Alena Žáková

Separation of HCl+NiCl2 Mixture by Diffusion Dialysis

Abstract Separation of an aqueous solution of HCl+NiCl2 by diffusion dialysis was investigated in a two‐compartment mixed cell with an anion‐exchange membrane Neosepta‐AFN. The experiments proved that this membrane can be considered a good separator for the mixture mentioned, because nickel chloride is efficiently rejected, while hydrochloric acid permeates well through the membrane. The separation is very effective at high acid concentrations and low concentrations of nickel chloride. The separation efficiency of the membrane was evaluated by the partial flux of nickel chloride. The experiments revealed that the partial flux is very low, i.e. below 3.2%—it decreases with increasing acid concentration, but it increases with increasing content of salt in the solution separated. Moreover, the separation process was quantified by the permeability of the membrane based on four phenomenological coefficients which depend on the initial acid and salt concentrations.

Apparent diffusivity of some inorganic acids in anion-exchange membrane

Abstract The paper deals with the determination of apparent diffusivity of H 2 SO 4 , HCl, HNO 3 , H 3 PO 4 and HF on the basis of the experiments carried out in a batch mixed cell with an anion-exchange membrane NEOSEPTA-AFN. The dependence of apparent diffusivity of the inorganic acid upon its concentration in the membrane has been approximated by the second degree polynomial whose coefficients have been determined with the help of models based on Fick’s first and second laws. Using all the experimental data obtained at various initial acid concentrations and rotational speeds of the stirrers, it has been shown that apparent diffusivity of the inorganic acid is concentration-dependent and decreases in the series HCl, HNO 3 , H 2 SO 4 , HF, H 3 PO 4 .

Transport of hydrochloric acid through anion-exchange membrane NEOSEPTA-AFN: Application of Nernst–Planck equation

Abstract The paper deals with the determination of mobility of H3O+ and Cl− ions on the basis of experiments with hydrochloric acid carried out in a batch mixed cell with an anion-exchange membrane NEOSEPTA-AFN, which have been completed by measurements of the membrane conductivity. The dependencies of mobility of H3O+ and Cl− ions upon the acid concentration in the membrane have been approximated by the second degree polynomial, whose coefficients have been determined with the help of a model based on the Nernst–Planck equation — the membrane being modeled as a homogeneous gel phase containing fixed positive charges, water molecules and mobile H3O+ and Cl− ions. Using all the experimental data obtained at various acid concentrations and rotational speeds of the stirrers, it has been found that mobility of H3O+ and Cl− ions is strongly affected by the acid concentration in the membrane.

Transport of nitric acid through the anion-exchange membrane NEOSEPTA-AFN

Abstract The paper presents the determination of mobility of H3O+ and NO3− ions and diffusivity of the non-dissociated form of acid on the basis of experiments with nitric acid carried out in a batch mixed cell with an anion-exchange membrane NEOSEPTA-AFN, which have been completed by measurements of membrane conductivity. The dependencies of mobility of H3O+ and NO3− ions upon the acid concentration in the membrane were approximated by the second degree polynomial, whose coefficients were determined by the numerical integration of the differential equation describing the time dependence of nitric acid in the cell followed by an optimizing procedure. Diffusivity of the non-dissociated form was calculated from mobilities of H3O+ and NO3− ions. The model used is based on the Nernst-Planck electro-diffusion equation and takes into account ionic equilibrium between the species. Using all the experimental data obtained at various acid concentrations and rotational speeds ofthe stirrers, it was found that the transport characteristics mentioned above (except for mobility of H3O+ ions) were affected by the nitric acid concentration in the membrane.

Modelling the flow of liquid in continuous dialyzer

The paper deals with the modelling of the flow of liquid in a compartment of continuous dialyzer. Two simple models, the dispersion model and tanks-in-series model, were used. Their parameters Peclet number, the mean residence time of liquid in dialyzer compartment, the number of tanks and the mean residence time of liquid in each tank were determined from a nonideal step input of a tracer and its response. It has been found that in the range of the Reynolds number from 0.44 to 3.64, the Peclet number and the number of tanks are in the range from about 200 to 320 and from 100 to 310, respectively. Both these parameters and the mean residence time of liquid in the compartment of dialyzer and in each tank decrease with the increasing Reynolds number. Furthermore, it has been proved that the values of the mean residence time of liquid in the compartment of dialyzer calculated from the dispersion model agree well with those calculated from the tanks-in-series model. The obtained values of the Peclet number and the number of tanks indicate that the flow in the dialyzer does not significantly differ from the plug flow.

On conditions affecting correctness of the measurement of solution/membrane equilibrium

The paper deals with simulation of conditions affecting the correctness of the measurement of a solution/membrane equilibrium which is determined by the method based on saturation of the membrane with the solution and subsequent extraction of a component into water or a suitable solution. Attention has been paid to the step when the solution remaining at the membrane surface is removed by washing with water. In this step, an amount of the component can be transferred into rinsing water which represents a loss of the component in the membrane, and the equilibrium is measured incorrectly. In the numerical simulation, the membrane has been considered as a slab, and unsteady-state mass transfer from the membrane into water has been solved. The simulation, whose results are given graphically, has shown that the loss of the component into water increases with increasing washing time, diffusivity of the component in the membrane, and liquid mass transfer coefficient. On the contrary, the loss of the component decreases with increasing partition coefficient and the membrane thickness. Furthermore, it has been found that the relative loss of the component is independent of the initial concentration of the component in the membrane.