Effects and mechanism on cadmium adsorption removal by CaCl2-modified biochar from selenium-rich straw

[Display omitted] •CaCl2-modified selenium-rich straw biochar was prepared.•CaCl2-modified selenium-rich straw biochar could more effectively remove cadmium from water.•The adsorption effect was superior at a pyrolysis temperature of 700 °C than that was at 600 °C.•The primary adsorption processes are functional group complexation, electrostatic adsorption, and ion exchange. As every-one knows, cadmium contamination poses a significant and permanent threat to people and aquatic life. Therefore, research on how to remove cadmium from wastewater is essential to protect the natural environment. In this study, agricultural and forestry waste straw sprayed with selenium-enriched foliar fertilizer was prepared as biochar, which was altered by calcium chloride (CaCl2) to remove Cd2+ from water. The outcomes demonstrated that biochar generated by pyrolysis at 700 °C (BC700) had the best adsorption effect. Secondly, pseudo-second-order kinetics and Langmuir adsorption models were used to predict the Cd2+ adsorption. Finally, electrostatic adsorption, ion exchange, and complexation of oxygen functional groups (OFGs) were demonstratedto be the main adsorption mechanisms. These conclusions indicate that selenium-rich straw biochar is a novel adsorbent for agroforestry waste recovery. Meanwhile, this work will offer a promising strategy for the overall utilization of rice straw.