Speaker
Prof.
Yuri Mikhlin
(Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of sciences)
Description
Valleriite is a mineral composed of alternating layers of brucite-like phase yMg(OH)2•zAl(OH)3 and sulfide close to chalcopyrite CuFeS2. Generally, valleriite is not very abundant, but “coppery” ores of Noril’sk ore provenance contain up to 20% of this mineral, industrial values of copper, nickel and are enriched in platinum group metals. Flotation of the coppery ores is poor, and even small admixtures of valleriite to of other ores suppress the recovery of values. Valleriite is also of interest as a material with very special character in terms of the structure of “noncommensurate” sulfide and hydroxide layers, and their electronic and magnetic properties, including probable persistent electric charge of the layers.
Here, we report Cu K-, Fe K-edge XANES and EXAFS measured at BM23 beamline, ESRF, in combination with XPS, 57Fe Mössbauer spectroscopy and other techniques in order to get insights, first of all, into specific characteristics of the sulfide layers of two valleriite samples of Noril’sk ores. The sample 1 was associated with pyrrhotites Fe1-xS, and the sample 2 associated with chalcopyrite CuFeS2 was a product of its incomplete interaction with serpentine minerals. It was found, in particular, that the sulfide layers in both valleriites show the photoelectron and Cu K-edge XANES spectra slightly distinct from those of chalcopyrite. While the Cu+-S bonding in the first coordination sphere was similar, the differences in the Cu-Fe and Cu-Cu coordination were found for the two valleriites and chalcopyrite, interpreted mainly in terms of various concentrations and the state of iron. The Mössbauer spectra suggest that, in contrast to chalcopyrite with ordered positions of Cu+ and Fe3+ ions and the antiferromagnetic character, the sample 2 contains about 25% of Fe2+-S species responsible for the negative charge of the sulfide layers; the sample 1 appears to have more than 90% of Fe3+. The sulfide layers exhibit rather high conductivity and are in electron equilibrium with hydroxide entities, at least under the XPS experiment conditions. The negative charge of the sulfide “phase” affects the chemical properties of the mineral, in particular, promoting the reduction and deposition of platinum in elemental form.
Primary author
Prof.
Yuri Mikhlin
(Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of sciences)
Co-authors
Dr
Alexander Romanchenko
(Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of Sciences)
Dr
Maxim Likhatskiy
(ICCT SB RAS)
Mr
Mikhail Volochaev
(Kirensky Institute of Physics of the Siberian Branch of the Russian Academy of Sciences)
Dr
Oleg Bayukov
(Kirensky Institute of Physics of the Siberian Branch of the Russian Academy of Sciences)
Dr
Sergei Vorobyev
(Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of Sciences)
Dr
Yevgeny Tomashevich
(Institute of Chemistry and Chemical Technology of the Siberian Branch of the Russian Academy of Sciences)
