Crystal Chemistry of Vanadium-Bearing Ellestadite Waste Forms

Yanan Fang; Sam J Page; Gregory J Rees; Maxim Avdeev; John V Hanna; Tim J White

doi:10.1021/acs.inorgchem.8b01160

Crystal Chemistry of Vanadium-Bearing Ellestadite Waste Forms

Inorg Chem. 2018 Aug 6;57(15):9122-9132. doi: 10.1021/acs.inorgchem.8b01160. Epub 2018 Jul 16.

Authors

Yanan Fang¹, Sam J Page², Gregory J Rees², Maxim Avdeev³, John V Hanna², Tim J White¹

Affiliations

¹ School of Materials Science & Engineering , Nanyang Technological University , 50 Nanyang Avenue , 639798 Singapore.
² Department of Physics , University of Warwick , Gibbet Hill Road , Coventry CV4 7AL , United Kingdom.
³ Australian Nuclear Science and Technology Organisation , Locked Bag 2001, Kirrawee DC , New South Wales 2232 , Australia.

PMID: 30010324
DOI: 10.1021/acs.inorgchem.8b01160

Abstract

Vanadate ellestadites Ca₁₀(SiO₄) _x(VO₄)_{6-2 x}(SO₄) _xCl₂, serving as prototype crystalline matrices for the fixation of pentavalent toxic metals (V, Cr, As), were synthesized and characterized by powder X-ray and neutron diffraction (PXRD and PND), electron probe microanalysis (EPMA), Fourier transform infrared spectroscopy (FTIR), and solid-state nuclear magnetic resonance (SS-NMR). The ellestadites 0.19 < x < 3 adopt the P6₃/ m structure, while the vanadate endmember Ca₁₀(VO₄)₆Cl₂ is triclinic with space group P1̅. A miscibility gap exists for 0.77 < x < 2.44. The deficiency of Cl in the structure leads to short-range disorder in the tunnel. Toxicity characteristic leaching testing (TCLP) showed the incorporation of vanadium increases ellestadite solubility, and defined a waste loading limit that should not exceed 25 atom % V to ensure small release levels.