Optimization of pulp density and particle size in the biooxidation of a pyritic gold concentrate by Sulfolobus metallicus

Abstract

Although increasing pulp densities and decreasing particle sizes have positive effects in the volumetric rate of biooxidation of refractory gold concentrates, a variety of phenomena such as mechanical damage, metabolic stress and inhibition can limit this effect. The objective of this work was to determine pulp density and particle size values that maximize the volumetric solubilization rate of iron from a pyritic gold concentrate. The leaching was carried on in agitated flasks with the thermophilic archaeon Sulfolobus metallicus. The concentrate contained 66.7% pyrite, and the constant operation conditions were 220 rev/min, 68 °C and initial pH of 2.0. Pulp densities were 2.5, 5, 10 and 15% w/v and the size fractions were 150–106, 106–75, 75–38 and <38 μm. Total solubilized iron concentrations were in the range of 8–25 g/l. In the 2.5 and 5% pulp density runs, iron extractions were in the range of 80–100%. A complete experimental design of 16 runs allowed the building of response surfaces from which the optimal conditions that maximize the rate of iron solubilization were determined. These conditions are 7.8% pulp density and particle size of 35 μm.