A comprehensive treatment method for electroplating wastewater

Abstract

This invention discloses a combined treatment method for electroplating wastewater, the resulting dry gel, and its applications. The method includes the following steps: preparing an aluminum sulfate octadechydrate solution, adding it to the electroplating wastewater, and stirring until homogeneous; then adding water glass to the mixture and stirring until homogeneous; allowing the mixture to stand until it completely transforms into a gel; and dehydrating the gel to obtain a dry gel. This invention completely transforms the wastewater into a gel, converting all harmful substances in the wastewater into the gel, resulting in thorough and simple treatment of electroplating wastewater. This invention utilizes the flocculation effect of aluminum sulfate to first convert impurities in the wastewater into large clusters, and then, through the promoting effect of aluminum ions on the gelation of water glass, it can quickly form a gel solid. This not only promotes the gelation time of water glass but also reduces sludge production and the land area occupied by waste. The resulting dry gel can be reused, avoiding secondary pollution caused by solid waste generated during wastewater treatment, which aligns with the concept of green sustainability.

Description

Technical Field

[0001] This invention relates to a comprehensive treatment method for flocculation-gelation of acidic electroplating wastewater containing heavy metals using aluminum sulfate and water glass, and belongs to the field of environmental technology. Background Technology

[0002] The electroplating industry is one of the world's three most polluting industries, and chromium-containing electroplating wastewater is among the most harmful heavy metal wastewater. This type of wastewater mainly originates from cleaning water used in plating tanks and on plating parts, waste electroplating solutions, plating tank waste liquid, workshop rinsing water, ventilation condensate, and leaks caused by equipment leaks or improper operation. Among these, cleaning water for plating parts accounts for more than 80% of the total wastewater discharge from electroplating workshops. Currently, the treatment of chromium-containing and other heavy metal wastewater still faces many challenges, including long process flows, high treatment costs, ineffective recovery of chromium resources, and large consumption of reagents. However, chromium poses a significant threat to the ecological environment and human health. If not properly treated, it will cause serious damage to the ecological environment and accumulate through the food chain, posing a potential threat to human health.

[0003] The sol-gel method has proven effective in wastewater treatment, offering advantages such as low cost, simple operation, and low sludge production. For example, patent CN110590014A describes adding water glass to electroplating chromium wastewater to completely gel the wastewater. Factors influencing the gelation process of water glass include SiO2 content, pH value, temperature, and metal salt ions, with pH having a significant impact. Therefore, the pH value can be adjusted by adding acid or acidic salt solutions, thereby promoting the gelation process of water glass.

[0004] Aluminum sulfate is one of the oldest and most widely used inorganic salt coagulants. Its hydrolysis releases a large amount of hydrogen ions, making the aqueous solution acidic, which can modify water glass. However, in patent CN110590014A, calcium oxide is used to regulate the gelation process of water glass. The ratio of electroplating wastewater to water glass is 3:2 to 2:3, requiring a large amount of water glass and 0-20g of calcium oxide. This still results in high reagent consumption and high treatment costs. To achieve the goals of wastewater reduction, resource recovery of valuable components, deep wastewater purification, and near-zero discharge, further exploration of better combined processes is needed. Summary of the Invention

[0005] This invention addresses the shortcomings described above by optimizing existing technologies. Here, experiments are conducted using acidic heavy metal ions, primarily composed of chromium and zinc, as an example.

[0006] This invention is achieved through the following method: First, a certain amount of aluminum sulfate solution is added to electroplating wastewater and stirred until homogeneous. Then, an appropriate amount of water glass is added. Initially, large colloidal flocs (lump) are formed. After standing for a period of time, the water glass undergoes a sol-gel reaction in the wastewater mixture, causing the wastewater to completely gel. After standing for a period of time at room temperature and pressure, a dry gel solid is obtained.

[0007] 1. The specific operation steps of the electroplating wastewater purification method provided by the present invention are as follows:

[0008] (1) Add aluminum sulfate solutions of different volumes and mass fractions to electroplating wastewater and stir until homogeneous;

[0009] (2) Add a certain volume of water glass to the above mixed solution and stir to bring the pH value to a suitable range;

[0010] (3) After standing for a certain period of time, the mixed solution will completely gel;

[0011] (4) Dry the gel under room temperature pressure to form a dry gel; or: Dehydrate the gel in step (3) to obtain a dry gel.

[0012] The main components of the electroplating wastewater containing acidic heavy metal ions used in step (1) are: chromium 321.7 mg / L, zinc 253.9 mg / L, calcium 104.9 mg / L, etc., with a pH between 3.6 and 3.7.

[0013] Furthermore, in step (1), the aluminum sulfate solution is prepared by aluminum sulfate octadechydrate and deionized water, wherein the mass fraction of the aluminum sulfate solution is 10-26%, and the volume ratio of electroplating wastewater to aluminum sulfate solution is 50:1-25:4.3.

[0014] Furthermore, in step (2), the volume ratio of electroplating wastewater to added water glass is 25:2.5 to 25:10, and the commercially available water glass with a modulus of 3.3 is used.

[0015] Furthermore, after stirring for 5 minutes in step (2), the pH of the mixture stabilized between 4.15 and 11.04;

[0016] Furthermore, the stirring time in steps (1) and (2) above can be evenly distributed after the water glass and aluminum sulfate are mixed;

[0017] Furthermore, in step (3), the time is started from the time after the water glass is added, and complete gelation is defined as the absence of liquid flow, wherein the complete gelation time is within the range of 3 hours to 14 days;

[0018] Furthermore, in step (4), the gel can be dehydrated and dried by standing in a natural environment, standing at room temperature and pressure, or being placed in a drying oven for constant temperature drying, etc.

[0019] Experiments showed that as the amount of aluminum sulfate used increased, the gelation time first shortened and then increased; the higher the mass fraction of aluminum sulfate, the shorter the gelation time; and the fastest gelation time was observed at a pH range of 8–9. The more water glass and aluminum sulfate added, the more flocs formed, but excessive amounts of both would produce a large amount of flocs, hindering dispersion.

[0020] The specific composition of the dry gel obtained in Example 4 is as follows: the composition of the obtained dry gel solid is: SiO2 (58.7%), Na2O (16.8%), Cr2O3 (0.88%), Al2O3 (6.87%), SO3 (14.7%); the specific composition of the dry gel obtained in Example 6 is: SiO2 (68.2%), Na2O (16.8%), Cr2O3 (1.09%), Al2O3 (4.68%), SO3 (6.46%).

[0021] After the above steps, heavy metal ions such as Cr and Zn are fixed in the gel. Moreover, since the main components of the dry gel are sodium oxide, silicon dioxide, and aluminum oxide, all of which can be used as the main raw materials for glass production, and the solidified chromium ions can be used as colorants, clarifying agents, and crystallization promoters for green glass in glass production, the dry gel solid obtained from the aforementioned treatment of electroplating wastewater is also within the scope of protection of this invention.

[0022] Beneficial Effects: The method provided by this invention mixes water glass and aluminum sulfate, which utilizes the flocculation effect of aluminum salts to encapsulate harmful substances in electroplating wastewater within flocs. It also adjusts the pH value and salt effect to promote the gelation process of the water glass, both of which effectively treat toxic substances in electroplating wastewater. Due to the gelation of the water glass, sludge production is reduced, minimizing waste and land occupation. The dried gel obtained after natural air drying can be reused, avoiding secondary pollution caused by solid waste generated during wastewater treatment, thus aligning with green production principles. This method, by adding an acidic salt solution, alters the pH of the mixture, accelerating the gelation rate, and improves upon the treatment method described in patent CN110590014A. Specific implementation methods

[0023] The following specific embodiments provide a more detailed description of the present invention. These embodiments are only used to illustrate the technical solution of this patent more clearly and should not be used to limit the scope of protection of the present invention.

[0024] In the following examples and comparative examples, the electroplating wastewater containing heavy metal ions used came from a company's waste electroplating solution. The basic characteristics of the wastewater were as follows: chromium 321.7 mg / L, zinc 253.9 mg / L, calcium 104.9 mg / L, sulfur 95.7 mg / L, magnesium 25.9 mg / L, sodium 25.4 mg / L, phosphorus 25.2 mg / L, absorbance 0.024, conductivity 1.5633 mS / cm, viscosity 15 cp, and pH between 3.6 and 3.7.

[0025] Example 1

[0026] (1) Add 0.5 mL of 10% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0027] (2) Add 2.5 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture and find it to be 11.02.

[0028] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 13 days.

[0029] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0030] Example 2

[0031] (1) Add 2.5 mL of 20% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0032] (2) Add 2.5 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture to be 4.15.

[0033] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 11 days.

[0034] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0035] Example 3

[0036] (1) Add 2.5 mL of 10% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0037] (2) Add 2.5 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture to be 9.86.

[0038] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 4 days.

[0039] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0040] Example 4

[0041] (1) Add 2 mL of 15% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0042] (2) Add 2.5 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture to be 9.59.

[0043] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 12 hours.

[0044] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0045] The composition of the obtained dry gel solid was analyzed and found to be: SiO2 (58.7%), Na2O (16.8%), Cr2O3 (0.88%), Al2O3 (6.87%), and SO3 (14.7%).

[0046] Example 5

[0047] (1) Add 2.5 mL of 20% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0048] (2) Add 2.5 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture to be 4.15.

[0049] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 11 days.

[0050] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0051] Example 6

[0052] (1) Add 1 mL of 15% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0053] (2) Add 2.5 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture and find it to be 10.88.

[0054] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 9 days.

[0055] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0056] The composition of the obtained dry gel solid was analyzed and found to be: SiO2 (68.2%), Na2O (16.8%), Cr2O3 (1.09%), Al2O3 (4.68%), and SO3 (6.46%).

[0057] Example 7

[0058] (1) Add 1.2 mL of 20% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0059] (2) Add 2.5 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture to be 9.74.

[0060] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 3 hours.

[0061] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0062] Example 8

[0063] (1) Add 4 mL of 20% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0064] (2) Add 7 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture to be 8.30.

[0065] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 4 hours.

[0066] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0067] Example 9

[0068] (1) Add 2 mL of 20% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0069] (2) Add 4 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture to be 9.30.

[0070] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 40 minutes.

[0071] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0072] Example 10

[0073] (1) Add 5 mL of 20% aluminum sulfate to 25 mL of electroplating wastewater containing chromium and zinc, and stir for 30 s;

[0074] (2) Add 10 mL of water glass to the mixture and stir for 5 min. Measure the pH of the mixture to be 8.55.

[0075] (3) Stir for 15 minutes and let stand. Start timing from the time after adding water glass. The gelation time is 20 hours.

[0076] (4) The wet gel is left to stand at room temperature and pressure to obtain a dry gel solid.

[0077] Comparative Example 1

[0078] (1) Add 2.5 mL of water glass to 25 mL of electroplating wastewater containing heavy metal ions and stir for 30 s;

[0079] (2) Let the mixed solution stand. The gelation time for the mixed solution to completely transform into gel is 20 days, starting from the time the water glass is added.

[0080] (3) Let the wet gel stand at room temperature and pressure to obtain a dry gel solid.

Claims

1. A purification method for treating acidic electroplating wastewater containing heavy metal ions such as chromium and zinc. Its features include the following steps: (1) Add aluminum sulfate solution to electroplating wastewater and stir until homogeneous; (2) Continue to add an appropriate amount of water glass solution and stir for 5 minutes; (3) Let stand until the mixture in (2) completely gels; (4) Dry the wet gel to obtain a dry gel solid.

2. The method according to claim 1, characterized in that: In step (1), the aluminum sulfate solution is prepared by mixing solid aluminum sulfate octadechydrate with deionized water; the mass fraction of the aluminum sulfate solution is 10-26%, and the volume ratio of electroplating wastewater to aluminum sulfate solution is 50:1-25:4.

3.

3. The method according to claim 1, characterized in that: In step (2), the ratio of electroplating wastewater to water glass is 25:2 to 25:

10.

4. The method according to claim 1, characterized in that: The pH range of the mixed solution is between 4.15 and 11.

04.

5. The method according to claim 1, characterized in that: The gelling time is from 1 hour to 14 days.

6. A dry gel solid obtained according to any one of claims 1-5, characterized in that: The main components are silicon dioxide, sodium oxide, aluminum oxide, and sulfur trioxide.

7. The use of the dry gel of claim 6 as a clarifying agent in colored glass or as a coloring agent and / or crystallization promoter in glass-ceramics.