Method for separating inorganic salts from a sodium-magnesium-sulfate mixed solution

Abstract

The application belongs to the technical field of wastewater treatment, and particularly relates to a method for separating inorganic salts in a sodium-magnesium sulfate mixed solution. A magnesium salt with relatively large solubility is added to a feed liquid containing sodium-magnesium sulfate, and magnesium sulfate heptahydrate is precipitated at normal temperature and low temperature, respectively, and sodium salt is precipitated at high temperature in the heating and evaporation process, thereby forming a continuous zero-emission disposal sodium-magnesium sulfate separation process. The process has strong universality, is suitable for an aqueous solution system with a mass ratio of magnesium sulfate to sodium sulfate of 1-4, has zero emission in the process, does not pollute the environment, and is an environmentally friendly new technology for separating sodium-magnesium sulfate.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for separating inorganic salts from a sodium magnesium sulfate mixed solution. Background Technology

[0002] Magnesium sulfate and sodium sulfate are frequently found in mine and chemical wastewater. Direct discharge of this wastewater causes environmental pollution, while resource recovery of magnesium sulfate and sodium sulfate from wastewater can achieve certain economic benefits. When the mass ratio of magnesium sulfate to sodium sulfate in the feed solution is between 1 and 4, there are currently two main methods for separating sodium magnesium sulfate: the first method is to directly freeze the solution to precipitate nitrate, and then heat it to evaporate and precipitate magnesium salt; the second method is to add a large amount of water to the feed solution, freeze it at low temperature to precipitate nitrate, then heat it to evaporate and concentrate, and finally cool it to precipitate magnesium salt.

[0003] Regarding the first method, direct freezing precipitation is suitable when the magnesium sulfate content is low. However, when the magnesium sulfate concentration is high, the magnesium sulfate may quickly become saturated after cooling, resulting in the precipitation of magnesium salts. Furthermore, during subsequent evaporation and concentration, sodium magnesium sulfate double salts are often obtained, leading to product impurity. Therefore, this method has a narrow scope of application, and product purity is difficult to guarantee.

[0004] For the second method, when the magnesium sulfate content is high, water is added to the mixed solution, followed by low-temperature freezing to precipitate nitrate. Adding water to the mixed solution reduces the concentrations of sodium sulfate and magnesium sulfate to very low levels, and freezing to around -10°C precipitates sodium sulfate decahydrate, while the magnesium sulfate remains unsaturated. The mother liquor is then heated, evaporated, and concentrated, and cooled to obtain magnesium salts. However, this process requires a large amount of water, resulting in additional energy consumption during evaporation, leading to high energy consumption. Summary of the Invention

[0005] In view of this, the present invention discloses a method for separating inorganic salts in a sodium magnesium sulfate mixed solution. By adding a magnesium salt with high solubility to the sodium magnesium sulfate-containing solution, magnesium sulfate heptahydrate is precipitated at room temperature and low temperature, while sodium salt is precipitated at high temperature during heating and evaporation, thus forming a continuous zero-emission sodium magnesium sulfate separation process.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for separating inorganic salts from a sodium magnesium sulfate mixed solution, for an aqueous solution with a magnesium sulfate to sodium sulfate mass ratio between 1 and 4, when the magnesium sulfate concentration is greater than 150 g / L, the steps are as follows:

[0008] S1. Magnesium salt precipitation at room temperature

[0009] A magnesium salt with high water solubility is added to the sodium magnesium sulfate mixed solution to be separated. The mixture is stirred at room temperature until homogeneous, and magnesium sulfate heptahydrate precipitates. After solid-liquid separation, magnesium sulfate heptahydrate and mother liquor are obtained. The magnesium salt with high water solubility includes magnesium chloride or magnesium chloride hexahydrate. The amount of magnesium in the added magnesium salt is 25% to 75% of the amount of sodium ions in the raw material solution.

[0010] S2. Cryogenic Magnesium Salt Deposition

[0011] The mother liquor obtained from magnesium salt precipitation at room temperature in step S1 is cooled and frozen, with the temperature controlled between -10℃ and 0℃, to continue precipitating magnesium sulfate heptahydrate. After solid-liquid separation, magnesium sulfate heptahydrate and mother liquor are obtained.

[0012] Furthermore, the cooling and freezing temperature is -10℃ to 0℃, and the freezing time is 30 to 90 minutes.

[0013] S3. Evaporation to precipitate sodium salt

[0014] The mother liquor obtained by freezing magnesium salt in step S2 is heated, and the termination temperature is controlled at 105-115℃. Sodium salt is extracted by evaporating water. After solid-liquid separation, sodium salt and mother liquor are obtained.

[0015] Furthermore, the heating and evaporation temperature is 105℃~115℃, the amount of water evaporated is 20%~65% of the mass before evaporation, and the mother liquor obtained from evaporation is used as a circulating mother liquor to be added to the sodium magnesium sulfate solution to be separated.

[0016] Repeating the process of S1 (at room temperature) magnesium salt precipitation, S2 (freezing) magnesium salt precipitation, and S3 (evaporation) sodium salt precipitation forms a continuous, zero-emission sodium magnesium sulfate separation process.

[0017] For aqueous solutions with a low initial concentration and a magnesium sulfate to sodium sulfate mass ratio between 1 and 4, the raw water can be evaporated first until the magnesium sulfate concentration is greater than 150 g / L, and then steps S1, S2, and S3 can be used to separate the magnesium and sodium salts.

[0018] The separation principle of inorganic salts in a sodium magnesium sulfate mixed solution disclosed in this invention is as follows:

[0019] Magnesium salts with high solubility are added, and magnesium sulfate heptahydrate is precipitated at room temperature by utilizing the common ion effect of magnesium. Then, the temperature is lowered to continue precipitating magnesium sulfate heptahydrate, reducing the concentration of magnesium sulfate in the solution to an extremely low level. Finally, the sodium salt is saturated by heating and evaporating water, and precipitated, thereby achieving the purpose of separating sodium magnesium sulfate.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0021] The process of this invention is highly versatile and applicable to aqueous solution systems where the mass ratio of magnesium sulfate to sodium sulfate is between 1 and 4. The process is zero-emission and pollution-free, making it an environmentally friendly new technology for the separation of sodium magnesium sulfate. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 This is a process flow diagram of the separation of inorganic salts in a sodium magnesium sulfate mixed solution disclosed in this invention. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in the embodiments of this application, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in this application is merely for describing particular implementations and is not intended to limit the scope of this disclosure.

[0026] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; other experimental methods and technical means not specifically mentioned herein refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0027] In the description of this invention, it should be understood that the terms "middle", "upper", "lower", "rise", "fall", "vertical", "surface", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0028] To better illustrate the content of this application, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that this application can be implemented even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail in order to highlight the main points of this application.

[0029] Without conflict, the technical features disclosed in the embodiments of this application can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of this application.

[0030] This invention discloses a method for separating inorganic salts from a sodium magnesium sulfate mixed solution.

[0031] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0032] Example 1

[0033] Take 6500g of raw material solution with magnesium sulfate content of 256g / L and sodium sulfate content of 140g / L, add 2800g of magnesium chloride hexahydrate, stir at room temperature of 25℃ for 15min, carry out the magnesium precipitation step at room temperature, and precipitate solid. After solid-liquid separation of solution and solid, 2500g of magnesium sulfate heptahydrate and 6800g of magnesium precipitation solution at room temperature are obtained.

[0034] The magnesium precipitation solution at room temperature was frozen at -5℃ for 1 hour to carry out the freezing magnesium precipitation step, and the solid was precipitated. After solid-liquid separation of the solution and solid, 800g of magnesium sulfate heptahydrate and 6000g of freezing mother liquor were obtained.

[0035] The frozen mother liquor was heated to carry out the evaporation and salt precipitation step. 1400g of water was evaporated by boiling at 108℃ to obtain 130g of sodium chloride.

[0036] After mixing the remaining 4470g of mother liquor with the new raw material liquor, magnesium chloride hexahydrate was added, and the S1, S2, and S3 operations continued.

[0037] The obtained magnesium sulfate heptahydrate and sodium chloride have a purity greater than 92%, and their purity can be further improved by purification.

[0038] Example 2

[0039] Take 6500g of raw material solution with magnesium sulfate content of 318g / L and sodium sulfate content of 88g / L, add 766g of magnesium chloride, stir at room temperature of 25℃ for 15min, carry out the magnesium precipitation step at room temperature, and precipitate solid. After solid-liquid separation of solution and solid, 3055g of magnesium sulfate heptahydrate and 4211g of magnesium precipitation solution at room temperature are obtained.

[0040] The magnesium precipitation solution at room temperature was frozen at -4.5℃ for 1 hour to carry out the freezing magnesium precipitation step, and solid was precipitated. After solid-liquid separation of the solution and solid, 798g of magnesium sulfate heptahydrate and 3413g of freezing mother liquor were obtained.

[0041] The frozen mother liquor was heated to carry out the evaporation and salt precipitation step. 1700g of water was evaporated by boiling at 110℃ to obtain 103g of sodium chloride.

[0042] After mixing the remaining 1610g of mother liquor with the new raw material liquor, magnesium chloride hexahydrate was added, and the S1, S2, and S3 operations continued.

[0043] The obtained magnesium sulfate heptahydrate and sodium chloride have a purity greater than 92%, and their purity can be further improved by purification.

[0044] Example 3

[0045] Take 19.5 kg of raw material solution with magnesium sulfate content of 106 g / L and sodium sulfate content of 29.7 g / L, first boil it at 105℃ to evaporate 13.0 kg of water, and obtain 6500 g of evaporation mother liquor;

[0046] Add 1077g of magnesium chloride, stir at 25℃ for 15min to carry out the magnesium precipitation step at room temperature, and precipitate solid. After solid-liquid separation of solution and solid, 2723g of magnesium sulfate heptahydrate and 4854g of magnesium precipitation solution at room temperature are obtained.

[0047] The magnesium precipitation solution at room temperature was frozen at -4℃ for 1 hour to carry out the freezing magnesium precipitation step, and solid was precipitated. After solid-liquid separation of the solution and solid, 960g of magnesium sulfate heptahydrate and 3894g of freezing mother liquor were obtained.

[0048] The frozen mother liquor was heated to carry out the evaporation and salt precipitation step. 2460g of water was evaporated by boiling at 113℃ to obtain 415g of sodium chloride.

[0049] After mixing the remaining 1019g of mother liquor with the new raw material liquor, magnesium chloride hexahydrate was added, and the S1, S2, and S3 operations were continued.

[0050] The obtained magnesium sulfate heptahydrate and sodium chloride have a purity greater than 92%, and their purity can be further improved by purification.

[0051] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for separating inorganic salts from a sodium magnesium sulfate mixed solution, characterized in that, The method specifically includes the following steps: S1. Magnesium salt precipitation at room temperature Adding a magnesium salt with high solubility in water to a mixed solution of sodium and magnesium sulfates to be separated is often... Stirring at room temperature precipitates magnesium sulfate heptahydrate. The magnesium salts with high water solubility include magnesium chloride or magnesium chloride hexahydrate, and the added... The amount of magnesium in magnesium salts is 25% to 75% of the amount of sodium ions in the raw material solution; S2. Cryogenic Magnesium Salt Deposition The mother liquor obtained from the S1 step at room temperature for magnesium salt precipitation was cooled and frozen to continue precipitating magnesium sulfate heptahydrate. S3. Evaporation to precipitate sodium salt The mother liquor obtained from the freezing and precipitation of magnesium salt in step S2 is heated to evaporate the water and precipitate sodium salt; the mother liquor obtained from evaporation is used as a circulating mother liquor and is added to the sodium magnesium sulfate solution to be separated in step S1. Repeating the process of S1 (at room temperature) magnesium salt precipitation, S2 (freezing) magnesium salt precipitation, and S3 (evaporation) sodium salt precipitation forms a continuous zero-emission sodium magnesium sulfate separation process. The method is applicable to aqueous solutions with a magnesium sulfate to sodium sulfate mass ratio between 1 and 4, and when the magnesium sulfate concentration is greater than 150 g / L. For aqueous solutions with a lower initial concentration, the original water can be evaporated first until the magnesium sulfate concentration is greater than 150 g / L, and then steps S1, S2, and S3 can be used to separate the magnesium salt and sodium salt.

2. The method for separating inorganic salts from a sodium magnesium sulfate mixed solution according to claim 1, characterized in that, The cooling and freezing temperature in S2 is -10℃ to 0℃, and the freezing time is 30 to 90 minutes.

3. The method for separating inorganic salts from a sodium magnesium sulfate mixed solution according to claim 1, characterized in that, The heating and evaporation temperature in S3 is 105℃~115℃, and the amount of water evaporated is 20%~65% of the mass before evaporation.

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