A method for purifying potassium bicarbonate mother liquor containing chloride

Abstract

The present invention belongs to the field of inorganic chemical engineering, and particularly relates to a method for purifying potassium bicarbonate mother liquor containing chlorides. In the present invention, the potassium bicarbonate mother liquor containing chlorides is passed through an ammonium-type resin (NH4-R) in a countercurrent manner for ion exchange to convert the resin into a potassium type (K-R), and a mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride is obtained. The potassium-type (K-R) resin and the ammonium bicarbonate solution are subjected to conventional ion exchange to obtain a potassium bicarbonate solution free of chlorides, and the resin is converted into an ammonium type (NH4-R), and then the next cycle of operation is carried out. The mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride obtained by ion exchange is subjected to a thermal decomposition method to thermally decompose the ammonium bicarbonate therein, and through spray absorption, a mixed solution of ammonium carbonate and ammonium bicarbonate is obtained, which is subjected to carbonation and concentration adjustment to obtain the ammonium bicarbonate solution required for ion exchange. The bottom liquid of the thermal decomposition tower is ammonium chloride solution, which is used for evaporation crystallization to recover ammonium chloride.

Description

Technical Field

[0001] The present invention belongs to the field of inorganic chemical industry, and particularly relates to the purification and production technology of potassium bicarbonate, and more particularly to a method for purifying potassium bicarbonate mother liquor containing chloride. Background Art

[0002] Potassium carbonate and potassium bicarbonate are basic chemical raw materials for inorganic salts, and are raw materials for producing potassium acetate, potassium fluoride, potassium arsenite and potassium sorbate. They are also commonly used in chemical industry, medicine, pesticides and fertilizers. With the development of technology, the uses of potassium carbonate are becoming more and more extensive. With the decreasing demand in industries such as pesticides and building materials, potassium carbonate and potassium bicarbonate are mainly concentrated in high-end industries such as medicine, new materials and new energy. The high-end demand has increased rapidly in recent years, but higher requirements are also put forward for product quality. Among them, more stringent requirements are put forward for the content, clarity, and the contents of potassium chloride and sulfate impurities.

[0003] At present, the commercial production processes of potassium bicarbonate and potassium carbonate are: ion exchange method and ion-exchange membrane electrolysis carbonization method.

[0004] Ion-exchange membrane electrolysis carbonization method: In the process of producing potassium bicarbonate and potassium carbonate, the raw material potassium chloride undergoes refined treatment, electrolysis, evaporation and concentration, carbonization and drying processes. Due to the need for electrolysis, the energy consumption is very high, and coupled with the large fluctuations in the market demand for by-product liquid chlorine, the cost of producing potassium carbonate or potassium bicarbonate by the ion-exchange membrane electrolysis method is not competitive.

[0005] Ion exchange method: The ion exchange method uses potassium chloride and ammonium bicarbonate as raw materials, and through an ion exchange tower, potassium bicarbonate and ammonium chloride solutions are obtained respectively. However, during the exchange process, in order to reduce production energy consumption and reduce wastewater discharge, it is necessary to strictly control the washing water volume. Therefore, it is very difficult to thoroughly clean the residual potassium chloride or ammonium chloride in the ion exchange resin, and more or less potassium chloride and ammonium chloride will be brought into the potassium bicarbonate solution.

[0006] Although high-specification potassium carbonate or potassium bicarbonate can be obtained by evaporation recrystallization or centrifugal rinsing, once potassium chloride and ammonium chloride enter the potassium bicarbonate solution, they cannot be separated (because eutectics or double salts will be formed). Previously, due to the relatively loose requirements for chloride indexes for qualified products and first-class products, and the proportion of qualified products and first-class products in the total output was as high as 60%, therefore, qualified products could be produced through simple purification in production, and the content of chloride impurities would not have too much impact on production.

[0007] However, in recent years, the demand for low-grade products such as first-class and qualified industrial potassium carbonate has been decreasing, and the proportion has dropped from the original 60% to 30%. This poses higher requirements for production. Otherwise, products that meet customer requirements cannot be produced. Through process improvement and adjustment of ion exchange in production, the introduction of potassium chloride and ammonium chloride can be reduced to a certain extent. However, due to the process, it is impossible to completely eliminate potassium chloride and ammonium chloride, so it can only be solved through subsequent purification. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a method for purifying potassium bicarbonate mother liquor containing chloride with simple process, high product yield and cost reduction.

[0009] To solve the above technical problem, the present invention provides a method for purifying potassium bicarbonate mother liquor containing chloride, which includes the following steps:

[0010] 1), Mix the potassium bicarbonate mother liquor containing chloride with pure water or with the low-concentration potassium bicarbonate solution II containing chloride obtained from the ion exchange tower in step 2) to obtain a potassium bicarbonate solution III containing chloride with a density of 1.20 ± 0.05 g / ml;

[0011] 2), Let the potassium bicarbonate solution III containing chloride obtained in step 1) flow through the ion exchange tower (resin model is 001×7, ammonium form) countercurrently, with a flow rate of 0.4 ± 0.1 BV / h (resin volume multiple), and the volume of the potassium bicarbonate solution III containing chloride is 1.0 ± 0.1 BV of the resin in the ion exchange tower; a mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride is obtained from the top of the ion exchange tower;

[0012] After the countercurrent flow of the potassium bicarbonate solution III containing chloride is completed, then use pure water with a volume of 0.5 ± 0.1 BV of the resin to flow through the ion exchange tower for top washing (top washing the potassium bicarbonate solution containing chloride in the ion exchange tower) in the forward direction, with a flow rate of 0.5 ± 0.1 BV / h, and a low-concentration potassium bicarbonate solution II containing chloride is obtained from the bottom of the ion exchange tower;

[0013] 3), The mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride obtained in step 2) enters the decomposition tower and undergoes thermal decomposition to respectively obtain a mixed gas containing ammonia, water vapor and carbon dioxide and an ammonium chloride solution;

[0014] The mixed gas enters the circulating absorption tower and is absorbed by sufficient pure water to obtain a mixed solution I of ammonium bicarbonate and ammonium carbonate;

[0015] 4) After step 2) rinsing the ion exchange column with pure water (rinsing the potassium bicarbonate solution containing chloride in the ion exchange column), the resin in the ion exchange column changes from ammonium form to potassium form, and then the ammonium bicarbonate solution with a concentration of 250 ± 10 g / L or the ammonium bicarbonate solution II obtained in the subsequent step 7) is fed into the ion exchange column in a co-current manner at a flow rate of 0.5 ± 0.1 BV / h (resin volume multiple) and a volume of 1.5 ± 0.1 BV to obtain a potassium bicarbonate solution containing ammonium bicarbonate;

[0016] After the ammonium bicarbonate solution or ammonium bicarbonate solution II is fed completely, the ion exchange column is rinsed in a co-current manner with pure water having a volume of 0.5 ± 0.1 BV (rinsing the potassium bicarbonate solution containing ammonium bicarbonate in the ion exchange column) to obtain a potassium bicarbonate solution containing ammonium bicarbonate;

[0017] 5) The potassium bicarbonate solution containing ammonium bicarbonate obtained in step 4) is subjected to evaporation crystallization, and the resulting slurry (potassium bicarbonate slurry) is cooled and then separated by centrifugation to obtain potassium bicarbonate (wet product);

[0018] During the evaporation crystallization process, ammonium bicarbonate decomposes into ammonia and carbon dioxide, which are then absorbed through a circulation absorption tower to obtain a mixed solution II of ammonium carbonate and ammonium bicarbonate;

[0019] 6) After the mixed solution I of ammonium bicarbonate and ammonium carbonate obtained in step 3) and the mixed solution II of ammonium carbonate and ammonium bicarbonate obtained in step 5) are mixed, they are carbonated with carbon dioxide to obtain ammonium bicarbonate solution I; during the carbonation process, the temperature is controlled at 40 - 50 °C, the pressure is 0.3 - 0.5 MPa, and the end point is controlled at a pH value of 8.2 - 8.3;

[0020] 7) The ammonium bicarbonate solution I obtained by carbonation in step 6) is put into an ammonium bicarbonate dissolution adjustment tank, and ammonium bicarbonate raw material (solid) or pure water is added with stirring at 30 - 35 °C, so that the concentration of ammonium bicarbonate in the resulting ammonium bicarbonate solution II is 250 ± 10 g / L.

[0021] As an improvement to the method for purifying the potassium bicarbonate mother liquor containing chloride of the present invention: the ammonium chloride solution obtained in step 3) is subjected to evaporation crystallization and then ammonium chloride is recovered.

[0022] As a further improvement to the method for purifying the potassium bicarbonate mother liquor containing chloride of the present invention: the temperature of the thermal decomposition in step 3) is 98 - 103 °C.

[0023] As a further improvement to the method for purifying the potassium bicarbonate mother liquor containing chloride of the present invention: the evaporation crystallization in step 5) is multi-effect continuous evaporation crystallization, for example, reference can be made to 2011103310383.

[0024] As a further improvement of the method for purifying potassium bicarbonate mother liquor containing chloride in the present invention: the potassium bicarbonate obtained in step 5) is a wet product, and is subsequently dried or calcined to obtain a finished product of potassium bicarbonate or a finished product of potassium carbonate.

[0025] The "potassium bicarbonate mother liquor containing chloride" used as the raw material in the present invention is a by-product obtained from the process of producing potassium carbonate by the ion exchange method, and the content of each component thereof is as follows: the potassium chloride content is 10 - 50 g / L, the potassium bicarbonate concentration is 220 - 350 g / L, the potassium carbonate concentration is 200 - 300 g / L, the sodium carbonate concentration is 15 - 30 g / L, and the rest is water and other trace impurities.

[0026] In order to solve the problems existing in the prior art, the present invention passes the potassium bicarbonate mother liquor containing chloride through an ammonium-type resin (NH4-R) in a countercurrent manner for ion exchange, converts the resin into a potassium-type (K-R), and obtains a mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride. The potassium-type (K-R) resin and the ammonium bicarbonate solution are subjected to conventional ion exchange to obtain a potassium bicarbonate solution without chloride (i.e., a potassium bicarbonate solution containing ammonium bicarbonate), and the resin is converted into an ammonium-type (NH4-R), and then the next cycle of operation is carried out. The mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride obtained by ion exchange is subjected to thermal decomposition, and the ammonium bicarbonate therein is thermally decomposed (in a decomposition tower) and absorbed by spraying (in a circulating absorption tower) to obtain a mixed solution of ammonium carbonate and ammonium bicarbonate, and after carbonation and concentration adjustment (in a carbonation tower and an ammonium bicarbonate dissolution adjustment tank respectively), an ammonium bicarbonate solution required for ion exchange is obtained. The bottom liquid of the thermal decomposition tower is an ammonium chloride solution, which is used for evaporation crystallization to recover ammonium chloride.

[0027] After the above treatment, while the potassium bicarbonate mother liquor containing chloride is purified, the resource utilization of all anions and cations is also realized.

[0028] In summary, the present invention uses the ion exchange method to convert the potassium bicarbonate mother liquor containing chloride into a mixed solution of ammonium bicarbonate, ammonium carbonate containing ammonium chloride and a potassium bicarbonate solution without chloride. The mixed solution of ammonium bicarbonate, ammonium carbonate containing ammonium chloride is further separated from ammonium bicarbonate, ammonium carbonate and chloride by thermal decomposition, and the recycling of ammonium bicarbonate and ammonium carbonate is realized.

[0029] The present invention has the characteristics of simple process, high conversion rate and excellent quality. It not only solves the problem of the outlet of the potassium bicarbonate mother liquor containing chloride, but also can significantly reduce the production cost of potassium bicarbonate, and has good economic and social benefits. The present invention adds a synthetic route with lower raw material cost and more concise for the production of high-quality potassium bicarbonate. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The following further details the specific embodiments of the present invention with reference to the accompanying drawings.

[0031] Figure 1 This is the process flow chart of the present invention. Specific embodiments

[0032] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0033] In the following text, the rotational speed of centrifugal separation is 500 - 1200 revolutions per minute.

[0034] Example 1: A method for purifying potassium bicarbonate mother liquor containing chloride, which successively performs the following steps:

[0035] 1), Mix 10 m 3 Potassium bicarbonate mother liquor containing chloride and 2.1 m 3 Pure water in a dilution batching tank to obtain potassium bicarbonate solution III containing chloride with a density of 1.18 g / ml;

[0036] The potassium bicarbonate mother liquor containing chloride, in which the potassium chloride content is 20.8 g / L, the potassium bicarbonate concentration is 350 g / L, the potassium carbonate concentration is 208.1 g / L, the sodium carbonate concentration is 22.5 g / L, and the rest is water and other trace impurities.

[0037] 2), Take 12 m 3 The potassium bicarbonate solution III containing chloride with a density of 1.18 g / ml obtained in step 1) and make it flow countercurrently through an ion exchange tower (resin model: 001×7, ammonium form, resin volume: 12 m 3 ), with a flow rate of 6.0 m 3 / h (0.5 BV / h). From the top of the ion exchange tower, a mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride is obtained, about 12 m 3 . In this mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride, the ammonium chloride content is 8.7 g / L, the ammonium bicarbonate content is 161.3 g / L, and the ammonium carbonate content is 96.2 g / L. This mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride is stored in storage tank 1.

[0038] When the potassium bicarbonate solution III containing chloride has finished flowing countercurrently, then use 6.0 m 3 (0.5 BV resin volume) of pure water to perform a forward flushing of the potassium bicarbonate solution containing chloride in the ion exchange tower, with a flow rate of 6.0 m 3 / h (0.5 BV / h). In the forward flow, thus from the bottom of the ion exchange tower, a low-concentration potassium bicarbonate solution II containing chloride is obtained, with a volume of 6.0 m 3 . This low-concentration potassium bicarbonate solution II containing chloride is stored in storage tank 2.

[0039] The potassium bicarbonate solution II containing chloride at low concentration has a potassium chloride content of 10.4 g / L, a potassium bicarbonate concentration of 175 g / L, a potassium carbonate concentration of 104 g / L, a sodium carbonate concentration of 11.3 g / L, and the rest is water and other trace impurities.

[0040] 3), the 12 m obtained in step 2) 3 The mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride enters the decomposition tower and undergoes thermal decomposition at 98 - 103 °C, so as to obtain a mixed gas containing ammonia, water vapor and carbon dioxide from the top of the decomposition tower respectively, and obtain 2.4 m of ammonium chloride solution from the bottom of the decomposition tower. 3 ; The mixed gas of ammonia, water vapor and carbon dioxide obtained from the top enters the circulation absorption tower and is absorbed with sufficient pure water to obtain 15.2 m of the mixed solution I of ammonium bicarbonate and ammonium carbonate. 3 and is stored in storage tank three.

[0041] In the mixed solution I of ammonium bicarbonate and ammonium carbonate, the ammonium bicarbonate is 63.65 g / L and the ammonium carbonate is 120.3 g / L.

[0042] In the ammonium chloride solution, the ammonium chloride content is 43.5 g / L, the ammonium carbonate is 5.6 g / L, and the rest is water, which can be used for evaporation crystallization to recover ammonium chloride.

[0043] 4), after the potassium bicarbonate solution containing chloride in the ion exchange tower is washed (top - washed) with pure water in step 2), the resin in the ion exchange tower changes from ammonium type to potassium type, and then 18 m 3 (1.5 times the resin volume) of ammonium bicarbonate solution with a concentration of 250 g / L or the ammonium bicarbonate solution II obtained in subsequent step 7) is fed into the ion exchange tower in a co - current manner, and the flow rate is 0.5 BV / h (resin volume multiple).

[0044] Note: When producing for the first time, the ammonium bicarbonate solution with a concentration of 250 g / L is obtained by dissolving ammonium bicarbonate solid raw materials in pure water, and in subsequent production, the ammonium bicarbonate solution II obtained in step 7) is used.

[0045] After the ammonium bicarbonate solution (or ammonium bicarbonate solution II) is fed, 0.5 BV of pure water with the volume of the resin is used to top - wash the potassium bicarbonate solution containing ammonium bicarbonate in the ion exchange tower in a co - current manner, and a total of 18 m 3 of potassium bicarbonate solution containing ammonium bicarbonate is obtained. In this potassium bicarbonate solution containing ammonium bicarbonate, the potassium chloride concentration is 0.03 g / L, the ammonium bicarbonate concentration is 28.3 g / L, the potassium bicarbonate concentration is 253 g / L, the sodium bicarbonate concentration is 13.8 g / L, and the rest is water and other trace impurities. This potassium bicarbonate solution containing ammonium bicarbonate is stored in storage tank four.

[0046] 5) The potassium bicarbonate solution containing ammonium bicarbonate obtained in step 4) is subjected to evaporation crystallization using a 4-effect continuous evaporation crystallizer (reference can be made to 2011103310383). The potassium bicarbonate solution containing ammonium bicarbonate is pumped into a desorption self-carbonation tower for low-temperature desorption self-carbonation. The outflowing material is pumped into the III-effect evaporator for evaporation and concentration. The material concentrated by the III-effect evaporator is pumped into the II-effect evaporator for evaporation and concentration. The material concentrated by the II-effect evaporator is pumped into the I-effect evaporator for evaporation and concentration. The material concentrated by the I-effect evaporator is pumped into the IV-effect evaporator for concentration and flash evaporation crystallization.

[0047] Among them, the temperature of the decomposition self-carbonation tower is controlled at 60 - 65 °C, the vacuum degree is controlled at a negative pressure of 0.078 - 0.082 MPa, and the steam pressure is controlled at 0.4 MPa; the temperature of the I-effect evaporator is controlled at 85 - 87 °C, the temperature of the II-effect evaporator is controlled at 73 - 75 °C, the temperature of the III-effect evaporator is controlled at 63 - 65 °C, and the temperature of the IV-effect evaporator is controlled at 53 - 59 °C; the vacuum degree of the I-effect evaporator is controlled at a negative pressure of 0.056 - 0.060 MPa, the vacuum degree of the II-effect evaporator is controlled at a negative pressure of 0.070 - 0.074 MPa, the vacuum degree of the III-effect evaporator is controlled at a negative pressure of 0.078 - 0.082 MPa, and the vacuum degree of the IV-effect evaporator is controlled at a negative pressure of 0.088 - 0.092 MPa to obtain a potassium bicarbonate slurry.

[0048] During the evaporation crystallization process, ammonium bicarbonate in the potassium bicarbonate solution containing ammonium bicarbonate decomposes into ammonia and carbon dioxide, and then is absorbed by pure water through a circulating absorption tower to obtain 2.2 m 3 A mixed solution II of ammonium carbonate and ammonium bicarbonate, where the concentration of ammonium bicarbonate is 142 g / L, the concentration of ammonium carbonate is 55.3 g / L, and the rest is water; it is also stored in storage tank three, that is, mixed with the mixed solution I of ammonium bicarbonate and ammonium carbonate obtained in step 3) to form a mixed solution of ammonium bicarbonate and ammonium carbonate.

[0049] The above potassium bicarbonate slurry is cooled to 45 °C and then centrifuged to obtain 4854 Kg of potassium bicarbonate (wet product). After drying (fluidized bed drying at 100 - 120 °C), 4712 Kg of potassium bicarbonate is obtained, among which potassium chloride is 0.011%, potassium bicarbonate is 96.6%, sodium carbonate is 3.3%, and water is 0.03%; it meets the requirements of the qualified product of the industrial potassium bicarbonate (HG / T2828 - 2010) industry standard.

[0050] 6) The mixed solution of ammonium bicarbonate and ammonium carbonate enters a carbonation tower and undergoes a carbonation reaction with carbon dioxide. The carbonation reaction temperature is controlled at 40 - 50 °C, the pressure is 0.3 - 0.5 MPa, and the end point controls the pH value to be 8.3; the carbonation time is about 45 min; to obtain 17.6 m 3 Ammonium bicarbonate solution I.

[0051] 7), the 17.6 m obtained by carbonation in step 6 3 The ammonium bicarbonate solution I obtained in step 6 is put into the ammonium bicarbonate dissolution and adjustment tank, and an appropriate amount of water (about 0.4 m 3 ) is added and stirred at 30 - 35 °C to obtain 18 m 3 ammonium bicarbonate solution II. The ammonium bicarbonate concentration of this ammonium bicarbonate solution II is 249.6 g / L, and the ammonium carbonate concentration is 0.36 g / L. This ammonium bicarbonate solution II is stored in the ammonium bicarbonate solution storage tank.

[0052] Note: The above results are the results obtained by "using the ammonium bicarbonate solution II obtained in step 7)" in step 4), and the results obtained by using an ammonium bicarbonate solution with a concentration of 250 g / L during the first production have no significant difference from the above results.

[0053] Example 2, A method for purifying a potassium bicarbonate mother liquor containing chloride, which successively performs the following steps:

[0054] 1), Mix 9.6 m 3 of the potassium bicarbonate mother liquor containing chloride and 2.5 m 3 of pure water in a dilution and batching tank to obtain a potassium bicarbonate solution III containing chloride with a density of 1.18 g / ml;

[0055] The potassium bicarbonate mother liquor containing chloride, in which the potassium chloride content is 25.3 g / L, the potassium bicarbonate concentration is 286 g / L, the potassium carbonate concentration is 253.1 g / L, the sodium carbonate concentration is 18.7 g / L, and the rest is water and other trace impurities.

[0056] 2), Take 12 m 3 of the potassium bicarbonate solution III containing chloride with a density of 1.18 g / ml obtained in step 1) and pass it through an ion exchange tower (resin model 001×7, ammonium type, resin volume 12 m 3 ) in countercurrent, with a flow rate of 6.0 m 3 / h (0.5 BV / h). From the top of the ion exchange tower, a mixed solution of ammonium chloride, ammonium bicarbonate, and ammonium carbonate of about 12 m 3 is obtained. In this mixed solution of ammonium chloride, ammonium bicarbonate, and ammonium carbonate, the ammonium chloride is 10.02 g / L, the ammonium bicarbonate is 124.2 g / L, and the ammonium carbonate is 102.3 g / L. This mixed solution of ammonium chloride, ammonium bicarbonate, and ammonium carbonate is stored in storage tank 1.

[0057] After the countercurrent of the potassium bicarbonate solution III containing chloride is completed, then use 6.0 m 3 (0.5 BV resin volume) of pure water to perform a co-current top wash on the potassium bicarbonate solution containing chloride in the ion exchange tower, and the flow rate is also 6.0 m 3 / h (0.5 BV / h), in the downflow direction. Therefore, a total of 6.0 m³ of a low-concentration potassium bicarbonate solution II containing chloride is obtained from the bottom of the ion exchange column. 3 This potassium bicarbonate solution II containing chloride is stored in storage tank II.

[0058] This low-concentration potassium bicarbonate solution II containing chloride has a potassium chloride content of 12.6 g / L, a potassium bicarbonate concentration of 143 g / L, a potassium carbonate concentration of 126.6 g / L, a sodium carbonate concentration of 9.4 g / L, and the rest is water and other trace impurities.

[0059] 3) The 12 m³ of the mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride obtained in step 2) enters the decomposition column and is thermally decomposed at 98 - 103 °C. As a result, a mixed gas containing ammonia, water vapor, and carbon dioxide is obtained from the top of the decomposition column, and 2.8 m³ of ammonium chloride solution is obtained from the bottom of the decomposition column. 3 The mixed gas of ammonia, water vapor, and carbon dioxide obtained from the top of the column enters the circulating absorption column and is absorbed with sufficient pure water to obtain 14.7 m³ of a mixed solution I of ammonium bicarbonate and ammonium carbonate. 3 which is stored in storage tank III. 3 In the mixed solution I of ammonium bicarbonate and ammonium carbonate, the ammonium bicarbonate content is 60.85 g / L, and the ammonium carbonate content is 108.1 g / L.

[0060] In the ammonium chloride solution, the ammonium chloride content is 42.9 g / L, the ammonium carbonate content is 3.1 g / L, and the rest is water, which is used for evaporation and crystallization to recover ammonium chloride.

[0061] 4) After washing (top washing) the potassium bicarbonate solution containing chloride in the ion exchange column with pure water in step 2), the resin in the ion exchange column is converted from the ammonium form to the potassium form. Then, 18 m³

[0062] (1.5 times the resin volume) of an ammonium bicarbonate solution with a concentration of about 250 g / L or the ammonium bicarbonate solution II obtained in subsequent step 7) is fed into the ion exchange column in the downflow direction at a flow rate of 0.5 BV / h (resin volume multiple). 3 Note: When first producing, an ammonium bicarbonate solution with a concentration of 250 g / L is obtained by dissolving ammonium bicarbonate solid raw materials in pure water. In subsequent production, the ammonium bicarbonate solution II obtained in step 7) is used.

[0063] After the ammonium bicarbonate solution (or ammonium bicarbonate solution II) is completely fed, 0.5 BV of pure water with the volume of the resin is used to perform a downflow top wash on the potassium bicarbonate solution containing ammonium bicarbonate in the ion exchange column, and a total of 18 m³ is obtained.

[0064] 3 ​A potassium bicarbonate solution containing ammonium bicarbonate, in which the potassium chloride concentration is 0.04 g / L, the ammonium bicarbonate concentration is 40.6 g / L, the potassium bicarbonate concentration is 251.7 g / L, the sodium bicarbonate concentration is 10.84 g / L, and the rest is water and other trace impurities.

[0065] 5), The potassium bicarbonate solution containing ammonium bicarbonate obtained in step 4) is subjected to evaporation crystallization using a 4-effect continuous evaporation crystallizer, specifically as described in Example 1, to obtain a potassium bicarbonate slurry.

[0066] During the evaporation crystallization process, ammonium bicarbonate in the potassium bicarbonate solution containing ammonium bicarbonate decomposes into ammonia and carbon dioxide, and then is absorbed by pure water through a circulating absorption tower to obtain 3.2 m 3 A mixed solution II containing ammonium carbonate and ammonium bicarbonate, in which the ammonium bicarbonate concentration is 136.8 g / L and the ammonium carbonate concentration is 55.4 g / L, and the rest is water; it is also stored in storage tank three, that is, mixed with the mixed solution I of ammonium bicarbonate and ammonium carbonate obtained in step 3) to form a mixed solution of ammonium bicarbonate and ammonium carbonate.

[0067] The above potassium bicarbonate slurry is cooled to 45 °C and then centrifuged to obtain 4796 Kg of potassium bicarbonate (wet product), and after drying, 4653 Kg of potassium bicarbonate is obtained, in which potassium chloride is 0.015%, potassium bicarbonate is 97.4%, sodium carbonate is 2.6%, and water is 0.04%, meeting the requirements of qualified products in the industrial potassium bicarbonate industry standard.

[0068] 6), The mixed solution of ammonium bicarbonate and ammonium carbonate enters the carbonation tower and undergoes a carbonation reaction with carbon dioxide to obtain 18.3 m 3 Ammonium bicarbonate solution I. During the carbonation process, the temperature is controlled at 40 - 50 °C, the pressure is 0.3 - 0.5 MPa, and the end point is controlled at a pH value of 8.2; the carbonation time is about 55 min.

[0069] 7), The 18.3 m 3 Ammonium bicarbonate solution I obtained by carbonation in step 6) is put into the ammonium bicarbonate dissolution adjustment tank, and 270 Kg of raw material ammonium bicarbonate is added and stirred at 30 - 35 °C to obtain 18.5 m 3 Ammonium bicarbonate solution II, in which the ammonium bicarbonate concentration is 250.6 g / L and the ammonium carbonate concentration is 0.47 g / L. This ammonium bicarbonate solution II is stored in the ammonium bicarbonate solution storage tank.

[0070] Note: The above results are the results obtained in step 4) by "using the ammonium bicarbonate solution II obtained in step 7)", and there is no significant difference between the results obtained using an ammonium bicarbonate solution with a concentration of 250 g / L during the first production and the above results.

[0071] Example 3. A method for purifying potassium bicarbonate mother liquor containing chloride. In step 1), the low-concentration potassium bicarbonate solution II containing chloride obtained from the ion exchange tower in step 2) of Example 2 is mixed with the potassium bicarbonate mother liquor containing chloride. Specifically, the following steps are carried out in sequence:

[0072] 1), Take 4.0 m 3 The low-concentration potassium bicarbonate solution II containing chloride obtained from the ion exchange tower in step 2) of Example 2 (the potassium chloride content is 12.6 g / L, the potassium bicarbonate concentration is 143 g / L, the potassium carbonate concentration is 126.6 g / L, the sodium carbonate concentration is 9.4 g / L, and the rest is water and other trace impurities) and 8.2 m 3 of the potassium bicarbonate mother liquor containing chloride are mixed in a dilution batching tank to obtain a potassium bicarbonate solution III containing chloride with a density of 1.20 g / ml (the potassium bicarbonate solution III containing chloride, in which the potassium chloride content is 37.41 g / L, the potassium bicarbonate concentration is 200.26 g / L, the potassium carbonate concentration is 233.19 g / L, the sodium carbonate concentration is 22.2 g / L, and the rest is water and other trace impurities);

[0073] The potassium bicarbonate mother liquor containing chloride, in which the potassium chloride content is 48.6 g / L, the potassium bicarbonate concentration is 223.3 g / L, the potassium carbonate concentration is 279.5 g / L, the sodium carbonate concentration is 27.9 g / L, and the rest is water and other trace impurities.

[0074] 2), Take 12 m 3 The potassium bicarbonate solution III containing chloride with a density of 1.20 g / ml obtained in step 1) flows countercurrently through an ion exchange tower (resin model is 001×7, ammonium type, resin volume is 12 m 3 ), and the flow rate is 6.0 m 3 / h (0.5 BV / h). From the top of the ion exchange tower, a mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride is obtained, about 12 m 3 . In this mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride, ammonium chloride is 18.79 g / L, ammonium bicarbonate is 110.72 g / L, and ammonium carbonate is 113.38 g / L. This mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride is stored in storage tank 1.

[0075] When the potassium bicarbonate solution III containing chloride has flowed countercurrently, then 6.0 m 3 (0.5 BV resin volume) of pure water is used to wash the potassium bicarbonate solution containing chloride in the ion exchange tower in a co-current manner, and the flow rate is also 6.0 m 3 / h (0.5 BV / h), co-current. Therefore, from the bottom of the ion exchange tower, a total volume of 6.0 m 3 of the low-concentration potassium bicarbonate solution II containing chloride is obtained. This potassium bicarbonate solution II containing chloride is stored in storage tank 2.

[0076] The potassium bicarbonate solution II containing chloride at low concentration has a potassium chloride content of 22.45 g / L, a potassium bicarbonate concentration of 133.98 g / L, a potassium carbonate concentration of 139.9 g / L, a sodium carbonate concentration of 13.3 g / L, and the rest is water and other trace impurities.

[0077] 3), the 12 m obtained in step 2 3 The mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride enters the decomposition tower and undergoes thermal decomposition at 98 - 103 °C, so as to obtain a mixed gas containing ammonia, water vapor and carbon dioxide from the top of the decomposition tower respectively and obtain 3.2 m of ammonium chloride solution from the bottom of the decomposition tower. 3 ; The mixed gas of ammonia, water vapor and carbon dioxide obtained from the top of the tower enters the circulation absorption tower and is absorbed with sufficient pure water to obtain 13.6 m of the mixed solution I of ammonium bicarbonate and ammonium carbonate. 3 and is stored in storage tank three.

[0078] In the mixed solution I of ammonium bicarbonate and ammonium carbonate, the ammonium bicarbonate is 68.39 g / L and the ammonium carbonate is 116.2 g / L.

[0079] In the ammonium chloride solution, the ammonium chloride content is 70.46 g / L, the ammonium carbonate is 2.8 g / L, and the rest is water, which is used for evaporation and crystallization to recover ammonium chloride.

[0080] 4), after washing (top washing) the potassium bicarbonate solution containing chloride in the ion exchange tower with pure water in step 2), the resin in the ion exchange tower changes from ammonium type to potassium type, and then 18 m 3 (1.5 times the resin volume) of ammonium bicarbonate solution with a concentration of 250 g / L or the ammonium bicarbonate solution II obtained in subsequent step 7) is fed into the ion exchange tower in a co-current manner, and the flow rate is 0.5 BV / h (resin volume multiple).

[0081] Note: When producing for the first time, the ammonium bicarbonate solution with a concentration of 250 g / L is obtained by dissolving ammonium bicarbonate solid raw materials in pure water, and in subsequent production, the ammonium bicarbonate solution II obtained in step 7) is used.

[0082] After the ammonium bicarbonate solution (or ammonium bicarbonate solution II) is fed completely, then 0.5 BV of pure water with the volume of the resin is used to top wash the potassium bicarbonate solution containing ammonium bicarbonate in the ion exchange tower in a co-current manner, and a total of 18 m 3 of potassium bicarbonate solution containing ammonium bicarbonate is obtained. In this potassium bicarbonate solution containing ammonium bicarbonate, the potassium chloride concentration is 0.04 g / L, the ammonium bicarbonate concentration is 42.3 g / L, the potassium bicarbonate concentration is 274.52 g / L, the sodium bicarbonate concentration is 16.42 g / L, and the rest is water and other trace impurities. This potassium bicarbonate solution containing ammonium bicarbonate is stored in storage tank four.

[0083] 5), The potassium bicarbonate solution containing ammonium bicarbonate obtained in step 4) is subjected to evaporation crystallization using a 4-effect continuous evaporation crystallizer, specifically as described in Example 1, to obtain a potassium bicarbonate slurry.

[0084] During the evaporation crystallization process, ammonium bicarbonate in the potassium bicarbonate solution containing ammonium bicarbonate decomposes into ammonia and carbon dioxide, which are then absorbed through a circulating absorption tower (absorbed with pure water) to obtain 3.6 m 3 A mixed solution II containing ammonium carbonate and ammonium bicarbonate, in which the concentration of ammonium bicarbonate is 148.05 g / L, the concentration of ammonium carbonate is 38.52 g / L, and the rest is water; it is also stored in storage tank three, that is, mixed with the mixed solution I of ammonium bicarbonate and ammonium carbonate obtained in step 3), thereby forming a mixed solution of ammonium bicarbonate and ammonium carbonate.

[0085] The above-mentioned potassium bicarbonate slurry is cooled to 45 °C and then centrifuged to obtain 5281.7 Kg of potassium bicarbonate (wet product). After drying, 5128 Kg of potassium bicarbonate is obtained, in which potassium chloride is 0.014%, potassium bicarbonate is 96.5%, sodium carbonate is 3.38%, and water is 0.04%, meeting the requirements of qualified products in the industrial potassium bicarbonate industry standard.

[0086] 6), The mixed solution of ammonium bicarbonate and ammonium carbonate enters a carbonation tower and undergoes a carbonation reaction with carbon dioxide to obtain 18.0 m 3 Ammonium bicarbonate solution I. During the carbonation process, the temperature is controlled at 40 - 50 °C, the pressure is 0.3 - 0.5 MPa, and the end-point controlled pH value is 8.3; the carbonation time is about 65 min.

[0087] 7), The 18.0 m 3 Ammonium bicarbonate solution I obtained by carbonation in step 6) is put into an ammonium bicarbonate dissolution adjustment tank, 210 Kg of raw material ammonium bicarbonate is added, and it is stirred at 30 - 35 °C to obtain 18.1 m 3 Ammonium bicarbonate solution II, in which the concentration of ammonium bicarbonate is 250.1 g / L and the concentration of ammonium carbonate is 0.56 g / L. This ammonium bicarbonate solution II is stored in an ammonium bicarbonate solution storage tank.

[0088] Comparative Example 1: The carbonation process in step 6) is cancelled, and the others are the same as in Example 2; specifically as follows:

[0089] Preceding steps: First, prepare an ammonium bicarbonate solution III containing ammonium carbonate: Mix 14.7 m 3 Of the mixed solution I of ammonium bicarbonate and ammonium carbonate obtained in step 3) of Example 1 and 3.2 m 3 Of the mixed solution II of ammonium bicarbonate and ammonium carbonate obtained in step 5), and then add 0.8 m 3 Of pure water to obtain approximately 18.4 m 3 An ammonium bicarbonate solution III containing ammonium carbonate;

[0090] Steps 1) to 3) are the same as Steps 1) to 3) of Example 2;

[0091] Step 4), change "ammonium bicarbonate solution II with a concentration of about 250 g / L" in "the 18 m obtained in Step 7)" to "ammonium bicarbonate solution III containing ammonium carbonate obtained in the above-mentioned previous steps", and the rest is the same as Step 4) of Example 2; 3 Change "ammonium bicarbonate solution II with a concentration of about 250 g / L" in "the 18 m obtained in Step 7)" to "ammonium bicarbonate solution III containing ammonium carbonate obtained in the above-mentioned previous steps", and the rest is the same as Step 4) of Example 2; 3 The rest is the same as Step 4) of Example 2;

[0092] The obtained result is:

[0093] A total of 18 m 3 Potassium bicarbonate solution containing ammonium bicarbonate is obtained. In this potassium bicarbonate solution containing ammonium bicarbonate, the potassium chloride concentration is 0.035 g / L, the ammonium carbonate concentration is 16.6 g / L, the ammonium bicarbonate concentration is 13.3 g / L, the potassium bicarbonate concentration is 70.48 g / L, the potassium carbonate concentration is 126.0 g / L, the sodium bicarbonate concentration is 3.1 g / L, the sodium carbonate concentration is 4.9 g / L, and the rest is water and trace impurities.

[0094] 5), The potassium bicarbonate solution containing ammonium bicarbonate obtained in Step 4) is subjected to evaporation crystallization using a 4-effect continuous evaporation crystallizer to obtain a potassium bicarbonate slurry;

[0095] After the above potassium bicarbonate slurry is cooled to 45°C and centrifuged, 4012 Kg of potassium bicarbonate (wet product) is obtained. After drying, 3649 Kg of potassium bicarbonate is obtained, in which potassium chloride is 0.013%, potassium bicarbonate is 34.8%, potassium carbonate is 62.1%, sodium carbonate is 3.06%, and water is 0.18%. The product does not meet the requirements of the qualified product of the industrial potassium bicarbonate industry standard.

[0096] Moreover, during the evaporation crystallization process, since the potassium bicarbonate solution containing ammonium bicarbonate obtained in Step 4) contains a large amount of potassium carbonate, the boiling point rises by up to 18°C. Therefore, compared with Example 2, the steam consumption for evaporation increases by 30%, and the dry weight loss of the obtained wet potassium bicarbonate product is as high as 10% (containing crystal water), making centrifugation difficult.

[0097] Therefore, it is not feasible to cancel the carbonation process in Step 6).

[0098] Comparative Example 2: The potassium bicarbonate mother liquor containing chloride in Step 1) of Example 1 is purified by carbonation, cooling crystallization, and centrifugal separation to obtain potassium bicarbonate and mother liquor. The specific operation is as follows:

[0099] 1), The potassium bicarbonate mother liquor containing chloride is put into a carbonation tower. During the carbonation process, the temperature is controlled at 60 - 80°C, the pressure is 0.3 - 0.5 MPa, the end point is controlled at a pH value of 8.4, and the carbonation time is about 90 min to obtain carbonated slurry I;

[0100] The potassium bicarbonate mother liquor containing chloride contains 20.8 g / L potassium chloride, 350 g / L potassium bicarbonate, 208.1 g / L potassium carbonate, 22.5 g / L sodium carbonate, and the rest is water and other trace impurities.

[0101] 2) The carbonated slurry I obtained in step 1) is transferred into a cooling crystallizer, cooled by cooling water, stirred at a speed of 32 r / min, and the temperature is reduced to 45° C., to obtain a slurry II after cooling and crystallization;

[0102] 3) The slurry II after cooling and crystallization obtained in step 2) is separated by centrifugation to obtain wet potassium bicarbonate, and 2372 kg of potassium bicarbonate is obtained after drying, wherein the potassium chloride is 0.42%, the potassium bicarbonate is 93.48%, the sodium bicarbonate is 5.94%, and the water content is 0.06%, which does not meet the requirements of industrial potassium bicarbonate industry standard qualified products.

[0103] Therefore, it can be seen from Comparative Example 2 that a qualified product cannot be obtained by purifying using the direct carbonation method.

[0104] Comparative Example 3: The potassium bicarbonate mother liquor containing chloride in step 1) of implementation 1 is directly evaporated and cooled for crystallization, and the potassium bicarbonate obtained after centrifugation is rinsed and purified. The specific operation is as follows:

[0105] 1) Implement the 10m 3 The potassium bicarbonate mother liquor containing chloride is evaporated and crystallized to obtain potassium bicarbonate slurry; the potassium bicarbonate slurry is cooled to 45°C and then centrifuged to obtain 1657 kg of potassium bicarbonate wet product I.

[0106] 2) 1657 kg of potassium bicarbonate wet product I obtained in step 1) is put into a pulping and washing kettle, 500 L of pure water is added to the washing kettle in advance, stirred and pulped for 60 minutes, and then centrifuged to obtain potassium bicarbonate wet product II;

[0107] 3) The potassium bicarbonate wet product II obtained in step 2) is dried to obtain 1057 kg of potassium bicarbonate, which contains 0.37% potassium chloride, 82.6% potassium bicarbonate, 12.3% potassium carbonate, 4.29% sodium carbonate, and 0.36% water.

[0108] The product does not meet the industry standard requirements for industrial potassium bicarbonate (HG / T2828-2010).

[0109] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for purifying potassium bicarbonate mother liquor containing chloride, characterized in that It includes the following steps: 1), Mix the potassium bicarbonate mother liquor containing chloride with pure water or with the low-concentration potassium bicarbonate solution II containing chloride obtained from the ion exchange column in step 2) to obtain a potassium bicarbonate solution III containing chloride with a density of 1.20 ± 0.05 g / ml; 2), Let the potassium bicarbonate solution III containing chloride obtained in step 1) flow through the ion exchange column in a countercurrent manner at a flow rate of 0.4 ± 0.1 BV / h. The volume of the potassium bicarbonate solution III containing chloride is 1.0 ± 0.1 BV. A mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride is obtained from the top of the ion exchange column, and the resin in the ion exchange column is converted from the ammonium form to the potassium form; After the countercurrent flow of the potassium bicarbonate solution III containing chloride is completed, then use pure water with a volume of 0.5 ± 0.1 BV to perform a co-current top wash on the ion exchange column at a flow rate of 0.5 ± 0.1 BV / h, and a low-concentration potassium bicarbonate solution II containing chloride is obtained from the bottom of the ion exchange column; 3), The mixed solution of ammonium bicarbonate and ammonium carbonate containing ammonium chloride obtained in step 2) enters the decomposition column and undergoes thermal decomposition to respectively obtain a mixed gas containing ammonia, water vapor and carbon dioxide, and an ammonium chloride solution; The said mixed gas enters the circulation absorption column and is absorbed by sufficient pure water to obtain a mixed solution I of ammonium bicarbonate and ammonium carbonate; 4), After using pure water to top wash the ion exchange column in step 2), then co-currently hang the ammonium bicarbonate solution with a concentration of 250 ± 10 g / L or the ammonium bicarbonate solution II obtained in subsequent step 7) into the ion exchange column at a flow rate of 0.5 ± 0.1 BV / h and a volume of 1.5 ± 0.1 BV to obtain a potassium bicarbonate solution containing ammonium bicarbonate; After the ammonium bicarbonate solution or the ammonium bicarbonate solution II is hung up, then use pure water with a volume of 0.5 ± 0.1 BV to perform a co-current top wash on the ion exchange column to obtain a potassium bicarbonate solution containing ammonium bicarbonate; 5), The potassium bicarbonate solution containing ammonium bicarbonate obtained in step 4) is subjected to evaporation crystallization, and the obtained potassium bicarbonate slurry is cooled and then centrifuged to obtain potassium bicarbonate; During the evaporation crystallization process, ammonium bicarbonate decomposes into ammonia and carbon dioxide, and then is absorbed through the circulation absorption column to obtain a mixed solution II of ammonium carbonate and ammonium bicarbonate; 6), After the mixed solution I of ammonium bicarbonate and ammonium carbonate obtained in step 3) and the mixed solution II of ammonium carbonate and ammonium bicarbonate obtained in step 5) are mixed, they are subjected to a carbonation reaction with carbon dioxide to obtain ammonium bicarbonate solution I; During the carbonation process, the temperature is controlled at 40 - 50 °C, the pressure is 0.3 - 0.5 MPa, and the end point is controlled with a pH value of 8.2 - 8.3; 7), Put the ammonium bicarbonate solution I obtained by carbonation in step 6) into the ammonium bicarbonate dissolution adjustment tank, add ammonium bicarbonate or pure water under stirring and stir at 30 - 35 °C, so that the concentration of ammonium bicarbonate in the obtained ammonium bicarbonate solution II is 250 ± 10 g / L.

2. The method for purifying the potassium bicarbonate mother liquor containing chloride according to claim 1, wherein: The ammonium chloride solution obtained in step 3) is subjected to evaporation crystallization and then ammonium chloride is recovered.

3. The method for purifying the potassium bicarbonate mother liquor containing chloride according to claim 1 or 2, characterized in that: The temperature of the thermal decomposition in step 3) is 98 - 103 °C.

4. The method for purifying potassium bicarbonate mother liquor containing chloride according to claim 3, wherein: The evaporation crystallization in step 5) is multi-effect continuous evaporation crystallization.

5. The method for purifying potassium bicarbonate mother liquor containing chloride according to claim 4, wherein: The potassium bicarbonate obtained in step 5) is a wet product, and is subsequently dried or calcined to obtain a finished product of potassium bicarbonate or a finished product of potassium carbonate.

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