Vol 13, No 4 (2023)

The paper discusses the electrodialysis treatment of mixed nickel sulfate and sulfuric acid solution using polyaniline surface-modified cation exchange membranes. The modified membranes are obtained on the basis of industrial cation-exchange MK-40 heterogeneous and MF-4SK homogeneous membranes by in situ oxidative polymerization of aniline under electrodialysis conditions. The conductive and diffusion characteristics of the initial and modified membranes in solutions of sulfuric acid and nickel sulfate are studied. It is shown that the modification of membranes with polyaniline leads to a decrease in their electrical conductivity and diffusion permeability while maintaining high selectivity. The diffusion permeability of cation-exchange membranes is higher in nickel sulfate solutions compared to sulfuric acid one, while an inverse dependence is found for anion-exchange membranes. The competitive transfer of sulfuric acid and nickel sulfate during electrodialysis separation and concentration of their mixture using initial and modified cation-exchange membranes paired with anion-exchange MA-41 membrane are studied. It is shown that the applying a polyaniline layer with positively charged groups on the surface of the MK-40 or MF-4SK cation-exchange membranes suppresses the transport of doubly charged nickel ions both in the separation and concentration modes over the entire range of current densities. The greatest repulsion effect is observed for homogeneous modified membranes, where the selective permeability coefficient P(H₂SO₄/NiSO₄) increases from 0.7–1.7 to 32.5–19.7 depending on the current density. It is established that the use of polyaniline modified cation-exchange membranes permits to concentrate the solution containing 0.1 mol-eq/L (4.9 g/L) H₂SO₄ and 0.1 mol-eq/L (7.7 g/L) NiSO₄, with simultaneous separation into sulfuric acid with concentration about 2.4 mol-eq/L (120 g/L) and nickel sulfate solutions. The content of nickel sulfate in the concentrate does not exceed 0.13 mol-eq/L (10 g/L).

The influence of lactose on the basic transport characteristics of ion exchange membranes, including cation-exchange membranes modified by polyaniline, has been studied. A positive effect on biofouling by Bacillus sp. or Shewanella oneidensis MR-1 cell cultures of modified MK-40 and Ralex CMHPES membranes has been found. That is mainly due to the different area of the conductive surface of these membranes. It has been revealed that the presence of lactose in a solution leads to a decrease in the conductivity of all studied membranes. However, the most significant effect is manifested for MK-40 membrane modified by polyaniline: its electrical conductivity is reduced by 15–25%. The diffusion permeability of the anion-exchange and initial cation-exchange membranes is poorly dependent on the presence of lactose in the solution. However, its decrease is observed by 2–2.5 times in the case of cation-exchange membranes modified by polyaniline. A significant effect of lactose on the current-voltage characteristics of the anion-exchange membranes has been found. This fact indicates significant adsorption of lactose on membrane surface in an external electric field. It is shown that ion-exchange membranes remain quite effective for electrodialysis of hydrochloric serum solutions, but their use is more effective at under limiting current modes.

In this work, membranes were obtained from PAN with the addition of particles of graphene oxide (GO), PAN pyrolyzed under the influence of IR radiation (IR-PAN-a) and nanodiamonds (ND). The pore structure of the obtained membranes was studied. It has been shown that the addition of particles slightly reduces the average pore size of the membranes from 17 to 12–15 nm, which leads to a decrease in the membranes water permeance from 158 to 80.9–119.9 kg/m² h bar. At the same time, the addition of particles led to hydrophilization of the surface—the water contact angle decreased from 65° to 48°–55°, which contributed to an increase in the flow of oil solutions in toluene by 2–3 times compared to the PAN membrane. At the same time, the addition of GO and IR-PAN-a contributed to a significant increase in the irreversible membrane fouling. On the other hand, the addition of nanodiamonds not only reduced the overall membrane fouling and increased the permeability of the separation mixture from 4.93 to 8.47 kg/m² h bar, but also made it possible to recover more than 96% of the pure toluene flux. The membranes rejection with the addition of ND in the filtration of oil solutions in toluene 10 g/L was 85–89%.