Effect of surfactant on the growth and activity of microorganisms in a heap bioleaching system

Abstract

The presence of surfactants in the lixiviant solution has the potential to improve solution penetration into small pores and cracks of large ore particles by decreasing surface tension, thereby enhancing access of lixiviant to internal mineral grains and associated metal recovery from low grade sulphide ores. The effect of surfactants on the growth and activity of microorganisms implicated in bioleaching must also be considered, because of the microorganisms’ principal role in the regeneration of leaching reagents and facilitating metal recovery from an ore. The effect of surfactant addition on ferrous ion oxidation and microbially-mediated leaching of chalcopyrite by a mixed thermophilic microbial culture was investigated using five non-ionic surfactants: Tween® 20, Tween® 80, Plurafac® LF 120, Plurafac® LF 600 and Lutensol® XL 90 at concentrations of 5, 10 and 20 mg L−1. The addition of 5 and 10 mg L−1 Tween® 20 showed no negative effect on microbial ferrous ion oxidation and chalcopyrite bioleaching. Further, its presence was observed to reduce the initial leaching lag time. Microbial ferrous ion oxidation was inhibited in the presence of 10 mg L−1 Plurafac® LF 120 while a partial inhibition was observed with 10 mg L−1 Lutensol XL 90. Plurafac® LF 600 at 5 and 10 mg L−1 and Tween® 80 at 10 mg L−1 inhibited microbial growth completely, and thereby leaching, hence precluding it from a role in bioleaching.