Bauxite ore extraction process
Aluminum is found in varying amounts in nature as aluminosilicates (contains aluminum, silicon, and oxygen) in various types of clay. As the minerals are weathered they gradually breakdown into various forms of hydrated aluminum oxide, Al2O3.xH2O, known as bauxite.
The bauxite is purified by the Bayer Process. First the ore is mixed with a hot concentrated solution of sodium hydroxide. The NaOH will dissolve the oxides of aluminum and silicon but not other impurities such as iron oxides, which remains insoluble. The insoluble materials are removed by filtration.
The solution which now contains the oxides of aluminum and silicon are next treated by bubbling carbon dioxide gas through the solution. Carbon dioxide forms a weak acid solution of carbonic acid which neutralizes the sodium hydroxide from the first treatment. This neutralization selectively precipitates the aluminum oxide, but leaves the silicates in solution. Again filtration is used for the separation. After this stage the purified aluminum oxide is heated to evaporate the water.
Aluminum in the metal form is very difficult to obtain by using some of the traditional chemical methods involving carbon or carbon monoxide as reducing agents to reduce the aluminum ions to aluminum metal. One of the earliest and costly methods in 1850 was to reduce aluminum chloride with sodium metal to obtain aluminum metal and sodium chloride. (Sodium metal is not easy to obtain either). As a result some of the earliest aluminum metal was made into jewelry.
Aluminium is the third most abundant element in the Earth’s crust, but does not occur as a metal naturally. The first step in producing aluminium is mining its ore – bauxite.
Bauxite occurs mainly in tropical and sub-tropical areas, like Africa, the West Indies, South America and Australia – there are some small deposits located in Europe.
Australia is the largest producer of bauxite, with five mines supplying around 23 per cent of global production.
Bauxite mining has five steps: Preparation of the mining area; bauxite mining; crushing; ore transport; and rehabilitation.
Bauxite dressing processing
The bauxite dressing processing is the process that seperates the bauxite ore concentrate from the bauxite ore. The purpose is to eliminat the gangue minerals and harmful impurities, seperate the high aluminium mines and low aluminium mines to get the concentrate with high alumina-silica ratio. SBM Machinery is utilizing the professional bauxite dressing technology and bauxite processing equipments to give you the most economical and reasonable choice.
The process of bauxite dressing processing
The main dressing methods consist of ore washing, flotation, magnetic separation and chemical mineral processing.
The ore washing is the most simple and effective method that can improve the alumina-silica ratio in bauxite. Through ore washing, the alumina-silica radio in bauxite can be improved about 2 times than before. This method is more effective for the dressing of the ore stones with loose texture. The ore washing often combined with other dressing methods to make up the process, that is ore washing(sieving and washing)--classification--hand sorting.
The flotation can be used for separating diaspore and kaolinite and could use the oxidation paraffin wax soap and tall oil as catching agent in alkaline medium.
The magnetic separation is used for separating the minerals with ferrum.
The chemical mineral processing mainly consists of roasting and desilicification because the main minerals containing silicon in ore stones are water aluminum silicate. After roasting, parts of the SiO2 convert to oxidation silicon particles which is amorphism and alkali soluble so that the the alumina-silica ratio in materials can be improved.
The bauxite, also called alum earth, mainly consists of diaspore and kaolinite. The diaspore is fine scattered colloid mixture, which consists of three minerals in all kinds of propotions and the three minerals are diasporite, boehmite and gibbsite.
The bauxite often accretes with clay minerals, such as the oxide and hydroxide of ferrum, anatase, kaolinite and chlorite,sometimes containing some minerals such as calcium, magnesium and sulfur. According to the impurities, the bauxite can be classified as high alkali bauxite, high titanium bauxite and high iron bauxite.
The most economic dressing process designer---SBM
During the bauxite processing, the bauxite screening and crushing generating line of SBM is the most economic one. This line comes from our years of researching and practical experience and is the most effective and practical plan. Discarding the cone crusher in traditional processing production line, the screening and crushing system is utilized and the screening and crushing equipment handles the materials such as the bauxite easily.
The screening and crushing equipment in SBM has high output and utilizes the crushing way with shearing force that is stronger than impact force, which is more suitable for bauxite crushing. For this, the screening and crushing equipment is used more often than before. According to the different customer's demand for capacity, the equipment can be combined with impact crusher, hammer crusher or roll crusher, through crushing, sieving and grading to get the product that you want.
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