Experimental and modeling studies for adsorbing different species of fluoride using lanthanum-aluminum perovskite

We investigated the adsorption mechanisms for removing fluoride based on experimental and modeling studies. Lanthanum-aluminum perovskite was designed for treating wastewater contaminated by fluoride. A fluorine-species model was developed to calculate the concentrations of different species of fluorine: F^-, HF, HF₂^-. Multiple kinetic models were examined and the pseudo-second order model was found the best to fit the experimental data, implying fast-chemisorption. The thermodynamic data were fitted by the Langmuir model and Freundlich model at different temperatures, indicating heterogeneous adsorption at low temperature and homogeneous adsorption at high temperature. The La₂Al₄O₉ material had less influence from negative ions when adsorbing fluoride. The adsorption mechanisms were further studied using experiments and Density Functional Theory calculations. The adsorption experiments could be attributed to the lattice plane (1 2 1) and La, O, Al sites. More Al sites were required than La sites for the increase of fluoride concentration. By contrast, more La sites than Al sites were needed for increased pH.