Love is in the Earth: a review of tellurium (bio)geochemistry in surface environments

Abstract

Tellurium (Te) is a rare metalloid in the chalcogen group of the Periodic Table. Tellurium is regularly listed as acritical raw material both due to its increased use in the solar industry and to the dependence on other com-modities in its supply chain. A thorough understanding of the (bio)geochemistry of Te in surface environments isfundamental for supporting the search for future sources of Te (geochemical exploration); developing innovativeprocessing techniques for extracting Te; and quantifying the environmental risks associated with rapidly in-creasing anthropogenic uses. The present work links existing research in inorganic Te geochemistry and mi-neralogy with the bio(geo)chemical and biological literature towards developing an integrated Te cycling model.Although average crustal rocks contain only a few μg/kg of Te, hydrothermal fluids and vapours are able toenrich Te to levels in excess of mg/kg. Tellurium is currently recovered as a by-product of base-metal mining; inthese deposits, it occurs mainly in common sulfides substituting for sulfur. Extreme Te enrichment (up to wt.%)is found in association with the precious metals Au and Ag in the form of telluride and sulfosalt minerals.Tellurium also forms a large variety of oxygen-containing secondary minerals as a result of weathering of Te-containing ores in (near-)surface environments. Anthropogenic activities introduce significant amounts of Teinto surficial environments, both through processing materials that contain minor Te and through breakdown ofused Te-containing materials. Additionally, radioactive132Te is produced in nuclear reactors and can con-taminate surrounding and distal environments.Environmental contamination of Te poses concern to organisms due to the acute toxicity of some Te com-pounds, especially the soluble tellurite and tellurate anions. A small percentage of microorganisms, however, areable to tolerate elevated levels of Te by detoxifying it through precipitation or volatilisation. Bioaccumulation ofTe compounds can occur in some plants of the garlic family. A variety of interlinked organic and inorganicprocesses govern Te environmental chemistry. The Te cycle in surface environments incorporates (oxidative)dissolution of Te from primary ore minerals, inorganic precipitation and redissolution processes in which sec-ondary minerals are formed, and bioreductive reprecipitation and volatilisation processes governed mainly bymicrobes. Our integrated Te cycling model highlights the interplay between anthropogenic, geochemical andbiogeochemical processes on the distribution and mobility of Te in surface environments