『Abstract
Arsenopyrite (FeAsS) and enargite (Cu3AsS4) fractured in a nitrogen atmosphere were characterised
after acidic (pH 1.8), oxidative dissolution in both the presence
and absence of the acidophilic microorganism Leptospirillum
ferrooxidans. Dissolution was monitored through analysis of
the coexisting aqueous solution using inductively coupled plasma
atomic emission spectroscopy and coupled ion chromatography-inductively
coupled plasma mass spectrometry, and chemical changes at the
mineral surface observed using X-ray photoelectron spectroscopy
and environmental scanning electron microscopy (ESEM). Biologically
mediated oxidation of arsenopyrite and enargite (2.5 g in 25 ml)
was seen to proceed to a greater extent than abiotic oxidation,
although arsenopyrite oxidation was significantly greater than
enargite oxidation. These dissolution reactions were associated
with the release of 〜917 and 〜180 ppm of arsenic into solution.
The formation of Fe(III)-oxyhydroxides, ferric sulphate and arsenate
was observed for arsenopyrite, thiosulphate and an unknown arsenic
oxide for enargite. ESEM revealed an extensive coating of an extracellular
polymeric substance associated with the L.ferrooxidans
cells on the arsenopyrite surface and bacterial leach pits suggest
a direct biological oxidation mechanism, although a combination
of indirect and direct bioleaching cannot be ruled out. Although
the relative oxidation rates of enargite were greater in the presence
of L.ferrooxidans, cells were not in contact with the surface
suggesting an indirect biological oxidation mechanism. Cells of
L.ferrooxidans appear able to withstand several hundreds
of ppm of As(III) and As(V).』
1. Introduction
2. Experimental methods
2.1. Sample preparation and procedure
2.2. Analytical instrumentation
3. Results
3.1. XPS analysis of arsenopyrite and enargite surfaces
3.1.1. Freshly cleaved arsenopyrite
3.1.1.1. Fe 2p(3/2) spectrum
3.1.1.2. As 3d(5/2) spectrum
3.1.1.3. S 2p(3/2) spectrum
3.1.2. Freshly cleaved enargite
3.1.2.1. Cu 2p(3/2) spectrum
3.1.2.2. As 3d(5/2) spectrum
3.1.2.3. S 2p(3/2) spectrum
3.1.3. Surface treatment of arsenopyrite with L.ferrooxidans
vs abiotic control surfaces
3.1.3.1. Fe 2p(3/2) spectrum
3.1.3.2. As 3d(5/2) spectrum
3.1.3.3. S 2p(3/2) spectrum
3.1.4. Surface treatment of enargite with L.ferrooxidans
vs abiotic control surfaces
3.1.4.1. Cu 2p(3/2) spectrum
3.1.4.2. As 3d(5/2) spectrum
3.1.4.3. S 2p(3/2) spectrum
3.2. Auger parameter analysis
3.3. Arsenopyrite and enargite surface morphology and attachment
of L.ferrooxidans (ESEM)
3.3.1. Fresh and abiotically reacted surfaces
3.3.2. Leptspirillum ferrooxidans reacted surfaces
3.4. Aqueous phase chemistry
3.4.1. Major element analysis
3.4.1.1. Arsenopyrite
3.4.1.2. Enargite
3.4.2. Arsenic speciation analysis
4. Discussion
4.1. Influence of bacteria on the oxidative dissolution of
arsenopyrite
4.1.1. Abiotic vs bacterially mediated oxidative dissolution
4.1.2. Arsenopyrite geochemistry and biological response to
arsenic
4.2. Cell attachment and biofilm formation - implications for
direct vs indirect bioleaching
4.3. Influence of bacteria on the oxidative dissolution of enargite
5. Conclusions
Acknowledgments
References