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The biooxidation and cyanidation of a refractory arsenical gold concentrate:

University of British Columbia

A significant drawback to the application of biooxidation as a pretreatment for refractory gold concentrates is the problem of high cyanide consumption. The presence of cyanicides in biooxidized residues are commonly referred to in the literature, but specific mechanisms are not proposed. In this study, a four-stage continuous bench scale bioreactor apparatus was set up to generate a representative biooxidized product suitable for an extensive cyanidation study. In all, four biooxidation steady states were reached. Residence times ranged from 2 to 5 days, while temperature and pulp density remained constant at 35 °C and 20%, respectively. With the first two steady states, the primary stage pH was controlled at 1.8, whereas for the second two the pH was controlled at 1.5. Sulfide oxidation ranged from 70% to 93%. Cyanidation experiments were conducted on the final products, as well as on samples taken from the intermediate stages of the reactor. The solids were leached under varying conditions of pulp density, NaCN concentration, pH, temperature, and stirring speed. Gold extractions ranged from 46.1% to 95.6%. The sodium cyanide consumption varied from 2.70 to 12.07 kg/tonne-concentrate. Results indicated that the high cyanide consumption associated with this concentrate is the result of two separate reaction mechanisms: one forming thiocyanate (SCN") possibly from a reactive form of elemental sulfur, and the other forming hexacyanoferrates (Fe(CN)₆³⁻ and Fe(CN)₅⁴⁻) by decomposition of basic ferric sulfate precipitates. Cyanide use can be reduced by employing higher pulp densities, primary stage aeration, and shorter overall leach times.

Thesis/Dissertation

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2009-05-25

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http://hdl.handle.net/2429/8161

Materials Engineering

University of British Columbia

UBCV

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