63 / 2021-06-30 11:23:40

Artificial accelerated aging used to assess long-term potential of biochar to immobilize Cd in contaminated soils

Biochar,,Artificial aging,Immobilization,cadmium,natural aging,

Due to the long time required for natural aging, artificial accelerated aging methods are important for evaluating long-term environmental impacts of biochar. In this study, the impact of five artificial accelerated aging methods of original and KMnO₄-modified rice straw biochar on Cd transport and immobilization in soil were quantified. The artificial aging methods included four individual treatments, dry-wet cycling, freeze-thaw cycling, leaching, and acidification, and the combination of all four treatments. The biochars were aged in close contact with soil using a three-layer mesh method that allowed the soil and biochar to be easily separated after the various aging treatments. The four individual and the combined aging methods all had negative effects on the immobilization of Cd relative to the fresh biochar. The relatively stable Cd fraction decreased for biochar given the leaching (45.21%-51.15%) > acidification (34.41%-38.74%) > freeze-thaw cycling (26.07%-38.33%) > dry-wet cycling (22.41%-31.10%) > combined (10.28%-17.96%) aging treatments. Cd adsorption and immobilization was higher for samples receiving the freeze-thaw and dry-wet cycling treatments, lower for samples receiving the leaching and acidification treatments and lowest for samples receiving the combined aging treatment. Samples with the KMnO₄ modified biochar exhibited significantly higher adsorption and immobilization of Cd than the original biochar, especially for the combined aging treatment. We conclude that aging decreases sorption and immobilization of Cd by biochar and that KMNO₄ oxidation treatments can enhance the ability of biochar to immobilize Cd.