Abstract
Bioleaching of metal sulfides is an interfacial process where adhesion and subsequent biofilm formation are considered to be crucial for this process. In this study, adhesion and biofilm formation by several acidophiles (Acidithiobacillus, Leptospirillum and Sulfobacillus) isolated from different biotopes with sulfide ores in Armenia were studied. Results showed that: (1) these bacteria adhere to pyrite surfaces to various extents. A correlation between pyrite biooxidation and adhesion of S. thermosulfidooxidans 6, L. ferriphilum CC, L. ferrooxidans ZC on pyrite surfaces is shown. It is supposed that bioleaching of pyrite by S. thermosulfidooxidans 6, L. ferriphilum CC, L. ferrooxidans ZC occurs by means of indirect leaching: by ferric iron of bacterial origin; (2) cells of At. ferrooxidans 61, L. ferrooxidans ZC and St. thermosulfidooxidans 6 form a monolayer biofilm on pyrite surfaces. The coverage of pyrite surfaces varies among these species. The order of the biofilm coverage is: L. ferrooxidans ZC ≥ At. ferrooxidans 61 > St. thermosulfidooxidans 6; (3) the extracellular polymeric substances (EPS) analysis indicates that the tested strains produce EPS, if grown either on soluble ferrous iron or solid pyrite. EPS are mainly composed of proteins and carbohydrates. Cells excrete higher amounts of capsular EPS than of colloidal EPS. In addition, cells grown on pyrite produce more EPS than ones grown on ferrous iron.
Highlights
Biomining is the term used to describe the technology that uses microbes to achieve metal extraction from minerals or waste materials
The iron-oxidizing strains Leptospirillum ferrooxidans ZC, L. ferriphilum CC, and the iron and sulfur-oxidizing bacteria Acidithiobacillus ferrooxidans 61, At. ferrooxidans 13Zn, Sulfobacillus thermosulfidooxidans 6 were isolated from several natural biotopes with sulfide ores in Armenia (Figure S1)
The planktonic cells of L. ferriphilum CC grown on pyrite culture decreased by 1–2 × 108 cells/mL
Summary
Biomining is the term used to describe the technology that uses microbes to achieve metal extraction from minerals or waste materials. Biomining of gold or other precious metals normally involves a pre-treatment process using iron-oxidizing and/or sulfur-oxidizing bacteria or archaea prior to cyanide extraction [1]. Compared to the traditional mineral processing technology like ore smelting/toasting, biomining is more attractive regarding to its lower energy costs and is more environmentally friendly. Minerals 2019, 9, 69 autotrophs) compared to smelting operations (CO2 emission) [2]. Biomining is an increasingly applied biotechnological procedure for processing of ores in the mining industry (biohydrometallurgy) [3]
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