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

Abstract

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.