Purification of bayer process liquor with alumina coated with a layer or

Abstract

An economical process for the removal and destruction of organic impurities present in Bayer process liquor depends upon the use of a hybrid adsorbent. The hybrid adsorbent consists essentially of porous essentially anhydrous particles of alumina having deposited on the surfaces thereof including the pores, an ultrathin layer of carbon atoms which is essentially monomolecular. Such carbonization is effected by cracking a suitable hydrocarbon, preferably a gas, in contact with a hot turbulent fluidized bed of alumina particles. This layer has the unique property of adsorbing far more impurities than the equivalent weight of active carbon, and also oxalate ions which are known not to be adsorbed on carbon. As an ultrathin layer it is too thin to change either the average pore volume or the surface area of the alumina particles substantially, from before they are carbonized. Because a sidestream of hot calcined alumina product is withdrawn from the main processing plant, the sidestream may be carbonized with a minimum energy cost. After virgin carbonized alumina adsorbs impurities and is 'spent', the spent alumina is returned to be calcined and can either be recarbonized, or sold as smelting grade alumina.