Pore size increase in sol–gel prepared non-stochiometric magnesium ferrite composite during phosphorous removal from water

Phosphorous removal from water by two novel adsorbents was achieved with competitive efficiency. The adsorbents were synthesized using a Sol–Gel method by mixing both magnesium and iron chlorides in two proportions: (i) in a stoichiometric (S-MgFeO) ratio, yielding 90% of the MgFe 2 O 4 plus 10% of hematite and (ii) with an excess of Mg that favored a magnesium-oxide-rich composite (C-MgFeO) of MgFe 2 O 4 and MgO, as indicated by X-ray diffraction measurements. 57 Fe Mössbauer spectroscopy (at 300 and 15 K) and magnetization (at 300 K) data demonstrated the presence of ferrimagnetic MgFe 2 O 4 for both adsorbents. Due to the presence of Mg-rich species at the samples’ grain surfaces (or interfaces), as suggested by dispersive energy spectroscopy and 57 Fe Mössbauer data, one of the highest adsorption capabilities found in the literature (~ 60 mg.g −1 ) was measured at pH = 5.5 for the C-MgFeO adsorbent. The adsorption isotherm and kinetics results are consistent with a surface layer chemisorption limited by diffusion, increasing the average pore diameter caused by Mg erosion at the particle surface under a phosphate-rich solution. The samples were twice reused with no noticeable change in adsorption capacities and magnetic properties, indicating a strong potential for these materials for industrial applications in the magnetic remediation process. The synthetic effluent treatment with the C-MgFeO composite is estimated to cost ca. 0.05 USD.L −1 , a value about six times lesser than treatment with the S-MgFeO adsorbent. Graphical abstract