The β-cyclodextrin and chitosan modified rice hull biochar (β-CD/C-BC) are used to stabilize agricultural soil contaminated with Cd and Pyr. The dosage and curing time of β-CD/C-BC are tested in the whole cycle, and the best experimental conditions are selected. The β-CD/C-BC can achieve highest stabilization rate of HMs in the soil, thereby reducing their migration ability and ecological risk.

Abstract

The composite pollution of heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) in agricultural soil is increasingly severe. HMs can undergo surface adsorption, complexation, or chemical reactions to transform from bioavailable species to residual species, achieving chemical morphological stability. However, these processes have no effect on PAHs. Biochar (BC), due to its inherent characteristics, can significantly enhance the stability of PAHs and is recommended as a potential co-stabilizing material for both heavy metals and PAHs. In this study, rice husk biochar modified with β-cyclodextrin and chitosan (β-CD/C-BC) was utilized to stabilize agricultural soil contaminated by Cd and Pyrene (Pyr). One-way tests were conducted on the dosage and curing time of biochar after a complete cycle of treatment. The results demonstrated that the optimal effect was achieved when the dosage of β-CD/C-BC was 7.5 % or the curing time was 21 days. The removal efficiencies for Cd and Pyr were found to be 84.62 %, 64.22 % or 85.90 %, 65.78 %, respectively. Additionally, BCR testing revealed that β-CD/C-BC could convert HMs in soil into a residual state (from 32 % to 82 %) with the highest stabilization rate, thereby reducing their migration ability and ecological risk.