RU2218452C2 - Way to win magnesium from synthetic carnallite - Google Patents

Abstract

FIELD: non- ferrous metallurgy, winning of magnesium by electrolysis of molten chlorides. SUBSTANCE: proposed way includes crystallization of spent electrolyte removed from electrolyzer, its crushing, mixing with chlorine-magnesium solution and synthesis of carnallite. Then its dewatering with extraction of solid anhydrous and/or deeply dewatered carnallite and its loading for electrolysis. In correspondence with invention spent electrolyte is endured in molten state prior to crystallization with production of clarified part directed for crystallization, bottom residue and melt enriched with oxides. EFFECT: increased quality of synthetic carnallite, additional recovery of magnesium for production of potash-magnesium fertilizers and/or anti-sleet preparation. 4 cl

Description

 The invention relates to ferrous metallurgy, in particular to the production of magnesium by electrolysis of chloride salts.

 Currently, in the electrolytic production of magnesium, carnallite is one of the main sources of raw materials. In connection with the increase in prices for natural enriched carnallite, and the complexity of recycling production waste, it is of interest to produce magnesium from synthetic carnallite obtained from spent electrolyte and / or potassium chloride and chlorine-magnesium solutions.

 A known method of producing magnesium from synthetic carnallite, including obtaining chloramagnesium solutions, their purification and evaporation, mixing with pulps of spent electrolyte and potassium chloride, cooling the mixture, precipitation of carnallite, its dehydration and electrolysis / Lebedev O.A. Magnesium production by electrolysis. M .: Metallurgy, 1988.S. 33-34 /.

 The disadvantages of this method are significant losses of magnesium chloride (up to 15%), contamination of the resulting carnallite with impurities present in the starting materials: sulfates, magnesium oxide and others.

 The closest in essence and the achieved effect is a method for the production of magnesium from oxide-chloride raw materials / RF Patent 2118406 / - prototype. The essence of the method consists in leaching magnesium from oxide raw materials to obtain chloromagnesium solutions, their purification, concentration, mixing with anhydrous spent electrolyte, synthesis of carnallite, its dehydration, electrolysis to produce magnesium, spent electrolyte and chlorine, returned to the raw material production process.

The disadvantage of this method is the contamination of synthetic carnallite with impurities contained in the spent electrolyte (MgO, Mg, SiO ₂ , Al ₂ O ₃ , F ₂ O ₃ and others), which reduces the quality of the resulting carnallite and, accordingly, reduces current efficiency and performance electrolyzer.

 The proposed technical solution is aimed at solving the problem of improving the quality of synthetic carnallite due to the preliminary preparation of the spent electrolyte for synthesis.

 The solution to this problem is provided by the fact that in the method for producing magnesium from synthetic carnallite by electrolysis, including crystallization of the spent electrolyte removed from the electrolyzer, its crushing, mixing with a chlorine-magnesium solution and synthesis of carnallite, its dehydration to obtain solid anhydrous and / or deeply dehydrated carnallite and loading onto electrolysis , according to the invention, before crystallization, the spent electrolyte is kept in a molten state to obtain a clarified part of the guided crystallization, bottom residue and oxide-rich melt.

The solution of the problem is also ensured by the fact that
- the spent electrolyte in the molten state is maintained at a temperature of at least 660 ^o C to a residual content of magnesium oxide of not more than 0.08%;
- the spent electrolyte after crushing is additionally crushed to a particle size of not more than 100 microns;
- the bottom residue and the melt enriched with impurities are processed into potassium-magnesium fertilizer and / or anti-icing preparation.

The proposed method is as follows. The spent electrolyte is removed from the electrolyzer, sedimented at a temperature of at least 660 ^o C to the content of magnesium oxide in the clarified part of not more than 0.08%. Magnesium from the surface of the melt is removed in a known manner and sent for refining. The clarified part of the melt from the mixer is poured into boxes, cooled, crushed and ground to a particle size of not more than 100 microns and sent to the synthesis of carnallite.

At temperatures below 660 ^o C, the duration of sludge increases due to an increase in the viscosity of the electrolyte, a crust forms on the surface, which complicates the fusion of magnesium droplets and their extraction.

 When the content of magnesium oxide in the electrolyte is below 0.08%, the duration of the sludge increases and thereby reduces the productivity of the apparatus.

 An increase in the particle size of the spent electrolyte over 100 μm slows down the speed of the synthesis process.

 When using spent electrolyte without additional sludge, the content of magnesium oxide in carnallite increases 10 times. After dehydration, the MgO content in the obtained product is at the level of its content in dehydrated carnallite obtained from natural carnallite.

Bottom residue containing, wt.%: 4-6 MgCl ₂ , 60-65 KCl, 3-4 MgO, ost. NaCl, CaCl ₂ , etc., are removed, cooled, and sent to receive potassium-magnesium fertilizers or an anti-icing preparation.

 Analysis of the totality of the features of the claimed invention, the new order of actions and the result achieved in this case shows that the proposed method meets the criteria of "novelty" and "inventive step" in relation to the totality of essential features.

 Information confirming the possibility of implementing this method is given in the examples.

 Example 1 (by a known method).

1000 kg of spent electrolyte containing, wt. %: 5.5 MgCl ₂ , 0.8 MgO, 0.12 Mg, 71.6 KCl, 17.8 NaCl, 0.69 CaCl ₂ , the rest are oxides of Fe, Al, Si and others. The melt was cooled, crushed and ground mixed with 1.83 m ^{3 of a} magnesium chloride solution with a mass concentration of 500 g / dm ³ MgCl ₂ . After synthesis, 2895 kg of synthetic carnallite were obtained, containing, wt.%: 31.6 MgCl ₂ , 0.28 MgO, 24.7 KCl, 6.1 NaCl, 0.23 CaCl ₂ . After dehydration, 1831 kg of deeply dehydrated carnallite containing 0.8 MgO and 0.4 N ₂ O were obtained.

 Example 2

1000 kg of spent electrolyte composition, wt. %: 0.3 Mg, 0.8 MgO, 5.4 MgCl ₂ , 71.6 KCl, 17.9 NaCl, 0.9 CaCl ₂ , the rest are oxides of Fe, Al, Si, etc., were poured into a steel crucible and placed in an oven, kept at a temperature of 700 ^o C to a residual content of 0.08% MgO in the clarified portion. 2.8 kg of magnesium was removed from the surface of the electrolyte. Then, 800 kg of electrolyte of the composition, wt.%: 0.01 Mg, 0.08 MgO, 5.61 MgCl ₂ , 74.5 KCl, 18.59 NaCl, 0.9 CaCl _{2 were} pumped out with a vacuum bucket.

Spent electrolyte after crystallization, crushing and grinding to a particle size of 100 μm was mixed with 1430 dm ^{3 of a} magnesium chloride solution with a concentration of 500 g / dm ³ . As a result of synthesis, 2525 kg of crude carnallite were obtained. After dehydration in a fluidized bed furnace, 1521 kg of deeply dehydrated carnallite were obtained, containing, wt.%: 49.8 MgCl ₂ , 0.26 MgO, 39.0 KCl, 9.7 NaCl, 0.5 CaCl, 0.4 H ₂ 0 .

 Deeply dehydrated carnallite was loaded into the electrolyzer and magnesium, spent electrolyte, and chlorine were obtained.

The bottom residue in the amount of 192 kg of the composition, wt.%: 61.0 KCl, 4.6 MgCl, 3.7 MgO, 15.2 NaCl, 0.8 CaCl ₂ , 0.05 Mg, the rest are oxides Fe, Al, Si and others. They were pumped into the box, cooled, crushed to a particle size of 2-5 mm and sent as fertilizer.

 The proposed method for producing magnesium from synthetic carnallite due to the additional preparation of spent electrolyte will reduce by 2.5-3 times the content of magnesium oxide in the resulting carnallite, additionally extract magnesium and obtain potassium-magnesium fertilizer and / or anti-icing preparation, i.e. create a virtually waste-free technology for the production of magnesium.

Claims (5)

1. A method of producing magnesium from synthetic carnallite by electrolysis, including crystallization of spent electrolyte removed from the electrolyzer, crushing it, mixing it with a chlorine-magnesium solution and synthesizing carnallite, dehydrating it to obtain solid anhydrous and / or deeply dehydrated carnallite, and loading onto electrolysis, characterized in that before by crystallization, the spent electrolyte is kept in a molten state to obtain a clarified portion directed to crystallization, a bottom residue and enriched oxides of the melt. 2. The method according to claim 1, characterized in that the exposure of the spent electrolyte is carried out at a temperature of at least 660 ° C. 3. The method according to claim 1, characterized in that the spent electrolyte is maintained until the content of magnesium oxide is not more than 0.08%. 4. The method according to claim 1 or 2, characterized in that the spent electrolyte after crushing is further crushed to a particle size of 100 microns. 5. The method according to claim 1, characterized in that the bottom residue and the oxide-rich melt of the spent electrolyte are processed into an anti-icing preparation and / or potassium-magnesium fertilizer.