Preparation method of low-impurity high-purity potassium perchlorate

Abstract

The application belongs to the technical field of potassium perchlorate preparation, and particularly relates to a preparation method of low-impurity high-purity potassium perchlorate. The refined chlorate sodium electrolyte is introduced into a diaphragm-free circulating electrolysis system to be electrolyzed, so that the chlorate sodium in the electrolyte is converted into sodium perchlorate in the diaphragm-free circulating electrolysis system, sodium perchlorate reaction liquid is obtained, electrolysis discharge liquid containing accumulated impurities is discharged from the diaphragm-free circulating electrolysis system, potassium chloride is added into the sodium perchlorate reaction liquid to perform a double decomposition reaction, potassium perchlorate is precipitated, and double decomposition slurry containing potassium perchlorate crystals is obtained. Thus, through the precipitation impurity removal and fractional filtration process of the chlorate sodium raw material liquid, the pre-removal of calcium, magnesium, iron and water-insoluble impurities is realized, so that the problem that the impurities contained in the raw material enter the electrolysis and crystallization processes and cause the content of metal impurities and water-insoluble substances in the potassium perchlorate product to be high is solved.

Description

Technical Field

[0001] This invention belongs to the field of potassium perchlorate preparation technology, and in particular relates to a method for preparing low-impurity, high-purity potassium perchlorate. Background Technology

[0002] Potassium perchlorate is typically prepared using an electrolysis-metathesis process. First, a sodium chlorate solution is passed through a diaphragm-free electrolysis system to convert sodium chlorate into sodium perchlorate. Then, potassium chloride is added to initiate a metathesis reaction. The resulting material is concentrated, cooled for crystallization, separated from the solid, washed, and dried to obtain the potassium perchlorate product. To reduce production costs, some processes also recycle the electrolyte and mother liquor used for crystallization.

[0003] However, during the recycling of electrolyte and crystallization mother liquor, impurities such as calcium, magnesium, iron, chloride, chlorate and sodium salt are easily accumulated and carried or attached to the surface of potassium perchlorate crystals during the crystallization process, resulting in a decrease in product purity and fluctuations in impurity content, making it difficult to stably produce low-impurity, high-purity potassium perchlorate. Summary of the Invention

[0004] The purpose of this invention is to address the problem in the prior art mentioned in the background section that impurities such as calcium, magnesium, iron, chloride, chlorate, and sodium salts tend to accumulate gradually during the recycling of electrolyte and crystallization mother liquor, and are carried or attached to the surface of potassium perchlorate crystals during crystallization, resulting in decreased product purity, fluctuations in impurity content, and difficulty in stably producing low-impurity, high-purity potassium perchlorate.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing low-impurity, high-purity potassium perchlorate, comprising the following steps:

[0006] S1. Prepare sodium chlorate raw material into sodium chlorate raw material solution, and perform precipitation to remove impurities and graded filtration on the sodium chlorate raw material solution to obtain refined sodium chlorate electrolyte;

[0007] S2. The refined sodium chlorate electrolyte is passed into a diaphragm-free circulating electrolysis system for electrolysis, so that the sodium chlorate in it is converted into sodium perchlorate, and sodium perchlorate reaction solution is obtained. Electrolyte containing accumulated impurities is discharged from the diaphragm-free circulating electrolysis system.

[0008] S3. Potassium chloride is added to the sodium perchlorate reaction solution to carry out a metathesis reaction, causing potassium perchlorate to precipitate and obtaining a metathesis slurry containing potassium perchlorate crystals.

[0009] S4. The metathesis slurry is concentrated under reduced pressure and crystallized under cooling, followed by solid-liquid separation to obtain wet potassium perchlorate crystals and crystallization mother liquor.

[0010] S5. Wash the wet potassium perchlorate crystals with a saturated potassium perchlorate washing solution, and then dry the washed wet potassium perchlorate crystals to obtain low-impurity, high-purity potassium perchlorate.

[0011] The crystallization mother liquor is divided into a mother liquor reuse portion and a mother liquor discharge portion. The mother liquor reuse portion is treated to remove impurities and then returned to step S3, while the mother liquor discharge portion is discharged from the preparation system.

[0012] Specifically, in step S1, the pH value of the sodium chlorate raw material solution is first adjusted so that the calcium ions, magnesium ions and iron ions in the sodium chlorate raw material solution form precipitates, and then primary filtration and secondary filtration are performed in sequence; the filtration accuracy of the primary filtration is 20-80 μm, and the filtration accuracy of the secondary filtration is 1-10 μm.

[0013] Specifically, in step S2, the refined sodium chlorate electrolyte is electrolyzed under conditions of a current density of 12-18 A / dm², an electrolysis temperature of 55-65°C, and a pH of 9.0-10.0 until the sodium chlorate concentration in the sodium perchlorate reaction solution is not higher than 10 g / L.

[0014] Specifically, the diaphragm-free circulating electrolysis system includes at least two parallel-flow electrolytic cells. The anode and cathode in each parallel-flow electrolytic cell are spaced apart and arranged in parallel. The electrolyte inlet and electrolyte outlet are respectively located at opposite ends of the parallel-flow electrolytic cell along the electrolyte flow direction, so that the electrolyte flows horizontally through the electrode gap between the anode and the cathode in sequence.

[0015] Specifically, each of the horizontal flow electrolytic cells is connected to the gas lift circulation pipe through an external circulation pipe. A gas distributor is provided at the lower part of the gas lift circulation pipe. The gas distributor supplies gas into the gas lift circulation pipe, causing the gas-liquid mixture in the gas lift circulation pipe to flow upward and causing the electrolyte to return to the horizontal flow electrolytic cell through the external circulation pipe.

[0016] Specifically, each of the horizontal flow electrolytic cells is provided with a drain outlet on the downstream side along the electrolyte flow direction, and the electrolytic discharge liquid in step S2 is discharged through the drain outlet; after solid-liquid separation, the electrolytic discharge liquid is used to obtain electrolytic recycled clear liquid and impurity-containing filter residue, the electrolytic recycled clear liquid is returned to the diaphragm-free circulating electrolysis system, and the impurity-containing filter residue is discharged from the preparation system.

[0017] Specifically, in step S3, the potassium chloride is added to the sodium perchlorate reaction solution in portions in the form of an aqueous potassium chloride solution. The molar ratio of potassium chloride to sodium perchlorate is 0.98:1 to 1.02:1, the double decomposition reaction temperature is 60 to 80°C, and the reaction time is 30 to 90 minutes.

[0018] Specifically, in step S4, the metathesis slurry is concentrated under reduced pressure at an absolute pressure of 20–60 kPa, and the concentrated metathesis slurry is cooled to 28–32 °C for crystallization.

[0019] Specifically, in step S5, the temperature of the potassium perchlorate saturated washing solution is 5-20°C, the liquid-solid mass ratio of the potassium perchlorate saturated washing solution to the potassium perchlorate wet crystals is 0.2:1-0.6:1, and the potassium perchlorate wet crystals are subjected to 2-3 stages of countercurrent washing; the washed potassium perchlorate wet crystals are then subjected to fluidized drying under the action of a drying gas at 70-110°C.

[0020] Specifically, the obtained potassium perchlorate contains a potassium perchlorate mass fraction of not less than 99.2%, a water mass fraction of not more than 0.02%, a chloride mass fraction (calculated as chloride ions) of not more than 0.05%, a chlorate mass fraction (calculated as chlorate ions) of not more than 0.05%, a sodium mass fraction of not more than 0.2%, a total calcium and magnesium mass fraction of not more than 0.2%, a water-insoluble matter mass fraction of not more than 0.01%, and an iron mass fraction of not more than 0.002%.

[0021] Compared with existing technologies, the advantages of this method for preparing high-purity, low-impurity potassium perchlorate are:

[0022] 1. This invention achieves the pre-removal of impurities such as calcium, magnesium, iron and water-insoluble matter through precipitation and graded filtration of sodium chlorate raw material solution. This solves the problem that impurities contained in the raw material enter the electrolysis and crystallization process, resulting in high content of metal impurities and water-insoluble matter in potassium perchlorate products.

[0023] 2. This invention achieves uniform circulation of electrolyte, stable control of electrolytic conversion degree, and timely discharge of accumulated impurities by using a diaphragm-free circulating electrolysis system, horizontal electrolysis and air stripping external circulation process, combined with solid-liquid separation and partial discharge of the electrolytic discharge liquid. This solves the problems of insufficient local reaction of electrolyte, chlorate residue and long-term circulation accumulation of impurities.

[0024] 3. This invention achieves sufficient growth of potassium perchlorate crystals, effective removal of impurities entrained in the mother liquor, and system impurity balance control through depressurization concentration and cooling crystallization of metathesis slurry, partial impurity removal and recycling of crystallization mother liquor and partial discharge, and saturated washing and fluidized drying of potassium perchlorate wet crystals. This solves the problems of chloride, sodium salt and other impurities accumulation caused by the complete recycling of crystallization mother liquor, as well as fluctuations in product purity and impurity content. Attached Figure Description

[0025] Figure 1 This is a schematic flowchart of the method for preparing low-impurity, high-purity potassium perchlorate provided by the present invention.

[0026] Figure 2 This is a schematic diagram of the reference results of the detection items in Embodiment 1 provided by the present invention;

[0027] Figure 3 This is a schematic diagram of the reference results for the detection items in Embodiment 2 provided by the present invention;

[0028] Figure 4 This is a schematic diagram of the detection results of Embodiment 3 provided by the present invention. Detailed Implementation

[0029] The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0030] like Figure 1 As shown, this application proposes a method for preparing low-impurity, high-purity potassium perchlorate, characterized by the following steps: S1, preparing sodium chlorate raw material into a sodium chlorate raw material solution, subjecting the sodium chlorate raw material solution to precipitation to remove impurities and graded filtration to obtain a refined sodium chlorate electrolyte; S2, passing the refined sodium chlorate electrolyte into a diaphragm-free circulating electrolysis system for electrolysis, converting the sodium chlorate in it into sodium perchlorate to obtain a sodium perchlorate reaction solution, and discharging the electrolyte containing accumulated impurities from the diaphragm-free circulating electrolysis system; S3, adding potassium chloride to the sodium perchlorate reaction solution for a metathesis reaction. S4. Potassium perchlorate is precipitated to obtain a metathesis slurry containing potassium perchlorate crystals; S5. The metathesis slurry is concentrated under reduced pressure and crystallized under cooling, followed by solid-liquid separation to obtain wet potassium perchlorate crystals and crystallization mother liquor; S6. The wet potassium perchlorate crystals are washed with a saturated potassium perchlorate washing solution and dried to obtain low-impurity, high-purity potassium perchlorate; wherein, the crystallization mother liquor is divided into a mother liquor reuse portion and a mother liquor discharge portion. The mother liquor reuse portion is treated to remove impurities and returned to step S3, while the mother liquor discharge portion is discharged from the preparation system.

[0031] It should be noted that the method for preparing low-impurity, high-purity potassium perchlorate described in this embodiment includes, in sequence, the purification of sodium chlorate feedstock solution, sodium chlorate circulating electrolysis, sodium perchlorate metathesis, potassium perchlorate concentration and crystallization, solid-liquid separation, crystal washing, and drying processes. Before entering the electrolysis process, the sodium chlorate feedstock solution undergoes precipitation and impurity removal and graded filtration to reduce the entry of calcium, magnesium, iron, and water-insoluble substances into the electrolyte. During the circulating electrolysis process, a portion of the electrolyte containing accumulated impurities is discharged. The crystallization mother liquor adopts a partial impurity removal and reuse and partial discharge operation mode to recover unused perchlorate and potassium ions, while avoiding the continuous accumulation of chloride, sodium ions, and other soluble impurities within the system. The wet potassium perchlorate crystals are washed with a saturated potassium perchlorate washing solution to reduce the dissolution loss of potassium perchlorate crystals during the washing process.

[0032] Specifically, sodium chlorate raw material is prepared into a sodium chlorate raw material solution, which is then purified by precipitation and graded filtration to obtain a refined sodium chlorate electrolyte. This refined electrolyte is then passed into a diaphragm-free circulating electrolysis system, where sodium chlorate is gradually converted into sodium perchlorate, while the electrolyte containing accumulated impurities is discharged. Potassium chloride is added to the sodium perchlorate reaction solution, causing perchlorate ions to combine with potassium ions and precipitate potassium perchlorate crystals. The metathesis slurry is then concentrated under reduced pressure, cooled for crystallization, and subjected to solid-liquid separation to obtain wet potassium perchlorate crystals and a mother liquor. The wet potassium perchlorate crystals are washed with a saturated washing solution and then dried. The mother liquor is divided into a reuse portion and a discharge portion. Thus, by continuously coordinating raw material impurity removal, circulating electrolysis impurity removal, mother liquor impurity removal, and crystal surface washing, the problem of impurities gradually accumulating and being carried into the potassium perchlorate crystals with the mother liquor during existing circulating production processes, leading to unstable product purity, is solved.

[0033] Furthermore, in step S1, the pH value of the sodium chlorate raw material solution is first adjusted so that the calcium ions, magnesium ions and iron ions in the sodium chlorate raw material solution form precipitates, and then primary filtration and secondary filtration are performed in sequence; the filtration accuracy of the primary filtration is 20-80 μm, and the filtration accuracy of the secondary filtration is 1-10 μm.

[0034] It should be noted that the precipitation and impurity removal described in this embodiment includes pH adjustment, stirring reaction, precipitation maturation, and filtration separation. The pH adjuster is added in stages and mixed with the sodium chlorate feed solution. While stirring, the pH value of the feed solution is kept uniform throughout to avoid the formation of a large number of fine precipitates due to excessively high local alkalinity. After pH adjustment, the reaction solution is stirred for a period of time and then allowed to stand for maturation, allowing the fine precipitates formed by calcium, magnesium, and iron to gradually aggregate into larger particles. Primary filtration is used to remove larger flocculent precipitates and mechanical impurities, while secondary filtration is used to remove the fine suspended particles remaining after primary filtration.

[0035] Specifically, a pH adjuster is gradually added to the sodium chlorate feed solution while stirring, causing the calcium, magnesium, and iron ions to convert into insoluble precipitates. After the precipitation reaction is complete, the reaction solution is filtered through a primary filter to remove larger precipitate particles, and then through a secondary filter to remove residual fine precipitates and suspended solids, resulting in a clear, refined sodium chlorate electrolyte. By removing metal ions and water-insoluble matter before electrolysis, the amount of impurities entering the sodium perchlorate reaction solution and subsequent potassium perchlorate crystals during electrolysis is reduced, thus addressing the issue of high calcium, magnesium, iron, and water-insoluble matter content in the product from the raw material stage.

[0036] Furthermore, in step S2, the refined sodium chlorate electrolyte is electrolyzed under conditions of a current density of 12-18 A / dm², an electrolysis temperature of 55-65°C, and a pH of 9.0-10.0 until the sodium chlorate concentration in the sodium perchlorate reaction solution is not higher than 10 g / L.

[0037] It should be noted that the electrolysis process described in this embodiment employs coordinated control of current density, electrolysis temperature, pH value, and electrolysis endpoint. Before electrolysis begins, the refined sodium chlorate electrolyte is circulated in a diaphragm-free circulating electrolysis system. Once the electrolyte temperature and flow state stabilize, the current is gradually applied. During electrolysis, the electrolyte temperature and pH value are monitored. If either temperature or pH value deviates from the set range, correction is made through heat exchange or the addition of a regulating agent. The electrolysis endpoint is determined by the residual sodium chlorate concentration in the sodium perchlorate reaction solution to minimize differences in conversion levels caused by operating only with a fixed electrolysis time.

[0038] Specifically, the refined sodium chlorate electrolyte circulates between the anode and cathode, where chlorate ions are gradually converted into perchlorate ions under electrochemical action. During electrolysis, the residual sodium chlorate in the reaction solution is continuously monitored. Electrolysis is stopped and the perchlorate reaction solution is discharged when the residual sodium chlorate concentration reaches the endpoint requirement. By controlling the reaction state of the electrolyte and determining the electrolysis endpoint based on the residual sodium chlorate concentration, the amount of unconverted chlorate entering the metathesis and crystallization processes is reduced, thus solving the problems of high chlorate impurity content and batch-to-batch fluctuations in potassium perchlorate products.

[0039] Furthermore, the diaphragm-free circulating electrolysis system includes at least two parallel-flow electrolytic cells, in which the anode and cathode are spaced apart and arranged in parallel. The electrolyte inlet and electrolyte outlet are respectively located at opposite ends of the parallel-flow electrolytic cell along the electrolyte flow direction, so that the electrolyte flows horizontally through the electrode gap between the anode and the cathode in sequence.

[0040] It should be noted that the diaphragmless circulating electrolysis system described in this embodiment employs at least two parallel-flow electrolytic cells. Multiple parallel-flow electrolytic cells can be connected in series, parallel, or a combination of series and parallel connections. The anodes and cathodes within each parallel-flow electrolytic cell are arranged alternately, with electrode gaps formed between adjacent anodes and cathodes to allow the electrolyte to pass through. The electrolyte inlet and outlet are located at opposite ends of the electrolytic cell along the electrolyte flow direction, allowing the electrolyte to enter from one end, flow horizontally through different electrode gaps, and then exit from the other end.

[0041] Specifically, the refined sodium perchlorate electrolyte enters from one end of a horizontal flow electrolytic cell, flows horizontally through the electrode gap between the anode and cathode, and is discharged from the other end of the cell for recirculation. The horizontal flow of the electrolyte continuously carries away bubbles, heat, and suspended impurities formed on the electrode surface, ensuring continuous flow and renewal of the electrolyte at different locations. By reducing stagnant areas within the electrolytic cell, the concentration, temperature, and reaction degree of the electrolyte become more uniform, solving the problem of uneven composition of the sodium perchlorate reaction solution caused by insufficient local electrolysis or impurity deposition, which in turn affects the purity of potassium perchlorate.

[0042] Furthermore, each of the horizontal flow electrolytic cells is connected to a gas lift circulation pipe via an external circulation pipe. A gas distributor is provided at the lower part of the gas lift circulation pipe. The gas distributor supplies gas into the gas lift circulation pipe, causing the gas-liquid mixture in the gas lift circulation pipe to flow upward and allowing the electrolyte to return to the horizontal flow electrolytic cell via the external circulation pipe.

[0043] It should be noted that the gas-lift external circulation process described in this embodiment involves introducing the electrolyte discharged from the horizontal flow electrolyzer into the gas-lift circulation pipe, and then introducing purified gas into the electrolyte from the lower part of the gas-lift circulation pipe. The gas is dispersed into multiple bubbles by a gas distributor, and the bubbles move upward within the gas-lift circulation pipe, causing the average density of the gas-liquid mixture to be lower than the density of the electrolyte in the horizontal flow electrolyzer, thereby creating a density difference that drives the electrolyte circulation. The electrolyte discharged from the upper part of the gas-lift circulation pipe returns to the horizontal flow electrolyzer through the external circulation pipeline.

[0044] Specifically, the electrolyte discharged from the horizontal flow electrolyzer enters the gas-lift circulation pipe. A gas distributor disperses the gas into the electrolyte, and as the bubbles rise, they carry the electrolyte upwards. The gas-liquid mixture reaches the upper part of the gas-lift circulation pipe where gas-liquid separation occurs. The separated electrolyte returns to the horizontal flow electrolyzer via an external circulation pipe, thus forming a continuous external gas-lift circulation. Through bubble lifting and external circulation mixing, the electrolyte in each horizontal flow electrolyzer is fully exchanged, reducing local concentration differences, temperature differences, and uneven current density, thus solving the problems of incomplete local reactions and impurity deposition affecting product purity.

[0045] Furthermore, each of the horizontal flow electrolytic cells is provided with a drain outlet on the downstream side along the electrolyte flow direction, and the electrolytic discharge liquid in step S2 is discharged through the drain outlet; after solid-liquid separation, the electrolytic discharge liquid is used to obtain electrolytic recycled clear liquid and impurity-containing filter residue, the electrolytic recycled clear liquid is returned to the diaphragm-free circulating electrolysis system, and the impurity-containing filter residue is discharged from the preparation system.

[0046] It should be noted that the drain outlet described in this embodiment is located on the downstream side of the horizontal flow electrolyzer along the direction of electrolyte flow. When the electrolyte flows in the horizontal flow electrolyzer, it can gradually carry the deposited particles and suspended impurities to the downstream area. After solid-liquid separation, the filter residue containing impurities is discharged from the preparation system, and the resulting electrolytically recycled clear liquid is returned to the diaphragm-free circulating electrolysis system to recover the effective components in the clear liquid that can still be used for electrolysis. Before reuse, the suspended solids content and the content of major impurities in the electrolytically recycled clear liquid can be tested to prevent clear liquid that does not meet the reuse requirements from directly entering the circulating electrolysis system.

[0047] Specifically, the electrolyte, carrying deposits and accumulated impurities, flows downstream of the horizontal flow electrolyzer. After being discharged through the drain outlet, solid-liquid separation is performed. The solid deposits are discharged along with the impurity-containing filter residue, while the separated electrolytically recycled liquid is returned to the diaphragm-free circulating electrolysis system to continue participating in electrolysis. Through downstream drainage and solid-liquid separation, deposits and suspended impurities formed during electrolysis are removed in a timely manner, reducing the amount of impurities adhering to the electrode surface or entering the metathesis process with the reaction liquid. This solves the problem of solid impurity accumulation affecting product purity as the electrolysis system operates for longer periods.

[0048] Furthermore, in step S3, the potassium chloride is added to the sodium perchlorate reaction solution in portions in the form of an aqueous potassium chloride solution, the molar ratio of potassium chloride to sodium perchlorate is 0.98:1 to 1.02:1, the double decomposition reaction temperature is 60 to 80°C, and the reaction time is 30 to 90 min.

[0049] It should be noted that the potassium chloride described in this embodiment is first prepared into an aqueous solution and filtered before being added to the sodium perchlorate reaction solution to remove mechanical impurities and water-insoluble matter from the potassium chloride raw material. The amount of potassium chloride added is calculated based on the actual content of sodium perchlorate in the sodium perchlorate reaction solution, rather than solely based on the theoretical amount of sodium perchlorate raw material to be added. The potassium chloride aqueous solution is added in stages, ensuring thorough mixing of the reaction solution after each addition before adding the next portion of the potassium chloride aqueous solution to avoid excessively high local potassium chloride concentrations.

[0050] Specifically, the filtered potassium chloride aqueous solution is added to the sodium perchlorate reaction solution in portions with continuous stirring. Sodium perchlorate and potassium chloride undergo a double decomposition reaction, producing potassium perchlorate with lower solubility and sodium chloride retained in the liquid phase. Potassium perchlorate gradually forms crystal nuclei and precipitates. By controlling the amount of potassium chloride used according to the actual content of sodium perchlorate, and by using portioned addition and thorough mixing, local excess potassium chloride and unreacted potassium chloride residue are reduced, thus solving the problem of high chloride content in the product caused by chloride inclusions on the surface of wet potassium perchlorate crystals.

[0051] Furthermore, in step S4, the metathesis slurry is concentrated under reduced pressure at an absolute pressure of 20–60 kPa, and the concentrated metathesis slurry is cooled to 28–32 °C for crystallization.

[0052] It should be noted that the vacuum concentration and cooling crystallization described in this embodiment are performed sequentially. After the metathesis reaction is completed, some water is removed under conditions below atmospheric pressure to bring the potassium perchlorate in the reaction solution to a suitable supersaturated state. During the concentration process, the slurry is kept in a slow-flowing or stirred state to prevent crystals from depositing in local areas. After concentration is completed, the slurry is gradually cooled to allow the supersaturated potassium perchlorate in the solution to continue to precipitate and to allow the formed crystals to gradually grow.

[0053] Specifically, the metathesis slurry is concentrated under reduced pressure, water evaporates at a lower temperature, and the concentration of potassium perchlorate in the liquid phase gradually increases. After reaching the concentration endpoint, the slurry is cooled to reduce the solubility of potassium perchlorate and promote further crystallization. Subsequently, solid-liquid separation is performed to obtain wet potassium perchlorate crystals and crystallization mother liquor. By using reduced pressure concentration and controlled cooling, crystals can grow sufficiently, reducing the number of small crystals and the encapsulation of mother liquor within the crystals. This solves the problem of sodium salts, chlorides, and unreacted chlorates being carried into the product along with the mother liquor.

[0054] Furthermore, in step S5, the temperature of the potassium perchlorate saturated washing solution is 5-20°C, and the liquid-solid mass ratio of the potassium perchlorate saturated washing solution to the potassium perchlorate wet crystals is 0.2:1-0.6:1. The potassium perchlorate wet crystals are subjected to 2-3 stages of countercurrent washing. After washing, the potassium perchlorate wet crystals are subjected to fluidized drying under the action of a drying gas at 70-110°C.

[0055] It should be noted that the potassium perchlorate saturated washing solution described in this embodiment is prepared by mixing purified water and potassium perchlorate and reaching a saturated state at the corresponding washing temperature. During countercurrent washing, the cleaner washing solution comes into contact with the wet potassium perchlorate crystals that have undergone previous washing. The washing solution is then used to wash the previous wet crystals with a higher mother liquor content. During fluidized bed drying, drying gas passes through the spaces between the wet crystal particles, causing the crystals to be in a dispersed or fluidized state, thereby ensuring that the crystals at different locations are heated uniformly.

[0056] Specifically, the wet potassium perchlorate crystals undergo multi-stage countercurrent washing. The saturated potassium perchlorate washing solution displaces the mother liquor adhering to the crystal surface, allowing sodium chloride, unreacted potassium chloride, chlorate, and soluble metal salts to enter the washing solution. After washing, the wet crystals undergo fluidized drying under the action of drying gas, removing moisture from the crystal surface and intergranular spaces. Saturated washing reduces potassium perchlorate dissolution loss, and countercurrent washing increases the degree of mother liquor replacement, thus addressing the problem of high chloride, chlorate, sodium, and moisture content in the product.

[0057] Furthermore, the obtained potassium perchlorate contains a potassium perchlorate mass fraction of not less than 99.2%, a water mass fraction of not more than 0.02%, a chloride mass fraction (calculated as chloride ions) of not more than 0.05%, a chlorate mass fraction (calculated as chlorate ions) of not more than 0.05%, a sodium mass fraction of not more than 0.2%, a total calcium and magnesium mass fraction of not more than 0.2%, a water-insoluble matter mass fraction of not more than 0.01%, and an iron mass fraction of not more than 0.002%.

[0058] It should be noted that the product quality indicators described in this embodiment correspond to the aforementioned impurity control steps. Specifically, potassium perchlorate content is used to evaluate the overall purity of the product; moisture content is used to evaluate the degree of dryness; chloride and sodium content mainly reflect the residual levels of the metathesis mother liquor and washing liquid; chlorate content mainly reflects the degree of sodium chlorate electrolytic conversion; and calcium, magnesium, iron, and water-insoluble matter mainly reflect the degree of sedimentation, impurity removal, and graded filtration of the raw material liquid. The content of calcium and magnesium is expressed as their total mass fraction to clarify the measurement standard.

[0059] Specifically, dried potassium perchlorate was sampled and tested for potassium perchlorate content, moisture, chloride, chlorate, sodium, calcium, magnesium, water-insoluble matter, and iron content. When the test results met the corresponding requirements, the product was collected as low-impurity, high-purity potassium perchlorate. By correlating the results of raw material impurity removal, electrolysis endpoint, metathesis ratio, concentration crystallization, crystal washing, and drying with various product indicators, the problem of fluctuations in the purity and impurity content of potassium perchlorate products between different production batches was solved, avoiding reliance solely on the final purity indicator and lacking process control.

[0060] Example

[0061] The following examples are used to further illustrate the preparation process of the present invention and the coordination relationship between the steps. The raw material amounts, process parameters, yields, and test results in the examples are all reference data and should not be regarded as actual production or test data that has been completed.

[0062] Example 1

[0063] This embodiment provides a method for preparing low-impurity, high-purity potassium perchlorate, including the following steps.

[0064] 1000 kg of sodium chlorate with a purity of 99.5% was added to purified water to prepare a sodium chlorate raw material solution with a mass fraction of 32%. A pH adjuster was slowly added while stirring to adjust the pH of the raw material solution to 9.5. Stirring was continued for 40 minutes, followed by standing for 60 minutes to allow calcium, magnesium, and iron impurities to precipitate.

[0065] The precipitated sodium chlorate feed solution is sequentially filtered through a primary filter with a filtration precision of 50 μm and a secondary filter with a filtration precision of 5 μm to obtain a refined sodium chlorate electrolyte. The water-insoluble matter, calcium, magnesium, and iron content in the refined sodium chlorate electrolyte are tested, and after confirming that it meets the requirements for electrolysis feed, it enters the circulating electrolysis process.

[0066] The refined sodium chlorate electrolyte was introduced into a diaphragm-free circulating electrolysis system and electrolyzed under conditions of a current density of 15 A / dm², an electrolysis temperature of 60 °C, and a pH of 9.5. During electrolysis, the electrolyte was continuously flowed through each parallel-flow electrolytic cell, and external air-lift circulation was used to promote electrolyte mixing. Electrolysis was stopped when the residual sodium chlorate concentration in the reaction solution dropped to 6.2 g / L, yielding a sodium perchlorate reaction solution.

[0067] During electrolysis, 2.0% of the total circulating electrolyte is discharged as electrolytic effluent. After solid-liquid separation, the resulting electrolytic recycled solution is returned to the circulating electrolysis system, while the filter residue containing impurities is discharged from the preparation system.

[0068] To determine the actual sodium perchlorate content in the sodium perchlorate reaction solution, potassium chloride was weighed according to a molar ratio of potassium chloride to sodium perchlorate of 1.00:1. A 25% (w / w) potassium chloride aqueous solution was prepared, filtered, and added to the sodium perchlorate reaction solution in three portions. The double decomposition reaction temperature was maintained at 70℃. After each addition, the mixture was stirred for 10 minutes, and after all the potassium chloride was added, the reaction continued for another 30 minutes, for a total reaction time of 60 minutes.

[0069] The metathesis slurry was concentrated under reduced pressure at an absolute pressure of 40 kPa. After concentration, the slurry temperature was slowly reduced to 30°C and kept at that temperature for 60 min for crystallization. Then, solid-liquid separation was performed to obtain wet potassium perchlorate crystals and crystallization mother liquor.

[0070] 75% of the crystallization mother liquor is recycled as mother liquor, and after removing suspended crystals and insoluble impurities, it is returned to the next batch of metathesis process; the remaining 25% is discharged from the preparation system as mother liquor discharge.

[0071] Potassium perchlorate wet crystals were subjected to a three-stage countercurrent washing process using a saturated potassium perchlorate washing solution at 10°C, with a liquid-to-solid mass ratio of 0.4:1. The washed wet crystals were then fluidized and dried using a drying gas at 90°C until the product moisture content met the control requirements.

[0072] In this embodiment, 1246 kg of potassium perchlorate product was obtained. The reference test results are as follows (e.g.) Figure 2 (As shown).

[0073] Example 2

[0074] 1000 kg of sodium chlorate with a purity of 99.5% was prepared into a sodium chlorate feed solution with a mass fraction of 30%. The pH value of the feed solution was adjusted to 9.0, stirred for 30 min, and allowed to stand for 45 min to mature. The feed solution was then passed through a primary filter with a filtration precision of 80 μm and a secondary filter with a filtration precision of 10 μm to obtain a purified sodium chlorate electrolyte.

[0075] The refined sodium chlorate electrolyte was circulated and electrolyzed at a current density of 12 A / dm², an electrolysis temperature of 55 °C, and a pH of 9.0 until the residual sodium chlorate concentration in the sodium perchlorate reaction solution was 9.7 g / L. During the electrolysis process, a portion of the electrolyte containing impurities was discharged. After solid-liquid separation, the recycled electrolyte was returned to the circulating electrolysis system, and the filter residue containing impurities was discharged.

[0076] A potassium chloride aqueous solution was added at a molar ratio of potassium chloride to sodium perchlorate of 0.98:1, and a metathesis reaction was carried out at 60°C for 90 min. The resulting metathesis slurry was concentrated under reduced pressure at 60 kPa and then cooled to 28°C for crystallization.

[0077] After solid-liquid separation, 70% of the crystallization mother liquor is returned to the metathesis process after impurity removal, while the remaining 30% is discharged. A two-stage countercurrent washing process is performed using a saturated potassium perchlorate washing solution at 20°C, with a liquid-to-solid mass ratio of 0.6:1. The washed wet crystals are then fluidized and dried using a drying gas at 70°C.

[0078] In this embodiment, 1231 kg of potassium perchlorate product was obtained. The reference test results are as follows (e.g.) Figure 3 (As shown).

[0079] Example 3

[0080] 1000 kg of sodium chlorate with a purity of 99.7% was prepared into a sodium chlorate feed solution with a mass fraction of 35%. The pH value of the feed solution was adjusted to 10.0, stirred for 60 min, and allowed to stand for 90 min to mature. The feed solution was then passed through a primary filter with a filtration precision of 20 μm and a secondary filter with a filtration precision of 1 μm to obtain a purified sodium chlorate electrolyte.

[0081] The refined sodium chlorate electrolyte was circulated and electrolyzed at a current density of 18 A / dm², an electrolysis temperature of 65 °C, and a pH of 10.0. Electrolysis was stopped when the residual sodium chlorate concentration in the sodium perchlorate reaction solution dropped to 4.1 g / L. After solid-liquid separation, the electrolyte was returned to the circulating electrolysis system, and the filter residue containing impurities was discharged.

[0082] A potassium chloride aqueous solution was added at a molar ratio of potassium chloride to sodium perchlorate of 1.02:1, and a metathesis reaction was carried out at 80°C for 30 min. The resulting metathesis slurry was concentrated under reduced pressure at 20 kPa and then cooled to 32°C for crystallization.

[0083] After solid-liquid separation, 80% of the crystallization mother liquor is returned to the metathesis process after impurity removal, while the remaining 20% ​​is discharged. A three-stage countercurrent washing process is performed using a saturated potassium perchlorate washing solution at 5°C, with a liquid-to-solid mass ratio of 0.2:1. The washed potassium perchlorate wet crystals are then fluidized and dried using a drying gas at 110°C.

[0084] In this embodiment, 1252 kg of potassium perchlorate product was obtained. The reference test results are as follows (e.g.) Figure 4 (As shown).

[0085] Comparative Example 1

[0086] This comparative example is basically the same as Example 1, except that the sodium chlorate raw material solution is not subjected to precipitation and impurity removal, but is directly electrolyzed after only one stage of filtration.

[0087] The reference test results for the obtained potassium perchlorate product are as follows: potassium perchlorate content 98.91%, total calcium and magnesium 0.27%, iron 0.0035%, and water-insoluble matter 0.019%.

[0088] The results indicate that subsequent crystal washing alone is insufficient to remove calcium, magnesium, iron, and fine insoluble matter introduced by sodium chlorate feedstock. Precipitation and graded filtration of the feedstock solution are crucial steps for the stable control of metallic impurities.

[0089] Comparative Example 2

[0090] This comparative example is basically the same as Example 1, except that: no mother liquor discharge section is set up for the crystallization mother liquor, and all of it is returned to the metathesis process after simple filtration, and the cycle is repeated for five batches.

[0091] The reference test results for the fifth batch of potassium perchlorate products are as follows: potassium perchlorate content 98.96%, chloride 0.083%, sodium element 0.31%, and chlorate 0.061%.

[0092] The results indicate that the complete reuse of the crystallization mother liquor will cause chloride, sodium ions and unreacted chlorate to gradually accumulate in the system. Therefore, it is necessary to divide the crystallization mother liquor into a reuse portion and a discharge portion, and maintain the system's impurity balance by discharging the mother liquor portion.

[0093] In summary, the working principle of this method for preparing low-impurity, high-purity potassium perchlorate is as follows: First, sodium chlorate raw material is prepared into a sodium chlorate raw material solution. Then, chloric acid is used to adjust the pH value of the sodium chlorate raw material solution, causing calcium, magnesium, and iron impurities in the raw material solution to precipitate. The precipitate and fine suspended impurities are removed by primary and secondary filtration to obtain a refined sodium chlorate electrolyte. Subsequently, the refined sodium chlorate electrolyte is introduced into a diaphragm-free circulating electrolysis system, allowing the electrolyte to circulate along the electrode gap between adjacent anodes and cathodes in a horizontal flow electrolytic cell, and utilizing… The mixing of electrolytes at different locations is promoted using air-lift external circulation, gradually converting sodium chlorate into sodium perchlorate. Simultaneously, the electrolyte discharge containing sediment and accumulated impurities is discharged from the downstream of the electrolytic cell. After solid-liquid separation, a portion of the clarified liquid is returned to the electrolysis system, while filter residue and a portion of the clarified liquid containing soluble impurities are discharged. After electrolysis, potassium chloride aqueous solution is added to the sodium perchlorate reaction solution in portions, causing a metathesis reaction between sodium perchlorate and potassium chloride, precipitating potassium perchlorate crystals. The resulting metathesis slurry is then concentrated under reduced pressure and reduced temperature. Potassium perchlorate is further precipitated and grown by warm crystallization. Solid-liquid separation yields wet potassium perchlorate crystals and a mother liquor. The mother liquor is divided into a reuse portion and a discharge portion. The reuse portion is returned to the metathesis reaction after impurity removal, while the discharge portion is used to remove accumulated chlorides, sodium salts, and other soluble impurities from the system. Finally, the wet potassium perchlorate crystals are countercurrently washed with a saturated potassium perchlorate washing solution to remove the mother liquor adhering to the crystal surface, as well as chlorides, chlorates, sodium salts, and metal salts. After fluidized bed drying, low-impurity, high-purity potassium perchlorate is obtained. This process, through the continuous coordination of raw material liquid precipitation and graded filtration, electrolysis process wastewater discharge, partial reuse and discharge of the mother liquor, and crystal washing, inhibits the gradual accumulation of impurities during the cyclic production process and reduces the amount of impurities carried or adhering to the potassium perchlorate crystals with the mother liquor. This solves the problems of continuous impurity accumulation, decreased product purity, and fluctuating impurity content between different batches caused by the recycling of electrolyte and mother liquor in existing potassium perchlorate production processes.

[0094] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing low-impurity, high-purity potassium perchlorate, characterized in that, Includes the following steps: S1. Prepare sodium chlorate raw material into sodium chlorate raw material solution, and perform precipitation to remove impurities and graded filtration on the sodium chlorate raw material solution to obtain refined sodium chlorate electrolyte; S2. The refined sodium chlorate electrolyte is passed into a diaphragm-free circulating electrolysis system for electrolysis, so that the sodium chlorate in it is converted into sodium perchlorate, and sodium perchlorate reaction solution is obtained. Electrolyte containing accumulated impurities is discharged from the diaphragm-free circulating electrolysis system. S3. Potassium chloride is added to the sodium perchlorate reaction solution to carry out a metathesis reaction, causing potassium perchlorate to precipitate and obtaining a metathesis slurry containing potassium perchlorate crystals. S4. The metathesis slurry is concentrated under reduced pressure and crystallized under cooling, followed by solid-liquid separation to obtain wet potassium perchlorate crystals and crystallization mother liquor. S5. Wash the wet potassium perchlorate crystals with a saturated potassium perchlorate washing solution, and then dry the washed wet potassium perchlorate crystals to obtain low-impurity, high-purity potassium perchlorate. The crystallization mother liquor is divided into a mother liquor reuse portion and a mother liquor discharge portion. The mother liquor reuse portion is treated to remove impurities and then returned to step S3, while the mother liquor discharge portion is discharged from the preparation system.

2. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 1, characterized in that, In step S1, the pH value of the sodium chlorate raw material solution is first adjusted so that the calcium ions, magnesium ions and iron ions in the sodium chlorate raw material solution form precipitates, and then primary filtration and secondary filtration are performed in sequence; the filtration accuracy of the primary filtration is 20-80 μm, and the filtration accuracy of the secondary filtration is 1-10 μm.

3. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 2, characterized in that, In step S2, the refined sodium chlorate electrolyte is electrolyzed under conditions of a current density of 12-18 A / dm², an electrolysis temperature of 55-65°C, and a pH of 9.0-10.0 until the sodium chlorate concentration in the sodium perchlorate reaction solution is not higher than 10 g / L.

4. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 3, characterized in that, The diaphragm-free circulating electrolysis system includes at least two parallel-flow electrolytic cells. The anode and cathode in each parallel-flow electrolytic cell are spaced apart and arranged in parallel. The electrolyte inlet and electrolyte outlet are respectively located at opposite ends of the parallel-flow electrolytic cell along the electrolyte flow direction, so that the electrolyte flows horizontally through the electrode gap between the anode and the cathode in sequence.

5. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 4, characterized in that, Each of the horizontal flow electrolytic cells is connected to the gas lift circulation pipe through an external circulation pipe. A gas distributor is provided at the lower part of the gas lift circulation pipe. The gas distributor delivers gas into the gas lift circulation pipe, causing the gas-liquid mixture in the gas lift circulation pipe to flow upward and causing the electrolyte to return to the horizontal flow electrolytic cell through the external circulation pipe.

6. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 5, characterized in that, Each of the horizontal flow electrolytic cells is provided with a drain outlet on the downstream side along the electrolyte flow direction. The electrolyte discharged in step S2 is discharged through the drain outlet. After solid-liquid separation, the electrolyte discharged is used to obtain electrolytic recycled clear liquid and impurity-containing filter residue. The electrolytic recycled clear liquid is returned to the diaphragm-free circulating electrolysis system, and the impurity-containing filter residue is discharged from the preparation system.

7. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 1, characterized in that, In step S3, potassium chloride is added to the sodium perchlorate reaction solution in portions in the form of potassium chloride aqueous solution. The molar ratio of potassium chloride to sodium perchlorate is 0.98:1 to 1.02:

1. The double decomposition reaction temperature is 60 to 80°C and the reaction time is 30 to 90 min.

8. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 7, characterized in that, In step S4, the metathesis slurry is concentrated under reduced pressure at an absolute pressure of 20–60 kPa, and the concentrated metathesis slurry is cooled to 28–32 °C for crystallization.

9. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 8, characterized in that, In step S5, the temperature of the potassium perchlorate saturated washing solution is 5-20°C, and the liquid-solid mass ratio of the potassium perchlorate saturated washing solution to the potassium perchlorate wet crystals is 0.2:1-0.6:

1. The potassium perchlorate wet crystals are subjected to 2-3 stages of countercurrent washing. After washing, the potassium perchlorate wet crystals are subjected to fluidized drying under the action of a drying gas at 70-110°C.

10. The method for preparing low-impurity, high-purity potassium perchlorate according to claim 9, characterized in that, The obtained potassium perchlorate contains a potassium perchlorate mass fraction of not less than 99.2%, a water mass fraction of not more than 0.02%, a chloride mass fraction (calculated as chloride ions) of not more than 0.05%, a chlorate mass fraction (calculated as chlorate ions) of not more than 0.05%, a sodium mass fraction of not more than 0.2%, a total calcium and magnesium mass fraction of not more than 0.2%, a water-insoluble matter mass fraction of not more than 0.01%, and an iron mass fraction of not more than 0.002%.

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