[China Aluminum Network] So far, many methods have been proposed for extracting alumina from aluminum ore or other aluminum-containing raw materials. Due to technical and economic reasons, some methods have been eliminated and some are still in experimental research. The alumina production methods that have been proposed can be classified into four types, namely, alkali method, acid method, acid-base combination method and thermal method. Alkali methods are currently used for large-scale industrial production. Bauxite is the most important aluminum resource in the world, followed by alum, nepheline, and clay. At present, in the world alumina industry, except that Russia uses nepheline to produce part of alumina, almost all alumina in the world is produced from bauxite. Bauxite is an ore consisting mainly of gibbsite, boehmite, or dicalite. So far, the bauxite resources that can be used for alumina production in China are all diaspore-type bauxite. The content of alumina in bauxite varies greatly, being only about 30% lower and more than 70% higher. In addition to alumina, the main chemical impurities contained in bauxite are silicon oxide, iron oxide and titanium oxide. In addition, a small amount or a trace amount of calcium and magnesium carbonate, potassium, sodium, vanadium, chromium, zinc, phosphorus, antimony, bismuth, sulfur and other elements of the compounds and organic matter. Among them, the content of bismuth in bauxite is small, but it will gradually accumulate in the circulating mother liquor in the alumina production process, which can be effectively recovered and become the main source of production bismuth. One of the main indicators to measure the quality of bauxite is the ratio of alumina content and silica content in bauxite, commonly known as aluminum-silicon ratio. When the alumina is produced by the alkaline method, the aluminum ore is treated with an alkali (NaOH or Na2CO3) to convert the alumina in the ore to a sodium aluminate solution. Impurities such as iron and titanium in the ore and most of the silicon become insoluble compounds. The insoluble residue (red mud) is separated from the solution, discarded after washing or subjected to a comprehensive treatment to recover the useful components therein. The pure sodium aluminate solution can be used to separate out aluminum hydroxide. After separation, washing and calcination, alumina products are obtained. The decomposing mother liquor is recycled for processing another batch of ore. Alkali production of alumina includes Bayer process, sintering process and Bayer sintering combined process. The Bayer process is a method developed by Austrian chemist Bayer from 1889 to 1892 to extract alumina from bauxite. Over a hundred years, there have been many improvements in process technology, but the basic principles have not changed. In commemoration of Bayer’s great contribution, this method has always used the name Bayer Law. The Bayer process includes two major processes. The first is the dissolution of alumina from bauxite under certain conditions (the term used in the alumina industry, ie leaching, the same applies hereinafter), followed by the extraction of aluminum hydroxide from supersaturated sodium aluminate dissolved water. Process, this is Bayer's two patents. The essence of the Bayer process is the extraction of alumina from bauxite by hydrometallurgical methods. Silica-containing minerals cause loss of Al2O3 and Na2O during the production of alumina from the Bayer process. In the Bayer process, after the bauxite is crushed, it is wet milled with lime and recycled mother liquor to make a qualified pulp. The slurry is pre-desiliconized and preheated to the dissolution temperature for dissolution. After the dissolved pulp is cooled by auto-evaporation, it enters into the sedimentation and separation process of diluting and red mud (solid residue after dissolution). The secondary steam generated from the evaporation process is used for preheating of the pulp. After sedimentation and separation, the red mud is washed into the red mud storage yard, and the separated crude liquid (sodium aluminate solution containing solid float, the same below) is sent to the leaf filter. The crude solution is called semen after removing most of the suspended matter by leaf filtration. The semen enters the decomposition process and is decomposed by seed to give aluminum hydroxide. After the decomposed aluminum hydroxide is fractionated and separated and washed, part of it is returned to the seed decomposing process as a seed crystal, and the other part is calcined to obtain an alumina product. The decomposed mother liquor separated after the seed crystal is decomposed is evaporated to return to the dissolution process and a closed loop is formed. Aluminum hydroxide is calcined to give alumina. The dissolution conditions required for different types of bauxite vary widely. The gibbsite type bauxite can be dissolved well at 105°C. The boehmite type bauxite can have a faster dissolution rate at a dissolution temperature of 200°C. Alumina type bauxite must be dissolved at a temperature higher than 240°C, and its typical industrial dissolution temperature is 260°C. Dissolution time is not less than 60 minutes. The Bayer process is used to treat bauxite with a high aluminum to silicon ratio. The process is simple, the product quality is high, and its economic effect is far better than other methods. When dealing with easily-dissolved gibbsite-type bauxite, the advantages are even more outstanding. At present, more than 90% of the alumina and aluminum hydroxide produced in the world is produced by the Bayer process. Due to the special nature of China's bauxite resources, approximately 50% of China's alumina is produced by the Bayer process. The process that combines the Bayer process and the sintering process is called the combined production process. Joint law can be divided into parallel joint law, series joint law and mixed joint law. The method used to produce alumina is mainly determined by the grade of bauxite (ie, the ratio of aluminum to silicon of the ore). From a general technical and economic point of view, the ore-silica-silica ratio is usually about 3 for the sintering method; for the ore-silica ratio higher than 10, the Bayer process can be used; when the grade of the bauxite is between the two, the joint can be used. The law dealt with in order to give full play to the respective advantages of the Bayer process and the sintering process to achieve better technical and economic indicators. At present, the annual global alumina production is about 55 million tons, and China's alumina production is about 6.8 million tons. As China's aluminum capital, Henan Gongyi Aluminum's output accounted for a large part.