Helena Bendová

Continuous dialysis of sulphuric acid in the presence of zinc sulphate

Transport of sulphuric acid in the presence of zinc sulphate through the anion-exchange membrane Neosepta-AFN (Astom Corporation, Japan) was studied in a two-compartment counter-current dialyzer with single passes at steady state. The following characteristics were used to characterize the dialysis process: recovery yield of acid, rejection coefficient of salt, and permeability coefficient of the membrane. In case of the H2SO4 + ZnSO4 mixture, permeability of the membrane was quantified by four phenomenological coefficients which are functions of acid and salt concentrations in the feed. They were determined by numerical integration of differential equations describing the concentration profiles of both components in both compartments, which was combined with an optimizing procedure.

Continuous dialysis of hydrochloric acid and sodium chloride mixture

ABSTRACT Using a two-compartment counter-current dialyzer with single passes, the simultaneous transport of hydrochloric acid and sodium chloride through an anion-exchange membrane Neosepta-AFN was studied at steady state. The diffusion dialysis process was quantified by four membrane mass transfer coefficients, which were correlated with the hydrochloric acid and sodium chloride concentrations in the feed. These characteristics were calculated from the experimental data on dialysis using a two-step procedure combining the numerical integration of the basic differential equations and a multivariable optimization. The second step of this procedure ensured the best agreement between the experimental and calculated data.

Application of diffusion dialysis in hydrometallurgical separation of nickel from spent Raney Ni catalyst

ABSTRACT The hydrometallurgical separation of nickel from spent Raney Ni catalyst is based on the dissolution of separated nickel slurry in hot diluted sulphuric acid (H2SO4) with the addition of an appropriate oxidation agent. Consecutive diffusion dialysis, which was performed in a two-compartment countercurrent dialyzer with an anion-exchange membrane Neosepta-AFN at steady state, enables the removal of excess of H2SO4 from a solution of aluminium and nickel sulphate in H2SO4 and simple recycling of the isolated H2SO4. Next, the obtained dialysate was alkalized using excess of NaOH solution. Using this procedure, the Ni(OH)2 contaminated with only 8.9 wt.% Al was obtained.

Determination of diffusivity from mass transfer measurements in a batch dialyzer: numerical analysis of pseudo-steady state approximation

The presented paper deals with the numerical analysis of pseudo-steady state conditions used in the modelling of the batch dialysis process. First, under specified conditions, time dependences of component concentrations and liquid volumes in both compartments were generated using a rigorous model based on Fick’s second law. From these data, the diffusion coefficient of the component in the membrane was calculated using a simplified model based on Fick’s first law. The specified coefficient was then compared with the calculated one. Numerical analysis revealed that in case of not too thick membranes, sufficiently high values of the diffusion coefficient, high intensity of mixing and considering the concentration and volume data in compartments I and II, the pseudo-steady state conditions can be considered as a good approximation of the real state.