CN113044860A - Method for preparing anhydrous ammonium magnesium double salt by using brine - Google Patents
Method for preparing anhydrous ammonium magnesium double salt by using brine Download PDFInfo
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Abstract
The invention discloses a method for preparing anhydrous ammonium magnesium double salt by using brine, which comprises the following steps: s1, adding a certain amount of ammonium chloride into refined brine to prepare a saturated solution at the temperature of 80-90 ℃; s2, cooling the saturated solution prepared in the step S1 to 30-40 ℃, cooling and crystallizing, and performing solid-liquid separation to obtain a hydrous magnesium ammonium double salt crystal; s3, evaporating and concentrating the filtrate obtained after the solid-liquid separation in the step S2 to a saturated solution at the temperature of 80-90 ℃, mixing the saturated solution with the fresh saturated solution prepared in the step S1, and then performing cooling crystallization in the step S2 to realize the recycling of the filtrate; and S4, dynamically drying and deeply dehydrating the hydrous ammonium-magnesium double salt crystal obtained in the step S2 to obtain the anhydrous ammonium-magnesium double salt. The invention has low production cost and simple process, and the produced anhydrous ammonium magnesium double salt has high purity and stable quality.
Description
Technical Field
The invention belongs to the technical field of inorganic chemical industry, and particularly relates to a method for preparing anhydrous ammonium-magnesium double salt by using brine.
Background
At present, the thermal reduction method and the electrolytic method are two main industrial methods for smelting metal magnesium. Although the thermal reduction method has simple process and low production cost, the method has serious environmental impact and has the following defects because the production process discharges too much greenhouse gas. In contrast, the electrolytic process is cleaner. Because the raw material for smelting the metal magnesium by the thermal reduction method is dolomite, if brine resources taking magnesium chloride which is a byproduct in potassium chloride production in Qinghai salt lake in China as a main chemical component are used as the raw material for producing the metal magnesium, only the process of the electrolytic anhydrous magnesium chloride method can be selected. The electrolyte molten salt system for smelting magnesium by electrolysis is prepared by mixing anhydrous magnesium chloride and other salts (such as potassium chloride, sodium chloride, etc.) in proportion and melting. For a long time, the preparation of anhydrous magnesium chloride is a technical bottleneck in the process of smelting magnesium by an electrolytic method and is one of the main factors with high cost.
The preparation method of anhydrous magnesium chloride mainly comprises four methods according to different raw materials and processes:
(1) and (3) performing direct pyrolysis dehydration on the magnesium chloride hydrate under the atmosphere of hydrogen chloride gas. The brine raw material liquid is subjected to impurity removal and refining, solution evaporation, cooling and crystallization to obtain magnesium chloride hydrate crystals. If the hydrous magnesium chloride crystal is heated and dehydrated in the air atmosphere, the hydrous magnesium chloride crystal is completely hydrolyzed to generate magnesium oxide and hydrogen chloride gas; if the hydrous magnesium chloride crystal is heated and dehydrated in the atmosphere of a large amount of hydrogen chloride gas, serious hydrolysis can be avoided, and the obtained anhydrous magnesium chloride meets the requirements of the electrolytic magnesium-smelting process. At present, the dehydration of magnesium chloride hydrate under the protection of hydrogen chloride gas to prepare anhydrous magnesium chloride is a relatively mature process for preparing anhydrous magnesium chloride in the magnesium smelting process by an industrial electrolytic method. However, the main problem of this method is that hydrogen chloride is a corrosive gas, which causes severe corrosion of equipment at high temperatures; the side reaction can only be inhibited but can not be completely prevented, the content of magnesium oxide in the obtained anhydrous magnesium chloride is high, the purity of the anhydrous magnesium chloride is not high, and the current efficiency of the electrolysis process is influenced; in addition, the method has high cost and limits the competitiveness of the magnesium smelting process by an electrolytic method.
(2) Calcining magnesite, and chlorinating to prepare anhydrous magnesium chloride. The magnesite is calcined at high temperature to generate magnesium oxide, and the magnesium oxide reacts with chlorine at high temperature to generate anhydrous magnesium chloride. This method requires a large amount of chlorine gas, and thus safety and environmental pollution are two prominent problems. This process is now rarely used.
(3) Preparing anhydrous magnesium chloride by an ammonia complexing method. ZL200710179865.9 patent proposes that bischofite raw material is dissolved in organic solvent, water in the bischofite raw material is removed by distillation to form anhydrous magnesium chloride organic solution, then ammonia gas is introduced into the anhydrous magnesium chloride organic solvent to obtain magnesium chloride ammine complex crystal, and the ammine complex crystal is heated to deaminate to obtain high-purity anhydrous magnesium chloride. The obtained anhydrous magnesium chloride and other salts are melted together to prepare the electrolyte fused salt for smelting the gold by the electrolytic method. The method has the advantages of mild process conditions, high product purity, less waste discharge, easy large-scale production and the like, and is an advanced process for preparing the high-purity anhydrous magnesium chloride. The process has not been industrially applied.
(4) The anhydrous magnesium chloride is prepared by a double salt method. The magnesium chloride and other specific salts are subjected to solid phase reaction or solution crystallization to form water-containing double salt, and then the anhydrous magnesium chloride meeting the technical requirements of electrolytic magnesium smelting can be obtained by dehydration. ZL201110393808.7 provides a method for preparing anhydrous magnesium chloride from magnesium chloride hexahydrate, which comprises the steps of mixing and ball-milling magnesium chloride hexahydrate and ammonium chloride solid materials, and then heating and dehydrating to prepare the anhydrous magnesium chloride. ZL201710601232.6 proposes solid phase reaction between solid magnesium chloride hexahydrate and solid ammonium chloride at the temperature lower than 100 ℃ to form double salt, then adding proper amount of ammonium chloride to thoroughly dehydrate at the temperature of 200-350 ℃ to obtain a mixture of anhydrous double salt and ammonium chloride, and thermally decomposing and distilling to remove ammonium chloride under vacuum condition to obtain anhydrous magnesium chloride material. There is also a research report on the formation of double salt by magnesium chloride hydrate and aniline hydrochloride, followed by thermal decomposition to obtain anhydrous magnesium chloride material.
At present, the bottleneck problem of the magnesium smelting process by an electrolytic method is as follows: the electrolysis process has high requirement on the purity of the anhydrous magnesium chloride electrolyte fused salt, and the cost of the prepared anhydrous magnesium chloride electrolyte meeting the electrolysis requirement is high, so that the production cost of the electrolytic magnesium is overhigh, and the product lacks competitiveness. Therefore, it is required to minimize the content of magnesium oxide in the electrolyte molten salt by avoiding hydrolysis of hydrated magnesium chloride as much as possible in the process of preparing anhydrous magnesium chloride. More importantly, technical innovation is required, and a new technology with lower production cost is proposed.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a method for preparing anhydrous ammonium-magnesium double salt by using brine, aiming at the defects of the prior art, the method is low in production cost and simple in process, and the produced anhydrous ammonium-magnesium double salt is high in purity and stable in quality.
In order to solve the above technical problems, the present invention comprises:
a method for preparing anhydrous ammonium magnesium double salt by using brine comprises the following steps:
s1, firstly, determining the molar concentration of magnesium chloride in the refined brine solution at room temperature, and then adding solid ammonium chloride into the refined brine solution, wherein the molar ratio of the ammonium chloride to the magnesium chloride is 1-1.2; heating and stirring until the solid ammonium chloride is completely dissolved to obtain a new configuration saturated solution with the temperature of 80-90 ℃;
s2, pumping the newly-prepared saturated solution obtained in the step S1 into a cooling crystallizer, cooling to 30-40 ℃ for cooling crystallization, controlling the average residence time of the saturated solution in the cooling crystallizer to be 30-120 minutes, and leading out crystal slurry from the bottom of the cooling crystallizer for solid-liquid separation to obtain an ammonium-magnesium double salt crystal containing water;
s3, evaporating and concentrating the filtrate obtained after the solid-liquid separation in the step S2 to a circulating saturated solution at the temperature of 80-90 ℃, pumping the circulating saturated solution and the newly-configured saturated solution in the step S1 into a cooling crystallizer, mixing, and then performing cooling crystallization in the step S2 to realize the recycling of the filtrate;
and S4, dynamically drying and deeply dehydrating the crystal of the hydrous ammonium-magnesium double salt obtained in the step S2 to obtain the anhydrous ammonium-magnesium double salt.
Further, in step S1, the refined brine is prepared by removing impurities from a brine raw material solution: firstly, removing insoluble substances in brine raw material liquid by adopting filter pressing operation, and then removing trace impurity components in the brine raw material liquid to obtain refined brine solution; the trace impurity component includes boron and sulfate.
Further, the method for removing the boron element in the brine raw material liquid adopts a special boron removal resin adsorption removal method: according to the content of boron in the brine raw material liquid, performing one-stage or multi-stage boron removal operation, wherein each stage of boron removal operation is to pass the brine raw material liquid at the temperature of 30-40 ℃ through a boron removal resin tower to ensure that the retention time of the brine raw material liquid in the boron removal resin tower is 30-60 minutes; and when the boron content in the brine raw material liquid is less than 5ppm, ending the boron removal operation.
Further, the method for removing sulfate radicals in the brine raw material liquid adopts a barium chloride precipitation method.
Further, in the step S3, the evaporation and concentration of the filtrate adopts single-effect or multi-effect evaporation under negative pressure.
Further, in the step S3, the molar ratio of ammonium chloride to magnesium chloride in the mixed solution of the circulating saturated solution pumped into the cooling crystallizer and the newly prepared saturated solution is 1 to 1.2.
Further, in the step S3, the sum of the volumes of the circulating saturated solution pumped into the cooling crystallizer per unit time and the newly prepared saturated solution is equal to the volume of the solid-liquid separation crystal slurry drawn out in the step S2.
Further, in step S4, the dynamic drying is: the hydrous ammonium magnesium double salt crystal material is directly or indirectly contacted with a heat source with the temperature of 150 ℃ and 180 ℃ in a flowing state, and is dried for 30 to 60 minutes in a concurrent flow or countercurrent flow manner.
Further, in step S4, the deep dehydration is: the dried ammonium magnesium double salt crystal material is directly or indirectly contacted with a heat source with the temperature of 200-450 ℃, and is dehydrated for 30-60 minutes in the reactor in a concurrent flow or a countercurrent flow manner.
Further, in the step S4, after the water-containing ammonium-magnesium double salt is subjected to dynamic drying and deep dehydration, the water content of the obtained ammonium-magnesium double salt crystal is less than 1.0wt%
The invention has the beneficial effects that:
the method takes the brine as the raw material liquid, adopts the solution crystallization process to prepare the hydrous ammonium-magnesium double salt crystal, and obtains the ammonium-magnesium double salt with the water content of less than 1.0wt% through drying and deep dehydration, and has the advantages of low production cost, simple process, high purity of the produced anhydrous ammonium-magnesium double salt and stable quality. The anhydrous ammonium magnesium double salt prepared by the method can be used as a key ingredient of electrolyte molten salt for smelting magnesium by an electrolytic method.
Drawings
FIG. 1 is a process flow diagram for preparing anhydrous ammonium magnesium double salt by using brine;
fig. 2 is an XRD pattern of the ammonium magnesium double salt crystal prepared by the method of the present invention.
Detailed Description
For the purpose of promoting an understanding of the invention, reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
As shown in fig. 1, the present invention provides a method for preparing anhydrous ammonium magnesium double salt by using brine, comprising the following steps:
s1, firstly, determining the molar concentration of magnesium chloride in the refined brine solution at room temperature, and then adding solid ammonium chloride into the refined brine solution, wherein the molar ratio of the ammonium chloride to the magnesium chloride is 1-1.2; heating and stirring until the solid ammonium chloride is completely dissolved to obtain a new configuration saturated solution with the temperature of 80-90 ℃;
in step S1, the refined brine is prepared by removing impurities from brine raw material liquid: firstly, removing insoluble substances such as silt and the like in brine raw material liquid by adopting filter pressing operation, and then removing trace impurity components to obtain refined brine solution; the trace impurity component includes boron and sulfate.
The method for removing the boron element in the brine raw material liquid adopts a special boron removal resin adsorption removal method: according to the content of boron in the brine raw material liquid, performing one-stage or multi-stage boron removal operation, wherein each stage of boron removal operation is to pass the brine raw material liquid at the temperature of 30-40 ℃ through a boron removal resin tower, control the flow rate of fluid and ensure that the retention time of the brine raw material liquid in the boron removal resin tower is 30-60 minutes; and when the boron content in the brine raw material liquid is less than 5ppm, ending the boron removal operation.
The method for removing sulfate radicals in the brine raw material liquid adopts a barium chloride precipitation method. According to the concentration of sulfate radicals in the brine after boron removal, a proper amount of barium chloride solution is added into the brine, and the mixture is fully mixed and stood to generate barium sulfate precipitate, so that the sulfate radicals in the brine raw material liquid can be thoroughly removed. The brine raw material liquid has different sources and different production places, and the types and the contents of impurity ions in the brine raw material liquid are different. Impurity removal and refining of the brine, and also removal of other impurity ions which have adverse effects on the electrolytic magnesium smelting process.
S2, pumping the newly-prepared saturated solution obtained in the step S1 into a cooling crystallizer, cooling to 30-40 ℃ for cooling crystallization, controlling the average residence time of the saturated solution in the cooling crystallizer to be 30-120 minutes, and leading out crystal slurry from the bottom of the cooling crystallizer for solid-liquid separation to obtain an ammonium-magnesium double salt crystal containing water;
s3, evaporating and concentrating the filtrate obtained after the solid-liquid separation in the step S2 to a circulating saturated solution at the temperature of 80-90 ℃, pumping the circulating saturated solution and the newly-configured saturated solution in the step S1 into a cooling crystallizer, mixing, and then performing cooling crystallization in the step S2 to realize the recycling of the filtrate;
in step S3, the evaporation and concentration of the filtrate adopts single-effect or multi-effect evaporation under negative pressure. The molar ratio of ammonium chloride to magnesium chloride in the mixed solution of the circulating saturated solution pumped into the cooling crystallizer and the newly prepared saturated solution is 1-1.2.
In the step S3, the sum of the volumes of the circulating saturated solution pumped into the cooling crystallizer in unit time and the newly prepared saturated solution is equal to the volume of the solid-liquid separation crystal slurry led out in the step S2, the volume and the chemical composition of the material in the cooling crystallizer are kept stable, and the long-term continuous operation of the steps S1-S3 is realized.
And S4, dynamically drying the hydrous ammonium-magnesium double salt crystal obtained in the step S2 (removing part of water carried by the crystal, and then carrying out drying on the dried ammonium-magnesium double salt crystal) and deeply dehydrating to obtain the anhydrous ammonium-magnesium double salt.
In step S4, the dynamic drying is: the hydrous ammonium magnesium double salt crystal material is directly or indirectly contacted with a heat source with the temperature of 150 ℃ and 180 ℃ in a flowing state, and is dried for 30 to 60 minutes in a concurrent flow or countercurrent flow manner. After dynamic drying, all free water and part of crystal water are removed from the hydrous ammonium-magnesium double salt crystal, and meanwhile, the flowing property of the crystal material is improved. The deep dehydration comprises the following steps: the dried ammonium magnesium double salt crystal material is directly or indirectly contacted with a heat source with the temperature of 200-450 ℃, and is dehydrated for 30-60 minutes in a rotary kiln, a mechanical vibration bed, a bubbling bed, a fast fluidized bed and other reactors in a deep mode in a cocurrent or countercurrent mode.
In step S4, after the water-containing ammonium-magnesium double salt is subjected to dynamic drying and deep dehydration, the crystal of the obtained ammonium-magnesium double salt has a water content of less than 1.0wt%, and thus severe hydrolysis in the electrolyte molten salt preparation process can be avoided. The prepared anhydrous ammonium magnesium double salt can remove ammonium chloride at the temperature of more than 450 ℃ to obtain anhydrous magnesium chloride which is used for preparing electrolyte fused salt for electrolytic smelting of magnesium.
Example 1:
a filter area of 22m is used2Small plate-and-frame filter press filtering 10m3Brine raw material liquid to obtain clarified brine raw material liquid.
The boron content in the brine raw material liquid is measured to be 36ppm by adopting an azomethine-H acid spectrophotometry. At 2m3The flow rate of the raw brine is 10 cubic meters and the temperature of the raw brine is 30 ℃ and the raw brine passes through a boron removal resin tower which is 800 multiplied by 1200 to carry out boron removal operation. Sampling is carried out at the outlet of the tank once every 1 hour, and the average content of boron in the brine raw material liquid after boron removal operation is measured to be 7.5 ppm. And then carrying out secondary boron removal operation, and measuring that the average content of boron elements in the brine after secondary boron removal is less than 1 ppm. And (3) carrying out two resin boron removal operations on 10 cubic portions of brine raw material liquid to obtain the brine raw material liquid with boron elements completely removed.
The brine raw material solution used in the test has the content of sulfate radical and iron ion less than 0.01wt%, so that the special removal of sulfate radical and iron ion is not carried out.
The brine raw material liquid is subjected to filter pressing, resin boron removal and other impurity removal refining treatments to obtain 10m3Refined brine raw material liquid with the magnesium chloride concentration of 385 g/L is put into a brine raw material liquid storage tank for standby.
Example 2:
2m is3The refined brine prepared in example 1 was transferred to a preparation tank, and 435 kg of industrial ammonium chloride was added thereto, and while stirring was continued, steam was introduced into a jacket of the preparation tank to heat the brine. When the temperature rises to 86 ℃, the ammonium chloride is completely dissolved, the steam is stopped to be introduced, and the preparation of the crystallization saturated solution is finished.
And (3) introducing cooling water of 15 ℃ into a jacket of the liquid preparation tank, adjusting the rotating speed of the stirrer to be 5r/min, and modifying the liquid preparation tank into a crystallizer for use. The temperature of the crystallization solution is reduced from 85 ℃ to 35 ℃ in about 40 minutes, and then the cold water is stopped from being introduced into the jacket.
And pumping the slurry into a centrifugal separator in batches from a crystal slurry outlet at the bottom of the crystallizer for solid-liquid separation. The crystal material is packaged, sealed and stored for standby, and the filtrate is pumped into a storage tank for standby.
Weighing 20 g of crystal sample by an electronic balance (accurate to milligram), measuring magnesium ions in the crystal sample by using the national standard GB/T13025.6-2012, measuring chloride ions in the crystal sample by using the national standard GB/T13025.5-2012, and calculating the composition of the crystal sample by neglecting other ions: the content of the aqueous ammonium magnesium double salt is 96.20 wt%; 2.48wt% ammonium chloride and 1.32wt% free water. FIG. 2 is an XRD pattern of a crystal sample.
Example 3:
1.5m obtained by solid-liquid separation of example 23The filtrate was pumped into a single effect evaporator and after evaporating 300 l of water under negative pressure, the remaining 85 ℃ concentrate was sent to a make-up tank (also used as a crystallizer).
0.6m3The refined brine prepared in example 1 was transferred to a blending tank, mixed with the concentrate, and then 150 kg of industrial ammonium chloride was added thereto, while continuously stirring, and steam was introduced into a jacket of the blending tank to heat the brine. When the temperature rises to 83 ℃, the ammonium chloride is completely dissolved, and the introduction of the steam is stoppedAnd (5) steam.
And (3) introducing cooling water of 15 ℃ into a jacket of the crystallizer, and adjusting the rotating speed of the stirrer to be 5 r/min. Controlling the flow rate of cold water, controlling the temperature reduction rate, controlling the temperature of the crystallization solution to be between 83 ℃ and 35 ℃ in 120 minutes, and stopping introducing the cold water into the jacket.
And (5) carrying out solid-liquid separation on the crystal mush. The crystal material is packaged, sealed and stored for standby, and the filtrate is pumped into a storage tank.
And (3) measuring magnesium ions and chloride ions in the crystal sample, and neglecting other ions, calculating the composition of the crystal sample as follows: 95.74wt% of aqueous ammonium magnesium double salt; 2.62wt% ammonium chloride and 1.64wt% free water.
Example 4:
and starting hot air ventilation systems such as an electric heater, a blower, an induced draft fan and the like, introducing dry hot air into a bubbling bed with the specification of 3000 × 20mm, and controlling the macroscopic air speed to be 0.5 m/s. After 30 minutes, the ventilation system was stable and the inlet hot air temperature of the bubbling bed was stable at 180 ℃.
25 kg of ammonium magnesium double salt crystal material is weighed and fed through a bubbling bed feeding port. The crystal material is dynamically dried under the action of hot air to remove surface free water and a part of crystal water. And controlling the crystal material to stay in the bubbling bed for 60 minutes, raising the temperature of the crystal material from room temperature to 132 ℃, discharging the dried crystal from a discharge port, and sealing and packaging.
Sampling analysis shows that the molar ratio of ammonium chloride to magnesium chloride in the dried crystal is 1.02, and the crystal water content in 1 mol of double salt is 2.05 mol.
Example 5:
the same drying apparatus as in example 4 was charged with hot air at 150 ℃. After stabilization, 25 kg of ammonium magnesium double salt crystals were added. Drying the crystal material in a bubbling bed for 35 minutes, discharging, sealing and packaging.
Sampling analysis shows that the molar ratio of ammonium chloride to magnesium chloride in the dried crystal is 1.17, and the crystal water content in 1 mole of double salt is 3.96 moles.
Example 6:
the same bubbling bed apparatus as in examples 4 and 5. And starting hot air ventilation systems such as an electric heater, a blower, an induced draft fan and the like, introducing hot air into the bubbling bed, and controlling the macroscopic air speed to be 0.5 m/s. After 30 minutes, the ventilation system was stable and the inlet hot air temperature of the bubbling bed was stable at 280 ℃.
25 kg of dried ammonium magnesium double salt crystal material is weighed and fed through a charging opening of a bubbling bed. The crystal material is deeply dehydrated under the action of hot air. And controlling the crystal material to stay in the bubbling bed for 30 minutes, gradually raising the temperature of the crystal material from room temperature to 230 ℃, then discharging the completely dehydrated ammonium-magnesium double salt crystal from a discharge port, and sealing, packaging and storing.
Sampling and analyzing, wherein the molar ratio of ammonium chloride to magnesium chloride in the deeply dehydrated crystal is 1.05, and no water is detected in the double-salt crystal material.
Example 7:
the same bubbling bed apparatus as in example 4, example 5 and example 6. And starting hot air ventilation systems such as an electric heater, a blower, an induced draft fan and the like, introducing hot air into the bubbling bed, and controlling the macroscopic air speed to be 0.5 m/s. After 30 minutes, the ventilation system was stable and the inlet hot air temperature of the bubbling bed was stable at 230 ℃.
25 kg of dried ammonium magnesium double salt crystal material is weighed and fed through a charging opening of a bubbling bed. The crystal material is deeply dehydrated under the action of hot air. And controlling the crystal material to stay in the bubbling bed for 60 minutes, gradually raising the temperature of the crystal material from room temperature to 209 ℃, then discharging the dehydrated ammonium-magnesium double salt crystal from a discharge port, and sealing, packaging and storing.
Sampling and analyzing, wherein the molar ratio of ammonium chloride to magnesium chloride in the deeply dehydrated crystal is 1.07, and no water is detected in the double-salt crystal material.
Although the present invention is illustrated by the above examples to show the detailed process parameters and process flows of the present invention, the present invention is not limited to the above detailed process parameters and process flows, i.e., it is not meant that the present invention is necessarily dependent on the above detailed process parameters and process flows to be practiced. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (10)
1. A method for preparing anhydrous ammonium magnesium double salt by using brine is characterized by comprising the following steps: the method comprises the following steps:
s1, firstly, determining the molar concentration of magnesium chloride in the refined brine solution at room temperature, and then adding solid ammonium chloride into the refined brine solution, wherein the molar ratio of the ammonium chloride to the magnesium chloride is 1-1.2; heating and stirring until the solid ammonium chloride is completely dissolved to obtain a new configuration saturated solution with the temperature of 80-90 ℃;
s2, pumping the newly-prepared saturated solution obtained in the step S1 into a cooling crystallizer, cooling to 30-40 ℃ for cooling crystallization, controlling the average residence time of the saturated solution in the cooling crystallizer to be 30-120 minutes, and leading out crystal slurry from the bottom of the cooling crystallizer for solid-liquid separation to obtain an ammonium-magnesium double salt crystal containing water;
s3, evaporating and concentrating the filtrate obtained after the solid-liquid separation in the step S2 to a circulating saturated solution at the temperature of 80-90 ℃, pumping the circulating saturated solution and the newly-configured saturated solution in the step S1 into a cooling crystallizer, mixing, and then performing cooling crystallization in the step S2 to realize the recycling of the filtrate;
and S4, dynamically drying and deeply dehydrating the crystal of the hydrous ammonium-magnesium double salt obtained in the step S2 to obtain the anhydrous ammonium-magnesium double salt.
2. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 1, wherein the method comprises the following steps: in the step S1, the refined brine is prepared by removing impurities from a brine raw material solution: firstly, removing insoluble substances in brine raw material liquid by adopting filter pressing operation, and then removing trace impurity components in the brine raw material liquid to obtain refined brine solution; the trace impurity component includes boron and sulfate.
3. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 2, wherein the method comprises the following steps: the method for removing the boron element in the brine raw material liquid adopts a special boron removal resin adsorption removal method: according to the content of boron in the brine raw material liquid, performing one-stage or multi-stage boron removal operation, wherein each stage of boron removal operation is to pass the brine raw material liquid at the temperature of 30-40 ℃ through a boron removal resin tower to ensure that the retention time of the brine raw material liquid in the boron removal resin tower is 30-60 minutes; and when the boron content in the brine raw material liquid is less than 5ppm, ending the boron removal operation.
4. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 2, wherein the method comprises the following steps: the method for removing sulfate radicals in the brine raw material liquid adopts a barium chloride precipitation method.
5. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 1, wherein the method comprises the following steps: in the step S3, the evaporation and concentration of the filtrate adopts single-effect or multi-effect evaporation under negative pressure.
6. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 1, wherein the method comprises the following steps: in the step S3, the molar ratio of ammonium chloride to magnesium chloride in the mixed solution of the circulating saturated solution pumped into the cooling crystallizer and the newly prepared saturated solution is 1-1.2.
7. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 1, wherein the method comprises the following steps: in the step S3, the sum of the volumes of the circulating saturated solution pumped into the cooling crystallizer per unit time and the newly prepared saturated solution is equal to the volume of the solid-liquid separation crystal slurry extracted in the step S2.
8. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 1, wherein the method comprises the following steps: in step S4, the dynamic drying is: the hydrous ammonium magnesium double salt crystal material is directly or indirectly contacted with a heat source with the temperature of 150 ℃ and 180 ℃ in a flowing state, and is dried for 30 to 60 minutes in a concurrent flow or countercurrent flow manner.
9. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 1, wherein the method comprises the following steps: in step S4, the deep dehydration is: the dried ammonium magnesium double salt crystal material is directly or indirectly contacted with a heat source with the temperature of 200-450 ℃, and is dehydrated for 30-60 minutes in the reactor in a concurrent flow or a countercurrent flow manner.
10. The method for preparing the anhydrous ammonium magnesium double salt by using the brine as claimed in claim 1, wherein the method comprises the following steps: in step S4, after the water-containing ammonium-magnesium double salt is subjected to dynamic drying and deep dehydration, the water content of the obtained ammonium-magnesium double salt crystal is less than 1.0 wt%.
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| Title |
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| 周宁波 等: "铵光卤石复盐的制备及结晶动力学研究", 《无机盐工业》 * |
| 李坚: "《轻稀贵金属冶金学》", 31 March 2018, 冶金工业出版社 * |
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