Method for producing low-chlorine magnesium oxide

Abstract

The application discloses a preparation method of low-chlorine magnesium oxide. The method comprises the following steps: adding high-chlorine magnesium hydroxide slurry into an electrolytic cell, adding an anode liquid into an anode chamber, adding a cathode liquid into a cathode chamber, and adding a reinforcing agent into the high-chlorine magnesium hydroxide slurry. A direct current electric field is applied between the anode and the cathode by using a pulse power source to remove chlorine. Under the action of the electric field, the negative-charged chlorine ions move to the anode chamber by electromigration, and the chlorine moves to the cathode chamber by electrodialysis in the form of chlorides or other soluble ions, so as to reduce the concentration of the chlorine ions in the high-chlorine magnesium hydroxide slurry. After the chlorine is removed, the magnesium hydroxide is filtered and calcined to obtain the low-chlorine magnesium oxide. The method has the advantages that the high-energy-consumption processes such as ball milling and calcining in the traditional chlorine removal process of magnesium hydroxide are avoided, the harm of the chlorine ions to the equipment is reduced, the chlorine ions in the magnesium hydroxide are removed only by electromigration and electrodialysis, and the green and efficient preparation of the low-chlorine magnesium oxide is realized.

Description

Technical Field

[0001] The invention relates to a preparation process of low-chloride magnesium oxide, belonging to the technical field of preparation of new magnesium oxide materials. Background Art

[0002] The Qarhan Salt Lake in Qinghai Province is rich in potassium, lithium, and other resources. However, the development of the Qarhan Salt Lake produced a significant amount of bischofite, known locally as "magnesium damage." Qinghai Western Magnesium Co., Ltd. successfully addressed this "magnesium damage" issue by using bischofite as a raw material through ammonia precipitation of magnesium to produce magnesium hydroxide on a large scale.

[0003] Currently, the average chlorine content in the industrial-grade magnesium hydroxide produced by Qinghai Western Magnesium Industry Co., Ltd. using the ammonia process is 0.3% to 0.8%. The high chlorine content is due to the failure to effectively control the morphology and growth rate of the initial grains during the ammonia precipitation process using bischofite. The resulting magnesium hydroxide tends to form spherical particles that continuously agglomerate and grow, resulting in a large amount of chloride ions in the solution being encapsulated in the spherical particles. Even subsequent filtration and washing cannot reduce the chloride ion content to less than 0.1%.

[0004] High chloride ion content limits the large-scale application of magnesium hydroxide in high-value-added industries such as flame retardants. Furthermore, magnesium oxide, a key downstream product of magnesium hydroxide, requires the raw material magnesium hydroxide to have as low a chloride ion content as possible. For example, during the calcination of magnesium hydroxide and when magnesium oxide is used in high-temperature environments, high chloride ion content can easily generate large amounts of chlorine gas during production. Chlorine gas combines with water molecules to form hydrogen chloride gas. This hydrogen chloride gas not only severely corrodes production equipment and pollutes the environment, but also affects the health of employees.

[0005] With the demand for industrial upgrading and the development of the high-tech functional materials market, low-chloride magnesium oxide has found widespread application in high-end refractories, high-functional fine inorganic materials, food, medicine, advanced electromagnetic materials, and the IT industry. The development of low-chloride magnesium oxide materials will support the upgrading of salt lake industries and further expand the application range of magnesium hydroxide produced from salt lake bischofite.

[0006] At present, the key to the preparation of low-chloride magnesium oxide lies in the removal of chloride ions from the raw material magnesium hydroxide. There are three main methods: (1) Recrystallization: As reported in CN114804163A, the crystal lattice is destroyed by ball milling, and a strong base is added to promote the recrystallization of magnesium hydroxide, thereby releasing and reducing the chloride ions in magnesium hydroxide. This method has high alkali consumption and energy consumption, and the subsequent filtration of magnesium hydroxide is more challenging; (2) Single-stage or multi-stage washing: As reported in CN108190924B, high-chloride magnesium hydroxide is subjected to single-stage stirring washing or multi-stage countercurrent stirring washing, which can reduce the chloride content in magnesium hydroxide from 0.8% to below 0.2%. This method uses a large amount of water and has high subsequent water treatment costs. (3) Electrochemical deposition: Patent CN114717579A uses magnesium chloride as raw material and uses electrochemical deposition to prepare magnesium hydroxide at the cathode. This technology can obtain magnesium hydroxide with a chloride content of 0.03%, but this method cannot be directly used to remove chloride ions from magnesium hydroxide. Magnesium oxide with low chloride content can also be prepared using a traditional calcination process, as reported in CN106986359B. This process involves treating the chloride ions in magnesium hydroxide through multiple calcinations, resulting in the production of magnesium oxide with low chloride content. This method involves multiple calcinations, which results in high energy consumption. The chlorine and hydrogen chloride gases released during the calcination process also place high demands on equipment and materials. Therefore, how to efficiently and cost-effectively remove the chloride ions from magnesium hydroxide becomes the key to preparing magnesium oxide with low chloride content.

[0007] At present, in the field of new materials related to magnesium oxide, there are no reports on the use of electrochemical methods to directly hydroxide magnesium and remove the chloride ion content; there are no reports on the use of enhancers such as sodium hydroxide, potassium hydroxide, ammonia water, and anionic surfactants to accelerate the electromigration and electrodialysis of chloride ions in magnesium hydroxide; there are also no reports on the combination of electrochemical methods and calcination to prepare low-chloride magnesium oxide. Summary of the Invention

[0008] In view of the problem of high chloride ion content in magnesium hydroxide produced by bischofite in salt lakes in the prior art, and the defect that the release of chloride ions during the calcination of magnesium hydroxide poses a great threat to equipment and materials, especially the pain point of high chloride content in the downstream product magnesium oxide, the purpose of the present invention is to provide a method for preparing low-chloride magnesium oxide. This method combines electrodynamics and calcination technology to solve the pain points of the current high-chloride magnesium hydroxide produced by bischofite and the limited application of downstream high-chloride magnesium oxide products in high-end magnesium materials; it reduces the impact of chloride ions on equipment and the environment during the calcination of magnesium hydroxide, and the obtained low-chloride magnesium oxide product has stable quality and high production efficiency, meeting industrial production requirements.

[0009] This invention proposes a method for preparing low-chloride magnesium oxide using an electrokinetic method and calcination. This process can significantly reduce the chloride ion concentration in magnesium hydroxide, improving the production of low-chloride magnesium oxide and extending the salt lake magnesium industry chain. It has significant economic value and lays the foundation for the diversification, serialization, and scale-up of high-end magnesium-based compound production in my country. The chlorine content in the resulting magnesium oxide product can be as low as 0.01 wt%.

[0010] The present invention provides a method for preparing low-chloride magnesium oxide, comprising the following steps:

[0011] (1) The chlorine-containing magnesium hydroxide slurry is put into the electrolytic cell, the anolyte is added to the anode chamber, and the cathode chamber is added to the cathode chamber. Under stirring conditions, a pulse power supply is used to apply an electric field between the positive and negative electrodes to remove chlorine; a diaphragm or partition is provided between the chlorine-containing magnesium hydroxide slurry and the anode chamber and the cathode chamber.

[0012] (2) The magnesium hydroxide slurry after dechlorination is filtered and calcined to obtain low-chloride magnesium oxide.

[0013] In industrial applications, a pulsed power supply is used to apply a DC electric field between the cathode and anode to remove chlorine. Of course, AC can also be used, but AC needs to be filtered. The filtered current can only flow in one direction, which is equivalent to DC.

[0014] The preparation method of a low-chloride magnesium oxide of the present invention also includes the following preferred embodiments:

[0015] Preferably, as in step (1), the D50 particle size of the magnesium hydroxide is less than 60 μm and the chloride ion content is greater than 0.01 wt %. The reason for controlling the particle size of the raw materials in the present invention is to ensure that the magnesium hydroxide does not form a colloid or precipitate during the electric field dechlorination, otherwise the dechlorination effect will be greatly reduced.

[0016] In order to ensure the purity of subsequent products, the purity of the raw material magnesium hydroxide is preferably greater than 98%.

[0017] In order to improve production efficiency and connect with the existing process, the chloride ion content of the raw material magnesium hydroxide used in the present invention is preferably less than or equal to 1.0%. Of course, less than 0.8wt% can also be used in the present invention.

[0018] Preferably, the solid content of the magnesium hydroxide slurry in step (1) is 20-60%, that is, the content of magnesium hydroxide in the magnesium hydroxide slurry is 20-60 wt%.

[0019] Preferably, the electrolytic cell is divided into an anode chamber and a cathode chamber by a separator or a diaphragm as in step (1), and the magnesium hydroxide slurry is added to the space formed by the separator or the diaphragm and the electrolysis wall, and before power is applied, the magnesium hydroxide slurry is almost not in contact with the electrodes.

[0020] Preferably, as in step (1), the anode chamber and the cathode chamber are respectively connected to corresponding electrolyte storage tanks to form a continuous circulation loop.

[0021] Preferably, as in step (1), the anolyte is selected from at least one of deionized water, ammonia water, sodium hydroxide solution, and potassium hydroxide solution.

[0022] Preferably, as in step (1), the cathode liquid is selected from at least one of deionized water, ammonia water, sodium hydroxide solution, potassium hydroxide solution, and potassium nitrate solution.

[0023] Preferably, as in step (1), before the electric field dechlorination, a strengthening agent is added to the chlorine-containing magnesium hydroxide slurry, wherein the strengthening agent is selected from at least two of an anionic surfactant, sodium hydroxide solution, potassium hydroxide solution, and ammonia water. The strengthening agent competes with the chloride ions for adsorption, thereby promoting the removal of the chloride ions.

[0024] Preferably, as in step (1), before the electric field dechlorination, a strengthening agent is added to the chlorine-containing magnesium hydroxide slurry, and the strengthening agent is composed of an anionic surfactant and at least one of sodium hydroxide solution, potassium hydroxide solution, and ammonia water.

[0025] It is further preferred that, as in step (1), the hydrophilic group of the anionic surfactant in the enhancer is at least one of carboxylate, sulfonate, sulfate and phosphate.

[0026] It is further preferred that, as in step (1), the cathodic ionic surfactant is at least one of sodium lauryl sulfate, sodium petroleum sulfonate, sodium dodecyl sulfonate, sodium hexadecyl sulfonate, sodium octadecyl sulfonate, sodium oleate, sodium linoleate, sodium linolenate, sodium laurate, myristic acid, palmitic acid, stearic acid, cycloalkanoic acid, sodium undecylenate, potassium dodecyl phosphate, and sodium hexadecyl phosphate.

[0027] More preferably, the slurry is enhanced by a composition comprising an inorganic substance and an anionic surfactant in a mass ratio of 3-8:4-7; the inorganic substance is selected from at least one of sodium hydroxide solution, potassium hydroxide solution, and aqueous ammonia. Both hydroxide and anionic surfactants can competitively adsorb chloride ions, and their combined use allows them to occupy more sites. When the enhancer comprises an inorganic substance and anionic surfactant in a mass ratio of 3-8:4-7, the removal of chloride ions under the action of an electric field is optimal.

[0028] Preferably, in step (1), the mass ratio of the strengthening agent to the chlorine-containing magnesium hydroxide slurry is 1-100:100000. More preferably, it is 9-40:100000. At this ratio, the strengthening agent has a good effect on removing chloride ions, the amount of strengthening agent used is small, and the cost is low.

[0029] Preferably, as in step (1), the electric field strength of the pulsed electric field is 0.1-8 V / cm, and the pulse duty cycle is 20-80%. As a further preference, the electric field strength of the pulsed electric field is 0.5-2 V / cm, and the pulse duty cycle is 30-60%.

[0030] Preferably, as in step (1), the electrode is an inert electrode, and the electrode material is at least one of ruthenium-coated titanium mesh, graphite plate, carbon fiber cloth, platinum group alloy and alloy foil thereof.

[0031] Preferably, as in step (1), the partition or membrane is at least one of a microporous material, a porous plate, a nylon screen, a filter membrane, a non-woven fabric, nylon, vinylon, a polypropylene filter cloth and a sponge.

[0032] Preferably, as in step (1), the high chloride magnesium hydroxide slurry is mechanically stirred, or at least one of air, oxygen and nitrogen is blown into the slurry to make the slurry suspended.

[0033] Preferably, as in step (2), the magnesium hydroxide is filtered using a plate filter press after chlorine removal.

[0034] Preferably, as in step (2), the filtered low-chloride magnesium hydroxide is placed in a furnace and heated to 600-900° C. at a heating rate of 2-8° C. / min for calcination.

[0035] This invention proposes, for the first time, the use of pulsed voltage to drive chloride ions in magnesium hydroxide slurry to achieve the purpose of removing chloride from magnesium hydroxide. This avoids the high energy consumption of ball milling and calcination in traditional dechlorination processes, reducing the harm of chloride ions to equipment and worker health during the calcination of magnesium hydroxide to produce magnesium oxide. This invention is the first to adopt the concept of pulsed power supply regulation + calcination to achieve a short process and low cost for the preparation of low-chloride magnesium oxide.

[0036] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0037] 1. The present invention utilizes pulse voltage to reduce chloride ions in magnesium hydroxide, thereby avoiding the high energy consumption operation units of ball milling and multi-stage calcination in the traditional dechlorination process, and the process is green and energy-saving.

[0038] 2. The present invention utilizes strengthening liquids such as ammonia water, sodium hydroxide solution, potassium hydroxide solution and anionic surfactants to achieve the purpose of competitive adsorption with chloride ions in magnesium hydroxide slurry, thereby promoting the efficiency of chloride ion removal under the action of an electric field and effectively reducing the chloride ion content in high-chloride magnesium hydroxide.

[0039] 3. The present invention combines pulse voltage with calcination process, avoiding the harm of chloride ions to equipment and environment during the preparation of magnesium oxide by calcining magnesium hydroxide, and realizing low-cost and green preparation of low-chloride magnesium oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a process flow chart of the present invention.

[0041] Figure 2 Schematic diagram of the electrolytic cell. Specific embodiments

[0042] The present invention will be further described below with reference to the embodiments. It should be emphasized that the following description is merely illustrative and is not intended to limit the scope of the present invention and its application.

[0043] Example 1

[0044] Step (1): Use Figure 2 The electrolytic cell shown in the figure is filled with a 30% solid magnesium hydroxide slurry (D50 particle size 42 μm; chloride ion solid content 0.6%). Both ends of the slurry are sealed with non-woven fabric. Ammonia water and sodium dodecyl sulfate are added to the slurry at a mass ratio of 5:4:100,000. Air is bubbled through the slurry to maintain uniform dispersion. Ammonia water containing 0.2 mol / l is added to the anode chamber, and deionized water is added to the cathode chamber. A graphite anode and a titanium plate cathode are inserted into the anode and cathode chambers, respectively. Constant current pumps connect the anode and cathode chambers to corresponding storage tanks, forming a continuous circulation loop. A unidirectional pulse voltage with an electric field strength of 0.5 V / cm and a duty cycle of 40% is applied between the anode and cathode. The electrolysis lasts for 79 hours, and the slurry is continuously stirred to ensure a suspended state. The chloride content of the magnesium hydroxide after pulse dechlorination is 0.03%.

[0045] Step (2): The magnesium hydroxide after dechlorination is filtered using a plate filter press, and the filtered low-chloride magnesium hydroxide (the chlorine content in the filtered magnesium hydroxide is 0.03%) is placed in a furnace and heated to 850° C. at a heating rate of 6° C. / min for calcination to obtain low-chloride magnesium oxide with a chlorine content of 0.02%.

[0046] Example 2

[0047] Step (1): Use Figure 2The electrolytic cell shown in the figure is filled with a 36% solid magnesium hydroxide slurry (D50 particle size 3 μm; chloride ion solid content 0.5%). Both ends of the slurry are sealed with sponges. Sodium hydroxide and sodium oleate are added to the slurry at a mass ratio of 3:7:100,000. Nitrogen is bubbled through the slurry to maintain uniform dispersion. Sodium hydroxide containing 0.1 mol / L is added to the anode chamber, and deionized water is added to the cathode chamber. A graphite anode and cathode are inserted into the anode and cathode chambers, respectively. Constant current pumps connect the anode and cathode chambers to corresponding storage tanks, forming a continuous circulation loop. A unidirectional pulse voltage with an electric field strength of 1 V / cm and a duty cycle of 60% is applied between the anode and cathode. The electrolysis is continued for 72 hours. After pulse dechlorination, the chloride content of the magnesium hydroxide is 0.03%.

[0048] Step (2): The magnesium hydroxide after dechlorination is filtered using a plate filter press, and the filtered magnesium hydroxide (the chlorine content in the filtered magnesium hydroxide is 0.03%) is placed in a furnace and heated to 900° C. at a heating rate of 8° C. / min for calcination to obtain low-chlorine magnesium oxide with a chlorine content of 0.01%.

[0049] Example 3

[0050] Step (1): Use Figure 2 The electrolytic cell shown in the figure is filled with a 20% solid magnesium hydroxide slurry (D50 particle size 50 μm; chloride ion solid content 0.6%). Both ends of the slurry are sealed with polypropylene. Potassium hydroxide and potassium dodecyl phosphate are added to the slurry in a mass ratio of 8:7:100,000. Oxygen is bubbled into the slurry to maintain uniform dispersion. Potassium hydroxide containing 0.15 mol / l is added to the anode chamber, and deionized water is added to the cathode chamber. A graphite anode and a carbon fiber cloth cathode are inserted into the anode and cathode chambers, respectively. A constant current pump connects the anode and cathode chambers to corresponding storage tanks, forming a continuous circulation loop. A unidirectional pulse voltage with an electric field strength of 1.5 V / cm and a duty cycle of 50% is applied between the anode and cathode. The electrolysis is continued for 54 hours. After pulse dechlorination, the chloride content of the magnesium hydroxide is 0.03%.

[0051] Step (2): The magnesium hydroxide after dechlorination is filtered using a plate filter press, and the filtered magnesium hydroxide (the chlorine content in the filtered magnesium hydroxide is 0.03%) is placed in a furnace and heated to 700° C. at a heating rate of 7° C. / min for calcination to obtain low-chlorine magnesium oxide with a chlorine content of 0.02%.

[0052] Example 4

[0053] Step (1): Use Figure 2The electrolytic cell shown in the figure is filled with a 25% solid magnesium hydroxide slurry (D50 particle size 30 μm; chloride ion solid content 0.6%). Both ends of the slurry are sealed with non-woven fabric. Ammonia water and sodium cetyl phosphate are added to the slurry at a mass ratio of 3:5:100,000. Air is bubbled into the slurry to maintain uniform dispersion. Ammonia water containing 0.20 mol / l is added to the anode chamber, and deionized water is added to the cathode chamber. A graphite anode and cathode are inserted into the anode and cathode chambers, respectively. Constant current pumps connect the anode and cathode chambers to corresponding storage tanks, forming a continuous circulation loop. A unidirectional pulse voltage with an electric field strength of 2.0 V / cm and a duty cycle of 40% is applied between the anode and cathode. The electrolysis is continued for 70 hours. After pulse dechlorination, the chloride content in the magnesium hydroxide is 0.02%.

[0054] Step (2): The magnesium hydroxide after dechlorination is filtered using a plate filter press, and the filtered magnesium hydroxide (the chlorine content in the filtered magnesium hydroxide is 0.02%) is placed in a furnace and heated to 750° C. at a heating rate of 5° C. / min for calcination to obtain low-chlorine magnesium oxide with a chlorine content of 0.01%.

[0055] Comparative Example 1

[0056] This comparative example differs from Example 1 in that no electricity is applied and no strengthening agent is used. A slurry of magnesium hydroxide (D50 particle size: 42 μm; chloride ion solid content: 0.6%) with a solid content of 30% is washed with a large amount of deionized water. After filtration, the chloride content of the magnesium hydroxide is 0.55%, and the chloride content of the calcined magnesium oxide is 0.21%.

[0057] Comparative Example 2

[0058] This comparative example differs from Example 1 in that no electricity is applied and only aqueous ammonia is used as a strengthening agent. A slurry of magnesium hydroxide (D50 particle size: 42 μm; chloride ion solid content: 0.6%) with a solid content of 30% is added to the aqueous ammonia and stirred. The mass ratio of aqueous ammonia to slurry is 9:100,000. After filtration, the chloride ion content of the magnesium hydroxide is 0.42%, and the chloride content of the magnesium oxide after calcination is 0.13%.

[0059] Comparative Example 3

[0060] This comparative example differs from Example 1 in that no electricity is applied and only sodium dodecyl sulfate is used as a strengthening agent. A slurry of magnesium hydroxide (D50 particle size: 42 μm; chloride ion solid content: 0.6%) with a solid content of 30% is added to the sodium dodecyl sulfate and stirred. The mass ratio of sodium dodecyl sulfate to slurry is 9:100,000. After filtration, the chloride ion content of the magnesium hydroxide is 0.40%, and the chloride content of the magnesium oxide after calcination is 0.11%.

[0061] Comparative Example 4

[0062] This comparative example differs from Example 1 in that no electricity is applied. A slurry of magnesium hydroxide (D50 particle size: 42 μm; chloride ion solid content: 0.6%) with a solid content of 30% is added to the slurry, and ammonia water and sodium lauryl sulfate are added to the slurry and stirred. The mass ratio of ammonia water: sodium lauryl sulfate: slurry is 5:4:100,000. After filtration, the chloride ion content of the magnesium hydroxide is 0.36%, and the chloride content of the magnesium oxide after calcination is 0.08%.

[0063] Comparative Example 5

[0064] This comparative example differs from Example 2 in that no pulse current is used. The electrolysis process is maintained at a DC constant voltage of 1 V / cm. After 72 hours of continuous DC electrolysis, the chlorine content of the filtered magnesium hydroxide is 0.12%, and the chlorine content of the calcined magnesium oxide is 0.03%. Continuous DC is less effective in removing chlorine from magnesium hydroxide than pulsed DC.

[0065] The background section of the present invention may contain background information about the problem or environment of the present invention, but does not necessarily describe the prior art. Therefore, the inclusion of content in the background section is not an admission by the applicant that the prior art is present.

[0066] The above description is a further detailed description of the present invention in conjunction with specific embodiments, and the specific implementation of the present invention should not be construed as being limited to these descriptions. Persons skilled in the art will appreciate that, without departing from the spirit of the present invention, they may make several substitutions or modifications to the described embodiments, and these substitutions or modifications should be considered to fall within the scope of protection of the present invention. Throughout this specification, reference to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples" indicates that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Persons skilled in the art may combine and assemble the different embodiments or examples described in this specification, as well as features of different embodiments or examples, without conflicting opinions. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications may be made herein without departing from the scope of protection of the patent application.

Claims

1. A method for preparing low-chloride magnesium oxide, characterized in that: The method includes the following steps: (1) adding chlorine-containing magnesium hydroxide slurry to an electrolytic cell, adding anolyte to the anode chamber, adding catholyte to the cathode chamber, and applying an electric field between the positive and negative electrodes using a pulse power supply to remove chlorine under stirring conditions; a diaphragm or partition is provided between the chlorine-containing magnesium hydroxide slurry and the anode chamber and the cathode chamber. The raw material magnesium hydroxide D50 in step (1) has a particle size of less than 60 μm and a chloride ion content greater than 0.01 wt%; The solid content of the magnesium hydroxide slurry in step (1) is 20-60%; In step (1), the anolyte is selected from at least one of deionized water, ammonia water, sodium hydroxide solution, and potassium hydroxide solution; The cathode liquid in step (1) is at least one of deionized water, ammonia water, sodium hydroxide solution, potassium hydroxide solution, and potassium nitrate solution; The electric field strength of the pulsed electric field in step (1) is 0.1-8 V / cm, and the pulse duty cycle is 20-80%; In step (1), before the electric field dechlorination, a strengthening agent is added to the chlorine-containing magnesium hydroxide slurry, wherein the strengthening agent is selected from at least two of anionic surfactants, sodium hydroxide, potassium hydroxide, and ammonia water; The strengthening agent added to the slurry is composed of an inorganic substance and an anionic surfactant in a mass ratio of 3-8:4-7; In step (1), the mass ratio of the strengthening agent to the chlorine-containing magnesium hydroxide slurry is 1-100: 100000; (2) The magnesium hydroxide slurry after dechlorination is filtered and calcined to obtain low-chloride magnesium oxide.

2. The method for preparing low-chloride magnesium oxide according to claim 1, wherein: In step (1), the mass ratio of the strengthening agent to the chlorine-containing magnesium hydroxide slurry is 9-40:100000.

3. The method for preparing low-chloride magnesium oxide according to claim 1, wherein: The hydrophilic group of the anionic surfactant is selected from at least one of carboxylates, sulfonates, sulfates and phosphates.

4. The method for preparing low-chloride magnesium oxide according to claim 1, wherein: The electric field strength of the pulsed electric field in step (1) is 0.5-2 V / cm, and the pulse duty cycle is 30-60%.

5. The method for preparing low-chloride magnesium oxide according to claim 1, wherein: The electrode in step (1) is an inert electrode, and the electrode material is at least one of ruthenium-coated titanium mesh, graphite plate, carbon fiber cloth, platinum group alloy and alloy foil thereof.

6. The method for preparing low-chloride magnesium oxide according to claim 1, wherein: In step (1), the partition or membrane is at least one of a microporous material, a porous plate, a nylon screen, a filter membrane, a non-woven fabric, nylon, vinylon, a polypropylene filter cloth and a sponge.

7. The method for preparing low-chloride magnesium oxide according to claim 1, wherein: The chlorine-containing magnesium hydroxide slurry in step (1) is mechanically stirred, or at least one of air, oxygen and nitrogen is blown into the slurry to make it suspended.

8. The method for preparing low-chloride magnesium oxide according to claim 1, wherein: The filtered low-chloride magnesium hydroxide in step (2) is placed in a furnace and heated to 600-900° C. at a heating rate of 2-8° C. / min for calcination to obtain low-chloride magnesium oxide.

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