Title: The elution of gold from activated carbon at room temperatures using sulphide solutions
Abstract:One of the main bottlenecks in the carbon-in-pulp process for the recovery of gold is the elution procedure, which typically requires the heating of caustic cyanide eluants to high temperatures for 16...One of the main bottlenecks in the carbon-in-pulp process for the recovery of gold is the elution procedure, which typically requires the heating of caustic cyanide eluants to high temperatures for 16 to 24 hours. The present work demonstrates that sodium sulphide solution as an alternative eluant can effect complete elution in about 4 hours at ambient temperatures. Elution efficiencies of around 100 per cent were obtained in 4 hours with a single pass of eluant containing 0,2 M Na2S and 0,4 NaOH - about 10 bed-volumes of eluant The initial rate was slow over the first hour of elution, probably because the activated carbon catalysed the oxidation of sulphide to polysulphide. Elution efficiencies of around 100 per cent were also obtained in less than 4 hours during the batch elution of carbon at liquid-to-solid ratios of about 100. Lower liquid-to-solid ratios resulted in the re-adsorption of gold, probably owing to the oxidation of sulphide to polysulphide, with the resultant formation of gold complexes that were eluted less readily. Improved rates of elution were obtained at higher sulphide concentrations and pH values greater than about 13. Higher temperatures increased the initial elution rate, but lowered the overall extraction efficiency, probably because of the deposition of elemental gold on the carbon. Variation of the ionic strength by the addition of NaCl had no effect on the elution, which confirms that the elution mechanism in the case of sulphide is different from that when cyanide or hydroxide is used as the eluant. It is proposed that the elution of gold by sulphide solutions proceeds by means of an initial step that involves the reaction of polysulphide ions with the adsorbed aurocyanide species, forming AuCN on the carbon and thiocyanate in solution. This step is followed by the formation of poorly adsorbed complexes with sulphide ions, such as AuS3-2. The presence of polysulphides, whether generated in situ by the catalytic oxidation effect of activated carbon or by the addition of elemental sulphur, reduces the elution rate and efficiency dramatically. This is probably due to the formation of complexes such as AuS-3 and AuS-2, which have a high adsorption affinity.Read More
Publication Year: 1994
Publication Date: 1994-08-01
Language: en
Type: article
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Cited By Count: 1
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