The importance of thiosalt speciation in the management of tailing pond

Abstract

The presence of thiosalts in mining wastewaters is an environmental issue due to the resulting pH depression as these species degrade with time. Despite research in the area, reaction kinetics of thiosalt species under different pH and temperature conditions are not fully understood, especially in conditions common in receiving ponds. As a result, it is difficult to design ponds or develop treatment technologies to treat these compounds. Several studies have dealt with the reaction kinetics of major thiosalt species (thiosulfate, trithionate, tetrathionate) under various pH and temperature conditions. However, further research is required to better understand the fundamental behaviors of thiosalt species and identify probable reaction paths in temperatures below 30°C, pH range between 2 and 9 and in the presence of reagents. -- The overall objectives of this work have been to study the behavior of thiosalts in mining wastewaters and develop a model of their behavior under the conditions studied that includes pH and temperature as independent variables. The study is divided in four parts: the first part is a summary of relevant information in terms of generation and kinetics of thiosalts, analytical methods for measuring their concentrations, and treatment of thiosalt wastes. Despite extensive research in the area, generation and kinetic information of thiosalt species under different pH and temperature conditions is not fully understood, especially under the range of conditions likely to be encountered in receiving ponds. -- The second part of the study analyzes the behavior of thiosulfate, trithionate and tetrathionate and provides with mathematical models for their behavior as pure species under the specified conditions. The third part of the study consists of the analysis of the thiosalt behavior in mixtures following a decoupling approach; this analysis provided with additional information for the proposal of global reaction pathways for the species. Finally, the last chapter provides preliminary results from kinetic experiments with selected reagents, results from equilibrium simulations and an analysis of future work required to improve the understanding of thiosalt reactions, improve treatment efficiency and reduce the environmental impact of acid mine drainage.