Improved adsorption of fluorine on three typical saline-sodic soils by increasing functional groups with Al 2 (SO 4 ) 3 incorporation

Fluorine pollution in saline-sodic soils has become an important environmental problem, but little is known about the interaction between Al2(SO4)3 and fluorine when Al2(SO4)3 is used to improve saline-sodic soils. In this study, batch adsorption experiments were conducted to investigate the impacts of different saline-sodic soils with Al2(SO4)3 on fluorine adsorption, and the mechanisms of adsorption were characterized by SEM, BET, FTIR, and XPS analysis. The results showed that fluorine adsorption decreased with increasing soil salinity, and the addition of Al2(SO4)3 increased the adsorption of fluorine in soils. Among the three saline-sodic soils, Al2(SO4)3 contributed greatly to fluorine adsorption by mildly saline-sodic soils, with a range of 40.84%-69.70%. Fluorine adsorption isotherms could be properly described by the Langmuir and Freundlich models. At higher fluorine equilibrium concentrations, the adsorption amount of fluorine was greater for soils with Al→F. Both the soil porosity and the number of aggregates of saline-sodic soils were increased after adding Al2(SO4)3 for adsorption. Functional groups such as Si-O-Si, H-O-H, C-H, -OH, and Al-O-H were involved in the reaction process. Fluorine adsorption on saline-sodic soils refers to the ligand exchange and electrostatic adsorption, and F− replaces -OH on the soil surface. This work may provide a theoretical reference for the changes in fluorine chemical behavior when Al2(SO4)3 ameliorates saline-sodic soils.