In situ X-ray absorption spectroscopy measurement of vapour-brine fractionation of antimony at hydrothermal conditions

Abstract

Despite the growing geological evidence that fluid boiling and vapour-liquid separation affect the distribution of metals in magmatic-hydrothermal systems significantly, there are few experimental data on the chemical status and partitioning of metals in the vapour and liquid phases. Here we report on an in situ measurement, using X-ray absorption fine structure (XAFS) spectroscopy, of antimony speciation and partitioning in the system Sb2O3-H2O-NaCl-HCl at 400°C and pressures 270—300 bar corresponding to the vapour-liquid equilibrium. Experiments were performed using a spectroscopic cell which allows simultaneous determination of the total concentration and atomic environment of the absorbing element (Sb) in each phase. Results show that quantitative vapour-brine separation of a supercritical aqueous salt fluid can be achieved by a controlled decompression and monitoring the X-ray absorbance of the fluid phase. Antimony concentrations in equilibrium with Sb2O3 (cubic, senarmontite) in the coexisting vapour and liquid phases and corresponding SbIII vapour-liquid partitioning coefficients are in agreement with recent data obtained using batch-reactor solubility techniques. The XAFS spectra analysis shows that hydroxy-chloride complexes, probably Sb(OH)2Cl0, are dominant both in the vapour and liquid phase in a salt-water system at acidic conditions. This first in situ XAFS study of element fractionation between coexisting volatile and dense phases opens new possibilities for systematic investigations of vapour-brine and fluid-melt immiscibility phenomena, avoiding many experimental artifacts common in less direct techniques.

A new view on gold speciation in sulfur-bearing hydrothermal fluids from in situ X-ray absorption spectroscopy and quantum-chemical modeling

“…Total sulfur concentration was roughly estimated from the before-edge absorbance of the fluid phase as measured in transmission mode. Details about the reduction procedure and concentration measurements can be found in EA-1 and Pokrovski et al (2008b). …”

“…Experiments were carried out using a high T-P cell developed at the Institut Néel (Testemale et al, 2005) and described in detail elsewhere (see Electronic annex EA1 and Pokrovski et al, 2005aPokrovski et al, , 2006Pokrovski et al, , 2008b). The apparatus includes an inner glassy-carbon cell heated by electrical resistances and inserted in a stainless steel vessel pressurized with helium and equipped with a water-cooling jacket and three beryllium windows for X-ray passage.…”

“…Such spectroscopic approaches have recently become possible owing to the progress in synchrotron radiation techniques and optical cell design (e.g., Seward and Driesner, 2004;Testemale et al, 2005), and new developments in quantum-chemical and molecular dynamics simulations of species structures (e.g., see Sherman, 2001, for review). In addition, quite recently a number of in situ spectroscopic studies involving simultaneous measurement of solid phase solubilities and local atomic structures of solutes in hydrothermal fluids has been reported using Raman and X-ray absorption spectroscopy techniques (e.g., Zotov and Keppler, 2002;Pokrovski et al, 2005aPokrovski et al, , 2006Pokrovski et al, , 2008b). …”

Fluids in geological processes — The present state and future outlook

“…Recent work (e.g., Liu et al, 2008;Pokrovski et al, 2008) illustrates how in-situ Synchrotron Radiation-Induced X-ray Fluorescence (SXRF) studies provide information of mineral solution and nature of complex in situations that have traditionally been difficult to access experimentally (e.g., conditions near the critical point of the solvent; phase separation), but that are commonly encountered in for example ore deposits.…”

Synthesis of Nanoparticles via Solvothermal and Hydrothermal Methods

“…In the twenty-first century, the hydrothermal/solvothermal process has gained great successes in manufacturing nanomaterials with crystallinity, crystal phase, morphology, and size control, due to its outstanding advantages, including low process temperature, performance of reactions in liquid environments, low energy consumption, and environmental benignity [9,[10][11][12][13][14][15][16][17][18].…”