • a portion of NaBr or other halide salt may be advantageously incorporated into the solution.
  • the rate of dissolution of certain metals in the leaching solution is in some instances accelerated if the solution contains halide ions in a concentration that is even higher than that provided by a bromine saturated concentrate, in which instance, preparation of the leaching solution preferably involves incorporation of chloride salt or bromide salt from a source other than the concentrate. It may be noted that both the actual molecular bromine and the ultimate bromide ion content are also affected by the shifts in equilibria which accompany the acidification and dilution process.
  • equations 3, 5 and 6, supra are driven to the left,converting perbromide ion to bromide and molecular bromine; equation 7 is also driven to the left, converting bromate ion and bromide ion to molecular bromine. Dilution tends to drive equation 1 to the right, resulting in conversion of molecular bromine to bromide ion and hypobromous acid. As a net result, the hypobromous acid concentration is a significant component of the equivalent molecular bromine content of the leaching solution.
  • Eh/pH diagrams constructed from thermodynamic data show a progressively larger solubility field at lower Eh values for the formation of the complex ions (see equations 10-13 infra) as Br- ion concentration increases from 10 "5 to 1.0M. These observations are consistent with the requirement for multiple Br " ions to form the complex anions PdBr 4 2" , PdBr 6 2" , and PtBr 6 2" . It may be noted that, where the dilution ratio is modest, for example, 15:1 or less, the acidic or alkaline concentrate of the invention typically furnishes sufficient Br " ion to fully satisfy the requirement for co-ordinating the metal.
  • the equivalent molecular bromine content of the leaching solution is between about 0.01% and about 20% by weight equivalent molecular bromine, between about 0.005% and about 20% by weight bromide ion, and between about 0.005% and about 30% by weight total halide ion.
  • the solution preferably contains between about 0.01% and about 1% by weight, more preferably about 0.02% to about 0.5% by weight, equivalent molecular bromine, between about 0.005% and about 10%, more preferably about 0.01% to about 1%, by weight bromide ion, and between about 0.005% and about 15%, preferably about 0.01% to about 1.5%, by weight total halide ion.
  • a more concentrated leaching solution may be used to advantage. Such may be prepared from the above described concentrates by modest dilution with water.
  • a 0.5% Pd on alumina catalyst, or a concentrate containing 30-50 oz. Pd per ton may advantageously be leached with a solution prepared by diluting a Br 2 concentrate of the invention to an equivalent molecular bromine content of between about 8 and about 25 gpl, a Br " content of between about 5 and about 20 gpl, and a total halide content of between about 10 and about 40 gpl.
  • Platinum and palladium are recovered from a source thereof, such as comminuted ore, by contacting the source material with the aqueous bromine leaching solution. In the case of platinum, oxidation and complexing of the platinum is believed to proceed in accordance with the equations:
  • the relative proportions of ore (or other source material) and leaching agent may be such that the leaching slurry contains between about 1 and about 600 lbs. active agent per ton of source. Active agent in this instance is defined as the sum of the amounts of bromide, perbromide, metal hypobromite, hypobromous acid, and molecular bromine in the leaching solution.
  • active agent in this instance is defined as the sum of the amounts of bromide, perbromide, metal hypobromite, hypobromous acid, and molecular bromine in the leaching solution.
  • the Br 2 /Pd molar ratio is preferably between about 1 and about 8
  • the molar ratio of Br 2 /Pd+Pt is preferably between about 2 and about 40.
  • an oxidation reduction potential of about 850-1250 mV is required for dissolution of Pt from a Pt compound such as a platinum oxide.
  • the oxidation reduction potential required to dissolve Pd is about 500-750 mv.
  • Pd may be leached with solutions containing only HBr, sulfuric acid, and optionally another source of bromide or other halide ion.
  • a leaching solution for Pd may contain between about 10 and about 20 % by weight sulfuric acid, between about 15 and about 30% by weight HBr, between about 10 and about 25% by weight total bromide ion, and between about 20 and about 40% by weight total halide ion.
  • the presence of Br 2 in the proportions outlined above is preferred for complete, rapid and efficient leaching.
  • the source material is a refractory ore
  • Such may be accomplished by methods known to the art such as roasting or pressure oxidation.
  • Roasting may be sufficient pretreatment if carried out at a temperature of at least about 500°C.
  • the ore is roasted at a temperature of at least about 900°C, preferably at least about 1000°C.
  • roasting at a temperature in the range of about 500°C to about 750°C is preferred.
  • pressure oxidation is performed, it is preferably in an autoclave under 150-300 psi oxygen pressure and at a temperature in the range of from about 150°C to about 220°C.
  • the composition and method may be used for recovery of silver from various sources, including photographic film.
  • the composition and method may also be used for recovery of platinum and/or palladium from ores, Pd catalysts and other sources.
  • the slurry of ore in leaching solution is preferably agitated to promote transfer of the precious metals to the aqueous phase.
  • a leachate is thus produced containing platinum or palladium complexed with bromide ions.
  • leaching may be carried out for up to about 20 hours or longer, preferably for about 4 to about 15 hours, more preferably for about 6 to about 10 hours.
  • leaching is preferably carried out at a temperature in the range of from about 50°C to about 120°C, more preferably from about 60°C to about 90°C, most preferably from about 80°C to about 90°C.
  • the leachate is separated from the leached ore, catalyst substrate or other residue, as by filtration.
  • the filter cake is washed with an aqueous washing medium, the spent wash solution is combined with the filtrate (leachate), and the combined filtrate and wash solution is treated for recovery of the metal therefrom.
  • the filter cake is washed with a 2-4 molar HC1. Washing the filter cake in such fashion may be effective to remove further quantities of silver in the form of AgCl 2 ⁇ from the cake.
  • a washing solution of 4M HC1 is especially preferred.
  • Platinum and palladium may be recovered from the combined filtrate and wash solution by conventional means such as solvent extraction, ion exchange and precipitative methods.
  • bromine can be generated in aqueous solution to produce an aqueous bromine solution, and that the bromine solution generated can be used in an economically advantageous process for the leaching of platinum and palladium from sources thereof.
  • This solution has been demonstrated to be effective for recovery of these metals from ores in high yield and at commercially acceptable leaching rates.
  • Fig. 3 is a schematic flow sheet of the electrogeneration process.
  • a bromide solution prepared in a makeup tank 101 is transferred by a pump 103 to an electrolytic cell 105.
  • Power is applied to the cell by a direct current power source 107 via an anode 109 and a cathode 111.
  • the cell shown in Fig. 3 is an undivided cell, i.e., it contains no diaphragm or other impediment or obstruction to flo of electrolytic solution sufficient to cause a discontinuity in the concentration gradient between the anode and the cathode.
  • Bromine is generated at the anode by the reaction:
  • the electrogeneration system may comprise a cell bank containing a plurality of cells.
  • the cells of such a system may be arranged in a variety of ways, but are preferably connected electrically in series.
  • the desired equivalent bromine concentration of the product solution and electrical design considerations several banks of cells may be used with the cells of each bank electrically in series, and the banks arranged either in series or in parallel with respect to each other.
  • the cells may be hydraulically in series or hydraulically in parallel.
  • the feed solution entering the cell (or cell bank) from tank 101 has a pH of between about 0 and about 6, preferably between about 0 and about 3, and contains between about 0.5 and about 8.8 moles/1, preferably between about 0.5 and about 5 moles/1, bromide ion.
  • the feed solution preferably contains between about 0.25 and about 2.5 moles per liter bromide ion.
  • filter cake losses of bromide may be minimized by operating with a somewhat weaker feed solution, for example, a solution containing between about 0.0125 and about 0.625 moles per liter bromide solution.
  • the feed solution may be prepared by dissolving an alkali metal bromide in water and acidifying with an acid such as HBr, sulfuric acid, or HC1 to the desired pH.
  • the solution may contain between about 0.5 and about 8.8 moles/1 of sodium ion.
  • Turbulent flow velocity and/or mechanical agitation in the electrode region is established at a level sufficient to minimize overvoltages and maintain the individual cell voltage in the range of between about 4 and about 5 volts at a current density in the range of between about 1.0 and about 4.0, preferably between about 2.0 and about 4.0, more preferably about 2.5 and about 3.0, kA/m 2 .
  • feed solution is introduced into the cell at essentially ambient temperature.
  • Temperature rise in the cell (or bank of cells) is in the range of between about 4°C and about 20°C.
  • conditions are controlled to avoid increase of the cell discharge solution temperature to greater than about 50°C.
  • High current efficiency is maintained by controlling the relationship between current and the throughput of electrolytic solution through the system so that the conversion of bromide ion during passage through the cell bank is between about 4% and about 50%, preferably between about 5% and about 40%.
  • the current density should be in the range of between about 2.0 and about 4.0 kA/m 2 .
  • the product solution has a pH of less than 6, preferably less than about 4. If the product solution is to be used for the leaching of platinum or palladium, it has a pH of less than about 4, preferably less than about 1, most preferably less than about 0.
  • the product solution contains between about 0.01 and about 3.66 moles/l of equivalent bromine, between about 0.1 and about 4.0 moles/1 unreacted bromide ion, and between about 0.1 and about 4.0 moles/1 alkali metal ion.
  • the product solution containing between about Q.03 and about 2.5 moles/1, more preferably between about 0.1 and about 2.0 moles/1, equivalent bromine, between about 0.4 and about 3.0 moles/1, more preferably between about 0.6 and about 2.5 moles/1, bromide ion, and between about 0.4 and about 3.0 mole ⁇ /1, more preferably between about 0.6 and about 2.5 m ⁇ les/1, alkali metal ion.
  • a solution used for recovery of precious metal from a high grade source preferably contains between about 8 and about 15 gpl equivalent bromine, between about 6 and about 12 gpl Br " , and between about 10 and about 20 halide ion, while a solution used for recovery of precious metal from a low grade source, may suitably contain between about 0.01% and about 1%, preferably between about 0.02 and about 0.5%, by weight equivalent molecular bromine, between about 0.005% and about 10%, preferably between about 0.01% and about 1%, by weight bromide ion and between about 0.005% and about 15%, preferably between about 0.01% and about 1.5%, by weight total halide ion.
  • Product solutions containing more than about 15 gpl equivalent Br 2 can be generated if desired but, in undivided cells, current efficiencies begin to deteriorate at product solution concentrations of around 10 gpl, and fall off sharply at product solution concentrations above about 15 gpl equivalent Br 2 . If divided cells are used, current efficiencies of 90% or more can be realized in the generation of product solutions containing as high as 400 gpl or more equivalent Br 2 .
  • Equivalent bromine is defined as the sum of the molar concentrations of molecular bromine, perbromide ion (Br 3 ⁇ ), hypobromite ion, and hypobromous acid. It also includes any bromate ion present in the solution, but at the prevailing pH, no substantial bromate ion concentration would be anticipated.
  • the molar ratio of equivalent bromine to bromide ion in the product solution is between about 0.05 and 0.6, preferably between 0.2 and 0.6. Throughout this range, the solution has substantial oxidizing power, but does not have a substantial bromine vapor pressure.
  • a depleted bromide solution is produced which may optionally be recycled to tank 101 where it is replenished by addition of fresh bromide, preferably as hydrogen bromide, alkali metal bromide or a combination thereof, and adjusted with acid or base as necessary to provide a feed solution of the proper pH for electrolysis in cell 105.
  • the electrolytic solution fed to the cell contain at least about 0.65 moles per liter bromide ion. It will be noted that this is substantially in excess of the bromide content necessary for generation of the 1-5 gpl equivalent Br 2 solutions that are optimal for precious metal sources. In these circumstances, relatively high bromide ion consumption may result from the fraction of Br " in the spent ore residue discarded from the process.
  • bromide consumption and power consumption are both reduced by use of a mixed halide electrolytic solution, specifically a solution containing both chloride and bromide ion.
  • the bromide ion content of the cell feed solution is preferably between about 0.065 and about 0.25 moles per liter and the chloride content is at least about 0.56 moles per liter, preferably between about 1.25 and about 2.25 moles per liter.
  • the molar ratio of chloride ion to bromide ion is at least about 10, preferably at least about 25.
  • a portion of the current is utilized in the oxidation of chloride ion to Cl 2 , but the Cl 2 is quantitatively converted back to chloride by the oxidation of bromide to Br 2 .
  • the mixed halide process is preferably operated at a bromide to bromine conversion in the upper portion of above noted range, generally between about 20% and about 50%, more preferably between about 30% and about 50%.
  • the combination of high conversion and low bromide ion content in the feed solution results in advantageously low Br " consumption.
  • the total halide conversion is preferably in the low end of the 4 to 50% range, preferably between about 5% and about 15%.
  • the mixed halide process can also be operated at high current efficiency and moderate power consumption. By operation at modest current density, for example, in the range of about 1 to about 2 kA/m 2 , the mixed halide process can be operated with very low power consumption. By operation at higher current densities, high productivity is realized with modest power consumption.
  • electrolysis is conducted under the following conditions:
  • Feed Solution Composition 5wt% CI " , 0.5wt% Br "
  • the bromine-containing product stream produced by electrolysis of the mixed halide stream may then be used in the recovery of precious metals or treatment of water as described herein.
  • the electrogeneration system may comprise one or more banks of cells rather than the single cell that is illustrated in Fig. 1.
  • the electrogeneration system may operate on a continuous basis as shown in Fig. 1 or on a batch basis in which the electrolytic solution is circulated between the cell(s) and reservoir such as the bromide solution makeup tank until the desired conversion has been realized.
  • the cell(s) preferably operate on a flow basis, but in the latter (batch) case, recirculation is required to reach the desired conversion.
  • the relationship between electric current and throughput is such that the conversion of bromide ion is in the desired range described herein.
  • the throughput is the flow rate through the electrogeneration system, while in a recirculation or other batch operation the throughput is determined from the batch volume and time of application of power to recirculating solution.
  • mass transport coefficient (k.,) for transfer of bromide ions from the bulk solution to the anode surface is at least about 5xl0 "4 cm/sec. typically 5xl0 "4 to about 5xl0 "3 cm/sec. for the relationship:
  • Fig. 2 is a schematic illustration of a type of undivided cell that can be utilized effectively to provide the desired electrical efficiency and productivity discussed above.
  • a cell of the type illustrated is available from Electrocatalytic, Inc., of Union New Jersey under the trade designation "Chloropac".
  • the apparatus depicted in Fig. 2 is a bipolar dual cell assembly which comprises an outer electrode subassembly 113 that includes two outer cylindrical electrodes 115 and 117 that are substantially axially aligned and mechanically attached to each other through an insulating spacer 119.
  • the cell assembly further comprises an inner cylindrical electrode 121 that is of smaller diameter than either of electrodes 115 and 117, is concentric therewith, and is substantially coextensive longitudinally with subassembly 113.
  • the annular space 123 between subassembly 113 and electrode 121 provides the path along which electrolytic solution may be caused to flow through the cell.
  • outer electrode 115 serves as an anode to which current is supplied to the bipolar dual cell assembly and outer electrode 117 serves as a cathode from which current is withdrawn.
  • the portion 125 of inner electrode 121 facing anode 115 serves as a cathode and the portion 127 of the inner electrode facing cathode 117 serves as an anode.
  • each of electrodes 115, 117 and 121 is constructed of titanium, and both anode 115 and anodic portion 127 of electrode 121 are coated with platinum.
  • the platinized surface catalyzes the anodic reaction and promotes generation of bromine at high current efficiency and minimum overvoltage.
  • an electrolytic feed solution containing bromide ions is caused to flow through annular path 123 between the electrodes and a direct current is applied to the flowing solution. Bromide ions are oxidized to bromine at anodes 115 and 127, while hydrogen is generated in the solution at cathodes 117 and 125.
  • the velocity through the cell is preferably about 1.22 to 2.44 m/sec, more preferably between about 1.52 and about 2.13 m/sec.
  • the cells illustrated in Fig. 2 are particularly preferred, a variety of different cell designs may provide the high rates of mass transfer, even potential and current distribution and high ratio of electrode area to working volume that characterize the Chloropac type unit.
  • Electrogeneration system 105 may consist of a single electrolysis cell or comprise a plurality of banks of cells, but in any case comprises paired anode and cathode means which may be either monopolar or bipolar, and which may be arranged in a variety of electrical and hydraulic configurations as discussed above.
  • Aqueous bromine solution produced in system 105 is transferred by discharge pump 129 to a leaching tank 131 where it contacts a solid particulate source of gold, such as crushed gold ore. This causes the gold contained in the source to react with elemental bromine, perbromide ions, hypobromite ions and bromide ions to produce an aqueous auriferous solution containing AuBr 4 " ions and a particulate residue.
  • the resulting slurry is transferred from tank 131 by a pump 133 through a filter or other solid/liquid separation means 135 for separation of the solid residue from the pregnant leach solution, and thence to a pregnant leach solution tank 137.
  • Gold may be recovered from the pregnant leach solution by a variety of means, including zinc precipitation, carbon adsorption, solvent extraction, electrowinning, or ion exchange.
  • the process of Fig. 3 causes the gold to be removed by ion exchange.
  • Pregnant leach solution is transferred by a pump 139 to a pair of ion exchange columns 141 loaded with an ion exchange resin.
  • AuBr 4 " ions are removed from the solution and collected on the column. Residual bromine in the pregnant leach solution is reduced to bromide ion in the columns.
  • Depleted bromide solution is returned to the barren tank 101, where it is replenished by addition of fresh bromide.
  • a very similar process may be used for the recovery of platinum and palladium from sources thereof.
  • the electrolytic cells are operated with a feed composition and conversion effective to provide the leaching solution compositions described hereinabove.
  • Sulfuric acid is preferably incorporated in the leaching solution, either by incorporation in the feed solution to the cells or by addition to the product solution to provide a leaching solution.
  • the leaching solution is preferably heated to a temperature of at least about 60°C, preferably to 80-90°C, either in the leaching vessel or immediately upstream thereof.
  • the leaching tank is preferably a closed tank which contains heating coils for heating the leaching slurry to the desired temperature.
  • a heat exchanger in the slurry discharge line from the leaching tank (or filtrate discharge line from the filter) may be provided to cool the Pt bearing leachate.
  • An especially preferred gold leaching embodiment of the process of the invention is illustrated in Fig. 4.
  • gold ore is loaded into an ore bin 143 from which it is transferred by a conveyor 145 to a ball mill 147. Milled ore passes to a classifier 149. A fines fraction from the classifier is subjected to leaching for recovery of gold while a coarse fraction is recycled to ball mill 147. The fines fraction is delivered to the first of two cascade agitated leaching tanks 151 and 153 where it is contacted with an aqueous bromine solution. The resultant leaching slurry overflows tank 151 to tank 153 and overflows tank 153 to solids/liquid separation means comprising a thickener 155.
  • Solids residue drawn from the bottom of thickener 155 is passed through a countercurrent washing system comprising thickeners 157, 159, and 161.
  • An aqueous washing medium is fed to the last of the series of thickeners, thickener 161.
  • Solids/liquid contact and separation in each thickener yields a liquid fraction that is transferred to the next thickener nearer the leaching system and a solids fraction which is transferred to the next thickener more remote from the leaching system.
  • operation of the countercurrent washing system provides a liquid stream which moves with progressively increasing gold content from thickener 161 to thickener 155 and a solids stream which moves with progressively decreasing gold content from thickener 155 to thickener 161.
  • Solid tailings are withdrawn from the bottom of thickener 161.
  • the wash liquor containing soluble gold recovered from the residue mixes with the pregnant leach solution from leaching tank 153 to produce an auriferous solution that is transferred to ion exchange columns 141. Removal of gold by ion exchange produces a depleted bromide solution which is recycled for use in generating additional aqueous bromine solution.
  • the depleted bromide solution is concentrated by passing all or part of the solution through a reverse osmosis unit 162. Water removed by the reverse osmosis unit is used in the circuit or purged from the process. The concentrated bromide solution is transferred to the electrogeneration system 163.
  • Electrogeneration system 163 includes a makeup tank (not shown) and one or a plurality of cells in which bromide is converted to bromine as discussed above.
  • the spent bromide solution is replenished by addition of alkali metal bromide and acid in the makeup tank, thus producing fresh feed solution for the cells of the electrogeneration system.
  • the aqueous bromine solution leaving system 163 has the composition described hereinabove and is effective for the removal of gold from ore. This solution is recycled to leaching tank 151 for further recovery of gold from ore.
  • Ion exchange columns 141 contain a commercial anion exchange resin such as the resin comprising secondary amine functional groups combined with a phenol-formaldehyde matrix sold under the trade designations "PAZ-4" by Sela, Inc., the resin comprising trimethylamine functional groups combined with a styrene/divinylbenzene matrix sold under the trade designation "D0WEX-21K” by Dow Chemical Company, and the polyester resin sold under the trade designation "Amberlite XAD-7" by Rohm and Haas.
  • the gold loading capacity of PAZ-4 and D0WEX-21K is in the neighborhood of 80-120 oz./cubic foot, while that of XAD-7 is in range of about 10-20 oz./cubic foot.
  • 80% loading is typically achieved in 1-2 hr. and maximum loading is reached in about 3-6 hr.
  • An acidic ketone solution for example an acetone/HCl solution, is preferably used for elution of the column.
  • Other eluents such as thiourea/HCl may also be used.
  • Fig. 5 Illustrated in Fig. 5 is an alternative embodiment of the invention in which a slurry of leaching solution and particulate gold-bearing material is circulated between a leaching zone (contained within leaching tank 165) and an electrogeneration system 167 by operation of a high volumetric capacity circulating pump 169.
  • the driving force for gold leaching may be enhanced by maintaining (or restoring) a high bromine content in the leaching solution.
  • Conditions for operation of the cell or cells of the electrogeneration system are comparable to those for the processes of Figs. 3 and 4, except that back mixing in the leaching tank causes the feed solution to the cells to have a somewhat lower bromine content than in the other processes.
  • Fig. 6 shows how the principle of the process of Fig. 5 can be implemented in a continuous operation.
  • each of a series of cascaded leaching tanks 165, 171, and 173 is associated with an electrogeneration system, and leaching slurry is circulated between each leaching tank and its associated cell(s) 167, 175, and 177 respectively by means of pumps 169, 179 and 181, while leaching slurry moves forward progressively from tank to tank.
  • Such a scheme may be integrated into the process of Fig. 4, with or without an electrolytic system for regeneration of depleted bromide solution passing from the ion exchange column to the first leaching tank.
  • the processes illustrated in Figs. 3-6 can also be used for the recovery of Pd and Pt from sources thereof.
  • the feed solutions and cell operating conditions are controlled to produce product solutions that have the desired compositions of Pd/Pt leaching solutions, or which may be readily modified to produce such leaching solutions.
  • leaching solutions for Pd/Pt preferably contain HC1, HBr or H 2 S0 4 , most preferably H 2 S0 4 in a proportion of between about 10% and _ about 20% by weight.
  • acid may be added to either the feed solution or the product solution. Regardless of which acid predominates in the leaching solution HBr is advantageously used for makeup in a recirculating system of the type illustrated in Figs. 3 or 4.
  • HBr provides a suitable source of both.
  • Sulfate ion is consumed, for example, through environmental losses, with catalyst substrate or spent ore residue, in the acidulation of a catalyst substrate or ore gangue, or in competition with the complexed metal anion for ion exchanger resin sites.
  • makeup of sulfuric acid is required. Whatever acid or combination of acids is used, acid makeup may be either before or after electrolysis, but is preferably done before.
  • alkali metal bromide is commonly used as a source of bromide ion. Alkali metal is lost only marginally, primarily by environmental losses or with catalyst substrate or spent ore residue. Alkali metal bromide is added to compensate for these marginal losses of alkali metal ion, and is preferably added upstream of the electrolytic cells.
  • electro-generation of bromine to produce an aqueous bromine solution can also be conducted in divided cells.
  • Such process may be carried out in a conventional plate and frame cell construction, using a diaphragm that preferably comprises a cation exchange membrane such as the perfluorosulfonic acid membrane sold under the trade designation "Nafion" by E.I. du Pont de Nemours & Co.
  • the anode is preferably constructed of graphite, vitreous carbon, or the ceramic sold under the trade designation Ebonex by Ebonex Technology, Inc., or platinum, ruthenium dioxide, or iridium dioxide on a titanium substrate.
  • bromide ion content of the feed solution to the anode compartment of the cell is substantially the same as that of the solution described above for feed to an undivided cell.
  • bromide ion can be supplied either in the form of an alkali metal bromide, in which case the pH of the feed solution is between about 0 and about 6, preferably about 0 to about 3, or hydrobromic acid, in which case the pH of the feed solution is approximately 0 or less.
  • a proton source such as sulfuric acid or hydrochloric acid is fed to the cathode side of the cell.
  • the conversion of bromide ion in the electrogeneration system is typically between about 4% and about 50%, preferably between 20% and 40%.
  • the equivalent bromine content of the product solution is between about 0.01 and about 3.66 moles/1, preferably between about 0.4 and about 3.0 moles/1, more preferably between about 0.2 and about 1.0 moles/1.
  • the product solution has a pH of between about 0 and about 6, preferably between about 0 and about 3, and an alkali metal ion content of between about 0.1 and about 4.0 moles/1, preferably between about 0.4 and about 3.0 moles/1, more preferably between about 0.3 and about 1.5 moles/1.
  • the product of a divided cell is particularly advantageous in such applications as industrial water treatment, such as cooling tower water, where the higher equivalent bromine concentration facilitates treatment of substantial volumes of water with modest volumes of aqueous bromine solution. It is also advantageous for such leaching applications as recovery of Au from jewelry scraps, Pd from catalyst substrate, and Pt/Pd from high grade ore concentrates.
  • EXAMPLE 1 Precursor compositions were prepared by adding a 48% HBr solution and a 46% NaBr solution to water. Liquid bromine was added to the precursor solution to produce acidic concentrates containing 34% by weight equivalent molecular bromine. Satisfactory solutions were prepared from the proportions of water, HBr solution, NaBr solution and liquid bromine set forth in Table 1.
  • EXAMPLE 2 Using the method generally described in Example 1, acidic concentrates containing 34% by weight equivalent molecular bromine were prepared from water, a 46% by weight NaBr solution, and a 37% by weight HCl solution. Satisfactory compositions were prepared from the proportions set forth in Table 2.
  • compositions were prepared from CaBr 2 , Br 2 , methanol, either HBr or HCl and, optionally, water. Satisfactory compositions were prepared from the proportions set forth in Table 4.
  • Acidic concentrates were prepared from water or organic solvent, 46% by weight NaBr solution, 48% HBr solution, and liquid bromine. NaBr and HBr solution were added to the water or organic solvent, and liquid bromine was added at a modest rate to the precursor mixture. The mixture was stirred constantly but not too vigorously during the addition of Br 2 .
  • Four separate concentrates were prepared, each of which was a stable, clear liquid. The partial vapor pressures were measured 24 hours after the concentrates were formulated. The compositions of these concentrates, their bromine partial vapor pressures and the thermodynamic crystallization temperatures are set forth in Table 5.
  • a solution was prepared by dissolving sodium bromide (27.7 grams) in water (29.3 grams).
  • a sodium perbromide solution was prepared by adding liquid bromine in an amount (43.0 grams) sufficient to saturate the bromide ion, i.e., stoichiometrically equivalent to the initial bromide ion content, in the solution.
  • the resulting sodium perbromide component solution contained 43% equivalent molecular bromine.
  • a sodium hydroxide solution was prepared containing 16.7% by weight sodium hydroxide. Liquid bromine (25.0 grams) was added to this solution (75.0 grams) producing a composition which contained 6.7% by weight bromate ion (7.9% by weight as sodium bromate; 25% by weight equivalent molecular bromine) .
  • a concentrate was prepared by mixing equal parts by weight of the perbromide and bromate component solutions.
  • the concentrate so prepared contained 31.82% by weight sodium perbromide, 2.14% by weight bromine, 14.80% by weight sodium bromide, 3.94% by weight sodium bromate and 47.30% by weight water. It had an equivalent molecular bromine concentration of 34% by weight.
  • the total vapor pressure was measured as a function of temperature for liquid Br 2 , the sodium perbromide component solution of this example, and the precursor concentrate of this example. From the data
  • Sodium perbromide and sodium bromate component solutions were prepared in the manner described in Example 6. A series of concentrates was prepared using varying proportions of the two component solutions. The composition of the concentrates obtained are set forth in Table 8.
  • EXAMPLE 8 In order to compare the vapor pressure of solutions containing bromate ion prepared according to the invention with previously known aqueous bromine-based solutions, a solution was prepared by a formulation method comparable to Bahl, et al. U.S. Patent No. 4,190,489, and a composition was prepared according to the invention, each containing 34% by weight equivalent bromine.
  • a composition was prepared according to the invention, each containing 34% by weight equivalent bromine.
  • 26 g KBr was dissolved in 40 g water and then 34 g Br 2 was added to the resulting solution.
  • 14.26 g NaBr, 45.49 g H 2 0, 6.25 g NaOH and 34 g Br 2 were mixed.
  • Bromate content and vapor pressure were calculated as follows: Titration with Thiosulfate-KI using a weak acid determines actual Br 2 content (Br 2 + Br 3 " ) while titration with Thiosulfate-KI using a strong acid converts bromate to bromine and determines the sum of bromate and bromine concentration. Therefore, the bromate content of the two solutions was determined by Thiosulfate-KI titration first with acetic acid to determine the actual bromine concentration, and then by Thiosulfate-KI titration with H 2 S0 4 to determine the total equivalent molecular bromine (Br 2 + Br 3 " + Br0 3 " ) and subtracting the difference. Solution vapor pressure at 25°C was obtained by using the Isoteniscope method. The results obtained are set forth in Table 9.
  • composition A of the invention * vs. Bahl Formulation ** Parameter A
  • a solubilizing reagent having the composition of that prepared in accordance with Example 4, composition #31 (using 46% NaBr) (hereinafter the "PGM Reagent") was used to demonstrate the ability of the present composition to solubilize palladium.
  • Samples of a precious metal scrap, comprising a hydrocracking catalyst (estimated 0.5% Pd) were used in the following tests to evaluate the effect of pH, pH adjuster, time, bromide concentration, reagent source, temperature and mixing speed. pH/pH Adjuster
  • the bromide concentration variable was controlled by using 46% NaBr.
  • 2.5 g catalyst was contacted with a solution of 5 g PGM Reagent, 10 g cone. H 2 S0 4 and 100 g H 2 0 for 10 hrs at 85°C with a shaker bath mixing speed of 280 rpm.
  • the results of this set of tests, provided in Table 12, show that NaBr in addition to that provided by the PGM reagent did not improve palladium dissolution.
  • a refractory concentrate containing platinum, palladium, rhodium and gold was used (after roasting overnight at 800°C) in this example to evaluate the efficacy of the — inventive compositions for solubilizing gold, platinum, and palladium.
  • the analysis of this concentrate by Hazen Research Laboratories was 50.6 oz/ton Pd, 15.6 oz/ton Pt, 0.83 oz/ton Au, and 0.44 oz/ton Rh. Due to the high sulfur content, roasting of the concentrate was deemed necessary, and several tests were performed on the calcine concentrate.
  • PGM Reagent Concentration Three concentrations of PGM Reagent were tested. 10 g of calcine concentrate was dissolved in a solution containing varying amounts of PGM Reagent, 10 g cone. H 2 S0 4 5 and 100 g H 2 0 for 16 hrs at 85°C and at a mixing speed of 200 rpm. The results are shown in Table 16. Based on these tests, 5 g or 5% PGM Reagent was selected as the optimum concentration for the remaining tests. Rh was not detectable by ICP analysis throughout all tests.
  • Preleaching Because a high concentration of base metals was thought to be inhibiting platinum and palladium dissolution, the effect of acid preleaching to remove these metals, followed by bromine leaching, was studied. The two preleaches compared were a 20% H 2 S0 4 preleach to a 10% H 2 S0 4 /24% HBr preleach. Each was followed by a 5% PGM Reagent bromine leach. 10 g ore was preleached in 20 g cone. H 2 S0 4 and 80 g H 2 0 for 3 hrs at room temperature. 10 g ore was also preleached in a solution containing 10 g cone.
  • H 2 S0 4 50 g 48% HBr and 50 g H 2 0 for 16 hrs at 85°C.
  • each sample was leached in a solution containing 5 g PGM Reagent, 10 g cone.
  • the 20% sulfuric acid preleach helped palladium dissolution, but not platinum.
  • the bromine leach following the HBr/H 2 S0 4 preleach improved the platinum dissolution only slightly.
  • a stir plate and heating mantle apparatus was compared to the shaker bath method for agitating ore slurries.
  • the H 2 S0 4 concentration variable was tested simultaneously. 20 g ore was slurried in a solution containing 10 g PGM Reagent and 100 g H 2 0 at 85°C for 6 hrs using stir bars. The results of these tests are presented in Table 20.
  • Fire assay results were obtained and metallurgical balances calculated for the following three tests.
  • the conditions were: LEACH-A: 10 g ore; 10 g cone. H 2 S0 4 ; 5 g PGM Reagent; 90 g H 2 0; 85°C (shaker bath); and 16 hours.
  • LEACH-B 20 g ore; 40 g cone. H 2 S0 4 ; 10 g PGM Reagent; 150 g H 2 0; 85°C (stir plate); and 16 hours.
  • LEACH-C Same as B, except time was only 6 hours. The results are presented in Table 21. Pd Solubilized
  • Au Solubilized EXAMPLE 11 As for the PGM Reagent used in the preceding Examples, the various other compositions of the present invention provide high levels of molecular bromine for dissolution of platinum and palladium. Repetition of the foregoing Examples 9 and 10 using each of the compositions of Examples 1-7 provides suitable platinum and palladium recoveries.
  • the initial PGM reagent includes water, at least about 25% by weight bromine, between about 4% and about 30% by weight hydrobromic acid, and between about 4% and about 15% by weight of lithium bromide, sodium bromide, potassium bromide or calcium bromide, a molar excess of bromide ion over bromine of at least about 30%, and a pH of not greater than about 1.0.
  • This reagent is diluted with water to prepare the leaching solution, which is thereafter contacted with the Pt/Pd source.
  • the initial PGM reagent includes a precursor composition initially having a pH of between about 6.5 and about 7.5 and comprising bromide ion, perbromide ion, molecular bromine, at least about 2% by weight bromate ion, and an alkali metal or alkaline earth metal ion, the precursor composition having an equivalent molecular bromine content of between about 10% and about 40% by weight and the ratio of the molar concentration of bromate ion to the sum of the molar concentrations of molecular bromine and perbromide ion being between about 0.05 and about 0.8.
  • the precursor composition is acidified, producing a leaching solution having a pH of between about 0 and about 6 and containing between about 0.01% and about 20% by weight equivalent molecular bromine, between about 0.005% and about 20% by weight bromide ion, and between about 0.005% and about 30% by weight total halide ion, which leaching solution is then contacted with the PGM source.
  • EXAMPLE 12 Referring to the Figures 7 and 8, there are shown Eh/pH diagrams for representative platinum group metals in the systems H 2 0-10 "4 M Pd-O.lMBr " (Fig. 7) and H 2 0-10 "4 M Pt-O.IM Br " (Fig. 8).
  • a simulated barren solution was prepared having a composition typical of that which would be obtained after recovery of gold by ion exchange from a pregnant leach solution produced by bromine leaching.
  • sodium bromide and 48% hydrobromic acid were mixed with water to produce a solution containing 5% by weight bromide ion and having a pH of 3.
  • this solution was circulated at a flow rate of 125 L/sec. between a 300 gal. pilot scale reservoir for the solution and a Chloropac cell operated at a constant amperage of 100A. At this amperage, the Chloropac cell is rated to produce 1/2 lb. Cl 2 per hour. Velocity through the annular portion of the Chloropac cell between the electrodes was about 1.83 m/sec.
  • Example 13 Further electrolysis runs were conducted in the manner described in Example 13, except that the simulated barren solution was buffered with 6 mol dm "1 sulfuric acid instead of 48% HBr. The results were essentially identical to those of Example 13. These results indicate that the depletion of Br " from the system has a negligible effect on current efficiency at low conversion. Loss in current efficiency with conversion in this low range can be substantially attributed to reduction of Br 2 to Br " at the cathode.
  • Example 16 Runs were made according to the general procedure of Example 14 except that the concentration of Br " was varied. In Example 15 the concentration was 4%, in Example 16 it was 3%, and in Example 17 it was 2.5%. To maintain conductivity, the solutions of Examples 16 and 17 further contained sodium sulfate as an auxiliary electrolyte. In Example 16, the Na 2 S0 4 concentration was 0.25 mol dm “3 and in Example 17 it was 0.33 mol dm "3 .
  • Example 15 the electrolysis was carried out to a conversion of 15.1% and bromine content of about 58 mmol dm "3 . At this point the cumulative current efficiency was about 83-85%.
  • Example 16 the conversion was 18%, the bromine content about 48 mmol dm "3 , and the cumulative current efficiency about 79%, while in Example 17 the conversion was 12.3%, the bromine content about 24 mmol dm "3 , and the cumulative current efficiency about 84%.
  • a black sand concentrate (100 g) containing 6 kg/tonne Au was contacted in an agitation bottle with a bromine leaching solution (8.0 g) having a composition typical of a solution that may be prepared from the electrolysis of a sodium bromide solution as described hereinabove.
  • the leaching solution had a pH of about 2 and contained about 0.68% by weight equivalent molecular bromine, about 0.43% by weight bromide ion, and about 0.43% by weight sodium ion.
  • the resultant leaching slurry was agitated in the capped bottle using an overhead mixer at slurry temperature of about 22°C for 24 hours.
  • the repulped slurry was then filtered and the cake was washed with a volume of water equal to the solids weight.
  • the gold values in the leaching samples, filtrate, wash, and residue were determined by inductively coupled plasma spectrometry (ICP) and fire assay. The results indicated that 90% of the gold was dissolved during the first two hours, and that dissolution reached a maximum in about 4 hours.
  • the residue (“tails") was releached twice with fresh leaching solution under conditions comparable to the initial leaching operation.
  • Fresh leaching solution restores the ORP to the 800-900 mV range in which effective removal of gold from the source is realized.
  • a simulated pregnant gold bromide solution 146.6 ppm Au
  • 12 dm 3 containing 5% Br " ion and residual Br 2 (not determined) was the catholyte, and a 5% H 2 S0 4 solution served as the anolyte.
  • the streams were recirculated (140 dm 3 hr _1 ) through a plate and frame-type cell equipped with a cation exchange membrane.
  • Nickel foams (30 pores per inch) served as the cathode, and anodized lead shot (Pb0 2 ) was the anode.
  • the counter reac- tion is the oxidation of water to oxygen.
  • anodic oxidation of Br " to Br 2 at, for example, graphite anodes could also have been the reaction of choice.

Abstract

Procédé de lessivage de platine et de palladium, selon lequel une solution de lessivage aqueuse contenant du brome et des ions de bromure entre en contact avec une source de métal précieux pour former un produit de lessivage aqueux. L'invention se rapporte également à une composition précurseur, servant à produire une solution de lessivage aqueuse pour lessiver le platine et le palladium, ainsi qu'à un procédé d'électrogénération de brome et à un procédé de lessivage de platine et de palladium au cours duquel du brome est électrogénéré et entre en contact avec une source de métal précieux pour former un produit de lessivage aqueux. L'invention se rapporte en outre à un procédé de lessivage d'or, d'argent, de platine et de palladium, selon lequel du brome est électrogénéré à partir d'une solution contenant des ions de chlorure et de bromure.
EP93918586A 1992-07-29 1993-07-28 Compositions de perbromure inorganique et procedes d'utilisation. Withdrawn EP0652979A4 (fr)

Applications Claiming Priority (3)

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US92203592A 1992-07-29 1992-07-29
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JP2003247028A (ja) 2001-11-21 2003-09-05 Shipley Co Llc 触媒金属を回収する方法
MX2016014770A (es) 2014-05-12 2017-05-25 Summit Mining Int Inc Proceso de lixiviado de salmuera para la recuperacion de metales valiosos de materiales de oxido.

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4904358A (en) * 1988-02-16 1990-02-27 Inland Aqua-Tech Co., Inc. Gold and silver recovery processes by electrolytic generation of active bromine
EP0476862A1 (fr) * 1990-09-04 1992-03-25 Great Lakes Chemical Corporation Production électrolytique de brome et son utilisation dans la récupération de métaux précieux et le traitement des eaux
WO1992018422A1 (fr) * 1991-04-12 1992-10-29 Great Lakes Chemical Corporation Compositions de perbromures inorganiques et leurs procedes d'utilisation

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1495931A (en) * 1973-12-07 1977-12-21 Matthey Rustenburg Refines Refining of metals
US3957601A (en) * 1974-05-17 1976-05-18 Mineral Research & Development Corporation Electrochemical mining
IL88367A0 (en) * 1988-03-07 1989-06-30 Great Lakes Chemical Corp Composition and method for recovery of gold and silver from sources thereof
AU619680B2 (en) * 1988-03-07 1992-01-30 Great Lakes Chemical Corporation Compositions and method for recovery of gold and silver from sources thereof
US4997532A (en) * 1988-12-30 1991-03-05 Satec Ltd. Process for extracting noble metals
CA1340169C (fr) * 1989-08-31 1998-12-08 Ahmad Dadgar Procede hydrometallurgique pour extraire l'or et l'argent de minerais a l'aide de solutions de bromate/perbromure; compositions utiles a cette fin
ZA933784B (en) * 1992-06-10 1993-12-22 Bhp Minerals Int Inc Recovery of precious metals from materials containing said metals

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4904358A (en) * 1988-02-16 1990-02-27 Inland Aqua-Tech Co., Inc. Gold and silver recovery processes by electrolytic generation of active bromine
EP0476862A1 (fr) * 1990-09-04 1992-03-25 Great Lakes Chemical Corporation Production électrolytique de brome et son utilisation dans la récupération de métaux précieux et le traitement des eaux
WO1992018422A1 (fr) * 1991-04-12 1992-10-29 Great Lakes Chemical Corporation Compositions de perbromures inorganiques et leurs procedes d'utilisation

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
DATABASE WPI Derwent Publications Ltd., London, GB; AN 90-354914 & AU-A-5 572 290 (GREAT LAKES CHEM. CORP.) *
DATABASE WPI Derwent Publications Ltd., London, GB; AN 93-053100 & ZA-A-9 006 900 (GREAT LAKES CEM. CORP.) 27 May 1992 *
See also references of WO9403649A1 *

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ZA935409B (en) 1994-02-16
CA2141312A1 (fr) 1994-02-17
WO1994003649A1 (fr) 1994-02-17
EP0652979A4 (fr) 1995-09-27
MX9304565A (es) 1994-04-29
AU680201B2 (en) 1997-07-24

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