Estudo do efeito da concentração de inibidores de nucleação no licor do processo bayer.

Abstract

The alumina produced through the extraction of the gibbsite from the bauxite ore by caustic liquor is constrained by the soluble sodium aluminate instability in the supersaturated liquor processed in alumina refineries. The aluminum hydrate precipitation, when takes place inside equipments not designed to this purpose, like press filters, washers or thickeners, will generate significant losses to the refinery. Therefore, the stabilization of the soluble sodium aluminate will reduce the liquor supersaturation and, as consequence, the driving force to the aluminum hydrate precipitation will be reduced as well. The supersaturation decrease was obtained from the usage of stabilizers, named nucleation inhibitors. The precipitation performance will not suffer negative impacts from the stabilizers usage due to the extremely elevated driving force caused by the temperature drop and aluminum hydrate seed addition. Stability trials were carried out dosing nucleation inhibitors under two distinct forms: a polymer which is soluble in water and a metallic cation solution. It was demonstrated that the elevated supersaturation of the liquors in the filtration feed and first mud washer of the mud washers train was reduced. The evidence for that was the significant ratio drop decrease. The influence of the stabilizer amount dosed and the liquor solids concentration were evaluated. The solids concentration presented a large potential to reduce the liquor instability. The effects generated by the solids were the precipitation rate increase and bigger ratio drop. The amount of stabilizer dosed presented a small impact over the resultant stability. The stabilization effect obtained from the metallic cation usage can be obtained only if it remains soluble. After the addition of the metallic cation dosage into the liquor, the concentration of this specie raised. However, this concentration started to drop tending to stabilize in an equilibrium concentration. The results obtained from the plant trial using the polymer as stabilizer were similar to the ones obtained in laboratory. This study concluded that nucleation inhibitors present a large potential to increase sodium aluminate concentration in Bayer liquor and, as consequence, the refinery production. Besides this, the residual life of some equipments can be increased as well.