TELLURIUM BEHAVIOR IN HISTORICAL MINE TAILINGS

Alternative resources are needed to address the predicted shortfalls in global supply of tellurium (Te), which is used in solar panels and thermoelectric devices. Tellurium is currently mostly recovered as a byproduct of Cu extraction, but is enriched in some types of gold deposits and, consequently, Te-enriched legacy mine wastes could represent a future Te resource. Under surficial conditions, mine wastes undergo oxidative weathering and telluride (Te^<0) minerals oxidize to phases containing tellurite (Te^IV) and/or tellurate (Te^VI). Thus, documenting the Te oxidation state and host minerals in weathered mine waste samples collected under a variety of environmental conditions is an important first step in evaluating recoverability of Te from mine tailings. To that end, eight historical mine tailings samples, containing between 6 and900 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 deposit types (Comstock epithermal vein, quartz-alunite epithermal vein, and alkaline Au-Te). During simulated weathering experiments, the US EPA 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, with smaller particle size and higher total sulfur in the solid positively correlating with high conductivity and ion release during the SPLP leach. Grain-scale mineral identification using scanning electron microscopy and electron microprobe revealed a wide variety of Te-bearing minerals, although few residual primary telluride minerals were detected. Some Te-essential minerals were detected, but in most Te-containing particles, Te is associated with phases that do not contain stoichiometric Te, such as iron (oxy)hydroxides, tripuhyite (FeSbO₄), and beaudantite [PbFe₃(AsO₄)(SO₄)(OH)₆]. Further, 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 relative fractions of species varied. 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.