Abstract: A process and an apparatus for the continuous decoposition of a supersaturated sodium aluminate liquor forming a suspension in the presence of aluminium trihydroxide seed characterised by:(a) bringing into contact in a non-agitated grading decomposer a feed flow formed by the suspension and a recycling flow which is taken off in the underflow zone of the decomposer,(b) simultaneously drawing off a production flow in the same underflow zone,(c) extraction of an overflow flow at the overflow of the grading decomposer, and(d) suitable regulation in dependence on the flow rate of the feed flow, the flow rate of the recycling flow, the speed of discharge flow of the suspension in the underflow zone and the speed of rise of the suspension in the overflow zone.

Abstract: A grading decomposer apparatus for continuously decomposing a liquor of sodium aluminate supersaturated in alumina comprises a cylindrical-conical tank for containing the liquor, having an upper cylindrical portion and an overflow generally peripherally disposed in the upper portion. A centrally disposed tubular element passes from above into the upper portion of the tank; the tubular member terminates in the cylindrical portion of the tank below the overflow. The apparatus also includes an off-take from the lower portion of the tank to an outlet; liquor is recycled from the lower portion of the tank to the upper portion within the tubular element and below the overflow, and liquor is introduced into the upper portion of the tank within the tubular element and below the overflow. A static disperser is disposed within the tubular element, the liquor feed and the recycled liquor inlet in order to create a feed and tranquilization zone within the tubular element.

Abstract: A method and apparatus for decomposing a sodium aluminate liquor supersaturated with alumina, obtained from alkaline action on bauxite by the Bayer process, is initiated by introduction of alumina trihydrate seed, thereby forming a suspension. The suspension is fed in at the top of a non-agitated reactor described as a "decomposer", and removed from the bottom of the decomposer; the speed at which the suspension moves downwardly is regulated at 1.5 to 10 meters per hour. The apparatus comprises a cylindrical-conical reactor which is fitted with an arrangement for feeding in the suspension at the top, and with an arrangement for taking out the suspension at the bottom. In one embodiment of the apparatus the suspension is taken from the base of the decomposer through an internal tube, with air injected into the bottom of it, is raised to the level of the top of the decomposer and is then sent downstream.