Experimental studies of the solubility and complexing of selected ore elements (Au, Ag, Cu, Mo, As, Sb, Hg) in aqueous solutions

Abstract

The importance of complexing in controlling the solubility, transport and precipitation of ore metals in aqueous solutions is a recurrent theme of this book. In this chapter experimental results obtained at the Institute of the Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of the Russian Academy of Sciences, Moscow during the past ten years are reviewed. The results presented here, on the solubility and complexing of a disparate range of metals in aqueous solutions, are linked together by a common methodological approach: the investigation, where possible, of simple systems to determine equilibrium constants for specific complex formation. The scope of this paper is unashamedly idiosyncratic. Some elements have received detailed and extensive study, others only limited investigation. However, the authors attempt to describe the results of many years work to characterize some Fluids in the Crust: Equilibrium and transport properties.

Stability of AuCl2− from 25 to 1000 °C at Pressures to 5000 bar and Consequences for Hydrothermal Gold Mobilization

“…The measured Au solubilities are best described by the formation of the AuCl 2 − complex. The equilibrium Au solubility constants calculated for the contrasting redox states are in perfect agreement with each other and fall between the values reported by Zotov et al [5] and Stefánsson and Seward [6]. The experimental values of the Au solubility constant were fitted together with Au solubility data available in the literature for temperatures from 25 to 1000 • C and pressures up to 2 kbar to a simple density model equation.…”

“…* Au-NaCl-HCl-H2-H2O system; ** Au-NaCl-HCl-H2SO4-SO2-H2O system. The experiments reported here fall within the T-P range of the key studies of Au solubility in chloride fluids performed by Zotov et al [5] and Stefánsson and Seward [6] (Supplementary Material Section 3.5). Our Au solubility data are 0.5 log units lower than those of [5].…”

“…• values predicted by Equation (5) and data of [5] increases to one log unit. This disagreement can be explained by partial loss of hydrogen, whose concentration was calculated, but …”

Antimony speciation in saline hydrothermal fluids: A combined X-ray absorption fine structure spectroscopy and solubility study

“…On the basis of many solubility studies of Sb III oxide and sulphide solids, aqueous hydroxide and sulphide complexes are believed to be the main Sb species in hydrothermal environments. Despite the somewhat uncertain stoichiometries for sulphide complexes which range from monomers to dimers according to different studies (e.g., Krupp, 1988;Spycher and Reed, 1989;Wood, 1989;Zotov et al, 1995), the majority of authors agree that sulfide species dominate only in H 2 S-rich (>0.01-0.1 m) low-to-moderate temperatures (<200-250°C) solutions of neutral-to-alkaline pH (Zotov et al, 2003;references therein). In most high-temperature hydrothermal fluids, the neutral Sb III hydroxide, Sb(OH) 3 , whose thermodynamic properties are well known to at least 450°C, is believed to be largely responsible for Sb transport in a wide pH range (Zotov et al, 2003;references therein).…”

The physical and chemical evolution of low-salinity magmatic fluids at the porphyry to epithermal transition: a thermodynamic study

“…For this modelling study, Gibbs free energy functions of temperature at 500 bar have been fitted to the experimental equilibrium constants given by Stefa´nsson (2003) Copper complexation experiments involving hydroxy, bisulphide and chloride ligands were evaluated by Akinfiev and Zotov (2001) who fitted published experiments to the HKF formulation for extrapolation. The most important copper(I) species in medium-salinity fluids are chloride complexes, whose thermodynamic data were derived from the largely concordant solubility experiments by Xiao et al (1998) and Zotov et al (1995) up to 350°C. The complex CuCl 3 À was ignored (cf.…”