The materials physical and chemical analysis of the reasons of instability particle size distribution of productional of aluminum hydroxide in the processing of bauxite by Bayer process. Shown that the frequency of changes in the properties precipitate Al(OH)3, formed during the precipitation of aluminate solutions determined by the dependence of the growth processes on the relative supersaturation of the system per unit area of the seed. Found determines the influence of concentration injected seed aluminum hydroxide and its active surface (which varies under the influence of impurities in the aluminate solution) on the parameters of the periodic changes in the properties of sediment.