A process for treating mercapto-containing electroplating silver wastewater

Abstract

The present invention belongs to the technical field of wastewater treatment, and in particular to a process for treating wastewater from electroplated silver containing mercapto groups. The process comprises the following steps: (1) taking electroplated silver containing mercapto groups and adjusting the pH to 7-9; (2) adding hydrogen peroxide, stirring and reacting for 10-30 minutes; (3) adjusting the pH to 11-11.5 again; (4) adding sodium chloride, stirring and reacting for 10-30 minutes; (5) adding 100-150 ppm polyaluminium chloride, stirring and reacting for 5-20 minutes; adding 2-3 ppm polyacrylamide, stirring and reacting for 5-20 minutes; (6) filter pressing; (7) discharging after adjusting the pH. The present invention is directed to the wastewater generated by the silver plating process using mercapto-containing drugs as additives, and a set of treatment processes are specially designed to first solve the problem of the silver component in the drainage meeting the discharge standard, and secondly solve the problem of difficult control of process parameters, and the use of dangerous sulfuric acid drugs in the treatment process, and the low treatment efficiency.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a process for treating mercapto-containing electroplated silver wastewater. Background Art

[0002] The production process of electroplating silver will produce silver-containing cleaning wastewater. Since silver is a Class I heavy metal and a heavy metal that is subject to environmental control, the discharge must meet the regulatory standard of ≤0.3mg / L. In addition, in order to ensure the quality of the electroplated coating, electroplating chemicals often require the use of organic additives. These additives can cooperate with metals, making it difficult to treat heavy metals using conventional chemical precipitation processes for wastewater treatment. Therefore, when treating wastewater containing heavy metals, the impact of organic additives on the chemical precipitation effect must be considered first.

[0003] There are many processes for electroplating silver, and each process uses different organic additives. There are currently no separate technical specifications for these additives. The existing technical specification "Fenton Oxidation Wastewater Treatment Engineering Technical Specification HJ1095" is a general technical specification for all difficult-to-degrade organic matter in electroplating wastewater. Figure 1 As shown, the Fenton oxidation process is first used to oxidize and decompose the organic matter, and then the conventional chemical precipitation process is used to precipitate the metallic silver. Among them, the Fenton oxidation process uses ferrous sulfate as a catalyst, hydrogen peroxide as an oxidant, and sulfuric acid to adjust the pH value, so that the organic matter is gradually oxidized and decomposed into small molecules, which lose the coordination effect with heavy metals. Among them, the specific process parameters of the Fenton oxidation process are: acid adjustment: adjust the pH to 3-4 with sulfuric acid; catalyst mixing: ferrous sulfate, the addition amount is based on process tests, usually H2O2 (mg / L): COD (mg / L) = 1:1~2:1, H2O2 (mg / L):Fe 2+ (mg / L)=1:1~10:1; Oxidant: hydrogen peroxide (H2O2), the dosage of the drug is the same as above, and the reaction time is 2-6h; Neutralization: use alkali solution, and the pH value meets the requirements of subsequent processes. The wastewater after Fenton oxidation uses conventional chemical precipitation process to remove heavy metal silver. The main process is: adjust pH → add polyaluminium chloride (PAC) → add polyacrylamide (PAM) → filter press → adjust pH value and discharge it externally. Among them, sodium hydroxide is used to adjust pH value, adjust pH to 11-11.5, and stir for 10 minutes; polyaluminium chloride (PAC) is an inorganic coagulant, the addition amount is 100-150ppm, and stir for 5 minutes after adding; polyacrylamide (PAM) is an organic flocculant, the addition amount is 2-3ppm, and stir for 5 minutes after adding; filter press: mud and water separation.

[0004] When using the Fenton oxidation process to treat silver-plated wastewater containing thiol drugs as additives, there are disadvantages such as unstable process, difficult to control process parameters, unsatisfactory treatment effects, use of dangerous sulfuric acid drugs in the treatment process, and low treatment efficiency. Specifically, the Fenton oxidation and conventional chemical precipitation processes for treating silver-containing wastewater have the following disadvantages:

[0005] (1) The process is unstable and the drainage is likely to exceed the standard

[0006] Fenton oxidation is difficult to completely oxidize, and various intermediates and other chemicals have a great influence on the removal of metallic silver. The laboratory has conducted many experiments to treat thiol-containing silver-containing wastewater. The silver content was 25ppm before treatment and 1.24ppm-4ppm after treatment, which did not meet the requirement of ≤0.3mg / L, and the data fluctuated greatly and was unstable.

[0007] (2) Process parameters are difficult to determine

[0008] The dosage of ferrous sulfate and hydrogen peroxide is difficult to determine due to the COD content in the wastewater and other process conditions (pH value, temperature, reaction time, etc.). Whether the water quality or process conditions fluctuate, it is difficult to determine the dosage of the drug, and at the same time it brings great uncertainty to the treatment effect, which brings difficulties to actual production.

[0009] (3) Sulfuric acid is used to adjust the pH value during production. Sulfuric acid is a highly dangerous chemical and creates a major safety risk during production.

[0010] (4) The treatment efficiency is low, and it takes at least 4 hours to treat once. Summary of the invention

[0011] In view of the above shortcomings of the prior art, the object of the present invention is to provide a process for treating mercapto-containing electroplating silver wastewater.

[0012] To achieve the above objectives, the technical solutions adopted are:

[0013] The object of the present invention is to provide a process for treating mercapto-containing electroplating silver wastewater, comprising the following steps:

[0014] (1) Take the mercapto-containing silver electroplating wastewater and adjust the pH to 7-9;

[0015] (2) Add hydrogen peroxide and stir to react for 10-30 minutes;

[0016] (3) Adjust the pH to 11-11.5 again;

[0017] (4) Add sodium chloride and stir to react for 10-30 minutes;

[0018] (5) Add 100-150 ppm polyaluminium chloride and stir for 5-20 minutes; add 2-3 ppm polyacrylamide and stir for 5-20 minutes;

[0019] (6) Filter pressing;

[0020] (7) Adjust pH before discharge.

[0021] The beneficial effects of adopting the above technical scheme are as follows: before adding hydrogen peroxide, the pH is adjusted to 7-9. Within this pH range, the decomposition speed of hydrogen peroxide is relatively fast, and the thiol component in the organic matter coordinated with the heavy metal silver can be destroyed. The thiol is easily oxidized and reacts with hydrogen peroxide to dissociate the silver; the pH is adjusted again, and a chemical precipitation process is adopted to precipitate the silver. Sodium chloride reacts with silver ions to form insoluble silver chloride, so that the silver content is further reduced; polyaluminium chloride can polymerize and coagulate silver chloride and other silver inorganic substances; polyacrylamide allows further flocculation to form a large precipitate; the purpose of filter pressing is to separate mud and water.

[0022] Among them, sodium hydroxide is preferred for adjusting pH.

[0023] Preferably, the following steps are further included between step (2) and step (3): adjusting the pH to 7-9, adding sodium pyrosulfite, and the mass ratio of sodium pyrosulfite to hydrogen peroxide is 2.4-2.7:1.

[0024] Preferably, the following steps are further included between step (6) and step (7): adjusting the pH to 7-9, adding sodium pyrosulfite, and the mass ratio of sodium pyrosulfite to hydrogen peroxide is 2.4-2.7:1.

[0025] The beneficial effect of adopting the above two-step optimization technical solution is that sodium metabisulfite can neutralize excess hydrogen peroxide. Excessive use of sodium metabisulfite will cause the decomposed sulfite to dissolve in the wastewater with heavy metal silver, resulting in excessive silver in the drainage. The above provides two timings for adding sodium metabisulfite. Compared with adding sodium metabisulfite after adding hydrogen peroxide and before adjusting the pH, adding sodium metabisulfite after filter pressing has a better reduction effect, which will reduce the influence of sulfite and other intermediates formed after the reaction of sodium metabisulfite on the formation of soluble complexes with silver, thereby further reducing the silver content in the drainage.

[0026] Preferably, the silver ion content in the mercapto-containing silver electroplating wastewater is 20-80 ppm, more preferably 20-50 ppm.

[0027] Preferably, the amount of hydrogen peroxide added is 150-300 ppm.

[0028] The beneficial effect of adopting the above two-step optimal technical scheme is that the amount of hydrogen peroxide used varies with the silver content in the mercapto-containing electroplating silver wastewater. For example, if the silver ion content is 20-50ppm, 150ppm of hydrogen peroxide is added. If the silver content increases to 80ppm, the amount of hydrogen peroxide added increases to 300ppm and above.

[0029] Preferably, the amount of sodium chloride added is 250-500 ppm, more preferably 250 ppm.

[0030] Preferably, the pH is adjusted after filter pressing and the waste is discharged after reaching the discharge standard.

[0031] Compared with the prior art, the beneficial effect of the present invention is that the present invention specifically designs a set of treatment processes for wastewater generated in the silver plating process using mercapto-containing drugs as additives. The present invention first solves the problem of silver components in wastewater meeting the discharge standards, and secondly solves the problem of difficult control of process parameters and low treatment efficiency due to the use of dangerous sulfuric acid drugs in the treatment process.

[0032] (1) The process is stable and the drainage index is far lower than the national standard.

[0033] The present invention is completely feasible after actual production and use, the silver content in drainage is basically below the middle limit, and the one-side CP value of the process capability index reaches 1.89 (unqualified rate 0.0059ppm), that is, it takes 69.93 million times of processing before an exceeding of the standard may occur once, and the process is very stable.

[0034] The silver content in the wastewater is below 0.15 mg / L, which is far lower than the national emission standard of 0.3 mg / L. Moreover, the process is stable, and the risk of exceeding the standard is almost zero during the effective period of the device.

[0035] (2) The process conditions are easy to control and the drugs are suitable for a wide range of wastewaters

[0036] The added drugs have a wide range of applications, can be easily controlled using instruments and metering pumps, and the process is stable. When the silver content in the wastewater changes, only the amount of hydrogen peroxide and sodium metabisulfite needs to be adjusted, and the other drugs do not need to be changed. In addition, the process has a wide range of application. When the silver content in the wastewater is 25-50ppm, the drug use parameters do not need to be changed to meet the emission standards.

[0037] (3) This process does not use sulfuric acid, eliminating major unsafe factors in production.

[0038] (4) The treatment efficiency is high, and it only takes 1 hour for each treatment, which is 3 times higher than the Fenton oxidation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is the Fenton oxidation wastewater treatment process;

[0040] Figure 2 It is the process capability index of the process of the present invention for treating silver-containing wastewater. DETAILED DESCRIPTION

[0041] The present invention is described below in conjunction with examples, which are only used to explain the present invention and are not used to limit the scope of the present invention.

[0042] Example 1

[0043] (1) Take mercapto-containing electroplating silver wastewater, in which the silver ion content is 22.9 ppm, and use sodium hydroxide to adjust the pH to 8.40;

[0044] (2) Add 150 ppm hydrogen peroxide and stir for 20 minutes;

[0045] (3) Using sodium hydroxide to adjust the pH to 8.3, adding sodium pyrosulfite, the mass ratio of sodium pyrosulfite to hydrogen peroxide is 2.5:1;

[0046] (4) Use sodium hydroxide to adjust the pH to 11.4;

[0047] (5) Add 250 ppm sodium chloride and stir to react for 15 minutes;

[0048] (6) Add 125 ppm polyaluminium chloride and stir for 5 minutes;

[0049] (7) Add 2.5 ppm polyacrylamide and stir for 5 minutes.

[0050] (8) Filter press and adjust the pH to meet the standards before discharge.

[0051] The detection showed that the silver ion content in the silver wastewater was 0.15ppm, which is far below the national standard.

[0052] Example 2

[0053] (1) Take mercapto-containing electroplating silver wastewater, in which the silver ion content is 38.2 ppm, and use sodium hydroxide to adjust the pH to 8.11;

[0054] (2) Add 160 ppm hydrogen peroxide and stir to react for 20 minutes;

[0055] (3) Use sodium hydroxide to adjust the pH to 8.05, add sodium pyrosulfite, and the mass ratio of sodium pyrosulfite to hydrogen peroxide is 2.5:1;

[0056] (4) Use sodium hydroxide to adjust the pH to 11.2;

[0057] (5) Add 250 ppm sodium chloride and stir to react for 15 minutes;

[0058] (6) Add 125 ppm polyaluminium chloride and stir for 5 minutes;

[0059] (7) Add 2.5 ppm polyacrylamide and stir for 5 minutes.

[0060] (8) Filter press and adjust the pH to meet the standards before discharge.

[0061] The detection showed that the silver ion content in the silver wastewater was 0.1ppm, which is lower than the national standard.

[0062] Example 3

[0063] (1) Take mercapto-containing electroplating silver wastewater, in which the silver ion content is 49.2 ppm, and use sodium hydroxide to adjust the pH to 8.48;

[0064] (2) Add 200 ppm of hydrogen peroxide and stir to react for 20 minutes;

[0065] (3) Using sodium hydroxide to adjust the pH to 8.4, adding sodium pyrosulfite, the mass ratio of sodium pyrosulfite to hydrogen peroxide is 2.5:1;

[0066] (4) Use sodium hydroxide to adjust the pH to 11.31;

[0067] (5) Add 250 ppm sodium chloride and stir to react for 15 minutes;

[0068] (6) Add 125 ppm polyaluminium chloride and stir for 5 minutes;

[0069] (7) Add 2.5 ppm polyacrylamide and stir for 5 minutes.

[0070] (8) Filter press and adjust the pH to meet the standards before discharge.

[0071] The detection showed that the silver ion content in the silver wastewater was 0.17ppm, which is lower than the national standard.

[0072] Example 4

[0073] (1) Take mercapto-containing electroplating silver wastewater, in which the silver ion content is 22.9 ppm, and use sodium hydroxide to adjust the pH to 8.40;

[0074] (2) Add 150 ppm hydrogen peroxide and stir for 20 minutes;

[0075] (3) Use sodium hydroxide to adjust the pH to 11.4;

[0076] (4) Add 250 ppm sodium chloride and stir to react for 15 minutes;

[0077] (5) Add 125 ppm polyaluminium chloride and stir for 5 minutes;

[0078] (6) Add 2.5 ppm polyacrylamide and stir for 5 minutes.

[0079] (7) Filter press, use sodium hydroxide to adjust the pH to 8.3, add sodium metabisulfite, the mass ratio of sodium metabisulfite to hydrogen peroxide is 2.5:1; adjust the pH to meet the standard before discharge.

[0080] The detection showed that the silver ion content in the silver wastewater was 0.10ppm, which is lower than the national standard.

[0081] Example 5

[0082] (1) Take mercapto-containing electroplating silver wastewater, in which the silver ion content is 80 ppm, and use sodium hydroxide to adjust the pH to 7.8;

[0083] (2) Add 600 ppm of hydrogen peroxide and stir for 20 minutes;

[0084] (3) Use sodium hydroxide to adjust the pH to 7.8, add sodium pyrosulfite, and the mass ratio of sodium pyrosulfite to hydrogen peroxide is 2.5:1;

[0085] (4) Use sodium hydroxide to adjust the pH to 11.3;

[0086] (5) Add 500 ppm sodium chloride and stir to react for 15 minutes;

[0087] (6) Add 125 ppm polyaluminium chloride and stir for 5 minutes;

[0088] (7) Add 2.5 ppm polyacrylamide and stir for 5 minutes.

[0089] (8) Filter press and adjust the pH to meet the standards before discharge.

[0090] The detection showed that the silver ion content in the silver wastewater was 0.24ppm, which is lower than the national standard.

[0091] Comparative Example 1

[0092] The only difference from Example 1 is that the mass ratio of sodium pyrosulfite to hydrogen peroxide is 2.8:1.

[0093] The detection showed that the silver ion content in the silver wastewater was 0.24ppm.

[0094] Comparative Example 2

[0095] (1) Take mercapto-containing electroplating silver wastewater, in which the silver ion content is 80 ppm, and use sodium hydroxide to adjust the pH to 7.8;

[0096] (2) Add 600 ppm of hydrogen peroxide and stir for 20 minutes;

[0097] (3) Use sodium hydroxide to adjust the pH to 7.6;

[0098] (4) Using sodium hydroxide to adjust the pH to 11.33, adding sodium metabisulfite, the mass ratio of sodium metabisulfite to hydrogen peroxide is 2.5:1;

[0099] (5) Add 500 ppm sodium chloride and stir to react for 15 minutes;

[0100] (6) Add 125 ppm polyaluminium chloride and stir for 5 minutes;

[0101] (7) Add 2.5 ppm polyacrylamide and stir for 5 minutes.

[0102] (8) Filter press and adjust the pH to meet the standards before discharge.

[0103] The test showed that the silver ion content in the silver wastewater was 0.35ppm, which is higher than the national standard.

[0104] Through the above embodiments and comparative examples, it can be found that the silver ion content of the mercapto-containing electroplated silver-containing wastewater to be treated in Examples 1 to 4 of the present invention is 20-50ppm, which can be reduced to below 0.2ppm after treatment. The silver ion content of the mercapto-containing electroplated silver-containing wastewater to be treated in Example 5 is 80ppm. Under the condition of reasonable adjustment of parameters, the standard of Ag≤0.3ppm can still be guaranteed. Figure 2 The process capability index diagram of the process of treating silver-containing wastewater of the present invention is shown in the figure. The curve in the figure is the result of taking 18 sets of data for testing continuously when the production is stable. The horizontal axis represents the silver ion content in ppm. The USL (upper specification limit) of the silver ion content is 0.3ppm, and the LSL (lower specification limit) is not set. Cpu (upper capability index) is an indicator specifically used to evaluate the capability of the process near the upper specification limit. Cpk (process capability index) is an indicator that measures the process capability while considering the process mean shift, which reflects the actual capability of the process. There is a corresponding relationship between Cpu and Cpk and the unqualified rate. The higher the Cpu and Cpk values, the stronger the process capability, the higher the proportion of qualified products produced, and the lower the unqualified rate. The values ​​of Cpu and Cpk in the process of the present invention are 1.89, which means that the unqualified rate is extremely low and the process is stable. The difference between Comparative Example 2 and Example 5 lies in the timing of adding sodium metabisulfite. In Comparative Example 2, sodium metabisulfite is added after sodium chloride is added, and then sodium metabisulfite is added, which reacts with hydrogen peroxide to generate sulfuric acid, causing the pH value to decrease, causing some heavy metal precipitation and dissolution, and increasing the heavy metal content in the solution, so the precipitation effect is not good.

[0105] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for treating mercapto-containing electroplating silver wastewater, characterized in that: The following steps are involved: (1) Take the mercapto-containing silver electroplating wastewater and adjust the pH to 7-8.40; (2) Add hydrogen peroxide and stir to react for 10-30 minutes; (3) Adjust the pH to 11-11.5 again; (4) Add sodium chloride and stir to react for 10-30 minutes; (5) Add 100-150 ppm polyaluminium chloride and stir for 5-20 minutes; add 2-3 ppm polyacrylamide and stir for 5-20 minutes; (6) Filter pressing; (7) Discharge after adjusting pH; The following steps are also included between step (6) and step (7): adjusting the pH to 7-9, adding sodium pyrosulfite, and the mass ratio of sodium pyrosulfite to hydrogen peroxide is 2.4-2.7:1; The amount of hydrogen peroxide added is 150-300ppm; The amount of sodium chloride added is 250-500ppm.

2. The process for treating mercapto-containing electroplating silver wastewater according to claim 1, wherein: The silver ion content in mercapto-containing silver electroplating wastewater is 20-80ppm.

3. The process for treating mercapto-containing electroplating silver wastewater according to claim 2, wherein: The silver ion content in mercapto-containing silver electroplating wastewater is 20-50ppm.

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