Deep treatment of secondary wastewater from electroless nickel plating ponds with two new chelating resins: Enhancement of complexed Ni(II) removal efficiency and mechanism study

This study presents two novel chelating resins for achieving ultra-low discharge standards in electroplating wastewater treatment, addressing the critical challenge of reducing Ni concentration from about 1 mg/L to <0.1 mg/L in secondary effluent. SDC-1 and SDC-2 were innovatively synthesized by functionalizing styrene-divinylbenzene (SDC) white spheres with hydroxamic acid and sodium dithiocarbamate groups, respectively. Both resins demonstrated exceptional performance in removing complexed Ni(II) from secondary effluent to below 0.1 mg/L, with SDC-2 achieving remarkably low concentrations of 0.03 mg/L, meeting national ultra-low emission standards. Comprehensive characterization using FTIR, FESEM, BET, and XPS, combined with thermodynamic and kinetic modeling and DFT calculations, revealed the superior adsorption mechanisms. The adsorption behaviors of both resins fitted well with the Freundlich isotherm model and the pseudo-second-order kinetic model. DFT calculations unveiled that both resins possess abundant active sites capable of decomposing Ni(II) complexes for deep wastewater treatment. Mechanistic insights showed that SDC-1 forms stable five-membered cyclic coordination complexes through O and N atoms of -CONHOH groups, while SDC-2 creates more structurally stable polydentate complexes via simultaneous coordination of N and S atoms in -HN-C(=S)-S-Na + groups with Ni(II). This work establishes a promising new strategy for deep removal of complexed heavy metal ions to achieve ultra-low discharge standards in industrial wastewater treatment.