Specific mechanism of Acidithiobacillus caldus extracellular polymeric substances in the bioleaching of copper-bearing sulfide ore.

Shoushuai Feng,Zhuangzhuang Huang,Yanjun Tong,Hailin Yang,Kaijun Li,Yogendra Kumar Mishra

doi:10.1371/journal.pone.0213945

Abstract

This study aimed to reveal the specific mechanism of extracellular polymeric substances (EPS) in the bioleaching of copper-bearing sulfide ore by moderately thermophilic bacterium Acidithiobacillus caldus. The bioleaching performance of blank control (BC), planktonic cell deficient (PD), attached cell deficient (AD), and EPS deficient (ED) systems were compared, to investigate the specific functions of “non-contact” and “contact” (including direct contact and, EPS-mediated contact) mechanisms. The detailed mechanics of bioleaching were studied using μx of cell growth, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The μx of cell growth demonstrated that EPS favors planktonic and attached cell growth. SEM observation revealed that intensive micro-pores on slag benefitted from the “EPS-mediated contact” mechanism. XRD identification indicated that additional chemical derivatives were produced via “EPS-mediated contact” mechanism, because of the active iron/sulfur metabolism. FTIR analysis revealed that the absorption peaks of C-O-S, sulfate, and S = O, which are closely associated with sulfur metabolism, have significant influences of EPS secretion. Taken together, the “EPS-mediated contact” mechanism contributed to almost half of the “contact” mechanism efficiency and a quarter of the total bioleaching efficiency. The proposed specific mechanism of EPS can deepen our understanding of similar bioleaching processes.

Highlights

With continuous decline in copper rich ore reserves, reprocessing of low-grade copper-bearing sulfide ores, accounting for >70% of the global copper reserves, has become inevitable [1,2,3]
In the blank control (BC) system, sulfur metabolism was active with a better comprehensive bioleaching mechanism, and the value of pH was maintained at about 1.50 in the early phase
The highest value of sulfate ion concentration was determined in the EPS deficient (ED) system (16.40 g/ L), compared to 28.60 g/L (BC), 19.46 g/L (PD) and 18.70 g/L (AD) in the other systems

Summary

Introduction

With continuous decline in copper rich ore reserves, reprocessing of low-grade copper-bearing sulfide ores, accounting for >70% of the global copper reserves, has become inevitable [1,2,3]. Metal extraction from these low-grade ores using traditional smelting techniques is uneconomical. Most low-grade ores have been discarded [4,5,6]. Biotechnology, Ministry of Education (KLCCBKF201601), the Priority Academic Program Development of Jiangsu Higher Education Institutions, and Program of Introducing Talents of Discipline to Universities (No 111-2-06) and national first-class discipline program of Light Industry Technology and Engineering (LITE201823)

Objectives

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Results

Conclusion