Influence Of Impurity Content Of Brown Fused Alumina On Its Quality

The types and quantities of impurities have different effects on brown fused alumina crystals, see the table below:

1. The Utilization of Silica in Containing Calcium Bauxite 

Calcium oxide present in bauxite is hardly reduced by carbon and almost all enters the melt. If there are only calcium oxide and alumina in the melt, then the impurity calcium oxide will all crystallize out as calcium hexaaluminate during the cooling process, and each calcium oxide molecule will consume 6 alumina molecules, that is, each mass of calcium oxide will consume 10.91 parts by mass of alumina produce 11.91 parts by mass of calcium hexaaluminate. If there is a certain amount of silica impurities in the melt at the same time, the crystals may be precipitated as calcium plagioclase, and each calcium oxide molecule only consumes 1 molecule of alumina, that is, each mass of calcium oxide consumes only 1.818 parts by mass alumina, generating 4.96 parts of calcium plagioclase.

2. Utilization of silicon oxide in magnesia-containing

Magnesium oxide in the melt has a strict restriction on the crystallization of brown aluminum oxide. In the crystallization zone of brown fused alumina, the crystallization route of brown aluminum oxide shortens with the increase of MgO content. If the MgO content exceeds 3%, the first crystallization zone is not brown fused alumina but magnesium aluminum spinel. When there is a certain amount of silicon dioxide in the melt, the first crystallization region can be returned to the brown aluminum oxide crystallization region, or the crystallization route of brown fused alumina can be increased, and more alumina can be precipitated in the brown aluminum oxide phase.

3. Silica and Sodium Oxide

In the smelting of white fused alumina, the sodium oxide in the alumina powder will form sodium peraluminate (Na₂O·11Al₂O₃) with alumina after melting, and each molecule of sodium oxide will consume 11 molecules of alumina, that is, each The mass of sodium oxide consumes 18.10 mass parts of alumina and produces 19.10 mass parts of sodium peraluminate. If a certain amount of silicon oxide is added to the melt to crystallize sodium oxide as Sanclineline (Na₂O·Al₂O₃·2SiO₂), each molecule of sodium oxide only consumes 1 molecule of alumina, that is, each mass The sodium oxide only consumes 1.645 parts of alumina by quality, and generates 4.584 parts of sanclinite.