Potential High-Risk Release Sources of Thallium and Arsenic from Surrounding Rocks of a Typical Thallium and Arsenic Mining Area in Southwest China

Abstract

Abundant naturally and anthropogenically exposed surrounding rocks (NESRs and AESRs) in mining areas may pose persistent threats as sources of potentially toxic elements (PTEs), but this has been historically overlooked, especially for thallium (Tl) and arsenic (As). Here, the release risks of Tl and As from both NESRs and AESRs in a typical Tl-As sulfide mining area were investigated. In a single leaching process, AESRs released 10.4% of total Tl (157 μg L–1) and 32.5% of total As (4089 μg L–1), 2–3 orders of magnitude higher than NESRs. Prolonged alternate drying and wetting leaching test revealed notable and long-term risks of release of Tl and As from AESRs, associated with iron-bearing mineral dissolution and acid production. Substantial release of PTEs was linked to the transformation/degradation of the -OH functional group and extensive dissolution of secondary sulfate minerals in AESRs. Ultrafiltration and STEM-EDS indicate that 18.4% of water-extracted As released from AESRs existed as natural nanoparticles consisting of iron-sulfur minerals. This study highlights the high risks of Tl and As release from anthropogenically exposed surrounding rocks and the importance of nanoparticles in PTE transport, and provides insights into the control of PTEs in mining areas.

Keywords: Surrounding rock, Thallium (Tl), Arsenic (As), leachability, Nanoparticles