Thermally induced changes in solubility and speciation of lead and iron minerals in a contaminated soil

Abstract

This study investigated the effects of thermal treatment on the solubility and speciation of lead (Pb) adsorbed on synthesized hematite (Pb‐Hm) and in an anthropogenically contaminated soil. The temperature of thermal treatment ranged from 100 to 900 °C, and the speciations of Pb and iron were determined using X‐ray absorption fine structure spectroscopy. In Pb‐Hm samples, the concentration of water‐extractable Pb significantly decreased after being treated at 300 and 600 °C (∼0.50 mg Pb L–1) compared with the untreated sample (9.83 mg Pb L–1). Under this temperature range, about 50% of the Pb‐Hm was transformed into massicot (β‐PbO). At 700 °C and above, a slight increase of water‐extractable Pb was probably caused by the formation of minium (Pb3O4). In the contaminated soil, water‐extractable Pb increased gradually from 0.30 to 0.40 mg Pb L–1 with increasing temperature from 25 to 200 °C; then it decreased rapidly to 0.09 mg Pb L–1 at 300 °C and further decreased to 0.004 mg Pb L–1 at 900 °C. Cerussite (PbCO3) and Pb associated with hematite were the major Pb species in the contaminated soil. In the process of thermal treatment, the significant decrease of water‐extractable Pb in the contaminated soil was caused by the transformation of cerussite into hematite‐associated Pb, accompanied by the transformation from ferrihydrite to hematite.