CC BY
7ХИМИЯ (CHEMISTRY)
УДК 669.72
Egamberdiyeva A.E.
Lecturer at the Department of Applied Chemistry Engineering and Technology University of Turkmenistan named after Oguzhana
(Turkmenistan, Ashgabat)
Dovranova E.A.
Lecturer at the Department of Applied Chemistry Engineering and Technology University of Turkmenistan named after Oguzhana
(Turkmenistan, Ashgabat)
POSSIBILITIES OF EBENEFICATION ALUMINUM OXIDE FROM LOCAL KAOLIN RAW MATERIALS
Abstract: this article discusses the features of the development of the modern technological process of enrichment and production of aluminum oxide. A cross and comparative analysis of the influence of the choice of the direction of development of the chemical industry was carried out. Recommendations for the implementation of developments in chemistry are given.
Keywords: analysis, method, research, systems, aluminum, chemistry.
Aluminum is one of the most abundant elements in the earth's crust. The clark of aluminum is 8.05, which is about 15% in terms of Al203 [8].
Due to its high chemical activity, it occurs in nature only in the form of compounds, mainly with oxygen and silicon, that is, in aluminosilicates, which include sodium, potassium, calcium and other elements. Aluminum is part of about 250 minerals, 40% of which are aluminosilicates. The most common compounds in nature are aluminum compounds with oxygen.
Currently, the main source of aluminum production are bauxites containing aluminum in the form of hydrated alumina (Al 2 Oz • nH 2 O), as well as nephelines and alunites. In the future, it is possible to use alkali-free aluminosilicates (kyanites, clays, kaolins) and some industrial wastes - high-alumina ash, slag and tailings from coal enrichment.
Abroad, almost all aluminum is obtained from bauxite ores. In Russia, for the production of aluminum, in addition to bauxites, nephelines are also used.
Bauxite, which consists mainly of hydrated oxides of aluminium, iron, silicon, titanium and some other elements, may also contain calcium and magnesium carbonates, sulfur, phosphorus, chromium compounds, and also in small quantities compounds of rare elements (vanadium, gallium, zirconium, niobium, etc.). In total, 42 elements were found in the composition of bauxite ores.
The chemical composition of bauxite varies over a very wide range both in different deposits and within the same deposit. The content of Al 2 Oz in bauxites ranges from 34 to 60%; SiO 2 - from tenths to 25%; Fe 2 Oz - from 2 to 40%; TiO 2 - from traces to 11%. The content of many accompanying elements is measured in hundredths and even thousandths of a percent.
In appearance, bauxites are similar to clay. They can have various colors and shades - from white to dark red.
The most important characteristics that determine the quality of bauxites are the content of aluminum oxide and the silicon modulus, which is expressed as the ratio of the content of Al 2 Oz to SiO 2 . The higher the silicon modulus, that is, the greater the content of Al 2 Oz and the less SiO 2 , the higher the quality of the bauxite.
According to the mineralogical composition, there are low-water (corundum), one-water (diaspore and boehmite), three-water (hydrargillite) and mixed types of bauxites. Usually, two minerals containing aluminum oxide are present simultaneously in bauxites.
Apatite-nepheline ores of the Kola Peninsula are subjected to flotation enrichment to obtain apatite and nepheline concentrates. The average composition of
the nepheline concentrate, %: Al 2 0 3 - 29; SiO 2 - 44; Fe 2 O 3 -3; (Na 2 O + K 2 O) -20%.
Siberian nepheline syenites are high-quality raw materials and do not require preliminary enrichment.
Due to the low content of Al 2 O 3 in nepheline ores and concentrates, their processing into alumina is expedient only with the associated production of soda, potash and the use of waste from complex technology for the production of cement.
Alunite ores are complex raw materials containing, in addition to aluminum, alkali and sulfuric anhydride SO 3 - Their processing into alumina is advisable only with the integrated use of all valuable components. The content of Al 2 Oz in alunite ores does not exceed 20-22%.
Clays and kaolins are widely used in many industries in the production of ceramics, refractories and other products. The best grades of kaolins, containing up to 49% Al 2 O 3 , are used either in the aluminum industry to obtain aluminum-silicon alloys by direct reduction, or as a raw material for the production of alumina.
Kyanites are not used for the production of alumina, but they are a very good raw material for the direct production of silicoaluminum.
Alumina - pure aluminum oxide (Al 2 O 3 ), {Basic, starting material for the production of aluminum by electrolysis.
Depending on the composition and physical and chemical properties of raw materials, alumina can be obtained in industry by alkaline, acid and acid-base methods.
Currently, almost all alumina is obtained by the alkaline method, which in turn is divided into hydrochemical, thermal and combined. The Bayer method, developed in Russia and used for the processing of low-silicon bauxites, has become the most widely used.
According to this method, bauxite after crushing and fine grinding is leached with sodium hydroxide solution in autoclaves heated with superheated steam with a capacity of up to 35 m 3 at a temperature of 250°C and a pressure of up to 3 MPa.
Under these conditions, aluminum hydroxide from bauxite dissolves quite quickly and completely with the formation of sodium aluminate according to the reaction:
Al (OH) 3 + NaOH -> NaAlO 2 + 2H 2 O
The silica contained in bauxite is also dissolved by sodium hydroxide to form sodium silicate Na 2 SiO 3 , which reacts with sodium aluminate and water, resulting in a complex chemical compound - sodium aluminosilicate Na 2 * Al 2 O 3 * 2SiO 2 * nH 2 Oh, which precipitates. Therefore, the more silica is contained in bauxite, the less alumina goes into solution.
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