Aluminum refining steps (8 step) - rosenburg Aluminium | manufacturing extrusion aluminium

Aluminum refining steps

How to refine aluminum   for use in the laboratory is as follows. Today in Rosenburg Aluminum we examined the refining stages of aluminum.

Aluminum refining steps – refining process

1. Milling in Aluminum refining steps

Bauxite
Bauxite is washed and crushed, reducing particle size and increasing surface area during digestion. Lime and “edible liquor” (soda soda returns from the deposition stage) are pumped in factories to make slurry.

2. cleaning

Bauxites with high levels of silica (SiO 2) are made through a process to remove this impurity. Silica can cause problems with the scale and quality of the final product.

3. Digestion

Sodium hydroxide solution (NaOH) is used to dissolve aluminum minerals in bauxite (gibcite, bumite, and diaspora) to form an excess solution of sodium aluminate, or “pregnant liquor.”

Gibbsite:
Al (OH Al (OH) 3 + Na + + OH- → Al (OH) 4- + Na +

Bumite and Diaspora:
AlO (OH) + AlO (OH) + Na + + OH- + H2O → Al (OH) 4- + Na +

The conditions inside the hydraulics (sodium concentration, temperature and pressure) are adjusted based on the properties of the bauxite ore.

Ore with a high gibbsite content can be processed at 140 ° C, while betmite bauxite requires temperatures between 200 and 280 ° C. The pressure is not as important for this process, but is defined by the vapor saturation pressure of the process. At 240 ° C the pressure is approximately 3.5 MPa.

Aluminum refining steps – refining process

The slurry is then cooled in a series of metal tanks to a temperature of 106 ° C at atmospheric pressure and with the steam off. This steam is used to preheat the consumed liquids. In some high-temperature digestion refineries, high-quality bauxite is injected into the flash train to increase production. This “sweetening” process also reduces energy consumption per ton of production.
Although higher temperatures are often theoretically advantageous, there are potential drawbacks, including the possibility of oxidation other than alumina in the alcoholic beverage solution.

4. On / off

The first step is to clarify the separation of solids (bauxite residues) from the charged solution (sodium aluminate remaining in solution) by precipitation. Chemical additives (flexion) are added to aid the deposition process. The bauxite residue falls to the bottom of the drainage tanks, then is transferred to the wash tanks, where there are several washing steps to recover the caustic soda (used in the re-digestion process).

Most separation of pregnant beverages from bauxite residues is done using a series of security filters. The purpose of security filters is to ensure that the final product is not contaminated with impurities in the residue.

Depending on the requirements of the storage facility, thicker effluents, filtration and / or neutralization are used before being pumped to the bauxite disposal site.

5. Rainfall

At this stage, alumina is recovered by crystallization from charged liquor, which is saturated with sodium alumina.

The crystallization process is driven by the advanced cooling of the charged liquor, leading to the formation of small crystals of aluminum trihydroxide (Al (OH) 3, commonly known as “hydrate”), which then grow and agglomerate to form larger crystals. The inverse precipitation reaction is the dissolution reaction of gibsite in the digestion stage:

Al (OH Al (OH) 4- + Na + → Al (OH) 3 + Na + + OH

6. Evaporation

The consumed liqueur is heated by a series of heat exchangers and then cooled in a series of metal tanks. Gas condensate in heaters is reused in the process, for example as boiler feed water or to wash bauxite residues. Sodium The residual sodium is washed away and re-digested.

7. Classification

Gibbsite crystals formed in sediments are classified into different sizes. This is typically done using cyclones or gravity classification tanks (a set of thickeners using the same immigrant / washer principles in the light stage).

The crystals are the size of small crystals for calibration after separation from alcohol using vacuum filtration, where solids are washed with hot water.
The fine crystals are returned to the precipitation stage after washing to remove organic impurities as granules that can be agglomerated.

8. Digestion

The filter cake is fed to calciners and formed at a temperature of 1100 ° C to prevent free moisture and chemically bound water and to produce alumina solids. There are various coupon style technologies, including gas suspension calciners, liquid bed calciners and rotary kilns.

The following equation describes the calcium response:

2Al (OH) 3 → Al2O3 + 3H2O

Aluminum a white powder, is the product of this stage and the final product of the waste process, ready for transport to molten aluminum or the chemical industry.