Method for recycling high-COD (Chemical Oxygen Demand) and high-total-nitrogen waste sulfuric acid

Abstract

The invention provides a recycling method of high-COD (Chemical Oxygen Demand) and high-total-nitrogen waste sulfuric acid. The recycling method comprises the following steps: diluting the high-COD and high-total-nitrogen waste sulfuric acid, and then sequentially carrying out BDD electrolysis, distillation and concentration to obtain regenerated sulfuric acid and regenerated nitric acid. The recycling method provided by the invention not only is low in cost, simple in process and environment-friendly, but also can realize resource recycling of the sulfuric acid and the nitric acid, so that the utilization rate of resources is increased. Moreover, the sulfuric acid component can be reserved to the maximum extent through the method, the obtained regenerated sulfuric acid is high in purity and low in COD content, high efficiency and selectivity of the method in the aspect of impurity removal are shown, and the method has high economic value and practical application significance.

Description

Technical Field

[0001] The present invention belongs to the field of secondary utilization of resources, and particularly relates to a method for recycling high-COD and high-total-nitrogen waste sulfuric acid. Background Art

[0002] At present, in the production industries of pharmaceutical intermediates, pesticide intermediates, etc., there are sulfonation and other reaction processes, which will generate a large amount of high-COD (chemical oxygen demand, that is, the amount of oxidant consumed when treating a sample with a strong oxidant under certain conditions) and high-total-nitrogen waste sulfuric acid. It has high acidity, strong peculiar smell, and a dark brown appearance, and is difficult to treat.

[0003] In the prior art, the treatment methods for high-COD and high-total-nitrogen waste sulfuric acid include: waste sulfuric acid concentration. During the process of heating and concentrating waste sulfuric acid, inorganic impurities in the waste sulfuric acid will crystallize out, and organic impurities will undergo oxidation, polymerization and other reactions, turning into dark-colored colloids or suspensions. Generally, filtration is used to remove these impurities, so as to achieve the dual purposes of removing impurities and concentrating dilute sulfuric acid. This treatment method has high requirements for equipment materials, large equipment investment, and large consumption of steam, water and electricity, high operating costs, complex operation, difficult maintenance and high costs, small treatment volume of waste sulfuric acid, extremely easy blockage of evaporation pipelines, and unstable operation; high-temperature pyrolysis, decomposing waste sulfuric acid thermally into SO2 or SO3 gas, and then producing sulfuric acid. This method can treat high-concentration waste sulfuric acid with high impurity content that cannot be recycled by the concentration process, has a large treatment volume of waste sulfuric acid, can treat ammonium sulfate in waste sulfuric acid, and can directly produce 98% sulfuric acid or fuming sulfuric acid. However, this method has large investment, high energy consumption, and F - , Cl - and metal ions (especially Na + ) are likely to cause corrosion and blockage of equipment and pipelines. Therefore, it is not suitable for treating waste sulfuric acid with high contents of fluorine, chlorine and metal salts; chemical oxidation, using an oxidant to oxidize and decompose organic impurities in waste sulfuric acid under appropriate conditions, turning them into carbon dioxide, water, nitrogen oxides, and then separating them from sulfuric acid, so as to purify and recycle waste sulfuric acid. This treatment method will cause environmental pollution, and at the same time will consume a certain amount of sulfuric acid, reducing the sulfuric acid recovery rate and increasing production costs. Therefore, its application is greatly limited and generally needs to be used in combination with other processes. In addition to the above methods, there are also extraction methods, crystallization methods or neutralization methods, etc. However, when the above prior art treats high-COD and high-total-nitrogen waste sulfuric acid, there are problems such as high costs, complex operation and serious environmental pollution.

[0004] Therefore, there is an urgent need to provide a treatment method for high-COD and high-total-nitrogen waste sulfuric acid with low cost, simple process and environmental protection. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a resource utilization method for waste sulfuric acid with high COD and high total nitrogen. The resource utilization method provided by the present invention not only has low cost, simple process and is environmentally friendly, but also can realize the resource recovery of both sulfuric acid and nitric acid, improving the resource utilization rate. Moreover, through this method, the sulfuric acid component can be retained to the greatest extent, and the regenerated sulfuric acid obtained has high purity and low COD content, demonstrating the high efficiency and selectivity of this method in impurity removal, and having high economic value and practical application significance.

[0006] To achieve the object of the present invention, the following technical solutions are adopted:

[0007] The present invention provides a resource utilization method for waste sulfuric acid with high COD and high total nitrogen, and the resource utilization method includes the following steps:

[0008] Dilute the waste sulfuric acid with high COD and high total nitrogen, and then successively carry out BDD electrolysis, distillation and concentration to obtain regenerated sulfuric acid and regenerated nitric acid.

[0009] The resource utilization method provided by the present invention not only has low cost, simple process and is environmentally friendly, but also can realize the resource recovery of both sulfuric acid and nitric acid, improving the resource utilization rate. Moreover, through this method, the sulfuric acid component can be retained to the greatest extent, and the regenerated sulfuric acid obtained has high purity and low COD content, demonstrating the high efficiency and selectivity of this method in impurity removal, and having high economic value and practical application significance.

[0010] In the present invention, BDD electrolysis is the electrolytic oxidation method with a boron-doped diamond (BDD) electrode. Its principle is that under the condition of an externally applied low electric field, by controlling conditions such as voltage or current, the BDD electrode oxidizes organic substances into CO2 and some simple inorganic substances, thereby reducing the chemical oxygen demand (COD) of organic substances. At the same time, the BDD electrode can form a layer of hydroxyl radicals with strong oxidizing properties on the surface of the electrode, which has a strong oxidizing effect on refractory organic wastewater such as phenols, heterocyclics, dyes, pesticides and surfactants, and can completely mineralize organic substances.

[0011] Features of BDD electrodes: 1) Wide electrochemical potential window and high oxygen evolution potential: The wider the potential window and the higher the oxygen evolution potential, the more difficult the oxygen evolution reaction occurs, and the greater the probability of organic pollutants being oxidized at the anode, which can improve the efficiency of sewage treatment and reduce energy consumption; 2) Low background current and double-layer capacitance: It is beneficial for diamond electrodes to detect trace pollutants in the electrolyte; 3) Stable electrochemical performance and corrosion resistance: BDD electrodes can still maintain good stability and electrode activity under acidic, neutral, and alkaline conditions; 4) Not easily contaminated and having a self-cleaning effect: The surface of the BDD electrode is not easily "poisoned" and contaminated, maintaining the performance of the electrode. The "reagent" for electrochemical oxidation is electrons, which is a clean reactant, and the oxidant does not need to be added during this process, so there is no secondary pollution.

[0012] It should be noted that the present invention does not specifically limit the cathode material for BDD electrolysis. Exemplarily, for example, it can be sulfuric acid-resistant materials such as stainless steel, titanium, graphite, or platinum.

[0013] In the present invention, if the high-COD and high-total-nitrogen waste sulfuric acid is not diluted, due to the too high acidity and poor fluidity, it is not conducive to completing the subsequent BDD electrolysis process.

[0014] Preferably, the high-COD and high-total-nitrogen waste sulfuric acid includes, by mass percentage:

[0015] The COD content is 50000 - 100000 ppm, for example, it can be 50000 ppm, 60000 ppm, 70000 ppm, 80000 ppm, 90000 ppm, or 100000 ppm, etc.; the organic nitrogen content is 1000 - 4000 ppm, for example, it can be 1000 ppm, 2000 ppm, 3000 ppm, or 4000 ppm, etc.; the ammonia nitrogen content is 5 - 10 ppm, for example, it can be 5 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, or 10 ppm, etc.; sulfuric acid is 50 - 70%, for example, it can be 50%, 55%, 60%, 65%, or 70%, etc.; the rest is water.

[0016] Preferably, the diluent used in the dilution process includes water. Exemplarily, for example, it can be pure water, etc.

[0017] Preferably, the target concentration for diluting the high-COD and high-total-nitrogen waste sulfuric acid is 30 - 40 wt%, for example, it can be 30 wt%, 32 wt%, 34 wt%, 36 wt%, 38 wt%, or 40 wt%, etc. It should be noted that the target concentration refers to the mass percentage of sulfuric acid in the high-COD and high-total-nitrogen waste sulfuric acid.

[0018] Preferably, in the BDD electrolysis, the boron doping concentration of the boron-doped diamond electrode is 0.01-1 wt%, for example, it can be 0.01 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt% or 1 wt% etc., and preferably 0.03-0.1 wt%.

[0019] In the present invention, too high or too low boron doping concentration of the boron-doped diamond electrode is not conducive to the performance of the electrode. If the boron doping concentration is too low, the conductivity of the diamond is poor and the charge transfer during the electrolysis process cannot be effectively achieved; if the boron doping concentration is too high, it will cause serious lattice distortion of the diamond, affecting the physical properties such as the hardness and stability of the electrode, and may also change the electrochemical activity of the electrode.

[0020] Preferably, in the BDD electrolysis, the boron-doped diamond electrode comprises a substrate and a BDD coating (boron-doped diamond coating) plated on the surface of the substrate.

[0021] Preferably, in the BDD electrolysis, the BDD coating is a porous structure.

[0022] In the present invention, the porous BDD coating helps to increase the effective area of the electrode and improve the electrolysis effect.

[0023] It should be noted that the present invention does not limit the material of the substrate. Exemplarily, for example, it can be graphite, silicon or metal (such as titanium) etc.

[0024] Preferably, the thickness of the BDD coating is 6-15 μm, for example, it can be 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm etc.

[0025] In the present invention, too high or too low thickness of the BDD coating is not conducive to the performance of the electrode. If the thickness is too small, the conductivity of the diamond is poor and the charge transfer during the electrolysis process cannot be effectively achieved; if the thickness is too large, it will cause serious lattice distortion of the diamond, affecting the physical properties such as the hardness and stability of the electrode, and may also change the electrochemical activity of the electrode.

[0026] Preferably, the parameters of the BDD electrolysis include:

[0027] The current density is 100-300 mA / cm 2 , for example, it can be 100 mA / cm 2 , 150 mA / cm 2 , 200 mA / cm 2 , 250 mA / cm 2 or 300 mA / cm 2etc., the electrolysis time is 1 - 3 h, and for example, it can be 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc.

[0028] In the present invention, under appropriate current density and electrolysis time, it helps to fully convert the COD in the waste sulfuric acid with high COD and high total nitrogen into carbon dioxide and water, and the total nitrogen is converted into nitrate. The electrolysis effect is excellent, and the conversion rates of COD and total nitrogen can reach more than 99%, which is beneficial to achieving better economic and environmental benefits. In addition, appropriate current density and electrolysis time help to achieve the energy-saving goal and reduce the treatment cost.

[0029] Preferably, during the BDD electrolysis process, the voltage is 3 - 5 V, and for example, it can be 3 V, 3.5 V, 4 V, 4.5 V or 5 V, etc.

[0030] In the present invention, controlling the BDD electrolysis process within an appropriate voltage range can not only maximize the conversion rates of COD and total nitrogen, but also reduce the occurrence of side reactions, improve the current efficiency, make the electric energy more effectively used for the treatment of waste sulfuric acid with high COD and high total nitrogen, and at the same time extend the service life of the electrode.

[0031] Preferably, the distillation method is single-effect distillation.

[0032] Preferably, the vacuum degree of the single-effect distillation is 0.05 - 0.1 MPa, and for example, it can be 0.05 MPa, 0.06 MPa, 0.07 MPa, 0.08 MPa, 0.09 MPa or 0.1 MPa, etc.

[0033] Preferably, the temperature of the single-effect distillation is 100 - 120 °C, and for example, it can be 100 °C, 105 °C, 110 °C, 115 °C or 120 °C, etc.

[0034] In the present invention, performing single-effect distillation under specific vacuum degree and temperature conditions helps to maintain a stable distillation process, reduce production interruptions or efficiency reduction caused by temperature fluctuations or other factors, and at the same time enables nitric acid to volatilize sufficiently, improving the separation effect. And it can significantly reduce the energy cost and improve the energy utilization efficiency.

[0035] Preferably, the concentration method includes any one or a combination of at least two of distillation concentration, membrane separation concentration, heating evaporation concentration or freeze-drying concentration.

[0036] Preferably, the parameters in the distillation concentration include:

[0037] The vacuum degree is 0.07 - 0.1 MPa, for example, it can be 0.07 MPa, 0.075 MPa, 0.08 MPa, 0.085 MPa, 0.09 MPa, 0.095 MPa or 0.1 MPa, etc., and the temperature is 100 - 200 °C, for example, it can be 100 °C, 105 °C, 110 °C, 115 °C or 120 °C, etc.

[0038] The present invention further distills and concentrates the sulfuric acid after distillation under specific vacuum degree and temperature, which can not only further remove the moisture in the sulfuric acid to increase its concentration and meet the requirements of different industrial productions for high-concentration sulfuric acid, but also further reduce the COD content, thereby improving the purity and quality of the sulfuric acid.

[0039] Preferably, after the BDD electrolysis, the COD content in the obtained mixed solution of sulfuric acid and nitric acid is 500 - 1000 ppm, for example, it can be 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm or 1000 ppm, etc.

[0040] Preferably, the purity of the regenerated sulfuric acid ≥ 97%, for example, it can be 97%, 97.5%, 98%, 98.5% or 99%, etc.

[0041] Preferably, the COD content in the regenerated sulfuric acid ≤ 500 ppm, for example, it can be 500 ppm, 400 ppm, 300 ppm, 200 ppm or 100 ppm, etc.

[0042] Preferably, the resource utilization method includes the following steps:

[0043] (1) Mix the high-COD and high-total-nitrogen waste sulfuric acid with water and dilute it so that the sulfuric acid concentration of the high-COD and high-total-nitrogen waste sulfuric acid is diluted to 30 - 40 wt%; wherein, the high-COD and high-total-nitrogen waste sulfuric acid includes by mass percentage:

[0044] The COD content is 50000 - 100000 ppm, the organic nitrogen content is 1000 - 4000 ppm, the ammonia nitrogen content is 5 - 10 ppm, sulfuric acid is 50 - 70%, and the rest is water.

[0045] (2) Perform BDD electrolysis on the diluted high-COD and high-total-nitrogen waste sulfuric acid in step (1) so that COD is converted into carbon dioxide and water, and total nitrogen is converted into nitrate, and then separate to obtain a mixed solution of sulfuric acid and nitric acid.

[0046] Among them, the boron doping concentration of the boron-doped diamond electrode is 0.01 - 1 wt%, and the parameters of the BDD electrolysis include: the current density is 100 - 300 mA / cm 2, the electrolysis time is 1 - 3 h, and the voltage is 3 - 5 V; the COD in the obtained mixed solution of sulfuric acid and nitric acid is 500 - 1000 ppm.

[0047] (3) Under a vacuum degree of 0.05 - 0.1 MPa and a temperature of 100 - 120 °C, perform single - effect distillation on the mixed solution of sulfuric acid and nitric acid obtained in step (2) to respectively obtain regenerated nitric acid and sulfuric acid after distillation.

[0048] (4) Under a vacuum degree of 0.07 - 0.1 MPa and a temperature of 100 - 200 °C, distill and concentrate the sulfuric acid after distillation to obtain regenerated sulfuric acid, and the purity of the regenerated sulfuric acid ≥ 97% (calculated according to 75% sulfuric acid), and the COD content ≤ 500 ppm.

[0049] The numerical ranges described in the present invention not only include the above - listed point values, but also include any point values between the above - mentioned numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention does not exhaustively list the specific point values included in the ranges.

[0050] Compared with the prior art, the present invention has the following beneficial effects:

[0051] The resource - based method provided by the present invention not only has low cost, simple process, and is environmentally friendly, but also can realize the resource - based recovery of both sulfuric acid and nitric acid, improving the resource utilization rate. Moreover, through this method, the sulfuric acid component can be retained to the greatest extent, and the obtained regenerated sulfuric acid has high purity and low COD content, demonstrating the high efficiency and selectivity of this method in impurity removal, and having high economic value and practical application significance. Brief Description of the Drawings

[0052] Figure 1 It is the process flow chart provided in Example 1 of the present invention. Detailed Embodiments

[0053] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0054] Example 1

[0055] This example provides a resource - based method for high - COD and high - total - nitrogen waste sulfuric acid, and its process flow chart is as Figure 1 shown, and the resource - based method includes the following steps:

[0056] (1) Mix high - COD and high - total - nitrogen waste sulfuric acid with pure water for dilution so that the sulfuric acid concentration of the high - COD and high - total - nitrogen waste sulfuric acid is diluted to 35 wt%; wherein, the high - COD and high - total - nitrogen waste sulfuric acid includes by mass percentage:

[0057] The COD content is 70,000 ppm, the organic nitrogen content is 3,000 ppm, the ammonia nitrogen content is 10 ppm, sulfuric acid is 60%, and the rest is water.

[0058] (2) Perform BDD electrolysis on the diluted high-COD and high-total-nitrogen waste sulfuric acid in step (1) so that COD is converted into carbon dioxide and water, and total nitrogen is converted into nitrate. After separation, a mixed solution of sulfuric acid and nitric acid is obtained.

[0059] Among them, the boron doping concentration of the boron-doped diamond electrode is 0.05 wt%, and the parameters of BDD electrolysis include: the current density is 200 mA / cm 2 , the electrolysis time is 2 h, and the voltage is 4 V; the COD in the obtained mixed solution of sulfuric acid and nitric acid is 700 ppm; the boron-doped diamond electrode includes a graphite substrate and a BDD coating plated on the surface of the graphite substrate, and the thickness of the BDD coating is 10 μm.

[0060] (3) Under a vacuum of 0.07 MPa and a temperature of 110 °C, perform single-effect distillation on the mixed solution of sulfuric acid and nitric acid obtained in step (2) to obtain regenerated nitric acid and distilled sulfuric acid respectively.

[0061] (4) Under a vacuum of 0.08 MPa and a temperature of 150 °C, distill and concentrate the distilled sulfuric acid to obtain regenerated sulfuric acid.

[0062] Example 2

[0063] This example provides a resource utilization method for high-COD and high-total-nitrogen waste sulfuric acid, and the resource utilization method includes the following steps:

[0064] (1) Mix the high-COD and high-total-nitrogen waste sulfuric acid with pure water and dilute it so that the sulfuric acid concentration of the high-COD and high-total-nitrogen waste sulfuric acid is diluted to 30 wt%; among them, the high-COD and high-total-nitrogen waste sulfuric acid includes by mass percentage:

[0065] The COD content is 70,000 ppm, the organic nitrogen content is 3,000 ppm, the ammonia nitrogen content is 10 ppm, sulfuric acid is 60%, and the rest is water.

[0066] (2) Perform BDD electrolysis on the diluted high-COD and high-total-nitrogen waste sulfuric acid in step (1) so that COD is converted into carbon dioxide and water, and total nitrogen is converted into nitrate. After separation, a mixed solution of sulfuric acid and nitric acid is obtained.

[0067] Among them, the boron doping concentration of the boron-doped diamond electrode is 0.01 wt%, and the parameters of BDD electrolysis include: the current density is 100 mA / cm 2, the electrolysis time is 1 h and the voltage is 3 V; the COD in the obtained mixed solution of sulfuric acid and nitric acid is 1000 ppm; the boron-doped diamond electrode includes a graphite substrate and a BDD coating plated on the surface of the graphite substrate, and the thickness of the BDD coating is 6 μm.

[0068] (3) At a vacuum degree of 0.05 MPa and a temperature of 100 °C, perform single-effect distillation on the mixed solution of sulfuric acid and nitric acid obtained in step (2) to obtain regenerated nitric acid and sulfuric acid after distillation respectively.

[0069] (4) At a vacuum degree of 0.07 MPa and a temperature of 100 °C, distill and concentrate the sulfuric acid after distillation to obtain regenerated sulfuric acid.

[0070] Example 3

[0071] This example provides a resource utilization method for high-COD and high-total-nitrogen waste sulfuric acid. The resource utilization method includes the following steps:

[0072] (1) Mix high-COD and high-total-nitrogen waste sulfuric acid with pure water for dilution so that the sulfuric acid concentration of the high-COD and high-total-nitrogen waste sulfuric acid is diluted to 40 wt%; among them, the high-COD and high-total-nitrogen waste sulfuric acid includes by mass percentage:

[0073] The COD content is 70000 ppm, the organic nitrogen content is 3000 ppm, the ammonia nitrogen content is 10 ppm, sulfuric acid is 60%, and the rest is water.

[0074] (2) Perform BDD electrolysis on the diluted high-COD and high-total-nitrogen waste sulfuric acid in step (1) so that COD is converted into carbon dioxide and water, and total nitrogen is converted into nitrate ions. After separation, a mixed solution of sulfuric acid and nitric acid is obtained.

[0075] Among them, the boron doping concentration of the boron-doped diamond electrode is 1 wt%, and the parameters of BDD electrolysis include: the current density is 300 mA / cm 2 , the electrolysis time is 3 h, and the voltage is 5 V; the COD in the obtained mixed solution of sulfuric acid and nitric acid is 500 ppm; the boron-doped diamond electrode includes a graphite substrate and a BDD coating plated on the surface of the graphite substrate, and the thickness of the BDD coating is 15 μm.

[0076] (3) At a vacuum degree of 0.1 MPa and a temperature of 120 °C, perform single-effect distillation on the mixed solution of sulfuric acid and nitric acid obtained in step (2) to obtain regenerated nitric acid and sulfuric acid after distillation respectively.

[0077] (4) At a vacuum degree of 0.1 MPa and a temperature of 200 °C, distill and concentrate the sulfuric acid after distillation to obtain regenerated sulfuric acid.

[0078] Example 4

[0079] The difference between this embodiment and Embodiment 1 is that the BDD coating is a porous structure.

[0080] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0081] Embodiment 5

[0082] The difference between this embodiment and Embodiment 1 is that the boron doping concentration of the boron-doped diamond electrode is 0.005 wt%.

[0083] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0084] Embodiment 6

[0085] The difference between this embodiment and Embodiment 1 is that the boron doping concentration of the boron-doped diamond electrode is 1.5 wt%.

[0086] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0087] Embodiment 7

[0088] The difference between this embodiment and Embodiment 1 is that the current density in step (2) is 50 mA / cm 2 .

[0089] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0090] Embodiment 8

[0091] The difference between this embodiment and Embodiment 1 is that the current density in step (2) is 350 mA / cm 2 .

[0092] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0093] Embodiment 9

[0094] The difference between this embodiment and Embodiment 1 is that the voltage in step (2) is 2 V.

[0095] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0096] Embodiment 10

[0097] The difference between this embodiment and Embodiment 1 is that the voltage in step (2) is 7 V.

[0098] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0099] Embodiment 11

[0100] The difference between this embodiment and Embodiment 1 is that the temperature in step (3) is 80 °C.

[0101] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0102] Embodiment 12

[0103] The difference between this embodiment and Embodiment 1 is that the temperature in step (3) is 150 °C.

[0104] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0105] Comparative Example 1

[0106] The difference between this comparative example and Embodiment 1 is that step (1) is not carried out, that is, the high-COD and high-total-nitrogen waste sulfuric acid is not diluted.

[0107] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0108] Comparative Example 2

[0109] The difference between this comparative example and Embodiment 1 is that step (2) is not carried out, that is, the high-COD and high-total-nitrogen waste sulfuric acid is not subjected to BDD electrolysis.

[0110] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0111] Comparative Example 3

[0112] The difference between this comparative example and Embodiment 1 is that step (3) is not carried out, that is, single-effect distillation is not carried out.

[0113] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0114] Comparative Example 4

[0115] The difference between this comparative example and Embodiment 1 is that step (4) is not carried out, that is, distillation concentration is not carried out.

[0116] The remaining resource utilization methods and parameters are the same as those in Embodiment 1.

[0117] Performance Test

[0118] The regenerated sulfuric acid obtained from the above embodiments and comparative examples was tested for concentration, COD content and recovery rate. The recovery rate refers to the percentage of the mass of sulfuric acid in the regenerated sulfuric acid to the mass of sulfuric acid in the high-COD and high-total-nitrogen waste sulfuric acid.

[0119] Among them, the concentration was tested by acid-base titration, the COD content was tested by the potassium dichromate method, and the mass of sulfuric acid in the recovery rate test was also tested by acid-base titration.

[0120] The test results are shown in Table 1.

[0121] Table 1

[0122]

[0123]

[0124] Analysis:

[0125] As can be seen from Table 1, the resource utilization method provided by the present invention not only has low cost, simple process and is environmentally friendly, but also can recycle sulfuric acid and nitric acid resourcefully, improving the resource utilization rate. Moreover, through this method, the sulfuric acid component can be retained to the greatest extent, and the regenerated sulfuric acid obtained has high purity and low COD content, demonstrating the high efficiency and selectivity of this method in impurity removal, and having high economic value and practical application significance.

[0126] Comparing Example 1 with Examples 5 - 6, it can be seen that if the boron doping concentration of the boron-doped diamond electrode is too low, the conductivity of the diamond is poor, and the charge transfer during the electrolysis process cannot be effectively achieved, and the electric field cannot be formed normally to provide the conditions for the electrochemical reaction, resulting in a high COD content; if the boron doping concentration of the boron-doped diamond electrode is too high, it will cause serious lattice distortion of the diamond, affecting the physical properties such as the hardness and stability of the electrode, and may also change the electrochemical activity of the electrode, resulting in a smaller electrochemical window and the inability to remove COD in a broad spectrum, leaving more COD residues.

[0127] Comparing Example 1 with Examples 7 - 8, it can be seen that if the current density in step (2) is too low, the COD content is high and the recovery rate decreases; if the current density in step (2) is too high, the COD content is high and the recovery rate decreases.

[0128] Comparing Example 1 with Examples 9 - 10, it can be seen that if the voltage in step (2) is too low, the COD content is high and the recovery rate decreases; if the voltage in step (2) is too high, the COD content is high and the recovery rate decreases.

[0129] Comparing Example 1 with Examples 11 - 12, it can be seen that if the temperature in step (3) is too low, the effect of single-effect distillation is poor, the COD content is high and the recovery rate decreases; if the temperature in step (3) is too high, the effect of single-effect distillation is poor, the COD content is high and the recovery rate decreases.

[0130] Comparing Example 1 with Comparative Example 1, it can be seen that if the high-COD and high-total-nitrogen waste sulfuric acid is not diluted in acidity, due to the too high acidity and poor fluidity, it is not conducive to completing the subsequent BDD electrolysis process, the current efficiency becomes low, the sulfuric acid purity becomes low, and the COD content cannot be effectively removed.

[0131] As can be seen from the comparison between Example 1 and Comparative Example 2, if the BDD electrolysis process is not carried out, there will be more COD residues and a high COD content, which will affect the product quality.

[0132] As can be seen from the comparison between Example 1 and Comparative Example 3, if the single-effect distillation is not carried out, the purity of sulfuric acid will be low, the COD content will be high, and nitric acid cannot be separated.

[0133] As can be seen from the comparison between Example 1 and Comparative Example 4, if the distillation and concentration are not carried out, the purity of sulfuric acid is relatively low, the COD content is high, and the quality requirements cannot be met.

[0134] It should be noted that the present invention uses the above-mentioned examples to illustrate the process method of the present invention, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A resource utilization method for waste sulfuric acid with high COD and high total nitrogen, characterized in that The resource utilization method includes the following steps: Dilute the waste sulfuric acid with high COD and high total nitrogen, and then successively carry out BDD electrolysis, distillation and concentration to obtain regenerated sulfuric acid and regenerated nitric acid.

2. The resource utilization method according to claim 1, wherein The waste sulfuric acid with high COD and high total nitrogen includes, by mass percentage: COD content is 50,000 - 100,000 ppm, organic nitrogen content is 1,000 - 4,000 ppm, ammonia nitrogen content is 5 - 10 ppm, sulfuric acid is 50 - 70%, and the rest is water.

3. The resource utilization method according to claim 1 or 2, characterized in that The diluent used in the dilution process includes water; Preferably, the target concentration for diluting the waste sulfuric acid with high COD and high total nitrogen is 30 - 40 wt%.

4. The resource utilization method according to any one of claims 1-3, characterized in that, In the BDD electrolysis, the boron doping concentration of the boron-doped diamond electrode is 0.01 - 1 wt%, preferably 0.03 - 0.1 wt%; Preferably, in the BDD electrolysis, the boron-doped diamond electrode includes a substrate and a BDD coating plated on the surface of the substrate; Preferably, the thickness of the BDD coating is 6 - 15 μm.

5. The resource utilization method according to any one of claims 1-4, characterized in that The parameters of the BDD electrolysis include: The current density is 100 - 300 mA / cm 2 , and the electrolysis time is 1 - 3 h; Preferably, during the BDD electrolysis, the voltage is 3 - 5V.

6. The resource utilization method according to any one of claims 1-5, characterized in that The distillation method is single-effect distillation; Preferably, the vacuum degree of the single-effect distillation is 0.05 - 0.1 MPa; Preferably, the temperature of the single-effect distillation is 100 - 120°C.

7. The resource utilization method according to any one of claims 1-6, characterized in that, The concentration method includes any one or a combination of at least two of distillation concentration, membrane separation concentration, heating evaporation concentration or freeze-drying concentration; Preferably, the parameters in the distillation concentration include: Vacuum degree is 0.07 - 0.1 MPa, and temperature is 100 - 200°C.

8. The resource utilization method according to any one of claims 1-7, characterized in that After the BDD electrolysis, the COD content in the obtained mixed solution of sulfuric acid and nitric acid is 500 - 1,000 ppm.

9. The resource utilization method according to any one of claims 1-8, characterized in that, The purity of the regenerated sulfuric acid ≥ 97%; Preferably, the COD content in the regenerated sulfuric acid ≤ 500 ppm.

10. The resource utilization method according to any one of claims 1-9, characterized in that, The resource utilization method includes the following steps: (1) Mix the waste sulfuric acid with high COD and high total nitrogen and water, and carry out dilution to dilute the sulfuric acid concentration of the waste sulfuric acid with high COD and high total nitrogen to 30 - 40 wt%; wherein, the waste sulfuric acid with high COD and high total nitrogen includes, by mass percentage: COD content is 50,000 - 100,000 ppm, organic nitrogen content is 1,000 - 4,000 ppm, ammonia nitrogen content is 5 - 10 ppm, sulfuric acid is 50 - 70%, and the rest is water; (2) Carry out BDD electrolysis on the waste sulfuric acid with high COD and high total nitrogen diluted in step (1) to convert COD into carbon dioxide and water, and total nitrogen into nitrate, and then separate to obtain a mixed solution of sulfuric acid and nitric acid; Among them, the boron doping concentration of the boron-doped diamond electrode is 0.01-1 wt%, and the parameters of BDD electrolysis include: the current density is 100-300 mA / cm 2 , the electrolysis time is 1-3 h, and the voltage is 3-5 V; the COD in the obtained mixed solution of sulfuric acid and nitric acid is 500-1000 ppm; (3) Carry out single-effect distillation on the mixed solution of sulfuric acid and nitric acid obtained in step (2) under a vacuum degree of 0.05 - 0.1 MPa and a temperature of 100 - 120°C to respectively obtain regenerated nitric acid and sulfuric acid after distillation; (4) Carry out distillation concentration on the sulfuric acid after distillation under a vacuum degree of 0.07 - 0.1 MPa and a temperature of 100 - 200°C to obtain regenerated sulfuric acid, and the purity of the regenerated sulfuric acid ≥ 97%, and the COD content ≤ 500 ppm.

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