Antimony isotope fractionation and thermodynamics during oxidative weathering of stibnite ores

• Applicants: Dr. Marina Lazarov; Professor Dr. Juraj Majzlan, Ph.D.
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 422759556

Oxidative weathering of stibnite, the most common mineral of antimony, is the major pathway of the human-driven introduction of the element antimony into the environment. Stibnite transforms in natural outcrops or mining waste through a sequence of phases to the ultimate inorganic sink of antimony, the mineral tripuhyite (FeSbO4). This sequence includes sulfoxides, mixed-valence (Sb3+/Sb5+) oxides and hydroxides, and phases of Sb5+ with other cations. The mineralogy of oxidative weathering progress is a measure of the transformation progress. Here, we propose to track the progress of weathering by quantitative determination of Sb isotopic composition in the individual phases of this sequence. In the proposed work, a solution and laser-ablation MC-ICP-MS analytical protocol for isotopic analysis of antimony will be tested, developed, and implemented. This protocol will be applied to a previously thoroughly studied model system (mining waste with abundant stibnite and its weathering products) to determine the isotopic changes during the progression from initial to mature weathering stages, changes in mineralogy, and oxidation state of antimony. The rich redox chemistry of Sb is expected to induce large variations in the Sb isotopic composition (as indicated by sparse previous literature) and thus provide an excellent tracer of antimony weathering and dispersal in nature. Furthermore, we aim at the examination of the presence or absence of the Sb3+/Sb5+ oxides (a group of minerals with pyrochlore structure) by the evaluation of the saturation state of contaminated water, using thermodynamic (calorimetric) measurements. The overall goal of the project is better understanding of the behavior of antimony under oxidizing conditions.

• DFG Programme: Research Grants
• Cooperation Partner: Professor Dr. Stefan Weyer, Ph.D.