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Hol A.,Wageningen University | Van Der Weijden R.D.,Wageningen University | Weert G.V.,Oretome Ltd | Kondos P.,Barrick Gold Corporation | Buisman C.J.N.,Wageningen University
Minerals Engineering | Year: 2011

Gold is commonly liberated from sulfide minerals via oxidative destruction techniques. To circumvent the formation of sulfuric acid and to reduce the amount of energy required for these processes two alternative anaerobic processes based on sulfate reducing bacteria are investigated for arsenopyrite in this study. The first alternative, "bio-reduction" is expected to alter the structure of arsenopyrite via reduction of the mineral-sulfur to hydrogen sulfide, yielding a sulfur depleted residue that probably contains the gold. The second alternative "anaerobic oxidation" focuses on the mineral-arsenic which under anaerobic conditions can be oxidized to arsenite and subsequently precipitates as orpiment, which may contain the gold. Both alternatives were investigated with gas lift loop reactor experiments performed at pH 5 and 35 °C. These experiments showed that sulfate reducers were able to reduce sulfate from the reactor fluid, but that they were not able to use arsenopyrite as an electron acceptor (bio-reduction) or donor (anaerobic oxidation) under the selected conditions. As a result the gold leachability of the ore concentrate was not improved. To make the mineral more accessible for the leach solution the solubilization of lattice constituents from arsenopyrite that can be biologically reduced/anaerobically oxidized, should be stimulated. In addition, the concentration of arsenite needs to be limited to preserve the activity of sulfate reducing bacteria. © 2010 Elsevier Ltd. All rights reserved. Source


Hol A.,Wageningen University | Van Der Weijden R.D.,Wageningen University | Van Weert G.,Oretome Ltd | Kondos P.,Barrick Gold Corporation | Buisman C.J.N.,Wageningen University
Environmental Science and Technology | Year: 2011

Gold is commonly liberated from sulfide minerals by chemical and biological oxidation. Although these technologies are successful, they are costly and produce acidic waste streams. Removal of mineral-sulfur to overcome the mineralogical barrier could also be done by bioreduction, producing hydrogen sulfide (H 2S). To make the sulfur within these minerals available for bioreduction, the use of partial bio-oxidation as a pretreatment to oxidize the sulfides to elemental sulfur was investigated in gas lift loop reactor experiments. Experiments at 35 °C using a refractory concentrate showed that at pH 2 arsenopyrite is preferentially partially oxidized over pyrite and that elemental sulfur can be subsequently converted into H 2S at pH 5 via bioreduction using H 2 gas. A single partial bio-oxidation/ bioreduction treatment increased the gold recovery of the concentrate from 6% to 39%. As elemental sulfur seems to inhibit further oxidation by covering the mineral surface, several treatments may be required to reach a gold recovery >90%. Depending on the number of treatments this method could be an interesting alternative to bio-oxidation. © 2011 American Chemical Society. Source


Hol A.,Wageningen University | van der Weijden R.D.,Wageningen University | Van Weert G.,Oretome Ltd | Kondos P.,Barrick Gold Corporation | Buisman C.J.N.,Wageningen University
International Journal of Mineral Processing | Year: 2010

To liberate gold from refractory pyrite, oxidative destruction techniques that consume lots of energy and generate acidic waste streams are custom. As an alternative the "bio-reduction" of pyrite is proposed and investigated in this study. Bio-reduction is an anaerobic process based on sulfate/sulfur reducing bacteria which are thought to be able to use pyrite-sulfur as a possible electron acceptor. The conversion of pyrite-sulfur into hydrogen sulfide is advantageous because energy is saved and the generation of an acidic waste stream is prevented. In addition, the generated H2S can be used to produce elemental sulfur, or even gold lixiviants such as thiosulfate or bisulfide. Batch experiments under anaerobic conditions showed that two effects can inhibit bio-reduction; methane formation and sulfide accumulation. In a gas lift loop reactor operated at pH 5, temperature of 35 °C, and with continuous sulfide removal no evidence of pyrite bio-reduction was found. Though the sulfate reducing bacteria survived, they did not utilize pyrite-sulfur as an electron acceptor under the chosen conditions. © 2010 Elsevier B.V. All rights reserved. Source

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