Effect of thermal treatment on stabilization and solidification of heavy metal contaminated clayey soil

Heavy metal pollution, particularly from copper, is a significant environmental challenge. This study investigates the impact of thermal treatment on the geotechnical and geo-environmental properties of copper-contaminated dispersive soil under temperatures ranging from 25 °C to 900 °C. The results demonstrate that temperature significantly alters soil properties, including pH, electrical conductivity (EC), unconfined compressive strength (UCS), thermal gravimetric, plasticity, and permeability. Among the factors influencing copper absorption and retention, cation exchange capacity (CEC), specific surface area (SSA), and carbonate content play critical roles, with carbonate content being the most influential. At 500 °C, despite a 56% reduction in CEC and a 37% decrease in SSA, the ability to absorb and retain copper increases significantly. Structural changes observed via SEM and XRD analyses reveal a transition from dispersed to flocculated, and ultimately to crystalline and porous structures, with the formation of new phases such as copper oxide (CuO) and mullite at higher temperatures. Notably, 300 °C shows the most effective pollutant retention, with a 13% increase in permeability and a fourfold increase in UCS, while 96% of the copper pollutant is absorbed. The soil remains classified in the CL range. This study highlights the potential of thermal treatment for improving the properties of copper-contaminated soil, reducing environmental risks, and enabling the stabilization and recycling of contaminated soils for use in construction materials.