Method for degrading cyanide-containing wastewater

Abstract

The invention belongs to the technical field of sewage treatment, and particularly relates to a method for degrading cyanide-containing wastewater. When the cyanogen-containing wastewater is cyanogen-containing complex wastewater, the method for degrading the cyanogen-containing wastewater comprises the following steps: sequentially carrying out photolysis reaction and first oxidation reaction on the cyanogen-containing wastewater under the condition that the pH value is 9.5-13.0; when the cyanide-containing wastewater is free cyanide-containing wastewater, the method for degrading the cyanide-containing wastewater comprises the following steps: sequentially carrying out a second oxidation reaction on the cyanide-containing wastewater under the condition that the pH value is 9.5-13.0; oxidizing agents for the first oxidation reaction and the second oxidation reaction are solutions of peracetic acid; the second oxidation reaction is carried out under the condition of ultraviolet irradiation. The method provided by the invention can destroy stable coordinate bonds (Fe-CN) of ferricyanide, improves the degradation efficiency, and does not generate secondary pollution.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, and specifically relates to a method for degrading cyanide-containing wastewater. Background Technology

[0002] Cyanide, as an important industrial raw material, is widely used in various industries, especially metallurgy and mining. The cyanide-containing wastewater and metal complexes (mainly Fe-CN) formed in cyanide tailings from gold extraction are difficult to degrade. Current treatment methods pose risks of releasing highly toxic HCN under acidic conditions, or they may have low selectivity, failing to break down the metal-cyanide complex, resulting in low degradation efficiency, or they may generate toxic byproducts, causing secondary pollution. Summary of the Invention

[0003] The purpose of this invention is to provide a method for degrading cyanide-containing wastewater. The method provided by this invention can break the stable coordination bond (Fe-CN) of ferricyanide, improve the degradation efficiency, and avoid secondary pollution.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for degrading cyanide-containing wastewater, wherein the cyanide-containing wastewater is divided into two types: wastewater containing free cyanide and wastewater containing cyanide complexes.

[0006] When the cyanide-containing wastewater is cyanide complex-containing wastewater, the method for degrading the cyanide-containing wastewater includes the following steps:

[0007] The cyanide-containing wastewater was subjected to photolysis and primary oxidation reactions sequentially under conditions of pH 9.5–13.0.

[0008] Both the photolysis reaction and the first oxidation reaction are carried out under ultraviolet light irradiation; the photolysis reaction takes 0.5 to 3 hours.

[0009] When the cyanide-containing wastewater is wastewater containing free cyanide, the method for degrading the cyanide-containing wastewater includes the following steps:

[0010] The cyanide-containing wastewater was subjected to a second oxidation reaction sequentially under conditions of pH 9.5–13.0;

[0011] The oxidant in both the first and second oxidation reactions is a solution of peracetic acid;

[0012] The second oxidation reaction is carried out under ultraviolet light irradiation.

[0013] Preferably, the temperature of the photolysis reaction is 10–35°C, the wavelength of the ultraviolet light is 200–450 nm, and the light intensity is 0.85–100 mW / cm². 2 .

[0014] Preferably, the photolysis reaction, the first oxidation reaction, and the second oxidation reaction are carried out under stirring conditions; the stirring speed is 200-1000 rpm.

[0015] Preferably, the temperature of the first oxidation reaction is 25-30°C and the time is 4-6 hours; the temperature of the second oxidation reaction is 25-30°C and the time is 10 minutes to 6 hours.

[0016] Preferably, the cyanide complex includes one or more of ferrocyanide, ferricyanide, and cobalt cyanide.

[0017] Preferably, the concentration of the peracetic acid solution is 0.1 to 5 g / L.

[0018] Preferably, when the cyanide-containing wastewater is wastewater containing free cyanide, the mass ratio of peracetic acid to free cyanide is 2 to 5:1.

[0019] Preferably, when the cyanide-containing wastewater is cyanide complex-containing wastewater, the mass ratio of peracetic acid to cyanide complex is 10 to 40:1.

[0020] Preferably, when the cyanide-containing wastewater is cyanide complex-containing wastewater, CN... - The concentration of cyanide complex in the cyanide-containing wastewater is calculated to be 1–100 mg / L.

[0021] Preferably, when the cyanide-containing wastewater is wastewater containing free cyanide, the concentration of free cyanide in the cyanide-containing wastewater is 1 to 100 mg / L.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. In the UV-activated peracetic acid (UV / PAA) system of this invention, under alkaline conditions (pH 9.5–13.0), UV light can drive ligand-metal charge transfer (LMCT) in metal-cyanide complexes (such as ferricyanide, ferrousyanide, cobalt cyanide, etc.), thereby achieving photolytic complex breakdown. Utilizing the coupling effect of UV / PAA, more abundant active free radicals (organic active free radicals (RC·), hydroxyl radicals (HO·), etc.) are generated, achieving complete degradation and removal of cyanide. Furthermore, the final products of peracetic acid (PAA) are formic acid and acetic acid, with no toxic byproducts and no secondary pollution.

[0024] 2. High environmental safety. Due to the pH self-stabilizing mechanism in the system, it overcomes the limitations of conventional UV / PAA processes under neutral or acidic conditions. The alkalinity released by the O-→·OH conversion of PAA effectively neutralizes the acidification effect of ligand dissociation and oxidative denitrification. Therefore, the pH fluctuation is small throughout the cyanide degradation process (ΔpH<0.17), while the formation and release risk of hydrogen cyanide (HCN) (pKa=9.2) can be suppressed in an alkaline environment with pH>10.

[0025] 3. Short reaction time and high removal efficiency. Addressing the difference in reaction kinetics between PAA and ferricyanide, this invention employs a delayed PAA addition strategy (UV complex disruption for 0.5–3 hours followed by PAA addition), which significantly improves treatment efficiency. The total cyanide removal rate is increased by 18% compared to simultaneous treatment, and the treatment time is shortened by 50%. This invention achieves, for the first time, the decoupling of the "complex disruption-oxidation" dual pathway, providing a new paradigm for the engineering optimization of advanced oxidation processes.

[0026] Data from the examples show that after treatment with the UV-activated peracetic acid system (UV / PAA) of the present invention, the total cyanide (TCN) in the cyanide-containing wastewater is ≤0.004 mg / L, and the TCN removal rate is >99%, which is far below the Class I discharge standard for total cyanide wastewater (GB 8978-1996). Compared with other existing treatment modes (such as alkaline chlorination, hydrogen peroxide, and ozone oxidation), it breaks through the bottleneck of the difficulty in degrading the strong coordination bonds of metal cyanide complexes, and does not produce secondary pollution. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 The effect of different peracetic acid addition amounts on the removal of free cyanide;

[0029] Figure 2 The effect of different pH values ​​on the removal of free cyanide (a. UV; c. UV / peracetic acid) and the reaction rate constant (b. UV; d. UV / peracetic acid);

[0030] Figure 3 The effect of peracetic acid addition on ferricyanide removal (a) and reaction rate constant (b);

[0031] Figure 4The effects of different pH values ​​on the photolysis of ferricyanide (a) and the removal of total cyanide (c) in the UV system, as well as the reaction rate constants (b. photolysis rate; d. degradation rate);

[0032] Figure 5 The effect of different peracetic acid addition times on ferricyanide removal;

[0033] Figure 6 The effect of ultraviolet light on the speciation of cyanide in alkaline washing wastewater;

[0034] Figure 7 The effect of peracetic acid addition on cyanide removal from alkaline washing wastewater;

[0035] Figure 8 The effect of peracetic acid addition time on cyanide removal from alkaline washing wastewater;

[0036] Figure 9 The removal efficiency of free cyanide in different systems (a) and the reaction rate constant (b) are shown.

[0037] Figure 10 The removal efficiency of ferricyanide in different systems (a) and the reaction rate constant (b) are shown.

[0038] Figure 11 Fe(CN)6 in the UV / peracetic acid and UV / hydrogen peroxide systems 3- and CN - The concentration changes. Detailed Implementation

[0039] This invention provides a method for degrading cyanide-containing wastewater, comprising the following steps:

[0040] The cyanide-containing wastewater includes two types: wastewater containing free cyanide and wastewater containing cyanide complexes.

[0041] When the cyanide-containing wastewater is cyanide complex-containing wastewater, the method for degrading the cyanide-containing wastewater includes the following steps: subjecting the cyanide-containing wastewater to a photolysis reaction and a first oxidation reaction sequentially under conditions of pH 9.5 to 13.0; both the photolysis reaction and the first oxidation reaction are carried out under ultraviolet light irradiation; the photolysis reaction takes 0.5 to 3 hours.

[0042] When the cyanide-containing wastewater is wastewater containing free cyanide, the method for degrading the cyanide-containing wastewater includes the following steps: subjecting the cyanide-containing wastewater to a second oxidation reaction sequentially under conditions of pH value of 9.5 to 13.0; the oxidant for both the first and second oxidation reactions is a solution of peracetic acid; and the second oxidation reaction is carried out under ultraviolet light irradiation.

[0043] When the cyanide-containing wastewater is cyanide complex wastewater, the method for degrading the cyanide-containing wastewater includes the following steps: subjecting the cyanide-containing wastewater to photolysis and a first oxidation reaction sequentially under conditions of pH 9.5 to 13.0.

[0044] In one embodiment of the present invention, the wastewater containing cyanide complexes may include alkaline washing wastewater from smelting slag. In another embodiment of the present invention, CN... - The concentration of cyanide complex in the cyanide-containing wastewater can be 1–100 mg / L; as one embodiment of the present invention, the pH adjusting agent for adjusting the cyanide-containing wastewater includes sodium hydroxide or sulfuric acid.

[0045] In one embodiment of the present invention, both the photolysis reaction and the first oxidation reaction are carried out under ultraviolet light irradiation; the photolysis reaction takes 0.5 to 3 hours.

[0046] In one embodiment of the present invention, the wavelength of the ultraviolet light can be 200–450 nm, specifically 254 nm; the light intensity can be 0.85–100 mW / cm². 2 Specifically, it can be 0.85mW / cm 2 The temperature of the photolysis reaction can be 25–30°C; the time of the photolysis reaction can be 0.5–3 hours, specifically 0.5 hours, 1 hour, 2 hours, or 3 hours. In one embodiment of the invention, the photolysis reaction can be carried out under stirring conditions; the stirring speed can be 200–1000 rpm.

[0047] In one embodiment of the present invention, the oxidant in the first oxidation reaction is a solution of peracetic acid. In another embodiment of the present invention, the concentration of the peracetic acid solution can be 0.1–5 g / L, specifically 1–2 g / L; the mass ratio of peracetic acid to the cyanide complex can be 10–40:1, specifically 10:1, 20:1, 30:1, or 40:1.

[0048] In one embodiment of the present invention, the temperature of the first oxidation reaction can be 25–30°C, and the time can be 4–6 hours. In another embodiment of the present invention, the first oxidation reaction can be carried out under stirring conditions; the stirring speed can be 200–1000 rpm.

[0049] When the cyanide-containing wastewater is wastewater containing free cyanide, the method for degrading the cyanide-containing wastewater includes the following steps: subjecting the cyanide-containing wastewater to a second oxidation reaction sequentially under conditions of pH 9.5 to 13.0; the oxidant for the second oxidation reaction is a solution of peracetic acid; and the second oxidation reaction is carried out under ultraviolet light irradiation.

[0050] In one embodiment of the present invention, when the cyanide-containing wastewater is wastewater containing free cyanide, the concentration of free cyanide in the cyanide-containing wastewater can be 1 to 100 mg / L.

[0051] In one embodiment of the present invention, during the second oxidation reaction, the mass ratio of peracetic acid to free cyanide can be 2 to 5:1; the wavelength and intensity parameters of the ultraviolet light are preferably the same as those of the first oxidation reaction, and will not be repeated here. In another embodiment of the present invention, the temperature of the second oxidation reaction can be 25 to 30°C, and the time can be 10 min to 6 h.

[0052] To further illustrate the present invention, the following detailed description of the invention's solutions, in conjunction with the accompanying drawings and embodiments, is provided, but should not be construed as limiting the scope of protection of the present invention.

[0053] Reagents and devices involved in the embodiments

[0054] pH adjuster: NaOH (industrial grade, 98% purity) or H2SO4;

[0055] Standard solutions: potassium cyanide standard solution, potassium ferricyanide solution, initial cyanide concentration (in CN). - (Calculated), potassium cyanide standard solution (5-50 mg / L), potassium ferricyanide standard solution (50 mg / L).

[0056] Example 1

[0057] 1. Ultraviolet light-driven dissociation of ferricyanide under alkaline conditions

[0058] ① Alkaline aqueous solution: Adjust the pH of the 50 mg / L potassium ferricyanide standard solution to 10.5-12.0 with sodium hydroxide.

[0059] ② Photolysis of ferricyanide (carried out in an ultraviolet reaction apparatus equipped with a magnetic stirrer (200 rpm): 25 mL of alkaline aqueous solution (initial pH adjusted to 10.5, 11, 11.5, and 12 respectively) was added to a 50 mL quartz reactor, and after sealing, ultraviolet irradiation was performed (254 nm ultraviolet light source (light intensity 0.85 mW·cm⁻¹)). -2 Samples were taken at set time points to determine the concentration of ferricyanide in the solution.

[0060] The results showed that under alkaline conditions, 254 nm ultraviolet irradiation could efficiently achieve ligand dissociation of ferricyanides. This process was mainly driven by direct photolysis, with negligible contribution from hydroxyl radicals (·OH). Furthermore, the dissociation efficiency showed a weak but stable increasing trend with increasing pH. After 1.5 h of irradiation, [Fe(CN)6] under various pH conditions... 3-The dissociation rates all exceeded 87%, fully demonstrating the powerful direct dissociation ability of ultraviolet light on ferrocyanide. Although UV photolysis technology alone can efficiently dissociate ferrocyanide and break down complexes, its ability to oxidize and degrade the released free cyanide is significantly insufficient (total cyanide (ferrocyanide and dissociated free cyanide) removal rate <35%), making it difficult to achieve complete mineralization of cyanide. A stronger oxidation pathway needs to be coupled to jointly drive the deep transformation of cyanide to low-toxicity / non-toxic forms.

[0061] Example 2

[0062] 1. To investigate the efficiency of UV-activated peracetic acid in degrading free cyanide, optimize process parameters (PAA addition amount, pH value) and obtain the optimal process parameters for free cyanide degradation.

[0063] ① Effect of peracetic acid addition on the degradation of free cyanide

[0064] Add potassium cyanide solution to a 50 mL quartz glass tube to control the initial concentration of free cyanide (in CN). - The concentration of peracetic acid (calculated as 10 mg / L) was added sequentially, followed by sodium hydroxide, maintaining the initial pH at 12. The concentrations of peracetic acid in the system were 0 mg / L, 5 mg / L, 10 mg / L, 20 mg / L, and 50 mg / L, with a total reaction volume of 25 mL. The tube was sealed and plugged, and then placed in a UV apparatus (254 nm UV light source, 0.85 mW·cm²) for the reaction. -2 The rotation speed is 200 rpm. After a set time, the quartz glass tube is removed and the content of free cyanide is measured.

[0065] The results show that: Figure 1 As shown, when the amount of peracetic acid added increased from 0 to 20 mg / L, under pH 12 conditions, the removal rate of free cyanide increased from 19.37% to 100% after 1 hour of reaction. The pseudo-first-order reaction rate constant (Kobs) for free cyanide degradation increased from 3.09 × 10⁻⁶. -3 min -1 Increased to 1.36 × 10 -1 min -1 When the amount of peracetic acid added is further increased to 50 mg / L, the removal rate of the pseudo-first-order reaction rate constant of free cyanide degradation is directly proportional to the amount of peracetic acid added.

[0066] ② The effect of initial pH on the degradation of free cyanide

[0067] The pKa value of the free cyanide is 9.20. When the solution pH is less than 9.20, the free cyanide mainly exists as HCN; when the solution pH is greater than 9.20, the free cyanide mainly exists as CN. - It exists in a certain form. Therefore, the study is conducted within the alkaline range.

[0068] UV system test: Add potassium cyanide solution to a 50 mL quartz glass tube to control the initial concentration of free cyanide (in CN). - The concentration of the solution was 10 mg / L. The initial pH was adjusted to 10.5, 11, 11.5, and 12 using sodium hydroxide and sulfuric acid, respectively. The tube was then sealed and capped. The quartz glass tube was placed in an ultraviolet (UV) apparatus for the reaction (254 nm UV light source, 0.85 mW·cm²). -2 The rotation speed is 200 rpm. After a set time, the quartz glass tube is removed and the content of free cyanide is measured.

[0069] In the UV / PAA system: add potassium cyanide solution to a 50 mL quartz glass tube to control the initial concentration of free cyanide (in CN). - The concentration of peracetic acid (CPA) was 10 mg / L. Peracetic acid was added to control the concentration of peracetic acid in the system to 20 mg / L. The initial pH was then adjusted to 10.5, 11, 11.5, and 12 using sodium hydroxide and sulfuric acid, respectively. The total reaction volume was 25 mL. The tube was sealed and stoppered, and the quartz glass tube was placed in a UV apparatus for reaction at 200 rpm. After the set time, the quartz glass tube was removed, and the content of free cyanide was measured.

[0070] Experimental results Figure 2 As shown, in the UV system, at pH values ​​of 10.5, 11, 11.5, and 12, the removal rates of free cyanide after 1 hour of reaction were 18.10%, 18.61%, 18.45%, and 17.91%, respectively, indicating that UV light alone has a very limited effect on the removal of free cyanide. The pseudo-first-order kinetic rate constant (Kobs) for the degradation of free cyanide is 3.09 × 10⁻⁶. - 3 min -1 3.19×10 -3 min -1 3.15×10 -3 min -1 3.13×10 -3 min -1 This indicates that the removal of free cyanide by ultraviolet light is not affected by pH changes.

[0071] In the UV / PAA system, when the amount of peracetic acid added was 20 mg / L, the removal rate of free cyanide was close to 100% within the studied pH range, and the pseudo-first-order kinetic rate constant for the degradation of free cyanide was 1.40 × 10⁻⁶. -1 min -1 1.39×10 -1 min -1 1.38×10 -1min -1 1.36×10 -1 min -1 This indicates that pH changes have no significant effect on the degradation of free cyanide in the UV / PAA system. Detailed kinetic equations are shown in Table 1.

[0072] Table 1. Kinetic equations for the degradation of free cyanide under different pH conditions.

[0073]

[0074]

[0075] 2. The efficiency of UV-activated peracetic acid in degrading ferricyanide

[0076] The effects of peracetic acid addition amount, initial pH on ferricyanide degradation, and the effect of peracetic acid addition time point on ferricyanide degradation were investigated to further optimize process parameters.

[0077] ① The effect of peracetic acid addition on ferricyanide degradation.

[0078] Add potassium ferricyanide solution to a 50 mL quartz glass tube, then add peracetic acid and sodium hydroxide sequentially, controlling the initial concentration of ferricyanide (in CN). - The concentration of peracetic acid in the system was 50 mg / L, the initial pH was 12, and the concentrations of peracetic acid in the system were 0.05 g / L, 0.1 g / L, 0.5 g / L, 1 g / L, 2.5 g / L, and 10 g / L, with a total reaction volume of 25 mL. The system was sealed and plugged, and the quartz glass tube was placed in a UV apparatus for the reaction (254 nm UV light source, intensity 0.85 mW·cm²). -2 The rotation speed was 200 rpm. The quartz glass tube was removed after a set time, and the total cyanide content was measured.

[0079] The results showed that the removal rate of ferricyanide first increased and then decreased with increasing peracetic acid dosage. The experiment investigated the effect of different peracetic acid dosages on ferricyanide degradation. The experimental results are as follows: Figure 3 As shown, when the amount of peracetic acid added was increased to 1 g / L, under pH 12 conditions, the removal rate of ferricyanide increased to 91.50% after 12 hours of reaction. The pseudo-first-order reaction rate constant for cyanide degradation was 2.08 × 10⁻⁶. -1 h -1 However, when the amount of peracetic acid added was further increased to 10 g / L, the removal rate of ferricyanide decreased to 78.24%, and the pseudo-first-order reaction rate constant Kobs for ferricyanide degradation decreased to 1.26 × 10⁻⁶. -1 h -1When excess peracetic acid is added to the system, the generation of free radicals increases significantly. At this point, the reactions between free radicals and between free radicals and peracetic acid are significantly enhanced, leading to a large consumption of free radicals and a decrease in their effective utilization rate. Therefore, the degradation effect of ferricyanide cannot be further optimized. Furthermore, excess peracetic acid competes with ferricyanide for ultraviolet light, significantly reducing the number of ultraviolet photons that ferricyanide can absorb, thereby inhibiting its photolysis reaction.

[0080] ②The effect of initial pH on the degradation of ferricyanide.

[0081] Add potassium ferricyanide solution to a 50 mL quartz glass tube to control the initial concentration of ferricyanide (in CN). - The concentration of peracetic acid (calculated as 50 mg / L) was 50 mg / L. Peracetic acid was added at a concentration of 1 g / L. The initial pH was adjusted to 10.5, 11, 11.5, and 12 using sodium hydroxide and sulfuric acid, respectively. The total reaction volume was 25 mL. The tube was sealed and stoppered, and then placed in a UV apparatus (254 nm UV light source, 0.85 mW·cm²) for the reaction. -2 The rotation speed was 200 rpm. After a set time, the quartz glass tube was removed, and the contents of free cyanide, ferricyanide, and total cyanide were measured.

[0082] The results showed that as pH increased, the photolysis rate of ferricyanide gradually accelerated, and the removal rate of total cyanide (ferricyanide and free cyanide) also increased accordingly. Experimental results are as follows... Figure 4 As shown, under ultraviolet light, at pH values ​​of 10.5, 11, 11.5, and 12, the photolysis rates of ferricyanide after 12 hours of reaction were 98.18%, 98.14%, 99.14%, and 99.24%, respectively, with pseudo-first-order kinetic rate constants of 7.93 × 10⁻⁶. -1 h -1 8.25×10 -1 h -1 8.82×10 -1 h -1 8.83×10 -1 h -1 The removal rates of total cyanide (ferricyanide and free cyanide) were 56.98%, 66.83%, 79.35%, and 91.50%, respectively, and the pseudo-first-order kinetic rate constants for cyanide degradation were 6.29 × 10⁻⁶. -2 h -1 8.45×10 -2 h -1 1.26×10 -1 h -1 2.08×10 -1 h -1The results suggest that the above findings may be related to the differences in the photolysis rate of ferricyanide under different pH conditions.

[0083] ③ The effect of the time point of peracetic acid addition on the degradation of ferricyanide.

[0084] The experiment investigated the effect of different peracetic acid addition times on the degradation of ferricyanide.

[0085] First, potassium ferricyanide solution was added to a 50 mL quartz glass tube. Different peracetic acid addition time points were set (0 h, 0.5 h, 1 h, 1.5 h, 2 h). Then, peracetic acid and sodium hydroxide were added sequentially, controlling the initial cyanide concentration (in CN). - The concentration of peracetic acid (to ferricyanide) was 50 mg / L, the initial pH was 12, the mass ratio of peracetic acid to ferricyanide was 20:1, and the total reaction volume was 25 mL. The tube was sealed and stoppered, and then placed in a UV apparatus (254 nm UV light source, 0.85 mW·cm²) for the reaction. -2 The rotation speed is 200 rpm. After a set time, the quartz glass tube is removed and the content of free cyanide is measured.

[0086] The results show that: Figure 5 As shown, under a total reaction time of 6 hours, when the time point for adding peracetic acid was extended from 0 hours to 1.5 hours, the removal rate of total cyanide (ferricyanide and free cyanide) increased from 77.25% to nearly 100%. When the time point for adding peracetic acid was further extended to 2 hours, the removal rate of total cyanide (ferricyanide and free cyanide) remained unchanged at 100%. The reason for these results is that, without the interference of peracetic acid, ferricyanide is almost completely photolyzed within 1.5 hours, at which point the cyanide in the solution is mainly CN. - Due to CN - The reaction rate with free radicals is very fast and it does not compete with peracetic acid for ultraviolet photons, making CN... - It can be completely removed in a relatively short time. Therefore, the optimized degradation process of ferricyanide after the addition time of peracetic acid is as follows: firstly, ultraviolet light is used to photodecompose all the ferricyanide into CN. - Peracetic acid was then added, causing the free radicals generated by the peracetic acid to react with CN. - The rapid reaction improves the removal efficiency of ferricyanide and also shortens the reaction time.

[0087] 3. Optimization of UV-activated peracetic acid degradation of cyanide tailings alkaline washing wastewater

[0088] ① Alkaline washing wastewater from cyanide tailings of gold concentrate in the gold smelting industry (referred to as alkaline washing wastewater): The cyanide in the gold concentrate cyanide tailings is transferred to an alkaline solution using the alkaline leaching method in ISO 11262-2011, resulting in alkaline washing wastewater; the alkaline washing wastewater mainly contains ferrocyanide (Fe(CN)6). 3- (accounting for >90%) and a small amount of free cyanide (CN) - Total cyanide (T) CN ): 46.45 mg / L; Ferricyanide (Fe(CN)6) 3- 44.80 mg / L; pH: 13;

[0089] ② The effect of ultraviolet light on the speciation of cyanide in alkaline washing wastewater

[0090] Take 20 mL of alkaline washing wastewater and place it in a 50 mL quartz glass tube. Seal the tube and stopper it. Place the quartz glass tube in an ultraviolet (UV) apparatus to carry out the reaction (254 nm UV light source, 0.85 mW·cm²). -2 The rotation speed was 200 rpm. After the set time, the quartz glass tube was removed, the solution was transferred to a brown plastic bottle and placed in a 4°C refrigerator. Finally, the contents of total cyanide, free cyanide and ferricyanide were determined.

[0091] The results showed that ultraviolet radiation was the main driving force behind the speciation of ferricyanide in alkaline washing wastewater. Because alkaline washing wastewater contains various metal ions and other impurity ions, these substances interfere with the absorption of ultraviolet light by ferricyanide, thus delaying its photolysis process. Therefore, ferricyanide in alkaline washing wastewater requires 2 hours to be completely photolyzed.

[0092] Depend on Figure 6 It can be seen that under ultraviolet irradiation alone, the total cyanide content in the alkaline washing wastewater changed very little, decreasing only slightly from 46.45 mg / L to 44.09 mg / L after 3 hours of reaction. Simultaneously, ferricyanide rapidly underwent photolysis to generate CN. - After 2 hours of reaction, the ferricyanide concentration dropped sharply from an initial 44.80 mg / L to 1.34 mg / L, while the corresponding CN concentration increased. - The content increased significantly from 1.08 mg / L to 43.26 mg / L. Subsequently, as the reaction proceeded, the ferricyanide content tended to stabilize.

[0093] ③ The effect of peracetic acid addition on the degradation of cyanide tailings alkaline washing wastewater

[0094] Take 20 mL of alkaline washing wastewater and place it in a 50 mL quartz glass tube. Add peracetic acid, controlling the peracetic acid concentration in the system to be 0.1 g / L, 0.5 g / L, 1 g / L, and 2 g / L. The total reaction volume is 25 mL. Seal and stopper the tube, and place it in an ultraviolet (UV) apparatus for the reaction (254 nm UV light source, 0.85 mW·cm²). -2 The total cyanide content was determined by rotating the instrument at 200 rpm.

[0095] The results show that, due to the large amount of pyrite in the tailings, the sulfur element readily reacts with CN. - Combine to form SCN - Therefore, alkaline washing wastewater contains a large amount of SCN. - SO4 2- Impurity ions. Due to SCN - It competes with cyanide for reactive species such as ·OH, thereby increasing the consumption of peracetic acid, inhibiting the degradation of cyanide, and resulting in the need for a higher concentration of peracetic acid to completely remove total cyanide from alkaline washing wastewater.

[0096] like Figure 7 As shown, when peracetic acid was added at a time point of 2 hours, the removal rate of total cyanide in the alkaline washing wastewater gradually increased with the increase of peracetic acid dosage. When the peracetic acid concentration reached 2 g / L, the removal rate of total cyanide almost reached 100%. In contrast, a pure ferricyanide solution with an initial concentration of 50 mg / L only required 1 g / L of peracetic acid to completely remove the cyanide.

[0097] ④ The effect of the timing of peracetic acid addition on the degradation of cyanide tailings alkaline washing wastewater.

[0098] The degradation effect of total cyanide in alkaline washing wastewater was compared under two operating conditions: PAA addition time points of 0h and 2h, to verify the optimization of degradation effect by delayed addition.

[0099] First, potassium ferricyanide solution was added to a 50 mL quartz glass tube. Different peracetic acid addition time points were set (0 h and 2 h). Then, peracetic acid and sodium hydroxide were added sequentially, controlling the initial cyanide concentration (in CN). - The concentration of peracetic acid (to ferricyanide) was 50 mg / L, the initial pH was 12, the mass ratio of peracetic acid to ferricyanide was 20:1, the total reaction volume was 25 mL, the tube was sealed and capped, and the quartz glass tube was placed in an ultraviolet light device (254 nm ultraviolet light source, light intensity 0.85 mW·cm²) for the reaction. -2 The total cyanide content was determined by rotating the instrument at 200 rpm.

[0100] The results showed that optimizing the timing of peracetic acid addition had a significant advantage in improving the removal efficiency of total cyanide in alkaline washing wastewater. Figure 8As shown, in the UV / PAA system, when peracetic acid was added at 0 h, the removal rate of total cyanide in the alkaline washing wastewater was only 82.49% after 10 h of reaction. However, when peracetic acid was added at 2 h, the removal rate of total cyanide significantly increased, reaching almost 100%. Furthermore, the pH value at the reaction endpoint was 11.92, which not only effectively prevented the escape of the highly toxic substance HCN, but also allowed for the recycling of the alkaline solution after the reaction, thus saving on reagent costs.

[0101] In summary, this invention optimizes the UV / PAA system by adjusting the UV irradiation duration, pH level, oxidant dosage, and addition sequence to arrive at the optimal solution. This invention has been validated in treating free cyanide model wastewater, ferricyanide model wastewater, and alkaline washing wastewater from actual cyanide tailings, significantly improving ferricyanide removal efficiency. Secondly, it achieves highly efficient cyanide degradation under strongly alkaline conditions, overcoming the limitations of the UV / PAA process under neutral or acidic conditions. Furthermore, UV / PAA effectively inhibits self-acidification during cyanide degradation, with the pH change throughout the reaction process being less than 0.3, avoiding the risk of leaching of the highly toxic substance HCN due to pH fluctuations. Finally, the UV / PAA process effectively disrupts the stable coordination bonds (Fe-CN) of ferricyanide, achieving deep mineralization of ferricyanide, providing a new approach and method for treating cyanide-containing wastewater, and offering significant economic and environmental benefits.

[0102] Comparative Example

[0103] To investigate the degradation of free cyanide and ferricyanide in different systems, five reaction systems were set up: UV, peracetic acid, hydrogen peroxide, UV / PAA, and UV / hydrogen peroxide. The degradation of free cyanide and ferricyanide in different systems was evaluated.

[0104] ① Degradation of free cyanide in different systems

[0105] The ultraviolet system is as follows: potassium cyanide concentration (in CN). - The concentration of the substance was 10 mg / L, the pH was 12, and the UV light source was 254 nm (intensity 0.85 mW·cm). -2 It does not contain peracetic acid.

[0106] The peracetic acid system is as follows: only peracetic acid is added, no light is used, the peracetic acid concentration is 20 mg / L, and the potassium cyanide concentration (as CN) is... - The concentration of the sample was 10 mg / L, and the initial pH was 12.

[0107] The hydrogen peroxide system is as follows: only hydrogen peroxide is added, with a hydrogen peroxide concentration of 22 mg / L, and potassium cyanide concentration (as CN). - The concentration of the sample was 10 mg / L, and the initial pH was 12.

[0108] The UV / PAA system is as follows: First, add potassium cyanide solution (10 mg / L, with CN...) - (Calculation), then add PAA solution to control the system concentration to 20 mg / L, and finally add sodium hydroxide to adjust the pH to 12; irradiate the reaction apparatus with ultraviolet light (254 nm ultraviolet light source (light intensity 0.85 mW·cm). -2 The reaction begins.

[0109] The UV / hydrogen peroxide system is as follows: First, add potassium cyanide solution (10 mg / L, with CN) - (Calculation), then add hydrogen peroxide to control its concentration at 22 mg / L, and finally add sodium hydroxide to adjust the pH to 12. Irradiate the reaction apparatus with ultraviolet light (254 nm ultraviolet light source (light intensity 0.85 mW·cm). -2 The reaction begins.

[0110] Figure 9 Removal efficiency of free cyanide in different systems (a) and reaction rate constant (b); from Figure 9 It can be seen that under ultraviolet light, the removal rate of free cyanide is 17.91%, and its pseudo-first-order reaction rate constant (K) is... obs The value is 3.13 × 10 -3 min -1 Ultraviolet light has a certain effect on the degradation of free cyanide, possibly because ultraviolet radiation can excite free cyanide to a state that is easier to degrade than the ground state. The removal rates of free cyanide in the peracetic acid and hydrogen peroxide systems were 30.80% and 31.12%, respectively, and the pseudo-first-order reaction rate constants for cyanide degradation were 5.93 × 10⁻⁶. -3 min -1 5.87×10 -3 min -1 Experimental results show that the removal efficiency of free cyanide is almost the same in both systems, but both are superior to the UV system.

[0111] When ultraviolet light and an oxidant are combined, the removal rate of free cyanide is significantly improved. The removal rates of free cyanide in both the UV / PAA system and the UV / hydrogen peroxide system are close to 100%, and the pseudo-first-order reaction rate constants for cyanide degradation are 1.36 × 10⁻⁶. -1 min -1 and 1.33×10 -1 min -1The catalytic effect of ultraviolet light on oxidants, specifically ultraviolet-activated peracetic acid or hydrogen peroxide, generates a large number of free radicals, which promote the removal of free cyanide. Compared with other cyanide removal technologies, both the UV / PAA and UV / hydrogen peroxide systems can efficiently degrade free cyanide.

[0112] ② Degradation of ferricyanide in different systems

[0113] The ultraviolet system is as follows: potassium ferricyanide concentration (in CN). - The concentration of the substance was 50 mg / L, the pH was 12, and the UV light source was 254 nm (intensity 0.85 mW·cm). -2 It does not contain peracetic acid.

[0114] The peracetic acid system is as follows: only peracetic acid is added, no light is applied, the peracetic acid concentration is 1 g / L, and the potassium ferricyanide concentration (as CN) is... - The concentration of the sample was 50 mg / L, and the initial pH was 12.

[0115] The hydrogen peroxide system is as follows: only hydrogen peroxide is added, with a hydrogen peroxide concentration of 1.13 g / L, and potassium ferricyanide concentration (as CN). - The concentration of the sample was 50 mg / L, and the initial pH was 12.

[0116] The UV / PAA system is as follows: first add potassium ferricyanide solution (in CN... - The concentration was calculated to be 50 mg / L. Then, PAA solution was added to control the system concentration to 1 g / L. Finally, sodium hydroxide was added to adjust the pH to 12. The reaction apparatus was then irradiated with ultraviolet light (254 nm ultraviolet light source, light intensity 0.85 mW·cm). -2 The reaction begins.

[0117] The UV / hydrogen peroxide system is as follows: first add potassium ferricyanide solution (in CN...) - The concentration was calculated to be 50 mg / L. Then hydrogen peroxide was added to control its concentration at 1.13 g / L. Finally, sodium hydroxide was added to adjust the pH to 12. The reaction apparatus was then irradiated with ultraviolet light (254 nm ultraviolet light source, light intensity 0.85 mW·cm). -2 The reaction begins.

[0118] Figure 10 To illustrate the removal efficiency (a) and reaction rate constant (b) of ferricyanide in different systems, from... Figure 10 It can be seen that in the ultraviolet light system, the cyanide removal rate (based on total cyanide) after 12 hours of reaction is 31.91%, and the pseudo-first-order reaction rate constant Kobs for cyanide degradation is 3.14 × 10⁻⁶. -2 h -1Compared to free cyanide, ultraviolet light showed better removal efficiency for ferricyanide, which may be related to the duration of ultraviolet irradiation. The removal rates of ferricyanide in the peracetic acid and hydrogen peroxide systems were 8.17% and 9.94%, respectively, with pseudo-first-order rate constants (Kobs) for cyanide degradation of 7.20 × 10⁻⁶. -3 h -1 8.30×10 -3 h -1 Unlike the removal of free cyanide, peracetic acid and hydrogen peroxide are less effective than ultraviolet light in removing ferricyanide. This may be because ferricyanide is chemically very stable, and ordinary oxidants are unlikely to oxidize and decompose it.

[0119] When ultraviolet light and an oxidant are combined, the removal efficiency of ferricyanide is significantly improved. The removal rates of ferricyanide in the UV / PAA and UV / hydrogen peroxide systems are 91.50% and 66.94%, respectively, and the pseudo-first-order reaction rate constants (Kobs) for cyanide degradation are 2.08 × 10⁻⁶. -1 h -1 and 9.82×10 -2 h -1 Experimental results show that there are significant differences in the removal efficiency of ferricyanide between the UV / PAA and UV / hydrogen peroxide systems. The degradation process of ferricyanide mainly consists of two steps: first, under the action of ultraviolet light, ferricyanide decomposes and releases CN. - Subsequently, CN - It is further oxidized by reactive species such as free radicals to produce CNO. - Such substances. Therefore, the reasons for the above results can be mainly attributed to two categories: one is the difference in the photolysis rate of ferricyanide, and the other is CN. - Differences in oxidation rates.

[0120] To analyze the reasons for the above results, the concentrations of Fe(CN)6 in the UV / PAA system and the UV / hydrogen peroxide system were experimentally determined. 3- and CN - The concentration changes are shown in the figure. Figure 11 After 12 hours of reaction, the photolysis rates of ferricyanide in the UV / PAA and UV / hydrogen peroxide systems were 99.24% and 99.52%, respectively. The results indicate that the photolysis effect of ferricyanide is almost identical in different systems, thus eliminating the influence of differences in the photolysis rate of ferricyanide. Further analysis revealed that CN in the UV / hydrogen peroxide system... - The generation amount of CN was significantly higher in the UV / PAA system than in the UV / PAA system, indicating that CN was generated more abundantly in the UV / PAA system. - The degradation effect is better. Based on the above analysis, it can be considered that the main reason for the difference in ferricyanide degradation effect is the different CN content in the different systems. -Differences between oxidation rates.

[0121] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for degrading cyanide-containing wastewater, characterized in that, The cyanide-containing wastewater is divided into two categories: wastewater containing free cyanide and wastewater containing cyanide complexes. When the cyanide-containing wastewater is cyanide complex-containing wastewater, the method for degrading the cyanide-containing wastewater includes the following steps: The cyanide-containing wastewater was subjected to photolysis and primary oxidation reactions sequentially under conditions of pH 9.5–13.

0. Both the photolysis reaction and the first oxidation reaction are carried out under ultraviolet light irradiation; the photolysis reaction takes 0.5 to 3 hours. When the cyanide-containing wastewater is wastewater containing free cyanide, the method for degrading the cyanide-containing wastewater includes the following steps: The cyanide-containing wastewater was subjected to a second oxidation reaction sequentially under conditions of pH 9.5–13.0; The oxidant in both the first and second oxidation reactions is a solution of peracetic acid; The second oxidation reaction is carried out under ultraviolet light irradiation.

2. The method as described in claim 1, characterized in that, The photolysis reaction is carried out at a temperature of 10–35°C, and the ultraviolet light has a wavelength of 200–450 nm and an intensity of 0.85–100 mW / cm². 2 .

3. The method as described in claim 1, characterized in that, The photolysis reaction, the first oxidation reaction, and the second oxidation reaction are carried out under stirring conditions; the stirring speed is 200-1000 rpm.

4. The method as described in claim 1, characterized in that, The temperature of the first oxidation reaction is 25-30℃ and the time is 4-6h; the temperature of the second oxidation reaction is 25-30℃ and the time is 10min-6h.

5. The method as described in claim 1, characterized in that, The cyanide complex includes one or more of ferrocyanide, ferricyanide, and cobalt cyanide.

6. The method as described in claim 1, characterized in that, The concentration of the peracetic acid solution is 0.1–5 g / L.

7. The method as described in claim 1, characterized in that, When the cyanide-containing wastewater is wastewater containing free cyanide, the mass ratio of peracetic acid to free cyanide is 2 to 5:

1.

8. The method as described in claim 1, characterized in that, When the cyanide-containing wastewater is cyanide complex-containing wastewater, the mass ratio of peracetic acid to cyanide complex is 10 to 40:

1.

9. The method as described in claim 1, characterized in that, When the cyanide-containing wastewater is cyanide complex-containing wastewater, CN - The concentration of cyanide complex in the cyanide-containing wastewater is calculated to be 1–100 mg / L.

10. The method as described in claim 1, characterized in that, When the cyanide-containing wastewater is wastewater containing free cyanide, the concentration of free cyanide in the cyanide-containing wastewater is 1-100 mg / L.

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