Application of Box–Behnken Design to Optimize Phosphate Adsorption Conditions from Water onto Novel Adsorbent CS-ZL/ZrO/Fe(3)O(4): Characterization, Equilibrium, Isotherm, Kinetic, and Desorption Studies

Phosphate (PO(4)(3−)) 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/Fe(3)O(4) was synthesized using a crosslinking method as a novel adsorbent for the removal of phosphate (PO(4)(3−)) 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 PO(4)(3−) onto CS-ZL/ZrO/Fe(3)O(4) was significant (p ≤ 0.05), with good mechanical stability. pH, dosage, and time were the three most important factors for the removal of PO(4)(3−). Freundlich isotherm and pseudo-second-order kinetic models generated the best equivalents for PO(4)(3−) adsorption. The presence of coexisting ions for PO(4)(3−) removal was also studied. The results indicated no significant effect on PO(4)(3−) removal (p ≤ 0.05). After adsorption, PO(4)(3−) 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 PO(4)(3−) from water.