Process for producing agglomerates from dusts

Abstract

A process for producing agglomerates from dust (especially electrostatic precipitator dust) collected from a process involving the thermal conversion of a material containing gibbsite to sub-alpha alumina and alpha alumina, and the agglomerates so formed. The process involves binding the dust particles together using water and undercalcined alumina taken from an intermediate stage of the same thermal conversion that originally produces the dust. The added undercalcined alumina is ground, in order to create fresh surfaces, to a median particle size of less than 30 microns and a specific surface area of about 130 to 300 m.sup.2 /g. About 1-4 parts by weight of the dust are mixed with every part by weight of the ground undercalcined alumina. A special procedure is employed for mixing the solids and water which makes use of intensive mixing. At first about 50-80% by weight of the estimated amount of water required is mixed with the solids in a single addition and the mixing is carried out for at least about 30 minutes. The remainder of the water is then added at a slow rate of addition while the mixing is continued. The resulting agglomerates are aged for at least 2 hours at a temperature of at least 80.degree. C. in an atmosphere of high relative humidity in order to strengthen the agglomerates. Calcining without sintering may also be carried out. The resulting dust agglomerates can be handled without significant fracturing or dust generation, contain no added contaminants, are inexpensive to produce and can be returned to the product stream of the thermal conversion process that initially produced the dust.