Metal sulfide precipitation mediated by an elemental sulfur-reducing thermoacidophilic microbial culture from a full-scale anaerobic reactor

Abstract

Biological sulfidogenic systems are advantageous over hydroxide precipitation methods to recover base metals from hot and acidic metallurgical streams. Sulfide precipitation is not widely used in the hydrometallurgical industry for the high operational and capital expenses associated with compartmentalizing the sulfidogenic and metal precipitation process. A single-stage elemental sulfur-reducing process in which sulfidogenesis and metal precipitation occur concurrently could significantly decrease these costs. This study examines the effect of metals on the sulfidogenic activity of an adapted thermoacidophilic sulfur-reducing culture. Batch tests were conducted with Cu2+, Ni2+, and Zn2+ in concentrations up to 100, 570, and 525 mg L−1, respectively. All metal ions were completely precipitated (LOQ < 0.1 mg L−1) with higher volumetric sulfide production rates than in the experiments without metals. Dissolved metals appear to stimulate the sulfur reduction metabolism in a redox-dependent process. Additionally, we investigated the use of an unadapted microbial inoculum from a full-scale anaerobic reactor as a fast start-up inoculum for a sulfidogenic process under high temperature (80 °C), low pH (pH 3), and high Cu2+ concentrations (up to 1143 mg L−1). After seven days of operation, we found equivalent sulfidogenic rates to those obtained after 75 days of adaptation with the same inoculum. These results encourage the development of a single-stage metal precipitation and sulfur-reducing process under conditions suitable for thermoacidophilic microorganisms.