Enrichment of tin and tungsten ores and placers. Maintenance of the main method of enrichment of tungsten ores and the use of auxiliary dehydration processes in the technological scheme

The chemical element is tungsten.

Before describing the production of tungsten, it is necessary to make a short digression into history. The name of this metal is translated from German as “wolf cream”, the origin of the term goes back to the late Middle Ages.

When obtaining tin from various ores, it was noticed that in some cases it was lost, passing into a foamy slag, "like a wolf devouring its prey."

The metaphor took root, giving the name to the later received metal, it is currently used in many languages ​​​​of the world. But in English, French and some other languages, tungsten is called differently, from the metaphor "heavy stone" (tungsten in Swedish). The Swedish origin of the word is associated with the experiments of the famous Swedish chemist Scheele, who first obtained tungsten oxide from an ore later named after him (scheelite).

Swedish chemist Scheele, who discovered tungsten.

The industrial production of tungsten metal can be divided into 3 stages:

• ore beneficiation and production of tungsten anhydrite;
• reduction to powder metal;
• obtaining a monolithic metal.

Ore enrichment

Tungsten is not found in the free state in nature, it is present only in the composition of various compounds.

• wolframite
• scheelites

These ores often contain small amounts of other substances (gold, silver, tin, mercury, etc.), despite the very low content of additional minerals, sometimes their extraction during enrichment is economically feasible.

1. Enrichment begins with crushing and grinding of rock. Then the material goes to further processing, the methods of which depend on the type of ore. Enrichment of wolframite ores is usually carried out by the gravitational method, the essence of which is the use of the combined forces of earth gravity and centrifugal force, minerals are separated by chemical and physical properties - density, particle size, wettability. This is how waste rock is separated, and the concentrate is brought to the required purity using magnetic separation. The content of wolframite in the resulting concentrate ranges from 52 to 85%.
2. Scheelite, unlike wolframite, is not a magnetic mineral, so magnetic separation is not applied to it. For scheelite ores, the enrichment algorithm is different. The main method is flotation (the process of separating particles in an aqueous suspension) followed by the use of electrostatic separation. The concentration of scheelite can be up to 90% at the outlet. Ores are also complex, containing wolframites and scheelites at the same time. For their enrichment, methods are used that combine gravity and flotation schemes.
   
   If further purification of the concentrate to established standards is required, different procedures are used depending on the type of impurities. To reduce phosphorus impurities, scheelite concentrates are treated in the cold with hydrochloric acid, while calcite and dolomite are removed. To remove copper, arsenic, bismuth, roasting is used, followed by treatment with acids. There are other cleaning methods as well.

In order to convert tungsten from a concentrate to a soluble compound, several different methods are used.

1. For example, a concentrate is sintered with an excess of soda, thus obtaining sodium wolframite.
2. Another method can be used - leaching: tungsten is extracted with a soda solution under pressure at high temperature, followed by neutralization and precipitation.
3. Another way is to treat the concentrate with gaseous chlorine. In this process, tungsten chloride is formed, which is then separated from the chlorides of other metals by sublimation. The resulting product can be converted into tungsten oxide or directly processed into elemental metal.

The main result of various enrichment methods is the production of tungsten trioxide. Further, it is he who goes to the production of metallic tungsten. Tungsten carbide is also obtained from it, which is the main component of many hard alloys. There is another product of direct processing of tungsten ore concentrates - ferrotungsten. It is usually smelted for the needs of ferrous metallurgy.

Recovery of tungsten

The resulting tungsten trioxide (tungsten anhydrite) at the next stage must be reduced to the state of the metal. Restoration is most often carried out by the widely used hydrogen method. A moving container (boat) with tungsten trioxide is fed into the furnace, the temperature rises along the way, hydrogen is supplied towards it. As the metal is reduced, the bulk density of the material increases, the volume of container loading decreases by more than half, therefore, in practice, a run in 2 stages is used, through different types of furnaces.

1. At the first stage, dioxide is formed from tungsten trioxide, at the second stage, pure tungsten powder is obtained from dioxide.
2. Then the powder is sieved through a mesh, large particles are additionally ground to obtain a powder with a given grain size.

Sometimes carbon is used to reduce tungsten. This method somewhat simplifies production, but requires higher temperatures. In addition, coal and its impurities react with tungsten, forming various compounds that lead to metal contamination. There are a number of other methods used in production around the world, but in terms of parameters, hydrogen reduction has the highest applicability.

Obtaining monolithic metal

If the first two stages of industrial production of tungsten are well known to metallurgists and have been used for a very long time, then the development of a special technology was required to obtain a monolith from powder. Most metals are obtained by simple melting and then cast into molds, with tungsten due to its main property - infusibility - such a procedure is impossible. The method for obtaining compact tungsten from powder, proposed at the beginning of the 20th century by the American Coolidge, is still used with various variations in our time. The essence of the method is that the powder turns into a monolithic metal under the influence of an electric current. Instead of the usual melting, to obtain metallic tungsten, several stages have to be passed. At the first of them, the powder is pressed into special bars-rods. Then these rods are subjected to a sintering procedure, and this is done in two stages:

1. 1. First, at temperatures up to 1300ºС, the rod is pre-sintered to increase its strength. The procedure is carried out in a special sealed furnace with a continuous supply of hydrogen. Hydrogen is used for additional reduction, it penetrates into the porous structure of the material, and with additional exposure to high temperature, a purely metallic contact is created between the crystals of the sintered bar. The shtabik after this stage is significantly hardened, losing up to 5% in size.
   2. Then proceed to the main stage - welding. This process is carried out at temperatures up to 3 thousandºC. The post is fixed with clamping contacts, and an electric current is passed through it. Hydrogen is also used at this stage - it is needed to prevent oxidation. The current strength is very high, for rods with a cross section of 10x10 mm, a current of about 2500 A is required, and for a cross section of 25x25 mm - about 9000 A. The voltage used is relatively small, from 10 to 20 V. For each batch of monolithic metal, a test rod is first welded, it is used to calibrate the welding mode. The duration of welding depends on the size of the rod and usually ranges from 15 minutes to an hour. This stage, like the first one, also leads to a reduction in the size of the rod.

The density and grain size of the resulting metal depend on the initial grain size of the rod and on the maximum welding temperature. The loss of dimensions after two sintering steps is up to 18% in length. The final density is 17–18.5 g/cm².

To obtain high-purity tungsten, various additives are used that evaporate during welding, for example, oxides of silicon and alkali metals. As they heat up, these additives evaporate, taking other impurities with them. This process contributes to additional purification. When using the correct temperature regime and the absence of traces of moisture in the hydrogen atmosphere during sintering, with the help of such additives, the degree of purification of tungsten can be increased to 99.995%.

Manufacture of products from tungsten

Obtained from the original ore after the described three stages of production, monolithic tungsten has a unique set of properties. In addition to refractoriness, it has a very high dimensional stability, strength retention at high temperatures and the absence of internal stress. Tungsten also has good ductility and ductility. Further production most often consists in drawing the wire. These are technologically relatively simple processes.

1. The blanks enter the rotary forging machine, where the material is reduced.
2. Then, by drawing, a wire of various diameters is obtained (drawing is pulling a rod on special equipment through tapering holes). So you can get the thinnest tungsten wire with a total degree of deformation of 99.9995%, while its strength can reach 600 kg / mm².

Tungsten began to be used for the filaments of electric lamps even before the development of a method for the production of malleable tungsten. The Russian scientist Lodygin, who had previously patented the principle of using a filament for a lamp, in the 1890s proposed using a tungsten wire twisted into a spiral as such a filament. How was tungsten obtained for such wires? First, a mixture of tungsten powder with some kind of plasticizer (for example, paraffin) was prepared, then a thin thread was pressed out of this mixture through a hole of a given diameter, dried, and calcined in hydrogen. A rather fragile wire was obtained, the rectilinear segments of which were attached to the lamp electrodes. There were attempts to obtain a compact metal by other methods, however, in all cases, the fragility of the threads remained critically high. After the work of Coolidge and Fink, the manufacture of tungsten wire gained a solid technological base, and the industrial use of tungsten began to grow rapidly.

An incandescent lamp invented by the Russian scientist Lodygin.

World tungsten market

Tungsten production volumes are about 50 thousand tons per year. The leader in production, as well as in consumption, is China, this country produces about 41 thousand tons per year (Russia, for comparison, produces 3.5 thousand tons). An important factor at present is the processing of secondary raw materials, usually scrap tungsten carbide, shavings, sawdust and powdered tungsten residues, such processing provides about 30% of the world's consumption of tungsten.

Filaments from burned-out incandescent lamps are practically not recycled.

The global tungsten market has recently shown a decline in demand for tungsten filaments. This is due to the development of alternative technologies in the field of lighting - fluorescent and LED lamps are aggressively replacing conventional incandescent lamps both in everyday life and in industry. Experts predict that the use of tungsten in this sector will decrease by 5% per year in the coming years. Demand for tungsten as a whole is not decreasing, the drop in applicability in one sector is offset by growth in others, including innovative industries.

Tungsten minerals, ores and concentrates

Tungsten is a rare element, its average content in the earth's crust is Yu-4% (by mass). About 15 minerals of tungsten are known, however, only minerals of the wolframite group and scheelite are of practical importance.

Wolframite (Fe, Mn)WO4 is an isomorphic mixture (solid solution) of iron and manganese tungstates. If there is more than 80% iron tungstate in the mineral, the mineral is called ferberite, in the case of the predominance of manganese tungstate (more than 80%) - hübnerite. Mixtures lying in composition between these limits are called wolframites. Minerals of the wolframite group are colored black or brown and have a high density (7D-7.9 g/cm3) and a hardness of 5-5.5 on the mineralogical scale. The mineral contains 76.3-76.8% W03. Wolframite is weakly magnetic.

Scheelite CaWOA is calcium tungstate. The color of the mineral is white, gray, yellow, brown. Density 5.9-6.1 g/cm3, hardness according to the mineralogical scale 4.5-5. Scheelite often contains an isomorphic admixture of powellite, CaMo04. When irradiated with ultraviolet rays, scheelite fluoresces blue - blue light. At a molybdenum content of more than 1%, fluorescence becomes yellow. Scheelite is non-magnetic.

Tungsten ores are usually poor in tungsten. The minimum content of W03 in ores, at which their exploitation is profitable, is currently 0.14-0.15% for large and 0.4-0.5% for small deposits.

Together with tungsten minerals, molybdenite, cassiterite, pyrite, arsenopyrite, chalcopyrite, tantalite or columbite, etc. are found in ores.

According to the mineralogical composition, two types of deposits are distinguished - wolframite and scheelite, and according to the shape of ore formations - vein and contact types.

In vein deposits, tungsten minerals mostly occur in quartz veins of small thickness (0.3-1 m). The contact type of deposits is associated with zones of contact between granite rocks and limestones. They are characterized by deposits of scheelite-bearing skarn (skarns are silicified limestones). The skarn-type ores include the Tyrny-Auzskoye deposit, the largest in the USSR, in the North Caucasus. During the weathering of vein deposits, wolframite and scheelite accumulate, forming placers. In the latter, wolframite is often combined with cassiterite.

Tungsten ores are enriched to obtain standard concentrates containing 55-65% W03. A high degree of enrichment of wolframite ores is achieved using various methods: gravity, flotation, magnetic and electrostatic separation.

When enriching scheelite ores, gravity-flotation or purely flotation schemes are used.

The extraction of tungsten into conditioned concentrates during the enrichment of tungsten ores ranges from 65-70% to 85-90%.

When enriching complex or difficult-to-enrich ores, it is sometimes economically advantageous to remove intermediate products with a content of 10-20% W03 from the enrichment cycle for chemical (hydrometallurgical) processing, as a result of which "artificial scheelite" or technical tungsten trioxide is obtained. Such combined schemes provide a high extraction of tungsten from ores.

The state standard (GOST 213-73) provides for the content of W03 in tungsten concentrates of the 1st grade not less than 65%, the 2nd grade - not less than 60%. They limit the content of impurities P, S, As, Sn, Cu, Pb, Sb, Bi in the range from hundredths of a percent to 1.0%, depending on the grade and purpose of the concentrate.

The explored reserves of tungsten as of 1981 are estimated at 2903 thousand tons, of which 1360 thousand tons are in the PRC. The USSR, Canada, Australia, the USA, South and North Korea, Bolivia, Brazil, and Portugal have significant reserves. Production of tungsten concentrates in capitalist and developing countries in the period 1971 - 1985 fluctuated within 20 - 25 thousand tons (in terms of metal content).

Methods for processing tungsten concentrates

The main product of the direct processing of tungsten concentrates (in addition to ferrotungsten, smelted for the needs of ferrous metallurgy) is tungsten trioxide. It serves as the starting material for tungsten and tungsten carbide, the main constituent of hard alloys.

Production schemes for the processing of tungsten concentrates are divided into two groups depending on the accepted method of decomposition:

Tungsten concentrates are sintered with soda or treated with aqueous soda solutions in autoclaves. Tungsten concentrates are sometimes decomposed with aqueous solutions of sodium hydroxide.

Concentrates are decomposed by acids.

In cases where alkaline reagents are used for decomposition, solutions of sodium tungstate are obtained, from which, after purification from impurities, end products are produced - ammonium paratungstate (PVA) or tungstic acid. 24

When the concentrate is decomposed by acids, precipitation of technical tungstic acid is obtained, which is purified from impurities in subsequent operations.

Decomposition of tungsten concentrates. alkaline reagents Sintering with Na2C03

Sintering wolframite with Na2C03. The interaction of wolframite with soda in the presence of oxygen proceeds actively at 800-900 C and is described by the following reactions: 2FeW04 + 2Na2C03 + l/202 = 2Na2W04 + Fe203 + 2C02; (l) 3MnW04 + 3Na2C03 + l/202 = 3Na2W04 + Mn304 + 3C02. (2)

These reactions proceed with a large loss of Gibbs energy and are practically irreversible. With the ratio in wolframite FeO:MnO = i:i AG ° 1001C = -260 kJ / mol. With an excess of Na2C03 in the charge of 10-15% in excess of the stoichiometric amount, complete decomposition of the concentrate is achieved. To accelerate the oxidation of iron and manganese, sometimes 1-4% nitrate is added to the charge.

Sintering wolframite with Na2C03 at domestic enterprises is carried out in tubular rotary kilns lined with fireclay bricks. In order to avoid the melting of the charge and the formation of deposits (growths) in the zones of the furnace with a lower temperature, tailings from the leaching of cakes (containing iron and manganese oxides) are added to the charge, reducing the content of W03 in it to 20-22%.

The furnace, 20 m long and with an outer diameter of 2.2 m, at a rotation speed of 0.4 rpm and an inclination of 3, has a capacity of 25 t/day in terms of charge.

The components of the charge (crushed concentrate, Na2C03, saltpeter) are fed from the hoppers to the screw mixer using automatic scales. The mixture enters the furnace hopper, from which it is fed into the furnace. After exiting the kiln, the sinter pieces pass through the crushing rolls and the wet grinding mill, from which the pulp is sent to the upper polisher (Fig. 1).

Scheelite sintering with Na2C03. At temperatures of 800-900 C, the interaction of scheelite with Na2C03 can proceed according to two reactions:

CaW04 + Na2CQ3 Na2W04 + CaCO3; (1.3)

CaW04 + Na2C03 *=*■ Na2W04 + CaO + C02. (1.4)

Both reactions proceed with a relatively small change in the Gibbs energy.

Reaction (1.4) proceeds to an appreciable extent above 850 C, when decomposition of CaCO3 is observed. The presence of calcium oxide in the sinter leads, when the sinter is leached with water, to the formation of poorly soluble calcium tungstate, which reduces the extraction of tungsten into solution:

Na2W04 + Ca(OH)2 = CaW04 + 2NaOH. (1.5)

With a large excess of Na2CO3 in the charge, this reaction is largely suppressed by the interaction of Na2CO4 with Ca(OH)2 to form CaCO3.

To reduce the consumption of Na2C03 and prevent the formation of free calcium oxide, quartz sand is added to the mixture to bind calcium oxide into insoluble silicates:

2CaW04 + 2Na2C03 + Si02 = 2Na2W04 + Ca2Si04 + 2C02;(l.6) AG°100IC = -106.5 kJ.

Nevertheless, in this case, too, to ensure a high degree of tungsten extraction into the solution, a significant excess of Na2CO3 (50–100% of the stoichiometric amount) must be introduced into the charge.

The sintering of the scheelite concentrate charge with Na2C03 and quartz sand is carried out in drum furnaces, as described above for wolframite at 850–900°C. To prevent melting, leaching dumps (containing mainly calcium silicate) are added to the charge at the rate of reducing the content of W03 to 20-22%.

Leaching of soda specks. When cakes are leached with water, sodium tungstate and soluble salts of impurities (Na2Si03, Na2HP04, Na2HAs04, Na2Mo04, Na2S04), as well as an excess of Na2C03, pass into the solution. Leaching is carried out at 80-90 ° C in steel reactors with mechanical agitation, operating in hierio-

Concentrates with soda:

Elevator feeding the concentrate to the mill; 2 - ball mill operating in a closed cycle with an air separator; 3 - auger; 4 - air separator; 5 - bag filter; 6 - automatic weight dispensers; 7 - conveying auger; 8 - screw mixer; 9 - charge hopper; 10 - feeder;

Drum oven; 12 - roll crusher; 13 - rod mill-leacher; 14 - reactor with stirrer

Wild mode, or continuous drum rotary lixiviators. The latter are filled with crushing rods for crushing pieces of cake.

The extraction of tungsten from the sinter into the solution is 98-99%. Strong solutions contain 150-200 g/l W03.

Autoclave o-c One method of decomposition of tungsten concentrates

The autoclave-soda method was proposed and developed in the USSR1 in relation to the processing of scheelite concentrates and middlings. Currently, the method is used in a number of domestic factories and in foreign countries.

The decomposition of scheelite with Na2C03 solutions is based on the exchange reaction

CaW04CrB)+Na2C03(pacTB)^Na2W04(pacTB)+CaC03(TB). (1.7)

At 200-225 °C and the corresponding excess of Na2C03, depending on the composition of the concentrate, decomposition proceeds with sufficient speed and completeness. The concentration equilibrium constants of reaction (1.7) are small, increase with temperature, and depend on the soda equivalent (i.e., the number of moles of Na2C03 per 1 mole of CaW04).

With a soda equivalent of 1 and 2 at 225 C, the equilibrium constant (Kc = C / C cq) is 1.56 and

0.99 respectively. It follows from this that at 225 C the minimum required soda equivalent is 2 (i.e., the excess of Na2C03 is 100%). The actual excess of Na2C03 is higher, since the rate of the process slows down as equilibrium is approached. For scheelite concentrates with a content of 45-55% W03 at 225 C, a soda equivalent of 2.6-3 is required. For middlings containing 15-20% W03, 4-4.5 moles of Na2C03 per 1 mole of CaW04 are required.

CaCO3 films formed on scheelite particles are porous and up to a thickness of 0.1-0.13 mm their influence on the rate of scheelite decomposition by Na2CO3 solutions was not found. With intensive stirring, the rate of the process is determined by the rate of the chemical stage, which is confirmed by the high value of the apparent activation energy E = 75+84 kJ/mol. However, in case of insufficient stirring speed (which

Occurs in horizontal rotating autoclaves), an intermediate regime is realized: the rate of the process is determined both by the rate of supply of the reagent to the surface and the rate of chemical interaction.

0.2 0.3 0, it 0.5 0.5 0.7 0.8

As can be seen from Fig. 2, the specific reaction rate decreases approximately in inverse proportion to the increase in the ratio of molar concentrations of Na2W04:Na2C03 in solution. it

Ryas. Fig. 2. Dependence of the specific rate of scheelite decomposition by a soda solution in an autoclave j on the molar ratio of Na2W04/Na2C03 concentrations in the solution at

Causes the need for a significant excess of Na2C03 against the minimum required, determined by the value of the equilibrium constant. To reduce the consumption of Na2C03, a two-stage countercurrent leaching is carried out. In this case, the tailings after the first leaching, in which there is little tungsten (15-20% of the original), are treated with a fresh solution containing a large excess of Na2C03. The resulting solution, which is circulating, enters the first stage of leaching.

Decomposition with Na2C03 solutions in autoclaves is also used for wolframite concentrates, however, the reaction in this case is more complicated, since it is accompanied by hydrolytic decomposition of iron carbonate (manganese carbonate is only partially hydrolyzed). The decomposition of wolframite at 200-225 °C can be represented by the following reactions:

MnW04(TB)+Na2C03(paCT)^MiiC03(TB)+Na2W04(paCTB); (1.8)

FeW04(TB)+NaC03(pacT)*=iFeC03(TB)+Na2W04(paCTB); (1.9)

FeC03 + HjO^FeO + H2CO3; (1.10)

Na2C03 + H2C03 = 2NaHC03. (l. ll)

The resulting iron oxide FeO at 200-225 ° C undergoes a transformation according to the reaction:

3FeO + H20 = Fe304 + H2.

The formation of sodium bicarbonate leads to a decrease in the concentration of Na2CO3 in the solution and requires a large excess of the reagent.

To achieve satisfactory decomposition of wolframite concentrates, it is necessary to finely grind them and increase the consumption of Na2C03 to 3.5-4.5 g-eq, depending on the composition of the concentrate. High-manganese wolframites are more difficult to decompose.

The addition of NaOH or CaO to the autoclaved slurry (which leads to causticization of Na2C03) improves the degree of decomposition.

The decomposition rate of wolframite can be increased by introducing oxygen (air) into the autoclave pulp, which oxidizes Fe (II) and Mil (II), which leads to the destruction of the crystal lattice of the mineral on the reacting surface.

secondary steam

Ryas. 3. Autoclave unit with a horizontally rotating autoclave: 1 - autoclave; 2 - loading pipe for the pulp (steam is introduced through it); 3 - pulp pump; 4 - pressure gauge; 5 - pulp reactor-heater; 6 - self-evaporator; 7 - drop separator; 8 - pulp input into the self-evaporator; 9 - chipper made of armored steel; 10 - pipe for pulp removal; 11 - pulp collector

Leaching is carried out in steel horizontal rotating autoclaves heated with live steam (Fig. 3) and vertical continuous autoclaves with stirring of the pulp with bubbling steam. Approximate process mode: temperature 225 pressure in the autoclave ~ 2.5 MPa, ratio T: W = 1: (3.5 * 4), duration at each stage 2-4 hours.

Figure 4 shows a diagram of an autoclave battery. The initial autoclave pulp, heated by steam to 80-100 °C, is pumped into autoclaves, where it is heated to

secondary steam

Ditch. Fig. 4. Scheme of a continuous autoclave plant: 1 - reactor for heating the initial pulp; 2 - piston pump; 3 - autoclave; 4 - throttle; 5 - self-evaporator; 6 - pulp collector

200-225 °C live steam. In continuous operation, the pressure in the autoclave is maintained by discharging the slurry through a throttle (calibrated carbide washer). The pulp enters the self-evaporator - a vessel under pressure of 0.15-0.2 MPa, where the pulp is rapidly cooled due to intensive evaporation. The advantages of autoclave-soda decomposition of scheelite concentrates before sintering are the exclusion of the furnace process and a somewhat lower content of impurities in tungsten solutions (especially phosphorus and arsenic).

The disadvantages of the method include a large consumption of Na2C03. A high concentration of excess Na2C03 (80-120 g/l) entails an increased consumption of acids for the neutralization of solutions and, accordingly, high costs for the disposal of waste solutions.

Decomposition of tungstate conc.

Sodium hydroxide solutions decompose wolframite according to the exchange reaction:

Me WC>4 + 2Na0Hi=tNa2W04 + Me(0 H)2, (1.13)

Where Me is iron, manganese.

The value of the concentration constant of this reaction Kc = 2 at temperatures of 90, 120 and 150 °C is equal to 0.68, respectively; 2.23 and 2.27.

Complete decomposition (98-99%) is achieved by treating the finely divided concentrate with 25-40% sodium hydroxide solution at 110-120°C. The required excess of alkali is 50% or more. The decomposition is carried out in steel sealed reactors equipped with stirrers. The passage of air into the solution accelerates the process due to the oxidation of iron (II) hydroxide Fe (OH) 2 into hydrated iron (III) oxide Fe203-«H20 and manganese (II) hydroxide Mn (OH) 2 into hydrated manganese (IV) oxide Mn02-lH20 .

The use of decomposition with alkali solutions is advisable only for high-grade wolframite concentrates (65-70% W02) with a small amount of silica and silicate impurities. When processing low-grade concentrates, highly contaminated solutions and hard-to-filter precipitates are obtained.

Processing of sodium tungstate solutions

Solutions of sodium tungstate containing 80-150 g/l W03, in order to obtain tungsten trioxide of the required purity, have so far been mainly processed according to the traditional scheme, which includes: purification from compounds of impurity elements (Si, P, As, F, Mo); precipitation

Calcium tungsten mag (artificial scheelite) with its subsequent decomposition with acids and obtaining technical tungstic acid; dissolution of tungstic acid in ammonia water, followed by evaporation of the solution and crystallization of ammonium paratungstate (PVA); calcination of PVA to obtain pure tungsten trioxide.

The main drawback of the scheme is its multi-stage nature, carrying out most of the operations in a periodic mode, and the duration of a number of redistributions. An extraction and ion-exchange technology for converting Na2W04 solutions into (NH4)2W04 solutions has been developed and is already being used at some enterprises. The main redistributions of the traditional scheme and new extraction and ion-exchange variants of the technology are briefly considered below.

Purification of impurities

Silicon cleaning. When the content of Si02 in solutions exceeds 0.1% of the content of W03, preliminary purification from silicon is necessary. Purification is based on the hydrolytic decomposition of Na2Si03 by boiling a solution neutralized to pH=8*9 with the release of silicic acid.

The solutions are neutralized with hydrochloric acid, added in a thin stream with stirring (to avoid local peroxidation) to a heated solution of sodium tungstate.

Purification of phosphorus and arsenic. To remove phosphate and arsenate ions, the method of precipitation of ammonium-magnesium salts Mg (NH4) P04 6H20 and Mg (NH4) AsC) 4 6H20 is used. The solubility of these salts in water at 20 C is 0.058 and 0.038%, respectively. In the presence of an excess of Mg2+ and NH4 ions, the solubility is lower.

The precipitation of phosphorus and arsenic impurities is carried out in the cold:

Na2HP04 + MgCl2 + NH4OH = Mg(NH4)P04 + 2NaCl +

Na2HAsQ4 + MgCl2 + NH4OH = Mg(NH4)AsQ4 + 2NaCl +

After a long standing (48 hours), crystalline precipitates of ammonium-magnesium salts precipitate from the solution.

Purification from fluoride ions. With a high content of fluorite in the original concentrate, the content of fluoride ions reaches 5 g/L. Solutions are purified from fluoride - ions by precipitation with magnesium fluoride from a neutralized solution, to which MgCl2 is added. Purification of fluorine can be combined with hydrolytic isolation of silicic acid.

Molybdenum cleaning. Solutions of sodium tungstate" must be purified from molybdenum if its content exceeds 0.1% of the W03 content (i.e. 0.1-0.2 t / l). At a molybdenum concentration of 5-10 g / l ( for example, in the processing of scheelite-powellite Tyrny-Auzsky concentrates), the isolation of molybdenum is of particular importance, since it is aimed at obtaining a molybdenum chemical concentrate.

A common method is to precipitate the sparingly soluble molybdenum trisulfide MoS3 from a solution.

It is known that when sodium sulfide is added to solutions of tungstate or sodium molybdate, sulfosalts Na23S4 or oxosulfosalts Na23Sx04_x (where E is Mo or W) are formed:

Na2304 + 4NaHS = Na23S4 + 4NaOH. (1.16)

The equilibrium constant of this reaction for Na2Mo04 is much larger than for Na2W04(^^0 » Kzr). Therefore, if an amount of Na2S is added to the solution, sufficient only for interaction with Na2Mo04 (with a slight excess), then molybdenum sulfosalt is predominantly formed. With the subsequent acidification of the solution to pH = 2.5 * 3.0, the sulfosalt is destroyed with the release of molybdenum trisulfide:

Na2MoS4 + 2HC1 = MoS3 j + 2NaCl + H2S. (1.17)

Oxosulfosalts decompose with the release of oxosulfides (for example, MoSjO, etc.). Together with molybdenum trisulfide, a certain amount of tungsten trisulfide co-precipitates. By dissolving the sulfide precipitate in a soda solution and re-precipitating molybdenum trisulfide, a molybdenum concentrate is obtained with a W03 content of not more than 2% with a loss of tungsten 0.3-0.5% of the initial amount.

After partial oxidative roasting of the precipitate of molybdenum trisulfide (at 450-500 ° C), a molybdenum chemical concentrate is obtained with a content of 50-52% molybdenum.

The disadvantage of the method of precipitation of molybdenum in the composition of trisulfide is the release of hydrogen sulfide according to reaction (1.17), which requires expenses for the neutralization of gases (they use the absorption of H2S in a scrubber irrigated with a sodium hydroxide solution). The selection of molybdenum trisulfide is carried out from a solution heated to 75-80 C. The operation is carried out in sealed steel reactors, gummed or coated with acid-resistant enamel. The trisulfide precipitates are separated from the solution by filtration on a filter press.

Obtaining tungstic acid from solutions of sodium tungstate

Tungstic acid can be directly isolated from a solution of sodium tungstate with hydrochloric or nitric acid. However, this method is rarely used due to the difficulty of washing precipitates from sodium ions, the content of which in tungsten trioxide is limited.

For the most part, calcium tungstate is initially precipitated from the solution, which is then decomposed with acids. Calcium tungstate is precipitated by adding a CaCl2 solution heated to 80-90 C to a sodium tungstate solution with a residual alkalinity of the solution of 0.3-0.7%. In this case, a white finely crystalline, easily settled precipitate falls out, sodium ions remain in the mother liquor, which ensures their low content in tungstic acid. 99-99.5% W precipitates from the solution, mother solutions contain 0.05-0.07 g/l W03. The CaW04 precipitate washed with water in the form of a paste or pulp enters for decomposition with hydrochloric acid when heated to 90 °:

CaW04 + 2HC1 = H2W04i + CaCl2. (1.18)

During decomposition, a high final acidity of the pulp is maintained (90–100 g/l HCI), which ensures the separation of tungstic acid from impurities of phosphorus, arsenic, and partly molybdenum compounds (molybdic acid dissolves in hydrochloric acid). Precipitates of tungstic acid require thorough washing from impurities (especially from calcium salts

and sodium). In recent years, continuous washing of tungstic acid in pulsating columns has been mastered, which greatly simplified the operation.

At one of the enterprises in the USSR, when processing sodium tungstate solutions, instead of hydrochloric acid, nitric acid is used to neutralize the solutions and decompose CaW04 precipitates, and the precipitation of the latter is carried out by introducing Ca(N03)2 into the solutions. In this case, the nitric acid mother liquors are disposed of, obtaining nitrate salts used as fertilizer.

Purification of technical tungstic acid and obtaining W03

Technical tungstic acid, obtained by the method described above, contains 0.2-0.3% impurities. As a result of acid calcination at 500-600 C, tungsten trioxide is obtained, suitable for the production of hard alloys based on tungsten carbide. However, the production of tungsten requires trioxide of a higher purity with a total impurity content of no more than 0.05%.

The ammonia method for purifying tungstic acid is generally accepted. It is easily soluble in ammonia water, while most of the impurities remain in the sediment: silica, iron and manganese hydroxides, and calcium (in the form of CaW04). However, ammonia solutions may contain an admixture of molybdenum, alkali metal salts.

From the ammonia solution, as a result of evaporation and subsequent cooling, a crystalline precipitate of PVA is isolated:

Evaporation

12(NH4)2W04 * (NH4)10H2W12O42 4Н20 + 14NH3 +

In industrial practice, the composition of PVA is often written in the oxide form: 5(NH4)20-12W03-5H20, which does not reflect its chemical nature as an isopoly acid salt.

Evaporation is carried out in batch or continuous devices made of stainless steel. Usually 75-80% of tungsten is isolated into crystals. Deeper crystallization is undesirable in order to avoid contamination of the crystals with impurities. It is significant that most of the molybdenum impurity (70-80%) remains in the mother liquor. From the mother liquor enriched with impurities, tungsten is precipitated in the form of CaW04 or H2W04, which is returned to the appropriate stages of the production scheme.

PVA crystals are squeezed out on a filter, then in a centrifuge, washed with cold water and dried.

Tungsten trioxide is obtained by thermal decomposition of tungstic acid or PVA:

H2W04 \u003d "W03 + H20;

(NH4) 10H2W12O42 4H20 = 12W03 + 10NH3 + 10H20. (1.20)

Calcination is carried out in rotary electric furnaces with a pipe made of heat-resistant steel 20X23H18. The calcination mode depends on the purpose of tungsten trioxide, the required size of its particles. So, to obtain tungsten wire grade VA (see below), PVA is calcined at 500-550 ° C, wire grades VCh and VT (tungsten without additives) - at 800-850 ° C.

Tungstic acid is calcined at 750-850 °C. Tungsten trioxide derived from PVA has larger particles than trioxide derived from tungstic acid. In tungsten trioxide, intended for the production of tungsten, the content of W03 must be at least 99.95% for the production of hard alloys - at least 99.9%.

Extraction and ion-exchange methods for processing solutions of sodium tungstate

The processing of sodium tungstate solutions is greatly simplified when tungsten is extracted from solutions by extraction with an organic extractant, followed by re-extraction from the organic phase with an ammonia solution with separation of PVA from an ammonia solution.

Since in a wide range of pH=7.5+2.0 tungsten is found in solutions in the form of polymeric anions, anion-exchange extractants are used for extraction: salts of amines or quaternary ammonium bases. In particular, the sulfate salt of trioctylamine (i?3NH)HS04 (where R is С8Н17) is used in industrial practice. The highest rates of tungsten extraction are observed at pH=2*4.

Extraction is described by the equation:

4 (i? 3NH) HS04 (opr) + H2 \ U120 * "(aq) + 2H + (aq) ї \u003d ї

Ї \u003d ї (D3GSh) 4H4 \ U12O40 (org) + 4H80; (aq.). (l.2l)

The amine is dissolved in kerosene, to which a technical mixture of polyhydric alcohols (C7 - C9) is added to prevent the precipitation of a solid phase (due to the low solubility of amine salts in kerosene). The approximate composition of the organic phase: amines 10%, alcohols 15%, kerosene - the rest.

Solutions purified from mrlibden, as well as impurities of phosphorus, arsenic, silicon and fluorine, are sent for extraction.

Tungsten is re-extracted from the organic phase with ammonia water (3-4% NH3), obtaining solutions of ammonium tungstate, from which PVA is isolated by evaporation and crystallization. The extraction is carried out in mixer-settler type apparatuses or in pulsating columns with packing.

The advantages of extraction processing of sodium tungstate solutions are obvious: the number of operations of the technological scheme is reduced, it is possible to carry out a continuous process for obtaining ammonium tungstate solutions from sodium tungstate solutions, and production areas are reduced.

Wastewater from the extraction process may contain an admixture of 80-100 mg/l of amines, as well as impurities of higher alcohols and kerosene. To remove these environmentally harmful impurities, froth flotation and adsorption on activated carbon are used.

Extraction technology is used at foreign enterprises and is also implemented at domestic plants.

The use of ion-exchange resins is a direction of the scheme for processing sodium tungstate solutions that competes with extraction. For this purpose, low-basic anion exchangers containing amine groups (often tertiary amines) or amphoteric resins (ampholytes) containing carboxyl and amine groups are used. At pH=2.5+3.5, tungsten polyanions are sorbed on resins, and for some resins the total capacity is 1700-1900 mg W03 per 1 g of resin. In the case of resin in the 8C>5~ form, sorption and elution are described by the equations, respectively:

2tf2S04 + H4W12044; 5^"4H4W12O40 + 2SOf; (1.22)

I?4H4WI2O40 + 24NH4OH = 12(NH4)2W04 + 4DON + 12H20. (l.23)

The ion-exchange method was developed and applied at one of the enterprises of the USSR. The required contact time of the resin with the solution is 8-12 hours. The process is carried out in a cascade of ion-exchange columns with a suspended resin bed in a continuous mode. A complicating circumstance is the partial isolation of PVA crystals at the stage of elution, which requires their separation from the resin particles. As a result of elution, solutions containing 150–170 g/l W03 are obtained, which are fed to the evaporation and crystallization of PVA.

The disadvantage of ion-exchange technology compared to extraction is the unfavorable kinetics (contact time 8-12 hours versus 5-10 minutes for extraction). At the same time, the advantages of ion exchangers include the absence of waste solutions containing organic impurities, as well as the fire safety and non-toxicity of resins.

Decomposition of scheelite concentrates with acids

In industrial practice, mainly in the processing of high-grade scheelite concentrates (70-75% W03), direct decomposition of scheelite with hydrochloric acid is used.

Decomposition reaction:

CaW04 + 2HC1 = W03H20 + CoCl2 (1.24)

Almost irreversible. However, the acid consumption is much higher than the stoichiometrically required one (250–300%) due to the inhibition of the process by tungstic acid films on scheelite particles.

The decomposition is carried out in sealed reactors with stirrers, lined with acid-resistant enamel and heated through a steam jacket. The process is carried out at 100-110 C. The duration of decomposition varies from 4-6 to 12 hours, which depends on the degree of grinding, as well as the origin of the concentrate (scheelites of various deposits differ in reactivity).

A single treatment does not always lead to a complete opening. In this case, after dissolving tungstic acid in ammonia water, the residue is re-treated with hydrochloric acid.

During the decomposition of scheelite-powellite concentrates containing 4-5% molybdenum, most of the molybdenum passes into the hydrochloric acid solution, which is explained by the high solubility of molybdic acid in hydrochloric acid. So, at 20 C in 270 g/l HC1, the solubilities of H2Mo04 and H2WO4 are 182 and 0.03 g/l, respectively. Despite this, complete separation of molybdenum is not achieved. Precipitates of tungstic acid contain 0.2-0.3% molybdenum, which cannot be extracted by re-treatment with hydrochloric acid.

The acid method differs from the alkaline methods of scheelite decomposition by a smaller number of operations of the technological scheme. However, when processing concentrates with a relatively low content of W03 (50-55%) with a significant content of impurities, in order to obtain conditioned ammonium paratungstate, two or three ammonia purifications of tungstic acid have to be carried out, which is uneconomical. Therefore, decomposition with hydrochloric acid is mostly used in the processing of rich and pure scheelite concentrates.

The disadvantages of the method of decomposition with hydrochloric acid are the high consumption of acid, the large volume of waste solutions of calcium chloride and the complexity of their disposal.

In the light of the tasks of creating waste-free technologies, the nitric acid method of decomposition of scheelite concentrates is of interest. In this case, the mother solutions are easy to dispose of, obtaining nitrate salts.

Tungsten is the most refractory metal with a melting point of 3380°C. And this determines its scope. It is also impossible to build electronics without tungsten, even the filament in a light bulb is tungsten.

And, of course, the properties of the metal determine the difficulties in obtaining it ...

First, you need to find the ore. These are just two minerals - scheelite (calcium tungstate CaWO 4) and wolframite (iron and manganese tungstate - FeWO 4 or MnWO 4). The latter has been known since the 16th century under the name "wolf foam" - "Spuma lupi" in Latin, or "Wolf Rahm" in German. This mineral accompanies tin ores and interferes with the smelting of tin, converting it into slag. Therefore, it is possible to find it already in antiquity. Rich tungsten ores usually contain 0.2 - 2% tungsten. In reality, tungsten was discovered in 1781.

However, finding this is the simplest thing in tungsten mining.
Next - the ore needs to be enriched. There are a bunch of methods and they are all quite complex. First, of course. Then - magnetic separation (if we have wolframite with iron tungstate). Next is gravity separation, because the metal is very heavy and the ore can be washed, much like when mining gold. Now they still use electrostatic separation, but it is unlikely that the method will be useful to a hitman.

So, we have separated the ore from the waste rock. If we have scheelite (CaWO 4), then the next step can be skipped, and if wolframite, then we need to turn it into scheelite. To do this, tungsten is extracted with a soda solution under pressure and at elevated temperature (the process takes place in an autoclave), followed by neutralization and precipitation in the form of artificial scheelite, i.e. calcium tungstate.
It is also possible to sinter wolframite with an excess of soda, then we get not calcium, but sodium tungstate, which is not so significant for our purposes (4FeWO 4 + 4Na 2 CO 3 + O 2 = 4Na 2 WO 4 + 2Fe 2 O 3 + 4CO 2).

The next two steps are water leaching of CaWO 4 -> H 2 WO 4 and hot acid decomposition.
You can take different acids - hydrochloric (Na 2 WO 4 + 2HCl \u003d H 2 WO 4 + 2NaCl) or nitric.
As a result, tungsten acid is isolated. The latter is calcined or dissolved in an aqueous solution of NH 3, from which paratungstate is crystallized by evaporation.
As a result, it is possible to obtain the main raw material for the production of tungsten - WO 3 trioxide with good purity.

Of course, there is also a method for obtaining WO 3 using chlorides, when a tungsten concentrate is treated with chlorine at an elevated temperature, but this method will not be simple for a hitman.

Tungsten oxides can be used in metallurgy as an alloying additive.

So, we have tungsten trioxide and one stage remains - reduction to metal.
There are two methods here - hydrogen reduction and carbon reduction. In the second case, coal and the impurities it always contains react with tungsten to form carbides and other compounds. Therefore, tungsten comes out “dirty”, brittle, and for electronics it is very desirable clean, because having only 0.1% iron, tungsten becomes brittle and it is impossible to pull out the thinnest wire for filaments from it.
The technical process with coal has another drawback - a high temperature: 1300 - 1400 ° C.

However, production with hydrogen reduction is also not a gift.
The reduction process takes place in special tube furnaces, heated in such a way that, as it moves along the pipe, the “boat” with WO3 passes through several temperature zones. A stream of dry hydrogen flows towards it. Recovery occurs both in "cold" (450...600°C) and in "hot" (750...1100°C) zones; in the "cold" - to the lowest oxide WO 2, then - to the elemental metal. Depending on the temperature and duration of the reaction in the "hot" zone, the purity and size of the grains of powdered tungsten released on the walls of the "boat" change.

So, we got pure metal tungsten in the form of the smallest powder.
But this is not yet an ingot of metal from which something can be made. The metal is obtained by powder metallurgy. That is, it is first pressed, sintered in a hydrogen atmosphere at a temperature of 1200-1300 ° C, then an electric current is passed through it. The metal is heated to 3000 °C, and sintering into a monolithic material occurs.

However, we rather need not ingots or even rods, but thin tungsten wire.
As you understand, here again, not everything is so simple.
Wire drawing is carried out at a temperature of 1000°C at the beginning of the process and 400-600°C at the end. In this case, not only the wire is heated, but also the die. Heating is carried out by a gas burner flame or an electric heater.
At the same time, after drawing, the tungsten wire is coated with graphite grease. The surface of the wire must be cleaned. Cleaning is carried out by annealing, chemical or electrolytic etching, electrolytic polishing.

As you can see, the task of obtaining a simple tungsten filament is not as simple as it seems. And here only the main methods are described, for sure there are a lot of pitfalls.
And, of course, even now tungsten is an expensive metal. Now one kilogram of tungsten costs more than $50, the same molybdenum is almost two times cheaper.

Actually, there are several uses for tungsten.
Of course, the main ones are radio and electrical engineering, where tungsten wire goes.

The next one is the manufacture of alloy steels, which are distinguished by their special hardness, elasticity and strength. Added together with chromium to iron, it gives the so-called high-speed steels, which retain their hardness and sharpness even when heated. They are used to make cutters, drills, cutters, as well as other cutting and drilling tools (in general, there is a lot of tungsten in a drilling tool).
Interesting alloys of tungsten with rhenium - high-temperature thermocouples are made from it, operating at temperatures above 2000 ° C, although only in an inert atmosphere.

Well, another interesting application is tungsten welding electrodes for electric welding. Such electrodes are non-consumable and it is necessary to supply another metal wire to the welding site to provide a weld pool. Tungsten electrodes are used in argon arc welding - for welding non-ferrous metals such as molybdenum, titanium, nickel, as well as high-alloy steels.

As you can see, the production of tungsten is not for ancient times.
And why is there tungsten?
Tungsten can only be obtained with the construction of electrical engineering - with the help of electrical engineering and for electrical engineering.
No electricity - no tungsten, but you don't need it either.

Cassiterite SnO 2- the main industrial mineral of tin, which is present in tin-bearing placers and bedrock ores. The content of tin in it is 78.8%. Cassiterite has a density of 6900…7100 kg/t and a hardness of 6…7. The main impurities in cassiterite are iron, tantalum, niobium, as well as titanium, manganese, pigs, silicon, tungsten, etc. The physicochemical properties of cassiterite, for example, magnetic susceptibility, and its flotation activity depend on these impurities.

Stannin Cu 2 S FeS SnS 4- tin sulfide mineral, although it is the most common mineral after cassiterite, has no industrial value, firstly, because it has a low tin content (27 ... 29.5%), and secondly, the presence of copper and iron sulfides in it complicates the metallurgical processing of concentrates and, thirdly, the proximity of the flotation properties of the bed to sulfides makes it difficult to separate them during flotation. The composition of tin concentrates obtained at concentrating plants is different. Gravity concentrates containing up to 60% tin are released from rich tin placers, and sludge concentrates obtained by both gravity and flotation methods can contain from 15 to 5% tin.

Tin-bearing deposits are divided into placer and primary. Alluvial tin deposits are the main source of world tin mining. About 75% of the world's tin reserves are concentrated in placers. Indigenous tin deposits have a complex material composition, depending on which they are divided into quartz-cassiterite, sulfide-quartz-cassiterite and sulfide-cassiterite.

Quartz-cassiterite ores are usually complex tin-tungsten. Cassiterite in these ores is represented by coarse, medium and finely disseminated crystals in quartz (from 0.1 to 1 mm or more). In addition to quartz and cassiterite, these ores usually contain feldspar, tourmaline, micas, wolframite or scheelite, and sulfides. The sulfide-cassiterite ores are dominated by sulfides - pyrite, pyrrhotite, arsenopyrite, galena, sphalerite and stanin. It also contains iron minerals, chlorite and tourmaline.

Tin placers and ores are enriched mainly by gravity methods using jigging machines, concentration tables, screw separators and locks. Placers are usually much easier to be enriched by gravity methods than ores of primary deposits, because. they do not require expensive crushing and grinding processes. Fine-tuning of rough gravity concentrates is carried out by magnetic, electrical and other methods.

Enrichment at locks is used when the grain size of cassiterite is more than 0.2 mm, because smaller grains are poorly caught on locks and their extraction does not exceed 50 ... 60%. More efficient devices are jigging machines, which are installed for primary enrichment and allow you to extract up to 90% of cassiterite. Fine-tuning of rough concentrates is carried out on concentration tables (Fig. 217).

Fig. 217. Scheme of enrichment of tin placers

The primary enrichment of placers is also carried out on dredges, including sea dredges, where drum screens with holes of 6 ... To enrich the undersize product of screens, jigging machines of various designs are used, usually with an artificial bed. Gateways are also installed. Primary concentrates are subjected to cleaning operations on jigging machines. Finishing, as a rule, is carried out at coastal finishing stations. Extraction of cassiterite from placers is usually 90…95%.

Enrichment of primary tin ores, which are distinguished by the complexity of the material composition and uneven dissemination of cassiterite, is carried out according to more complex multi-stage schemes using not only gravity methods, but also flotation gravity, flotation, and magnetic separation.

When preparing tin ores for enrichment, it is necessary to take into account the ability of cassiterite to sludge due to its size. More than 70% of the loss of tin during enrichment is accounted for by sludged cassiterite, which is carried away with drains from gravity apparatuses. Therefore, the grinding of tin ores is carried out in rod mills, which operate in a closed cycle with screens. At some factories, enrichment in heavy suspensions is used at the head of the process, which makes it possible to separate up to 30 ... 35% of host rock minerals into tailings, reduce grinding costs and increase tin recovery.

To isolate coarse-grained cosmiterite in the head of the process, jigging is used with a feed size of 2…3 to 15…20 mm. Sometimes, instead of jigging machines, with a material size of minus 3 + 0.1 mm, screw separators are installed, and when enriching a material with a size of 2 ... 0.1 mm, concentration tables are used.

For ores with uneven dissemination of cassiterite, multi-stage schemes are used with sequential regrinding of not only tailings, but also poor concentrates and middlings. In tin ore, which is enriched according to the scheme shown in Fig. 218, cassiterite has a particle size of 0.01 to 3 mm.

Rice. 218. Scheme of gravitational enrichment of primary tin ores

The ore also contains iron oxides, sulfides (arsenopyrite, chalcopyrite, pyrite, stanin, galena), wolframite. The nonmetallic part is represented by quartz, tourmaline, chlorite, sericite, and fluorite.

The first stage of enrichment is carried out in jigging machines with an ore size of 90% minus 10 mm with the release of coarse tin concentrate. Then, after regrinding the tailings of the first stage of enrichment and hydraulic classification according to equal fall, enrichment is carried out on concentration tables. The tin concentrate obtained according to this scheme contains 19 ... 20% of tin with an extraction of 70 ... 85% and is sent for finishing.

When finishing, sulfide minerals, minerals of host rocks, are removed from coarse tin concentrates, which makes it possible to increase the tin content to the standard.

Coarsely disseminated sulfide minerals with a particle size of 2…4 mm are removed by flotation gravity on concentration tables, before which the concentrates are treated with sulfuric acid (1.2…1.5 kg/t), xanthate (0.5 kg/t) and kerosene (1…2 kg/t). t).

Cassiterite is recovered from gravity concentration sludge by flotation using selective collectors and depressants. For ores of complex mineral composition containing significant amounts of tourmaline, iron hydroxides, the use of fatty acid collectors makes it possible to obtain poor tin concentrates containing no more than 2–3% tin. Therefore, when flotation of cassiterite, such selective collectors as Asparal-F or aerosol-22 (succinamates), phosphonic acids and reagent IM-50 (alkylhydroxamic acids and their salts) are used. Water glass and oxalic acid are used to depress the minerals of the host rocks.

Before flotation of cassiterite, material with a particle size of minus 10–15 µm is removed from the sludge, then sulfides are flotation from the tails of which, at pH 5, when oxalic acid, liquid glass and Asparal-F reagent (140–150 g/t) are fed into as a collector, cassiterite is floated (Fig. 219). The resulting flotation concentrate contains up to 12% tin when extracting up to 70...75% tin from the operation.

Bartles-Moseley orbital locks and Bartles-Crosbelt concentrators are sometimes used to extract cassiterite from sludge. The rough concentrates obtained on these devices, containing 1 ... 2.5% of tin, are sent for finishing to slurry concentration tables with the production of commercial slurry tin concentrates.

Tungsten in ores it is represented by a wider range of minerals of industrial importance than tin. Of the 22 tungsten minerals currently known, four are the main ones: wolframite (Fe,Mn)WO 4(density 6700 ... 7500 kg / m 3), hubnerite MnWO 4(density 7100 kg / m 3), ferberite FeWO 4(density 7500 kg / m 3) and scheelite CaWO 4(density 5800 ... 6200 kg / m 3). In addition to these minerals, molybdoscheelite, which is scheelite and an isomorphic admixture of molybdenum (6...16%), is of practical importance. Wolframite, hübnerite and ferberite are weakly magnetic minerals; they contain magnesium, calcium, tantalum and niobium as impurities. Wolframite is often found in ores along with cassiterite, molybdenite, and sulfide minerals.

The industrial types of tungsten-containing ores include vein quartz-wolframite and quartz-cassiterite-wolframite, stockwork, skarn and alluvial. In deposits vein type contain wolframite, hubnerite and scheelite, as well as molybdenum minerals, pyrite, chalcopyrite, tin, arsenic, bismuth and gold minerals. AT stockwork In deposits, the content of tungsten is 5 ... 10 times less than in vein deposits, but they have large reserves. AT skarn ores, along with tungsten, represented mainly by scheelite, contain molybdenum and tin. Alluvial tungsten deposits have small reserves, but they play a significant role in the extraction of tungsten. The industrial content of tungsten trioxide in placers (0.03 ... 0.1%) is much lower than in primary ores, but their development is much simpler and economically more profitable. These placers, along with wolframite and scheelite, also contain cassiterite.

The quality of tungsten concentrates depends on the material composition of the enriched ore and the requirements that apply to them when used in various industries. So for the production of ferrotungsten, the concentrate must contain at least 63% WO3, wolframite-huebnerite concentrate for the production of hard alloys must contain at least 60% WO3. Scheelite concentrates typically contain 55% WO3. The main harmful impurities in tungsten concentrates are silica, phosphorus, sulfur, arsenic, tin, copper, lead, antimony and bismuth.

Tungsten placers and ores are enriched, as well as tin, in two stages - primary gravity enrichment and refinement of rough concentrates by various methods. With a low content of tungsten trioxide in the ore (0.1 ... 0.8%) and high requirements for the quality of concentrates, the total degree of enrichment is from 300 to 600. This degree of enrichment can only be achieved by combining various methods, from gravity to flotation.

In addition, wolframite placers and primary ores usually contain other heavy minerals (cassiterite, tantalite-columbite, magnetite, sulfides), therefore, during primary gravity concentration, a collective concentrate containing from 5 to 20% WO 3 is released. When finishing these collective concentrates, standard monomineral concentrates are obtained, for which flotation gravity and flotation of sulfides, magnetic separation of magnetite and wolframite are used. It is also possible to use electrical separation, enrichment on concentration tables, and even flotation of minerals from displacement rocks.

The high density of tungsten minerals makes it possible to effectively use gravity enrichment methods for their extraction: in heavy suspensions, on jigging machines, concentration tables, screw and jet separators. In enrichment and especially in the refinement of collective gravitational concentrates, sagnite separation is widely used. Wolframite has magnetic properties and therefore separates in a strong magnetic field, for example, from non-magnetic cassiterite.

The original tungsten ore, as well as tin ore, is crushed to a particle size of minus 12 + 6 mm and enriched with jigging, where coarsely disseminated wolframite and part of the tailings with a tailings content of tungsten trioxide are released. After jigging, the ore is fed to rod mills for grinding, in which it is crushed to a fineness of minus 2+ 0.5 mm. To avoid excessive sludge formation, grinding is carried out in two stages. After crushing, the ore is subjected to hydraulic classification with the release of sludge and the enrichment of sand fractions on concentration tables. The middlings and tailings received on the tables are crushed and sent to the concentration tables. The tailings are also subsequently crushed and enriched on concentration tables. The enrichment practice shows that the extraction of wolframite, hübnerite and ferberite by gravity methods reaches 85%, while scheelite inclined to sludge is extracted by gravity methods only by 55 ... 70%.

When enriching finely disseminated wolframite ores containing only 0.05 ... 0.1% of tungsten trioxide, flotation is used.

Flotation is especially widely used to extract scheelite from skarn ores, which contain calcite, dolomite, fluorite and barite, floated by the same collectors as scheelite.

Collectors in the flotation of scheelite ores are fatty acids of the oleic type, which is used at a temperature of at least 18 ... 20 ° C in the form of an emulsion prepared in soft water. Often, oleic acid is saponified in a hot solution of soda ash at a ratio of 1:2 before being fed into the process. Instead of oleic acid, tall oil, naphthenic acids, and the like are also used.

It is very difficult to separate scheelite from alkaline earth minerals containing calcium, barium and iron oxides by flotation. Scheelite, fluorite, apatite and calcite contain calcium cations in the crystal lattice, which provide chemical sorption of the fatty acid collector. Therefore, selective flotation of these minerals from scheelite is possible within narrow pH ranges using depressants such as liquid glass, sodium silicofluoride, soda, sulfuric and hydrofluoric acid.

The depressing effect of liquid glass during the flotation of calcium-containing minerals with oleic acid consists in the desorption of calcium soaps formed on the surface of the minerals. At the same time, the floatability of scheelite does not change, while the floatability of other calcium-containing minerals deteriorates sharply. Increasing the temperature to 80...85°C reduces the contact time of the pulp with a solution of liquid glass from 16 hours to 30...60 minutes. Liquid glass consumption is about 0.7 kg/t. The process of selective scheelite flotation, shown in Fig. 220, using the steaming process with liquid glass, is called the Petrov method.

Rice. 220. Scheme of scheelite flotation from tungsten-molybdenum ores using

fine-tuning according to the Petrov method

The concentrate of the main scheelite flotation, which is carried out at a temperature of 20°C in the presence of oleic acid, contains 4...6% tungsten trioxide and 38...45% calcium oxide in the form of calcite, fluorite and apatite. The concentrate is thickened to 50-60% solid before steaming. Steaming is carried out sequentially in two vats in a 3% solution of liquid glass at a temperature of 80 ... 85 ° C for 30 ... 60 minutes. After steaming, cleaning operations are carried out at a temperature of 20 ... 25 ° C. The resulting scheelite concentrate may contain up to 63...66% of tungsten trioxide with its recovery of 82...83%.

Tungsten ores in our country were processed at large GOKs (Orlovsky, Lermontovsky, Tyrnauzsky, Primorsky, Dzhidinsky VMK) according to the now classic technological schemes with multi-stage grinding and enrichment of material divided into narrow size classes, as a rule, in two cycles: primary gravitational enrichment and fine-tuning of rough concentrates by various methods. This is due to the low content of tungsten in the processed ores (0.1-0.8% WO3) and high quality requirements for concentrates. Primary enrichment for coarsely disseminated ores (minus 12+6 mm) was carried out by jigging, and for medium-, fine- and finely disseminated ores (minus 2+0.04 mm) screw apparatuses of various modifications and sizes were used.

In 2001, the Dzhida tungsten-molybdenum plant (Buryatia, Zakamensk) ceased its activity, having accumulated after it the Barun-Naryn technogenic tungsten deposit, multimillion in terms of sand volume. Since 2011, Zakamensk CJSC has been processing this deposit at a modular processing plant.

The technological scheme was based on enrichment in two stages on Knelson centrifugal concentrators (CVD-42 for the main operation and CVD-20 for cleaning), middlings regrinding and flotation of the bulk gravity concentrate to obtain a KVGF grade concentrate. During operation, a number of factors were noted in the operation of Knelson concentrators that negatively affect the economic performance of sand processing, namely:

High operating costs, incl. energy costs and the cost of spare parts, which, given the remoteness of production from generating capacities and the increased cost of electricity, this factor is of particular importance;

Low degree of extraction of tungsten minerals into gravity concentrate (about 60% of the operation);

The complexity of this equipment in operation: with fluctuations in the material composition of the enriched raw materials, centrifugal concentrators require intervention in the process and operational settings (changes in the pressure of the fluidizing water, the speed of rotation of the enrichment bowl), which leads to fluctuations in the quality characteristics of the obtained gravity concentrates;

Significant remoteness of the manufacturer and, as a result, a long waiting time for spare parts.

In search of an alternative method of gravitational concentration, Spirit conducted laboratory tests of the technology screw separation using industrial screw separators SVM-750 and SVSH-750 manufactured by LLC PK Spirit. Enrichment took place in two operations: main and control with the receipt of three enrichment products - concentrate, middlings and tailings. All enrichment products obtained as a result of the experiment were analyzed in the laboratory of ZAO Zakamensk. The best results are presented in table. one.

Table 1. Results of screw separation in laboratory conditions

The data obtained showed the possibility of using screw separators instead of Knelson concentrators in the primary enrichment operation.

The next step was to conduct semi-industrial tests on the existing enrichment scheme. A pilot semi-industrial plant was assembled with screw devices SVSH-2-750, which were installed in parallel with Knelson CVD-42 concentrators. Enrichment was carried out in one operation, the resulting products were sent further according to the scheme of the operating enrichment plant, and sampling was carried out directly from the enrichment process without stopping the operation of the equipment. Indicators of semi-industrial tests are presented in table. 2.

Table 2. Results of comparative semi-industrial tests of screw apparatuses and centrifugal concentratorsknelson

Indicators	Source food	Concentrate
Recovery, %

The results show that the enrichment of sands is more efficient on screw apparatus than on centrifugal concentrators. This translates into a lower concentrate yield (16.87% versus 32.26%) with an increase in recovery (83.13% versus 67.74%) into tungsten mineral concentrate. This results in a higher quality WO3 concentrate (0.9% versus 0.42%),