Kinetics of selenium and tellurium removal with cuprous ion from copper sulfate-sulfuric acid solution by Mohammad Mokmeli A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Materials Engineering) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April 2014 © Mohammad Mokmeli, 2014 Abstract Dissemination of selenium and tellurium in pyritic ores and many of the sulphide minerals results in the contamination of pregnant leach solutions and electrolytes in hydrometallurgical treatment of sulphide ores and residues. In an effort to reduce the detrimental effects of selenium and tellurium, it has been of great interest to remove selenium and tellurium from contaminated solutions to lower levels than allowed in regulations, product specifications or process requirements. The selenium and tellurium content of the solution may be reduced into insoluble precipitates of copper selenides and tellurides using cuprous ion. Cuprous ion has uses as a reducing agent in hydrometallurgical applications and can be specifically used to remove selenium and tellurium ions from copper sulphate-sulfuric acid solutions. In this study, the chemistry and kinetics of the removal of selenium and tellurium from copper sulfate-sulfuric acid solutions by cuprous ion reduction and precipitation was pursued. At first, a study of equilibrium cuprous concentrations for the cupric–copper metal reaction was performed and an empirical function capable of predicting the saturated [Cu +] was suggested at different temperatures, cupric and sulfuric acid concentrations. Secondly, the kinetics of the selenium removal with cuprous was studied and the mechanism of the reduction reaction and the rate law was determined over a wide range of acidity and temperature. The effects of temperature, acidity, cupric concentration and ionic strength on selenium removal rate were also studied. Subsequently, rate constants as functions of temperature, acidity and ionic strength were suggested. Thirdly, the tellurium reduction chemistry and reaction kinetics by means of cuprous in a wide range of conditions were investigated. The mechanism of the reaction, rate ii constants and activation energies were also determined. Similarly to selenium, effects of temperature and acidity on tellurium removal rate were also studied and rate constants as a function of temperature and acidity were suggested. Selenium and tellurium reduction reaction times can be estimated at different acidities and temperatures using the suggested rate laws and rate constant functions. iii Preface Much of the work presented in this thesis has been previously published in Hydrometallurgy journal, or is under review for publication or has been presented at the conference. The overall supervision of this research was provided by Dr. Dreisinger and Dr. Wassink. The experimental apparatus and some of the experimental procedures have been developed by Dr. Wassink. All the testing, data analysis and manuscript writing were conducted by the candidate. All publications were prepared by the candidate and edited by Dr. Dreisinger and Dr. Wassink, prior to submission for publication. This thesis manuscript is mainly composed of the publications listed below: Mokmeli M., Wassink B., Dreisinger D. B., (2012), Equilibrium cuprous concentrations in copper sulfate–sulfuric acid solutions containing 50–110 g/L Cu 2+ and 10–200 g/L H2SO 4 at 50–95 °C, Hydrometallurgy, Volume 121-124, pp. 100–106. Portions of this paper appear in sections 2.1, 3.2 and 4.1. Mokmeli M., Wassink B., Dreisinger D. B., (2013), Cuprous sulfate thermodynamics and cuprous perchlorate oxidation kinetics, European Metallurgical Conference 2013, Weimar, Germany, pp. 69-84. Portions of this paper appear in sections 1.1, 3.2, 4.1 and 4.2. iv Mokmeli M., Wassink B., Dreisinger D. B., (2013), Kinetics study of selenium removal from copper sulfate-sulfuric acid solution, Hydrometallurgy, Volume 139, pp 13-25. Portions of this paper appear in section 2.2 and chapter 5. Mokmeli M., Dreisinger D. B., Wassink B., (under consideration), Thermodynamics and kinetics study of tellurium removal with cuprous ion, submitted to Hydrometallurgy journal, September 26, 2013. Parts of this manuscript appear in section 2.3 and chapter 6. Mokmeli M., Dreisinger D. B., Wassink B., (2014) Fundamental studies in selenium and tellurium removal from copper sulphate-sulphuric acid solutions with application to industrial purification circuits, Hydrometallurgy Conference 22-25 June 2014, Victoria, Canada v Table of Contents Abstract...........................................................................................................................ii Preface ...........................................................................................................................iv Table of Contents ...........................................................................................................vi List of Tables .................................................................................................................ix List of Figures .................................................................................................................x List of Symbols and Abbreviations...............................................................................xiii Acknowledgments........................................................................................................xiv Dedication....................................................................................................................xvi Chapter 1 Introduction .................................................................................................1 1.1 Background......................................................................................................1 1.2 Problem Definition...........................................................................................5 1.3 Objectives of the Research...............................................................................6 Chapter 2 Chemistry and Kinetics of Cuprous, Selenium and Tellurium.......................7 2.1 Thermodynamics and Kinetics of Cuprous Generation Reaction ......................7 2.2 Selenium Chemistry.......................................................................................12 2.2.1 Selenium Reduction Chemistry and Kinetics ..........................................16 2.2.2 Selenium Reduction Chemistry and Kinetics in Copper Sulfate-Sulfuric Acid Solutions.......................................................................................................19 2.2.3 Chemistry of Cuprous Selenide Reaction with Cupric Ion ......................22 2.3 Tellurium Chemistry......................................................................................25 2.3.1 Tellurium-Copper -Water System...........................................................30 2.3.2 Tellurium Reduction Chemistry and Kinetics .........................................35 2.4 Selenium and Tellurium Removal at VALE (Canada) ....................................40 2.5 Summary .......................................................................................................45 Chapter 3 Experimental..............................................................................................49 3.1 Materials........................................................................................................49 3.2 Experimental Procedures................................................................................50 3.2.1 Generation, Sampling and Analysis of Cuprous Ion................................50 3.2.2 Determination of Equilibrium Cuprous Concentration............................52 3.2.3 Kinetics of Cuprous Oxidation with Perchlorate.....................................54 3.2.4 Kinetics Study of Selenium Reduction ...................................................55 3.2.5 Kinetics Study of Tellurium Reduction...................................................58 3.2.6 Repeatability and Accuracy of the Thermodynamics and Kinetics Experiments...........................................................................................................59 Chapter 4 Cuprous Sulfate Thermodynamics and Cuprous Perchlorate Oxidation Kinetics……….. ...........................................................................................................61 4.1 Equilibrium Cuprous Concentrations in Copper Sulfate-Sulfuric Acid Solutions…................................................................................................................61 4.1.1 Objectives..............................................................................................61 4.1.2 Experimental..........................................................................................62 4.1.3 Results and Discussion...........................................................................62 4.2 Kinetics of Cuprous Oxidation with Perchlorate.............................................68 4.2.1 Objectives..............................................................................................68 4.2.2 Experimental..........................................................................................69 4.2.3 Results and Discussion...........................................................................69 vi 4.3 Summary .......................................................................................................75 Chapter 5 Kinetics