[Characteristics and Heavy Metal Adsorption Performance of Sewage Sludge-derived Biochar from Co-pyrolysis with Transition Metals].

: To enhance the heavy metal cation adsorption capacity of sewage sludge-derived biochar in an aqueous medium with a high concentration of Ca2+, modified biochars were obtained from co-pyrolysis of sewage sludge and transition metal oxides (with a sewage sludge:transition metal mass ratio of 10:1), such as Fe2O3, MnO2, and ZnO. The properties of the modified biochars were characterized, and the Cd2+ adsorption effect of the modified biochars was determined as well. The H/C atom ratios of the modified biochars were all lower than 0.31, indicating that the transition metal oxides catalyzed the decomposition and volatilization of organic matter in sewage sludge. The majority of the added Fe and Mn remained in the modified biochars, and existed as a simple substance and oxide, respectively; while significant loss of Zn occurred. The pores of the modified biochars were mainly mesopores with an average pore size of approximately 3.8 nm, and the specific surface area of the modified biochars was larger than 50 m2·g-1. When the initial Cd2+ concentration was increased from 0 mg·L-1 to approximately 200 mg·L-1, the Cd2+ adsorption capacity of the Fe-modified biochar declined from 43.17 mg·g-1 to 27.88 mg·g-1, which was still higher than that of the unmodified biochar by at least 10 mg·g-1. In aqueous media with a high concentration of Ca2+, the Fe-modified biochar showed better Cd2+ adsorption performance; thus, compared to MnO2 and ZnO, Fe2O3 was the best choice to enhance the heavy metal adsorption performance of the sewage sludge-derived biochar.