GOLD RECOVERY

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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] 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:

[0063] FIG. 1 illustrates an apparatus for carrying out the gold recovery method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0064] 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.

[0065] 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. By way of example, 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. Naturally, the conduit 104 will be manufactured from a material that is incapable of being corroded by chlorine gas.

[0066] 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.

[0067] A second pump 113 feeds the cathode electrolyte or catholyte 114 to the cathode 109. Typically, 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.

[0068] In the embodiment shown, 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).

[0069] Conduit 122 provides an outlet for any excess chlorine gas.

[0070] In use, the NaCl electrolyte 111 delivered to the anode 108 is oxidised to yield chlorine gas:

2NaCl.fwdarw.Cl.sub.2+2Na.sup.++2e.sup.

[0071] 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.fwdarw.Br.sub.2+2Na.sup.++2e.sup.

2NaI.fwdarw.I.sub.2+2Na.sup.++2e.sup.

I.sub.2+Cl.sub.2.fwdarw.2ICl

Br.sub.2+Cl.sub.2.fwdarw.2BrCl

[0072] At the cathode 109, hydrogen gas is generated from the electrolyte 114 according to the following equation:

2H.sub.2O+2e.sup..fwdarw.H.sub.2+2OH.sup.

[0073] 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.

[0074] 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. 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.

[0075] 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 along conduit 121 to a collection flask/container.

[0076] 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.

[0077] Conduit 121 may internally house 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,

[0078] A reiteration of the process can be easily commenced by recharging the vessel 102 with new waste electronic materials 103.

[0079] 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.

[0080] 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.