Method for decalcification and carbon sequestration of fly ash water washing solution

Abstract

The application discloses a method for removing calcium and fixing carbon in fly ash washing liquid. The method uses the extraction of insoluble organic amine on acid to improve the pH value of the washing liquid system, continuously absorbs CO2, and realizes the complete removal of calcium in the fly ash washing liquid. The amine in the organic phase is regenerated by alkali, and the small amount of mixed organic diluent in the washing liquid is separated by azeotropic distillation to realize the reuse. The calcium carbonate product prepared by the method has small particles and high purity, is a high-quality globular aragonite type calcium carbonate particle, and can be used as a good adsorbent and additive material and has wide application in many fields.

Description

Technical Field

[0001] This invention belongs to the field of fly ash resource utilization technology, specifically relating to a method for enhancing the decalcification and carbon fixation of fly ash washing liquid using organic amines as a medium. Background Technology

[0002] Co-processing technology for cement kiln fly ash is currently an important treatment pathway for waste incineration fly ash. However, fly ash also contains a large amount of chlorides, which affects the quality of cement products and can also corrode cement kilns. Therefore, waste incineration fly ash needs to undergo pretreatment with water washing and dechlorination before being fed into cement kiln production. The fly ash washing liquid can be concentrated, evaporated, and crystallized to obtain chloride products, enabling resource recovery. At the same time, the desalinated water can also be reused.

[0003] However, the high calcium ion concentration (0.5–2%) in the washing solution can cause scaling in the evaporation system, affecting the stable operation of the equipment. Furthermore, the presence of calcium will affect the subsequent crystallization of sodium chloride and potassium chloride, leading to disruption of the entire system's circulation. Therefore, decalcification treatment is necessary. The commonly used soda ash decalcification method requires approximately 120 kg of soda ash per ton of washing solution. On the other hand, the washing solution is alkaline, with a pH of around 11.8, and has strong buffering capacity; neutralizing each ton of washing solution requires approximately 30–40 kg of hydrochloric acid.

[0004] Carbon sequestration is a process that converts CO2 into stable mineral carbonates through chemical reactions, and is an important method of carbon capture and storage (CCS). This technology utilizes alkaline minerals or solutions rich in calcium and magnesium ions to react with CO2, generating minerals such as calcium carbonate or magnesium carbonate, enabling long-term CO2 sequestration and reducing its concentration in the atmosphere. In this process, alkalinity is required to convert dissolved CO2 into carbonate ions; the reaction formula is as follows:

[0005]

[0006] When the solution pH > 10

[0007]

[0008] When the solution pH < 10

[0009]

[0010] Consuming the alkali content in the washing liquid through CO2 absorption can save on the use of hydrochloric acid for neutralization (e.g., patent CN118754344A, a method for carbon fixation and calcium removal from waste incineration fly ash washing liquid). However, it can only remove 10-15% of the calcium in the washing liquid; further decalcification requires the addition of additional alkali, and the choice of alkali source directly affects the cost of fly ash resource utilization. Invention patent CN117303425A proposes a method for indirectly preparing calcium carbonate from fly ash via an organic phase-mediated process. This involves leaching calcium from the fly ash with an acid solution and adding an organic amine phase to the leachate to promote CO2 absorption and calcium carbonate production. However, it does not consider that during the carbonation reaction in contact between the two phases, some organic diluent will dissolve into the decalcification purification liquid, resulting in organic matter loss, or the impact of the presence of organic matter on the evaporation and crystallization process. In recent years, the utilization of alkali from waste such as carbide slag has received widespread attention. However, its composition is mainly calcium hydroxide; directly using it in the process of absorbing CO2 to generate calcium carbonate will simultaneously introduce an equal amount of new calcium, thus failing to achieve decalcification. Summary of the Invention

[0011] The purpose of this invention is to address the limitations of current technologies by providing a method for decalcification and carbon fixation of fly ash washing liquid. This method utilizes the extraction effect of insoluble (or slightly soluble) organic amines on acids to increase the pH value of the washing liquid system, enabling continuous CO2 absorption and complete removal of calcium from the fly ash washing liquid. The amines in the organic phase are regenerated by alkali treatment, while a small amount of organic diluent mixed in the washing liquid is separated by azeotropic distillation at the top of the column, resulting in the distillation of low-boiling-point azeotropes containing the organic diluent for reuse. This invention adjusts the characteristics of the calcium carbonate byproduct of decalcification using organic amines, producing high-quality aragonite-type calcium carbonate particles, which are excellent adsorbents and additives with wide applications in various fields. Furthermore, it can simultaneously control the crystal form of the prepared calcium carbonate, resulting in small-particle, high-purity calcium carbonate.

[0012] The technical solution adopted in this invention is as follows:

[0013] A method for decalcification and carbon fixation of fly ash washing liquid, the method comprising the following steps:

[0014] (1) Mix organic amine and diluent at a volume ratio of 1:1 to 3 to obtain organic amine phase, and mix organic amine phase with water washing liquid at a volume ratio of 1 to 3:1. After continuous stirring, an oil-water mixture system is obtained.

[0015] The organic amine is a secondary amine or a tertiary amine, preferably a tertiary amine, and more preferably trioctylamine; the diluent is a saturated monohydric fatty alcohol, kerosene or solvent oil with not less than 3 carbon atoms, preferably a saturated monohydric fatty alcohol, and more preferably n-butanol.

[0016] (2) CO2 gas is introduced into the above continuously stirred oil-water mixture until the pH value is 7.5 to 9.0, and then the mixture is stopped to obtain an organic phase containing organic amine hydrochloride and an aqueous phase mixed with calcium carbonate.

[0017] (3) After standing, the liquid is separated, and the aqueous phase is filtered to obtain calcium carbonate and decalcified washing liquid. The calcium carbonate is washed and dried to obtain calcium carbonate product.

[0018] In addition, the organic phase containing organic amine hydrochloride is added to the organic phase and stirred for 10 to 90 minutes to regenerate the organic amine; after regeneration, it is mixed with a diluent and used as the organic amine phase in the next cycle step (1);

[0019] The molar amount of the base is 2 to 5 times that of the organic amine;

[0020] The alkali mentioned is sodium hydroxide, ammonia, or alkaline solid waste (the amount of alkali is expressed in terms of OH-). - (in moles);

[0021] The solid waste residue is industrial alkali residue or carbide residue;

[0022] (4) The decalcified washing liquid containing a small amount of diluent is fed into a distillation column for azeotropic distillation. The diluent and water are distilled off at the top of the column as a low-boiling-point azeotrope. After phase separation, the aqueous phase is refluxed back to the distillation column, and the oil phase is the regenerated diluent. The refined decalcified washing liquid is obtained at the bottom of the distillation column. The recovered diluent is mixed with the regenerated organic amine and then recycled in step (1). The refined decalcified washing liquid at the bottom of the column is sent to the MVR system for salt separation and crystallization to obtain sodium chloride and potassium chloride.

[0023] The distillation column is a plate column, filled with spray-type trays; the number of trays is 10 to 15, the feed position is the 1st to 3rd tray, the reflux ratio is 0.8 to 1.2, the top operating temperature is 92 to 94°C, the bottom operating temperature is 103 to 105°C, and the operating pressure is 102 to 113 kPa; the feed liquid is preheated with MVR evaporation condensate (88 to 92°C);

[0024] The main components and mass percentages of the fly ash washing solution are as follows: Ca 2+ 0.5-2%, Cl - 4-9%, K + 1-3%, Na + 1-5%.

[0025] The CO2 introduced in step (2) of the above method can be pure CO2 gas or a mixed gas containing CO2, such as purified kiln gas. The role of continuously stirring the mixed system of organic amine phase and fly ash washing liquid during the gas introduction process is to make the two fully mixed, which is conducive to maintaining the alkalinity of the aqueous phase and CO2 absorption.

[0026] The washing process of calcium carbonate obtained in step (3) of the above method includes water washing and ethanol washing. The purpose of ethanol washing is to remove the organic phase adsorbed by the calcium carbonate product.

[0027] The essential features of this invention are:

[0028] This invention uses an organic amine phase composed of organic amines and diluents mixed with fly ash washing liquid. During the CO2 decalcification and carbon fixation process, the acid produced by the reaction is continuously absorbed, and the generated organic amine salts are regenerated with alkali. The organic diluent dissolved in the washing liquid is recovered by distillation, realizing the closed-loop use of insoluble organic amines and their diluents in the entire treatment system. By using insoluble organic amines as an intermediary, industrial waste alkali, such as Ca(OH)2 in carbide slag, can be used as an alkali source for regeneration without introducing calcium ions, thus saving on alkali reagent costs.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) The insoluble organic amine extracts the acid, so that carbon fixation and decalcification can continue, and decalcification of fly ash washing liquid can be achieved. The decalcification rate can reach more than 99%, and high-purity calcium carbonate products (purity can reach more than 95%) are obtained. Compared with the process of decalcification with soda ash and then neutralization with hydrochloric acid, the annual cost of reagents alone can be saved by more than RMB 2 million per year for a factory with an annual fly ash processing capacity of 50,000 tons.

[0031] (2) Insoluble amines can be regenerated using various alkali sources, including waste alkali, utilizing the OH- in the waste alkali. - Without introducing additional calcium, the regenerated organic amine can be recycled after being mixed with the recovered diluent, and the recovery rate of the organic phase can reach more than 98%. Using carbide slag and industrial waste alkali slag as regenerators for organic amines can save the cost of alkali in the system.

[0032] (3) By using the small amount of organic diluent dissolved in the washing liquid by distillation, the organic matter can be recovered and recycled, which can effectively ensure the smooth progress of the subsequent MVR evaporation and crystallization process, minimize the loss of organic matter, and improve the economic efficiency of the process. Attached Figure Description

[0033] Figure 1 This is a schematic flowchart of the method for decalcification and carbon fixation of fly ash washing liquid enhanced by organic amines according to the present invention.

[0034] Figure 2 This is the XRD pattern of the calcium carbonate product obtained in Example 1;

[0035] Figure 3 This is a scanning electron microscope image of the calcium carbonate product obtained in Example 1. Detailed Implementation

[0036] The present invention will be further described below with reference to embodiments.

[0037] The fly ash washing solution in this invention comes from the washing solution obtained during the dechlorination process of fly ash from municipal solid waste incineration, and can also be other calcium-rich industrial wastewater. The fly ash washing solution in the following examples is from Wuhu Conch Environmental Protection Co., Ltd., and its main components and concentrations include a calcium ion concentration of 0.9%, a potassium ion content of 2.2%, a sodium ion content of 2.6%, a chloride ion content of 6.46%, and a pH value of 11.8. However, it is not limited to these components.

[0038] Example 1

[0039] A method for decalcification and carbon fixation of fly ash washing liquid enhanced with organic amines includes the following steps:

[0040] (1) Mix trioctylamine and n-butanol at a volume ratio of 1:2 to form an organic amine phase, mix it with fly ash washing liquid at a volume ratio of 2:1, and introduce pure CO2 gas to carry out a mineralization reaction. Stop the reaction when the pH reaches 8.8 to obtain a mixed solution.

[0041] (2) The mixture obtained in step (1) is allowed to stand and separate into phases. The aqueous phase is filtered to obtain decalcified washing liquid and solid calcium carbonate. The calcium carbonate is washed with water, washed with alcohol and dried to obtain calcium carbonate product.

[0042] (3) The organic phase containing organic amine hydrochloride obtained in step (2) is mixed with carbide slag slurry (according to the OH content in carbide slag). - The organic phase is regenerated by mixing and stirring for 60 minutes with the content of organic amine hydrochloride (the molar ratio of the acid content in the organic amine hydrochloride is greater than 3). The regenerated organic phase is then mixed with the recovered diluent and used in the mineralization reaction of step (1) to achieve the recycling of the organic phase.

[0043] The process achieved a calcium ion removal rate of 98.2%, a CO2 fixation rate of 51.5%, an organic amine regeneration rate of 97.7%, and a total organic phase recovery rate of 98.5% in the fly ash washing solution.

[0044] (4) The calcium carbonate product obtained in step (2) was characterized using X-ray diffraction and scanning electron microscopy; the X-ray diffraction results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the obtained calcium carbonate products are all in the spheroidal aragonite form; scanning electron microscope images are shown below. Figure 3 As shown, by Figure 3 It can be seen that the particle size of the obtained calcium carbonate product is about 3 micrometers; the purity test result of calcium carbonate is 96.2%;

[0045] (5) The decalcified washing liquid containing a small amount of diluent is fed into a distillation column for azeotropic distillation at room temperature. The diluent and water are distilled off at the top of the column in the form of a low-boiling-point azeotrope. After phase separation, the aqueous phase is refluxed back to the distillation column, and the oil phase is the regenerated diluent. The refined decalcified washing liquid is obtained in the bottom of the distillation column. The recovered diluent is mixed with the regenerated organic amine and then recycled in step (1). The refined decalcified washing liquid in the bottom of the column is sent to the MVR system for salt separation and crystallization to obtain sodium chloride and potassium chloride.

[0046] The distillation column is a plate column with spray-type trays; it has 12 trays, the feed position is the 3rd tray, the reflux ratio is 0.8, the top operating temperature is 93℃, the bottom operating temperature is 104℃, and the operating pressure is 102kPa; it is preheated with condensate evaporated at 90℃ using MVR as the heat source.

[0047] The azeotropic distillation apparatus further includes a reboiler, a column body, a top condenser, and a phase separator.

[0048] During the process, n-butanol and water are distilled off at the top of the column in the form of an azeotrope (92.7℃, n-butanol 57.5%). After phase separation in the phase separator, the recovered n-butanol is returned to step (1) for reuse. The aqueous phase after phase separation is refluxed to the distillation column, and a refined decalcified washing liquid with a n-butanol content of <50ppm is obtained in the bottom of the column.

[0049] The purpose of distillation is twofold: firstly, to recover the diluent, reduce its loss, and enable its reuse; and secondly, to prevent the diluent from entering the steam in the MVR and affecting the compressor and steam temperature.

[0050] Example 2

[0051] A method for decalcification and carbon fixation of fly ash washing liquid enhanced with organic amines includes the following steps:

[0052] (1) Mix diisobutylamine and n-butanol at a volume ratio of 1:2 to form an organic phase, mix it with fly ash washing liquid at a volume ratio of 1:1, and introduce pure CO2 gas to carry out a mineralization reaction. Stop the reaction when the pH reaches 8.5 to obtain a mixed solution.

[0053] (2) The mixture obtained in step (1) is allowed to stand and separate into phases. The aqueous phase is filtered to obtain decalcified washing liquid and solid calcium carbonate. The calcium carbonate is washed with water, washed with alcohol and dried to obtain calcium carbonate product.

[0054] (3) The organic phase containing organic amine hydrochloride obtained in step (2) is reacted with ammonia water (in accordance with OH) - The organic phase is regenerated by mixing and stirring for 30 minutes with the content of organic amine hydrochloride in a ratio of 3.0 to the content of acid in organic amine hydrochloride. The regenerated organic phase is then mixed with the recovered diluent and used in the mineralization reaction of step (1) to achieve the recycling of the organic phase.

[0055] The process achieved a calcium ion removal rate of 86.6%, a CO2 fixation rate of 63.8%, and an organic amine regeneration rate of 90.6% in fly ash washing solution.

[0056] (4) The calcium carbonate product obtained in step (2) was characterized by X-ray diffraction and scanning electron microscopy. The X-ray diffraction results and scanning electron microscopy images show that the obtained calcium carbonate product is mainly composed of aragonite with a small amount of calcite. The purity test result of calcium carbonate is 97.5%.

[0057] The organic matter recovery process of the decalcified washing solution is the same as in Example 1; the refined decalcified washing solution is directly fed into the MVR for evaporation, crystallization and salt separation to obtain potassium chloride and sodium chloride products.

[0058] Example 3

[0059] A method for decalcification and carbon fixation of fly ash washing liquid enhanced with organic amines includes the following steps:

[0060] (1) Mix trioctylamine and n-butanol in a volume ratio of 1:1 to form an organic phase, mix it with fly ash washing liquid in a volume ratio of 1.5:1, and introduce pure CO2 gas to carry out a mineralization reaction. Stop the reaction when the pH reaches 9 to obtain a mixed solution.

[0061] (2) The mixture obtained in step (1) is allowed to stand and separate into phases. The aqueous phase is filtered to obtain decalcified washing liquid and solid calcium carbonate. The calcium carbonate is washed with water, washed with alcohol and dried to obtain calcium carbonate product.

[0062] (3) The organic phase containing organic amine hydrochloride obtained in step (2) is mixed with industrial waste alkali slurry (according to the OH content in the waste alkali). - The organic phase is regenerated by mixing and stirring for 60 minutes with a concentration greater than 3 (the molar ratio of the concentration of the organic amine hydrochloride to the concentration of the acid in the organic amine hydrochloride). The regenerated organic phase is then mixed with the recovered diluent and used in the mineralization reaction of step (1) to achieve the recycling of the organic phase.

[0063] The process achieved a calcium ion removal rate of 80.5%, a CO2 fixation rate of 36.5%, and an organic amine regeneration rate of 95.6% in fly ash washing solution.

[0064] (4) The calcium carbonate product obtained in step (2) was characterized by X-ray diffraction and scanning electron microscopy. The X-ray diffraction results and scanning electron microscopy images show that the obtained calcium carbonate product is in the form of spheroidal aragonite. The purity test result of calcium carbonate is 97.1%.

[0065] The organic matter recovery process of the decalcified washing solution is the same as in Example 1; the refined decalcified washing solution is directly fed into the MVR for evaporation, crystallization and salt separation to obtain potassium chloride and sodium chloride products.

[0066] Example 4

[0067] A method for decalcification and carbon fixation of fly ash washing liquid enhanced with organic amines includes the following steps:

[0068] (1) Mix trioctylamine and n-butanol at a volume ratio of 1:2 to form an organic phase, mix it with fly ash washing liquid at a volume ratio of 2.5:1, and introduce pure CO2 gas to carry out a mineralization reaction. Stop the reaction when the pH reaches 7.8 to obtain a mixed solution.

[0069] (2) The mixture obtained in step (1) is allowed to stand and separate into phases. The aqueous phase is filtered to obtain decalcified washing liquid and solid calcium carbonate. The calcium carbonate is washed with water, washed with alcohol and dried to obtain calcium carbonate product.

[0070] (3) The organic phase containing organic amine hydrochloride obtained in step (2) is reacted with sodium hydroxide solution (according to OH) - The organic phase is regenerated by mixing and stirring for 30 minutes with the content of organic amine hydrochloride in a ratio of 3.0 to the content of acid in organic amine hydrochloride. The regenerated organic phase is then mixed with the recovered diluent and used in the mineralization reaction of step (1) to achieve the recycling of the organic phase.

[0071] The process achieved a calcium ion removal rate of 69.5%, a CO2 fixation rate of 32.2%, and an organic amine regeneration rate of 94.3% in fly ash washing solution.

[0072] (4) The calcium carbonate product obtained in step (2) was characterized by X-ray diffraction and scanning electron microscopy. The X-ray diffraction results and scanning electron microscopy images show that the calcium carbonate product obtained is in the form of spheroidal aragonite. The purity test result of calcium carbonate is 96.6%.

[0073] The organic matter recovery process of the decalcified washing solution is the same as in Example 1; the refined decalcified washing solution is directly fed into the MVR for evaporation, crystallization and salt separation to obtain potassium chloride and sodium chloride products.

[0074] Example 5

[0075] A method for decalcification and carbon fixation of fly ash washing liquid enhanced with organic amines includes the following steps:

[0076] (1) Mix diisobutylamine and n-octanol in a volume ratio of 1:2 to form an organic phase, mix it with fly ash washing liquid in a volume ratio of 1:1, and introduce pure CO2 gas to carry out a mineralization reaction. Stop the reaction when the pH reaches 8.5 to obtain a mixed solution.

[0077] (2) The mixture obtained in step (1) is allowed to stand and separate into phases. The aqueous phase is filtered to obtain decalcified washing liquid and solid calcium carbonate. The calcium carbonate is washed with water, washed with alcohol and dried to obtain calcium carbonate product.

[0078] (3) The organic phase containing organic amine hydrochloride obtained in step (2) is mixed with carbide slag slurry (according to the OH content in carbide slag). - The organic phase is regenerated by mixing and stirring the organic phase with the concentration of organic amine hydrochloride (the molar ratio of the concentration of organic amine hydrochloride to that of acid is greater than 3). The regenerated organic phase is then mixed with the recovered diluent and used in the mineralization reaction of step (1) to achieve the recycling of the organic phase.

[0079] The process achieved a calcium ion removal rate of 99.8%, a CO2 fixation rate of 71.3%, and an organic amine regeneration rate of 94.4% in fly ash washing solution.

[0080] (4) The calcium carbonate product obtained in step (2) was characterized by X-ray diffraction and scanning electron microscopy. The X-ray diffraction results and scanning electron microscopy images show that the obtained calcium carbonate product is mainly composed of aragonite with a small amount of calcite. The purity test result of calcium carbonate is 94.6%.

[0081] Octanol has low solubility in water, approximately 0.1% at room temperature, which has little impact on subsequent processes. The washing liquid after decalcification is directly fed into the MVR system for evaporation, crystallization, and salt separation.

[0082] Matters not covered in this invention are common knowledge.

Claims

1. A method for decalcification and carbon fixation of fly ash washing liquid, characterized in that the method includes the following steps: (1) The organic amine and the diluent are mixed at a volume ratio of 1:1 to 3 to obtain the organic amine phase, and the organic amine phase is mixed with the water washing liquid at a volume ratio of 1 to 3:

1. After continuous stirring, an oil-water mixture system is obtained. in, The organic amine is trioctylamine, and the diluent is n-butanol; (2) CO2 is introduced into the above continuously stirred oil-water mixture until the pH value is 7.5~9.0, and then stopped to obtain an organic phase containing organic amine hydrochloride and an aqueous phase mixed with calcium carbonate; (3) After standing, the liquid is separated and the aqueous phase is filtered to obtain calcium carbonate and decalcified washing liquid. The calcium carbonate is washed and dried to obtain calcium carbonate product. In addition, after adding alkali to the organic phase containing organic amine hydrochloride and stirring for 10 to 90 minutes, the organic amine is regenerated; after regeneration, it is mixed with diluent and used as the organic amine phase in the next cycle step (1); The molar amount of the base is 2 to 5 times that of the organic amine; The alkali mentioned is sodium hydroxide, ammonia, or alkaline solid waste (the amount of alkali is expressed in terms of OH). - (in moles); (4) The decalcified washing liquid containing a small amount of diluent is fed into the distillation column for azeotropic distillation. The diluent and water are distilled off at the top of the column in the form of a low-boiling-point azeotrope. After phase separation, the aqueous phase is refluxed back to the distillation column, and the oil phase is the regenerated diluent. The refined decalcified washing liquid is obtained in the bottom of the distillation column. The recovered diluent is mixed with the regenerated organic amine and then recycled in step (1). The refined decalcified washing liquid in the bottom of the column is sent to the MVR system for salt separation and crystallization to obtain sodium chloride and potassium chloride. In step (3), the solid waste residue is industrial alkali residue or carbide residue; In step (4), the distillation column is a plate column, filled with spray-type trays; the number of trays is 10~15, the feed position is the 1st~3rd tray, the reflux ratio is 0.8~1.2, the top operating temperature is 92~94℃, the bottom operating temperature is 103~105℃, and the operating pressure is 102~113kPa; the feed liquid is preheated with MVR evaporation condensate (88~92℃); In step (1), the main components and mass percentages of the fly ash washing solution are as follows: Ca 2+ 0.5~2%, Cl - 4~9%, K + 1~3%, Na + 1~5%.

2. The method for decalcification and carbon fixation of fly ash washing liquid as described in claim 1, characterized in that, The CO2 introduced in step (2) is pure CO2 gas or purified kiln gas.

3. The method for decalcification and carbon fixation of fly ash washing liquid as described in claim 1, characterized in that, The washing of calcium carbonate in step (3) includes washing with water and washing with ethanol.

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