Statistical optimization and batch studies on adsorption of phosphate using Al-eggshell:

This work provides a simple and convenient method to manufacture the sorbent of Al-eggshell. The influence of AlC1(3) concentration and pH values as well as the dosage of sorbent and their interactions on adsorption of phosphate was investigated. Therefore, Box-Behnken design coupled with response surface method was adopted to explore the empirical model for phosphate species removal. It was observed that there is an optimal point, C(AlCl3)(0.29 mol/l)-pH(6.12)-dosage(6.72 g/l), for the goal of maximizing phosphate species removal. The second-order polynomial model for phosphate reduction was given as Removal(%) = 96.43 + 10.82X1 + 4.29X2 - 0.70X3 + 2.06X1X2 - 1.72X1X3 + 8.24X2X3 - 13.10X1(2 )- 17.26X2(2 )- 1.72X3(2) . Contour pictures implied that the interaction between pH values and sorbent dosage was the strongest, followed by C(AlCl3) versus dosage and C(AlCl3) versus pH. The adsorption of phosphate data had a good agreement with the Freundlich isotherm equation at 313 and 323 K. Otherwise, Langmuir-Freundlich model described the best fitness at the temperature of 293, 298, and 303 K. The process of adsorption of phosphate on Al-eggshell fitted a pseudo-second-order kinetic equation, which indicates the exothermic reaction. In conclusion, the present work suggests Al-eggshell as an efficient and environmental friendly sorbent for phosphate species adsorption from aqueous solutions.