Correlations between crystallization and dissolution of aluminium potassium sulphate.

Abstract

Growth and dissolution rates of a potash alum crystal have been measured at a constant temperature of 30°C. The diffusion theory for both growth and dissolution is discussed, based upon the experimental results. Based upon observations of the solution-crystal interfacial concentration for growth and dissolution, it is shown that the diffusion step in the growth process was second-order with respect to the driving force, and the presence of a separation step of solute or cluster from crystal lattice for the dissolution process is proposed because the interfacial concentration was not equal to saturated condition. Agreement between the dimensionless concentrations, which included the solution-crystal interfacial concentrations for growth or dissolution, related these phenomena and gave the relations among the transfer rate coefficients. And it was shown that the interfacial concentrations could be estimated even at a solution temperature other than 30°C by using the relations obtained at 30°C. Therefore, the transfer coefficients of reaction and diffusion steps for the growth process can also be determined. The transfer coefficients of separation and diffusion steps for the dissolution process and interfacial concentration can also be calculated by measuring the overall rate coefficient for dissolution.