A treatment process for cyanide-containing wastewater

Abstract

The application provides a treatment process of cyanide-containing wastewater, and belongs to the technical field of industrial wastewater treatment. The process comprises the following steps: firstly, pretreating the cyanide-containing wastewater to obtain cyanide-containing pretreated effluent; then, mixing the cyanide-containing pretreated effluent with passivation wastewater; and finally, sequentially performing low-chlorine pre-oxidation, composite catalytic complex-oxidation, residual chlorine regulation, heavy metal instant capture and coagulation sedimentation treatment. The process can improve the removal stability of complex cyanide and copper, nickel, zinc and other heavy metals, reduce the consumption of oxidants and residual chlorine, and improve the adaptability of subsequent biochemical treatment.

Description

Technical Field

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

[0002] In electroplating, metal surface treatment, and passivation processes, wastewater containing cyanide, chromium, passivation, nickel, copper, zinc, and complexing agents is typically generated. These wastewaters originate from different sources and have significantly different pollutant compositions. If they are mixed directly without separation, it can easily lead to problems such as the release of toxic gases, interference between redox reactions, complex heavy metal complexation, and reduced efficiency of subsequent precipitation treatment. Therefore, in engineering practice, different pretreatment units are usually set up according to the wastewater source and the main pollutant types before the pretreated wastewater, which is then ready for comprehensive treatment, is sent to the subsequent comprehensive treatment system.

[0003] Cyanide-containing wastewater typically originates from cyanide-containing electroplating, cyanide-containing cleaning, cyanide-containing stripping, cyanide-containing rinsing, or cyanide-containing surface treatment processes. In addition to free cyanide, this wastewater may also contain metallic cyanide complexes such as copper-cyanide complexes, nickel-cyanide complexes, and zinc-cyanide complexes. Due to the high toxicity of cyanide-containing wastewater and the risk of generating hydrogen cyanide gas under inappropriate pH conditions, it is usually collected separately and pretreated in engineering practice. The existing "Technical Specification for Electroplating Wastewater Treatment Engineering" (HJ 2002-2010) also stipulates that cyanide-containing wastewater should be treated separately and should not be mixed with other wastewater before treatment; after treatment and when the free cyanide content reaches the control requirements, the cyanide-containing wastewater can enter a mixed wastewater treatment system for further removal of heavy metal ions.

[0004] Pretreatment typically includes cyanide removal followed by heavy metal capture, coagulation, and sedimentation to reduce the concentration of free cyanide and remove some heavy metal ions and suspended solids. The supernatant obtained after the above pretreatment is generally referred to as cyanide-containing pretreated effluent. This cyanide-containing pretreated effluent may still contain residual complexed cyanide, copper, nickel, zinc, and other heavy metal ions, as well as residual chlorine and organic pollutants. Its water quality usually does not meet the requirements for direct discharge or direct entry into a biological treatment system, and therefore still needs to be further treated by a subsequent integrated treatment system.

[0005] Chinese patent publication number CN104291493B discloses a method for treating electroplating wastewater. The method involves collecting general electroplating wastewater, cyanide-containing electroplating wastewater, and chromium-containing electroplating wastewater separately. The cyanide-containing wastewater undergoes cyanide removal treatment to obtain pretreated cyanide-containing electroplating wastewater. This pretreated wastewater is then passed into the general electroplating wastewater system to form a combined electroplating wastewater system for further treatment. This scheme essentially involves pretreating cyanide-containing wastewater before incorporating it into a combined wastewater system for subsequent treatment.

[0006] Passivation wastewater typically originates from trivalent chromium passivation, hexavalent chromium passivation, post-passivation cleaning, sealing cleaning, passivation rinsing, or related washing processes. This type of wastewater is an important component of the electroplating and surface treatment wastewater system.

[0007] Publicly available technologies indicate that, in addition to chromium ions, passivation wastewater may also contain heavy metal ions such as copper, nickel, and zinc, as well as complex components such as fluoride ions, organic acid complexing agents, and organic additives. For example, Chinese patent publication number CN110642425A discloses a method for treating trivalent chromium passivation wastewater, which explicitly states that the passivation wastewater contains trivalent chromium ions, zinc ions, hydrofluoric acid, and carboxylic acids. Furthermore, Chinese patent publication number CN114751582B also indicates that electroplating mixed wastewater may include trivalent chromium passivation wastewater, hexavalent chromium passivation wastewater, and electroplating wastewater containing copper, nickel, and zinc, and may contain complexing agents such as citrates, tartrates, and organic amines.

[0008] Therefore, passivation wastewater is usually characterized by a variety of heavy metal ions, high content of complexing agents, and complex water composition. Its treatment process usually requires a combination of processes such as oxidation-reduction regulation, heavy metal capture, coagulation and sedimentation, and subsequent biochemical treatment.

[0009] For surface treatment wastewater treatment plants equipped with passivation wastewater treatment units, the cyanide-containing pretreatment effluent and passivation wastewater share certain commonalities in their subsequent treatment requirements, both potentially involving heavy metal removal, complex breakdown, organic pollutant degradation, and suspended solids removal. Therefore, in practical engineering, the cyanide-containing pretreatment effluent is typically introduced into the front end of the passivation system and mixed with the passivation wastewater for unified treatment. On the one hand, this allows the existing large-volume integrated treatment unit to continue removing residual heavy metals, complexed pollutants, and organic pollutants; on the other hand, it avoids the need to set up a separate complete end-of-pipe treatment system for the low-concentration cyanide-containing pretreatment effluent, thereby improving the overall economic efficiency and stability of the wastewater treatment system.

[0010] However, after the cyanide-containing pretreatment effluent is incorporated into the passivation system, the pollutant forms in the mixed wastewater become more complex. The residual complexed cyanide, residual chlorine, and heavy metal ions in the cyanide-containing pretreatment effluent interact with chromium, copper, nickel, zinc, fluoride ions, carboxylic acid complexing agents, organic amine complexing agents, and organic additives in the passivation wastewater. This can easily lead to problems such as insufficient further removal efficiency of complexed cyanide, inadequate precipitation of heavy metals, high oxidant consumption, and inhibition of subsequent biological treatment by residual chlorine. Existing processes such as simple alkaline chlorination to break down cyanide, conventional reduction neutralization, or ordinary coagulation and sedimentation still have insufficient capacity for the synergistic treatment of complexed cyanide and complexed heavy metals in the aforementioned mixed system.

[0011] Therefore, there is a need to provide a treatment process suitable for cyanide pretreatment effluent after it is incorporated into a passivation system, so as to improve the efficiency of breaking down complexed cyanide in mixed wastewater, reduce oxidant consumption and residual chlorine, and simultaneously improve the precipitation and removal stability of heavy metals such as copper, nickel, and zinc without significantly changing the existing main wastewater treatment process. Summary of the Invention

[0012] To address the problems of insufficient removal efficiency of complexed cyanide, unstable heavy metal removal, high oxidant consumption, and residual chlorine affecting subsequent biochemical treatment when cyanide-containing wastewater is mixed with pretreated effluent and passivation wastewater, this invention provides a treatment process for cyanide-containing wastewater that can improve the removal stability of complexed cyanide and heavy metals, reduce oxidant consumption and residual chlorine, and improve the adaptability to subsequent biochemical treatment.

[0013] To solve the above problems, the present invention adopts the following technical solution.

[0014] A process for treating cyanide-containing wastewater includes the following steps: S1. Pre-treat the cyanide-containing wastewater to obtain cyanide-containing pre-treated effluent; S2. The cyanide-containing pretreated effluent is sent to the front end of the passivation system and mixed with the passivation wastewater to obtain mixed wastewater; S3. Perform low-chlorine pre-oxidation treatment on the mixed wastewater; S4. Add persulfate to the wastewater after low-chlorine pre-oxidation and contact the wastewater with the iron-manganese composite catalyst to carry out composite catalytic complex-breaking oxidation treatment. S5. Adjust the residual chlorine in the wastewater after composite catalytic complex-breaking oxidation. S6. Add a heavy metal precipitant to the wastewater after residual chlorine control to form insoluble precipitates of heavy metal ions released after composite catalytic complex-breaking oxidation. S7. The wastewater after the addition of heavy metal precipitating agent is subjected to coagulation, flocculation and sedimentation treatment, and the sedimented effluent enters the subsequent treatment system.

[0015] Furthermore, the cyanide-containing wastewater originates from cyanide-containing electroplating, cyanide-containing cleaning, cyanide-containing stripping, cyanide-containing rinsing, or cyanide-containing surface treatment processes; The passivation wastewater originates from trivalent chromium passivation, hexavalent chromium passivation, post-passivation cleaning, closed cleaning, passivation rinsing, or passivation-related washing processes, and contains one or more of the following: chromium, copper, nickel, zinc, fluoride ions, complexing agents, organic additives, oxidizing substances, or reducing substances.

[0016] Further, in step S1, the cyanide-containing wastewater is collected separately and homogenized, then subjected to primary cyanide removal treatment, secondary cyanide removal treatment, and solid-liquid separation treatment to obtain the cyanide-containing pretreated effluent.

[0017] Furthermore, the primary cyanide removal treatment is carried out under conditions of pH 10.5–11.5 and redox potential of +300–+450 mV; The secondary cyanide removal treatment was carried out under conditions of pH 7.5–8.8 and redox potential of +550–+750 mV; Before the solid-liquid separation treatment, heavy metal precipitating agents, PAC and PAM are added to the wastewater after the secondary cyanide crushing treatment, so that some heavy metal ions and suspended solids in the wastewater precipitate and are separated.

[0018] Further, in step S2, the volume ratio of the cyanide-containing pretreated effluent to the passivation wastewater is 1:4 to 1:15; The mixed wastewater has a pH of 8.5–10.5, a total cyanide concentration of 0.5–10 mg / L, and a combined concentration of copper, nickel, and zinc of 1–30 mg / L.

[0019] Further, in step S3, the pH of the mixed wastewater is controlled to be 9.8-10.5, sodium hypochlorite is added as an oxidant, the oxidation-reduction potential is controlled to be +360-+430mV, the free residual chlorine is 0.3-0.8mg / L, and the reaction time is 20-30min; The sodium hypochlorite has an effective chlorine content of 5-12 wt%, and the dosage is 0.7-1.0 times the theoretical oxidation amount of total cyanide in the mixed wastewater.

[0020] Further, in step S4, the persulfate is one or more of sodium persulfate, potassium persulfate, and potassium peroxymonosulfate, and the dosage of the persulfate is 60-160 mg / L. The composite catalytic complex-breaking oxidation treatment was carried out under conditions of pH 9.2–9.8 and redox potential of +540–+620 mV, with a reaction time of 30–50 min.

[0021] Furthermore, the iron-manganese composite catalyst is a supported iron-manganese composite catalytic packing material; The supported iron-manganese composite catalytic packing includes a porous support and an iron-manganese composite oxidation active component supported on the surface of the porous support. The porous carrier is one or more of ceramic particles, zeolite, activated carbon, volcanic rock, or porous alumina; The iron-manganese composite oxidation active component includes at least two of FeOOH, Fe2O3, MnO2, and MnOOH, and the mass ratio of iron to manganese is 1:0.6 to 1:1.2. The iron-manganese composite oxidation active component accounts for 8% to 25% of the total mass of the supported iron-manganese composite catalytic packing.

[0022] Furthermore, the supported iron-manganese composite catalytic packing is configured as a fixed-bed catalytic packing layer; The height of the fixed-bed catalytic packing layer is 0.8–1.5 m, the packing particle size is 1–3 mm, and the empty bed contact time is 20–40 min; The persulfate is added at two points. The first addition point is located at the water inlet of the fixed bed catalytic packing layer, and the second addition point is located at 1 / 2 to 2 / 3 of the height of the fixed bed catalytic packing layer. The amount of persulfate added at the second addition point accounts for 20% to 45% of the total amount of persulfate added.

[0023] Further, in step S5, one or more of sodium bisulfite, sodium metabisulfite, and sodium thiosulfate are added to the wastewater to regulate residual chlorine, so that the free residual chlorine is reduced to below 0.2 mg / L and the oxidation-reduction potential is reduced to +220 to +360 mV. In step S6, within 5 to 30 minutes after the residual chlorine adjustment is completed, the pH of the wastewater is adjusted to 9.0 to 9.6, and a heavy metal precipitant is added for immediate heavy metal precipitant collection. The heavy metal scavenger is one or two of dithiocarbamate scavengers and trithiotriazine scavengers, and the dosage is 1.1 to 2.0 times the total molar amount of copper, nickel and zinc in the mixed wastewater. No oxidizing agent is added during the immediate heavy metal capture process. The capture reaction time is 15-30 minutes. Step S7 is performed after the capture reaction is completed.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention prioritizes the reduction of free and easily oxidized cyanide in mixed wastewater through a low-chlorine pre-oxidation step, avoiding the ineffective consumption of oxidant and the accumulation of residual chlorine caused by directly using high doses of sodium hypochlorite. Through the synergistic effect of persulfate and an iron-manganese composite catalyst, it performs composite catalytic complex-breaking oxidation on the complexed cyanide, metal cyanide complexes, and organic complexing agents remaining after low-chlorine pre-oxidation, transforming stable complexed pollutants into forms that can be further oxidized or captured and precipitated. A residual chlorine control step switches the wastewater system from an oxidative and complex-breaking state to a low-residual chlorine state suitable for heavy metal capture, reducing the adverse effects of residual chlorine on the capture agent and subsequent biological treatment system. A heavy metal immediate capture step fixes copper, nickel, zinc, and other metal ions into insoluble precipitates after release and before they re-complex, thereby improving the stability of heavy metal removal. Therefore, this invention can improve the removal efficiency of complexed cyanide and the precipitation removal effect of heavy metals such as copper, nickel, and zinc while reducing sodium hypochlorite dosage and residual chlorine, and improves the adaptability to subsequent biological treatment. Attached Figure Description

[0025] Figure 1 This is a process flow diagram of a cyanide-containing wastewater treatment process according to the present invention. Detailed Implementation

[0026] The present invention will be further described below in conjunction with the specific processing procedure. It should be understood that the following content is used to illustrate the technical solution of the present invention and is not intended to limit the scope of protection of the present invention. Without departing from the technical concept of the present invention, those skilled in the art can make adaptive adjustments to the type of reagent, dosage, reaction time, and treatment unit form according to the actual wastewater quality, quantity, equipment layout, and discharge requirements.

[0027] like Figure 1 As shown, this invention provides a treatment process for cyanide-containing wastewater. This process is not aimed at conventional cyanide removal treatment of raw cyanide-containing wastewater, but rather at complex mixed wastewater formed by mixing cyanide-containing pretreated effluent with passivation wastewater. This mixed wastewater typically contains free cyanide, complexed cyanide, heavy metal ions such as copper, nickel, and zinc, chromium, fluoride ions, carboxylic acid complexing agents, organic amine complexing agents, organic additives, residual chlorine, and other redox pollutants. These pollutants easily interact through complexation, competitive oxidation, re-complexation, and precipitation inhibition, making it difficult to achieve stable synergistic treatment effects with simple high-chlorination oxidation, persulfate oxidation alone, or ordinary coagulation and sedimentation.

[0028] Based on the pollutant characteristics of the above-mentioned mixed system, this invention constructs a continuous treatment path consisting of cyanide-containing wastewater pretreatment, mixing of cyanide-containing pretreated effluent and passivated wastewater, low-chlorine pre-oxidation, composite catalytic complex-breaking oxidation, residual chlorine regulation, immediate heavy metal capture, and coagulation sedimentation. This allows cyanide pollutants and heavy metal pollutants to be gradually transformed along the path of "selective pre-oxidation of free cyanide, catalytic complex-breaking of complexed pollutants, switching of redox states, immediate capture of released metals, and floc sedimentation separation".

[0029] I. Pretreatment of Cyanide-Containing Wastewater First, the cyanide-containing wastewater is collected and pretreated separately to obtain cyanide-pretreated effluent. This cyanide-containing wastewater originates from cyanide electroplating, cyanide cleaning, cyanide stripping, cyanide rinsing, or cyanide surface treatment processes. This type of wastewater typically contains free cyanide and may also contain complexed cyanides such as copper-cyanide complexes, nickel-cyanide complexes, and zinc-cyanide complexes. Because cyanide-containing wastewater is highly toxic and poses a risk of forming hydrogen cyanide gas under inappropriate pH conditions, it requires separate pretreatment before entering the subsequent integrated treatment system.

[0030] In a preferred embodiment, the cyanide-containing wastewater is collected separately and then enters a conditioning unit for homogenization to stabilize the water volume and quality. The homogenized wastewater then enters a primary cyanide removal unit, where it undergoes primary cyanide removal treatment under conditions of pH 10.5–11.5 and redox potential of +300–+450 mV. This process preferentially oxidizes free cyanide into cyanate or other low-toxicity intermediates, thereby reducing the acute toxicity of the cyanide-containing wastewater.

[0031] After primary cyanide removal treatment, the wastewater pH is adjusted to 7.5–8.8, and secondary cyanide removal treatment is carried out under conditions of +550–+750 mV redox potential to further reduce residual cyanide and some easily oxidized complexed cyanide. The wastewater after secondary cyanide removal treatment enters the heavy metal capture and solid-liquid separation treatment stage. By adding heavy metal capture agents, PAC, and PAM, some heavy metal ions such as copper, nickel, and zinc, as well as suspended solids in the wastewater, precipitate and separate. The resulting supernatant is the cyanide-containing pretreated effluent.

[0032] After the above pretreatment, the risk of direct mixing of cyanide-containing wastewater is reduced. However, a certain amount of complexed cyanide, heavy metal ions such as copper, nickel, and zinc, residual chlorine, and organic pollutants may still remain in the cyanide-containing pretreated effluent. Its water quality usually still needs to be further treated in the subsequent integrated treatment system.

[0033] II. Mixing cyanide pretreatment effluent with passivation wastewater The cyanide-containing pretreated effluent is fed into the front end of the passivation system and mixed with the passivation wastewater to obtain mixed wastewater. The front end of the passivation system can be the mixing and conditioning unit, homogenization unit, or influent unit before entering the low-chlorine pre-oxidation treatment of the passivation wastewater treatment system. Passivation wastewater can originate from trivalent chromium passivation, hexavalent chromium passivation, post-passivation cleaning, closed cleaning, passivation rinsing, or passivation-related washing processes. In addition to chromium, this type of wastewater may also contain copper, nickel, zinc, fluoride ions, carboxylic acid complexing agents, organic amine complexing agents, organic additives, and other oxidizing or reducing substances.

[0034] In a preferred embodiment, the volume ratio of cyanide-containing pretreated effluent to passivation wastewater is 1:4 to 1:15. The resulting mixed wastewater has a pH of 8.5 to 10.5, a total cyanide concentration of 0.5 to 10 mg / L, and a combined concentration of copper, nickel, and zinc of 1 to 30 mg / L.

[0035] After the cyanide-containing pretreatment effluent is mixed with the passivation wastewater, the forms of pollutants in the wastewater system become more complex. On the one hand, residual complexed cyanide and metal ions in the cyanide-containing pretreatment effluent enter the passivation wastewater system; on the other hand, carboxylic acids, organic amine complexing agents, and organic additives in the passivation wastewater may continue to stabilize heavy metal ions such as copper, nickel, and zinc, making them difficult to remove completely by ordinary coagulation and sedimentation. If high-dose sodium hypochlorite oxidation is directly used at this stage, the oxidant will be consumed by free cyanide, complexing agents, organic additives, and reducing pollutants, easily leading to increased reagent consumption and residual chlorine accumulation. Therefore, this invention does not use a one-time high-dose oxidation or direct capture and precipitation treatment method after the mixed wastewater is formed, but instead sequentially performs low-chlorine pre-oxidation, composite catalytic complex-breaking oxidation, residual chlorine control, and immediate capture of heavy metals.

[0036] III. Low-chlorine pre-oxidation treatment The mixed wastewater is subjected to low-chlorine pre-oxidation treatment. Specifically, the pH of the mixed wastewater is controlled at 9.8–10.5, sodium hypochlorite is added as an oxidant, the oxidation-reduction potential is controlled at +360–+430 mV, the free residual chlorine is 0.3–0.8 mg / L, and the reaction time is 20–30 min. The available chlorine content of sodium hypochlorite is preferably 5–12 wt%, and its dosage is 0.7–1.0 times the theoretical oxidation amount of total cyanide in the mixed wastewater.

[0037] In this step, sodium hypochlorite is mainly used for the selective oxidation of free cyanide and easily oxidized cyanide. By controlling the redox potential and free residual chlorine within a low range, sodium hypochlorite can preferentially act on free cyanide, reducing the free cyanide load in the mixed wastewater, while avoiding the ineffective consumption of large amounts of sodium hypochlorite by organic additives, reducing substances, and complexing agents in the passivation wastewater.

[0038] This low-chlorine pre-oxidation step is not intended to achieve deep oxidation of complexed cyanide using sodium hypochlorite. Its purpose is to pre-regulate the pollutant speciation in the mixed wastewater through low-dose oxidation. After this step, the main target of treatment in the mixed wastewater changes from a state where free cyanide and complexed cyanide coexist to a state where complexed cyanide, complexed heavy metals, and organic complexing agents are the primary targets, thus providing a more concentrated reaction basis for subsequent composite catalytic complex-breaking oxidation.

[0039] In this step, the theoretical total cyanide oxidation capacity refers to the theoretical oxidant consumption calculated by converting the total cyanide concentration in the mixed wastewater into CN⁻ and then into the available chlorine equivalent required to oxidize CN⁻ to CNO⁻, expressed as available chlorine. The sodium hypochlorite dosage of 0.7 to 1.0 times the theoretical total cyanide oxidation capacity means that the sodium hypochlorite dosage, expressed as available chlorine, is 0.7 to 1.0 times the theoretical amount.

[0040] IV. Composite Catalytic Complex-Breaking Oxidation Treatment After low-chlorine pre-oxidation, the wastewater enters the composite catalytic complex-breaking oxidation treatment stage. In this stage, persulfate is added to the wastewater, and the wastewater is brought into contact with an iron-manganese composite catalyst to further break down the complexed cyanides, metal complexes, and organic complexing agents that remain after low-chlorine pre-oxidation.

[0041] The persulfate can be one or more of sodium persulfate, potassium persulfate, and potassium peroxymonosulfate, with a preferred dosage of 60–160 mg / L. The composite catalytic complex-breaking oxidation treatment is preferably carried out under conditions of pH 9.2–9.8, redox potential of +540–+620 mV, and reaction time of 30–50 min.

[0042] In this reaction, the iron-manganese composite catalyst promotes the activation of persulfate and maintains the catalytic oxidation interface through the valence state cycle of the iron and manganese active components. This catalytic oxidation interface can disrupt the coordination structures of copper-cyanide complexes, nickel-cyanide complexes, zinc-cyanide complexes, and heavy metal complexes formed by carboxylic acid and organic amine ligands, causing the complexed cyanide to dissociate and further oxidize, while simultaneously releasing heavy metal ions such as copper, nickel, and zinc from their complexed state. Thus, pollutants in the mixed wastewater gradually transform from a stable complexed state into cyanide intermediates that can be further oxidized and metal ions that can be captured and precipitated.

[0043] In a preferred embodiment, the iron-manganese composite catalyst is a supported iron-manganese composite catalytic packing. The supported iron-manganese composite catalytic packing includes a porous support and an iron-manganese composite oxidation active component supported on the surface of the porous support. The porous support can be one or more of ceramic particles, zeolite, activated carbon, volcanic rock, or porous alumina. The iron-manganese composite oxidation active component includes at least two of FeOOH, Fe2O3, MnO2, and MnOOH, with a mass ratio of iron to manganese of 1:0.6 to 1:1.2. The iron-manganese composite oxidation active component accounts for 8% to 25% of the total mass of the supported iron-manganese composite catalytic packing.

[0044] Furthermore, the supported iron-manganese composite catalytic packing is configured as a fixed-bed catalytic packing layer, through which wastewater flows from bottom to top or from top to bottom. The height of the fixed-bed catalytic packing layer is 0.8–1.5 m, the packing particle size is 1–3 mm, and the empty bed contact time is 20–40 min.

[0045] To prevent the rapid consumption of persulfate in the front section of the fixed-bed catalytic packing layer, which could lead to insufficient oxidation capacity in the later stages, the persulfate is preferably added at two points. The first addition point is located at the inlet end of the fixed-bed catalytic packing layer to establish an initial catalytic oxidation environment in the front section. The second addition point is located at 1 / 2 to 2 / 3 of the height of the fixed-bed catalytic packing layer to replenish the persulfate concentration in the later stages. Preferably, the amount of persulfate added at the second addition point accounts for 20% to 45% of the total persulfate added.

[0046] By employing the aforementioned two-point addition method—fixed-bed catalytic packing layer and persulfate—wastewater can continuously contact the catalytically active sites and oxidant as it passes through the packing layer, creating a continuous catalytic oxidation zone within the packing layer. This arrangement is not simply about increasing the amount of persulfate added, but rather about controlling the spatial distribution of persulfate within the fixed bed. This reduces the likelihood of concentrated consumption of the oxidant at the front end of the packing layer, ensuring that the middle and later sections of the packing layer maintain effective complex-breaking oxidation capabilities, thereby improving the stability of the complexed cyanide and complexing agent.

[0047] V. Residual Chlorine Control Treatment After the complex-breaking oxidation by the composite catalytic oxidation, the wastewater enters the residual chlorine control stage. Specifically, one or more of sodium bisulfite, sodium metabisulfite, and sodium thiosulfate are added to the wastewater to reduce the free residual chlorine in the wastewater to below 0.2 mg / L and to reduce the oxidation-reduction potential to +220 to +360 mV.

[0048] The reason for setting up a residual chlorine control step is that after the composite catalytic complex-breaking oxidation, free residual chlorine and other oxidizing components may remain in the wastewater. If heavy metal scavengers are added directly under these conditions, the residual chlorine will oxidize the sulfur coordination groups in dithiocarbamate or trithiotriazine scavengers, reducing the scavenger's ability to coordinate and precipitate heavy metal ions such as copper, nickel, and zinc. Furthermore, residual chlorine entering subsequent biological systems may also inhibit microbial activity.

[0049] Therefore, this step is not only used to reduce residual chlorine concentration, but also to switch the wastewater system from a complex catalytic oxidation state to a reaction state suitable for heavy metal capture and precipitation. The previous stage requires a strong oxidizing environment to break down complexed pollutants, while the subsequent stage requires a lower oxidizing environment to ensure the effectiveness of the heavy metal capture agent. By controlling residual chlorine, the consumption of the capture agent by the residual oxidant is reduced, and the copper, nickel, zinc, and other metal ions released from the broken complexes can preferentially react with the capture agent in subsequent steps to form insoluble precipitates.

[0050] VI. Real-time capture of heavy metals After residual chlorine adjustment, the wastewater enters the immediate heavy metal capture stage. Specifically, within 5 to 30 minutes after the residual chlorine adjustment is completed, the pH of the wastewater is adjusted to 9.0 to 9.6, and a heavy metal capture agent is added to cause the heavy metal ions released after the composite catalytic complex-breaking oxidation to form insoluble precipitates.

[0051] The heavy metal scavenging agent can be one or both of dithiocarbamate scavengers and trithiotriazine scavengers. The dosage of the heavy metal scavenging agent is 1.1 to 2.0 times the total molar amount of copper, nickel, and zinc in the mixed wastewater. Preferably, no strong oxidant is added during the immediate heavy metal scavenging process, and the scavenging reaction time is 15 to 30 minutes.

[0052] In this invention, unless otherwise stated, the concentrations of copper, nickel, and zinc refer to the mass concentration of the corresponding metal elements in the wastewater in all forms, including free, complexed, and other detectable forms. The total molar amount of copper, nickel, and zinc is the sum of the amounts of copper, nickel, and zinc in the mixed wastewater after converting them into amounts of substance according to their respective mass concentrations. When the mass concentrations of copper, nickel, and zinc are CCu, CNi, and CZn, respectively, the total molar amount of copper, nickel, and zinc can be calculated as follows: n_total = CCu / MCu + CNi / MNi + CZn / MZn Wherein, ntotal represents the total molar concentration of copper, nickel, and zinc, and MCu, MNi, and MZn represent the molar masses of copper, nickel, and zinc, respectively. In actual calculations, the unit of mass concentration should be uniformly converted to g / L. The dosage of heavy metal scavenging agent is calculated as 1.1 to 2.0 times the total molar amount of copper, nickel, and zinc, referring to the molar amount of effective functional groups in the scavenging agent capable of coordinating or precipitating with metal ions.

[0053] After composite catalytic oxidation, the metal cyanide complexes and organically complexed heavy metals are destroyed, releasing heavy metal ions such as copper, nickel, and zinc. If these released metal ions remain in a system containing residual carboxylic acid or organic amine ligands for an extended period, they may re-complex, leading to a decrease in subsequent coagulation and precipitation removal efficiency. This invention performs immediate collection within 5–30 minutes after residual chlorine control, allowing the released metal ions to react with the collector before re-complexation, forming insoluble precipitates and thus improving the stability of heavy metal removal.

[0054] VII. Coagulation, flocculation and sedimentation treatment After immediate heavy metal capture, the wastewater enters the coagulation, flocculation, and sedimentation treatment stage. Specifically, PAC and PAM are added to the wastewater after the capture reaction for coagulation, flocculation, and sedimentation treatment. The dosage of PAC is 60–180 mg / L, the dosage of PAM is 1–3 mg / L, the coagulation reaction time is 3–8 min, the flocculation reaction time is 10–20 min, and the sedimentation time is 1.5–3 h.

[0055] After immediate heavy metal capture, the wastewater forms metal precipitates, metal hydroxide precipitates, fine colloidal particles, and some oxidation products. Through PAC coagulation and PAM flocculation, these fine particles and colloidal pollutants further aggregate to form larger flocs, which are then separated into solid and liquid phases by sedimentation. The effluent can then undergo further treatment in one or more of the following units: hydrolysis acidification, anoxic treatment, aerobic treatment, biological sedimentation, multi-media filtration, and ion exchange treatment.

[0056] Through the above continuous processing, this invention forms a multi-step synergistic system consisting of "low-chlorine selective pre-oxidation, composite catalytic complex-breaking oxidation, redox state switching, immediate heavy metal capture, and flocculation sedimentation separation". The steps are not simply connected in series, but rather form a continuous matching relationship in terms of reactants, reaction intensity, oxidant distribution, redox state, and capture timing.

[0057] Specifically, the low-chlorine pre-oxidation step reduces the load of free cyanide and easily oxidized cyanide while inhibiting the accumulation of high residual chlorine; the composite catalytic complex-breaking oxidation step deeply destroys the complexed cyanide and complexing agent remaining after low-chlorine pre-oxidation, transforming stable complexed pollutants into forms that can be further oxidized or precipitated and captured; the residual chlorine control step switches the system from an oxidative complex-breaking state to a low residual chlorine state suitable for capture and precipitation; the heavy metal immediate capture step achieves precipitation and fixation after the release of metal ions and before they re-complex; and the coagulation, flocculation, and precipitation steps further separate the captured products, metal hydroxides, colloidal particles, and some oxidation products into solid and liquid components.

[0058] Compared to conventional high-chlorine oxidation processes for cyanide removal, this invention does not rely solely on sodium hypochlorite for deep complex-breaking oxidation. Instead, sodium hypochlorite is primarily used for the pre-oxidation of free and easily oxidized cyanides, while a persulfate and iron-manganese composite catalyst handles the deep destruction of complexed pollutants. Therefore, this invention can improve the removal efficiency of complexed cyanides and reduce residual chlorine accumulation with lower sodium hypochlorite dosages.

[0059] Compared to the standalone persulfate oxidation process, this invention reduces the load of free cyanide and easily oxidizable substances through pre-oxidation with low-chlorine, and improves the utilization efficiency of persulfate within the catalytic packing layer through a fixed-bed catalytic packing and a two-point addition method, allowing the persulfate to act more concentratedly on the complexed cyanide and organic complexing agents. This process reduces the risk of rapid or ineffective consumption of persulfate in localized areas and improves the stability of the composite catalytic complex-breaking oxidation.

[0060] Compared to conventional heavy metal capture and precipitation processes, this invention first regulates residual chlorine after complex breaking, and then performs immediate capture within 5–30 minutes. This reduces the likelihood of the capture agent being destroyed by residual oxidants and lowers the possibility of metal ions re-complexing with residual complexing agents. Therefore, the stability of precipitation removal of heavy metals such as copper, nickel, and zinc is improved.

[0061] Therefore, this invention can produce comprehensive technical effects that exceed the expectations of conventional process combinations: while reducing the dosage of sodium hypochlorite and residual chlorine, it improves the efficiency of breaking down complexed cyanide, and simultaneously enhances the capture and precipitation of heavy metals such as copper, nickel, and zinc, reducing the risk of subsequent biochemical treatment being inhibited by residual chlorine and complexed pollutants. This effect stems from the temporal coordination and continuous reaction state transitions between low-chlorine pre-oxidation, composite catalytic complex-breaking oxidation, residual chlorine control, and immediate heavy metal capture, exhibiting a clear synergistic effect.

[0062] The present invention will be further illustrated below through specific embodiments. In all embodiments and comparative examples, the mixed wastewater formed by mixing cyanide-containing pretreated effluent and passivation wastewater is used as the treatment object. For ease of comparison, the initial water quality control of the mixed wastewater used in each group of experiments is as follows:

[0063] Example 1: This example uses the cyanide-containing wastewater treatment process of the present invention. After primary cyanide removal, secondary cyanide removal, heavy metal capture, and solid-liquid separation, the cyanide-containing wastewater is pretreated to obtain cyanide-containing pretreated effluent; the cyanide-containing pretreated effluent is mixed with passivation wastewater to obtain mixed wastewater.

[0064] The mixed wastewater was subjected to low-chlorine pre-oxidation treatment, with the pH controlled at 9.8, the oxidation-reduction potential at +360mV, the free residual chlorine at 0.30mg / L, the reaction time at 20min, and the sodium hypochlorite dosage at 0.70 times the theoretical oxidation amount of total cyanide.

[0065] After low-chlorine pre-oxidation, sodium persulfate is added to the wastewater, which is then passed through a supported iron-manganese composite catalytic packing layer for composite catalytic complex-breaking oxidation treatment. The sodium persulfate dosage is 60 mg / L, the reaction pH is 9.2, the redox potential is +540 mV, and the reaction time is 30 min. The mass ratio of iron to manganese in the supported iron-manganese composite catalytic packing is 1:0.6, and the iron-manganese composite oxidation active component accounts for 8% of the total mass of the packing. The fixed-bed catalytic packing layer height is 0.8 m, the packing particle size is 1 mm, and the empty bed contact time is 20 min. Sodium persulfate is added at two points, with the second addition point located at 1 / 2 of the packing layer height, and the amount added at the second point accounting for 20% of the total sodium persulfate dosage.

[0066] After complex-breaking oxidation by composite catalysis, sodium bisulfite is added to regulate residual chlorine, reducing free residual chlorine to 0.08 mg / L and the redox potential to +220 mV. Within 5 minutes of residual chlorine regulation, the wastewater pH is adjusted to 9.0, and a dithiocarbamate heavy metal scavenger is added at a dosage of 1.1 times the total molar amount of copper, nickel, and zinc. The scavenging reaction time is 15 minutes. No oxidizing agent is added during the scavenging process.

[0067] After collection, PAC and PAM were added for coagulation, flocculation and sedimentation treatment. The dosage of PAC was 60 mg / L and the dosage of PAM was 1 mg / L. The coagulation reaction time was 3 min, the flocculation reaction time was 10 min, and the sedimentation time was 1.5 h.

[0068] Example 2: This example uses the same overall process as Example 1, except that the low-chlorine pre-oxidation treatment controls the pH to 10.2, the oxidation-reduction potential to +395mV, the free residual chlorine to 0.55mg / L, the reaction time to 25min, and the sodium hypochlorite dosage to be 0.85 times the theoretical total cyanide oxidation amount.

[0069] In the composite catalytic complex-breaking oxidation treatment, the sodium persulfate dosage was 110 mg / L, the reaction pH was 9.5, the redox potential was +580 mV, and the reaction time was 40 min. The supported iron-manganese composite catalytic packing had an iron to manganese mass ratio of 1:0.9, and the iron-manganese composite oxidation active component accounted for 16% of the total packing mass. The fixed-bed catalytic packing layer height was 1.15 m, the packing particle size was 2 mm, and the empty bed contact time was 30 min. The second addition point was located approximately 3 / 5 of the packing layer height, and the dosage at this second addition point accounted for 32% of the total sodium persulfate dosage.

[0070] After residual chlorine adjustment, the free residual chlorine decreased to 0.05 mg / L, and the oxidation-reduction potential decreased to +300 mV. Within 18 minutes of residual chlorine adjustment, the wastewater pH was adjusted to 9.3, and a trithiotriazine heavy metal scavenger was added at a dosage of 1.5 times the total molar amount of copper, nickel, and zinc. The scavenging reaction time was 22 minutes. After scavenging, 120 mg / L of PAC and 2 mg / L of PAM were added for coagulation, flocculation, and sedimentation treatment. The sedimentation time was 2.2 hours.

[0071] Example 3: This example uses the same overall process as Example 1, except that the low-chlorine pre-oxidation treatment controls the pH to 10.5, the oxidation-reduction potential to +430mV, the free residual chlorine to 0.80mg / L, the reaction time to 30min, and the sodium hypochlorite dosage to be 1.00 times the theoretical total cyanide oxidation amount.

[0072] In the composite catalytic complex-breaking oxidation treatment, the sodium persulfate dosage was 160 mg / L, the reaction pH was 9.8, the redox potential was +620 mV, and the reaction time was 50 min. The supported iron-manganese composite catalytic packing had an iron to manganese mass ratio of 1:1.2, and the iron-manganese composite oxidation active component accounted for 25% of the total packing mass. The fixed-bed catalytic packing layer height was 1.5 m, the packing particle size was 3 mm, and the empty bed contact time was 40 min. The second addition point was located at 2 / 3 of the packing layer height, and the dosage at this second addition point accounted for 45% of the total sodium persulfate dosage.

[0073] After residual chlorine adjustment, the free residual chlorine decreased to 0.04 mg / L, and the redox potential decreased to +360 mV. Within 30 minutes of residual chlorine adjustment, the wastewater pH was adjusted to 9.6, and a dithiocarbamate heavy metal scavenger was added at a dosage of 2.0 times the total molar amount of copper, nickel, and zinc. The scavenging reaction time was 30 minutes. After scavenging, 180 mg / L of PAC and 3 mg / L of PAM were added for coagulation, flocculation, and sedimentation treatment. The sedimentation time was 3 hours.

[0074] Comparative Example 1: This comparative example uses a traditional high-chlorine oxidation process to remove cyanide. The pH of the mixed wastewater was adjusted to 10.0, and sodium hypochlorite was directly added for oxidation treatment. The amount of sodium hypochlorite added was 2.0 times the theoretical oxidation amount of total cyanide. The oxidation-reduction potential was controlled at +650mV, and the reaction time was 60min. After oxidation, heavy metal scavengers, PAC, and PAM were directly added for coagulation and sedimentation treatment.

[0075] This comparative example did not employ the steps of low-chlorine pre-oxidation, synergistic complex-breaking oxidation with persulfate and iron-manganese composite catalyst, residual chlorine control, and immediate collection.

[0076] Comparative Example 2: This comparative example is basically the same as Example 2, except that the mixed wastewater is not subjected to low-chlorine pre-oxidation treatment, but directly enters the composite catalytic complex-breaking oxidation treatment of persulfate and supported iron-manganese composite catalytic packing. The remaining steps are the same as in Example 2.

[0077] Comparative Example 3: This comparative example is basically the same as Example 2, except that in the composite catalytic complex-breaking oxidation step, only sodium persulfate is added, and the supported iron-manganese composite catalyst packing is not used. The remaining steps are the same as in Example 2.

[0078] Comparative Example 4: This comparative example is basically the same as Example 2, except that the sodium persulfate is not added at two points, but is added all at once at the inlet end of the fixed-bed catalytic packing layer. The remaining steps are the same as in Example 2.

[0079] Comparative Example 5: This comparative example is basically the same as Example 2, except that after the composite catalytic complex-breaking oxidation, residual chlorine control is not performed, and heavy metal scavenging agent is directly added for scavenging. The remaining steps are the same as in Example 2.

[0080] Comparative Example 6: This comparative example is basically the same as Example 2, except that after the composite catalytic complex-breaking oxidation and residual chlorine control are completed, the heavy metal scavenger is added after a 60-minute delay. The remaining steps are the same as in Example 2.

[0081]

[0082] As shown in Table 2, although the traditional high-chlorine oxidation process involves a relatively high dosage of sodium hypochlorite, the removal effect of complexed cyanide is still limited, and the residual free chlorine is significantly higher. Examples 1 to 3, with a lower sodium hypochlorite dosage than the traditional process, still achieved lower concentrations of total cyanide and complexed cyanide, indicating a synergistic effect between low-chlorine pre-oxidation and composite catalytic complex-breaking oxidation.

[0083] In Comparative Example 2, after eliminating the low-chlorine pre-oxidation, the treatment effect of the composite catalytic complex-breaking oxidation was lower than that in Example 2, indicating that low-chlorine pre-oxidation can reduce the load of free cyanide and easily oxidized substances, allowing the persulfate and iron-manganese composite catalyst to act more concentratedly on the complexed pollutants. In Comparative Example 3, after eliminating the iron-manganese composite catalytic packing, the removal effect of complexed cyanide decreased, indicating that the iron-manganese composite catalytic packing plays an important role in the activation of persulfate and complex-breaking oxidation. In Comparative Example 4, persulfate was added in a single step, and its effect was weaker than that in Example 2, indicating that two-point addition can improve the oxidant distribution in the fixed bed and improve the stability of complex-breaking oxidation.

[0084]

[0085] As shown in Table 3, the traditional high-chlorine oxidation process has a poor removal effect on complexed heavy metals, indicating that simply increasing the oxidant dosage cannot effectively solve the problem of difficult precipitation of complexed heavy metals. Examples 1 to 3 used composite catalytic oxidation to break down the complex and release metal ions, and then immediately captured them after residual chlorine control, resulting in a significant reduction in the concentrations of copper, nickel, and zinc.

[0086] In Comparative Example 5, no residual chlorine control was performed, and the trapping agent was easily consumed by residual chlorine oxidation, resulting in a lower heavy metal removal efficiency than in Example 2. In Comparative Example 6, after delayed trapping, the residual concentrations of copper, nickel, and zinc increased, indicating that if the metal ions released by complexation are not trapped within an appropriate time, they are likely to re-form a stable form with the residual complexing agent, affecting the subsequent precipitation effect.

[0087]

[0088] As shown in Table 4, Comparative Example 1, due to its high level of free residual chlorine, exhibited a significant inhibitory effect on the subsequent biochemical system. Comparative Example 5, despite undergoing composite catalytic complex-breaking oxidation treatment, still showed a high inhibition rate of biochemical oxygen consumption rate without residual chlorine control. Examples 1 to 3 reduced free residual chlorine to a lower level through residual chlorine control, while simultaneously weakening some organic complexing agents through composite catalytic complex-breaking oxidation, thus improving subsequent biochemical adaptability.

[0089] The above embodiments and comparative examples demonstrate that the technical effects of the present invention arise from the continuous synergy between low-chlorine pre-oxidation, composite catalytic complex-breaking oxidation, residual chlorine regulation, and immediate heavy metal capture. Low-chlorine pre-oxidation reduces the load of free cyanide and easily oxidizable substances; composite catalytic complex-breaking oxidation destroys complexed cyanide and complexed heavy metals; residual chlorine regulation reduces the oxidation loss of the capture agent and improves its biochemical adaptability; and immediate capture achieves precipitation and fixation before metal ions re-complex.

[0090] Compared with traditional high-chlorination oxidation processes, this invention achieves lower total cyanide and complexed cyanide residues with lower sodium hypochlorite dosage, while improving the precipitation and removal efficiency of heavy metals such as copper, nickel, and zinc, and reducing the adverse effects of residual chlorine on subsequent biochemical treatment. This comprehensive effect is not simply achieved by the sum of individual treatment steps, but rather by the interaction of multiple steps, including the reactants, oxidation intensity, oxidant distribution, residual chlorine state, and collection timing.

Claims

1. A treatment process for cyanide-containing wastewater, characterized in that, Includes the following steps: S1. Pre-treat the cyanide-containing wastewater to obtain cyanide-containing pre-treated effluent; S2. The cyanide-containing pretreated effluent is sent to the front end of the passivation system and mixed with the passivation wastewater to obtain mixed wastewater; S3. Perform low-chlorine pre-oxidation treatment on the mixed wastewater; S4. Add persulfate to the wastewater after low-chlorine pre-oxidation and contact the wastewater with the iron-manganese composite catalyst to carry out composite catalytic complex-breaking oxidation treatment. S5. Adjust the residual chlorine in the wastewater after composite catalytic complex-breaking oxidation. S6. Add a heavy metal precipitant to the wastewater after residual chlorine control to form insoluble precipitates of heavy metal ions released after composite catalytic complex-breaking oxidation. S7. The wastewater after the addition of heavy metal precipitating agent is subjected to coagulation, flocculation and sedimentation treatment, and the sedimented effluent enters the subsequent treatment system.

2. The treatment process for cyanide-containing wastewater according to claim 1, characterized in that, The cyanide-containing wastewater originates from cyanide-containing electroplating, cyanide-containing cleaning, cyanide-containing stripping, cyanide-containing rinsing, or cyanide-containing surface treatment processes. The passivation wastewater originates from trivalent chromium passivation, hexavalent chromium passivation, post-passivation cleaning, closed cleaning, passivation rinsing, or passivation-related washing processes, and contains one or more of the following: chromium, copper, nickel, zinc, fluoride ions, complexing agents, organic additives, oxidizing substances, or reducing substances.

3. The treatment process for cyanide-containing wastewater according to claim 1, characterized in that, In step S1, the cyanide-containing wastewater is collected separately and homogenized, then subjected to primary cyanide removal treatment, secondary cyanide removal treatment, and solid-liquid separation treatment to obtain the cyanide-containing pretreated effluent.

4. The treatment process for cyanide-containing wastewater according to claim 3, characterized in that, The primary cyanide removal treatment was carried out under conditions of pH 10.5–11.5 and redox potential of +300–+450 mV. The secondary cyanide removal treatment was carried out under conditions of pH 7.5–8.8 and redox potential of +550–+750 mV; Before the solid-liquid separation treatment, heavy metal precipitating agents, PAC and PAM are added to the wastewater after the secondary cyanide crushing treatment, so that some heavy metal ions and suspended solids in the wastewater precipitate and are separated.

5. The treatment process for cyanide-containing wastewater according to claim 1, characterized in that, In step S2, the volume ratio of the cyanide-containing pretreated effluent to the passivation wastewater is 1:4 to 1:

15. The mixed wastewater has a pH of 8.5–10.5, a total cyanide concentration of 0.5–10 mg / L, and a combined concentration of copper, nickel, and zinc of 1–30 mg / L.

6. The treatment process for cyanide-containing wastewater according to claim 1, characterized in that, In step S3, the pH of the mixed wastewater is controlled to be 9.8-10.5, sodium hypochlorite is added as an oxidant, the oxidation-reduction potential is controlled to be +360-+430mV, the free residual chlorine is 0.3-0.8mg / L, and the reaction time is 20-30min. The sodium hypochlorite has an effective chlorine content of 5-12 wt%, and the dosage is 0.7-1.0 times the theoretical oxidation amount of total cyanide in the mixed wastewater.

7. A treatment process for cyanide-containing wastewater according to claim 1 or 6, characterized in that, In step S4, the persulfate is one or more of sodium persulfate, potassium persulfate, and potassium peroxymonosulfate, and the dosage of the persulfate is 60-160 mg / L. The composite catalytic complex-breaking oxidation treatment was carried out under conditions of pH 9.2–9.8 and redox potential of +540–+620 mV, with a reaction time of 30–50 min.

8. The treatment process for cyanide-containing wastewater according to claim 7, characterized in that, The iron-manganese composite catalyst is a supported iron-manganese composite catalytic packing. The supported iron-manganese composite catalytic packing includes a porous support and an iron-manganese composite oxidation active component supported on the surface of the porous support. The porous carrier is one or more of ceramic particles, zeolite, activated carbon, volcanic rock, or porous alumina; The iron-manganese composite oxidation active component includes at least two of FeOOH, Fe2O3, MnO2, and MnOOH, and the mass ratio of iron to manganese is 1:0.6 to 1:1.

2. The iron-manganese composite oxidation active component accounts for 8% to 25% of the total mass of the supported iron-manganese composite catalytic packing.

9. The treatment process for cyanide-containing wastewater according to claim 8, characterized in that, The supported iron-manganese composite catalytic packing is configured as a fixed-bed catalytic packing layer; The height of the fixed-bed catalytic packing layer is 0.8–1.5 m, the packing particle size is 1–3 mm, and the empty bed contact time is 20–40 min; The persulfate is added at two points. The first addition point is located at the water inlet of the fixed bed catalytic packing layer, and the second addition point is located at 1 / 2 to 2 / 3 of the height of the fixed bed catalytic packing layer. The amount of persulfate added at the second addition point accounts for 20% to 45% of the total amount of persulfate added.

10. A treatment process for cyanide-containing wastewater according to any one of claims 7 to 9, characterized in that, In step S5, one or more of sodium bisulfite, sodium metabisulfite, and sodium thiosulfate are added to the wastewater to regulate residual chlorine, thereby reducing free residual chlorine to below 0.2 mg / L and reducing the redox potential to +220 to +360 mV. In step S6, within 5 to 30 minutes after the residual chlorine adjustment is completed, the pH of the wastewater is adjusted to 9.0 to 9.6, and a heavy metal precipitant is added for immediate heavy metal precipitant collection. The heavy metal scavenger is one or two of dithiocarbamate scavengers and trithiotriazine scavengers, and the dosage is 1.1 to 2.0 times the total molar amount of copper, nickel and zinc in the mixed wastewater. No strong oxidant is added during the immediate heavy metal capture process. The capture reaction time is 15-30 minutes. Step S7 is performed after the capture reaction is completed.

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