Study On Technology And Mechanism Of Desilication In Sodium Aluminate Solution With High Alumina Concentration

Sintering process takes a very important place in China alumina industry. Elevating the alumina concentration in solution is an effective technological direction to promote the production efficiency, desilication process is one of the most important procedures of alumina production in sintering process, which directly affects the product quatity and procuction efficiency, and thus, it's of great significance to study the desilication of sodium aluminate solution with high alumina concentration(about 180g/L). In this case, the following aspects have been studied systematically in the dissertation:1. Kinetics analysis of desilication processResearch on the macro-kinetics of desilication with the formaton of DSP of sodium aluminate solution with high Al₂O₃ concentration illustrates that the process is controlled by chemical reaction step with the apparent activation energy 91.10kJ/mol. Research on the macro-kinetics of deep desilication with the formaton of hydrogarnet of sodium aluminate solution with high concentration shows that the apparent activation energy is 96.77kJ/mol and elevation of temperature deserts a positive effect on desilication process.2. Study on desilication process with the formation of DSPFactors influencing desilication process with the formation of sodium aluminosilicate hydrate (DSP) of sodium aluminate solution with high Al₂O₃ concentration were thoroughly investigated. The results show that elevation of temperature and prolongation of the reaction time can increase the mass ratio of alumina to silica in solution. Increasing amount of DSP added accelerates the desilication process. However, it can not reduce the concentration of silica in solution. Na₂O_S and Na₂O_C in solution have a positive effect on desilication process. The optimized technological conditions for the first-stage desilication in sodium aluminate solution with high concentration are as follows: desilication temperature is 170℃, solid content of DSP added is 50g/L, and desilication duration time is 1h, mass ratio of alumina to silica of the purified liquor after first-stage desilication can reach more than 250.3. Study on deep desilication process with the formation of hydrogarnetFactors influencing desilication process with the formation of hydrogarnet of sodium aluminate solution with high Al₂O₃ concentration were thoroughly studied. The results show that it should add CaO for deep desilication in sodium aluminate solution with high concentration; it deserts a positive effect on deep desilication process that increasing the amount of CaO added,elevating the reaction temperature and prolonging the reaction time. On the other hand, it deserts a negative effect on deep desilication that elevating the alumina concentration,the causitic ratio and the concentration of Na₂O_C and Na₂O_S in solution. The optimized technological conditions for the second-stage deep desilication in sodium aluminate solution with high concentration are as follows: the amount of CaO added is 7～9g/L, desilication temperature is 110℃, and desilication duration time is 2h, mass ratio of alumina to silica of the purified liquor after deep desilication can reach more than 800.