Comparison of adsorption behaviors of Fe-La oxides co-loaded MgO nanosheets for the removal of methyl orange and phosphate in single and binary systems

Fe-La oxides co-loaded MgO (Fe-La/MgO) nanosheets were prepared for the adsorption of methyl orange and phosphate in single and binary systems. The Fe-La oxides content, concentration ratio of methyl orange to phosphate, inorganic ions, and pH values greatly affect the competitive adsorption performance of Fe-La/MgO in binary system. Among these obtained Fe-La/MgO composites, Fe-La/MgO-2 with a total Fe-La oxides content of 4.0 wt% and a Fe/La molar ratio of 1:1 presents the best adsorption capacity of phosphate (38.82 mg g(-1)) within 120 min, and La2O3/MgO with a La2O3 content of 2.0 wt% exhibits the highest adsorption activity of methyl orange (30.38 mg g(-1)) within 40 min in single system. However, the adsorption capacities of Fe-La/MgO-2 for phosphate and methyl orange in binary system are respectively 39.51 mg g(-1) and 16.52 mg g(-1) within 40 min due to the competitive adsorption between phosphate and methyl orange. The low pH is favorable for the separation of phosphate and methyl orange in binary system. Langmuir isotherm and second-order model can well fit with the adsorption isotherms and kinetics in single system. In addition, these adsorption processes of Fe-La/MgO-2 for methyl orange and phosphate in single system are the physisorption and chemisorption governed by the intra-particle diffusion and external mass transfer, respectively.