Membrane Properties of Montmorillonite, Saponite and Clinoptilolite During Electroosmotic Fractionation of Hydrogen Isotopes

Abstract

Based on experimental studies, the possibility and efficiency of usage of montmorillonite, saponite, and clinoptilolite as separation membranes during electroosmotic fractionation of hydrogen isotopes in an aqueous electrolyte solution was evaluated. For the experiments, the following samples were used: bentonite (Cherkasy deposit) with a content of montmorillonite of 75% (hereinafter referred to as montmorillonite), saponite (Varvariv deposit) and clinoptilolite (Sokyrnytsya deposit). It was found that under the influence of an electric field, electroosmotic filtration of the tritiated electrolyte occurs through weakly permeable membranes. Depending on the structural features of the mineral substance, various proton conductivity of the membranes was recorded, which determines the different intensity of the redistribution of ions of dissociated HTO molecules between the anode and cathode chambers. The largest difference between the specific activity of tritium in the anolyte and catholyte was obtained in the system where the mineral membrane was made of saponite (11% and 26% of the specific activity of tritium in the initial HTO, respectively). The least was the stability of the montmorillonite membrane. Its destruction upon interaction with a Na2CO3 solution led to electrolyte leakage and a decrease in the extraction of tritium from the filtrate (catholyte). The use of clinoptilolite when creating a composite with montmorillonite made it possible to increase the stability of the membrane and additional possibilities for fractionating hydrogen isotopes in an electrolyte. Electroosmotic filtration of the electrolyte was accompanied by fractionation of hydrogen isotopes in the mineral membranes of the experimental systems. The largest isotope effect was obtained in montmorillonite and composite montmorillonite-zeolite membranes, where the fractionation coefficient α in the fraction extracted from the interlayer space was 1.16 and 1.12, respectively. In a composite membrane, where the amount of clinoptilolite was 67.5%, isotopic hydrogen fractionation was also observed in the surface-adsorbed fraction (α = 1.5) and in a structurally bound form (α = 1.1). The use of saponite as an electroosmotic membrane leads to a smaller isotope effect than in a montmorillonite membrane, and is manifested in surface-adsorbed water (α = 1.08) and in the interlayer space (α = 1.02). The addition of quartz sand to montmorillonite reduces the efficiency of fractionation of hydrogen isotopes detected only in the surface-adsorbed fraction (α = 1.02).