The effect of the synergistic thermal treatment and stabilization on the transformation and transportation of arsenic, chromium, and cadmium in soil.

Thermal treatments commonly used to remedy organic-contaminated soils can inadvertently impact the behavior of non-targeted pollutants, notably heavy metal(loid)s in soil. This study introduces an integrated calcination-stabilization remediation strategy employing steel slag as a stabilizing agent, with a focus on elucidating the transformations and remobilization tendencies of As, Cr, and Cd. Thermal treatment alters the mobility of these elements by modifying soil properties, with pH and redox conditions playing pivotal roles. After anaerobic calcination, the leaching concentrations of As reached 163 μg L-1, far surpassed 7.57 μg L-1 after the aerobic calcination. Although Cr and As share oxygen-containing anion forms, they display opposing leaching tendencies after thermal treatment. At 400 °C, Cr leaching from aerobically treated soil reaches 64.5 mg L-1, dropping to 6.63 mg L-1 after anaerobic heating due to pH-induced Cr(OH)3 formation. Thermal treatment significantly amplifies the leaching of Cd cations. In contrast to the leaching concentration of 122 μg L-1 in the untreated soil, aerobic and anaerobic heating (400 °C) resulted in leaching concentrations of 896 μg L-1 and 132 μg L-1, respectively. Noteworthy, the integrated treatment (400 °C anaerobically) decreases leached As and Cd concentrations to 68.3 μg L-1 and 15.4 μg L-1, attributed to stabilizer alkalinity and porosity. Column leaching shows initial rapid release followed by continuous behavior for As and Cd, with the average leaching concentrations of the remediated soil decreasing to 60.5 μg L-1 and 1.32 μg L-1, ensuring safe backfilling. In conclusion, this study contributes to the understanding of the mobility and stabilization of heavy metal(loid)s subsequent to the integrated calcination-stabilization process.