A FLUIDIZED-BED REACTOR AS A TOOL FOR THE INVESTIGATION OF OXYGEN AVAILABILITY ON THE BIOOXIDATION RATE OF SULFIDE MINERALS AT HIGH SOLIDS CONCENTRATIONS

Researchers investigating the bio-oxidation of a variety of sulphide ores have reported finding a maximum reactor solids concentration above which the bio-oxidation rate declines. Due to the economic benefits of operating reactors at as high a solids concentration as possible, a fluidised bed reactor has been used to study the effect of oxygen availability, one of the factors thought to inhibit the oxidation rate at high solids concentrations. Different fluidisation flowrates allow the bed solids concentration to be altered without any change in the overall solids-to-liquid ratio, or liquor composition. Initial tests have been performed at the same overall liquid-to-solid ratio, but at bed solids concentrations ranging between 20 and 45 per cent. The dissolved oxygen concentration was above 1,0 ppm throughout, ensuring that conditions were not oxygen limited. The iron concentration varied between 4 and 10 g.l-1 and the reactor was inoculated with 10(8) bacteria/ml. Under these conditions, the specific bio-oxidation rate was found to be independent of the bed solids concentration. This strongly indicated that oxygen transfer is a major cause of the limitation in bio-oxidation rate during the oxidation of high sulphide content ores at high solids concentrations in stirred tank reactors.