ENVIRONMENTAL BEHAVIOR OF TELLURIUM IN MINE TAILINGS

Tellurium (Te) is a critical element used in solar panels and thermoelectric devices, and is enriched in some types of gold deposits. 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. Telluride (Te^<0) minerals, which are typically not bioaccessible, can oxidize to tellurite (Te^IV), and/or tellurate (Te^VI) in the surficial environment, with Te^IV being approximately 10x more toxic. Predicting the dominant oxidation state under surficial conditions is complicated by limited, often inconsistent, thermodynamic datasets. Thus, documenting Te-behavior in natural samples collected under a variety of environmental conditions is important. To that end, eight historical mine tailings samples, containing between 6-900 mg kg^-1 Te, were examined to assess Te behavior in the surficial environment. These tailings were collected from a range of climates (arid to alpine) and, during 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. Smaller particle size and higher total sulfur in the solid were correlated (correlation coefficients >0.87) with high conductivity and ion release duing the SPLP leach. 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, 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.