Kinetics of Defluoridation of Aqueous Waste-streams of the Aluminium Industry with a Modified Chelating Resin

Ion-exchange technology offers a low-energy potential route to the recovery of fluoride from aluminium industry leachate. This study presents an investigation into the kinetics of fluoride uptake from a simulant leachate and for comparison, from a simple NaF solution, using a lanthanum-loaded chelating resin. Experimental data were found to follow the Ho pseudo 2nd-order rate law and the Elovich equation, suggesting that, although multiple uptake mechanisms occurred on heterogeneous binding sites, the process was chemical reaction-controlled. The maximum observed rate constants were calculated as 0.760 ± 0.01 g mg-1 min-1 (NaF solution) and 0.0724 ± 0.0125 mg-1 min-1 (leachate). However, the maximum calculated equilibrium uptake for the leachate was 26.9 ± 0.2 mg g-1, which was almost twice as high as for NaF solution (14.0 ± 0.9 mg g-1).