Cristalizacao do NaCl a partir de solucoes multicomponentes

This work aims the study of the influence of different ionic species K"+,Mg"2"+ ad Al"3"+ added as chlorides, on growth of NaCl crystals. The experimental work was carried out in a fluidized-bed crystallizer at 303 K, for different hydrodynamic conditions and concentrations of the impurity. The evaluation of the effect of the impurities on the growth and dissolution processes of NaCl was done by comparing the corresponding rates measured in pure aqueous solution and in the presence of admixtures. To calculate the thermodynamic driving-force for crystallization, the activity coefficients of NaCl and its solubility were obtained as a function of the temperature and of the second-salt content in the system. The interpretation of the experimental results required the prediction of the ternary solutions densities. To evaluate these quantities, the Pitzer model developed for the thermodynamics of electrolytes was, therefore, used. Parameters estimation was done based on experimental data measured for binary and ternary solutions. The experimental work allowed us to conclude that the presence of impurities changes the growth and dissolution kinetics of NaCl. The reduction observed in both rates was directly related to the cation charge. Therefore, it was possible to conclude that the resistance to the diffusion of the main solute in the system, as well as the blocking effect of the foreign ions upon the surface integration step increases with cation chargeAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga