Method for recovering magnesium resource in solid industrial salt

Abstract

The invention belongs to the field of salt chemical industry production, and relates to a method for recovering magnesium resources in solid industrial salt. According to the method, a high-quality magnesium hydroxide product is obtained through countercurrent salt leaching, hydrolysis under the alkaline condition, secondary filtering separation, dehydration drying and packaging, and pure salt and pure brine obtained after salt leaching serve as production raw materials and return to a production system. Compared with the prior art, the method does not change the existing salt chemical industry production process, does not affect the existing production, only washes the solid raw material salt of the salt chemical industry with water, recycles magnesium hydroxide in the washing water, is easy to implement technical improvement and large in operation tolerance, improves the existing production stability of the salt chemical industry, and simultaneously reduces the production cost of the salt chemical industry. And the recovered magnesium resource can bring certain economic value to enterprises, and meanwhile, the discharge amount of the salty mud is reduced, so that the magnesium resource in the solid industrial salt is possibly recovered, and the method has certain environmental protection and social benefits.

Description

Technical Field

[0001] The invention belongs to the field of salt chemical production, and in particular relates to a method for recovering magnesium resources in solid industrial salt. Background Art

[0002] In the salt-making process, as sodium chloride continues to crystallize, the concentration of magnesium salts such as magnesium chloride and magnesium sulfate gradually increases, and eventually reaches a supersaturated state, crystallizing and precipitating on the surface of sodium chloride crystals. Although there is a process of draining the old brine when drying sea salt, the finished salt still contains a large amount of magnesium chloride and magnesium sulfate crystals. In contrast, lake salt is a fully crystalline salt, and the sodium chloride in its finished product contains more magnesium salt crystals.

[0003] The national standard for qualified sodium chloride is magnesium ≤ 0.15%. In the production system of caustic soda and soda ash, the magnesium salt brought in with the raw salt will be hydrolyzed into solid magnesium hydroxide. The production process of the caustic soda industry includes primary brine refining and secondary brine refining, aiming to control the total amount of calcium and magnesium in the saturated brine to below 20ppb to ensure the quality of caustic soda. The primary brine refining process is to separate magnesium hydroxide and calcium carbonate solids from the brine to obtain refined brine and calcium and magnesium salt mud that meet the requirements of secondary refining. However, these calcium and magnesium salt mud mixtures are usually treated as solid waste because they have no practical use. The secondary brine refining process uses chelating resin to adsorb calcium and magnesium ions, and resolves them through acid washing, and then returns them to the primary brine refining system. The soda ash industry lacks effective means to remove magnesium salts. Whether it is salting out in the combined alkali process or saturation of dissolved salts in the ammonia-alkali process, the magnesium salts brought in with solid sodium chloride will eventually enter the sodium carbonate product, thereby seriously affecting the quality of the sodium carbonate product.

[0004] At the end of the last century, some salt chemical companies used the salt washing process, the main purpose of which was to remove water-insoluble matter from the raw salt. However, due to the limitations of separation technology at the time, the sediment could only be removed by simple sedimentation, and the dissolved magnesium chloride returned to the production system. With the continuous development and widespread application of membrane technology, membrane products of various materials and pore sizes have been introduced, providing new solutions to technical problems that were difficult to solve in the past.

[0005] Magnesium hydroxide particles are small and difficult to separate by natural sedimentation. If membrane filtration technology is used, a very dense filter cake will be formed, which will seriously affect the filtration efficiency. Therefore, in the chlor-alkali industry, a floating clarification barrel pre-treatment is often used to separate most of the magnesium hydroxide from the brine by flotation. However, since this process requires the use of iron hydroxide to flocculate magnesium hydroxide, and the sludge is mixed with calcium carbonate salt mud for dehydration, the final calcium and magnesium salt mud is difficult to further separate and has no recycling value, which has become a major environmental problem currently faced by chlor-alkali companies. In addition, due to the wide application of magnesium resources in many fields such as aerospace and the growth of demand, the recycling of magnesium resources has once again become a focus of attention in the industry.

[0006] If magnesium resources can be recovered from the raw salt, the remaining calcium carbonate will be easier to separate. By separating calcium carbonate through sedimentation, the quality of soda ash can be significantly improved. In addition, chlor-alkali companies do not need to use flotation clarification tank pre-treaters or coarse filtration equipment for pre-treatment, which not only saves investment costs and floor space, but also improves the stability of the production process.

[0007] Patent CN111204780A provides a method for resource utilization of salt mud in the chlor-alkali industry, including pretreatment, washing, pickling, solid-liquid separation, recovery of calcium oxalate, and recovery of magnesium hydroxide. This method is said to have a short process. While achieving the reduction of solid waste of salt mud produced by the chlor-alkali industry, it fully recovers the calcium and magnesium components in the salt mud, turning waste into treasure, reducing the environmental pollution caused by waste discharge, and the obtained calcium oxalate and magnesium hydroxide can be used as valuable industrial raw materials. However, this patent is only used for salt mud treatment. First of all, it is of no help to the production of primary brine in chlor-alkali, and it is impossible to cancel the floating clarification pretreatment device or metal wire mesh coarse filter in the primary brine refining process; secondly, the primary brine refining process needs to first add sodium hydroxide to hydrolyze magnesium ions into magnesium hydroxide precipitation into salt mud; after drying, washing and acidifying the salt mud, magnesium hydroxide is dissolved into magnesium ions, and then oxalic acid or oxalate is added to react with calcium ions to form calcium oxalate, and after separating calcium oxalate, sodium hydroxide is added to hydrolyze magnesium ions into magnesium hydroxide again. The process of this patent is actually not simple. It adds soda ash once to remove calcium to form salt sludge, adds oxalic acid or oxalate once to recover calcium oxalate, adds sodium hydroxide twice to remove magnesium, and performs pickling once. The consumption of reagents is large, the salt sludge needs to be dried and ground, and the energy consumption is high. Summary of the invention

[0008] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a method for recovering magnesium resources in solid industrial salt, while recovering magnesium resources, improving the quality of magnesium hydroxide products, reducing the investment, land occupation and operating costs of the brine refining system, reducing solid waste emissions, and improving production stability.

[0009] The purpose of the present invention can be achieved by the following technical solutions:

[0010] The present invention provides a method for recovering magnesium resources in solid industrial salt, comprising the following steps:

[0011] S1, using brine A to countercurrently wash industrial salt B to obtain brine C and clean salt Q;

[0012] S2, using the first membrane separation device to separate the brine C, remove water-insoluble matter, obtain brine H and brine slurry E, the brine slurry E is dehydrated separately to obtain dry brine slurry G and filtrate F, and the filtrate F is circulated back to the first membrane separation device;

[0013] S3, adding sodium hydroxide I to the salt water H, reacting to obtain alkaline salt water J, whose pH value is 9-11, magnesium ions are hydrolyzed into solid magnesium hydroxide in the alkaline salt water J, and calcium ions remain in the alkaline salt water J;

[0014] S4, using a second membrane separation device to intercept magnesium hydroxide solid to obtain magnesium hydroxide slurry L and clean brine O;

[0015] S5, the magnesium hydroxide slurry L is dehydrated separately to obtain magnesium hydroxide solid residue N and filtrate M. The magnesium hydroxide solid residue N is dried and packaged to obtain a magnesium hydroxide product P. The filtrate M is circulated back to the second membrane separation device.

[0016] Furthermore, the clean brine O and the clean brine Q are returned to the production system as production raw materials.

[0017] Furthermore, in step S1, the washing salt water A is neutral or weakly acidic water with low salt content, and its pH is ≤7, and is selected from any one of the following: light salt water after acid neutralization of chlorine alkali, salt water after sodium bicarbonate is separated from soda ash, industrial water or evaporated condensed water. The washing salt water A dissolves magnesium chloride, calcium chloride, magnesium sulfate, sodium sulfate and part of sodium chloride on the surface of industrial salt B into salt water C to prevent magnesium ions from being hydrolyzed into magnesium hydroxide during the salt washing process, so that the magnesium hydroxide is dehydrated and lost together with the salt mud.

[0018] Furthermore, in step S1, the industrial salt B is a magnesium-containing solid salt that meets national standards, and is selected from sea salt, lake salt, regenerated salt or any other magnesium-containing solid salt that meets national standards.

[0019] Furthermore, in step S1, the countercurrent cleaning method of industrial salt B is: industrial salt B is cleaned by an auger screw conveyor, industrial salt B is rotated and transported upward from the bottom of the auger screw conveyor, and brine A is added from the top of the auger screw conveyor and flows downward by gravity to dissolve magnesium chloride, calcium chloride, magnesium sulfate, sodium sulfate and part of sodium chloride on the surface of salt particles, and the concentration gradually increases, and finally flows out from the bottom of the auger screw conveyor into the first membrane separation device; the material of the contact part of the auger screw conveyor with industrial salt B and brine A is any one of titanium, high silicon cast iron, high nickel cast iron or SS2205 duplex stainless steel.

[0020] Furthermore, in step S2, the first membrane separation device adopts any one of a microfiltration membrane device or an ultrafiltration membrane device, and its material is any one of a ceramic membrane, a silicon carbide membrane, polytetrafluoroethylene, polyvinylidene fluoride, polysulfone or polyethersulfone, and its structure is any one of a tubular type, a hollow fiber immersed type or a flat plate type; the first membrane separation device has a pore size of 0.02 to 0.1 microns and a filtration pressure of 0.02 to 0.2 MPa.

[0021] Furthermore, in step S2, the salt sludge E is dehydrated separately by a sludge dehydration device, which includes at least any one of a plate and frame filter press, a screw press, a vacuum filter or a belt filter.

[0022] Furthermore, in step S3, the mass concentration of the sodium hydroxide I is 5% to 32%, and the reaction time is 20 to 30 min.

[0023] Furthermore, in step S4, the second membrane separation device adopts any one of a microfiltration membrane device or an ultrafiltration membrane device, and its material is any one of a ceramic membrane, a silicon carbide membrane, polytetrafluoroethylene, polyvinylidene fluoride, polysulfone or polyethersulfone, and its structure is any one of a tubular type, a hollow fiber immersed type or a flat plate type; the second membrane separation device has a pore size of 0.02 to 0.1 microns and a filtration pressure of 0.02 to 0.2 MPa.

[0024] Further, in step S4, the magnesium hydroxide slurry L is dehydrated separately by a sludge dehydration device, which includes at least any one of a plate and frame filter press, a screw press, a vacuum filter or a belt filter.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention does not change the existing salt chemical production process and does not affect the existing production. It only washes the solid raw material salt of the salt chemical industry with water and recovers magnesium hydroxide in the washing water. The technical transformation is easy to implement and the operation tolerance is large. High-quality magnesium hydroxide products can be obtained, which brings certain economic value to the enterprise.

[0027] (2) The present invention can eliminate pretreatment methods such as flotation clarification and wire mesh coarse filtration, simplify the process of primary brine refining, reduce investment, land occupation and energy consumption; while improving the existing production stability of salt chemical industry, it reduces the discharge of salt mud, making it possible to recover magnesium resources in solid industrial salt, and has certain environmental and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a process flow chart of the present invention;

[0029] Figure 2 The invention discloses a salt washing machine (auger screw conveyor) which has a working principle.

[0030] Description of the markings in the figure:

[0031] A-wash brine before treatment by salt washer, B-industrial salt, C-brine after treatment by salt washer, D-brine separated to the first membrane separation device, E-salt sludge retained by the first membrane separation device, F-filtrate of salt sludge, G-dry salt sludge, H-recovered brine after preliminary separation of water-insoluble matter by the first membrane separation device, I-sodium hydroxide, J-alkaline brine, K-brine separated to the second membrane separation device, L-magnesium hydroxide slurry retained by the second membrane separation device, M-filtrate of magnesium hydroxide slurry, N-magnesium hydroxide solid residue, O-clean brine returned to the production system, P-magnesium hydroxide product, Q-clean salt returned to the production system. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0033] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0034] The present invention provides a method for recovering magnesium resources in solid industrial salt, such as Figure 1 As shown, the following steps are included:

[0035] S1, using brine A to countercurrently wash industrial salt B to obtain brine C and clean salt Q. The brine A is low-salt neutral or weakly acidic water with a pH of ≤7, selected from any one of the following: light brine after acid neutralization with chlorine and alkali, brine after sodium bicarbonate is separated with soda ash, industrial water, or evaporation condensate water; the industrial salt B is a magnesium-containing solid salt that meets national standards, selected from any one of sea salt, lake salt, regenerated salt, or other magnesium-containing solid salts that meet national standards; Figure 2 As shown, the method of countercurrent cleaning of industrial salt B by washing brine A is as follows: industrial salt B is cleaned by an auger screw conveyor, industrial salt B is rotated and transported upward from the bottom of the auger screw conveyor, and washing brine A is added from the top of the auger screw conveyor and flows downward by gravity to dissolve magnesium chloride, calcium chloride, magnesium sulfate, sodium sulfate and part of sodium chloride on the surface of salt particles into brine C, and the concentration gradually increases to prevent magnesium ions from being hydrolyzed into magnesium hydroxide during the salt washing process, so that magnesium hydroxide is dehydrated and lost together with the salt mud, and brine C finally flows out from the bottom of the auger screw conveyor into the first membrane separation device; the material of the contact part of the auger screw conveyor with industrial salt B and washing brine A is any one of titanium, high silicon cast iron, high nickel cast iron or SS2205 duplex stainless steel.

[0036] S2, using the first membrane separation device to separate the brine C, remove the water insoluble matter, obtain brine H and salt slurry E, and dehydrate the salt slurry E separately through the sludge dehydration equipment to obtain dry salt slurry G and filtrate F, and the filtrate F is circulated back to the first membrane separation device. The first membrane separation device adopts any one of a microfiltration membrane device or an ultrafiltration membrane device, and its material adopts any one of a ceramic membrane, a silicon carbide membrane, polytetrafluoroethylene, polyvinylidene fluoride, polysulfone or polyethersulfone, and its structural form is any one of a tubular type, a hollow fiber submerged type or a flat plate type, and its pore size is 0.02 to 0.1 microns, and the filtration pressure is 0.02 to 0.2 MPa; the sludge dehydration equipment includes at least any one of a plate and frame filter press, a screw press, a vacuum filter or a belt filter.

[0037] S3, adding sodium hydroxide I with a mass concentration of 5% to 32% to the brine H, reacting for 20 to 30 minutes, to obtain alkaline brine J, whose pH value is 9 to 11, magnesium ions are hydrolyzed into solid magnesium hydroxide in the alkaline brine J, and calcium ions remain in the alkaline brine J.

[0038] S4, using a second membrane separation device to intercept magnesium hydroxide solids to obtain magnesium hydroxide slurry L and clean brine O. The second membrane separation device is any one of a microfiltration membrane device or an ultrafiltration membrane device, and its material is any one of a ceramic membrane, a silicon carbide membrane, polytetrafluoroethylene, polyvinylidene fluoride, polysulfone or polyethersulfone, and its structure is any one of a tubular type, a hollow fiber submerged type or a flat plate type, and its pore size is 0.02 to 0.1 microns, and the filtration pressure is 0.02 to 0.2 MPa.

[0039] S5, the magnesium hydroxide slurry L is dehydrated separately by a sludge dehydration device to obtain a magnesium hydroxide solid residue N and a filtrate M. The magnesium hydroxide solid residue N is dried and packaged to obtain a magnesium hydroxide product P, and the filtrate M is circulated back to the second membrane separation device. The sludge dehydration equipment includes at least any one of a plate and frame filter press, a screw press, a vacuum filter or a belt filter.

[0040] The clean brine O and clean brine Q are returned to the production system as production raw materials.

[0041] Example 1

[0042] The specific steps of this embodiment are as follows:

[0043] Industrial water is used to wash magnesium-containing solid salt of a chlor-alkali enterprise in reverse flow. The solid salt is rotated upward from the bottom of the auger screw conveyor. Normal temperature industrial water is added from the top of the auger screw conveyor and flows downward by gravity to dissolve magnesium chloride, calcium chloride, magnesium sulfate, sodium sulfate and part of sodium chloride on the surface of solid salt particles into crude brine. The material of the auger screw conveyor in contact with solid salt and crude brine is titanium. The crude brine required for primary brine refining is obtained by dissolving salt saturation. The Ca in the solid salt 2+ Mg 2+ The crude brine flows out from the bottom of the auger screw conveyor and is filtered through a ceramic flat membrane with a pore size of 100 nanometers. The filtration pressure is 0.02MPa. All water-insoluble substances brought in with the solid salt are intercepted by the ceramic flat membrane filtration device. Salt mud and crude brine saturated with dissolved salt are filtered out. The salt mud is dehydrated separately using a plate and frame filter press to obtain dry salt mud and filtrate. The filtrate is circulated back to the ceramic flat membrane filtration device. For the crude brine saturated with dissolved salt, the components in the crude brine are measured as follows: sodium chloride 305g / L, sodium sulfate 7.4g / L, Ca 2+ 300mg / L, Mg 2+ 250mg / L.

[0044] Then add 0.1g / L of sodium hydroxide (except Mg 2+ ) and 0.3 g / L sodium carbonate (in addition to Ca 2+ ) and adjust the pH value of the saturated crude brine to 11, stir and react for 30 minutes to obtain alkaline crude brine, in which magnesium ions are hydrolyzed into solid magnesium hydroxide, and calcium ions are reacted and precipitated into solid calcium carbonate. Subsequently, the alkaline crude brine is filtered again using a silicon carbide flat membrane with a pore size of 100 nanometers, and the filtration pressure is 0.02MPa to obtain a refined primary brine, a slurry of magnesium hydroxide and calcium carbonate, and a vacuum filter is used to dehydrate and recover the slurry of magnesium hydroxide and calcium carbonate, and the filtrate is circulated back to the silicon carbide flat membrane filtration device. For the refined brine, the components in the brine are measured: sodium chloride 305g / L, sodium sulfate 7.4g / L, Ca 2+ +Mg 2+ ≤1mg / L, Mg 2+ ≤0.01mg / L, suspended solids (SS) ≤1mg / L, indicating that more than 99.9% of magnesium ions are converted into magnesium hydroxide and are intercepted and recovered by the silicon carbide flat membrane. The magnesium content in the refined brine meets the national standard for qualified sodium chloride products, and it is returned to the production system of the chlor-alkali enterprise as a production raw material.

[0045] Example 2

[0046] A chlor-alkali plant currently produces 250,000 tons of ion-exchange membrane caustic soda per year. Its raw materials are mainly lake salt, and the primary brine refining adopts the brine refining process of pre-reaction-pretreatment-post-reaction-polytetrafluoroethylene membrane filtration. However, its primary brine refining system was built earlier and has been in operation for more than ten years. The equipment is seriously aged, especially the pre-processor is seriously damaged by corrosion. There is no space on site to build a new pre-processor. Once the pre-processor cannot operate, the system will face the risk of suspension of production. In addition, because the lake salt used by the enterprise is fully crystalline salt, Ca 2+ Mg 2+ The content of impurities such as magnesium hydroxide and sulfate is high. If there is no pre-treatment to remove magnesium hydroxide, the filter cake formed by magnesium hydroxide particles will be very dense, which seriously affects the filtration flux and makes it difficult for the subsequent polytetrafluoroethylene membrane to filter stably. The process of the present invention is now used to refine the raw salt of the chlor-alkali plant.

[0047] The specific steps of this embodiment are as follows:

[0048] Industrial water is used to wash the raw lake salt of the chlor-alkali plant in reverse flow. The lake salt is rotated upward from the bottom of the auger screw conveyor. Industrial water at room temperature is added from the top of the auger screw conveyor and flows downward by gravity to dissolve the magnesium chloride, calcium chloride, magnesium sulfate, sodium sulfate and part of the sodium chloride on the surface of the lake salt particles into the crude brine. The material of the auger screw conveyor that contacts the solid salt and the crude brine is SS2205 duplex stainless steel. The black and turbid washing brine is obtained and the inorganic flat plate with a pore size of 100 nanometers is used. Plate membrane filtration. In this embodiment, a silicon carbide flat membrane is used to filter the turbid washed salt water. The filtration pressure is 0.1 MPa. All water insoluble substances brought in with the lake salt are retained by the silicon carbide flat membrane to obtain salt mud and clear, transparent and colorless salt water solution. The salt mud is dehydrated separately using a belt filter to obtain dry salt mud and filtrate. The filtrate is circulated back to the silicon carbide flat membrane filtration device. The Mg content of the obtained clear, transparent and colorless salt water solution is analyzed by EDTA titration. 2+ , Mg 2+ The content is 340.89 mg / L. Then, 0.2 g / L of sodium hydroxide is added to adjust the pH value of the salt solution to 10, and the reaction is stirred for 30 minutes to obtain an alkaline salt solution, which is then filtered again using an inorganic flat membrane with a pore size of 100 nanometers. In this embodiment, a silicon carbide flat membrane is used to filter the alkaline salt solution. The filtration pressure is 0.1 MPa to obtain magnesium hydroxide slurry and a clear, transparent and colorless aqueous solution. The aqueous solution is returned to the chlor-alkali plant production system as a production raw material. The magnesium hydroxide slurry is dehydrated and recovered using a spiral stacking machine, and the filtrate is circulated back to the silicon carbide flat membrane filtration device. For the obtained aqueous solution, the Mg in the obtained aqueous solution is analyzed again by EDTA titration. 2+ Content, found no Mg 2+, indicating that almost all magnesium resources entering the brine with the raw salt are recovered.

[0049] If the process of the present invention is used to wash the solid raw materials in the salt chemical industry and recover magnesium hydroxide therefrom, according to the 250,000 tons / year ion-exchange membrane caustic soda scale of the chlor-alkali plant, the annual consumption of solid salt exceeds 380,000 tons. If all the solid salt is lake salt, the Mg content is 2+ At 0.15%, the magnesium resources brought into the solid salt in terms of magnesium ions will reach 577.5 tons / year, and nearly 1,400 tons / year of high-purity magnesium hydroxide can be obtained, which will bring economic benefits to the enterprise and reduce the discharge of salt mud by 1,400 tons / year (dry basis). At the same time, the pre-treatment unit can be eliminated, the process of primary brine refining can be simplified, and about 500m 2 of industrial land.

[0050] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for recovering magnesium resources from solid industrial salt, characterized in that: The steps include: S1, using brine A to countercurrently wash industrial salt B to obtain brine C and clean salt Q; S2, using the first membrane separation device to separate the brine C, remove water-insoluble matter, obtain brine H and brine slurry E, the brine slurry E is dehydrated separately to obtain dry brine slurry G and filtrate F, and the filtrate F is circulated back to the first membrane separation device; S3, adding sodium hydroxide I to the salt water H, reacting to obtain alkaline salt water J, whose pH value is 9-11, magnesium ions are hydrolyzed into solid magnesium hydroxide in the alkaline salt water J, and calcium ions remain in the alkaline salt water J; S4, using a second membrane separation device to intercept magnesium hydroxide solid to obtain magnesium hydroxide slurry L and clean brine O; S5, the magnesium hydroxide slurry L is dehydrated separately to obtain magnesium hydroxide solid residue N and filtrate M. The magnesium hydroxide solid residue N is dried and packaged to obtain a magnesium hydroxide product P. The filtrate M is circulated back to the second membrane separation device.

2. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: In step S1, the brine A is low-salt neutral or weakly acidic water with a pH of ≤7, and is selected from any one of the following: brine obtained by neutralization of chlorine and alkali with acid, brine obtained by separation of sodium bicarbonate from soda ash, industrial water, or evaporated condensed water.

3. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: In step S1, the industrial salt B is a magnesium-containing solid salt that meets national standards, and is selected from sea salt, lake salt, regenerated salt or any other magnesium-containing solid salt that meets national standards.

4. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: In step S1, the countercurrent cleaning method of industrial salt B is: industrial salt B is cleaned by an auger screw conveyor, industrial salt B is rotated upward from the bottom of the auger screw conveyor, and washing brine A is added from the top of the auger screw conveyor and flows downward by gravity; the material of the contact part of the auger screw conveyor with industrial salt B and washing brine A is any one of titanium, high silicon cast iron, high nickel cast iron or SS2205 duplex stainless steel.

5. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: In step S2, the first membrane separation device adopts any one of a microfiltration membrane device or an ultrafiltration membrane device, and its material is any one of a ceramic membrane, a silicon carbide membrane, polytetrafluoroethylene, polyvinylidene fluoride, polysulfone or polyethersulfone, and its structure is any one of a tubular type, a hollow fiber immersed type or a flat plate type; the first membrane separation device has a pore size of 0.02 to 0.1 microns and a filtration pressure of 0.02 to 0.2 MPa.

6. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: In step S2, the salt sludge E is dehydrated separately by a sludge dehydration device, which includes at least one of a plate and frame filter press, a screw press, a vacuum filter or a belt filter.

7. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: In step S3, the mass concentration of the sodium hydroxide I is 5% to 32%, and the reaction time is 20 to 30 minutes.

8. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: In step S4, the second membrane separation device adopts any one of a microfiltration membrane device or an ultrafiltration membrane device, and its material is any one of a ceramic membrane, a silicon carbide membrane, polytetrafluoroethylene, polyvinylidene fluoride, polysulfone or polyethersulfone, and its structure is any one of a tubular type, a hollow fiber immersed type or a flat plate type; the second membrane separation device has a pore size of 0.02 to 0.1 microns and a filtration pressure of 0.02 to 0.2 MPa.

9. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: In step S5, the magnesium hydroxide slurry L is dehydrated separately by a sludge dehydration device, which includes at least one of a plate and frame filter press, a screw press, a vacuum filter or a belt filter.

10. A method for recovering magnesium resources in solid industrial salt according to claim 1, characterized in that: The clean brine O and clean brine Q are returned to the production system as production raw materials.

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