Low-silica aluminium fluoride soln. for cryolite prodn. - prepd. by reacting hexafluorosilicic acid with aluminium contg. material

摘要

Prodn. of AlF3 soln. by treating 10-30 wt. % soln. of H2SiF6 with an excess of an Al- contg. material at an elevated temp. is improved in that this reaction is carried out at 90-100 degrees C with intensive stirring; the pH at the end is between 2.5 and 3.5; a ferric salt is added in an amt. of 0.005-0.2 mole (pref. 0.01-0.05 mole) per mile of H2Si F6; the reaction mixt. is rapidly cooled below 60 degrees C; and the pptd. silicic acid is sepd. by filtration. The AlF3 soln. is suitable for the prodn. of cryolite (by addition of NaCl) because of the very low silica content (as required for the aluminium prodn.); the pptn. of colloidal silica is promoted by the presence of a ferric salt. Cheap alumina hydrate or low-iron bauxite can be used as the aluminium source.