Efficient extraction and recovery method for chloride ions in desulfurization wastewater

Abstract

The invention discloses a method for efficiently extracting and recycling chloride ions in desulfurization wastewater, and belongs to the technical field of industrial wastewater treatment and recycling. The method comprises the following steps: firstly, constructing a composite extraction system which takes tertiary amine N235 as a main extraction agent, n-decanol as a modifier and a mixed solution of kerosene and benzene as a diluent; then, the desulfurization wastewater is subjected to multi-stage extraction, and the chloride ion removal rate is stabilized at 68.9%-69.4%; after extraction, ammonia water is used as a back-extraction agent to carry out back extraction on an organic phase loaded with chloride ions, the back-extraction rate can reach 90% or above, and the organic phase can be recycled. The extraction system disclosed by the invention has strong anti-interference capability on common cations such as Ca < 2 + >, Mg < 2 + > and Na < + > in wastewater, solves the problems of low extraction efficiency, poor stability and high cost in the prior art, and is simple in process flow and suitable for industrial application.

Description

Technical Field

[0001] This invention relates to a method for efficient extraction and recovery of chloride ions in desulfurization wastewater, specifically a method for efficient extraction and recovery of chloride ions in high-chlorine wastewater generated by wet desulfurization in coal-fired power plants, belonging to the field of industrial wastewater treatment and resource utilization technology. Background Technology

[0002] The wet desulfurization process in coal-fired power plants generates a large amount of desulfurization wastewater. This wastewater has a complex composition, characterized by high chloride ion content, high hardness, and high salt content. Excessive chloride ion concentration can lead to severe corrosion of desulfurization system equipment, pipe scaling, and reduced desulfurization efficiency, directly impacting the safe and stable operation of the system. Therefore, effectively removing chloride ions from desulfurization wastewater is a crucial step in achieving zero wastewater discharge and resource reuse.

[0003] Currently, common methods for treating high-chlorine wastewater include chemical precipitation, evaporation crystallization, ion exchange, and membrane separation. However, these methods all have certain limitations: chemical precipitation consumes a large amount of reagents and produces a large amount of sludge; evaporation crystallization is extremely energy-intensive; ion exchange resins are easily fouled and require frequent regeneration; and membrane separation has stringent requirements for influent water quality and is difficult to treat concentrated wastewater.

[0004] Solvent extraction, as a highly efficient separation technique, is widely used in metal extraction and wastewater treatment. Its principle is based on the difference in the partition ratio of solutes in immiscible aqueous and organic phases for separation and enrichment. This method has advantages such as good selectivity, high recovery rate, mild operating conditions, and large processing capacity. Applying extraction to dechlorination of desulfurization wastewater has broad application prospects. However, existing extraction systems, when applied to actual desulfurization wastewater, generally suffer from low extraction efficiency, significant dissolution loss of the organic phase in the aqueous phase, and problems with other coexisting ions in the wastewater (such as Ca2+). 2+ Mg 2+ Na + Problems such as poor anti-interference ability and high cost of extractant have limited the industrial promotion of this technology.

[0005] Therefore, developing a dedicated extraction system and supporting process that is efficient, stable, cost-effective, and highly resistant to interference is of great significance for promoting the application of extraction methods in the field of dechlorination of desulfurization wastewater. Summary of the Invention

[0006] To address the shortcomings of existing technologies, such as low extraction efficiency, significant organic phase dissolution and loss in the aqueous phase, and poor performance regarding other ions (e.g., Ca2+), 2+ Mg 2+ Na +To address the problems of poor anti-interference ability and high cost of extractants, this invention provides a highly efficient extraction and recovery method for chloride ions (content in the range of 5000-20000 mg / L) in desulfurization wastewater. This method has high extraction efficiency, good stability, strong anti-interference ability, and low operating cost.

[0007] This invention develops an extraction system based on N235, optimizes the extractant formulation, extraction and back-extraction operating conditions, and clarifies its reaction mechanism: the performance of amine extractants is mainly determined by their basicity and steric hindrance. When alkyl groups replace hydrogen atoms in amine molecules, the electron cloud density of nitrogen atoms is enhanced through an inductive effect, increasing basicity and thus facilitating proton binding and improving extraction efficiency. However, with the increase of the number of alkyl groups and the size of the substituents, the steric hindrance effect becomes increasingly significant, hindering the effective approach and binding of amines to protons, potentially reducing extraction efficiency. Therefore, the overall performance of amine extractants depends on the balance between increased basicity and steric hindrance. N235, after acidification with sulfuric acid, forms an amine salt (R3NH)2SO4. This amine salt, through an anion exchange mechanism, releases SO42-... 2- With Cl in wastewater - An exchange reaction occurs, generating a neutral ion-pair extractant R3NHCl, thereby achieving chloride ion extraction. The reaction is as follows (in the reaction, N235 is written as R3N):

[0008]

[0009] Before extraction, the peak at m / z = 354.4142 corresponds to the N235 monomer (M+H) in mass spectrometry analysis. + This confirmed that the extractant existed in the form of free tertiary amine R3N. After extraction, the peak at m / z = 424.3525 confirmed the formation of a 1:1 supported Cl... - Extraction compound. The extraction mechanism involves the amine being protonated by H₂SO₄ to form the amine salt (R₃NH)₂SO₄, followed by anion exchange with Cl₂. - The results support the extraction composition at a 1:1 ratio (N235:Cl). - The proportion exists.

[0010] This invention provides a method for efficient extraction and recovery of chloride ions in desulfurization wastewater, comprising the following: (1) Preparation of extractant: The present invention develops a composite extraction system consisting of a main extractant, a diluent and a modifier; the main extractant is a tertiary amine extractant N235; the modifier is n-decyl alcohol; the diluent is a mixture of kerosene and benzene in a volume ratio of 1:3.

[0011] (2) Extraction process: The extractant prepared in step (1) is mixed with the desulfurization wastewater to be treated at a volume ratio of organic phase to aqueous phase (O / A) 1: (3~8), and the extraction reaction is carried out at room temperature. After the reaction is completed, the phases are separated by standing to obtain the organic phase loaded with chloride ions and the raffinate aqueous phase. (3) Back-extraction process: The organic phase obtained in step (2) is mixed with an ammonia solution with a mass fraction of 25% at a volume ratio of organic phase to water phase (O / A) of 6:1, and back-extracted for 15 minutes to achieve the back-extraction of chloride ions and the regeneration of the organic phase.

[0012] The above method is further explained as follows: This invention optimizes the formulation of the extractant. Through systematic comparison of n-decyl alcohol, n-octanol and isooctanol, it was found that n-decyl alcohol can maintain stable and good extraction efficiency under chloride ion concentration conditions of 5000-20000 mg / L, and has the most balanced performance. Therefore, this invention selects n-decyl alcohol as the modifier.

[0013] The diluent combination exhibits higher extraction efficiency and lower organic phase loss compared to a single TBP (tributyl phosphate) or other high-carbon alkane mixture.

[0014] In common extractant formulations, the extractant accounts for 40%–85%, while the diluent and modifier account for 15%–60%. Therefore, the proposed volume ratio of the extractant, diluent, and modifier used in the screening is within the range of 5:4:1–8:1:1. Experimental testing revealed that the optimal volume ratio of the extractant formulation described in this invention is: N235 : diluent : n-decyl alcohol = 6 : 3 : 1. This ratio ensures high extraction efficiency while effectively saving on the amount of N235 used, reducing costs, and avoiding the problem of organic phase adhesion to the walls due to insufficient diluent.

[0015] This invention optimizes the extraction process conditions: extraction experiments were conducted with O / A volume ratios of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, and 1:8. Considering economic factors, the optimal volume ratio of organic phase to aqueous phase in this invention is 1:4. Under this condition, the chloride ion removal rate is significantly improved, and further increasing the amount of organic phase has limited effect on efficiency improvement; therefore, this is the optimal point from an economic perspective.

[0016] The extractant system provided by this invention has strong anti-interference performance. This extraction system is effective against common Ca in wastewater. 2+ Mg 2+ Na + Plasma exhibits extremely strong anti-interference capabilities. It is particularly effective for wastewater containing Ca concentrations ranging from 400–2000 mg / L. 2+ 1000–9000 mg / L of Mg 2+500–20000 mg / L Na + It exhibits strong anti-interference properties, with the chloride ion extraction rate remaining between 68.9% and 69.4%, showing minimal fluctuation.

[0017] In step (3) of the back-extraction process, the back-extraction agent is ammonia water with a mass fraction of 25%, which ensures a high back-extraction rate while having low corrosivity to the equipment. Although NaOH has a slightly higher back-extraction rate at the same concentration, ammonia water, as a weak alkali, has a much lower corrosivity to equipment (especially carbon steel equipment) than NaOH, which can significantly reduce equipment investment and maintenance costs.

[0018] The optimal back-extraction ratio (O / A) is 2:1 (organic phase: aqueous phase). This ratio ensures a high back-extraction rate while avoiding organic phase loss and subsequent processing burden caused by excessive aqueous phase volume.

[0019] Back-extraction time: preferably 15 minutes. The back-extraction process is a rapid reaction, and 15 minutes ensures that the reaction proceeds fully.

[0020] Optional pretreatment solutions: Highly efficient pretreatment solutions are provided for calcium ions in wastewater.

[0021] The beneficial effects of this invention are: (1) High efficiency and high stability: Through optimized extractant formulation and process conditions, efficient and stable extraction of chloride ions is achieved, with strong resistance to water quality fluctuations.

[0022] (2) Low cost: Low-cost n-decyl alcohol and kerosene-benzene diluent are preferred, and a cost-saving ratio of 6:3:1 is adopted. At the same time, ammonia water with low corrosivity is selected as the back-extraction agent, which significantly reduces the cost of reagents and equipment investment.

[0023] (3) Resource recovery and environmental protection: Chloride ions can be enriched and recovered through back extraction, and the regenerated organic phase can be recycled, realizing resource recovery and greening of the process.

[0024] (4) The process is simple and easy to promote: the whole process flow is clear, the operating conditions are mild, and it is easy to modify and integrate on the basis of existing wastewater treatment systems, and it has good prospects for industrial application. Attached Figure Description

[0025] Figure 1 This is the mass spectrum of the extractant monomer N235 before extraction in Example 2; Figure 2 This is the mass spectrum of the saturated loaded organic phase after extraction in Example 2; Figure 3 The image shows the Fourier transform infrared spectrum of the organic phase after extraction in Example 2. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] Example 1: Screening and Determination of Extractant Formulation I. Selection of Modifiers: First, in a basic system where the main extractant is N235 and the diluent is kerosene-benzene, the effects of n-decyl alcohol, n-octanol, and isooctanol as modifiers on chloride ion extraction efficiency were investigated, with the extractant, diluent, and modifier in a ratio of 7:2:1.

[0028] The specific experimental procedure is as follows: 42 ml of N235, 12 ml of kerosene, and 6 ml of modifiers (n-decyl alcohol, n-octanol, and isooctanol, respectively) were accurately measured and mixed to prepare three extractants with different modifiers. Extraction experiments were then conducted with 240 ml of water samples.

[0029] The experiment employed a three-stage countercurrent extraction simulation. 240 mL of wastewater (with a chloride ion concentration of 7907 mg / L in the desulfurization wastewater) was added to 0.8 mL of concentrated sulfuric acid. After heating to 60°C, 20 mL of extractant was added. The reaction was allowed to proceed for 15 minutes, after which stirring was stopped, and the mixture was allowed to stand at a constant temperature for 15 minutes. The aqueous phase and extract were then separated, constituting the first-stage extraction. This process was repeated twice with the separated aqueous phase, constituting the second-stage and third-stage extractions. The results showed that isooctanol exhibited high efficiency in the first-stage extraction (high chloride ion concentration), but its efficiency decreased significantly in the third-stage extraction (low concentration). n-Octanol showed the opposite effect, performing better at low concentrations. n-Decanol maintained stable and good extraction efficiency under both high and low chloride ion concentrations, demonstrating the most balanced performance. Therefore, n-Decanol was selected as the optimal modifier.

[0030] II. Selection of the proportions of each component in the extractant Next, based on the determination of n-decyl alcohol as the modifier, the effect of different ratios on the efficiency of three-stage chloride ion extraction was studied in a system of N235: diluent: n-decyl alcohol. The diluent was kerosene: benzene = 1:3.

[0031] The specific experimental procedure is as follows: 60 mL of extractant with different ratios (5:4:1, 5:3:2, 5:2:3, 5:1:4, 6:3:1, 6:2:2, 6:1:3, 7:2:1, 7:1:2, 8:1:1) was prepared, with the volume ratio of extractant, diluent, and modifier ranging from 5:4:1 to 8:1:1. A three-stage countercurrent extraction simulation was used. 240 mL of wastewater (chloride ion concentration of 7907 mg / L in desulfurization wastewater) was added to 0.8 mL of concentrated sulfuric acid, heated to 60°C, and then 20 mL of extractant was added. After reacting for 15 minutes, stirring was stopped, and the mixture was allowed to stand at a constant temperature for 15 minutes. The aqueous phase and extract were then separated, representing the first stage of extraction. The above operation was repeated twice with the separated aqueous phase, representing the second and third stages of extraction. The experiment showed that the extraction efficiency was better when the ratio of N235:diluent:n-decyl alcohol was 7:2:1 or 6:3:1. To save on N235 usage and control costs, a 6:3:1 ratio was ultimately chosen as the optimal solution.

[0032] III. Selection of Diluent Finally, the diluents were screened.

[0033] The specific experimental procedure is as follows: 42 mL of N235, 12 mL of diluent (in this example, three compound systems of sulfonated kerosene + benzene, kerosene + benzene, and kerosene + xylene were compared in the experiment), and 6 mL of n-decyl alcohol were accurately measured and mixed to prepare three extractants with different modified formulations. Extraction experiments were carried out with 240 mL of water sample respectively.

[0034] The experiment employed a three-stage countercurrent extraction simulation. 240 mL of wastewater (chloride ion concentration of 7907 mg / L in desulfurization wastewater) was added to 0.8 mL of concentrated sulfuric acid. After heating to 60°C, 20 mL of extractant was added. The reaction was allowed to proceed for 15 minutes, then stirring was stopped, and the mixture was allowed to stand at a constant temperature for 15 minutes. The aqueous phase and extract were then separated, constituting the first-stage extraction. This process was repeated twice with the separated aqueous phase, constituting the second-stage and third-stage extractions. Results showed that the kerosene-benzene complex system (volume ratio 1:3) achieved the highest removal rate (99.18%) in the three-stage extraction, exhibiting overall stability. The first-stage extraction rate reached 66.23%, and the second-stage extraction rate reached 94.05%. This formulation simultaneously achieved the triple objectives of high extraction efficiency, rapid phase separation, and system stability, laying the foundation for subsequent experiments.

[0035] Example 2: Optimization of Extraction Conditions – Determination of O / A Ratio Using the optimal extractant formulation determined in Example 1 (N235:(kerosene:benzene=1:3):n-decyl alcohol=6:3:1), the effect of the organic phase to aqueous phase volume ratio (O / A) on the chloride ion extraction efficiency was systematically investigated.

[0036] The specific experimental procedure is as follows: 42 mL of N235, 12 mL of diluent (kerosene:benzene = 1:3), and 6 mL of n-decanol were precisely measured and mixed to prepare the extractant. This extractant was then used in the three-stage countercurrent extraction experiment (chloride ion concentration 7907 mg / L) with different volumes (420 mL, 360 mL, 300 mL, 240 mL, and 180 mL) of the same water sample, as described in Example 1. The experimental results clearly showed that the chloride ion removal rate increased with increasing O / A ratio. The increase in removal rate was most significant when the O / A ratio increased from 1:7 to 1:5; however, the increase in removal rate tended to level off when the O / A ratio was further increased to 1:3. Considering both extraction efficiency and treatment cost, an O / A ratio of 1:4 (60 mL extractant, 240 mL water sample) was selected as the optimal operating condition.

[0037] Example 3: Interference resistance test of the extraction system Under optimal extractant formulation and O / A = 1:4 conditions, the effects of common cations in water (Ca) were systematically investigated. 2+ Mg 2+ Na + The effect of concentration changes on chloride ion extraction rate.

[0038] The specific experimental procedure is as follows: Measure 42 mL of N235, 12 mL of diluent (kerosene:benzene = 1:3, volume ratio), and 6 mL of n-decyl alcohol, mix them to prepare the extractant, and then react it with different Ca... 2+ Mg 2+ Na + The three-stage countercurrent extraction experiment in Case 1 was performed on a water sample of the desired concentration. The results showed that: Control Ca 2+ With concentrations of 400, 800, 1200, 1600, and 2000 mg / L, the chloride ion extraction rates were measured to be stable at 69.0%, 69.3%, 69.0%, 69.0%, and 68.9%, respectively.

[0039] Controlling Mg 2+ With concentrations of 1000, 3000, 5000, 7000, and 9000 mg / L, the chloride ion extraction rates were measured to be stable at 69.0%, 69.0%, 68.9%, 69.4%, and 69.0%, respectively.

[0040] Control Na + With concentrations of 500, 5000, 10000, 15000, and 20000 mg / L, the chloride ion extraction rates were measured to be stable at 68.5%, 69.1%, 69.0%, 69.0%, and 69.3%, respectively.

[0041] The above results fully demonstrate that the extraction system has excellent adaptability to changes in the concentration of common cations in the influent water and strong anti-interference ability.

[0042] Example 4: Optimization of back-extraction process parameters Back-extraction experiments were conducted using an organic phase loaded with chloride ions. First, the type and concentration of the back-extraction agent were determined. Back-extraction was performed using 5%, 15%, and 25% (w / w) NH3·H2O and 5%, 15%, and 25% (w / w) NaOH, respectively.

[0043] The specific experimental procedure is as follows: The extract (60 mL) obtained after the three-stage extraction in Example 3 was heated to 60°C, and 2.5 mL of back-extraction agent was added. After reacting for 15 minutes, stirring was stopped, and the mixture was allowed to stand at a constant temperature for 15 minutes. The aqueous phase and extract were then separated, which constituted the first-stage back-extraction. The above operation was repeated for the second-stage back-extraction. The chloride ion concentration in the back-extraction agent was measured.

[0044] The results showed that the back-extraction rates of both back-extraction agents increased with increasing concentration, reaching equilibrium at 20%. Although NaOH had a slightly higher back-extraction rate, its strong corrosiveness would increase equipment costs and maintenance difficulties, so 25% NH3·H2O was chosen as the back-extraction agent.

[0045] Performance testing: Samples obtained under the optimal operating conditions determined in Example 2 were tested, and the data are as follows: Figure 1 The image shows the mass spectrum of the extractant monomer N235 before extraction in Example 2. The mass spectrum peak at m / z=354.4142 is the molecular ion peak of N235 extractant obtaining a proton (M+H), corresponding to one extractant monomer N235.

[0046] Figure 2 This is the mass spectrum of the saturated loaded organic phase after extraction in Example 2. The mass peak at m / z = 424.3525 represents the Cl-loaded organic phase after extraction with N235 extractant. - The mass spectrum. This result indicates that the extractant N235 and Cl in the saturated supported organic phase... - The existence of the 1:1 extraction ratio in the above analysis was verified.

[0047] Figure 3 This is the Fourier transform infrared spectrum of the organic phase after extraction in Example 2; infrared spectroscopy analysis revealed that the extracted organic phase at 1034 cm⁻¹... -1 Cl appears at the location - Characteristic peaks indicate that Cl - Extracted into the organic phase; simultaneously, 1128 cm -1 SO4 2-The characteristic peak intensity decreased significantly, indicating that SO4 in the aqueous phase... 2- The reduction was confirmed by the presence of Cl during the extraction process. - With SO4 2- Ion exchange reactions.

[0048] The extraction mechanism of this invention was confirmed by Fourier transform infrared spectroscopy (FT-IR) and energy-efficient intramural chromatography-mass spectrometry (ESI-MS).

Claims

1. A method for efficient extraction and recovery of chloride ions from desulfurization wastewater, characterized in that... Includes the following: (1) Preparation of the extractant: a composite extraction system consisting of a main extractant, a diluent and a modifier; the main extractant is a tertiary amine extractant N235; the modifier is n-decyl alcohol; the diluent is a mixture of kerosene and benzene; the volume ratio of the main extractant, diluent and modifier is (5~8):(1~4):1; (2) Extraction process: The extractant prepared in step (1) is mixed with the desulfurization wastewater to be treated at a volume ratio of organic phase to aqueous phase of 1: (3~8). The extraction reaction is carried out at room temperature. After the reaction is completed, the phases are separated by standing to obtain the organic phase loaded with chloride ions and the raffinate aqueous phase. (3) Back-extraction process: The organic phase obtained in step (2) is back-extracted with an ammonia solution to achieve the back-extraction of chloride ions and the regeneration of the organic phase; the mass percentage of the ammonia solution is 5%~25%.

2. The method for efficient extraction and recovery of chloride ions in desulfurization wastewater according to claim 1, characterized in that, In step (1), kerosene and benzene are mixed at a volume ratio of 1:3; the chloride ion concentration is 5000-20000 mg / L.

3. The method for efficient extraction and recovery of chloride ions in desulfurization wastewater according to claim 1, characterized in that, The optimal volume ratio of the extraction system formulation is: main extractant, diluent, and modifier = 6:3:

1.

4. The method for efficient extraction and recovery of chloride ions in desulfurization wastewater according to claim 1, characterized in that, In step (2), the volume ratio of the organic phase to the aqueous phase before extraction is 1:

4.

5. The method for efficient extraction and recovery of chloride ions in desulfurization wastewater according to claim 1, characterized in that, In step (3), the volume ratio of the organic phase to the aqueous phase in the back-extraction is 6:

1.

6. The method for efficient extraction and recovery of chloride ions in desulfurization wastewater according to claim 1, characterized in that, In step (3) back-extraction, the back-extraction agent is ammonia water with a mass fraction of 25%.

7. The method for efficient extraction and recovery of chloride ions in desulfurization wastewater according to claim 1, characterized in that, In step (3) back-extraction, the back-extraction ratio is: organic phase: aqueous phase volume ratio is 2:

1.

8. The method for efficient extraction and recovery of chloride ions in desulfurization wastewater according to claim 7, characterized in that, The back-extraction time is 15 minutes.

9. The method for efficient extraction and recovery of chloride ions in desulfurization wastewater according to claim 1, characterized in that, The extraction system exhibits strong resistance to changes in cation concentration in the influent, and is effective for Ca2+ concentrations in wastewater ranging from 400 to 2000 mg / L. 2+ 1000–9000 mg / L of Mg 2+ 500–20000 mg / L Na + It has strong anti-interference capabilities.

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