Effect of biochar aging and co-existence of diethyl phthalate on the mono-sorption of cadmium and zinc to biochar-treated soils

In this study, the influence of the aging process of pig-(PB) and P. orientalis-(POB) derived biochars on the sorption capacity of the biochar-treated soils for cadmium (Cd) and zinc (Zn) with and without the co-existence of diethyl phthalate (DEP) was investigated. Additionally, the surface and internal characteristics of biochars were determined before and after their aging in soils. The PB-treated soil had a higher sorption capacity for Cd2+ and Zn2+ than the POB-treated soil. The sorption capacity of the biochar-treated soils for Cd2+ and Zn2+ increased with biochar application rates. After aging, the abundance of oxygen-containing functional groups on the biochar surface, and the pH and organic carbon content of the biochar-treated soils significantly increased, thereby improving the sorption capacity for Cd2+ and Zn2+. The sorption capacities of biochar-treated soils for Cd2+ and Zn2+ followed the order of 1-month aging > 6-month aging > fresh. The co-existence of DEP enhanced the sorption capacity of the fresh biochar-treated soils for Cd2+ and Zn2+, whereas this enhancing effect disappeared for the aged biochar treatments. Our findings provide insights into the interactions between mixed contaminants in biochar-amended soils and the long-term efficacy of biochar treatments on metal sorption to soils.