Abstract
Adhesion plays an important role in bacterial dissolution of metal sulfides, since the attached cells initiate the dissolution. In addition, biofilms, forming after bacterial attachment, enhance the dissolution. In this study, interactions between initial adhesion force, attachment behavior and copper recovery were comparatively analyzed for Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans during bioleaching of chalcopyrite. The adhesion forces between bacteria and minerals were measured by atomic force microscopy (AFM). L. ferrooxidans had the largest adhesion force and attached best to chalcopyrite, while A. ferrooxidans exhibited the highest bioleaching of chalcopyrite. The results suggest that the biofilm formation, rather than the initial adhesion, is positively correlated with bioleaching efficiency.
Highlights
Chalcopyrite is the primary and most abundant copper sulfide mineral
Each curve is composed of two parts: the approach curve and the retraction curve
Since the cells on the cantilever tips were soft and compressible, no sharp single point represented the “jump to contact” event on the approach curve. This repulsive force kept increasing until the cell probe contacted with the chalcopyrite surface. This observation is in agreement with other research, where the authors investigated the interactions between an atomic force microscopy (AFM)
Summary
Because of various requirements (high temperature, complicated pretreatment) and formation of passivating layers (elemental sulfur, copper-rich polysulfide, or iron sulfate-type precipitates), it is recalcitrant to be leached via hydrometallurgical processing [1,2,3,4,5]. The dissolution of metal ions from insoluble metal sulfides by microorganisms is known as bioleaching [9]. It can be achieved through two modes: contact and non-contact leaching. In both modes, bacteria oxidize ferrous ion to ferric ion, ferric ion attack minerals. Ferrous ion is re-oxidized by iron oxidizing bacteria. RISCs are oxidized to sulfates by sulfur-oxidizing bacteria, which causes the environment acidify. The contact leaching mode is accepted to be more effective because the micro space, filled with extracellular polymeric substances (EPS) between mineral surface and biofilm cells, Minerals 2018, 8, 406; doi:10.3390/min8090406 www.mdpi.com/journal/minerals
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