University of Alaska Fairbanks

Tellurium is classified as a (near-)critical element due to low average crustal abundance (3 μg kg-1), extraction as a byproduct, and increasing use in high technology applications, particularly high efficiency solar panels. Currently, nearly all Te is recovered as a byproduct of Cu extraction, but Te is also enriched in, but not recovered from, some Au/Ag ore bodies. The goals of the present study are (1) to perform a mass balance to identify inefficient extraction steps and high concentration waste streams where Te recovery could be initiated or improved, and (2) to assess the distribution of Te between host minerals throughout the extraction process. Preliminary results indicate less than 2% of Te present in Cu ore is recovered, with particularly high losses during initial concentration of Cu ore minerals by flotation. Tellurium is principally present in the ore in tellurides (e.g., PbTe, Bi₂Te₃, and Ag-S-Se-Te phases identified using electron microprobe) with low substitution into sulfides (~10 mg kg-1 Te in bulk pyrite and chalcopyrite). This work has also identified Te accumulation in solid-phase intermediates that could be further processed to recover Te, inducing: smelter dusts (200 mg kg-1) and a precious metal concentrate (1300 mg kg-1), where Te is present in both reduced and oxidized forms, as determined by x-ray absorption spectroscopy. One of the several high-grade Au/Ag telluride deposits in the US has an estimated capability to recovery tens of tons Te per year. However, Te is not currently being recovered, largely due to a lack of knowledge of Te behavior during the Au extraction process and only marginally profitable economics. However, there is substantial enrichment of Te (100 mg kg-1 relative to 6 mg kg-1 in average ore) in several solid-phase extraction intermediates, suggesting the potential for Te recovery. These results clearly indicate that relatively small gains in Te recovery from operating mines would result in a substantial increase in Te available to high technology industries. We have also identified several points during the extraction process where Te recovery might be initiated or improved.