Metal wastewater refers to the wastewater containing heavy metals that is discharged during the production processes of industries such as mining and metallurgy, machinery manufacturing, chemical engineering, electronics, and instrumentation. The heavy metals in the heavy metal wastewater generally cannot be decomposed or destroyed; they can only change their location of existence and their physical and chemical forms. The treatment methods for heavy metal wastewater are to be carried out on-site at the production location. Commonly used treatment methods include chemical precipitation and ion exchange. After treatment, if the heavy metals in the water are below the discharge standards, it can be discharged or reused.

Technological process

1. Chemical precipitation method: The principle of the chemical precipitation method is to convert the dissolved heavy metals in the wastewater into insoluble heavy metal compounds through chemical reactions. Then, through filtration and separation, the precipitate is removed from the aqueous solution. This method includes neutralization precipitation method, sulfide precipitation method, and ferrite co-precipitation method. Due to the influence of the precipitant and environmental conditions, the effluent concentration of the precipitation method often fails to meet the requirements. Further treatment is necessary. The generated precipitate must be properly treated and disposed of; otherwise, it will cause secondary pollution. 

2. Ion Exchange Method: The ion exchange method involves the exchange of heavy metal ions with ion exchange agents, thereby achieving the removal of heavy metal ions from wastewater. Commonly used ion exchange agents include cation exchange resins, anion exchange resins, and chelating resins, among others. Over the past few years, scholars both at home and abroad have conducted extensive research on the development of ion exchange agents. With the continuous emergence of ion exchange agents, this method has increasingly demonstrated its advantages in the deep treatment of electroplating wastewater and the recovery of high-valent metal salts. The ion exchange method is an important method for treating electroplating wastewater, featuring large treatment capacity, good effluent quality, and the ability to recover heavy metal resources, without causing secondary pollution to the environment. However, ion exchange agents are prone to oxidation and failure, require frequent regeneration, and have high operating costs. 

3. Solvent Extraction Method: The solvent extraction method is a commonly used technique for separating and purifying substances. Due to the liquid-liquid contact, it can be operated continuously and the separation effect is good. When using this method, a selective solvent with high selectivity should be chosen. Heavy metals in wastewater generally exist in the form of cations or anions. For example, under acidic conditions, they undergo complexation reactions with the extractant, being extracted from the aqueous phase to the organic phase, and then being re-extracted from the organic phase to the aqueous phase under alkaline conditions, allowing the solvent to be regenerated for recycling. This requires attention to the selection of the acidity of the aqueous phase during the extraction operation. Although the solvent extraction method has significant advantages, the loss of solvent during the extraction process and the high energy consumption during the regeneration process make this method have certain limitations and its application is greatly restricted.