Microbial ferrous ion oxidation versus ferric ion precipitation at low temperature conditions

Abstract

Ferric ion precipitation in a typical bioleach operation is known to be inevitable. However, its management has been emphasized as critical to efficiently maximize the potential that bioleach technique offers, especially in heap bioleach systems. Although there are some studies on ferric ion precipitation, limited studies exist in the context of a cold condition which often prevails in some operations. This study investigated ferrous ion biooxidation and ferric ion precipitation under cold temperature conditions. The results showed that maximum ferrous ion oxidation rates of 1.05, 1.25, 1.51 and 1.60 mmol/L/h at 6, 7, 8 and 10°C respectively were achieved in packed column reactor. The results further showed a simultaneous ferric ion precipitation during the oxidation process. The kinetics of ferric ion precipitation follows a first order kinetics with the rate constants of 0.0066, 0.0074, 0.0080 and 0.011 h-1. Activation energies of 68 and 77 kJ/mol were obtained for both ferrous ion biooxidation and ferric ion precipitation respectively. Although slow kinetics are expected for both processes, the kinetics information may be useful for design management consideration at least to predict when bioleach liquor would likely run out of dissolved ferric ion.