Cyanide-containing wastewater treatment method

Abstract

The invention discloses a cyanogen-containing wastewater treatment method, which adopts an electrochemical combined oxidation method to treat cyanogen-containing wastewater, and comprises the following steps: combining cathode electrochemical in-situ generated hydrogen peroxide oxidation treatment of cyanogen-containing wastewater and anode oxidation treatment of cyanogen-containing wastewater, wherein pollutants in the cyanogen-containing wastewater comprise total cyanogen and thiocyanogen. According to the cyanide-containing wastewater treatment method, the cathode can also indirectly participate in the decomposition reaction of cyanide through hydrogen peroxide generated in situ at the cathode, the removal rate of total cyanogen and thiocyanogen in the cyanide-containing wastewater is increased, and more efficient utilization of electric energy is achieved. In addition, on-site generation and on-site use of hydrogen peroxide are realized, so that risks in storage and transportation processes are avoided.

Description

Technical Field

[0001] The invention relates to the technical field of wastewater treatment, and in particular to a method for treating cyanide-containing wastewater. Background Art

[0002] Cyanidation is still a commonly used gold extraction method in gold mines. Cyanidation is a method of using alkaline cyanide solution to dissolve the gold in the ore and then precipitate it to extract the gold. In the cyanidation leaching process, due to the coexistence of a variety of complex sulfide minerals in the mine, the tailings contain not only free cyanide, but also a large amount of heavy metals such as copper and iron, as well as a large amount of thiocyanide. - ) During the cyanidation process, as the leachate is recycled and accumulated, cyanide wastewater containing high content of thiocyanate is produced. The accumulation of thiocyanate has a great adverse effect on the recycling of the leachate and the treatment of cyanide-containing wastewater.

[0003] Among the many technologies for treating cyanide-containing wastewater, the hydrogen peroxide method is favored because it can effectively deal with cyanide wastewater with large concentration fluctuations, has significant treatment effects on inorganic cyanide and metal cyanide complexes, and has a simple process and high degradation efficiency. However, as a strong oxidant, hydrogen peroxide has the risk of explosion during transportation and storage, and is easily decomposed or reacts with other substances, resulting in high reagent costs.

[0004] The traditional electrolysis method has the advantages of short process, simple operation and no secondary pollution. However, this method mainly relies on the anode to oxidize cyanide, while the cathode is only used for the electronic reduction of metal ions and fails to directly participate in the decomposition process of cyanide, resulting in a waste of some electrical energy. Summary of the invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0006] To this end, the present invention provides a method for treating cyanide-containing wastewater, which uses an electrochemical combined oxidation method to treat cyanide-containing wastewater, comprising:

[0007] In-situ cathode electrochemical generation of hydrogen peroxide for the treatment of cyanide-containing wastewater;

[0008] Anodic oxidation treatment of cyanide-containing wastewater;

[0009] Among them, pollutants in cyanide-containing wastewater include total cyanide and thiocyanate.

[0010] Furthermore, the electrochemical combined oxidation method specifically comprises:

[0011] Place the cyanide-containing wastewater in an electrolytic cell, add an electrolyte solution, and control the initial pH of the solution to be 11-12;

[0012] A graphite plate is used as the anode and a gas diffusion electrode is used as the cathode;

[0013] The power supply is turned on and air is introduced to the cathode. Oxygen reduction is performed on the cathode to generate hydrogen peroxide. The generated hydrogen peroxide is oxidized to treat the cyanide-containing wastewater, and an oxidation reaction occurs on the anode to treat the cyanide-containing wastewater.

[0014] Furthermore, the gas diffusion electrode is prepared by:

[0015] Pretreatment of the stainless steel mesh: immerse the stainless steel mesh in a dilute sulfuric acid solution with a mass fraction of 8% to 15%, ultrasonic cleaning, then rinse with deionized water and dry;

[0016] Preparation of the diffusion layer: weigh carbon black and pore-forming agent, add anhydrous ethanol, and mix them evenly by ultrasonic treatment; then add PTFE emulsion, ultrasonic treatment again, evaporate the ethanol until the mixture is in a paste state, and roll it in a mold to obtain a diffusion layer with a thickness of 1 mm to 3 mm;

[0017] Preparation of the catalytic layer: adding anhydrous ethanol to carbon black, and mixing by ultrasonic treatment; then adding PTFE emulsion, and ultrasonic treatment again, evaporating the ethanol until the mixture is in a paste state, and rolling in a mold to obtain a catalytic layer with a thickness of 1 mm to 3 mm;

[0018] Gas diffusion electrode forming: The obtained diffusion layer and catalyst layer are placed on both sides of the stainless steel mesh respectively, and cold pressed to achieve forming, and then dried and calcined to finally obtain a gas diffusion electrode.

[0019] Furthermore, the electrochemical combined oxidation method has a current density of 2 mA / cm 2 ~5mA / cm 2 , the air flow rate is 20mL / min~120mL / min, the electrolyte solution is sodium sulfate solution, the electrolyte solution concentration is 0.05mol / L~0.30mol / L, and the electrolysis time is 4h~24h.

[0020] Furthermore, when the cyanide-containing wastewater is treated by the electrochemical combined oxidation method, the total cyanide concentration in the cyanide-containing wastewater is adjusted to ≤5000 mg / L, and the thiocyanate concentration is adjusted to ≤2 g / L.

[0021] Furthermore, the electrochemical combined oxidation method,

[0022] When the total cyanide content is 500mg / L-1000mg / L, the removal rate of total cyanide is 77%-85%. When the total cyanide content is 2000mg / L, the removal rate of total cyanide drops to 61.6%. When the total cyanide content is 400mg / L, the removal rate of total cyanide is 69.8%.

[0023] When the thiocyanate content is 400mg / L~500mg / L, the removal rate of thiocyanate is 79%~86%; when the thiocyanate content is 2000mg / L, the removal rate of thiocyanate is 9.1%; when the thiocyanate content is 1000mg / L, the removal rate of thiocyanate is 13.9%.

[0024] Furthermore, in the electrochemical combined oxidation method, when the total cyanide content is 500 mg / L, the removal rate of total cyanide reaches more than 84%; when the thiocyanate content is 400 mg / L, the removal rate of thiocyanate reaches more than 85%.

[0025] Furthermore, the electrochemical combined oxidation method has a removal rate of 68% to 74% for copper at 400 mg / L to 1000 mg / L, a removal rate of 65% to 73% for iron at 400 mg / L to 1000 mg / L, and a removal rate of 58% to 66% for zinc at 400 mg / L to 1000 mg / L.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] The invention provides a method for treating cyanide-containing wastewater, which adopts cathode electrochemical in-situ generated hydrogen peroxide to oxidize and treat the cyanide-containing wastewater, and combines it with anode oxidation to jointly treat the cyanide-containing wastewater, thereby improving the removal rate of total cyanide and thiocyanate in the cyanide-containing wastewater and achieving more efficient use of electric energy; and also achieving on-site generation and on-site use of hydrogen peroxide, thereby avoiding risks in the storage and transportation of hydrogen peroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments recorded in the embodiments of the present invention. For ordinary technicians in this field, other drawings can also be obtained based on these drawings.

[0029] Figure 1 (a) SCN under different oxidation methods provided in Example 1 of the present invention - Effect on total cyanide removal.

[0030] Figure 1 (b) SCN under different oxidation methods provided in Example 1 of the present invention - The removal rules.

[0031] Figure 1 (c) is the variation pattern of pH under different oxidation modes provided in Example 1 of the present invention.

[0032] Figure 2 The removal effects of various components in cyanide wastewater with different concentration gradients under combined oxidation are provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0033] In order to better understand the above-mentioned technical scheme, the technical scheme of the embodiments of the present application is described in detail below through the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present application and the specific features in the embodiments are detailed descriptions of the technical scheme of the embodiments of the present application, rather than limitations on the technical scheme of the present application. In the absence of conflict, the embodiments of the present application and the technical features in the embodiments may be combined with each other.

[0034] An embodiment of the present invention provides a method for treating cyanide-containing wastewater, which adopts an electrochemical combined oxidation method to treat cyanide-containing wastewater, including: in-situ electrochemical generation of hydrogen peroxide to treat cyanide-containing wastewater; and anodic oxidation to treat cyanide-containing wastewater; wherein the pollutants in the cyanide-containing wastewater include total cyanide and thiocyanate.

[0035] Compared with the conventional electrochemical oxidation method for treating cyanide-containing wastewater, the cathode is only used for the electronic reduction of metal ions in the treatment method of cyanide-containing wastewater in the embodiment of the present invention. In the embodiment of the present invention, the cathode can also indirectly participate in the decomposition reaction of cyanide by generating hydrogen peroxide in situ at the cathode, thereby improving the removal rate of total cyanide and thiocyanate in cyanide-containing wastewater and achieving more efficient use of electrical energy. In addition, the on-site generation and on-site use of hydrogen peroxide are achieved, thereby avoiding risks during storage and transportation.

[0036] In some embodiments, the electrochemical combined oxidation method specifically includes:

[0037] Place the cyanide-containing wastewater in an electrolytic cell, add an electrolyte solution, and control the initial pH of the solution to be 11-12;

[0038] A graphite plate is used as the anode and a gas diffusion electrode is used as the cathode;

[0039] The power supply is turned on and air is introduced to the cathode. Oxygen reduction is performed on the cathode to generate hydrogen peroxide. The generated hydrogen peroxide is oxidized to treat the cyanide-containing wastewater, and an oxidation reaction occurs on the anode to treat the cyanide-containing wastewater.

[0040] The current density was controlled to be 2 mA / cm 2 ~5mA / cm 2 , the air flow rate is 20mL / min~120mL / min, the electrolyte solution is sodium sulfate solution, the electrolyte solution concentration is 0.05mol / L~0.30mol / L, and the electrolysis time is 4h~24h. As a preferred embodiment, the current density is 3mA / cm 2, the air flow rate is 60mL / min, the concentration of the electrolyte sodium sulfate solution is 0.10mol / L, the electrolysis time is 8h, and the initial pH of the cyanide-containing wastewater solution is adjusted to 12. It can be understood that in order to improve the treatment efficiency, when the electrochemical combined oxidation method is used to treat cyanide-containing wastewater, the total cyanide concentration in the cyanide-containing wastewater is adjusted to ≤5000mg / L, and the thiocyanate concentration is adjusted to ≤2g / L.

[0041] Optionally, the preparation method of the gas diffusion electrode comprises:

[0042] (1) Pretreatment of 316 stainless steel mesh: First, the stainless steel mesh is precisely cut to the appropriate size according to the required specifications. Next, the stainless steel mesh is immersed in a 10% dilute sulfuric acid solution and ultrasonically cleaned for 10 minutes to remove inorganic dirt on the surface. Subsequently, the mesh is taken out and thoroughly rinsed with deionized water. To further remove oil and organic solvent residues on the surface, the stainless steel mesh needs to be ultrasonically cleaned in an ethanol solution and deionized water for 10 minutes respectively. After completing the above steps, the stainless steel mesh is placed in an electric hot air drying oven for drying to ensure that all surface moisture is removed.

[0043] (2) Preparation of diffusion layer: 1.2 g of carbon black and 0.12 g of ammonium bicarbonate (pore former) were weighed and placed in a beaker. Subsequently, anhydrous ethanol was added to completely immerse the materials and ultrasonically treated for 15 min to ensure that the components were evenly mixed. Next, 0.6 g of 60% PTFE emulsion was added and ultrasonically treated again for 20 min, which not only made all the components evenly distributed, but also achieved the demulsification of the emulsion. After that, the beaker was placed in a water bath and heated at 80 ° C (ethanol evaporated at a low temperature of 25 ° C after adding the pore former ammonium bicarbonate), and stirred continuously so that the ethanol could be completely evaporated until the mixture was in a paste state. At this time, the paste was taken out and placed in a homemade mold, and it was molded into a suitable size and shape with a thickness of 1 to 3 mm by continuously rolling it with a glass rod until the expected fibrous structure was formed, that is, the desired diffusion layer was successfully prepared.

[0044] (3) Preparation of the catalytic layer: 1.2 g of carbon black was weighed and placed in a beaker, followed by adding sufficient anhydrous ethanol to completely immerse it, and ultrasonically treated for 15 min to ensure that it was evenly distributed in the solution. Subsequently, 0.6 g of 60% PTFE emulsion was added and ultrasonically treated for 20 min, which not only ensured the uniform distribution of the components in the mixture, but also achieved the demulsification process of the emulsion. After that, the beaker was placed in a water bath and heated at a constant temperature of 80 ° C. During this process, the mixture needs to be stirred continuously so that the ethanol can be completely evaporated until the mixture forms the desired paste. Once the paste is ready, it is taken out and placed in a homemade mold. Use a glass rod to continuously roll it and shape it into a suitable size and shape with a thickness of 1 to 3 mm until it presents the expected fibrous structure, and the preparation of the catalytic layer is completed.

[0045] (4) Forming of gas diffusion electrode: The obtained diffusion layer and catalyst layer are placed on both sides of the stainless steel mesh respectively. Then, with the assistance of a liquid-cooled press, it is subjected to cold pressing for 10 minutes to achieve forming. Subsequently, the preliminarily prepared gas diffusion electrode is placed in an electric hot air drying oven to completely evaporate the residual ethanol therein. After the drying process is completed, the electrode is placed in a muffle furnace and calcined at 330°C for 1 hour. After natural cooling, the final gas diffusion electrode is obtained.

[0046] Example 1 Total cyanide (CN) under combined oxidation and anodic oxidation - ) and thiocyanate (SCN - ) Removal rate

[0047] Simulated wastewater composition: NaCN as CN - Source, CN - Concentration 500mg / L, other components SCN - About 1g / L, Cu about 80mg / L, Fe about 65mg / L, Zn about 44mg / L, Cl - About 60mg / L. When the electrode is energized with aeration flow rate of 0, the reaction system H 2 O 2 The yield is 0, that is, under non-ventilated conditions, the reaction in the system is mainly an oxidation reaction at the anode, hereinafter referred to as anodic oxidation; while under ventilation conditions, H 2 O 2 The case of anodic oxidation and H 2 O 2 The combined action is hereinafter referred to as combined oxidation.

[0048] The solution pH was selected as 12 and the current density was 3 mA / cm 2 Under the conditions of -) and the addition of thiocyanate (SCN - ), combined oxidation and anode oxidation alone have a significant effect on total cyanide (CN - ) degradation and removal effect, and total cyanide (CN - ) in the presence of thiocyanate (SCN - ) removal rules. The results are as follows Figure 1 shown.

[0049] Figure 1 a, add thiocyanate (SCN - ) and then combined with oxidation to total cyanide (CN - The removal effect of SCN is comparable to that of anodic oxidation in the first 2 hours, and is much better than that of anodic oxidation in the range of 2 to 8 hours. This is because the concentration of hydrogen peroxide is low in the early stage of electrolysis, and the total cyanide is mainly removed by the oxidation of the anode. As the electrolysis proceeds, the cumulative concentration of hydrogen peroxide gradually increases, thereby accelerating the removal rate of total cyanide. Whether it is combined oxidation or anodic oxidation, adding SCN - The total cyanide removal rate after addition was lower than that without adding SCN. - This is due to SCN - It not only reacts with hydrogen peroxide, but also oxidizes on the anode and releases CN - , which leads to SCN - Oxidative degradation of CN - Competition will occur between the oxidative degradation reactions, resulting in a decrease in the removal rate of total cyanide.

[0050] Figure 1 b) The combined oxidation of SCN in the first 6 h of electrolysis - The removal rate of SCN in the combined oxidation was lower than that in the anodic oxidation, while the removal rate of SCN in the combined oxidation exceeded that in the anodic oxidation in the last 2 hours. This may be because in the combined oxidation process, the hydrogen peroxide produced by the gas diffusion cathode is oxidized and decomposed on the anode to react with SCN. - The electrochemical reaction of anodic oxidation competes with each other, leading to SCN - The degradation rate of SCN is slower than that of anodic oxidation. As the electrolysis proceeds, the cumulative concentration of hydrogen peroxide increases and gradually oxidizes SCN. - , making SCN - The removal rate is improved.

[0051] Figure 1 Add SCN in c - The pH value of the last two oxidation methods decreased much faster than that without adding SCN. - This is due to SCN - When it reacts with hydrogen peroxide or is oxidized at the anode, H + , resulting in a rapid drop in the pH value of the solution.

[0052] Example 2 Treatment of gold cyanide wastewater with different concentrations

[0053] The properties of the initial cyanide wastewater used in the experiment are shown in Table 1.

[0054] Table 1 Main indicators of cyanide-containing wastewater used in the experiment

[0055]

[0056]

[0057] Deionized water was used to dilute the samples to different concentration gradients (based on the total cyanide concentration) at a current density of 3 mA / cm 2 , the air flow rate was 60mL / min, the electrolyte solution was sodium sulfate solution, the concentration was 0.10mol / L, and the pH value of each wastewater was adjusted to 12, and the electrolysis treatment was carried out for 8h. - , copper, iron, zinc, Cl - The removal rate of ions determined the concentration range of cyanide wastewater that can be effectively treated by electrochemical in-situ hydrogen peroxide generation combined with anode co-oxidation. Figure 2 shown.

[0058] Through Figure 2 From the analysis of the experimental results in the experiment, it can be seen that the removal rate of total cyanide shows a trend of first increasing and then decreasing with the increase of the concentration of cyanide wastewater. In the range of 500mg / L to 1000mg / L, the removal rate of total cyanide is between 77.5% and 84.1%, with the highest reaching 84.1% at 500mg / L. However, in high-concentration cyanide wastewater of 2000mg / L, the removal rate of total cyanide drops to 61.6%, and is 69.8% at 400mg / L.

[0059] SCN - The removal rate of SCN decreased with the increase of cyanide wastewater concentration. - The removal rates of SCN were relatively poor, at 9.1% and 13.9% respectively. - The removal effects were good, at 79.5% and 85.1% respectively.

[0060] The removal rate of copper was the worst at a concentration of 2000 mg / L, but remained basically stable within the concentration range of 400 mg / L to 1000 mg / L, ranging from 68.4% to 73.1%. The highest removal rate of copper was 73.1% at 500 mg / L.

[0061] The iron removal rate fluctuated between 62.1% and 72.8% in the entire concentration range, and showed better removal effects at 1000 mg / L and 500 mg / L, which were 72.8% and 72.6%, respectively.

[0062] The removal rate of zinc reached its maximum at 2000 mg / L, which was 97.0%, and in the concentration range of 400 mg / L to 1000 mg / L, the removal rate remained at the same level, ranging from 58.4% to 65.5%.

[0063] Finally, the removal effect of chloride ions was not ideal in the entire concentration range, especially at a high concentration of 2000 mg / L, where the removal rate was only 6.6%, while it was slightly better at 400 mg / L and 500 mg / L, which were 20.7% and 18.7%, respectively.

[0064] In summary, the electrochemical combined oxidation method showed significant removal effects on cyanide wastewater with a total cyanide concentration ranging from 400 mg / L to 1000 mg / L. In all concentration gradient ranges, the optimal removal effect was achieved when the total cyanide concentration was 500 mg / L, with a total cyanide removal rate of up to 84.1%. - The removal rates of copper, iron and zinc also reached a high level at this concentration, which were 79.5%, 73.1%, 72.6% and 62.5% respectively. Although the removal rate of chloride ions was relatively low, it still had a removal effect of 18.7%.

[0065] It is easy for those skilled in the art to understand that, under the premise of no conflict, the above-mentioned advantageous methods can be freely combined and superimposed. The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application. The above are only preferred implementation methods of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and variations can be made without departing from the technical principles of the present application, and these improvements and variations should also be regarded as the protection scope of the present application.

Claims

1. A method for treating cyanide-containing wastewater, characterized in that: The electrochemical combined oxidation method is used to treat cyanide-containing wastewater, including: In-situ cathode electrochemical generation of hydrogen peroxide for the treatment of cyanide-containing wastewater; Anodic oxidation treatment of cyanide-containing wastewater; Among them, pollutants in cyanide-containing wastewater include total cyanide and thiocyanate.

2. The method for treating cyanide-containing wastewater according to claim 1, characterized in that: The electrochemical combined oxidation method specifically comprises: Place the cyanide-containing wastewater in an electrolytic cell, add an electrolyte solution, and control the initial pH of the solution to be 11-12; A graphite plate is used as the anode and a gas diffusion electrode is used as the cathode; The power supply is turned on and air is introduced to the cathode. Oxygen reduction is performed on the cathode to generate hydrogen peroxide. The generated hydrogen peroxide is oxidized to treat the cyanide-containing wastewater, and an oxidation reaction occurs on the anode to treat the cyanide-containing wastewater.

3. The method for treating cyanide-containing wastewater according to claim 2, characterized in that: The gas diffusion electrode, the preparation method comprises: Pretreatment of the stainless steel mesh: immerse the stainless steel mesh in a dilute sulfuric acid solution with a mass fraction of 8% to 15%, ultrasonic cleaning, then rinse with deionized water and dry; Preparation of the diffusion layer: weigh carbon black and pore-forming agent, add anhydrous ethanol, and mix them evenly by ultrasonic treatment; then add PTFE emulsion, ultrasonic treatment again, evaporate the ethanol until the mixture is in a paste state, and roll it in a mold to obtain a diffusion layer with a thickness of 1 mm to 3 mm; Preparation of the catalytic layer: adding anhydrous ethanol to carbon black, and mixing by ultrasonic treatment; then adding PTFE emulsion, and ultrasonic treatment again, evaporating the ethanol until the mixture is in a paste state, and rolling in a mold to obtain a catalytic layer with a thickness of 1 mm to 3 mm; Gas diffusion electrode forming: The obtained diffusion layer and catalyst layer are placed on both sides of the stainless steel mesh respectively, and cold pressed to achieve forming, and then dried and calcined to finally obtain a gas diffusion electrode.

4. The method for treating cyanide-containing wastewater according to claim 3, characterized in that: The electrochemical combined oxidation method has a current density of 2 mA / cm 2 ~5mA / cm 2 , the air flow rate is 20mL / min~120mL / min, the electrolyte solution is sodium sulfate solution, the electrolyte solution concentration is 0.05mol / L~0.30mol / L, and the electrolysis time is 4h~24h.

5. The method for treating cyanide-containing wastewater according to claim 4, characterized in that: When electrochemical combined oxidation is used to treat cyanide-containing wastewater, the total cyanide concentration in the cyanide-containing wastewater is adjusted to ≤5000mg / L, and the thiocyanate concentration is adjusted to ≤2g / L.

6. The method for treating cyanide-containing wastewater according to claim 5, characterized in that: The electrochemical combined oxidation method, When the total cyanide content is 500mg / L-1000mg / L, the removal rate of total cyanide is 77%-85%. When the total cyanide content is 2000mg / L, the removal rate of total cyanide drops to 61.6%. When the total cyanide content is 400mg / L, the removal rate of total cyanide is 69.8%. When the thiocyanate content is 400mg / L~500mg / L, the removal rate of thiocyanate is 79%~86%; when the thiocyanate content is 2000mg / L, the removal rate of thiocyanate is 9.1%; when the thiocyanate content is 1000mg / L, the removal rate of thiocyanate is 13.9%.

7. The method for treating cyanide-containing wastewater according to claim 5, characterized in that: In the electrochemical combined oxidation method, when the total cyanide content is 500 mg / L, the total cyanide removal rate reaches more than 84%; when the thiocyanate content is 400 mg / L, the thiocyanate removal rate reaches more than 85%.

8. The method for treating cyanide-containing wastewater according to claim 5, characterized in that: The electrochemical combined oxidation method has a removal rate of 68% to 74% for copper at a concentration of 400 mg / L to 1000 mg / L.

9. The method for treating cyanide-containing wastewater according to claim 5, characterized in that: The electrochemical combined oxidation method has a removal rate of 65% to 73% for iron at a concentration of 400 mg / L to 1000 mg / L.

10. The method for treating cyanide-containing wastewater according to claim 5, characterized in that: The electrochemical combined oxidation method has a removal rate of 58% to 66% for zinc at a concentration of 400 mg / L to 1000 mg / L.

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