Continuous bioleaching of arsenopyrite from mine tailings using an adapted mesophilic microbial culture

Abstract

The present study aimed to develop a mesophilic microbial culture that grows effectively in solutions with high solid loading and to develop an optimized continuous-bioleaching system for the treatment of arsenic-rich mine tailings. The mesophilic microbial consortium was composed mainly of L. ferriphilum (90%) and A. caldus (5%). Following an adaptation process of serial sub-culturing, the microbes were capable of tolerating 20 g/L of arsenic. The inoculum used in the CSTR experiment after the adaptation process was mainly composed of A. caldus, L. ferriphilum, Methylophaga spp., and Sphingomonas spp. Subsequently, an optimization test was performed at 15% (w/w) solid concentration in a three-stage reactor unit. The subsequent study proceeded in two phases, with tests at 7 days total residence time and a further test at 5 days total residence time. Agitation speed, air-flow rate, and temperature were varied to test their effect on arsenic removal, and the ensuing bioleaching was studied. To quantify the reactor performance, the arsenic (As) solubilization efficiency, the ferrous-to-ferric oxidation rate, the microbial cell concentration, the dissolved oxygen, and the redox potential were measured. These measurements indicated that oxygen supply played the most important role in the bioleaching efficiency. The reactor operated at 5 days residence time displayed the greatest leaching rate (96 mg/L/d).