A method and system for producing food-grade potassium chloride

Abstract

The application relates to a production method of food-grade potassium chloride, and relates to the field of food additives. Raw materials are obtained from industrial potassium chloride or agricultural potassium chloride. Most of the potassium chloride is obtained by a flotation method from potassium-containing brine. Since nitrogen-containing collectors and anti-caking agents are added in the whole production process, the ammonium content of the finally produced potassium chloride product seriously exceeds the standard, and the grade of the potassium chloride is only 93-98%, which is difficult to meet the requirement that the purity of the food-grade potassium chloride is greater than or equal to 99%. In the application, the step-by-step ammonium removal process is used for the saturated potassium chloride solution. Most of the organic amines and magnesium and sodium ions adsorbed on the surface of the potassium chloride are removed by the washing+physical adsorption method, then the inorganic ammonium mixed in the potassium chloride crystals is removed by the dissolution+crystallization method, and finally the high-purity food-grade potassium chloride is obtained. The process flow of the application is simple, the operation cost is relatively low, the obtained potassium chloride has coarse granularity and high quality, the by-product ammonium magnesium phosphate can be used as a slow-release fertilizer, and tailing discharge is truly avoided.

Description

Technical Field

[0001] This invention relates to the field of food additives, and specifically to a method and system for producing food-grade potassium chloride. Background Technology

[0002] Food-grade potassium chloride is a very common product with a wide range of applications in the food industry. For example, it can be used as a salt substitute, nutritional supplement, gelling aid, yeast feed, flavoring agent, aroma enhancer, and pH control agent. It is one of the high-end products that can be derived from the potash fertilizer industry, and the market development potential of the food-grade potassium chloride industry is huge in the future.

[0003] Currently, the raw materials for producing food-grade potassium chloride both domestically and internationally are mostly industrial-grade potassium chloride. The production process basically follows the evaporation crystallization process, which includes dissolution, impurity removal, crystallization, filtration, and drying. This process can produce products that meet quality requirements, but it has high requirements for the quality of raw materials. Although my country is a country with severe potassium resource scarcity, the current domestic potassium chloride production capacity of the Qarhan Salt Lake is sufficient for self-sufficiency in the production of food-grade potassium chloride. However, according to research, most domestic manufacturers of food-grade potassium chloride use imported potassium as raw material, rather than relying on local sources. The reason for this is that most potassium chloride produced in my country is produced using conventional flotation methods, resulting in potassium chloride products containing a large number of impurities that cannot be removed by simple physical methods. These impurities mainly include ammonium chloride, magnesium chloride, octadecylamine flotation reagents, dodecylmorpholine flotation reagents, and calcium sulfate insoluble matter. In particular, the content of inorganic ammonium and organic amines is seriously excessive. Organic amines are irritating to the skin and mucous membranes and also have a certain stimulating effect on the central nervous system. These factors greatly limit the application of this potassium chloride in the pharmaceutical and food additive industries. Therefore, if food-grade potassium chloride is to be produced using this salt lake potash fertilizer as raw material, the removal process of inorganic ammonium and organic amines must be studied first.

[0004] Several Chinese patents disclose methods for removing ammonium from potassium chloride. These methods employ chemical separation, macroporous resin adsorption, and nanofiltration membrane separation to remove organic nitrogen compounds, such as octadecylamine, dodecylmorpholine, and No. 2 oil, from industrial potassium chloride. While these methods can theoretically effectively remove ammonia nitrogen from industrial potassium chloride, the processes are complex and costly, hindering industrialization. The inventors discovered in their experiments that when using a direct hot-dissolution method, the solubility of octadecylamine or alkylmorpholine increases with temperature. This organic matter remains in the liquid phase until it is adsorbed onto the surface of potassium chloride crystals during cooling and crystallization, becoming mixed into the product and difficult to remove. CN105668592A discloses a method for producing low-sodium, high-purity potassium chloride. Using potassium chloride with a weight content ≥96% as raw material, a three-stage flash evaporation continuous cooling crystallization process is employed to produce low-impurity, low-sodium, and low-carbon high-purity potassium chloride. This invention leverages the principle that the solubility of various substances varies greatly with temperature, rationally controlling the crystallization temperature of each effect in the crystallizer to effectively reduce the content of various impurities in the finished product. During the crystallization process, fresh saturated potassium chloride solution is continuously replenished to strictly control the content of impurity ions such as calcium, magnesium, and sodium in the mother liquor. By adjusting the feed flow rate, circulation flow rate, temperature difference between effects, and vacuum degree, the crystallization rate and the residence time of the material in the crystallizer are controlled, ensuring that the crystallization process is always in the optimal and most stable crystallization state. During the centrifugation process, deionized water is used to wash the surface of the potassium chloride crystals, reducing the amount of mother liquor adhering to the crystal surface and further reducing the impurity content of the finished product. However, this method cannot effectively control impurity ions within a certain range, resulting in unstable product quality. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by proposing a method for producing food-grade potassium chloride. This method is simple, has low production cost, and can effectively remove sodium magnesium ammonium, organic amines and other organic matter from the raw potassium chloride.

[0006] Another technical problem to be solved by the present invention is to address the shortcomings of the prior art by proposing a production system for food-grade potassium chloride using the above method.

[0007] The technical problem to be solved by this invention is achieved through the following technical solution. This invention is a method for producing food-grade potassium chloride, characterized in that the method adopts a stepwise ammonium removal process. First, organic amines and magnesium and sodium ions adsorbed on the surface of potassium chloride are removed by washing and physical adsorption. Then, inorganic ammonium mixed in the potassium chloride crystals is removed by dissolution and crystallization, finally obtaining high-purity food-grade potassium chloride.

[0008] A further preferred embodiment of the method for producing food-grade potassium chloride according to the present invention comprises the following specific steps: (1) Washing: The solid raw material potassium chloride is washed with fresh water to remove sodium and magnesium ions and organic amines and organic matter adsorbed on the surface. The temperature of the fresh water is 10℃~60℃. Then it is fed into the thickening process. The underflow of the thickening process is fed into the filtration process. After filtration, crude potassium chloride is obtained. (2) Physical adsorption: The overflow of the thickening operation is fed into the activated carbon filter, and the mother liquor after adsorption is fed into the ion exchange resin column. The mother liquor after sodium removal by the resin column is fed into the stirring tank. A pH adjuster is added to the stirring tank to adjust the pH to 10~12, and then fed into the subsequent dehydration operation. The filtrate after dehydration, which is the adsorption mother liquor, is fed into the hot melt tank. (3) Dissolution: Take crude potassium chloride and add an appropriate amount of fresh water and / or cooling crystallization mother liquor produced in the later process to prepare a potassium chloride saturated solution, or add an appropriate amount of adsorption mother liquor. The dissolution temperature is controlled at 50℃~110℃ to obtain potassium chloride saturated solution I. Add pH adjuster to potassium chloride saturated solution I. After the pH is adjusted to 8~12, add strong oxidant to convert the inorganic ammonium in the solution into ammonium monochloride and ammonium dichloride to obtain potassium chloride saturated solution II. The filter cake is dry-piled for later use. Potassium chloride saturated solution II is fed into the ammonium stripping tower. Compressed air is blown into the ammonium stripping tower by a blower. After condensation, ammonium monochloride and ammonium dichloride liquid are recovered. After stripping, potassium chloride saturated solution III is fed into the tail salt filtration operation. The filter cake is used as roadbed material. The filtrate is fed into the neutralization tank. Hydrochloric acid is added to the neutralization tank to adjust the pH to 6-8, thus obtaining potassium chloride saturated solution IV. (4) Crystallization: A saturated potassium chloride solution IV is fed into a multi-effect flash evaporation cooling crystallization process to obtain KCL crystal slurry; after the crystal slurry is concentrated, dehydrated and dried, a high-quality food-grade potassium chloride with an ammonium content of 1-20 ppm is obtained, and the cooled crystallization mother liquor is returned to the potassium chloride dissolving tank.

[0009] The preferred technical solution of the production method of food-grade potassium chloride of the present invention is that, in step (3) during dissolution, crude potassium chloride is mixed with adsorption mother liquor, cooling crystallization mother liquor and fresh water in a mass ratio of 1:1.6:8-24:0.05 to prepare a saturated potassium chloride solution.

[0010] A further preferred technical solution of the method for producing food-grade potassium chloride according to the present invention is that the pH adjuster in step (2) or (3) is one or more combinations of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and the alkali and organic amine are reacted with NH4+. + The molar ratio is 1~2:1, and the pH value is greater than 9.

[0011] The preferred technical solution of the method for producing food-grade potassium chloride according to the present invention is that the strong oxidant in step (3) is one or more of ozone, hydrogen peroxide, hypochlorite, peracetic acid, nitrite, nitrite, chlorine, and chlorine water; the strong oxidant is added under acidic conditions or under alkaline conditions.

[0012] A further preferred technical solution of the method for producing food-grade potassium chloride according to the present invention is that the ion exchange resin in step (2) is one or more combinations of a strong acid cation exchange resin or a weak acid cation exchange resin.

[0013] The preferred technical solution of the production method of food-grade potassium chloride of the present invention is that the solid raw material potassium chloride in step (1) is industrial grade or agricultural grade potassium chloride; and the multi-effect flash evaporation cooling crystallization in step (4) adopts a 2-4 effect DTB type vacuum crystallizer.

[0014] A further preferred technical solution of the method for producing food-grade potassium chloride according to the present invention is that, in step (2), the filtrate after dehydration, i.e., the adsorption mother liquor, is input into the washing tank for slurry preparation; when the adsorption mother liquor is turbid, it is introduced into an activated carbon filter for filtration and then into the washing tank for slurry preparation.

[0015] This invention also discloses a method for producing sodium chloride as a byproduct of the production of food-grade potassium chloride using any of the above technical solutions. The method is characterized by: mixing the mother liquor after desorption from the activated carbon filter, the mother liquor after desorption from the resin column, and the filter cake after dehydration of the adsorption mother liquor with the condensed and recovered ammonium chloride and dichloride liquids; then adding NaOH and phosphate to react and convert the inorganic ammonium and magnesium ions into magnesium ammonium phosphate precipitate; then performing oil-water separation and solid-liquid separation to obtain organic matter and magnesium ammonium phosphate fertilizer, respectively; then adding hydrochloric acid to adjust the neutrality and feeding it to a salt-drying pond to produce sodium chloride; the added phosphate is one or more combinations of phosphoric acid, sodium phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, or other inorganic phosphates, with a molar ratio of phosphate ions to ammonium ions of 0.8~2.0.

[0016] This invention also discloses a food-grade potassium chloride production system using the production method of any of the above technical solutions, characterized in that the system comprises: The washing tank is equipped with a potassium chloride feeding mechanism, a water supply pipeline, a cooling crystallization mother liquor recycling pipeline, and a washing discharge pipeline. The thickener is connected to the washing discharge pipe at the top and to the thickened underflow discharge pipe at the bottom. The activated carbon filter is connected to the thickener via piping. The first centrifuge is connected to the thick underflow discharge pipeline; An ion exchange resin column is connected to an activated carbon filter via pipeline; The mixing tank is connected to the ion exchange resin column, the first centrifuge, and the strong alkali feeder via pipelines. The second centrifuge is connected to the mixing tank via pipeline; The adsorption mother liquor tank is connected to the second centrifuge, washing tank, and activated carbon filter via pipelines. The hot melt tank is connected to the adsorption mother liquor tank, the water replenishment pipeline, the first centrifuge, the oxidant dosing mechanism, and the strong alkali dosing mechanism via pipelines. The ammonium stripping tower is connected to the hot melt tank via pipelines; The neutralization tank is connected to the lower part of the ammonium stripping tower via pipelines. The neutralization tank is also connected to a hydrochloric acid dosing mechanism. The multi-effect flash cooling crystallizer is connected to the neutralization tank via pipeline; The third filter is connected to the multi-effect flash cooling crystallizer via a pipeline; The crystallization mother liquor tank is connected to the third filter and the hot melt tank via pipelines; The dryer is connected to the third filter via a material conveying mechanism.

[0017] In this invention, During the freshwater washing stage, the temperature of the freshwater can be controlled between 20℃ and 45℃ before being fed into the thickening process. A thickener is selected as the thickening equipment, and insulation is added. A small amount of freshwater is added to the thickener to maintain the mother liquor in an unsaturated state. The underflow from the thickener is fed to the centrifuge. After dehydration, the filter cake is conveyed to the dissolving tank by a conveyor. The overflow from the thickener and the filtrate from the centrifuge can be fed to the activated carbon filter. Large-pore activated carbon is preferred.

[0018] The mother liquor after treatment by an activated carbon filter is fed into an ion exchange resin, which can be a strong acid cation exchange resin or a weak acid cation exchange resin. The potassium chloride slurry obtained from multi-effect flash evaporation concentration and crystallization is fed into a secondary dehydration process for solid-liquid separation. The dehydrated product is washed with fresh water and then fed into a tertiary dehydration process to obtain a wet potassium chloride solid. The obtained wet potassium chloride is then fed into a drying process to obtain high-quality food-grade potassium chloride with a moisture content of less than 1%.

[0019] The potassium chloride used can be industrial grade or agricultural grade. Further preferred raw materials are agricultural or industrial grade potassium chloride produced in Qinghai, China, with a potassium chloride content of 93-98%, sodium ion content of 0.1-2.0%, magnesium ion content of 0.1-0.5%, and ammonium content of 400-2500 mg / kg.

[0020] For concentration operations, a thickener can be used; for dehydration operations, a centrifuge can be used. For drying operations, a fluidized bed dryer or a rotary drum dryer can be used as the drying equipment.

[0021] The method of this invention can produce high-quality food-grade potassium chloride with a potassium chloride content ≥99.8%, sodium ion content ≤0.5%, total calcium and magnesium ion content ≤100mg / kg, ammonium ≤20mg / kg, heavy metals ≤1mg / kg, and organic matter content ≤1mg / kg.

[0022] The inventors discovered that agricultural potassium chloride products contain a large number of impurities that cannot be removed by simple physical methods. These impurities mainly include ammonium chloride, magnesium chloride, octadecylamine flotation reagent, dodecylmorpholine flotation reagent, and calcium sulfate insoluble matter. Among these, magnesium chloride, sodium chloride, octadecylamine flotation reagent, dodecylmorpholine flotation reagent, and some ammonium chloride are primarily adsorbed on the surface of potassium chloride crystals. Calcium sulfate insoluble matter is mixed in the potassium chloride product, while some ammonium chloride exists in a mixed crystal form within the potassium chloride crystals. While reverse flotation washing can remove the adsorbed ammonium chloride, magnesium chloride, octadecylamine flotation reagent, and dodecylmorpholine flotation reagent from the potassium chloride crystal surface, it cannot remove the ammonium chloride mixed into the potassium chloride crystal lattice or some calcium sulfate insoluble matter. Furthermore, the potassium chloride washing mother liquor contains magnesium... 2+ Na + Organic matter, NH4 + It needs to be removed before it can be returned to the process for continued use.

[0023] The principle of this invention: (1) When the temperature exceeds 80℃, octadecylamine will undergo an ammonia evolution reaction, releasing NH3. This reaction accelerates with increasing temperature, especially the stronger the alkalinity, the faster the ammonia evolution reaction rate.

[0024] (2) At pH = 8~10, phosphates can react with Mg(OH)2 and NH4. + The reaction produces MgNH4PO4·H2O precipitate, which can achieve the simultaneous removal of magnesium and ammonium by a single agent.

[0025] (3) Strong oxidants can react with amine molecules on organic amines and inorganic ammonium to produce ammonium monochloride and ammonium dichloride. Ammonium monochloride and ammonium dichloride can be hydrolyzed to produce NH3.

[0026] (4) The acid-insoluble matter is removed by dehydration equipment under hot melting conditions using a hot melting and cold crystallization process, and then high-quality food-grade potassium chloride is obtained by vacuum crystallization process.

[0027] (5) The washing mother liquor can remove organic matter and Mg(OH)2 through two-stage adsorption, and then it can be recycled separately.

[0028] Currently, the commonly used process for obtaining food-grade potassium chloride is as follows: first, the potassium chloride raw material of this invention is thermally dissolved to prepare a saturated solution, and then Mg carried in the solution is removed by adding alkali. 2+ Inorganic ammonium is removed by stripping, and then organic amines are adsorbed by activated carbon and ion exchange resin. Finally, qualified food-grade potassium chloride is obtained by cold crystallization.

[0029] Compared with the prior art, the method of the present invention has the following advantages: (1) The present invention adopts a stepwise purification process, which can effectively solve the problem of Mg 2+ Na + The impact of organic matter on subsequent food-grade potassium chloride products.

[0030] (2) Mg can be removed in one step by adding phosphate under alkaline conditions. 2+ and NH4 + Furthermore, the resulting MgNH4PO4·H2O is an excellent slow-release multi-element compound fertilizer, which can turn waste into treasure and reduce environmental pollution.

[0031] (3) By adding a strong oxidant to a saturated potassium chloride solution, the amine molecules of organic amines can be recovered in the form of ammonium chloride and dichloride, and then recovered through a precipitation reaction.

[0032] (4) Sodium chloride mixed in the potassium chloride raw material is recovered separately by sun-drying in the salt fields. Overall, this invention, through multiple improvements, produces high-purity potassium chloride products. The byproduct magnesium ammonium phosphate can be used as a slow-release compound fertilizer, the organic matter can be used as biofuel, and the sodium chloride produced from salt fields can be used in the chlor-alkali industry. It does not produce environmental pollution and is a green production process. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the production system for food-grade potassium chloride according to the present invention. Detailed Implementation

[0034] Example 1: A method for producing food-grade potassium chloride, the specific steps of which include: (1) Add industrial potassium chloride with a potassium chloride grade of 94%, an ammonium content of 2600 mg / kg, a sodium chloride content of 6.0%, and a magnesium chloride content of 2.0% to the crystallization mother liquor to prepare a 40% concentration, add 15% (by weight of raw potassium chloride) of fresh water and wash for 60 min to remove sodium and magnesium ions, and then feed the crystal slurry to the thickener.

[0035] (2) The underflow from the thickener is fed to the filtration process. The filter is a centrifuge. The filter cake from the centrifuge is fed to the dissolution process. The overflow from the thickener and the filtrate from the centrifuge are fed into the activated carbon filter. The slurry is fed from the top of the activated carbon filter. Most of the suspended solids and organic impurities are removed by the activated carbon filter. The bottom of the activated carbon filter is equipped with a heat exchange device to prevent crystallization after the mother liquor cools down. The adsorption time is 30 minutes. The adsorbed mother liquor is then fed into a weakly acidic ion exchange resin column for adsorption. The replacement time is 30 minutes. The mother liquor after sodium removal from the resin column is fed into a stirring tank. NaOH is added to the stirring tank. The pH was adjusted to 11, and then fed into the subsequent dehydration process. After dehydration, the filtrate was fed into a hot dissolving tank. The crude potassium chloride was mixed with the mother liquor obtained from adsorption, the mother liquor from cooling crystallization, and fresh water in a ratio of 1:1.6:8:0.05 to prepare a potassium chloride saturated solution. The dissolution temperature was controlled at 95℃ to obtain potassium chloride saturated solution I. Sodium hydroxide, a pH adjuster, was added to potassium chloride saturated solution I. After the pH was adjusted to 10, sodium hypochlorite, a strong oxidant, was added. The molar ratio of sodium hypochlorite to total amine was 2:1. The inorganic ammonium in the solution was converted into ammonium monochloride and ammonium dichloride to obtain potassium chloride saturated solution II. (3) Potassium chloride saturated solution II is fed into the ammonium stripping tower. Compressed air is blown into the ammonium stripping tower by a blower. After condensation, ammonium monochloride and ammonium dichloride liquid are recovered. After stripping, potassium chloride saturated solution III is fed into the tail salt filtration operation. The filter cake is used as roadbed material. The filtrate is fed into the neutralization tank. Hydrochloric acid is added to the neutralization tank to pH 7 to obtain potassium chloride saturated solution IV. Then, the potassium chloride is subjected to flash cooling and concentration crystallization through triple-effect flash crystallization operation. The crystallization equipment is a DTB type vacuum crystallizer. (4) The potassium chloride crystal slurry obtained by triple-effect flash evaporation concentration and crystallization is fed into a centrifuge for solid-liquid separation. The solid material is fed into the centrifuge to obtain potassium chloride solid wet material. (5) The obtained wet potassium chloride material is fed into the drying process. After drying, high-quality food-grade potassium chloride is obtained with a potassium chloride content of 99.9%, sodium ion content of 0.45%, total calcium and magnesium ion content of 91 mg / kg, ammonium content of 15 mg / kg, heavy metal content of 0.5 mg / kg, and organic matter content of 0.5 mg / kg. The drying equipment is a flash dryer.

[0036] (6) The mother liquor after the activated carbon filter is desorbed, the mother liquor after the resin column is desorbed, and the filter cake after the adsorption mother liquor is dehydrated are mixed with the liquid of ammonium chloride and ammonium dichloride recovered after condensation. Then NaOH and sodium hydrogen phosphate are added to react and convert the inorganic ammonium and magnesium ions in it into magnesium ammonium phosphate precipitate. Then oil-water separation and solid-liquid separation are performed to obtain organic matter and magnesium ammonium phosphate fertilizer respectively. Then hydrochloric acid is added to adjust the neutrality and fed to the salt pond for tailings recovery. The molar ratio of phosphate ions to ammonium ions is 1:1.

[0037] Example 2: A method for producing food-grade potassium chloride, the specific steps of which include: (1) Add industrial potassium chloride with a potassium chloride grade of 95%, an ammonium content of 1800 mg / kg, a sodium chloride content of 3.0%, and a magnesium chloride content of 1.8% to the crystallization mother liquor to prepare a 40% concentration, add 15% fresh water (by weight of the raw potassium chloride), wash for 45 min to remove sodium and magnesium ions, and then feed the crystal slurry to the thickener.

[0038] (2) The underflow from the thickener is fed to the filtration process. The filter is a centrifuge. The filter cake from the centrifuge is fed to the dissolution process. The overflow from the thickener and the filtrate from the centrifuge are fed into the activated carbon filter. The slurry is fed from the top of the activated carbon filter. Most of the suspended solids and organic impurities are removed by the activated carbon filter. The bottom of the activated carbon filter is equipped with a heat exchange device to prevent crystallization after the mother liquor cools down. The adsorption time is 20 minutes. The adsorbed mother liquor is then fed into a weakly acidic ion exchange resin column for adsorption. The replacement time is 30 minutes. The mother liquor after sodium removal by the resin column is fed into a stirring tank. Sodium carbonate is added to adjust the pH to 10.5, and then the solution is fed into the subsequent dehydration process. After dehydration, the filtrate is fed into a hot dissolving tank. Crude potassium chloride is mixed with the mother liquor obtained from adsorption, the mother liquor from cooling crystallization, and fresh water in a ratio of 1:1.6:10:0.05 to prepare a saturated potassium chloride solution. The dissolution temperature is controlled at 90℃ to obtain saturated potassium chloride solution I. Sodium carbonate is added as a pH adjuster to saturated potassium chloride solution I. After the pH is adjusted to 10, hydrogen peroxide, a strong oxidant, is added. The molar ratio of hydrogen peroxide to total amine is 4:1 to convert the inorganic ammonium in the solution into ammonium monochloride and ammonium dichloride to obtain saturated potassium chloride solution II. (3) Potassium chloride saturated solution II is fed into the ammonium stripping tower. Compressed air is blown into the ammonium stripping tower by a blower. After condensation, ammonium chloride monochloride and ammonium dichloride liquid are recovered. After stripping, potassium chloride saturated solution III is fed into the tail salt filtration operation. The filter cake is used as roadbed material. The filtrate is fed into the neutralization tank. Hydrochloric acid is added to the neutralization tank to pH 7 to obtain potassium chloride saturated solution IV. Then, the potassium chloride is subjected to flash cooling and concentration crystallization through a double-effect flash crystallization operation. The crystallization equipment is a DTB type vacuum crystallizer. (4) The potassium chloride crystal slurry obtained by double-effect flash evaporation concentration and crystallization is fed into a centrifuge for solid-liquid separation. The solid material is fed into the centrifuge to obtain potassium chloride solid wet material. (5) The obtained wet potassium chloride material is fed into the drying process. After drying, high-quality food-grade potassium chloride is obtained with a potassium chloride content of 99.9%, sodium ion content of 0.4%, total calcium and magnesium ion content of 85 mg / kg, ammonium content of 12 mg / kg, heavy metal content of 0.6 mg / kg, and organic matter content of 0.8 mg / kg. A rotary drum dryer is selected as the drying equipment.

[0039] (6) The mother liquor after the activated carbon filter is desorbed, the mother liquor after the resin column is desorbed, and the filter cake after the adsorption mother liquor is dehydrated are mixed with the liquid of ammonium chloride and ammonium dichloride recovered after condensation. Then sodium carbonate and sodium hydrogen phosphate are added to react and convert the inorganic ammonium and magnesium ions in them into magnesium ammonium phosphate precipitate. Then oil-water separation and solid-liquid separation are performed to obtain organic matter and magnesium ammonium phosphate fertilizer respectively. Then hydrochloric acid is added to adjust the neutrality and feed it to the salt pond for tailings recovery. The molar ratio of phosphate ions to ammonium ions is 1.5:1.

[0040] Example 3: A method for producing food-grade potassium chloride, the specific steps of which include: (1) Add industrial potassium chloride with a potassium chloride grade of 93%, an ammonium content of 3000 mg / kg, a sodium chloride content of 5.0%, and a magnesium chloride content of 2.5% to the crystallization mother liquor to prepare a 40% concentration, add 25% fresh water (by weight of the raw potassium chloride), wash for 45 min to remove sodium and magnesium ions, and then feed the crystal slurry to the thickener.

[0041] (2) The underflow from the thickener is fed to the filtration process. The filter is a centrifuge. The filter cake from the centrifuge is fed to the dissolution process. The overflow from the thickener and the filtrate from the centrifuge are fed into the activated carbon filter. The slurry is fed from the top of the activated carbon filter. Most of the suspended solids and organic impurities are removed by the activated carbon filter. The bottom of the activated carbon filter is equipped with a heat exchange device to prevent crystallization after the mother liquor cools down. The adsorption time is 45 minutes. The adsorbed mother liquor is then fed into a weakly acidic ion exchange resin column for adsorption. The replacement time is 20 minutes. The mother liquor after sodium removal by the resin column is fed into a stirring tank. NaOH is added to adjust the pH to 11, and then the solution is fed into the subsequent dehydration process. After dehydration, the filtrate is fed into a hot dissolving tank. Crude potassium chloride is mixed with the mother liquor obtained from adsorption, the mother liquor from cooling crystallization, and fresh water in a ratio of 1:1.6:9:0.05 to prepare a potassium chloride saturated solution. The dissolution temperature is controlled at 95℃ to obtain potassium chloride saturated solution I. Potassium hydroxide is added to potassium chloride saturated solution I as a pH adjuster. After the pH is adjusted to 11, chlorine gas, a strong oxidant, is added. The molar ratio of chlorine gas to total amine is 2:1 to convert the inorganic ammonium in the solution into ammonium monochloride and ammonium dichloride to obtain potassium chloride saturated solution II. (3) Potassium chloride saturated solution II is fed into the ammonium stripping tower. Compressed air is blown into the ammonium stripping tower by a blower. After condensation, ammonium monochloride and ammonium dichloride liquid are recovered. After stripping, potassium chloride saturated solution III is fed into the tail salt filtration operation. The filter cake is used as roadbed material. The filtrate is fed into the neutralization tank. Hydrochloric acid is added to the neutralization tank to pH 7 to obtain potassium chloride saturated solution IV. Then, the potassium chloride is flash cooled and concentrated by a four-effect flash crystallization operation. The crystallization equipment is a DTB type vacuum crystallizer. (4) The potassium chloride crystal slurry obtained by four-effect flash evaporation concentration and crystallization is fed into a centrifuge for solid-liquid separation. The solid material is fed into the centrifuge to obtain potassium chloride solid wet material. (5) The obtained wet potassium chloride material is fed into the drying process. After drying, high-quality food-grade potassium chloride is obtained with a potassium chloride content of 99.9%, sodium ion content of 0.3%, total calcium and magnesium ion content of 80 mg / kg, ammonium content of 6 mg / kg, heavy metal content of 0.5 mg / kg, and organic matter content of 0.7 mg / kg. The drying equipment is a flash dryer.

[0042] (6) The mother liquor after the activated carbon filter is desorbed, the mother liquor after the resin column is desorbed, and the filter cake after the adsorption mother liquor is dehydrated are mixed with the liquid of ammonium chloride and ammonium dichloride recovered after condensation. Then NaOH and sodium hydrogen phosphate are added to react and convert the inorganic ammonium and magnesium ions in it into magnesium ammonium phosphate precipitate. Then oil-water separation and solid-liquid separation are performed to obtain organic matter and magnesium ammonium phosphate fertilizer respectively. Then hydrochloric acid is added to adjust the neutrality and feed it to the salt pond for tailings recovery. The molar ratio of phosphate ions to ammonium ions is 1.5:1.

[0043] Example 4, a production system for food-grade potassium chloride, used to produce food-grade potassium chloride (excluding byproducts) for any of Examples 1-3.

[0044] Reference Figure 1 The system includes: Washing tank 1 is connected to a potassium chloride feeding mechanism, a water supply pipe 2, a cooling crystallization mother liquor recycling pipe, and a washing discharge pipe. Thickener 3 is connected to the washing discharge pipe at the top and to the thickened underflow discharge pipe at the bottom; Activated carbon filter 4 is connected to thickener 3 via pipeline; The first centrifuge 9 is connected to the thick underflow discharge pipeline; The ion exchange resin column 5 is connected to the activated carbon filter 4 via a pipeline; The mixing tank 10 is connected to the ion exchange resin column 5, the first centrifuge 9, and the strong alkali feeder 8 via pipelines. The second centrifuge 6 is connected to the mixing tank 10 via a pipeline; The mother liquor adsorption tank 7 is connected to the second centrifuge 6, the washing tank 10, and the activated carbon filter 4 via pipelines. The hot melt tank 14 is connected to the adsorption mother liquor tank 7, the water replenishment pipeline 12, the first centrifuge 9, the oxidant dosing mechanism 13, and the strong alkali dosing mechanism 11 via pipelines. The ammonium stripping tower 15 is connected to the hot melt tank 14 via a pipeline; Neutralization tank 17 is connected to the lower part of ammonium stripping tower 15 via pipeline. Neutralization tank 17 is also connected to hydrochloric acid dosing mechanism 16. The multi-effect flash cooling crystallizer 18 is connected to the neutralization tank 17 via a pipeline; The third filter 20 is connected to the multi-effect flash cooling crystallizer 18 via a pipeline; The crystallization mother liquor tank 19 is connected to the third filter 20 and the hot melting tank 14 via pipelines; The dryer 21 is connected to the third filter 20 via a material conveying mechanism.

[0045] This food-grade potassium chloride production system can produce food-grade potassium chloride, ensuring stable and efficient production.

[0046] The embodiments of the present invention can be understood to be subject to various changes, modifications, substitutions and variations without departing from the principles of the present invention. The scope of the present invention is defined by the claims and their equivalents.

Claims

1. A method for producing food-grade potassium chloride, characterized in that, This method employs a stepwise ammonium removal process. First, organic amines and magnesium and sodium ions adsorbed on the surface of potassium chloride are removed by washing and physical adsorption. Then, inorganic ammonium mixed in with potassium chloride crystals is removed by dissolution and crystallization, ultimately obtaining high-purity food-grade potassium chloride. The specific steps are as follows: (1) Washing: The solid raw material potassium chloride is washed with fresh water to remove sodium and magnesium ions and organic amines and organic matter adsorbed on the surface. The temperature of the fresh water is 10℃~60℃. Then it is fed into the thickening process. The underflow of the thickening process is fed into the filtration process. After filtration, crude potassium chloride is obtained. (2) Physical adsorption: The overflow of the thickening operation is fed into the activated carbon filter, and the mother liquor after adsorption is fed into the ion exchange resin column. The mother liquor after sodium removal by the resin column is fed into the stirring tank. A pH adjuster is added to the stirring tank to adjust the pH to 10~12, and then fed into the subsequent dehydration operation. The filtrate after dehydration, which is the adsorption mother liquor, is fed into the hot melt tank. (3) Dissolution: Take crude potassium chloride and add fresh water, cooling crystallization mother liquor and adsorption mother liquor to prepare potassium chloride saturated solution. The dissolution temperature is controlled at 50℃~110℃ to obtain potassium chloride saturated solution I. Add pH adjuster to potassium chloride saturated solution I. After the pH is adjusted to 8~12, add strong oxidant to convert the inorganic ammonium in the solution into ammonium monochloride and ammonium dichloride to obtain potassium chloride saturated solution II. Potassium chloride saturated solution II is fed into an ammonium stripping tower. Compressed air is blown into the ammonium stripping tower by a blower. The stripping gas at the top of the tower is condensed and then recovered as ammonium monochloride and ammonium dichloride liquid. After stripping, potassium chloride saturated solution III is fed into the tailings filtration operation. The filter cake is used as roadbed material. The filtrate is fed into a neutralization tank. Hydrochloric acid is added to the neutralization tank to adjust the pH to 6-8, thus obtaining potassium chloride saturated solution IV. (4) Crystallization: A saturated potassium chloride solution IV is fed into a multi-effect flash evaporation cooling crystallization process to obtain KCL crystal slurry; after the crystal slurry is concentrated, dehydrated and dried, a high-quality food-grade potassium chloride with an ammonium content of 1-20 ppm is obtained, and the cooled crystallization mother liquor is returned to the potassium chloride dissolving tank. In step (3) during dissolution: a saturated potassium chloride solution is prepared by mixing crude potassium chloride with adsorption mother liquor, cooling crystallization mother liquor, and fresh water at a mass ratio of 1:1.6:8-24:0.05; The pH adjuster in step (2) or (3) is one or more combinations of sodium hydroxide, potassium hydroxide, sodium carbonate, and potassium carbonate, and the alkali is reacted with an organic amine in the form of NH4+. + The molar ratio is 1~2:1, and the pH value is greater than 9; The strong oxidant mentioned in step (3) is one or a combination of ozone, hydrogen peroxide, hypochlorite, peracetic acid, nitrite, nitrite, chlorine, and chlorine water.

2. The method for producing food-grade potassium chloride according to claim 1, characterized in that: The ion exchange resin mentioned in step (2) is one or more combinations of a strong acid cation exchange resin or a weak acid cation exchange resin.

3. The method for producing food-grade potassium chloride according to claim 1, characterized in that: The solid raw material potassium chloride mentioned in step (1) is industrial grade or agricultural grade potassium chloride; the multi-effect flash evaporation cooling crystallization in step (4) adopts a 2-4 effect DTB type vacuum crystallizer.

4. A food-grade potassium chloride production system employing the production method of any one of claims 1-3, characterized in that, The system includes: The washing tank is equipped with a potassium chloride feeding mechanism, a water supply pipeline, a cooling crystallization mother liquor recycling pipeline, and a washing discharge pipeline. The thickener is connected to the washing discharge pipe at the top and to the thickened underflow discharge pipe at the bottom. The activated carbon filter is connected to the thickener via piping. The first centrifuge is connected to the thick underflow discharge pipeline; An ion exchange resin column is connected to an activated carbon filter via pipeline; The mixing tank is connected to the ion exchange resin column, the first centrifuge, and the strong alkali feeder via pipelines. The second centrifuge is connected to the mixing tank via pipeline; The adsorption mother liquor tank is connected to the second centrifuge, washing tank, and activated carbon filter via pipelines; the hot melting tank is connected to the adsorption mother liquor tank, water replenishment pipeline, first centrifuge, oxidant dosing mechanism, and strong alkali dosing mechanism via pipelines. The ammonium stripping tower is connected to the hot melt tank via pipelines; The neutralization tank is connected to the lower part of the ammonium stripping tower via pipeline, and a hydrochloric acid dosing mechanism is also connected to the neutralization tank; the multi-effect flash cooling crystallizer is connected to the neutralization tank via pipeline; The third filter is connected to the multi-effect flash cooling crystallizer via a pipeline; The crystallization mother liquor tank is connected to the third filter and the hot melt tank via pipelines; The dryer is connected to the third filter via a material conveying mechanism.

Images