Chromatographic formation of a triadic band of lithium in hydrated LTA zeolite: An investigation on lithium isotope separation effects by ion exchange

Abstract

Lithium concentrations [Li] and isotopic ratios [7Li]/[6Li] were measured for effluent fractions from a biphasic zeolite column. The biphasic state was ascribed to a mixture of hydrated Linde Type A (LTA) zeolites, [Li0.08(NH4)0.92]A and [Li0.33(NH4)0.67]A, which were formed by Li ion exchange from hydrated ammonium in the form (NH4)12[Al12Si12O48]·nH2O (NH4A). The biphasic Li band of the column was displaced by ion exchange with a solution of NH4NO3. A constant [Li] with a much lower level than the concentration of NH4+ in the displacer (NH4NO3) was observed for the effluent from a short column. This constant lower level of [Li] was attributable to the biphasic state. On this [Li] plateau of the effluent, the level of [7Li] shifted higher than the original isotopic composition of the Li feed, whereas 6Li was concentrated on the biphasic zeolite solid. The accumulation of 6Li in the zeolite proceeded by a mechanism of differential elution of 7Li from the biphasic zeolite. For the long column experiment, a significant enrichment of 6Li in the zeolite was observed, whereby a triadic band of Li was probably formed in the column. Two monophasic and a biphasic state were assigned. The biphasic band was deemed to push the monophasic bands forward, thereby enriching the monophasic bands with 7Li, while 6Li accumulated at the end of the biphasic band. The trio structure of the Li band and isotopic discrimination in the band were analyzed.