Novel predicting methods for the removal of divalent metal ions by magnetite/amorphous iron oxide composite systems

Several multi-regressive equations for the quantitative prediction of the percentage of divalent metal ions removal by magnetite/amorphous iron oxide composite systems have been established in the present study. The systems were synthesized from ferrous sulfate mixing with aqueous Mg2+, Ca2+, Mn2+, Zn2+, Cd2+ and Pb2+ nitrate solutions. The results showed that using the thermodynamic properties of divalent metal ions, the predicting model with the best linear regression result (correlation coefficient (r)=0.9345) can be obtained from: M2+ Removal%=−1.15984×ΔG°solv+339.91154×RM2+−984.57433. where ΔG°solv and RM2+ are the experimental solvation free energies and Shannon–Prewitt ionic radii of divalent metal ions, respectively. Obeying our previous ‘linear atomization energy relationships (LAER)’, the atomization energies of metal ions (AEcation) and metal monoaquo complexes (AEcomplex) can supply well governing parameters for universally predicting various kinds of aqueous reactions of metal ions. The density functional calculated results thus revealed that the atomization energies of metal ions (AEcation) and metal monoaquo complexes (AEcomplex), coupling with the interatomic metal–oxide bond lengths (RMO) in metal monoaquo complexes, can accurately predict the removal percentage of divalent metal ions by magnetite/amorphous iron oxide composite systems (correlation coefficient (r)=0.9935). The linear predicting model can be expressed as: M2+ Removal%=−2.43375×AEcation+2.40201×AEcomplex+235.44139×RMO−1164.56703.