New insights into interfacial dynamics and mechanisms of biochar-derived dissolved organic matter on arsenic redistribution in Schwertmannite

Biochar is extensively utilized for the remediation of environments contaminated with heavy metals (HMs). However, its derived-dissolved organic matter (BDOM) can interact with iron oxides, which may adversely influence the retention of HMs. This study investigates the effect of BDOM derived from tobacco stalk (TS) and tobacco petiole (TP) biochar on the redistribution behavior of As(V) in acid mine drainage (AMD)-impacted environments, particularly concentrating on the interactions with Schwertmannite (Sch). Results showed that TP-BDOM, abundant in lignin-like compounds, led to a low-amplitude release of As(V) from Sch under acidic conditions, reaching a maximum value (19.84 μg L^-1), significantly lower than the release caused by TS-BDOM (87.46 μg L^-1). Subsequently, 88.2% of the released As(V) were re-adsorbed in the TS-BDOM system, while 47.5% were retained in the TP-BDOM system. XRD analysis, in conjunction with SEM and STEM characterizations, confirmed that there were no additional crystalline phases or alterations in the microscopic morphological features of the particles throughout the reaction process. In-situ ATR-FTIR, complemented by 2D-COS analysis, demonstrated that aromatic N-OH groups and carboxylic in BDOMs coordinated to As-Sch, enhancing sulfate and As(V) release. It was also noted that no As(III) was detected under the influences of TP- and TS-BDOM. XPS results indicated that As(V) remained the predominant redox species even in the presence of BDOMs. These findings enhance our insight into BDOM's role in As(V) fate and transport within AMD-contaminated environments.