Electroregeneration Of Ni (ii) -loaded
ELECTROREGENERATION OF Ni (II) -LOADED
ION-EXCHANGE RESINS
Yu. Dzyazko, V. Belyakov
Institute of General and Inorganic Chemistry, Ukrainian National Academy of Sciences, Palladin avenue 32-34, 03680 Kiev, Ukraine
Regeneration of Ni (II) loaded ion-exchange resins by electrodialysis was investigated. Dowex MSC-1, Dowex HCR-S, Purolite C100 E, КU-2-8, Dowex MAC-3 cation-exchange resins were used. The compartment containing the ion-exchanger was separated from the cathode and anode compartments with a cation- and anion-selective membrane respectively. Both the cathode and anode compartments were filled with a H2SO4 solution. During the experiment Ni (II) ions were concentrated into the cathode compartment due to electromigration process.
The main regularities of regeneration of Ni-loaded ion-exchangers, namely dependence of the process efficiency on the cell voltage, the rate of the solution passed through the desalination chamber, concentration of the solutions in the outer compartment, Ni (II) content in the ion-exchanger phase were investigated. Increase in cell voltage from 10 V to 50 V was found to result in reducing of the process efficiency due to Ni (II) hydroxide formation on the surface of the cation-exchange membrane. The process of hydroxide deposition takes place if a 0.1-1 M H2SO4 solution fills the electrode compartments. It was found that it is possible to avoid Ni(OH)2 deposition using a 3 M H2SO4 solution.
It was found that increase in the linear rate of the solution passed through the central compartment from 0.067 to 0.67 cm s-1 results in the increase in current efficiency. For instance, the differential current efficiency of regeneration of Dowex MSC-1 ion-exchange resin containing 0.5 mmol g-1 Ni (II) reaches 80% at 0.67 cm s-1 flow rate.
The diffusion coefficients (D) of Ni (II) ions in the ion-exchanger phase was determined by investigation of sorption kinetics [1] and electromigration during the electrodialysis process [2] (Table 1).
The mathematical apparatus of the Boyd-Adamson theory [4] was applied for treatment of the sorption kinetics data. According to this theory, the rate of ion exchange is described by the following equation:
, (1)
where F is a degree of process completion; n is an integer number, 1
, (2)
where r is the radius of a particle. The D values obtained for different ion-exchangers by sorption method increases in the order: Purolyte C100 E> Dowex MAC-3> Dowex MCS-1> KU-2-8> Dowex HCR-S.
The Nernst-Plank equation was used for treatment of data obtained by electrodialysis method. The lower values of diffusion coefficients were obtained using this method at 5 V, 0.067 cm s-1 flow rate through the ion-exchanger bed and 1 M H2SO4 solution in the electrode compartments. In this case the Ni (II) diffusion coefficients increases in the order: Dowex HCR-S > KU-2-8 > Dowex MCS-1 > Dowex MAC-3 >Purolyte C100 E.. It was shown that a change of the order is connected with diffusion limitation of electrodialysis process. Minimization of diffusion limitation, for instance by increasing of acid concentration in the electrode compartments, allows to obtain a good agreement between the orders of ion-exchangers obtained by electrodialysis and sorption methods.
Table 1. Effective diffusion coefficients (D) of Ni (II) ions in ion-exchanger phase
Ion-exchanger
D / m2 s-1
sorption method
electrodialysis method
Dowex MCS-1
7.2×10-12
3.9×10-13
Dowex HCR-S
1,04×10-11
1.7×10-13
Purolyte C100 E
6.3×10-12
1.6×10-12
KU-2-8
9.1×10-12
1.3×10-12
Dowex MAC-3
6.6×10-12
3.9×10-12
References
1. Boyd G.E, Adamson A.W., Myers L.S. J. Amer. Chem. Soc., (1947), 69, pp. 2836-2848.
2. P.B.Spoor, L.J.J.Janssen J. of Applied Electrochemistry, in press.
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