Effect of Activation Time on the Performance and Mechanism of CO2-Activated Wheat Straw Char for the Removal of Cd2+

The removal behavior and characteristic of cadmium (Cd2+) on wheat straw char activated by CO2 were investigated in this study. The equilibrium, kinetics, and removal isotherms were studied. The results of batch experiments revealed that the removal of Cd2+ was described well by pseudo-second-order and Langmuir models. The increase in activation time improved the removal of Cd2+, especially for the activation time of 84min. The results suggested that chemisorption of Cd2+ on activated carbon was the main reaction mechanism. The maximum removal capacity of Cd2+ onto activated WSC-84 was 75.55mg/g, which was much higher than other three samples activated by CO2 with other amounts of time. According to the results of SEM, XPS, and FT-IR, complexation with surface oxygen-containing functional groups, ion exchange, and precipitation were the possible mechanisms of the removal process. It is suggested that the experimental results will enhance the comprehensive understanding of the activation of biomass and its utilization in the restoration of Cd-contaminated soil.