Treatment of Waste Solutions from Electrolytic-Plasma Polishing Decontamination to Remove Cr(III) Radionuclide Using Ultrafiltration Membranes

The paper presents the results of using ultrafiltration for purification of solutions simulating liquid radioactive waste, produced during decontamination of parts by electrolytic-plasma treatment, to remove chromium(III) radionuclides (⁵¹Cr(III)). The main performance characteristics and transport properties of ultrafiltration membranes made of hydrophilized polysulfone, polyethersulfone, and regenerated cellulose with different molecular weight cutoff (MWCO) values have been determined. The dependences of membrane flux and ⁵¹Cr(III) rejection coefficient on the pH of solutions and thermostatting time have been established. It has been shown that in 8% (NH₄)₂SO₄ solution at pH 7–8, the ⁵¹Cr(III) radionuclide occurs in the form of polynuclear hydroxo complexes, which are retained by ultrafiltration membranes and precipitate during centrifugation. A regenerated-cellulose membrane with MWCO = 10 is the most effective, rejecting ∼97% of ⁵¹Cr(III) at pH 8. Increasing the time of solution thermostatting before membrane separation leads to an increase in the rejection of ⁵¹Cr(III) due to a deeper hydrolysis process with the formation of polynuclear hydroxo complexes.