RU2241670C1 - Serpentinite processing method - Google Patents

Abstract

FIELD: inorganic compounds technology and nonferrous metallurgy.

SUBSTANCE: method of processing serpentinite into magnesium and silica powder comprises leaching serpentinite with aqueous hydrochloric acid to give suspension containing dissolved magnesium chloride and undissolved silica. Suspension is separated into liquid (magnesium chloride solution) and solid (silica) phases. Magnesium chloride solution is freed of impurities by neutralization. Precipitated impurities (iron, nickel, and chromium hydroxides) are separated and remaining magnesium chloride solution is processed to produce anhydrous carnallite, which is subjected to electrolysis producing magnesium, anodic chlorine, and spent electrolyte. Carbon-containing blend prepared from silica is chlorinated with chlorine and resulting silicon tetrachloride is purified and subjected to vapor-phase hydrolysis to give silica powder and hydrogen chloride. The latter is used in preparation of anhydrous carnallite, after which is absorbed in water to give aqueous hydrochloric acid used for leaching of serpentinite.

EFFECT: achieved complete utilization of raw materials.

1 dwg

Description

The invention relates to the field of metallurgy and chemical technology of inorganic substances and can be used for the processing of serpentinite to obtain marketable products - magnesium and aerosil.

A known method of extracting magnesium compounds from asbestos waste by leaching with mineral acid (UK Patent No. 2033364; C 01 F 5/00; 05/21/1980).

The resulting suspension is filtered. Complex processing of asbestos waste is not conducted - the solid phase is not processed.

A known method for the production of magnesium from oxide raw materials, in particular serpentinite (asbestos waste) by leaching with hydrochloric acid obtained by the absorption of hydrogen chloride from water from the products of the conversion of anode chlorine in a natural gas combustion torch (Patent RF 2118406, С 25 С 3/04; 27.08.89, BI No. 24).

The resulting chloro-magnesium solution is purified, concentrated and synthetic carnallite is obtained, and magnesium, chlorine and spent electrolyte are obtained by electrolysis of dehydrated carnallite. Complex processing of serpentinite is not carried out - the silicon-containing residue (SiO ₂ content in the processed sample is 34.3%) is not processed.

A known method of producing a solution of magnesium chloride by leaching of serpentinite (asbestos waste) with hydrochloric acid (US Patent No. 5980854; C 01 F 5/30, C 22 B 26/22, 11/09/1999). The resulting suspension is neutralized and separated into solid and liquid phases to extract a pure solution of magnesium chloride containing 1 ppm or less of each impurity.

According to this method, complex processing of serpentinite is not carried out - the solid phase is not processed.

The closest known analogues in terms of technical nature and the achieved result is a method for processing serpentinite using magnesium production technology by Bedrand M. The Production of Magnesium by Noranda. 58 ^th Annual World International Magnesium Assotiation Conference. May 20-22, 2001, Brussels Belgium , pp57-64, prototype).

According to the prototype method, serpentinite is leached with hydrochloric acid, the suspension is neutralized and filtered to obtain a chlorine-magnesium solution (Brain) and silicon dioxide. Silica is sent to a secure storage facility built on top of a pile of serpentinite dumps. This eliminates the use of agricultural land for waste storage.

The magnesium chloride solution is purified, then dried in a fluidized bed to obtain granules of magnesium chloride dihydrate.

The granules are loaded into a chlorinator for dehydration, hydrogen chloride is fed into the chlorinator.

Anhydrous magnesium chloride is charged into the electrolyzer to produce magnesium metal and chlorine. Chlorine from the electrolyzer is washed and purified before being burned with hydrogen in a hydrogen chloride reactor. The resulting hydrochloric acid is condensed to remove traces of hydrogen. Anhydrous hydrogen chloride is obtained from hydrochloric acid in stripping columns and sent to a chlorinator. The chlorine effluent gases containing harmful organic compounds are re-condensed to remove impurities from hydrochloric acid by adsorption of activated carbon.

The purified and prepared hydrochloric acid is recycled to leach serpentinite at the beginning of the process.

The disadvantages of this method of processing serpentinite are:

- low complexity of the use of raw materials, because all silicon dioxide is not disposed of (sent to the dump);

- the need for washing chlorine before conversion to hydrogen chloride;

- the need for hydrogen chloride by the reaction of chlorine with hydrogen;

- the need for additional purification of hydrogen chloride from traces of hydrogen.

An object of the invention is to increase the complexity of the use of raw materials and simplify the preparation of chlorine and hydrogen chloride for use in the synthesis of Hcl and dehydration of carnallite.

The technical result obtained by the implementation of the claimed invention is to reduce the production of waste products during processing of serpentinite, eliminating the washing of chlorine and purification of hydrogen chloride from hydrogen.

The specified technical result is achieved by implementing the proposed method for processing serpentinite, the essence of which is expressed by the following set of essential features:

- leaching of magnesium from serpentinite with hydrochloric acid to obtain a suspension;

- filtering the suspension to obtain a magnesium chloride solution and a precipitate of silicon dioxide;

- purification of the magnesium chloride solution from impurities by neutralization, filtration, obtaining synthetic carnallite from the filtrate and spent electrolyte;

- dehydration of carnallite using hydrogen chloride;

- electrolysis of carnallite to produce magnesium, spent electrolyte and chlorine;

- production of hydrogen chloride from chlorine by chlorination of silicon dioxide to obtain silicon tetrachloride and the vapor-phase hydrolysis of silicon tetrachloride in the combustion products of an air-hydrogen or air-hydrocarbon mixture to produce aerosil and hydrogen chloride;

- the allocation of dust-gas mixture of aerosil;

- dehydration of carnallite in the presence of hydrogen chloride contained in the vapor-gas mixture of the vapor-phase hydrolysis process;

- absorption of hydrogen chloride by water from the exhaust gases after dehydration of carnallite to obtain hydrochloric acid, which is sent to leach serpentinite.

Significant distinguishing features of the proposed method is that hydrogen chloride is produced in two stages from chlorine generated during the electrolysis of carnallite: by chlorination of a carbon-containing mixture prepared from silicon dioxide, followed by vapor-phase hydrolysis of silicon tetrachloride to obtain aerosil and hydrogen chloride, which is sent to dehydrate carnallite .

It should be noted that the washing of chlorine and the synthesis of hydrogen chloride using hydrogen and, accordingly, cleaning of traces of hydrogen are excluded.

From a comparison of the considered methods it follows that the above new methods of performing actions and a new procedure for performing actions ensure the achievement of a technical result in carrying out the invention.

The drawing shows a flow diagram of the processing of serpentinite with obtaining magnesium and aerosil.

Serpentinite is crushed and then leached with a solution of hydrochloric acid obtained after absorption of exhaust gases from dehydration of carnallite. After leaching, the suspension is filtered, the silica precipitate is separated, and the magnesium chloride solution is purified by neutralization, the pulp is filtered, and the precipitate of Fe, Ni, and Cr hydroxides is separated, and the nickel-iron concentrate is sent to the consumer.

The purified chlorine-magnesium solution is supplied for preparation by mixing six-water carnallite with the spent electrolyte. The obtained KCl · MgCl ₂ · 6H ₂ O is directed to fluidized bed dehydration in a stream of hydrogen chloride obtained by vapor-phase hydrolysis of silicon tetrachloride.

During the electrolysis of carnallite, magnesium is formed, which is sent to the consumer, spent electrolyte supplied to prepare the six-water carnallite, and chlorine, which is sent to the two-stage production of hydrogen chloride: by chlorination of silicon dioxide by the reaction of SiO ₂ + 2Cl ₂ + C → SiCl ₄ + CO ₂ and vapor-phase by hydrolysis of silicon tetrachloride in the products of the combustion of hydrogen (or hydrocarbon) at a temperature of 1100-1400 ° C according to the reaction SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4НСl.

During vapor-phase hydrolysis, aerosil (finely divided silica) is formed, which is sent to the consumer, and hydrogen chloride, which is sent to dehydrate the six-water carnallite and the subsequent production of hydrochloric acid (16-25% Hcl) to leach serpentinite.

Chlorides formed upon separation by selective condensation of chlorides, purification and isolation of silicon tetrachloride are neutralized and disposed of.

Exhaust gases after dehydration of carnallite and absorption of hydrogen chloride are discharged into the pipe, the exhaust gases of chlorination are neutralized and discharged into the pipe.

Example. 500 g of serpentinite containing 21.8% Mg were charged to the reactor; 5.7% Fe; 0.25% Ni; 0.2% Cr; 2% Ca; 38.3% SiO ₂ , particle size less than 1.2 mm and 1.4 dm ³ hydrochloric acid (25 wt.% Hcl). The suspension was leached at 80-90 ° C; after filtration, 1.7 dm ^{3 of a} magnesium chloride solution filtrate (g / dm ³ ) was obtained: MgCl ₂ - 249; Fe - 16.1; CaCl ₂ - 13.2; Ni - 0.7; Cr 0.26 and 203.8 g of a silica precipitate (wt.%): StO ₂ 85.3; MgO - 0.8; Fe ₂ O ₃ - 0.6; CaO - 1.3; Cr ₂ O ₃ - 0.1; NiO - 0.03.

The chlorine-magnesium solution was neutralized with brucite and sodium hydroxide, the pulp was filtered, the precipitate was calcined at 700 ° C. 62.9 g of a product was obtained containing (wt.%): Fe ₂ O ₃ - 62.2; NiO - 2.4; Cr ₂ O ₃ - 2.1. Such a material is a high-quality oxidized raw material for the production of nickel and ferronickel.

Purified chlorine-magnesium solution [filtrate] (volume 1.9 dm ³ ) containing (g / dm ³ ): MgCl ₂ - 230; CaCl ₂ - 2.2; NaCl - 15; Ni - 0.0005; Cr 0.0005; Si <0,0002; Fe - 0.0005, was processed according to the generally accepted scheme: evaporated at a temperature of 110-120 ° С to the content of magnesium chloride 36 wt.%, Then 466 g of spent electrolyte containing (wt.%) Was added: MgCl ₂ - 6; KCl 74.9; NaCl - 18; CaCl ₂ - 0.5, the mixture was heated to 136 ° C. The resulting synthetic carnallite was cooled to 65 ° C and dehydrated in a fluidized bed furnace. A mixture of hydrogen chloride with flue gases was fed into the furnace. The content of HCl in the gas mixture was 6 vol.%, The temperature in the fluidized bed was maintained within the range of 300-350 ° C. 912 g of dehydrated carnallite was obtained, containing (wt.%): MgCl ₂ - 49.2; KCl - 37.6; CaCl ₂ - 0.5; NaCl - 12.3; MgO - 0.2; H ₂ O - 0.1.

Dehydrated carnallite of this composition is a quality raw material for the production of magnesium and chlorine in the usual electrolytic manner.

100 g of the obtained precipitate of X-ray amorphous active silicon dioxide was crushed to a particle size of less than 160 μm, calcined at 400-450 ° C, mixed with carbon and 130 g of a mixture containing (wt.%) Were obtained: SiO ₂ - 65; C is 30.5. The resulting mixture was chlorinated at a temperature of 920-970 ° C with a chlorine-air mixture containing 80 vol.% Cl ₂ and 20 vol.% Air. The degree of chlorination of silicon dioxide was 93.4%. Fractional condensation of the components of a gas-vapor mixture of metal chloride impurities (FeCl ₃ , AlCl ₃ , chromium, manganese, magnesium chlorides, etc.) was separated from technical silicon tetrachloride, from which 201 g of purified SiCl ₄ were obtained by distillation and rectification, in which the iron content and aluminum amounted to <0.001 wt.% each, the chlorine content of 0.02 wt.%.

The obtained silicon tetrachloride was evaporated, the vapor was fed into the burner by a stream of transporting air, where vapor-phase hydrolysis of SiCl _{4 was} carried out in a hydrogen-air flame at a temperature of 1150-1200 ° C. 67 g of aerosil were isolated from the reaction products, the specific surface area of the product determined by the BET method on a GHP device, amounted to 270 m ² / g A product of this quality is used as a filler in the manufacture of rubber products, plastics, as a thickener for paints, lubricants and other liquids.

The resulting gas mixture (590 L) after separation of Aerosil contains (vol.%): Hcl - 18; H ₂ O - 4; nitrogen and air - the rest. Such a gas mixture, diluted with hot flue gases to 6-10 vol.% Hcl, provides deep dehydration of carnallite with minimal hydrolysis of magnesium chloride.

Thus, the technological scheme described above allows us to solve the problem of processing serpentinite with an increase in the complexity of using raw materials while simplifying the preparation of chlorine and hydrogen chloride for use in the processes of producing HCl and dehydration of carnallite. Moreover, in comparison with the Noranda method, a reduction in the amount of production waste is achieved due to the possibility of using silicon dioxide for the production of aerosil and iron-nickel concentrate to produce nickel or ferronickel.

Claims (1)

A method of processing serpentinite, including leaching with hydrochloric acid, filtering the suspension to obtain a magnesium chloride solution and silicon dioxide, purifying the filtrate by neutralization, obtaining dehydrated carnallite, electrolysis of carnallite to obtain magnesium, spent electrolyte and chlorine, obtaining hydrogen chloride from chlorine to dehydrate carnallite and salt leaching, characterized in that the production of hydrogen chloride is carried out in two stages: by chlorination of silicon dioxide to obtain tetrachloride and silica and vapor-phase hydrolysis of silicon tetrachloride and aerosil to obtain hydrogen chloride.