Method and device for producing particles with a high magnesium content from sea water
Patent Information
- Application Number
- EP2023704976
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-01-11
- Filing Date
- 2023-02-13
- Publication Date
- 2025-02-12
AI Technical Summary
Existing methods for extracting magnesium from seawater are costly, inefficient, and result in contaminated products due to high pH values and the use of expensive reagents, leading to the need for a more cost-effective and efficient process for producing high magnesium content particles.
A method using calcium hydroxide to raise the pH of seawater to 12, combined with a specialized nozzle system to control particle size, allowing for the precipitation of magnesium hydroxide with minimal contamination, and the use of electrolysis to further reduce salt content, enabling the production of small, uniformly sized magnesium particles.
This approach reduces production costs, minimizes contamination, and allows for the efficient production of high magnesium content particles with controlled sizes, making the process more economically viable and scalable for industrial applications.
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Figure 1.1
Abstract
Description
[0001] Method and apparatus for producing particles with a high magnesium content from seawater
[0002] Description
[0003] The present invention relates to a method and a technical device for extracting particles from seawater that have a high magnesium content. Such particles can be, for example, magnesium hydroxide or other water-insoluble magnesium salts such as magnesium sulfate, magnesium carbonate, etc.
[0004] According to the invention, the particles are produced in a precipitation process using a suitable alkaline reagent. If this precipitation is carried out with the aid of a nozzle structure according to the invention and / or with the addition of auxiliary reagents, the size of the obtained particles and their yield can be influenced. The aqueous suspension obtained from the process can be further processed into various products using known technical methods, including metallic magnesium for metallurgy.
[0005] Magnesium-containing raw materials, especially magnesium hydroxide, are very important raw materials for industry. Magnesium hydroxide occurs naturally in crystalline form as 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, while the demand for magnesium-containing raw materials, especially magnesium hydroxide, is constantly increasing, other methods for its extraction are increasingly gaining attention. These include, in particular, the precipitation of water-soluble magnesium salts, such as magnesium chloride with a hydroxide in an aqueous solution.
[0006] The world's oceans contain large amounts of various salts. Their average salt content is approximately 3.5%, or 35 g / liter. The composition of seawater is virtually the same in all regions of the world. The proportion of magnesium chloride in seawater is approximately 11% of the salt content. This makes seawater a virtually inexhaustible source of raw materials for magnesium salts.
[0007] It's therefore only logical that research into magnesium extraction from seawater has been ongoing for decades. Below are some examples of relevant intellectual property rights.
[0008] In the process according to DE 11 96 172 B, magnesium hydroxide is extracted from seawater by precipitation with a 5 to 10% aqueous suspension of calcium carbide liquor (consisting mainly of calcium oxide, aluminum oxide, iron oxide, and silicon oxide). The process involves the following steps:
[0009] 1. Separation of calcium carbide liquor in a milky state into less pure and purer fractions.
[0010] 2. Conversion of seawater with the resulting less pure portion of the calcium carbide liquor to carbonic acid-free seawater
[0011] 3. Conversion of the carbonic acid-free seawater with the purer portion of the calcium carbide liquor to magnesium hydroxide and
[0012] 4. Separation of the obtained magnesium hydroxide into a pure and a less pure fraction.
[0013] The conversion / precipitation takes place discontinuously in clarification tanks, followed by mechanical separation (liquid cyclone) of the precipitated magnesium hydroxide. The use of calcium carbide liquor instead of, for example, calcium hydroxide, which is much more cost-effective, is likely to make the process even more expensive.
[0014] GB 543 665 A describes a process for extracting magnesium salts from seawater, as well as a process for pretreating the seawater to reduce its carbon dioxide, bicarbonate, and carbonate content by adding calcium hydroxide or oxide. After the calcium carbonate has precipitated, the Mg(II) solution can be further processed. This patent essentially discloses a process for pretreating seawater to extract the named salts. A technical process for actually extracting these salts is not described.
[0015] US Pat. No. 3,111,376 describes a continuous process for the production of magnesium hydroxide from a magnesium chloride solution with dolomite (CaMgCCO3). The precipitation of the magnesium hydroxide occurs at elevated temperatures (up to 90°C), where dolomite is converted in situ into the corresponding hydroxides (Ca(OH)2).
[0016] However, due to the relatively high temperatures and the reagents used, the process is likely to be quite expensive and uneconomical for broad technical applications.
[0017] Seawater is pretreated with sodium carbonate in accordance with GB 535 852 A to precipitate calcium salts. After separating the calcium carbonates, the seawater is then mixed with sodium hydroxide to obtain the desired magnesium hydroxide, which is then filtered off.
[0018] Due to the use of sodium hydroxide as a precipitating reagent and the resulting high pH value in the system, precipitation of all multivalent ions is to be expected, resulting in a highly contaminated product.
[0019] US 240 50 55 describes a method for extracting magnesium hydroxide from seawater. Here, seawater is directly mixed with a (super)stoichiometric amount of calcium hydroxide milk of lime and stirred in a reactor until complete conversion to magnesium hydroxide occurs. The precipitated magnesium hydroxide is then separated.
[0020] Due to the nature of the method, the resulting particles are relatively large. Freshwater is also used in the production of lime milk, which increases production costs.
[0021] WO 0029326 A1 describes a process for producing magnesium hydroxide from seawater, in which the magnesium hydroxide is precipitated with sodium hydroxide solution obtained from seawater by electrodialysis.
[0022] The use of sodium hydroxide as a precipitating reagent will also cause a number of other salts to precipitate due to the resulting high pH value, leading to significant contamination of the product.
[0023] WO 2016 / 193087 A1 describes how micro- and nanoparticles can be produced from solutions of two salts by precipitation using a specially designed nozzle. The particle size can be influenced by changing the flow rates and adding surfactants.
[0024] The process described uses almost exclusively salt solutions. The use of alkalis as a precipitating agent is not planned.
[0025] DE 10 2004 026 725 A1 discloses a modular nozzle system for generating droplets from liquids of varying viscosity. The arrangement described therein relates to a gas-liquid nozzle in which the liquid is pumped through internal capillaries, and the gas flowing around the liquid serves to ensure droplet detachment.
[0026] From the above, it is therefore an object of the invention to provide a further developed method in the sense of a practically applicable technical process and a device for obtaining particles from seawater, wherein the particles have a high magnesium content.
[0027] The object of the invention is achieved with the teachings or features and groups of features of the independent claims, wherein the dependent claims comprise at least expedient embodiments and further developments.
[0028] Based on the known prior art, the present invention relates to a method and a device for producing small particles with a high magnesium content from seawater. The basic idea of the invention is to convert the highly water-soluble magnesium chloride contained in seawater into a virtually water-insoluble form, for example, magnesium hydroxide, and thus precipitate it.
[0029] Magnesium chloride can be converted, for example, into the virtually water-insoluble magnesium hydroxide by simply raising the pH of the system above 12. If the pH is further increased to, say, 14, magnesium hydroxide is still formed. However, at this high pH, almost all other salts present in seawater are converted into water-insoluble hydroxides, which leads to undesirable contamination of the desired magnesium hydroxide.
[0030] A simple and cost-effective solution to limit the pH to 12 is to use the poorly water-soluble calcium hydroxide instead of, for example, sodium hydroxide. Calcium hydroxide is only soluble in water up to approximately 1.7 g / liter at room temperature, which limits the pH of the solution to 12.
[0031] Another way to adjust the pH value is to increase the pH value by applying a voltage.
[0032] It is therefore possible to adjust the pH of seawater to the required value of 12 not only by adding Ca(OH)2, but also by applying an electrical voltage in the sense of electrolysis.
[0033] If the voltage is increased above an experimentally determined limit, a large portion of the dissolved salts will precipitate. This would make it possible to produce a salt mixture or significantly reduced-salt seawater, which could be further processed or used in conventional ways.
[0034] The process according to the invention differs from the prior art in that, by using an excess of Ca(OH)2 in the first process step, a saturated Ca(OH)2 solution can be produced directly from seawater. The use of freshwater is not required. The nozzle, described in more detail below, enables the production of very small particles, the size of which can also be influenced by the flow parameters of the reaction liquids. A combination of the nozzle according to the invention, which serves to produce the particles directly from seawater, is neither known nor obvious from the prior art.
[0035] If you stir a saturated calcium hydroxide solution with seawater, magnesium hydroxide immediately precipitates. However, the particles are quite large and their size distribution is very broad.
[0036] To produce small particles with a narrow size distribution of magnesium chloride, the present invention uses a special nozzle. This nozzle allows the seawater to be brought into contact with the saturated calcium hydroxide solution in a controlled manner within defined parameters, rather than in an uncontrolled manner, such as through simple stirring.
[0037] The invention will be explained in more detail below using exemplary embodiments and with the aid of figures.
[0038] Here we show:
[0039] Fig. 1 shows an exemplary explanation of a plant for carrying out a technical process for the extraction of magnesium particles from seawater;
[0040] Fig. 2 is a schematic representation of a technical process for exemplary implementation of the method according to the third example and
[0041] Fig. 3 is a sectional view and a detailed view of the nozzle or multiple nozzle according to the invention, in which capillaries are located in the center of several vertical, cylindrical channels.
[0042] According to the invention, a multiple nozzle is used which is designed as follows (Fig. 3): Capillaries are located at the center of several vertical, cylindrical channels. The inner diameter of the capillaries and the free cross-section of the cylindrical channels has a diameter of a few millimeters. One of the reaction liquids (K1 and K2) each flows through the capillaries and the cylindrical channels. The dimensions of the resulting cross-sections through which the liquids flow are comparable and selected such that even with laminar flow the throughput per channel is in the range of a few liters per minute. The individual cylindrical channels and the capillaries inside them are connected to one another within the nozzle by horizontal channels such that the flow conditions in each channel and in each capillary are almost identical.
[0043] The nozzle is designed so that the two fluid streams only come into contact in the outer outlet area, i.e., outside the nozzle (MZ). This prevents nozzle clogging and increases the reliability of the process.
[0044] If the pre-pressure of both liquids K1 and K2 flowing through such a nozzle is changed, the flow parameters through the capillaries and through the vertical, cylindrical channels also change.
[0045] It has been experimentally demonstrated that in laminar flows through the nozzle, i.e. with Reynolds number values below 10,000, the diameter of the resulting particles is determined by the flow velocity.
[0046] For example, using the same nozzle at low flow rates, particle diameters in the pm range are obtained, while at higher flow rates, which are close to the boundary of turbulent flow, particles with a significantly smaller diameter are produced. In the turbulent flow range, the particle diameter always remains almost constant.
[0047] By adding a surface-active liquid, such as a detergent, the diameter of the resulting particles can be further reduced. The higher the detergent concentration in both solutions fed to the nozzle, the smaller the particles become. Similar effects can be observed by changing the concentration and / or temperature of the reaction solutions. To achieve a sufficient volume throughput for industrial applications, several of the multi-capillary nozzles described here can be combined in nozzle heads. In these nozzle heads, both the capillaries for liquid transport and the channels for the gas flowing concentrically around them are incorporated into stacked plates or planes.
[0048] Example 1:
[0049] A saturated calcium hydroxide solution is prepared by stirring, for example, 4 g of calcium hydroxide into one liter of fresh water. The solution is then filtered and poured into a storage container. Seawater, which has also been previously filtered, is poured into a second container. These two clear solutions are then fed to a nozzle constructed as described above, with one solution flowing through the capillary and the other through the surrounding cylindrical channel. Magnesium hydroxide is obtained as an aqueous suspension at the nozzle outlet. By varying the pre-pressure on the nozzle, different flow conditions are created inside the nozzle. This leads to different particle sizes in the resulting suspension. The powdered magnesium hydroxide can be obtained from the suspension by simple sedimentation or by filtration.
[0050] Example 2:
[0051] A saturated calcium hydroxide solution is prepared by stirring, for example, 4 g of calcium hydroxide into one liter of seawater, then filtered and poured into a storage vessel. Using the seawater precipitates several of the salts contained in the water, including the magnesium chloride it contains. For this reason, the suspension is decanted before filtering. Seawater, which has also been previously filtered, is poured into a second vessel. These two clear solutions are then fed to a nozzle constructed as described above, with one solution flowing through the capillary and the other through the surrounding cylindrical channel. Magnesium hydroxide is obtained as an aqueous suspension at the nozzle outlet. By varying the pre-pressure on the nozzle, different flow conditions are created inside the nozzle. This leads to different particle sizes in the resulting suspension.The powdered magnesium hydroxide can be obtained from the suspension by simple sedimentation or by filtration.
[0052] Example 3:
[0053] If you want to work at a pH of 14 and not 12 as in the above examples, proceed as follows: A saturated sodium hydroxide solution is prepared by stirring, for example, 4 g of calcium hydroxide and 6 g of sodium carbonate into one liter of water. The solution is then filtered and poured into a storage container. If seawater is used instead of freshwater, the suspension must be allowed to settle and the supernatant filtered as in Example 2 before further use; otherwise, simple filtration is sufficient. Seawater, which has also been filtered beforehand, is poured into a second container. These two clear solutions are then fed to a nozzle constructed as described above, with one solution flowing through the capillary and the other through the surrounding cylindrical channel. An aqueous suspension is obtained at the nozzle outlet.By varying the pre-pressure on the nozzle, different flow conditions are created inside the nozzle. This leads to different particle sizes in the resulting suspension. The solids content of the suspension contains only approximately 80% magnesium hydroxide. This can be separated from the suspension by simple sedimentation or filtration.
[0054] Example 4:
[0055] If the method described in Example 2 is implemented in a technical process, it can be constructed as shown in Fig. 1:
[0056] To prepare the basic solution with a pH of 12, the basic reagent (e.g. calcium hydroxide) is placed in the mixing tank M2 and stirred into seawater (MW), which has previously been filtered through the filter F3 to produce a clear liquid. The aqueous supernatant in M2 is fed to the sink vessel (decanter) Dl. The aqueous supernatant from Dl is transferred via the filter F4 to the storage tank V2, from where it is pumped as a clear solution into the reaction vessel R. The second liquid stream pumped into R is seawater. To increase the yield, a small amount (below the solubility limit) of a basic reagent, such as calcium hydroxide, is added to this liquid to raise its pH to approximately 10 (see the upper part of the flow diagram in Figure 1). For this purpose, seawater MW is filtered through the filter Fl and pumped into the mixing tank Ml.1 g / liter is stirred into this water. The solution obtained in this way is transferred via filter F2 into storage tank VI and from there into reaction vessel R. Inside reaction vessel R there is a nozzle head as described above, through which the two liquids are pumped into the vessel and at the outlet of which the desired particles (e.g. magnesium hydroxide) are formed. If no defined, small particles are desired, the two liquids can also be passed past the nozzle head into R and mixed with the agitator from R. The suspension from R is fed into sink vessel D2 where it is concentrated. The aqueous supernatant MW* is disposed of, while the product (e.g. magnesium hydroxide) is separated from the sink fraction using filter F5.The magnesium hydroxide obtained in this way can then be dried and used in other industrial processes, such as the electrolytic extraction of metallic magnesium.
[0057] Example 5:
[0058] If the method described in Example 3 is implemented in a technical process, it can be structured as shown in Fig. 2. This largely corresponds to that of Example 4. The information given there also applies here.
[0059] In contrast, the suspension obtained in R (here RI) is mixed with seawater a second time to convert the hydroxide contained in its aqueous supernatant to magnesium hydroxide. For this purpose, the hydroxide is pumped into R2 and reacted there with the seawater treated via Fl, Ml, F2, and VI. The suspensions from D2 and R2 are then combined in M4 and concentrated in sink tank D3. The aqueous supernatant MW* is disposed of, while the product (e.g., magnesium hydroxide) is separated from the sink fraction using filter F5. The magnesium hydroxide thus obtained can then be dried and used in other industrial processes, such as the electrowinning of metallic magnesium.
Claims
Claims: A process for producing particles with 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, furthermore, this conversion is carried out by raising the pH value in the system to a range equal to or above pH 12, and the precipitated particles are fed to a nozzle arrangement to achieve particle size control and a uniformity of the size distribution of the obtained particles. The process according to claim 1, characterized in that the conversion of the magnesium chloride into water-insoluble magnesium hydroxide is carried out by limiting the pH value to 12, and for this purpose, the seawater is introduced, in particular stirred, into a saturated calcium hydroxide solution.Method according to claim 1, characterized in that the pH value of the seawater is adjusted to a value in the range of pH 12 by applying an electrical voltage. Device for obtaining particles from seawater with a high magnesium content, based on a precipitation process with a suitable alkaline reagent, in particular according to a method according to claim 1, characterized in that, for providing small particles with a narrow size distribution, a nozzle arrangement is provided to bring seawater into controlled contact with saturated calcium hydroxide solution, wherein the nozzle has capillaries in the center of several vertical cylindrical channels, the inner diameter and the free cross-section of the cylindrical channels being in the range of a few millimeters, and each of the reaction liquids can be supplied to the capillaries and the cylindrical channels, wherein the cylindrical Channels and capillaries within the nozzle are interconnected by channels such that the flow conditions in each channel and in each capillary are nearly identical, and the particle size of the reaction fluids can be predetermined by adjusting the flow parameters. The device according to claim 4 is characterized in that the fluid flows of the reaction fluids merge or come into contact outside the nozzle in the opening region of the respective cylindrical channel with an internal capillary, forming a mixing zone (MZ).