Applying bio-oxidation waste solution into two-stage oxidation process to enhance the bio-oxidation of pyrite: Insight on enhanced mechanism

Abstract

Chemical oxidation that applies the bio-oxidation waste solution (BOS) as oxidation system, a simple and environmentally friendly method, can significantly enhance the bio-oxidation efficiency of pyrite (FeS2) in two-stage oxidation process. To clarify the dissolution process of pyrite and reveal the enhanced mechanism, the present study provided an in-depth analysis of oxidation results, physical and chemical changes on the pyrite surface during chemical oxidation. The microbial community structure and kinetic analysis were also performed for the bio-oxidation. Study indicated that the oxidation of Fe3+ resulted in the destruction of pyrite surface chemical structure and the reduction of particle size. The nitrogenous substances were also generated on pyrite surface. Kinetic analysis suggested that the dissolution rate of pyrite in bio-oxidation was mainly limited by interfacial chemical reaction step. Therefore, both physical and chemical factors caused by Fe3+ oxidation were conducive to accelerating the dissolution of pyrite. Additionally, releasing more Fe2+ as energy source and the generated nitrogenous substances as N or C source, greatly improved the microbial community structure and growth rate, thus leading to a rapid increase of oxidant-Fe3+ concentration. These factors greatly enhanced the dissolution kinetics of pyrite in bio-oxidation. As a result, the extraction levels of Fe and S elements for pyrite in two-stage oxidation process could reach 89.1 ± 1.5 % and 87.3 ± 1.2 %, respectively, which were significantly increased by 70.1 ± 0.2 % and 62.3 ± 0.1 % compared with the values in one-stage bio-oxidation process. These findings provide theoretical support for using BOS in the two-stage oxidation process for high‑sulfur refractory gold ores.