[Heavy Metal Ion Adsorption Properties and Stability of Amine-sulfur Modified Biochar in Aqueous Solution]

A novel biochar was prepared by modification with corn straw, ethylene triamine, and carbon disulfide, and its adsorption properties and stability with respect to heavy metal ions in single and mixed systems (Pb²⁺, Ni²⁺, and Cd²⁺) were investigated. Characterization analysis confirmed the successful modification of an amine-sulfur double group on the surface of the biochar, which had abundant functional groups with a large specific surface area. Adsorption experiments under the single system indicated that the adsorption equilibrium time was 4 h and the optimum dosages were 1, 0.8, and 1.2 g·L^-1. The adsorption met the conditions of the quasi-second-order kinetic equation. Under the ternary system, the adsorption equilibrium time was reduced to 1.5 h, the optimum dosages were 0.4, 1.6, and 0.8 g·L^-1, and the adsorption sequence was Pb²⁺ > Cd²⁺ > Ni²⁺. The total amount of adsorption was 0.67 mmol·g^-1, which was higher than that of single heavy metal ions, indicating that amine-sulfur modified straw biochar (BC-SN) has an improved treatment effect on polluted water under the coexistence of three heavy metal ions. The Pb²⁺ and Cd²⁺ adsorbed by the biochar was stably bound in the form of heavy metal sulfide and a chelated amino group. In contrast, the adsorption of Ni²⁺ was via the mixed adsorption of various functional groups. When Pb²⁺ and Cd²⁺ compete for adsorption, the binding energy is higher and adsorption stability is more reliable.