Process of titanium extraction

Titanium is produced by a magnesium-thermal method, the essence of which is enrichment of titanium ores, smelting titanium slag from them, followed by the production of titanium tetrachloride and the reduction of magnesium from the last metallic titanium.

The raw material for the production of titanium is titanomagnetite ores, from which an ilmenite concentrate containing 40-45% TiO2, ~ 30% FeO, 20% Fe2O3 and 5-7% of the waste rock is recovered. The name of this concentrate was obtained by the presence in it of the ilmenite mineral FeO * TiO2.

The ilmenite concentrate is melted in a mixture with charcoal, anthracite in ore-thermal furnaces, where iron and titanium oxides are reduced.
The resulting iron is enriched in carbon, and cast iron is produced, and the lower oxides of titanium turn into slag. Cast iron and slag are poured separately into molds.

The main product of this process is titanium slag. A by-product of this process is cast iron used in metallurgical production. The resulting titanium slag is subjected to chlorination in special furnaces. In the lower part of the furnace there is a carbon nozzle, which is heated by passing an electric current through it. Briquettes of titanium slag are fed into the furnace, and chlorine through the tuyeres. At a temperature of 800 – 1250 ° C in the presence of carbon, titanium tetrachloride and also chlorides are formed.

Titanium tetrachloride is separated and purified from the remaining chlorides due to the difference in the boiling point of these chlorides by rectification in special installations.

Titanium tetrachloride titanium is reduced in the reactors at a temperature of 950-1000 ° C. Magnesium is charged into the reactor; After evacuation of air and filling the cavity of the reactor with argon, a vaporous titanium tetrachloride is fed into it. Between the liquid magnesium and titanium tetrachloride there is a reaction of 2Mg + TiCl4 = Ti + 2MgCl2.

Solid titanium particles are sintered into a porous mass-sponge, and liquid MgCl2 is discharged through the tap of the reactor. The titanium sponge contains 35-40% magnesium and magnesium chloride.

To remove these impurities from the titanium sponge, it is heated to a temperature of 900-950 ° C in a vacuum. Titanium sponge is melted by vacuum-arc remelting.

Vacuum in the furnace protects titanium from oxidation and helps to clean it from impurities. The resulting ingots of titanium have defects, so they are re-melted again, using both consumable electrodes. After that, the purity of titanium is 99.6 – 99.7%. After secondary remelting, ingots are used for pressure treatment.

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Process of magnesium extraction

Magnesium is a silvery white metal. Its most important physical property is a low density (p = 1.74 g / cm at 20 ° C). There are twelve electrons in the electron shell of the magnesium atom. Two electrons 3s located in the outer orbit can easily be torn off, which leads to the formation of the Mg’2 + ion, so magnesium is divalent in all known compounds.

Natural magnesium consists of a mixture of three stable isotopes. Moreover, the artificial isotope Mg with a half-decay of 10.2 h can be used as a radioactive indicator. Magnesium crystals have a compact hexagonal structure.

When magnesium is stored in dry air, an oxide film is formed on its surface, protecting the metal with a slight heating (up to 200 ° C) from further oxidation; In these conditions, the corrosion resistance of pure magnesium exceeds the resistance of low-carbon steel. However, in the humid air, its corrosion is greatly enhanced. It is practically not affected by kerosene, gasoline and mineral oils. However, it is not stable in aqueous solutions of salts (except fluorides) and is soluble in many mineral and organic acids.

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Magnesium in the form of ingots or products is not flammable. The ignition of magnesium can occur only at a temperature close to its melting point (651 ° C) or after melting, if it is not isolated from the oxygen of the air. Covered with a flux, the metal can be heated and melted. Powdered magnesium or a thin magnesium tape easily lights up from the match and burns with a dazzling white flame. Magnesium is non-magnetic and does not spark at impacts or friction.
In its free form it does not occur, but it comes in the form of carbonates, silicates in many rocks, and is also dissolved in sea and lake water in the form of chlorides and sulfates.

Currently, magnesia, dolomite, carnallite, as well as sea water and waste from a number of industries are used to produce magnesium.
Natural mineral magnesite, in addition to magnesium carbonate, MgCO3 usually contains calcium carbonate, quartz, and also impurities of other minerals, including aluminum and iron oxides. For the production of magnesium, only pure caustic magnesite obtained by the reaction MgCO3 = MgO + CO2 is used when the natural magnesite is heated (roasted) to 700-900 ° C.

Dolomite is a rock, which is a double calcium and magnesium carbonate MgCO3-CaCO3. Dolomites usually contain impurities of quartz, calcite, gypsum, etc. The content and color of the impurities determine the color of the rock. Dolomite is widespread in nature and accounts for about 0.1% of all rocks that make up the earth’s crust. Dolomite, like magnesite, is preliminarily fired to obtain a mixture of oxides of MgO and CaO.
Carnallite is a natural magnesium chloride and potassium is a very hygroscopic crystalline substance, usually colored with impurities in pink, yellow or gray. Carnallite is subjected to hydrochemical treatment to separate bromine and some sodium chloride and potassium from it, resulting in the so-called artificial carnallite, which is used in the magnesium industry.
Inexhaustible reserves of magnesium in the form of bishofite MgCl2 * 6H, 0 in seawater; On average, 0.38% of MgCl2 is contained therein. In addition, in sea water there are magnesium compounds MgS04 (0.17%) and MgBr2 (0.01%).

Sea water is still rarely used to produce bischofite, as in many countries there are salt lakes, in which the content of magnesium chloride is much higher. In some ozepax of the Perekop group, for example, the content of magnesium chloride reaches 15% by the end of summer. In addition, a number of productions are now used as raw materials for the production of magnesium. In this case, especially, magnesium chloride, obtained by extracting titanium from its ores, is widely used.

The concept of an electrolytic process for the production of magnesium. In general, magnesium is produced by the electrolytic method, the most important stages of which are:
A) Preparation of pure anhydrous magnesium salts;
B) electrolysis of the melt of these salts
C) refining of magnesium.

Variants of the electrolytic method for the production of magnesium differ in the composition of the salts supplied to the electrolysis (carnallite, magnesium chloride, etc.), and by the method of obtaining these salts (chlorination of magnesite, dehydration of bischofite or carnallite). Chlorination of magnesite can be carried out similarly to chlorination of titanium oxide. Dehydration of carnallite is usually carried out in two stages: first by slow heating of natural carnallite in tubular furnaces, and then by melting the compound KCl * MgCl2 * H2O until the hydrated moisture is completely removed.

Electrolysis is carried out in molten chlorides of magnesium, potassium, sodium and calcium, since during the electrolysis of aqueous solutions of its salts, due to the negative magnesium potential, only hydrogen is released on the cathode.

Magnesium can be obtained by electrolysis of pure molten anhydrous magnesium chloride, but the high melting point, low electrical conductivity and other adverse properties of this salt force the use of electrolytes of more complex composition. It is more convenient to conduct electrolysis of carnallite, which usually contains sodium chloride as an impurity. This electrolyte has a lower melting point, a higher electrical conductivity and less dissolves magnesium. Therefore, when working with it, less energy is consumed.
Magnesium baths are connected in series in a series of 60-100 pcs. The number of baths in a series is determined by the voltage of a source of direct electric current; The tension of the bath, which depends on its design, the distance between poles, the composition of the electrolyte, varies between 5.5-7.5 V.

Maintenance of baths is to perform the following basic operations:
A) feeding with electrolyte;
B) temperature control;
C) extraction of magnesium;
D) removal of sludge.

Power baths with electrolyte. In the process of electrolysis there is a continuous decomposition of magnesium chloride, therefore fresh water is added to the bath periodically to fill fresh molten salt salts. It is most convenient to add anhydrous magnesium chloride to the electrolyte resulting from the reduction of titanium chloride by magnesium. In the case of an autonomous location of the magnesium plant bischofite must first be dehydrated. You can enter into the bath and anhydrous carnallite, but then you need to drain some of the electrolyte, since otherwise it will have an excess of potassium chloride. Potassium fertilizers are obtained from the spent electrolyte.

Temperature control. Electrolysis should proceed at a temperature of 690-720 ° C, with the lower limit desirable to adhere to when feeding the baths with magnesium chloride, and the top – when feeding carnallite. In the process of electrolysis, it is necessary to observe the temperature of the electrolyte, since a deviation from the norm, especially upward, considerably worsens the process parameters.

In magnesium baths, temperature regulation does not change the interpolar distance, as is customary in the electrolytic production of aluminum, but changes the composition, and with it the conductivity of the electrolyte. So, for example, to raise the temperature of the electrolyte, it is necessary to fill it with more pure magnesium chloride, which will increase the resistance of the electrolyte. Changes in temperature within 20-30 ° C can be achieved by varying the amount of aspirated gases from the cathode space of the bath.

In case of overheating of the electrolyte, the loading of solid sodium chloride is used; When the temperature drops excessively, for example, when the bath is turned off, the electrolyte is heated by alternating current, lowering the nichrome spirals into the cathode cells.

Extraction of magnesium from the cell. This is usually done at least once a day, using vacuum ladles. The bucket is preheated by the heating elements incorporated in it and then fed to the baths by a bridge crane. After creating a vacuum of 730-800 kPa in the cell of the bath, lower the suction pipe and open the valve. Metal and some of the electrolyte are sucked into the bucket. Then the valve is closed and the operation is repeated in the other cells of the bath.

Sludge removal. In the electrolyte with magnesium chloride, magnesium oxide also enters; In addition, hydrolysis of the electrolyte may occur to form magnesium oxide. It settles on the bottom of the cell, dragging along with other products and forming sludge. The sludge is removed once every two to three days, without allowing a significant accumulation of it on the bottom of the bath, as this sometimes leads to the closure of the anode with the cathode and worsens the conditions for the deposition of magnesium on the cathode.

Electrolytic method of magnesium production

General information about magnesium

Magnesium is a silvery white metal. Its most important physical property is a low density, equal to 1.738 g / cm3 (at 20 ° C).
Natural magnesium consists of a mixture of three stable isotopes. Moreover, the artificial isotope Mg28 with a half-decay of 21.3 h can be used as a radioactive indicator. Magnesium crystals have a compact hexagonal structure.

Magnesium in the form of ingots or products is not flammable. The ignition of magnesium can occur only at a temperature close to its melting point (651 ° C) or after melting, if it is not isolated from the oxygen of the air. Magnesium is not magnetic and does not spark when struck or rubbed.

The strength and other mechanical properties of magnesium depend very much on its purity and the way the sample is prepared.
Currently, magnesium is used for magnesium, dolomite, carnallite, as well as sea water and waste from a number of industries.

Magnesite – magnesium carbonate MgCO3. Natural mineral magnesite usually contains calcium carbonate, quartz, and also impurities of other minerals, including aluminum and iron oxides.
For the production of magnesium, only pure caustic magnesite obtained by the reaction of MgCO3 = MgO + CO is used, when natural magnesite is heated (roasted) to 700-900 ° C

Dolomite is a rock, which is a double calcium and magnesium carbonate MgCO3-CaCO3. Dolomites usually contain impurities of quartz, calcite, gypsum, etc. The content and color of the impurities determine the color of the rock. Dolomite is widespread in nature and accounts for about 0.1% of all rocks that make up the earth’s crust. Dolomite, as well as magnesite, used magnesium industry, pre-fired to obtain a mixture of oxides of MgO and CaO.

Carnallite MgC12 • KC1 • 6H2O – natural chloride of magnesium and potassium is a very hygroscopic crystalline substance, usually colored with impurities in pink, yellow or gray.

The concept of an electrolytic method for the production of magnesium

In general, magnesium is produced by the electrolytic method, the most important stages of which are: a) obtaining pure anhydrous magnesium salts; B) electrolysis of these salts in the molten state and c) refining of magnesium.

Variants of the electrolytic process for the production of magnesium are known, differing in composition of the salts supplied to electrolysis (carnallite, magnesium chloride, etc.), and by the method of obtaining these salts (chlorination of magnesite, dehydration of magnesium chloride, etc.). Electrolysis is carried out in molten chlorides of magnesium, potassium, sodium and calcium, since during the electrolysis of aqueous solutions of its salts, due to the negative magnesium potential, only hydrogen is released on the cathode.

Anodes are graphite plates 4, cathodes are steel plates 2. Since the density of the molten electrolyte is greater than the density of magnesium under the same temperature conditions, the liquid magnesium released on the cathode, not dissolving in the electrolyte, floats up onto its surface. At the anode, gaseous chlorine is released, which also rises and is ejected from the electrolyte. In order to avoid the interaction of chlorine and magnesium and the short circuit of the anode and cathode with molten magnesium, a septum is installed at the top, which is usually called a diaphragm. During the electrolysis, magnesium chloride is used, periodically added to the electrolyte.

The magnesium that is collected on the surface of the cathode space is periodically removed. The chlorine liberated in the anode space is sucked through the pipes 3 and used, for example, for the chlorination of magnesium oxide or titanium oxide.

Power baths with electrolyte. In the process of electrolysis there is a continuous decomposition of magnesium chloride, so to fill it in the bath, fresh molten chloride salts are periodically introduced.

Temperature control. Electrolysis should proceed at a temperature of 690-720 ° C, with the lower limit desirable to adhere to when feeding the baths with magnesium chloride, and the top – when feeding carnallite. In the process of electrolysis it is necessary to observe the temperature of the electrolyte, since the deviation from the norm, especially upward, considerably worsens the indices.

Extraction of magnesium from the cell. This is usually done at least once a day, using vacuum buckets (Fig. 173).
Sludge removal. In the electrolyte with magnesium chloride, magnesium oxide also enters; In addition, hydrolysis of the electrolyte may occur to form magnesium oxide. Magnesium oxide settles on the bottom of the cell, dragging along with other products and forming sludge.

The impurities contained in the magnesium can be divided into two groups.

The first group is metal impurities that enter magnesium when it is obtained. The most important of them are iron, sodium and potassium, which fall into magnesium as a result of the electrolytic decomposition of their compounds, which are present in the electrolyte composition or that have got into it with the raw material.

The second group is nonmetallic impurities mechanically trapped during the extraction of magnesium from the bath. These include mainly chlorides of calcium, magnesium, sodium and potassium, magnesium oxide, as well as magnesium nitride and silicide.

Many different fluxes have been proposed for refining magnesium. An example is the flux VI-2, containing 38-46% MgCl2; 32-40% KCl; 3-5% CaF2; 5-8% BaCl2, used for melting magnesium, for melting its alloys in stationary crucibles and in induction furnaces. This flux refines the metal well and melts at 420 ° C. The VI-3 flux usually contains 34-40% MgCl2; 25-36% of KC1; 15-20% of CaP2; 7-10% MgO; It is universal for the melting of magnesium alloys in withdrawable crucibles. When refining to the end of the process as the metal slowly quenches, the slag formed by it solidifies, turning into a solid crust.
The best results of refining can be obtained by subliming magnesium in a vacuum, which is described in the purification of sponge titanium after its reduction with magnesium.

Refractory materials in the metallurgical industry

The materials used to lining the working space of these devices are called refractory (refractories). They are made mainly from stable natural minerals, giving them the form of bricks, powders and various shaped products. By chemical properties refractory materials are divided into acidic, basic and neutral.

A typical acid refractory is a dinas bricks made of quartz (93-96% SiO2) with a small addition of lime (2-3% CaO) for bonding. It has refractoriness (softening point by its own weight) 1650-1730 ° C and is used for laying furnaces working with acidic slags containing a large amount of SiO2.

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A characteristic basic refractory is magnesite brick made from natural magnesite baked at high temperature (91-94% MgO, the rest is CaO, A12OS, SiO2, Fe2O3). In addition, the basic refractory-dolomite (CaO-fMgO) is widely used as a crushed and calcined natural mineral. The basic refractories are resistant to lime (basic) slags and dust to a temperature of 1800-1900 ° C.

The carbon refractories that can withstand heating to 2000 ° C and interact little with very aggressive slags can be referred to as neutral ones. They are made of anthracite and other pure carbonaceous materials. They contain about 90% of carbon and are divided into coal and graphite. They are made of crucibles, electrodes or by them lining electrolytic baths for aluminum production and separate parts of other furnaces.
The chromites made of natural chromium iron ore are neutral. Chromite brick contains about 30% Cr2O3 and 25% MgO and Fe2O3.

A stable refractory is chromium-magnesite brick, made of a mixture of chromite and magnesite; Its chemical properties approach neutral with a chromite content of at least 28%, with a lower chromite content, these refractories have a weakly basic character.

The most common and cheap refractory is chamotte, made of baked clay (kaolinite Al2O3 • 2SiO2-2H2O), its chemical and refractory properties vary widely, depending on the chemical composition. Shamottes containing less than 60% SiO2 and 40% Al2O3 are resistant to acidic and basic slags and almost almost neutral. Shamottes containing more than 60% SiO2 and 30% A12O3, have weakly expressed acid properties, and clay refractories containing more than 65% SiO2 are called semi-acidic; They have the least refractoriness, but are cheap.

High-alumina refractories (А12О3 more than 45%) have very high refractoriness (up to 2000 ° С), high resistance to temperature drop and greater resistance against acidic and basic slags, but they are expensive.

Processing of constructional materials by cutting

The purpose of processing structural materials by cutting

The processing of structural materials by cutting refers to the process of separating a layer of material from a workpiece with cutting tools to obtain a part of the desired shape, given dimensions and surface roughness.
At present, most parts of machines receive the final shape and dimensions by machining by cutting machines. Only this treatment satisfies the increasing requirements for the accuracy of the dimensions and thoroughness of the surface finish.
Cutting processing determines the quality of the machines manufactured, their accuracy, durability, as well as reliability and cost. Despite the fact that the methods of obtaining blanks and processing them on metal cutting machines are continuously improved, the labor intensity of machine-tool operations in engineering constitutes the largest part, reaching 30-50% of the total laboriousness of manufacturing machines.

Types of workpieces and processing allowances

On metal-cutting machines from the blanks get the finished parts. Depending on the material, shape and dimensions of the workpiece machined on the machine, and also the nature of production, the main types of metal blanks are: castings of cast iron, steel and non-ferrous alloys; Forging and stamping of steel and non-ferrous alloys; Long products from steel and non-ferrous alloys, which comes in the form of rods and is cut into individual blanks.
The allowance is a layer of metal that is removed from the workpiece during processing. From the correct choice of allowances, rational consumption of metal and cost-effectiveness of processing depend.

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Working, adjusting and auxiliary movements in metal cutting machines

1. Types of movements in metal cutting machines

For machining by cutting (turning, drilling, milling, etc.), the workpiece and the cutting tool must perform certain movements. They are subdivided into working, or cutting movements, installation (adjustment) and auxiliary. Work movements are designed to remove chips, and installation and auxiliary – to prepare for this process.
Installation – the movements of the working organs of the machine, with the help of which the tool in relation to the workpiece occupies a position that allows it to remove a certain layer of material from it.
Auxiliary – the movements of the working organs of the machine, not having a direct relationship to cutting. Examples are: rapid displacement of working organs, switching of cutting speeds and feeds, etc.

2. Main movement and feed motion

Work movements are divided into main movement and feed motion. With the help of the main movement, the chips are removed, and the feed motion makes it possible to extend the cutting start to the untreated sections of the workpiece surface. For example, during drilling, the rotation of the drill is the main movement that allows cutting to start when the drill is in contact with the workpiece, and moving the drill along the axis is a feed motion that makes it possible to extend the process to subsequent volumes of metal and thus drill the required hole.

3. Types of main movement and feed motion

In metal-cutting machines, the main motion is most often rotational (turning, drilling, milling, grinding machines) or rectilinear (reciprocating – planing and grooving machines). The main movement can be communicated to the workpiece (lathe lathes, planing machines) or cutting tools (milling, drilling, cross-planing machines).
In machines with a main rotary motion, the feed is continuous and the cutting is also continuous. In machines with reciprocating motion, the working stroke alternates with idling, the feed movement is carried out before the beginning of each working stroke and, consequently, the cutting is intermittent.