Batista, Maria Joao

Figueiredo, M. Ondina

Oliveira, Daniel P. S.

Silva, Teresa

Veiga, JP

de Oliveira, Daniel Pipa Soares

Repositório do LNEG

  2nd Meeting of Synchrotron Radiation Users from Portugal and ESRF-Day       2nd ENURS & ESRF-Day     Rhenium incorporation in molybdenite: first results of a XANES study  Teresa Pereira da Silva 1 (*), Maria-Ondina Figueiredo 2,1, Daniel de Oliveira 1,  João Pedro Veiga 2, Maria João Batista 1  1 National Laboratory of Energy & Geology (LNEG), Research Unit of Mineral Resources & Geophysics, Apartado 7586, 2610-999 Amadora, Portugal  2 Centre for Materials Research (CENIMAT/I3N), Materials Science Department, Faculty of Sciences &Technology, New University of Lisbon, 2829-516 Caparica, Portugal (*) E-mail: teresa.pena@lneg.pt Scientific Research Area: CHEMISTRY  Keywords: Rhenium; molybdenite; Re L3 absorption edge; XANES; polytypes  Rhenium (Re) is a scarce element that occurs mainly in porphyry copper-molybdenum ore deposits associated with the mineral molybdenite, MoS2 (recognized as the main Re-carrier in Nature) but also in granite pegmatites and quartz veins as well as in volcanic gases. The unique combination of physical and chemical properties of rhenium and its alloys makes this element extremely attractive thus highly demanded. It has been applied in a great diversity of industrial fields in recent years – aerospace, electrical, chemical production (catalysts) nuclear and biomedical [1]. Molybdenite structure was determined ninety years ago [2]. It is based on the stacking of [S-Mo-S] layers with Mo4+ cations in prismatic coordination between two superimposed closest-packed layers of S= anions, giving rise to polytypism [3,4] - namely 2H, hexagonal, and 3R, trigonal, the first polytype being more common in Nature but the second, incorporating higher Re-contents [5]. Between successive prismatic planar modules, additional octahedral and tetrahedral interstices are available in molybdenite which could locally accommodate ions with suitable coordination requirements, thus giving rise either to a solid-solution or to dispersed nanodomains of another phase.  With the aim of clarifying these possibilities, an X-ray absorption spectroscopy (XANES) study using synchrotron radiation was performed at the Re L3-edge of rhenium-rich 2H-molybdenite samples from different provenances [6]. Obtained results are developed supporting the generally accepted structural perspective that rhenium is mainly carried by molybdenite through the isomorphous replacement of Mo, rather than by the formation of dispersed Re-specific nanophase(s).  Further spectroscopic experiments are foreseen to study the incorporation of rhenium in 3R- molybdenite samples, namely from the wolframite-cassiterite mineralization of Panasqueira, northern Portugal, where the rhombohedral polytype was assigned fifty years ago [7]. References [1] Naor, A., et al. (2010) Properties and applications of rhenium and its alloys. AMMTIAC Quart. 5, 11-15.  [2] Dickinson, R.G. & Pauling, L. (1923) The crystal structure of molybdenite. J. Am. Chem. Soc. 45, 1466-1471. [3] Traill, R.J. (1963) A rhombohedral polytype of molybdenite. Canad. Min. 7, 524-526. [4] Takeuchi, Y. & Nowacki, W. (1964) Detailed crystal structure of rhombohedral MoS2 and systematic deduction of possible polytypes of molybdenite. Schweiz. Miner. Petrol. Mitt. 44, 105-120. [5] Newberry, R.J.J. (1979) Polytypism in molybdenite (I): a non-equilibrium impurity-induced phenomenon. Amer. Min. 64, 758-767. [6] Silva, T.P., et al. (2013) Molybdenite as a rhenium carrier: first results of a spectroscopic approach using synchrotron radiation. Submitted, J. Electron Spectroscopy and Related Phenomena. [7] Clark, A.H. (1965) Rhombohedral molybdenite from the Minas da Panasqueira, Beira Baixa, Portugal. Min. Mag. 35, 69-71. 

Rhenium incorporation in molybdenite : first results of a XANES study

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