Insight of Cadmium Solidification by Mineral-Based Soil Conditioner

In response to the environmental concerns posed by cadmium (Cd) contamination, the application of nano-submicron mineral-based soil conditioner (MSC) as a potential soil amendment has garnered interest due to its promising Cd mitigation properties. In this study, we aimed to investigate the solidification capacity and mechanism of Cd in MSC and examine the phase and morphology changes following solidification. Systematic experiments were conducted to assess the solidification capacity of MSC for Cd, revealing an impressive efficiency of nearly 100 % even at Cd concentrations of approximately 800 mg/L. The solidification efficiency was found to be positively correlated with the pH value, significantly declining as the environment shifted from pH>7 to pH<7. Notably, under alkaline conditions (pH>7), Cd solidification in MSC was primarily attributed to the Cd-OH complex formed on the surface of MSC and aided by cation-exchange reaction. In contrast, under acidic conditions (pH<7) and exposure to extreme Cd concentrations, Cd(OH)Cl precipitation became the dominant mechanism for solidification. Interestingly, the presence of KCdCl3, a water-soluble phase, did not significantly contribute to the overall solidification efficiency. These findings provide valuable insights into the solidification mechanism of Cd in MSC and offer potential implications for soil remediation efforts targeting Cd contamination.