Resource recycling method of ammonium-containing waste sulfuric acid

Abstract

The invention provides a resource recycling method of ammonium-containing waste sulfuric acid, which comprises the following steps: (1) respectively introducing a solvent and ammonium-containing waste sulfuric acid into two sides of a dialysis membrane for diffusion dialysis treatment, and respectively obtaining a sulfuric acid solution and an acidic ammonium sulfate solution on two sides of the dialysis membrane; and (2) carrying out bipolar membrane electrolysis treatment on the acidic ammonium sulfate solution to obtain ammonia water and ammonium-containing sulfuric acid. According to the method disclosed by the invention, sulfuric acid and ammonium ions (converted into ammonia water) in the ammonium-containing waste sulfuric acid can be efficiently and greenly recovered, the obtained ammonium-containing sulfuric acid can also be repeatedly recovered, and resource recovery of the ammonium-containing waste sulfuric acid is realized under the condition of ensuring low cost.

Description

Technical Field

[0001] The invention belongs to the technical field of resource recovery and relates to a resource recovery method for ammonium-containing waste sulfuric acid. Background Art

[0002] Ion exchange resins are widely used in many industrial fields. For example, they are used in the food industry for sugar production, MSG, wine refining, and biological product production; in the pharmaceutical industry, they play an important role in developing a new generation of antibiotics and improving the quality of existing antibiotics; in the synthetic chemistry and petrochemical industries, they are often used as acid and base catalysts in esterification, hydrolysis, transesterification, hydration and other reactions.

[0003] The ion exchange resin production process involves a sulfuric acid treatment process, which introduces ammonium into the atmosphere, forming waste sulfuric acid. The sulfuric acid concentration in this mixed hydrolyzate ranges from 45% to 48.0%. Directly discharging this ammonium-containing waste sulfuric acid would create numerous serious problems. From a resource perspective, this would result in a significant waste of resources. After all, sulfuric acid is a critical chemical raw material, and its direct disposal means that the resources invested initially are not fully utilized. From an economic perspective, the discharge of large amounts of ammonium-containing waste sulfuric acid leads to a dramatic increase in production waste. The high cost of treating this waste significantly increases production costs and reduces the company's economic returns. Environmentally, the treatment of ammonium-containing waste sulfuric acid is challenging. Improper handling can cause severe pollution to soil, water, and other ecological environments, impacting the ecological balance and potentially exposing the company to risks of environmental penalties. Furthermore, complex wastewater treatment processes can disrupt normal production operations and reduce productivity.

[0004] CN115784172A discloses a method for treating waste sulfuric acid with an ion exchange resin, comprising the following steps: S1: preparing an ion exchange resin and waste sulfuric acid to be treated; S2: adding one of aniline, p-phenylenediamine, phenylhydrazine or hydrazine hydrate to the waste sulfuric acid solution, stirring at room temperature and filtering to obtain a sulfate precipitant containing an amino compound and a filtrate.

[0005] CN111825062A discloses a method for recovering waste sulfuric acid, which first separates insoluble matter from the waste sulfuric acid by filtration, extracts the remaining organic matter in the waste sulfuric acid with benzene, separates the extractant by distillation, and then concentrates it through ion exchange to obtain a high-purity sulfuric acid solution; the organic phase in the waste sulfuric acid is stripped of the waste sulfuric acid by extraction, and then the metal ions in the solution are intercepted by ion exchange to reduce the salt content in the solution to a minimum, thereby filtering impurities in the solution and recovering the waste sulfuric acid.

[0006] The above scheme uses extraction or chemical precipitation to recover waste sulfuric acid, but the extraction method is not effective. The chemical precipitation method adds organic matter such as aniline to the waste sulfuric acid solution to form a precipitate with sulfuric acid, and then recovers concentrated sulfuric acid through thermal decomposition precipitation. The precipitation separation and subsequent treatment of the filtrate are relatively cumbersome, and the treatment cost needs to be further optimized.

[0007] In summary, the existing methods for treating ammonium-containing waste sulfuric acid have varying degrees of deficiencies in terms of resource recovery efficiency, cost control, and environmental compliance. There is an urgent need for an efficient, low-cost, and environmentally friendly ammonium-containing waste sulfuric acid recovery technology to meet the needs of sustainable development of the ion exchange resin-related industry. Summary of the Invention

[0008] The object of the present invention is to provide a resource recovery method for ammonium-containing waste sulfuric acid. The method of the present invention can efficiently and environmentally recover sulfuric acid and ammonium ions (converted into ammonia water) in the ammonium-containing waste sulfuric acid. The obtained ammonium-containing sulfuric acid can also be repeatedly recovered, thereby achieving resource recovery of ammonium-containing waste sulfuric acid while ensuring low cost.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for recycling ammonium-containing waste sulfuric acid, the method comprising the following steps:

[0011] (1) passing a solvent and ammonium-containing waste sulfuric acid into both sides of a dialysis membrane for diffusion dialysis treatment, thereby obtaining a sulfuric acid solution and an acidic ammonium sulfate solution on both sides of the dialysis membrane;

[0012] (2) The acidic ammonium sulfate solution is subjected to bipolar membrane electrolysis to obtain ammonia water and ammonium-containing sulfuric acid.

[0013] The ammonium-containing waste sulfuric acid contains a large amount of acid. The present invention preliminarily performs diffusion dialysis treatment on the ammonium-containing waste sulfuric acid, and introduces a solvent and the ammonium-containing waste sulfuric acid into both sides of the dialysis membrane respectively. The acid in the ammonium-containing waste sulfuric acid enters pure water through the dialysis membrane to obtain sulfuric acid, and the ammonium in the ammonium-containing waste sulfuric acid is intercepted to obtain an ammonium sulfate solution containing part of the sulfuric acid, i.e., an acidic ammonium sulfate solution. The acidic ammonium sulfate solution is subjected to bipolar membrane electrolysis to obtain ammonia water and low-concentration ammonium-containing sulfuric acid in the cathode chamber and the anode chamber, respectively.

[0014] Preferably, the ammonium-containing waste sulfuric acid in step (1) is subjected to ultrafiltration treatment before being introduced.

[0015] Preferably, the pore size of the filter membrane used in the ultrafiltration treatment is 10 μm to 100 μm, for example, 10 μm, 20 μm, 50 μm, 80 μm or 100 μm, etc., and is not limited to the listed values. Other values not listed within this numerical range are also applicable.

[0016] In order to alleviate the membrane pollution caused by diffusion dialysis, the ammonium-containing waste sulfuric acid described in the present application needs to be subjected to ultrafiltration treatment before diffusion dialysis to remove impurities therein, and the filter membrane includes a PTFE filter membrane.

[0017] Preferably, the solvent in step (1) comprises pure water.

[0018] Preferably, the flow ratio of the solvent to the ammonium-containing waste sulfuric acid is (1-5):1, for example: 1:1, 2:1, 3:1, 4:1 or 5:1, etc., and is not limited to the listed values. Other unlisted values within this numerical range are also applicable.

[0019] Preferably, the dialysis membrane in step (1) comprises a perfluorosulfonic acid resin membrane and / or a polystyrene-divinylbenzene quaternized membrane.

[0020] Preferably, the thickness of the dialysis membrane in step (1) is 30 μm to 50 μm, for example, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0021] Preferably, the sulfuric acid solution in step (1) is concentrated and then reused.

[0022] The sulfuric acid obtained by the diffusion dialysis treatment in the present invention has a low concentration and is difficult to use directly, so it needs to be reused after being concentrated.

[0023] Preferably, the concentration temperature is 100°C to 200°C, for example, 100°C, 120°C, 150°C, 180°C or 200°C, etc., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0024] Preferably, the concentration time is 0.5 h to 1.5 h, for example, 0.5 h, 0.8 h, 1 h, 1.2 h or 1.5 h, etc., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0025] Preferably, the mass concentration of sulfuric acid obtained after the concentration is 55% to 65%, for example, 55%, 58%, 60%, 62% or 65%, etc., and is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0026] Preferably, the current density of the bipolar membrane electrolysis treatment in step (2) is 200 mA / cm 2 ~400mA / cm 2 , for example: 200mA / cm 2 , 250mA / cm 2 、300mA / cm 2、350mA / cm 2 or 400mA / cm 2 The present invention is not limited to the numerical values listed, and other numerical values not listed within the numerical range are also applicable.

[0027] Preferably, the anion exchange membrane used in the bipolar membrane electrolysis treatment in step (2) has a membrane area of 600 cm 2 ~1000cm 2 , for example: 600cm 2 , 700cm 2 , 800cm 2 , 900cm 2 or 1000cm 2 The present invention is not limited to the numerical values listed, and other numerical values not listed within the numerical range are also applicable.

[0028] Preferably, the material of the anion exchange membrane used in the bipolar membrane electrolysis treatment in step (2) includes polystyrene-divinylbenzene.

[0029] Preferably, the stacking method of the anion exchange membrane used in the bipolar membrane electrolysis treatment in step (2) includes flat-plate stacking.

[0030] The bipolar membrane electrolysis process described in the present invention employs a bipolar membrane interfacial layer between the anode and cathode chambers of the electrolysis process. Under the influence of an electric field, water dissociates in the interfacial layer, generating hydrogen and hydroxide ions. Hydrogen ions migrate through the cation exchange layer toward the cathode chamber, participating in the cathode reaction; hydroxide ions migrate through the anion exchange layer toward the anode chamber, participating in the anodic reaction. Furthermore, the ion exchange layers on both sides of the bipolar membrane selectively allow the passage of specific ions, thereby achieving the separation and transmission of different ions.

[0031] Preferably, the ammonium-containing sulfuric acid obtained in step (2) is returned to step (1) for use as ammonium-containing waste sulfuric acid.

[0032] The ammonium-containing sulfuric acid obtained by the resource recovery method of the present invention still contains a small amount of sulfuric acid and ammonium ions, which can be directly concentrated and then repeatedly subjected to the above resource recovery, or added to other ammonium-containing waste sulfuric acid for resource recovery.

[0033] Preferably, the ammonia water in step (2) is concentrated and then reused.

[0034] The concentration of the ammonia water obtained by resource recovery in the present invention is relatively low, and therefore it needs to be concentrated before being reused.

[0035] Preferably, the concentration method comprises mixing a sodium hydroxide solution having a mass concentration of 30% to 50%, for example, 30%, 35%, 40%, 45% or 50%, etc., not limited to the listed values, and other values within the numerical range not listed are also applicable, with aqueous ammonia, heating to generate ammonia gas, and using deionized water to absorb the ammonia gas to obtain aqueous ammonia with a mass concentration of 15% to 25%, for example, 15%, 18%, 20%, 22% or 25%, etc., not limited to the listed values, and other values within the numerical range not listed are also applicable.

[0036] Preferably, the molar ratio of sodium hydroxide in the sodium hydroxide solution to ammonia gas in the ammonia water is 1:(0.5-1), for example: 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9 or 1:1, etc., and is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0037] Preferably, the heating temperature is 40°C to 60°C, for example, 40°C, 45°C, 50°C, 55°C or 60°C, etc., and is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] (1) The method of the present invention can recover sulfuric acid and ammonium ions (converted into ammonia water) in ammonium-containing waste sulfuric acid, and the obtained ammonium-containing sulfuric acid can also be repeatedly recovered, thereby realizing the resource recovery of ammonium-containing waste sulfuric acid.

[0040] (2) The sulfuric acid recovery rate of the resource recovery method of ammonium-containing waste sulfuric acid of the present invention can reach more than 93%, and the ammonium recovery rate can reach more than 93%. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The present invention provides a process flow chart of a method for recycling ammonium-containing waste sulfuric acid. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0043] The mass concentration of ammonium sulfate in the ammonium-containing waste sulfuric acid in the examples of the present invention and the comparative examples is 5%, and the mass concentration of sulfuric acid is 42%.

[0044] Example 1

[0045] This embodiment provides a method for recycling ammonium-containing waste sulfuric acid. The process flow chart of the recycling method is as follows: Figure 1As shown, the resource recovery method includes the following steps:

[0046] (1) After ultrafiltration treatment of ammonium-containing waste sulfuric acid using a filter membrane with a pore size of 80 μm, pure water and ammonium-containing waste sulfuric acid are passed through both sides of a polystyrene-divinylbenzene quaternary ammonium membrane dialysis membrane with a thickness of 40 μm at a flow ratio of 3:1 for diffusion dialysis treatment, respectively obtaining a sulfuric acid solution and an acidic ammonium sulfate solution on both sides of the dialysis membrane, and the sulfuric acid solution is concentrated and concentrated at 150° C. for 1 hour to obtain a sulfuric acid solution with a mass concentration of 60%;

[0047] (2) The acidic ammonium sulfate solution was subjected to bipolar membrane electrolysis, and the current density of the bipolar membrane electrolysis was 300 mA / cm 2 The anion exchange membrane used includes polystyrene-divinylbenzene, with a thickness of 800 cm 2 The stacking method of the anion exchange membrane is flat-plate stacking, and dilute ammonia water and ammonium-containing sulfuric acid are added. The dilute ammonia water is mixed with a sodium hydroxide solution with a mass concentration of 40% according to the molar ratio of NaOH:NH3=1:0.8, and heated at 50°C. The generated ammonia gas is absorbed by deionized water to obtain ammonia water with a mass concentration of 20%.

[0048] Example 2

[0049] This embodiment provides a method for recycling ammonium-containing waste sulfuric acid. The process flow chart of the recycling method is as follows: Figure 1 As shown, the resource recovery method includes the following steps:

[0050] (1) After ultrafiltration treatment of ammonium-containing waste sulfuric acid using a filter membrane with a pore size of 100 μm, pure water and ammonium-containing waste sulfuric acid are passed through both sides of a polystyrene-divinylbenzene quaternary ammonium membrane dialysis membrane with a thickness of 30 μm at a flow ratio of 1:1 for diffusion dialysis treatment, respectively obtaining a sulfuric acid solution and an acidic ammonium sulfate solution on both sides of the dialysis membrane, and the sulfuric acid solution is concentrated and concentrated at 100° C. for 1.5 hours to obtain a sulfuric acid solution with a mass concentration of 55%;

[0051] (2) The acidic ammonium sulfate solution was subjected to bipolar membrane electrolysis, and the current density of the bipolar membrane electrolysis was 200 mA / cm 2 The anion exchange membrane used includes polystyrene-divinylbenzene, with a thickness of 600 cm 2 The stacking method of the anion exchange membrane is flat-plate stacking, and dilute ammonia water and ammonium-containing sulfuric acid are added. The dilute ammonia water is mixed with a sodium hydroxide solution with a mass concentration of 30% according to the molar ratio of NaOH:NH3=1:1, and heated at 60°C. The generated ammonia gas is absorbed by deionized water to obtain ammonia water with a mass concentration of 18.6%.

[0052] Example 3

[0053] This embodiment provides a method for recycling ammonium-containing waste sulfuric acid. The process flow chart of the recycling method is as follows: Figure 1 As shown, the resource recovery method includes the following steps:

[0054] (1) After ultrafiltration treatment of ammonium-containing waste sulfuric acid using a filter membrane with a pore size of 10 μm, pure water and ammonium-containing waste sulfuric acid are passed through both sides of a 50 μm thick perfluorosulfonic acid resin membrane dialysis membrane at a flow ratio of 5:1 for diffusion dialysis treatment, respectively obtaining a sulfuric acid solution and an acidic ammonium sulfate solution on both sides of the dialysis membrane, and the sulfuric acid solution is concentrated at 200° C. for 0.5 h to obtain a sulfuric acid solution with a mass concentration of 63%;

[0055] (2) The acidic ammonium sulfate solution was subjected to bipolar membrane electrolysis, and the current density of the bipolar membrane electrolysis was 400 mA / cm 2 The anion exchange membrane used includes polystyrene-divinylbenzene, with a thickness of 1000 cm 2 The stacking method of the anion exchange membrane is flat-plate stacking, and dilute ammonia water and ammonium-containing sulfuric acid are added. The dilute ammonia water is mixed with a sodium hydroxide solution with a mass concentration of 50% according to the molar ratio of NaOH:NH3=1:0.5, and heated at 40°C. The generated ammonia gas is absorbed by deionized water to obtain ammonia water with a mass concentration of 22.8%.

[0056] Example 4

[0057] The only difference between this embodiment and embodiment 1 is that the flow ratio of pure water to ammonium-containing waste sulfuric acid in step (1) is 0.5:1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0058] Example 5

[0059] The only difference between this embodiment and embodiment 1 is that the flow ratio of pure water to ammonium-containing waste sulfuric acid in step (1) is 8:1, and other conditions and parameters are exactly the same as those in embodiment 1.

[0060] Example 6

[0061] The only difference between this embodiment and embodiment 1 is that the current density of the bipolar membrane electrolysis treatment in step (2) is 100 mA / cm 2 , other conditions and parameters are exactly the same as those in Example 1.

[0062] Example 7

[0063] The only difference between this embodiment and embodiment 1 is that the current density of the bipolar membrane electrolysis treatment in step (2) is 500 mA / cm 2 , other conditions and parameters are exactly the same as those in Example 1.

[0064] Comparative Example 1

[0065] The only difference between this comparative example and Example 1 is that no diffusion dialysis is performed and bipolar membrane electrolysis is performed directly. Other conditions and parameters are exactly the same as those in Example 1.

[0066] Comparative Example 2

[0067] The only difference between this comparative example and Example 1 is that the bipolar membrane electrolysis treatment is replaced by ordinary electrolysis treatment, and the other conditions and parameters are exactly the same as those in Example 1.

[0068] Performance testing:

[0069] The recovery rates of sulfuric acid and ammonium in the test examples and comparative examples were tested. The test results are shown in Table 1:

[0070] Table 1

[0071] Sulfuric acid recovery rate (%) Ammonium recovery rate (%) Example 1 98 97 Example 2 97 98 Example 3 98 97 Example 4 95 94 Example 5 96 95 Example 6 94 93 Example 7 93 94 Comparative Example 1 80 10 Comparative Example 2 60 30

[0072] As can be seen from Table 1, from Examples 1-7, the sulfuric acid recovery rate of the resource recovery method of ammonium-containing waste sulfuric acid of the present invention can reach more than 93%, and the ammonium recovery rate can reach more than 93%.

[0073] By comparing Example 1 with Examples 4-5, it can be seen that in the resource recovery method of ammonium-containing waste sulfuric acid according to the present invention, the flow ratio of the solvent to the ammonium-containing waste sulfuric acid in step (1) affects the recovery effect. When the flow ratio of the pure water to the ammonium-containing waste sulfuric acid in step (1) is controlled at (1-5):1, the recovery effect is better. If the flow rate of pure water is too large, the acidity of the recovered acid becomes lower, affecting the sulfuric acid recovery rate and recovery cost. If the flow rate of pure water is too small, ammonium and water molecules are more likely to pass through the anion exchange membrane, the interception rate becomes lower, and the ammonium recovery rate is low.

[0074] By comparing Example 1 with Examples 6-7, it can be seen that in the resource recovery method of ammonium-containing waste sulfuric acid of the present invention, the current density of the bipolar membrane electrolysis treatment in step (2) will affect the recovery effect. The current density of the bipolar membrane electrolysis treatment in step (2) is controlled at 200 mA / cm 2 ~400mA / cm 2 , the recovery effect is better. If the current density of the bipolar membrane electrolysis treatment is too large, there will be an exothermic effect, the current efficiency will become lower, and the ammonium recovery rate will become lower. If the current density of the bipolar membrane electrolysis treatment is too small, the separation of ammonium and sulfuric acid will not be complete, and the sulfuric acid recovery will become lower.

[0075] By comparison between Example 1 and Comparative Example 1, it can be seen that ammonium-containing waste sulfuric acid contains a large amount of acid. In the present invention, the ammonium-containing waste sulfuric acid is pre-diffusion dialysis treated, and a solvent and ammonium-containing waste sulfuric acid are respectively introduced on both sides of the dialysis membrane. The acid in the ammonium-containing waste sulfuric acid enters the pure water through the dialysis membrane to obtain sulfuric acid, and the ammonium in the ammonium-containing waste sulfuric acid is intercepted to obtain an acidic ammonium sulfate solution. If bipolar membrane electrolysis is directly performed without diffusion dialysis treatment, the acidity in the system is too high and the electrolysis effect is greatly reduced, and a large amount of hydrogen is easily generated, resulting in danger.

[0076] From the comparison between Example 1 and Comparative Example 2, it can be seen that the resistance becomes larger at high concentrations, and hydrogen side reactions are easily generated, the efficiency of generating ammonia is low, and the ammonium recovery rate is extremely low.

[0077] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for recycling ammonium-containing waste sulfuric acid, characterized in that: The resource recovery method comprises the following steps: (1) passing a solvent and ammonium-containing waste sulfuric acid into both sides of a dialysis membrane for diffusion dialysis treatment, thereby obtaining a sulfuric acid solution and an acidic ammonium sulfate solution on both sides of the dialysis membrane; (2) The acidic ammonium sulfate solution is subjected to bipolar membrane electrolysis to obtain ammonia water and ammonium-containing sulfuric acid.

2. The resource recovery method according to claim 1, wherein: The ammonium-containing waste sulfuric acid in step (1) is subjected to ultrafiltration treatment before being introduced; Preferably, the pore size of the filter membrane used in the ultrafiltration treatment is 10 μm to 100 μm.

3. The resource recovery method according to claim 1 or 2, characterized in that: The solvent in step (1) includes pure water.

4. The resource recovery method according to any one of claims 1 to 3, characterized in that: The flow ratio of the solvent to the ammonium-containing waste sulfuric acid is (1-5):

1.

5. The resource recovery method according to any one of claims 1 to 4, characterized in that: The dialysis membrane in step (1) comprises a perfluorosulfonic acid resin membrane and / or a polystyrene-divinylbenzene quaternary ammonium membrane; Preferably, the thickness of the dialysis membrane in step (1) is 30 μm to 50 μm.

6. The resource recovery method according to any one of claims 1 to 5, characterized in that: The sulfuric acid solution in step (1) is concentrated and then reused; Preferably, the concentration temperature is 100°C to 200°C; Preferably, the concentration time is 0.5h to 1.5h; Preferably, the mass concentration of sulfuric acid obtained after the concentration is 55% to 65%.

7. The resource recovery method according to claim 6, characterized in that: The current density of the bipolar membrane electrolysis treatment in step (2) is 200 mA / cm 2 ~400mA / cm 2 .

8. The resource recovery method according to any one of claims 1 to 7, characterized in that: The anion exchange membrane used in step (2) bipolar membrane electrolysis has a membrane area of 600 cm 2 ~1000cm 2 ; Preferably, the material of the anion exchange membrane used in the bipolar membrane electrolysis treatment in step (2) comprises polystyrene-divinylbenzene; Preferably, the stacking method of the anion exchange membrane used in the bipolar membrane electrolysis treatment in step (2) includes flat-plate stacking.

9. The resource recovery method according to any one of claims 1 to 8, characterized in that: The ammonium-containing sulfuric acid obtained in step (2) is returned to step (1) for use as ammonium-containing waste sulfuric acid.

10. The resource recovery method according to any one of claims 1 to 9, characterized in that: The ammonia water in step (2) is concentrated and then reused; Preferably, the concentration method comprises mixing a sodium hydroxide solution having a mass concentration of 30% to 50% with aqueous ammonia, heating to generate ammonia gas, and using deionized water to absorb the ammonia gas to obtain aqueous ammonia with a mass concentration of 15% to 25%; Preferably, the molar ratio of sodium hydroxide in the sodium hydroxide solution to ammonia gas in the ammonia water is 1:(0.5-1); Preferably, the heating temperature is 40°C to 60°C.

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