Gas–liquid mass transfer phenomena in bio-oxidation experiments of sulphide minerals: A critical review of literature data

Abstract

It was examined whether gas–liquid transfer of oxygen or carbon dioxide has determined the bacterial oxidation rate of sulphide minerals in the kinetic experiments reported in the literature. Correlations available in the literature were used to estimate the gas–liquid mass transfer coefficients of oxygen and carbon-dioxide, k L a (s −1), in the reported experimental equipment (e.g. shake flasks or aerated stirred tanks). The maximum oxygen and carbon dioxide transfer rates were estimated for reported kinetic experiments with pyrite and compared with estimated maximum oxygen and carbon dioxide consumption rates that occurred in those experiments. It was concluded that gas–liquid carbon dioxide transfer limitation and exhaustion of carbon dioxide in the gas-phase, often occurred. Therefore, the observed decrease of the bacterial oxidation rate constant at increasing slurry densities was probably caused by carbon dioxide limitation. Consequently, the method presented in this work needs to be applied in order to ensure that the bioleaching kinetics are properly measured in the absence of carbon dioxide and/or oxygen transfer limitation.