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Bacterial oxidation of a pyrite-arsenopyrite-gold ore concentrate was carried out in 14 l continuous-flow stirred tank reactors. Oxygen and carbon dioxide consumption rates, mineral dissolution rates and bacterial concentrations were measured at various steady-state residence times and with 6, 11 and 16 wt.% solids in the feed slurry. Mineral oxidation was found to be strongly dependant on bacterial activity. Arsenopyrite was found to be preferentially oxidised at the higher pulp densities., Bacterial oxidation of a pyrite-arsenopyrite-gold ore concentrate was carried out in 14 l continuous-flow stirred tank reactors. Oxygen and carbon dioxide consumption rates, mineral dissolution rates and bacterial concentrations were measured at various steady-state residence times and with 6, 11 and 16 wt.% solids in the feed slurry. Mineral oxidation was found to be strongly dependant on bacterial activity. Arsenopyrite was found to be preferentially oxidised at the higher pulp densities.

Bacterial oxidation of an arsenopyritic gold-ore concentrate was carried out with continuous-flow operation in 14 l, mechanically agitated reactors. Samples from the slurry reactors were separated into solid and liquid fractions and analysed separately to determine the electrochemical rates of sulphide conversion by the bacteria and the rates of direct bacterial oxidation of sulphide. The rates of the individual mechanisms are compared to the overall rates of biooxidation in the continuous-flow slurry reactors. The results show that the commonly hypothesised direct and indirect mechanisms of biooxidation both play a significant role in the bacterial oxidation of sulphide ores., Bacterial oxidation of an arsenopyritic gold-ore concentrate was carried out with continuous-flow operation in 14 l, mechanically agitated reactors. Samples from the slurry reactors were separated into solid and liquid fractions and analysed separately to determine the electrochemical rates of sulphide conversion by the bacteria and the rates of direct bacterial oxidation of sulphide. The rates of the individual mechanisms are compared to the overall rates of biooxidation in the continuous-flow slurry reactors. The results show that the commonly hypothesised direct and indirect mechanisms of biooxidation both play a significant role in the bacterial oxidation of sulphide ores.

Oxygen and carbon dioxide consumptions drop sharply at dissolved oxygen levels below 10% of saturation, but are relatively stable above 20% of saturation. An optimum oxygen uptake rate (and mineral dissolution rate) is observed at a residence time near 40 hours. Oxygen uptakes are directly proportional to the mineral solubilisation rates. Carbon dioxide uptakes are directly associated with bacterial growth. The stoichiometry of oxygen to carbon dioxide uptakes, though not constant, is very reproducible over wide variations in residence time., Oxygen and carbon dioxide consumptions drop sharply at dissolved oxygen levels below 10% of saturation, but are relatively stable above 20% of saturation. An optimum oxygen uptake rate (and mineral dissolution rate) is observed at a residence time near 40 hours. Oxygen uptakes are directly proportional to the mineral solubilisation rates. Carbon dioxide uptakes are directly associated with bacterial growth. The stoichiometry of oxygen to carbon dioxide uptakes, though not constant, is very reproducible over wide variations in residence time.

Radian Corporation has developed a process for treating hexavalent chromium contaminated soils that involves: soil washing using an alkaline extractant; biological reduction of Cr(VI) to Cr(III) in the soil wash effluent; and separation of Cr(III) from the biologically treated effluent. Biological treatment has been demonstrated for immobilised cells (fixed-film) in fluidised bed bioreactors and suspended cells in slurry bioreactors for Cr(VI) levels ranging from 30-600 mg/l which have been reduced to non-detectable levels (less than 0.05 mg/l). The resulting Cr(III) effluent was chemically treated to precipitate chromium hydroxide for removal by physical separation., Radian Corporation has developed a process for treating hexavalent chromium contaminated soils that involves: soil washing using an alkaline extractant; biological reduction of Cr(VI) to Cr(III) in the soil wash effluent; and separation of Cr(III) from the biologically treated effluent. Biological treatment has been demonstrated for immobilised cells (fixed-film) in fluidised bed bioreactors and suspended cells in slurry bioreactors for Cr(VI) levels ranging from 30-600 mg/l which have been reduced to non-detectable levels (less than 0.05 mg/l). The resulting Cr(III) effluent was chemically treated to precipitate chromium hydroxide for removal by physical separation.