Selective and enhanced nickel adsorption from sulfate- and calcium-rich solutions using chitosan

Abstract

• Chitosan effectively adsorbed Ni from a real Ni/Ca/SO 4 2− bearing leachate. • Sulfate had a positive effect on Ni adsorption while Ca did not have any effect. • Formation of NiSO 4 0 species contributed to the enhanced Ni adsorption onto chitosan. • Chitosan has a Ni q max of 1.49 mmol/g even with 500 mM SO 4 2− and 10 mM Ca present. • Chitosan was selective for Ni over Ca as validated in a column setup. Nickel (Ni) is an economically important metal characterized by its mechanical strength and anticorrosion properties. With the increasing industrial demand for Ni and the depleting accessible Ni primary ores, sustainable technologies are required for the recovery of this metal from alternative resources. In this study, adsorption using chitosan was investigated as a sustainable technique to recover Ni from sulfate (SO 4 2− ) and calcium (Ca) rich secondary resources. The effects of pH, contact time, and the presence of SO 4 2− and Ca on Ni adsorption were investigated in batch experiments. Chemical speciation modeling was performed to analyze how the predominant Ni species present under different conditions may affect the efficiency of the adsorption process. The comparison of chitosan’s maximum Ni adsorption capacities in the absence (1.00 mmol/g) and presence (1.49 mmol/g) of 500 mM SO 4 2− and 10 mM Ca indicated the positive effect of these ions on Ni adsorption. The predominance of the neutrally charged NiSO 4 0 species in Ni/SO 4 2− system has contributed to the enhanced Ni adsorption on chitosan as verified by X-ray photoelectron spectroscopy (XPS) analysis. However, kinetic studies confirmed that the Ni adsorption rate decreased by 4.5 times when SO 4 2− was present. The subsequent continuous Ni adsorption from a real SO 4 2− -rich leachate in a column setup revealed that chitosan is selective for Ni over Ca and Cr with selectivity quotients of 9.6 ( K Ni/Ca ) and 3.0 ( K Ni/Cr ). Overall, this study indicated that Ni complexation with SO 4 2− enhances the Ni adsorption capacity of chitosan, but slows down the adsorption process.