A method for producing high-dispersion magnesium hydroxide from a magnesium-containing brine

Abstract

The present application relates to a method for preparing high-dispersion magnesium hydroxide from magnesium-containing brine, comprising: removing insoluble substances from the magnesium-containing brine; adding a chelating agent, stirring the reaction, and allowing the chelating agent to form stable magnesium chelate with magnesium ions in the magnesium-containing brine; gradually adding a compound or solution thereof that can dissociate hydroxyl ions, allowing the magnesium chelate to undergo dechelation to generate high-dispersion magnesium hydroxide, filtering to harvest the magnesium hydroxide, washing, and drying to obtain high-dispersion magnesium hydroxide. The present application utilizes the electrostatic repulsion between chelates and the gradual release of magnesium ions, even in a monodispersed manner, which is conducive to the uniform nucleation of magnesium hydroxide and avoids agglomeration, ultimately resulting in high-dispersion magnesium hydroxide. The present application can take into account the dispersion and particle size of the magnesium hydroxide product, and can also improve the purity of the product under strict control of the amount of hydroxyl ions added, thereby preparing high-value-added high-dispersion magnesium hydroxide products.

Description

Technical Field

[0001] This invention pertains to methods for preparing magnesium hydroxide from mixed salts, specifically relating to a method for preparing highly dispersed magnesium hydroxide from magnesium-containing brine. Background Technology

[0002] In recent years, with the rapid development of the new energy field, the extraction of lithium from salt lake resources has become a hot topic. However, salt lakes also contain abundant magnesium resources. Reports indicate that the annual output of old brine from the Qinghai Qarhan Salt Lake alone amounts to 80 million tons of magnesium chloride, and the resources are of high quality, suitable for developing various high-purity and high-quality magnesium products. However, for a long time, due to technical and other reasons, magnesium resources have not been well developed and utilized. This has resulted in the waste of magnesium resources and has also caused serious "magnesium hazards" to the production of salt lake potash fertilizer and lithium products (the discharge of concentrated magnesium water after lithium extraction from salt lakes leads to a sharp increase in magnesium concentration, a higher magnesium-to-lithium ratio, and increased difficulty in lithium extraction). Therefore, in today's increasingly focused development of a circular economy, actively developing and utilizing waste brine resources to turn waste into treasure, while simultaneously solving major key technical problems in the industrialization process, is an urgent task for researchers. This is not only related to the sustainable development of salt lake resources in my country, but also of great significance to the improvement of the ecological environment of salt lake resources and the development of the social economy.

[0003] Magnesium hydroxide is non-toxic, possesses high thermal stability, and is safe and environmentally friendly. Magnesium hydroxide with regular morphology, small particle size, and good dispersibility has extremely high application value. It can be used as a flame retardant in polymer materials and can also be used in the preparation of magnesium oxide. Magnesium oxide obtained after light calcination has high activity and can be used for adsorption or low-temperature sintering. Magnesium hydroxide prepared by traditional precipitation methods is difficult to control, resulting in irregular, easily agglomerated, large-sized, and widely distributed magnesium hydroxide, making it unsuitable for direct application. A common solution is the hydrothermal method. The hydrothermal process involves dissolving and recrystallizing magnesium hydroxide under conditions of a specific temperature and the addition of a certain concentration of mineralizing agent, resulting in magnesium hydroxide with regular morphology and low agglomeration. However, the hydrothermal method requires resistance heating or provides heat from gas or fuel oil, resulting in high energy consumption and a long heating process; furthermore, for large volumes of magnesium-containing solutions, it easily leads to uneven heating, which is not conducive to large-scale production applications.

[0004] Currently, the main method for producing magnesia in salt lake areas is the lime slurry precipitation method, which involves directly reacting brine with lime slurry to obtain magnesium hydroxide. While this method seems simple, it requires extremely high-quality lime slurry. Lime contains burnt calcium oxide, underburned calcium carbonate, and other impurities such as iron and aluminum, all of which can enter the product and result in low purity. More seriously, the magnesium hydroxide obtained from the direct reaction of brine and lime slurry easily forms a gel, resulting in poor filtration performance and thus very low production efficiency.

[0005] Furthermore, patent application CN104609449A discloses using agglomerated magnesium hydroxide with an average original particle size of 0.1-3 micrometers and an average agglomerated particle size of 5-50 micrometers as raw material, mixing it with an inorganic flux, heating it to 300-700℃ in an air atmosphere at a rate of 1-50℃ / min, and calcining it at a constant temperature for 0.5-6 hours to obtain dispersed ultrafine active magnesium oxide; preparing an aqueous solution containing 0.01-20% dispersant and 0-20wt% morphology control agent, adding the dispersed ultrafine active magnesium oxide at a temperature of 10-100℃ and under stirring conditions to form a suspension with a solid content of 0.5-40wt%, performing a hydration conversion reaction for 0.5-6 hours, filtering, washing and drying to obtain highly dispersed magnesium hydroxide powder with an average original particle size of 0.1-3 micrometers, an average agglomerated particle size of 0.5-4.0 micrometers, and a magnesium hydroxide main content ≥95wt% and a regular morphology. The process of preparing magnesium hydroxide using this method is rather complicated, and the raw materials are limited to magnesium hydroxide with a specific original particle size. It is not suitable for directly preparing highly dispersed magnesium hydroxide from brines of magnesium, lithium, calcium, etc. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for preparing highly dispersed magnesium hydroxide from magnesium-containing brine. This method involves adding a chelating agent to bind with magnesium ions to form a stable magnesium chelate, and then gradually adding a compound or solution capable of dissociating hydroxide ions to dechelate the magnesium chelate and generate highly dispersed magnesium hydroxide. The magnesium hydroxide is then collected by filtration, washed, and dried to obtain highly dispersed magnesium hydroxide. This invention solves the problems of existing lime slurry methods, such as high requirements for lime slurry quality, low product purity, poor filtration performance, or overly cumbersome processes.

[0008] (II) Technical Solution

[0009] A method for preparing highly dispersed magnesium hydroxide from magnesium-containing brine includes:

[0010] S1. Remove insoluble substances from magnesium-containing brine;

[0011] S2. Add a chelating agent to the purified pretreated magnesium-containing brine, stir and react to form a stable magnesium chelate with the magnesium ions in the magnesium-containing brine.

[0012] S3. Gradually add compounds or solutions that can dissociate hydroxide ions to cause magnesium chelates to dechelate and generate highly dispersed magnesium hydroxide precipitate.

[0013] S4. Filter to collect magnesium hydroxide, wash and dry to obtain highly dispersed magnesium hydroxide.

[0014] According to a preferred embodiment of the present invention, in S1, the magnesium-containing brine is surface brine, underground brine, petroleum brine, or industrially produced brine containing Mg. 2+ Wastewater containing mixed ions.

[0015] According to a preferred embodiment of the present invention, in S1, the magnesium-containing brine,

[0016] The metal cation is magnesium ion; or,

[0017] The metal cation is a mixture of magnesium ions and monovalent alkali metal cations; or,

[0018] The metal cation is a mixture of magnesium ions and other divalent and / or polyvalent metal cations;

[0019] Alternatively, the metal cation may be a mixture of magnesium ions, monovalent alkali metal cations, and other divalent and / or polyvalent metal cations.

[0020] According to a preferred embodiment of the present invention, in S1, the magnesium-containing brine is surface brine, underground brine, petroleum brine, or industrially produced brine containing Mg. 2+ Salt water.

[0021] According to a preferred embodiment of the present invention, when the metal cation in the magnesium-containing brine to be treated is magnesium ion or a mixture of magnesium ion and monovalent alkali metal cation, a compound or solution of which can dissociate hydroxide ions is gradually added in step S3 to obtain high-purity, highly dispersed magnesium hydroxide.

[0022] When the divalent metal ion other than magnesium in the magnesium-containing brine to be treated is calcium ion and the mass concentration of calcium ion is less than 0.5% of the mass concentration of magnesium ion, a compound or its solution that can dissociate hydroxide ions is gradually added in step S3, and the pH of the magnesium-containing brine is controlled in real time to be 11.0-14.0 to obtain high-purity, high-dispersibility magnesium hydroxide. At this time, since there is no calcium ion interference in the magnesium-containing brine (or the calcium ion concentration is very low), the pH can be adjusted to 11.0-14.0, and the magnesium chelate dechelates to generate high-purity (>98%), high-dispersibility magnesium hydroxide.

[0023] When the divalent metal ion in the magnesium-containing brine to be treated is calcium ion (excluding magnesium) and the calcium ion mass concentration accounts for 0.5%-2% of the magnesium ion mass concentration, a compound or solution capable of dissociating hydroxide ions is gradually added in step S3, and the pH of the magnesium-containing brine is controlled in real time to 11.0-13.0 to obtain high-purity, highly dispersed magnesium hydroxide. Although calcium ions interfere with the magnesium-containing brine, magnesium chelates and calcium chelates have different stability. By adjusting the pH of the magnesium-containing brine to 11.0-13.0, the magnesium chelates preferentially undergo dechelation and release magnesium ions, resulting in high-purity (>98%), highly dispersed magnesium hydroxide. Controlling the pH of the magnesium-containing brine within the range of 11.0-13 avoids simultaneous dechelation and precipitation of calcium and magnesium.

[0024] When the divalent metal ion in the magnesium-containing brine to be treated is calcium ion (excluding magnesium) and the calcium ion concentration exceeds 2% of the magnesium ion concentration, calcium precipitation should be performed first to remove impurities before proceeding to steps S2-S3. The calcium precipitation process involves using carbonates or sulfates to generate a calcium precipitate, which is then removed through methods such as settling, stepwise precipitation, centrifugation, and membrane separation to reduce the calcium concentration. After this process, the magnesium hydroxide is treated as described above, which is beneficial for obtaining highly dispersed magnesium hydroxide.

[0025] According to a preferred embodiment of the present invention, in S1, when the metal cation in the magnesium-containing brine is magnesium ion or a mixture of magnesium ion and monovalent alkali metal cation, and the magnesium ion concentration is 0.1-5 g / L, preferably 0.5-2.0 g / L, the S2 treatment is directly performed. If the magnesium ion concentration is greater than 5 g / L, a dilution operation is first performed to bring the magnesium ion concentration to 0.1-5 g / L, preferably 0.5-2.0 g / L.

[0026] When the magnesium-containing brine in S1 contains magnesium ions and is a mixture of magnesium ions and other divalent and / or polyvalent metal ions, or a mixture of magnesium ions, monovalent alkali metal ions, and other divalent and / or polyvalent metal ions, and the total concentration of the other divalent and / or polyvalent metal ions does not exceed 0.5% of the magnesium ion mass concentration, dilution is performed according to the magnesium ion concentration, or S2 treatment is directly carried out. For example, dilution is performed until the magnesium ion concentration reaches 0.1-5 g / L, preferably 0.5-2.0 g / L. When the total concentration of the other divalent and / or polyvalent metal ions exceeds 0.5% of the magnesium ion mass concentration, the other divalent and / or polyvalent metal ions can be removed first, and then dilution is performed according to the magnesium ion concentration, or S2 treatment is directly carried out. The removal of impurities includes centrifugation or membrane separation after precipitation, and the dilution method is to dilute until the magnesium ion concentration reaches 0.1-5 g / L, preferably 0.5-2.0 g / L.

[0027] Among them, other divalent ions can be one or more of calcium ions, copper ions, barium ions, lead ions, manganese ions, zinc ions, and ferrous ions; polyvalent metal cations can be one or more of trivalent aluminum, iron, and chromium ions, and tetravalent chromium ions.

[0028] According to a preferred embodiment of the present invention, in S2, the chelating agent is one or a combination of several of the following: aminocarboxylic acid chelating agents, organophosphonic acid chelating agents, and water-soluble polymer chelating agents.

[0029] Among them, organophosphonic acid chelating agents are one or more combinations of ethylenediaminetetramethylenephosphonic acid (EDTMPA), diethylenetriaminepentamethylenephosphonic acid (DETPMP), polyol phosphate ester (PAPE), phosphonoylhydroxyacetic acid (HDTMPA), and their salts; aminocarboxylic acid chelating agents are one or more combinations of N-carboxyethyl ethylenediaminetetraacetic acid (HEDTA), ethylene glycol diaminoethyl ether tetraacetic acid (EGTA), 1,2-cyclohexanediaminetetraacetic acid (CDTA), and their salts; water-soluble polymer chelating agents are one or more combinations of polyacrylic acid (PAA), polyacrylic acid salts, polyethyleneimine (PEI), hydroxyethyl cellulose (HEC), and polyacrylamine (PPI).

[0030] According to a preferred embodiment of the present invention, in S2, before adding the chelating agent to the magnesium-containing brine, the magnesium ion concentration is measured; when the selected chelating agent is a small molecule aminocarboxylic acid chelating agent or an organophosphonic acid chelating agent, the molar ratio of the chelating agent to the magnesium ion molar concentration is 0.5-1.2:1;

[0031] When the selected chelating agent is a macromolecular water-soluble polymer chelating agent, the molar ratio of the chelating agent to the magnesium ion molar concentration is 0.1-0.5:1.

[0032] According to a preferred embodiment of the present invention, in S3, the alkaline solution is one or a combination of sodium hydroxide, ammonia and potassium hydroxide; the concentration of hydroxide ions in the alkaline solution is 0.1-10 mol / L, preferably 1-3 mol / L, based on the concentration of ionizable hydroxide ions; the amount of alkaline solution added, calculated as hydroxide ions, is 1.5-3.0 times the molar amount of magnesium ions.

[0033] In S3, for every 1L of magnesium chelate solution, the alkaline solution dropping rate is 0.1-50mL / min, with the optimal dropping rate being 0.25-2mL / min; specifically, this is achieved by controlling the pH of the magnesium-containing salt solution within the required range in real time.

[0034] According to a preferred embodiment of the present invention, in step S3, the alkali solution is added while stirring, and the alkali solution addition lasts for 15-120 minutes. The stirring speed during this process is 400-5000 rpm, preferably 500-1000 rpm. Furthermore, after the alkali solution is added, stirring continues at a relatively high speed (3000-5000 rpm) for a period of time, which can further improve the magnesium hydroxide yield and make the particle size distribution more uniform.

[0035] According to a preferred embodiment of the present invention, the pH of the clarified liquid obtained from filtration in step S4 is further adjusted to allow other divalent or polyvalent metal ions to dechelate; the chelating agent recovery liquid is obtained by filtration and is reused in step S2. By further adjusting the pH, other divalent or polyvalent metal ions can be removed after filtration, preventing the accumulation of other divalent or polyvalent metal ions in the chelating agent recovery liquid in step S2, which would affect the purity of the magnesium hydroxide product. The filter membrane used to obtain the chelating agent recovery liquid is a microfiltration membrane or ultrafiltration membrane, used to retain the hydroxides of divalent or polyvalent metal ions, producing a relatively pure chelating agent solution. This process achieves a chelating agent recovery rate of up to 97-100%, and the chelating agent recovery liquid can be returned to S2 for recycling, thereby reducing the amount of chelating agent used and saving reagent costs.

[0036] According to a preferred embodiment of the present invention, in S4, the drying method is vacuum drying, and the drying temperature is 40-80°C; or the harvested magnesium hydroxide precipitate is further added with water and slurryed before spray drying to obtain a highly dispersed magnesium hydroxide product.

[0037] Preferably, morphology modifiers, such as PEG, can be added during the slurry preparation process.

[0038] (III) Beneficial Effects

[0039] (1) In this invention, a chelating agent is added to magnesium-containing salt water. Taking advantage of the electrostatic repulsion between chelates and the high stability of magnesium chelates, magnesium chelates are dispersed and gradually release magnesium ions during the dechelation process. Therefore, magnesium ions are in an extremely dispersed state (even released in a monodisperse manner), which is conducive to the uniform nucleation of magnesium hydroxide and avoids agglomeration. Finally, nano-sized magnesium hydroxide with extremely high dispersion is obtained.

[0040] (2) When the magnesium-containing brine contains only monovalent alkali metals other than magnesium or does not contain other metal cations, steps S2-S3 can be carried out directly. In S3, it is not necessary to accurately control the pH range of the brine, and high-purity, highly dispersed nano-sized magnesium hydroxide can also be obtained.

[0041] When magnesium-containing brine contains divalent or polyvalent metal ions other than magnesium, if the concentration of these other divalent or polyvalent ions is low (below 0.5%), the chelating agent can selectively chelate with magnesium ions and other divalent or polyvalent metal cations to form stable chelates (without chelating with monovalent cations). However, the stability of chelates varies among different metal ions, and the proportion of impurity metal ions is low. By adding alkali to dechelate the magnesium chelate, magnesium ions are preferentially dissociated and react with hydroxide ions provided by the alkali solution to generate magnesium hydroxide. In this way, the purity of the product can be further improved on the basis of obtaining highly dispersed nano-sized magnesium hydroxide, achieving a high-purity grade.

[0042] When magnesium-containing brine contains divalent or polyvalent metal ions other than magnesium, if the concentration of other divalent or polyvalent ions is relatively high compared to the concentration of magnesium ions, some impurity metal ions can be removed beforehand by chelation with alkali to obtain high-purity, highly dispersed nano-sized magnesium hydroxide.

[0043] When the only divalent or polyvalent metal ion in the magnesium-containing brine is calcium, even if the calcium ion concentration is higher than 0.5% but lower than 2%, it is not necessary to remove calcium beforehand. By precisely controlling the pH range of the brine during alkali chelation, magnesium hydroxide is preferentially formed within the pH range, which avoids the simultaneous precipitation of calcium and magnesium and can also produce a high-purity, highly dispersed magnesium hydroxide product, thus eliminating the need for calcium removal.

[0044] Therefore, the present invention employs a method of chelation with chelating agents and dechelation with alkali solution followed by precipitation, which can achieve both high dispersibility and high purity of magnesium hydroxide products.

[0045] (3) During dechelation, the concentration of magnesium ions in the brine affects the morphology of magnesium hydroxide in the product. Specifically: 1) When the magnesium ion concentration is 0-1000 mg / L, the magnesium hydroxide product exhibits regular spherical shapes with a diameter of 50-250 nm; 2) When the magnesium ion concentration is greater than 1000 mg / L, the magnesium hydroxide exhibits petal-like shapes with a particle size of about 200-400 nm. The purity of the products with the above two different morphologies is greater than 98.0%, meeting the high purity index of magnesium hydroxide. It can be seen that the present invention can prepare products with good dispersibility, high purity, and different micromorphologies according to the magnesium ion concentration in the brine, with a yield of 97-100%, which can greatly increase the added value of magnesium hydroxide.

[0046] (4) The method of the present invention is simple, easy to operate and highly efficient, environmentally friendly and suitable for large-scale batch preparation of high-value-added, high-purity and high-dispersion nano-grade magnesium hydroxide products in plateau salt lakes, thus solving the problem of magnesium hazard in the utilization of salt lake resources.

[0047] (5) This invention proposes a method for the comprehensive utilization of brine (including salt lake brine or various industrial saline wastewater), which can be used alone or in combination with other processes, such as coupling with a salt lake brine lithium extraction process to produce high-value-added magnesium hydroxide. The process of this invention has no strict requirements on the composition of magnesium-containing brine and can directly use salt lake brine as a production raw material, resulting in low production costs. In the process, the chelating agent is dechelated, filtered, recovered, and recycled, which can save on reagent input. Magnesium completes the precipitation reaction at room temperature during the process, requiring no heat input throughout, resulting in low energy consumption costs. Attached Figure Description

[0048] Figure 1 The image shows the XRD pattern of the magnesium hydroxide product from Example 1.

[0049] Figure 2 This is a SEM image of the magnesium hydroxide product in Example 1.

[0050] Figure 3 The image shows the SEM image of the magnesium hydroxide product from Comparative Example 1.

[0051] Figure 4 This is a SEM image of the magnesium hydroxide product from Example 2.

[0052] Figure 5 SEM image of magnesium hydroxide product in Example 3.

[0053] Figure 6 Example 4: SEM image of magnesium hydroxide product.

[0054] Figure 7 Example 5: SEM image of magnesium hydroxide product. Detailed Implementation

[0055] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0056] Example 1

[0057] In this embodiment, the brine contains only magnesium ions as the metal cation, with a concentration of 300 mg / L (molar concentration 12.343 mmol / L). The method for preparing highly dispersed nano-sized magnesium hydroxide from this brine is as follows:

[0058] (1) Take the salt water and perform simple filtration to remove mud, sand, insoluble suspended matter, etc.

[0059] (2) The concentration of magnesium ions in the brine was measured, and an aminocarboxylic acid chelating agent, HEDTA-3Na, was added accordingly. The molar ratio of the chelating agent to the magnesium ion concentration was 0.9:1. To promote sufficient contact between the chelating agent and magnesium ions and to completely chelate the magnesium ions, the mixture was stirred at room temperature at a stirring speed of 1000 rpm for 30 min.

[0060] (3) Add a 1.0 mol / L sodium hydroxide solution to the chelated brine at a rate of 10 mL / min. The molar ratio of hydroxide ions to magnesium ions is 2.1:1. The sodium hydroxide solution is fed for 30 min. After the alkali solution is fed, continue to react at room temperature and stirring at 4000 rpm for 60 min.

[0061] (4) After the reaction was completed, the precipitate was filtered, washed, and dried under vacuum at 60℃ to obtain a well-formed spherical magnesium hydroxide product with a particle size of 50-70 nm. The yield was 99.17%, and the purity was 99.87%. The XRD and SEM results of the product are as follows: Figure 1 and Figure 2 As shown.

[0062] Finally, sodium hydroxide solution was added to the filtered solution until no more suspended particles were produced. The filtered solution was then returned to step (2) as a chelating agent for recycling, and the chelating agent recovery rate reached 98.46%.

[0063] Comparative Example 1

[0064] In this comparative example, the brine treated with magnesium ions as the sole cation had a concentration of 300 mg / L (molar concentration 12.343 mmol / L). Unlike Example 1, no chelating agent was added to the brine in this example. The method for preparing magnesium hydroxide from this brine was as follows:

[0065] (1) Take the salt water and perform simple filtration to remove mud, sand, insoluble suspended matter, etc.

[0066] (2) Add a 1.0 mol / L sodium hydroxide solution at a stirring speed of 1000 rpm at a rate of 10 mL / min. The molar ratio of hydroxide ions to magnesium ions is 2.1:1. The sodium hydroxide solution is fed for 30 min. After the alkali solution is fed, continue to react at room temperature at a stirring speed of 4000 rpm for 60 min.

[0067] (3) After the reaction was complete, the precipitate was filtered, washed, and dried under vacuum at 60°C to obtain magnesium hydroxide with uneven size distribution and severe agglomeration. The purity was determined to be 99.47%. The SEM results of the product are shown below. Figure 3 As shown.

[0068] Example 2

[0069] In this embodiment, the brine treated had a magnesium ion concentration of 4000 mg / L (molar concentration 164.575 mmol / L), and the mass concentrations of lithium ions, sodium ions, and potassium ions were 0.07, 2.6, and 0.3 times the mass concentration of magnesium ions, respectively. The method for preparing highly dispersed magnesium hydroxide from this salt lake brine is as follows:

[0070] (1) Take the brine from the salt lake and perform simple filtration to remove mud, sand, insoluble suspended matter, etc.

[0071] (2) The concentrations of magnesium ions and polyvalent cations in the brine were measured, and hydroxyethyl cellulose (HEC), a macromolecular water-soluble polymer chelating agent, was added accordingly. The molar ratio of the chelating agent to the magnesium ion concentration was 0.25:1. To promote sufficient contact between the chelating agent and magnesium ions and to completely chelate the magnesium ions, the mixture was stirred at room temperature at a stirring speed of 1500 rpm for 10 min.

[0072] (3) Add a 2.50 mol / L potassium hydroxide solution to the chelated brine at a rate of 9 mL / min. The molar ratio of hydroxide ions to magnesium ions is 1.86:1. The potassium hydroxide solution is fed for 120 min. After the alkali solution is fed, continue to react at room temperature and stirring at 2000 rpm for 100 min.

[0073] (4) After the reaction was completed, the precipitate was filtered, washed, and spray-dried at 45°C to obtain a regular petal-shaped magnesium hydroxide product with a particle size of 300-400 nm. The yield was 99.53%, and the purity was 99.84%. The SEM results of the product are shown below. Figure 4 As shown.

[0074] Finally, potassium hydroxide solution was added to the filtered solution until no more suspended particles were produced. The filtered solution was then returned to step (2) as a chelating agent for recycling, and the chelating agent recovery rate reached 99.07%.

[0075] Example 3

[0076] In this embodiment, the brine treated had a magnesium ion concentration of 800 mg / L (molar concentration of 32.915 mmol / L), and the mass concentrations of lithium ions, sodium ions, and potassium ions were 0.16, 9.43, and 2.44 times the mass concentration of magnesium ions, respectively. The method for preparing highly dispersed magnesium hydroxide from this brine is as follows:

[0077] (1) Take the brine and perform simple filtration to remove mud, sand, insoluble suspended matter, etc.

[0078] (2) The concentrations of magnesium ions and polyvalent cations in the brine were measured, and accordingly, a small-molecule amino acid chelating agent, tetrasodium 1,2-cyclohexanediaminetetraacetate (CDTA-4Na), and a large-molecule water-soluble polymer, polyacrylamide (PAM-10000), were added sequentially. The molar ratios of the two chelating agents to the molar concentration of magnesium ions were 0.54:1 and 0.1:1, respectively. To promote sufficient contact between the chelating agent and magnesium ions for complete chelation of magnesium ions, the mixture was stirred at room temperature for 60 min at a stirring rate of 2500 rpm.

[0079] (3) Add a 1.5 mol / L sodium hydroxide solution to the chelated brine at a rate of 40 mL / min. The molar ratio of hydroxide ions to magnesium ions is 1.97:1. The potassium hydroxide solution is fed for 15 min. After the alkaline solution is fed, continue to react at room temperature with a stirring speed of 5000 rpm for 100 min.

[0080] (4) After the reaction was completed, the precipitate was filtered, washed, and spray-dried at 50°C to obtain a well-formed spherical magnesium hydroxide product with a particle size of 100-150 nm. The yield was 98.47%, and the purity was 99.04%. The SEM results of the product are shown below. Figure 5 As shown.

[0081] Finally, sodium hydroxide solution was added to the filtered solution until no more suspended particles were produced. The filtered solution was then returned to step (2) as a chelating agent for recycling, and the chelating agent recovery rate reached 98.63%.

[0082] Example 4

[0083] In this embodiment, the magnesium ion concentration in the brine is 5000 mg / L (molar concentration 205.719 mmol / L), and the calcium ion concentration is 0.48% of the magnesium ion concentration. The method for preparing highly dispersed magnesium hydroxide from this brine is as follows:

[0084] (1) Take the brine and perform simple filtration to remove mud, sand, insoluble suspended matter, etc.

[0085] (2) The concentrations of magnesium ions and polyvalent cations in the brine were measured, and an organophosphonic acid chelating agent—polyol phosphate (PAPE)—was added accordingly. The ratio of the chelating agent to the molar amount of magnesium ions and polyvalent cations was 0.65:1. To promote sufficient contact between the chelating agent and magnesium ions and to completely chelate the magnesium ions, the mixture was stirred at room temperature for 120 min at a stirring speed of 600 rpm.

[0086] (3) Add 3.0 mol / L ammonia water to the chelated brine at a rate of 40 mL / min, precisely control the pH of the brine between 11.0 and 14.0, the molar ratio of hydroxide ions to magnesium ions is 2.05:1, the ammonia water feeding time is 15 min, and after the alkali solution is fed, continue to react at room temperature and stirring speed of 2500 rpm for 300 min.

[0087] (4) After the reaction was complete, the precipitate was eluted, filtered, washed, and dried under vacuum at 80℃ to obtain a petal-shaped magnesium hydroxide product with a particle size of 300-320 nm. The yield was 99.62%, and the purity was 99.87%. The SEM results of the product are shown below. Figure 6 As shown.

[0088] Finally, sodium hydroxide solution was added to the filtered solution until no more suspended particles were produced. The filtered solution was then returned to step (2) as a chelating agent for recycling, and the chelating agent recovery rate reached 98.40%.

[0089] Example 5

[0090] In this embodiment, the brine treated has a magnesium ion concentration of 10000 mg / L (molar concentration 411.437 mmol / L), a calcium ion concentration of 10% of the magnesium ion concentration, and an iron ion and trace amounts of other metal cations concentration of 1.07% of the magnesium ion concentration. The method for preparing highly dispersed magnesium hydroxide from this brine is as follows:

[0091] (1) Take the brine and perform simple filtration to remove mud, sand, insoluble suspended matter, etc.

[0092] (2) Referring to the stepwise precipitation method in patent US1968737A, the brine was first pretreated to partially reduce the content of calcium ions and polyvalent cations in the brine. The magnesium ion concentration of the pretreated water was 9750 mg / L (molar concentration 401.15 mmol / L), the mass concentration of calcium ions was 1.1% of the mass concentration of magnesium ions, and the mass concentration of the remaining polyvalent cations was 0.013% of the mass concentration of magnesium ions. Then the pretreated water was diluted 10 times, and the magnesium ion concentration in the brine was 975 mg / L (molar concentration 40.115 mmol / L).

[0093] (3) Based on the concentrations of magnesium ions and polyvalent cations in the pretreated product water, add an aminocarboxylic acid chelating agent, ethylene glycol diaminoethyl ether tetraacetic acid tetrasodium (EGTA-4Na). The molar ratio of the chelating agent to the total molar amount of magnesium ions and polyvalent cations is 1.05:1. To promote sufficient contact between the chelating agent and magnesium ions for complete chelation of magnesium ions, stir at room temperature for 50 min at a stirring speed of 1500 rpm.

[0094] (4) Add 5 mol / L ammonia water to the chelated brine at a rate of 50 mL / min, control the pH of the brine between 11.0 and 13.0 to precipitate magnesium ions while preventing calcium ion precipitation, the molar ratio of hydroxide ions to magnesium ions is 1.69:1, the ammonia water feeding time is 20 min, and after the alkali solution is fed, continue to react at room temperature with a stirring speed of 5000 rpm for 25 min.

[0095] (5) After the reaction was complete, the precipitate was filtered, washed, and dried under vacuum at 80℃ to obtain a well-formed spherical magnesium hydroxide product with a particle size of 200-250 nm. The yield was 96.41%, and the purity was 98.83%. The SEM results of the product are shown below. Figure 7 As shown.

[0096] Finally, sodium hydroxide solution was added to the filtered solution until no more suspended particles were produced. The filtered solution was then returned to step (2) as a chelating agent for recycling, and the chelating agent recovery rate reached 99.57%.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing highly dispersed magnesium hydroxide from magnesium-containing brine, characterized in that, include: S1. Remove insoluble substances from magnesium-containing brine; The magnesium-containing brine is surface brine, underground brine, petroleum brine, or industrially produced brine containing magnesium. 2+ Salt water; When the metal cation in the magnesium-containing brine is magnesium ion or a mixture of magnesium ion and monovalent alkali metal cation, and the magnesium ion concentration is 0.1-5 g / L, S2 treatment is performed directly. If the magnesium ion concentration is greater than 5 g / L, a dilution operation is performed first to bring the magnesium ion concentration to 0.1-5 g / L. When the metal cation in the magnesium-containing brine is a mixture of magnesium ions and other divalent and / or polyvalent metal cations, or a mixture of magnesium ions, monovalent alkali metal cations and other divalent and / or polyvalent metal cations, and the total concentration of other divalent and / or polyvalent metal cations does not exceed 2% of the magnesium ion mass concentration, the brine is diluted according to the magnesium ion concentration or directly subjected to S2 treatment. When the total concentration of other divalent metal cations and / or polyvalent metal cations exceeds 2% of the magnesium ion mass concentration, the other divalent metal cations and / or polyvalent metal cations are first removed to remove impurities, and then diluted according to the magnesium ion concentration or directly subjected to S2 treatment. S2. Add a chelating agent to the purified pretreated magnesium-containing brine and stir to react, so that the chelating agent and magnesium ions in the magnesium-containing brine form a stable magnesium chelate; the chelating agent is HEDTA-3Na, hydroxyethyl cellulose HEC, 1,2-cyclohexanediaminetetraacetic acid tetrasodium CDTA-4Na, polyol phosphate PAPE or ethylene glycol diaminoethyl ether tetraacetic acid tetrasodium EGTA-4Na. S3. Gradually add a compound or solution that can dissociate hydroxide ions to cause the magnesium chelate to dechelate and form magnesium hydroxide precipitate; when the metal cation in the magnesium-containing brine to be treated is magnesium ion or a mixture of magnesium ion and monovalent alkali metal cation, gradually add a compound or solution that can dissociate hydroxide ions in step S3 to obtain high-purity, high-dispersibility magnesium hydroxide. When the divalent metal ion other than magnesium in the magnesium-containing brine to be treated is calcium ion and the mass concentration of calcium ion is less than 0.5% of the mass concentration of magnesium ion, a compound or its solution that can dissociate hydroxide ions is gradually added in step S3, and the pH of the magnesium-containing brine is controlled in real time to 11.0-14.0 to obtain high-purity, high-dispersibility magnesium hydroxide. When the divalent metal ion other than magnesium in the magnesium-containing brine to be treated is calcium ion and the mass concentration of calcium ion accounts for 0.5%-2% of the mass concentration of magnesium ion, in step S3, a compound or solution that can dissociate hydroxide ions is gradually added, and the pH of the magnesium-containing brine is controlled in real time to 11.0-13.0, so as to obtain high-purity and highly dispersed magnesium hydroxide. S4. Filter to collect magnesium hydroxide, wash and dry to obtain magnesium hydroxide with high dispersion and purity greater than 98%.

2. The method according to claim 1, characterized in that, In S2, the magnesium ion concentration is measured before the chelating agent is added to the magnesium-containing brine. When the selected chelating agent is a small molecule aminocarboxylic acid chelating agent or an organophosphonic acid chelating agent, the molar ratio of the chelating agent to the magnesium ion molar concentration is 0.5-1.2:

1. When the selected chelating agent is a macromolecular water-soluble polymer chelating agent, the molar ratio of the chelating agent to the magnesium ion molar concentration is 0.1-0.5:

1.

3. The method according to claim 1, characterized in that, In S3, the solution of the compound that can dissociate hydroxide ions is one or a combination of sodium hydroxide solution, ammonia water and potassium hydroxide solution; based on the concentration of ionizable hydroxide ions, the hydroxide ion concentration is 0.1-10 mol / L, and the amount added is 1.5-3.0 times the molar amount of magnesium ions.

4. The method according to claim 1, characterized in that, The pH of the clarified liquid obtained from filtration in S4 is further adjusted to induce the dechelation reaction of other divalent ions or polyvalent metal cations; the chelating agent recovery liquid is obtained by filtration; the chelating agent recovery liquid is reused in step S2; In S4, the drying method is vacuum drying at a temperature of 40-80°C; or the harvested magnesium hydroxide precipitate is further mixed with water and slurryed before spray drying to obtain a highly dispersed magnesium hydroxide product.

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