The kinetics of desilication of synthetic spent Bayer liquor seeded with cancrinite and cancrinite/sodalite mixed-phase crystals

Isothermal, batch desilication kinetics of synthetic, sodium aluminate solu tion (spent Bayer liquor) via cancrinite and cancrinite/sodalite mixed-phas e crystal growth, have been studied under conditions at which sodium alumin osilicate scale forms at the surfaces of steel heat exchangers of alumina p lant. Seeding with the pure cancrinite and mixed-phase crystals results in the suppression of scale formation and a faster rate of liquor desilication in comparison with its sodalite dimorph. Cancrinite seed crystals prepared from NO3--rich solutions exhibited crystal growth mechanism and kinetic be haviour different from dimorphic mixed-phase crystals prepared from CO32--r ich solutions, when both were used to desilicate CO32--rich spent Bayer liq uor. The rate of desilication due to crystal growth on CO32- -cancrinite/so dalite mixed phase crystals followed a second-order dependence on the relat ive supersaturation of SiO2. An activation energy of 52 kJ mol(-1) was esti mated for the crystal growth process. For desilication kinetics involving N O3--cancrinite seed crystal growth, a third-order dependence on relative su persaturation of SiO2 and an activation energy of 63 kJ mol(-1) were obtain ed. (C) 1999 Elsevier Science B.V. All rights reserved.