Rates of Growth and Dissolution of Barium Nitrate in a Vertical Cone-Type Vessel

Abstract

By use of a vertical cone-type vessel, the rates of growth and dissolution of Ba(NOs)2 in aqueous solution were studied in the temperature range from 38 to 69eC.
It was deduced from the vessel characteristics that mass transfer coeMcient of solute, kd, in the vessel is not affected by flow rate and crystal size, ands hence it was necessary to know the value of kd, in advance, for the analysis of the rates as a function of the diffusiQn rate, From the results of the dissolution of fixed spherical fused samples, the following Ranz Marshall-type dimmensionless expression was obtained.
76(ptFPFD)1/3(112)
where Ls, D, u, pF and ptF are radius of the sample (cm), diffusion coefllicient (cm2/sec), linear velocity (cm/sec), density (g/cmS) andiviscosity (g/cm. sec) of solution, reSpectively. Comparing the dissolution rates of the suspended crystal particles with those of the fused samples regardless of the method of preparation, the activation energies were 4. O kcal/mol in both cases, the average shape factor of the crystals used was estimated to be 1.84, which was consistent with the observation by a microscope.
The rates of growth of the suspended crystal were controlled by the rate of surface reaction as well as by the rate of mass transfer. The activation energy of the. surface reaction was 27.5kcal/mol. The effects of the operational conditions on the performance of the vertica.1cone crystallizer were discussed.