Effect of Fe(III)-modified montmorillonite on arsenic oxidation and anthracene transformation in soil

Studies have shown that Fe(III)-modified montmorillonite can oxidize arsenite (As(III)) and also degrade anthracene. However, the application of Fe(III)-modified montmorillonite to remediate soil contaminated by arsenic and/or polycyclic aromatic hydrocarbons (PAHs) has not been reported. In this study, we first investigated the transformation of arsenic and anthracene on the surface of Fe(III)-modified montmorillonite, and then added Fe(III)-modified montmorillonite to spiked soil to examine its effect on arsenic oxidation and anthracene transformation. The experiments included treatments with As(III) and anthracene added separately or combined (both at a rate of 100 mg/kg). Compared with Na-modified montmorillonite, Fe(III)-modified montmorillonite significantly promoted As(III) oxidation and anthracene transformation on its surface. After 15 days of incubation, the proportion of As(V) (As(V)/[As(III) + As(V)]) on Na-modified montmorillonite was approximately 60%, and the transformation extent of anthracene was < 30%; on Fe(III)-modified montmorillonite, on the other hand, the proportion of As(V) was approximately 90%, and almost all anthracene was transformed. Adding 5% Fe(III)-modified montmorillonite to spiked soil also significantly enhanced As(III) oxidation and anthracene transformation. After 15 days, in the soil with added Fe(III)-modified montmorillonite, the proportion of As(V) was approximately 40%, the transformation extent of anthracene was > 60%, and approximately half of the initial added anthracene was transformed to anthraquinone. By contrast, after 15 days, in the soil without added Fe(III)-modified montmorillonite, the proportion of As(V) was only approximately 20%, the transformation extent of anthracene was < 25%, and anthraquinone was not detected. In both the montmorillonite and soil systems, the transformation of arsenic and anthracene had little influence on each other. The results showed that Fe(III)-modified montmorillonite has the potential to remediate soil contaminated by arsenic and PAHs.