[Preparation of Magnetic Iron Oxide/Mulberry Stem Biochar and Its Effects on Dissolved Organic Carbon and Arsenic Speciation in Arsenic-Contaminated Soils].

Abstract

In this study, original mulberry-biochar (M-BC) and magnetic iron oxide/mulberry stem biochar (Fe-BC) materials were prepared and characterized using mulberry stems as the raw material. The effects of carbonized temperature of Fe-BC and M-BC on dissolved organic carbon (DOC) and arsenic(As) speciation in soil leaching solutions were studied using soil incubation experiments. The results showed that:① Fe-BC was mainly composed of Fe₃O₄ and was magnetic, and the main functional groups were a C＝O double bond, O-H bond, C-O bond, and Fe-O bond. The point of zero charge values (pH_zpc) of Fe-BC-400, Fe-BC-500, and Fe-BC-600 were 8.92, 8.74, and 9.19, respectively, and the specific surface areas of Fe-BC-400, Fe-BC-500, and Fe-BC-600 were 447.412, 482.697, and 525.708 m²·g^-1, respectively. ② With the increase in the carbonization temperature of M-BC and Fe-BC, the ρ(DOC) of soil leaching solution decreased 11.6-315.6 mg·L^-1 and 78-365.6 mg·L^-1, respectively. The DOC concentration of soil leaching solution was negatively correlated with soil EC. On day 35 of the incubation experiments, compared with that in soil after incubation without biochar (control), the As concentration of the soil leaching solution with Fe-BC-600 decreased by 55.96%, and there was no significant correlation between the As concentration of the soil leaching solution and the DOC concentration of the soil. ③ The available As concentration on day 35 in soil after incubation with Fe-BC was lower than that of the control group; the available As concentration on day 35 in soil incubated with Fe-BC-600 was reduced by 39.21%. ④ The residue As concentration on day 35 in soil incubated with M-BC decreased by 17.76%-49.11%. The residue As content on day 35 in soil incubated with Fe-BC-600 increased by 80%. Fe-BC-600 was most beneficial to reduce the DOC concentration and the available As content in soil leaching solution and increased the residue As content, thus reducing the bioavailability of soil arsenic. Therefore, this study can provide a theoretical basis for magnetic iron oxide/biochar remediation in arsenic-contaminated soil.