LIQUIDUS TEMPERATURES OF CRYOLITE MELTS WITH LOW CRYOLITE RATIO

摘要

Multi-component fluoride mixtures are the only possible media for the development of new ecologically clean and energy saving technologies for aluminum production. A radical decrease of operating temperature is impossible in the frame of existing technology in which sodium cryolite is a basic component of electrolyte. In order to obtain essential decrease of the electrolyte liquidus temperature the potassium cryolite can be used as a basic component. Sodium, lithium and calcium fluorides additions significantly change the properties of a bath. Therefore liquidus temperatures in the ternary KF-LiF-AlF_3 and quaternaries KF-rnLiF-AlF_3-CaF_2 and KF-NaF-AlF_3-CaF_2 systems with cryolite ratio 1.3 and 1.5 have been determined. Any additions of CaF_2 to the KF-NaF-AlF_3 mixture with low CR increase the electrolyte primary crystallization temperature when KF concentration is above 30 mol.%. The calcium fluoride solubility in the KF-NaF-rnAlF_3 system rises with cryolite ratio and NaF content. The NaF or LiF additions to the KF-AlF_3 melt with CR 1.3-1.5 increase melting points of the electrolytes. CaF_2 is more soluble in the KF- LiF-AlF_3 system than in the KF-NaF-AlF_3 system.