Artashes A. Migdisov

An experimental study of the stability of copper chloride complexes in water vapor at elevated temperatures and pressures

Abstract The solubility of copper chloride in liquid-undersaturated HCl-bearing water vapor was investigated experimentally at temperatures of 280 to 320°C and pressures up to 103 bars. Results of these experiments show that the solubility of copper in the vapor phase is significant and increases with increasing fH2O, but is retrograde with respect to temperature. This solubility is attributed to the formation of hydrated copper-chloride gas species, interpreted to have a copper-chlorine ratio of 1:1 (e.g., CuCl, Cu3Cl3, etc.) and a hydration number varying from 7.6 at 320°C, to 6.0 at 300°C, and 6.1 at 280°C. Complex formation is proposed to have occurred through the reaction: A1 3 CuCl solid +nH 2 O gas ⇋ Cu 3 Cl 3 ·(H 2 O) n gas Log K values determined for this reaction are −21.46 ± 0.05 at 280°C (n = 7.6), −19.03 ± 0.10 at 300°C (n = 6.0), and −19.45 ± 0.12 at 320°C (n = 6.1), if it is assumed that the vapor species is the trimer, Cu3Cl3(H2O)6–8. Calculations based on the above data indicate that at 300°C and HCl fluxes encountered in passively degassing volcanic systems, the vapor phase could transport copper in concentrations as high as 280 ppm. Theoretically, this vapor could form an economic copper deposit (e.g., 50 million tonnes of 0.5% Cu) in as little as ∼20,500 yr.

The stability of Au-chloride complexes in water vapor at elevated temperatures and pressures

Abstract The solubility of gold in liquid-undersaturated HCl-bearing water vapor was investigated experimentally at temperatures of 300 to 360°C and pressures up to 144 bars. Results of these experiments show that the solubility of gold in the vapor phase is significant and increases with increasing fHCl and fH2O. This behavior of gold is attributed to formation of hydrated gold-chloride gas species, interpreted to have a gold-chlorine ratio of 1:1 and a hydration number varying from 5 at 300°C to 3 at 360°C. These complexes are proposed to have formed through the following reaction: (A1) Au solid + m · HCl gas + n · H 2 O gas = AuCl m ·( H 2 O ) n gas + m 2 · H 2 gas which was determined to have log K values of −17.28 ± 0.36 at 300°C, −18.73 ± 0.66 at 340°C, and −18.74 ± 0.43 at 360°C. Gold solubility in the vapor was retrograde, i.e., it decreased with increasing temperature, possibly as a result of the inferred decrease in hydration number. Calculations based on our data indicate that at 300°C and fO2-pH conditions, encountered in high sulfidation epithermal systems, the vapor phase can transport up to 6.6 ppb gold, which would be sufficient to form an economic deposit (e.g., Nansatsu, Japan; 36 tonnes) in ∼ 30,000 yr.

The Chemistry of Metal Transport and Deposition by Ore-Forming Hydrothermal Fluids

The chapter presents an overview of the chemistry of transport and deposition of metals by aqueous fluids under hydrothermal conditions that are responsible for the formation of ore deposits throughout the Earths crust. Metal complex equilibria at elevated temperatures and pressures are considered in relation to modern knowledge of water solvent structure and properties as well as electrolyte solution behavior under extreme conditions. The recent advances in our knowledge of the stoichiometry and stability of metal complexes from experimental and ab initio studies are discussed within the context of hydrothermal fluids having liquid-like densities and those having gas-like densities.

Steel slag carbonation in a flow-through reactor system: the role of fluid-flux.

Steel production is currently the largest industrial source of atmospheric CO2. As annual steel production continues to grow, the need for effective methods of reducing its carbon footprint increases correspondingly. The carbonation of the calcium-bearing phases in steel slag generated during basic oxygen furnace (BOF) steel production, in particular its major constituent, larnite {Ca2SiO4}, which is a structural analogue of olivine {(MgFe)2SiO4}, the main mineral subjected to natural carbonation in peridotites, offers the potential to offset some of these emissions. However, the controls on the nature and efficiency of steel slag carbonation are yet to be completely understood. Experiments were conducted exposing steel slag grains to a CO2-H2O mixture in both batch and flow-through reactors to investigate the impact of temperature, fluid flux, and reaction gradient on the dissolution and carbonation of steel slag. The results of these experiments show that dissolution and carbonation of BOF steel slag are more efficient in a flow-through reactor than in the batch reactors used in most previous studies. Moreover, they show that fluid flux needs to be optimized in addition to grain size, pressure, and temperature, in order to maximize the efficiency of carbonation. Based on these results, a two-stage reactor consisting of a high and a low fluid-flux chamber is proposed for CO2 sequestration by steel slag carbonation, allowing dissolution of the slag and precipitation of calcium carbonate to occur within a single flow-through system.