Combined thermal desorption and stabilisation is a major choice for the remediation of soil polluted by heavy metals and organic toxicants. Coupled, these processes physically and chemically affect the stability of heavy metals. For this study, polluted soil containing cadmium (Cd) around a lead-zinc smelter was chosen as the subject. To determine the coupling influence of combining thermal desorption and stabilisation to stabilise the Cd in the soil, the stability of Cd in the soil after thermal desorption, stabilisation, and combined treatment was examined based on the leaching rate, chemical speciation, and soil microstructure. The results showed that the stability of Cd was directly related to the temperature of thermal desorption and the stabilisation agent dose. The influence of the two combined stabilisation‒thermal desorption and thermal desorption‒stabilisation processes on the stability of Cd was analysed. The proportion of residual Cd of the former was 1.14 times higher than those of the latter, and the soil particles in the former process crystalized more significantly than those in the latter. Multiple regression analysis was used to construct the Cd stability model. In order to make the stabilised fraction of Cd consistent, compared with the stabilisation‒thermal desorption process, the agent dose in the thermal desorption‒stabilisation process should increase by 1.39-5.55 times higher, or the desorption temperature should increase by 28.3 °C-69.5 °C. Therefore, the combined stabilisation‒thermal desorption process is more conducive to stabilising Cd in the soil, a phenomenon that saves energy and reduces carbon emissions.
Keywords: Agent dose; Chemical speciation; Desorption temperature; Leaching rate; Soil microstructure.
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