INFLUENCE OF ADMIXTURES AND OPERATING-CONDITIONS ON THE CRYSTALLIZATION OF AMMONIUM-CHLORIDE

Effects of specific admixtures and operating conditions on the crystal lization of ammonium chloride from aqueous solutions were experimental ly investigated. The metastable zone width was measured and crystalliz ation runs were performed in continuous and batch mode in the presence of Al3+, Fe2+ and Mn2+, the latter seeming to be the most effective o ne: in fact it enlarges the metastable range, improves the NH4Cl cryst al habit and reduces the production of fines both from batch and conti nuous crystallization. A strong influence of the temperature, in the r ange 30-55 degrees C, on the yields of continuous crystallization was also noticed. The best results were obtained at 30 degrees C. Finally, continuous runs allowed to determine the ratio between growth and nuc leation rate, g/n, at various temperatures and in the presence of Mn2 as admixture.