Bauxite is main material in aluminium making. Silica is main detrimental impurities in alumina making. Bauxite ores has many uses and the most important one is that bauxite is used as metal aluminium refining and refractory material and abrasive materials and high aluminium cement material in aluminum industry.

Bauxite Ore processing flowchart

Bauxite processing is relatively simple and hand dressing is used commonly. The design is that: washing for three times, crushing for two times and hand dressing for one time. Along with the development of refractory material and alumina industry in our country, the production of bauxite raw materials is put forward higher and higher demand.

For bauxite is regarded as smelting aluminium material, different smelting methods have different quality demands. The ratio of SiO2/Al2O3 is more than 8 ~ 10 in bayer process, 5～7 in combined process and 3.5～5.0 in sintering process. Therefore as smelting aluminium material, the primary task in bauxite dressing is to improve the ratio of SiO2/Al2O3. At the same time, iron oxide in ores will reduce productivity of dissolution kettle in bayer process and reduce clinker temperature in sintering process and prevent alumina from becoming sodium aluminate. At present, after the raw ore is fine ground, then through desilicication flotation, high gradient strong magnetic deironing and corresponding measures to removing impurities such as potassium and sodium, inferior bauxite will become bauxite with good quality.

Alumina production process

In industry, the way for metal aluminium refining is that: get alumina from bauxite and then through electrolysis the alumina will become metal aluminium. Different alumina production methods have different requirements of the ore quality. And the general requirement like followings:

Sintering process

This method is suitable for treating low grade ores with high silicon content. It requires that the Al2O3/SiO2 is 3～5(3.5 or so)　and the Fe2O3 content is below 10%. In modern industry, the sintering process is alkali-lime sintering process. The bauxite is mixed with certain soda ash and lime (or limestone). Then through high temperature sintering, oxidation silicon and lime synthesize original calcium silicate that is insoluble in water and iron oxide synthesizes iron acid sodium which is easily hydrolyzed. Alumina and soda ash can synthesize sodium metaaluminate that is water soluble. When the sintering products clinker is leached out, sodium metaaluminate comes into solution so that it can seperate from original calcium silicate and hydrate ferric oxide. Sodium aluminate solution(refined solution), which had come through desilicication refining, can be decomposed by carbon dioxide to get aluminium hydroxide. Then through calcination, the final product --alumina can be got through aluminium hydroxide.

Bayer process

Bayer process is the main industrial method in alumina producing. Bayer process is suitable for processing low silicon bauxite with good quality but is not suitable for goethite with aluminum. The production process is that: in the pressure cooking device, caustic alkali is used to leach bauxite so that we can get sodium aluminate solution. Then the sodium aluminate solution is diluted. Then through stirring with aluminum hydroxide crystal seed(or seed), the sodium aluminate is be decomposed to get aluminium hydroxide. Product alumina will be got through calcination. After evaporation, the mother solution in which the crystal seed is decomposed comes back for leaching bauxite. Bayer process is suitable for processing low silicon bauxite with good quality.

Combining process

Combining process is suitable for processing bauxite with medium grade. In our country, mixture process is mainly used. It is that adding some ores that is low grade into red muds that is used in bayer process so that can improve the ratio of SiO2/Al2O3 in sintering process.