Количественное влияние затравки на показатели массовой кристаллизации химических осадков

Abstract

One of the problems to be solved in the course of exsolution of crystal sediments is to re-ceive products with desired technological properties. Two fundamentally different approaches can be applied for its resolution depending on method of supersaturation and requirements to the crystal sediments quality. In case of high supersaturation growth centers arise spontaneously and their number determines the properties of the final product to a large degree. The crystallization in the metastable region of solutions prevents spontaneous crystal nucleation and an introduc-tion of the seed phase becomes inevitable in this case. The nature of this phase determines the properties of the final product to some extent. During the real process there are mechanisms that disrupt the normal growth of crystals, causing distortion, leading to heterogeneous nucleation and recrystallization with degradation of seed material even. The line between these trends is the limiting supersaturation value, attrib-uted to the unit of phase interface. In this case the development of appropriate growth mecha-nisms is proportional to the deviation of the specific supersaturation of the solution from its value limit. The traditional source of heterogeneous nucleation is the mechanical interaction of the particles. The interaction probability is proportional to their concentration. Particles’ mass and their size becomes the most significant heterogeneous nucleation factor for seed particles of the same nature and morphology at the conditions of reproducible stream turbulence. Mathe-matical description of these trends has allowed to establish the dependence of the final particles’ size on the seed concentration in the feed pulp and to show the existence of a minimum number of particles of the final product. Experimental study of the of chemical sediments’ properties that depend on the seed amount, was carried out in relation to the breaking-up of aluminate solutions of alumina production. The process of selection of aluminum hydroxide has allowed to establish the amount of the seed aluminum hydrox-ide, resulting in a product of maximum size, and thus to confirm the theoretical conclusions.