A production process for producing metallic magnesium and industrial silicon by decomposing serpentine using the hydrochloric acid method.

Abstract

This invention provides a production process for manufacturing metallic magnesium and industrial silicon by decomposing serpentine using the hydrochloric acid method. [Solution] The present invention provides a method for processing serpentine ore as a raw material using a two-stage countercurrent hydrochloric acid leaching process. The wet process steps include storage and filtration of the slurry after ore dressing, two-stage hydrochloric acid leaching under atmospheric pressure, washing and filtration of the silicon slag after leaching, removal of iron and nickel precipitation from the leaching solution, separation, washing and filtration of the obtained iron hydroxide and nickel hydroxide, crystallization and evaporation of the magnesium chloride solution, and production of hydrochloric acid using the gas generated after the thermal decomposition of magnesium chloride. The present invention has developed a serpentine decomposition technology using hydrochloric acid, a metallic magnesium production process using a drying-electrolytic method, and a process for producing industrial silicon by smelting silicon slag in an electric furnace.

Description

[Technical Field]

[0001] This invention relates to a comprehensive utilization technology for serpentine, and more particularly to a production process for producing metallic magnesium and industrial silicon by decomposing serpentine using the hydrochloric acid method. [Background technology]

[0002] With the rapid development of modern industry, traditional metal resources are becoming depleted. Therefore, it is necessary to search for and develop new metal resources.

[0003] Magnesium is one of the most abundant elements on Earth, making up approximately 2.3% of the metallic minerals in the Earth's crust, and is also extremely abundant in salt lakes and oceans. Therefore, accelerating the development of magnesium metal materials is one of the important measures for achieving sustainable development. The demand for magnesium metal, which possesses excellent properties, is increasing year by year, and its application fields are expanding more and more. Magnesium has now emerged as the "metal of the age" on the stage of metallurgical materials, and stands out among non-ferrous metals. Today, it has established itself as the fifth major non-ferrous metal, after copper, aluminum, lead, and zinc. However, although the magnesium metal industry, which has an advantage in abundant resources, is developing rapidly, its market potential remains largely untapped. Therefore, promoting the further development of the magnesium industry and developing new metallic magnesium smelting processes is now a key focus of research worldwide.

[0004] Conventional magnesium and magnesium-based materials are primarily derived from magnesite-based magnesium carbonate ore. These ores require a high-temperature calcination (roasting) process to convert them into magnesium oxide (MgO). The specific production process consists of the following steps. 1. Mining: Ore is extracted from magnesite or dolomite mines. 2. Crushing and pulverization: The mined ore is crushed and pulverized to become a fine powder. 3. Pre-treatment: Pre-treat the powder to remove impurities and foreign matter. 4. Roasting: The pre-treated powder is placed in a high-temperature furnace and roasted to convert it into magnesium oxide. 5. Purification: The magnesium oxide after calcination is purified to remove any remaining impurities. 6. Materialization: Refined magnesium oxide is a major basic raw material for magnesium-based refractory materials, magnesium sulfate, and magnesium salts. 7. Conventional magnesium ingot manufacturing methods use the pigeon process, which involves reducing and firing silicon iron and dolomite at high temperatures. This process consumes a large amount of coal and simultaneously emits a large amount of carbon dioxide.

[0005] From the perspective of current environmental protection requirements, such conventional production processes have serious drawbacks and problems. These processes consume large amounts of energy and generate large amounts of carbon dioxide (CO2) during the firing process. As a result, the supply of metallic magnesium and magnesium-based materials faces significant pressure in terms of both energy and environmental impact.

[0006] Therefore, the development of new chemical industrial processes and process routes is extremely important for the development of the magnesium and magnesium-based materials industry. By using serpentine as a raw material instead of conventional magnesium carbonate ore, it becomes possible to open up new sources of magnesium and magnesium-based materials.

[0007] China's serpentinite resources are extremely abundant, and many of them belong to ultramafic serpentinite deposits. These deposits are characterized by their large number, size, wide distribution, and favorable texture and structural conditions of the ore. Serpentinite is classified as a 1:1 type layered silicate mineral, composed of Si-O tetrahedral sheets and Mg-O octahedral sheets, and its main mineral species include chrysotile (fiber serpentinite), lizardite (leaf serpentinite), and antigorite (granular serpentinite). The main mineral composition of serpentinite, serpentinite tailings, and asbestos tailings is primarily serpentinite, accompanied by small amounts of magnetite, talc, magnesium hydroxide, dolomite, and calcite. The main chemical composition is SiO2 and MgO, with small amounts of Fe2O3, Al2O3, NiO, and Cr2O3. Among these, the main metal oxide is magnesium oxide (MgO).

[0008] Currently, the most commonly used method for the effective utilization of serpentine resources is to add organic or inorganic acids to the serpentine raw material and directly acid-treat it to produce various magnesium-containing compound products. Furthermore, the residue remaining after extracting magnesium oxide from serpentine can be reacted directly with sodium hydroxide to produce chemical products such as sodium metasilicate and white carbon.

[0009] To date, there are no reports of a technology that involves decomposing serpentine using hydrochloric acid, producing metallic magnesium by high-temperature drying-electrolysis, and then smelting silicon slag in an electric furnace to produce industrial silicon. Despite these technologies being processes that involve minimal environmental pollution, low energy consumption, and low costs, there are currently no publicly disclosed examples of their use. [Overview of the project]

[0010] The technical problem that this invention aims to solve is to provide a production process for producing metallic magnesium and industrial silicon by decomposing serpentine using the hydrochloric acid method.

[0011] The present invention is realized as follows. A production process that uses serpentine ore as a raw material and decomposes serpentine using the hydrochloric acid method to produce metallic magnesium and industrial silicon, Step (1) involves concentrating and filtering the slurry obtained after wet grinding of serpentine ore to obtain a raw material slurry, Step (2) involves performing a two-step atmospheric pressure hydrochloric acid leaching on the pre-treated raw material slurry, Step (3) involves CCD washing, filtration, and drying of the leached crude silica slag to obtain silicon slag, further reducing and smelting to remove impurities through purification, and crushing to obtain industrial silicon. Step (4) involves removing iron and precipitation of nickel from the leachate, separating the precipitated iron hydroxide and nickel hydroxide, washing and filtering, Step (4) involves removing secondary impurities and purifying the crystals, then evaporating them to concentrate the magnesium chloride, and obtaining a magnesium chloride solution with a mass concentration of 45%-55% as the raw material for the dry magnesium chloride in step (5). Step (6) involves drying the magnesium chloride, Step (7) electrolyzes magnesium chloride sent from the drying system into metallic magnesium and chlorine gas, Step (8) of purifying magnesium, A production process characterized by including the following.

[0012] Furthermore, in step (1), the slurry is a slurry with a mass concentration of 8-15%, and is obtained by mixing serpentine ore fine powder raw material with hydrochloric acid to form a slurry.

[0013] Furthermore, in step (2), the two-stage atmospheric pressure hydrochloric acid leaching is carried out by a hydrochloric acid-based two-stage countercurrent leaching process, specifically including the following steps A to C: In step A, the pre-treated raw material slurry is sent to a single-stage leaching process, the slurry temperature in the single-stage leaching process is controlled to 80°C-85°C, and the leaching time is 2h-3h. In step B, after the first leaching, the concentrated overflow liquid is sent to the neutralization and iron removal process, and if the residual acid from the leaching is between 5-15 g / L, the underflow liquid from the first leaching is sent to the second leaching process. In step C, the slurry temperature in the two-stage leaching process is controlled to 95°C-100°C, the leaching time is set to 2h-3h, the crude silica slag obtained after the two-stage leaching separation is sent to the CCD process for washing, and the overflow liquid from the two-stage leaching process is returned to the single-stage leaching process.

[0014] Furthermore, in step (3), after the crude silica slag is slurryed, countercurrent washing is performed using a concentrator, and the washing system uses a 5-stage countercurrent washing system, controlling the washing ratio (weight ratio of washing water to solids entering the concentrator) to 2:1.

[0015] Furthermore, in step (3), the reduction smelting is carried out using silicon slag as the main raw material, modified coke powder and wood lumps as reducing agents, and smelting in a semi-closed electric furnace.

[0016] Furthermore, in step (3), the purification and impurity removal is carried out by a bottom-blowing method using oxygen and compressed air, in which compressed air is first blown in from the bottom of the silicon ladle, followed by oxygen, to perform oxidative refining on the molten silicon.

[0017] Furthermore, in step (4), the iron removal employs a two-step process, including the following steps a and b: In step a, after neutralizing the residual acid using magnesium hydroxide slurry as a neutralizing agent, in the first stage of iron removal, the endpoint pH value is controlled to 3.0-3.5, and trivalent iron and aluminum are hydrolyzed and precipitated, while silica is co-precipitated and removed. The slurry after iron removal is then concentrated and separated. In step b, the end point pH value of the second-stage iron removal is controlled to be 4.0 - 4.5. By blowing compressed air, ferrous iron is oxidized to ferric iron, and iron and aluminum in the primary slurry are further hydrolyzed and removed. The overflow liquid of the second-stage iron removal is sent to the nickel precipitation process. After the underflow liquid of the second-stage iron removal passes through the CCD washing process, the overflow liquid after slurrying is returned to the first-stage iron removal process to recover valuable metals in the slag.

[0018] Furthermore, in step (6), for the drying, a cooling granulation, one-stage air-flow dehydration, and one-stage molten salt dehydration process are adopted to obtain anhydrous magnesium chloride.

[0019] Furthermore, for the molten salt dehydration, a hydrochloric acid drying system is adopted to gradually remove water molecules in magnesium chloride, obtain a magnesium chloride molten salt, and recover the dried HCl-containing gas to produce hydrochloric acid.

[0020] Furthermore, the process adopts a system for comprehensively utilizing serpentine ore. The system includes a two-stage countercurrent leaching reactor. A solid-liquid separation and washing device is connected to the leaching liquid outlet of the two-stage countercurrent leaching reactor. A metallic magnesium production line is connected to the overflow port of the solid-liquid separation and washing device. An industrial silicon production line is connected to the silicon slag outlet of the solid-liquid separation and washing device. The metallic magnesium production line includes a sequentially connected iron removal device, nickel precipitation device, evaporation concentration device, magnesium chloride drying device, and magnesium chloride electrolysis device. The industrial silicon production line includes a sequentially connected silicon slag drying device, reduction smelting device, and refining impurity removal device.

[0021] The present invention has the following advantages. This invention develops a serpentine decomposition technique using hydrochloric acid, a metallic magnesium production process using a drying-electrolytic method, and a process for producing industrial silicon by smelting silicon slag in an electric furnace. The resulting metallic magnesium product meets the chemical composition requirements of the Chinese national standards, and the industrial silicon product conforms to the standards for chemical silicon. This invention has the characteristics of a short process, minimal environmental pollution, low energy consumption, and relatively low cost, opening up a new direction for the comprehensive utilization of serpentine resources. [Brief explanation of the drawing]

[0022] The present invention will be further described below with reference to the drawings and examples. [Figure 1] This is a schematic diagram of the system structure of the present invention.

[0023] Explanation of the symbols Two-stage countercurrent leaching reactor 1, solid-liquid separation and washing apparatus 2, iron removal apparatus 3, nickel precipitation apparatus 4, evaporative concentration apparatus 5, magnesium chloride dryer 6, granulation centrifuge 61, air-fluidized bed dryer 62, HCl gas drying mechanism 63, magnesium chloride electrolytic apparatus 7, silicon slag dryer 8, reduction smelting apparatus 9, refining impurity removal apparatus 10, hydrochloric acid absorption tower 11, chlorine compressor 12, hydrochloric acid synthesis apparatus 13, water electrolytic apparatus 14, metallic magnesium refining and casting apparatus 15, dust removal apparatus 16. [Modes for carrying out the invention]

[0024] The technical aspects of the present invention will be described clearly and completely below with reference to the drawings and specific embodiments. Unless otherwise specified in the embodiments, the procedures were followed under normal conditions or conditions suggested by the manufacturer. The equipment used, unless otherwise specified by manufacturer, is all a standard, commercially available product.

[0025] The process of the present invention employs a system that comprehensively utilizes serpentine. This system includes a two-stage counterflow leaching reactor 1. A solid-liquid separation and washing device 2 is connected to the leaching outlet of the two-stage counterflow leaching reactor 1. The overflow port of the solid-liquid separation and washing device 2 is connected to a metallic magnesium production line, and the silicon slag outlet of the solid-liquid separation and washing device 2 is connected to an industrial silicon production line. The metallic magnesium production line includes, in sequence, an iron removal device 3, a nickel precipitation device 4, an evaporation and concentration device 5, a magnesium chloride dryer 6, and a magnesium chloride electrolytic device 7. The industrial silicon production line includes, in sequence, a silicon slag dryer 8, a reduction smelting device 9, and a refining and impurity removal device 10.

[0026] Furthermore, the solid-liquid separation and washing apparatus 2 is a CCD (Counter Current Decantation) concentrator.

[0027] Furthermore, the gas outlet of the magnesium chloride dryer 6 is connected to the hydrochloric acid absorption tower 11. The hydrochloric acid output port of the hydrochloric acid absorption tower 11 is connected to the recovered hydrochloric acid inlet of the two-stage counterflow leaching reactor 1.

[0028] Furthermore, the magnesium chloride drying apparatus 6 includes a granulation centrifuge 61, an air-fluidized bed dryer 62, and an HCl gas drying mechanism 63. The granulation centrifuge 61 is connected to the air-fluidized bed dryer 62 via a particle transport mechanism. The discharge port of the air-fluidized bed dryer 62 is connected to the supply port of the HCl gas drying mechanism 63.

[0029] Specifically, the air-fluidized bed dryer 62 includes a discharge hopper, a conveyor, a vibrating screen, a wet raw material hopper, and a supply pipe (all known configurations, not shown) provided along the particle transport path.

[0030] Furthermore, the gas outlet of the magnesium chloride electrolytic device 7 is connected to the chlorine gas inlet of the hydrochloric acid synthesis device 13 via the chlorine compressor 12, and the hydrogen gas inlet of the hydrochloric acid synthesis device 13 is connected to the water electrolytic device 14.

[0031] Furthermore, the magnesium chloride electrolytic apparatus 7 is further connected to the metallic magnesium refining and casting apparatus 15.

[0032] Furthermore, the flue gas outlet of the reduction smelting apparatus 9 is connected to the dust removal device 16 via a preheating boiler.

[0033] The specific process of this invention is as follows: 1. Slurry storage and filtration Serpentine ore is transported to the smelting yard, where it undergoes coarse and fine crushing to obtain serpentine ore with a particle size of approximately 10 mm. The obtained coarse powder is stored in the coarse powder hopper of the crushing system and then introduced into the crushing system. The coarse powder is sent to the vertical mill via a quantitative feeder, belt conveyor, and bucket elevator for crushing. The fine powder is collected by a bag filter dust collector and transported to the fine powder hopper via an air slide and bucket elevator for temporary storage. The particle size of the fine powder is controlled so that particles of 0.074 mm or smaller account for more than 85% of the total. The fine powder is slurryed in a slurry preparation tank located at the top of the hopper and then sent to the leaching process.

[0034] Slurry storage and filtration primarily involves processing a slurry of approximately 10% concentration sent from the raw material pretreatment area to meet the supply requirements of the subsequent leaching process, and includes steps such as slurry concentration, storage, filtration, and slurring. For slurring of the filtered cake, hydrochloric acid is used as the slurring solution. During the slurring process, small amounts of oxides in serpentine, such as MgO, FeO(OH), and NiO, react with the hydrochloric acid, resulting in a small overflow of HCl during the slurring process. This HCl is collected and then washed and recovered.

[0035] 2. Hydrochloric acid leaching From the perspective of the composition of serpentine ore, metallic elements exist mainly in the form of metal oxides in minerals, such as MgO, FeO(OH), NiO, CoO, CaO, FeO, MnO, and ZnO. Under normal pressure conditions (temperature ~95°C), most metallic oxides of Me (Mg, Ni, Co, Mn, Ca, Al) react with hydrochloric acid to form soluble chlorides (MeCl). nIt generates ) and enters the solution. The reaction equation is as follows: Me2O n (s) + 2nH + →2Me n+ +nH2O Here, Me represents Ni, Co, Mn, etc., and n is the valence of the metal ion. Since magnesium is mainly present in lizardite, which is a silicate mineral, most of the magnesium enters the leachate when the lizardite dissolves. Mg3Si2O5(OH)4(s)+6H + →3 Mg 2+ +2SiO2(s)+5H2O.

[0036] According to the results of serpentine leaching tests, the present invention employs a two-stage countercurrent atmospheric pressure hydrochloric acid leaching process. The pre-treated raw material slurry is first introduced into the first leaching process. The slurry temperature for the first leaching is controlled to approximately 80-85°C, and the leaching time is 2-3 hours. In this stage, most of the metal oxides are leached out. After the first leaching, the overflow of the concentrated slurry is sent to the neutralization and iron removal process, where the residual acid concentration is maintained in the range of 5-15 g / L. Meanwhile, the underflow from the first leaching is sent to the second leaching process. The slurry temperature for the second leaching is controlled to approximately 95-100°C, and the leaching time is 2-3 hours. The crude silica slag obtained by the separation operation after the second leaching is sent to the CCD washing process, and the overflow from the second leaching is returned to the first leaching process.

[0037] 3. Filtration of CCD and silica slag The crude silica slag obtained in the leaching process is slurryed and then washed in a countercurrent manner using a concentrator. Washing water is supplied from the product washing process and the recovered liquid after exhaust gas washing. To improve the efficiency of CCD washing, the washing system employs a five-stage countercurrent washing method, and the washing ratio (weight ratio of washing water to solids fed into the concentrator) is controlled to 2:1. The overflow liquid from CCD1 (first-stage CCD) is sent to the iron removal and nickel precipitation process to slurry the iron slag from the second-stage iron removal process, and then sent to the first-stage leaching process. On the other hand, the underflow from CCD5 is sent to the filtration process, and the filtered water-containing crude silica is transported by a belt conveyor to the dry metallurgy process for further manufacturing of silicon products.

[0038] 3.1 Production Process of Metallic Magnesium 3.1.1 Iron removal and nickel precipitation process The iron removal and nickel precipitation process primarily uses a magnesium oxide slurry to neutralize residual acid in the first-stage leaching overflow solution. Subsequently, the pH value is adjusted to remove impurity elements such as iron, aluminum, and silicon, and nickel is precipitated to recover valuable metals.

[0039] The iron removal process consists of two stages, using magnesium oxide slurry as a neutralizing agent. After neutralizing residual acid, the first stage of iron removal controls the endpoint pH to 3.0-3.5, hydrolyzing and precipitating ferric iron and aluminum, while co-precipitating and removing silica. The iron-removed slurry is then concentrated and separated. To facilitate the settling of precipitate particles, a portion of the underflow from the concentrator is used as seed crystals in the iron removal process. The underflow from the first stage of iron removal is sent to the product filtration and separation process for further treatment.

[0040] In the second stage of iron removal, the endpoint pH is controlled to 4.0-4.5, and compressed air is blown in to further hydrolyze the iron and aluminum in the first stage slurry by oxidizing divalent iron to trivalent iron. The overflow liquid from the second stage of iron removal is sent to the nickel precipitation process. A portion of the underflow from the second stage of iron removal is reused as seed crystals, and the remainder is slurryed with the overflow liquid of CCD6 and then returned to the first stage of iron removal to recover valuable metals such as nickel contained in the residue.

[0041] By further selecting magnesium oxide slurry as the precipitant for nickel precipitation and controlling the endpoint pH value of nickel precipitation to 8.0-8.5, nickel in the solution forms a hydroxide precipitate, and a small amount of manganese also precipitates simultaneously. The precipitated slurry is then sent to a concentrator for solid-liquid separation.

[0042] 3.1.2 Separation and Filtration of Products Product separation includes the concentration and separation of certain iron-free products, the concentration and separation of nickel precipitates, the filtration and separation of the underflow after concentration, and product packaging.

[0043] In the first stage of the iron removal product concentration and separation process, the overflow liquid from the concentrator is sent to the second stage of iron removal in the iron removal and nickel precipitation process. A portion of the underflow from the concentrator is reused as seed crystals, and the remainder is sent to the product filtration and washing process. After two stages of washing and two stages of pressure filtration, a wet iron powder is obtained, and this iron powder is sent to the iron concentrate drying process for drying. Secondary steam condensate of magnesium chloride is used for washing.

[0044] In the concentration and separation process of nickel precipitate products, a portion of the overflow liquid from the concentrator is sent to the magnesium chloride evaporation process via microfiltration, while the remainder is used as a preparation solution for precipitants and flocculants. A portion of the underflow liquid from the concentrator is reused as seed crystals, and the remainder is sent to the product filtration and washing process. In the filtration and washing process, nickel products are obtained through two washing and two pressurized filtration stages, and the products are automatically packaged. Secondary steam condensate of magnesium chloride is used for washing. Packaged nickel products can be stored in the nickel product warehouse.

[0045] The manufacturing of flocculants primarily involves providing flocculant solutions that can be used for operations in the concentration of raw materials, CCD, and product concentration and separation processes, and transporting them by pump to each point of use of the flocculant.

[0046] 3.1.3 Evaporative Concentration of Magnesium Chloride The magnesium chloride solution is introduced into the evaporation and concentration system after storage and preheating. The magnesium chloride evaporation and concentration system employs a quadruple-effect evaporation method to obtain a magnesium chloride solution with a concentration of 48-51%. Subsequently, cooling and granulation are performed in a granulation column to obtain 4,8-hydrate magnesium chloride solid. The obtained solid is transported by conveyor to a magnesium chloride dryer for drying. The secondary steam condensate after evaporation is returned to the system and used as washing water. The discharged mother liquor is returned to the iron removal and nickel precipitation process.

[0047] 3.1.4 Smelting Process of Metallic Magnesium 3.1.4.1 Magnesium chloride and auxiliary components (1) Magnesium chloride solution Magnesium chloride is evaporated and concentrated using a forced-circulation evaporator to obtain a magnesium chloride solution with a magnesium chloride content of 48%-51%, which is then used as a raw material in the magnesium chloride drying process.

[0048] Specifically, the magnesium chloride solution after wet purification contains approximately 25.44% MgCl2, and is concentrated to approximately 51% magnesium chloride solution using a multi-effect forced evaporation concentrator.

[0049] (2) Concentrated sulfuric acid The hydrated chlorine gas produced by electrolysis of magnesium chloride needs to be adsorbed and compressed. Therefore, 98% concentrated sulfuric acid is purchased, and 93% concentrated sulfuric acid is produced and sold.

[0050] 3.1.4.2 Smelting Process of Metallic Magnesium (1) Magnesium chloride drying system Since the MgCl2 solution produced by wet evaporation concentration has a content of approximately 51%, the present invention provides anhydrous magnesium chloride by a cooling granulation + one-stage air-flow dehydration + one-stage molten salt dehydration process.

[0051] The purpose of granulation is to convert concentrated liquid brine into solid granules. Magnesium chloride brine is introduced into a granulation centrifuge and sprayed into the granulation column in droplet form. The droplet magnesium chloride brine descends within the granulation column, making countercurrent contact with the cooling airflow introduced through a louver system, and parallel contact with the airflow at the top of the column. In this way, the particles fall in an umbrella-shaped trajectory, and the temperature of the air discharged from the top of the column can be controlled. The droplet brine forms solid particles during the cooling and crystallization process. An outlet hopper is provided at the bottom of the granulation column to receive the granulated wet particles. The particles are discharged from the bottom of the granulation column and sent to a vibrating sieve device via a conveying system using a belt conveyor and bucket elevator, where large particles are removed. The large particles are redissolved and returned to the granulation process. The remaining particles are sent to a wet material hopper and then supplied to an air-fluidized bed dryer.

[0052] The primary purpose of the air drying apparatus is to partially dry MgCl2 particles, reducing their water content from approximately 4.8 mol H2O / mol MgCl2 to approximately 1.8 mol H2O / mol MgCl2. Water-containing magnesium chloride particles in the wet particle hopper are introduced into the air drying apparatus via a supply pipe. The particles are then fed into the upper plate of a two-stage vertical fluidized bed, which uses hot air as the heating and drying medium. Hot air is introduced from the bottom of each stage to form the fluidized bed. An electric heater in the air drying apparatus heats compressed air, and this hot air is supplied to a slit-shaped feeder in the upper plate, uniformly dispersing the wet particles across the fluidized bed surface.

[0053] The generated MgCl2 enters a hydrogen chloride drying tower, where water molecules are gradually removed to obtain molten magnesium chloride, which meets the demands of the electrolytic cell and improves its lifespan.

[0054] In the drying process, HCl gas is obtained by chemically synthesizing hydrogen gas produced by water electrolysis and Cl2 generated from a magnesium electrolytic cell at high temperature. The resulting hydrated HCl gas undergoes multi-stage washing and concentration to obtain 36% hydrochloric acid, which is then returned to the leaching process.

[0055] (2) Metal Magnesium Smelting System In the magnesium electrolysis process, magnesium chloride (MgCl2) supplied from the drying system is electrolyzed to produce metallic magnesium and chlorine gas. The resulting metallic magnesium is refined, cast into ingots, and sold. Meanwhile, the generated chlorine gas is combusted with hydrogen gas in the synthesis process to produce hydrogen chloride (HCl).

[0056] MgCl2 is electrolyzed in an electrolytic cell and decomposed into magnesium (Mg) and chlorine gas (Cl2). The generated chlorine gas is discharged through chlorine gas piping and sent to the chlorination process via a chlorine compressor chamber. Meanwhile, the molten magnesium is removed by suction using a vacuum magnesium ladle at a predetermined time.

[0057] In magnesium electrolysis, a multi-stage tank magnesium manufacturing process is employed. During the production process, argon gas is introduced into the furnace to maintain a slight positive pressure state in order to prevent oxidation of molten magnesium. In addition, a purification tower is used to purify residual chlorine gas discharged during equipment maintenance, chlorine gas generated during the initial stages of operation, and chlorine gas in the event of an accident.

[0058] The chlorine compressor is used to transport chlorine gas produced by electrolysis. The medium in the chlorine compressor is concentrated sulfuric acid. The chlorine gas discharged from the electrolytic cell contains sublimations of the electrolyte. After leaving the electrolytic cell, the chlorine gas is collected in the chlorine gas main line via a chlorine gas branch line, and then introduced into a bag filter. After the sublimations are removed in the bag filter, the gas is pumped under pressure by the chlorine compressor, pressurized in the turbine room, and sent to the synthesis process. Dust collection in the bag filter is performed using a pulsed backwashing method with compressed air. The chlorine gas main line and bag filter are cleaned every few days, and the removed sublimations are processed together with waste salt discharged from the chlorination furnace and reused as a metallurgical auxiliary raw material.

[0059] (3) Metal Magnesium Refining System Molten magnesium is pumped into a refining furnace, where refining flux is added according to a predetermined mixing ratio. Approximately 20 kg of flux is added per ton of magnesium, and the mixture is thoroughly stirred to achieve the refining effect. The refining time is approximately 10-20 minutes. Afterward, the temperature is controlled to 10¹³-10²³ K, and the mixture is allowed to stand for 15-20 minutes to separate impurities from the magnesium. During the refining process, the magnesium in the furnace may burn, but oxidation of the magnesium can be prevented by implementing gas protection.

[0060] The refined molten magnesium is sent to a continuous casting machine where it is cast. The machine rotates slowly, and the cast metallic magnesium is rapidly cooled. Sulfur powder is sprayed onto the surface of the magnesium ingot to prevent oxidation, ultimately forming the magnesium ingot.

[0061] The surface of the metallic magnesium ingots is treated to make them smooth, and finally they are packaged and stored in a warehouse.

[0062] 3.2 Industrial Silicon Smelting Process 3.2.1 Silicone slag and auxiliary components The raw materials for industrial silicon production include silica, carbon-based reducing agents, and electrodes. Since impurities in the raw materials are ultimately carried over to the final product, very strict restrictions are placed on the content of impurities such as iron, aluminum, and calcium during raw material selection. Because impurities are not removed during the refining process, all impurities in the raw materials remain in the industrial silicon product and furnace slag. Therefore, to guarantee the quality of industrial silicon products, it is necessary to use high-purity raw materials with low levels of harmful impurities.

[0063] To ensure that the maximum amount of silica is converted to silicon, the selected carbon reducing agent (low-sulfur, low-ash coal, wood lumps, etc.) must have good reactivity.

[0064] The reaction layer between silica and carbon in the electric furnace must maintain high permeability, ensuring sufficient reaction between silicon dioxide and carbon. The carbon-based reducing agent must have sufficient strength to prevent it from crumbling into fine particles or powder upon introduction. Furthermore, the carbon must maintain its strength even at high temperatures in the electric furnace. The power required for the reaction process is supplied by carbon electrodes. The electrodes are deeply inserted into the furnace material, and the power is released from the tips of the carbon electrodes within the electric furnace. The high-temperature region of the arc is formed near the bottom of the electric furnace, which becomes the reaction zone. The molten silicon produced by the reaction forms a molten pool at the bottom of the furnace. By inserting the electrodes sufficiently into the furnace material, the reaction area can be expanded and the electrodes can penetrate the molten pool at the bottom of the furnace.

[0065] If the electrical conductivity of the carbon-based reducing agent in the furnace material is high, the resistivity of the furnace material decreases, resulting in excessive electrode current. As a result, the electrodes cannot be inserted sufficiently, the high-temperature region shifts upward, and the reaction zone rises accordingly. This raises the furnace bottom, increases branch current, and negatively impacts the stable operation of the furnace. Therefore, it is necessary to ensure appropriate electrical conductivity by selecting a carbon-based reducing agent with low electrical conductivity, or by appropriately blending low-sulfur, low-ash coal and wood lumps and adjusting the particle size.

[0066] (1) Silicon slag origin and components After wet hydrochloric acid leaching, pressure filtration and washing are performed to obtain high-silicone slag. The moisture content of the obtained silicone slag is 25%.

[0067] (2) Carbon reducing agent Carbon-based reducing agents used in the production of industrial silicon include low-ash bituminous coal, petroleum coke, semi-coke, and wood lumps. The physical and chemical properties of carbon-based reducing agents have a significant impact on the refining performance and product quality of industrial silicon.

[0068] In this invention, modified coke powder is selected as a reducing agent, mixed with silica slag to produce a compacted powder, and then fed into an electric furnace.

[0069] (3) Wood block The raw materials sourced from the market meet the particle size requirements for furnace input (approximately 20 x 20 x 50 mm), and no crushing or sieving is performed in the factory. The raw materials are transported to the factory by automobile and stored in auxiliary material storage shelves. Wood lumps are an excellent reducing agent, and machine-made wood lumps have very low ash content (usually less than 3%), high reactivity, and high resistivity. Adding wood lumps to the furnace material suppresses the sintering of the furnace material.

[0070] The wood blocks must be controlled to contain 30-65% fixed carbon, less than 3% ash, and 26-45% volatile matter.

[0071] (4) Electrode Graphite is procured from the market and transported by automobile to the factory warehouse for storage. Graphite electrodes are manufactured by graphitizing carbon electrodes, which are made from petroleum coke and tar pitch, in a graphitization resistance furnace at a temperature of 2273-2773K. The role of graphite electrodes is to supply power to the electric furnace and they are one of the main components of the electric furnace design. The physical and chemical properties of the electrodes directly affect the quality of the smelted products and the technoeconomic indicators in production. Electrodes must have high electrical conductivity, sufficient mechanical strength, high oxidation resistance, and low wear resistance. Cylindrical electrodes are generally used, and the shape of the electrodes is designed to geometrically ensure complete contact between the electrode and the copper laminate (copper clamp), achieving stable current flow and preventing arc generation.

[0072] 3.2.2 Industrial Silicon Smelting Process In this invention, silicon slag is used as the main raw material, modified coke powder and wood lumps are used as reducing agents, and smelting production is carried out using a semi-closed electric furnace. The process is divided into five stages: drying of silicon slag, preparation of raw materials, smelting, refining, and product processing.

[0073] (1) Drying of silicone slag The silica slag obtained through the wet process has a high moisture content and cannot be used directly in electric furnace smelting. In this invention, silicon slag is dried using a rotary kiln, and natural gas is used as fuel. The moisture content of the dried silica slag is less than 1%.

[0074] (2) Raw material preparation process Modified coke powder purchased from an external source is dumped into silos by truck. To increase production efficiency and reduce energy consumption, this invention employs a fully automated blending system in the blending process of an 8x33 MVA class industrial silicon electric furnace. After drying, the silicon slag and modified coke powder are weighed and mixed by a quantitative feeder, controlling the blending ratio and maintaining a weighing accuracy of within 0.5%. Subsequently, they are pressure-molded by a roll press to obtain high-strength briquette-like raw materials. Each process of raw material supply, weighing, and blending is automatically controlled by a DCS (Distributed Control System). The blended raw materials are transported to the elevated platform of the electric furnace by a large inclined belt conveyor, and then fed into the furnace top hopper by a distribution belt conveyor. The furnace material is intermittently supplied into the furnace through raw material pipes, and smelting is carried out continuously, with metallic silicon being tapped periodically. Each electric furnace is equipped with 12 high-level hoppers, each connected to 12 raw material pipes. One of the raw material tubes is the central raw material tube, and three are the outer raw material tubes. To prevent the generation of vortices, non-magnetic stainless steel is used extensively in the raw material tubes and the parts of the electrode holder below the short-circuit net. In addition, the lower part of the raw material tubes is water-cooled to ensure a stable supply.

[0075] (3) Smelting process The mixed raw materials are sent into the electric furnace via a supply pipe through the top hopper and input pipe, and subjected to the smelting process. Smelting is carried out in continuous operation, with the material being fed in batches, and silicon tapping occurring intermittently. Depending on the operating status of the electric furnace, the material is fed in increments, and a high-temperature arc is generated between the electrodes and the material by passing an electric current through the electrodes, heating and melting the material and promoting the reduction reaction. During the smelting process, furnace scraping is performed according to the sintering state of the furnace surface to increase the electrical resistance of the material, improve permeability, and accelerate the melting rate. To reduce the workload on the workers, this invention uses furnace scraping machines placed on three operating surfaces to perform automatic furnace scraping. During operation, the electrodes are continuously consumed, so it is necessary to add electrodes periodically. Graphite electrodes are lifted from ±0.00m floors to the electrode extension platform by a 10t overhead crane, and connection work is performed. The electric furnace is equipped with five tapping outlets (silicon tapping outlets), which are used alternately. Molten silicon is tapped out approximately every 2-3 hours. When a certain amount of liquid silicon has accumulated at the bottom of the furnace, the tap is opened using a furnace opening device or burner drilling machine, and the silicon solution is poured directly into the silicon pots on the silicon pot vehicle. Inside the silicon pots outside the furnace, oxygen-rich bottom-blowing refining is performed using synthetic slag to further improve the purity of the silicon.

[0076] The exhaust gas generated from the electric furnace first recovers its residual heat by passing it through a preheating boiler, then is dust-removed by a dust collection system and released into the atmosphere. The electric furnace exhaust gas contains a large amount of highly volatile SiO2 gas (boiling point approximately 1880°C). After being discharged from the furnace, these gases cool rapidly and condense, undergoing a disproportionation reaction. As a result, fine powders of Si and SiO2, i.e., silicon fine powder, are produced. After being recovered by the dust collection system, the powder is densified using a densification device, packaged, and stored in a silicon fine powder warehouse. It can be sold as a by-product, or reused in compounding systems as needed.

[0077] Each workshop will be equipped with one set of silicon fine powder densification system. This system consists of three densification hoppers and densification devices, with each densification hopper having a capacity of 175 m³. 3It is as follows. The dust that has not been densified is first put into the high-density ash storage tank, and gas-fluidized by the densification device in the tank. By this treatment, the bulk density of the silicon fine powder increases from the original 0.2 t / m 3 to 0.6 t / m 3 while its physical and chemical properties do not change.

[0078] (4) Refining process In the refining process of the present invention, a method of bottom-blowing oxygen and compressed air is adopted. The ventilation bricks for bottom-blowing oxygen are installed at the bottom of the ladle, and a large number of thin copper tubes are arranged inside the ventilation bricks. Oxygen and compressed air are blown into the molten silicon from these thin tubes to carry out refining. In this refining process, stirring is not required. By blowing oxygen from the bottom of the molten silicon, the kinetic conditions of the reaction between the slag and metal elements are improved, the reaction is promoted, impurities are removed quickly, and heat loss and ladle adhesion of the molten silicon can be reduced.

[0079] The oxygen and compressed air sent from the oxygen supply station and the compressed air station are introduced into the bottom of the silicon ladle and the ventilation bricks through heat-resistant rubber hoses, react with the molten silicon that has just come out of the furnace, and remove the impurities Ca and Al. About 2 to 3 minutes before the molten metal is discharged, first blow compressed air into the bottom of the ladle to prevent the molten silicon from flowing into the ventilation holes. When the molten metal reaches about 1 / 3 of the ladle depth, open the oxygen to start oxidative refining. Close the molten metal discharge hole of the furnace. When the refining is completed (when the contents of Al and Ca etc. reach below the specified values), stop the oxygen supply. Then, the ladle is moved to the casting yard by the molten metal transfer cart for secondary refining. Even after the pouring of the molten silicon is completed, in order to prevent the blockage of the air diffuser holes, blow compressed air for another 3 to 5 minutes, and then remove the heat-resistant rubber hose after a little time. Then, remove the silicon slag to prepare for the next furnace's molten metal discharge. This oxidative refining process can effectively remove aluminum and calcium, which are the main impurities in industrial silicon. Since the process is simple and the combustion loss rate of silicon is also low, generally the out-of-furnace ladle bottom-blowing oxidative refining method is adopted.

[0080] (5) Finishing process After the blowing of the silicon solution is complete, it is transported to the casting room, left to settle to allow the slag to settle, and casting is carried out using a crane while sampling and analysis are performed simultaneously. The resulting lumpy industrial silicon products are stacked in the semi-finished product section according to grade and stored. The semi-finished products are fed into a jaw crusher by hand or a belt conveyor and crushed, then sent to a high-efficiency vibrating sieve by a belt conveyor. After sieving, industrial silicon with a particle size of 50 mm or more is bagged via an electro-hydraulic fan-shaped gate and transported to the product warehouse by forklift. Industrial silicon with a particle size of less than 50 mm undergoes secondary sieving via a belt conveyor, and industrial silicon with a particle size of 10 mm or more is fed into a hopper, similarly bagged via an electro-hydraulic fan-shaped gate, and transported to the finished product warehouse by forklift. After casting, the silicon molds are cleaned and repaired in preparation for the next silicon tapping.

[0081] 4. Products (1) Main product: metallic magnesium The metallic magnesium products obtained in this invention meet the chemical composition requirements specified in the national standard "Raw Magnesium Ingot" (GB / T3499-2023). The surface of the crude magnesium ingot must be smooth and clean and free from residual solvents, intercalated slag, cold cracks, burrs, shrinkage cracks, oxidative combustion products, and other defects that would impair its use. Furthermore, no residual acid should be present, and no moisture should be contained within the pores.

[0082] (2) Industrial silicon, a by-product Industrial silicone products generally have a particle size of 5 to 120 mm and are stored in product warehouses in bagged form. Product quality conforms to the chemical silicone standards of the "Industrial Silicone" (GB / T2881-2014) standard.

[0083] Although specific embodiments of the present invention have been described above, those skilled in the art should understand that the described embodiments are merely illustrative and do not limit the scope of the present invention, and that equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the invention should all be included within the scope of protection of the claims of the present invention.

Claims

1. A production process that uses serpentine ore as a raw material and decomposes serpentine using the hydrochloric acid method to produce metallic magnesium and industrial silicon, Step (1) involves concentrating and filtering the slurry obtained after wet grinding of serpentine ore to obtain a raw material slurry, Step (2) involves performing a two-step atmospheric pressure hydrochloric acid leaching on the pre-treated raw material slurry, Step (3) involves washing the leached crude silica slag with a CCD, filtering and drying it to obtain silicon slag, further reducing and smelting it to remove impurities through purification, and crushing it to obtain industrial silicon. Step (4) involves removing iron and precipitation of nickel from the leachate, separating the precipitated iron hydroxide and nickel hydroxide, washing, and filtering. Step (4) involves removing secondary impurities and purifying the crystals, then evaporating them to concentrate the magnesium chloride, and obtaining a magnesium chloride solution with a mass concentration of 45%-55% as the raw material for the dried magnesium chloride in step (5). Step (6) of drying magnesium chloride, Step (7) involves electrolyzing magnesium chloride sent from the drying system into metallic magnesium and chlorine gas, Step (8) of purifying magnesium, A production process characterized by including the following.

2. The production process according to claim 1, characterized in that in step (1), the slurry is a slurry with a mass concentration of 8-15%, and is obtained by mixing serpentine ore fine powder raw material with hydrochloric acid to form a slurry.

3. In step (2), the two-stage atmospheric pressure hydrochloric acid leaching is carried out by a hydrochloric acid-based two-stage countercurrent leaching process, specifically including the following steps A to C: In step A, the pre-treated raw material slurry is sent to a single-stage leaching process, the slurry temperature in the single-stage leaching process is controlled to 80°C-85°C, and the leaching time is 2h-3h. In step B, after the first leaching, the concentrated overflow liquid is sent to the neutralization and iron removal process, and if the residual acid from the leaching is between 5 and 15 g / L, the underflow liquid from the first leaching is sent to the second leaching process. The production process according to claim 1, characterized in that in step C, the slurry temperature of the two-stage leaching process is controlled to 95°C-100°C, the leaching time is set to 2h-3h, the crude silica slag obtained after the two-stage leaching separation is sent to the CCD process for washing, and the overflow liquid from the two-stage leaching process is returned to the one-stage leaching process.

4. The production process according to claim 1, characterized in that, in step (3), after slurrying the crude silica slag, countercurrent washing is performed using a concentrator, the washing system uses a five-stage countercurrent washing, and the washing ratio (weight ratio of washing water to solids entering the concentrator) is controlled to 2:

1.

5. The production process according to claim 1, characterized in that in step (3), the reduction smelting is carried out using silicon slag as the main raw material, modified coke powder and wood lumps as reducing agents, and smelted in a semi-closed electric furnace.

6. The production process according to claim 1, characterized in that in step (3), the purification and impurity removal is carried out by a bottom-blowing method of oxygen and compressed air, and oxidative refining is performed on the molten silicon by first blowing compressed air from the bottom of the silicon ladle, followed by blowing oxygen.

7. In step (4), the iron removal employs a two-step process, including the following steps a and b: In step a, after neutralizing the residual acid using magnesium hydroxide slurry as a neutralizing agent, in the first stage of iron removal, the endpoint pH value is controlled to 3.0-3.5, and trivalent iron and aluminum are hydrolyzed and precipitated, while silica is co-precipitated and removed. The slurry after iron removal is then concentrated and separated. The production process according to claim 1, characterized in that in step b, the endpoint pH value of the second stage iron removal is controlled to 4.0 to 4.5, compressed air is blown in to oxidize divalent iron to trivalent iron, further hydrolyze and remove iron and aluminum in the primary slurry, send the overflow liquid of the second stage iron removal to the nickel precipitation step, the underflow liquid of the second stage iron removal has gone through the CCD washing step and then the overflow liquid has been slurryed and returned to the first stage iron removal step to recover valuable metals in the slag.

8. The production process according to claim 1, characterized in that in step (6), the drying is performed by employing a cooling granulation, a one-stage air-flow dehydration, and a one-stage molten salt dehydration process to obtain anhydrous magnesium chloride.

9. The production process according to claim 1, characterized in that the molten salt dehydration employs a hydrochloric acid drying system to gradually remove water molecules from magnesium chloride, obtain a molten magnesium chloride salt, and recover the water-containing HCl gas after drying to produce hydrochloric acid.

10. The production process according to claim 1, characterized in that the process employs a system that comprehensively utilizes serpentine ore, the system includes a two-stage countercurrent leaching reactor, a solid-liquid separation and washing device is connected to the leaching outlet of the two-stage countercurrent leaching reactor, a metallic magnesium production line is connected to the overflow port of the solid-liquid separation and washing device, an industrial silicon production line is connected to the silicon slag outlet of the solid-liquid separation and washing device, the metallic magnesium production line includes, in sequence, an iron removal device, a nickel precipitation device, an evaporation and concentration device, a magnesium chloride dryer, and a magnesium chloride electrolyzer, and the industrial silicon production line includes, in sequence, a silicon slag dryer, a reduction smelting device, and a refining impurity removal device.

Images