A redox process for efficient recovery of chromium complexes from Cr(III)-EDTA-containing wastewater

Abstract

The application discloses a kind of redox processes for realizing the efficient recovery of chromium complex in Cr (III) -EDTA-containing wastewater, first, appropriate sodium percarbonate, formic acid is added to Cr (III) -EDTA-containing wastewater containing heavy metal chromium, and stirring is dissolved;Immediately, ozone is introduced into the mixed solution, and the oxidation of active species hydroxyl radical and carbonate radical, the reduction of active species carbon dioxide radical is generated by ozone / sodium percarbonate / formic acid advanced oxidation reduction method, which realizes the rapid complex breaking of chromium complex in wastewater, the reduction of hexavalent chromium, and the rapid removal of chromium ions in wastewater;At the same time, the organic ligand EDTA in wastewater is rapidly mineralized and decomposed under the oxidation of highly active free radicals.The application can realize the efficient complex breaking of chromium complex in Cr (III) -EDTA-containing wastewater and the synchronous removal of heavy metal chromium, and the heavy metal chromium is recycled, which has the advantages of economic efficiency, simple operation, easy engineering application, etc.

Description

Technical Field

[0001] This invention relates to the field of heavy metal industrial wastewater treatment technology, and in particular to an oxidation-reduction process for achieving efficient recovery of chromium complexes from Cr(III)-EDTA-containing wastewater. Background Technology

[0002] Chromium is one of the major heavy metal pollutants, and chromium-containing wastewater accounts for about 8% of total industrial wastewater. Over 85% of leather processing requires the use of chromium tanning agents; however, about 40% of this chromium wastewater remains in the form of organic chromium in production wastewater and waste materials. The concentration of trivalent chromium in the wastewater can reach 3000-6000 mg / L, and the large amount of amino, carboxyl, and hydroxyl-containing organic ligands (such as EDTA and NTA) present in chromium tanning wastewater readily reacts with chromium. 3+ It forms a metal complex. Metal complexes typically have the following properties: (1) Strong migration ability: Complexes formed by the combination of organic ligands such as amino, carboxyl or hydroxyl groups with heavy metal ions usually have strong water solubility, making the pollutant highly mobile in the aquatic environment, thus causing more widespread potential hazards. (2) High stability: Cr 3+ The metal complexes formed by complexing with organic ligands exhibit strong stability, which makes the complexed Cr... 3+ It is difficult to remove by traditional heavy metal ion treatment methods (such as adsorption or precipitation). (3) High biotoxicity: high concentration of complexed Cr 3+ It exhibits strong biotoxicity. Furthermore, the complexed Cr... 3+ In aquatic environments, it is easily oxidized by oxidants (such as O2, high-valence Mn, microorganisms, etc.) into Cr(VI), which is even more toxic.

[0003] Currently, the advanced oxidation-coupled reduction precipitation method is commonly used to treat wastewater containing Cr(III)-EDTA. The reaction principle involves first using advanced oxidation technology (such as the Fenton process) to break down the complexes of Cr(III)-EDTA, releasing free chromium ions (such as Cr...). 3+ and CrO4 2- Simultaneously, the ligand EDTA is degraded into small molecule acids; then Fe is added to the system. 2+ The highly toxic Cr(VI) is reduced to Cr(III); finally, sodium hydroxide is added to adjust the pH of the wastewater to alkaline, and the free Cr(III) ions react with OH-. -The reaction produces chromium hydroxide precipitate. However, the advanced oxidation-coupling reduction precipitation method for treating Cr(III)-EDTA wastewater has the following drawbacks: First, the operation process is complex, the efficiency of treating Cr(III)-EDTA wastewater is low, and the wastewater treatment time and cost are increased; Second, the advanced oxidation-coupling reduction precipitation method generates a large amount of iron sludge containing heavy metal chromium during the treatment of Cr(III)-EDTA wastewater, which is a hazardous waste. The treatment cost is high, and improper treatment can cause "secondary pollution".

[0004] It is worth noting that chromium is a strategic metal widely used in metallic materials, electronic equipment, and surface treatment. However, my country's chromium ore resources are extremely scarce, with relevant statistics showing that my country's dependence on imported chromium minerals is as high as 99%. Therefore, effectively recovering metallic chromium during the treatment of Cr(III)-EDTA-containing wastewater can not only reduce its environmental pollution but also help alleviate my country's chromium resource shortage. Therefore, there is an urgent need to invent a Cr(III)-EDTA-containing wastewater treatment process that features a fast reaction rate, simple operation, stable treatment effect, low operating cost, and the ability to recover metallic chromium. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems existing in the prior art and to provide an oxidation-reduction process for the efficient recovery of chromium complexes from Cr(III)-EDTA-containing wastewater.

[0006] To achieve the above objectives, the technical solution provided by this invention is: a redox process for the efficient recovery of chromium complexes from Cr(III)-EDTA wastewater. This process first involves adding appropriate amounts of sodium percarbonate and formic acid to the Cr(III)-EDTA wastewater, stirring to dissolve them, and then immediately introducing ozone into the mixture. Through an advanced redox process using ozone / sodium percarbonate / formic acid, oxidizing reactive species hydroxyl radicals and carbonate radicals, and reducing reactive species carbon dioxide radicals, are generated, rapidly breaking down the chromium complexes in the wastewater and reducing hexavalent chromium. Finally, free trivalent chromium ions react with carbonate and hydroxide ions under alkaline conditions to form insoluble carbonate and hydroxide precipitates. Through settling and simple filtration, the heavy metal chromium in the Cr(III)-EDTA wastewater can be rapidly separated. Simultaneously, the EDTA organic ligands in the wastewater undergo rapid mineralization and decomposition under the oxidation of highly active free radicals, thereby achieving rapid and efficient purification of the Cr(III)-EDTA wastewater.

[0007] The process specifically includes the following steps:

[0008] Step 1: Heavy metal complexing wastewater containing heavy metal chromium and complexing agent ethylenediaminetetraacetic acid is added to the reactor;

[0009] Step 2: Add appropriate amounts of sodium percarbonate and formic acid to the reactor, and use a magnetic stirrer to ensure that the sodium percarbonate is completely dissolved;

[0010] Step 3: Once the sodium percarbonate and formic acid have completely dissolved and mixed, immediately introduce ozone generated by the ozone generator into the reaction tank. The reactor is connected to the external ozone generator and the tail gas absorption device through a gas pipe.

[0011] Step 4: After the ozone / sodium percarbonate / formic acid reaction is complete, let it stand for a period of time, and finally use a microporous membrane filter to filter and separate the solid and liquid, so as to achieve simultaneous complex breaking and heavy metal removal.

[0012] Preferably, the sodium percarbonate in step 2 is any commercially available sodium percarbonate, and the amount of sodium percarbonate added is 1 to 5 times the molar concentration of metallic chromium in the Cr(III)-EDTA wastewater; the formic acid in step 2 is any commercially available formic acid, and the amount of formic acid added is 5 to 50 times the molar concentration of metallic chromium in the Cr(III)-EDTA wastewater.

[0013] Preferably, the concentration of ozone introduced in step 3 is 0.5–8 mg / (L·min), more preferably 0.06 g / (L·min); the reaction time is 210 min.

[0014] Preferably, the micropore diameter of the microporous membrane device in step 4 is less than or equal to 0.22 μm; it can effectively achieve solid-liquid separation and obtain better treatment results.

[0015] Beneficial effects of this invention:

[0016] 1. The ozone / sodium percarbonate / formic acid advanced oxidation-reduction method of the present invention can achieve efficient complex breaking, reduction and simultaneous removal of heavy metal ions of chromium complexes, simplify the treatment process of chromium complexes in Cr(III)-EDTA wastewater, improve treatment efficiency, and is an economical, efficient, easy-to-operate, wide pH applicable range, and easy-to-engineer Cr(III)-EDTA wastewater treatment technology.

[0017] 2. The present invention provides an ozone-sodium percarbonate oxidation method for generating highly oxidizing OH and CO3. ·- and CO2 ·- This further enhances the breaking of chromium complexes, the reduction of hexavalent chromium, and the mineralization by EDTA, enabling rapid separation of precipitates after wastewater treatment.

[0018] 3. The ozone / sodium percarbonate / formic acid oxidation-reduction method of the present invention has the advantages of low chemical reagent dosage, economy, and high removal rate. The released trivalent chromium ions react with carbonate ions to form metal carbonate precipitates, which can be separated into solid and liquid by simple filtration. Typically, metal carbonates have a relatively small solubility product (K). sp <10-10 Metal ions in Cr(III)-EDTA wastewater can be completely precipitated after treatment with ozone / sodium percarbonate / formic acid oxidation-reduction method.

[0019] 4. Compared with existing methods for treating Cr(III)-EDTA-containing wastewater, this invention achieves the recovery of valuable chromium from the wastewater for the first time during the treatment process, which not only reduces its pollution to the environment but also helps alleviate the current shortage of chromium resources in my country. Attached Figure Description

[0020] The accompanying drawings, which are provided to further illustrate the invention and constitute a part of this invention, are illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention.

[0021] Figure 1 The graphs show the total Cr removal efficiency of Cr(III)-EDTA in the ozone / sodium percarbonate / formic acid redox system and the change of Cr(VI) concentration over time under different initial pH conditions according to the present invention.

[0022] Figure 2 This is an X-ray crystal diffraction pattern of the reaction precipitate of the present invention.

[0023] Figure 3 The graph shows the total Cr removal effect of the present invention in a system with different sodium percarbonate dosages using Cr(III)-EDTA.

[0024] Figure 4 The diagram shows the total Cr removal effect of the present invention in a system with different formic acid dosages using Cr(III)-EDTA.

[0025] Figure 5 The graph shows the total Cr removal effect of Cr(III)-EDTA under different ozone concentrations, with sodium percarbonate dosage of 3.2 mM and formic acid dosage of 30.8 mM.

[0026] Figure 6 The diagram shows the total Cr removal effect of Cr ions forming Cr coordination complexes with different complexing agents (ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), diethyltriaminepentaacetic acid (DTPA), and citric acid) in the ozone-sodium percarbonate oxidation system under the conditions of sodium percarbonate dosage of 3.2 mM, formic acid dosage of 30.8 mM, and ozone concentration of 0.06 g / (L·min).

[0027] Figure 7The figure shows the total Cr removal effect of Cr(III)-EDTA in a coexisting anion and cation system under the conditions of sodium percarbonate dosage of 3.2 mM, formic acid dosage of 30.8 mM, and ozone concentration of 0.06 g / (L·min).

[0028] Figure 8 This is a schematic diagram of the overall process of the present invention. Detailed Implementation

[0029] This section will describe in detail specific embodiments of the present invention. Preferred embodiments of the present invention are shown in the accompanying drawings. The purpose of the drawings is to supplement the textual description with graphics, so that people can intuitively and vividly understand each technical feature and overall technical solution of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0030] Reference Figures 1-8 A preferred embodiment of the present invention provides an oxidation-reduction process for the efficient recovery of chromium complexes from Cr(III)-EDTA wastewater. This process first involves adding appropriate amounts of sodium percarbonate and formic acid to the Cr(III)-EDTA wastewater, stirring to dissolve them, and then immediately introducing ozone into the mixture. Through an ozone / sodium percarbonate / formic acid advanced oxidation-reduction method, oxidizing reactive species hydroxyl radicals and carbonate radicals, and reducing reactive species carbon dioxide radicals are generated, rapidly breaking down the chromium complexes in the wastewater and reducing hexavalent chromium. Finally, free trivalent chromium ions react with carbonate and hydroxide ions under alkaline conditions to form insoluble carbonate and hydroxide precipitates. Through settling and simple filtration, the heavy metal chromium in the Cr(III)-EDTA wastewater can be rapidly separated. Simultaneously, the EDTA organic ligands in the wastewater are rapidly mineralized and decomposed under the oxidation of highly active free radicals. This achieves rapid and efficient purification of Cr(III)-EDTA wastewater.

[0031] The process specifically includes the following steps:

[0032] Step 1: Heavy metal complexing wastewater containing heavy metal chromium and complexing agent ethylenediaminetetraacetic acid is added to the reactor;

[0033] Step 2: Add appropriate amounts of sodium percarbonate and formic acid to the reactor, and use a magnetic stirrer to ensure that the sodium percarbonate is completely dissolved;

[0034] Step 3: Once the sodium percarbonate and formic acid have completely dissolved and mixed, immediately introduce ozone generated by the ozone generator into the reaction tank. The reactor is connected to the external ozone generator and the tail gas absorption device through a gas pipe.

[0035] Step 4: After the ozone / sodium percarbonate / formic acid reaction is complete, let it stand for a period of time, and finally use a microporous membrane filter to filter and separate the solid and liquid, so as to achieve simultaneous complex breaking and heavy metal removal.

[0036] In this embodiment, the sodium percarbonate in step 2 is any commercially available sodium percarbonate, and the amount of sodium percarbonate added is 1 to 5 times the molar concentration of metallic chromium in the Cr(III)-EDTA wastewater; the formic acid in step 2 is any commercially available formic acid, and the amount of formic acid added is 5 to 50 times the molar concentration of metallic chromium in the Cr(III)-EDTA wastewater.

[0037] In this embodiment, the concentration of ozone introduced in step 3 is 0.5–8 mg / (L·min), and the reaction time is 210 min.

[0038] In this embodiment, the micropore diameter of the microporous filter membrane device in step 4 is less than or equal to 0.22 μm.

[0039] Sodium percarbonate (SPC), with the chemical formula Na₂CO₃·1.5H₂O₂, commonly known as solid hydrogen peroxide, is widely used in disinfection, cleaning, and bleaching. Compared to H₂O₂, SPC is easier to transport and store, and has a wider pH range. Sodium percarbonate decomposes in water, releasing H₂O₂ and Na₂CO₃. Passing ozone into an aqueous solution containing sodium percarbonate can generate highly selective oxide CO₃²⁻. ·- (E0=1.78V vs SHE)) can achieve rapid complex breaking of Cr(III)-EDTA and mineralization of ligand EDTA. Formic acid is a common small molecule acid. When formic acid is oxidized by ozone, it generates highly reducing carbon dioxide free radicals (CO2). ·- CO2 ·- It has strong reducing properties and can reduce hexavalent chromium through single-electron transfer. Furthermore, CO2... ·- The direct product of its reaction with pollutants is carbon dioxide, with no secondary pollution generated, making it the most ideal strong reducing agent. Based on the above analysis, this invention provides an ozone / sodium percarbonate / formic acid advanced oxidation / reduction technology, generating oxidizing reactive species hydroxyl radicals and carbonate radicals, and reducing reactive species carbon dioxide radicals, achieving efficient complex breaking of Cr(III)-EDTA and simultaneous reduction of Cr(VI). Furthermore, CO3 in the solution... 2- Easily reacts with free Cr 3+ The formation of insoluble carbonate precipitates can improve the removal efficiency of metallic chromium, thereby achieving efficient recovery of metallic chromium.

[0040] The technical principle of this invention: Sodium percarbonate combines the properties of both sodium carbonate and hydrogen peroxide, and its solubility in water provides an alkaline environment. Under alkaline conditions, H₂O₂ dissociates to produce HO₂. - HO2 -It reacts with ozone to generate highly reactive ·OH, as shown in formulas (1)-(6). ·OH can also react with carbonate ions to produce CO3. ·- As shown in formula (7), relevant literature reports CO3 ·- It primarily attacks electron-rich sites such as the N-COOH group of metal complexes, achieving rapid decarboxylation and complex disruption to release metal ions (see literature: Environment Science & Technology 2023, 57, 12, 5034-5045). In addition, CO3... · - It can also target and attack the electron-rich sites of Cr(III)-EDTA complexes to generate free Cr(VI) (i.e., CrO4). 2- This further improved the complex-breaking efficiency of Cr(III)-EDTA. Meanwhile, HCOOH reacts with ozone to generate CO2. ·- (E0 = -2.0V vs SHE) Formulas (8) and (9). CO2 ·- Capable of reducing Cr(VI) to Cr 3+ ions, Cr 3+ It reacts with carbonate ions in water to form insoluble carbonates, thereby achieving the precipitation and recovery of chromium ions, as shown in formula (10). Theoretically, two negatively charged free radicals, namely CO32-, react to form insoluble carbonates, thus achieving the precipitation and recovery of chromium ions. ·- and CO2 ·- The ability to coexist in the reaction system ensures that the aforementioned redox reactions can proceed simultaneously. Based on the above analysis, the ozone / sodium percarbonate / formic acid advanced redox technology is expected to achieve efficient complex disruption of chromium complexes in Cr(III)-EDTA-containing wastewater, simultaneous reduction of hexavalent chromium, and efficient precipitation and recovery of chromium.

[0041] Na2CO3·1.5H2O2→Na2CO3+1.5H2O2 (1)

[0042] O3+OH - →HO4 - (2)

[0043]

[0044] O2 - +O3→O2+O3 - · (4)

[0045] O3 - ·→O2+O - · (5)

[0046] O - · + H₂O → ·OH + OH - (6)

[0047] HO·+CO3 2- →OH - +CO3 ·- k2 = 4.2 × 10 8 M -1 S -1 (7)

[0048] HO·+HCOO - →CO2 ·- +H₂O k₂=3.2×10 9 M -1 S -1 (8)

[0049] CO3 ·- +HCOO - →CO2 ·- +HCO3 - k2 = 1.5 × 10 5 M -1 S -1 (9)

[0050] Cr 3+ +CO3 2- →Cr2(CO3)3↓ (10)

[0051] The ozone / sodium percarbonate / formic acid advanced oxidation-reduction method of the present invention can achieve efficient complex breaking, reduction and simultaneous removal of heavy metal ions of chromium complexes, simplify the treatment process of chromium complexes in Cr(III)-EDTA wastewater, improve treatment efficiency, and is an economical, efficient, easy-to-operate, wide pH applicable range, and easy-to-engineer Cr(III)-EDTA wastewater treatment technology.

[0052] The present invention provides an ozone-sodium percarbonate oxidation method for generating highly oxidizing OH and CO3. ·- and CO2 ·- This further enhances the breaking of chromium complexes, the reduction of hexavalent chromium, and the mineralization by EDTA, enabling rapid separation of precipitates after wastewater treatment.

[0053] This invention provides an ozone / sodium percarbonate / formic acid oxidation-reduction method, which has the advantages of low chemical reagent dosage, economy, and high removal rate. The released trivalent chromium ions react with carbonate ions to form a metal carbonate precipitate, which can be separated into solid and liquid phases by simple filtration. Typically, metal carbonates have a relatively small solubility product (K). sp <10 -10 Metal ions in Cr(III)-EDTA wastewater can be completely precipitated after treatment with ozone / sodium percarbonate / formic acid oxidation-reduction method.

[0054] Compared with existing methods for treating Cr(III)-EDTA-containing wastewater, this invention is the first to achieve the recovery of valuable chromium from the wastewater during the treatment process. This not only reduces its environmental pollution but also helps alleviate the current shortage of chromium resources in my country.

[0055] Example 1

[0056] Based on the properties of actual Cr(III)-EDTA-containing wastewater, a simulated reaction solution with an initial Cr(III)-EDTA concentration of 2 mmol / L was prepared. At room temperature (25±3℃), 1000 mL of the 2 mmol / L Cr(III)-EDTA solution was transferred into the reactor using a graduated cylinder, and the reactor was placed on a magnetic stirrer. The initial pH of the reaction solution was adjusted to specified values ​​(pH = 3, 5, 7, 9, 10, 11) using NaOH solution (10 mol / L) and H₂SO₄ solution (10 mol / L). Then, sodium percarbonate and formic acid were added to the reactor, with an initial concentration of 3.2 mM for sodium percarbonate and 30.8 mM formic acid. After the sodium percarbonate and formic acid were completely dissolved and mixed, O₃ was immediately introduced into the reactor at a concentration of 0.06 g / (L·min). After the reaction started, 1 mL of reaction sample was transferred from the reaction system at specified reaction time points (10, 20, 30, 40, 50, and 60 min). The sample was filtered through a 22 μm microporous membrane and the total Cr and Cr(VI) concentrations in the supernatant were analyzed. All experiments were repeated at least three times, and the mean and standard error of the experimental data were calculated.

[0057] Experimental results are as follows Figure 1 As shown, within an initial pH range ≥ 5, the ozone / sodium percarbonate / formic acid advanced oxidation-reduction method for treating Cr(III)-EDTA reaction solution achieved good total chromium removal efficiency. Furthermore, the total chromium removal efficiency gradually increased with increasing pH. When the initial pH of the system was 3, 5, 7, 9, 10, and 11, the total chromium removal efficiencies were 89%, 90%, 92.5%, 93.8%, 96%, and 99.8%, respectively. This indicates that the ozone / sodium percarbonate / formic acid advanced oxidation-reduction method has a wide applicable pH range for treating Cr(III)-EDTA wastewater. In addition, we monitored the concentration changes of Cr(VI) in the system and found that the concentration of Cr(VI) first increased and then decreased with reaction time, preliminarily confirming that Cr(III)-EDTA oxidatively broke down the complex to generate Cr(VI), which was subsequently reduced to Cr by the reducing species generated in the system. 3+ Ions. Cr 3+ via CO3 2- and OH -Under the combined action of various factors, a green precipitate was formed. Solid-liquid separation was achieved through filtration. The collected precipitate was then dried, ground, and calcined. X-ray diffraction (XRD) analysis revealed that the green precipitate was high-purity Cr2O3. Figure 2 ), and calculations confirmed that the chromium recovery rate was as high as 99%.

[0058] Example 2

[0059] The dosage of sodium percarbonate was varied (1.6, 2, 3.2, 8, 16 mmol / L) to treat 2 mmol / L Cr(III)-EDTA solution. Other experimental conditions were the same as in Case 1. The total Cr removal effect before and after the reaction was as follows: Figure 3 As shown in the figure, the experimental results indicate that the total Cr removal efficiency gradually increases with increasing sodium percarbonate dosage. It is noteworthy that the total Cr removal efficiency decreases when the sodium percarbonate dosage exceeds 3.2 mM. Therefore, considering economic costs, the optimal sodium percarbonate dosage is 3.2 mM.

[0060] Example 3

[0061] Under the optimal condition of sodium carbonate dosage of 3.2 mM, the dosage of formic acid was varied (7.7, 15.4, 23.1, 30.8 mmol / L) to treat 2 mmol / L Cr(III)-EDTA solution. Other experimental conditions were the same as in Case 1. The total Cr removal effect before and after the reaction was as follows: Figure 3 As shown in the figure, the experimental results indicate that the total Cr removal efficiency gradually increases with increasing formic acid dosage. Therefore, the optimal dosage of formic acid is 30.8 mM.

[0062] Example 4

[0063] Under the preferred conditions of an initial sodium percarbonate concentration of 3.2 mM and an initial formic acid concentration of 30.8 mM, a 2 mmol / L Cr(III)-EDTA solution was treated by varying the O3 gas concentration (0.01, 0.02, 0.06, 0.08, 0.1 g / (L·min)), with other experimental conditions the same as in Case Study 1. Figure 4 Experimental results show that the higher the O3 gas concentration, the higher the total Cr removal efficiency. However, when the O3 gas concentration is greater than 0.06 g / (L·min), the improvement in total Cr removal efficiency is not significant. Therefore, considering the economic cost of treatment and to ensure the maximum optimization of chemical reagents, 0.06 g / (L·min) was selected as the optimal O3 gas concentration for further research.

[0064] Example 5

[0065] Chromium coordination complexes formed by chromium ions and different complexing agents (ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), citric acid, and diethyltriaminepentaacetic acid (DTPA)) were treated under preferred conditions of an initial sodium percarbonate concentration of 3.2 mM, an initial formic acid concentration of 30.8 mM, and an O3 gas concentration of 0.06 g / (L·min). Figure 6 As shown, the ozone / sodium percarbonate / formic acid advanced oxidation-reduction method for treating chromium-containing coordination complex reaction solutions all achieved good total Cr removal effects.

[0066] Example 6

[0067] Under optimal conditions of an initial sodium percarbonate concentration of 3.2 mM, an initial formic acid concentration of 30.8 mM, and an O3 gas concentration of 0.06 g / (L·min), the study investigated common coexisting anions and cations (Cl-) in wastewater. - SO4 2- NO3 - NH4 + The effect of ozone / sodium percarbonate / formic acid advanced oxidation-reduction process on the removal of Cr(III)-EDTA. Figure 7 As shown, the coexistence of anions and cations had no significant inhibitory effect.

[0068] In summary, this invention utilizes an ozone / sodium percarbonate / formic acid advanced redox method to generate oxidizing reactive species hydroxyl radicals and carbonate radicals, and reducing reactive species carbon dioxide radicals. This enables rapid complex breakdown of chromium complexes in wastewater and reduction of hexavalent chromium. Ultimately, free trivalent chromium ions react with carbonate and hydroxide ions under alkaline conditions to form insoluble carbonate and hydroxide precipitates, achieving rapid removal and recovery of chromium ions from wastewater. Simultaneously, EDTA organic ligands in the wastewater undergo rapid mineralization and decomposition under highly active free radical oxidation. The heavy metal content in the treated wastewater is within the emission limits specified in the "Electroplating Pollutant Discharge Standard (GB21900-2008)". This method treats Cr(III)-EDTA-containing wastewater without generating secondary pollutants while simultaneously recovering valuable chromium, offering advantages such as being green, efficient, and low-cost.

[0069] Without causing conflict, those skilled in the art can freely combine and use the above-mentioned additional technical features.

[0070] The above description is only a preferred embodiment of the present invention. Any technical solution that achieves the purpose of the present invention by essentially the same means is within the protection scope of the present invention.

Claims

1. A redox process for efficient recovery of chromium complexes from Cr(III)-EDTA-containing wastewater, characterized in that: The process first adds appropriate amount of sodium percarbonate and formic acid in Cr(III)-EDTA-containing wastewater, stirs and dissolves, and then immediately introduces ozone into the mixture, so as to generate oxidizing active species hydroxyl radical and carbonate radical and reducing active species carbon dioxide radical by ozone / sodium percarbonate / formic acid advanced oxidation and reduction method, so as to realize rapid complex breaking of chromium complex in wastewater, reduction of hexavalent chromium, and finally reaction of free trivalent chromium ion with carbonate radical and hydroxyl radical to generate difficultly soluble carbonate and hydroxide precipitate under alkaline conditions, so as to realize rapid separation of heavy metal chromium in Cr(III)-EDTA-containing wastewater by standing and simple filtration; meanwhile, EDTA organic ligand in the wastewater is rapidly mineralized and decomposed under the oxidation of high-activity free radical, so as to realize rapid and efficient purification of Cr(III)-EDTA-containing wastewater. The process specifically comprises the following steps: Step 1: heavy metal complex wastewater containing heavy metal chromium and complexing agent ethylenediaminetetraacetic acid is added into a reactor; Step 2: appropriate amount of sodium percarbonate and formic acid are added into the reactor, and a magnetic stirrer is used to ensure complete dissolution of the sodium percarbonate; Step 3: after the sodium percarbonate and formic acid are completely dissolved and mixed, ozone generated by an ozone generator is immediately introduced into the reactor, wherein the reactor is connected with the external ozone generator and tail gas absorption device through a gas pipe; Step 4: after the ozone / sodium percarbonate / formic acid reaction is completed, the mixture is allowed to stand for a period of time, and finally microfiltration membrane device is used for filtration to realize simultaneous complex breaking and heavy metal removal.

2. The redox process for efficient recovery of chromium complex from Cr(III)-EDTA containing wastewater according to claim 1, characterized by: The sodium percarbonate in step 2 is any commercial sodium percarbonate, and the addition amount of the sodium percarbonate is 1 to 5 times the molar concentration of the metal chromium in the Cr(III)-EDTA-containing wastewater.

3. The redox process for efficient recovery of chromium complex from Cr(III)-EDTA containing wastewater according to claim 1, characterized by: The formic acid in step 2 is any commercial formic acid, and the addition amount of the formic acid is 5 to 50 times the molar concentration of the metal chromium in the Cr(III)-EDTA-containing wastewater.

4. The redox process for efficient recovery of chromium complex from Cr(III)-EDTA containing wastewater according to claim 1, characterized by: The concentration of the ozone introduced in step 3 is 0.5-8 mg / (L·min), and the reaction time is 210 min.

5. The redox process for efficient recovery of chromium complex from Cr(III)-EDTA containing wastewater according to claim 1, characterized by: The microfiltration membrane device in step 4 has a micro-pore diameter of less than or equal to 0.22 μm.

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