KR100829798B1 - Plating wastewater treatment method using vacuum evaporation concentration method - Google Patents

Abstract

The present invention provides a method for treating Zn-Cr plating wastewater using vacuum evaporation concentration method, and more specifically, a method for separating and removing heavy metal ions and COD components from Zn-Cr plating wastewater using vacuum evaporation concentration method. Silver can be used as a plating flush and concentrated water can be recycled into the plating solution to effectively remove heavy metal ions and COD components in Zn-Cr plating wastewater while minimizing sludge.

Zn-Cr Plating Wastewater, Vacuum Evaporation Concentration

Description

Recycling method of electroplating wastewater by evaporator system

1 is a schematic view showing a treatment step of Zn-Cr plating wastewater according to the present invention.

Figure 2 is a graph showing the effect of removing heavy metal ions in Zn-Cr plating wastewater using the slaked lime of Comparative Example 1.

Figure 3 is a graph showing the COD value of the organic matter removal effect in Zn-Cr plating wastewater by the Fenton oxidation method of Comparative Example 2.

The present invention relates to a Zn-Cr plating wastewater treatment method using a vacuum evaporation concentration method, more specifically, to separate heavy metal ions and COD components in Zn-Cr plating wastewater using a vacuum evaporation concentration method as a plating solution and condensate The present invention relates to a method for reusing the water into a plating flush.

In general, plating factories produce beautiful cold rolled and plated products using hot rolled coils through pickling, cold rolling, electric cleaning, annealing, and plating processes. At this time, in order to remove heavy metal ions and chemically oxidizable substances (hereinafter referred to as COD components) in the plating waste water, conventional flocculation sedimentation methods and chemical oxidation methods have been used.

Agglomeration sedimentation is a method of agglomeration and precipitation of heavy metal ions in wastewater using aluminum salt or iron salt, and chemical oxidation is a method of chemically oxidizing and removing organic substances in wastewater using oxidizing agents such as hydrogen peroxide and potassium permanganate. (Journal of KSEE, Vol. 18, p 43-54 (1996)).

However, such a conventional method has a problem in that the cost of the chemical cost is generated by using a chemical such as a flocculant to increase the wastewater treatment cost and a large amount of sludge, as well as to treat the sludge generated separately.

In order to solve the problems of the prior art as described above, the present invention is to provide a method for treating Zn-Cr plating wastewater by vacuum evaporation concentration method.

It is still another object of the present invention to separate heavy metal ions and COD components in Zn-Cr plating wastewater by vacuum evaporation, and to use the obtained condensed water as the plating wash water and to plate the concentrated water containing heavy metal ions and COD components. It is to provide a method for reuse in solution.

In order to achieve the above object, the present invention is a method for treating Zn-Cr plating wastewater, by vacuum evaporation of the COD component and heavy metal ions in the Zn-Cr plating wastewater in a vacuum evaporation concentrator, the COD component and heavy metal ions The present invention relates to a method for treating Zn-Cr plating wastewater using a vacuum evaporative concentration method for separating concentrated water and condensate.                     

The present invention also relates to a method for treating Zn-Cr plating wastewater in which the condensed water obtained by the vacuum evaporation concentrate is used as a plating flush and the concentrated water is reused as a plating solution.

Hereinafter, the present invention will be described in more detail.

Zn-Cr plating wastewater contains heavy metal ions including Zn, Cr, Fe and the like, and various COD components. The heavy metal ions and COD components should be lowered below the allowable concentration in the wastewater as water pollutants.

In one example of the present invention, the Zn-Cr plating wastewater is heated to 70 ~ 80 ℃ by a heat exchanger and introduced into the separator, the water evaporated in the separator is condensed in the condenser is stored in the condensate tank as condensate water and the water is removed plating wastewater When the new plating waste water is introduced again and the above process is repeated, the plating waste water is gradually concentrated to include heavy metal ions of a predetermined concentration or more, and thus, the plating waste water is reused by being introduced into the plating process.

As an example of the present invention, an example of a vacuum evaporation concentrator will be described with reference to the process diagram of FIG. 1. A basic element constituting the vacuum evaporation concentrator includes a separator, a circulation pump, a heat exchanger, a vacuum pump, a condenser, a cooling tower, and the like. Can be mentioned. The plating waste water is transferred to the heat exchanger by a feed pump and is controlled to a temperature of 70-80 ° C. by heat exchange by hot water supplied from a hot water generation tank. After the heat exchanged plating wastewater enters the separator and expands and evaporates, it is cooled in the condenser to collect condensate in the condensate tank.                     

The hot water temperature supplied to the vacuum evaporation concentrator in the present invention is 70 ~ 80 ℃, preferably 70 ~ 75 ℃. The plating waste water is transferred to a heat exchanger by a feed pump and is controlled to a temperature of 70-80 ° C. by hot water supplied from a hot water generation tank. The temperature of the incoming wastewater is related to the degree of vacuum in the separator. If the temperature of the wastewater flowing into the vacuum evaporator is less than 70 ° C, the degree of vacuum in the separator should be relatively increased. By disabling the pump, the temperature of the wastewater is adjusted to 70-80 ° C., preferably 70-75 ° C. That is, the heat-exchanged plated wastewater (70-80 ° C) flows into the separator, expands and evaporates, and then cools in the condenser to collect condensate in the condensate tank, and the concentrated water is reconcentrated in the separator. Recirculated to the separator.

The vacuum degree of the separator of the vacuum evaporation concentrator is in the range of -500 ~ -600 mmHg, which is -500 ~ -600 mmHg, preferably 70-75 ℃ when the temperature of the incoming plating waste water is 70-80 ℃ If influent wastewater is used, the vacuum degree of -550 to -600 mmHg is more effectively evaporated.

In addition, the amount of plating wastewater flowing into the vacuum evaporation concentrator is 10 to 20 l / hr to maintain the level stability of the separator and prevent the plating wastewater from flowing to the condenser, and the circulating pump shear operation pressure is 0.5-0.6kg /. cm ² , the back end operating pressure of the circulation pump may be 2.0-2.5kg / cm ² .

Hereinafter, the present invention will be described in more detail with reference to the following exemplary embodiments, but the protection scope of the present invention is not intended to be limited to the following examples.

EXAMPLE

Example 1 Treatment of Zn-Cr Plating Wastewater Using Vacuum Evaporation Concentration

The vacuum evaporator used in the present invention is a pilot device having a processing capacity of up to 30 L / hr, the plating wastewater is introduced into the range of 10-20 L / hr for level stability of the separator, and the hot water temperature is 70-75. The experiment was performed while automatically adjusting with a temperature controller in the range of ℃. The pressure range of the circulating pump was 0.5 to 0.6 kg / cm ² and the vacuum degree was -550 to -600mmHg for 8 hours of continuous operation experiments to show the electrical conductivity, COD and heavy metal ion concentrations of condensate and concentrated water. Represented in each.

division Wastewater Condensate Concentrated water Condensate % Removal Concentrated water Content percentage (%) * COD (mg / L) 12000 11.24 99.9 59100 98.5 Zn (mg / L) 8500 4.03 99.9 40970 96.4 Cr (mg / L) 2500 1.26 99.9 12000 96 Fe (mg / L) 1100 0.62 99.9 5335 97 Electrical Conductivity (㎲ / ㎝) 13830 113 99.2 67.1 97

Note *) The content set is calculated by the formula:

[Concentrated water concentration / (raw wastewater concentration X 5)] X100

As can be seen in Table 1, the electrical conductivity of the condensed water, heavy metal ions, COD component removal rate of 99% or more can be reused as the plating wash water. In addition, the COD concentration, heavy metal ion concentration, and electrical conductivity of the concentrated water after 8 hours of operation time can maintain the quality of 96% or more of the plating solution concentration, it is judged that it is possible to recycle the plating solution. Therefore, it can be seen from Table 1 that the concentrated water can be recycled to the plating solution, and the condensate can be reused as the washing water using the vacuum evaporation concentration method.

Comparative Example 1: Zn-Cr Plating Wastewater Treatment Using Slaked Lime

The lime was injected into Zn-Cr plating wastewater to raise the pH to 8-10 to form a hydroxide precipitate. The injection of slaked lime is shown in the results of the injection concentration of Cr and Zn ion removal rate used in Table 2 and Figure 2 below.

Slaked lime injection concentration (mg / L) 0 300 600 800 1000 1200 Cr ion removal rate (%) 0 48 54 60 97 98 Zn ion removal rate (%) 0 45 51 57 95 96

As can be seen in the graphs of Table 2 and Figure 2, the initial Cr and Zn ion concentration was 432.9mg / L, 920mg / L Zn-Cr plating waste water should be at least pH 8.8 by injecting lime more than 1000mg / L It can be seen that the removal rate of Cr and Zn ions is almost completely removed at 95% or more, and the removal rate of Cr and Zn ions is not very high when the slaked lime is injected at 1000 mg / L or less.

Comparative Example 2: Fenton Oxidation of Zn-Cr Plating Wastewater

Zn-Cr plating wastewater was treated by Fenton Oxidation method using hydrogen peroxide and iron salt. Specifically, the experiment was performed while changing the hydrogen peroxide concentration as shown in Table 3 while maintaining the iron salt concentration to 500 mg / L. It was. The results obtained are shown in Table 3 below. In addition, it is shown as the COD concentration according to the injection concentration of hydrogen peroxide used in FIG.                     

H ₂ O ₂ (mg / L) Fe ⁺² (500mg / L) 0 400 500 600 700 800 COD concentration (mg / L) 2000 1260 1150 968 1310 1704

As can be seen in the graph of Table 3 and Figure 3, the initial COD concentration was 2000mg / L Zn-Cr plating wastewater treated water when the peroxide injection concentration is 600mg / L even after oxidative decomposition of organic matter with hydrogen peroxide and iron salt The COD concentration of 968mg / L or more and the COD removal rate was 52%, indicating that the removal efficiency of COD components in the wastewater was not very high.

As described above, by separating and removing heavy metal ions and COD components in Zn-Cr wastewater using vacuum evaporation concentration, sludge generation is reduced as compared to conventional flocculation and chemical oxidation methods, and at the same time, the heavy metal ions and COD components in wastewater are effectively Can be removed. Furthermore, the condensed water by vacuum evaporation concentration can be reused as the plating washing water, and the final concentrated water can be recycled as the plating solution.

Claims (4)

delete delete delete In the method of treating Zn-Cr plating wastewater, The temperature of the inflow plating wastewater in the vacuum evaporation concentrator is 70 ~ 80 ℃, the degree of vacuum is -500 ~ -600 mmHg, the inflow of the plating wastewater is 10 ~ 20ℓ / hr, and the operating pressure of the circulating pump shear pressure of the concentrator is 0.5 ~ 0.6kg / cm ² and the operation pressure of the circulating pump after the circulating pump is 2.0 ~ 2.5kg / cm ² to vacuum evaporate the water of the Zn-Cr plating wastewater, and the concentrated water containing the COD component and heavy metal ions and A method for treating Zn-Cr plating wastewater using a vacuum evaporative concentration method, characterized in that it is separated by condensate.

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