Data analysis and estimation of thermodynamic properties of aqueous monovalent metal-glycinate complexes

Abstract

Recently, an aqueous glycine solution has been proposed as a non-toxic environmentally friendly lixiviant to leach precious metals such as gold. In confined spaces, gold can be leached effectively using cyanide as a lixiviant. However, in unconfined applications, cyanide poses detrimental environmental effects due to its high level of toxicity. In order to investigate the effectiveness of lixiviant systems containing glycine and examine their potential, it is essential to identify the thermodynamic properties and stability domains of metal-glycinate complexes. Numerous studies have been conducted on the thermodynamic equilibrium of divalent metal-glycinate formations but those of monovalent metal-glycinate are scarce in general and inexistent for most precious metals including gold. In this study, we use data analysis to relate the standard partial molal properties of metal-glycinate complexes to the standard partial molal properties of various metals and estimate the equilibrium constants of monovalent metal-glycinate formation at ambient conditions. Finally, the standard partial molal properties of the metal-glycinate complexes and their revised Helgeson-Kirkham-Flowers (HKF) equations of state have been estimated and used to deduce the equilibrium constants of metal-glycine systems at different temperatures. The proposed method has been tested using existing experimental data and showed excellent consistency.