Carbon Sources as a Factor Determining the Activity of Microbial Oxidation of Sulfide Concentrate at Elevated Temperature

Aleksandr Bulaev,Anna Boduen

doi:10.3390/min12020110

Abstract

The goal of the present work was to evaluate the possibility of improving the efficiency of the stirred tank reactor biooxidation of sulfide gold-bearing concentrate by means of addition of carbon sources required for the constructive metabolism of microorganisms. Biooxidation experiments were performed on gold-bearing pyrite-arsenopyrite concentrate in continuous mode at 45 °C to determine the influence of additional carbon sources (carbon dioxide and molasses) on sulfide mineral oxidation. The use of CO2 allowed increasing the efficiency of the biooxidation and the extents of sulfide sulfur (Ss) oxidation and gold recovery were 79% and 84%, respectively. Biooxidation in a control experiment (without additional carbon sources) and when using molasses allowed achieving 39% and 66% oxidation of Ss as well as 73% and 81% of gold recovery. Analysis of the microbial populations formed in biooxidation reactors using NGS methods demonstrated that CO2 application led to an increase in the relative abundance of the genus Sulfobacillus. Thus, it was determined that application of additional carbon source makes it possible to manage the biooxidation process, affecting both sulfide mineral oxidation and microbial population composition.

Highlights

Biooxidation in stirred tank reactors (STR biooxidation) has been successfully used at a commercial scale to extract gold and some non-ferrous metals from sulfide concentrates [1,2,3,4,5,6]
The curves demonstrate that both carbon dioxide and molasses influenced these parameters, which may be used for indirect evaluation of biooxidation activity
The comparison of the data obtained in the present work (45 ◦ C) with those from the previous work (40 ◦ C) [33] demonstrated that at 40 ◦ C liquid phase parameters corresponded to higher biooxidation activity, while the increase in the temperature up to 45 ◦ C led to the increase in the pH and ferrous iron concentration

Summary

Introduction

Biooxidation in stirred tank reactors (STR biooxidation) has been successfully used at a commercial scale to extract gold and some non-ferrous metals (cobalt, nickel) from sulfide concentrates [1,2,3,4,5,6]. STR biooxidation of sulfide concentrates is performed by aerobic acidophilic iron- and sulfur-oxidizing microorganisms, which oxidize sulfide gold-bearing minerals (arsenopyrite, pyrite, pyrrhotite) to obtain energy. These processes may be carried out in stirred tank reactors connected in series under controlled conditions (oxygen and mineral nutrition supply, pH, and temperature maintenance) that provide stable biooxidation performance [3,4,7,8,9]. Industrial STR biooxidation processes are usually carried out at temperatures of 40–45 ◦ C as heat is generated during microbial sulfide mineral biooxidation. STR biooxidation is always performed by mixed populations of different acidophilic microorganisms [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]

Objectives

Methods

Results

Discussion

Conclusion