A Study On Fluidization Separating-washing Of Leached Slurry And Its Effect On Secondary Reactions

In the sintering process of producing alumina, the slurry after sinter leaching must be separated and washed. Nowadays, settling tank is widely used in the process of separating slurry and washing red mud. A12O3 concentration of the green liquor is 120-130g/L, and the underflow should be washed for 6 to 8 times. It needs about 20 hours, so the secondary reaction loss is serious. An efficient means for reducing energy consumption is to increase A12O3 concentration of wet method system, its pivotal technique involves the process of the rapid separation of solid and liquid which can reduce the secondary reaction loss. However, settling tank process can not be used to separate high Al2O3 concentration slurry. Researchers have been looking for a better technology which can meet rapid separation and washing. In this study, fluidization technology is introduced into the processes of slurry separation and red mud washing. The effect of fluidization separation-washing and secondary reaction loss have been studied systematically in the dissertation. The main research contents and conclusions of the paper are as follows:(1) The fluidization separating-washing of leached slurry was studied. The results show that:Na2O concentration and mass ratio of liquid to solid in the underflow can reach 0.5-10g/L and 2.5-3, respectively, and Na2O concentration of the overflow is 85-140g/L, when the Na2O concentration of the leached slurry is 120-180g/L; Na2O concentration and mass ratio of liquid to solid in the underflow can reach 5-20g/L and 2.5-3.5, respectively, and A12O3 concentration of the overflow is 160-220g/L, when the A12O3 concentration of the leached slurry is 240-270g/L. The efficiency of separating-washing is more than 99%.(2) The separating-washing of high alumina concentration leached slurry was studied based on the fluidization. The results show that the average secondary loss is 0.16%. (3) Mathematical model of slurry fluidized separation-washing is established. The model can predict the overflow concentration and underflow concentration, especially the axial concentration distribution in the solution.Equation (1) can predict the alkali concentration in the overflow.Equation (2) can predict the alkali concentration in the underflow.Equation (3) can predict the axial concentration distribution in the procedure.(4) The fluidization separation-washing has many advantages such as higher handling capacity per unit area, good separating-washing effect, capacity of handing high concentration slurry and less secondary reaction loss.