Adsorption of Phosphate by Calcinated Mg-Fe Layered Double Hydroxide

概要

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Phosphorus resources are limited in the world and there have been some alarming reports that deposits of high-grade phosphate ores are likely to be depleted in the next few decades. Layered double hydroxides (LDHs), known as hydrotalcite-like compound or anionic clays, have drawn much attention on their high adsorption capacity to various anions from aqueous solution, such as AsO43-, CrO42-, PO43-, SeO32- due to their large surface area, high anion-exchange capacities and flexible interlayer space. In this present research, a series of Mg-Fe LDHs after calcination were synthesized to adsorb phosphate from solution. The highest phosphate adsorption capacity was obtained with Mg/Fe ratio of 3 and calcined at 573 K. The adsorption kinetics which was studied by using the pseudo-second-order model showed a high adsorption capacity of 76 mg-P/g at equilibrium time of 72 h. Adsorption isotherms revealed that the phosphate uptake process was better fit to Freundlich model than Langmuir model. Distribution coefficient (Kd) revealed good adsorption selectivity to phosphate in a mixed anion solution. The adsorbed phosphate can be effectively desorbed (73%) by adding a 0.1 M NaOH solution.