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

摘要

In the continuous multistage prodn. of dust-free AlF3 (I) from its hydrates (II), esp. AlF3.3H2O (IIA), by drying and calcination, (II) is predried and/or precalcined, freed from fines and completely dehydrated and calcined in an (indirectly heated) rotary calciner. 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. 60 (max. 40) microns and the particle size distribution of the end prod. varied accordingly. Dehydration is completed at a temp. gradient rising continuously to the calcination temp. of 500-600 deg.C within a time span of up to 45 min. The fines are granulated in an intensive mixer with metastable AlF3 soln. with a concn. of 5 to max. 30 (10-15) wt.% and completely dehydrated and calcined as above, pref. after mixing with the prod. freed from fines. 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.