Application of Box–Behnken Design to Optimize Phosphate Adsorption Conditions from Water onto Novel Adsorbent CS-ZL/ZrO/Fe3O4: Characterization, Equilibrium, Isotherm, Kinetic, and Desorption Studies

Abstract

Phosphate (PO43−) is an essential nutrient in agriculture; however, it is hazardous to the environment if discharged in excess as in wastewater discharge and runoff from agriculture. Moreover, the stability of chitosan under acidic conditions remains a concern. To address these problems, CS-ZL/ZrO/Fe3O4 was synthesized using a crosslinking method as a novel adsorbent for the removal of phosphate (PO43−) from water and to increase the stability of chitosan. The response surface methodology (RSM) with a Box–Behnken design (BBD)-based analysis of variance (ANOVA) was implemented. The ANOVA results clearly showed that the adsorption of PO43− onto CS-ZL/ZrO/Fe3O4 was significant (p ≤ 0.05), with good mechanical stability. pH, dosage, and time were the three most important factors for the removal of PO43−. Freundlich isotherm and pseudo-second-order kinetic models generated the best equivalents for PO43− adsorption. The presence of coexisting ions for PO43− removal was also studied. The results indicated no significant effect on PO43− removal (p ≤ 0.05). After adsorption, PO43− was easily released by 1 M NaOH, reaching 95.77% and exhibiting a good capability over three cycles. Thus, this concept is effective for increasing the stability of chitosan and is an alternative adsorbent for the removal of PO43− from water.