阅读说明：本技术 从氯化钠和硫酸镁的混合盐中提取一水硫酸镁和工业盐的方法 (Method for extracting magnesium sulfate monohydrate and industrial salt from mixed salt of sodium chloride and magnesium sulfate ) 是由 李守江 雷光元 谭秀民 董广峰 张秀峰 马松亮 伊跃军 杨玉明 李敬芳 于 2020-12-30 设计创作，主要内容包括：本发明公开了一种从氯化钠和硫酸镁的混合盐中提取一水硫酸镁和工业盐的方法,属于无机化工分离技术领域。通过调制具有选择性的溶剂,使得混合盐中硫酸镁最大限度溶解,同时抑制氯化钠的溶解,固液分离后实现氯化钠和硫酸镁的分离,硫酸镁进入溶解母液中、氯化钠进入溶解渣中,溶解母液经常规的降温结晶、洗涤、干燥制得一水硫酸镁产品,溶解渣经洗涤精制、干燥回收得到工业盐产品。本发明提供的方法可以有效地实现氯化钠和硫酸镁的混合物中氯化钠和硫酸镁的分离,对硫酸镁具有良好的选择性,具有较高的镁回收率,操作容易,易于实现大规模工业化生产。(The invention discloses a method for extracting magnesium sulfate monohydrate and industrial salt from a mixed salt of sodium chloride and magnesium sulfate, belonging to the technical field of inorganic chemical separation. The selective solvent is prepared, so that magnesium sulfate in the mixed salt is dissolved to the maximum extent, the dissolution of sodium chloride is inhibited, the separation of sodium chloride and magnesium sulfate is realized after solid-liquid separation, magnesium sulfate enters a dissolving mother solution, sodium chloride enters dissolving slag, the dissolving mother solution is subjected to conventional cooling crystallization, washing and drying to prepare a magnesium sulfate monohydrate product, and the dissolving slag is subjected to washing, refining, drying and recovery to obtain an industrial salt product. The method provided by the invention can effectively realize the separation of sodium chloride and magnesium sulfate in the mixture of the sodium chloride and the magnesium sulfate, has good selectivity on the magnesium sulfate, has higher magnesium recovery rate, is easy to operate, and is easy to realize large-scale industrial production.)

1. The method for extracting the magnesium sulfate monohydrate and the industrial salt from the mixed salt of the sodium chloride and the magnesium sulfate is characterized by sequentially comprising the following steps:

preparing a solvent: preparing a solvent with high selectivity by using various inorganic salts such as sodium chloride, magnesium sulfate or sodium sulfate and fresh water or brine;

thermal dissolution: heating the solvent prepared in the step (1) to a required temperature, adding a mixed salt of sodium chloride and magnesium sulfate, stirring and dissolving for 30-60min, and selectively dissolving magnesium sulfate and sodium chloride;

solid-liquid separation: after the thermal dissolution is finished, carrying out solid-liquid separation, wherein the filtrate is dissolved mother liquor and enters the step (4), and the filter cake is crude sodium chloride and enters the step (5);

preparation of magnesium sulfate monohydrate: cooling and crystallizing the dissolved mother liquor to separate out magnesium sulfate heptahydrate, filtering to obtain crude magnesium sulfate after crystallization is finished, returning the filtered crystallized mother liquor to the step (1) for recycling, washing and refining the crude magnesium sulfate by adopting fresh water pulping to obtain wet magnesium sulfate heptahydrate, and drying the wet magnesium sulfate heptahydrate to obtain a magnesium sulfate monohydrate product;

recovery of industrial salt: and (4) washing and refining the crude sodium chloride generated in the step (3) by adopting a saturated sodium chloride solution, and then drying to obtain an industrial salt product.

2. The method for extracting magnesium sulfate monohydrate and industrial salts from a mixed salt of sodium chloride and magnesium sulfate according to claim 1, wherein the solvent prepared in step (1) is a low-sodium high-magnesium solution, wherein Mg is present²⁺The mass percentage of the content is 7.3% -8.7%, and Cl^-The content mass percentage is 19.4% -25.8%.

3. The method for extracting magnesium sulfate monohydrate and industrial salts from a mixed salt of sodium chloride and magnesium sulfate according to claim 1, wherein the thermal dissolution temperature of the step (2) is 60 ℃ to 75 ℃.

4. The method for extracting the magnesium sulfate monohydrate and the industrial salt from the mixed salt of the sodium chloride and the magnesium sulfate according to claim 1, wherein in the step (4), the dissolution mother liquor is cooled to 10-35 ℃ through natural cooling or forced cooling for cold crystallization.

5. The method for extracting magnesium sulfate monohydrate and industrial salts from a mixed salt of sodium chloride and magnesium sulfate according to claim 1, wherein in the step (4), the crystallization mother liquor after precipitation of magnesium sulfate heptahydrate is returned to the step (1) for recycling as a solvent required for thermal dissolution in the step (2).

6. The method for extracting the magnesium sulfate monohydrate and the industrial salt from the mixed salt of the sodium chloride and the magnesium sulfate according to claim 1, wherein in the step (4), the liquid-solid ratio of the fresh water pulping and washing crude magnesium sulfate is 0.33-0.4: 1, and the washing temperature is 0-30 ℃.

7. The method for extracting the magnesium sulfate monohydrate and the industrial salt from the mixed salt of the sodium chloride and the magnesium sulfate according to claim 1, wherein the mass percent of Mg in the recovered magnesium sulfate monohydrate product is more than or equal to 16.5%, the mass percent of Cl in the recovered magnesium sulfate monohydrate product is less than or equal to 1.50%, and the mass percent of NaCl in the recovered industrial salt product is more than or equal to 98.5%.

8. The method for extracting magnesium sulfate monohydrate and industrial salts from a mixed salt of sodium chloride and magnesium sulfate according to claim 1, wherein the content of NaCl in the mixed salt of sodium chloride and magnesium sulfate is not less than 10% by mass.

Technical Field

The invention relates to a method for extracting magnesium sulfate monohydrate and industrial salt from a mixed salt of sodium chloride and magnesium sulfate, belonging to the field of inorganic chemical separation.

Background

Magnesium sulfate monohydrate is a double-element fertilizer (containing Mg and S), sulfur and magnesium are medium-amount nutrient elements required by plants, are necessary for increasing the yield and improving the quality of crops, and are high-quality agricultural fertilizers. In addition, magnesium sulfate monohydrate is also used in the fields of pharmacy, food, feed additives, fermentation industry, printing and dyeing, ceramics, paper making and the like. The main method for producing magnesium sulfate monohydrate is an ore sulfuric acid method, which is obtained by directly reacting magnesium oxide ore with sulfuric acid. In recent years, with the development of domestic salt lake resources, such as natural magnesium sulfate resources of salt lakes in Yuancheng, Shanxi and sulfate type salt lakes in Chaudu basin, magnesium sulfate heptahydrate is produced by naturally cooling and crystallizing nitrate-making mother liquor in winter, and magnesium sulfate monohydrate is obtained by high-temperature drying. Meanwhile, the high-temperature salt which is a byproduct in the process of producing potassium chloride by using bittern in the sea salt chemical industry and the epsomite which is separated out in the process of sun curing salt lake brine and contains sodium chloride are both raw material sources of magnesium sulfate monohydrate.

Patent CN101554618B discloses a process for extracting magnesium sulfate heptahydrate from mixed salt containing magnesium sulfate heptahydrate by direct flotation, ammonium and amine cation mixed collectors are adopted to separate magnesium sulfate heptahydrate and sodium chloride by flotation, flotation concentrate is magnesium sulfate heptahydrate, and flotation tailings are sodium chloride. For such soluble salt flotation, since magnesium sulfate has high solubility and is extremely sensitive to temperature, a slight change in ambient temperature causes the flotation solvent to be unsaturated with respect to sodium chloride and magnesium sulfate, and a change in temperature causes precipitation of magnesium sulfate in the flotation solvent or dissolution of magnesium sulfate in the mixed salt, which is difficult to realize in industrial practice. Therefore, the separation of mixed salts of sodium chloride and magnesium sulfate by flotation has not been seen in industrial practice.

For the separation of magnesium sulfate and sodium chloride, a hot-melt crystallization method is generally adopted, namely, the magnesium sulfate is hot-melted by utilizing the characteristics of the solubility difference of the magnesium sulfate and the magnesium sulfate, the solubility of the sodium chloride is not changed greatly along with the temperature, the solubility of the magnesium sulfate is changed greatly along with the temperature, the sodium chloride is removed by solid-liquid separation, and the magnesium sulfate heptahydrate is obtained by mother liquor crystallization. A process experiment research of producing magnesium sulfate heptahydrate by a hot melt crystallization method is published in journal of inorganic salt industry in 2013 in Highen, a technology of extracting magnesium sulfate heptahydrate from potassium magnesium fertilizer workshop flotation tailings containing sodium chloride and magnesium sulfate by the hot melt crystallization method is introduced, and a magnesium sulfate heptahydrate product with the purity of 99.1% is obtained. However, the separation of sodium chloride and magnesium sulfate by the technology is not complete, the magnesium content in the dissolved slag is more than 8%, and a large part of magnesium still remains in the slag, so that the recovery rate of magnesium is low, and the technical economy is poor.

Disclosure of Invention

The invention aims to solve the defects in the prior art and provide the method for extracting the magnesium sulfate monohydrate and the industrial salt from the mixture of sodium chloride and magnesium sulfate, which has the advantages of mild operation conditions, thorough sodium-magnesium separation and high magnesium recovery rate.

The invention relates to a method for extracting magnesium sulfate monohydrate and industrial salt from mixed salt of sodium chloride and magnesium sulfate, which comprises the following steps:

(1) preparing a solvent: preparing a solvent with high selectivity by using various inorganic salts such as sodium chloride, magnesium sulfate or sodium sulfate and fresh water or brine;

(2) thermal dissolution: heating the solvent prepared in the step (1) to a required temperature, adding a mixed salt of sodium chloride and magnesium sulfate, stirring and dissolving for 30-60min, and selectively dissolving magnesium sulfate and sodium chloride;

(3) solid-liquid separation: after the thermal dissolution is finished, carrying out solid-liquid separation, wherein the filtrate is dissolved mother liquor and enters the step (4), and the filter cake is crude sodium chloride and enters the step (5);

(4) preparation of magnesium sulfate monohydrate: cooling and crystallizing the dissolved mother liquor to separate out magnesium sulfate heptahydrate, filtering to obtain crude magnesium sulfate after crystallization is finished, returning the filtered crystallized mother liquor to the step (1) for recycling, washing and refining the crude magnesium sulfate by adopting fresh water pulping to obtain wet magnesium sulfate heptahydrate, and drying the wet magnesium sulfate heptahydrate to obtain a magnesium sulfate monohydrate product;

(5) recovery of industrial salt: and (4) washing and refining the crude sodium chloride generated in the step (3) by adopting a saturated sodium chloride solution, and then drying to obtain an industrial salt product.

In the method, the solvent prepared in the step (1) is a low-sodium high-magnesium solution, wherein Mg²⁺The mass percentage of the content is 7.3% -8.7%, and Cl^-The content of the sodium chloride-magnesium sulfate solvent is 19.4-25.8% by mass, the solvent has high selectivity on magnesium sulfate, magnesium sulfate in a mixture of sodium chloride and magnesium sulfate can be dissolved to the maximum extent, the dissolution of sodium chloride is inhibited, and the high-efficiency separation of sodium chloride and magnesium sulfate can be realized by using the solvent.

According to the method, the thermal dissolution temperature in the step (2) is 60-75 ℃, the sodium-magnesium separation efficiency is high in the temperature range, 95% of magnesium sulfate in the mixture of sodium chloride and magnesium sulfate is dissolved into the solution, 95% of sodium chloride is remained in the dissolved slag solid, and the mass percentage of NaCl in the dissolved slag is more than or equal to 87%.

In the method, in the step (4), the dissolved mother liquor is cooled to 10-35 ℃ through natural cooling or forced cooling for cold crystallization, 95-100% of magnesium sulfate in the dissolved mother liquor is crystallized and separated out to form crude magnesium sulfate, and the crude magnesium sulfate contains 8-10% of sodium chloride and 9-9.5% of Mg.

In the method, in the step (4), the crystallization mother liquor after the magnesium sulfate heptahydrate is separated out is returned to the step (1) for recycling and is used as a solvent required by the thermal dissolution in the step (2), and the crystallization mother liquor is returned to 100% for recycling, so that fresh water resources are effectively saved.

In the method, in the step (4), the liquid-solid ratio of the fresh water pulping and washing crude magnesium sulfate is 0.33-0.4: 1, the washing temperature is 0-30 ℃, and the Cl content in wet magnesium sulfate heptahydrate obtained after washing is less than or equal to 0.85% by mass.

According to the method, the mass percent of Mg in the recovered magnesium sulfate monohydrate product is more than or equal to 16.5%, the mass percent of Cl is less than or equal to 1.50%, the mass percent of NaCl in the recovered industrial salt product is more than or equal to 98.5%, the magnesium sulfate monohydrate product meets the requirements of HG/T2680-2017 industrial magnesium sulfate and GB/T26568-.

In the method, the NaCl content in the mixed salt of sodium chloride and magnesium sulfate is more than or equal to 10 percent by mass.

Compared with the prior art, the invention has the remarkable improvements that:

(1) by preparing a unique solvent with high selectivity, the mixture of sodium chloride and magnesium sulfate is effectively separated by adopting a traditional hot melt crystallization method, the magnesium sulfate can be dissolved by the solvent to the maximum extent, the dissolution of the sodium chloride is inhibited, 95% of the magnesium sulfate is dissolved into the solution, and 95% of the sodium chloride is remained in the dissolved slag solid.

(2) The crystallization mother liquor of the prepared solvent after the mixed salt is dissolved in heat and the magnesium sulfate is separated out by crystallization is the same as the solvent prepared initially, the selectivity for the magnesium sulfate is still good, the solvent can be recycled by 100 percent, a closed cycle process is formed, the solvent consumption is less, and the fresh water resource is saved.

(3) By adopting the method, the magnesium sulfate monohydrate product meeting the requirements of HG/T2680-2017 industrial magnesium sulfate and GB/T26568-2011 agricultural magnesium sulfate and the refined industrial salt product meeting the requirements of GB/T3462-2016 industrial salt are finally recovered, the impurity content of the product is low, the recovery rates of sodium chloride and magnesium sulfate are high, the recovery rate of magnesium is more than or equal to 70 percent, and the recovery rate of sodium is more than or equal to 85 percent.

In conclusion, the method is suitable for treating the mixed salt of sodium chloride and magnesium sulfate, including the high-temperature salt which is a byproduct in the process of producing potassium chloride by using bittern in the sea salt chemical industry and the epsomite which is separated out in the process of sun-curing salt lake brine and contains sodium chloride. The method has the advantages of simple process, high separation efficiency, high recovery rate, easy operation and easy realization of large-scale industrial production.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

In order to make the above objects, features and advantages of the present invention more comprehensible, the following description will be given of a method for extracting magnesium sulfate monohydrate and industrial salts from a mixed salt of sodium chloride and magnesium sulfate according to the present invention with reference to examples. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. The present invention may be embodied in many different forms other than those herein described and it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention and these changes and modifications are to be considered in the light of the above teachings.

Example 1

(1) Preparing a solvent: preparing solvent with high selectivity to magnesium sulfate from inorganic salts such as sodium chloride, magnesium chloride and magnesium sulfate and fresh water²⁺7.3 percent of Cl^-The content mass percentage is 19.4%;

(2) thermal dissolution: heating the solvent prepared in the step (1) to 75 ℃, adding a mixed salt of sodium chloride and magnesium sulfate, stirring and dissolving for 60min, and selectively dissolving magnesium sulfate and sodium chloride;

(3) solid-liquid separation: after the thermal dissolution is finished, carrying out solid-liquid separation, wherein the filtrate is dissolved mother liquor and enters the step (4), and the filter cake is crude sodium chloride and enters the step (5);

(4) preparation of magnesium sulfate monohydrate: cooling the dissolved mother liquor to 35 ℃ to crystallize and separate out magnesium sulfate heptahydrate, filtering to obtain crude magnesium sulfate after crystallization is finished, returning the filtered crystallized mother liquor to the step (1) for recycling, pulping and washing the crude magnesium sulfate by adopting fresh water with a liquid-solid ratio of 0.33:1 at 0 ℃ to obtain wet magnesium sulfate heptahydrate, and drying the wet magnesium sulfate heptahydrate to obtain a magnesium sulfate monohydrate product;

(5) recovery of industrial salt: and (4) washing and refining the crude sodium chloride generated in the step (3) by adopting a saturated sodium chloride solution, and then drying to obtain an industrial salt product.

The relevant material chemistry data for example 1 are shown in table 1.

Example 2

(1) Preparing a solvent: preparing solvent with high selectivity to magnesium sulfate, Mg, from inorganic salts such as sodium chloride, magnesium sulfate and sodium sulfate and bittern²⁺8.7 percent of Cl^-The content mass percentage is 25.8%;

(2) thermal dissolution: heating the solvent prepared in the step (1) to 60 ℃, adding a mixed salt of sodium chloride and magnesium sulfate, stirring and dissolving for 30min, and selectively dissolving magnesium sulfate and not dissolving sodium chloride;

(3) solid-liquid separation: after the thermal dissolution is finished, carrying out solid-liquid separation, wherein the filtrate is dissolved mother liquor and enters the step (4), and the filter cake is crude sodium chloride and enters the step (5);

(4) preparation of magnesium sulfate monohydrate: crystallizing the dissolved mother liquor to separate magnesium sulfate heptahydrate by cooling to 0 ℃, filtering to obtain crude magnesium sulfate after crystallization, returning the filtered crystallized mother liquor to the step (1) for recycling, pulping and washing the crude magnesium sulfate by adopting fresh water with a liquid-solid ratio of 0.4:1 at 30 ℃ to obtain wet magnesium sulfate heptahydrate, and drying the wet magnesium sulfate heptahydrate to obtain a magnesium sulfate monohydrate product;

(5) recovery of industrial salt: and (4) washing and refining the crude sodium chloride generated in the step (3) by adopting a saturated sodium chloride solution, and then drying to obtain an industrial salt product.

The chemical composition data of the relevant materials for example 2 are shown in table 2.

Example 3

(1) Preparing a solvent: preparing solvent with high selectivity to magnesium sulfate, Mg, from inorganic salts such as sodium chloride, magnesium sulfate and sodium sulfate and bittern²⁺8.01 percent of Cl^-The content mass percentage is 21.19%;

(2) thermal dissolution: heating the solvent prepared in the step (1) to 65 ℃, adding a mixed salt of sodium chloride and magnesium sulfate, stirring and dissolving for 40min, and selectively dissolving magnesium sulfate and sodium chloride;

(3) solid-liquid separation: after the thermal dissolution is finished, carrying out solid-liquid separation, wherein the filtrate is dissolved mother liquor and enters the step (4), and the filter cake is crude sodium chloride and enters the step (5);

(4) preparation of magnesium sulfate monohydrate: cooling the dissolved mother liquor to 25 ℃, crystallizing to separate out magnesium sulfate heptahydrate, filtering to obtain crude magnesium sulfate after crystallization is finished, returning the filtered crystallized mother liquor to the step (1) for recycling, pulping and washing the crude magnesium sulfate by adopting fresh water with a liquid-solid ratio of 0.35:1 at 25 ℃ to obtain wet magnesium sulfate heptahydrate, and drying the wet magnesium sulfate heptahydrate to obtain a magnesium sulfate monohydrate product;

(5) recovery of industrial salt: and (4) washing and refining the crude sodium chloride generated in the step (3) by adopting a saturated sodium chloride solution, and then drying to obtain an industrial salt product.

The relevant material chemistry data for example 3 is shown in table 3.