The mineralogical and chemical composition determines the openability (extraction of Al2O3 from bauxite); alkali consumption; temperature, leaching time; concentration of Na2Ok solutions; bauxite processing method; structure, density, hardness, moisture content of bauxite, etc.
The hardness of bauxite determines the energy consumption for crushing and grinding bauxite. Bauxites with low hardness can be crushed/grinded in one stage, harder ones - in two stages.
Humidity affects the grinding process and the transportation of bauxite in winter. Bauxite with high humidity can clog equipment (crushers, screens, etc.) due to the adhesion of bauxite mass to working surfaces. Freezing makes unloading bauxite from railway cars much more difficult. Bauxite freezes into large monolithic pieces, the unloading and crushing of which requires manual labor.
The chemical composition determines the quality of bauxite, the silicon module, the consumption of bauxite for the production of 1 ton of alumina, the loss of alkali per 1 ton of alumina, the method of processing bauxite, the yield of red mud, the conditions for storing and transporting bauxite.
Well-opening bauxites are those from which the extraction of alumina into solution is close to or equal to the theoretical:
where ηt is the theoretical extraction of alumina (theoretical yield); Al2O3(B), SiO2(B) - content of components in bauxite, % (by weight); Y is the number of moles of SiO2 bonding with 1 mole of Al2O3 in the red mud.
Theoretical extraction of alumina shows the ratio of the amount of alumina that passed into solution over a certain period of time to its amount in the original bauxite.
To calculate the actual extraction of alumina, we proceed from the condition that Fe2O3 of bauxite remains completely in the solid phase during leaching. In this case, the chemical extraction (actual yield) of Al2O3 into the solution during leaching or the degree of extraction is calculated using the formula
In relation to low-iron bauxites, more accurate results are obtained when calculating extraction not by Fe2O3, but by SiO2.
The chemical yield is lower than theoretical, since the leaching residue (red mud) always contains some amount of unleached alumina in the form of hydroxides, corundum, aluminoferrite, etc.
The breakability of bauxite is mainly determined by its mineralogical composition, the structure and density of the rock, as well as the presence of impurities. These factors determine the difference between the theoretical and actual extraction of Al2O3 into solution. This difference is usually between 2 and 8%.
Diaspore bauxites are among the most difficult to open, while gibbsite bauxites are among the easiest to open.
According to their chemical activity, aluminum hydroxides and oxides are arranged in the following sequence:
gibbsite (hydrargillite) → boehmite → diaspore → alumina → corundum.
This is related to the technology of bauxite processing, in particular the choice of leaching conditions. The lower leaching temperature of gibbsite bauxite is determined by the fact that gibbsite dissolves well in an alkaline solution at a temperature of 95-105 ° C and Na2Ok = 100-200 g/l (at atmospheric pressure), boehmite - at 150-230 ° C and Na2Ok = 200 -250 g/l (Pu = 1.4-2.9 MPa), and the diaspore dissolves at a temperature of 230-240 °C and Na2Ok = 250-300 g/l (Pu = 2.8-3 MPa).
Dense, jasper-shaped bauxite, which has almost no pores, leaches much more slowly than loose, porous ores. It has been established that organic impurities of bauxite (soluble in benzene) reduce the leachability of diaspore bauxites, which is apparently due to their enveloping ability. The harmful effects of these impurities can be eliminated by increasing the dosage of lime.
The weight of the sludge that is formed after leaching of bauxite is determined by the formula
where Q(B) is the amount of bauxite supplied for leaching; Fe2O3 - Fe2O3 content in bauxite and sludge, respectively.
The yield of red mud η is determined by the formula
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Bauxite is the most important raw material for alumina production.
Bauxite is a rock consisting mainly of hydrous oxides of aluminum, iron and small amounts of oxides of silicon, titanium and some other elements, as well as hydrous aluminosilicates. Bauxites, by their origin, are divided into two main groups, residual and sedimentary. Residual bauxites are formed during the process of lateritic weathering of syenites, granites, diorites, basalts, dolerites, crystalline shales, clays, as well as during the leaching of limestones.
Lateritization is the process of weathering of aluminosilicate rocks under conditions of a leveled topography, a hot climate with alternating rainy and dry periods. This process involves the decomposition of aluminosilicates, the removal of silicic acid, the formation and accumulation of free hydrates of aluminum and iron oxides. Typical laterite bauxites are unknown in Russia. They are widespread in tropical and subtropical zones.
Sedimentary bauxites were formed in coastal sea lagoons, continental lakes and river valleys due to solutions, suspensions and colloidal compounds of aluminum, iron, titanium and many other elements carried by rivers and groundwater.
Characteristic of bauxites is the cryptocrystalline and often amorphous state of most of the minerals included in their composition. Many mineral forms are represented by hardened simple and complex hydrogels. The color of bauxite ranges from almost white to dark red and black. Bauxites have bean, oolitic, clot, fine-grained and pore structures. Bauxites of different structures are often found in deposits close to each other.
In addition to some varieties, appearance, without special study methods (in thin sections, using chemical, differential thermal, X-ray analyses), bauxites are difficult to determine. The hardness of bauxite varies greatly and is determined by its mineralogical composition and structure. Bauxites are characterized by significant porosity, sometimes turning into cavernousness, which determines their significant moisture content
42 chemical elements were found in bauxites, including ten (O, H, C, Al, Si, Ti, Ca, Mg, Fe and S) that are found in bauxites the largest quantities and the content of each of them exceeds 1%, five elements (P, V, Cr, Na and K) are included in amounts up to 1%, the content of the remaining elements does not exceed 0.1% (Cu, Zn, Zr, Ca, Co, Mn , Ge, Sr, Be, Ba, U, Th).
The chemical composition of bauxite varies widely both in different deposits and within one deposit.
The mineralogical composition of bauxite is very complex. They contain about 100 minerals. However, the following are of rock-forming importance, depending on the type of bauxite: diaspore, boehmite, hydrargillite or gibbsite, kaolinite, chlorites, calcite, siderite, hematite, goethite, pyrite.
Typically, bauxite contains two aluminum oxide minerals.
Depending on the degree of hydration of aluminum oxide, bauxite is divided into:
1) low-water - corundum,
2) single-water - diasporic and boehmite,
3) three-hydrate - hydrargillite or gibbsite.
The sizes of the deposits are extremely different and are determined by the size of the accumulation basins, the eroded nature of the area and, to a lesser extent, depend on their genesis. Maximum known length The deposit reaches a strike length of 10 km and a width of 2 km. The greatest extent is covered by residual bauxite of lateritic origin. The thickness of deposits without bulges and pockets is usually about 5 m.
The thickness of pockets in sheet-like deposits reaches 65 m, and in deposits located in limestone - up to 250 m. Reserves of individual deposits of all types usually do not exceed 20-25 million tons. The structure of deposits depends on the genesis of the deposit. The simplest structure is found in sedimentary deposits of lagoonal origin, occurring among limestones. Typically they have a flat upper contact and an extremely sinuous lower contact. These deposits are characterized by consistent quality in width, strike and thickness. The most complex deposits are sedimentary and mixed, of lake-swamp origin. They usually represent several layers of bauxite interspersed with bauxite and ordinary clays.
Lake-marsh and valley deposits are characterized by zonality of their structure. Deposits of some deposits have the form of lenses of scaly or concentrically zonal structure (Tikhvin basin).
The industry places a number of requirements on bauxite as a raw material for alumina production. In Russia, these requirements are determined by the state standard GOST 972-50 (Table 1).
2. For bauxite intended for the production of alumina, the following limits for sulfur content are established: for bauxite grades B-1, B-2, B-7, B-8 - no more than 0.7%; for bauxite grades B-3, B-5, B-4 - no more than 1.0%.
3. Bauxite grades B-1, B-2, B-7 and B-8 are produced depending on the carbon dioxide content, in two grades: the first grade - with a carbon dioxide content of up to 1.3%, the second grade - with a carbon dioxide content of over 1, 3% by weight of dry bauxite.
4. In bauxite intended for the production of alumina by sintering (grades B-3, B-4, B-5), a reduced content of aluminum oxide is allowed due to an increase in the content of calcium carbonate
5. In bauxite intended for the production of electrocorundum, the following calcium oxide content is established: for bauxite grades BV and V-O - no more than 0.5%, for bauxite grade B-1 - no more than 0.8%. Sulfur content no more than 0.3%.
6. In bauxite intended for open-hearth production, the sulfur content should not exceed 0.2%, the phosphorus content should not exceed 0.6% based on P2O6.
7. In bauxite intended for the production of fused refractories, the calcium oxide content should not exceed 1.5%, the sulfur content should not exceed 0.5%.
8. In bauxite intended for the production of aluminous cement, the sulfur content should not exceed 0.5%.
Bauxite deposits in Russia
Bauxites were first discovered in Russia in 1916 (Tikhvinskoye). In the early 30s, bauxite was discovered in the Northern Urals. This was followed by a series of bauxite finds in various parts Russia.
Currently, we can talk about the following bauxite-bearing regions of Russia:
1 North Ural - bauxites of boehmite-diaspore type, have an average composition of 51.0-57.0% AbO3, 2.5-8.5% SiO2, 20.0-22.0% Fe2O3, 2.5-3, 0% TiO2. Pyrite-containing varieties are common, containing 6-8% sulfur.
2 South Ural - bauxites of boehmite-diaspore type, have an average composition: 48.0-60.0% Al2O3, 5.0-12.0% SiO2, 18.0-20.0% Fe2O3, 2.5-3 .0% TiO2. There are pyrite-containing varieties.
3. Middle Ural - bauxites of the hydrargillite type, have an average composition: 33.0-39.0% Al2O3, 6-8% SiO2, 15.0-20.0% Fe2O3, 3.0-4.0 TiO2. There are varieties containing Fe2O3 in the form of siderite.
4. Yenisei - bauxites of the hydrargillite type, have an average composition. 32.0-46.0% Al2O2, 6.0-10.0% SiO2, 25-35% Fe2O3, 4.8-5.5% TiO2. There are varieties containing corundum along with hydrargillite.
5. North-Western - bauxites of the hydrargillite-boehmite type, have an average composition of 39.0-46.0% AbO3, 8-15% SiO2, 14.C-16.0% Fe2O3, 2.0-3.0% TiO2 .
6. North Kazakhstan - bauxites of the hydrargillite type, have an average composition, 40.0-50.0% Al2O3, 5.0-15.0% SiO2, 10.0-12.0% Fe2O3, 2.3-2, 5% TiO2 Varieties are common where the main amount of iron is in the form of siderite.
In addition, low-quality bauxite is known in Russia that does not meet the requirements of GOST:
1. Onega - bauxites of the hydrargillite-boehmite type.
2. Sayan - bauxites of boehmite-diaspore type, etc.
Bauxite deposits of foreign countries
USA. Although the country ranks first in the production of aluminum metal, the American alumina industry is largely dependent on imports. For example, in 1960, bauxite was imported into the United States from: Suriname 3,317,240 tons; Jamaica 4,257,040 tons and British Guiana 335,280 tons.
Bauxite in the USA was discovered in the state of Georgia in 1883. Two bauxite-bearing areas are known. Central Arkansas and the southeastern states of Georgia, Alabama, Mississippi, Tennessee and Virginia.
Diasloric bauxites, which are not considered alumina raw materials in the United States, are known in Pennsylvania and Missouri.
Bauxite reserves (as of 1950) are: Arkansas - 39 million tons, Alabama - 700 thousand tons, Georgia - 1 million tons, Pennsylvania - 5 million tons. In 1957, 1,437,000 tons were mined, of which 9 /10 - from deposits in Arkansas. Average composition of Arkansas bauxite: 56-59% Al2O3, 5-8% SiO2, 2-6% Fe2O3, 29-31% p.p.
Canada- the world's second-largest aluminum producer. It does not have its own deposits. Bauxite is imported from British Guiana, Suriname and the USA. In 1956, 2,159,000 tons of bauxite were imported into Canada.
Jamaica. A strip of deposits stretches here across the entire island from east to west. The volume of deposits ranges from several thousand tons to many millions of tons, on average 500 thousand tons. Total reserves - about 600 million tons. Production in 1952 - 420,000 g, and in 1960 g. has already reached 5,836,920 tons Average composition. 46-50% Al2O3, 0.4-3.5% SiO2, 17-23% Fe2O3. Bauxite is mainly exported. There are two alumina refineries in Jamaica. One in Kirchwann with a capacity of 550,000 tons per year, and the other in the St. Catherine region with a capacity of 250,000 tons.
British Guiana. The main deposits are located along the river. Demerera, between Christianburg and Akima, along the river. Esquibo, along the river. Berbays and its tributary river. Ituni. The significance of the deposits is very different. Reserves are estimated at 65-100 million tons. Exploitation began in 1914. In 1960, 2,510,730 tons were produced. Average composition: 50-61% Al2O3, 3-12% SiO2, 1.0-2.5% Fe2O3 . An alumina plant with a capacity of 230,000 tons per year was built in the Mekenzi area.
Suriname. Bauxite was discovered in 1915. The main deposits are located along the Kottika and Suriname rivers. The largest deposit is Moengro. Bauxites represent surface deposits (covers on the tops of low hills). Total reserves are determined at 50-100 million tons Composition: 55-57% Al2O3, 2-3% SiO2, 8-12% Fe2O3, 30-31% p.p. Operation began in 1922. Production in 1951 was 2,699,000 tons, and in 1960 it was already 3,454,400 tons. The construction of alumina and aluminum plants is planned.
Brazil. Bauxite deposits are found in many parts of the country, but the largest are located on the Pozos de Caldos plateau. Reserves are estimated at about 200 million tons.
In 1960, production amounted to only 99,000 tons. Bauxite composition: 45-65% Al2O3, 2-20% SiO2, 0.3-10% Fe2O3.
Hawaiian Islands. Bauxite deposits are known on many islands of the archipelago. Bauxite of hydrargillite type. Total reserves are estimated at 600 million g. Composition: 40-46% Al2O3, 2% SiO2, 35-40% Fe2O3.
Ghana. The deposits represent a strip stretching parallel to the ocean coast, 100-150 km from it into the interior of the continent. The four most interesting areas are Ncisreso, Affo (Sefwi-Bekwai), Yenakhin and the Yehuanojoya Mountains. The Yenakhin region has the largest reserves - 168 million tons, in Affo there are about 32.5 million tons, in the Eyuanahem mountains - 4 million tons. Composition - 51% Al2O3, 1-1.5% SiO2, 19% Fe2O3, 1.5% TiO2.
Bauxite is exported to England. In 1960, production was 191,008 tons. The presence of large hydropower resources makes it possible to organize large production aluminum Construction of a plant with a capacity of 210,000 tons of aluminum per year has begun.
Republic of Guinea. Bauxite deposits are known in a number of places in the republic, but mining is carried out only on the island of Los. Bauxite of hydrargillite type. Composition: 51% Al2O3, 6% SiO2, 11% Fe2O3.
Possible reserves are estimated at approximately 1 billion tons. Production in 1960 amounted to 1,377,696 tons, of which 385,000 tons were exported to Canada
In 1960, an alumina refinery with a capacity of 480,000 tons per year was launched.
Indonesia. Bauxite is known on many islands: Bintan, Banka, Batam, Singkap. The most significant ones are located on the island. Bintan with reserves of 23 million tons. Total reserves of bauxite are about 30 million tons.
Bauxite composition: 53-55% Al2O3, 4% SiO2, 9-13% Fe2O3. All mined ore is exported. An aluminum smelter with a capacity of 10,000 tons per year is planned to be built in East Sumatra.
India. The main reserves are concentrated in the states of Bihar, Madhcha Pradesh, Orissa, Madras, Bombay, Jami and Kashmir. Total reserves exceed 250 million tons, of which only 27 million tons are high-quality. Bauxites are of the hydrargillite type, except for Kashmir, which are diasporic.
Composition of hydrargillite bauxite: 56-68% Al2O3, 0.3-7.0% SiO2, 0.3-6.0% Fe2O3, 1-10% TiO2.
Composition of diaspore bauxite: 79% Al2O3, ~1% SiO2, 2.1% Fe2O3.
Australia. Bauxite deposits were discovered in 1952 in the northern part of the continent and are found in a number of other places. Bauxite of hydrargillite type. The average composition is 46% Al2O3, 5-6% SiO2. Possible reserves are estimated at more than a billion tons.
France. Bauxite was discovered in 1821. The deposits are located in the departments of Var, Bouches-du-Rhône, Hérault, Eastern Pyrenees and Ariège and extend approximately parallel to the Mediterranean coast. The main reserves are in the Bap department, which is the main producer of bauxite, providing 6/7 of France's total production. Proven reserves are 20 million tons, probable reserves are 40 million tons. The main type of bauxite is boehmite. Mined bauxite has a composition. 51-58% Al2O3, 3.5-5.5% SiO2, 18-25% Fe2 O3.
The exploitation of the deposits began in 1873, production in 1960 amounted to more than 2,038,096 tons.
Italy. The deposits are mainly concentrated in the central part of the Apennine Peninsula. Three bauxite-bearing zones are distinguished: Abruzza, Campania, and the Gargano Mountains. Reserves are estimated at 30 million tons. In 1957, 261,000 tons were mined. Boehmite-type bauxite. Composition 43-53% Al2O3, 2-6% SiO2.
Greece. The deposits represent an intermittent strip stretching from northwest to southeast, from the island of Amorgos in the Tsoklida archipelago to Phthiotis in the Pindus mountain range, crossing Attica, Boeotia and Phosida. Diaspore-boehmite type bauxite. Composition: 56-59% Al2O3, 3-7% SiO2, 18.0% Fe2O3. Production in 1960 was 949,960 tons. Bauxite is completely exported to Germany, Great Britain and Russia.
Yugoslavia. The deposits are located in Istria, Dalmatia, Bosnia, Herzegovina and Montenegro. Type of bauxite: Dalmatian - hydrargillite; Istra, Montenegrin, Herzegovinian - boehmite. Explored reserves are about 130 million tons, possible 270 million tons. Average composition: 59.7% Al2O3, 3.4% SiO2, 18.2% Fe2O3. In 1960, 1,025,144 tons of bauxite were mined; a significant part of bauxite is exported to Germany and Italy.
Hungary. The deposits stretch in a strip from the southern end of Lake Balaton to the villages. Negra north of Budapest. The bulk of the reserves are located in the Bakony Forest region, where 15 deposits are known, of which Halimba is one of the largest in Europe.
Bauxites of hydrargillite-boehmite type Composition: 48-63% Al2O3, 2-14% SiO2, 20-30% Fe2O3. Hungarian bauxites are characterized by increased contents of P2Os, V2O5 and Cr2O3. Reserves are estimated at 200-250 million tons.
Mining is concentrated in the Gant and Iskaszent-Dverd deposits, which provide up to 80% of all bauxite production in Hungary. In 1960, more than 1,150,000 tons were mined.
Romania. The most important deposits are located in Transylvania in the Bihar mountains. The size of individual deposits is small. Bauxite is mainly of the diaspore type. Composition: 49-71% Al2O3, 2-9% SiO2, 3-30% Fe2Oa. Total reserves are estimated at 40 million tons.
China. Bauxite deposits are located within the Korea-China platform. There are two known genetic types of deposits - sedimentary and residual (laterite), as well as two mineralogical types - diaspore and hydrargillite. The most important of them are located in the provinces of Shandong, Henan, and Gui-Zhou. Bauxite composition is 63-70% Al2O3, 20% SiO2, 1-5% Fe2O3. The reserves are very significant, but due to poor knowledge of the deposits, they are not completely taken into account. Deposits of high-alumina diasporic shales are large in scale.
Federal Republic of Germany. The only bauxite deposit, with reserves of only a few hundred thousand tons, is located in Hesse. Annual production is 7-8 thousand tons. The fairly powerful aluminum industry of Germany depends entirely on imports, mainly from Yugoslavia, France, and Italy. In 1956, Germany imported 1,312,100 tons of bauxite.
Switzerland, Sweden, Norway. They do not have their own bauxite deposits. The significant aluminum industry of these countries is based on the import of bauxite and alumina.
Great Britain. There are no bauxite deposits in England and Scotland proper. Bauxite has long been known in Northern Ireland(Antrim area). Currently, the best deposits have been developed and the scale of production is extremely small. Operation stopped completely in 1934, but resumed during the Second World War.
These bauxites are mainly supplied to the chemical industry. The type of bauxite is hydrargillite. Composition: 40-60% Al2O3, 3-7% SiO2, 1-20% Fe2O3, 17-28% p.p.
Imported bauxite is used to produce alumina. In 1957, bauxite imports amounted to 360 thousand tons. Bauxites are imported mainly from Ghana.
Bauxite is a rock composed of various minerals, mainly hydroxides and oxides of aluminum (alumina). In addition, they contain oxides, hydroxides and silicates of iron, silica (silicon oxide), quartz and other chemicals. Total chemical elements, found as part of this breed - about a hundred. Since bauxite has a complex composition, it does not have a clearly defined chemical formula.
What is bauxite
Bauxite was discovered by French geologist Pierre Berthier in 1821 near the village of Le Beau, where the researcher spent his summer vacation. The rock got its name in honor of this village. Berthier himself did not attach much importance to his discovery. He had no idea that this rock would in the future become the most important raw material for the production of aluminum.
Appearance and physical properties
In appearance, this rock is similar to clay, but can also have a rocky appearance. Their color is very diverse - from almost white to almost black, but the most common are dark red, gray or brown. Opaque, insoluble in water. Density depends on iron content and usually ranges from 2900–3500 kg/m3, but can be significantly less. When mixed with water, bauxite does not form a plastic mass, unlike clay.
Their structure may be dense or porous. Often you can find small inclusions in them in the form of rounded bodies formed by iron oxides or alumina. Such bauxites look very decorative. The hardness of the rock ranges from 2 to 7 units on the Mohs scale.
Chemical composition
In addition to the main components - aluminum hydroxide, iron and silicon compounds, bauxite contains many chemical elements- sodium, potassium, magnesium, chromium, zirconium, gallium, vanadium, as well as compounds such as carbonates, calcites, titanites. From a human point of view, the most important are aluminum compounds - the more of them, the more valuable the ore. Silicon oxide, on the contrary, worsens the quality of the rock.
Part may include such minerals, like diaspora, boehmite, gibbsite. They are rock-forming. In addition, the composition often contains associated minerals - for example, goethite, chlorites, kaolinite and others.
Bauxites are similar to clays, but they also have significant difference- aluminum is contained in them in the form of hydroxide, and in clays - in the form of kaolinite.
Main varieties
Depending on their chemical composition, all bauxites can be divided into three main groups:
- Monohydroxide (rock-forming minerals - diaspores or boehmite).
- Trihydroxide (gibbsites).
- Mixed, combining the properties of both the first and second groups.
The latter are the most common.
According to the method of formation, bauxites are divided into lateritic - also called residual - and redeposited (or sedimentary). The first ones are formed in areas with tropical climates as a result of deep chemical processes, occurring in aluminosilicate rocks under conditions of high humidity and temperature, and the second - as a result of the transfer and redeposition of weathering products. They often occur in layers. Since these layers differ in quality, it is more difficult to process such ore.
Usage
The main application of bauxite ore is the production of aluminum. In addition, it is used as a flux in ferrous metallurgy, in the production of paints, in the abrasive industry, for the production of electrocorundum, high-alumina refractories. Bauxite is also used to make aluminous cement - a fast-hardening composition with high astringent properties, which has proven itself during construction work at low temperatures.
Application in jewelry
Bauxite is not a promising stone for jewelers; it can only be found occasionally designer jewelry made from it. However, by giving the stone a ball shape and polishing it, they get beautiful souvenirs. No healing or magical qualities are attributed to bauxite.
How bauxite is formed
This rock is formed by the weathering of minerals containing aluminum, such as feldspars. They usually collapse, forming clays, but the hot climate and high humidity promote the removal of silica and alkalis, therefore in tropical countries Most of the bauxite deposits are concentrated. There are two ways of formation of this rock - residual-chemogenic and sedimentary-chemogenic. Sedimentary bauxites are formed as a result of the accumulation of weathering products in lowlands and pits.
Place of Birth
About 90 percent of the world's bauxite reserves are found in laterite deposits. With prolonged weathering of aluminosilicate rocks in hot and humid climates, so-called lateritic crusts are formed. The leaders in bauxite reserves are Guinea, Australia and Brazil. India, Vietnam, Indonesia, Jamaica, Mali and Cameroon also have significant numbers of them.
Bauxite reserves in Russia
There are few bauxite deposits in Russia, so most of this raw material has to be purchased abroad. The best quality Russian bauxites are mined in the North Ural bauxite-bearing region. These reserves were discovered in 1931 year by geologist N.A. Karzhavin. The ore lies at a depth of 700–1000 m and is mined using the mining method. There is one deposit in Leningrad region. IN
Arkhangelsk region produces high alumina bauxite and low silicon content, their development is underway open method. Their main disadvantage is the high percentage of chromium and gypsum in the rock composition. The Vislovskoye deposit is located in the Belgorod region, the quality of the ore is low due to great content carbonates.
The deposits discovered in the late 60s in the north-west of the Komi Republic are considered promising, however their ore quality is average Moreover, their extraction is complicated by the uninhabited nature of the area and poor transport infrastructure. Despite this, in 1997, the first batch of bauxite raw materials from Komi was delivered to the Ural Aluminum Smelter, having successfully passed industrial tests. In addition to aluminum, the raw materials from these deposits contain rare metals, which gives them additional value. Bauxite is also mined in the Angara region; its distinctive feature is high content free aluminum oxide in the form of corundum (up to 10%).
Extraction and processing
Most often they are mined by open pit mining, but underground mining is also used. The choice of bauxite processing technology depends on its quality. In any case, the process includes two stages:
- obtaining alumina (chemical methods);
- release of aluminum (electrolysis).
Alumina from ore High Quality mine using the Bayer process, in which finely ground bauxite is treated with a sodium hydroxide solution to form a sodium aluminate solution. The resulting solution is purified from red mud, and alumina (aluminum hydroxide) is precipitated from it.
To process low quality bauxite it is necessary apply more complex method - they are crushed, mixed with limestone and soda and sintered in special rotary kilns. The resulting product is treated with alkali, the precipitated hydroxide is separated and filtered.
At one plant they can used in parallel both of these processes. This allows you to process ore of different qualities at the same time. It is also possible to use these methods sequentially, sintering the remaining slag after using the Bayer method and extracting additional alumina from it.
BOXITES [called area of Les Baux in the south of France, where bauxite deposits were first discovered], bauxite, consisting mainly of aluminum hydroxides (aluminum gel, gibbsite, boehmite, diaspores, etc.), oxides and hydroxides of iron and clay minerals. The color is red in various shades, brownish-brown, less often white, yellow, gray (to black). They are found in the form of dense (rocky) or porous formations, as well as in the form of loose earthy and clay-like masses. Based on their structure, they are classified as clastic (pelite, sandstone, gravelite, conglomerate) and concretionary (oolitic, pisolite, leguminous); by texture - homogeneous, layered and other bauxites. Density varies from 1800 kg/m 3 (loose) to 3200 kg/m 3 (rocky). According to the predominant mineral composition, bauxites are distinguished: monohydroxide (diaspore, boehmite), trihydroxide (gibbsite) and mixed composition (diaspore-boehmite, boehmite-gibbsite, chamosite-boehmite, chamosite-gibbsite, gibbsite-kaolinite, goethite-chamosite-boehmite, etc.). ).
Bauxites are formed during deep chemical transformations (lateritization) of aluminosilicate rocks in a humid tropical climate (lateritic or residual bauxites) or during the transfer of lateritic weathering products and their redeposition (sedimentary bauxites). As a result of the superposition of these processes, bauxites of a mixed (polygenic) type are formed. The deposits are sheet-like, lens-shaped or irregularly shaped (karst pockets). The quality of lateritic bauxites is usually high (50% $\ce(Al_2O_3)$ and higher), sedimentary bauxites can range from high-grade (55–75% $\ce(Al_2O_3)$) to substandard (less than 37% $\ce (Al_2O_3)$ ). In Russia, the quality requirements for mined (commercial) bauxite are determined by GOST, as well as contractual terms between suppliers and consumers. Depending on the ratio (by weight) of alumina and silica content (the so-called silicon module), bauxite is divided into 8 grades. For the lowest grade (B-6, 2nd grade), the silicon module must be over 2 with an alumina content of at least 37%; for high-grade bauxites (B-0, B-00) the silicon module must be over 10 with an alumina content of 50% and more. In foreign classifications, bauxite with a silicon modulus of over 7 is classified as high-quality.
Bauxite deposits according to reserves are divided into large (over 50 million tons), medium (5–50 million tons) and small (up to 5 million tons). The reserves of the world's largest deposit, Boke (Guinea), are estimated at 2.5 billion tons. 83.7% of reserves are concentrated in lateritic deposits, 9.5% in polygenic deposits and 6.8% in sedimentary deposits.
Bauxite deposits have been explored in more than 50 countries around the world. Total bauxite reserves are estimated at 29.3 billion tons, confirmed reserves at 18.5 billion tons (2nd half of the 2000s). The largest confirmed reserves are in: Guinea (7.4 billion tons; over 40% of world reserves), Jamaica (2 billion tons; 10.8%), Brazil (1.9 billion tons; 10.3%) , Australia (1.8 billion tons; 9.7%), India (0.77 billion tons; 4.2%), Guyana (0.7 billion tons; 3.8%), Greece (0. 6 billion tons; 3.2%), Suriname (0.58 billion tons; 3.1%), China (0.53 billion tons; 2.8%). The largest bauxite province in the world is the West African bauxite province (or Guinea).
In Russia, the total reserves of bauxite are over 1.4 billion tons, proven reserves are over 1.1 billion tons (beginning of 2013). There are 57 deposits (including 4 large and 7 medium). The main bauxite reserves are concentrated in the Sverdlovsk region (about 1/3 of the reserves of the Russian Federation; sedimentary deposits of the North Ural bauxite-bearing region - large Cheremukhovskoye, medium - Red Cap, Kalinskoye, Novokalinskoye), the Komi Republic (26% of the reserves of the Russian Federation; polygenic deposits of the Vorykvinsky group of the Timan bauxite-bearing zones - large Vezhayu-Vorykvinskoye, medium - Verkhneshugorskoye, Vostochnoye), Arkhangelsk region (18% of reserves of the Russian Federation; large Iksinsky sedimentary deposit), Belgorod region (about 16% of reserves of the Russian Federation; large Vislovskoye laterite deposit, medium - Melikhovo-Shebekinskoye). Bauxite reserves have also been identified in the Krasnoyarsk and Altai territories, the Kemerovo region, the Republic of Bashkortostan, and the Leningrad region. Ores from Russian deposits, compared to foreign analogues, are of lower quality and more difficult development conditions. The richest ores ($\ce(Al_2O_3)$ 56%) are in the deposits of the Northern Urals; The largest (approx. 18% of Russian reserves) Iksinsky deposit is composed of low-quality bauxites.
World bauxite production exceeded 196 million tons/year (2nd half of the 2000s). Main producing countries: Australia (62.6 million tons/year), China (27 million tons/year), Brazil (22.8 million tons/year), Guinea (18.2 million tons/year), Jamaica (14.9 million tons/year), India (13.9 million tons/year). In Russia, the extraction of bauxite from the subsoil in 2012 amounted to 5.14 million tons; 9 deposits were developed, 6 of them in the Sverdlovsk region.
Alumina and aluminum are extracted from bauxite. Bauxite is also used in the production of paints, artificial abrasives (electrocorundum), as fluxes in ferrous metallurgy, and sorbents for purifying petroleum products from various impurities; low-iron bauxites - for producing high-alumina refractories, quick-hardening cements, etc. Bauxites are complex raw materials; in addition to aluminum and iron, they contain gallium, as well as titanium, chromium, zirconium, niobium, and rare earth elements.
According to the mineralogical composition, bauxites are divided into: 1) monohydrate - boehmite and diaspore, 2) trihydrate - gibbsite and 3) mixed. Both alumina monohydrates and trihydrates may be present in these types of ores. In some deposits, along with trihydrate, anhydrous alumina (corundum) is present.
Bauxite deposits in Eastern Siberia belong to two completely different types in terms of age, genesis, appearance and mineralogical composition. The first is a kind of argillite-like metamorphosed rocks with an unclear bean microstructure, and the second has a typical bean structure.
The main components of bauxite are oxides of aluminum, iron, titanium and silicon; oxides of magnesium, calcium, phosphorus, chromium and sulfur are contained in quantities from tenths of a percent to 2%. The content of gallium, vanadium and zirconium oxides is thousandths of a percent.
In addition to Al 2 O 3, boehmite-diaspore bauxites of Eastern Siberia are characterized by high contents of SiO 2 and Fe 2 O 3, and sometimes titanium dioxide (gibbsite type).
Technical requirements for bauxite are regulated by GOST, which standardizes the alumina content and its ratio to silica (silicon module). In addition, GOST provides for the content of harmful impurities in bauxite, such as sulfur, calcium oxide, and phosphorus. These requirements may vary depending on the processing method, the type of deposit and its technical and economic conditions for each deposit.
In diaspore-boehmite bauxites of Eastern Siberia, the characteristic bean structure is observed mainly only under a microscope, and the cementing material predominates over the beans. Among bauxites of this type, two main varieties are distinguished: diaspore-chlorite and diaspore-boehmite-hematite.
In deposits of the gibbsite type, bauxites with a typical bean structure predominate, among which there are: dense, rocky and weathered, destroyed, called loose. In addition to stony and friable bauxites, a significant portion consists of clayey bauxites and clays. The legume part of stony and friable bauxites is composed mainly of hematite and magnetite. The sizes of the beans range from fractions of a millimeter to a centimeter. The cementing part of stony bauxites, as well as bauxite varieties, is composed of fine-grained and finely dispersed clay minerals and gibbsite, usually colored reddish-brown by iron hydroxides.
The main rock-forming minerals of bauxite of the diaspore-boehmite type are chlorite-daphnite, hematite, diaspore, boehmite, pyrophyllite, illite, kaolinite; impurities - sericite, pyrite, calcite, gypsum, magnetite, zircon and tourmaline. The presence of chlorite, as well as high-silica aluminosilicates - illite and pyrophyllite, determines the high content of silica in bauxites. Mineral grain sizes from fractions of a micron to 0.01 mm. Minerals in bauxite are in close association, forming finely dispersed mixtures, and only in certain areas and thin layers do some minerals form segregations (chlorite) or beans. In addition, various substitutions and changes in minerals are often observed due to the processes of weathering and metamorphism.
The rock-forming minerals of gibbsite-type bauxites are aluminum trihydrate - gibbsite, hematite (hydrohematite), goethite (hydrogoethite), maghemite, kaolinite, halloysite, hydromicas, quartz, rutile, ilmenite and anhydrous alumina (corundum). Impurities are represented by magnetite, tourmaline, apatite, zircon, etc.
The main mineral of alumina - gibbsite - is observed in the form of a finely dispersed, weakly crystallized mass and, less often, relatively large ones (0.1–0.3 mm) crystals and grains. Finely dispersed gibbsite is usually colored by iron hydroxides in yellowish and brown colors and almost does not polarize under a microscope. Large gibbsite grains are characteristic of stony bauxites, where they form crustified rims around the beans. Gibbsite is closely associated with clay minerals.
Titanium minerals are represented by ilmenite and rutile. Ilmenite is present both in the cementing part of bauxite and in the legume part in the form of grains ranging in size from 0.003–0.01 to 0.1–0.3 mm. Rutile in bauxite is finely dispersed, ranging in size from fractions to 3–8 mk And
2. Study of material composition
When studying the material composition of bauxites, as follows from the above, we are dealing with amorphous, finely dispersed and fine-grained minerals located in close paragenetic intergrowths and almost always colored by iron oxides and hydroxides. Therefore, in order to carry out qualitative and quantitative mineralogical analysis of bauxite, it is necessary to use various research methods.
From the original ore sample ground to -0.5 or -1.0 mm, take samples: one –10 G for mineralogical, second -10 g for chemical and third -5 G for thermal analyses. Samples of diaspore-boehmite bauxite are crushed to 0.01–0.07 mm and gibbsite – up to 0.1–0.2 mm.
Mineralogical analysis of the crushed sample is carried out after its preliminary decolorization, i.e. dissolution of iron oxides and hydroxides in oxalic and hydrochloric acid.
acids or alcohol saturated with hydrogen chloride. If carbonates are present, samples are first treated with acetic acid. In the resulting solutions, the content of oxides of iron, aluminum, silicon and titanium is determined chemically.
The mineralogical composition of the insoluble residue can be studied by separation in heavy liquids after preliminary disintegration and elutriation and by separation in heavy liquids without preliminary elutriation.
For a more complete study of clay minerals, elutriation (option I) is used, while clay fractions can be studied by other methods of analysis (thermal, X-ray diffraction) and without separation in heavy liquids. Option II analysis is the fastest, but less accurate.
Below we describe the main operations and analytical methods used in studying the material composition of bauxite.
Study under a microscope produced in transparent and polished sections and in immersion preparations. In a laboratory study, the entire complex of analyzes must be preceded by the study of bauxite in thin sections. Using thin sections prepared from various bauxite samples, the mineralogical composition, the degree of dispersion of minerals, the relationship of minerals with each other, the degree of weathering, structure, etc. are determined. In polished thin sections, minerals of iron oxides and hydroxides, ilmenite, rutile and other ore minerals are studied. It should be taken into account that minerals of iron oxides and hydroxides are almost always in close connection with clay and alumina minerals, therefore, as our studies have shown, their optical properties do not always coincide with the data of reference samples.
When studying the mineralogical composition of bauxites, especially their loose varieties, the immersion method is widely used. In immersion preparations, the mineralogical composition is studied mainly by the optical properties of minerals, and the quantitative ratio of minerals in the sample is also determined.
The study of bauxite rocks under a microscope in transparent and polished sections and immersion preparations must be carried out at maximum magnification. Even then, it is not always possible to determine the necessary morphological and optical properties of minerals and the nature of their fine intergrowths. These problems can be solved only with the simultaneous use of electron microscopic and electron diffraction research methods.
Exhaustion used to separate relatively coarse-grained fractions from fine-grained ones, which require other methods of study. For colored bauxites (brown, greenish), this analysis is carried out only after bleaching. The finest-grained bauxites, densely cemented, are elutriated after preliminary disintegration.
Disintegration of the bleached sample is carried out by boiling with a peptizer in Erlenmeyer flasks under reflux. Can be used as a peptizer whole line reagents (ammonia, liquid glass, soda, sodium pyrophosphate, etc.). The ratios of liquid and solid are assumed to be the same as for clays. In some cases, as, for example, in diaspore-boehmite bauxites, disintegration does not completely occur even with the help of a peptizer. Therefore, the non-disaggregated part is additionally ground in a mortar with light pressure with a rubber pestle.
There are various elutriation methods. For clayey rocks they are most fully described by M. F. Vikulova. We carried out elutriation of bauxite samples in liter glasses, as described by I. I. Gorbunov. Marks are made on the walls: top - for 1 l, 7 below her cm - for draining particles<1 mk and 10 “g below the liter mark - to drain particles > 1 mk. The exhausted liquid is drained using a siphon: the top 7 cm layer after 24 h(particles less than 1 mk), 10 cm layer after 1 h 22 min(particles 1–5 mk) and after 17 min 10 sec(particles 5–10 m.k). Factions larger than 10 mk scattered on sieves. To prevent the suspension from being sucked in from a depth below the design level, a tip designed by V. A. Novikov is placed on the lower end of the siphon lowered into the suspension.
From a fraction smaller than 1 mk or 5 mk in some cases using a supercentrifuge (with a rotation speed of 18–20 thousand. rpm) it is possible to isolate fractions enriched with particles of hundredths of a micron in size. This is achieved by changing the rate at which the suspension is fed into the centrifuge. The principle of operation and application of a supercentrifuge for granulometric analysis are described by K. K. Nikitin.
Gravity analysis for bauxite rocks is produced on electric centrifuges at 2000–3000 rpm in liquids specific gravity 3.2; 3.0; 2.8; 2.7; 2.5.
Separation of samples into monomineral fractions by centrifugation in heavy liquids without preliminary elutriation is almost impossible to achieve. Thin classes (1–5 mk) even after elutriation they are poorly separated in heavy liquids. This happens, apparently, due to high degree dispersion, as well as the finest accretion of minerals. Thus, before gravity analysis, it is necessary to separate samples into classes by elutriation. Thin classes (1–5 mk and sometimes 10 mk are studied by thermal, X-ray diffraction, microscopic and other methods without separation in heavy liquids. From larger fractions in heavy liquids, it is possible to separate diaspores from boehmite (liquid specific gravity 3.0), pyrite, ilmenite, rutile, tourmaline, zircon, epidote, etc. (in liquid specific gravity 3.2), boehmite to gibbsite and kaolinite (liquid specific gravity 2.8), gibbsite from kaolinite (liquid specific gravity 2.5).
It should be noted that for better separation in heavy liquids, bleached samples or fractions after elutriation are not dried to dryness, but are filled with heavy liquid in a wet state, since the dried sample may lose its ability to disperse. The use of gravity analysis in studying the mineralogical composition of bauxites is described in detail by E. V. Rozhkova et al.
Thermal analysis is one of the main methods for studying bauxite samples. As you know, bauxite is composed of minerals containing water. Depending on the change in temperature, various phase transformations occur in the sample, accompanied by the release or absorption of heat. The use of thermal analysis is based on this property of bauxite. The essence of the method and working methods are described in specialized literature.
Thermal analysis is carried out using various methods, most often using the heating curve method and the dehydration method. Recently, installations have been designed in which heating and dehydration (weight loss) curves are simultaneously recorded. Thermal curves are recorded both for the original samples and for fractions separately isolated from them. As an example, the thermal curves of the greenish-gray chlorite variety of diaspore bauxite and its individual fractions are given. Here, on the thermal curve of diaspore fraction II,
endothermic effect at a temperature of 560°, which corresponds to endothermic effects on curves I and III at temperatures of 573 and 556°. On the heating curve of clay fraction IV, the endothermic stops at 140, 652 and 1020° correspond to illite. The endothermic stop at 532° and weak exothermic effects at 816 and 1226° can be explained by the presence of a small amount of kaolinite. Thus, the endothermic effect at 573° on the original sample (curve I) corresponds to both diaspore and kaolinite, and at 630° – illite (652° on curve IV) and chlorite. When the sample has a polymineral composition, thermal effects superimpose; as a result, it is impossible to obtain a clear idea of the composition of the original rock without analyzing its constituent parts or fractions.
In gibbsite bauxites, the mineralogical composition is determined much more simply from thermal curves. All thermograms show an endothermic effect in the range from 204 to 588 ° with a maximum at 288–304 °, indicating the presence of gibbsite. In the same temperature range, iron hydroxides—goethite and hydrogoethite—lose water, but since the amount of water in them is approximately 2 times less than in gibbsite, the depth of the effect corresponding to iron hydroxides will be influenced by the amount of gibbsite. The second endothermic effect in the range of 500–752° with a maximum at 560–592° and the corresponding exothermic effect at 980–1020° characterize kaolinite.
Halloysite and muscovite, present in small quantities in the bauxites under study, are not reflected in the thermograms, except for a small endothermic effect at 116–180°, which apparently belongs to halloysite. The reason for this is small contents specified minerals and the imposition of a number of effects. In addition, if kaolinite and micas are present in the samples, then, as is known, even an insignificant admixture of kaolinite in mica is expressed in thermograms by the kaolinite effect.
The amount of gibbsite can be determined by the areas of the first endothermic effect. Areas are measured using a planimeter. The sample most enriched in gibbsite with the maximum content of alumina and water, and the lowest content of silica and iron oxides, can be taken as a standard. The value of A1 2 O 3 gibbsite in other samples is determined from the calculation
Where X- the value of the determined gibbsite A1 2 O 3;
S is the area of the endothermic gibbsite effect of the sample under study on the thermogram, cm 2,
A- content of A1 2 O 3 of the gibbsite reference sample;
K is the area of the reference sample on the thermogram, cm 2.
The dependence of the endothermic effect areas on the gibbsite content can be expressed graphically. To do this, the A1 2 O 3 content in percent is plotted along the abscissa axis, and the corresponding areas in square centimeters are plotted along the ordinate axis. By measuring the area of the endothermic effect corresponding to gibbsite on the curve, it is possible to calculate the A1 2 O 3 content in the test sample from the graph.
The dehydration method is based on the fact that minerals containing water tend to lose weight at certain temperatures. The amount of mineral in the sample is determined by weight loss. In some cases, especially when the temperature ranges of mineral dehydration overlap, this method is unreliable. Therefore, it should be used simultaneously with the recording of heating curves, although such a combined method is not always available due to the lack of special installations.
The simplest method for determining weight loss was developed at VIMS. To do this, you need to have a drying cabinet, muffle, thermocouple, torsion balance, etc. The method of work, the course of analysis and the results of its application for clays and bauxites are described in detail by V. P. Astafiev.
Weight loss during heating in each temperature range can be recalculated not by the amount of mineral, as V.P. Astafiev recommends, but by the amount of A1 2 O 3. contained in this mineral. The results obtained can be compared with chemical analysis data. The recommended 2-hour exposure at 300° for samples enriched with gibbsite is insufficient. The sample reaches a constant weight within 3–4 hours of heating, i.e., when all the gibbsite water is released. In clay varieties poor in gibbsite, its dehydration at 300° occurs completely in 2 h. Losses in the weight of samples at different temperatures can be expressed graphically if the temperature values (from 100 to 800°) are plotted along the abscissa axis, and the corresponding weight loss (H 2 O) as a percentage is plotted along the ordinate axis. The results of the quantitative determination of minerals using the method of V.P. Astafiev usually coincide well with the results of thermal analysis by area of effects and with the conversion to the mineral composition of chemical analysis of samples.
Chemical analysis gives the first idea of the quality of bauxites when studying their material composition.
The weight ratio of alumina to silica determines the value of the silicon modulus, which is a criterion for the quality of bauxite. The larger this module, the better the quality of bauxite. The modulus value for bauxite ranges from 1.5 to 12.0. The ratio of alumina content to loss on ignition (LOI) gives some idea of the type of bauxite. Thus, in gibbsite bauxites, the loss on ignition is significantly higher than in diaspore-boehmite bauxites. In the first, it ranges from 15 to 25%, and in the second, from 7 to 15%. Loss on ignition in bauxite is usually taken as the amount of H 2 O, since SO 3, CO 2 and organic matter are only rarely found in large quantities. Diaspore-boehmite bauxites contain calcite and pyrite as impurities. The sum of SO 3 and CO 2 in them is 1–2%. Gibbsite-type bauxites sometimes contain organic matter, but its amount does not exceed 1%. This type of bauxite is characterized by high contents of iron oxide (10–46%) and titanium dioxide (2–9%). Iron is presented mainly in the form of oxide and is part of hematite, goethite, magnetite and their hydrate forms. Diaspore-boehmite bauxites contain ferrous iron, the content of which ranges from 1 to 17%. Its high content is due to the presence of chlorite and small amounts of pyrite. In gibbsite-type bauxites, ferrous iron is part of ilmenite.
The presence of alkalis may indicate the presence of micas in bauxite rock. Thus, in diaspore-boehmite bauxites, the relatively high content of alkalis (K 2 O + Na 2 O = 0.5–2.0%) is explained by the presence of hydromicas of the illite type. Oxides of calcium and magnesium can be found in carbonates, clay minerals and chlorite. Their content usually does not exceed 1–1.5%. Chromium and phosphorus also constitute minor impurities in bauxite. Other impurity elements Cr, Mn, Cu, Pb, Ni, Zn, As, Co, Ba, Ga, Zr, V are present in bauxite in negligible quantities (thousandths and ten-thousandths of a percent).
When studying the material composition of bauxite, a chemical analysis of individual monomineral fractions is also performed. For example, in boehmite-diaspore and gibbsite fractions, the alumina content, losses on ignition and impurities - silica, oxides of iron, magnesium, vanadium, gallium and titanium dioxide - are determined. Fractions enriched in clay minerals are analyzed for silica content, total alkalis, alumina, calcium, magnesium, iron oxides and losses on ignition. High silica contents in the presence of alkalis in clay fractions from diaspore-boehmite bauxites indicate the presence of illite-type hydromicas. In the clay fractions of kaolinite-gibbsite bauxites, if alkalis and free silica minerals are absent, a high SiO 2 content may indicate high silica content of kaolinite.
According to chemical analysis, it is possible to recalculate the mineral composition. Chemical analysis of monomineral fractions is converted into molecular quantities, from which calculations are made chemical formulas studied minerals. Conversion of the chemical composition of bauxite to minerals is carried out to control other methods or as an addition to them. For example, if the main silica-containing minerals in a sample are quartz and kaolinite, then, knowing the amount of quartz, the remaining silica bound in kaolinite is determined. Based on the amount of silica per kaolinite, it is possible to calculate the amount of alumina required to bind it into the kaolinite formula. Based on the total content of kaolinite, it is possible to determine the amount of Al 2 O 3 present in the form of alumina hydrates (gibbsite or others). For example, the chemical composition of bauxite: 51.6% A1 2 O 3; 5.5% SiO 2; 13.2% Fe 2 O 3; 4.3% TiO 2 ; 24.7% p.p.p.; amount 99.3%. The amount of quartz in the sample is 0.5%. Then the amount of SiO 2 in kaolinite will be equal to the difference between its total content in the sample (5.5%) and SiO 2 of quartz (0.5%), i.e. 5.0%.
and the amount of A1 2 O 3 per 5.0% SiO 2 kaolinite will be
The difference between the total content of A1 2 O 3 in the rock (51.6) and A1 2 O 3 per kaolinite (4.2) is Ai 2 O 3 of alumina hydrates, i.e. 47.4%. Knowing that in the bauxites under study the alumina hydrate mineral is gibbsite, from the amount of A1 2 O 3 obtained for alumina hydrates (47.4%) we calculate the amount of gibbsite based on its theoretical composition (65.4% A1 2 O 3; 34.6 % H 2 O). In this case, the amount of alumina will be equal to
The data obtained can be monitored by the loss in weight upon ignition, which is taken here as the amount of H 2 O. Thus, to bind A1 2 O 3 = 47.4% into gibbsite, it is necessary
According to chemical analysis general content H 2 0 in the sample is 24.7 (pp. p.), i.e., it approximately coincides with the H 2 0 content in gibbsite. In this case, there is no water left for other minerals (kaolinite, iron hydroxides). Consequently, the amount of alumina equal to 47.4%, in addition to the trihydrate, also includes some amount of monohydrate or anhydrous alumina. The above example only shows the principle of recalculation. In reality, most bauxites are more complex in their mineralogical composition. Therefore, when converting a chemical analysis to a mineralogical analysis, data from other analyzes are also used. For example, in gibbsite bauxites, the amount of gibbsite and clay minerals should be calculated from dehydration or thermal analysis, taking into account their chemical composition.
However, despite the complexity of the mineralogical composition, for some bauxites it is possible to convert the chemical composition to the mineralogical one.
Phase chemical analysis. The basic principles of chemical phase analysis of bauxite are set out in the book by V.V. Dolivo-Dobrovolsky and Yu.V. Klimenko. When studying bauxites in Eastern Siberia, it turned out that this method in each specific case requires some changes and improvements. This is explained by the fact that the rock-forming minerals of bauxite, especially clayey ones, have wide solubility limits in mineral acids.
Chemical phase analysis for the study of bauxite is carried out mainly in two versions: a) incomplete chemical phase analysis (selective dissolution of one or a group of minerals) and b) complete chemical phase analysis.
Incomplete chemical phase analysis is performed, on the one hand, for the purpose of pre-processing samples for subsequent study of insoluble residues under a microscope, thermal, X-ray diffraction and other analyses, and on the other hand, for the quantitative determination of one or two components. The amount of minerals is determined by the difference in weights before and after dissolution or by recalculating the chemical composition of the dissolved part of the sample.
Using selective dissolution, the amount of iron oxides and hydroxides (sometimes chlorite) is determined. The issue of deferrization of bauxite is covered in detail in the works of VIMS. In diaspore-boehmite type bauxites, iron oxides and chlorites are dissolved in 6 N. HCl. In gibbsite bauxites, hydroxides and iron oxides are maximally (90–95%) extracted into solution when dissolved in alcohol saturated with hydrogen chloride (3 N), at L: T = 50. In this case, 5–10% of the total alumina passes into the solution its amount in bauxite, and titanium dioxide up to 40%. Bauxite decolorization can be carried out in 10% oxalic acid by heating in a water bath for 3–4 h at L: T = 100. Under these conditions, titanium-containing minerals dissolve less (about 10-15% TiO 2), but more are extracted into the alumina solution (25–40%), with iron oxides being extracted by 80–90%. Thus, to maximize the preservation of titanium minerals during bauxite bleaching, you need to use 10% oxalic acid, and to preserve alumina minerals, you need to use an alcohol solution saturated with hydrogen chloride.
The carbonates (calcite) present in some bauxites dissolve in 10% acetic acid when heated for 1 h at F: T=100 (see chapter “Copper sandstones”). Their dissolution should precede the bleaching of bauxite.
Incomplete chemical phase analysis is also used to quantify alumina minerals. There are several methods for their determination based on selective dissolution. In some bauxites, the amount of gibbsite can be determined fairly quickly by dissolving samples in 1 N. KOH or NaOH according to the method described by V.V. Dolivo-Dobrovolsky and Yu.V. Klimenko. Low-water and anhydrous alumina minerals - diaspores and corundum in bauxite can be determined by dissolving samples in hydrofluoric acid without heating, similar to the method for determining sillimanite and andalusite, described below. A. A. Glagolev and P. V. Kulkin indicate that corundum and diaspores from secondary quartzites of Kazakhstan in hydrofluoric acid in the cold for 20 h practically do not dissolve.
A complete chemical phase analysis, due to the unique material composition of bauxites and the different behavior during dissolution of the same minerals from different deposits, has its own specifics for each type of bauxite. After dissolving the kaolinite, A1 2 O 3 and SiO 2 are determined in the residue. Based on the content of the latter, the amount of pyrophyllite is calculated, while it must be borne in mind that silica is almost always present in the diaspora itself (up to 11%).
For gibbsite bauxites, in which monohydrate alumina minerals are absent or constitute a minor proportion, chemical phase analysis can be reduced to two or three stages. According to this scheme, gibbsite is dissolved by double treatment with alkali. Based on the content of A1 2 O 3 in the solution, the amount of gibbsite in the sample is calculated. But using the example of gibbsite bauxites in Eastern Siberia, it turned out that in individual samples more alumina is leached than is contained in the form of gibbsite. In these bauxites, free alumina, formed during the physicochemical decomposition of kaolinite, apparently passes into alkaline extracts. Taking into account the characteristics of gibbsite bauxites, when conducting chemical phase analysis, it is necessary to conduct parallel analysis without treating samples with alkali. First, the sample is dissolved in HCl of specific gravity 1.19 when heated for 2 h. Under these conditions, gibbsite, iron oxides and hydroxides are completely dissolved.
Spectral, X-ray diffraction and other analyzes are very effective in studying bauxite. As is known, spectral analysis gives a complete picture of the elemental composition of the ore. It is performed both for initial samples and for individual fractions isolated from them. Spectral analysis in bauxite determines the content of the main components (Al, Fe, Ti, Si), as well as trace elements Ga, Cr, V, Mn, P, Zr, etc.
X-ray diffraction analysis is widely used, making it possible to determine the phase composition of various fractions. Electron diffraction and electron microscopic studies are used for the same purpose. The essence of these analyses, methods for preparing drugs, and methods for interpreting the results are described in the specialized literature. It should be noted here that when studying with these methods great importance has a sample preparation method. For X-ray diffraction and electron diffraction methods of analysis, it is necessary to obtain more or less monomineral fractions, as well as to separate particles by size. For example, in diaspore-boehmite bauxites in a fraction of less than 1 mk X-ray diffraction analysis reveals only illite, and electron diffraction analysis reveals only kaolinite. This is due to the fact that illite is in the form of large particles that cannot be examined by electron diffraction (particles larger than 0.05 mk), and kaolinite, on the contrary, due to its high degree of dispersion, is detected only by electron diffraction. Thermal analysis confirmed that this fraction is a mixture of illite and kaolinite.
The electron microscopic method does not give a definite answer, since in bauxites, especially densely cemented ones, the natural shape of the particles is not preserved after grinding and dissolving the samples in acids. Therefore, viewing under an electron microscope has an auxiliary or controlling value for electron diffraction and X-ray diffraction analyses. It makes it possible to judge the degree of homogeneity and dispersion of a particular fraction, the presence of impurities, which can be reflected by the above-mentioned analyses.
Among other research methods, magnetic separation should be noted. Maghemite-hematite beans are isolated by a permanent magnet.