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

ABSTRACT Titanium dioxide (TiO 2 ) 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. TiO 2 nanoparticles, biochar, and a blend of biochar+TiO 2 were investigated as amendments for an alkaline V‐contaminated soil. Treatments involved mixing (weight basis) 1% TiO 2 (T1), 5% biochar (T2), 1% TiO 2 + 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 NaVO 3 . 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 TiO 2 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 TiO 2 , biochar, and combined TiO 2 +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 TiO 2 +biochar. The labile V fraction decreased, and the nonlabile V fraction increased, significantly in the TiO 2 +biochar amended soil compared to the unamended soil. Applying a blend of biochar+TiO 2 reduced the mobility of V in a neutral‐alkaline soil, thereby preventing it from contaminating the nearby soil and water bodies.