Evaluation of phosphate ion adsorption from aqueous solution by nickel-aluminum complex hydroxides

We prepared a variety of nickel-aluminum complex hydroxides, investigated their physicochemical properties, and evaluated their ability to adsorb phosphate ions (the molar ratios of nickel to aluminum, 1:2, 1:1, 2:1, 3:1, and 4:1, are referred to as NA12, NA11, NA21, NA31, and NA41). NA12 and NA11 have amorphous structures; their specific surface areas and the concentration of associated hydroxyl groups were greater than those of other adsorbents. The number of phosphate ions adsorbed onto NA12 and NA11 was greater than that onto other adsorbents. These results indicated that the phosphate ion adsorption is related to the specific surface area and the amount of hydroxyl groups. The adsorption isotherm data, and the effects of contact time and pH on the adsorption were investigated; our results implied that both the Freundlich equation model and the pseudo-second-order kinetic model describe the adsorption of phosphate ions by NA11. We showed that phosphate ions adsorbed onto NA11 can be desorbed by sodium hydroxide solution at different concentrations and that NA11 could be reused for at least three repeated cycles of phosphate ion adsorption and desorption. This study illustrates that NA11 has the potential for practical application as an adsorbent for phosphate ions from wastewater.