Biochar–nZVI nanocomposite: optimization of grain size and Fe0 loading, application and removal mechanism of anionic metal species from soft water, hard water and groundwater

This work for the first time evaluates the efficiency of biochar-supported nanoscale zerovalent iron (nZVI) particles combinedly as a function of biochar grain size and iron loading for the removal of anionic metal species, i.e., HCrO4− and CrO42−. Both the factors are crucial and have to be optimized in order to achieve the highest and fastest removal. Not only that, it is also crucial to check the applicability of that composite in complex aqueous solutions. For that, nZVI particles were supported on biochar grains of different size ranges, i.e.,   SW (21.54 mg/g) > HW (17.00 mg/g) > DW (16.30 mg/g). Cr(VI) removal mechanisms were chemisorption, reduction and simultaneous coprecipitation as confirmed through various kinetic and isotherm modeling and through pXRD of reaction precipitates.