Polishing alumina prepn. from bayerite and/or nordstrandite - by grinding continuously in two-chamber ball mill. heating and cooling

摘要

Polishing alumina prepn. from Al(OH)3 takes place by using a bayerite and/or nordstrandite raw material having residual moisture content less than 3 wt.% and grain-size 45-125 micron. The raw material is ground in a continuously working ball-mill contg. at least 2 series-connected grinding chambers, for 10-50 (30) min. in each grinding chamber, with degree of comminution 8-10, w.r.t. average grain dia. The ground material is then heated 36-40 hrs. to 620-700 deg.C and cooled in 24 hrs. to 20-30 deg.C. The initial structure is maintained. Surface-activation takes place. Alpha-alumina formation is prevented. A quality-prod. is obtd. in yields over 80% by an energy-saving process. Annealing can take place in metal capsules. Cooling need not be controlled gradually.