ISSN:
0001-1541
Keywords:
Chemistry
;
Chemical Engineering
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Single seed crystals of potassium chloride were grown from aqueous solutions under conditions of constant temperature, supersturation, and impurity concentration. With emission spectrography as the method of analysis, the distribution of various metal ion impurities between the grown potassium chloride crystal and the solution was studied. The distribution coefficients of Pb++, defined as the ratio of the impurity concentration in the crystal to the concentration in solution, were found to be greater than unity at very low concentrations. The lead distribution coefficients varied between 2,700 for solutions containing 10-8 moles of lead/mole of potassium chloride to 28 (for solutions of 10-5 moles of lead/mole of potassium chloride).The results suggest a mechanism of nonequilibrium capture of the impurity. The magnitude of the distribution coefficient is shown to depend on the equilibrium distribution coefficient between the solution and surface of the crystal, the rate of growth of the crystal, and the rate of diffusion of the impurity through the crystal lattice. These results are believed to be of significance in the purification of materials by fractional crystallization. For instance, they indicate that in order to produce crystals of lead-free potassium chloride, the conventional techniques or recrystallization should be modified to include rejection of the first crystals grown.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/aic.690130432
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