Sorption of perchlorate on Mg-Al-CO3 layered double hydroxides prepared via fine inorganic sol-gel process: The treatment of aqueous solutions with pH 5, 7 and 8

Perchlorate anion is dangerous to human and able to affect the brain functions. Ion exchange is one of the main approaches, which allows separating ClO4 - anion and controlling its concentration in water solutions. In this work, we evaluated the ability of Mg-Al-CO3 layered double hydroxides (LDHs) to remove perchlorate ions at various, yet relevant to drinking water treatment conditions, pH values: 5, 7 and 8. LDHs were prepared via an original fine inorganic synthesis which includes sol-gel routes. It was shown that Mg-Al-CO3 LDHs can effectively sorb perchlorate even at pH 8, whereas most inorganic anion exchangers exhibited much lower adsorptive potential to anions. Experimental adsorption isotherms obeyed the Freundlich model and the Linear equation which confirmed favorable sorption. The process proceeds according to the mechanism of physical sorption based on an electrostatic interaction of an adsorbent and an adsorbate. Although these Mg-Al-CO3 LDHs demonstrated high adsorptive capacity to perchlorate (as compared with the literature) which is equal to 37 mg of ClO4 - per 1 gram of dry adsorbent at pH 5, an improvement in their adsorptive affinity can be achieved by the optimization of the material chemical composition and/or its calcination. To improve the removal properties of the anion exchanger toward ClO4 -, several pathways have been suggested. One of them is a thermal treatment of these unique LDHs, which maintain their layered structure even after calcination at 300-6000C. The paper also presents an overview of the literature data on perchlorate sorption by various materials.