Bacterial-mediated recovery of copper from low-grade copper sulfide using fly ash and bacterial community dynamics

Abstract

Bioleaching is confronted with problems, such as low efficiency, long production cycle length, and vegetation destruction. In order to solve problems above, fly ash and low-grade copper sulfide ores were used to investigate bioleaching behaviors and bacterial community succession. Results showed that copper recovery, bacterial concentration, total proportion of main leaching bacteria including Acidithiobacillus ferrooxidans, Acidibacillus ferrooxidans, and Leptospirillum ferriphilum, were improved through using appropriate dosage of fly ash. The maximum copper recovery of 79.87% and bacterial concentration of 7.08 × 107 cells·mL−1 were obtained after using 0.8 g·L−1 fly ash. Exclusive precipitation including Zn(Fe3(SO4)2(OH)6)2 and Mg(Fe3(SO4)2(OH)6)2 was found in sample added 0.8 g·L−1 fly ash, which reduced the effect of hazardous ions on bacteria and thus contributing to bacterial proliferation. Bacterial community structure was differentiated, which indicated difference between original inoculation and sample used 0.8 g·L−1 fly ash was less than others. Total proportion of the three microorganism above accounted for more than 95% in all tests, especially in sample with 0.8 g·L−1 fly ash up to 99.81%. Cl− and Ag+ contained in fly ash can act as catalytic agent, which contributed to conversion from smooth and dense passivation layer to sparse and scattered one, and therefore improving contact between ores, lixiviant, and bacteria. Using appropriate dosage of fly ash showed prospects in bioleaching.

1. Introduction

Copper is the fundamentally strategic non-ferrous metal and cornerstone of national defense construction, playing a significant role in development of economy and society [1–2]. There are abundant copper reserves around the whole world, and the production of copper concentrate increases with each passing year [3]. As the largest producer and consumer of copper, China takes the fourth place of the global copper reserves today [4]. However, characteristics such as low grade, complex structure, difficult to recover has seriously hampered the development of copper-extraction industry [5]. There are many methods to recover copper from low-grade resources, including pyrometallurgy, hydrometallurgy, and biohydrometallurgy [6]. However, the requirement for substantial energy, as well as the toxic gas emission during pyrometallurgical process, and the reliance of chemical agents including cyanide in the hydrometallurgical method and the generation of dangerous byproducts, result in the need for environmentally-friendly method to recover copper [7]. Biohydrometallurgy (bioleaching), on the other hand, has been recognized as an eco-friendly, economically-sustainable, and strongly-reliable alternative to the conventional pyrometallurgy and hydrometallurgy to recover copper from low-grade reserves over the recent years [8–10].

Low-grade copper sulfides including chalcopyrite and bornite are the prominent, economically-significant, and copper-bearing resources, and its judicious utilization to meet the ever growing demand of copper assumes great significance [11–12]. Given that the significance of low-grade copper sulfides and its recalcitrant performance to bioleaching, many attempts to enhance copper recovery in the presence of additives have been made [13]. The utilization of chloride ion to enhance copper recovery through bioleaching was reported by Martins and Leão [14] and Zhang et al. [15]. Except chloride ion, the utilization of silver ion and ferric ion as catalysts to improve copper recovery from low-grade chalcopyrite has been put forward [16–17]. Furthermore, using acid-pretreated sargassum and seawater to accelerate bioleaching process and improve bacterial community structure have been recently proposed [18–19]. In addition, bioleaching of low-grade resources in the presence of acid-processed rice straw has been investigated [20]. Additives above have responded to improved copper recovery from low-grade copper sulfides, they are occasionally away from resource-saving or uneconomical, however [21]. If substitutable additives are found which can realize improved copper recovery, reduced environmental-pollution and waste resource re-use, then it would greatly contribute to copper recovery from low-grade copper sulfides.