RU2290457C2 - Method of complex processing of magnesium silicates - Google Patents

Abstract

FIELD: metallurgy; chemical engineering of inorganic agents; complex processing of magnesium silicate-serpentinite.

SUBSTANCE: proposed method consists in classification of ground serpentinite into fractions followed by magnetic separation of calcium-containing nonmagnetic minerals. Magnetic fraction of serpentinite is leached out by hydrochloric acid. Magnesium chloride solution thus obtained is separated from amorphous sediment of silicon dioxide, after which it is washed and dried. Magnesium chloride solution is cleaned from admixtures, thus obtaining iron-nickel concentrate. Cleaned magnesium chloride solution and ground waste potassium electrolyte are used for production of synthetic carnallite-KCl·MgCl₂·6H₂O which is dehydrated to content of water lesser than 0.2% and is fed for electrolysis. As a result, metallic magnesium, chlorine gas and waste potassium electrolyte are obtained. Electrolyte is returned to carnallite production stage. Chlorine gas is subjected to conversion into hydrogen chloride which is directed for dehydrating of carnallite. Hydrogen chloride is separated from dehydration gases obtaining hydrochloric acid which is used for leaching-out of serpentinite.

EFFECT: waste-free ecologically safe process.

23 cl, 1 dwg, 1 tbl, 1 ex

Description

The invention relates to the field of non-ferrous metallurgy and chemical technology of inorganic substances. It can be used for complex processing of silicates of magnesium serpentinite - 3MgO · 2SiO ₂ · 2H ₂ O - waste products of asbestos production with the production of marketable products: metallic magnesium, amorphous silicon dioxide and iron-nickel concentrate.

In terms of metal, serpentinite contains 21.5-23% of magnesium, and, for example, carnallite ore only 5%. The presence of multimillion reserves of crystalline serpentinite is an extremely favorable moment in terms of ensuring the production of magnesium with cheap raw materials.

According to the International Magnesium Association, world consumption of primary magnesium in 2003 amounted to about 464 thousand tons. During the current decade, an annual increase in its consumption is projected in the range of 5-6%. The highest growth rate of metal consumption of more than 8% per year is expected in the automotive industry. Consumers are interested in not only the quality of magnesium, but also such an important factor as its price. The increase in magnesium consumption will be largely determined by the level of world prices for this metal.

The purpose of the invention is the creation of a technological process that provides a significant reduction in the cost of production of magnesium.

The feedstock for the electrolytic method for producing magnesium may be magnesite, dolomite or brines of magnesium chloride, or solid natural carnallite - KCl · MgCl ₂ · 6H ₂ O.

A known method of producing magnesium by the electrolytic method from carnallite, H.L. Strelets "Electrolytic production of magnesium", Moscow, Metallurgy, 1972, pp. 58-261.

The technology has been successfully mastered at Russian enterprises. Over an almost 70-year period of work, high-performance equipment has been created and all technological processes have been debugged. The raw material for this technology is the natural carnallite of the Verkhnekamsk deposit of potassium and magnesium salts. The Russian experience in the production of magnesium from carnallite was successfully used in the construction of a magnesium plant in Israel.

Launched in 1996 by DSM, the company successfully operates producing magnesium by electrolysis of dehydrated carnallite, the raw material for which is salt brine from the Dead Sea.

When evaluating the technological scheme should focus on such important points as:

- the need to create chlorine-consuming redistributions and, as a result, a rigid bunch of these industries;

- high losses of magnesium in the technological process from ore to finished metal. The production of 1 ton of magnesium requires about 25 tons of carnallite ore.

- low use of chlorine and, as a result, high costs of environmental protection measures. As a result, the cost of raw materials costs about 30% of magnesium.

US Pat. No. 4,269,816 for the production of anhydrous MgCl ₂ provides a process for chlorinating lump magnesite in a shaft furnace using carbon monoxide as a reducing agent. In this process, calcination of magnesite to MgO and briquetting of a mixture of magnesium oxide and coke are excluded. To obtain magnesium chloride with a minimum content of impurities, high-quality magnesite or additional purification of the melt before electrolysis is required. The process is characterized by low productivity and the release of chlorinated hydrocarbons into the atmosphere.

The company Norsk Hydro has developed a process for the production of anhydrous MgCl ₂ from solutions obtained by leaching magnesite with hydrochloric acid, US patent No. 3742199, including:

- evaporation of a solution of magnesium chloride to a concentration of 55% MgCl ₂ to obtain crystalline bischofite with 4-6 molecules of water;

- dehydration in a fluidized bed with air to powdered MgCl ₂ · 2H ₂ O;

- three-stage dehydration of MgCl ₂ · 2H ₂ O with anhydrous hydrogen chloride at 300 ° C to obtain MgCl ₂ containing not more than 0.2% MgO and H ₂ O each.

The process is implemented on an industrial scale and requires the recirculation of large volumes of gaseous hydrogen chloride and the use of special materials that are resistant to hydrogen chloride and water vapor at temperatures above 350 ° C. The technological process is complex and requires large material costs.

A Canadian firm, Noranda, developed a process for producing magnesium from serpentinite (Bedard M. The Production of Magnesium by Noranda. 58 ^th Annual World International Magnesium Association Conference. May 20-22, 2001, Brussels Belgium, pp. 57-64). The main redistributions of this technological scheme:

- leaching of serpentinite with hydrochloric acid;

- neutralization and filtration of the suspension to obtain a solution of magnesium chloride and silicon dioxide;

- cleaning and filtering the solution of heavy metals;

- evaporation and drying of a solution of magnesium chloride to MgCl ₂ · 2H ₂ O;

- mixing hydrate of magnesium chloride with spent electrolyte;

- dehydration of the mixture using hydrogen chloride and obtaining anhydrous chlorides of magnesium, potassium and sodium;

- electrolysis of magnesium chloride to produce magnesium and chlorine and spent electrolyte;

- the conversion of chlorine and hydrogen to hydrogen chloride;

- return of hydrogen chloride and electrolyte to the process.

The main disadvantages of this method:

- only magnesium (~ 40% of the composition) is extracted from serpentinite, the remaining components: silica and iron, nickel and chromium concentrate are sent to the solid waste storage, polluting the environment, reducing the economic efficiency of raw materials processing;

- the process of dehydration of magnesium chloride hydrate in a molten medium at 650-700 ° C leads to high hydrolysis of MgCl ₂ , complicates the hardware design of the process, increases the loss of raw materials and energy consumption.

A known method of producing magnesium from silicon-containing waste (RF patent No. 2237111), including grinding and fractionation, leaching with hydrochloric acid to obtain a suspension of magnesium chloride, separation of the solution and washing of the precipitate, two-stage purification and concentration of the solution, its multi-stage dehydration to obtain anhydrous raw materials for electrolysis, electrolysis to produce magnesium, chlorine and electrolyte, the conversion of chlorine to hydrogen chloride and its direction to the stage of preparation of raw materials for electrolysis.

The disadvantages of this method:

- Leaching of the material with an interval of fineness of + 0 ÷ 3 mm does not ensure uniformity of the obtained silica in chemical composition, which reduces its consumer properties. Increasing the leaching time to 12 hours creates serious difficulties in organizing large-scale production.

- The exclusion of the carnallite synthesis operation from the technological scheme creates similar problems in the dehydration of magnesium chloride dihydrate, as in the production of serpentinite magnesium by the method of Noranda, Canada.

- Purification of a solution of magnesium chloride from heavy metals in the second stage at pH 10.0-11.0 leads to significant losses of magnesium chloride due to its precipitation in the form of hydroxide and reduces the quality of the concentrate of heavy metals.

- There is no operation to remove calcium from a solution of magnesium chloride, which, given the return of spent electrolyte, will lead to its accumulation and disruption of the process.

The closest known analogues in technical essence and the achieved result is a method for the production of magnesium from oxide-chloride raw materials (RF patent No. 2118406, C 25 C 3/04, publ. 08.28.896 BI No. 24).

According to the prototype method, the oxide feedstock, in particular serpentinite, is leached with hydrochloric acid, the purified magnesium chloride solutions are mixed with crushed potassium electrolyte or potassium chloride before dehydration to obtain synthetic carnallite - KCl · MgCl ₂ · 6H ₂ O, which is dehydrated in two stages, s using hydrogen chloride on the latter.

Dehydrated carnallite with a magnesium oxide and water content of less than 0.5% is subjected to electrolysis to produce magnesium metal, chlorine gas, and spent potassium electrolyte.

Chlorine gas (80-85% vol. Cl ₂ , the rest is air) is burned in a natural gas flare by the reaction CH ₄ + 2Cl ₂ + O ₂ = CO ₂ + 4HCl. Hydrogen chloride is sent to the stage of dehydration of carnallite and after absorption by water in the form of a 15-20% solution of hydrochloric acid, it is returned to the leaching of oxide raw materials.

Spent potassium electrolyte is used to produce synthetic carnallite. Thus, the most important elements of the prototype method according to the patent of the Russian Federation No. 2118406 are:

- synthesis of carnallite;

- return of chlorine and spent potassium electrolyte to the process.

The disadvantages of this method of processing oxide raw materials in relation to serpentinite are:

- Relatively low extraction of magnesium during leaching of raw materials ~ 80-85%. As a result of this, amorphous silicon dioxide contains up to 5-8% of magnesium oxide, 0.5-0.8% of the total nickel, chromium and iron. To obtain a product with a purity of at least 98% SiO ₂ , the organization of the second leaching stage is required, which complicates the hardware design of the process.

- The degree of conversion of chlorine to hydrogen chloride in the flare of combustion of natural gas is 95-97%. The capture of chlorine from conversion products is associated with additional material costs.

- When recycling potassium spent electrolyte, the problem of removing calcium chloride from the process arises, the accumulation of which upsets the process of synthesis of carnallite.

An object of the invention is the integrated processing of magnesium silicates - serpentinite, to produce salable metallic magnesium, amorphous silicon dioxide and iron-nickel concentrate.

The technical result obtained by the implementation of the claimed invention is to create a non-waste environmentally friendly and highly profitable production of the above commercial products.

The specified technical result is achieved by the fact that in the method of complex processing of magnesium silicates - serpentinite, including leaching of serpentinite with hydrochloric acid in the apparatus, separation of the magnesium chloride solution from the amorphous precipitate of silicon dioxide, washing and drying it, purification of the magnesium chloride solution from impurities, its concentration, synthesis carnallite, its dehydration and electrolysis to produce magnesium, chlorine and spent potassium electrolyte, before leaching, the crushed serpentinite is classified and magnetic separation, while leaching using the magnetic fraction of serpentinite, and the purification of the magnesium chloride solution is carried out with the release of iron-Nickel precipitate.

And also because prior to magnetic separation, the material is classified into fractions by size, the lower limit of the first fraction is 0.2 ± 0.05 mm, the upper limit is 1.2 ± 0.05 mm, and the particle pitch is 0.3 ± 0.05 mm.

And also by the fact that at the same time only one of the fractions is supplied for leaching.

And also by the fact that the leaching of the magnetic fraction of serpentinite is carried out in a continuous countercurrent, pulsating mode.

As well as the fact that leaching is carried out with hydrochloric acid with a concentration of 15-20% and a temperature of 50-70 ° C supplied to the lower part of the apparatus, and the magnetic fraction of serpentinite is loaded into its upper part, while in the middle part of the apparatus the temperature is due to the reaction heat support in the range of 90-105 ° C.

And also the fact that a solution of magnesium chloride containing 5-10 g / l of free hydrochloric acid is removed at a temperature of 70-85 ° C from the upper part of the apparatus, and the precipitate of amorphous silicon dioxide is unloaded from its lower part.

And also the fact that the washing of the precipitate of amorphous silicon dioxide is carried out in a continuous, countercurrent, pulsating mode with a 0.01-0.05% solution of hydrochloric acid with a flow rate of 1-1.1 m ³ / t of sediment.

And also the fact that the precipitate of amorphous silicon dioxide after drying has a specific surface area of 230-320 m ² / g

And also the fact that the purification of the magnesium chloride solution from impurities is carried out at a temperature of 70-85 ° C by neutralization to a pH of 3.5-4.5, then the oxidation of ferrous iron, manganese and nickel to higher valency, followed by neutralization to a pH of 6-7, 5 and filtering the magnesium chloride solution from the nickel-iron precipitate.

And also the fact that neutralization is carried out with the natural mineral brucite, previously calcined at 500-550 ° C and crushed to a particle size <50 microns.

And also the fact that the neutralization is carried out with magnesium hydroxide obtained from a solution of magnesium chloride.

And also the fact that the oxidation is carried out with chlorine or sodium hypochlorite at pH 3.5 ÷ 4.5.

And also the fact that the washing of the iron-nickel precipitate is carried out in a continuous, countercurrent, pulsating mode with a water flow rate of 1.1-1.2 m ³ / t of sediment.

And also by the fact that the washed iron-nickel precipitate is dried at a temperature of 500-550 ° C and a concentrate is obtained for the production of metallic nickel or ferronickel alloys.

And also the fact that the synthesis of carnallite is carried out from a solution of magnesium chloride and ground spent potassium electrolyte in the presence of hydrochloric acid to obtain, after separation of carnallite, a mother solution of magnesium chloride.

And also by the fact that the spent potassium electrolyte is crushed to a fraction <0.5 mm and the metal magnesium rings are separated> 0.5 mm in size.

And also the fact that the mother liquor of magnesium chloride after separation of carnallite is purified from calcium compounds.

As well as the fact that the carnallite is dehydrated in fluidized bed furnaces in two stages, in the first one to obtain the two-water product KCl · MgCl ₂ · 2H ₂ O, and in the second, when hydrogen chloride is fed into the chambers of the fluidized bed furnace to produce carnallite containing no more than 0.2% of water.

And also the fact that the second stage of carnallite dehydration is carried out in the mode of discrete supply of hydrogen chloride, depending on the temperature of the material in the chambers of the fluidized bed furnace.

And also the fact that hydrogen chloride is obtained in a separate apparatus by the conversion of chlorine gas and water vapor in a natural gas flare in the temperature range 950-1300 ° C.

And also the fact that the conversion of chlorine gas to hydrogen chloride is carried out at a volume ratio of CH ₄ : Cl ₂ : H ₂ O = 1: 4: 2 to obtain a gas containing at least 85 vol.% Hydrogen chloride.

And also by the fact that carnallite is introduced into the anode space of the working flow of electrolyzers.

And also by the fact that in the electrolytic cells together with dehydrated carnallite, carbon-containing material is loaded in an amount of 0.05-0.1% by weight of the raw material.

The drawing shows a flow chart of the integrated processing of magnesium silicates - serpentinite to obtain marketable products.

The development of technological regimes for all stages of the integrated processing of magnesium silicates-serpentinite was carried out in laboratory and pilot plants.

EXAMPLE: to remove calcium, ground serpentinite fraction 0.2-0.5 was subjected to electromagnetic enrichment at a field strength of 1500 _erst . The results, in terms of the anhydrous product, are presented in the table.

The problem of balance is explained by the presence in serpentinite in addition to the listed components of the following substances, wt.%: MnO - 0.08-0.12; CoO - 0.05-0.07; CO ₂ 0.8-1.0; SO ₃ ^2- - 0.2-0.25; TiO ₂ - 0.01-0.02 and others. Given the permissible error in the methods for determining the components, the data presented completely characterize the compositions of the products of electromagnetic separation. Redistribution of particle size of serpentinite particles in fractions during magnetic separation does not occur.

From the data of the table it follows that during electromagnetic enrichment the content of silicon, magnesium and nickel oxides in the magnetic and non-magnetic fractions is preserved as in the original serpentinite. The content of iron and chromium in the magnetic material increases by about 10%. The calcium content in the magnetic fraction to the initial serpentinite decreases by 2 times.

The magnetic fraction of serpentinite composition,%: 45.47 - MgO; 42.21 - SiO ₂ ; 0.49 - CaO; 10.04 - Fe ₂ O ₃ ; 0.37 - Cr ₂ O ₃ ; 0.35 - NiO with a particle size of +0.2 ÷ -0.5 mm was leached in countercurrent pulsation mode. For the experiment, 10 kg of this material and 35 l of 18% hydrochloric acid were consumed. The use of hydrochloric acid with a concentration of at least 15% is associated with the need to obtain solutions containing more than 250 g / l of magnesium chloride, with a maximum degree of extraction and leaching rate. Acid was supplied to the bottom of the column at a temperature of 70 ° C. Due to the heat of reaction, the pulp temperature in the middle part of the apparatus rose to 95 ° C. At the outlet, the solution had a temperature of 80 ° C. After separation of silica, 40 l of a filtrate of the composition was obtained, g / l: MgCl ₂ - 260; CaCl ₂ ~ 2; FeCl ₃ - 33.7; FeCl ₂ - 13; NiCl ₂ - 1.4; CrCl ₃ - 1.9; free HCl - 9. Washed and calcined at 800 ° C, amorphous silicon dioxide contained 98.15% silicon dioxide; 0.2% calcium oxide; 0.85% magnesium oxide; 0.3% iron trioxide; 0.02% chromium trioxide and 0.015% nickel oxide. This product is a raw material for the production of liquid glass, a sorbent for purifying water from oil products, silicon tetrachloride, soot, etc.

A solution of magnesium chloride at a temperature of 80 ° C was neutralized by brucite calcined at 500 ° C and crushed to a particle size of less than 50 μm to pH = 3.5. To convert ferrous iron, nickel and manganese to higher oxidation states, the solution was treated with gaseous chlorine and the brucite was adjusted to pH 7.5.

After the precipitate was isolated by filtration of iron hydroxides and heavy metals, 35 L of a solution of the composition was obtained, g / l: MgCl ₂ - 309; CaCl ₂ - 2.3; Fe <0.0005; Mn - 0.005; Ni 0.0007; Co - 0.0013.

0.8 l of 18% hydrochloric acid was poured into the solution at a temperature of 70 ° C and 11.3 kg of ground spent electrolyte of the composition were fused,%: KCl - 75; MgCl ₂ - 5.5; NaCl 18.51; CaCl ₂ - 0.5; Mg 0.18; MgO 0.25. To transfer metallic magnesium and its oxide contained in the electrolyte into chloride, the pulp was stirred for 1 hour. The solution was evaporated and carnallite-KCl · MgCl ₂ · 6H ₂ O was synthesized in an amount of 36.5 kg of the composition,%: MgCl ₂ - 31.5; KCl - 25.1; H ₂ O svob-2.8; SO ^-2 ₄ <0.02; Fe ³⁺ <0.005. X-ray phase analysis of the obtained product showed the presence of a single phase - carnallite. Synthetic carnallite was dehydrated in a fluidized bed furnace in two stages in the temperature range of 60-120 ° C and 120-350 ° C with the supply of hydrogen chloride. Received 22.1 kg of dehydrated carnallite with a content,%: MgCl ₂ - 50.8%; KCl - 39.8%; NaCl - 9.45%; MgO - 0.21%; H ₂ O - 0.14%.

A product of this composition is a high-quality raw material for the production of magnesium by the electrolytic method.

The precipitate of iron hydroxides and heavy metals was washed with water and calcined at a temperature of 550 ° C. Received 1,254 kg of concentrate containing, wt.%: Fe ₂ O ₃ - 76.31; NiO - 2.51; Cr ₂ O ₃ - 2.6; MgO 9.26; CaO 0.32; Al ₂ O ₃ - 3.25; SiO ₂ - 1.4; Cl - 0.3; Mn ₂ O ₃ 0.64; P ₂ O ₅ <0.05.

The product is a raw material for the production of metallic nickel or ferronickel alloys. On the above product received a positive conclusion.

The technology for producing hydrogen chloride from chlorine gas, natural gas and water vapor has been tested in a pilot plant with a capacity of 25 kg Cl ₂ per hour. When 1.6 m ³ / h of natural gas, 6.5 m ³ / h of chlorine gas and 3.25 m ³ / h of water vapor with a temperature of 210 ° C and a torch temperature of 1150-1200 ° C were supplied to the burner, 100% conversion of chlorine gas to hydrogen chloride was achieved with the content in the reaction products, vol.%: HCl - 85.2; CO ₂ - 10.6; Cl ₂ - absence; the rest is nitrogen. The presence of nitrogen is explained by the presence of air in the chlorine gas.

The technological mode of the electrolytic production of magnesium was tested on an experimental electrolyzer with a current strength of 10 kA. As a raw material, dehydrated synthetic carnallite of the above composition was used. The feed was loaded into the anode space of the electrolyzer with the addition of ground petroleum coke in an amount of 1 kg / t of dehydrated carnallite. Technological mode of electrolysis: melt temperature - 670-680 ° C; the content of MgCl ₂ in the electrolyte is 5-12%; a sample of magnesium - 3 times a day. For the experiment received 465 kg of metallic magnesium. When feeding the electrolyzer with solid dehydrated carnallite in comparison with the melt, it was possible to increase the current load on the electrolyzer by 6% and increase the current output of magnesium by 5%.

Thus, the flow diagram shown in the figure was tested in experimental plants and allowed us to solve the problem of complex processing of serpentinite to produce marketable products: magnesium metal, amorphous silicon dioxide, and iron-nickel concentrate. Provides non-waste and environmental safety of production.

Compared with current technological schemes, the implementation of the invention will significantly reduce the cost of magnesium production.

Table Enrichment products Exit, % Content,% Recovery,% SiO ₂ MgO Cao Fe ₂ O ₃ Cr ₂ O ₃ Nio Σ SiO ₂ MgO Cao Fe ₂ O ₃ Cr ₂ O ₃ Nio Magnetic fraction 81.4 42.21 45.47 0.49 10.04 0.37 0.35 98.93 80.32 82.15 43.0 89.19 89.11 84.79 Non-magnetic fraction 18.6 45.24 43.24 2.84 5.32 0.198 0.27 97,108 19.68 17.85 57.0 10.81 10.89 15.21 Source serpentinite one hundred 42.76 45.06 0.927 9.16 0.338 0.336 98,581 one hundred one hundred one hundred one hundred one hundred one hundred

Claims (23)

1. The method of complex processing of magnesium silicates - serpentinite, including leaching of serpentinite with hydrochloric acid in the apparatus, separation of the magnesium chloride solution from the amorphous precipitate of silicon dioxide, washing and drying it, purification of the magnesium chloride solution from impurities, its concentration, carnallite synthesis, its dehydration and electrolysis obtaining magnesium, chlorine and spent potassium electrolyte, characterized in that before leaching, the crushed serpentinite is subjected to classification and magnetic separation, for leaching Bani use magnetic fraction serpentinite, purification magnesium chloride solution is carried out with the release of iron-nickel precipitate. 2. The method according to claim 1, characterized in that prior to magnetic separation the material is classified into fractions by size, the lower limit of the first fraction is (0.2 ± 0.05) mm, the upper one is (1.2 ± 0.05) mm and the step of the particles does not exceed (0.3 ± 0.05) mm. 3. The method according to claim 2, characterized in that at the same time only one of the fractions is supplied for leaching. 4. The method according to claim 1, characterized in that the leaching of the magnetic fraction of serpentinite is carried out in a continuous countercurrent pulsating mode. 5. The method according to claims 1, 4, characterized in that the leaching is carried out with hydrochloric acid with a concentration of 15-20% and a temperature of 50-70 ° C supplied to the lower part of the apparatus, and the magnetic fraction of serpentinite is loaded into its upper part, in the middle part of the apparatus due to the heat of reaction, the temperature is maintained in the range of 90-105 ° C. 6. The method according to claim 5, characterized in that the magnesium chloride solution containing 5-10 g / l of free hydrochloric acid is removed at a temperature of 70-85 ° C from the upper part of the apparatus, and the precipitate of amorphous silicon dioxide is unloaded from its lower part . 7. The method according to claim 6, characterized in that the washing of the precipitate of amorphous silicon dioxide is carried out in a continuous countercurrent pulsating mode with 0.01-0.05% hydrochloric acid solution with a flow rate of 1-1.1 m ³ / t of sediment. 8. The method according to claim 7, characterized in that the precipitate of amorphous silicon dioxide after drying has a specific surface area of 230-320 m ² / year 9. The method according to claim 1, characterized in that the purification of the magnesium chloride solution from impurities is carried out at a temperature of 70-85 ° C by neutralization to a pH of 3.5-4.5, then the oxidation of ferrous iron, manganese and nickel to higher valency, followed by neutralization to a pH of 6-7.5 and separation by filtration of a solution of magnesium chloride from an iron-nickel precipitate. 10. The method according to claim 9, characterized in that the neutralization is carried out with a natural mineral brucite, previously calcined at 500-550 ° C and crushed to a particle size <50 μm. 11. The method according to claim 9, characterized in that the neutralization is carried out with magnesium hydroxide obtained from a solution of magnesium chloride. 12. The method according to claim 9, characterized in that the oxidation is carried out with chlorine or sodium hypochlorite at a pH of 3.5-4.5. 13. The method according to claim 9, characterized in that the washing of the iron-nickel precipitate is carried out in a continuous countercurrent pulsating mode with a water flow rate of 1.1-1.2 m ³ / t of sediment. 14. The method according to item 13, wherein the washed iron-nickel precipitate is dried at a temperature of 500-550 ° C and receive a concentrate for the production of metallic nickel or ferronickel alloys. 15. The method according to claim 1, characterized in that the synthesis of carnallite is carried out from a solution of magnesium chloride and ground spent potassium electrolyte in the presence of hydrochloric acid to obtain, after separation of carnallite, a mother liquor of magnesium chloride. 16. The method according to p. 15, characterized in that the spent potassium electrolyte is crushed to a fraction <0.5 mm, and the kings of metallic magnesium> 0.5 mm are separated. 17. The method according to p. 15, characterized in that the mother liquor of magnesium chloride after separation of carnallite is purified from calcium compounds. 18. The method according to claim 1, characterized in that the dehydration of carnallite is carried out in fluidized bed furnaces in two stages, in the first - to obtain the two-water product KCl · MgCl ₂ · 2H ₂ O, in the second - when hydrogen chloride is fed into the chamber of a boiling furnace layer to obtain carnallite containing not more than 0.2% water. 19. The method according to p. 18, characterized in that the second stage of carnallite dehydration is carried out in the mode of discrete supply of hydrogen chloride, depending on the temperature of the material in the chambers of the fluidized bed furnace. 20. The method according to claim 19, characterized in that the hydrogen chloride is obtained in a separate apparatus by the conversion of chlorine gas and water vapor in a natural gas flare in the temperature range 950-1300 ° C. 21. The method according to claim 20, characterized in that the conversion of chlorine gas to hydrogen chloride is carried out at a volume ratio of CH ₄ : Cl ₂ : H ₂ O = 1: 4: 2 to obtain a gas containing at least 85 vol.% Hydrogen chloride. 22. The method according to claim 1, characterized in that carnallite is introduced into the anode space of the working cells in the stream. 23. The method according to item 22, wherein the electrolytic cells together with dehydrated carnallite load carbon-containing material in an amount of 0.05-0.1% by weight of the raw material.