A method for advanced treatment of cadmium-containing wastewater

Abstract

The application discloses a kind of deep treatment methods of cadmium-containing wastewater, it is related to wastewater treatment method field, the treatment method includes the following steps: S1, raw water pretreatment: acid cadmium-containing wastewater is collected separately, after adding precipitant, stirring and aeration standing, obtain supernatant and sediment;S2, deep treatment: the wastewater after pretreatment is treated by advanced oxidation process and is broken complex;S3, subsequent treatment: special chelating agent is added to the wastewater after deep treatment and is treated;S4, detection and discharge: after being treated, wastewater is discharged to intermediate pool after detection is qualified.The application can efficiently remove cadmium ions and other harmful substances in wastewater by using complex breaking agent and heavy metal capturing agent for deep treatment of cadmium-containing wastewater, realize the deep purification of wastewater, ensure that effluent quality meets discharge standard, solve the problem that cadmium-containing wastewater discharge standard is low and difficult to handle, meet the needs of long-term operation of sewage plant, bring significant economic benefits and social benefits.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of wastewater treatment methods, in particular to a deep treatment method for cadmium-containing wastewater. BACKGROUND

[0002] With the rapid development of modern industrial production, especially the rapid development of metal smelting, mining, electroplating and other industries, the discharge of cadmium-containing wastewater has increased significantly. Cadmium is a toxic and harmful heavy metal element, which has great harm to human body and environment. Therefore, the treatment of cadmium-containing wastewater has become a problem to be solved. At present, the treatment methods of cadmium-containing wastewater mainly include physical method, chemical method and biological method. The physical method mainly includes precipitation, filtration, adsorption, etc.; the chemical method mainly includes oxidation-reduction, neutralization precipitation, complex precipitation, etc.; the biological method mainly uses microorganisms or plants to absorb and transform cadmium in wastewater. However, these traditional methods have some problems in treatment effect, treatment efficiency, cost and secondary pollution. Because the enterprise exists acid plating cadmium, its complexing ability is strong, and the emission concentration is very low. In order to ensure that the drainage meets the standard, a deep treatment method for cadmium-containing wastewater is urgently needed to carry out deep treatment on cadmium-containing wastewater.

[0003] The existing method has the following problems:

[0004] The traditional method has great difficulty in treating high-concentration cadmium-containing wastewater, and it is often difficult to achieve ideal removal effect. Some methods need a long treatment time, and a large amount of energy and chemical reagents are consumed in the treatment process. The precipitates, waste residues and other substances generated in the treatment process may cause secondary pollution to the environment. SUMMARY

[0005] The present application provides a deep treatment method for cadmium-containing wastewater to solve the problems in the above-mentioned background method.

[0006] To solve the above-mentioned method problems, the method scheme adopted by the present application is:

[0007] A deep treatment method for cadmium-containing wastewater, the treatment method comprising the following steps:

[0008] S1, raw water pretreatment: separately collect acid cadmium-containing wastewater, add a precipitating agent, stir and aerate, and then stand to obtain supernatant and sediment;

[0009] S2, deep treatment: the pretreated wastewater is subjected to high-level oxidation treatment to break the complex;

[0010] S3, subsequent treatment: adding a special chelating agent to the wastewater after deep treatment for treatment;

[0011] S4, detection and discharge: the treated wastewater is discharged to an intermediate pool after passing the detection.

[0012] Preferably, the precipitant is one or more of calcium oxide, sodium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate solution with a concentration of ≥5%.

[0013] Preferably, after adding the medicament in S1, the pH value of the wastewater is adjusted to 5-9, and the aeration time is 10-20 min.

[0014] Preferably, S2 comprises the following steps:

[0015] 0.5% of a complex breaking agent is added to the pretreated wastewater for stirring, and after 30 min of reaction, the wastewater is pumped to a cadmium concentration reduction line for concentration reduction treatment, and the ions with strong complexing ability are collected for further treatment;

[0016] The pH of the cadmium-containing wastewater after concentration reduction treatment is adjusted to 3-4, and 0.5% of a complex breaking agent is added again for stirring, and after 30 min of reaction, the wastewater is pumped to a cadmium treatment line, a heavy metal capturing agent is added for treatment, and a filter is used for filtration to obtain supernatant and sediment;

[0017] If the complexing ability of the cadmium-containing wastewater after concentration reduction is strong in the process experiment, and the complex breaking agent cannot achieve the expected complex breaking effect, the complex breaking agent in the second step needs to be changed to a Fenton reagent for Fenton oxidation process treatment.

[0018] Preferably, the heavy metal capturing agent comprises inorganic salt heavy metal capturing agents and organic heavy metal capturing agents, the inorganic salt heavy metal capturing agents include but are not limited to sodium sulfide, polyaluminum chloride, iron salt, phosphate, and the organic heavy metal capturing agents include but are not limited to organic sulfur TMT heavy metal capturing agent and polyamine heavy metal capturing agent.

[0019] Preferably, the Fenton reagent is ferrous sulfate and hydrogen peroxide, the ferrous sulfate is added first and then the hydrogen peroxide in the Fenton oxidation process, and the process parameters of the Fenton oxidation process are as follows:

[0020] The ferrous sulfate dosage is 20 mg / L;

[0021] The hydrogen peroxide dosage is 100 mg / L;

[0022] The pH value is 3-5;

[0023] The reaction time is 20-30 min.

[0024] Preferably, the special chelating agent is a composite chelating agent prepared by compounding trisodium trithiocyanate and sodium dimethyl dithiocarbamate, and the mass ratio of trisodium trithiocyanate and sodium dimethyl dithiocarbamate is 20%-65% and 35%-80%, respectively.

[0025] Preferably, the S3 comprises: adding a special chelating agent into the deeply treated wastewater, the mass ratio of the special chelating agent to the wastewater being 1:200-1:5000, stirring for 5-30 min, then adding polyaluminum oxide, the mass ratio of the polyaluminum oxide to the wastewater being 1:200-1:5000, stirring again for 5-30 min, then standing at normal temperature for 0.5-12 h, and filtering by using a filter.

[0026] Due to the adoption of the above method scheme, the method progress achieved by the present application relative to the prior art is:

[0027] The present application provides a kind of deeply treated wastewater containing cadmium, by using breaking agent and heavy metal capture agent, the deeply treated wastewater containing cadmium can be efficiently removed cadmium ion and other harmful substances in wastewater, realize the deep purification of wastewater, ensure that effluent quality meets discharge standard, solve the problem of low discharge standard of wastewater containing cadmium, difficult to handle, meet the needs of long-term operation of sewage plant, bring significant economic benefits and social benefits, simple process flow.

[0028] The present application provides a kind of deeply treated wastewater containing cadmium, by using special chelating agent and heavy metal ion in wastewater form stable chelate, remove it from wastewater, the cadmium concentration in treated wastewater is far lower than national discharge standard, and chelate precipitate is stable, reduce the secondary pollution caused by cadmium precipitate to environment, with environmental protection, high efficiency energy saving, less precipitation, non-toxicity, reduce the processing cost.

[0029] The present application provides a kind of deeply treated wastewater containing cadmium, by optimizing wastewater treatment process, improve processing efficiency, reduce the processing cost of wastewater containing cadmium, in process experiment, when the complexing ability of wastewater containing cadmium after concentration reduction is strong, breaking agent cannot achieve the expected breaking effect, change breaking agent to fenton reagent for fenton oxidation process treatment, ensure that treatment effect is stable and reliable, shorten the treatment time of wastewater, at the same time avoid consuming a large amount of energy and chemical reagent.

[0030] The present application provides a kind of deeply treated wastewater containing cadmium, by using precipitating agent to remove part of cadmium ion in wastewater, then using deep treatment method to remove cadmium, can effectively reduce the dosage of precipitating agent, reduce the fouling speed of on-site process, reduce the descaling maintenance time, improve production efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The process flow chart of the deeply treated wastewater containing cadmium of the present application. DETAILED DESCRIPTION

[0032] To make the method means, creative features, purposes and effects achieved by the present application easy to understand, the present application is further described below in combination with specific embodiments.

[0033] As Figure 1 shown, a kind of cadmium-containing wastewater advanced treatment method, the treatment method includes the following steps:

[0034] S1, raw water pretreatment: separately collect acidic cadmium-containing wastewater, after adding precipitant, stirring and aeration standing, obtain supernatant and sediment;

[0035] S2, advanced treatment: the wastewater after pretreatment is treated by advanced oxidation treatment and is broken complexed;

[0036] S3, subsequent treatment: adding special chelating agent to the wastewater after advanced treatment;

[0037] S4, detection and discharge: after the treated wastewater is detected and qualified, it is discharged to intermediate pool.

[0038] By raw water pretreatment, advanced treatment, subsequent treatment, detection and discharge and other steps, cadmium-containing wastewater is treated, which can effectively remove cadmium ions in wastewater, realize the deep purification and reuse of wastewater, help to realize the effective treatment of cadmium-containing wastewater and the sustainable development of environment, use precipitant to remove part of cadmium ions in wastewater, and then use advanced treatment method to remove cadmium deeply, which can effectively reduce the dosage of precipitant, reduce the fouling speed of on-site process, reduce the descaling maintenance time, improve the production efficiency, since the implementation of the process scheme, a total of 6720 tons of cadmium-containing wastewater has been treated, the reagent cost is 9.35 yuan / ton, and the total cost of sewage plant is about 50 yuan / ton, which can basically meet the long-term operation demand of sewage plant, cadmium is the necessary electroplating process for aerospace and military enterprises, and its wastewater treatment has been a long-standing problem for the development of the industry, this process solves the problem of cadmium-containing wastewater treatment, which also has a great promoting effect on the development of the above industries, thereby bringing significant economic and social benefits.

[0039] The precipitant is one or more of calcium oxide, sodium hydroxide, calcium hydroxide, sodium carbonate and sodium bicarbonate solution with a concentration of ≥5%.

[0040] After adding reagent in S1, adjust the wastewater ph to 5-9, and the aeration time is 10-20 min.

[0041] S2 includes the following steps:

[0042] 0.5% of the complexing agent is added to the pretreated wastewater and stirred, and after 30 min of reaction, it is pumped to the cadmium-containing concentration line for concentration reduction treatment, the purpose of this step is to separate the part of cadmium ions with weak complexing property and easy to handle in cadmium-containing wastewater, and the ions with strong complexing property are collected and further treated;

[0043] The PH of the cadmium-containing wastewater after the concentration reduction treatment is adjusted to 3-4, and 0.5% of a complex breaker is added again for stirring. After 30 minutes of reaction, the cadmium-containing wastewater is pumped to the cadmium treatment line, and a heavy metal capturing agent is added for treatment. Filtration equipment is used for filtration to obtain supernatant and sediment;

[0044] If the cadmium-containing wastewater after the concentration reduction treatment has strong complexing properties in the process experiment, and the complex breaker cannot achieve the expected complex breaking effect, the complex breaker in the second step needs to be replaced with Fenton reagent for Fenton oxidation process treatment. The high-efficiency oxidation and degradation capability of the Fenton oxidation process can be fully utilized to improve the removal rate of cadmium ions and purify the water quality, which helps to improve the overall efficiency of wastewater treatment, meets the requirements of environmental protection and sustainable development, optimizes the wastewater treatment process, improves the treatment efficiency, and reduces the treatment cost of cadmium-containing wastewater.

[0045] The complex breaker is an oxidizing agent, which mainly oxidizes and decomposes the complexes in the wastewater to free metal ions, creating conditions for subsequent heavy metal capture and chelation processes;

[0046] The heavy metal capturing agent chelates heavy metal ions through various chelating groups to form stable insoluble precipitates, achieving the purpose of removing heavy metal ions. In addition, under the action of the high-molecular-weight structure of the heavy metal capturing agent, the precipitation speed and removal rate can be significantly improved through flocculation and net capture;

[0047] By using the complex breaker and the heavy metal capturing agent for deep treatment of cadmium-containing wastewater, cadmium ions and other harmful substances in the wastewater can be efficiently removed, achieving deep purification of the wastewater and ensuring that the effluent water quality meets the discharge standards. This solves the problem of low discharge standard and high treatment difficulty of cadmium-containing wastewater, meets the long-term operation requirements of sewage plants, and brings significant economic and social benefits.

[0048] The heavy metal capturing agent includes inorganic salt heavy metal capturing agents and organic heavy metal capturing agents. The inorganic salt heavy metal capturing agents include but are not limited to sodium sulfide, polyaluminum chloride, iron salt, and phosphate. The organic heavy metal capturing agents include but are not limited to organic sulfur TMT heavy metal capturing agent and polyamine heavy metal capturing agent.

[0049] The Fenton reagent is ferrous sulfate and hydrogen peroxide. In the Fenton oxidation process, ferrous sulfate is added first, followed by hydrogen peroxide. The process parameters of the Fenton oxidation process are as follows:

[0050] The ferrous sulfate dosage is 20 mg / L;

[0051] The hydrogen peroxide dosage is 100 mg / L;

[0052] The pH value is 3-5;

[0053] The reaction time is 20-30 minutes.

[0054] The special chelating agent is a composite chelating agent prepared by compounding trisodium trithiocyanate and sodium dimethyl dithiocarbamate, and the mass ratio of trisodium trithiocyanate and sodium dimethyl dithiocarbamate is 20%-65% and 35%-80% respectively.

[0055] S3 comprises: adding the special chelating agent into the wastewater after deep treatment, the mass ratio of the special chelating agent to the wastewater is 1:200-1:5000, stirring for 5-30 min, then adding polyaluminum hydroxide, the mass ratio of the polyaluminum hydroxide to the wastewater is 1:200-1:5000, stirring again for 5-30 min, then standing at normal temperature for 0.5-12 h, and filtering by using a filter.

[0056] By using the special chelating agent to form stable chelates with heavy metal ions in the wastewater, the heavy metal ions are removed from the wastewater, the cadmium concentration in the treated wastewater is far lower than the national discharge standard, the chelates are stable in precipitation, the secondary pollution caused by cadmium precipitates to the environment is reduced, and the chelates have the advantages of environmental protection, high efficiency and energy saving, less precipitation, non-toxicity and reduced treatment cost.

[0057] In summary, the acidic cadmium-containing wastewater is collected alone, the pH value of the wastewater is adjusted to 5-9, a precipitant is added for stirring and aeration for 10-20 min, and after standing, the supernatant and sediment are obtained, 0.5% of a complex breaking agent is added to the pretreated wastewater for stirring, and after 30 min of reaction, the wastewater is pumped to a cadmium concentration reduction line for concentration reduction treatment. The purpose of this step is to separate the easily treated part of the cadmium ions with weak complexing ability from the cadmium-containing wastewater, and to collect the ions with strong complexing ability for further treatment. The pH of the cadmium-containing wastewater after concentration reduction treatment is adjusted to 3-4, and 0.5% of a complex breaking agent is added for stirring. After 30 min of reaction, the wastewater is pumped to a cadmium treatment line, a heavy metal capturing agent is added for treatment, and a filtering device is used for filtration to obtain the supernatant and sediment. If the cadmium-containing wastewater after concentration reduction has strong complexing ability in the process experiment, the complex breaking agent in the second step needs to be replaced with a Fenton reagent for Fenton oxidation process treatment. The high efficient oxidation and degradation ability of the Fenton oxidation process is fully utilized to improve the removal rate of cadmium ions and purify the water quality, while avoiding the consumption of a large amount of energy and chemical reagents, which helps to improve the overall efficiency of wastewater treatment, optimize the wastewater treatment process, reduce the treatment cost of cadmium-containing wastewater, and use a complex breaking agent and a heavy metal capturing agent for deep treatment of cadmium-containing wastewater to efficiently remove cadmium ions and other harmful substances in the wastewater, achieve deep purification of the wastewater, and ensure that the effluent water quality meets the discharge standard. A special chelating agent is added to the wastewater after deep treatment, and the mass ratio of the special chelating agent to the wastewater is 1:200-1:5000. After stirring for 5-30 min, polyaluminum oxide is added, and the mass ratio of the polyaluminum oxide to the wastewater is 1:200-1:5000. After stirring for 5-30 min again, the wastewater is left to stand at room temperature for 0.5-12 h, and then filtered using a filter. The treated wastewater is discharged to an intermediate tank after passing the detection. The process flow is simple, solves the problems of low discharge standard and high treatment difficulty of cadmium-containing wastewater, uses a special chelating agent to form stable chelates with heavy metal ions in the wastewater to remove them from the wastewater, the cadmium concentration in the treated wastewater is far below the national discharge standard, and the chelate precipitate is stable, reducing the secondary pollution of cadmium precipitate to the environment. The deep treatment method can shorten the treatment time of the wastewater, the use of a precipitant to remove part of the cadmium ions in the wastewater, and the use of a deep treatment method to deeply remove cadmium can effectively reduce the amount of precipitant used, reduce the on-site process scaling speed, reduce the descaling maintenance time, and improve the production efficiency. Since the implementation of the process scheme, a total of 6720 tons of cadmium-containing wastewater has been treated, the cost of reagents is 9.35 yuan / ton, and the total cost of the sewage plant is about 50 yuan / ton, which basically meets the long-term operation needs of the sewage plant. Cadmium is an essential electroplating process for the aerospace and military industries, and the treatment of its wastewater has been a long-standing problem for the development of the industry. This process solves the problem of treating cadmium-containing wastewater and has a great promoting effect on the development of the above industries, thereby bringing significant economic and social benefits.

[0058] The above detailed description of the application is given in general terms but modifications or improvements can be made to it which will be apparent to those skilled in the art of the method. Therefore, any modifications or improvements made without departing from the spirit of the application are within the scope of the present application.

Claims

1. A method for advanced treatment of cadmium-containing wastewater, characterized by: The treatment method comprises the following steps: S1, raw water pretreatment: separately collect the acidic cadmium-containing wastewater, add a precipitant, stir and aerate and stand, and then obtain supernatant and sediment; S2, advanced treatment: perform high-level oxidation treatment on the pretreated wastewater to break the complexation; S3, subsequent treatment: add a special chelating agent to the wastewater after the advanced treatment; S4, detection and discharge: after the treated wastewater is detected to be qualified, discharge it to an intermediate pool; The S2 comprises the following steps: Add 0.5% of a complex breaking agent to the pretreated wastewater and stir, after 30 minutes of reaction, draw it to a cadmium concentration reduction line for concentration reduction treatment, collect ions with strong complexing properties and further treat them; After the PH of the cadmium-containing wastewater after the concentration reduction treatment is adjusted to 3-4, add 0.5% of a complex breaking agent again for stirring, after 30 minutes of reaction, draw it to a cadmium treatment line, add a heavy metal capturing agent for treatment, and use a filter to filter, to obtain supernatant and sediment; If, in the process experiment, the cadmium-containing wastewater after the concentration reduction has strong complexing properties, and the complex breaking agent cannot achieve the expected complex breaking effect, then the complex breaking agent in the second step needs to be changed to a Fenton reagent for Fenton oxidation process treatment; The special chelating agent is a composite chelating agent prepared by compounding trisodium trithiocyanate and sodium dimethyl dithiocarbamate, and the mass ratio of the trisodium trithiocyanate and the sodium dimethyl dithiocarbamate is 20%-65% and 35%-80% respectively.

2. The method for advanced treatment of cadmium-containing wastewater according to claim 1, characterized in that: The precipitant is one or more of calcium oxide, sodium hydroxide, calcium hydroxide, sodium carbonate and sodium bicarbonate solution with a concentration of ≥5%.

3. The method according to claim 1, wherein the method is characterized by: After adding the medicament in the S1, adjust the PH of the wastewater to 5-9, and the aeration time is 10-20 minutes.

4. The method for advanced treatment of cadmium-containing wastewater according to claim 1, characterized in that: The heavy metal capturing agent comprises inorganic salt heavy metal capturing agents and organic heavy metal capturing agents, the inorganic salt heavy metal capturing agents include but are not limited to sodium sulfide, polyaluminum chloride, iron salt and phosphate, and the organic heavy metal capturing agents include but are not limited to organic sulfur TMT heavy metal capturing agent and polyamine heavy metal capturing agent.

5. The method for advanced treatment of cadmium-containing wastewater according to claim 1, characterized in that: The Fenton reagent is ferrous sulfate and hydrogen peroxide, the Fenton oxidation process first adds ferrous sulfate and then hydrogen peroxide, and the process parameters of the Fenton oxidation process are as follows: The ferrous sulfate dosage is 20 mg / L; The hydrogen peroxide dosage is 100 mg / L; The PH value is 3-5; The reaction time is 20-30 minutes.

6. The method according to claim 5, wherein the method is characterized by: The S3 comprises: adding the special chelating agent to the wastewater after the advanced treatment, the mass ratio of the special chelating agent to the wastewater is 1:200-1:5000, stirring for 5-30 minutes, then adding polyaluminum chloride, the mass ratio of the polyaluminum chloride to the wastewater is 1:200-1:5000, stirring for 5-30 minutes again, and then standing at room temperature for 0.5-12 hours, and using a filter to filter.

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