Method for removing oxalic acid and salts thereof in wastewater by using hydrogen peroxide

Abstract

The invention discloses a method for removing oxalic acid and salts thereof in wastewater by using hydrogen peroxide. The method comprises the following steps: pretreating wastewater containing oxalic acid and salts thereof, and adjusting the pH value to 3.5-4.0; adding hydrogen peroxide into the adjusted wastewater, and uniformly stirring to obtain mixed wastewater; and feeding the mixed wastewater into an activated carbon reaction column in a pulse water feeding manner, and removing oxalic acid and salts thereof in the water. According to the method, the removal efficiency of oxalic acid is effectively improved, and compared with the prior art, the method has the advantages that the process is simple, secondary pollution is avoided, and the wastewater treatment efficiency and environmental friendliness are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method for removing oxalic acid and its salts from wastewater using hydrogen peroxide. Background Technology

[0002] Oxalic acid (scientific name: ethanedioic acid, molecular formula: H₂C₂O₄) is a common saturated dicarboxylic acid widely used in various industries such as chemical engineering, pharmaceuticals, fine chemicals, daily chemicals, printing and dyeing, and the manufacture of lithium battery cathode materials. Oxalic acid possesses strong acidity, reducing properties, and complexing properties, and can form soluble complexes with metals, often used for the extraction of rare earth elements. Oxalic acid and its salts (such as sodium oxalate) are also widely present in industrial wastewater.

[0003] Currently, methods for treating oxalic acid and its salts in water mainly include electrochemical methods, chemical oxidation methods, adsorption methods, biochemical methods, and precipitation recovery methods. However, each of these existing methods has certain limitations. For example, precipitation and adsorption methods may generate hazardous waste, while electrolysis and ozone catalytic oxidation methods usually require expensive equipment investment; biochemical methods have high requirements for the salinity, heavy metals, and pH of the water; in addition, the treatment effect of ozone catalytic oxidation method is limited and requires the use of catalysts.

[0004] In some industrial wastewater treatment processes, residual oxalic acid can cause scaling in membrane systems, affecting normal treatment procedures. For example, in a wastewater resource recovery project, residual oxalic acid caused scaling problems when wastewater entered the RO system, as oxalate ions reacted with calcium ions to form a supersaturated solution. Traditional oxalic acid treatment methods, such as oxidation and adsorption, cannot completely and effectively remove oxalic acid and may introduce new impurities, affecting subsequent treatment.

[0005] Patent document CN 118929718 A discloses a method for removing oxalate from a sodium aluminate solution, comprising: mixing an oxalate removal agent with a solvent at a set temperature to obtain a mixed solution with a set concentration; and adding the mixed solution to a sodium aluminate solution to cause the oxalate removal agent to react with the oxalate in the sodium aluminate solution to undergo a precipitation reaction, followed by solid-liquid separation to obtain a purified sodium aluminate solution. The oxalate removal agent includes one or more of barium hydroxide, barium chloride, and calcium chloride. However, the above method has the following drawbacks: firstly, the oxalate removal agent is difficult to remove oxalic acid; secondly, it easily introduces impurity ions such as barium and calcium. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this invention provides a method for removing oxalic acid and its salts from wastewater using hydrogen peroxide. This method can effectively remove oxalic acid and its salts from industrial wastewater. It effectively solves some obvious drawbacks such as the difficulty in completely removing oxalic acid and its salts, high investment costs in the treatment process, and the introduction of new impurity ions during the treatment process.

[0007] This invention provides a method for removing oxalic acid and its salts from wastewater using hydrogen peroxide. The technical solution steps are as follows: (1) After pretreatment of the wastewater containing oxalic acid and its salts, adjust the pH value to 3.5~4.0; (2) Add hydrogen peroxide to the adjusted wastewater and stir evenly to obtain mixed wastewater; (3) The mixed wastewater is fed into the activated carbon reaction column through a pulse inlet method to remove oxalic acid and its salts from the water.

[0008] In one alternative embodiment, the wastewater pretreatment to remove suspended solids is carried out by ultrafiltration (UF), which can efficiently remove solid impurities from the wastewater and provide cleaner wastewater for subsequent oxidation reactions.

[0009] In one optional embodiment, the hydrogen peroxide has a mass fraction of 30%, and the mass ratio of hydrogen peroxide to sodium oxalate is 1:1.9 to 2.1, preferably 1:2. This ratio ensures the oxidation reaction efficiency of hydrogen peroxide while avoiding excessive use of hydrogen peroxide.

[0010] In one optional embodiment, the granular activated carbon (columnar) has a particle size of 2-4 mm, preferably 4 mm, and an iodine value of 800-1200 mg / g, preferably 1000 mg / g, which can provide sufficient surface area and catalytic reaction capacity to improve the removal efficiency of oxalic acid and its salts.

[0011] In one optional embodiment, the height-to-diameter ratio (height of activated carbon fixed bed: inner diameter of activated carbon fixed bed) of the activated carbon reaction column is controlled at (10~15):1, preferably 12:1. This ratio can ensure that the wastewater is evenly distributed between the activated carbon bed layers, prevent the wastewater flow rate from being too fast, ensure stable removal effect, optimize the filling amount, and reduce the cost of activated carbon and equipment.

[0012] In one alternative implementation, the water sample is subjected to a combination of co-current and gravity flow, allowing the wastewater to achieve sufficient contact and treatment as it passes through the activated carbon reaction column, thereby improving the efficiency of oxalic acid removal.

[0013] In one alternative implementation, the flow rate and residence time of wastewater through the activated carbon reaction column are the same in each cycle, and the residence time t1 is between 5 and 10 seconds. This ensures that the wastewater and activated carbon are in full contact, thereby improving the reaction efficiency.

[0014] In one optional implementation, the pulse influent time is 5-10 seconds, the total duration of a single cycle is 2t1, and the number of pulse cycles is n, where n ranges from 15 to 20. This design optimizes wastewater flowability, avoids short-circuiting and concentration polarization within the activated carbon column, and ensures highly efficient treatment.

[0015] The intermittent pulse influent oxidation step includes: pretreated wastewater is pumped into the activated carbon reaction column by an influent pump with a volume of Q within an influent time t1. After gravity flow treatment in the activated carbon reaction column, the water sample is collected and returned to the front-end pH adjustment step. The same influent and treatment process is repeated, and the reaction is carried out in n cycles. Finally, the treated effluent meets the standards and is discharged or utilized.

[0016] The actual filling volume V1 of the activated carbon bed is calculated using the following formula: T=n·t1 M=Q·C m1 = M / (v·T) V1=m1 / ρ Where T is the total residence time of the reaction column in seconds; t1 is the residence time of a single pulse reaction column in seconds; n is the number of pulse cycles; M is the mass of oxalic acid and its salts in the waste liquid (calculated as sodium oxalate) in mg; Q is the circulating water volume in L; C is the sodium oxalate concentration in the influent in mg / L; m1 is the mass of granular activated carbon in g; v is the oxidation removal rate of oxalic acid and its salts (calculated as sodium oxalate) in mg (sodium oxalate) / g activated carbon·s, with a value range of 0.02~0.022; V1 is the activated carbon bed volume in cm³. 3 ρ represents the actual bulk density of granular activated carbon, in g / cm³. 3 .

[0017] The technical principle of this invention is that the treatment of oxalic acid and its salts in water by the "activated carbon-hydrogen peroxide" system is a complex process, and the removal of oxalic acid mainly involves two processes.

[0018] First, adsorption. Granular activated carbon has a rich microporous structure and a large specific surface area. At the same time, the oxygen-containing functional groups on the surface of activated carbon also affect the adsorption behavior of activated carbon for organic matter. Due to the special physical and chemical structure of its surface, granular activated carbon has a good adsorption effect on oxalic acid.

[0019] Secondly, catalytic oxidation. The oxidation potential of hydroxyl radicals is as high as 2.8V, far exceeding that of hydrogen peroxide and second only to sulfur dioxide (F). Hydroxyl radicals can non-selectively attack most organic compounds, preferentially targeting sites with high electron cloud density, such as double bonds and aromatic rings, thereby initiating oxidation, addition, and substitution reactions, ultimately decomposing them into harmless substances such as CO2 and H2O. Therefore, hydroxyl radicals are considered to be highly efficient active substances for removing target pollutants. In the "hydrogen peroxide-activated carbon" system, the surface of activated carbon contains relatively abundant oxygen-containing functional groups such as hydroxyl and ether groups. These functional groups can promote the generation of hydroxyl radicals from hydrogen peroxide. Moreover, these functional groups are fixed on the surface of activated carbon and are not easily eliminated, thus allowing activated carbon to continuously exert relatively stable catalytic properties. In addition, trace amounts of metal elements, such as Fe and Al, are also embedded on the surface of activated carbon. Fe in activated carbon may exist in the form of Fe3O4, while Al exists in the form of Al2O3. 3+ And Al 3+ It also has the function of catalyzing the decomposition of H2O2 into hydroxyl radicals. Under the continuous generation of hydroxyl radicals, oxalic acid may be gradually oxidized.

[0020] Therefore, oxalic acid reacts not only in solution through molecular and free radical collisions, but hydroxyl radicals may also attack oxalic acid molecules originally adsorbed within the activated carbon pores. As the oxalic acid molecules originally adsorbed and fixed on the activated carbon pores are oxidized and removed, the vacated adsorption sites regain their adsorption capacity and continue to adsorb free oxalic acid molecules in the solution. Because of the simultaneous occurrence of "adsorption," "free radical attack oxidation," and "adsorption-oxidation," the treatment efficiency and rate of oxalic acid in water samples are greatly improved.

[0021] Furthermore, the pulsed water inlet and outlet method results in a relatively high water flow velocity, an increased Reynolds number, and a flow state similar to turbulence. According to fluid mechanics principles, a higher Reynolds number corresponds to a thinner viscous sublayer. This significantly thins the liquid boundary layer (mainly composed of the viscous sublayer) on the activated carbon surface, leading to a substantial increase in water flow shear force. Simultaneously, the trajectories of liquid particles flowing across the activated carbon surface are extremely chaotic, involving mixing and collisions. The pulsed water inlet method ensures more uniform water distribution and a larger effective reaction area. The combined effect of these factors greatly promotes the mass transfer efficiency of oxalic acid molecules / ions from the aqueous phase to the carbon surface.

[0022] The technical solution of this invention has the following advantages: (1) This invention effectively removes oxalic acid from wastewater by using hydrogen peroxide and activated carbon in combination. The oxidation effect of hydrogen peroxide and the adsorption effect of activated carbon are combined to efficiently degrade oxalic acid in wastewater. This technology solves the problem that oxalic acid is difficult to completely remove and secondary pollution may occur during the treatment process in the prior art, thereby greatly improving the efficiency and environmental friendliness of wastewater treatment.

[0023] (2) In the wastewater pretreatment process, the present invention uses ultrafiltration (UF) to remove suspended solids, which can effectively remove solid impurities in wastewater and provide a clean water quality foundation for subsequent hydrogen peroxide oxidation and activated carbon adsorption. This technology ensures the stability and efficiency of the subsequent treatment process and avoids the clogging of activated carbon by particulate matter.

[0024] (3) The present invention explores a hydrogen peroxide mass fraction of 30% and a hydrogen peroxide to sodium oxalate mass ratio of 1:1.9~2.1. This ratio optimizes the use efficiency of hydrogen peroxide, ensures that the oxidation reaction is sufficient and not wasted, thereby reducing the cost of using chemical agents.

[0025] (4) This invention uses columnar coal-based granular activated carbon as the adsorbent material. By combining co-current and gravity flow for water intake, the problem of activated carbon caking caused by high salinity is effectively avoided, short-circuiting is reduced, and the adsorption and catalytic effects of activated carbon are improved. This design ensures the stability of the reaction process and extends the service life of the activated carbon.

[0026] (5) The present invention, through pulsed water inlet, can ensure sufficient contact between wastewater and activated carbon, thereby improving the removal efficiency of oxalic acid. This technology optimizes the distribution of fluid in the activated carbon column, avoids saturation of activated carbon adsorption and decrease in reaction rate, and improves the efficiency of the entire treatment process.

[0027] (6) This invention optimizes the pulse influent time and pulse cycle, thereby improving wastewater flowability, avoiding short-circuiting within the activated carbon column, and ensuring efficient treatment.

[0028] (7) The present invention has high engineering application feasibility, simple equipment, low investment, easy control of reaction conditions, and high expected degree of automation of equipment in the later stage.

[0029] (8) The wastewater treatment method of the present invention is applicable to the removal of low to medium concentrations of oxalic acid from wastewater in various industries, and is particularly suitable for wastewater treatment in the chemical, pharmaceutical, and metallurgical industries. It has broad industrial application prospects. Attached Figure Description

[0030] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the process flow of Embodiments 1-5 of the present invention. Detailed Implementation

[0032] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0033] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0034] Example 1 In this embodiment, wastewater with a sodium oxalate concentration of 503.23 mg / L is first treated by ultrafiltration (UF) to remove suspended solids, and the pH value of the wastewater is adjusted to 3.5 using dilute sulfuric acid. Next, 30% hydrogen peroxide (by mass) is added, with a hydrogen peroxide to sodium oxalate mass ratio of 1:1.9, and the mixture is stirred thoroughly to obtain a mixed wastewater. Figure 1 As shown, mixed wastewater was fed into an activated carbon reaction column for treatment. The activated carbon particles (columnar) had a diameter of 2 mm, and the height-to-diameter ratio of the column was 10:1. The iodine value was 800 mg / g. A multi-cycle "adsorption-oxidation" reaction was employed. The average residence time of the water sample in the activated carbon reaction column after influent in a single pulse cycle was set to 5 seconds, the single pulse influent cycle was 10 seconds, and the number of cycles n=15. The experimental results showed that the sodium oxalate concentration was 57.25 mg / L, and the oxalic acid removal rate was 88.62%.

[0035] The volume V1 of activated carbon and the total residence time are calculated using the following formulas: The volume of water to be treated is Q=0.5L, the activated carbon removal rate is preset to 0.021mg / (g·s), and the actual measured bulk density of the granular activated carbon used is ρ=0.806g / cm³.

[0036] T = n·t1 = 15 × 5 = 75s M = Q·C = 0.5 × 503.23 = 251.615 mg m1=M / (v·T)=251.615 / (0.021×75)=159.76g V1=m1 / ρ=159.76 / 0.806=198.21cm³ Example 2 In this embodiment, wastewater with a sodium oxalate concentration of 501.11 mg / L was first treated by ultrafiltration (UF) to remove suspended solids, and the pH of the wastewater was adjusted to 4.0 using dilute sulfuric acid. Next, 30% hydrogen peroxide was added, with a hydrogen peroxide to sodium oxalate mass ratio of 1:2.1, and the mixture was stirred thoroughly to obtain a mixed wastewater. Figure 1 As shown, mixed wastewater was fed into an activated carbon reaction column for treatment. The activated carbon particles (columnar) had a diameter of 4 mm and an iodine value of 1200 mg / g. The height-to-diameter ratio of the activated carbon column was 15:1. A multi-cycle "adsorption-oxidation" reaction was employed. The average residence time of the water sample in the activated carbon reaction column after influent in a single pulse cycle was set to 10 seconds, the single pulse influent cycle was 20 seconds, and the number of cycles n=20. Experimental results showed that the sodium oxalate concentration was 7.12 mg / L, and the oxalic acid removal rate was 98.58%.

[0037] The volume V1 of activated carbon and the total residence time are calculated using the following formulas: The volume of water to be treated is Q=0.5L, the activated carbon removal rate is preset to 0.021mg / (g·s), and the actual measured bulk density of the granular activated carbon used is ρ=0.806g / cm³.

[0038] T = n·t1 = 20 × 10 = 200 s M = Q·C = 0.5 × 501.11 = 250.555 mg m1=M / (v·T)=250.555 / (0.021×200)=59.67g V1=m1 / ρ=74.06cm 3 Example 3 In this embodiment, wastewater with a sodium oxalate concentration of 497.87 mg / L is first treated by ultrafiltration (UF) to remove suspended solids, and the pH of the wastewater is adjusted to 4 using dilute sulfuric acid. Next, 30% hydrogen peroxide (mass ratio of hydrogen peroxide to sodium oxalate) is added, with a mass ratio of 1:2, and the mixture is stirred thoroughly to obtain a mixed wastewater. Figure 1As shown, mixed wastewater was fed into an activated carbon reaction column for treatment. The activated carbon particles (columnar) had a diameter of 4 mm and an iodine value of 1000 mg / g. The height-to-diameter ratio of the activated carbon column was 12:1. A multi-cycle "adsorption-oxidation" reaction was employed. The average residence time of the water sample in the activated carbon reaction column after influent in a single pulse cycle was set to 7 seconds, the single pulse influent cycle was 14 seconds, and the cycle number n=15. Experimental results showed that with a sodium oxalate concentration of 0.27 mg / L, the oxalic acid removal rate was 99.95%.

[0039] The volume V1 of activated carbon and the total residence time are calculated using the following formulas: The volume of water to be treated is Q=0.5L, the activated carbon removal rate is preset to 0.021mg / (g·s), and the actual measured bulk density of the granular activated carbon used is ρ=0.806g / cm³.

[0040] T = n·t1 = 15 × 7 = 105 s M = Q·C = 0.5 × 497.87 = 248.935 mg m1 = M / (v·T) = 112.9g V1 = m1 / ρ = 140.07cm 3 Example 4 In this embodiment, wastewater with a sodium oxalate concentration of 500.66 mg / L is first treated by ultrafiltration (UF) to remove suspended solids, and the pH value of the wastewater is adjusted to 3.8 using dilute sulfuric acid. Next, 30% hydrogen peroxide (mass fraction) is added, with a hydrogen peroxide to sodium oxalate mass ratio of 1:1.9, and the mixture is stirred thoroughly to obtain a mixed wastewater. Figure 1 As shown, mixed wastewater was fed into an activated carbon reaction column for treatment. The activated carbon particles (columnar) had a diameter of 3 mm and an iodine value of 1000 mg / g. The height-to-diameter ratio of the activated carbon column was 10:1. A multi-cycle "adsorption-oxidation" reaction was employed. The average residence time of the water sample in the activated carbon reaction column after influent in a single pulse cycle was set to 6 seconds, the single pulse influent cycle was 12 seconds, and the cycle number n=16. Experimental results showed that the sodium oxalate concentration was 10.88 mg / L, and the oxalic acid removal rate was 97.83%.

[0041] The volume V1 of activated carbon and the total residence time are calculated using the following formulas: The volume of water to be treated is Q=0.5L, the activated carbon removal rate is preset to 0.021mg / (g·s), and the actual measured bulk density of the granular activated carbon used is ρ=0.806g / cm³.

[0042] T = n·t1 = 16 × 6 = 96 s M = Q·C = 0.5 × 500.66 = 250.33 mg m1=M / (v·T)=250.33 / (0.021×96)=124.17g V1 = m1 / ρ = 154.06cm 3 Example 5 In this embodiment, wastewater with a sodium oxalate concentration of 548.42 g was first treated by ultrafiltration (UF) to remove suspended solids, and the pH of the wastewater was adjusted to 4.0 using dilute sulfuric acid. Next, 30% hydrogen peroxide (by mass) was added, with a hydrogen peroxide to sodium oxalate mass ratio of 1:2.1, and the mixture was stirred thoroughly to obtain a mixed wastewater. Figure 1 As shown, mixed wastewater was treated using an activated carbon reaction column. The activated carbon particles (columnar) had a diameter of 4 mm and an iodine value of 1200 mg / g. The height-to-diameter ratio of the activated carbon column was 14:1. A multi-cycle "adsorption-oxidation" reaction was employed. The average residence time of the water sample in the activated carbon reaction column after influent in a single pulse cycle was set to 8 seconds, with a single pulse influent cycle of 16 seconds and a cycle number of n=18. Experimental results showed that the sodium oxalate concentration was 8.23 ​​mg / L, and the oxalic acid removal rate was 98.50%.

[0043] The volume V1 of activated carbon and the total residence time are calculated using the following formulas: The volume of water to be treated is Q=0.5L, the activated carbon removal rate is preset to 0.021mg / (g·s), and the actual measured bulk density of the granular activated carbon used is ρ=0.806g / cm³.

[0044] T = n·t1 = 18 × 8 = 144 s M = Q·C = 0.5 × 548.42 = 274.21 mg m1=M / (v·T)=274.21 / (0.021×144)=90.68g V1 = m1 / ρ = 112.5cm 3 Comparative Example 1 This comparative study aimed to verify the removal efficiency of hydrogen peroxide alone on sodium oxalate under different pH conditions. Sodium oxalate solutions with a concentration of 200.5 mg / L were divided into four groups, with different concentrations of hydrogen peroxide added (55.5 mg / L, 101.2 mg / L, 100.1 mg / L, and 100.7 mg / L), and the pH was adjusted to 2.98, 2.98, 6.32, and 9.07, respectively. After 22 hours of stirring, the change in sodium oxalate concentration was measured. The experimental results showed that the concentration of sodium oxalate hardly changed, indicating that hydrogen peroxide alone cannot effectively remove sodium oxalate.

[0045] Table 1. Experiments on the oxidation of sodium oxalate by hydrogen peroxide in acidic / neutral / alkaline environments.

[0046] Comparative Example 2 This comparative example aims to verify the removal efficiency of sodium oxalate by combined treatment with activated carbon and hydrogen peroxide when the influent flow is from bottom to top countercurrent (without pulses). Table 2 shows that the sodium oxalate removal rate is no higher than 55%, indicating that sodium oxalate cannot be effectively and completely removed under pulse-free influent conditions.

[0047] Table 2. Experiment on the combined treatment of sodium oxalate with activated carbon and hydrogen peroxide (without pulse).

[0048] Methods or standards for detecting effect data Oxalic acid can be determined by titration, colorimetry, and chromatography. Considering the convenience of laboratory reagent procurement and operation, this patent employs a relatively convenient colorimetric method with high accuracy and precision for determining oxalate ions. The principle primarily utilizes the strong complexation between oxalic acid and ferric ions. In a potassium chloride-hydrochloric acid buffer solution with a pH of 1.8-2.5, ferric ions react with sulfosalicylic acid to form a purple-red complex. Because oxalate ions have a stronger complexing ability with ferric ions, they can compete with the ferric ions originally complexed with sulfosalicylic acid. Through this competitive complexation of oxalate with ferric ions, the original purple-red color of the solution lightens, and the degree of lightening increases with increasing oxalic acid concentration. The absorbance of the mixed solution at a specific wavelength shows a linear relationship with the oxalic acid concentration, thus allowing for the quantitative determination of the oxalic acid concentration in the solution.

[0049] Required reagents: Anhydrous sodium oxalate solution = 200 mg / L (each mL contains 0.2 mg of sodium oxalate, equivalent to 0.1343 mg / mL of oxalic acid); Ferric trivalent solution: 0.1 mol / L (each mL contains 5.6 mg of ferric ions, prepared using ferric chloride hexahydrate; a suitable amount of concentrated hydrochloric acid needs to be added during preparation to promote dissolution, but excessive concentrated hydrochloric acid should not be added, otherwise the solution will become too acidic, affecting the use of this spectrophotometric method); pH=2 buffer solution (6.5 mL of 0.2 mol / L hydrochloric acid solution + 25 mL of 0.2 mol / L potassium chloride solution, diluted to 100 mL); Sulfosalicylic acid solution: 0.5% wt.

[0050] Experimental equipment: spectrophotometer; 25mL colorimetric tubes.

[0051] Dosing procedure: Add 0.2 mL of iron solution to a 25 mL colorimetric tube → add 10 mL of buffer solution → 1.2 mL of sulfosalicylic acid solution (at this point the solution has developed a reddish-brown color) → add the sample to be tested / sodium oxalate standard solution → make up to volume → mix well and let stand for 3 min → measure at a wavelength of 504 nm.

[0052] The test results show that the absorbance at each concentration gradient at a wavelength of 504 nm is a function of concentration, yielding a linear equation: Abs = -0.0087[C] + 1.3074, with a correlation coefficient R = -0.999. Based on this function, the oxalate concentration in the solution can be deduced from the absorbance.

[0053] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for removing oxalic acid and its salts from wastewater using hydrogen peroxide, characterized in that, Includes the following steps: (1) After pretreating the wastewater containing oxalic acid and its salts, adjust the pH value to 3.5~4.0; (2) Add hydrogen peroxide to the adjusted wastewater and stir evenly to obtain mixed wastewater; (3) The mixed wastewater is fed into the activated carbon reaction column through a pulse inlet method to remove oxalic acid and its salts from the water.

2. The method according to claim 1, characterized in that, In step (1) wastewater pretreatment, suspended solids are removed; preferably, the method for removing suspended solids is ultrafiltration.

3. The method according to claim 1, characterized in that, The hydrogen peroxide mass fraction in step (2) is 30%, and the ratio of the amount of hydrogen peroxide added to the mass concentration of oxalic acid and its salt (calculated as sodium oxalate) is 1:1.9~2.

1.

4. The method according to any one of claims 1, characterized in that, The activated carbon reaction column in step (3) is filled with activated carbon particles with a diameter of 2-4 mm and an iodine value of 800-1200 mg / g.

5. The method according to claim 1, characterized in that, The height-to-diameter ratio of the activated carbon reaction column is controlled at (10~15):

1.

6. The method according to claim 1, characterized in that, The water entering the activated carbon reaction column is pumped into the upper part of the activated carbon reaction column by a pulse pump, and then passes through the activated carbon by a combination of co-current and gravity flow.

7. The method according to claim 1, characterized in that, In a single pulse cycle of the pulsed water inlet, the average residence time t1 of the water sample in the activated carbon reaction column after water inlet is controlled at 5~10s.

8. The method according to claim 6, characterized in that, The period of a single pulse water inlet in the pulsed system is t2, where t2 = 2·t1, and the number of pulse periods is n, where n ranges from 15 to 20.

9. The method according to claim 4, characterized in that, The bed packing volume V1 of the activated carbon is calculated using the following formula: T=n·t1 M=Q·C m1 = M / (v·T) V1=m1 / ρ Where T is the total residence time of the reaction column, in seconds; t1 is the residence time of a single pulse reaction column, in seconds; n is the number of pulse cycles; M is the mass of oxalic acid and its salts in the wastewater (calculated as sodium oxalate), in mg; Q is the circulating water volume, in L; C is the influent sodium oxalate concentration, in mg / L; m1 is the mass of granular activated carbon, in g; v is the oxidation removal rate of oxalic acid and its salts (calculated as sodium oxalate), in mg (sodium oxalate) / g activated carbon·s, ranging from 0.02 to 0.022; V1 is the activated carbon bed packing volume, in cm³. 3 ρ represents the actual bulk density of granular activated carbon, in g / cm³. 3 .

10. The method according to any one of claims 1-9, characterized in that, The concentration of oxalic acid and its salts in the wastewater is controlled at ≤550 mg / L (calculated as sodium oxalate).

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