Method and apparatus for producing particles with high magnesium content from seawater
By using calcium hydroxide to adjust pH value and special nozzle design in seawater, the high cost and pollution problems of high magnesium content particles in seawater are solved, and a process of efficient production of small-particle magnesium hydroxide is realized.
Patent Information
- Application Number
- CN202380038981.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-01-11
- Filing Date
- 2023-02-13
- Publication Date
- 2024-12-20
AI Technical Summary
The prior art has problems of high costs, pollution and increased production costs when extracting particles with high magnesium content from seawater, especially due to ineconomic and pollution problems caused by high temperatures and high pH values.
The pH of seawater is adjusted to 12 by using calcium hydroxide which is hard to dissolve in water, and using a dedicated nozzle design, the seawater is contacted with a saturated calcium hydroxide solution under controlled conditions, thereby precipitating small particles with narrow particle size distribution. Magnesium hydroxide.
The efficient production of small-particle magnesium hydroxide at room temperature is achieved, reducing production costs and reducing pollution, providing a feasible process to obtain particles with high magnesium content from seawater.
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Abstract
Description
Technical Field
[0001] The present invention relates to a method and a technical device for extracting particles with a high magnesium content from seawater. Such particles can be, for example, magnesium hydroxide, or other water-insoluble magnesium salts, such as magnesium sulfate, magnesium carbonate, etc.
[0002] According to the invention, the particles are produced in a precipitation process using a suitable alkaline agent. If this precipitation is carried out with the aid of a nozzle assembly according to the invention and / or by adding auxiliary agents, the size of the resulting particles and their yield can be influenced. The aqueous suspension obtained by this method can be further processed into different products using known technical processes, up to magnesium metal for metallurgy. Background Art
[0003] Magnesium-containing raw materials, in particular magnesium hydroxide, are very important raw materials in industry. In nature, magnesium hydroxide exists in crystalline form as so-called brucite and is also mined industrially as an ore. Since brucite can only be mined on an industrial scale in a few regions of the world, but the demand for magnesium-containing raw materials, in particular magnesium hydroxide, is increasing, other ways of obtaining it are gaining more and more attention. These include, in particular, the precipitation of water-soluble magnesium salts, such as magnesium chloride, from aqueous solutions of hydroxides.
[0004] The world's oceans contain a large number of different salts. Their average salt content is about 3.5%, or 35 g / l. The composition of seawater is almost the same all over the world. The proportion of magnesium chloride in seawater is about 11% of the salt content. This makes seawater an almost inexhaustible source of raw magnesium salts.
[0005] Therefore, it is clear that in the field of obtaining magnesium from seawater, research has been carried out for decades. Some representative related patent documents are listed below.
[0006] In the process according to DE 11 96 172 B, magnesium hydroxide is obtained from seawater by precipitation with a 5 to 10% aqueous suspension of calcium carbid waste liquor (consisting mainly of calcium oxide, aluminum oxide, iron oxide and silicon oxide). The process comprises the following steps:
[0007] 1. Separate the milky white calcium carbide waste alkali liquor into a lower purity part and a higher purity part;
[0008] 2. using the less pure portion of the resulting carbide waste liquor to convert seawater to produce carbonic acid-free seawater;
[0009] 3. converting the carbonate-free seawater with a higher purity portion of the carbide waste liquor to produce magnesium hydroxide; and
[0010] 4. Separating the resulting magnesium hydroxide into a pure fraction and a fraction of lower purity.
[0011] The conversion / precipitation is carried out discontinuously in clarifiers, with subsequent mechanical separation (liquid cyclone) of the precipitated magnesium hydroxide. The use of carbide waste liquor instead of, for example, much cheaper calcium hydroxide would likely make the process additionally more expensive.
[0012] GB 543 665 A describes a method for extracting magnesium salts from seawater and a method for pretreating seawater to reduce its carbon dioxide, bicarbonate and carbonate content by adding calcium hydroxide or calcium oxide. After precipitation of calcium carbonate, the Mg(II) solution can be further processed.
[0013] The patent basically discloses a method for pre-treating seawater, from which the mentioned salts can be obtained. No technical method is disclosed for actually obtaining these salts.
[0014] US 3 111 376 relates to a continuous process for preparing magnesium hydroxide from a magnesium chloride solution using dolomite (CaMg(CO3)2). The precipitation of magnesium hydroxide is carried out at elevated temperatures (up to 90° C.), with the dolomite being converted in situ into the corresponding hydroxide (Ca(OH)2).
[0015] However, due to the relatively high temperatures and reagents used, this method can be quite expensive and uneconomical for widespread technical applications.
[0016] According to GB 535 852 A, seawater is pretreated with sodium carbonate to precipitate calcium salts. After separation of the calcium carbonate, the seawater is then mixed with sodium hydroxide to obtain the desired magnesium hydroxide, which is finally filtered off.
[0017] Due to the sodium hydroxide used as precipitation agent and the high pH value thus generated in the system, all multivalent ions are expected to precipitate, which leads to severe contamination of the product.
[0018] US 240 50 55 describes a method for obtaining magnesium hydroxide from seawater. Here, seawater is directly mixed with a (super)stoichiometric amount of calcium hydroxide lime milk and stirred in a reactor until it is completely converted into magnesium hydroxide. Finally, the precipitated magnesium hydroxide is separated.
[0019] Due to the nature of the process, the resulting particles are relatively large. Fresh water is also used in the production of milk of lime, which results in increased production costs.
[0020] WO 0029326 A1 describes a process for producing magnesium hydroxide from seawater, in which the magnesium hydroxide is precipitated with a sodium hydroxide solution obtained from seawater by electrodialysis.
[0021] By using sodium hydroxide as precipitation agent, many other salts will also precipitate due to the resulting high pH values, which leads to significant contamination of the product.
[0022] WO 2016 / 193087 A1 describes how microparticles and nanoparticles can be produced by precipitation from a solution of two salts using a specially designed nozzle. The particle size can be influenced by varying the flow rate and by adding surface-active substances.
[0023] In the process described, almost exclusively salt solutions are used. The use of alkali solution as precipitation agent is not proposed.
[0024] DE 10 2004 026 725 A1 discloses a modular nozzle system for producing droplets from liquids of different viscosities. The arrangement described therein relates to a gas-liquid nozzle, in which the liquid is pumped through an internal capillary and a gas flowing around the liquid is used to ensure droplet break-off. Summary of the invention
[0025] Based on the above, the object of the present invention is therefore to provide a method and a device for obtaining particles from seawater which are further developed in the sense of a practically applicable technical process, wherein the particles have a high magnesium content.
[0026] The technical problem of the present invention is solved by the teaching or features and feature groups of the independent claims, wherein the dependent claims contain at least advantageous embodiments and improvements.
[0027] Starting from the known prior art, the present invention relates to a method and a device by means of which small particles having a high magnesium content can be produced from seawater.
[0028] The basic idea of the present invention is to convert the readily water-soluble magnesium chloride contained in seawater into a form which is hardly water-soluble, such as magnesium hydroxide, and thereby precipitate it.
[0029] Magnesium chloride is converted, for example, into magnesium hydroxide, which is barely soluble in water, simply by increasing the pH in the system to values above 12. Magnesium hydroxide is still formed if the pH is further increased, for example to 14. However, at such high pH values, almost all other salts contained in the seawater are converted into water-insoluble hydroxides, which leads to undesirable contamination of the desired magnesium hydroxide.
[0030] A simple and inexpensive solution to limit the pH to 12 is to use sparingly water-soluble calcium hydroxide instead of, for example, sodium hydroxide. Calcium hydroxide is only soluble in water up to approximately 1.7 g / l at room temperature, which limits the pH value of the solution to 12.
[0031] Another possible way to adjust the pH value is to increase the pH value by applying a voltage.
[0032] It is thus possible to adjust the pH of seawater to the desired value of 12 not only by adding Ca(OH)2, but also by applying a voltage in the sense of electrolysis.
[0033] If the voltage is increased above an experimentally determined limit value, most of the dissolved salts will precipitate. In this way, it is possible to provide a salt mixture or highly salt-reduced seawater, which can be further processed or used in a manner known per se.
[0034] The method according to the invention differs from the prior art in that, by using an excess of Ca(OH)2 in the first method step, a saturated Ca(OH)2 solution can be produced directly from seawater. No fresh water needs to be used. The nozzle explained in more detail below enables very small particles to be provided, the size of which can also be influenced by the flow parameters of the reaction liquid. The combined use of a nozzle according to the invention for the direct production of particles from seawater is neither known nor obvious from the prior art.
[0035] If a saturated calcium hydroxide solution is stirred with seawater, magnesium hydroxide precipitates immediately. However, the particles are rather large and their size distribution is very broad.
[0036] In order to produce small particles with a narrow particle size distribution from magnesium chloride, a special nozzle is used in the present invention. With the help of this nozzle, seawater is contacted with a saturated calcium hydroxide solution in a controlled manner within defined parameters, rather than in an uncontrolled manner, such as by simple stirring.
[0037] The invention is explained in more detail below with reference to exemplary embodiments and with the aid of the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS
[0038] Figure 1 An exemplary representation of an apparatus for carrying out the technical process of obtaining magnesium particles from seawater is shown;
[0039] Figure 2 A schematic diagram showing a technical process for exemplarily implementing the method according to the third embodiment, and
[0040] Figure 3 Cross-sectional views and detail views of a nozzle or multiple nozzles according to the invention are shown, in which the capillary is located in the center of several vertical cylindrical channels.
[0041] According to the present invention, a multiple nozzle designed as follows is used ( Figure 3): The capillary is located in the center of a plurality of vertical cylindrical channels. The inner diameter of the capillary and the free cross section of the cylindrical channel have a diameter of several millimeters. The capillary and the cylindrical channel are each flowed through by one of the reaction liquids (K1 and K2). The dimensions of the resulting cross section through which the liquid flows are comparable and are selected so that the flow rate per channel is in the range of several liters per minute even in the case of laminar flow. The individual cylindrical channels and the capillaries therein are connected to each other in the nozzle by horizontal channels so that the flow conditions in each channel and each capillary are almost the same.
[0042] The nozzle is designed so that the two liquid streams meet only in the outer outlet region, ie outside the nozzle (MZ). This prevents clogging of the nozzle and increases the reliability of the method.
[0043] If the inlet pressure (Vordruck) of the two liquids K1 and K2 flowing through such a nozzle is now changed, the flow parameters through the capillary and through the vertical cylindrical channel also change.
[0044] Experiments have shown that, in the case of laminar flow through a nozzle, ie in the case of values of the Reynolds parameter below 10,000, the diameter of the resulting particles is predetermined by the flow velocity.
[0045] For example, with the same nozzle, particle diameters in the µm range are obtained at low flow rates, while at higher flow rates close to the turbulence limit, particles with significantly smaller diameters are produced. In the turbulent range, the particle diameter always remains almost constant.
[0046] The diameter of the resulting particles can be further reduced by adding a surface-active liquid, such as a detergent. Here, the higher the detergent concentration in the two solutions supplied to the nozzle, the smaller the particles become. Similar effects can be observed by varying the concentration and / or temperature of the reaction solution.
[0047] In order to achieve sufficient volume throughput for industrial applications, several multi-capillary nozzles described herein can be combined in a nozzle head. In these nozzle heads, the capillaries for liquid delivery and the channels for making the gas flow concentrically around them are introduced into plates or planes superimposed one above the other. DETAILED DESCRIPTION Embodiment 1:
[0048] A saturated calcium hydroxide solution is prepared by stirring, for example, 4 grams of calcium hydroxide into 1 liter of fresh water, which is then filtered out and loaded into a storage container. Seawater, which has also been pre-filtered, is loaded into a second container. The two clarified solutions are then fed into a nozzle, which is constructed as described above and in which one solution flows through a capillary and the other flows through a surrounding cylindrical channel. At the outlet of the nozzle, magnesium hydroxide is obtained as an aqueous suspension. By varying the inlet pressure on the nozzle, different flow conditions are produced inside the nozzle. This results in different particle sizes in the resulting suspension. Powdered magnesium hydroxide can be obtained from this suspension by simple sedimentation or by filtration. Embodiment 2:
[0049] A saturated calcium hydroxide solution is prepared by stirring, for example, 4 grams of calcium hydroxide into 1 liter of seawater, which is then filtered out and loaded into a storage container. Many salts contained in the water, including the magnesium chloride contained therein, are precipitated by using seawater. The suspension is therefore decanted before filtering. The seawater, which has also been pre-filtered, is loaded into a second container. The two clarified solutions are then fed into a nozzle, which is constructed as described above and in which one solution flows through a capillary and the other solution flows through a surrounding cylindrical channel. At the outlet of the nozzle, magnesium hydroxide is obtained as an aqueous suspension. By changing the inlet pressure on the nozzle, different flow conditions are produced inside the nozzle. This results in different particle sizes in the resulting suspension. Powdered magnesium hydroxide can be obtained from the suspension by simple sedimentation or by filtration. Embodiment 3:
[0050] If it is necessary to operate at pH 14 instead of pH 12 as in the above example, the following procedure is adopted: a saturated sodium hydroxide solution is prepared by stirring, for example, 4 grams of calcium hydroxide and 6 grams of sodium carbonate into 1 liter of water, then filtered out and loaded into a storage container. If seawater is used instead of fresh water, the suspension must be settled and the supernatant filtered as in Example 2 before its further use, otherwise simple filtration is sufficient. The seawater, which has also been pre-filtered, is loaded into a second container. The two clarified solutions are then fed into a nozzle, which is constructed as described above and in which one solution flows through a capillary and the other solution flows through a surrounding cylindrical channel. An aqueous suspension is obtained at the outlet of the nozzle. By changing the inlet pressure on the nozzle, different flow conditions are generated inside the nozzle. This results in different particle sizes in the resulting suspension. Only about 80% of the solid content of the suspension is magnesium hydroxide. It can be separated from the suspension by simple sedimentation or filtration. Embodiment 4:
[0051] If the method described in Example 2 is implemented in a technical process, this can be done as follows Figure 1 The construction shown in:
[0052] To prepare an alkaline solution with a pH value of 12, an alkaline agent (e.g. calcium hydroxide) is transferred to a mixing tank M2 and stirred into seawater (MW) there which has been previously filtered through a filter F3 to form a clear liquid. The aqueous supernatant present in M2 is fed to a settling vessel (decanter) D1. The aqueous supernatant from D1 is transferred via a filter F4 to a storage tank V2, from where it is pumped as a clear solution into a reaction vessel R. The second liquid stream pumped into R is seawater. To increase the yield, a small amount (below the solubility limit) of an alkaline agent, e.g. calcium hydroxide, is added to this liquid to raise its pH to about 10 (for this see Figure 1 ). For this purpose, seawater MW is filtered through a filter F1 and pumped into a mixing tank M1. An alkaline reagent BR, such as calcium hydroxide, is stirred into this water in M1 at a concentration of up to about 1 g / l. The solution obtained in this way is transferred via a filter F2 to a storage container V1 and from there to a reaction vessel R. Inside the reaction vessel R there is a nozzle head as described above, through which the two liquids are pumped into the container and the desired particles (e.g. magnesium hydroxide) are produced at its outlet. If defined small particles are not required, the two liquids can also be fed to R over the nozzle head and mixed using a stirrer from R. The suspension from R is introduced into a sedimentation vessel D2, where it is concentrated. The aqueous supernatant MW* is discarded, while the product (e.g. magnesium hydroxide) is separated from the sedimentation fraction using a filter F5. The magnesium hydroxide obtained in this way can then be dried and fed to other industrial processes, such as the electrolytic acquisition of metallic magnesium. Embodiment 5:
[0053] If the method described in Example 3 is implemented in a technical process, this can be done as follows Figure 2 This corresponds largely to the method of Example 4. The information given there also applies accordingly here.
[0054] In contrast, the suspension obtained in R (here R1) is mixed with seawater for a second time to convert the hydroxide contained in its aqueous supernatant into magnesium hydroxide. To this end, it is pumped into R2 and reacted here with seawater treated with F1, M1, F2 and V1. The suspensions from D2 and R2 are then combined in M4 and concentrated in the sedimentation tank D3. The aqueous supernatant MW* is discarded, while the product (e.g. magnesium hydroxide) is separated from the sedimentation fraction using a filter F5. The magnesium hydroxide obtained in this way can then be dried and supplied to other industrial processes, such as electrolytic acquisition of metallic magnesium.
Claims
1. A method for producing particles having a high magnesium content from seawater, wherein the readily water-soluble magnesium chloride contained in the seawater is converted into a water-insoluble form and precipitated, further wherein the conversion is carried out by raising the pH value in the system to a range equal to or higher than pH 12, and the precipitated particles are fed into a nozzle arrangement to achieve particle size adjustment and homogenization of the particle size distribution of the resulting particles.
2. The method according to claim 1, characterized in that: The magnesium chloride is converted into water-insoluble magnesium hydroxide by limiting the pH value to 12 and for this purpose seawater is introduced, in particular stirred, into a saturated calcium hydroxide solution.
3. The method according to claim 1, characterized in that The pH value of seawater is adjusted to a value around pH-12 by applying voltage.
4. A device for obtaining particles with a high magnesium content from seawater, based on a precipitation process using a suitable alkaline agent, in particular by a method according to claim 1, characterized in that In order to provide small particles with a narrow particle size distribution, a nozzle arrangement is provided for contacting seawater with a saturated calcium hydroxide solution in a controlled manner, wherein the nozzle has a capillary in the center of a plurality of vertical cylindrical channels, the inner diameter of the capillary and the free cross section of the cylindrical channel being in the range of a few millimeters, into which capillary and cylindrical channel each one of the reaction liquids can be fed, wherein in addition the cylindrical channel and the capillary inside the nozzle are connected to each other via a channel so that the flow conditions in each channel and each capillary are almost identical and the particle size can be preset by adjusting the flow parameters of the reaction liquid.
5. The device according to claim 4, characterized in that The flows of the reaction liquids merge or come into contact outside the nozzle in the opening region of the corresponding cylindrical channels with the inner capillaries and form a mixing zone (MZ).