Enhanced removal of Cr(VI) from aqueous solution by nano- zero-valent iron supported by KOH activated sludge-based biochar

Abstract

In this study，aiming at the problems of limited specific surface area and surface functional groups of sludge-based biochar and easy aggregation and oxidation of nano zero-valent iron, the sludge-based biochar activated by KOH supported nano-zero-valent iron (nZVI@SBC-KOH) was prepared and used to remove Cr(VI) from aqueous solution. By KOH activation, the specific surface area of SBC and the number of oxygen-containing functional groups on its surface are greatly increased, and by loading nZVI, nZVI is widely distributed on the surface and in the pores of SBC-KOH, which effectively solves its problem of easy agglomeration and oxidation. The adsorption process of Cr(VI) on nZVI@SBC-KOH is a spontaneous endothermic process, which is in line with the pseudo-second-order kinetic model and Langmuir adsorption isotherm model, and the maximum adsorption capacity at 298 K is 63.59 mg g−1. The nZVI@SBC-KOH adsorbs Cr(VI) to its surface through the electrostatic interaction of oxygen-containing functional groups, then Cr(VI) is reduced to Cr(III) partly by nZVI, and finally Cr(III) and Fe(III) co-precipitates in the form of CrxFe1−x(OH)3 on the surface of nZVI@SBC-KOH.