Quantitative transport and immobilization of cadmium in saturated-unsaturated soils with the combined application of biochar and organic fertilizer

In this study, cadmium (Cd) transport and immobilization on passivators (biochar, organic fertilizer) and soils under saturated-unsaturated conditions were independently analyzed. The results showed that the Cd adsorption capacities of biochar and organic fertilizer were comparable in acidic soils. But in alkaline soils, the Cd adsorption capacity of organic fertilizer was significantly larger than that of biochar. In acidic soils, passivators effectively immobilized Cd, and the total net effects were in the order: combination (44.05-58.13%) > 3% biochar (31.96-46.88%) > 3% organic fertilizer (28.78-41.82%). In alkaline soils, all treatments had negative effects on Cd immobilization. For acidic soils, the immobilization of Cd was mainly attributed to the passivators, and the positive contribution percentages of relatively stable Cd increase by passivators were 81.05-100%, while those by soils were 0-18.95%. For alkaline soils, after the treatments of passivators, although a considerable amount of Cd was immobilized inside the passivator, Cd was activated more inside the soil. Therefore, it is noteworthy that soil conditions must be fully considered when applying biochar and organic fertilizers for Cd remediation.

Automated summary

In this study, the transport and immobilization of cadmium (Cd) on passivators (biochar, organic fertilizer) and soils under different conditions were analyzed independently. The adsorption capacity of Cd by biochar and organic fertilizer was comparable in acidic soils, but in alkaline soils, organic fertilizer had a significantly higher adsorption capacity. In acidic soils, passivators effectively immobilized Cd, with the combination treatment showing the highest immobilization effect. In alkaline soils, all treatments had negative effects on Cd immobilization as Cd became more activated in the soil. Therefore, considering soil conditions is crucial when using biochar and organic fertilizers for Cd remediation.