Production process for preparing magnesium metal and industrial silicon by decomposing serpentine through hydrochloric acid method

Abstract

The invention relates to a serpentine comprehensive utilization technology, in particular to a production process for preparing magnesium metal and industrial silicon by decomposing serpentine through a hydrochloric acid method. Serpentine ore is used as a raw material, and a hydrochloric acid system two-stage countercurrent leaching process is adopted for treatment. The wet process comprises the following steps: storage and filtration of slurry after mineral separation and wet grinding, two-stage normal-pressure hydrochloric acid leaching, washing and filtration of leached silicon slag, iron removal and nickel precipitation of leachate, separation, washing and filtration of ferric hydroxide and nickel hydroxide obtained by precipitation, crystallization and evaporation of a magnesium chloride solution, and preparation of hydrochloric acid from flue gas after thermal decomposition of magnesium chloride. The invention develops a process for decomposing serpentine by a hydrochloric acid method and producing magnesium metal by a drying-electrolysis method, and a process for producing industrial silicon by smelting silicon slag in an electric furnace. The produced magnesium metal product meets the requirements of related chemical components of the national standard, and the quality of the industrial silicon product meets the chemical silicon standard. The method has the characteristics of short flow, small environmental pollution, low energy consumption, lower cost and the like.

Description

Technical Field

[0001] The invention relates to a serpentine comprehensive utilization technology, in particular to a production process for preparing metallic magnesium and industrial silicon by decomposing serpentine using a hydrochloric acid method. Background Art

[0002] With the rapid development of modern industry, traditional metal resources are on the verge of exhaustion. Therefore, it is imperative to find and develop new metal resources.

[0003] Magnesium is one of the most abundant elements on earth. In addition to the 2.3% content of metal ore in the surface layer of the earth's crust, its content in salt lakes and oceans is also considerable. Therefore, accelerating the development of magnesium metal materials is one of the important measures to achieve sustainable development. Due to its excellent properties, the use of magnesium metal is increasing, and its application areas are constantly expanding. Magnesium is appearing on the stage of metallurgical materials as a "metal of the times" and has become a leader among non-ferrous metals. Now magnesium has become the fifth largest non-ferrous metal after copper, aluminum, lead and zinc. However, although magnesium metal with resource advantages has developed rapidly, its market potential has not yet been fully tapped. Therefore, how to further accelerate the development of the magnesium industry and develop new magnesium metal smelting processes has become a hot topic of research in countries around the world.

[0004] Traditional magnesium and magnesium materials are mainly derived from magnesite-type magnesium carbonate ores, which need to be roasted at high temperatures to convert them into magnesium oxide. The specific production process includes the following steps:

[0005] 1. Mining: Mining ore from magnesite or dolomite mines.

[0006] 2. Crushing and grinding: crush and grind the ore to make it into powder.

[0007] 3. Pretreatment: Pretreat the powder to remove impurities and impurities.

[0008] 4. Calcination: The pretreated powder is placed in a high-temperature furnace for calcination to convert it into magnesium oxide.

[0009] 5. Purification: Purify the calcined magnesium oxide to remove impurities and impurities.

[0010] 6. Made of materials: Purified magnesium oxide is an important basic material for magnesium refractory materials, magnesium sulfate and magnesium salts.

[0011] 7. The traditional magnesium ingot production process is the Pidgeon process, which uses ferrosilicon and dolomite for reduction roasting at high temperature, consuming a large amount of coal and releasing a large amount of carbon dioxide.

[0012] According to current environmental protection requirements, this traditional production process has serious deficiencies and problems. First, this process consumes a lot of energy and produces a lot of carbon dioxide during roasting, which puts the supply of magnesium metal and magnesium materials under great pressure.

[0013] Therefore, the development of new chemical processes and process routes is crucial for the industrial development of magnesium and magnesium materials. Using serpentine instead of traditional magnesium carbonate ore can create a new source of magnesium and magnesium materials.

[0014] my country is rich in serpentine mineral resources, most of which are ultrabasic serpentine deposits, with many deposits, large scale, wide distribution, and good texture conditions. Serpentine belongs to a 1:1 type layered silicate, composed of silicon-oxygen tetrahedral sheets and magnesium-oxygen octahedral sheets, mainly including chrysotile, antigorite and lizardite. The main mineral composition of serpentine, serpentine tailings and asbestos tailings is serpentine containing a small amount of magnetite, talc, brucite, dolomite, calcite, etc. The main chemical composition is SiO2, MgO, containing a small amount of Fe2O3, Al2O3, NiO, Cr2O3, etc., among which the metal oxide is mainly magnesium oxide.

[0015] At present, the common method for serpentine resource utilization is to add organic acid and inorganic acid to the serpentine raw material for direct acid leaching to prepare magnesium-containing compound products. The residue after extracting magnesium oxide from serpentine is directly reacted with sodium hydroxide to prepare chemical products such as sodium metasilicate or white carbon black.

[0016] So far, there have been no public reports on technologies that use hydrochloric acid to decompose serpentine, high-temperature drying-electrolysis to produce metallic magnesium, and silicon slag electric furnace smelting to produce industrial silicon, which have low environmental pollution, low energy consumption, and low cost. Summary of the invention

[0017] The technical problem to be solved by the present invention is to provide a production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid.

[0018] The present invention is achieved in that:

[0019] A production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid, using serpentine ore as raw material, and the process includes:

[0020] (1) The slurry after wet grinding of mineral processing is concentrated and filtered to obtain raw material slurry;

[0021] (2) the pretreated raw material slurry is subjected to two-stage atmospheric pressure hydrochloric acid leaching;

[0022] (3) The leached crude silica slag is washed with CCD, filtered, and dried to obtain silicon slag, and then industrial silicon is obtained through reduction smelting, refining, impurity removal, and crushing;

[0023] (4) removing iron from the leaching solution and precipitating nickel, and separating, washing and filtering the precipitated iron hydroxide and nickel hydroxide;

[0024] (5) After secondary impurity removal and purification in step (4), the magnesium chloride is concentrated by crystallization and evaporation to obtain a magnesium chloride solution with a mass concentration of 45% to 55%, which is used as a raw material for drying magnesium chloride;

[0025] (6) drying magnesium chloride;

[0026] (7) electrolyzing the magnesium chloride sent from the drying system into metallic magnesium and chlorine gas;

[0027] (8) Magnesium refining.

[0028] Furthermore, the slurry in step (1) is a slurry with a mass concentration of 8-15%, which is obtained by mixing serpentine ore fine powder with hydrochloric acid.

[0029] Furthermore, the two-stage atmospheric pressure hydrochloric acid leaching in step (2) is carried out by using a two-stage countercurrent leaching process of a hydrochloric acid system, which specifically comprises the following steps:

[0030] A. The pretreated raw material slurry first enters the first stage of leaching, the slurry temperature of the first stage of leaching is controlled at 80℃~85℃, and the leaching time is 2h~3h;

[0031] B. The overflow after the first stage leaching and thickening is sent to neutralization and iron removal, and the residual acid in the leaching is between 5-15g / L; the bottom flow of the first stage leaching is sent to the second stage leaching;

[0032] C. The slurry temperature of the second stage leaching is controlled at 95℃~100℃, and the leaching time is 2h~3h; the crude silica slag obtained after the second stage leaching separation is sent to CCD for washing; the overflow of the second stage leaching returns to the first stage leaching.

[0033] Furthermore, in step (3), the crude silica is slurried and then subjected to countercurrent washing using a thickener. The washing system uses a five-stage countercurrent washing system, and the washing ratio is controlled at 2:1 (the weight ratio of wash water to solids entering the thickener).

[0034] Furthermore, the reduction smelting in step (3) uses silicon slag as the main raw material, upgraded coke powder and wood blocks as reducing agents, and adopts a semi-enclosed electric furnace for smelting production.

[0035] Furthermore, the refining and impurity removal in step (3) is carried out by bottom blowing of oxygen and compressed air, and compressed air and oxygen are blown to the bottom of the silicon bag in sequence to perform oxidative refining on the silicon solution.

[0036] Furthermore, the iron removal in step (4) adopts a two-stage process, comprising the following steps:

[0037] a. Use magnesium hydroxide slurry as a neutralizing agent, neutralize the residual acid, and then remove iron in one stage to control the end point pH value to 3.0-3.5, so that trivalent iron and aluminum are hydrolyzed and precipitated, and silicon dioxide is co-precipitated and removed. After iron removal, the slurry is densely separated;

[0038] b. The endpoint pH value of the second-stage iron removal is 4.0-4.5. Compressed air is blown in to oxidize divalent iron into trivalent iron, so that the iron and aluminum in the first-stage slurry are further hydrolyzed. The overflow of the second-stage iron removal is sent to nickel precipitation; the overflow liquid of the second-stage iron removal bottom flow CCD is slurried and returned to the first-stage iron removal to recover the valuable metals in the slag.

[0039] Furthermore, the drying in step (6) adopts cooling granulation, one-stage air fluidized dehydration, and one-stage molten salt dehydration process to obtain anhydrous magnesium chloride.

[0040] Furthermore, the molten salt dehydration adopts a hydrochloric acid drying system to gradually remove water molecules from the magnesium chloride to obtain magnesium chloride molten salt, and the dried aqueous HCl gas is recovered to prepare hydrochloric acid.

[0041] Furthermore, the process adopts a serpentine ore comprehensive utilization system, which includes a two-stage countercurrent leaching reaction device, the leachate outlet of the two-stage countercurrent leaching reaction device is connected to a solid-liquid separation and washing device, the overflow port of the solid-liquid separation and washing device is connected to a metal magnesium production line, and the silicon slag outlet of the solid-liquid separation and washing device is connected to an industrial silicon production line; the metal magnesium production line includes an iron removal device, a nickel precipitation device, an evaporation and concentration device, a magnesium chloride drying device, and a magnesium chloride electrolysis device connected in sequence; the industrial silicon production line includes a silicon slag drying device, a reduction smelting device, and a refining and impurity removal device connected in sequence.

[0042] The present invention has the following advantages: the present invention develops a process for decomposing serpentine by hydrochloric acid method, producing metal magnesium by drying-electrolysis method, and a process for producing industrial silicon by smelting silicon slag in an electric furnace. The produced metal magnesium product meets the requirements of the national standard for chemical composition, and the quality of the industrial silicon product meets the standard for chemical silicon. The present invention has the characteristics of short process, small environmental pollution, low energy consumption, and low cost, and has opened up a new development idea for the comprehensive utilization of serpentine resources in my country. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described below in conjunction with embodiments with reference to the accompanying drawings.

[0044] Figure 1 It is a schematic diagram of the system structure of the present invention.

[0045] The numbers in the figure are: two-stage countercurrent leaching reaction device 1, solid-liquid separation and washing device 2, iron removal device 3, nickel precipitation device 4, evaporation concentration device 5, magnesium chloride drying device 6, granulation centrifuge 61, air fluidized bed dryer 62, HCl gas drying mechanism 63, magnesium chloride electrolysis device 7, silicon slag drying device 8, reduction smelting device 9, refining and impurity removal device 10, hydrochloric acid absorption tower 11, chlorine compressor 12, hydrochloric acid synthesis device 13, water electrolysis device 14, magnesium metal refining casting device 15, dust removal device 16. DETAILED DESCRIPTION

[0046] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings and specific embodiments. If no specific conditions are specified in the embodiments, the conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the instruments used is not specified, they are all conventional products that can be purchased commercially.

[0047] The process of the present invention adopts a system for comprehensive utilization of serpentine, which includes a two-stage countercurrent leaching reaction device 1, the leachate outlet of the two-stage countercurrent leaching reaction device 1 is connected to a solid-liquid separation and washing device 2, the overflow port of the solid-liquid separation and washing device 2 is connected to a metal 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 metal magnesium production line includes an iron removal device 3, a nickel precipitation device 4, an evaporation and concentration device 5, a magnesium chloride drying device 6, and a magnesium chloride electrolysis device 7 connected in sequence; the industrial silicon production line includes a silicon slag drying device 8, a reduction smelting device 9, and a refining and impurity removal device 10 connected in sequence.

[0048] Furthermore, the solid-liquid separation and washing device 2 is a CCD thickener.

[0049] Furthermore, the gas outlet of the magnesium chloride drying device 6 is connected to the hydrochloric acid absorption tower 11, and the hydrochloric acid output port of the hydrochloric acid absorption tower 11 is connected to the recovery hydrochloric acid input port of the second-stage countercurrent leaching reaction device 1.

[0050] Furthermore, the magnesium chloride drying device 6 includes a granulating centrifuge 61, an air fluidized bed dryer 62, and an HCl gas drying mechanism 63. The granulating centrifuge 61 is connected to the air fluidized bed dryer 62 through a particle transmission mechanism, and the discharge port of the air fluidized bed dryer 62 is connected to the feed port of the HCl gas drying mechanism 63.

[0051] Specifically, the air fluidized bed dryer 62 includes a discharge hopper, a conveyor, a vibrating screen, a wet material bin, and a feed pipe (conventional, not shown) arranged along the particle transportation route.

[0052] Furthermore, the gas outlet of the magnesium chloride electrolysis device 7 is connected to the chlorine inlet of the hydrochloric acid synthesis device 13 through the chlorine compressor 12 , and the hydrogen inlet of the hydrochloric acid synthesis device 13 is connected to the water electrolysis device 14 .

[0053] Furthermore, the magnesium chloride electrolysis device 7 is further connected to a magnesium metal refining casting device 15 .

[0054] Furthermore, the flue gas outlet of the reduction smelting device 9 is connected to the dust removal device 16 via a waste heat boiler.

[0055] The specific process steps of the present invention are as follows:

[0056] 1. Slurry storage and filtration

[0057] Serpentine ore is transported to the smelting yard, and after coarse and fine crushing, serpentine ore with a particle size of about 10mm is obtained, which is stored in the coarse powder silo of the grinding system and then enters the grinding system. The coarse powder is sent to the vertical mill through the quantitative feeder, belt conveyor, and bucket elevator. The fine powder is collected by the bag dust collector and temporarily stored in the fine powder silo through the pneumatic chute and bucket elevator. The fine powder particle size is controlled to be more than 0.074mm for more than 85%. The fine powder is sent to the leaching process after slurry mixing in the slurry mixing tank on the top of the silo.

[0058] Slurry storage and filtration mainly treat the 10% concentration slurry delivered from the raw material pretreatment area to meet the feed requirements of the subsequent leaching process, including slurry concentration, storage, filtration, slurrying and other steps. Filter cake slurrying uses hydrochloric acid as the slurrying liquid. During the slurrying process, a small amount of oxides in serpentine such as MgO, FeO(OH), NiO, etc. react with hydrochloric acid. A small amount of HCl will overflow during the slurrying process, which will be collected, washed and recycled.

[0059] 2. Hydrochloric acid leaching

[0060] From the composition of serpentine ore, metal elements mainly exist in the form of metal oxides, such as MgO, FeO(OH), NiO, CoO, CaO, FeO, MnO, ZnO, etc. Under normal pressure conditions (temperature ~ 95°C), most metal Me (Mg, Ni, Co, Mn, Ca, Al) oxides react with hydrochloric acid to form soluble chloride salts (MeCl n ) and enter the solution, and the reaction formula is as follows:

[0061] Me2O n (s)+2nH + →2Me n+ +nH2O

[0062] Me: Ni, Co, Mn, etc., n: metal ion valence. Magnesium mainly exists in the silicate mineral lizardite, so the dissolution of lizardite allows most of the magnesium to enter the leachate.

[0063] Mg3Si2O5(OH)4(s)+6H + →3Mg 2+ +2SiO2(s)+5H2O.

[0064] According to the results of the serpentine leaching test, the present invention adopts a two-stage countercurrent normal pressure hydrochloric acid leaching process:

[0065] The pretreated raw material slurry first enters the first stage of leaching. The slurry temperature of the first stage of leaching is controlled at about 80℃~85℃, and the leaching time is 2h~3h. Most of the metal oxides are leached in the first stage. After the first stage of leaching is concentrated, the overflow is sent to neutralization and iron removal, and the leaching residual acid is between 5-15g / L. The underflow of the first stage of leaching is sent to the second stage of leaching. The slurry temperature of the second stage of leaching is controlled at about 95℃~100℃, and the leaching time is 2h~3h. The crude silica slag obtained after the second stage of leaching separation is sent to CCD for washing; the overflow of the second stage of leaching returns to the first stage of leaching.

[0066] 3. CCD and silicon slag filtration

[0067] The crude silica slag obtained from the leaching workshop is slurried and then counter-current washed by a thickener. The washing water comes from the product washing water and the liquid after tail gas washing. In order to improve the washing efficiency of CCD, the washing system adopts a 5-stage counter-current washing method, and the washing ratio is controlled at 2:1 (the weight ratio of washing water to solid entering the thickener). The overflow liquid of CCD1 is sent to the iron removal and nickel precipitation workshop to slurry the iron slag of the second stage of iron removal, and then sent to the first stage of leaching. The underflow of CCD5 is filtered, and the crude silica containing water after filtration is sent to the pyrometallurgical workshop by belt for further production of silicon products.

[0068] 3.1 Magnesium Metal Production Process

[0069] 3.1.1 Iron removal and nickel precipitation workshop

[0070] The iron removal and nickel precipitation process mainly utilizes magnesium oxide slurry to neutralize the residual acid in a leaching overflow liquid, and then adjusts the pH value to remove impurity elements such as iron, aluminum, and silicon, and then precipitates nickel to recover valuable metals.

[0071] The iron removal process adopts a two-stage process. Magnesium hydroxide slurry is used as a neutralizer. After neutralizing the residual acid, the first stage of iron removal controls the end point pH value to 3.0-3.5, so that trivalent iron and aluminum are hydrolyzed and precipitated, and silicon dioxide is co-precipitated and removed. After iron removal, the slurry is densely separated. In order to make the precipitate particles easier to settle, a part of the thickener bottom flow is used as a seed in the iron removal process; the first stage of iron removal bottom flow is processed in the product filtration and separation process.

[0072] The final pH value of the second-stage iron removal is 4.0-4.5. Compressed air is blown in to oxidize divalent iron into trivalent iron, so that the iron and aluminum in the first-stage slurry are further hydrolyzed. The overflow of the second-stage iron removal is sent to nickel precipitation; a part of the bottom flow of the second-stage iron removal is returned for use as crystal seeds, and the rest is slurried with CCD6 overflow liquid and returned to the first-stage iron removal to recover valuable metals such as nickel in the slag.

[0073] The precipitant for nickel precipitation is magnesium oxide slurry. The endpoint pH value of nickel precipitation is controlled at 8.0-8.5, so that the nickel in the solution forms hydroxide precipitation, and a small amount of manganese is also precipitated. After precipitation, the slurry is sent to a thickener for liquid-solid separation.

[0074] 3.1.2 Product separation and filtration

[0075] Product separation includes the first stage of iron removal product thickening separation, nickel precipitation thickening separation and thickening bottom flow filtration separation and product packaging.

[0076] The first stage of iron removal product thickening and separation process, the overflow of the thickener is sent to the second stage of iron removal in the iron removal and nickel precipitation workshop. Part of the underflow of the thickener is returned as a seed crystal, and the rest enters the product filtration and washing. After two stages of washing and two stages of filter pressing, the wet iron concentrate is sent to the iron concentrate drying workshop for drying. The washing uses the secondary steam condensate of magnesium chloride.

[0077] In the thickening and separation process of nickel precipitation products, part of the overflow of the thickener is sent to the magnesium chloride evaporation workshop after precision filtration, and part of it is used as a precipitant and flocculant preparation liquid. Part of the underflow of the thickener is returned as a seed crystal, and the rest enters the product filtration and washing. After two stages of washing and two stages of filter pressing, the nickel product is produced and automatically packaged. The washing uses the secondary steam condensate of magnesium chloride. The packaged nickel products can be stored in the nickel product warehouse.

[0078] Flocculant preparation is mainly to provide usable flocculant solution for the operation of raw material thickening, CCD and product thickening separation processes, and pump it to various flocculant use points.

[0079] 3.1.3 Evaporation and concentration of magnesium chloride

[0080] After storage and preheating, the magnesium chloride solution enters the evaporation and concentration system. The magnesium chloride evaporation and concentration system adopts four-effect evaporation to obtain a magnesium chloride solution with a concentration of 48%-51%, and then uses a granulation tower to cool and granulate to obtain 4.8 water magnesium chloride solid, which is sent to the magnesium chloride drying device through a conveyor for magnesium chloride drying. After evaporation, the secondary steam condensate returns to the system for use as slag washing water. The discharged mother liquor returns to the iron removal and nickel precipitation workshop.

[0081] 3.1.4 Magnesium Metal Smelting Process

[0082] 3.1.4.1 Magnesium chloride and auxiliary ingredients

[0083] (1) Magnesium chloride solution

[0084] The above-mentioned forced circulation evaporator is used to evaporate and concentrate the magnesium chloride to obtain a magnesium chloride solution with a magnesium chloride content of 48%-51%, which is used as a raw material for drying the magnesium chloride.

[0085] Specifically, the magnesium chloride solution after wet purification contains about 25.44% MgCl2, and a magnesium chloride solution of about 51% is obtained by multi-effect forced evaporation concentration.

[0086] (2) Concentrated sulfuric acid

[0087] The aqueous chlorine gas produced by the electrolysis of magnesium chloride needs to be adsorbed and compressed. 98% concentrated sulfuric acid is purchased and 93% concentrated sulfuric acid is produced for sale.

[0088] 3.1.4.2 Magnesium Metal Smelting Process

[0089] (1) Magnesium chloride drying system

[0090] Since the MgCl2 solution produced by wet evaporation concentration has a content of about 51%, the present invention adopts a cooling granulation + a stage of air fluidization dehydration + a stage of molten salt dehydration process to obtain anhydrous magnesium chloride.

[0091] The purpose of granulation is to convert the concentrated liquid brine into solid particles. The magnesium chloride brine enters the granulation centrifuge, and the magnesium chloride brine is sprayed from the centrifuge into the granulation tower in the form of droplets, and enters the granulation tower in the form of droplets. The droplet-shaped magnesium chloride brine falls in the granulation tower, contacts the ambient air cooling airflow introduced through the shutter system in countercurrent, and contacts the airflow at the top of the tower in parallel, thereby controlling the particles to fall in an umbrella-shaped trajectory and the temperature of the air discharged from the top of the tower. As the droplet-shaped brine cools and crystallizes, solid particles are formed. A discharge hopper is set at the bottom of the granulation tower to receive the granulated wet particles. The particles come out of the bottom of the granulation tower and are sent to a group of vibrating screens through a belt and bucket conveyor transportation system to screen out and remove large particles. The large particles are re-dissolved and granulated again. The remaining particles are sent to the wet material bin and then to the air fluidized bed dryer.

[0092] The main purpose of the air dryer is to partially dry the MgCl2 particles from about 4.8 mol H2O / mol MgCl2 to about 1.8 mol H2O / mol MgCl2. The hydrous magnesium chloride particles in the wet particle storage bin are added to the air dryer through a feed pipe, and the particles are added to the top plate of a two-stage vertical fluidized bed using hot air. The hot air as a heating / drying medium is added through the bottom of each stage. The electric heater of the air dryer heats the compressed air and supplies it to the gill-shaped feeder in the top plate, so that the wet particles are evenly spread on the surface of the fluidized bed.

[0093] The produced MgCl2 enters the hydrogen chloride drying tower to gradually remove water molecules from MgCl2 to obtain magnesium chloride molten salt, which meets the needs of the electrolytic cell and increases the life of the electrolytic cell.

[0094] The drying process uses HCl gas, which is synthesized by high-temperature chemical reaction between hydrogen produced by water electrolysis and Cl2 produced by a magnesium electrolytic cell. After drying, the aqueous HCl gas is washed and concentrated in multiple stages to obtain 36% hydrochloric acid, which is returned to the leaching process.

[0095] (2) Magnesium Metal Smelting System

[0096] Magnesium electrolysis mainly electrolyzes MgCl2 sent from the drying system into metallic magnesium and chlorine. After refined magnesium is cast into ingots for sale, and chlorine is burned with hydrogen through a synthesis process to produce HCl.

[0097] MgCl2 is electrolyzed into Mg and Cl2 in the electrolytic cell. Chlorine is discharged from the chlorine pipe and sent to the chlorination section through the chlorine compressor room. The molten magnesium is regularly extracted by vacuum magnesium ladle.

[0098] Electrolytic magnesium adopts multi-electrode magnesium production process. In order to protect the molten magnesium from oxidation during the production process, argon is filled into the furnace to a slightly positive pressure. The purification tower is also used to purify residual chlorine discharged during equipment maintenance, chlorine generated during the start-up period, and accidental chlorine.

[0099] The chlorine compressor is used to transport electrolytic chlorine. The medium of the chlorine compressor is concentrated sulfuric acid. The chlorine from the electrolytic cell contains electrolyte sublimates. The chlorine comes out of the electrolytic cell, passes through the chlorine branch pipe and is collected in the chlorine delivery main pipe, and then enters the bag filter. After the sublimates are removed, the chlorine compressor sends it to the turbine room for pressurization and then to the synthesis process. The bag filter is cleaned by compressed air pulse backwashing. The chlorine main pipe and bag filter are cleaned every few days, and the sublimates removed are processed together with the waste salt discharged from the chlorination furnace into metallurgical auxiliary materials for recycling.

[0100] (3) Magnesium metal refining system

[0101] The magnesium metal liquid is pumped to the refining furnace, and refining flux is added according to the ratio, with the flux amount being 20kg per ton of magnesium, and fully stirred to achieve the purification effect. The refining time is about 10-20 minutes, and then the temperature is controlled at 1013-1023K, and it is left to stand for 15-20 minutes to separate the impurities from the magnesium. During the refining process, the magnesium in the refining furnace will burn, and gas protection can be used to prevent magnesium oxidation.

[0102] The refined magnesium liquid is transported to the continuous casting machine for pouring. The continuous casting machine rotates slowly and continuously. The casted metallic magnesium cools down quickly, and sulfur powder is sprayed on the surface of the magnesium ingot to prevent magnesium oxidation, and finally a magnesium ingot is formed.

[0103] The metal magnesium ingots are surface treated to make them smooth and finally packaged for storage.

[0104] 3.2 Industrial silicon smelting process

[0105] 3.2.1 Silicon slag and auxiliary materials composition

[0106] The raw materials for industrial silicon production include silica, carbonaceous reducing agent and electrodes. Since impurities in the raw materials will eventually be introduced into the product, the content of impurities such as iron, aluminum and calcium is strictly restricted when selecting raw materials. Because impurities are not removed during the smelting process, all impurities in the raw materials will remain in the industrial silicon products and slag. To ensure the quality of industrial silicon products, raw materials with high purity and low content of harmful impurities must be used.

[0107] To ensure that the maximum amount of silica is converted to silicon, the selected carbon reductant (low-sulfur, low-ash coal, wood chips, etc.) must be highly reactive.

[0108] The silica and carbon reaction bed in the electric furnace must maintain a high degree of permeability to facilitate the most complete reaction between silicon dioxide and carbon. The carbon reductant must have sufficient strength to avoid being broken into fine particles or powder when charging. At the same time, when the temperature in the electric furnace is very high, the carbon must also maintain its strength. The electrical energy required for the reaction process is provided by the carbonaceous electrode. The electrode penetrates deep into the charge, and the electrical energy is released from the end of the carbonaceous electrode in the electric furnace. The high-heat area of ​​the arc is close to the bottom of the electric furnace, forming a reaction zone. The molten silicon liquid produced by the reaction forms a molten pool at the bottom of the furnace. The electrode must penetrate deep into the charge to expand the reaction area and make the molten pool at the bottom of the furnace penetrate.

[0109] If the conductivity of the carbonaceous reducing agent in the charge is high, the charge specific resistance is small, the electrode current is too large, and the electrode cannot penetrate deeply, which will cause the high-heat zone to move upward, the reaction zone will also move upward, the furnace bottom will rise, the branch current will increase, and the furnace condition will be affected. Therefore, it is necessary to choose a carbon reducing agent with lower conductivity or adjust the ratio and particle size of low-sulfur and low-ash coal and wood blocks to achieve the appropriate conductivity.

[0110] (1) Source and composition of silicon slag

[0111] After wet hydrochloric acid leaching, filtration and washing, high silicon slag is obtained, and the moisture content of the silicon slag is 25%.

[0112] (2) Carbon reducing agent

[0113] Carbonaceous reducing agents used in the production of industrial silicon include low-ash bituminous coal, petroleum coke, semi-coke, and wood blocks. The physical and chemical properties of carbonaceous reducing agents have a great influence on the smelting index and quality of industrial silicon.

[0114] The invention selects upgraded coke powder as a reducing agent, mixes it with silicon slag and presses it into blocks before entering an electric furnace.

[0115] (3) Wood blocks

[0116] The incoming material is purchased from the market, and the particle size meets the furnace requirements, about 20×20×50mm. The factory no longer performs crushing and screening. The car is pulled to the auxiliary material shed in the factory for storage. Wood blocks are an excellent reducing agent. Mechanical wood blocks contain very low ash content (usually less than 3%), have high reactivity and extremely high specific resistance. The presence of wood blocks in the charge reduces the sintering of the charge.

[0117] The wood blocks are required to have 30%-65% fixed carbon, less than 3% ash, and volatile matter controlled at 26%-45%.

[0118] (4) Electrode:

[0119] Graphite is purchased from the market. It is transported by car to the factory warehouse for storage. Graphite electrodes are made of petroleum coke and asphalt tar as raw materials to form carbon electrodes, which are then placed in a graphitization resistance furnace at a temperature of 2273-2773K and made into graphitization cloth. The function of graphite electrodes is to transmit electrical energy to the electric furnace, and they are the main components of the electric furnace design. The physical and chemical properties of the electrodes substantially affect the quality of smelting products and the technical and economic indicators of production. The electrodes should have high electrical conductivity, sufficient mechanical strength, high anti-oxidation temperature, and low consumption. Cylindrical electrodes are usually used, and the shape of the electrodes should geometrically ensure complete contact between the electrodes and the copper tiles to facilitate power supply without arcing.

[0120] 3.2.2 Industrial silicon smelting process

[0121] The present invention uses silicon slag as the main raw material, upgraded coke powder and wood blocks as reducing agents, and adopts a semi-enclosed electric furnace for smelting production. The process flow can be divided into five stages: silicon slag drying, material preparation, smelting, refining and finished product processing.

[0122] (1) Silicon slag drying

[0123] The silicon slag produced by the wet method has a high moisture content and cannot be directly used for electric furnace smelting. The present invention adopts a rotary kiln to dry the silicon slag, and the fuel is natural gas. After drying, the moisture content of the silicon slag is less than 1%.

[0124] (2) Material preparation process

[0125] The purchased upgraded coke powder is unloaded from the truck to the silo. In order to improve production efficiency and reduce energy consumption, the design of the batching of the 8×33MVA industrial silicon electric furnace adopts automatic batching. The dried silicon slag and the upgraded coke powder are measured by the quantitative feeder and mixed and proportioned, and the metering accuracy is controlled to 0.5%. Then, the roller press is used to press to obtain high-strength block materials. DCS automatic control is adopted between feeding, weighing and batching. The mixed material after batching is sent to the high-span platform of the electric furnace by the large-angle feeding belt conveyor, and then the mixed material is unloaded to the top silo of the furnace by the cloth belt. The furnace charge is intermittently added to the furnace through the material pipe, and the smelting is continuous and the iron is tapped at a fixed time. Each electric furnace is equipped with 12 high-level silos, 12 material pipes are set below, including one central material pipe and three external material pipes. In order to prevent the generation of eddy currents, the material pipe and the part below the short net of the electrode holder are made of non-magnetic stainless steel materials, and the lower part of the material pipe is cooled by water.

[0126] (3) Smelting process

[0127] The mixed material is sent to the electric furnace through the top silo and the discharge pipe for smelting. The smelting is continuous production, with batch feeding and intermittent silicon output. According to the smelting situation of the electric furnace, the charge is added to the electric furnace in batches, and the current is passed through the electrode to generate a high-temperature arc between the electrode and the charge. The charge is heated, melted, and a reduction reaction occurs. During the smelting process, in order to increase the resistance of the charge, improve the permeability of the charge, and speed up the smelting speed, it is necessary to perform a furnace tamping operation according to the bonding situation of the material surface. In order to reduce the labor intensity of the workers, a furnace tamping machine is used to tamping the furnace on three large operating surfaces. During the smelting process, the electrode is continuously consumed, and the electrode needs to be regularly extended to supplement the continuously consumed graphite electrode. The graphite electrode is lifted from ±0.00m to the electrode connection platform by a 10t suspension crane for electrode extension. The electric furnace is equipped with 5 silicon outlets, which are used alternately. The electric furnace discharges silicon liquid every 2 to 3 hours. When there is a certain amount of liquid Si at the bottom of the furnace, the silicon outlet is opened with a furnace eye opener or a burn-through device, and the silicon liquid flows directly into the silicon bag on the silicon bag car, and oxygen-enriched bottom blowing refining is carried out in the silicon bag using synthetic slag outside the furnace.

[0128] The flue gas from the electric furnace is first recycled through the waste heat boiler, and then dedusted through the dust removal system before being discharged. The flue gas from the electric furnace contains a large amount of highly volatile SiO2 (boiling point is 1880℃). After the gas is discharged, it is quickly condensed and undergoes a disproportionate reaction when it is cooled, and the generated Si and SiO2 powder, i.e., microsilica powder, is recycled through the dust removal system, encrypted and packaged with encryption equipment, and stored in the microsilica powder warehouse. It can be sold as a by-product or returned to the batching system.

[0129] Each workshop is equipped with a micro-silica powder encryption system. The micro-silica powder encryption system consists of three encryption bins and encryption devices. The volume of each encryption bin is 175m 3 After the undensified dust is input into the densified ash storage tank, the dust is fluidized by the gas in the densification device in the tank, which can increase the density of the microsilica powder from the original 0.2t / m3 Increased to 0.6t / m 3 , without changing its physical and chemical properties.

[0130] (4) Refining process

[0131] The refining process of the present invention adopts the bottom blowing method of oxygen and compressed air. The air-permeable bricks for bottom blowing oxygen are installed in the bottom of the ladle. There are many thin copper tubes in the air-permeable bricks. Oxygen and air are blown from the thin copper tubes to the silicon solution for refining. The refining process does not require stirring. Oxygen is blown from the bottom of the silicon ladle. The purpose is to improve the kinetic conditions of the slag-metal element phase reaction, accelerate the reaction to remove impurities as soon as possible, and reduce heat loss and silicon liquid sticking to the ladle.

[0132] The oxygen and compressed air delivered from the oxygen station and the air compressor station are input into the bottom of the silicon bag and the diffuser bricks through the heat-resistant rubber tube to react with the silicon liquid just out of the furnace to remove the impurities Ca and Al. 2-3 minutes before the furnace is out, the compressed air is first introduced into the bottom of the bag to prevent the silicon liquid from pouring into the air vents. When the silicon liquid reaches 1 / 3 of the bottom depth of the silicon bag, the oxygen can be turned on for oxidation refining. After the furnace is out of the plugging eyes and the refining is completed (the content of aluminum, calcium, etc. reaches below the required value), the oxygen can be turned off, and the silicon bag is pulled from the furnace trolley to the casting span for secondary refining. After pouring the silicon liquid, continue to introduce compressed air for 3 to 5 minutes to prevent the diffuser holes from being blocked. Later, the heat-resistant rubber tube can be pulled out, and the silicon slag can be removed, waiting to be out of the furnace. The oxidation refining process can effectively remove the main impurities of aluminum and calcium in industrial silicon, and the process is simple and the silicon burn-out rate is low, so the oxidation bottom blowing refining of the silicon bag outside the furnace is generally adopted.

[0133] (5) Finished product processing

[0134] After the silicon liquid is blown, it is transported to the casting room, where the sediment is left to stand, and samples are taken for testing. At the same time, the casting is carried out by crane. The cast block industrial silicon products are stored in the semi-finished product area according to grade. After the semi-finished products are crushed by hand or by a belt conveyor, they enter the high-efficiency vibrating screen through a belt conveyor. After screening, industrial silicon larger than 50mm is bagged through an electro-hydraulic fan-shaped gate and transported to the product warehouse by forklift. Industrial silicon smaller than 50mm passes through a belt conveyor, and after secondary screening, industrial silicon larger than 10mm enters the hopper, and then is bagged through an electro-hydraulic fan-shaped gate and transported to the finished product warehouse by forklift. The silicon bag after casting is cleaned and repaired to prepare for the next furnace of silicon.

[0135] 4. Products

[0136] (1) Main product: Magnesium metal

[0137] The magnesium metal product produced by the present invention meets the relevant chemical composition requirements of the national standard "Primary Magnesium Ingot" (GB / T3499-2023). The surface of the crude magnesium ingot should be flat and clean, and no residual solvent, slag inclusion, cold shut, flash, shrinkage cracks, oxidation combustion products and other use defects are allowed, no residual acid is allowed, and no moisture is allowed in the shrinkage cavity.

[0138] (2) By-product industrial silicon

[0139] The general particle size of industrial silicon products is 5 to 120 mm, and they are stored in bags in the finished product warehouse. The product quality complies with the chemical silicon standard in the "Industrial Silicon" (GB / T2881-2014) standard.

[0140] Although the specific implementation modes of the present invention are described above, those skilled in the art should understand that the specific implementation modes described are only illustrative and are not intended to limit the scope of the present invention. Equivalent modifications and changes made by those skilled in the art in accordance with the spirit of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid, characterized in that: Using serpentine ore as raw material, the process includes: (1) The slurry after wet grinding of mineral processing is concentrated and filtered to obtain raw material slurry; (2) the pretreated raw material slurry is subjected to two-stage atmospheric pressure hydrochloric acid leaching; (3) The leached crude silica slag is washed with CCD, filtered, and dried to obtain silicon slag, and then industrial silicon is obtained through reduction smelting, refining, impurity removal, and crushing; (4) removing iron from the leaching solution and precipitating nickel, and separating, washing and filtering the precipitated iron hydroxide and nickel hydroxide; (5) After secondary impurity removal and purification in step (4), the magnesium chloride is concentrated by crystallization and evaporation to obtain a magnesium chloride solution with a mass concentration of 45% to 55%, which is used as a raw material for drying magnesium chloride; (6) drying magnesium chloride; (7) electrolyzing the magnesium chloride sent from the drying system into metallic magnesium and chlorine gas; (8) Magnesium refining.

2. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: The slurry in step (1) is a slurry with a mass concentration of 8-15%, which is obtained by mixing serpentine ore fine powder with hydrochloric acid.

3. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: The two-stage normal pressure hydrochloric acid leaching in step (2) is carried out by using a two-stage countercurrent leaching process of a hydrochloric acid system, which specifically comprises the following steps: A. The pretreated raw material slurry first enters the first stage of leaching, the slurry temperature of the first stage of leaching is controlled at 80℃~85℃, and the leaching time is 2h~3h; B. The overflow after the first stage leaching and thickening is sent to neutralization and iron removal, and the residual acid in the leaching is between 5-15g / L; the bottom flow of the first stage leaching is sent to the second stage leaching; C. The slurry temperature of the second stage leaching is controlled at 95℃~100℃, and the leaching time is 2h~3h; the crude silica slag obtained after the second stage leaching separation is sent to CCD for washing; the overflow of the second stage leaching returns to the first stage leaching.

4. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: In step (3), the crude silicon dioxide is slurried and then subjected to countercurrent washing using a thickener. The washing system uses a five-stage countercurrent washing system, and the washing ratio is controlled at 2:1 = the weight ratio of wash water to the solids entering the thickener.

5. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: The reduction smelting in step (3) uses silicon slag as the main raw material, upgraded coke powder and wood blocks as reducing agents, and adopts a semi-enclosed electric furnace for smelting production.

6. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: The refining and impurity removal in step (3) is carried out by bottom blowing of oxygen and compressed air, and compressed air and oxygen are blown to the bottom of the silicon bag in sequence to perform oxidative refining on the silicon solution.

7. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: The iron removal in step (4) adopts a two-stage process, comprising the following steps: a. Use magnesium hydroxide slurry as a neutralizing agent, neutralize the residual acid, and then remove iron in one stage to control the end point pH value to 3.0-3.5, so that trivalent iron and aluminum are hydrolyzed and precipitated, and silicon dioxide is co-precipitated and removed. After iron removal, the slurry is densely separated; b. The endpoint pH value of the second-stage iron removal is 4.0-4.

5. Compressed air is blown in to oxidize divalent iron into trivalent iron, so that the iron and aluminum in the first-stage slurry are further hydrolyzed. The overflow of the second-stage iron removal is sent to nickel precipitation; the overflow liquid of the second-stage iron removal bottom flow CCD is slurried and returned to the first-stage iron removal to recover the valuable metals in the slag.

8. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: The drying in step (6) adopts cooling granulation, one-stage air fluidization dehydration, and one-stage molten salt dehydration process to obtain anhydrous magnesium chloride.

9. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: The molten salt dehydration adopts a hydrochloric acid drying system to gradually remove water molecules from the magnesium chloride to obtain magnesium chloride molten salt, and the dried water-containing HCl gas is recovered to prepare hydrochloric acid.

10. The production process for preparing metallic magnesium and industrial silicon by decomposing serpentine with hydrochloric acid according to claim 1, characterized in that: The process adopts a serpentine ore comprehensive utilization system, which includes a two-stage countercurrent leaching reaction device, the leachate outlet of the two-stage countercurrent leaching reaction device is connected to a solid-liquid separation washing device, the overflow port of the solid-liquid separation washing device is connected to a metal magnesium production line, and the silicon slag outlet of the solid-liquid separation washing device is connected to an industrial silicon production line; The metal magnesium production line includes an iron removal device, a nickel precipitation device, an evaporation concentration device, a magnesium chloride drying device, and a magnesium chloride electrolysis device connected in sequence; the industrial silicon production line includes a silicon slag drying device, a reduction smelting device, and a refining and impurity removal device connected in sequence.

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