Purification of a diluted nickel solution containing nickel by a process combining ion exchange and electrodialysis

The removal of nickel ions from diluted solution using some ion-exchange resins (Dowex MSC-1, Purolite C 100E, KU 2-8 and Dowex HCR-S) was studied. The purification process involved the use of an electrodialysis-type cell in which the centre compartment was filled with a packed bed of ion-exchanger particles. The Dowex HCR-S resin was shown to be the most suitable material for use in electrodeionization processes. The current efficiency under constant rate of nickel transport to the catholyte reached 14%. The energy consumption, which is needed for removal of 0.35 mol Ni (II) from 1 m3 solution containing 1 mol NiSO4, was estimated as 208 Wh. The apparent diffusion coefficients of Ni(II) ions in the ion exchangers were determined with the electromigration method. These values increased with decrease of the effluent pH and reached 1.30@10!12 (Dowex MSC-1), 1.36@10!12 (Purolite C 100E), 2.69@10!12 (KU 2-8), and 4.07@10!12 (Dowex HCR-S) m2 s!1 at pH 2.3–2.5. The largest magnitude of the nickel diffusion coefficient was obtained for the Dowex HCR-S resin, which contains the maximum quantity of functional groups per volume unit. It was found that the mobility of sorbed ions determines the efficiency of the purification process.

Fig. 10. Ni(II) diffusion coefficient in Purolite C 100E ("), Dowex MSC-1 (—), KU 2-8 (L), Dowex HCR-S (#) resins as a function of the effluent pH. The initial H2SO4 concentrations in the electrode compartments were equal. It was found that an increase in effluent acidity due to leakage of the acid through the anion-selective membrane caused a decrease in the Ni(II) amount deposited on the cationselective membrane. As a result, the nickel flux through the cation-exchange membrane increases. The apparent diffusion coefficients of Ni(II) ions in the ion exchangers containing an 8% cross-linking agent were determined with the electromigration method. The increased with the decrease of the effluent pH. The values of Ni(II) diffusion coefficients obtained at pH 2.3– 2.5 reached 1.30@10!12 (Dowex MSC-1), 1.36@ 10!12 (Purolite C 100E), 2.69@10!12 (KU 2-8) and 4.07@10!12 (Dowex HCR-S) m2 s!1. This is the same order of magnitude as self-diffusion coefficients of divalent cations through an ionexchange resin of the same type [21]. The largest value of nickel diffusion coefficient was found for the Dowex HCR-S, which contains the maximum quantity of functional groups per volume unit. All the investigated ion exchangers were tested in the process of Ni(II) removal from diluted solution. The Dowex HCR-S resin was found to be the most suitable material for use in electrodeionization processes. The current efficiency under a constant rate of nickel transport to the catholyte reached 14%. The energy consumption, which is needed for removal of 0.35 mol Ni(II) from 1 m3 solution containing 1 mol NiSO4, was estimated as 208 W h. Thus the mobility of sorbed ions determines the efficiency of the purification process. Further development of a technology for nickel removal from diluted solutions using Dowex HCR-S resin is possible and connected with optimization of the electrodeionization process.