Study On The Desilication Of Raw Liquid In Sintering Process Alumina Production

Three-stage desilication of raw liquor is adopted in sintering process alumina production in Shandong Aluminum Corporation. The first stage is operated under high pressure. The second stage is adding lime without separating sodium-silicon residue. Then the third stage is processed by adding lime once again after separating silicon residue. The technology is quite unreasonable because the energy consumption of the first stage is very high caused by high pressure. The second stage is processed without separating sodium-silicon residue because the solubility of sodium-silicon residue is lower than that of hydrated garnet, during the second stage sodium-silicon is re-dissolved into solution. Extra loss of alumina occurs and desilication effect is bad.Based on the analysis of desilication by process dynamics and thermodynamics, the chemical principles of desilication under air pressure by separating sodium-silicon residue during the first stage and adding lime after separation during the second stage is studied according to the present desilication situation during the sintering process in Shandong Aluminum Corporation. On the basis of this, the regularities of some influences including concentration, seed quantity, activation of seeds, floating material quantity, desilication time on the desilication quantity is studied and the technical situation during the first stage desilication is gained, gamely seed quantity: 100¹50g/l; temperature: 95¹00℃; time: 3⁴ h; the A/S of the first refined liquor: 300; adopting high effective flocculant and the floating material quantity below 0.5g/l; the seeds should be milled in order to avoid decreasing activation of seeds after several cycles of seeds. the second desilication stage under air pressure: quantity of added effective calcium oxide: 8¹0g/l; temperature: 95⁹8℃; time: 2 h; A/S of the second stage refined liquor :1000. By calculation ahead of time, when the first stage desilication is altered from high pressure to air pressure, steam consumption of about 55kg/m³-raw liquor are reduced and when the second and third stage is substituted by adding lime after separation of sodium-silicon residue, net benefit of 45yuan/t-Al₂O₃ can be obtained. So annual benefit of about 27 million Yuan can be achieved.At the same time, this paper shows that it is not necessary to activate or grind all kinds of silicon residue seeds gotten from practical production and seeds will affect the desilication effect only when the seeds experience close cycle for several times and the activation is decreased. During practical production, it is demanded to grind and activate seeds. But it is enough to grind seeds simply by the hydro- miller in that firstly, the seed structure after cycles are not very stronge and are easy to become thinner after grinding. Moreover, the technical situation in this paper does not need high activation seeds. During the second stage desilication under air pressure, high effective flocculant is adopted to reduce the floating material quantity of the first refined liquor to improve the desilicatin effect of the second stage.New technology of desilication under air pressure is studied . The first stage is changed from high pressure to air pressure. Then energy consumption can be saved. In addition, The second stage is changed by adding lime after separating sodium-silicon residue and the third stage is cancelled. Then extra loss of alumina and operation procedure are reduced, and the A/S of refined liquor obtained by thus can attain or even be higher than the current third refined liquor.