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

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 similar to 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.