Continuous prodn. of dust free anhydrous aluminium fluoride - by predrying and precalcining, removing fibres and final drying and calcination

摘要

In the multistage prodn. of dust-free AlF3 (I) with a low SiO2 and Al2O3 content by drying and calcining AlF3 hydrates (II), esp. AlF3.3H2O (IIA), the fines are removed from the (II) dried and/or precalcined in the first stage, before complete dehydration. If a disc drier is used in the first stage, the fines are sepd. by air sepn. and deposition on a cloth filter. With a flow drier, a cyclone and cloth filter are employed for sepn. The hydrate obtd. by precalcination in the first stage is in the AlF3.3H2O to AlF3.O.3H2O range. The size of the fines sepd. is max. 40 (max.20) microns. The formation of deposits retarding heat transfer on the walls of the calciner is prevented. A purer prod. is obtd. by sepn. of the fines, which include a considerable amt. of SiO2, which is desirable for (I) used in Al mfr. by electrolysis of a (I) melt.