US20170218478A1 - Gold recovery - Google Patents
Gold recovery Download PDFInfo
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- US20170218478A1 US20170218478A1 US15/487,107 US201715487107A US2017218478A1 US 20170218478 A1 US20170218478 A1 US 20170218478A1 US 201715487107 A US201715487107 A US 201715487107A US 2017218478 A1 US2017218478 A1 US 2017218478A1
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- gold
- vessel
- chlorine gas
- reaction vessel
- substrate
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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
- C22B11/00—Obtaining noble metals
- C22B11/06—Chloridising
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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
- C22B11/00—Obtaining noble metals
- C22B11/02—Obtaining noble metals by dry processes
- C22B11/021—Recovery of noble metals from waste materials
- C22B11/025—Recovery of noble metals from waste materials from manufactured products, e.g. from printed circuit boards, from photographic films, paper, or baths
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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
- C22B11/00—Obtaining noble metals
- C22B11/04—Obtaining noble metals by wet processes
- C22B11/042—Recovery of noble metals from waste materials
- C22B11/046—Recovery of noble metals from waste materials from manufactured products, e.g. from printed circuit boards, from photographic films, paper or baths
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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
- C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
- C22B7/001—Dry processes
- C22B7/002—Dry processes by treating with halogens, sulfur or compounds thereof; by carburising, by treating with hydrogen (hydriding)
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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
- C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
- C22B7/006—Wet processes
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/24—Halogens or compounds thereof
- C25B1/26—Chlorine; Compounds thereof
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- 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
- the present invention relates to a method of recovering gold from waste sources thereof, in particular waste electrical goods. Also disclosed herein is an apparatus for recovering gold from said waste sources.
- Gold is typically recovered from ores and other impure sources using cyanide, aqua regia or smelting. Such methods suffer from inter alia, toxicity issues, disposal costs and high energy input.
- U.S. Pat. No. 3,834,896 describes a process for recovering gold involving injecting chlorine into an aqueous slurry of carbonaceous ore at high temperature in the presence of iron, aluminium or gallium promoters.
- U.S. Pat. No. 4,723,998 discloses a two-step process for extracting gold from carbonaceous or metal oxide based ores.
- the process comprises using chlorine to dissolve the gold from the ores and subsequently absorbing the gold on to ion exchange resins.
- U.S. Pat. No. 3,495,976 communicates a method of recovering gold that has been plated or coated on to non-ferrous metals such as tungsten, molybdenum, or copper.
- the gold plated material is treated with an aqueous solution of potassium iodide and dissolved iodine.
- the gold is recovered by adding conc. sulphuric acid and distilling of the iodine. When all the iodine has been removed, the gold is separated from the remaining solution as a powder.
- U.S. Pat. No. 3,957,505 discloses a process for extracting gold from gold bearing material comprising: treating the gold bearing material in an aqueous solution consisting essentially of iodine and a water soluble iodide salt to dissolve gold from said gold bearing material; mixing a reducing agent with said aqueous solution to reduce dissolved gold iodide salts to gold metal and precipitate said gold metal in substantially pure form from said aqueous solution. The precipitated gold metal is removed from the aqueous solution. An oxidizing agent is subsequently added to the aqueous solution to restore the solution to substantially its original condition for dissolving gold from further gold bearing material.
- G.B. Patent No. 20471 discloses a method of extracting gold from ores thereof.
- the method discloses utilising an undivided electrolytic cell to generate a leaching material. Once the gold has been leached from the ore it is subsequently electrodeposited on the cathode. This method suffers in that the cathode has to be removed from the electrochemical cell to recover the gold and the cell will have to be cleaned out regularly to remove unwanted sludge, salts and other contaminants.
- gaseous chlorine as used in the present invention can circulate freely and penetrate into small nooks and crannies of the electronic scrap to leach and dissolve the surface gold.
- Much smaller volumes of water can be used to merely moisten the surfaces to facilitate reaction.
- a further object of the present invention is to provide for a gold recovery process that affords an aqueous solution of gold withoutenvironmently unfriendly process or treatment chemicals, used to produce the leaching material.
- Another object of the present invention further is to provide for a method and apparatus in which the chlorine gas is generated externally to a reactor vessel and subsequently pumped into the reactor vessel comprising the waste gold materials.
- the present invention provides for a method of extracting gold from waste substrates or sources comprising gold, the method comprising the step of:
- the vessel comprising a vessel inlet through which the chlorine gas is delivered and a vessel outlet,
- the chlorine gas, substrate comprising gold and moisture present in the vessel interact to provide a gold solution which may be recovered from the vessel via the vessel outlet.
- the gold solution may flow directly into the vessel outlet.
- the gold solution may be actively forced into the vessel outlet.
- the substrate comprising gold is a waste source.
- the waste source is decommissioned or scrap electrical goods or electrical goods which are being recycled.
- the substrate comprising gold may be a substrate on to which the gold is plated or coated.
- the substrate may be a metal, plastic or ceramic material on which gold has been plated or coated.
- the substrate comprising gold may be a metal or metal alloy substrate on to which gold is plated or coated. Suitable metals include ferrous and non-ferrous metals.
- the metal substrate on to which gold is plated or coated may be selected from the group consisting of nickel, copper, and alloys thereof.
- the substrate comprising gold comprises waste electronic materials, for example printed circuit boards. From an environmental perspective it is highly advantageous to efficiently recycle gold from waste electronic materials.
- water vapour or moisture may be charged into the vessel by any means known to a person skilled in the art.
- the substrate comprising gold may be sprayed with water prior to being placed in the vessel.
- moisture is pumped into the vessel as a fine water mist, spray or steam to create a moist atmosphere.
- the presence of steam may also speed up the gold extraction process.
- the vessel may further comprise a water inlet for pumping said spray, steam, or mist into the vessel.
- gold can be recovered in a low volume solution free of any additives. Furthermore, once the gold has been recovered from the solution the resultant waste liquid that must be treated before final discharge is low in volume. Consequently, costs are reduced.
- PCBs scrap printed circuit boards
- the method of the present invention avoids toxic materials such as cyanide solutions.
- Prior art processes for gold recovery are based on leaching and have utilised aqueous environments in which gold containing substrates are submerged in an aqueous solution in an aqueous leaching bath.
- the lower water volumes associated with the method of the present invention allow for vessels of smaller volume to be used than prior art gold recovery methods.
- the method of the present invention can be industrially scaled up without having to provide excessively large vessels to hold the waste gold materials, and water. The vessel must simply be large enough to hold the waste gold material. Thus, costs involved in setting up and maintaining the process are lower.
- the process of the present invention uses much lower water volumes than prior art processes, effluent treatment costs are minimised.
- the lower water volumes also enables better control of the gold leaching process. Initially the gold concentration in the outlet stream would be high but would decrease towards zero when all the gold is leached. When it is apparent that all the gold has been leached off, either by visual inspection or by measurement of the gold content in the reactor outlet stream, it is easy to quench the reaction by purging the reactor vessel of chlorine gas by passing air or another gas through the vessel. This minimises leaching of other substrate metals such as copper, nickel etc. Such almost instant quenching is not possible with an aqueous leaching bath.
- the method of the present invention also provides for gaseous inter-halogen compounds being delivered in to the vessel along with the chlorine gas through the vessel inlet.
- inter-halogen compounds is used to refer to gaseous materials comprising two distinct halogen atoms.
- compounds such as iodine chloride (ICl) and bromide chloride (BrCl).
- ICl iodine chloride
- BrCl bromide chloride
- the presence of inter-halogen compounds has been shown to increase the efficiency of the leaching/recovery process relative to chlorine on its own.
- the inter-halogen compounds may be introduced by doping the chlorine gas with amounts of elemental iodine or bromine, or they may be produced electrolytically, vide infra.
- the chlorine gas may be prepared in an electrolytic cell external to the vessel.
- the chlorine can be prepared in the electrolytic cell and delivered into the vessel, upon preparation, to provide a constant stream of chlorine into the vessel.
- the electrolytic cell may be a divided electrolytic cell, i.e. the anode electrolyte and cathode electrolyte are separated from one another.
- the electrolyte used for chlorine preparation can be of optimum purity and concentration.
- the gold leaching step can be performed without the build-up of salts and contaminants from the electrolytic process.
- the chlorine gas prepared by the electrolytic cell may be delivered along a conduit to the vessel inlet.
- the gaseous inter-halogen compounds may be prepared in the electrolytic cell and may be deliverable along the conduit to the vessel.
- Inter-halogen compounds may be generated by adding amounts of bromide salts, for example NaBr, and iodide salts, for example, NaI, to the electrolyte.
- the conduit is manufactured from a material that is incapable of being corroded by chlorine gas.
- the method of the present invention may further comprise a quenching process such that when water exiting the vessel via the vessel outlet no longer comprises gold the process can be shut down quickly.
- a sensor may be utilised to detect the presence of gold in water exiting, the vessel via the vessel outlet.
- the quenching process may comprise cutting off the supply of chlorine gas to the vessel and flushing the vessel with inert gas prior to discharge of the vessel.
- inert gas is used to represent a non-toxic, non-reactive gas.
- the inert gas may be selected from the group consisting of air, nitrogen, argon and combinations thereof.
- the current to the electrolytic cell can be switched off to halt the production of chlorine.
- the vessel can be flushed with air, or another non-reactive, inert gas such as nitrogen or argon to purge it of any residual chlorine gas.
- the scrap materials can be unloaded from the vessel, and the vessel can be charged with new waste materials to recommence the process again.
- the gold solution which exits the vessel via the vessel outlet may be further treated to recover solid gold metal from the gold solution.
- the skilled person will be familiar with a number of different methods of reducing the gold solution to gold metal.
- the gold solution may be treated with reducing agents such as sulphur dioxide gas, hydroxylamine, hydrazine, hydrogen peroxide.
- the gold solution may be refined electrochemically, for example by electrowinning or electroplating.
- reducing agents such as sulphur dioxide gas, hydroxylamine, hydrazine, hydrogen peroxide.
- the gold solution may be refined electrochemically, for example by electrowinning or electroplating.
- a number of different methods of reducing a gold solution to provide gold metal are disclosed in U.S. Pat. No. 3,957,505.
- the process of the invention operates at ambient or slightly above ambient temperatures whereas some prior art processes for gold recovery require temperatures of between 200 and 800° C. to volatilise gold chloride, thus requiring a high and therefore expensive energy input.
- the reaction of the invention will proceed more rapidly at higher temperatures. Temperatures from ambient to 70° C. give good results but
- the present invention provides for an apparatus for extracting gold from a substrate comprising gold, the apparatus comprising:
- reaction vessel configured to receive the substrate comprising gold, the reaction vessel comprising a vessel inlet, through which chlorine gas is delivered into the reaction vessel and a vessel outlet,
- a water inlet adapted to deliver water spray, steam, or mist into the vessel
- a source of chlorine gas in fluid communication with the vessel;
- the substrate comprising gold, chlorine gas and moisture present in the vessel interact to provide a gold solution which may be recovered from the vessel via the vessel outlet.
- a conduit may extend from the vessel inlet to the source of chlorine gas to establish fluid communication therebetween.
- the conduit is manufactured from a material that is incapable of being corroded by chlorine gas.
- the substrate comprising gold may be a substrate on to which the gold is plated or coated.
- the substrate may be a metal, plastic or ceramic material on which gold has been plated or coated.
- the substrate comprising gold may be a metal or metal alloy substrate on to which gold is plated or coated. Suitable metals include ferrous and non-ferrous metals.
- the metal substrate on to which gold is plated or coated may be selected from the group consisting of nickel, copper, and alloys thereof.
- the substrate comprising gold comprises waste electronic materials, for example printed circuit boards. From an environmental perspective it is highly advantageous to efficiently recycle gold from waste electronic materials.
- moisture may be charged into the vessel by any means known to a person skilled in the art.
- the substrate comprising gold may be sprayed with water prior to being placed in the vessel.
- moisture is pumped into the vessel as a fine water mist, spray, or steam.
- the vessel may further comprise a water inlet for pumping said spray, steam, or mist into the vessel.
- the presence of steam may also speed up the gold extraction process
- the source of chlorine gas may be an electrolytic cell disposed external to the vessel.
- the chlorine can be prepared in the electrolytic cell and delivered into the vessel, upon preparation, to provide a constant stream of chlorine into the vessel.
- the electrolytic cell may be a divided electrolytic cell, i.e. the anode electrolyte and cathode electrolyte are separated from one another.
- the build-up of chlorine gas in the electrolytic cell may generate sufficient pressure to urge the chlorine gas from the electrolytic cell along the conduit and into the vessel.
- the apparatus of the present invention may further comprise an urging means for urging chlorine gas from the source of chlorine gas along the conduit and in to the reaction vessel.
- the urging means may be a pump.
- the source of chlorine in the apparatus of the present invention may further comprise a source of inter-halogen compounds.
- a source of inter-halogen compounds for example, compounds such as iodine chloride (ICl) and bromide chloride, BrCl.
- ICl iodine chloride
- BrCl bromide chloride
- the presence of inter-halogen compounds has been shown to increase the efficiency of the process relative to chlorine on its own.
- the gaseous inter-halogen compounds may be prepared in the electrolytic cell.
- Inter-halogen compounds may be generated by adding amounts of bromide salts, for example NaBr, and iodide salts, for example, Nal, to the electrolyte.
- the vessel of the apparatus of the present invention may further comprise an inlet for flushing the vessel with an inert gas prior to discharge of the vessel.
- the inert gas may be selected from the group consisting of air, nitrogen, argon and combinations thereof.
- the apparatus of the present invention may further comprise a collector for the gold solution.
- FIG. 1 illustrates an apparatus for carrying out the gold recovery method of the present invention.
- FIG. 1 illustrates an embodiment of the present invention.
- An electrolytic cell 101 is disposed external to a (reactor) vessel 102 , the latter being charged with substrates comprising gold 103 .
- the substrates comprising gold 103 may be waste electrical goods, for example printed circuit boards, in which gold is plated or coated onto another material such as copper or nickel.
- a conduit 104 allows for fluid communication between the vessel 102 and the electrolytic cell 101 .
- the conduit 104 will be manufactured from a material that is incapable of being corroded by chlorine gas.
- the electrolytic cell 101 is a divided cell having an anode chamber 105 and cathode chamber 106 .
- a membrane 107 divides the anode 108 and cathode 109 .
- a pump 110 feeds the anode electrolyte or anolyte 111 to the anode 108 .
- the anode electrolyte 111 primarily consists of chloride salts, such as NaCl or KCl. However, the anode electrolyte 109 may also comprise small amounts of bromide and iodide salts, e.g. NaBr, NaI, KBr or KI to provide a source of inter-halogen compounds.
- a flow meter 112 regulates the flow of chlorine gas produced at the anode away from the anode 108 .
- a second pump 113 feeds the cathode electrolyte or catholyte 114 to the cathode 109 .
- the cathode electrolyte 114 is a NaOH or KOH solution.
- a flow meter 115 regulates the flow of hydrogen gas produced at the cathode away from the cathode 109 .
- An outlet 116 provides an exhaust for hydrogen gas generated during the electrolytic process.
- the vessel 102 has a chlorine gas inlet 117 and a water inlet 118 . Water is fed to the water inlet 118 through conduit 119 . An outlet 120 provides an exit for an aqueous solution of recovered gold. The gold solution travels along conduit 121 to a collection flask or container (not shown).
- Conduit 122 provides an outlet for any excess chlorine gas.
- the NaCl electrolyte 111 delivered to the anode 108 is oxidised to yield chlorine gas:
- inter-halogen compounds BrCl and ICl.
- the presence of these compounds improves the efficiency of the chlorine leaching process.
- the inter-halogen compounds may be formed by reaction of halogens in elemental form as follows:
- the membrane 107 prevents the analyte and the catholyte mixing, and it stops the chlorine forming at the anode 108 from mixing with the sodium hydroxide and the hydrogen formed at the cathode.
- the hydrogen gas generated as a by-product of the electrolytic process exits the cell via outlet 116 .
- Chlorine gas generated at the anode 108 flows into the conduit 104 and into the vessel 102 via vessel inlet 117 .
- Water is introduced into the vessel 102 through water inlet 118 from water conduit 119 .
- Water inlet 118 may comprise a nozzle to pump the water in as a fine mist, spray, or steam.
- a fine water mist, spray or steam the final volume of the gold solution is vastly reduced compared to prior art methods of gold recovery.
- a low volume solution is cheaper to treat prior to discharging it as effluent.
- the chlorine gas (and any inter-halogen compounds present), gold and water react to afford an aqueous solution of gold recovered from the waste materials.
- the aqueous gold solution exits the vessel through outlet 120 and passes along conduit 121 to a collection flask/container.
- the gold solution which exits the vessel via the vessel outlet 120 may be further treated to recover solid gold metal from the gold solution.
- the skilled person will be familiar with a number of different methods of reducing the gold solution to gold metal.
- the gold solution may be treated with reducing agents such as sulphur dioxide gas, hydroxylamine, hydrazine, hydrogen peroxide.
- the gold solution may be refined electrochemically, for example by electrowinning or electroplating.
- a number of different methods of reducing a gold solution to provide gold metal are disclosed in U.S. Pat. No. 3,857,505.
- Conduit 121 may internally house a gold sensor or detector.
- a gold sensor or detector When solution exiting the vessel 102 through outlet 120 no longer contains any gold, current to the electrolytic cell 101 can be stopped to halt chlorine production.
- the vessel 102 can be flushed with a non-reactive gas such as air, nitrogen or argon to expel any residual chlorine gas and the now gold depleted waste electronic materials 103 can be discharged from the vessel 102 to be replaced by new materials,
- a reiteration of the process can be easily commenced by recharging the vessel 102 with new waste electronic materials 103 .
Abstract
The cost of precious metals, such as gold, makes recovery or recycling of these materials economically viable and desirable. Disclosed herein is a method of recovering gold from waste sources thereof, in particular waste electrical goods. Also disclosed herein is an apparatus for recovering gold from said waste sources. In particular, disclosed herein is a method and apparatus in which gold leaching chlorine gas is generated externally to a reactor vessel and subsequently pumped into the reactor vessel comprising the waste gold materials.
Description
- The present invention relates to a method of recovering gold from waste sources thereof, in particular waste electrical goods. Also disclosed herein is an apparatus for recovering gold from said waste sources.
- The cost of precious metals, such as gold, makes recovery or recycling of these materials economically viable and desirable. Gold is typically recovered from ores and other impure sources using cyanide, aqua regia or smelting. Such methods suffer from inter alia, toxicity issues, disposal costs and high energy input.
- Prior art patents addressing the problem of improving efficiency in gold extraction and recovery are numerous. For example, U.S. Pat. No. 3,834,896 describes a process for recovering gold involving injecting chlorine into an aqueous slurry of carbonaceous ore at high temperature in the presence of iron, aluminium or gallium promoters.
- U.S. Pat. No. 4,723,998 discloses a two-step process for extracting gold from carbonaceous or metal oxide based ores. The process comprises using chlorine to dissolve the gold from the ores and subsequently absorbing the gold on to ion exchange resins.
- U.S. Pat. No. 3,495,976 communicates a method of recovering gold that has been plated or coated on to non-ferrous metals such as tungsten, molybdenum, or copper. The gold plated material is treated with an aqueous solution of potassium iodide and dissolved iodine. The gold is recovered by adding conc. sulphuric acid and distilling of the iodine. When all the iodine has been removed, the gold is separated from the remaining solution as a powder.
- U.S. Pat. No. 3,957,505 discloses a process for extracting gold from gold bearing material comprising: treating the gold bearing material in an aqueous solution consisting essentially of iodine and a water soluble iodide salt to dissolve gold from said gold bearing material; mixing a reducing agent with said aqueous solution to reduce dissolved gold iodide salts to gold metal and precipitate said gold metal in substantially pure form from said aqueous solution. The precipitated gold metal is removed from the aqueous solution. An oxidizing agent is subsequently added to the aqueous solution to restore the solution to substantially its original condition for dissolving gold from further gold bearing material.
- G.B. Patent No. 20471 discloses a method of extracting gold from ores thereof. The method discloses utilising an undivided electrolytic cell to generate a leaching material. Once the gold has been leached from the ore it is subsequently electrodeposited on the cathode. This method suffers in that the cathode has to be removed from the electrochemical cell to recover the gold and the cell will have to be cleaned out regularly to remove unwanted sludge, salts and other contaminants.
- Hoffmann, JOM, Springer N.Y., vol 44, no. 7 p 43-48 describes methods for recovering precious metals from electronic scrap involving slurrying the scrap in water and sparging chlorine gas into the slurry. WO 01/83835 A2 describes a gold recovery process in which gold scrap is mixed with water and hydrocloric acid and chlorine gas is blown into the reactor, to dissolve the gold. Both methods use large amounts of water.
- In gold leaching, using for example cyanide, it is essential to carry out the reaction in an aqueous system to facilitate ionisation of the sodium cyanide used to cyanide ions. Waste electronic scrap contains irregularly shaped pieces and will take up more volume than it would if compacted. But if compacted the leachant solution could not act on all the surfaces.
- As an example, 382 grams of computer connector slots occupied a volume of 1000 cm3 in a beaker. To fill the same beaker to the 1000 cm3 mark required an additional volume of 770 cm3 of water. Based on these figures, 1 tonne of waste electronic scrap would occupy a volume of approximately 2.6 m3 and would require a volume of 2 m3 leachant to fill the container. In practical terms a larger tank with a larger volume of leachant would be needed to allow for agitation.
- In contrast, gaseous chlorine as used in the present invention can circulate freely and penetrate into small nooks and crannies of the electronic scrap to leach and dissolve the surface gold. Much smaller volumes of water can be used to merely moisten the surfaces to facilitate reaction.
- Notwithstanding the state of the art there remains a need for alternative methods for recovering gold that mitigate some or all of the above mentioned problems.
- It is an object of the present invention to provide for a method and apparatus for recovering gold from waste sources thereof, in particular, waste electronic materials.
- It is further object of the present invention to allow for the recovery of gold in solutions of small volume. Consequently, consumption of resources, such as water is minimal.
- A further object of the present invention is to provide for a gold recovery process that affords an aqueous solution of gold withoutenvironmently unfriendly process or treatment chemicals, used to produce the leaching material.
- Another object of the present invention further is to provide for a method and apparatus in which the chlorine gas is generated externally to a reactor vessel and subsequently pumped into the reactor vessel comprising the waste gold materials.
- In a first aspect the present invention provides for a method of extracting gold from waste substrates or sources comprising gold, the method comprising the step of:
- delivering chlorine gas to a vessel containing the substrate comprising gold, the vessel comprising a vessel inlet through which the chlorine gas is delivered and a vessel outlet,
- delivering water vapour to the vessel, such that
- the chlorine gas, substrate comprising gold and moisture present in the vessel interact to provide a gold solution which may be recovered from the vessel via the vessel outlet.
- The gold solution may flow directly into the vessel outlet. Alternatively, the gold solution may be actively forced into the vessel outlet.
- The substrate comprising gold is a waste source. In particular the waste source is decommissioned or scrap electrical goods or electrical goods which are being recycled.
- The substrate comprising gold may be a substrate on to which the gold is plated or coated. For example, the substrate may be a metal, plastic or ceramic material on which gold has been plated or coated. For example, the substrate comprising gold may be a metal or metal alloy substrate on to which gold is plated or coated. Suitable metals include ferrous and non-ferrous metals. For example, the metal substrate on to which gold is plated or coated may be selected from the group consisting of nickel, copper, and alloys thereof.
- In one particular embodiment, the substrate comprising gold comprises waste electronic materials, for example printed circuit boards. From an environmental perspective it is highly advantageous to efficiently recycle gold from waste electronic materials.
- With reference to the method of the present invention, water vapour or moisture may be charged into the vessel by any means known to a person skilled in the art. For example, the substrate comprising gold may be sprayed with water prior to being placed in the vessel. In a preferred embodiment, moisture is pumped into the vessel as a fine water mist, spray or steam to create a moist atmosphere. Advantageously, the presence of steam may also speed up the gold extraction process. In order to pump moisture into the vessel it may further comprise a water inlet for pumping said spray, steam, or mist into the vessel.
- Advantageously, by providing a source of chlorine that is external to the vessel and delivering the chlorine into the vessel, small volumes of water can be utilised to recover the gold. Where chlorine generation and gold recovery occurring the same vessel lame volumes of water and additives are required.
- Accordingly, using the method of the present invention gold can be recovered in a low volume solution free of any additives. Furthermore, once the gold has been recovered from the solution the resultant waste liquid that must be treated before final discharge is low in volume. Consequently, costs are reduced.
- The absence of dissolved chemicals and additives in the water fed into the vessel also greatly reduces the costs associated with treating the water prior to discharge.
- For example, approximately 2000 L of prior art cyanide leaching solution would be required to recover gold from a cubic metre of scrap printed circuit boards (PCBs). Using the method of the present invention, gold could be recovered from the same quantity of PCBs with 200 L of water.
- Naturally, the costs associated with treating and handling 2000 L of cyanide solution prior to discharge are considerable. Such large volumes of a potentially toxic material are undesirable in any industrial process. Advantageously, the method of the present invention avoids toxic materials such as cyanide solutions.
- Prior art processes for gold recovery are based on leaching and have utilised aqueous environments in which gold containing substrates are submerged in an aqueous solution in an aqueous leaching bath. Advantageously, the lower water volumes associated with the method of the present invention allow for vessels of smaller volume to be used than prior art gold recovery methods. The method of the present invention can be industrially scaled up without having to provide excessively large vessels to hold the waste gold materials, and water. The vessel must simply be large enough to hold the waste gold material. Thus, costs involved in setting up and maintaining the process are lower.
- Since the process of the present invention uses much lower water volumes than prior art processes, effluent treatment costs are minimised. The lower water volumes also enables better control of the gold leaching process. Initially the gold concentration in the outlet stream would be high but would decrease towards zero when all the gold is leached. When it is apparent that all the gold has been leached off, either by visual inspection or by measurement of the gold content in the reactor outlet stream, it is easy to quench the reaction by purging the reactor vessel of chlorine gas by passing air or another gas through the vessel. This minimises leaching of other substrate metals such as copper, nickel etc. Such almost instant quenching is not possible with an aqueous leaching bath.
- The method of the present invention also provides for gaseous inter-halogen compounds being delivered in to the vessel along with the chlorine gas through the vessel inlet. As used herein, the term inter-halogen compounds is used to refer to gaseous materials comprising two distinct halogen atoms. For example, compounds such as iodine chloride (ICl) and bromide chloride (BrCl). Advantageously, the presence of inter-halogen compounds has been shown to increase the efficiency of the leaching/recovery process relative to chlorine on its own. The inter-halogen compounds may be introduced by doping the chlorine gas with amounts of elemental iodine or bromine, or they may be produced electrolytically, vide infra.
- With reference to the method of the present invention, the chlorine gas may be prepared in an electrolytic cell external to the vessel. For example, the chlorine can be prepared in the electrolytic cell and delivered into the vessel, upon preparation, to provide a constant stream of chlorine into the vessel. The electrolytic cell may be a divided electrolytic cell, i.e. the anode electrolyte and cathode electrolyte are separated from one another.
- Advantageously, by separating the chlorine preparation step from the gold leaching step in the vessel, the electrolyte used for chlorine preparation can be of optimum purity and concentration. Moreover, the gold leaching step can be performed without the build-up of salts and contaminants from the electrolytic process.
- The chlorine gas prepared by the electrolytic cell may be delivered along a conduit to the vessel inlet. Furthermore, the gaseous inter-halogen compounds may be prepared in the electrolytic cell and may be deliverable along the conduit to the vessel. Inter-halogen compounds may be generated by adding amounts of bromide salts, for example NaBr, and iodide salts, for example, NaI, to the electrolyte.
- Suitably, the conduit is manufactured from a material that is incapable of being corroded by chlorine gas.
- The method of the present invention may further comprise a quenching process such that when water exiting the vessel via the vessel outlet no longer comprises gold the process can be shut down quickly.
- A sensor may be utilised to detect the presence of gold in water exiting, the vessel via the vessel outlet.
- The quenching process may comprise cutting off the supply of chlorine gas to the vessel and flushing the vessel with inert gas prior to discharge of the vessel. As used herein, the term inert gas is used to represent a non-toxic, non-reactive gas. For example, the inert gas may be selected from the group consisting of air, nitrogen, argon and combinations thereof.
- For example, the current to the electrolytic cell can be switched off to halt the production of chlorine. The vessel can be flushed with air, or another non-reactive, inert gas such as nitrogen or argon to purge it of any residual chlorine gas. The scrap materials can be unloaded from the vessel, and the vessel can be charged with new waste materials to recommence the process again.
- The gold solution which exits the vessel via the vessel outlet may be further treated to recover solid gold metal from the gold solution.
- The skilled person will be familiar with a number of different methods of reducing the gold solution to gold metal. For example, the gold solution may be treated with reducing agents such as sulphur dioxide gas, hydroxylamine, hydrazine, hydrogen peroxide. Alternatively, the gold solution may be refined electrochemically, for example by electrowinning or electroplating. A number of different methods of reducing a gold solution to provide gold metal are disclosed in U.S. Pat. No. 3,957,505. Advantageously, the process of the invention operates at ambient or slightly above ambient temperatures whereas some prior art processes for gold recovery require temperatures of between 200 and 800° C. to volatilise gold chloride, thus requiring a high and therefore expensive energy input. The reaction of the invention will proceed more rapidly at higher temperatures. Temperatures from ambient to 70° C. give good results but the use of higher temperatures are not excluded, subject to practical problems involved with higher pressures at higher temperatures.
- In a further aspect, the present invention provides for an apparatus for extracting gold from a substrate comprising gold, the apparatus comprising:
- a reaction vessel configured to receive the substrate comprising gold, the reaction vessel comprising a vessel inlet, through which chlorine gas is delivered into the reaction vessel and a vessel outlet,
- a water inlet adapted to deliver water spray, steam, or mist into the vessel; and
- a source of chlorine gas in fluid communication with the vessel; such that
- the substrate comprising gold, chlorine gas and moisture present in the vessel interact to provide a gold solution which may be recovered from the vessel via the vessel outlet.
- In one embodiment a conduit may extend from the vessel inlet to the source of chlorine gas to establish fluid communication therebetween.
- Suitably, the conduit is manufactured from a material that is incapable of being corroded by chlorine gas.
- With reference to the apparatus of the present invention the substrate comprising gold may be a substrate on to which the gold is plated or coated. For example, the substrate may be a metal, plastic or ceramic material on which gold has been plated or coated. For example, the substrate comprising gold may be a metal or metal alloy substrate on to which gold is plated or coated. Suitable metals include ferrous and non-ferrous metals. For example, the metal substrate on to which gold is plated or coated may be selected from the group consisting of nickel, copper, and alloys thereof.
- In one particular embodiment, the substrate comprising gold comprises waste electronic materials, for example printed circuit boards. From an environmental perspective it is highly advantageous to efficiently recycle gold from waste electronic materials.
- With reference to the apparatus of the present invention, moisture may be charged into the vessel by any means known to a person skilled in the art. For example, the substrate comprising gold may be sprayed with water prior to being placed in the vessel. In a preferred embodiment, moisture is pumped into the vessel as a fine water mist, spray, or steam. The vessel may further comprise a water inlet for pumping said spray, steam, or mist into the vessel. Advantageously, the presence of steam may also speed up the gold extraction process
- With reference to the apparatus of the present invention, the source of chlorine gas may be an electrolytic cell disposed external to the vessel. For example, the chlorine can be prepared in the electrolytic cell and delivered into the vessel, upon preparation, to provide a constant stream of chlorine into the vessel. The electrolytic cell may be a divided electrolytic cell, i.e. the anode electrolyte and cathode electrolyte are separated from one another.
- The build-up of chlorine gas in the electrolytic cell may generate sufficient pressure to urge the chlorine gas from the electrolytic cell along the conduit and into the vessel.
- The apparatus of the present invention may further comprise an urging means for urging chlorine gas from the source of chlorine gas along the conduit and in to the reaction vessel. The urging means may be a pump.
- The source of chlorine in the apparatus of the present invention may further comprise a source of inter-halogen compounds. For example, compounds such as iodine chloride (ICl) and bromide chloride, BrCl. Advantageously, the presence of inter-halogen compounds has been shown to increase the efficiency of the process relative to chlorine on its own.
- The gaseous inter-halogen compounds may be prepared in the electrolytic cell. Inter-halogen compounds may be generated by adding amounts of bromide salts, for example NaBr, and iodide salts, for example, Nal, to the electrolyte.
- The vessel of the apparatus of the present invention may further comprise an inlet for flushing the vessel with an inert gas prior to discharge of the vessel. The inert gas may be selected from the group consisting of air, nitrogen, argon and combinations thereof.
- The apparatus of the present invention may further comprise a collector for the gold solution.
- Where suitable, it will be appreciated that all optional and/or preferred features of one embodiment of the invention may be combined with optional and/or preferred features of another/other embodiment(s) of the invention.
- Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the invention and from the drawings in which:
-
FIG. 1 illustrates an apparatus for carrying out the gold recovery method of the present invention. - It should be readily apparent to one of ordinary skill in the art that the examples disclosed herein below represent generalised examples only, and that other arrangements and methods capable of reproducing the invention are possible and are embraced by the present invention.
-
FIG. 1 illustrates an embodiment of the present invention. Anelectrolytic cell 101 is disposed external to a (reactor)vessel 102, the latter being charged withsubstrates comprising gold 103. By way of example, thesubstrates comprising gold 103 may be waste electrical goods, for example printed circuit boards, in which gold is plated or coated onto another material such as copper or nickel. Aconduit 104 allows for fluid communication between thevessel 102 and theelectrolytic cell 101. Naturally, theconduit 104 will be manufactured from a material that is incapable of being corroded by chlorine gas. - The
electrolytic cell 101 is a divided cell having ananode chamber 105 andcathode chamber 106. Amembrane 107 divides theanode 108 andcathode 109. Apump 110 feeds the anode electrolyte oranolyte 111 to theanode 108. Theanode electrolyte 111 primarily consists of chloride salts, such as NaCl or KCl. However, theanode electrolyte 109 may also comprise small amounts of bromide and iodide salts, e.g. NaBr, NaI, KBr or KI to provide a source of inter-halogen compounds. Aflow meter 112 regulates the flow of chlorine gas produced at the anode away from theanode 108. - A
second pump 113 feeds the cathode electrolyte orcatholyte 114 to thecathode 109. Typically, thecathode electrolyte 114 is a NaOH or KOH solution. Aflow meter 115 regulates the flow of hydrogen gas produced at the cathode away from thecathode 109. Anoutlet 116 provides an exhaust for hydrogen gas generated during the electrolytic process. - In the embodiment shown, the
vessel 102 has achlorine gas inlet 117 and awater inlet 118. Water is fed to thewater inlet 118 throughconduit 119. Anoutlet 120 provides an exit for an aqueous solution of recovered gold. The gold solution travels alongconduit 121 to a collection flask or container (not shown). -
Conduit 122 provides an outlet for any excess chlorine gas. - In use, the
NaCl electrolyte 111 delivered to theanode 108 is oxidised to yield chlorine gas: -
2NaCl→Cl2+2Na++2e− - As indicated supra, the presence of chloride and bromide salts, such as NaBr and NaI can result in the formation of gaseous inter-halogen compounds BrCl and ICl. The presence of these compounds improves the efficiency of the chlorine leaching process. The inter-halogen compounds may be formed by reaction of halogens in elemental form as follows:
-
2NaBr→Br2+2Na++2e− -
2NaI→I2+2Na++2e− -
I2+Cl2→2ICl -
Br2+Cl2→2BrCl - At the
cathode 109, hydrogen gas is generated from theelectrolyte 114 according to the following equation: -
2H2O+2e−→H2+2OH− - The
membrane 107 prevents the analyte and the catholyte mixing, and it stops the chlorine forming at theanode 108 from mixing with the sodium hydroxide and the hydrogen formed at the cathode. The hydrogen gas generated as a by-product of the electrolytic process exits the cell viaoutlet 116. - Chlorine gas generated at the
anode 108 flows into theconduit 104 and into thevessel 102 viavessel inlet 117. Water is introduced into thevessel 102 throughwater inlet 118 fromwater conduit 119.Water inlet 118 may comprise a nozzle to pump the water in as a fine mist, spray, or steam. By using a fine water mist, spray or steam the final volume of the gold solution is vastly reduced compared to prior art methods of gold recovery. Advantageously, a low volume solution is cheaper to treat prior to discharging it as effluent. - Upon contact with the waste electrical materials comprising gold, the chlorine gas (and any inter-halogen compounds present), gold and water react to afford an aqueous solution of gold recovered from the waste materials. The aqueous gold solution exits the vessel through
outlet 120 and passes alongconduit 121 to a collection flask/container. - The gold solution which exits the vessel via the
vessel outlet 120 may be further treated to recover solid gold metal from the gold solution. The skilled person will be familiar with a number of different methods of reducing the gold solution to gold metal. For example, the gold solution may be treated with reducing agents such as sulphur dioxide gas, hydroxylamine, hydrazine, hydrogen peroxide. Alternatively, the gold solution may be refined electrochemically, for example by electrowinning or electroplating. A number of different methods of reducing a gold solution to provide gold metal are disclosed in U.S. Pat. No. 3,857,505. -
Conduit 121 may internally house a gold sensor or detector. When solution exiting thevessel 102 throughoutlet 120 no longer contains any gold, current to theelectrolytic cell 101 can be stopped to halt chlorine production. Thevessel 102 can be flushed with a non-reactive gas such as air, nitrogen or argon to expel any residual chlorine gas and the now gold depleted wasteelectronic materials 103 can be discharged from thevessel 102 to be replaced by new materials, - A reiteration of the process can be easily commenced by recharging the
vessel 102 with new wasteelectronic materials 103. - The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.
- It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.
Claims (5)
1. An apparatus for extracting gold from a substrate comprising gold, the apparatus comprising:
a reaction vessel configured to receive the substrate comprising gold, the reaction vessel comprising a vessel inlet through which chlorine gas is deliverable into the reaction vessel, the reaction vessel further comprising a vessel outlet;
a water inlet adapted to deliver water spray, steam, vapor, and/or mist into the vessel; and
a source of chlorine gas in fluid communication with the reaction vessel, wherein the substrate comprising gold, the chlorine gas and moisture present in the reaction vessel interact to provide a gold solution which is recovered from the reaction vessel via the vessel outlet.
2. The apparatus of claim 1 , wherein a conduit extends from the verse inlet to the source of chlorine gas to establish fluid communication therebetween.
3. The apparatus of claim 1 , wherein the apparatus further comprises an urging means for urging chlorine gas from the source of chlorine gas along the conduit and into the reaction vessel.
4. The apparatus of claim 1 , wherein the source of chlorine gas is an electrolytic cell.
5. The apparatus of claim 1 , further comprising a collector for gold solution.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US15/487,107 US20170218478A1 (en) | 2012-05-09 | 2017-04-13 | Gold recovery |
Applications Claiming Priority (5)
Application Number | Priority Date | Filing Date | Title |
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EP12167381.8 | 2012-05-09 | ||
EP20120167381 EP2662464A1 (en) | 2012-05-09 | 2012-05-09 | Gold recovery |
PCT/EP2013/059687 WO2013167714A1 (en) | 2012-05-09 | 2013-05-09 | Gold recovery |
US201414399565A | 2014-11-07 | 2014-11-07 | |
US15/487,107 US20170218478A1 (en) | 2012-05-09 | 2017-04-13 | Gold recovery |
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US14/399,565 Division US9689054B2 (en) | 2012-05-09 | 2013-05-09 | Gold recovery |
PCT/EP2013/059687 Division WO2013167714A1 (en) | 2012-05-09 | 2013-05-09 | Gold recovery |
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US20170218478A1 true US20170218478A1 (en) | 2017-08-03 |
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US14/399,565 Active 2033-08-11 US9689054B2 (en) | 2012-05-09 | 2013-05-09 | Gold recovery |
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US14/399,565 Active 2033-08-11 US9689054B2 (en) | 2012-05-09 | 2013-05-09 | Gold recovery |
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EP (2) | EP2662464A1 (en) |
CN (1) | CN104302793A (en) |
HK (1) | HK1208505A1 (en) |
PT (1) | PT2847360T (en) |
WO (1) | WO2013167714A1 (en) |
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JP2014529500A (en) * | 2011-12-15 | 2014-11-13 | アドバンスドテクノロジーマテリアルズ,インコーポレイテッド | Apparatus and method for stripping solder metal during recycling of waste electrical and electronic equipment |
CN104263940B (en) * | 2014-09-09 | 2016-08-24 | 中国电器科学研究院有限公司 | The de-golden clothes of a kind of gold for reclaiming in waste and old circuit board are put |
US9777346B2 (en) | 2015-09-03 | 2017-10-03 | Battelle Energy Alliance, Llc | Methods for recovering metals from electronic waste, and related systems |
US10648062B1 (en) | 2017-03-23 | 2020-05-12 | George Meyer | Strategic metal and mineral element ore processing using mixing and oxidant treatment |
Family Cites Families (16)
Publication number | Priority date | Publication date | Assignee | Title |
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GB190920471A (en) | 1909-09-07 | 1910-09-01 | William Frederick Cobb | Improvements in the Extraction and Separation of Gold and Silver from their Ores. |
US1869830A (en) * | 1931-09-02 | 1932-08-02 | George Fiske Hammond | Apparatus for the treatment of ore |
GB1087067A (en) | 1964-12-22 | 1967-10-11 | Moscovsky Zd Vtorichnykh Drago | Method of separating a layer of gold from a base of high melting transition metal element or non-ferrous alloy thereof |
US3834896A (en) | 1972-06-21 | 1974-09-10 | Us Interior | Recovery of gold |
US3957505A (en) | 1974-08-05 | 1976-05-18 | Bayside Refining And Chemical Company | Gold reclamation process |
US4723998A (en) | 1985-11-29 | 1988-02-09 | Freeport Minerals Co | Recovery of gold from carbonaceous ores by simultaneous chlorine leach and ion exchange resin adsorption process |
JPH01142038A (en) * | 1987-11-30 | 1989-06-02 | Tanaka Kikinzoku Kogyo Kk | Method for recovering au |
US4979986A (en) * | 1988-02-22 | 1990-12-25 | Newmont Gold Company And Outomec U.S.A., Inc. | Rapid oxidation process of carbonaceous and pyritic gold-bearing ores by chlorination |
JPH1136020A (en) * | 1997-07-15 | 1999-02-09 | Justy:Kk | Treatment of waste printed circuit board |
WO2001083835A2 (en) * | 2000-04-28 | 2001-11-08 | Mintek | Gold recovery process with hydrochloric acid lixiviant |
DE10121946C1 (en) * | 2001-05-05 | 2002-09-05 | Heraeus Gmbh W C | Process for dissolving precious metals contained in residues comprises slurrying the residues with concentrated hydrochloric acid, and feeding hydrogen chloride gas and chlorine gas through the slurry |
CA2435779A1 (en) * | 2003-07-22 | 2005-01-22 | Institut National De La Recherche Scientifique | A process for recovering platinum group metals from ores and concentrates |
FI118302B (en) * | 2006-02-17 | 2007-09-28 | Outotec Oyj | Procedure for the extraction of gold |
AU2009219115B2 (en) * | 2008-02-29 | 2013-10-31 | Australian Nuclear Science And Technology Organisation | Selective gold extraction from copper anode slime with an alcohol |
KR100876682B1 (en) * | 2008-06-24 | 2009-01-07 | 한국지질자원연구원 | The dissolution apparatus for noble metals |
KR101229766B1 (en) * | 2010-11-23 | 2013-02-05 | 한국지질자원연구원 | Selective Recovery Method of Gold from Scrapped Printed Circuit Boards(PCBs) |
-
2012
- 2012-05-09 EP EP20120167381 patent/EP2662464A1/en not_active Withdrawn
-
2013
- 2013-05-09 CN CN201380024425.XA patent/CN104302793A/en active Pending
- 2013-05-09 PT PT13723070T patent/PT2847360T/en unknown
- 2013-05-09 US US14/399,565 patent/US9689054B2/en active Active
- 2013-05-09 EP EP13723070.2A patent/EP2847360B1/en active Active
- 2013-05-09 WO PCT/EP2013/059687 patent/WO2013167714A1/en active Application Filing
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2015
- 2015-09-16 HK HK15109080.5A patent/HK1208505A1/en unknown
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2017
- 2017-04-13 US US15/487,107 patent/US20170218478A1/en not_active Abandoned
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EP2662464A1 (en) | 2013-11-13 |
US20150114182A1 (en) | 2015-04-30 |
EP2847360B1 (en) | 2019-06-19 |
HK1208505A1 (en) | 2016-03-04 |
US9689054B2 (en) | 2017-06-27 |
PT2847360T (en) | 2019-09-24 |
CN104302793A (en) | 2015-01-21 |
EP2847360A1 (en) | 2015-03-18 |
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