HCl-assisted KOH activated Chinese medicine residue biochar as a new method to improve the purification capacity of lead- containing wastewater: Experimental and mechanism studies

Activated biochar (CMRBKOH) was prepared by activating Chinese medicine residue with KOH. And modified by HCl. XRD, SEM, and BET characterization were used to investigate the physiochemical properties of CMRB and CMRBKOH. The best concentration of hydrochloric acid as modifier is 2.5%. The adsorption capacity is 74.38 mg g-1 under the condition that the dose of the adsorbent is 0.4 g L-1, the initial concentration is 100 mg L-1, and pH 5.0. The pseudo-second-order kinetic model (R2 = 1.00) and Langmuir isotherm model (R2 = 1.00) were found to be highly consistent with the data by data fitting. The thermodynamic analysis revealed that chemisorption dominated the adsorption process. The surface functional groups (C-O, C=O, and O-H) on the surface of the original biochar were dramatically improved by activation, enables CMRBKOH to adsorb Pb(II) with more effective surface complexation, electrostatic attraction, ion exchange, coprecipitation, and coordination. Compared with the work done in other literatures, the material properties of this study are excellent. In addition, after eight cycles of experiments, the adsorption capacity is still 87.22%, and the adsorbent shows excellent regeneration capacity. As a whole, CMRBKOH could be considered an emerging Pb(II) adsorbent material with significant promise for Chinese medicine residue resource utilization, environmental quality, and public health protection.