A process for the recovery of potassium nitrate from a potassium containing waste stream or by-product

Abstract

The application discloses a method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-product, and comprises the following steps: step one, flowing the potassium-containing waste liquid through a modified special ion exchange column to obtain tail liquid and the ion exchange column after adsorption; step two, washing the ion exchange column after adsorption with an eluent until all the adsorbed substances are washed down to obtain potassium chloride eluent; and step three, mixing the potassium chloride eluent with a dilute nitric acid solution, adding an organic extractant for extraction, evaporating the extracted solution through three-stage vacuum evaporation to separate salt, and performing plate heat exchange between the high-temperature concentrated solution after evaporation and the extracted solution, then reducing to 35 DEG C and entering a vacuum flash evaporation cooling crystallization system to obtain potassium nitrate. The ammonium-type clinoptilolite and potassium selective chelating resin mixture cooperate with the extraction process, greatly reduce impurities, and cooperate with three-stage evaporation to remove trace impurities step by step, so that the product purity is improved step by step, and the solubility of potassium nitrate sharply decreases with temperature.

Description

Technical Field

[0001] This invention relates to the field of potassium nitrate recovery technology, and in particular to a method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products. Background Technology

[0002] Recovering potassium resources from potassium-containing wastewater, especially the production of high-value-added potassium nitrate (KNO3), is an important issue for comprehensive resource utilization and environmental protection. Existing potassium recovery processes are mostly based on precipitation or direct evaporation crystallization methods, but they generally suffer from problems such as low recovery rates, poor product purity, high energy consumption, or secondary pollution.

[0003] Potassium nitrate is an important inorganic chemical raw material, widely used in molten salt energy storage, optical glass, electronic ceramics, high-end fertilizers, gunpowder, and food preservation, with a large market demand. Currently, the mainstream industrial routes for potassium nitrate preparation fall into three categories: mineral conversion, potassium chloride-nitric acid metathesis extraction, and ammonium nitrate metathesis recycling. All of these processes use purchased refined potassium chloride solid as raw material, resulting in high raw material procurement costs. Furthermore, industries such as chemical production, metallurgical processing, and potash fertilizer processing continuously generate large quantities of potassium-containing wastewater and potassium salt byproduct leachate. These wastes contain a certain concentration of potassium ions; direct discharge not only causes significant potassium resource loss but also leads to environmental problems such as eutrophication of water bodies and soil salinization. Simple collection and stockpiling results in solid byproducts occupying space and posing a risk of leachate pollution. Therefore, developing a process for the resource-based recovery and preparation of potassium nitrate from waste potassium-containing wastewater and potassium byproducts has significant economic and environmental value.

[0004] Existing technologies for recovering potassium salts from potassium-containing waste liquids have many drawbacks: Direct evaporation crystallization process: This process requires no pretreatment, directly heating and evaporating potassium-containing waste liquid to precipitate salt. However, the waste liquid commonly contains impurities such as calcium, magnesium, sodium, heavy metals, and suspended solids. During concentration, scale-forming ions continuously accumulate, making the evaporator heat exchange tubes prone to scaling and blockage, requiring frequent shutdowns for acid washing and maintenance. Simultaneously, the potassium ion concentration in the waste liquid is low, the evaporation volume is huge, steam energy consumption is high, and the total potassium recovery rate is only 70%~78%. Chloride ions continuously accumulate during concentration, and hydrogen chloride volatilizes in large quantities under high-temperature conditions, causing strong corrosion to the evaporation and crystallization equipment. The entire system requires high-specification titanium materials for corrosion protection, significantly increasing equipment investment. The resulting product contains a large amount of mixed salts, with chloride ion and calcium / magnesium levels exceeding standards, making it only suitable as low-end agricultural potassium salt and unable to meet the requirements for high-purity industrial potassium nitrate. There is no heat recovery design, and the cooling stage relies on large chiller units, resulting in high refrigeration energy consumption.

[0005] Simple Organic Extraction Metathesis Process (IMI Extraction Method): This route relies on an organic extractant to separate hydrochloric acid generated from the reaction of potassium chloride and nitric acid, driving the metathesis reaction forward. However, the process lacks a pre-treatment enrichment unit, allowing calcium, magnesium, suspended solids, and heavy metals from potassium-containing wastewater to directly enter the extraction system. This easily leads to extractant emulsification, stratification, and failure, resulting in high extractant consumption and short replacement cycles. It also has high raw material requirements, only allowing the use of purchased refined potassium chloride solids, and cannot treat waste potassium-containing wastewater and potassium byproducts, limiting resource utilization. Furthermore, the downstream process only includes a single-stage evaporation and concentration, leading to the continuous accumulation of trace impurities in the mother liquor and limiting product purity. The high-temperature concentrated feed solution is directly cooled by water, resulting in complete heat energy waste and a lack of heat recovery system, leading to consistently high overall energy consumption.

[0006] In summary, existing technologies have four major pain points: First, they cannot efficiently adapt to low-impurity, low-concentration industrial potassium-containing waste liquids and potassium by-products, making it difficult to achieve high-value recovery of waste potassium resources; second, the purification unit is singular, impurities are not thoroughly removed, product purity is low, and industrial-grade high-purity potassium nitrate cannot be produced; third, reaction conversion efficiency is limited, potassium recovery rate is low, the combined energy consumption of steam, refrigeration, and reagents is high, equipment corrosion and scaling are severe, and operation and maintenance costs are high; fourth, by-product waste acid and high-salinity tailwater cannot be reused in a closed loop, resulting in large emissions of waste gas, wastewater, and solid waste, and significant environmental pressure. Summary of the Invention

[0007] In order to overcome the above-mentioned shortcomings of the prior art, the present invention proposes a method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products, comprising the following steps: Step 1: Pass the potassium-containing waste liquid through a modified special ion exchange column to obtain the tail liquid and the adsorbed ion exchange column; Step 2: Rinse the ion exchange column after adsorption with eluent until all the adsorbed substances are washed off to obtain potassium chloride eluent. Step 3: Mix potassium chloride eluent with dilute nitric acid solution, add organic extractant for extraction, and then pass the extracted solution through a three-stage vacuum evaporation process to precipitate salt. After evaporation, the high-temperature concentrated solution is subjected to plate heat exchange with the extracted solution. After cooling to 35°C, it enters a vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

[0009] Potassium ions are separated from a large number of other cations in the waste liquid using a modified ion exchange column. The modified ion exchange column selectively adsorbs potassium ions, and then a high-concentration potassium chloride solution is obtained through eluent. After mixing with dilute nitric acid, extraction is performed using an extractant to reduce impurity ions in the filtrate entering the evaporation. If extraction is not performed, the chloride ions will be directly lost during evaporation. -A large amount of NaCl mixed crystals will precipitate out; after extraction, the organic phase will carry away some of the Cl. - Impurities may be introduced, resulting in a higher proportion of KNO3 in the aqueous phase, thereby significantly improving the purity of KNO3 crystals after three-stage evaporation. Combined with plate heat exchange after three-stage evaporation, a dual heat energy cycle is achieved. Byproduct hydrochloric acid, extractant, and waste heat from heat exchange are all internally recycled and reused, and all waste liquid is recycled. There is no discharge of high-salt wastewater or hazardous residue. Existing processes alone cannot achieve a closed-loop chain. The extraction process in this invention is a mature process in the field, so it is not described in detail in this invention. Furthermore, in this invention, both the extractant and the ion exchange column can be recycled.

[0010] Preferably, in step three, the concentration of the dilute nitric acid solution is 20-25%, and the mass ratio of the dilute nitric acid solution, potassium chloride eluent, and organic extractant is 1-1.5:1:1.2-1.5.

[0011] Preferably, in step three, the three-stage vacuum evaporation salt precipitation includes: In the first stage, under a vacuum of 0.085-0.09 MPa and a temperature of 75-85℃, the reaction solution is introduced, the water is evaporated, and the first filtrate and the first mother liquor are precipitated. In the second stage, under a vacuum of 0.07-0.08 MPa and a temperature of 55-65℃, the first mother liquor from the first stage is further evaporated to precipitate the second filtrate and the second mother liquor. In the third stage, under a vacuum of 0.092-0.096 MPa and a temperature of 30-40℃, the second mother liquor from the second stage is further evaporated to precipitate the third filtrate and the high-temperature concentrate. After evaporation, the high-temperature concentrate is subjected to plate heat exchange with sodium nitrate and potassium chloride solutions. After cooling to 35℃, it enters the vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

[0012] After adopting the above technical solution, the first stage involves low-temperature dehydration and trace solvent extraction; the second stage involves medium-temperature precipitation and filtration of trace impurities; and the third stage involves deep high-temperature saturated concentration. Segmented temperature control avoids carbonization of organic matter and localized explosive precipitation, gradually removing trace impurities and improving product purity step by step. The solubility of potassium nitrate drops sharply with temperature, and the 35℃ mild vacuum flash evaporation relies on the latent heat of vaporization for self-cooling, eliminating the need for large-scale refrigeration units. The vacuum environment isolates air, preventing nitric acid oxidation and discoloration. The mild crystallization environment produces large and uniform crystals with fewer impurities in the mother liquor, eliminating the need for multiple recrystallizations.

[0013] Preferably, in step three, the three-stage vacuum evaporation salt precipitation includes: In the first stage, under a vacuum of 0.085 MPa and a temperature of 80°C, the reaction solution is introduced, the water is evaporated, and the first filtrate and the first mother liquor are precipitated. In the second stage, under a vacuum of 0.075 MPa and a temperature of 60°C, the first mother liquor from the first stage is further evaporated to precipitate the second filtrate and the second mother liquor. In the third stage, under a vacuum of 0.094 MPa and a temperature of 35°C, the second mother liquor from the second stage is further evaporated to precipitate the third filtrate and the high-temperature concentrate. After evaporation, the high-temperature concentrate is subjected to plate heat exchange with sodium nitrate and potassium chloride solutions. After cooling to 35°C, it enters the vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

[0014] Preferably, the modified ion exchange column is filled with a mixture of ammonium clinoptilolite and potassium selective chelating resin.

[0015] Preferably, the eluent is a 3-6% sodium chloride solution.

[0016] Preferably, the organic extract is tributyl phosphate.

[0017] Preferably, the tail liquid obtained in step one is refluxed back into the modified ion exchange column to obtain a secondary tail liquid and an ion exchange column after secondary adsorption.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The present invention uses a mixture of ammonium-type clinoptilolite and potassium selective chelating resin in an extraction process to significantly reduce impurities. Combined with three-stage evaporation, trace impurities are removed step by step, resulting in a progressively higher product purity. The solubility of potassium nitrate decreases sharply with temperature.

[0019] 2. Resin elution yields a high-concentration potassium chloride enriched solution, which significantly increases the potassium concentration compared to the original waste liquid, greatly reducing the amount of dilute nitric acid and organic extractant required, and lowering the subsequent evaporation water volume and reagent consumption.

[0020] 3. Plate heat exchangers recover the waste heat of high-temperature concentrate to preheat the feed, combined with three-stage vacuum evaporation and flash evaporation for secondary steam recovery. The overall steam energy consumption is significantly reduced compared to direct evaporation and single extraction processes; it also eliminates the need for external large-scale chillers, thus reducing refrigeration energy consumption. Detailed Implementation

[0021] The invention will now be described in detail with reference to the embodiments.

[0022] Example 1 A method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products includes the following steps: Step 1: Pass the potassium-containing waste liquid through a modified special ion exchange column to obtain the tail liquid and the adsorbed ion exchange column; The modified ion exchange column is filled with a mixture of ammonium-type clinoptilolite and potassium selective chelating resin. Step 2: Rinse the ion exchange column after adsorption with an eluent until all the adsorbed substances are washed off to obtain potassium chloride eluent. The eluent is a 3% sodium chloride solution. Step 3: Mix potassium chloride eluent with dilute nitric acid solution and add organic extractant for extraction. The extracted solution is then subjected to three-stage vacuum evaporation to precipitate salt. The high-temperature concentrate after evaporation is then subjected to plate heat exchange with the extracted solution. After cooling to 35°C, the solution is then introduced into a vacuum flash cooling crystallization system to obtain potassium nitrate. The organic extract is tributyl phosphate. The concentration of the dilute nitric acid solution is 20%, and the mass ratio of the dilute nitric acid solution, potassium chloride eluent, and organic extractant is 1:1:1.2.

[0023] The three-stage vacuum evaporation salt precipitation includes: In the first stage, under a vacuum of 0.085 MPa and a temperature of 75°C, the reaction solution is introduced, the water is evaporated, and the first filtrate and the first mother liquor are precipitated. In the second stage, under a vacuum of 0.07 MPa and a temperature of 55°C, the first mother liquor from the first stage is further evaporated to precipitate the second filtrate and the second mother liquor. In the third stage, under a vacuum of 0.092 MPa and a temperature of 30°C, the second mother liquor from the second stage is further evaporated to precipitate the third filtrate and the high-temperature concentrate. After evaporation, the high-temperature concentrate is subjected to plate heat exchange with sodium nitrate and potassium chloride solutions. After cooling to 35°C, it enters the vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

[0024] Example 2 A method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products includes the following steps: Step 1: Pass the potassium-containing waste liquid through a modified special ion exchange column to obtain the tail liquid and the adsorbed ion exchange column; The modified ion exchange column is filled with a mixture of ammonium-type clinoptilolite and potassium selective chelating resin. Step 2: Rinse the ion exchange column after adsorption with an eluent until all the adsorbed substances are washed off to obtain potassium chloride eluent. The eluent is a 5% sodium chloride solution. Step 3: Mix potassium chloride eluent with dilute nitric acid solution and add organic extractant for extraction. The extracted solution is then subjected to three-stage vacuum evaporation to precipitate salt. The high-temperature concentrate after evaporation is then subjected to plate heat exchange with the extracted solution. After cooling to 35°C, the solution is then introduced into a vacuum flash cooling crystallization system to obtain potassium nitrate. The organic extract is tributyl phosphate. The concentration of the dilute nitric acid solution is 20%, and the mass ratio of the dilute nitric acid solution, potassium chloride eluent, and organic extractant is 1.5:1:1.2.

[0025] The three-stage vacuum evaporation salt precipitation includes: In the first stage, under a vacuum of 0.085 MPa and a temperature of 80°C, the reaction solution is introduced, the water is evaporated, and the first filtrate and the first mother liquor are precipitated. In the second stage, under a vacuum of 0.075 MPa and a temperature of 60°C, the first mother liquor from the first stage is further evaporated to precipitate the second filtrate and the second mother liquor. In the third stage, under a vacuum of 0.094 MPa and a temperature of 35°C, the second mother liquor from the second stage is further evaporated to precipitate the third filtrate and the high-temperature concentrate. After evaporation, the high-temperature concentrate is subjected to plate heat exchange with sodium nitrate and potassium chloride solutions. After cooling to 35°C, it enters the vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

[0026] Example 3 A method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products includes the following steps: Step 1: Pass the potassium-containing waste liquid through a modified special ion exchange column to obtain the tail liquid and the adsorbed ion exchange column; The modified ion exchange column is filled with a mixture of ammonium-type clinoptilolite and potassium selective chelating resin. Step 2: Rinse the ion exchange column after adsorption with an eluent until all the adsorbed substances are washed off to obtain potassium chloride eluent. The eluent is a 6% sodium chloride solution. Step 3: Mix potassium chloride eluent with dilute nitric acid solution and add organic extractant for extraction. The extracted solution is then subjected to three-stage vacuum evaporation to precipitate salt. The high-temperature concentrate after evaporation is then subjected to plate heat exchange with the extracted solution. After cooling to 35°C, the solution is then introduced into a vacuum flash cooling crystallization system to obtain potassium nitrate. The organic extract is tributyl phosphate. The concentration of the dilute nitric acid solution is 25%, and the mass ratio of the dilute nitric acid solution, potassium chloride eluent, and organic extractant is 1.5:1:1.5.

[0027] The three-stage vacuum evaporation salt precipitation includes: In the first stage, under a vacuum of 0.09 MPa and a temperature of 85°C, the reaction solution is introduced, the water is evaporated, and the first filtrate and the first mother liquor are precipitated. In the second stage, under a vacuum of 0.08 MPa and a temperature of 65°C, the first mother liquor from the first stage is further evaporated to precipitate the second filtrate and the second mother liquor. In the third stage, under a vacuum of 0.096 MPa and a temperature of 40°C, the second mother liquor from the second stage is further evaporated to precipitate the third filtrate and the high-temperature concentrate. After evaporation, the high-temperature concentrate is subjected to plate heat exchange with sodium nitrate and potassium chloride solutions. After cooling to 35°C, it enters the vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

[0028] Comparative Example 1 Compared with Example 2, in Comparative Example 1, the potassium-containing waste liquid was not effluented through a modified special ion exchange column, but nitric acid was added directly. The rest was the same as in Example 2.

[0029] Comparative Example 2 Compared with Example 2, Comparative Example 2 did not undergo organic extraction, but was otherwise the same as Example 2.

[0030] Comparative Example 3 Compared with Example 2, Comparative Example 3 did not pass through an ion exchange column before extraction, but instead eluted and then added nitric acid before evaporation. The rest was the same as Example 2.

[0031] Comparative Example 4 Compared with Example 2, Comparative Example 4 did not undergo three-stage evaporation, but was otherwise the same as Example 2.

[0032] Comparative Example 5 Compared with Example 2, Comparative Example 5 did not use plate heat exchange between the high-temperature concentrated liquid after evaporation and the solution after extraction; otherwise, it was the same as Example 2.

[0033] Using the same batch of waste liquid as raw material, it was divided into 8 portions and the recovery methods of Examples 1-3 and Comparative Examples 1-5 were used for process recovery. The final potassium nitrate recovery rate and potassium nitrate concentration were calculated. The specific data are shown in Table 1. Table 1 ; As can be seen from Table 1, Examples 1-3 are the optimal solutions.

[0034] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the patent and its protection scope should be determined by the appended claims.

Claims

1. A method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products, characterized in that, Includes the following steps, Step 1: Pass the potassium-containing waste liquid through a modified special ion exchange column to obtain the tail liquid and the adsorbed ion exchange column; Step 2: Rinse the ion exchange column after adsorption with eluent until all the adsorbed substances are washed off to obtain potassium chloride eluent. Step 3: Mix potassium chloride eluent with dilute nitric acid solution, add organic extractant for extraction, and then pass the extracted solution through a three-stage vacuum evaporation process to precipitate salt. After evaporation, the high-temperature concentrated solution is subjected to plate heat exchange with the extracted solution. After cooling to 35°C, it enters a vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

2. The method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products as described in claim 1, characterized in that, In step three, the concentration of the dilute nitric acid solution is 20-25%, and the mass ratio of the dilute nitric acid solution, potassium chloride eluent, and organic extractant is 1-1.5:1:1.2-1.

5.

3. The method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products as described in claim 2, characterized in that, In step three, the three-stage vacuum evaporation salt precipitation includes: In the first stage, under a vacuum of 0.085-0.09 MPa and a temperature of 75-85℃, the reaction solution is introduced, the water is evaporated, and the first filtrate and the first mother liquor are precipitated. In the second stage, under a vacuum of 0.07-0.08 MPa and a temperature of 55-65℃, the first mother liquor from the first stage is further evaporated to precipitate the second filtrate and the second mother liquor. In the third stage, under a vacuum of 0.092-0.096 MPa and a temperature of 30-40℃, the second mother liquor from the second stage is further evaporated to precipitate the third filtrate and the high-temperature concentrate. After evaporation, the high-temperature concentrate is subjected to plate heat exchange with sodium nitrate and potassium chloride solutions. After cooling to 35℃, it enters the vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

4. The method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products as described in claim 2, characterized in that, In step three, the three-stage vacuum evaporation salt precipitation includes: In the first stage, under a vacuum of 0.085 MPa and a temperature of 80°C, the reaction solution is introduced, the water is evaporated, and the first filtrate and the first mother liquor are precipitated. In the second stage, under a vacuum of 0.075 MPa and a temperature of 60°C, the first mother liquor from the first stage is further evaporated to precipitate the second filtrate and the second mother liquor. In the third stage, under a vacuum of 0.094 MPa and a temperature of 35°C, the second mother liquor from the second stage is further evaporated to precipitate the third filtrate and the high-temperature concentrate. After evaporation, the high-temperature concentrate is subjected to plate heat exchange with sodium nitrate and potassium chloride solutions. After cooling to 35°C, it enters the vacuum flash evaporation cooling crystallization system to obtain potassium nitrate.

5. A method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products as described in any one of claims 3 or 4, characterized in that, The modified ion exchange column is filled with a mixture of ammonium-type clinoptilolite and potassium selective chelating resin.

6. A method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products as described in any one of claims 3 or 4, characterized in that, The eluent is a 3-6% sodium chloride solution.

7. A method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products as described in any one of claims 3 or 4, characterized in that, The organic extract is tributyl phosphate.

8. A method for recovering and preparing potassium nitrate from potassium-containing waste liquid or by-products as described in any one of claims 3 or 4, characterized in that, The tail liquid obtained in step one is refluxed back into the modified ion exchange column to obtain a secondary tail liquid and a secondary adsorption ion exchange column.