Study on Cadmium Adsorption and Passivation Capacity of Struvite

Research on the treatment of cadmium-contaminated soil is of great significance due to the potential ecological hazards posed by cadmium. This study investigated the cadmium (Cd²⁺) adsorption capacity of struvite and the factors influencing this process, as well as the passivation effect of struvite on cadmium in contaminated soil. The results indicate that the removal efficiency of Cd²⁺ by struvite increased with pH (from 6 to 9), reaching 93.55% at pH 9 when 4 g·L^-1 of struvite was added to a 50 mg·L^-1 Cd²⁺ solution. The adsorption process followed the pseudo-second-order kinetic model and fitted well with the Langmuir isotherm model, with a maximum adsorption capacity of 49.857 mg·g^-1. This capacity was 5.8 times greater than that of rice straw biochar. In soil experiments, compared to untreated soil, the application of struvite reduced cadmium content in the above-ground and below-ground parts of peas by 32.12% and 2.74%, respectively, and decreased the stem/root translocation factor (TF_S/R) by 30.24%. The reduction in TF_S/R was higher than that achieved by bamboo biochar (17.91%). The cadmium passivation rate following struvite application was 22.72%, potentially due to enhanced conversion of weak acid-extractable cadmium into the residual fraction. Additionally, phosphorus and nitrogen content in the above-ground parts of peas increased by 4.9% and 9.7%, respectively. These findings suggest that struvite functions as a slow-release fertilizer with notable cadmium passivation capacity.