Thermal Treatment of Mercury Mine Wastes Using a Rotary Solar Kiln

Thermal desorption, by a rotary kiln of mercury contaminated soil and mine wastes, has been used in order to volatilize mercury from the contaminated medium. Solar thermal desorption is an innovative treatment that uses solar energy to increase the volatility of contaminants, which are removed from a solid matrix by a controlled air flow system. Samples of soils and mine wastes used in the experiments were collected in the abandoned Valle del Azogue mine (SE, Spain), where a complex ore, composed mainly of cinnabar, arsenic minerals (realgar and orpiment) and stibnite, was mined. The results showed that thermal treatment at temperatures >400 °C successfully lowered the Hg content (2070–116 ppm) to <15 mg kg. The lowest values of mercury in treated samples were obtained at a higher temperature and exposition time. The samples that showed a high removal efficiency (>99%) were associated with the presence of significant contents of cinnabar and an equivalent diameter above 0.8 mm.