1. Chemical precipitation
The chemical precipitation method is a more economical and effective method in the treatment of electroplating wastewater. Because of its mature technology and simple operation and management, it can simultaneously remove many metals in electroplating wastewater, so it is widely used. Add chemical agents to the sewage to convert the heavy metal ions in the original sewage into heavy metal compounds that are insoluble in water, and then precipitate to separate it from the sewage to achieve the purpose of removal, such as hydroxide precipitation method, sulfide precipitation method Ferrite method, etc.
2. Hydroxide precipitation method
The hydroxide precipitation method is the most commonly used chemical precipitation method. This process has the advantages of simple operation, low cost, and easy control of PH. It adds alkaline precipitation agent to the wastewater to make heavy metals in the wastewater generate water-insoluble hydroxide precipitate, which is separated and removed. The reagents such as lime and sodium carbonate are widely used and low in price.
Nevertheless, the use of the hydroxide precipitation method has its own limitations. There is a large amount of sludge generated during use, which is easy to cause secondary pollution; additional chemical agents are required; for heavy metals with a large hydroxide dissolution constant, the pH needs to be adjusted to 11-12, and when discharged Transfer back 6 to 9 to increase processing costs and other shortcomings.
3. Sulfide precipitation method
Sulfide precipitation is also an effective method for removing heavy metal ions in water. Commonly used sulfides are Na2S, NaHS, H2S, etc. In a certain pH range, the suitability of the sulfide precipitation method depends on the solubility product of the sulfide, the valence state and concentration of metal ions, etc. The adjustment of the pH of the solution can selectively precipitate the metal sulfide with a smaller solubility product Thing.