Dissolving aluminium oxide involves the use of an organic solvent. Using recycled organic solvents for this purpose helps separate organic impurities from the aluminium oxide solution.
The solvent must be able to dissolve the organic components of the aluminum oxide. This is achieved through a process called extraction.
Various chemicals are used for this purpose. The most common solutions used are nitric-based and sulfuric-based acid solutions. These types of deoxidizers are more environmentally friendly and tend to passivate other solutions.
When the aluminium is dissolved in sulphuric or nitric acid, a mixture of insoluble matter and soluble aluminium is formed. The soluble component is filtered, and the insoluble part is collected as waste.
The dissolving process is further improved by heating the reaction mixture. By increasing the temperature, the amount of aluminium oxidized and the rate of reaction is enhanced.
A preferred method of preparing impure aluminium oxide is shown in the patent application 4 027 159. It comprises three steps: a screening step, a dilution step, and a neutralization step. The result is a filtrate containing purified aluminium oxide and aluminium sulphate in soluble form.
Adding nitric acid to the solution increases the speed of the reaction. The resulting mixture is granulated in the granulation step. After the granulation step, the acid solution is diluted with water.
The acid solution is then neutralized. During neutralization, a thin layer of the oxide forms to prevent further reactions. At the same time, a low tension current is introduced into the crucible.