What is the production method of alumina?

” >Alumina production methodSo far, many methods for refining alumina from aluminum ores or other aluminum-containing raw materials have been proposed, but Due to various technical and economic reasons, only a few methods are currently used in industrial production. Due to the two properties of alumina, either alkaline solution or acidic solution can be used to dissolve the alumina in bauxite. The production methods of alumina can be roughly divided into alkali method, acid method, acid-base combined method and thermal method. However, only the alkali method is used in industry.

” >Alkali method uses alkali (industrial caustic sodaNaOH or soda ash Na2CO3) treats bauxite to convert the alumina in the ore into sodium aluminate solution. Impurities such as iron and titanium and most of the silicon in the ore become insoluble compounds and enter the residue (red mud). It is separated from the solution and then discarded or reused comprehensively.

” >From purified sodium aluminate (called Semen) can be decomposed to release aluminum hydroxide, and the decomposed mother liquor can be recycled in production. The alkali process produces alumina and there are many processes such as alkali method, soda-lime sintering method and -sinter combined method. The method directly uses the circulating mother liquor containing a large amount of free caustic alkali to treat bauxite, dissolves the alumina to obtain a sodium aluminate solution, and adds aluminum hydroxide (seed crystal) to the sodium aluminate solution. Aluminum hydroxide crystals can be separated out by stirring for a long time. The decomposition mother liquor is evaporated and then used to dissolve the next batch of bauxite.

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” >The soda lime sintering method is used in bauxite Add limestone (or lime) and caustic soda (carbon denominator solution containing a large amount of Na2CO3), sinter at high temperature to obtain the material containing solid sodium aluminate, and dissolve the material with water or dilute alkali solution to obtain sodium aluminate solution. After the sodium aluminate solution is desiliconized and purified, the crystallized aluminum hydroxide can be decomposed by introducing carbon dioxide gas. The decomposed mother liquor is evaporated and recycled. The method has relatively simple process, low energy consumption, good product quality and low cost. But it is limited to processing high-grade bauxite (A/S should be greater than 7).

” >The soda-lime sintering method is complex and consumes high energy , product quality and cost are inferior to law. But it can handle high-silica bauxite. Due to the decrease in the aluminum-silicon ratio of the ore, the consumption of various raw materials has increased, equipment has increased, and various technical and economic indicators have also declined. Therefore, the aluminum-silicon ratio of ores currently treated by soda-lime sintering method should not be lower than 3 to 3.5. Practice has proved that in some cases, the joint production process of the sintering method and the sintering method is adopted, that is, the sintering combined method.�It can combine the advantages of the casting method and the sintering method, and obtain better economic results than a single casting method or the sintering method. The acid methodProduction of alumina is to treat aluminum-containing raw materials with inorganic acids such as nitric acid, sulfuric acid, and hydrochloric acid to obtain the corresponding acidic aqueous solution of aluminum salts.

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” >Then these aluminum salts are precipitated from the solution into hydrate crystals (crystallization by evaporation) or basic aluminum salts (crystallization by hydrolysis). These aluminum salts can also be neutralized with alkali. The aqueous solution of the salt precipitates aluminum as aluminum hydroxide, and the obtained aluminum hydroxide or the hydrated crystals or basic aluminum salts of each aluminum salt are calcined to obtain anhydrous aluminum oxide. The acid method is used to treat widely distributed aluminum-containing raw materials with high silicon and low iron, such as clay, kaolin, etc., and is reasonable in principle.

” >However, compared with the alkali method, the acid method to produce alumina requires expensive acid-resistant equipment. The recovery of the acid is generally more complicated, and impurities such as iron and titanium are removed from the aluminum salt solution. Can’t wait. Therefore, industrialization has not been achieved so far. In recent years, some countries lacking bauxite resources have been using the acid process as a technical reserve for processing non-bauxite raw materials to produce alumina, and have actively studied it and made certain progress.

” >The acid-base combined method is to first use the acid method to prepare aluminum hydroxide containing iron, titanium and other impurities from high-silicon aluminum ore, and then use the alkali method (method )deal with. The essence of this process is to use acid method to remove silicon and alkali method to remove iron. Some recent literature considers this to be a method of industrial value. Thermal method (also known as Pederson method) was proposed for processing high-silicon and high-iron aluminum ore. Its essence is to reduce the smelting ore in an electric furnace or blast furnace to obtain ferrosilicon alloy (or pig iron) and Calcium aluminate slag, after the two are separated by the difference in specific gravity, the alumina is extracted from the slag using an alkali method. my country’s Fushun, the Soviet Union, and Norway all produced alumina according to this method in the 1940s, but later stopped production. Currently, research on this method is still ongoing.