Physicochemical modeling as applied to study of sulfoarsenide complexes in hydrothermal solutions

Abstract

System As–Na–S–Cl–H–O was studied. The research was carried out in three stages: (1) selection of the most likely complexes resulting from arsenic sulfide dissolution, (2) calculation of their thermodynamic constants, and (3) comparison of calculated data with thermodynamic database obtained in tests with the solution of inverse thermodynamic problems using the Selektor program complex. The system As–Na–S–Cl–H–O included more than 230 dependent components, which were divided into two groups, base and functional. The former group includes components of the solution (NaCl, NaOH, Na2S, NaHS, HCl, H2S, H2SO4, sulfates, H2SO3, sulfites, thiosulfates, Na+, Cl−,HS−, S2−), gas phase (43 components), and solid phase (orpiment, red arsenic, arsenolite, claudetite, arsenic, sulfur, sodium salts). Thermodynamic constants of the base components are contained in the Selektor database (they were borrowed from reference-books). The latter group includes 77 complexes labile in the solution but determining the solubility of arsenic and stability of its solid phases. Physicochemical modeling was performed in H2S (≥0.01 m, pH = 1–10), Na2S, and NaHS solutions at 25–250 °C and saturated-vapor pressure. It has been established that the dissolution of arsenic sulfide mineral phases in subneutral and alkaline solutions at low oxidation potential is favored by the formation of sulfoarsenides, which are more stable than arsenides and arsenates. Thermodynamic constants of functional complexes determining the orpiment solubility were calculated within the experimental error. It is shown that in hydrothermal iron-free systems with a low oxidation potential, the concentration of As in the solution decreases on cooling and with acidity increase.

Sulfoarsenide complexes of gold in hydrothermal solutions in the formation of gold ore deposits (thermodynamic modeling)

“…The calculations used numerical correlation of the data of the experimental system by means of the min imization of the difference in the calculated parame ters by the SELEKTOR SW and the values obtained in the experiments over the entire set of initial data, on the obligatory condition of the minimization of the isobar-isotherm of the Gibbs potential [12]. The ini tial thermodynamical constants of gold complexes at increased temperatures were calculated in the HKF system [13].…”

“…oxides of these elements) [12]. The selection of the initial approximation for the calculation of isobarisotherm potentials (the g T functions) of sulfoarsenide …”

“…The sulfoars enide complex of gold is formed on the basis of thio arsenite and Au hydrosulfide [12] by the scheme:…”

“…The activity of the interacting particles was determined using the experimental data from [2,10]. The g T functions of the complex calculated with the standard equation of free energy for on the basis of the g T functions for HS -hydrosulfide ion, gold hydrosulfide (Akinfiev and Zotov, 2001; Pal'yanova, 2008), and thioarsenite ion [12] at 25, 200, and 300°C were used in the calcula tions.…”