The characteristics of adsorption Cr(VI) by iron-modified and iron-doped phosphorus-based biochar biochar

Abstract

ABSTRACT In this study, we evaluated the effect of the modification of biochar on the adsorption of Cr(VI) under weakly acidic conditions. Sesame straw biochar (BC) was modified by treatment with ferric chloride to produce iron-modified biochar (FBC) and ferric chloride and chlorapatite to produce iron-doped chlorapatite-modified biochar (FBCP). Analysis by scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) showed that the adsorption mechanism of Cr(VI) by FBC and FBCP was reduction, physical adsorption, ion exchange, and functional group complexation. Experiments were performed to evaluate the kinetic, isothermal, and thermodynamic characteristics of adsorption, demonstrating that the adsorption of Cr(VI) by FBC and FBCP was a spontaneous endothermic reaction, consistent with the pseudo-second-order kinetic model and Langmuir model, and the process was dominated by monolayer chemical adsorption. The Langmuir model revealed maximum saturated adsorption capacities for Cr(VI) of 7.907 and 12.625 mg/g by FBC and FBCP, respectively, equating to 4.06 and 6.48 times the maximum saturated adsorption capacity of BC, respectively. Compared with FBC, the phosphate ions in FBCP also co-precipitated with Cr(III), further improving the removal efficiency of pollutants.