Synthesis of Al/Ce and Al/Nd hybrid mesoporous gels and their application in competitive adsorption of fluoride ions

Abstract

To produce well loaded mesoporous aluminum-based adsorbents for defluoridation of zinc sulfate solution, novel Al/Ce hybrid gel (AC) and Al/Nd hybrid gel (AN) were synthesized with high water-soluble pseudo-boehmite as the main raw material. The properties, optimal defluoridation conditions, synthesis principle and adsorption mechanism were studied via related characterizations, experiments, and models. The results obtained revealed that the main bodies of AN and AC are AlO(OH). Ce(CH3COO)3 and Nd(CH3COO)3 are embedded in the frameworks, forming large amounts of ink-bottle type mesopores. The experimental data of both AC and AN fitted well to the pseudo-second-order kinetic and Langmuir isotherm models. Maximum adsorption capacities of AC and AN for fluoride ions were 26.57 mg g−1 and 29.18 mg g−1, respectively. The larger adsorption capacity indicated that the aluminum-based adsorbent modified by Nd element for the first time has a promising application prospect in defluoridation. The adsorbents showed high fluoride ion adsorption speeds with the removal rates reaching 50.15% (AC) and 33.41% (AN) within 2 min at 50 °C, 3 g l−1. The mechanism analysis revealed that the electrostatic interaction of protonated hydroxyl with fluoride ions and coordination between rare earth ions and fluoride ions are involved in the adsorption. Ce(CH3COO)3 and Nd(CH3COO)3 embedded in the main body stabilize the structure of the adsorbents, enhance the defluoridation speeds, and provide adsorption sites for fluoride ions.