Co‐Application of Wood Biochar and Nano‐Titanium Dioxide to Immobilize Vanadium in Alkaline Soils

ABSTRACT Titanium dioxide (TiO2) and biochar have been used as amendments to adsorb vanadium (V) in aqueous solutions; however, their simultaneous application in the remediation of V‐contaminated neutral‐alkaline soils is rare. TiO2 nanoparticles, biochar, and a blend of biochar+TiO2 were investigated as amendments for an alkaline V‐contaminated soil. Treatments involved mixing (weight basis) 1% TiO2 (T1), 5% biochar (T2), 1% TiO2 + 5% biochar (T3) with soil, and an unamended soil (T4). An adsorption edge study was performed from pH 4 to 10 at the V concentration of 200 mg L−1. A standard vanadium (V) solution was prepared using NaVO3. An incubation study was conducted over 3 months with V‐contaminated soil at a rate of 200 mg kg−1, at 80% field capacity. At the end of the incubation period, the treated soils were subjected to V fractionation. X‐ray diffraction (XRD) patterns and FTIR spectra of TiO2 nanoparticles, biochar, uncontaminated soil, and four treated soils were obtained. The adsorption edge of V was below pH 4.6, suggesting reduced retention of V in alkaline soils. In the combined treatment, the adsorption edge was elevated by one unit compared to the control. V adsorption increased in TiO2, biochar, and combined TiO2+biochar treatments at 7%, 4%, and 20%, respectively, compared with the unamended soil (control) at a pH of ~7.6. Functional groups revealed the possibility of inner‐sphere and outer‐sphere adsorption mechanisms between vanadate and the mix amendment of TiO2+biochar. The labile V fraction decreased, and the nonlabile V fraction increased, significantly in the TiO2+biochar amended soil compared to the unamended soil. Applying a blend of biochar+TiO2 reduced the mobility of V in a neutral‐alkaline soil, thereby preventing it from contaminating the nearby soil and water bodies.