Method and apparatus for producing magnesium-rich particles from seawater

Abstract

The present invention relates to an apparatus and method for obtaining particles with a high magnesium content from seawater. The particles can be, for example, magnesium hydroxide, as well as other water-insoluble magnesium salts, such as, for example, magnesium sulfate, magnesium carbonate, etc. The particles are produced in a precipitation process using a suitable alkaline reagent. When the precipitation is carried out using the 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 within certain ranges. The aqueous suspension obtained from the method can be further processed using existing technological methods to produce different products, including up to metallic magnesium for metallurgy.

Description

[Technical field]

[0001] The present invention relates to a method and technical device for the extraction of 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 reagent. If this precipitation is carried out using a nozzle assembly according to the invention and / or with the addition of auxiliary reagents, the size of the particles obtained and their yield can be influenced. The aqueous suspension obtained from this method can be further processed into various articles using known technical methods, for example into metallic magnesium for metallurgy. [Background technology]

[0003] Magnesium-containing raw materials, especially magnesium hydroxide, are very important raw materials for industry. Originally, magnesium hydroxide exists in crystalline form as the so-called brucite and is mined industrially as an ore. In some areas of the world, brucite can only be mined on an industrial scale, but the demand for magnesium-containing raw materials and especially magnesium hydroxide is constantly increasing, and other methods of extracting it are attracting more and more attention. These include, in particular, the precipitation (precipitation) of water-soluble magnesium salts, such as magnesium chloride, by hydroxide in aqueous solution.

[0004] The world's oceans contain a large amount of different salts. Their average salt content is about 3.5%, i.e. 35 g / L. The composition of seawater is approximately the same in all parts of the world. The proportion of magnesium chloride in seawater is about 11% of the salt content. This makes seawater a practically inexhaustible source of raw material for magnesium salts.

[0005] It is therefore clear that research has been carried out for many decades in the field of magnesium extraction from seawater. Below is a representative list of relevant intellectual property rights:

[0006] In the process according to DE 1196172 B, magnesium hydroxide is obtained by precipitation from seawater using a 5-10% aqueous suspension of calcium carbide waste liquor (consisting mainly of calcium oxide, aluminium oxide, iron oxide and silicon oxide). The method includes the following steps: 1. Separating milky calcium carbonate waste liquor into a relatively low purity fraction and a relatively high purity fraction; 2. Transforming seawater with a relatively low purity portion of the resulting calcium carbonate waste liquor to produce non-carbonated seawater; 3. The conversion of non-carbonated seawater with a relatively pure portion of the calcium carbonate wastewater to produce magnesium hydroxide; and 4. Separating the resulting magnesium hydroxide into a pure fraction and a less pure fraction.

[0007] Here, the conversion / precipitation is carried out discontinuously in a refiner, with subsequent mechanical separation (hydrocyclone) of the precipitated magnesium hydroxide. The use of calcium carbonate waste liquor instead of, for example, calcium hydroxide, which is much cheaper, is likely to make this process even more expensive.

[0008] GB543665A describes a process for extracting magnesium salts from seawater, and for pre-treating 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.

[0009] The patent basically discloses a method for pre-treating seawater so that the described salts can be obtained therefrom. No technical method for the actual extraction of these salts is disclosed.

[0010] US3111376 deals with a continuous process for the preparation of magnesium hydroxide from magnesium chloride solutions containing dolomite (CaMg(CO3)2). Precipitation of magnesium hydroxide occurs at elevated temperatures (up to 90°C) where the dolomite is converted in situ to the corresponding hydroxide (Ca(OH)2).

[0011] However, due to the relatively high temperatures and reagents used, this method is likely to be rather expensive and uneconomical for widespread technical applications.

[0012] Seawater is pretreated with sodium carbonate to precipitate calcium salts according to GB535852A. After separating the calcium carbonate, the seawater is mixed with sodium hydroxide to obtain the desired magnesium hydroxide, which is then filtered off.

[0013] Due to the sodium hydroxide used as the precipitating reagent and the resulting high pH values ​​generated in the system, precipitation of all multivalent ions is expected, which results in a highly impure product.

[0014] US2405055 describes a method for extracting magnesium hydroxide from seawater. Seawater is mixed directly with calcium hydroxide milk in a (super)stoichiometric amount of lime and stirred in a reactor until complete conversion to magnesium hydroxide. Finally, the precipitated magnesium hydroxide is separated.

[0015] Due to the nature of this process, the particles obtained are relatively large. Fresh water is also used in the production of lime milk, which leads to increased production costs.

[0016] WO 0029326 describes a process for producing magnesium hydroxide from seawater, in which magnesium hydroxide is precipitated with a sodium hydroxide solution obtained from seawater by electrodialysis.

[0017] Due to the high pH values ​​produced by using sodium hydroxide as the precipitating reagent, many other salts also precipitate, which results in significant contamination of the product.

[0018] WO2016 / 193087A1 describes how micro- and nanoparticles can be produced from a solution of two salts by precipitation using specially designed nozzles. The particle size can be influenced by varying the flow rate and by adding surfactants.

[0019] In the described method, almost exclusively salt solutions are used: no provision is made for the use of the lysate as a precipitating reagent.

[0020] DE102004026725A1 discloses a modular nozzle system for producing droplets from liquids of different viscosities. The device described in this document relates to a gas-liquid nozzle, in which the liquid is pumped through an internal capillary and a gas flowing around the liquid serves to ensure the detachment of the droplets. Summary of the Invention [Problem to be solved by the invention]

[0021] In view of the above, the present invention therefore addresses the problem of providing a further developed method in terms of a practically applicable technological process and an apparatus for obtaining particles from seawater, said particles having a high magnesium content. [Means for solving the problem]

[0022] The problem addressed by the present invention is solved using the teachings or features and characteristics of the independent claims, while the dependent claims contain at least advantageous embodiments and developments. [Brief description of the drawings]

[0023] [Figure 1]FIG. 1 is an exemplary illustration of a system for carrying out a technological process for obtaining magnesium particles from seawater. [Diagram 2] FIG. 2 is a schematic diagram of a technical process for an exemplary implementation of the method according to the third embodiment. [Diagram 3] FIG. 3 shows a cross-section and a detailed view of a nozzle or nozzles according to the invention, in which a capillary is located in the center of several vertical cylindrical channels. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Proceeding from the known prior art, the present invention relates to a method and an apparatus by which small particles having a high magnesium content can be produced from seawater.

[0025] The basic idea of ​​the present invention is to convert the readily water-soluble magnesium chloride contained in seawater into a mostly water-insoluble form, such as magnesium hydroxide, and thus precipitate it.

[0026] For example, magnesium chloride is converted to the nearly water-insoluble magnesium hydroxide by simply raising the pH value in the system above a value of 12. If the pH value is further increased to 14, for example, magnesium hydroxide is still formed. However, at this high pH value, nearly all other salts contained in seawater are converted to water-insoluble hydroxides, which results in undesirable contamination of the desired magnesium hydroxide.

[0027] A simple and inexpensive solution to limit the pH to 12 is, for example, to use calcium hydroxide instead of sodium hydroxide, which does not dissolve easily in water. Calcium hydroxide is only soluble in water up to about 1.7 g / L at room temperature, which limits the pH value of the solution to 12.

[0028] Another way to adjust the pH value is to apply a voltage to increase the pH value.

[0029] Therefore, it is possible to adjust the pH value of seawater to the required value of 12 not only by adding Ca(OH)2, but also by applying a voltage in the sense of electrolysis.

[0030] If the voltage is increased above an experimentally determined limit value, most of the dissolved salts will precipitate, thus making it possible to provide a salt mixture or seawater with a highly reduced salinity, which can be further processed or used in a manner known per se.

[0031] The method according to the invention differs from the prior art in that by using excess Ca(OH)2 in the first method step, a saturated Ca(OH)2 solution can be produced directly from seawater. The use of fresh water is not necessary. The nozzles, which are described in more detail below, allow the provision of very small particles, the size of which can also be influenced by the flow parameters of the reaction liquid. The combination with the use of nozzles according to the invention serves to produce particles directly from seawater, which is neither known nor obvious from the prior art.

[0032] When saturated calcium hydroxide solution is mixed with seawater, magnesium hydroxide precipitates immediately, however the particles are very large and have a very wide size distribution.

[0033] In order to produce small particles with a narrow particle size distribution from magnesium chloride, a special nozzle is used in the present invention, by means of which seawater is contacted with a saturated calcium hydroxide solution in a controlled manner within defined parameters and not in an uncontrolled manner, such as, for example, by simple stirring.

[0034] The invention is explained in more detail below with reference to exemplary embodiments and by means of the drawings. The diagram shows: FIG. 1 is an exemplary illustration of a system for carrying out a technological process for obtaining magnesium particles from seawater; FIG. 2 is a schematic diagram of a technical process for an exemplary implementation of the method according to the third embodiment; FIG. 3 shows a cross-section and a detailed view of a nozzle or nozzles according to the invention, in which a capillary is located in the center of several vertical cylindrical channels.

[0035] According to the invention, a multiple nozzle is used, which is designed as follows (Figure 3): a capillary is located in the center of several vertical cylindrical channels. The inner diameter of the capillary and the free cross section of the cylindrical channels have a diameter of a few millimeters. One of the reaction liquids (K1 and K2) flows through each of the capillaries and cylindrical channels. The resulting dimensions of the cross sections through which the liquids flow are comparable and are selected so that the flow rate per channel is in the range of a few liters / min, even in laminar flow. The individual cylindrical channels and their internal capillaries are connected in the nozzle by horizontal channels in such a way that the flow conditions in each channel and in each capillary are approximately identical.

[0036] The nozzle is designed so that the two liquid streams only come into contact at the outer outlet region, i.e., the outer side of the nozzle (MZ), which prevents nozzle clogging and increases the reliability of the method.

[0037] If the inlet pressure of both liquids K1 and K2 flowing through such a nozzle is now changed, the flow parameters through the capillary and the vertical cylindrical channel will also change.

[0038] Experiments have shown that when laminar flow occurs through the nozzle, ie, when the Reynolds number is less than 10,000, the diameter of the resulting particles is determined by the flow velocity.

[0039] For example, low flow rates from the same nozzle can result in particle sizes in the μm range, while relatively high flow rates near the limit of turbulence produce particles with significantly smaller diameters. In the turbulent regime, the particle diameter remains approximately constant at all times.

[0040] The diameter of the resulting particles can be further reduced by adding a surface active liquid, e.g. a detergent. The higher the concentration of detergent in both solutions fed to the nozzle, the smaller the particles will be. Similar effects can be observed by varying the concentration and / or temperature of the reaction solutions.

[0041] To achieve sufficient volumetric throughput for industrial applications, several of the multi-capillary nozzles described herein can be combined in a nozzle head in which both the capillaries for liquid transport and the channels for gas flowing concentrically around them are incorporated in superimposed plates or planes. EXAMPLES

[0042] Example 1: For example, a saturated calcium hydroxide solution is prepared by stirring 4 g of calcium hydroxide in 1 liter of fresh water, then filtering and pouring into a storage container. The previously filtered seawater is poured into a second container. These two clear solutions are then fed into a nozzle, configured as described above, where one solution flows through the capillary and the other flows through the surrounding cylindrical channel. At the nozzle outlet, magnesium hydroxide is obtained as an aqueous suspension. By varying the inlet pressure on the nozzle, different flow conditions are created in the nozzle. This results in different particle sizes in the resulting suspension. From the suspension, powdered magnesium hydroxide can be obtained by simple settling or filtration.

[0043] Example 2: For example, a saturated calcium hydroxide solution is prepared by stirring 4 g of calcium hydroxide in 1 liter of seawater, then filtering and pouring into a storage container. Using seawater means that many of the salts contained in the water, such as the magnesium chloride contained therein, will precipitate. The suspension is therefore decanted before filtering. The previously filtered seawater is poured into a second container. These two clear solutions are then fed into a nozzle, configured as described above, where one solution flows through the capillary and the other flows through the 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 created in the nozzle. This results in different particle sizes in the resulting suspension. From the suspension, magnesium hydroxide in powder form can be obtained by simple settling or filtration.

[0044] Example 3: If it is desired to process at a pH of 14 instead of 12 as in the above example, the following approach should be adopted: a saturated sodium hydroxide solution is prepared, for example by stirring 4 g of calcium hydroxide and 6 g of sodium carbonate per liter of water, then filtered and poured into a storage container. If seawater is used instead of fresh water, the suspension must be precipitated as in example 2 before further use and the supernatant must be filtered, otherwise simple filtration is sufficient. The previously filtered seawater is poured into a second container. These two clear solutions are then fed into a nozzle, which is constructed as described above, one solution flows through the capillary and the other through the surrounding cylindrical channel. An aqueous suspension is obtained at the outlet of the nozzle. By varying the inlet pressure on the nozzle, different flow conditions are created in the nozzle. This results in different particle sizes in the resulting suspension. Only about 80% of the solids of the suspension are magnesium hydroxide. It can be separated from the suspension by simple precipitation or filtration.

[0045] Example 4: If the method according to example 2 is implemented in a technical process, it can be configured as shown in FIG. To prepare a basic solution of pH 12, a basic reagent (e.g. calcium hydroxide) is transferred to a mixing tank M2 and stirred into seawater (MW), which has previously been filtered through a filter F3 to form a clear liquid. The aqueous supernatant in M2 is fed to a precipitation vessel (decanter) D1. The aqueous supernatant from D1 is transferred through a filter F4 to a reservoir V2, from where it is pumped (pumped) as a clear solution into a reaction tank R. The second liquid stream pumped to R is seawater. To increase the yield, a small amount (below the solubility limit) of a basic reagent, e.g. calcium hydroxide, is added to this liquid, thereby raising its pH to about 10 (see the top of the flow diagram in Figure 1). For this purpose, seawater MW is filtered through a filter F1 and pumped into the mixing tank M1. A basic reagent BR, e.g. calcium hydroxide, is stirred into this water in M1 at a concentration of up to about 1 g / L. The solution thus obtained is transferred through a filter F2 to a storage vessel 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 vessel, at the outlet of which the desired particles (for example magnesium hydroxide) are produced. If certain small particles are not required, the two liquids can also be fed through the nozzle head to R and mixed with an agitator from R. The suspension from R is sent to a precipitation vessel D2, where it is concentrated. The aqueous supernatant MW * is discarded, 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 fed to other industrial processes, such as the electrolytic recovery of magnesium metal.

[0046] Example 5: When the method according to Example 3 is implemented in a technical process, it can be configured as shown in Figure 2. It corresponds largely to that of Example 4, and the information given there also applies accordingly.

[0047] In contrast, the suspension obtained in R (here R1) is mixed again with seawater in order to convert the hydroxides contained in its aqueous supernatant into magnesium hydroxide. It is pumped to R2, where it is reacted with the seawater prepared via F1, M1, F2 and V1. The suspensions from D2 and R2 are then combined in M4 and concentrated in a sink tank D3. The aqueous supernatant MW * is discarded, 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 fed to other industrial processes, such as the electrolytic recovery of magnesium metal.

Claims

1. 1. A method for producing particles having a high magnesium content from seawater, comprising the steps of: converting water-soluble magnesium chloride contained in the seawater into a water-insoluble form and precipitating it, and this conversion is carried out by increasing the pH value in the system to pH 12 or higher, and the precipitated particles are fed to a nozzle device to achieve particle size adjustment and homogenization of the particle size distribution of the obtained particles; method.

2. 2. A 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, the seawater is introduced into a saturated calcium hydroxide solution, in particular with stirring.

3. 2. The method according to claim 1, characterized in that the pH value of the seawater is adjusted to a value in the region of pH-12 by applying a voltage.

4. 1. An apparatus for obtaining particles with a high magnesium content from seawater based on a precipitation process with a suitable alkaline agent, in particular by the method according to claim 1, a nozzle arrangement is provided for contacting the seawater with the saturated calcium hydroxide solution in a controlled manner to provide small particles having a narrow size distribution; said nozzle having a capillary at the center of a plurality of vertical cylindrical channels, the internal diameter of which and the free cross section of said cylindrical channels are in the range of a few millimeters; one of the reaction fluids can be supplied to each of the capillary and the cylindrical channel; the cylindrical channel in the nozzle and the capillary are connected to each other by a channel such that flow conditions in each of the channels and the capillary are substantially identical, and particle size can be predetermined by adjusting flow parameters of the reaction solution; An apparatus comprising:

5. 5. The apparatus of claim 4, wherein the liquid streams of the reaction fluids meet or contact outside the nozzle at the opening region of the respective cylindrical channels with internal capillaries to form a mixing zone (MZ).

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