4 Beneficiation Processes to Obtain Aluminum from Bauxite
Aluminum products are one of the most widely used metals. The current output and consumption of aluminum (in tons) is second only to steel and has become the second-largest metal for human application.
The aluminum content in the crust is 8.3%
Bauxite is mainly used to extract aluminum. About 85% of bauxite can be refined into alumina and then smelted into aluminum, 8% for chemical alumina, and 7% for refractory materials, proppants, and cement.
Because of different grades of the ores, you can get 2 tons of alumina from 4-6 tons of bauxite and 1ton aluminum from 2 tons of alumina.
how much bauxite to make aluminum
Here are common 4 beneficiation methods of bauxite including ore washing, flotation separation, magnetic separation, and chemical beneficiation.
Ore-washing process for bauxite
Ore washing is the simplest and most effective method to improve the bauxite aluminum-silicon ratio by about 2 times. But you need to combine the ore washing process with other methods including classification -Manual selection process.
Step 1Use stone crushers to crush the primary bauxite then make a further grinding.
Step 2Stir and mix the ore pulp
Step 3Classify the ore pulp one or more times to get final products in which the fine-grade particle is discharged as tailings and the coarse-grade particle is used as a concentrate product.
complete bauxite washing process
Difficulties of bauxite ore washing process
There are a large number of low-grade gibbsite bauxite in the world such as Australia and Fiji.
The maximum particle size of the washed ore is 30mm. The surface of gibbsite is mainly iron-containing minerals with high hardness, and aluminum, silicon, and other minerals inside.
- 1So, the common ore-washing method is difficult to obtain high-grade concentrate because the impurities embedded in the core cannot be effectively removed.
- 2Existing ore washing technology can only recover coarse-grained ore with over 1 mm in size, resulting in a very low concentrate yield.
- 3There is a certain amount of recyclable ore smaller than 1 mm in size, which is always be wasted when being discarded as tailings.
Effective solutions for ore-washing process
1Firstly use grinding media such as steel balls or rod balls to remove the slime on the ore surface so that the slime can be easily dissolved, diluted, adjusted.
2Next, make the further grinding of the ore blocks.
3Control the concentration of the pulp, adjust the parameters of the classification equipment to achieve the separation of coarse and fine particles, and reduce the lower limit of recycled particle size.
The separation limit of coarse and fine particles is about 0.05 ~ 1mm, which breaks the traditional concept that particles over 1mm is mine while less than 1 mm is mud.
This bauxite washing method uses mining equipment combinations including ball mills,vibrating screen, spiral classifier, hydro-cyclone, shaker, and jig equipment in the classification process.
six common machines that you need in ore-washing process
Flotation separation methods
It is mainly used to separate diaspore and kaolinite, or for oxidized paraffin soap and Tar Oil as collectors, and the reaction is made in an alkaline medium.
Step 1Cush and grind bauxite to the required size.
Step 2Classify to get a raw pulp
Step 3Spray the raw pulp into a scavenging foam collecting tank then wash away the scavenging foam
Step 4Return the ore pulp to a roughing stirring barrel by a conveying pipe, and then bauxite pulp will react with the flotation agent.
Improtant parts of extract aluminum in folatation process
Disadvantages of flotation separation
1Because collecting agent contains the surface-active substances, the foam of each operation of bauxite flotation is very sticking and big-volume. So, the general quantity of water will consume alarge amount of foam flushing waters, finally reducing the concentration of the flotation system.
2The research shows that flotation pulp concentration is an important factor to ensure the flotation high target. The influences of the flotation pulp concentration are as follows:
- aeration of slurry
- concentration of agents
- flotation time
Easy ways to solve the problems
As long as you properly improve the flotation pulp concentration, you can greatly raise the processing capacity of the entire system.
Method for magnetic separation of aluminum and iron in bauxite
Step 1Mix and dry the finely ground high-iron bauxite and additives
Step 2Use coal as a reducing agent to make reduction roasting.
Step 3After reduction, give the bauxite another grinding and make a magnetic separation to obtain magnetic metal iron powder and non-magnetic aluminum-rich slag.
Step 4Mix leaching agent with aluminum slag to dissolve aluminum and silicon.
Step 5Adopt porous adsorbent to adsorb of silicon in leachate then processing the silicon to produce silicon-based products such as white carbon black and molecular sieve.
Step 6Extract chemical products such as alumina or aluminum sulfate from the solution after silicon separation.
How to get aluminum in bauxite magnetic separation
Obstacles in the process
In addition to aluminum and iron minerals, high iron bauxite is also accompanied by valuable metals such as gallium and vanadium, of which Ga content is 0.0044% ~ 0.0070%, V205 content is 0.148% ~ 0178%.
1However, the content of aluminum and iron is relatively low so that whether it is a single aluminum ore or a single iron ore, it is difficult to meet the basic requirements of industrial applications.
2Besides, the iron and aluminum minerals are embedded in a very fine grain size. Most minerals are poorly crystallized, some are colloidal and cemented with each other, and the embedding relationship is extremely complicated.
Therefore, the efficient separation of aluminum and iron is the first Step in the comprehensive utilization of bauxite.
Effective ways to resolve the difficulties
- 1Crush the high iron bauxite and grind it to a fineness of -0.074mm then mix it with Yuanming powder and sodium citrate in a mass ratio of 95 to 92: 5 to 8.
- 2Notice that the additive content is 17.5% ~ 25% of the dry base mass percentage of the high iron bauxite.
- 3After mixing, add the reducing agent which is 0.7 ~ 1.2 times of the dry material mass at 1000℃ ~ 1150℃ for 60min ～ 90min.
- 4Bauxite with -0.074mm and the mass percentage content is not less than 95%. Make a magnetic separation under the magnetic field strength of 97.5mT ～ 150mT.
- 5A sulfuric acid solution with a mass percentage concentration of 15% to 30% is used as the bleaching agent. that function is to stir and leach the aluminum-rich slag under the conditions of room temperature to 60 ° C with the mass liquid-solid ratio of 8: 1 to 10: 1 for 15min to 120min.
- 6Next, add 0.8g / L ～ 1.2g / L porous adsorbent activated carbon to adsorb the silicon in the leaching solution for 15min ～ 60min.
Chemical beneficiation to process bauxite
- 1Treat bauxite with sodium aluminate solution to fully dissociate aluminum minerals and silicon minerals by Bayer chemical separation methods
- 2Use classification equipment to classify according to the difference of particle size and a specific gravity of aluminum minerals and silicon minerals.
What are the difficulties?
- 1Calcine bauxite at a high temperature of 1000 ℃ in advance will cause energy consumption and make diaspore burn into α-Al2O3. Besides, it would greatly impact the Bayer method of dissolution.
- 2The desilication with alkali solution needs to be pressurized, but the process is complicated.
- 3The complicated process of desalinization for alkaline solution recovery prolongs the entire beneficiation process.
Using chemical and physical beneficiation methods
The chemical method means that we should fully dissociate aluminum minerals and silicon minerals in bauxite. The physical method uses classification equipment for bauxite concentrate. Outstanding features of the combination of the two ways:
- Simple and short process and low cost
- Greatly-improved A / S ore
- Bayer process alumina production process provides a concentrate for the alumina industry.
Details of Bayer process
Bayer process is important part in the chemical beneficiation
- The first process of the Bayer is to crush the bauxite ore into granules with a diameter of about 30 mm.
- Then wash away the impurities such as clay on the surface of the granules.
- The important thing is that you can mix the washed particles with the reused Bayer process liquid phase with a sodium hydroxide concentration of 30% -40% to form a suspension with a solid particle size below 300 microns by ball mill.
- As the particle size gradually becomes smaller, the specific surface area of bauxite greatly increases, which helps accelerate the speed of subsequent chemical reactions.
The suspension formed by the bauxite and high-concentration sodium hydroxide solution enters the reaction kettle.
By raising the temperature and pressure, the alumina in the bauxite reacts with sodium hydroxide to produce soluble sodium aluminate.
Alumina in bauxite can react with high-cincentration NaOH
Precipitation of aluminum hydroxide
- The hot solution enters the cooling device, and is diluted with water and gradually cooled.
- Sodium aluminate will be hydrolyzed to produce aluminum hydroxide. At this time, adding pure alumina powder will precipitate white aluminum hydroxide solid.
- After filtering off the generated aluminum hydroxide, the remaining sodium hydroxide solution with a relatively high concentration will be recycled and used to process another batch of bauxite to dissolve aluminum hydroxide.
- The aluminum hydroxide that has been produced can be decomposed into alumina at 1000°C
The crystal form and particle size of the desired alumina decide the specific calcination temperature. The alumina can be electrolyzed to produce metallic aluminum by the Hall-Ero process.