Rare and valuable minerals

How is alumina obtained from nepheline?

Aluminum oxide is one of the most common and sought-after substances on the planet. Metallic aluminum is extracted from natural raw materials containing it. It is used for the production of refractory, abrasive materials, lasers, and synthetic gemstones. Most importantly, it is indispensable as a catalyst and catalyst support for a number of key industrial processes. We have prepared informative material on aluminum oxide, which we will present in three parts. In the first article we will talk about the main properties of the substance and its areas of application. General properties of aluminum oxide Aluminum oxide (OA) is a binary compound of aluminum and oxygen. In nature, it is distributed as the main component of alumina, a non-stoichiometric mixture of oxides of aluminum, potassium, sodium, magnesium, etc. Alumina consists of up to 98% α – And γ – modifications of aluminum oxide and is a white crystalline powder. Chemical Formula: [Al2O3]
CAS registration number: 1344-28-1
HS codes: 2818200000 (main), 2818101100 There are several main types of aluminum oxide. Anhydrous aluminum oxide has several modifications of the crystalline form, differing in characteristics and areas of application. Installed α-, β- и γ-modifications of alumina, with α- and γ-Al2O3 are pure aluminum oxide, and β-Аl2O3 – a group of aluminates with a high content of aluminum oxide. α-aluminum oxide or corundum is a mineral in the form of large transparent crystals, trigonal system. Depending on the type of impurities, red corundum is distinguished – ruby ​​and blue – sapphire. Corundum crystals are the working fluids of lasers; stones for precision mechanisms are made from rubies. γ-alumina has a cubic shape. In nature γ-form was not detected, it is obtained by heat treatment of hydrates of aluminum oxide, boehmite (Al2О3·Н2O) and hydrargillite (Al2O3ZN2O). When heated γ-Аl2O3 passes irreversibly into α-form. Used as a catalyst carrier and desiccant in chemical and petrochemical production processes. β-Aluminum oxide has a hexagonal crystal lattice. A substance sometimes described as β-Al2O3, is in fact not pure aluminum oxide, but is a series of aluminates of alkali and alkaline earth metals, characterized by a very high aluminum oxide content, with the following general formulas: MeO 6Al2O3 and Me2O 11Al2O3, where MeO are oxides of calcium, barium, strontium, etc., and Me2O – oxides of sodium, potassium, lithium and other alkali metals. The content of alkali and alkaline earth oxides can be up to 8−10%. When heated to 1600−1700°C β-alumina decomposes into α- Al2O3 with the release of the corresponding oxide in a gaseous state. Presence β-alumina in the calcined corundum material reduces the mechanical strength and especially its electrical properties and is therefore undesirable. β-Al2O3 used as a metal-conducting solid electrolyte. There is also amorphous aluminum oxide – aluminum gel, formed by dehydration of gel-like Al (OH)3 and is a porous, sometimes transparent substance. Methods for producing aluminum oxide As a rule, bauxite, alunite, and nepheline are used as raw materials for the production of aluminum oxide. When the aluminum oxide content is more than 6-7%, production is carried out using the main method – the Bayer method, and with a lower content of the substance, the method of sintering ore with lime or soda is used. The Bayer method is a hydrochemical method for producing alumina from bauxite. It involves processing crushed rock in ball mills, then bauxite is treated with alkaline solutions at a temperature of 225−250°C. The sodium aluminate composition thus obtained is diluted with an aqueous solution and filtered. During the filtration process, sludge containing aluminum oxide, the properties of which correspond to standard ones, is subjected to decomposition in centrifuges. About ½ of the resulting Al (OH) is released3. It is filtered and calcined in rotary kilns or in a fluidized bed at a temperature of ~ 1200 °C. The result is alumina containing 15−60% α-Al2О3. The use of this method allows you to save the mother liquor for use in subsequent bauxite leaching operations. The method of sintering ore with lime or soda works as follows: high-silicon crushed ore (nepheline, etc.) is mixed with soda and limestone and sintered in rotary kilns at 1250−1300 °C. The resulting mass is leached with an aqueous alkaline solution. The Na aluminate solution is separated from the sludge, then freed from SiO2, precipitating it in an autoclave at a pressure of about 0,6 MPa, and then using lime at atmospheric pressure and decomposing the aluminate with CO gas2. Resulting Al(OH)3 separated from the solution and calcined at a temperature of about 1200 °C. When processing nepheline, in addition to alumina, Na2CO3, K2CO3 and cement. During the production of alumina from alunites, H2SO4 and K2SO4. Alunite ore is fired at 500−580°C in a reducing atmosphere and treated with NaOH solution according to the Bayer method. To produce high-strength corundum ceramics, aluminum oxide powder is used, obtained by thermal decomposition of certain aluminum salts, for example, aluminum nitrate, ammonia alum of varying degrees of purity. Aluminum oxide obtained from the decomposition of salts is a highly dispersed γ-Al powder2O3 (when calcined to 1200°C) and has great chemical activity. To obtain ultra- and nanodisperse Al powders2O3, which are used in the technology of structural and instrumental ceramics, the method of co-precipitation of hydroxides (CHD) and plasma-chemical synthesis (PCS) has become widespread. The essence of the SOG method is to dissolve aluminum salts, for example, AlCl3 in an ammonia solution and the subsequent precipitation of the resulting hydrates. The process is carried out at low temperatures and long holding times. The resulting hydroxides are dried and calcined, resulting in the formation of Al powder2O3 with a particle size of 10−100 nm. In PCS technology, an aqueous solution of Al (NO3)3 fed into the plasma torch nozzle. Extremely high temperature gradients arise in the drops of the solution, and a very rapid process of synthesis and crystallization of Al occurs2O3. The powder particles have a spherical shape and a size of 0,1−1 μm. Use: in the production of alumina. Essence: a nepheline-limestone charge is prepared, it is sintered, and the sinter is leached. The resulting aluminate solution is divided into two parts. Part of the solution is subjected to desiliconization in open mixers in the presence of a nepheline-limestone charge, the other part of the solution is desiliconized in two stages: at the first stage in autoclaves with the addition of nepheline-limestone sludge, the resulting precipitate is separated from the solution, the precipitate is sent for sintering, and the resulting solution is desiliconized the second stage in open mixers with the addition of lime with the release of hydrogarnet sludge into the sediment. Hydrogarnet slurry can be fed to the first stage of desiliconization. Nepheline-limestone mixture is fed to autoclaves. 2 salary f-ly.

Claim

1. METHOD FOR PRODUCING ALUMINA FROM NEPHELINE RAW MATERIALS, including the preparation of nepheline-limestone charge, its sintering, leaching of sinter, desiliconization of aluminate solutions in the presence of nepheline-limestone charge in open mixers to obtain nepheline-limestone slurry and aluminate solution, separation of aluminum hydroxide from aluminum atomic solution and its calcination, characterized in that part of the solution is subjected to desiliconization of aluminate solutions in the presence of nepheline-limestone charge, the other part of the solution is desiliconized in two stages: at the first stage in autoclaves with the addition of nepheline-limestone slurry, the resulting precipitate is separated from the solution, the precipitate is sent for sintering, and the resulting the solution is desiliconized at the second stage in open mixers with the addition of lime, releasing hydrogarnet sludge into the sediment. 2. The method according to claim 1, characterized in that the hydrogarnet slurry is fed to the first stage of desiliconization. 3. Method according to claims 1 and 2, characterized in that nepheline-limestone charge is supplied to the autoclaves.

Description of the invention for the patent

The invention relates to non-ferrous metallurgy. This production includes the preparation of the charge (USB), sintering of the charge, leaching of the cake, desiliconization of the aluminate solution, decomposition of the solution with the release of aluminum hydroxide into a precipitate, followed by calcination to obtain the finished product (alumina). A close analogue of the proposed method is the production tested and implemented at Pikalevsky JSC “Glinozem”, where the mixture is prepared by mixing and grinding nepheline, limestone and white sludge (desiliconization product). The charge is sintered in furnaces. Speck is leached in mills with a soda-alkaline solution. Filtered and washed belite sludge is used as a raw material component of cement, and the aluminate solution is subjected to desiliconization. Desiliconization is carried out in open bags in the presence of nepheline-limestone charge. The resulting nepheline-limestone sludge (sediment) is separated from the solution and returned for sintering along with the main charge flow. The desiliconized aluminate solution decomposes at the limit of decomposition with the release of aluminum hydroxide into a precipitate, which undergoes calcination to obtain the finished product (alumina). The proposed method also includes the preparation of nepheline-limestone charge (UPL), sintering of the charge, leaching of the cake, desiliconization of the aluminate solution, the essence of which is as follows: part of the solution is desiliconized in open mixers (-95 98 o C) in the presence of nepheline-limestone charge in the amount 30-50 g/l. Desiliconized solution M cr. 150-250 units. after separating the nepheline-limestone sludge (sediment), it decomposes in a co-alkaline battery at the decomposition stage, releasing aluminum hydroxide into the sediment. The other part is desiliconized in two stages. At the first stage, in autoclaves (150 o C) in the presence of nepheline-limestone sludge (in the absence of nepheline-limestone slurry, nepheline-limestone charge is supplied to the autoclaves). The resulting precipitate after desiliconization is separated from the solution and returned for sintering, and the clarified solution enters the second stage of desiliconization in open mixers in the presence of lime-containing pulp (lime milk). The sediment (hydrogen garnet slurry) is also fed to autoclaves, and the clarified solution (with a flint module of more than 2000) to the soda battery of the decomposition stage, where it decomposes with the release of aluminum hydroxide into a precipitate and obtaining a soda solution. Aluminum hydroxide is fed to calcination to produce Al 2 O 3 (alumina). The technical characteristics of the proposed method relative to its analogue (patent N 1736931) with a plant capacity of 270 thousand tons/year were:
1. The amount of recycled white sludge (desiliconization product) returned for sintering was: in the first case, 0,581 t/t Al 2 O 3 ; in the second 0,607 t/t Al 2 O 3. The irretrievable losses of alumina with it amounted to 0,0188 t/t Al 2 O 3; 0,021 t/t Al 2 O 3 . As a result, by reducing the irretrievable losses of Al 2 O 3 with white mud, the proposed method increases the production of Al 2 O 3 by 594 tons/year. 2. By reducing the turnover of white sludge, the productivity of sintering furnaces for raw materials also increases by 0,022 tons per 1 ton of Al 2 O 3, which ensures an increase in the output of finished products by 1422 tons of Al 2 O 3 /year. Total 2016 t/year.

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