Advantages and disadvantages of separate treatment or mixed treatment of electroplating wastewater
Advantages and disadvantages of separate treatment or mixed treatment of electroplating wastewater
During the electroplating production process, a large amount of rinsing water will be produced. These rinsing waters contain cyanide, chromium, cadmium, as well as heavy metal ions such as nickel and copper, surfactants, additives, and oils. There is also a waste liquid from various chemical treatment tanks and electroplating tanks. Although the quantity is not large, the concentration is relatively high.
1. Treatment of cyanide-containing electroplating wastewater
Cyanide-containing wastewater is generally collected and treated separately. Because the first step needs to be oxidized and broken down, if it is mixed with other wastewater, it will dilute the oxidant and increase the usage of the oxidant; if it is mixed with acidic substances and discharged, it will form a complex to complicate the wastewater treatment. Therefore, the wastewater containing cyanide should be discharged and treated separately. Some factories discharge together with alkali degreasing wastewater because the first step of cyanide treatment is carried out in an alkaline environment, which is also feasible.
2. Treatment of chromium-containing electroplating wastewater
Most factories also collect and treat chromium-containing electroplating wastewater separately. The first step of chromium-containing wastewater is reduction treatment, and separate treatment does not waste treatment agents. Second, the PH value of precipitation is easy to control, and some factories treat chromium-containing wastewater. It is mixed and discharged with pickling and activated rinsing water, because the first step of chromium-containing wastewater treatment is carried out under the condition of low pH value, and discharging with pickling water can save the cost of sulfuric acid required to adjust the pH value.
3. Treatment of nickel-containing electroplating wastewater
In qualified factories, nickel-containing wastewater should be collected and treated separately. Has the following advantages:
1. The PH value of the precipitation is not affected by the PH value required for the precipitation of other heavy metals. The precipitation is relatively sufficient, and the water quality after treatment can easily meet the discharge standard.
2. The sediment produced by the chemical method is relatively simple, which is beneficial to the comprehensive utilization in the next step. The sediment can be sold, which is economical.
3. Factories with better conditions can use ion exchange to treat nickel-containing electroplating wastewater, and nickel salts can be recycled as raw materials, and it is necessary to collect nickel-containing wastewater by diversion.
4. Factories with better economic conditions can use turning over and leaking treatment to recover nickel salts and pure water. Nickel-containing wastewater must be collected separately.
5. Manufacturers with less water volume and unacceptable conditions often adopt mixed discharge, which often makes the quality of discharged wastewater unstable, and the mixed waste produced needs to pay disposal fees to comprehensive utilization factories, wasting resources and increasing economic expenses.
4. Treatment of copper-containing electroplating wastewater
The separate treatment and mixed treatment of copper-containing electroplating wastewater are basically the same as those of nickel-containing wastewater.
5. Treatment of zinc-containing electroplating wastewater
1. Zinc-containing wastewater is treated by chemical method, and the diversion collection has certain significance. Due to the precipitation of Zn(OH)2
The optimum acidity value of the precipitate is PH=8.5. When the pH value reaches 10.5, Zn(OH)2 begins to dissolve. If it is mixed with Ni2+ and Cu2+, in order to make Zn2+ fully precipitate and not reach the PH value of redissolving, Then Ni2+ and Cu2+ are not sufficiently precipitated. If Ni2+ and Cu2+ are to be fully precipitated and the pH value is controlled to be 10.5-11, Zn2+ tends to dissolve.
2. Zinc and zinc compounds still have certain economic value, they are collected and processed separately, Zn(OH)2
The recycling of sediment is more convenient, and it can also bring certain economic benefits.
3. The zinc-containing electroplating wastewater is treated by ion exchange method, and it also needs to be collected and treated separately. Some
If the conditions do not allow the factory, the zinc-containing wastewater is mixed with copper and nickel wastewater. It is difficult to make the discharged water meet the stable discharge standard. The mixed waste generated must be paid to the comprehensive utilization factory for disposal.
6. Electroplating acid-base wastewater treatment
1. Chromium-containing wastewater is treated by chemical method. Many of them discharge pickling and activation wastewater together with chromium-containing wastewater. Some of them discharge a part of acid-washing and activation wastewater into the underground storage tank of chromium-containing wastewater according to the treatment needs of chromium-containing wastewater. , and part of it is discharged together with alkaline wastewater to neutralize acidic wastewater.
2. Some factories use chemical methods to treat nickel-containing wastewater, and part of the rinsing water in the degreasing process is mixed with nickel-containing wastewater.
The waste water is discharged together, the purpose is to save the caustic soda required to increase the pH value.
3. Some discharge and store the acid and alkali separately, and then process the required amount of acid and alkali according to the chemical method.
They are respectively sent to the relevant homogenization tank.
4. If the conditions do not allow, the acid-base rinsing water and the acid-base elimination liquid of the factory are discharged arbitrarily, sometimes acidic, sometimes alkaline, if not treated, it will cause great harm.
