Coating development on mine waste rocks as a protective sink to attenuate the off-site migration of antimony in the environment

This study explored the feasibility of depositing protective coatings with an Sb scavenger function on mine waste rocks derived from the exploitation of stibnite deposits. Encapsulation treatments were performed using ferrous sulfate as the coating precursor. Different Fe/Sb_leachable molar ratios (0.1, 1, and 10) were evaluated using hydrothermal and thermal processes at various temperatures (30, 50, 100, and 150 °C). The environmental characterization of the coated mine waste was established using standard leaching tests. The most effective coatings were analyzed for their mineralogy, chemical composition, and Sb attenuation using X-ray powder diffraction, scanning electron microscopy, and digestion/extraction processes. Additionally, stability tests were conducted to assess the effectiveness of encapsulation under changing environmental conditions. The Fe/Sb_leachable molar ratio was found to be a critical factor in reverting the toxic and hazardous characteristics of mine wastes, with an optimal value of 10. The coatings were primarily composed of Fe oxyhydroxy sulfates/Fe oxyhydroxides and calcium sulfate minerals with a bulk Sb content of approximately 1 %. The adsorbed Sb content in the coatings was a small fraction of the total Sb content (< 0.5 %), indicating a strong retention. Moreover, such coatings were stable under different pH (3-8) and redox (100 to -100 mV) conditions.