A treatment system and method for chemical nickel plating waste liquid

Abstract

The present application relates to the field of wastewater treatment, and specifically discloses a treatment system and treatment method for chemical nickel plating waste liquid. The treatment system includes: a complex breaking pretreatment system; an oxidation complex breaking system, including a redox reactor and a complex breaking reactor connected in sequence, wherein the oxidant of the redox reactor is oxygen, and the oxidant of the complex breaking reactor is hydrogen peroxide; a chemical precipitation system, including a neutralization reaction tank and a sedimentation tank connected in sequence, and the sedimentation tank is equipped with a filtration system; an evaporation crystallization system, including an evaporation device, a crystallization device and a separation device arranged in sequence. This treatment system and treatment method for chemical nickel plating waste liquid adopts a two-stage oxidation method to achieve oxidation and complex breaking of the waste liquid, and combines chemical precipitation treatment and evaporation crystallization treatment at the same time, which not only reduces the treatment cost of the waste liquid, but also does not bring in other impurities, and can separate nickel salts and phosphates, is easy and simple to operate, has low treatment cost, and high nickel removal rate, which is conducive to realizing nickel resource utilization.

Description

Technical Field

[0001] The present application relates to the field of wastewater treatment, and more specifically, to a treatment system and method for chemical nickel plating waste liquid. Background Art

[0002] There are three main types of reducing agents used in chemical nickel plating: (1) hypophosphites; (2) sodium borohydride-based boron-containing reducing agents; and (3) hydrazine. Among them, acidic chemical nickel plating using sodium hypophosphite as a reducing agent is the most widely used. During the nickel plating process, as the deposition reaction continues, sodium hypophosphite is continuously consumed and phosphite is continuously generated. At present, industrial chemical nickel plating is carried out in an acidic system with sodium hypophosphite as a reducing agent. In order to ensure the stability, service life and coating quality of the plating solution, complexing agents, stabilizers, accelerators, pH buffers and nickel plating brighteners need to be added to the plating solution. These substances are all organic substances, such as citric acid, tartaric acid, malic acid, glycolic acid, succinic acid, succinic acid, acetic acid, etc. Complexing agents are added in large quantities to the chemical plating solution. The presence of these substances has a strong complexation with nickel and is easy to form a stable complex with nickel, which brings difficulties to the treatment of the plating solution. Other additives added to the chemical plating solution, such as pH buffer (NaAc), have little effect on waste liquid treatment, and the amount of brightener and stabilizer added is small, which will not cause difficulties in the treatment of waste liquid and wastewater.

[0003] Since there are a lot of reducing hypophosphites and phosphites, complexing agents and reducing agents in the plating solution, the COD of the plating solution will increase sharply. At the same time, due to the accumulation of sulfates and phosphites generated by the reaction, the plating solution is prone to aging, which may cause the chemical nickel plating solution to be partially or completely scrapped. Therefore, there are many pollutants in the scrapped plating solution and the rinse water of the plated parts, which must be treated.

[0004] At present, the main methods for treating waste liquid and wastewater are: chemical precipitation, electrolysis, ion exchange, and catalytic reduction. In practical applications, two or more methods can be used in combination. Although some treatment methods have good effects, the cost of treating waste liquid is high, and it is difficult to promote and use them in chemical nickel plating enterprises; or other impurities will be introduced during the treatment process, which is not conducive to the resource utilization of nickel. Summary of the invention

[0005] In order to solve the above technical problems, the present application provides a treatment system and method for chemical nickel plating waste liquid.

[0006] This application adopts the following technical solutions:

[0007] A system for treating chemical nickel plating waste liquid, comprising the following systems connected in sequence:

[0008] A chelation breaking pretreatment system, including a regulating tank for adjusting the pH of the nickel plating waste liquid;

[0009] The oxidation and decomposition system comprises a redox reactor and a decomposition reactor which are connected in sequence, wherein the oxidant of the redox reactor is oxygen and the oxidant of the decomposition reactor is hydrogen peroxide;

[0010] The chemical precipitation system includes a neutralization reaction tank and a sedimentation tank connected in sequence, and the sedimentation tank is equipped with a filtration system;

[0011] The evaporation crystallization system comprises an evaporation device, a crystallization device and a separation device which are arranged in sequence.

[0012] Furthermore, the above-mentioned complex breaking reactor has a series-connected secondary reaction tank, and the oxidation complex breaking system also includes a circulation storage tank connected to the reaction tank.

[0013] Furthermore, the above-mentioned filtration system includes a primary filtration device and a fine filtration device. The primary filtration device is a plate and frame filter press or a bag filter, and the fine filtration device can use a precision filter of less than 100 microns.

[0014] Furthermore, the above-mentioned network breaking pretreatment system also includes a filtering and impurity removal device connected to the regulating tank.

[0015] A method for treating chemical nickel plating waste liquid, which utilizes the above-mentioned treatment system, comprises:

[0016] (1) adding acid solution in a regulating tank to obtain acidic nickel plating waste liquid;

[0017] Preferably, the acidity is adjusted to pH = 0-6 with sulfuric acid or hydrochloric acid solution;

[0018] (2) passing the acidic nickel plating waste liquid into the redox reactor for a first-stage oxidation, using oxygen to oxidize the hypophosphite and phosphite in the nickel plating waste liquid into hydrogen phosphate or dihydrogen phosphate; passing the nickel plating waste liquid after the first-stage oxidation into the complex breaking reactor for a second-stage oxidation, using hydrogen peroxide to break the organic complex to form a free Ni 2+ ;

[0019] The acidic nickel plating waste liquid is passed into a redox reactor for a first-stage oxidation, and the hypophosphite and phosphite in the nickel plating waste liquid are oxidized into phosphates by oxygen. The first-stage oxidation reaction can be carried out at room temperature. When the temperature is low, the reaction time is longer, and the oxidation reaction takes 12-18 hours to complete. The optimal reaction temperature is 50-90°C, which is conducive to accelerating the reaction speed and improving production efficiency. Under this temperature condition, the complete oxidation reaction time is 2-5 hours; the nickel plating waste liquid after the first-stage oxidation is passed into a complex breaking reactor for a second-stage oxidation, and hydrogen peroxide is used to destroy the stable nickel organic complex to form a free Ni 2+Since oxygen is used in the first stage of oxidation to oxidize most of the hypophosphite and phosphite into high-valent stable phosphates, the amount of expensive hydrogen peroxide used in the second stage of oxidation is greatly saved, thereby saving the cost of waste liquid treatment. After the second stage reaction is completed, the solution should be controlled to be weakly acidic, pH = 4-6, and nickel exists in the solution in the form of dihydrogen phosphate or hydrogen phosphate. 2+ No precipitation will occur;

[0020] (3) The nickel plating waste liquid after the second stage oxidation is transferred to the neutralization reaction tank, and a neutralization precipitant is added to adjust the pH of the system to 9-10 to remove the free Ni 2+ Converting into nickel phosphate or nickel hydroxide for precipitation, filtering to obtain nickel phosphate or nickel hydroxide and secondary wastewater;

[0021] Since nickel phosphate or sodium hydroxide has extremely low solubility and is a poorly soluble compound, the Ni 2+ ≦1mg / l, the precipitation is complete, solid-liquid separation is achieved after filtration, nickel resources are recovered, and the filtrate is further processed;

[0022] (4) The supernatant and filtrate wastewater from the sedimentation tank are transferred to an evaporation crystallization system for evaporation crystallization to obtain solid salts and distilled water.

[0023] Furthermore, in the second-stage oxidation process, the reaction time of the decomposition reactor is 0.7-1.3h.

[0024] Furthermore, in the chelation pretreatment system, the acid solution put into the regulating tank is sulfuric acid or hydrochloric acid solution, and the pH of the nickel plating waste liquid after adjustment is 0 to 6. During the oxidation process, attention should be paid to replenishing the consumed acid solution to maintain the acidity of the system.

[0025] Furthermore, in the decomposition treatment system, the acid solution put into the regulating tank is sulfuric acid or hydrochloric acid solution to maintain the pH of the nickel plating waste liquid ≤ 6, and the optimal range is pH = 4 to 6. During the oxidation process, attention should be paid to replenishing the consumed acid solution to maintain the acidity of the system.

[0026] Furthermore, the neutralization precipitant added to the neutralization reaction tank is a sodium hydroxide solution.

[0027] Furthermore, the method also includes adding a polymer flocculant into the sedimentation tank.

[0028] Furthermore, the polymer flocculant includes polyacrylamide or polyaluminium chloride.

[0029] Furthermore, the reaction temperature of the first stage oxidation is 50-90°C, and the reaction time is 2-5h.

[0030] In summary, this application has the following beneficial effects:

[0031] The treatment system and treatment method of the chemical nickel plating waste liquid provided by the present application adopts a two-stage oxidation method to achieve oxidation and decomposition of the waste liquid. The first stage of oxidation is carried out in a redox reactor, using oxygen to oxidize the hypophosphite and phosphite in the nickel plating waste liquid into phosphate; the second stage of oxidation is carried out in a decomposition reactor, using H2O2 to decompose the organic complex to form free Ni 2+ . Compared with the process of direct oxidation of H2O2 in the prior art, the present application can save a lot of H2O2 consumption. The industrial H2O2 concentration is mostly about 35%. The large amount of hydrogen peroxide used will bring more water into the reaction system, thereby increasing the steam consumption caused by the subsequent evaporation and desalination, and increasing the cost of waste liquid treatment; compared with the Fenton reaction and the addition of ferrous sulfate for oxidation, this method can avoid the introduction of impurities and the formation of additional precipitated solid waste (ferrous hydroxide), thereby reducing production costs. At the same time, chemical precipitation is used to separate nickel salts and soluble salts, and combined with evaporation and crystallization treatment, the COD, NH3-N and TN of the treated waste liquid (evaporation condensate) are reduced. According to the water quality of the evaporation condensate, it is selected to discharge directly or to meet the discharge standards after biochemical treatment.

[0032] The method is easy and simple to operate, has low processing cost, high nickel removal rate, is conducive to realizing nickel resource utilization, and has good economic and ecological benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a structural schematic diagram of a chemical nickel plating waste liquid treatment system provided in an embodiment of the present application; Figure 2 It is a flow chart of the method for treating chemical nickel plating waste liquid provided in an embodiment of the present application. DETAILED DESCRIPTION

[0034] The embodiments of the present invention will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. The specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0035] Industrial chemical nickel plating is carried out in an acidic system with sodium hypophosphite as a reducing agent. The characteristic pollutants of the electroplating waste liquid are mainly heavy metal nickel, sodium hypophosphite, ammonia nitrogen, total nitrogen COD and organic matter. Specifically, for example, the electroplating waste liquid targeted by the embodiment of the present application has the following characteristics: pH = 4-6, weak acidity, and the main components are: total phosphorus 30-34g / l, which is hypophosphite; chemical oxygen demand (COD) 60-77.5g / l; ammonia nitrogen 3.3-4.7g / l; total nitrogen 5.1-6.2g / l; nickel 6.8-8.7g / l; specific gravity 1.10-1.20.

[0036] Through analysis, it can be known that the main factors causing the excessive COD of electroplating waste liquid are mainly the following two points: one is caused by inorganic salts, such as the chemical oxygen demand consumed by the oxidation of hypophosphite and ammonium salts; the other is the chemical oxygen demand consumed when the organic complex is oxidized. Therefore, in the process of treatment, this application has made special improvements to the oxidation and decomposition process to further control the treatment cost and achieve: first, minimize the amount of solid waste generated during the treatment process; second, add as few chemical agents as possible to reduce disposal costs; third, separate nickel salts from other miscellaneous salts to achieve resource utilization and reduce treatment costs.

[0037] In the nickel plating waste liquid, the phosphorus in the sodium hypophosphite and phosphite has a chemical valence of +1 and +3, both of which are reducing and can be easily oxidized to +5 orthophosphate. The following is the redox potential of phosphorus under different valences:

[0038] O(0)-(-2) O2+4H + +4e - =2H2O 1.229

[0039] O(-1)-(-2) H2O2+2H + +2e - =2H2O 1.776

[0040] P(+3)-(+1) H3PO3+2H + +2e - =H3PO2+H2O -0.499

[0041] P(+5)-(+3) H3PO4+2H + +2e - =H3PO3+H2O -0.276

[0042] The chemical reaction equation for oxidation and complex breaking using hydrogen peroxide is as follows:

[0043] NaH2PO2+2H2O2+2H + →NaH2PO3+3H2O

[0044] NaH2PO3+2H2O2+2H + →NaH2PO4+3H2O

[0045] NaH2PO2+4H2O2+4H + →NaH2PO4+6H2O

[0046] [Ni 2+ +mL n- ]+H2O2+2H +→Ni 2+ +mk n- +2H2O

[0047] 3Ni 2+ +2PO4 3- →Ni3(PO4)2↓

[0048] In the formula, [Ni 2+ +mL n- ] represents a complex of nickel ions.

[0049] The solubility product of nickel phosphate at 25°C is 4.5×10 -35 , and the phosphate content in the solution is relatively high. Under acidic conditions, phosphate is mainly monohydrogen phosphate or dihydrogen phosphate, and has a large solubility. When the neutralizing precipitant NaOH is added to adjust the pH to 9-10, the hydrogen phosphate and dihydrogen phosphate in the solution are completely converted into phosphate, generating a nickel phosphate precipitate that is insoluble in water. Here, calcium hydroxide cannot be used as a neutralizing precipitant, because calcium hydroxide will be converted into calcium phosphate precipitate with phosphate ions in the waste liquid, thereby forming a co-precipitation with nickel phosphate, which is not conducive to the subsequent recycling of nickel resources.

[0050] In the process of using H2O2 to oxidize and break the complex, sodium hypophosphite and sodium phosphite consume a large amount of H2O2 during the oxidation process. Normally, in nickel plating waste liquid, hypophosphite accounts for 40% and phosphite accounts for 60%. It takes 4 molecules of hydrogen peroxide to oxidize 1 molecule of sodium hypophosphite into orthophosphate, and it takes 2 molecules of hydrogen peroxide to oxidize 1 molecule of sodium hypophosphite into orthophosphate. It can be seen that if only H2O2 is used for oxidation and breaking the complex, the amount of hydrogen peroxide used is large; and the concentration of industrial hydrogen peroxide is 35%, which will bring more water into the reaction system, bringing more steam consumption for subsequent evaporation and desalination, resulting in excessive waste liquid treatment costs. When using hydrogen peroxide alone to oxidize chemical nickel plating waste liquid, 200-400kg of 35% concentration industrial hydrogen peroxide is required for the oxidation of hypophosphite and phosphite per ton of waste liquid. At the same time, if the Fenton reaction is adopted, a large amount of ferrous sulfate needs to be added to generate a large amount of ferric sulfate precipitate, which results in too much precipitate, causing an increase in the subsequent solid waste disposal costs, and also making it impossible to realize the resource utilization of nickel and phosphorus, making the entire waste liquid treatment cost too high.

[0051] In order to solve the above problems, the present application optimizes the process and provides a treatment system and method for chemical nickel plating waste liquid, specifically:

[0052] The treatment system of the chemical nickel plating waste liquid is as follows: Figure 1 As shown, it includes the following systems connected in sequence:

[0053] 1. A chelation pretreatment system, including a regulating tank for adjusting the pH of nickel plating wastewater;

[0054] Among them, the regulating tank is connected to the waste liquid storage tank. The waste liquid tank is a temporary storage tank used by the chemical nickel plating producer to store waste liquid. It is made of fiberglass or steel-lined plastic. The temporary storage process can play a role in pre-precipitation and separation. The regulating tank is used to adjust the pH of the nickel plating waste liquid. Since the pH of the nickel plating waste liquid is weakly acidic, it is necessary to first add acid (such as H2SO4) to the regulating tank to adjust the pH value of the waste liquid to acidic (pH = 0-6). Since part of the acid will be consumed during the oxidation process, it needs to be supplemented. Most of the organic acid chelating agent can also be removed during the oxidation process; under acidic conditions, the oxidation capacity of oxygen can be improved, and at the same time, the precipitation of nickel phosphate during the oxidation process will not be caused. Preferably, in order to further improve the quality of the final nickel phosphate and ensure that the subsequent redox reactor and the decomposition reactor can operate normally, the decomposition pretreatment system also includes a primary filtration and impurity removal device, which includes a plate and frame filter press or a bag filter to deoil and remove insoluble impurities before the nickel plating waste liquid enters the oxidation decomposition system. The first stage oxygen oxidation reaction can be carried out at room temperature, but the reaction time is relatively long. For example, when the temperature is low in winter, a complete reaction takes 12-18 hours. The reaction process is an exothermic reaction. As the temperature rises, the oxidation reaction rate accelerates. The optimal initial reaction temperature is 60-90°C. At this temperature, the reaction can generally be completed in 2-4 hours.

[0055] (2) An oxidation and decomposition system, comprising a redox reactor and a decomposition reactor connected in sequence, wherein the oxidant of the redox reactor is oxygen and the oxidant of the decomposition reactor is hydrogen peroxide.

[0056] Among them, the redox reactor has a steel-lined polytetrafluoroethylene or steel-lined plastic, and is equipped with a temporary storage tank for storing waste liquid to be further treated after redox. The decomposition reactor has a series of secondary reaction tanks, and the decomposition reaction time is 0.7-1.3h, preferably the decomposition reaction time is 1h. However, after the oxidation decomposition reaction is completed, the solution pH should be maintained at 4-6. Too high acidity will affect the amount of sodium hydroxide used during neutralization and precipitation, resulting in an increase in processing costs. In order to further ensure the quality of the decomposition reaction, a circulation storage tank connected to the reaction tank is also provided. When the decomposition effect is found to be poor, it is used to return to re-decomposition.

[0057] (3) A chemical precipitation system, comprising a neutralization reaction tank and a sedimentation tank connected in sequence, wherein the sedimentation tank is equipped with a filtration system;

[0058] The neutralization reaction tank can be a series-type secondary reaction tank, made of fiberglass or PP or carbon steel with anti-corrosion treatment.

[0059] The sedimentation tank is used to quickly precipitate and separate the solid and liquid produced by the neutralization reaction to obtain nickel phosphate or hydroxide precipitate. The sedimentation tank is equipped with a filtration system, and a plate and frame filter press or a centrifugal filter is selected. Preferably, the plate and frame filter press is a diaphragm filter press, which filters the nickel phosphate or nickel hydroxide precipitate every day, and the filtrate enters the storage tank for temporary storage.

[0060] (4) An evaporation crystallization system, comprising an evaporation device, a crystallization device and a separation device arranged in sequence.

[0061] Since the filtered mother liquor after the neutralization and precipitation of nickel contains a large amount of sodium phosphate, sodium sulfate, sodium chloride, sodium nitrate, ammonium salts and a small amount of unoxidized organic matter, the COD and salt content of this waste liquid are very high, and it is impossible to use biochemical methods to treat this kind of sewage. Evaporation and desalination treatment is required. Depending on the COD of the evaporation condensate, it is selected to be discharged directly or to undergo biochemical treatment before meeting the discharge standards.

[0062] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0063] Example 1

[0064] This embodiment provides a method for treating chemical nickel plating waste liquid, which uses the above-mentioned treatment system, and the treatment process is as follows: Figure 2 As shown, specifically including:

[0065] (1) The waste liquid to be treated is passed into a regulating tank, acid is added to the regulating tank, the pH is adjusted to 0-1.0 with sulfuric acid or hydrochloric acid, and filtered to remove most of the insoluble impurities.

[0066] (2) The acidic nickel plating waste liquid is passed into a redox reactor for a first-stage oxidation, which can react at room temperature and the reaction is completed in 12 hours. The hypophosphite and phosphite in the nickel plating waste liquid are oxidized into phosphates using oxygen. During the oxidation process, part of the acid solution is added to keep the pH of the reaction system less than 6. The more thorough the first-stage oxidation reaction is, the less H2O2 is consumed in the second-stage oxidation process. The first-stage oxidation reaction consumes 25.3 kg of oxygen to treat 1 ton of waste liquid.

[0067] (3) Subsequently, the nickel plating waste liquid after the first stage oxidation is passed into the decomposition reactor for second stage oxidation. The reaction time is 1 h, and hydrogen peroxide is used to decompose the organic complex to form free Ni 2+ , keep the pH of the reaction system less than 6, and the amount of H2O2 consumed by oxidative decomposition of 1 ton of waste liquid is about 30 kg.

[0068] (4) The nickel plating waste liquid after the second stage oxidation is transferred to the neutralization reaction tank, sodium hydroxide is added as a neutralization precipitant, and the pH of the waste liquid system is adjusted to 9.5. The free Ni2+ Converted into nickel phosphate or nickel hydroxide precipitation. Then passed into the sedimentation tank, added with polymer flocculant polyacrylamide (PAM), the nickel phosphate or nickel hydroxide in the system was quickly precipitated, filtered to obtain nickel phosphate or nickel hydroxide. The amount of sodium hydroxide used in each ton of wastewater is 10kg, the amount of PAM used is 0.1kg, and 9.2kg of nickel phosphate or 7kg of nickel hydroxide can be recovered.

[0069] (5) The supernatant or filtrate of the separated nickel resources is transferred to the evaporation crystallization system for direct evaporation crystallization desalination. After centrifugation, solid impurities are obtained. The main components of the solid impurities are: Na3PO4, Na2SO4, NaCl, and NaNO3. The treated evaporation condensate water sample is then analyzed, and the COD, NH3-N and TN analysis reports of the distilled water are used to determine whether further biochemical treatment or direct discharge is required.

[0070] Example 2

[0071] This embodiment provides a method for treating chemical nickel plating waste liquid, which specifically includes:

[0072] (1) The waste liquid to be treated is passed into a regulating tank, acid is added to the regulating tank, the pH is adjusted to 1-2 with sulfuric acid, and filtered to remove most of the suspended matter and impurities.

[0073] (2) The acidic nickel plating waste liquid is passed into a redox reactor for a first oxidation, the reaction starting temperature is 50-60°C, and the reaction is completed in 4 hours. The hypophosphite and phosphite in the nickel plating waste liquid are oxidized into phosphates using oxygen, and part of the consumed acid is replenished during the reaction process to reduce the consumption of H2O2 in the subsequent oxidation process. 26 kg of oxygen is consumed to treat 1 ton of waste liquid.

[0074] (3) Subsequently, the nickel plating waste liquid after the first stage oxidation was passed into the decomposition reactor for second stage oxidation. The reaction time was 0.7 h, and hydrogen peroxide was used to decompose the organic complex to form free Ni 2+ The amount of H2O2 consumed for oxidation and decomposition of each ton of waste liquid is about 30kg.

[0075] (4) The nickel plating waste liquid after the second stage oxidation is then passed into the neutralization reaction tank, sodium hydroxide is added as a neutralization precipitant, and the pH of the waste liquid system is adjusted to 9. The free Ni 2+ The wastewater is converted into nickel phosphate or nickel hydroxide for precipitation and separation. Then, the wastewater is passed into a sedimentation tank to precipitate and separate the nickel phosphate or nickel hydroxide in the system, and the nickel phosphate or nickel hydroxide and the filtrate are obtained by filtration. The amount of sodium hydroxide used in 1 ton of wastewater is 10 kg, and 9.2 kg of nickel phosphate or 7 kg of nickel hydroxide can be recovered.

[0076] (5) The supernatant and filtrate of the sedimentation tank are passed into the evaporation crystallization system for direct evaporation crystallization desalination. After centrifugation, solid impurities are obtained. The main components of the solid impurities are: Na3PO4, Na2SO4, NaCl, and NaNO3. The treated water samples are then analyzed, and the COD, NH3-N and TN analysis reports of the evaporated condensed water are used to determine whether further biochemical treatment or direct discharge is required.

[0077] Example 3

[0078] This embodiment provides a method for treating chemical nickel plating waste liquid, which specifically includes:

[0079] (1) The waste liquid to be treated is passed into a regulating tank, hydrochloric acid is added to the regulating tank, the pH is adjusted to 2-4, and filtered to remove most of the organic acid complexing agent.

[0080] (2) The acidic nickel plating waste liquid is passed into a redox reactor for a first oxidation, and the hypophosphite and phosphite in the nickel plating waste liquid are oxidized into phosphate using oxygen. The reaction starting temperature is about 60°C and the reaction time is 3 hours to reduce the H2O2 consumption in the subsequent oxidation process. 26 kg of oxygen is required to treat 1 ton of waste liquid.

[0081] (3) The nickel plating waste liquid after the first stage oxidation is passed into the decomposition reactor for second stage oxidation. The reaction time is 1.3 h. The organic complex is broken by hydrogen peroxide to form free Ni 2+ .

[0082] (4) The nickel plating waste liquid after the second stage oxidation is then passed into the neutralization reaction tank, sodium hydroxide is added as a neutralization precipitant, and the pH of the waste liquid system is adjusted to 10. The free Ni 2+ It is converted into nickel phosphate or nickel hydroxide. Then it is passed into a sedimentation tank, and a polymer flocculant polyacrylamide (PAM) is added to precipitate the nickel phosphate or nickel hydroxide in the system, and the nickel phosphate or nickel hydroxide is obtained by filtration.

[0083] (5) The supernatant and filtrate wastewater from the secondary precipitation treatment are passed into the evaporation crystallization system for direct evaporation crystallization desalination. Solid impurities are obtained after centrifugal separation. The main components of the solid impurities are: Na3PO4, Na2SO4, NaCl, and NaNO3. The treated evaporation condensate water sample is then analyzed, and the COD, NH3-N and TN analysis reports of the distilled water are used to determine whether further biochemical treatment or direct discharge is required.

[0084] Application examples:

[0085] In this application example, the nickel plating waste liquid treatment method and treatment system provided in Example 1 are used to treat the waste liquid:

[0086] After the nickel plating waste liquid is homogenized in the regulating tank, the waste liquid pH is 4-6, weakly acidic; total phosphorus is 30-34g / L, mainly hypophosphite and phosphite; COD is 60-77.5g / L; ammonia nitrogen is 3.3-4.7g / L; total nitrogen is 5.1-6.2g / L; nickel is 6.8-8.7g / L; specific gravity is 1.10-1.20.

[0087] The pollutant emission standards refer to the "Electroplating Pollutant Emission Standards" (GB2I900-2008), as shown in Table 1. The maximum emission concentration of nickel is 0.5 mg / L, and the maximum emission concentration of phosphorus is 1.0 mg / L.

[0088] Table 1. Water pollution emission concentration limits for newly built enterprises

[0089]

[0090]

[0091] In the wastewater finally treated in this application example, the nickel concentration is 0.2 mg / L and the phosphorus emission concentration is 0.6 mg / L, which is in line with the "Electroplating Pollutant Emission Standards" and is far less than the maximum emission concentration specified in the standards.

[0092] Assuming that 30 tons of nickel plating waste liquid is processed daily, the conditions of the materials before and after daily processing are shown in Table 2 and Table 3:

[0093] Table 2. Daily consumption of materials for sewage treatment

[0094]

[0095] Table 3. Materials recovered from daily sewage treatment

[0096]

[0097] As shown in Table 2 and Table 3, 30 tons of nickel plating waste liquid need to be processed daily, 300 kg of sodium hydroxide, 800 kg of oxygen, 1000 kg of 35% hydrogen peroxide, and 20000 kg of evaporated water. After processing, 828 kg of 60% nickel hydroxide containing water is recovered, and about 13000 kg of crystalline salts are produced. It can be seen that the treatment method provided in Example 1 can greatly save the amount of 35% hydrogen peroxide, reduce the amount of evaporated water, and at the same time obtain a higher content of nickel hydroxide and crystalline salts.

[0098] At the same time, from the perspective of economic benefits, the raw material cost of treating one ton of chemical nickel plating waste liquid using the method provided in Example 1 is shown in Table 4:

[0099] Table 4. Raw material cost per ton of chemical nickel plating waste liquid

[0100] Drug Name Unit price (Yuan) Consumption <![CDATA[Recovery amount (kg / m J )]]> Cost (Yuan / <![CDATA[H202]]> 3 33 99 NaOH 3.5 10 35 PAM 6.5 0.1 0.65 Salt treatment 2 443 886 sulfuric acid 0.5 2 1 <![CDATA[O2]]> 1.2 27 32.4 cost 1044.05 yuan Ni recovery 190*0.6 7 798 income - - - 798 yuan

[0101] As can be seen from Table 4, the nickel recovery value is calculated based on 60% of the market price of nickel plates. The price of nickel plates is 190,000 yuan / ton. The material income for treating each ton of chemical nickel plating waste liquid is: income - cost = 798-1044.05 = -246.05, that is, 246.05 yuan / ton is required for material investment.

[0102] Steam consumption: Using single-effect evaporation equipment, 900kg of steam is required per ton, 300 yuan per ton, equivalent to 270 yuan. Using double-effect evaporation equipment, 700kg of steam is required per ton, equivalent to 210 yuan.

[0103] Electricity cost: Assuming a power of 60kw and an average working time of 16 hours, 960 kWh of electricity per day, 20 kWh per ton, at 0.80 yuan / kWh, the cost is 25.6 yuan / ton.

[0104] Comprehensive operating cost = material input + steam consumption + electricity cost = 246.05 + 270 (based on single-effect evaporation) + 25.6 = 541.65 yuan / ton.

[0105] Using direct H2O2 oxidation method, 400kg of hydrogen peroxide is needed to treat 1 ton of the above chemical nickel plating waste liquid, and 12 tons of 35% hydrogen peroxide are needed to treat 30 tons of waste liquid. Other chemical consumables are similar. The cost of hydrogen peroxide per ton is 1,200 yuan. Evaporation uses single-effect evaporation equipment, which requires 1,400kg of steam per ton and 300 yuan per ton of steam, equivalent to 420 yuan. Using double-effect evaporation equipment, 1,100kg of steam is needed per ton, equivalent to 330 yuan. The miscellaneous salt treatment fee is 886 yuan. Therefore, the comprehensive cost of conventionally treating 1 ton of waste liquid is more than 2,400 yuan.

[0106] In summary, the nickel plating wastewater treatment system and treatment method provided by this application only cost 541.65 yuan per ton of nickel plating wastewater. It can be seen that through this treatment system and treatment method, the waste liquid can not only meet the emission standards, but also further reduce the treatment cost, recover nickel and solid salts, which is conducive to the resource utilization of nickel and has good economic and ecological benefits.

[0107] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A system for treating chemical nickel plating waste liquid, characterized in that: It includes the following systems connected in sequence: A chelation breaking pretreatment system, including a regulating tank for adjusting the pH of the nickel plating waste liquid; The oxidation and decomposition system comprises a redox reactor and a decomposition reactor connected in sequence, wherein the oxidant of the redox reactor is oxygen, the reaction temperature is 50-90°C, and the reaction time is 2-5h; the oxidant of the decomposition reactor is hydrogen peroxide, the reaction time is 0.7-1.3h, and the pH of the solution is maintained at 4-6 at the end of the oxidation and decomposition reaction; The chemical precipitation system comprises a neutralization reaction tank and a sedimentation tank connected in sequence, wherein a sodium hydroxide solution is added into the neutralization reaction tank as a precipitant, and the sedimentation tank is equipped with a filtration system; The evaporation crystallization system comprises an evaporation device, a crystallization device and a separation device which are arranged in sequence.

2. The treatment system for chemical nickel plating waste liquid according to claim 1, characterized in that: The decomposition reactor has a series-type secondary reaction tank, and the oxidation decomposition system also includes a circulation storage tank connected to the reaction tank.

3. The treatment system for chemical nickel plating waste liquid according to claim 1, characterized in that: The filtration system comprises a primary filtration device and a fine filtration device, wherein the primary filtration device is a plate-and-frame filter press or a bag filter.

4. The treatment system for chemical nickel plating waste liquid according to claim 1, characterized in that: The network breaking pretreatment system also includes a filtering and impurity removal device connected to the regulating tank.

5. A method for treating chemical nickel plating waste liquid, characterized in that: It utilizes the treatment system of chemical nickel plating waste liquid according to any one of claims 1 to 4, and the treatment method comprises: Adding acid solution into the regulating tank to obtain acidic nickel plating waste liquid; The acidic nickel plating waste liquid is passed into the redox reactor for a first-stage oxidation, and the hypophosphite and phosphite in the nickel plating waste liquid are oxidized into hydrogen phosphate or dihydrogen phosphate by oxygen; the nickel plating waste liquid after the first-stage oxidation is passed into the complex breaking reactor for a second-stage oxidation, and the organic complex is broken by hydrogen peroxide to form a free Ni 2+ ; Then, the nickel plating waste liquid after the second stage oxidation is passed into the neutralization reaction tank, and a neutralization precipitant is added to adjust the pH of the system to 9-10, and the free Ni in the system is 2+ Converting into nickel phosphate or nickel hydroxide for precipitation, filtering to obtain nickel phosphate or nickel hydroxide and secondary wastewater; The secondary wastewater is introduced into the evaporation crystallization system for evaporation crystallization to obtain solid impure salts.

6. The method for treating chemical nickel plating waste liquid according to claim 5, characterized in that: In the two-stage oxidation process, the reaction time is 0.7-1.3h.

7. The method for treating chemical nickel plating waste liquid according to claim 5, characterized in that: In the chelation breaking pretreatment system, the acid solution put into the regulating tank is a sulfuric acid solution or a hydrochloric acid solution, and the pH of the nickel plating waste liquid after adjustment is 0-6.

8. The method for treating chemical nickel plating waste liquid according to claim 5, characterized in that: The neutralization precipitant added to the neutralization reaction tank is a sodium hydroxide solution.

9. The method for treating chemical nickel plating waste liquid according to claim 8, characterized in that: The method also includes adding a polymer flocculant into the sedimentation tank.

10. The method for treating chemical nickel plating waste liquid according to claim 9, characterized in that: The reaction temperature of the one-stage oxidation is 50-90°C, and the reaction time is 2-5h.

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