Industrial crystallization has some specialities different from diffusion operation in chemical engineering field and ideal crystal growth theory, and these specialities are very important to understand crystallization in a crystallizer. Design theories of crystallizer whose capacity is expressed by production rate and product crystal size, are proposed from two different concepts (ideal behaviors of crystal and solution in a crystallizer, and final product crystal estimated from average nucleation rate, average growth rate, average suspension density), using industrial crystallization theories. These theories are satisfactorily applied for design of industrial continuous crystallizers from laboratory tests' data. Some discussions on data of industrial and laboratory tests of sodium chloride have been done by these design theories, and correlations between product crystal size and production rate in the same continuous crystallizer are studied. newconcept for production of a desired crystal size which is obtained by adjustment of suspension density in the continuous crystallizer, production and nucleation rate, is proposed.
To verify the effectiveness of the rotating cylinder method as a laboratory testing apparatus of foulant and/or deposited scale, an annular geometry heat-transfer tube with indirect electric heating was tested in more practical fouling and cleaning conditions. Calcium sulfate foulant was used as a representative foulant of seawater, and experimentally expected to show typical asymptotic fouling curves, asymptotic value of which decreased with an increase of fluid velocity. A generalized fouling model was applied to estimate the fouling mechanism, and proved surface process to be a controlling mechanism of scale deposition. The effectiveness of mechanical cleaning against the formed scale was quantitatively evaluated by using particle abrasion method. The removal test verified that the removing rate decreased asymptotically in inverse proportion to the overall particle load, and also that the dependence of the removing rate per unit particle concentration on the particle load was affected by the fluid velocity. The observed final residual fouling resistance decreased asymptotically with an increase of the particle concentration, and the suitable concentration of particle for mild cleaning was very low as compared with the operating condition of the fluidized bed heat exchanger.
To develop potassium ion ion-memorizing inorganic-exchangers, potassium ions of specially synthesized KMo5O15OH·2H2O and KNbWO6 with tunnel structure or K2Mn2O8 and KMg2LiSi4O10F2·2H2O with layered structures were ion-exchanged for sodium ions in sodium chloride aqueous solution, protons in hydrochloric acid aqueous solution, or lithium ions in lithium chloride squeous solution at 70°C. Sodium ion-exchanged NaxK1-xMo5O15OH·2H2O, NaxK1-xMg2LiSi4O10F2·2H2O and proton-exchanged K2-xHxMn4O8 were found to have the selectivity for potassium ions in aqueous solution at room temperature. Especially, it was found that NaMg2LiSi4O10F2·2H2O has an outstanding selectivity for potassium ions in solution. This mica has the feasibility of a superior potassium ion ionmemorizing ion-exchanger. To develop bromide ion ion-memorizing ion-exchangers, Pb10(PO4)6Br2-xClx was synthesized and its anion-exchange characteristics of chloride ions in it for bromide ions in aqueous solutions were investigated.
It is difficult to selectively separate and uptake small amounts of K+ from seawater in the presence of a large amount of Na+. During investigation of the cation-exchange characteristics of inorganic ion exchangers, we have discussed that K⇔ in aqueous solution are strongly held on some synthetic fluorine tetrasilicic micas by a cation-exchange reaction at room temperature. From among the successfully synthesized micas, sodium ion-exchanged hectorite, Na1/3Mg8/3Li1/3Si4O10F2·H2O (Na+H), and sodium ion-exchanged taeniolite, NaMg2LiSi4O10F2·2H2O (Na+T), were found to be promising. Their removal behaviors of K+ from model aqueous solutions, apractical seawater, and some brines were examined by normal batch methods. It was found that ⇔ exchange isotherm of Na+T rises steeply and attains plateau above the diagonal line in low-concentration region of K+, which reveals that K+ are extremely preferred to Na+ in the low-concentration region. The order of K+ selectivity was Na+H<<Na+T in the lowcollcentration region. Further, the Na+T was found to selectivity take up a regular amount of K+independent of the concentrations of Na+ and K+ in solution. It is concluded that Na+T can be utilized in the separation and uptake of K+ from seawater (K+ 370ppm, Na+ 10,600ppm).
The limiting current densities in electrodialysis were measured for the rare-earth element solutions including one of lanthanum, praseodymium, neodymium, and yttrium (the single-component systems) and those including two of them and EDTA as a chelator (the multi-component systems). In the single-component systems, the observed values of limiting current densities for single rareearth elements were successfully correlated with the following equation under the experimental conditions studied: Ilim=kC0.80u0.76 where Ilim, k, C, and u are limiting current density, constant, solution concentration, and liquid velocity, respectively. In the multi-component systems, a bent point was observed in the currentdensity vs. cell-voltage curves, in which water dissociation did not occur. At the bent point, the observed fluxes of ionic species transferred through a cation-exchange membrane changed abruptly, which suggested that the bent point corresponded to one of limiting current densities for rare-earth elements. The calculation with the equation, mentioned above, for the single-component systems identified the current density at the bent point as one of the limiting current densities for the rare-earth elements.