Study On Carbonization Of Sodium Aluminate Solution With High AL2O3 Concentration

Alumina is one of the most important raw materials in the world economics. Since the alumina industry has developed with high speed from 1980's in the 20th century, nowadays the total output of alumina annually is up to 4,000,000 tone in our country, only junior to the iron & steel yields in the metallurgical industry.In the present dissertation, the technology of carbonization of sodium aluminate solution with high A12O3 concentration (130~210g.L~1) has been studied systematically based on the analysis of the mechanisms and technique characters. Results of the experiment and analysis are as following:1. The reaction Gibbs free energies (ArGr) of NaAl(OH)4 and the complicated compound Na2O A12O3- 2CO2- nH2O were calculated, and the variation character and influencing factors of equilibrium content of SiO2 in the carbonization process were also investigated.2. The liquor supersaturation, which influences both the precipitation speed and the percentage of impurities in the product, is the main impetus of carbonization of sodium aluminate solution with high A12O3 concentration. Improving carbonization temperature or choosing reasonable gas ventilating system may reduce the liquor supersaturation, and then the coarse grain aluminium trihydroxide with good crystallization and low content of impurities (Na2O, SiO2) can be produced.3. It is also demonstrated that the aluminium trihydroxide seeds can improve remarkably quality of the carbonization product. Seeds can decrease the interface energy between aluminium trihydroxide crystal and liquor, which is beneficial to the crystal growth and reduction of impurities absorption.4. The pickup behaviors of impurities (Na2O, SiO2) in the conditions of different temperatures, seeds charges and gas ventilating systems were analyzed in the process of carbonization. The product with good quality from carbonization of sodium aluminate solution with 130~200g.L"' A12O3 under the optimized conditions has been obtained.(Figures:38; Tables: 19 ; References:63 )...