Bauxite actually refers to the collective name for ores that can be used industrially and are composed of gibbsite, boehmite or diaspore as the main minerals. Its application fields include metals and non-metals.
Bauxite is the best raw material for producing metallic aluminum and is also the most important application field. Its consumption accounts for more than 90% of the world's total bauxite production.
The non-metallic uses of bauxite are mainly as raw materials for refractory materials, abrasive materials, chemicals and high-alumina cement. Although the proportion of bauxite used in non-metallic applications is small, its uses are very wide. For example: chemical products such as sulfate, trihydrate and aluminum chloride can be used in papermaking, water purification, ceramics and petroleum refining; activated alumina can be used as catalysts, catalyst carriers and Physical adsorbent for decolorization, dehydration, degassing, deacidification, drying, etc.; aluminum chloride produced with r-Al2O3 can be used in organic synthesis of dyes, rubber, medicine, petroleum, etc.; 3 to 5 Al2O3 in the glass composition can increase the melting point, Viscosity and strength; abrasive materials are the main raw materials for high-grade grinding wheels and polishing powders; refractory materials are indispensable furnace building materials in the industrial sector.
Metal aluminum is the second most important metal in the world after steel. In 1995, the world's per capita consumption reached 3.29kg. Aluminum is widely used in various sectors of the national economy because of its small specific gravity, good electrical and thermal conductivity, easy machining and many other excellent properties. At present, the construction, transportation and packaging sectors account for more than 60% of the total aluminum consumption in the world. Aluminum is an indispensable raw material for the electrical appliance industry, aircraft manufacturing industry, machinery industry and civil appliances.
The focus is on bauxite and its deposits that produce metallic aluminum. As for bauxite and its deposits used as refractory clay, see the discussion of non-metallic minerals "Refractory Clay".
1. Characteristics of mineral raw materials
Aluminum is one of the most widely distributed elements in the earth's crust and is a rock-loving and oxygen-loving element. Aluminum mostly exists in nature as oxides, hydroxides and oxygen-containing aluminum silicates, and the natural metal of aluminum is rarely found.
There are 258 kinds of aluminum-containing minerals known in nature, of which about 43 are common minerals. In fact, there are no aluminum deposits composed of pure minerals. They are generally distributed and mixed with impurities. From an economic and technical point of view, not all aluminum-containing minerals can become industrial raw materials. Bauxite, which is mainly composed of diaspore, boehmite or gibbsite, is used to extract metallic aluminum. Due to the lack of bauxite resources in the former Soviet Union, nepheline and alunite were used to refine alumina. my country's aluminum strontium phosphorus ore can comprehensively recover alumina.
Diasporite is also known as diaspore. Its structural formula and molecular formula are AlO(OH) and Al2O3·H2O respectively. Orthorhombic crystal system, those with intact crystals are columnar, plate-shaped, scaly, needle-shaped, prism-shaped, etc. The diaspore in the ore generally contains TiO2, SiO2, Fe2O3, Ga2O3, Nb2O5, Ta2O5, TR2O3 and other homogeneous mixtures in different amounts. Diaspore is soluble in acid and alkali, but it is very weakly soluble under normal temperature and pressure. It needs high temperature, high pressure and strong acid or alkali concentration to completely decompose. Diaspore is formed in acidic media and is produced with boehmite, hematite, goethite, kaolinite, chlorite, pyrite, etc. Its hydration can turn into gibbsite, dehydration can turn into alpha corundum, and can be replaced by kaolinite, pyrite, siderite, chlorite, etc.
Boehmite is also known as boehmite and boehmite. Its structural formula is AlO(OH) and its molecular formula is Al2O3·H2O. Orthorhombic crystal system, those with intact crystals are in the form of rhombus, facet, prism, needle, fiber and hexagonal plate. Boehmite in the ore often contains Fe2O3, TiO2, Cr2O, Ga2O3 and other homogeneous elements. Boehmite is soluble in acids and alkalis. This mineral is formed in acidic media, mainly in sedimentary bauxite, and is characterized by its association with siderite. It can be replaced by diaspore, gibbsite, kaolinite, etc., dehydrated and transformed into diaspore and alpha corundum, and hydrated into gibbsite.
Gibbsite is also known as allophane and hydroxide, with the structural formula Al(OH) and the molecular formula Al2O3·3H2O. Monoclinic crystal system, those with intact crystals are in the shape of hexagonal plates and prisms, often in the form of fine crystal aggregates or twin crystals. The gibbsite in the ore is mostly in the form of irregular aggregates, all containing different amounts of TiO2 and SiO2 , Fe2O3, Nb2O5, Ta2O5, Ga2O3 and other similar homogeneous or mechanical mixtures. Gibbsite is soluble in acid and alkali, and its powder can be completely dissolved after being heated to 100°C for 2 hours. This mineral is formed in acidic media. In weathered crust deposits, gibbsite is a primary mineral and the main ore mineral. It occurs with kaolinite, goethite, hematite, illite, etc. Dehydrated gibbsite can become boehmite, diaspore and α-corundum, and can be replaced by kaolinite, halloysite, etc.
The main chemical components of bauxite are Al2O3, SiO2, Fe2O3, TiO2, and H2O+. The total of the five accounts for more than 95% of the composition, generally >98. The minor components are S, CaO, MgO, and K2O. , Na2O, CO2, MnO2, organic matter, carbonaceous matter, etc., trace components include Ga, Ge, Nb, Ta, TR, Co, Zr, V, P, Cr, Ni, etc. Al2O3 mainly occurs in aluminum minerals—diaspore, boehmite, and gibbsite, and secondarily in silicon minerals (mainly kaolinite minerals).
Under endogenous conditions, due to the widespread presence of silica, Al2O3 and SiO2 are often closely combined to form various types of aluminosilicate minerals. These minerals generally have an aluminum-to-silicon ratio of less than 1, and industrial aluminum Ore generally requires Al2O3≥40 and Al/Si>1.8~2.6, so industrial aluminum deposits are rarely formed under endogenous conditions.
At present, most of the known industrial bauxite at home and abroad are formed under supergene conditions. There are two main forms of bauxite generation under supergene conditions: weathering-eluvial (residual) mineralization (laterite mineralization) and weathering-transportation-sedimentation mineralization or weathering-reformation-redeposition mineralization (sedimentation mineralization). mine). Weathering-eluvial (residual) mineralization is an aluminum-containing parent rock with favorable drainage terrain (such as residual hills, low mountains and platforms) under humid and hot climate conditions. Due to the weathering and decomposition of water, CO2 and organisms, the parent rock The medium-soluble substances K, Na, Ca, Mg and SiO2 are leached and discharged, while the less mobile substances Al, Fe and Ti remain in situ to form laterite-type bauxite. Weathering-transportation-sedimentary mineralization refers to mechanical or chemical weathering and erosion of aluminum-containing rocks, laterite weathering crusts or formed laterite deposits under the action of gravity, water and natural acids (sulfuric acid, carbonic acid, organic acids) etc. , transportation and other physical and chemical transformations, bauxite is formed in hillside depressions, valleys, offshore lake basins or coastal lagoons, and limited sea basins, and sedimentary bauxite is formed in a water medium environment.
Bauxite ore contains useful components such as gallium, vanadium, niobium, tantalum, titanium, cerium and radioactive elements. These valuable associated components can be comprehensively recovered. The sulfur, CO2, MgO, and P2O5 in the ore are harmful components and are not conducive to the smelting and recovery of aluminum.
Bauxite ore is divided into: gibbsite type, boehmite type and diaspore type according to the main aluminum-containing minerals it contains. Foreign bauxite ores are mainly gibbsite type, followed by boehmite type, and diaspore type bauxite is very rare. However, my country mainly has diaspore-type bauxite and gibbsite-type bauxite is very rare.
Foreign gibbsite-type bauxite has the characteristics of high aluminum, low silicon and high iron. The ore quality is good and suitable for the Bayer process with low energy consumption. The overall characteristics of my country's diaspore-type bauxite are high aluminum, high silicon, low sulfur and low iron, and medium-low aluminum to silicon ratio. The ore quality is poor and processing is difficult. Alumina production uses a high-energy-consuming combined method. .
2. Uses and technical and economic indicators
Bauxite ore has various uses, the most important of which are: refining metallic aluminum in the aluminum industry, making refractory materials and grinding materials, and Used as raw material for high alumina cement. Ore is used for different purposes and has different quality requirements. Table 3.9.1 is the industry standard for bauxite ore (YS/T78-94) released by China Nonferrous Metals Industry Corporation in 1994.
According to this standard, bauxite is divided into three types: sedimentary diaspore, accumulation diaspore and laterite gibbsite, and is divided into LK12-70, LK8-65, LK5- according to its chemical composition. 60. Nine grades including LK3-53, LK15-60, LK11-55, LK8-50, LK7-50, and LK3-40. In addition to stipulating the chemical composition of bauxite, the standard also requires that the moisture of sedimentary diaspore should not be greater than 7, and that of accumulation-type diaspore and laterite-type gibbsite should not be greater than 8. In addition, it is required that the particle size of bauxite ore shall not be greater than 150mm. Bauxite ore must not be mixed with dirt, limestone and other debris.
In industrial extraction of metallic aluminum, alumina is first extracted from bauxite, and then the alumina is electrolyzed into metallic aluminum. According to my country's practical production experience, different alumina production methods have different requirements for ore quality. The general requirements are:
1) Sintering method: suitable for processing low-grade ores with high silicon content. It is required that Al2O3/SiO2 is 3 to 5 (or around 3.5), and Fe2O3 <10.
2) Bayer method: suitable for processing rich ores with high Al2O3 content and low SiO2 content. Generally, Al2O3>65 and Al2O3/SiO2>7 are required. Iron oxide does not react with alkali in the Bayer process, but the iron content is high and the amount of red mud is large. The red mud washing is complicated, which can easily cause mechanical losses of alkali and alumina, but aluminum goethite is not suitable.
3) Combined method: suitable for processing medium-grade bauxite. my country mainly uses the mixed method, that is, adding some low-grade ores to the red mud of the Bayer method to increase the aluminum-silicon ratio of the sintering method. Generally, Al2O3＞60, Al2O3/SiO2 is 5~7, and Fe2O3＜10. For alumina production, sulfur is a very harmful impurity, and high-sulfur ores should not be used.
Bauxite used as grinding materials is required to contain high Al2O3 and low iron and titanium. Generally, it requires Al2O3≥70, Fe2O3≤5, TiO2≤4.5, CaO MgO≤1.0, Al2O3/SiO2≥12 .
The bauxite ore used as raw material for high alumina cement must have: Fe2O3<2.5, TiO2<3.5, R2O (monovalent metal oxide)<1.0, MgO<1.0.
3. A brief history of mining
The aluminum element was obtained in 1825 by Danish physicist H.C. Oersted using potassium amalgam to interact with aluminum chloride. Aluminum amalgam, and then using distillation to remove the mercury, was discovered to produce metallic aluminum for the first time.
The production of metallic aluminum was initially based on chemical methods. That is, the sodium chemical method founded by French scientist H. Sainte Claire Diwill in 1854 and the magnesium method founded by Russian physical chemist H.H. Beketov (Н.Н.Бекетов) in 1865 chemical method. France started industrial production using chemical methods in 1855 and was the first country in the world to produce aluminum.
The discovery of bauxite (1821) preceded the element aluminum and was mistakenly thought to be a new mineral at the time. To produce aluminum from bauxite, alumina must first be produced, and then aluminum must be produced electrolytically. The mining of bauxite began in France in 1873, and the production of alumina from bauxite began in 1894. The Bayer process was used, and the production scale was only more than 1 ton per day.
By 1900, countries such as France, Italy and the United States had a small amount of bauxite mining, with an annual output of only 90,000 tons. With the development of modern industry, aluminum as a metal and alloy was applied to the aviation and military industries, and then expanded to civilian industry. Since then, the aluminum industry has developed rapidly. By 1950, the world's aluminum metal production had reached 1.51 million tons. It increased to 20.92 million tons in 1996, becoming the second most important metal after steel.
The general search for bauxite in my country first began in 1924. At that time, the Japanese Toshio Itamoto and others conducted geological surveys of the bauxite shale in Liaoyang, Liaoning Province, and Yantai, Shandong Province.
Since then, the Japanese Yoshio Kouki and others, as well as Chinese scholars Wang Zhuquan, Xie Jiarong, Chen Hongcheng and others, have successively conducted research on aluminum in the Zibo area of ????Shandong, Tangshan and Kailuan areas of Hebei, Taiyuan, Xishan and Yangquan areas of Shanxi, and Benxi and Fuzhou Bay areas of Liaoning. Special geological surveys were conducted on earth minerals and bauxite shale. The investigation of bauxite mines in southern my country began in 1940. First, Bian Zhaoxiang investigated the bauxite mines near Banqiao Town, Kunming, Yunnan. Subsequently, from 1942 to 1945, Peng Qirui, Xie Jiarong, Lesen Wangxun and others successively conducted geological surveys and systematic sampling of bauxite and high-aluminum clay mines in Yunnan, Guizhou, Sichuan and other places. Generally speaking, most of the work done before the founding of New China was of a general reconnaissance and investigation research nature.
The real geological exploration work of bauxite began after the founding of New China. From 1953 to 1955, the geological teams of the Ministry of Metallurgy and the Ministry of Geology successively investigated the bauxite mines in Zibo, Shandong, the bauxite mines in the Xiaoguan area of ??Gongxian County, Henan (such as Zhulingou, Chadian, Shuitou and Zhongling mining areas), and the aluminum areas in Qianzhong, Guizhou. Geological exploration work has been carried out in soil mines (such as Linxi, Xiaoshanba, Yanlong and other mining areas), Baijiazhuang mining area in Yangquan, Shanxi, etc. However, due to the lack of bauxite exploration experience at that time, the bauxite specifications of the former Soviet Union were blindly applied without considering the actual situation of China’s bauxite mines. As a result, most geological exploration reports were downgraded during the review from 1960 to 1962. , the reserves have also been reduced a lot. After 1958, my country has accumulated certain experience in bauxite exploration. On the basis of the large-scale copper and aluminum census, many mining areas have been discovered and explored, among which the more important ones are: Henan Zhangyaoyuan, Guangxi Pingguo , Shanxi Xiaoyi Ke'er, Fujian Zhangpu, Hainan Penglai, and other bauxite mining areas.
The mining of bauxite in my country first began in 1911. At that time, the Japanese first mined Fuzhou Bay bauxite mine in Liaoning Province, my country, and then from 1925 to 1941, they mined Liaoyang and Shandong Province in Liaoning Province. The two layers of bauxite, A and G, are mined in the Yantai mining area. The above mining is mostly used as refractory materials. From 1941 to 1943, the Japanese mined the Tianzhuang and Hongtupo sections of the Hutian and Fengshui mining areas in Zibo, Shandong Province, my country, and the ore was used as raw material for aluminum smelting. Later, the Taiwan Aluminum Company also conducted small-scale mining for aluminum smelting.
The large-scale development and utilization of bauxite in my country began after New China. In 1954, the Fengshui Mine in Shandong Province, which had been mined by the Japanese on a small scale before, was first restored. After 1958, three major aluminum plants, 501, 502, and 503, were built in Shandong, Henan, Guizhou and other provinces. In order to meet the needs of these three major aluminum plants for bauxite, aluminum plants were built in Shandong, Henan, Shanxi, Guizhou and other provinces. Aluminum raw material bases include Zhangdian Aluminum Mine, Xiaoguan Aluminum Mine, Luoyang Aluminum Mine, Xiuwen Aluminum Mine, Qingzhen Aluminum Mine, and Yangquan Aluminum Mine.
In the 1980s, especially after the establishment of China Nonferrous Metals Industry Corporation in 1983, my country's bauxite geological exploration and aluminum industry have developed rapidly. Shanxi Aluminum Plant, Zhongzhou Aluminum Plant, etc. were newly built and expanded. A group of large-scale aluminum plants represented by the aluminum factory have increased my country's primary aluminum output from less than 2,000 tons in 1954 to 1.87 million tons now. A complete aluminum industry system has been established from geology, mining to smelting and processing. Aluminum metal and its processed products can basically meet the needs of my country's economic construction.