Simultaneous removal of cadmium, lead, chromate by biochar modified with layered double hydroxide with sulfide intercalation

Abstract

In this study, a novel KOH-activated biochar modified with Mg₂Al-LDH with S^2- intercalation (KBC-LDH-S) was proposed for simultaneous adsorption of anions and cations. The adsorption capacity, thermodynamic and kinetic studies, effects of initial temperature and solution pH were investigated. Furthermore, the adsorption characteristics in both single and ternary Pb-Cd-Cr systems were investigated. Comparing with bare biochar, the adsorption capacity of KBC-LDH-S was increased by 387.8 % for Cd²⁺ (190.4 mg/g), 358.1 % for Pb²⁺ (392.2 mg/g), 1106.0 % for total Cr (170.7 mg/g) and 4602 % for Cr⁶⁺ (833.8 mg/g). The S^2- intercalation effectively increased the adsorption capacity of CrO₄^2- by 3370 % and promoted simultaneous adsorption. The interlayer anion exchange and redox reaction occurred between CrO₄^2- and S^2- to generate Cr³⁺, and then promoted the adsorption of CrO₄^2-. Besides, the adsorption amount and total removal efficiency first increased and then decreased with the increasing concentration in the Pb-Cd-Cr ternary system.

Keywords: Adsorption stability; Biochar; Heavy metals; Layered double hydroxide (LDH); Simultaneous removal.