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.