Chalcopyrite bioleaching by an enriched microbial community in acidic artificial seawater

Abstract

The enhancement of chalcopyrite bioleaching with an enriched microbial community by acidified seawater was studied, and the enhancing mechanism was analyzed. The microbial community was enriched at the Dabaoshan mine site, and the treated ore sample had high concentrations of chalcopyrite and galena. The experimental results show that copper extraction from chalcopyrite with an enriched microbial community in seawater was promoted from 13.1% to 62.1% by acidification in comparison with that without acidification. Further analyses of the solutions, solid residues and microbial compositions by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and 16S rDNA sequencing revealed the promoting effects of acidified seawater. This acidification can increase the biodissolution of chalcopyrite to increase the concentration of iron ions and maintain the redox potential in the range of 360−410 mV. The latter produces an optimal redox environment conducive to chalcopyrite dissolution via Cu2S. The adaptability of the microbial community to a high-salt environment is improved. Chloride ions at 580 mmol/L improve the leaching kinetics of chalcopyrite by increasing the porosity and noncrystallinity of the intermediate elemental sulfur. This study provides a promising way to bioleaching copper minerals using seawater for areas with freshwater shortages.

1. Introduction

More than 80% of copper in the world is refined from copper-bearing sulfide ores [1]. Chalcopyrite constitutes the vast majority of copper resources and reserves of copper sulfide [2]. It is a mineralogical species with important economic significance. Copper extraction via traditional pyrometallurgical and hydrometallurgical processes has certain drawbacks, such as high energy consumption or low efficiency, because of its special crystal structure [3]. Compared with traditional methods, bioleaching has the advantages of being low cost and eco-friendly and has been successfully used in the copper extraction industry for some low-grade chalcopyrite ores [4 −6]. To date, many tests have been conducted to improve bioleaching efficiency, including the addition of Ag+ [7, 8], activated carbon [9], Cl– [10], and the surface-active agent Tween-80 [11]. The adjustment of the solution pH or redox potential is also used in a few cases [12, 13]. Among these methods, the addition of NaCl has received great attention because it has great application potential for freshwater shortages, where another challenge is the utilization of an alternative saline water source for the biohydrometallurgy process. For example, some mines from western Australia and parts of Chile often use seawater for mineral processing [14]. There are also several potential industrial applications of NaCl-resistant leaching bacteria for improving copper bioleaching [15, 16].

To date, several studies have attempted to utilize saline water at different temperatures for chalcopyrite bioleaching with typical bioleaching microorganisms. The bioleaching process of metal sulfides is significantly strengthened when the chloride ion concentration is low (<200 mmol/L) [17]. However, many bioleaching prokaryotes have relatively low tolerance to sodium chloride, which limits their growth and bioleaching performance under high-salt conditions. For example, for the typical mesophilic acidophilic iron-oxidizing bacterium Acidithiobacillus ferridurans (the optimum growth temperature is 30−35 ℃), the Rus operon is inactivated after a long period of growth with 500 mmol/L NaCl [18]. A high concentration of sodium chloride leads not only to the loss of microbial ferrous iron oxidation ability but also to the inability to reduce ferric iron