BEHAVIOR OF TELLURIUM IN SURFICIAL MINE TAILINGS

Tellurium (Te) is a critical element used in solar panels and thermoelectric devices with growing demand and uncertain future supply. Little is known about the behavior of Te in the surficial environment. Thus Te-enriched legacy mine wastes could represent a future Te resource or an environmental hazard or both. Telluride (Te^<0) minerals have low bioaccessibility and can oxidize to more toxic forms, such as tellurite (Te^IV), and/or tellurate (Te^VI), but predicting the dominant oxidation state under environmental conditions is complicated by limited, and often inconsistent, thermodynamic datasets. Eight historical mine tailings samples, containing between 6-900 mg kg^-1 Te, and collected from a range of climates (arid to alpine) were examined to document the mineralogical host and speciation of Te in natural samples and correlate that with bioaccessibility and lability. In simulated weathering experiments, the synthetic precipitation leach procedure (SPLP) produced leachates with a wide range of pH (2.7-9.0) and conductivity (0.01-4.8 mS cm^-1) values. Physiologically-based extraction tests (PBET) mimicking gastric conditions liberated between 1 and 88% of total Te, whereas the SPLP and lung PBET liberated less than 1% of total Te. Linear combination fits of Te K-edge X-ray absorption spectra provide strong evidence for the presence of both Te^IV and Te^VI in most bulk samples, although the fraction of each species varied. The X-ray absorption spectroscopy-estimated abundance of Te^VI in the samples positively correlated with leachate pH and correlated, albeit less strongly, with mean annual temperature at the sample site, suggesting that climate influences Te speciation, a hypothesis we will continue to explore using bulk and grain-scale mineralogical investigation. This ongoing work will lend insight into the behavior of Te under a broad range of environmental conditions, which is important when assessing the potential for Te recovery from legacy mine wastes, as well as risks to human health and the environment.