Effects of coexisting nickel ions on properties of spinel synthesized in wastewater containing chromium and insight into the effect mechanism

Ferrite process exhibits promising potential as a technological solution for the treatment of chromium-containing wastewater, owing to its dual functionality in both purifying the wastewater and facilitating resource utilization. Nickel ions often coexist in chromium-containing electroplating wastewater because of the need for an electroplating process. When the ferrite process treats chromium-containing electroplating wastewater, coexisting nickel ions will enter the synthetic spinel crystals and affect their properties. In the study, the effects of nickel ions on properties of spinel synthesized in mixed wastewater containing chromium were investigated by atomic absorption spectroscopy (AAS), toxicity characteristic leaching procedure (TCLP), physical property measurement system (PPMS), and the effect mechanism was clarified by X-ray diffraction (XRD), toxicity characteristic leaching procedure (TCLP), scanning electron microscope (SEM) and energy dispersion spectrum (EDS).The findings suggested that the presence of nickel ions had minimal impact on both the quality of the filtrate and the stability of chromium in the products synthesized under room temperature conditions and an initial pH level of 12. Interestingly, it was observed that a moderate concentration of nickel ions significantly enhanced the magnetic properties exhibited by these products. However, excessive nickel ions resulted in a reduction in the magnetic properties of the synthetic solid substance. The crystallinity degree of the synthetic solid substance gradually degenerated as the reaction time increased. Compared to nickel ions, chromium ions more quickly entered the synthetic spinel structure. Finally, the stable nickel-containing spinel was formed when the reaction time was over 20 min, but the crystallinity degree of the synthetic solid substance was inferior.