A novel biochar derived from Prunella vulgaris L. residue of Chinese herbs for eco-efficient removal of four heavy metals from water: Optimization, mechanism, assessment and recycle
Xingyi Yang, Dong Liang, Qiang Li, Huan J. Chang, Zhaoqiong Chen, Xin Liu
Abstract
Industrial development causing heavy metal contamination of wastewater may cause irreparable harm to the human beings and environment. In this research, the Chinese herbal residue of Prunella vulgaris L. was prepared as a novel biochar (PBC400) to effectively remove Pb 2+ , Cd 2+ , Cu 2+ and Zn 2+ from water. After optimizing conditions through Box-Behnken design (BBD), 99.02 % Pb 2+ , 98.63 % Cd 2+ , 91.86 % Cu 2+ and 88.24 % Zn 2+ were removed, respectively. Kinetic and isotherm studies revealed that Pb 2+ /Cu 2+ and Cd 2+ /Zn 2+ were dominated by chemisorption on a heterogeneous surface and homogeneous surface, respectively, and the maximum adsorption capacity of Pb 2+ , Cd 2+ , Cu 2+ and Zn 2+ were 163.12, 57.97, 47.07 and 40.61 mg·g −1 , respectively. The adsorption mechanisms included pore filling, cation exchange, mineral precipitation, cation-π interaction, complexation and electrostatic attraction, and DFT calculation further elucidated the dominant role of carboxyl and the ease adsorption order of Pb 2+ >Cu 2+ >Cd 2+ /Zn 2+ . The water quality after adsorption was assessed as clean according to the Nemerow pollution index. Furthermore, the prepared magnetic biochar (MPBC400) after six cycles, exhibited >99.72 % of removal rate for Pb 2+ /Cd 2+ /Cu 2+ /Zn 2+ . Overall, Prunella vulgaris L. residue can be prepared as an eco-friendly biochar adsorbent for both the efficient adsorption of heavy metal contaminants and sustainable utilization of waste Chinese medicine residue resources.