Efficient removal of Cr(VI) from wastewater by N-doped Fe-containing sludge biochar

In this work, N-doped Fe-containing sludge biochar (NSBC) was prepared by impregnation-pyrolysis of Fe-containing wastewater treatment plant residual sludge with ammonium chloride and employed to Cr(VI) removing from wastewater. Additionally, spectroscopic techniques were applied to investigate the characterization of adsorbents and the potential mechanism of removing Cr(VI). In the range of solutions pH 2 to 7, there was a inhibition of removing Cr(VI) by increasing the solution pH. The co-existing ions K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl⁻ and \({\text{NO}}_{3}^{ - }\) ${\text{NO}}_3^{-}$ showed no influence on removing Cr(VI), whereas the \({\text{SO}}_{4}^{2 - }\) ${\text{SO}}_4^{2-}$ , \({\text{PO}}_{4}^{3 - }\) ${\text{PO}}_4^{3-}$ and humic acid exhibited inhibitory effects on removing Cr(VI). The removal amounts of SBC and NSBC were 42.32 mg/g and 105.57 mg/g, respectively. The removal behavior of Cr(VI) by SBC and NSBC was consistent with the pseudo-second-order kinetic model and Langmuir model, which indicated the removal process was a homogeneous and single chemisorption. The thermodynamic results demonstrated that the Cr(VI) removal was both spontaneous and endothermic. The Cr(VI) removing by NSBC was affected by various mechanisms, such as electrostatic interaction, complexation and reduction. This provided novel material for Cr(VI) removal from wastewater.