An innovative pH-independent magnetically separable hydrogel for the removal of Cu(II) and Ni(II) ions from electroplating wastewater

A novel magnetic anionic hydrogel (nFeMAH), synthesized via a facile method, was characterized by XRD, VSM, SEM, TEM, FTIR, XPS, and zeta-potential measurement. Over the tested range of pH 2 to 12, the surface of the nFeMAH was permanently negative with a zeta-potential of -35 to -45 mV. The adsorption kinetics and capacity of nFeMAH were studied. Within 60 min, equilibrium was achieved with maximum adsorption capacities of 102 mg Cu(II)/g and 93 mg Ni(II)/g. The pseudo-second-order kinetics model was well-matched with the experimental data, whereas the Langmuir isotherm model agreed well with the isotherm data. The magnetic separation efficiency of nFeMAH remained above 90% after 20 cycles of adsorption-desorption, whereas the Ni(II) removal efficiency dropped from 92 to about 75% after the first cycle. The magnetic separation efficiency of nFeMAH was consistently high (99%). The major mechanism of metal removal by nFeMAH was ion exchange but there also was evidence for formation of metal oxides. Therefore, the application of nFeMAH for treating electroplating wastewater can be a desirable option when considering its superior performance in the adsorptive treatment, i.e., pH insensitivity, fast adsorption kinetics, high reusability, and consistency in magnetic separation.