Experimental Investigation and Thermodynamic Modeling of Zn+2 and Ni+2 Extraction from Zn Plant Residue using D2EHPA

Zinc plant filter cake contains valuable metals that can be reused as a source for obtaining these metals. This study  describes an experimental two stage study on the extraction of zinc and nickel from waste zinc filter cake which includes acid leaching of zinc filter cake followed by organic phase aided extraction of metals from the leaching solution. To determine the optimum leaching condition a comprehensive study of the recovery of chemical elements from spent plant residues was experimentally studied at different levels of acid concentrations at different temperatures while measuring chemical elements concentration with respect to time. Experimental results showed that 99% recovery of Ni2+, Zn2+ and 89% recovery of Pb2+ can be achieved at following optimum conditions: 2M nitric acid, T= 358.15 K after 1.5 h of acid leaching at S/L=1/10. Then, the extraction of Zn2+, Ni2+, and Pb2+ was carried out by di-(2-ethylhexyl) phosphoric acid (D2EHPA) that was diluted with kerosene in equal phase ratio and the effect of extractant concentration and pH was studied at T = 298.15 K. Results showed that an increase in pH and extractant concentration can greatly increase zinc and nickel extraction to a maximum achievable amount of 95% and 90 % for Zn2+ and Ni2+, respectively by 25 (v/v%) D2EHPA at pH = 5.5 and organic to aqueous phase ratio (O/A) = 1/1. For modeling of equilibrium concentrations in organic and aqueous phases and activity coefficients calculation, Electrolyte-UNIQUAC-NRF, UNIQUAC-NRF, NRTL and NRTL-based local composition models were used. After that, adjusted parameters were successfully used for calculation of the equilibrium constant of the unknown parameters and the extraction reaction. The obtained results of thermodynamic modeling were in well agreement with the experimental data.