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Open AccessArticle

Role of Ag+ in the Bioleaching of Arsenopyrite by Acidithiobacillus ferrooxidans

by Yan Zhang 1, Qian Li 1 and Xiaoliang Liu 2,*
1
School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China
2
College of Chemical and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, China
*
Author to whom correspondence should be addressed.
Metals 2020, 10(3), 403; https://doi.org/10.3390/met10030403
Received: 13 February 2020 / Revised: 15 March 2020 / Accepted: 19 March 2020 / Published: 22 March 2020
Arsenopyrite (FeAsS) is often associated with gold, but pre-treatment is necessary prior to gold leaching, mainly due to the gold encapsulation in the matrix of FeAsS. Bio-oxidation is attractive and promising, largely due to its simplicity, low cost and environmental friendliness. A critical problem that still impedes the large-scale applications of this green technology is its slow leaching kinetics. Some metal ions such as Ag+ have previously been found to expedite the bioleaching process. In this paper, the role of Ag+ in the arsenopyrite bioleaching by Acidithiobacillus ferrooxidans was investigated in detail by bioleaching experiments and a series of analyses including thermodynamics, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Experimental results suggested that addition of 5 mg/L Ag+ to the leaching system could significantly improve the final As leaching efficiency from 30.4% to 47.8% and shorten the bioleaching period from 19 days to 15 days. Thermodynamic analysis indicates that Ag+ destabilises As2S2, As2S3 and S0 via forming Ag2S, which is confirmed by the XRD analysis on the phase transformation during bioleaching. SEM and XPS analyses further showed that Ag+ removed the passivating film consisting mainly of As2S2, As2S3 and S0 because Ag2S formed on the arsenopyrite surface from the start bioleaching of 36 h. In the presence of Fe3+, Ag2S could easily be dissolved to Ag+ again, likely leading to the establishment of the Ag+/Ag2S cycle. The bacteria utilised the two synergistic cycles of Fe3+/Fe2+ and Ag+/Ag2S to catalyse the bioleaching of arsenopyrite. View Full-Text
Keywords: arsenopyrite; gold ore; bioleaching; passivating film; metal ion catalyst; silver arsenopyrite; gold ore; bioleaching; passivating film; metal ion catalyst; silver
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Zhang, Y.; Li, Q.; Liu, X. Role of Ag+ in the Bioleaching of Arsenopyrite by Acidithiobacillus ferrooxidans. Metals 2020, 10, 403.

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