Preparation method of modified carbon and application of modified carbon in separation of high-purity sodium nitrate from DMC wastewater

Abstract

The invention provides a preparation method of modified carbon and application of the modified carbon to separation of high-purity sodium nitrate in DMC wastewater, and relates to the field of DMC wastewater treatment.The modified carbon comprises modified granular activated carbon, coconut shell activated carbon and peanut shell activated carbon; wherein the modified carbon is obtained by modifying activated carbon with a ferric salt solution; the preparation method comprises the following steps: mixing activated carbon with water, boiling for 1 hour, and washing with ethanol for multiple times to remove ash and oil stains on the surface of the activated carbon; the preparation method comprises the following steps: pretreating activated carbon, adding 0.3-1.2 mol / L of an iron salt solution for modification, and drying the modified activated carbon in a drying oven at 105 DEG C. The modified activated carbon is obtained by loading active substances such as iron oxide and iron sulfide on the surface of the activated carbon, so that the affinity of the activated carbon to organic matters is improved, and the modified activated carbon is simple to prepare, low in cost and relatively good in adsorption effect.

Description

Technical Field

[0001] The present invention relates to the technical field of DMC wastewater treatment, and particularly relates to a preparation method of modified carbon and its application in separating high-purity sodium nitrate from DMC wastewater. Background Art

[0002] DMC high-salt wastewater refers to the wastewater discharged during the production process of dimethyl carbonate (DMC). Due to the presence of a large amount of refractory organic compounds and salts (sodium nitrate), it is difficult to remove the organic matter in DMC high-salt wastewater.

[0003] Among them, advanced oxidation, distillation, and membrane processes are common methods for removing organic matter and recovering salts from saline wastewater. However, these methods have problems such as difficulty in degrading macromolecular organic matter, high sludge volume, and high costs. In this regard, Chinese invention patent CN117923704 A discloses a resource utilization method for high-salt wastewater. This invention uses processes such as ozone oxidation, coagulation, reverse osmosis, and nanofiltration, effectively reducing the organic matter content and obtaining high-purity sodium sulfate and sodium chloride. However, the process is too long and the equipment maintenance cost is high.

[0004] CN109896685 B discloses a harmless treatment method for high-concentration printing and dyeing wastewater. This invention combines ozone oxidation and Fenton oxidation to remove organic matter in the wastewater, and recovers inorganic salts through electrodialysis and evaporation crystallization. This process has a high water recovery rate and no harmful substance emissions. However, the process equipment is difficult to be industrially applied, and the cost of the membrane in electrodialysis is relatively high.

[0005] In view of this, this paper proposes a preparation method of modified carbon and its application in separating high-purity sodium nitrate from DMC wastewater. The adsorbent is improved, and the adsorption-Fenton-gradient evaporation salt process is used to recover sodium nitrate from the wastewater. The process is simple, the cost is low, the purity of the recovered salt is high, and it is suitable for industrial application. Summary of the Invention

[0006] (1) Technical Problems to be Solved

[0007] Aiming at the deficiencies of the prior art, the present invention provides a preparation method of modified carbon and its application in separating high-purity sodium nitrate from DMC wastewater, solving the problem of low purity of sodium nitrate after separating high-purity sodium nitrate from DMC wastewater in the prior art.

[0008] (2) Technical Solutions

[0009] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0010] In the present invention, on the first hand, a preparation method of modified carbon is used to prepare modified carbon. The modified carbon includes modified granular activated carbon, coconut shell activated carbon, and peanut shell activated carbon;

[0011] Among them, the modified carbon is obtained by modifying activated carbon with an iron salt solution;

[0012] The preparation method includes: mixing activated carbon with water and boiling, and then washing it several times with ethanol to remove ash and oil on the surface of the activated carbon;

[0013] After the activated carbon is pretreated, 0.3 - 1.2 mol / L of iron salt solution is added for modification, and after modification, it is dried.

[0014] Furthermore, the iron salt solution is one of FeCl3, Fe(NO3)3, and FeSO4.

[0015] Furthermore, the liquid - solid ratio of the iron salt solution to the activated carbon used in the modification is 2 - 18 mL / g.

[0016] Furthermore, the modification time used in the modification is 0.5 - 4.5 h.

[0017] In a second aspect, an application of the modified carbon in separating high - purity sodium nitrate from DMC wastewater, using the prepared modified carbon to adsorb DMC wastewater, includes the following steps:

[0018] S1: Pump the acid solution and DMC wastewater into the regulation tank simultaneously, and adjust the pH of the wastewater;

[0019] After the pH is stable, add modified activated carbon to the wastewater for adsorption;

[0020] S2: After the DMC wastewater is adsorbed by the activated carbon, pump it, together with an oxidant and a catalyst, into the Fenton reaction tank for Fenton reaction. After the Fenton tank is full, pump the wastewater and an alkali solution into the neutralization tank simultaneously to precipitate sludge, and then pump the wastewater from the neutralization tank and a flocculant into the flocculation tank to settle the sludge;

[0021] S3: Perform primary vacuum distillation on the effluent from the flocculation tank, and stop distillation immediately when salts precipitate;

[0022] Then, slowly stir the concentrated solution, cool it down, filter and separate the salts therein, and perform secondary vacuum distillation on the concentrated solution;

[0023] S4: After salts precipitate, repeat the above process. The concentrated solution is returned to the adsorption - Fenton process for re - treatment, the distillate is discharged, and the precipitated sodium nitrate is dried and then recovered.

[0024] Furthermore, in step S1, the acid adjustment adopts an online acid - adjustment method, and the pH is monitored by a pH online detector. The acid solution is 1:1 HNO3.

[0025] Further, in step S1, the pH is 1.0 - 9.0. During the adsorption process, the dosage of the adsorbent is controlled to be 1.25 - 6.25 g / L, and the adsorption time is 5 - 100 min.

[0026] Further, in step S3, the temperature of the first-stage vacuum distillation is 90°C, the temperature of the second-stage vacuum distillation is 70°C, and the temperature for cooling is 25°C.

[0027] Further, in step S4, the drying temperature of sodium nitrate is 60°C.

[0028] Further, the inlet and outlet mode of the DMC high-salt wastewater is bottom-in and top-out, and the chemicals are all pumped into the bottom of the reaction tank.

[0029] (III) Beneficial effects

[0030] The present invention provides a preparation method of modified carbon and its application in separating high-purity sodium nitrate from DMC wastewater. Compared with the prior art, it has the following beneficial effects:

[0031] By loading active substances such as iron oxides and iron sulfides on the surface of activated carbon to obtain modified carbon, the affinity of activated carbon for organic substances is improved. The preparation of modified activated carbon is simple, with low cost and good adsorption effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 It is a process flow chart for separating high-purity sodium nitrate from DMC wastewater using modified carbon;

[0034] Figure 2 It is a comparison chart of the COD removal of particles, coconut shell, and peanut shell activated carbon modified by Fe(Cl)3, FeSO4, and Fe(NO3)3 solutions in Example 1;

[0035] Figure 3 It is an electron micrograph of coconut shell activated carbon, including (a) before modification, (b) after modification with FeSO4, and (c) after adsorption;

[0036] Figure 4 It is a comparison chart of the COD removal under different modification conditions with different FeSO4 concentrations in Example 2;

[0037] Figure 5It is a comparison chart of COD removal under different modified liquid-solid ratios in Example 3;

[0038] Figure 6 It is a comparison chart of COD removal under different modification times in Example 4;

[0039] Figure 7 It is a comparison chart of COD removal under different adsorption pH values in Example 5;

[0040] Figure 8 It is a comparison chart of COD removal under different dosages of adsorbent in Example 6;

[0041] Figure 9 It is a comparison chart of COD removal under different adsorption times in Example 7;

[0042] Figure 10 It is a comparison chart of COD removal and the change in sodium nitrate purity under different dosages of H2O2 (30%) in Example 8;

[0043] Figure 11 It is the GC-MS charts of the DMC stock solution and the treated effluent in Example 8, including (a) the raw DMC water and (b) the DMC effluent;

[0044] Figure 12 It is a comparison chart of COD removal and the change in sodium nitrate purity under different dosages of the catalyst (50 g / L FeSO4) in Example 9;

[0045] Figure 13 It is a comparison chart of COD removal and the change in sodium nitrate purity under different reaction times of Fenton in Example 10. Detailed implementation manners

[0046] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0047] By providing a preparation method of modified carbon and its application in separating high-purity sodium nitrate from DMC wastewater, the embodiments of the present application solve the problem that after separating high-purity sodium nitrate from DMC wastewater, the organic matter impurity rate in sodium nitrate is high, resulting in low purification purity of sodium nitrate, and improve the purification effect of extracting sodium nitrate from DMC wastewater.

[0048] To better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0049] As Figures 1-13 shown, a preparation method of modified carbon is used to prepare modified carbon, and the modified carbon includes modified granular activated carbon, coconut shell activated carbon and peanut shell activated carbon;

[0050] Among them, the modified carbon is obtained by modifying activated carbon with an iron salt solution;

[0051] The preparation method includes: mixing activated carbon with water and boiling for 1 h, and then washing it several times with ethanol to remove the ash and oil on the surface of the activated carbon;

[0052] After the activated carbon is pretreated, 0.3 - 1.2 mol / L iron salt solution is added for modification, and after modification, it is placed in an oven at 105 °C for drying.

[0053] Specifically, the iron salt solution can be one of FeCl3, Fe(NO3)3, and FeSO4;

[0054] The liquid - solid ratio of the iron salt solution to the activated carbon used in the modification is 2 - 18 mL / g, and the modification time is 0.5 - 4.5 h.

[0055] By loading active substances such as iron oxides and iron sulfides on the surface of the activated carbon to obtain the modified carbon, the affinity of the activated carbon for organic substances is improved. The preparation of the modified activated carbon is simple, the cost is low, and it has a good adsorption effect.

[0056] As Figure 1 shown, the application of modified carbon in separating high - purity sodium nitrate from DMC wastewater includes the following steps:

[0057] S1: Pump the acid solution and DMC wastewater into the adjustment tank at the same time, and adjust the pH of the wastewater;

[0058] After the pH is stable, add modified activated carbon to the wastewater for adsorption;

[0059] S2: After the DMC wastewater is adsorbed by the activated carbon, pump it into the Fenton reaction tank together with the oxidant and catalyst for Fenton reaction. After the Fenton tank is full, pump the wastewater in it and the alkali solution into the neutralization tank at the same time to precipitate the sludge. Then pump the wastewater from the neutralization tank and the flocculant into the flocculation tank at the same time to settle the sludge;

[0060] S3: Perform primary vacuum distillation on the effluent from the flocculation tank, and stop distillation immediately when salt crystals precipitate;

[0061] Then, slowly stir the concentrated solution, cool it down, filter and separate the salt in it, and perform secondary vacuum distillation on the concentrated solution;

[0062] S4: After the salt is precipitated, repeat the above process. The concentrated liquid is returned to the adsorption-Fenton process for reprocessing, the distillate is discharged, and the precipitated sodium nitrate is dried and then recycled.

[0063] Specifically, in step S1, the acid adjustment is carried out in an online manner, and the pH is monitored by a pH online detector. To avoid introducing impurities, the acid solution is 1:1 HNO3.

[0064] In step S1, the pH = 1.0 - 9.0. During the adsorption process, the dosage of the adsorbent is controlled at 1.25 - 6.25 g / L, and the adsorption time is 5 - 100 min.

[0065] In step S2, the oxidant is 30% H2O2, and the dosage is 0.50 - 1.50% (v / v). The catalyst is a FeSO4 (50 g / L) solution, and the dosage is 1.0 - 3.0% (v / v). The reaction time is 1 - 5 h.

[0066] In step S2, the alkali solution is a NaOH solution or a Ca(OH)2 suspension. Selecting a NaOH solution has less impact on the salt purity in the subsequent salt evaporation process. Selecting a Ca(OH)2 suspension can improve the sludge flocculation effect and accelerate the sedimentation speed. The pH of the wastewater is 7 - 10.

[0067] In step S2, the flocculant is a 1.5 g / L polyacrylamide solution, and the dosage is 0.3 - 0.9% (v / v).

[0068] In step S3, the temperature of the first-stage vacuum distillation is 90 °C, the temperature of the second-stage vacuum distillation is 70 °C, and the temperature reduction is 25 °C.

[0069] It should be noted that the temperature reduction here refers to reducing the temperature to 25 °C.

[0070] In step S4, the drying temperature of the sodium nitrate is 60 °C.

[0071] Among them, in step S3, vacuum distillation is used to reduce the energy consumption. At the same time, by controlling the temperature of the first-stage vacuum distillation at 90 °C and the temperature of the second-stage vacuum distillation at 70 °C, it can effectively prevent some organic matters from polymerizing due to too high distillation temperature, which affects the purity of sodium nitrate.

[0072] By applying the prepared modified carbon to the separation of high-purity sodium nitrate from DMC wastewater, the combination of modified carbon and the Fenton process can achieve the efficient removal of organic matters in DMC high-salt wastewater, and high-purity sodium nitrate can be obtained by gradient salt evaporation of the final effluent.

[0073] It should be noted that the inlet and outlet mode of DMC high-salt wastewater is from bottom to top, and the chemicals are all pumped into the bottom of the reaction tank.

[0074] The adsorption-Fenton process is carried out continuously by pumping, and the chemicals are directly pumped into the bottom of the reaction tank. The DMC high-salt wastewater flows in a bottom-up manner, enabling sufficient Fenton reaction and efficient degradation of organic matter. The salt evaporation process adopts gradient vacuum distillation, ensuring that the color and crystallization effect of sodium nitrate meet the standards. The process is safe, environmentally friendly, and the device is easy to assemble.

[0075] Example:

[0076] The DMC high-salt wastewater is the wastewater generated in the production process of dimethyl carbonate (DMC). During the experiment, the wastewater from a large wastewater treatment plant with a sodium nitrate content of 4-5% and a COD content of 1700-5000 mg / L and a pH of 9.8-10.2 was used as the experimental water:

[0077] Example 1:

[0078] A preparation method of modified carbon includes the following steps:

[0079] S01. Place the particles, coconut shell, and peanut shell activated carbon in beakers respectively, add water and boil for 1 h. After boiling, wash with ethanol several times and then dry at 80 °C for later use;

[0080] S02. Take 100 g of the three kinds of activated carbon after pretreatment, and add 1 L of 0.9 mol / L Fe(Cl)3, FeSO4, and Fe(NO3)3 solutions respectively. Stir slowly for 3.5 h. After the reaction ends, perform a filtration operation and wash the residual liquid on the surface of the activated carbon with water, and dry at 105 °C;

[0081] S03. Adjust the pH of the DMC high-salt wastewater to 7.0. Take 50 g of the three kinds of activated carbon modified by different modifiers respectively, and add them to 10 L of wastewater and stir for adsorption for 75 min.

[0082] Among them, in step S2, each kind of activated carbon has four equal portions. Three of each kind of activated carbon are respectively added with 1 L of 0.9 mol / L Fe(Cl)3, FeSO4, and Fe(NO3)3 solutions, and the remaining one of each kind of activated carbon is not added with iron salt solution for modification, and the activated carbon not added with iron salt solution is used as the initial control.

[0083] The COD removal of the wastewater adsorbed by different modified activated carbons and unmodified activated carbon is as Figure 2 shown. Modifying the coconut shell activated carbon with FeSO4 has the highest COD removal rate. Figure 3Scanning electron micrographs of coconut shell activated carbon before modification, after modification with FeSO4, and after adsorbing organic matter. It can be seen that under the same other conditions, the adsorption effect of coconut shell activated carbon modified with FeSO4 is better, and the COD removal rate from DMC high-salt wastewater is higher.

[0084] Example 2:

[0085] S01. Place the coconut shell activated carbon in a beaker, boil it with water for 1 h, wash it several times with ethanol after boiling, and then dry it at 80 °C for later use;

[0086] S02. Take 100 g of pretreated coconut shell activated carbon, add 1 L of FeSO4 solutions with concentrations of 0.3, 0.6, 0.9, and 1.2 mol / L respectively, stir slowly for 3.5 h, perform a filtration operation after the reaction ends, wash the residual liquid on the surface of the activated carbon with water, and dry it at 105 °C;

[0087] S03. Adjust the pH of the DMC high-salt wastewater to 7.0, take 50 g of the modified coconut shell activated carbon, and add it to 10 L of the wastewater and stir for adsorption for 75 min.

[0088] It should be noted that the coconut shell activated carbon without adding the iron salt solution is used as the initial control, and is compared with the coconut shell activated carbon modified after adding the iron salt solution.

[0089] Under the modification conditions with different concentrations of the modifier, the COD removal rates of the modified coconut shell activated carbon are 23.44%, 45.39%, 55.10%, and 54.12% respectively. The results are as Figure 4 shown. It can be seen that under the same other conditions, the adsorption effect is better after modifying the coconut shell activated carbon with 0.9 mol / L FeSO4 solution.

[0090] Example 3:

[0091] S01. Place the coconut shell activated carbon in a beaker, boil it with water for 1 h, wash it several times with ethanol after boiling, and then dry it at 80 °C for later use;

[0092] S02. Take 100 g of pretreated coconut shell activated carbon, add 0.2, 0.6, 1.0, 1.4, and 1.8 L of 0.9 mol / L FeSO4 solution respectively, stir slowly for 3.5 h, perform a filtration operation after the reaction ends, wash the residual liquid on the surface of the activated carbon with water, and dry it at 105 °C;

[0093] S03. Adjust the pH of the DMC high-salt wastewater to 7.0, take 50 g of the modified coconut shell activated carbon, and add it to 10 L of the wastewater and stir for adsorption for 75 min.

[0094] Under different modified liquid-solid ratios, the COD removal rates of the modified coconut shell activated carbon were 35.68%, 39.18%, 53.15%, 56.08%, and 56.98% respectively. The results are as Figure 5 shown. It can be seen that under the same other conditions, the adsorption effect is better after modifying the coconut shell activated carbon with 1.8 L of 0.9 mol / L FeSO4 solution.

[0095] It should be noted that the adsorption effect is the best after modifying the coconut shell activated carbon with 1.8 L of 0.9 mol / L FeSO4 solution, and the COD removal rate reaches 56.98%. However, under the 1.8 L condition, the removal rate only decreases by 0.9% compared with the 1.0 L condition. To save costs, 1.0 L of the modifier was selected to modify 100 g of activated carbon. In subsequent examples, 1.0 L of 0.9 mol / L FeSO4 solution was used to modify the coconut shell activated carbon.

[0096] Example 4:

[0097] S01. Place the coconut shell activated carbon in a beaker, boil it with water for 1 h, and after boiling, wash it several times with ethanol and then dry it at 80 °C for later use;

[0098] S02. Take 100 g of the pretreated coconut shell activated carbon, add 1.0 L of 0.9 mol / L FeSO4 solution respectively, stir slowly for 0.5, 1.5, 2.5, 3.5, and 4.5 h. After the reaction is completed, perform a filtration operation, and wash the residual liquid on the surface of the activated carbon with water, and dry it at 105 °C.

[0099] S03. Adjust the pH of the DMC high-salt wastewater to 7.0, take 50 g of the modified coconut shell activated carbon, and add it to 10 L of the wastewater and stir for adsorption for 75 min.

[0100] Under different modified time conditions, the COD removal rates of the modified coconut shell activated carbon were 9.55%, 30.02%, 41.36%, 53.18%, and 55.29% respectively. The results are as Figure 6 shown. It can be seen that under the same other conditions, the adsorption effect is better after modifying the coconut shell activated carbon with 1.0 L of 0.9 mol / L FeSO4 solution for 4.5 h.

[0101] Example 5:

[0102] S01. Place the coconut shell activated carbon in a beaker, boil it with water for 1 h, and after boiling, wash it several times with ethanol and then dry it at 80 °C for later use.

[0103] S02. Take 100 g of pretreated coconut shell activated carbon, add 1.0 L of 0.9 mol / L FeSO4 solution respectively, stir slowly for 3.5 h. After the reaction is completed, carry out the filtration operation, wash the residual liquid on the surface of the activated carbon with water, and dry it at 105 °C.

[0104] S03. Adjust the pH of the DMC high-salt wastewater to 1.0, 3.0, 5.0, 7.0, 9.0. Take 50 g of the modified coconut shell activated carbon, add it to 10 L of the wastewater, and stir for adsorption for 75 min.

[0105] Under different adsorption pH conditions, the COD removal rates of the modified coconut shell activated carbon are 30.11%, 43.61%, 45.27%, 53.73%, 24.17% respectively. The results are as Figure 7 shown. It can be seen that under the same other conditions, when the pH is 7.0, the activated carbon has the best COD removal effect. However, the subsequent Fenton process needs to adjust the pH to 3.0. Therefore, according to the actual needs, the adsorption pH can be selected as 3.0.

[0106] Example 6:

[0107] S01. Place the coconut shell activated carbon in a beaker, boil it with water for 1 h. After boiling, wash it with ethanol several times and then dry it at 80 °C for standby.

[0108] S02. Take 100 g of pretreated coconut shell activated carbon, add 1.0 L of 0.9 mol / L FeSO4 solution respectively, stir slowly for 3.5 h. After the reaction is completed, carry out the filtration operation, wash the residual liquid on the surface of the activated carbon with water, and dry it at 105 °C.

[0109] S03. Adjust the pH of the DMC high-salt wastewater to 3.0. Take 12.5, 25, 37.5, 50, 62.5 g of the modified coconut shell activated carbon, add it to 10 L of the wastewater, and stir for adsorption for 75 min.

[0110] Under different dosages of the adsorbent, the COD removal rates of the modified coconut shell activated carbon are 17.2%, 23.77%, 40.69%, 45.14%, 46.81% respectively. The results are as Figure 8 shown. It can be seen that under the same other conditions, when the dosage of the coconut shell activated carbon is 62.5 g, the COD removal effect is better.

[0111] Example 7:

[0112] S01. Place the coconut shell activated carbon in a beaker, boil it with water for 1 h. After boiling, wash it with ethanol several times and dry it at 80 °C for standby.

[0113] S02. Take 100 g of pretreated coconut shell activated carbon, add 1.0 L of 0.9 mol / L FeSO4 solution respectively, stir slowly for 3.5 h. After the reaction ends, carry out the filtration operation, wash the residual liquid on the surface of the activated carbon with water, and dry it under the condition of 105 °C.

[0114] S03. Adjust the pH of the DMC high-salt wastewater to 3.0. Take 50 g of modified coconut shell activated carbon and add it to 10 L of wastewater, stir and adsorb for 5, 25, 50, 75, 100 min.

[0115] At different adsorption times, the COD removal rates of the modified coconut shell activated carbon are 14.53%, 26.70%, 33.83%, 44.68%, 43.49% respectively. The results are as Figure 9 shown. It can be seen that under the same other conditions, when the adsorption time is 75 min, the adsorption effect of the coconut shell activated carbon is better.

[0116] In summary, Examples 1 to 7 are multiple examples of the preparation of modified carbon. It can be seen that when the modified carbon is prepared by the steps of Example 7 and the adsorption time is controlled at 75 min, the adsorption effect of the coconut shell activated carbon is better and the COD removal rate of the modified coconut shell activated carbon is higher.

[0117] Example 8:

[0118] S01. Adjust the pump speed of the DMC high-salt wastewater to 2.5 L / h. Pump the wastewater and 1:1 HNO3 into the acid adjustment tank at the same time, adjust the pH of the wastewater to 3.0. After the pH is stable, take 50 g of FeSO4-modified coconut shell activated carbon and place it in the adsorption reaction tank (10 L), and pump in the acidic wastewater.

[0119] S02. After the adsorption reaction tank is full, pump the wastewater in it into the Fenton reaction tank, and at the same time pump in 0.5 - 1.5% H2O2 (30%) and 2.5% FeSO4 solution (50 g / L). After the Fenton tank is full, pump the wastewater in it and 1.5 mol / L NaOH into the neutralization tank at the same time, adjust the pH of the wastewater to 8.0 for neutralization precipitation. Finally, pump the wastewater in the neutralization tank into the flocculation tank, and pump in 0.5% 1.5 g / L polyacrylamide for flocculation sedimentation at the same time. The residence time of the wastewater in each reaction tank is 4 h.

[0120] S03. Carry out the first-stage vacuum distillation on the effluent of the flocculation tank at 90 °C. Immediately stop the distillation after the salt is precipitated, slowly stir the concentrated solution until the temperature is 25 °C, filter and separate the salt. The concentrated solution continues to carry out the second-stage vacuum distillation at 70 °C. After the salt is precipitated, stir and cool down again, and separate the precipitated salt.

[0121] S04. The concentrated solution is returned to the adsorption-Fenton process for reprocessing, the distillate is discharged, and the precipitated sodium nitrate is dried at 70 °C.

[0122] Under the conditions of different dosages of oxidants, the remaining COD amounts are 1186, 807, 486, 147, and 194 mg / L respectively, and the purities of sodium nitrate are 89.70%, 94.55%, 96.97%, 98.05%, and 98.18% respectively. The results are as Figure 10 shown Figure 11 are the GC-MS diagrams of the DMC stock solution and the treated effluent.

[0123] Example 9:

[0124] S01. Adjust the pumping speed of the DMC high-salt wastewater to 2.5 L / h. Pump the wastewater and 1:1 HNO3 into the acid adjustment tank simultaneously, and adjust the pH of the wastewater to 3.0. After the pH is stable, place 50 g of FeSO4-modified coconut shell activated carbon in the adsorption reaction tank (10 L), and pump in the acidic wastewater.

[0125] S02. After the adsorption reaction tank is full, pump the wastewater in it into the Fenton reaction tank, and simultaneously pump in 1.25% H2O2 (30%) and 1.0 - 3.0% FeSO4 solution (50 g / L). After the Fenton tank is full, pump the wastewater in it and 1.5 mol / L NaOH into the neutralization tank simultaneously, adjust the pH of the wastewater to 8.0 for neutralization precipitation, and finally pump the wastewater in the neutralization tank into the flocculation tank, and simultaneously pump in 0.5% 1.5 g / L polyacrylamide for flocculation sedimentation. The residence time of the wastewater in each reaction tank is 4 h.

[0126] S03. Perform primary vacuum distillation on the effluent from the flocculation tank at 90 °C. Stop distillation immediately after the salt precipitates, slowly stir the concentrated liquid until the temperature reaches 25 °C, filter and separate the salt. Continue secondary vacuum distillation on the concentrated liquid at 70 °C, stir and cool down again after the salt precipitates, and separate the precipitated salt.

[0127] S04. Return the concentrated liquid to the adsorption-Fenton process for re-treatment, discharge the distillate, and dry the precipitated sodium nitrate at 70 °C.

[0128] Under the conditions of different dosages of catalysts, the remaining COD amounts are 1168, 1056, 767, 177, and 230 mg / L respectively, and the purities of sodium nitrate are 90.94%, 91.47%, 95.12%, 97.69%, and 97.43% respectively. The results are as Figure 12 shown.

[0129] Example 10:

[0130] S01. Adjust the pumping speed of the DMC high-salt wastewater to 2.5 L / h. Pump the wastewater and 1:1 HNO3 into the acid adjustment tank simultaneously, and adjust the pH of the wastewater to 3.0. After the pH is stable, place 50 g of FeSO4-modified coconut shell activated carbon in the adsorption reaction tank (10 L), and pump in the acidic wastewater;

[0131] After the S02 adsorption reaction tank is full, pump the wastewater in it into the Fenton reaction tank, and at the same time pump in 1.25% H2O2 (30%) and 2.5% FeSO4 solution (50 g / L). After the Fenton tank is full, pump the wastewater in it and 1.5 mol / L NaOH into the neutralization tank at the same time, adjust the pH of the wastewater to 8.0 for neutralization precipitation, and finally pump the wastewater in the neutralization tank into the flocculation tank, and at the same time pump in 0.5% 1.5 g / L polyacrylamide for flocculation sedimentation. The residence time of the wastewater in each reaction tank is 1 - 5 h;

[0132] S03: Conduct the first-stage vacuum distillation on the effluent from the flocculation tank at 90 °C. Stop the distillation immediately after the salt precipitates, slowly stir the concentrated solution until the temperature reaches 25 °C, filter and separate the salt. The concentrated solution continues the second-stage vacuum distillation at 70 °C. After the salt precipitates, stir and cool down again to separate the precipitated salt;

[0133] S04: Return the concentrated solution to the adsorption-Fenton process for reprocessing, discharge the distillate, and dry the precipitated sodium nitrate at 70 °C.

[0134] The remaining COD amounts under different reaction time conditions are 989, 555, 204, 146, 175 mg / L respectively, and the purities of sodium nitrate are 94.15%, 96.33%, 97.45%, 98.29%, 98.08% respectively. The results are as Figure 13 shown.

[0135] In summary, in Examples 8 - 10, the modified activated carbon after being modified with iron salts is used to adsorb the organic matter in the acidified high-salt DMC wastewater, which improves the affinity of the activated carbon for organic matter. The preparation of the modified activated carbon is simple, the cost is low, and it has a good adsorption effect. Moreover, combined with the Fenton process, the efficient removal of organic matter in the high-salt DMC wastewater can be realized, and high-purity sodium nitrate can be obtained by gradient evaporation of salt from the final effluent.

[0136] To sum up, compared with the prior art, the following beneficial effects are achieved:

[0137] 1. By loading active substances such as iron oxides and iron sulfides on the surface of the activated carbon to obtain the modified carbon, the affinity of the activated carbon for organic matter is improved. The preparation of the modified activated carbon is simple, the cost is low, and it has a good adsorption effect.

[0138] 2. The adsorption-Fenton process is carried out continuously by pumping, and the chemicals are directly pumped into the bottom of the reaction tank. The high-salt DMC wastewater flows in a bottom-up manner. The Fenton reaction is sufficient, and the organic matter is efficiently degraded. The evaporation of salt process adopts the method of gradient vacuum distillation to ensure that the color and crystallization effect of sodium nitrate meet the standards. The process is safe, environmentally friendly, and the device is easy to assemble.

[0139] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the existence of additional identical elements in the process, method, article or device comprising the said element.

[0140] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of modified carbon for preparing modified carbon, characterized in that, The modified carbon includes modified granular activated carbon, coconut shell activated carbon, and peanut shell activated carbon; Among them, the modified carbon is obtained by modifying activated carbon with an iron salt solution; The preparation method includes: mixing activated carbon with water and boiling, and then washing it several times with ethanol to remove ash and oil on the surface of the activated carbon; After the activated carbon is pretreated, an iron salt solution with a concentration of 0.3 - 1.2 mol / L is added for modification, and after modification, it is dried.

2. The preparation method of a modified carbon as described in claim 1, characterized in that, The iron salt solution is one of FeCl3, Fe(NO3)3, and FeSO4.

3. The preparation method of a modified carbon as claimed in claim 1, wherein, The liquid-solid ratio of the iron salt solution used in the modification to the activated carbon is 2 - 18 mL / g.

4. The preparation method of a modified carbon according to claim 1, characterized in that, The modification time used in the modification is 0.5 - 4.5 h.

5. Application of modified carbon in separating high-purity sodium nitrate from DMC wastewater, wherein the modified carbon prepared by the preparation method described in any one of claims 1-4 is used to adsorb DMC wastewater, characterized in that, It includes the following steps: S1: Pump the acid solution and DMC wastewater into the adjustment tank simultaneously, and adjust the pH of the wastewater; After the pH is stable, add modified activated carbon to the wastewater for adsorption; S2: After the DMC wastewater is adsorbed by the activated carbon, it is pumped into the Fenton reaction tank simultaneously with the oxidant and catalyst for Fenton reaction. After the Fenton tank is full, the wastewater in it and the alkali solution are pumped into the neutralization tank simultaneously to precipitate sludge. Then, the wastewater from the neutralization tank and the flocculant are pumped into the flocculation tank simultaneously to settle the sludge; S3: Perform primary reduced-pressure distillation on the effluent from the flocculation tank, and stop distillation immediately after salt precipitation; Next, slowly stir the concentrated solution, cool it down, filter and separate the salt in it, and perform secondary reduced-pressure distillation on the concentrated solution; S4: After salt precipitation, repeat the above process. The concentrated solution is returned to the adsorption-Fenton process for re-treatment, the distillate is discharged, and the precipitated sodium nitrate is dried and then recovered.

6. The application of the modified carbon as claimed in claim 5 in separating high-purity sodium nitrate from DMC wastewater, characterized in that, In step S1, the acid adjustment adopts an on-line acid adjustment method, and the pH is monitored by a pH on-line detector. The acid solution is 1:1 HNO3.

7. The application of the modified carbon as claimed in claim 5 in separating high-purity sodium nitrate from DMC wastewater, characterized in that, In step S1, the pH = 1.0 - 9.

0. During the adsorption process, the dosage of the adsorbent is controlled to be 1.25 - 6.25 g / L, and the adsorption time is 5 - 100 min.

8. The application of the modified carbon as claimed in claim 5 in separating high-purity sodium nitrate from DMC wastewater, characterized in that, The temperature of the primary reduced-pressure distillation in step S3 is 90 °C, the temperature of the secondary reduced-pressure distillation is 70 °C, and the cooling temperature is 25 °C.

9. The application of the modified carbon as claimed in claim 5 in separating high-purity sodium nitrate from DMC wastewater, characterized in that, The drying temperature of the sodium nitrate in step S4 is 60 °C.

10. The application of the modified carbon as claimed in claim 5 in separating high-purity sodium nitrate from DMC wastewater, characterized in that, The inlet and outlet mode of the DMC high-salt wastewater is bottom-in and top-out, and the chemicals are all pumped to the bottom of the reaction tank.

Images