UBC Theses and Dissertations

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UBC Theses and Dissertations

Recovery and production of high-purity tellurium from silver soda slag Mackowiak, Kristian David


The objective of the current research was the extraction and separation of silver and tellurium from an industrial slag by-product. The recovery of these elements presented an opportunity to extract additional value from the slag, as well as produce tellurium, an important metal in solar panel production. A 2N purity tellurium powder was produced using a three-stage process. The process first involved a pyrometallurgical processing step, which served to separate the silver from tellurium. A thermodynamic model was first produced in HSC 9.1 to determine the effects of temperature and various reagents on the pyrometallurgical system. Using the model results, a central composite design (CCD) methodology was utilized to determine the experimental tests to conduct. The results of the CCD testing were used to generate full quadratic statistical models using MATLAB®. From the experimental testing, the silver recovery during the pyrometallurgical step was 92% to the metal phase and 88% tellurium recovery to the slag phase. The remaining pyrometallurgically processed slag from the previous step was then crushed and prepared for leaching. The lixiviant used was deionized water, with the slurry consisting of 1 to 30% slag by weight. Approximately 30% of the Te in the slag would instantaneously leach, which was attributed to sodium tellurite dissolution. Following 24 hours of leaching, additional tellurium would leach into solution. It was found that a lower solids percentage in the slurry yielded over 60% Te recovery. The addition of sodium hydroxide or sodium sulphide also led to increases in the Te recovery. The resulting tellurium leach solution could then be purified in one of two ways. First, electrowinning of the solution could be conducted, which led to the production of the 2N purity Te powders. Recoveries typically around 70 to 90% were achieved in a single electrowinning step. It was found that using the leach solution containing sodium sulphide would lead to the highest Te recovery, at 91%, with a purity of nearly 3N. Combining all three steps, the overall Te recovery of the system was found to be 46%.

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