Study on the regularity of Se(IV) adsorption by bentonite from different regions

Abstract Bentonite exhibits obvious geological characteristics in different areas, and its chemical composition varies. To investigate the impact of these variations on the adsorption of Se(IV), the chemical structures and elemental contents of three types of bentonites were characterized using FTIR and XRF. By conducting a series of experiments and fitting the results with the kinetic adsorption model and the isothermal adsorption model, it was discovered that bentonite exhibits diverse adsorption modes for Se(IV). In acidic environments, the adsorption mode primarily involves forming an outer-sphere complex, whereas in neutral and alkaline environments, the primary mode is to form an inner-sphere complex. Zhi-Shin bentonite, which has low alumina content and high iron oxide content, demonstrates poor adsorption effectiveness on Se(IV) at low temperatures (less than 45 °C), but exhibits good adsorption effectiveness at high temperatures (more than 50 °C). Conversely, bentonite with high alumina content and low iron oxide content demonstrates the opposite effect. Furthermore, for bentonite with high iron oxide content, Se(IV) will form more inner-sphere complexes with iron oxide, and the adsorption behavior is not easily affected by changes in ionic strength and pH.