Batch and continous biooxidation kinetics of a refractory gold-bearing pyrite concentrate

Abstract

Batch and continuous biooxidation studies have been carried out on a refractory, gold-bearing pyrite concentrate. The batch results were obtained using approximately the same surface area concentration for three different narrow size fractions. These showed an almost constant mass biooxidation rate for pyrite of 3,22 kg m −3 3 d −1 or an area rate of 1,53 × 10 −3 kg m −2 2 d −1 . The logistic equation was found to fit the batch data well and gave values of km ranging from 1,259 to 1,277 d −1 with values of Xm from 0,597 to 0,942 for the largest and smallest size refractions respectively. For the single stage continuous bioreactor the logistic equation also gave a good fit of the data with mean values for km of 0,305 d −1 and a mean X m of 0,762. These are close to those obtained for the batch biooxidation data. Biooxidation of the pyrite proceeds with the development of pores which were observed both on polished sections and scanning electron micrographs. This biooxidation and pore formation appears to be selective in the gold-rich regions with the consequence that only 50% sulphide oxidation is required for 90% gold liberation. The concentrate contained traces of arsenic which appears to be closely associated with the gold.