Removal of phosphates from aqueous solution by sepiolite-nano zero valent iron composite optimization with response surface methodology

In this study, sepiolite-nano zero valent iron composite was synthesized and applied for its potential adsorption to remove phosphates from aqueous solution. This composite was characterized by different techniques. For optimization of independent parameters (pH=3-9; initial phosphate concentration=5-100mg/L; adsorbent dosage=0.2-1g/L; and contact time=5-100min), response surface methodology based on central composite design was used. Adsorption isotherms and kinetic models were done under optimum conditions. The results indicated that maximum adsorption efficiency of 99.43 and 92% for synthetic solution and real surface water sample, respectively, were achieved at optimum conditions of pH 4.5, initial phosphate concentration of 25mg/L, adsorbent dosage of 0.8g/L, and 46.26min contact time. The interaction between adsorbent and adsorbate is better described with the Freundlich isotherm (R-2=0.9537), and the kinetic of adsorption process followed pseudo-second-order model. Electrostatic interaction was the major mechanisms of the removal of phosphates from aqueous solution. The findings of this study showed that there is an effective adsorbent for removal of phosphates from aqueous solutions.