Solid Solutions in Aluminum Electrolytes with the Participation of LiF

The paper presents the investigation of the solid solutions formation in the fluoride system Na5Al3F14-Na3AlF6-K3AlF6 with the addition of LiF. Two local regions were under consideration. The first case concerns the possibility of potassium and sodium cations replacing with lithium in the elpasolite (K2NaAlF6) when LiF is added to the electrolyte. In the second, the effect of lithium fluoride on the chiolite (Na5Al3F14) was studied. The investigation was motivated by the need to control the composition of the electrolyte during the electrolytic production of aluminum. The electrolyte samples were obtained from the initial fluorides under laboratory conditions. Determination of crystal-chemical details of the structure of solid solutions was carried out by the method of full-profile analysis (Rietveld method) on multiphase polycrystalline samples. It was found that the addition of LiF in the structure of elpasolite is accompanied by a gradual substitution of lithium for sodium with the formation, ultimately, of the K2LiAlF6 phase with the lattice parameter a = 8.0779 Å. Potassium is not subject to substitution. No dissolution of LiF in the structure of cryolite (Na3AlF6) was found. It was shown that chiolite does not form solid solutions with LiF upon crystallization