XAFS measurements on zinc chloride aqueous solutions from ambient to supercritical conditions using the diamond anvil cell

Abstract

The structure and bonding properties of metal complexes in subcritical and supercritical fluids are still largely unknown. Conventional high pressure and temperature cell designs impose considerable limitations on the pressure, temperature, and concentration of metal salts required for measurements on solutions under supercritical conditions. In this study, we demonstrate the first application of the diamond anvil cell, specially designed for x-ray absorption studies of fn'st-row transition metal ions in supercritical fluids. Zn K-edge XAFS spectra were measured from aqueous solutions of 1-2m ZnC12 and up to 6m NaC1, at temperatures ranging from 25-660 °C and pressures up to 800 MPa. Our results indicate that the ZnC142-complex is predominant in the lm ZnC12/6m NaC1 solution, while ZnC12(H20)2 is similarly predominant in the 2m ZnC12 solution, at all temperatures and pressures. The Zn-C1 bond length of both types of chlorozinc(II) complexes was found to decrease at a rate of about 0.01 A/100 °C.

The effect of CO2 on the speciation of RbBr in solution at temperatures to 579°C and pressures to 0.26GPa

“…EXAFS spectra from the SFLINCS are worse than the best from hydrothermal and diamond anvil type experiments (e.g. Mayanovic et al, 1999Mayanovic et al, , 2001Simonet et al, 2002). Better SFLINCS are obtained using the 9mm Ag capsules than in the 5mm Pt capsules.…”

“…No conclusive evidence of any other changes in RbBr speciation with increasing temperature and pressure have been found, although molecular dynamics (MD) simulations (e.g. Wallen et al, 1997;Ferlat et al, 2001) suggest that ion-pairing should occur, and studies of ZnCl 2 and ZnBr 2 in Na-halide solutions have revealed ion pairing and other complexes, such as ZnCl 4 2À (Mayanovic et al, 1999(Mayanovic et al, , 2001Simonet et al, 2002).…”

Subseafloor phase equilibria in high-temperature hydrothermal fluids of the Lucky Strike Seamount (Mid-Atlantic Ridge, 37°17′N)

“…Several investigations, however, suggest the monochloro-zinc complex is relatively insignificant at the conditions considered herein (e.g. Wesolowski et al, 1998;Mayanovic et al, 1999) and we have therefore chosen to suppress formation of this complex. Solubility data for H 2 S (aq) are from Kishima (1989).…”

Speciation and thermodynamic properties for cobalt chloride complexes in hydrothermal fluids at 35–440°C and 600bar: An in-situ XAS study

“…In recent years, increasing evidence from in-situ X-ray absorption spectroscopy (XAS) studies have shown that the structure of the complexes formed by halide ions and the divalent first-row transition metals (e.g., Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ ) changes from octahedral to tetrahedral with increasing temperature and/or halide concentration (e.g., Anderson et al, 1995;Hoffmann et al, 1999;Mayanovic et al, 1999;Collings et al, 2000;Brugger et al, 2001;Simonet et al, 2002;Liu et al, 2007;Testemale et al, 2009). However, the precise structure and number of halide ligands in the tetrahedral species remain controversial.…”

“…However, the precise structure and number of halide ligands in the tetrahedral species remain controversial. For example, under which conditions (T, P, salinity) is the metal bonded with four halide ions (e.g., FeCl 4 2À , Testemale et al, 2009; ZnCl 4 2À , Mayanovic et al, 1999), or with both halide ions and water molecules (e.g., NiBr 3 (H 2 O) À , Hoffmann et al, 1999)? A similar coordination change from octahedral to tetrahedral-like upon increasing temperature and/or salinity was described by Bazarkina et al (2010) for Cd 2+ , with aqueous speciation at high temperature (>300°C) dominated by the tetrahedral complexes CdCl 2 (H 2 O) 2(aq) and CdCl 3 (H 2 O) À .…”