Alkali-process activated carbon multi-stage synergistic potassium removal method

Abstract

The invention relates to an alkaline activated carbon multi-stage synergistic potassium removal method, and belongs to the technical field of activated carbon materials. According to the method, a four-step synergistic process of water washing, acid pickling, ion exchange and nitrogen calcination is adopted, and a waste acid recycling closed-loop system is combined. The deep removal of residual potassium is realized through the synergistic effect of countercurrent water washing, pH (Potential of Hydrogen) staged regulation and control acid washing, deep potassium removal by ion exchange resin and nitrogen protection calcination, and meanwhile, the high specific surface area is maintained; the pickling waste liquid is neutralized, concentrated and crystallized to be converted into agricultural potash fertilizer, and mother liquid is recycled to form green circulation.

Description

Technical Field

[0001] The invention belongs to the technical field of activated carbon materials and relates to a multi-stage collaborative potassium removal method of alkaline activated carbon. Background Art

[0002] In the production of activated carbon, the residual potassium salt is a key issue. Alkali activated carbon is usually treated by soaking in an alkaline solution to remove harmful impurities, but potassium ions will still remain in the final product, which will have a negative impact on its subsequent application. Especially in high-end application areas such as supercapacitors, medicine, and the food industry, the potassium content of activated carbon must be strictly controlled. Potassium ions can cause short circuits and self-discharge in electrochemical equipment, affecting performance and safety. In the fields of medicine and food, high levels of potassium salts will cause products to fail to comply with relevant regulations and cannot be put on the market. Therefore, removing potassium salts from activated carbon is not only the key to improving product performance and safety.

[0003] Currently, the main methods for removing potassium salts from activated carbon include water washing, acid washing, and high-temperature calcination. Water washing usually involves counter-flushing the activated carbon with high-temperature water to help remove some soluble salts; acid washing uses an acidic solution to dissolve the potassium salts, thereby removing the potassium salts. The high-temperature calcination method heats the activated carbon to a certain temperature, decomposes the potassium salts in a reducing atmosphere, and repairs the carbon pore structure. Although these technologies can achieve the removal of potassium salts to a certain extent, they each have different limitations. For example, water washing may not be able to effectively remove deeply embedded potassium salts, acid washing can cause damage to the activated carbon surface, and high-temperature calcination requires high energy consumption and has limited effect on restoring the pore structure.

[0004] Although the existing technologies have solved the problem of potassium salt removal to a certain extent, they generally have some shortcomings that affect process efficiency and product quality. For example, a single pickling method easily leads to incomplete removal of potassium ions, and the use of acid solution and the treatment of waste acid increase production costs and environmental pressure. In addition, most of the existing technologies do not have an effective waste liquid recovery and resource utilization system, resulting in water resource waste and waste discharge problems. Therefore, there is an urgent need for a more efficient, economical and green multi-stage synergistic potassium removal process to cope with the increasingly stringent market demand and environmental protection requirements. Summary of the Invention

[0005] The object of the present invention is to provide a multi-stage collaborative potassium removal method for alkaline activated carbon, which can achieve deep removal of residual potassium while maintaining a high specific surface area of the activated carbon.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A multi-stage collaborative potassium removal method using alkaline activated carbon comprises the following steps: (1) Wash the alkaline activated carbon in hot water at 60-80°C; (2) washing the activated carbon treated in step (1) with a mixed acid solution containing HCl and HNO3; (3) The residual K on the activated carbon treated in step (2) is adsorbed by sodium cation exchange resin. + , the resin regeneration liquid is used to be added to the mixed acid solution containing solution; (4) calcining the activated carbon treated in step (4) at 380-420° C. in a nitrogen atmosphere; (5) neutralizing the pickling waste liquid obtained in step (2) to prepare potash fertilizer.

[0007] In this application, a multi-stage synergistic potassium removal method is used: first, hot water countercurrent washing is used to remove water-soluble salts, then acid washing is used to remove bound potassium such as K2CO3, ion exchange deep adsorption is performed, and finally, stubborn bound potassium such as K2O is removed by high-temperature decomposition.

[0008] As a preferred technical solution of the present invention, the mass ratio of the activated carbon to the washing water in step (1) is 1:5-8.

[0009] As a preferred technical solution of the present invention, the mixed acid solution in step (2) contains HCl and HNO3 in a volume ratio of 2-4:1.

[0010] As a preferred technical solution of the present invention, the acid washing in step (2) is based on the feedback of the pH electrode to adjust the acid flow rate. The pH is controlled at 1.5-2.0 during the pickling time of 0-30 minutes. The strong acid dissociates K2CO3. The pH is controlled at 2.0-2.5 during the pickling time of 30-60 minutes, further dissolving the free potassium and reducing the H + concentration, inhibit micropore corrosion, control the pH at 2.5-3.0 during pickling for 60-120 minutes, and transition to ion exchange to prevent strong acid from damaging the resin functional groups.

[0011] As a preferred technical solution of the present invention, the sodium type cation exchange resin in step (3) is a sodium type sulfonic acid resin column D001 type.

[0012] As a preferred technical solution of the present invention, the ion exchange flow rate in step (3) is 0.5-2 BV / h.

[0013] As a preferred technical solution of the present invention, the calcination time in step (4) is 40-80 minutes.

[0014] As a preferred technical solution of the present invention, the resin after ion exchange in step (3) is regenerated and backwashed with 8-12 wt% NaCl solution.

[0015] As a preferred technical solution of the present invention, the neutralization of the pickling wastewater to prepare potash fertilizer in step (5) specifically comprises the following steps: A1. Add MgO to the pickling wastewater to adjust the pH to 6.5-7.5 to generate heavy metal precipitates; A2, separate the precipitate, and evaporate the filtrate to concentrate to K + Concentration ≥ 200 g / L; A3. Cool to 25-30°C and add KCl seed crystals. Stir evenly and let stand for 3-6 hours. Centrifuge to obtain KCl crystals. A4. The mother liquor is returned to the pickling process in step (b) for recycling.

[0016] As a preferred technical solution of the present invention, the seed crystal is KCl powder with a particle size of 0.1-0.5 mm; the amount of seed crystal added is 0.3-1 wt%.

[0017] Beneficial effects of the present invention: (1) The present invention uses a multi-stage potassium removal method to reduce the potassium residue from >3000 ppm to ≤20 ppm and the specific surface area of the activated carbon after calcination is ≥1200 m 2 / g, adsorption performance retention rate ≥95%.

[0018] (2) The present invention removes water-soluble salts by washing with water and then removes bound potassium in the activated carbon by real-time pH control while avoiding corrosion of the activated carbon and damage to the ion exchange resin. The potassium residue is further reduced and the pore structure of the activated carbon is restored by calcination under nitrogen protection.

[0019] (3) The present invention realizes resource recycling by preparing potash fertilizer through water circulation and neutralization of pickling waste liquid. DETAILED DESCRIPTION

[0020] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0021] Example 1 A multi-stage collaborative potassium removal method using alkaline activated carbon comprises the following steps: (1) Wash the alkaline activated carbon in hot water at 75°C; (2) washing the activated carbon treated in step (1) with a mixed acid solution containing HCl and HNO3; (3) The residual K on the activated carbon treated in step (2) is adsorbed by sodium cation exchange resin. + , the resin regeneration liquid is used to be added to the mixed acid solution containing solution; (4) calcining the activated carbon treated in step (4) at 400° C. in a nitrogen atmosphere; (5) neutralizing the pickling waste liquid obtained in step (2) to prepare potash fertilizer.

[0022] The mass ratio of the activated carbon to the washing water in step (1) is 1:7.

[0023] The mixed acid solution in step (2) contains HCl and HNO3 in a volume ratio of 3:1.

[0024] The pickling in step (2) is based on the feedback of the pH electrode to adjust the flow rate of the acid solution. The pH is controlled at 1.8 during the pickling period of 0-30 minutes, at 2.2 during the pickling period of 30-60 minutes, and at 2.7 during the pickling period of 60-120 minutes.

[0025] The sodium type cation exchange resin in step (3) is a sodium type sulfonic acid resin column D001 type.

[0026] The ion exchange flow rate in step (3) is 1 BV / h.

[0027] The calcination time in step (4) is 60 minutes.

[0028] The resin after ion exchange in step (3) was regenerated by backwashing with 10 wt% NaCl solution.

[0029] The step (5) of neutralizing the pickling wastewater to prepare potash fertilizer specifically comprises the following steps: A1. Add MgO to the pickling wastewater to adjust the pH to 7.0 to generate heavy metal precipitates; A2, separate the precipitate, and evaporate the filtrate to concentrate to K + The concentration is 300g / L; A3. Cool to 28°C and add KCl seed crystals. Stir evenly and let stand for 5 hours. Centrifuge to obtain KCl crystals. A4. The mother liquor is returned to the pickling process in step (b) for recycling.

[0030] The seed crystal is KCl powder with a particle size of 0.1-0.5 mm; the added amount of the seed crystal is 0.7 wt %.

[0031] Example 2 A multi-stage collaborative potassium removal method using alkaline activated carbon comprises the following steps: (1) Wash the alkaline activated carbon in hot water at 75°C; (2) washing the activated carbon treated in step (1) with a mixed acid solution containing HCl and HNO3; (3) adsorbing the residual K+ on the activated carbon treated in step (2) through a sodium cation exchange resin, and adding the resin regeneration liquid to the mixed acid solution; (4) calcining the activated carbon treated in step (4) at 400° C. in a nitrogen atmosphere; (5) neutralizing the pickling waste liquid obtained in step (2) to prepare potash fertilizer.

[0032] The mass ratio of the activated carbon to the washing water in step (1) is 1:6.

[0033] The mixed acid solution in step (2) contains HCl and HNO3 in a volume ratio of 3:1.

[0034] The pickling in step (2) is based on the feedback of the pH electrode to adjust the flow rate of the acid solution. The pH is controlled at 1.6 during the pickling period of 0-30 minutes, at 2.3 during the pickling period of 30-60 minutes, and at 2.8 during the pickling period of 60-120 minutes.

[0035] The sodium type cation exchange resin in step (3) is a sodium type sulfonic acid resin column D001 type.

[0036] The ion exchange flow rate in step (3) is 1.5 BV / h.

[0037] The calcination time in step (4) is 60 minutes.

[0038] The resin after ion exchange in step (3) was regenerated by backwashing with 10 wt% NaCl solution.

[0039] The step (5) of neutralizing the pickling wastewater to prepare potash fertilizer specifically comprises the following steps: A1. Add MgO to the pickling wastewater to adjust the pH to 7.0 to generate heavy metal precipitates; A2, separate the precipitate, and evaporate the filtrate to concentrate to K + The concentration is 250g / L; A3. Cool to 27°C and add KCl seed crystals. Stir evenly and let stand for 4.5 hours. Centrifuge to obtain KCl crystals. A4. The mother liquor is returned to the pickling process in step (b) for recycling.

[0040] The seed crystal is KCl powder with a particle size of 0.1-0.5 mm; the added amount of the seed crystal is 0.6 wt %.

[0041] Example 3 A multi-stage collaborative potassium removal method using alkaline activated carbon comprises the following steps: (1) Wash the alkaline activated carbon in hot water at 60°C; (2) washing the activated carbon treated in step (1) with a mixed acid solution containing HCl and HNO3; (3) adsorbing the residual K+ on the activated carbon treated in step (2) through a sodium cation exchange resin, and adding the resin regeneration liquid to the mixed acid solution; (4) calcining the activated carbon treated in step (4) at 380° C. in a nitrogen atmosphere; (5) neutralizing the pickling waste liquid obtained in step (2) to prepare potash fertilizer.

[0042] The mass ratio of the activated carbon to the washing water in step (1) is 1:5.

[0043] The mixed acid solution in step (2) contains HCl and HNO3 in a volume ratio of 2:1.

[0044] The pickling in step (2) is based on the feedback of the pH electrode to adjust the flow rate of the acid solution. The pH is controlled at 1.5 during the pickling period of 0-30 minutes, at 2.0 during the pickling period of 30-60 minutes, and at 2.5 during the pickling period of 60-120 minutes.

[0045] The sodium type cation exchange resin in step (3) is a sodium type sulfonic acid resin column D001 type.

[0046] The ion exchange flow rate in step (3) is 0.5 BV / h.

[0047] The calcination time in step (4) is 40 minutes.

[0048] The resin after ion exchange in step (3) was regenerated by backwashing with 8 wt% NaCl solution.

[0049] The step (5) of neutralizing the pickling wastewater to prepare potash fertilizer specifically comprises the following steps: A1. Add MgO to the pickling wastewater to adjust the pH to 6.5 to generate heavy metal precipitates; A2, separate the precipitate, and evaporate the filtrate to concentrate to K + The concentration is 200g / L; A3. Cool to 25°C and add KCl seed crystals. Stir evenly and let stand for 3 hours. Centrifuge to obtain KCl crystals. A4. The mother liquor is returned to the pickling process in step (b) for recycling.

[0050] The seed crystal is KCl powder with a particle size of 0.1-0.5 mm; the added amount of the seed crystal is 0.3 wt %.

[0051] Example 4 A multi-stage collaborative potassium removal method using alkaline activated carbon comprises the following steps: (1) Wash the alkaline activated carbon in hot water at 80°C; (2) washing the activated carbon treated in step (1) with a mixed acid solution containing HCl and HNO3; (3) adsorbing the residual K+ on the activated carbon treated in step (2) through a sodium cation exchange resin, and adding the resin regeneration liquid to the mixed acid solution; (4) calcining the activated carbon treated in step (4) at 420° C. in a nitrogen atmosphere; (5) neutralizing the pickling waste liquid obtained in step (2) to prepare potash fertilizer.

[0052] The mass ratio of the activated carbon to the washing water in step (1) is 1:8.

[0053] The mixed acid solution in step (2) contains HCl and HNO3 in a volume ratio of 4:1.

[0054] The pickling in step (2) is based on the pH electrode feedback to adjust the acid flow rate, and the pH is controlled at 2.0 during the pickling period of 0-30 minutes, the pH is controlled at 2.5 during the pickling period of 30-60 minutes, and the pH is controlled at 3.0 during the pickling period of 60-120 minutes.

[0055] The sodium type cation exchange resin in step (3) is a sodium type sulfonic acid resin column D001 type.

[0056] The ion exchange flow rate in step (3) is 2 BV / h.

[0057] The calcination time in step (4) is 80 minutes.

[0058] The resin after ion exchange in step (3) was regenerated by backwashing with 12 wt% NaCl solution.

[0059] The step (5) of neutralizing the pickling wastewater to prepare potash fertilizer specifically comprises the following steps: A1. Add MgO to the pickling wastewater to adjust the pH to 7.5 to generate heavy metal precipitates; A2, separate the precipitate, and evaporate the filtrate to concentrate to K + The concentration is 400g / L; A3. Cool to 30°C and add KCl seed crystals. Stir evenly and let stand for 6 hours. Centrifuge to obtain KCl crystals. A4. The mother liquor is returned to the pickling process in step (b) for recycling.

[0060] The seed crystal is KCl powder with a particle size of 0.1-0.5 mm; the amount of seed crystal added is 1 wt %.

[0061] Comparative Example 1 On the basis of Example 1, step (2) pickling treatment was omitted, and the rest remained the same as Example 1.

[0062] Comparative Example 2 On the basis of Example 1, the pH value during pickling was always controlled at 1.8, and the rest was consistent with Example 1.

[0063] Comparative Example 3 On the basis of Example 1, the pH value during pickling was always controlled at 2.7, and the rest was consistent with Example 1.

[0064] Comparative Example 4 On the basis of Example 1, the calcination atmosphere in step (4) was changed from nitrogen to air, and the rest remained the same as Example 1.

[0065] Comparative Example 5 On the basis of Example 1, step A1 uses Ca(OH)2 instead of MgO, and the rest remains the same as Example 1.

[0066] Performance testing: Potassium residue: Weigh 0.4 g of sample into a digestion vessel, add 8 mL of HNO3 and 2 mL of HClO4, seal the vessel, and digest at elevated temperature (180°C for 2 hours). After cooling, transfer the sample to 50 mL and determine the potassium residue in the activated carbon using ICP-OES. Specific surface area: According to ASTM D6556-19 standard, BET nitrogen adsorption test; Iodine adsorption: tested according to GB / T 12496.8-2015 standard iodine solution titration method; Carbon tetrachloride adsorption rate: tested according to GB / T 7702.19-2008 standard; Organic solvent removal rate: tested according to the benzene / toluene solution adsorption-gravimetric method of the 2025 edition of the Chinese Pharmacopoeia.

[0067] It can be seen from the above test results that comparative example 1 was not pickled, and the potassium removal rate was seriously reduced; comparative examples 2-4 reflect the importance of real-time pH control during pickling. When the acidity is too strong, it is easy to cause micropore collapse and a serious reduction in specific surface area. When the acidity is weak, the potassium residue is higher; comparative example 4 is calcined and oxidized in air to lose the carbon skeleton, and the carbon tetrachloride adsorption rate is significantly reduced. Comparative example 5 uses Ca(OH)2 instead of MgO to introduce CaSO4, which may be an impurity, and the crystal purity is reduced and the evaporating dish is scaled.

[0068] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to equivalent embodiments using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any indirect modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A multi-stage collaborative potassium removal method using alkaline activated carbon, characterized in that: The following steps are involved: (1) Wash the alkaline activated carbon in hot water at 60-80°C; (2) washing the activated carbon treated in step (1) with a mixed acid solution containing HCl and HNO3; (3) The residual K on the activated carbon treated in step (2) is adsorbed by sodium cation exchange resin. + , the resin regeneration liquid is used to be added to the mixed acid solution containing solution; (4) calcining the activated carbon treated in step (4) at 380-420° C. in a nitrogen atmosphere; (5) neutralizing the pickling waste liquid obtained in step (2) to prepare potash fertilizer.

2. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 1, characterized in that: The mass ratio of the activated carbon to the washing water in step (1) is 1:5-8.

3. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 1, characterized in that: The mixed acid solution in step (2) contains HCl and HNO3 in a volume ratio of 2-4:

1.

4. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 1, characterized in that: The pickling in step (2) is based on the feedback of the pH electrode to adjust the flow rate of the acid solution. The pH is controlled at 1.5-2.0 during the pickling time of 0-30 minutes, the pH is controlled at 2.0-2.5 during the pickling time of 30-60 minutes, and the pH is controlled at 2.5-3.0 during the pickling time of 60-120 minutes.

5. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 1, characterized in that: The sodium type cation exchange resin in step (3) is a sodium type sulfonic acid resin column D001 type.

6. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 1, characterized in that: The ion exchange flow rate in step (3) is 0.5-2 BV / h.

7. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 1, characterized in that: The calcination time in step (4) is 40-80 minutes.

8. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 1, characterized in that: After the ion exchange in step (3), the resin is regenerated by backwashing with 8-12 wt% NaCl solution.

9. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 1, characterized in that: The step (5) of neutralizing the pickling wastewater to prepare potash fertilizer specifically comprises the following steps: A1. Add MgO to the pickling wastewater to adjust the pH to 6.5-7.5 to generate heavy metal precipitates; A2, separate the precipitate, and evaporate the filtrate to concentrate to K + Concentration ≥ 200 g / L; A3. Cool to 25-30°C and add KCl seed crystals. Stir evenly and let stand for 3-6 hours. Centrifuge to obtain KCl crystals. A4. The mother liquor is returned to the pickling process in step (b) for recycling.

10. The multi-stage synergistic potassium removal method using alkaline activated carbon according to claim 9, characterized in that: The seed crystal is KCl powder with a particle size of 0.1-0.5 mm; the amount of seed crystal added is 0.3-1 wt%.

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