The effects of the concentrations of shell constituent solutions and core mass of Fe3O4/MnxZnyFe3-x-yO4 on phosphate adsorption were investigated using response surface methodology. An empirical mathematical model was developed which relates the response, that is, phosphate adsorption from water to the independent variables, that is, concentrations of Mn2+ and Zn2+ solutions (shell constituent solutions), and core (Fe3O4) mass using Design Expert software (version 7). F and p-values showed the significance of the model. The adsorbent was synthesized based on one of the optimal points suggested by the software and characterized by inductively coupled plasma spectroscopy, X-ray crystallography, X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy, and vibrating sample magnetometery methods. The experimental data corresponded to the Langmuir adsorption model. Statistical analysis indicated that the quadratic term of Fe3O4 mass had the highest effect on the phosphate adsorption yield. Also, the interaction term between the Fe3O4 mass and the Mn2+ solution concentration and linear term of Zn2+ solution had significant effects on phosphate adsorption. The results confirmed interaction between variables. Accordingly, the adsorbent yield for phosphate removal is a strong function of Fe3O4/MnxZnyFe3-x-yO4 composition.
