Tl nano-minerals and their environmental significance

Thallium (Tl) is a toxic trace metal that can pose a serious threat to human and environmental health. Its maximum permissible levels are generally among the lowest of the regulated inorganic pollutants. In the scope of the TlNanoMin project, we aim at better understanding of this non-essential trace metal using mineralogy as our guide. Tl is used for various high-technology products (optics, electronics or even in radiology). It is only used in small amounts, but because of its unique characteristics it has become an important raw material in modern consumer electronics. Regarding Tl-retention in natural environments, its principal mineral associations are with sulphur, aluminosilicates and manganese oxides. Mine metallurgical wastes are one of the main sources of Tl contamination of soils, surface and groundwater. In areas affected by mining of Tl-rich sulphide ores, Tl contents in sulphide-rich mining wastes reach up to 20 000 mg/kg, which is in comparison with the Tl-concentration in arable soils of about 1 mg/kg enormous. In such areas, Tl is mostly retained in secondary Tl-bearing minerals. From mine waste piles, contaminated soils or sediments, Tl may be released into the groundwater and thus may enter the human food chain. The mobility and bioavailability of Tl in mine waste materials, soils and sediments are dependent on its speciation, i.e., on the chemical form in which the Tl is retained. In the case of secondary minerals, their solubility in water determines their effectiveness to retain Tl and prevent its further transfer. TlNanoMin targets nano- and microscale weathering of Tl-rich mineralisation and corresponding mining wastes, sediments and soils, with particular focus on the multi- component systems, where Tl is associated with other potentially toxic trace elements, such as arsenic (As), antimony (Sb) and/or mercury (Hg). The aim of this research is to investigate these weathering processes and their nano- and microcrystalline products, which are formed from Tl-rich ores, as well as synthetic, mineral-like Tl-bearing oxides and oxy salts of arsenic and sulphur. To achieve this goal, we will investigate both selected naturally Tl-bearing ore deposits and neighbouring mining wastes or soils from three Tl- rich localities in Europa as well as synthetic mineral-like Tl-compounds. For that matter, we will use a variety of complementary analytical techniques to assess the geochemical drivers of weathering in natural settings. The outreach of the TlNanoMin project will highlight the importance of the mineralogy and geochemistry to identify the environmental risks related to emerging pollutants. Modern technologies to determine the concentration and the way of retention of toxic materials in soil, water and food might become an integral part of environmental policy regarding to the growing population and the increased demand for land, soil and water.