Highly efficient sorption of selenate and selenite onto a cationic layered single hydroxide via anion exchange and inner-sphere complexation

Selenium is a double-edge sword element with a narrow dosage margin between as a nutrient and toxicant. Seeking efficient sorbents with high performance for reducing high content of selenium in wastewater is still highly desirable. In this work, we report a cationic layered single hydroxide that consists of only Al and O with free exchangeable Cl- in the interlayers with excellent sorption capability of selenate and selenite. The batch experiments including sorption isotherms, kinetics, selectivity, and desorption were systematically investigated. The maximum sorption capacities for selenate and selenite anions reached 164.7 mg Se/g and 190.3 mg Se/g respectively, which represented one of the highest values among the existing inorganic materials. It also showed superior removal depth under simulated environmental conditions in the presence of multiple competing anions (Cl-, NO3-, CO32-, SO42- and PO43- ). After close analysis by EXAFS and other characterization techniques, we fully revealed the sorption mechanism and found that the selenate and selenite anions were exchanged with Cl- in the interlayer space firstly and were immobilized onto the surface through inner-sphere complexation, resulting in such superior selenium removal performance.