Arsenopyrite and pyrite bioleaching: evidence from XPS, XRD and ICP techniques |
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Authors: | Fantauzzi Marzia Licheri Cristina Atzei Davide Loi Giovanni Elsener Bernhard Rossi Giovanni Rossi Antonella |
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Institution: | (1) Dipartimento di Chimica Inorganica e Analitica, INSTM Research Unit, Centro Grandi Strumenti Universit? di Cagliari, 09042 Monserrato, Cagliari, Italy;(2) Department of Medical Sciences Mario Aresu, Universit? di Cagliari, 09042 Monserrato, Cagliari, Italy;(3) Department of Geoengineering and Environmental Technologies, Universit? di Cagliari, 09100 Cagliari, Italy;(4) Dipartimento di Chimica Inorganica ed Analitica, SS 554 Bivio per Sestu, 09100 Cagliari, Italy; |
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Abstract: | In this work, a multi-technical bulk and surface analytical approach was used to investigate the bioleaching of a pyrite and
arsenopyrite flotation concentrate with a mixed microflora mainly consisting of Acidithiobacillus ferrooxidans. X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and X-ray-induced Auger electron spectroscopy mineral surfaces
investigations, along with inductively coupled plasma-atomic emission spectroscopy and carbon, hydrogen, nitrogen and sulphur
determination (CHNS) analyses, were carried out prior and after bioleaching. The flotation concentrate was a mixture of pyrite
(FeS2) and arsenopyrite (FeAsS); after bioleaching, 95% of the initial content of pyrite and 85% of arsenopyrite were dissolved.
The chemical state of the main elements (Fe, As and S) at the surface of the bioreactor feed particles and of the residue
after bioleaching was investigated by X-ray photoelectron and X-ray excited Auger electron spectroscopy. After bioleaching,
no signals of iron, arsenic and sulphur originating from pyrite and arsenopyrite were detected, confirming a strong oxidation
and the dissolution of the particles. On the surfaces of the mineral residue particles, elemental sulphur as reaction intermediate
of the leaching process and precipitated secondary phases (Fe–OOH and jarosite), together with adsorbed arsenates, was detected.
Evidence of microbial cells adhesion at mineral surfaces was also produced: carbon and nitrogen were revealed by CHNS, and
nitrogen was also detected on the bioleached surfaces by XPS. This was attributed to the deposition, on the mineral surfaces,
of the remnants of a bio-film consisting of an extra-cellular polymer layer that had favoured the bacterial action. |
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