Forced hydrolysis synthesis of a lanthanum oxyhydroxide/hydroxide-incorporated adsorbent for fluoride adsorption
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Around the world, concentrations of fluoride ions in water higher than 1.5 mg L−1 have been found, which cause disease. These problems have boosted the synthesis of new materials for use in efficient fluoride adsorption processes. Lathanum(III) oxyhydroxide/hydroxide incorporated into supporting material through precipitation has shown a high selectivity for the removal of fluoride ions. Forced hydrolysis can be an alternative to obtain these compounds on a carrier surface. In this work, forced hydrolysis was applied to produce La(III) oxyhydroxides/hydroxides on granular carbon to evaluate its performance on fluoride adsorption and the effect of the presence of Cl−, SO42−, and CO32− coions. La-incorporated compounds were characterized by X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, nitrogen physisorption, laser diffraction, and point of zero charge to determine the physicochemical and textural properties and determine the adsorption mechanism. Forced hydrolysis favors the formation and anchoring of La(OH)NO3 and LaOOH microparticles at the edges of and inside the porous carbon, increasing the particle size, volume, and size distribution of the pores. A kinetics study pointed to chemical adsorption, and the maximum adsorption capacity based on the Langmuir model was 12.178 mg g−1. The presence of carbonate ions in the aqueous medium notably affected the removal of fluoride ions. The proposed mechanism consists of anchoring lanthanum oxyhydroxides/hydroxides to acidic groups, where fluoride is adsorbed by displacing hydroxyl ions. Graphic Abstract: (Figure presented.)
