The chemical method of electroplating wastewater treatment is to dissolve harmful chemicals into non-toxic and harmless chemicals by means of redox reaction or neutralization sedimentation reaction, or remove metal cadmium from wastewater immediately by sedimentation or flotation.

1. Precipitation method

(1) Neutralization precipitation method. The neutralization reaction is carried out by adding alkali to the sewage containing metal cadmium, so that metal cadmium can be converted into insoluble water by hydroxide precipitation. Neutralization sedimentation method is easy to use and is a common way to solve sewage problems.

(2) Sulfide precipitation method. The addition of sulfide can transform the positive metal cadmium ion in the sewage into sulfide precipitation for removal. Compared with the neutralization precipitation method, the sulfide precipitation method has the advantage that the solubility of heavy metal sulfide is lower than that of its hydroxide, reflecting that the PH value is between 7 and 9, and the sewage after solution usually does not need neutralization, so the practical effect of solution is stronger. However, the defect of sulfide precipitation method is that the sulfide precipitated particles are small and easy to produce colloidal solution. The sulfide precipitated remains in water and will be converted into vapor when encountering acid, which will lead to pollution.

2. Air oxidation

According to the addition of reducing agent, the air of harmful chemicals in electroplating wastewater is oxidized to non-toxic or low harmful substances, which is suitable for solving the problems of CN -, Fe2+, Mn2+cheap positive ions in sewage and various organic compounds and pathogenic microorganisms that cause saturation, obscurity and smell. For example, when dealing with cyanide containing sewage, common hypochlorite oxidizes at least positive cyanide ion in the air under the partial alkali standard to convert it into low toxic cyanate, Zero discharge of electroplating wastewater And then further dissolved into non-toxic carbon dioxide and nitrogen.

3. Organic chemical reduction

The most typical organic chemical reduction method in the treatment of electroplating wastewater is the treatment of chromium containing wastewater. The method is to add oxidants FeS04, NaHS03, Na2S03, S02 or copper powder in the sewage to convert Cr (Ⅵ) into Cr (III), and then add NaOH or lime milk for precipitation and separation. The advantages of this method are simple machinery and equipment, less project investment and large sludge production, but it can avoid pollution caused by sediment and sludge.

4. Neutralization method

According to the neutralization reaction of strong acid and strong base, adjust the ph acidity and alkalinity of electroplating wastewater to make it weakly acidic or close to weakly acidic or the category of ph acidity and alkalinity suitable for the next step. The key is to solve the acid pickling and passivation wastewater in electroplating plants.