Sintering Liquid Crude Desilication New Technology Research,

Alumina output produced by sintering process in Zhongzhou Branch of Chalco is 900,000 tons per year, in which 72.5% of pregnant liquor are obtained by two-stage desilication method. The first stage is called as high-pressure desilication (direct and indirect heating); the second stage is run by directly adding lime milk into sodium aluminate solutions after removed sodium-silicon residue. However, it is found that energy consumption of current desilication technology of the first stage is so high. So a new process —two-stage normal-pressure desilication is put forward in this paper aiming at this shortcoming, in which normal-pressure desilication substituted for high-pressure desilication in the first stage and then still adding lime into sodium aluminate solutions after separating sodium-silicon residue in the second stage.On the basis of analyzing the thermodynamics and kinetics of coarse liquor desilication in the sintering process, this paper puts forward this new approach. Meanwhile, all pertinent factors were systemically investigated. The paper also disclosed the mechanism of two-stage desilication process via studying the phase graph of Na₂O-Al₂O₃-CaO-CO₂-SiO₂-H₂O system.Technical conditions suitable for two-stage normal-pressure desilication attained in this paper are as follows:The first stage: Seed addition: 100-500 g/l; Temperature: 95-100℃; Time: 3-4 hours; A/S of the primary pregnant liquor: 300 ±;Solid suspension after flocculation is less than 0.5g/l; the circulated seeds must be grinded to increase its activation.The second stage: Effective calcium addition: 8-10 g/l; Temperature: 95-98℃; Time: 2 hours; A/S of the secondary pregnant liquor :1000±.The new desilication process not only significantly decreases energyconsumption and workload of equipment, but also A/S of the secondary pregnant liquor can reach or transcend the existed level. Comparing to high-pressure desilication technology, the new two-stage normal-pressure desilication can reduce steam consumption by 45kg/m3-green liquor, significantly decrease the workload of cleaning and maintaining equipments, and raise net income by 26.78 yuan/t-Al2O3. Therefore the annual benefit of 18.7457 million yuan can be achieved.