Characteristics of Cd²⁺ Adsorption From Water by Sulfhydryl Group Modified Rice Hull Biochar

The rice hull biochar(RHB) was modified by (3-mercaptopropyl) trimethoxysilane, and analyzed for the Zeta potential, SEM-EDS, BET and FTIR before and after the modification. Effects of solution pH, reaction temperature and time, solid-liquid ratio and other factors on the adsorption of Cd²⁺ on the rice hull biochar before and after modification and the desorption were investigated. The adsorption kinetics and thermodynamics of modified rice hull biochar(MRHB) on Cd²⁺ in water were studied. Results show that both the MRHB surface pores and the negative charge increased, the structure was clearer, and the sulfhydryl group was successfully introduced. Under different influencing factors, the adsorption effect of sulphide-modified RHB on Cd²⁺ was excellent. Under the best condition, the maximum MRHB(14.95 mg·g^-1) was 76% higher than non-modified RHB(8.50 mg·g^-1) and the desorption rate reduced by 23%-53%. The whole adsorption process was more in line with the quasi-secondary kinetics(R²>0.99) and the Langmuir isotherm equation model(R²>0.99). The adsorption was a spontaneous endothermic process dominated by mono-layer adsorption.