WO1996000308A2 - Procede et appareil d'extraction de metaux precieux - Google Patents

Procede et appareil d'extraction de metaux precieux Download PDF

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Publication number
WO1996000308A2
WO1996000308A2 PCT/US1995/009199 US9509199W WO9600308A2 WO 1996000308 A2 WO1996000308 A2 WO 1996000308A2 US 9509199 W US9509199 W US 9509199W WO 9600308 A2 WO9600308 A2 WO 9600308A2
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Prior art keywords
bisulfide
ore
lixiviant
precious metal
reducing
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PCT/US1995/009199
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English (en)
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WO1996000308A3 (fr
Inventor
Robert M. Hunter
Frank M. Stewart
Tamara Darsow
Macgregor L. Fogelsong
Original Assignee
Hunter Robert M
Stewart Frank M
Tamara Darsow
Fogelsong Macgregor L
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Priority claimed from US08/265,322 external-priority patent/US5449397A/en
Application filed by Hunter Robert M, Stewart Frank M, Tamara Darsow, Fogelsong Macgregor L filed Critical Hunter Robert M
Priority to AU34899/95A priority Critical patent/AU700356B2/en
Priority to CA002194349A priority patent/CA2194349C/fr
Publication of WO1996000308A2 publication Critical patent/WO1996000308A2/fr
Publication of WO1996000308A3 publication Critical patent/WO1996000308A3/fr

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    • 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
    • C22B3/18—Extraction of metal compounds from ores or concentrates by wet processes with the aid of microorganisms or enzymes, e.g. bacteria or algae
    • 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
    • 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 a method and apparatus for extracting precious metals from their ores and the product thereof.
  • it relates to the following: (1) a biohydrometallurgical process and apparatus for extraction and recovery of gold, silver and platinum group elements from their ores; (2) the products of that process and apparatus.
  • the first step in precious metal production from ore involves preparing the ore for precious metal extraction. Preparation can take any one of a number of courses depending on the character of the ore. Gold and silver ores often contain metallic sulfides. Ores containing platinum-group elements (PGE) typically also contain metallic sulfides.
  • PGE platinum-group elements
  • refractory, non-oxidized (e.g., sulfide) gold and silver ores are oxidized at elevated temperatures and pressures in large autoclaves (i.e., "roasted"), prior to the extraction of precious metals by means of cyanide leaching, (see McQuiston, Jr., F.W., & Shoemaker, R.S., Gold and Silver Cyanidation Plant Practice, Vol. II, Baltimore: Port City Press, 1980).
  • Biooxidation process steps may include ore crushing, acid pretreatment, inoculation with appropriate sulfide-oxidizing bacteria, addition of nutrients, recirculating the biolixiviant and cooling the heap (for 3 to 8 days), and allowing the heap to "rest” (for 3 to 8 days).
  • Precious metal extraction by means of cyanidation may include the process steps of washing the heap for an extended period (e.g., 14 days) to remove residual acidity or iron content, breaking the heap apart in order to agglomerate it with cement and/or lime to make a new heap, leaching it with an alkaline cyanide or thiosulfate solution for 30 to 40 days, and recovery of gold and silver from the leach solution by adsorption on activated carbon or zinc dust precipitation.
  • an extended period e.g. 14 days
  • Rate controls on the bio-oxidation of heaps of pyritic material imposed by bacterial upper temperature limits were described by Pantelis, G. & Ritchie, A.I.M. in “Rate controls on the oxidation of heaps of pyritic material imposed by upper temperature limits on the bacterially catalysed process,” (FEMS Microbiology Reviews, 11, 183-190, 1993). Biooxidation bacteria have been characterized in detail. Brierly, C.L., & Brierly, J.A., in “A chemoautotrophic and thermophilic microorganism isolated from an acid hot spring,” (Canadian J.
  • Acetogens acetogenic bacteria
  • Methanogens methanogenic bacteria
  • Nitrate-reducing bacteria that produce nitrogen gas
  • ore refers to a composition that comprises precious metal values.
  • ore may be a mineral assemblage that is being mined in-situ (in place) or that has been mined conventionally; or it may be a waste product, such as obsolete or damaged electronic components.
  • precious metals refers to gold(Au), silver(Ag) and/or platinum-group elements (PGE).
  • platinum-group elements refers to platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Rh) and iridium (Ir).
  • bisufide lixiviant refers to an aqueous solution comprising HS- ions, and may also comprise dissolved H,S gas (H 2 S (aq) ).
  • bisulfide complex refers to a complex comprising a precious metal and bisulfide.
  • the present invention provides method and apparatus for leaching of precious metals from their ores by means of a leaching solution comprising a sulfide ion and having a low fugacity of hydrogen gas.
  • Leaching is accomplished by formation of precious metal complexes.
  • the complex Au(HS) 2 - predominates.
  • the solubility of gold is increased by the formation of the complex Au 2 S 2 -2 .
  • the solubility of gold is increased by the formation of the complex AuHS 0 .
  • formation of a variety of precious metal-sulfide complexes is possible.
  • the invention may be practiced on oxidized ore, sulfide ore, or otherwise refractory ore in a tank reactor or heap leach operation.
  • a bio-oxidation step for removing base-metal sulfides from precious metal ores is coupled with a bisulfide precious metal leaching step, but conventional roasting may also be used to remove base-metal sulfides and produce an acidic, sulfate stream.
  • the leaching solution is essentially neutral or alkaline.
  • the process of producing the leaching solution is biocatalyzed.
  • a first process step of bio-oxidation of ore particles is accomplished to free (liberate) precious metals dispersed or occluded within the ore.
  • a portion of the acidic, base-metal sulfate leach solution produced by the bio-oxidation step is introduced to an anaerobic reactor.
  • the anaerobic reactor is a side- stream reactor or a series of such reactors in series.
  • the anaerobic process may occur on-line.
  • One or more preferably non- toxic electron donors such as hydrogen gas, formate, acetate and/or methanol—which does not bind effectively to activated carbon
  • growth requirements such as vitamins and/or salts
  • the electron donors and/or growth requirements are derived from organic material deposited on the ore by sulfide- oxidizing bacteria during the bio-oxidation step.
  • the hydrogen fugacity in the ⁇ eactor, or at least in the last reactor in a series of such reactors, is maintained at a low level by at least one hydrogen-consuming bacterium.
  • the anaerobic reactor may be operated in a pH-stat mode by adding sufficient acidic sulfate solution to maintain a neutral pH in the reactor (see Hunter, R.M., Biocatalyzed Partial Demineralization of Acidic Metal-Sulfate Solutions, Ph.D. Thesis, Montana State University, 1989).
  • the anaerobic reactor may be operated in a sulfide-stat mode by adding sufficient sulfate solution to maintain a constant dissolved sulfide concentration in the reactor in response to signals from a sulfide sensor (e.g., sulfide ion selective electrode).
  • Base metals are preferably precipitated and removed and a portion of the hydrogen sulfide gas (H 2 S) produced in the anaerobic reactor is preferably removed.
  • oxyanion- reducing bacteria are used to create an essentially neutral leaching solution comprising a relatively high concentration bisulfide ions, a high fugacity of hydrogen sulfide gas, a low concentration of dissolved base metals and a low fugacity of hydrogen gas.
  • the precious metal leaching solution is produced in an anaerobic environment by contacting a stream of gas comprising hydrogen sulfide gas and essentially no hydrogen gas with the solution until the environment has an appropriately high concentration of hydrogen sulfide gas and an appropriately low fugacity of hydrogen gas.
  • the gas may be produced biotically by a culture of sulfate-reducing bacteria, or it may be produced abiotically by purifying H 2 S gas to remove H 2 gas.
  • the oxidized ore (possibly in a heap that is covered and submerged to exclude oxygen) is leached (by recirculating the neutral or alkaline bisulfide lixiviant comprising, or saturated with, H 2 S) in a leaching reactor.
  • the H 2 S partial pressure is increased by introducing the lixiviant under pressure at the bottom of a heap submerged in water, causing ion concentrations to increase in direct proportion to the increase in H 2 S partial pressure.
  • the anaerobic reactor and the leaching reactor are operated together as a single, essentially completely-mixed reactor.
  • a completely mixed reactor is one that produces an effluent concentration of a conservative tracer (e.g., a non-reactive dye) equal to 37 ⁇ 3 percent of the initial tracer concentration (i.e., tracer mass divided by liquid volume) one detention time (i.e., liquid volume divided by liquid volumetric flow rate) after an impulse input (i.e., slug addition) of the tracer.
  • a conservative tracer e.g., a non-reactive dye
  • the complexed precious metal e.g., gold and silver
  • the complexed precious metal e.g., gold and silver
  • Recovery may be accomplished in a conventional manner by adsorption on activated carbon or by modifying either the solution pH, hydrogen fugacity, or oxidation-reduction potential (ORP).
  • Recovered precious metals are converted into products. This may include the operations of separating, smelting and casting of each precious metal into bars, bullion or other forms.
  • the present invention offers a variety of advantages not provided by the prior art.
  • One object of the invention is to lower the monetary cost of gold, silver and platinum-group element production.
  • a waste product excess sulfuric acid from a roasting or bio-oxidation pretreatment step
  • the lixiviant a neutral bisulfide solution
  • Another object of the invention is to use both inorganic (salts) and organic (biofilm carbonaceous compounds) byproducts of bioxidization as inputs to a precious-metal solubilization process.
  • Another object of the invention is to lower the environmental risk of precious metal mining. This is the case because the actual and perceived environmental risk of maintaining a large inventory of a neutral bisulfide solution is much lower than that associated with maintaining an equivalent volume of caustic cyanide solution.
  • Another object of the invention is to provide a method and apparatus for both in-situ or ex-situ (conventional) mining. Further objects and advantages of the invention will become apparent from consideration of the drawings and the ensuing description.
  • Fig. 1 is a highly schematic block diagram illustrating a first representative embodiment of the present invention.
  • Fig. 2 is a highly schematic block diagram illustrating a second representative embodiment of the present invention.
  • Fig. 3 is a highly schematic block diagram illustrating a third representative embodiment of the present invention.
  • Fig. 4 is a highly schematic block diagram illustrating a fourth representative embodiment of the present invention.
  • Fig. 1 is a schematic block diagram illustrating a preferred embodiment of the invention, with the dashed lines representing possible variations in the process and apparatus.
  • Ore 2 is the input to the process and, under certain conditions, may be the only input to the process.
  • ore 2 is crushed and may be otherwise treated to optimize bio-oxidation.
  • bio-oxidation reactor 4 oxidation of metal sulfides is accomplished to free or mobilized precious metals dispersed or occluded within metallic sulfides in ore 2.
  • Bio-oxidation reactor 4 produces a sidestream comprising sulfate ions 6 and acidity.
  • the sidestream also comprises biofilm carbonaceous compounds.
  • bio-oxidation does not occur and sulfate ions 6 are an input to the process.
  • Sulfate ions 6 may be a component of a waste stream, such as acid mine drainage, or by-product of ore roasting.
  • electron donor 7 is added to sulfate reduction reactor 8 so that sulfate ions 6 are biologically reduced therein.
  • sulfate reduction reactor 8 is operated at a mean cell residence time low enough to cause essentially-complete (99+ percent) utilization of electron donor 7.
  • sulfate reduction reactor 8 is operated in a pH-stat mode so as to maintain an essentially constant pH ( ⁇ 0.1 pH unit) in reactor
  • Oxidized ore 20 is introduced to bisulfide leaching reactor 22.
  • precious metal values in oxidized ore 20 are dissolved and complexed by means of bisulfide lixiviant 10.
  • Pregnant solution 24 comprising precious metal values is introduced to precious metals recovery reactor 26 for precious metals recovery in a conventional manner by adsorption on activated carbon; or by modifying either the solution pH, hydrogen fugacity, or oxidation-reduction potential (ORP).
  • a product e.g., gold bullion
  • leached ore 28 is disposed of in a conventional manner (e.g., permanent storage) and need not be treated for removal of lixiviant.
  • leached ore 28 is washed and/or dewatered to remove residual lixiviant 10 prior to disposal. Lixiviant 10 removed from leached ore 28 is used to wet and/or neutralize the acidic pH of incoming oxidized ore 20 and/or it is returned to leaching reactor 22.
  • reactors 8 and 26 are preferably optimized for precious metal dissolution and complex formation.
  • design and/or operation are varied to achieve the following conditions in the reactor environment:
  • stability and equilibrium constants are used to predict the direction of a reversible chemical reaction under certain standard conditions and under other conditions.
  • the standard conditions are 1.0 molar (M) concentrations of dissolved reactants and products and 1.0 atmosphere (Atm) pressure of gaseous reactants and products.
  • the temperature is usually taken as 25°C (298°K), but stability and equilibrium constants are reported at other temperatures as well. ⁇
  • Equilibrium constants can be derived in a number of ways.
  • the stability constant for a reaction is related to the standard free energy change the reaction as follows:
  • T absolute temperature in degrees Kelvin (°K)
  • precious metal e.g., gold, silver, platinum and palladium
  • the equilibrium and stability constants for the platinum group element reactions can be estimated using the methods disclosed by Hancock, R.D., Finkelstein, N.P., & Evers, A., in "A linear free-energy relation involving the formation constants of palladium (II) and platinum (II),” (Journal of Inorganic and Nuclear Chemistry, 39, 1031-1034, 1977) and Mountain, B.W. & Wood, S.A., in “Chemical controls on the solubility, transport, and deposition of platinum and palladium in hydrothermal solutions: A thermodynamic approach," (Economic Geology, 83, 492- 510, 1988). They have demonstrated that, for metals in the group Au, Ag, Pt and Pd, plots of the logarithms of the stability constants of one metal versus another are linear for a variety of ligands.
  • [Pd(HS) 4 - 2 ] K Pd(HS)4 * [H 2 S (ag) ] 2 * [HS-] 2 /[H 2(g) ]
  • bisulfide ions are generated biologically (by naturally- occurring sulfate-reducing bacteria) at very low cost using an acidic waste product (bio- oxidation heap leach effluent) as the sulfate source.
  • an acidic waste product bio- oxidation heap leach effluent
  • formate ion as the electron donor, the following reaction occurs:
  • H 2 S gas can be recovered from spent lixiviant and/or leached ore by reducing the H 2 S gas partial pressure in the gas mixture in contact with said spent lixiviant and/or leached ore using a vacuum pump. More complete H 2 S gas recovery can be achieved by acidifying the spent lixiviant and/or leached ore to a pH below 7.0 and/or by increasing gas/liquid interfacial area, (e.g., by forming the liquid into droplets).
  • the optimal pH for the bisulfide lixiviant solution for precious metal recovery is the pH that maximizes the solubility of target precious metal compounds and the stability of their complexes.
  • Krauskopf, K.B. in "The solubility of gold” Economic Geology, (46, 858-870, 1951), noted that "one of the most perplexing facts about the chemistry of gold is its ability to dissolve in solutions of HS- of moderate concentration even at room temperature, whereas it dissolves in S -2 (i.e., more alkaline solutions) only in concentrated solutions at high temperature.” Schwarzenbach, von G.
  • Seward reported that for gold in solutions of reduced sulfur "a pronounced solubility maximum occurs in the region of pH about 7." (Seward, T.M., “Thio complexes of gold and the transport of gold in hydrothermal ore solutions,” Geochimica et cosmochimica Acta, 37, 379-399, 1973).
  • Hydrogen-consuming bacteria include such anion-reducing bacteria as acetogens, methanogens, sulfate-reducing bacteria and denitrifying (nitrate-reducing) bacteria. In natural ecosystems, these bacteria participate in "interspecies hydrogen transfer.” Examples of acetogens include Acetobacterium woodi (ATCC 29683, DSM 1030, or DSM 2396) and Clostridium aceticum (ATCC 35044 or DSM 1496).
  • Examples of hydrogen-consuming methanogens are numerous and include the mesophiles Methanobrevibacter ruminantmm (ATCC 35063 or DSM 1093) and Methanosarcina barken (ATCC 29786 or DSM 805), and the thermophile Methanobacterium thermoautotrophicum (ATCC 29096 or DSM 1053). Examples of hydrogen-consuming sulfate-reducing bacteria are shown in Table 4.
  • leaching solution is produced in an anaerobic reactor by culturing in the reactor sulfate-reducing bacteria capable of using formate or acetate, as well as hydrogen as electron donors, and both sulfate and nitrate as electron acceptors. Since anions, such as sulfate and nitrate, are reduced, such bacteria are oxyanion-reducing bacteria.
  • bacteria examples include mesophilic, fresh- water species such as Desulfobacterium catecholicum DSM 3882 (acetate and formate) and Desulfovibrio simplex DSM 4141 (formate); mesophilic, salt-water species, such as Desulfovibrio salexigens DSM 2638 (formate); and thermophilic, fresh- water species such as Desidfomacidum kuznetsovii DSM 6115 or VKM B-1805 (acetate and formate).
  • Microorganisms with ATCC accession numbers can be obtained from the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Maryland 20852-1776, tel 1-800- 638-6597, fax 1-301-231-5826.
  • Microorganisms with DSM accession numbers can be obtained from the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH, Mascheroder Weg lb, D-38124 Braunschweig, Germany, tel 011-49 (0)531-2616-336, fax 011-49 (0)531-
  • Microorganisms with VKM accession numbers can be obtained from the Institute of Biochemistry and Physiology of Microorganisms of the Russian Academy of Science,
  • additional hydrogen consumption is accomplished by purging the headspace of bisulfide leaching reactor 22 through aH 2 S-scrubbing means (e.g., a zinc acetate solution "bubbler") into a nitrate-fed reactor containing a culture of sulfate-reducing bacteria that are also capable of nitrate reduction, operated in parallel (side-stream) or in series with reactor 22.
  • aH 2 S-scrubbing means e.g., a zinc acetate solution "bubbler”
  • a nitrate-fed reactor containing a culture of sulfate-reducing bacteria that are also capable of nitrate reduction operated in parallel (side-stream) or in series with reactor 22.
  • a zinc acetate bubbler would not be required if the H,S concentration in reactor 22 were controlled independently by a side-stream bubbler controlled by a sulfide ion-selective electrode that would turn on a H 2 S-scrubbing bubbler loop when a high H 2 S setpoint was reached.
  • the H 2 S (aq) concentration and the HS- concentration may be increased to an appropriate level, and the H 2 fugacity may be reduced to an appropriate level in the environment provided by reactor 22 by contacting the contents of reactor 22 with a stream of gas having an appropriate H 2 S fugacity and effectively no H 2 .
  • This stream of gas may be produced biologically by a culture comprising sulfate-reducing bacteria or it may be produced abiotically using conventional means.
  • An equilibrium will be reached that partitions the constituents of reactor 22 of limited solubility between the gas and liquid phases in reactor 22. Henry's Law can be used to predict equilibrium and steady state constituent levels.
  • sulfate-reduction reactor 8 is operated in the thermophilic (50-100°C) and barophilic (over one atmosphere) ranges (e.g., in a submerged, covered heap).
  • sulfate-reduction reactor 8 If sulfate-reduction reactor 8 is operated at steady-state at relatively high total dissolved sulfide (H 2 S (aq) + HS- + S -2 ) concentrations (say over about 1,000 mg/l in the liquid), then sulfate-reducing bacteria will be enriched in reactor 8 that are relatively resistant to growth rate inhibition by such total sulfide concentrations.
  • H 2 S (aq) + HS- + S -2 total dissolved sulfide
  • sulfate-reducing bacteria will be enriched in reactor 8 that are relatively resistant to growth rate inhibition by such total sulfide concentrations.
  • Many investigators have reported that common sulfate-reducing bacteria can grow in media containing over 2,700 mg/1 of total sulfides (See Miller, L.P. (1950). Formation of metal sulfides through the activities of sulfate-reducing bacteria.
  • sulfate-reduction reactor 8 is operated at a relatively low total sulfide concentration (say less than about 1,000 mg/1 in the liquid) in order to minimize inhibition of the sulfate-reducing bacteria growing in it. This may be achieved by using a vacuum pump or purging gas stream to transfer H 2 S gas from the headspace of reactor 8 to the liquid in leaching reactor 22.
  • a H 2 S gas pump is used to increase the H 2 S partial pressure in the transferred gas stream.
  • the H 2 S gas removed from reactor 8 is absorbed in a basic (pH >7) solution as dissolved HS ions during the intake portion of the pumping cycle.
  • the solution containing dissolved HS ' ions is acidified to convert the dissolved HS- to H 2 S gas and the H 2 S is pumped into leaching reactor 22.
  • waste sulfuric acid produced by oxidation of metal sulfides is used to acidify the solution containing the dissolved HS- ions.
  • H 2 S gas pumping is accomplished by dissolving it in a liquid solution at a relatively low temperature (e.g., 10°C). The H 2 S is then driven out of the solution by heating the liquid to a relatively higher temperature (e.g., 60°C).
  • a relatively low temperature e.g. 10°C
  • the H 2 S is then driven out of the solution by heating the liquid to a relatively higher temperature (e.g., 60°C).
  • This form of H 2 S pumping is made possible by the significant change in Henry's law coefficient for H 2 S gas with temperature.
  • Precious metals recovery options include adsorption on activated carbon; adsorption on ion-exchange resin; and modification of the solution pH, hydrogen fugacity, or oxidation- reduction potential (ORP).
  • precious metals are adsorbed on the cell walls of bacteria and the bacteria are separated from the liquid in which they are suspended by settling and/or filtration of the liquid after settling of the ore particles.
  • Options that do not otherwise modify lixiviant solution chemistry are preferable. For this reason, in preferred embodiments, at least reactors 8 and 22, and preferably also reactor 26, are operated together as a single, essentially completely-mixed reactor.
  • pregnant solution 24 is degassed to reduce its total dissolved sulfide concentration before and/or concurrent with contacting it with granular activated carbon in precious metals recovery reactor 26.
  • Degassing may be accomplished by pumping gas from the headspace of reactor 26 into the liquid in leaching reactor 22.
  • Precious metals that have absorbed to the activated carbon are eluted into a concentrated solution that is a solvent for the precious metals. Precious metals are recovered from the concentrated solution by conventional means.
  • Recovered precious metals are converted into products. This may include the operations of separating, smelting and casting of each precious metal into bars or bullion.
  • Fig. 2 is a schematic diagram illustrating a second alternative representative embodiment of the invention, with dashed lines representing possible variations in the process and apparatus.
  • ore 30 preferably undergoes crushing 32 to facilitate exposure of precious metal values in the ore to processing solutions.
  • Crushed ore 34 then undergoes acid leaching 36 in aerobic reactor 37. If necessary, air 38 containing oxygen and carbon dioxide is added in the acid leaching step.
  • Acid-leach solution 40 is recirculated through the ore undergoing acid leaching by means of pump 42.
  • Acid-leached ore 44 then undergoes bisulfide leaching 46 in essentially completely- mixed, anaerobic reactor 47.
  • Bisulfide lixiviant 48 is recirculated through the ore undergoing bisulfide leaching by means of pump 50.
  • the pH of bisulfide lixiviant 48 is established at an optimum pH by pH controller 60 which controls the rate of addition of acid-leached ore 44 and acid-leach solution 40 to reactor 47 by means of valves 62 and 64.
  • the sulfate and/or the sulfide concentration in bisulfide lixiviant recirculation loop 76 is monitored by sensor/controller 82, which may comprise an ion-specific electrode.
  • Sensor/controller 82 is programmed to add up to a stoichiometric amount of electron donor 84, which is a sulfate-reducing bacteria growth substrate such as formate, acetate or methanol, to bisulfide lixiviant recirculation loop 76.
  • electron donor 84 which is a sulfate-reducing bacteria growth substrate such as formate, acetate or methanol
  • Pregnant bisulfide lixiviant 66 which contains precious metal values is subjected to gold and silver recovery 68. Recovered gold and silver is converted into products (e.g., bars of essentially pure metal).
  • Spent lixiviant 70 is returned to bisulfide lixiviant recirculation loop 76.
  • gold and silver recovery 68 is accomplished by passing pregnant bisulfide lixiviant 66 through activated carbon column 78.
  • Leached ore 80 undergoes dewatering 90 by conventional means, such as settling and/or vacuum filtration. Contained bisulfide lixiviant 92 is returned to bisulfide lixiviant recirculation loop 76. Waste ore 94 is disposed of by using conventional means.
  • acid-leach solution portion 96 undergoes base metal removal 98 in base metal removal reactor 100. Excess hydrogen sulfide gas 110 removed from anaerobic reactor 47 is introduced to base metal removal reactor 100 to precipitate iron and other base metals 104. Acid-leach solution portion 102 having a reduced base metal content may be returned to reactor 37, or optionally, to reactor 47.
  • excess hydrogen sulfide gas portion 112 undergoes sulfur recovery 114 in sulfur recovery reactor 116.
  • Recovery of element sulfur 120 may be accomplished by the conventional Claus process or by means of the process disclosed in U.S. Patent No. 4,666,852, which disclosure is incorporated herein as if fully set forth.
  • FIG. 3 is a schematic diagram illustrating a third alternative representative embodiment of the invention, with dashed lines representing possible variations in the process and apparatus.
  • sequential processing of heaps 200 and 202 of crushed ore 204 and 205 is accomplished.
  • heap 200 conventional bio-oxidation of crushed ore particles 200 is accomplished to free precious metals dispersed or occluded within the ore.
  • Air 206 may be introduced to heap 200 via plenum 208.
  • Acidic, base-metal sulfate leach solution 210 is collected from the bottom of heap 200 through plenum 208 by means of pump 212.
  • Portion 214 of leach solution is recirculated by means of pump 212 and distributor 216 to the top of heap 200.
  • bio-oxidation of heap 200 may include ore crushing, acid pretreatment, inoculation with appropriate sulfide-oxidizing bacteria, addition of nutrients, recirculating the biolixiviant and cooling the heap (for 3 to 8 days), and allowing the heap to "rest” (for 3 to 8 days). Additional process steps may include washing heap 200 for an extended period (e.g., 14 days) to remove residual acidity or iron content, and breaking heap 200 apart in order to agglomerate ore 202 with cement and/or lime to make a new heap, such as heap 202.
  • an extended period e.g. 14 days
  • Portion 220 of acidic, base-metal sulfate leach solution 210 produced by the bio- oxidation step is introduced to anaerobic, sulfate-reduction reactor 230.
  • reactor 230 is a side-stream reactor.
  • the rate of addition of portion 220 to reactor 230 may be controlled by pH controller 232 which operates valve 234 to create an optimum pH for precious metals leaching in bisulfide leach solution 238 produced by reactor 230.
  • non-toxic electron donor 240 such as formate, acetic acid (e.g., vinegar), acetate, or methanol- which does not bind effectively to activated carbon
  • anaerobic reactor 230 is added to anaerobic reactor 230 to enrich within reactor 230 a microbial culture comprising sulfate-reducing bacteria.
  • Anaerobic reactor 230 is preferably operated in a pH-stat mode by adding a sufficient portion 220 of acidic sulfate solution to maintain a neutral pH in reactor 230.
  • the concentration of dissolved sulfide (H,S, HS-, and S -2 ) in the anaerobic reactor is maintained below about 2,500 mg/1 to prevent inhibition of the microbial culture comprising sulfate-reducing bacteria.
  • base metals 244 (such as iron) are precipitated in
  • portion 252 of clarified bisulfide lixiviant 254 is recirculated to reactor 230.
  • the rate of recirculation of portion 252 is preferably chosen so that reactor 230 and settling tank 250 are operated together as a single, essentially completely-mixed reactor.
  • Headspace 260 of reactor 230 and headspace 262 of settling tank 250 are preferably connected by conduit 264.
  • Excess hydrogen sulfide gas (H 2 S) 266 produced in anaerobic reactor 230 e.g., that amount over about 2,700 mg/l
  • tank 250 is preferably removed.
  • excess hydrogen sulfide gas undergoes sulfur recovery 270 to produce elemental sulfur 272.
  • leaching solution 254 comprising bisulfide ions and a low concentration of dissolved and suspended base metals.
  • Bisulfide lixiviant 254 and headspace 260 comprise the reactor environment of reactor 230.
  • excess H 2 S gas produced in reactor 230 is removed from headspace 260 and/or headspace 262 by means of a H 2 S gas pump (not shown) and transferred into clarified bisulfide lixiviant 254 downstream from settling tank 250.
  • H 2 S gas pump not shown
  • concentrations of H 2 S (aq) and HS- in the lixiviant are increased after most of base metals 244 are removed from it.
  • heap 200 is undergoing bio-oxidation while a second heap 202, which has previously undergone bio-oxidation, undergoes leaching with bisulfide lixiviant.
  • oxidized ore 205 is preferably covered with cover 208 and submerged in bisulfide lixiviant 282 to exclude oxygen.
  • Heap 202 is leached by recirculating portion 292 of neutral bisulfide lixiviant 282 saturated with H 2 S through it by means of plenum 284, pump 286, and distributor 290.
  • the H 2 S partial pressure is increased by introducing the lixiviant [and/or H 2 S gas having a low concentration (less than 1,000 parts per million by volume) of H 2 gas] under pressure at the bottom of a heap via plenum 284 which is submerged in lixiviant 282, causing HS- ion concentrations to increase in direct proportion to the increase in H 2 S partial pressure.
  • This may increase the concentration of dissolved sulfide (H 2 S, HS-, and S -2 ) in heap 202 above 2,500 mg/l.
  • anaerobic reactor 230, settling tank 250, and heap 202 are operated together as a single, essentially completely- mixed reactor by recirculating portion 294, from heap 202, to reactor 230.
  • pressure sensors are placed at multiple points throughout the system for safety reasons. This provides a warning system for users of the system, since releases of H 2 S (g) can be toxic. Low pressures sound an alarm, indicating a leak somewhere, while high pressures indicate unsafe operation.
  • the use of multiple gauges pinpoints the source of the problem quickly.
  • the pressure gauges are also used to monitor and regulate the H 2 S (g) pressures to optimize the solubility of the gold and silver.
  • conductivity and total dissolved solids meters are placed in the effluent streams of the sulfate-reducing reactor in order to measure the ionic strength of the solvent.
  • the meters are used to monitor the ionic strength of the solvent, which controls the activity coefficients of the gold and silver complexes, H 2 S (aq) , HS-, and H 2(g) . Control of the activities of these compounds increases the efficiency of solubilizing the gold and silver.
  • Complexed gold and silver in pregnant portion 300 of lixiviant 282 is recovered continuously from the lixiviant solution in reactor 302. Recovery may be accomplished in a conventional manner by adsorption on activated carbon or by precipitation on zinc dust or by modifying either the solution pH, hydrogen fugacity, or oxidation-reduction potential (ORP). Metal that has been recovered from activated carbon eluent by electrowinning or zinc dust may be smelted to recover precious metal values as products such as jewelry or electronic system components. Barren lixiviant solution 306 is recycled to heap 202.
  • Working Example No. 1 Working Example No. 1
  • a chemostat having a working (liquid) volume of 5 liters and a headspace volume of 2.5 liters was operated at a dilution rte of 0.006 per hour for over 6 hydraulic detention times so that steady state conditions were achieved.
  • a sulfate-reducing bacteria growth medium comprising formate ions was pumped into the chemostat at a constant rate.
  • the pH of the liquid in the chemostat was maintained at 7.0 by means of a pH controller that added bio- oxidation process effluent (acidic metal sulfate solution) to the reactor as required.
  • H 2 S headspace H 2 S partial pressure of about 1 atmosphere. Achievement of this partial pressure of H 2 S was assured by purging the chemostat with a gas containing 99.5+ percent H 2 S at the beginning of the experiment.
  • the concentration of H 2 gas in the chemostat headspace before it was purged and in the gas used to purge the chemostat was measured by means of a gas chromatograph with a thermal conductivity detector.
  • the concentration of H 2 in the headspace was about 300 parts per million (ppm) by volume and the H 2 concentration in the purging gas was about 200 ppm.
  • the chemostat effluent contained about 200 mg/l of formate.
  • the effluent was discharged to a reservoir, the headspace of which was connected to the headspace of the chemostat.
  • a square of gold foil about 0.1 inch on a side and 0.025 inch thick was placed in a 160- milliliter (ml) serum bottle and a Teflon ® septum stopper was crimped on the bottle mouth.
  • the bottle was purged with oxygen-free nitrogen gas and 100 ml of chemostat effluent was transferred to the bottle without exposing it to air.
  • the contents of the bottle were then purged three times with the afore described H 2 S gas mixture at about 3-day intervals. Within four hours of the initial purging, the liquid in the bottle took on a bright yellow color. Testing of a six-ml sample of the liquid plus two ml of aqua regia revealed that the liquid contained about 0.3 mg/l of gold.
  • FIG. 4 is a schematic diagram illustrating a fourth alternative representative embodiment of the invention, with dashed lines representing possible variations in the process and apparatus.
  • Fig. 4 is a schematic diagram illustrating a fourth alternative representative embodiment of the invention, with dashed lines representing possible variations in the process and apparatus.
  • an experiment was conducted to illustrate the disclosed method and apparatus on low-grade samples of gold ore. Experimental procedures and results are presented below.
  • Bio-oxidation was accomplished in aerobic, stirred, batch reactor 312 having a working volume of 5 liters.
  • Batch reactor 312 was placed in a water bath (not shown) having a temperature of 35°C
  • About 1,000 grams of the ground ore was suspended in about 5 liters of an acidic Thiobacillus ferrooxidans medium in the reactor.
  • the acidic medium as described in ASTM Standard E 1357 contained the constituents shown in Table 5 and its pH was adjusted to pH 2 with concentrated sodium hydroxide (NaOH).
  • Air and carbon dioxide were introduced into the suspension by pumping air into it at a relatively high rate with air pump 314.
  • the suspension was inoculated with an active culture of Thiobacillus ferrooxidans, ATCC 13661, obtained from the American Type Culture Collection at the address given above.
  • the progress of bio-oxidation was monitored by measuring pH (with first pH monitor 318) and dissolved iron concentrations in the acidic medium.
  • a first representative portion of dried, bio- oxidized ore 324 was subjected to conventional cyanide extraction, and then assayed for gold content to provide a basis of comparison with the bisulfide extraction.
  • a leaching solution comprising dissolved hydrogen sulfide gas and bisulfide ions was produced in continuously stirred tank reactor (CSTR or chemostat) 326 having a working (liquid) volume of five liters and a headspace volume of 2.5 liters.
  • Chemostat 326 was placed in a water bath (not shown) having a temperature of 35°C. Chemostat 326 was started in a batch mode by placing a sulfate-reducing bacteria medium in the chemostat, inoculating the chemostat with wild sulfate-reducing bacteria and allowing the culture to acclimate for 5-7 days.
  • sulfate-reduction medium 328 containing the constituents shown in Table 6 and formate as a carbon source was pumped into reactor 326 by pump 330 at a rate that produced a dilution rate of about 0.005 per hour.
  • Liquid effluent was removed from the chemostat by pump 332 at the rate required to maintain the liquid level in the chemostat at a set level and discharged to effluent storage container 342. This dilution rate produced a mean cell residence time in the reactor that was much less than the maximum specific growth rate of the sulfate-reducing bacteria used to inoculate it.
  • Chemostat 326 was operated in a pH-stat mode at pH 7.0 by continuously monitoring the pH of the liquid in chemostat 326 with pH monitor/controller 336, and by intermittently pumping acidic supernatant 338 produced by the bio-oxidation step into chemostat 326 with pump 340.. Addition of acidic supernatant 338 to chemostat 326 increased the dilution rate to about 0.006 per hour.
  • the chemostat headspace was periodically purged with hydrogen sulfide from canister 334 to maintain positive pressure within the reactor. After chemostat 326 had been operating for about three hydraulic detention times and had reached steady state, the effluent from the reactor was used as solvent in leaching experiments.
  • Pyrex serum bottles 348 with a capacity of 160 ml were used as batch leaching reactors.
  • the reactors had previously been washed with aqua regia because Pyrex is known to adsorb gold complexes under certain conditions. Representative four-gram portions of the bio-oxidized ore were added to the reactors.
  • the reactors were augmented with 4 gram portions of prewashed 4-12 mesh activated carbon. Effluent collected from the chemostat was dispensed in 100 ml aliquots into the leaching reactors by pump 346.
  • the reactors were immediately capped, sealed, purged and pressurized to 1 atmosphere absolute with 99.5 percent pure hydrogen sulfide gas.
  • the reactors were then placed in both 35 and 65 °C incubators. The experiments were mixed by hand about two times daily and purged and pressurized with hydrogen sulfide gas at least every 48 hours.
  • the invention has utility as a means of extracting precious metals from ore that is being mined in situ or ex situ.
  • the invention can also be used to recover precious metals from scrap.

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Abstract

Procédé et appareil (4) d'extraction de métaux précieux de leurs minerais, et produit (26) ainsi obtenu. Un minerai oxydé contenant un métal précieux est exposé à une solution de lessivage (agent de lixiviation) (254), présentant une concentration (activité) relativement élevée de gaz d'acide sulfhydrique dissous, une concentration (activité) relativement élevée d'ions bisulfure, et une concentration relativement faible (fugacité) d'hydrogène gazeux dissous. Le gaz d'acide sulfhydrique et les ions bisulfure sont de préférence ajoutés à la solution au moyen de bactéries de réduction de sulfate croissant dans un milieu comprenant des ions sulfate et des ions nitrate dissous, mais des sources abiotiques peuvent également être utilisées. Des exemples de telles bactéries comprennent les espèces mésophiles d'eau douce telles que Desulfobacterium catecholicum DSM 3882, et Desulfovibrio simplex DSM 4141; les espèces mésophiles d'eau salée telles que Desulfovibrio salexigens DSM 2638; et les espèces thermophiles d'eau douce telles que Desulfomaculum kuznetsovii VKM B-1805.
PCT/US1995/009199 1994-06-24 1995-06-26 Procede et appareil d'extraction de metaux precieux WO1996000308A2 (fr)

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AU34899/95A AU700356B2 (en) 1994-06-24 1995-06-26 Method and apparatus for extracting precious metals from their ores and the product thereof
CA002194349A CA2194349C (fr) 1994-06-24 1995-06-26 Procede et appareil d'extraction de metaux precieux de leurs minerais, et produit ainsi obtenu

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US08/265,322 US5449397A (en) 1994-06-24 1994-06-24 Biocatalyzed leaching of precious metal values
US08/265,322 1994-06-24
US08/436,726 US5672194A (en) 1994-06-24 1995-05-08 Method and apparatus for extracting precious metals from their ores and the product thereof
US08/436,726 1995-05-08

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Cited By (7)

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Publication number Priority date Publication date Assignee Title
WO2008059439A1 (fr) * 2006-11-15 2008-05-22 University Of Cape Town Processus et appareil de sulfuration pour la récupération améliorée de minéraux à base de métaux précieux ou de métaux de base oxydés ou oxydés en surface
CN102719669A (zh) * 2012-07-06 2012-10-10 中国矿业大学(北京) 生物硫化剂硫化改性低品位氧化铜矿的工艺
RU2526511C2 (ru) * 2007-09-25 2014-08-20 Пасторал Гринхаус Гэз Рисерч Лтд Проникающие в клетку пептиды и полипептиды для клеток микроорганизмов
WO2018084723A2 (fr) 2016-11-03 2018-05-11 Mint Innovation Limited Procédé de récupération de métal
CN112375911A (zh) * 2020-11-02 2021-02-19 昆明理工大学 一种直接用活性炭回收（Au(S2O3)23-）的方法
US11591669B2 (en) 2016-10-31 2023-02-28 Mint Innovation Limited Metal recovery process
US11608544B2 (en) 2017-10-17 2023-03-21 Mint Innovation Limited Process for recovering metal from electronic waste

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US4822413A (en) * 1986-03-13 1989-04-18 Davy Mckee (Stockton) Limited Extraction of metal values from ores or concentrates
US4974816A (en) * 1986-02-07 1990-12-04 Envirotech Corporation Method and apparatus for biological processing of metal-containing ores
US5127942A (en) * 1990-09-21 1992-07-07 Newmont Mining Corporation Microbial consortium treatment of refractory precious metal ores

Patent Citations (3)

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US4974816A (en) * 1986-02-07 1990-12-04 Envirotech Corporation Method and apparatus for biological processing of metal-containing ores
US4822413A (en) * 1986-03-13 1989-04-18 Davy Mckee (Stockton) Limited Extraction of metal values from ores or concentrates
US5127942A (en) * 1990-09-21 1992-07-07 Newmont Mining Corporation Microbial consortium treatment of refractory precious metal ores

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008059439A1 (fr) * 2006-11-15 2008-05-22 University Of Cape Town Processus et appareil de sulfuration pour la récupération améliorée de minéraux à base de métaux précieux ou de métaux de base oxydés ou oxydés en surface
EA015581B1 (ru) * 2006-11-15 2011-10-31 Юниверсити Оф Кейптаун Способ обработки компонентсодержащего материала и устройство
US8883097B2 (en) 2006-11-15 2014-11-11 University Of Cape Town Sulfidisation process and apparatus for enhanced recovery of oxidised and surface oxidised base and precious metal minerals
RU2526511C2 (ru) * 2007-09-25 2014-08-20 Пасторал Гринхаус Гэз Рисерч Лтд Проникающие в клетку пептиды и полипептиды для клеток микроорганизмов
CN102719669A (zh) * 2012-07-06 2012-10-10 中国矿业大学(北京) 生物硫化剂硫化改性低品位氧化铜矿的工艺
US11591669B2 (en) 2016-10-31 2023-02-28 Mint Innovation Limited Metal recovery process
WO2018084723A2 (fr) 2016-11-03 2018-05-11 Mint Innovation Limited Procédé de récupération de métal
EP3535427A4 (fr) * 2016-11-03 2019-12-25 Mint Innovation Limited Procédé de récupération de métal
US11634788B2 (en) 2016-11-03 2023-04-25 Mint Innovation Limited Process for recovering metal
US11608544B2 (en) 2017-10-17 2023-03-21 Mint Innovation Limited Process for recovering metal from electronic waste
CN112375911A (zh) * 2020-11-02 2021-02-19 昆明理工大学 一种直接用活性炭回收（Au(S2O3)23-）的方法
CN112375911B (zh) * 2020-11-02 2022-07-05 昆明理工大学 一种直接用活性炭回收（Au(S2O3)23-）的方法

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CA2194349C (fr) 2006-05-30
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AU700356B2 (en) 1999-01-07
WO1996000308A3 (fr) 1996-02-15

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