| Description |
The rate of hydrolysis of aluminum sulfate has been investigated by using a high pressure autoclave and a reaction capillary. Hydrolysis of aluminum sulfate at temperatures higher than the normal boiling point of aqueous solution affords a very alightly soluble compound, hydronium alunite. The rate of hydrolysis is higherm the lower the inifial concentration, the higher the reaction temperature, and the higher the basicity of solution. The basicity is the most sensitive factor affecting the rate of hydrolysis of aluminum sulfate among the variables. At low temperature, the rate of hydrolysis is limited by a surface-controlled process, whereas above the limiting temperature the rate of hydrolysis is controlled by a diffusion process in the interfacial layer. The analysis of rate data reveals that the surface-controlled process has a high activation energy of the order of 22 kcal/mole, and the diffustion-controlled process has very low activation energy near zero. The criterion of the operating mechanism is apparently the size of the precipitate particle. The theory of the rate of precipitation of spherical particles has been developed for the growth stage of particles where no further nucleation is accounted for. The applicability of the theory has been tested by measuring the rate of precipitation of hydronium alumite from basic aluminum sulfate solution. Good agreement is found up to one hundred percent completion of precipitation. |
