Alcan International Limited

Robert L Clegg

Kwat I The

Andrew N Carruthers

Dirk Noteboom

Claude Boulanger

A process for producing strong, essentially dust-free agglomerates from dust created by an industrial operation carried out, for example, on an ore or mineral, e.g. during the thermal conversion of a material containing predominantly gibbsite to sub-alpha alumina by a multistage thermal process having at least one intermediate stage. The process comprises grinding particles of binder material containing undercalcined alumina to a median particle size of less than 30 microns and to a specific surface area in the range of 90-300 m.sup.2 /g; combining about 1-4 parts by weight of the dust with one part by weight of the ground binder material to form combined solids; mixing the combined solids with water to produce agglomerates, the total amount of added water being about 0.8-1.2 parts by weight for every part by weight of the ground binder material, plus about 0.08 to 0.12 parts by weight for every part by weight of the dust; and optionally aging the resulting agglomerates in a closed environment at a temperature of at least 80.degree. C. for at least one hour in at least 50% humidity. The water is mixed with the combined solids by intensive mixing in a mixer equipped with a mixing motor, the water being added according to the following scheme: (a) 40-80% of the total amount of water is added to the combined solids at a rate such that no more than 10 minutes are required for complete addition; (b) optionally allowing a period of time to pass after the addition of the water in step (a) before proceeding further while continuing the intensive mixing; (c) commencing the addition of the remainder of the water and measuring a characteristic of said mixture corresponding to its viscosity and using the measurement as a reference value; and (d) continuing the addition of the remainder of the water while continuing to measure the characteristic of the mixture, the water being added at such a rate that the characteristic of the mixture remains the same as the reference value during the addition or varies by less than .+-.5%.

Process for producing agglomerates from dusts

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.

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Chicoutimie-Nord, Canada

Robert L Clegg