Recovery of Zn(II) and Ni(II) Binary from Wastewater Using Integrated Biosorption and Electrodeposition

Abstract

The present study aimed to obtain best operational conditions for biosorption of Zn(II) and Ni(II) binary metal solution in a fixed bed packed with wheat straw as biosorbent. The effects of bed depths, liquid flow rates and mixture metal concentrations on biosorption service time were investigated. The results showed that breakthrough service time of the biosorption columns (Cb = 2 mg/L Zn and Ni) increased with increasing bed depth, while decreased with increasing influent concentrations and flow rates, as expected. This paper further extended the study to investigate the competition of Zn(II) and Ni(II) binary in solution by performing biosorption tests at varied ratio of the metal concentrations. For biomass regeneration, the effect of desorbing agents (hydrochloric acid, nitric acid and sulphuric acid), their concentrations (0.1–0.5 mol/L) and flow rates (0.05–0.1 L/min) on recovery of Zn(II) and Ni(II) binary mixture was investigated. The best performance in desorption of Zn(II) and Ni(II) binary solutions were 0.1 mol/L H2SO4 and a 0.05 L/min inlet flow rate. Moreover, after five sorption/desorption cycles, the biosorbent still maintained its high adsorption capability. Electrodeposition was also used to recover metal ions from concentrated Zn(II) and Ni(II) binary solutions (about 340 mg/L) from the desorption step. It was found that the electrodeposition could reduce the metal concentrations down to wastewater discharge limit of 2 mg/L Zn and Ni ions.