THE INFLUENCE OF SODIUM-CARBONATE ON SODIUM ALUMINOSILICATE CRYSTALLIZATION AND SOLUBILITY IN SODIUM ALUMINATE SOLUTIONS

Isothermal batch precipitation experiments have been carried out in sy nthetic Bayer liquors to investigate the effects of sodium carbonate c oncentration on both silica solubility and the crystallisation of sodi um aluminosilicates. At both 90 and 160 degrees C cancrinite (generica lly defined as a sodium aluminosilicate of space group P6(3)) is the s table solid phase. Sodalite (generically defined as a sodium aluminosi licate with space group <P(4)over bar 3n> seed transforms to cancrinit e at both these temperatures. A high concentration of sodium carbonate in the synthetic liquor causes a decrease in the rate of conversion o f sodalite to cancrinite. The solubility of both cancrinite and sodali te decreases as the concentration of sodium carbonate in the synthetic liquor is increased. For instance at 90 degrees C and with 40.0 g dm( -3) sodium carbonate in the synthetic liquor after 13 days the sodium aluminosilicate concentration is 0.52 g dm(-3) compared to 0.85 g dm(- 3) with 4.6 g dm(-3) of sodium carbonate in solution. At 160 degrees C the sodium aluminosilicate concentration is 0.47 g dm(-3) with 40.0 g dm(-3) sodium carbonate in solution after 13 days and 0.79 g dm(-3) w ith 4.6 g dm(-3) sodium carbonate in solution. Throughout all these ex periments a progressive loss of carbonate from the sodium aluminosilic ate crystallisation products was observed as a function of time.