[Remediation Effect of Two Iron-modified Biochars on Slightly Alkaline Arsenic and Cadmium Contaminated Soil]

As a good passivation agent for heavy metals, modified biochar has been widely used in environmental remediation. In order to explore the effects of different modification methods on arsenic (As) and cadmium (Cd) passivation in soil by biochar, this study used co-precipitation and impregnation pyrolysis to prepare iron-modified biochar. Through adsorption experiments and soil culture experiments, the properties of biochar, adsorption capacity, and the As and Cd passivation ability in soil were analyzed. The results showed that both modification methods could increase the iron (Fe) content and zero charge point of biochar, and the Fe minerals supported by Fe-modified biochar (FeBC-1) prepared by co-precipitation were mainly Fe₃O₄, FeO(OH), and γ-Fe₂O₃. The Fe-modified biochar (FeBC-2) prepared by impregnation pyrolysis mainly consisted of α-Fe₂O₃ and γ-Fe₂O₃. FeBC-1 showed strong adsorption and removal ability for As and Cd, with a removal rate of 21.40%-34.14%, which could significantly promote the conversion of non-obligate adsorbed As to residual As in soil, whereas FeBC-2 only had a good adsorption effect on As. The adsorption capacity of BC, FeBC-1, and FeBC-2 for Cd were proportional to their CEC. The adsorption and removal effect of BC on Cd was better than that of FeBC-1 and FeBC-2, which could significantly promote the conversion of soil acid-soluble Cd to stable residue Cd.