Integrating bi-pH operation to enhance Ni2+ removal and recovery in fluidized-bed non-seeded granulation process

Abstract

Anthropogenic activities and industrial processes generate large amounts of nickel in effluent, posing a threat to public and ecological health. Several processes have been developed to remove nickel and adhere to environmental limits. The fluidized-bed non-seeded granulation process has proven effective in removing and recovering metals including nickel. In this study, nickel was precipitated using phosphate while investigating bi-pH operation. The study compared single-pH and bi-pH and found that bi-pH was better. The effects of molar ratio ([Ni2+]:[PO43-]), initial nickel concentration, copper ion concentrations, and other co-existing chemical compounds were then investigated under bi-pH operation. The optimal conditions were observed at bi-pH 7.5 and 9.0, molar ratio of 1:1.3, and 300 mg/L initial nickel concentration. The results showed that bi-pH improved the granulation process by generating heterogeneous granulation through observed bi-layers. The effects of molar ratio and initial nickel concentrations were attributed to changes in the predominant saturation condition, dictating primary and secondary nucleation. Co-existing compounds had no significant effect on total nickel removal but reduced granulation efficiency due to nickel complexation, ionic competition, and precipitate dissolution.