Asenic (As) possess considerable toxicity to both aquatic ecosystem and human health; therefore, it needs to be treated effectively prior to reaching the environment. Herein, CoAl-LDH@boehmite was synthesized for the enhanced removal of arsenate from aqueous media by in situ coating of Co2+ on the boehmite surface under the optimum Co2+ loading condition. In addition, effects of key parameters such as Co2+ loading, pH, ionic strength, and competitive anions, sorbent dosage, and temperature on the adsorption behavior of CoAl-LDH were investigated comprehensively. To further elucidate the adsorption mechanism, mathematical models (kinetics, equilibrium isotherms, and thermodynamics) and X-ray absorption spectroscopy (XAS) were applied. Morphology and structure analyses indicated that nano-sized plate-like CoAl-LDH crystals were successfully formed on the boehmite surface resulting in higher arsenate adsorption capacity from aqueous media than that of raw boehmite. Experimental results showed that the adsorption affinity towards arsenate increased with increasing Co2+ loading, sorbent dosage, and temperature, while it decreased with increasing solution pH and ionic strength. Competitive anions (NO3−, Cl−, HCO3−, SO42−, and HPO42−) could significantly affects sorbent-sorbate interactions. It was found that the order of negative effect of competitive anions on the adsorption capacity of the CoAl-LDH@boehmite was HPO42− &gt; SO42− &gt; HCO3− &gt; Cl− &gt; NO3−. Sorption kinetics and isotherms studies delineated that the pseudo-second-order and Sips isotherm models accurately describe the adsorption behavior of the CoAl-LDH@boehmite. Thermodynamic analysis suggested that the sorption process was thermodynamically spontaneous and endothermic in nature. Removal mechanisms of arsenate by CoAl-LDH@boehmite were determined by a series of batch experiments and a combination of XRD, FT-IR, TEM and EXAFS analyses. In the case of boehmite, arsenate was only removed by adsorption on boehmite surface with inner-sphere surface complex, whereas both intercalation of arsenate ion into interlayer of LDH and adsorption on both surfaces of boehmite and LDH were concurrently responsible for removing arsenate from the weak basic solution by the CoAl-LDH@boehmite. After 5th regeneration of the used CoAl-LDH@boehmite, the 3D nanostructure of CoAl-LDH was preserved and arsenate sorption performance was also kept. grant number: 2018002470002

In situ Synthesis of 3D Nanostructured CoAl-LDH on Boehmite Surface: Improved Arsenate Removal and Investigation of the Removal Mechanisms

2019 Spring National Meeting

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