[China Aluminum Industry Net] Wastewater from the metal processing industry contains high concentrations of heavy metals that endanger the environment and pose a threat to public health and biology. Therefore, wastewater needs to be pretreated before it is discharged. Traditional treatment methods include chemical methods, heavy metal precipitation, flocculation, settling and discharge, which are very time consuming. The precipitation of heavy metals reduces the concentration of metals contained. The key is the solubility of the precipitated metal compound. That is, if a metal can form an insoluble compound, this compound can be removed by purification and filtration. The two heavy metal precipitation methods currently used are hydroxide and sulfidation. Both of these methods react with metal cations and OH- or S2- to form corresponding insoluble metal hydroxides or sulfides. The precipitation of heavy metals such as hydroxides is pH-sensitive. Therefore, it is necessary to determine the preferred pH before wastewater treatment. Most heavy metal hydroxides precipitate at pH 8.5-9.5. Outside of this range, metal hydroxides can re-dissolve or decompose. The heavy metal hydroxide precipitated as colloidal charged particles requires the addition of a coagulant to reduce the charge and make the precipitated particles larger in size. To promote sedimentation, coagulant particles are flocculated using flocculants. Metal flocs/muds settle in clarifiers or sedimentation tanks. If the supernatant meets regulatory discharge standards, it can be discharged and the sludge is filtered through a filter press to form a semi-solid waste. This process needs to be performed in a separate tank at each step. The entire process requires multiple adjustments of pH and addition of acid, coagulant, lime or alkali, and polymer flocculant. In addition, this process produces large amounts of harmful sludge/waste containing high concentrations of heavy metals that require further processing. 1. Sludge Disposal If the pH drops below the preferred range, the precipitated heavy metals will solidify again. Decomposition of municipal solid waste and humic substances generates organic acids (reduced pH), which in turn increases the solid solubility of heavy metals, and sulfides and cyanides react with these organic acids to produce toxic hydrogen sulfide, hydrogen cyanide gas. In general, the disposal of waste in refuse pits or landfills has little effect on groundwater. However, where these conditions are not available, a collection system must be installed to collect leachate and remove heavy metals by precipitation or other means. Chemical treatment was used to reduce the exudation rate of sludge containing heavy metals. Sludge containing heavy metals is treated with chemicals that make them stable or insoluble. Most landfills use this method. However, these treatments increase the cost of wastewater treatment, which usually accounts for 60%-80% of waste disposal costs. 2. Stabilization of Non-leaching Substrates The preferred technique for removing heavy metals and other harmful contaminants in wastewater is to maintain the stability of non-leaching matrices so that once the garbage is placed in landfills, these heavy metals and other harmful pollutants are It will not be dangerous to the environment. This is usually dealt with by emitting wastes that react with chemicals. The newer treatment is the use of chemicals to remove contaminants from the wastewater. This agent has a strong affinity for heavy metals and is less pH-limited than metal hydroxide precipitates. Metals react with the drug at levels as high as 10,000 mg/L or higher. High levels of metals are not limited by pH or oils, surfactants, chelating agents, complexing agents, suspended solids, and hardness. This process requires the addition of a chemical agent to the agitated wastewater of the treatment tank, rapid precipitation and dehydration after a dense flotation block is formed in the treatment tank, and can be performed on the existing equipment. The resulting waste does not require post-treatment. The chemical components in the treatment agent stabilize the contaminants, especially heavy metals, in the waste and reduce the solid solubility of the metal. Therefore, the waste passes the toxic leaching test to meet the regulatory requirements for non-hazardous materials. 3. Removal of heavy metals by metal removal technology (MRT) is a cost-effective technology for removing heavy metals from industrial wastewater. It is called MRT-100 and is a filter tank containing two parts: granular activated carbon (GAC) and methylbenzotriazole (MeBT). When metal-containing waste water flows through this tank, MeBT is combined with metal ions and adsorbed on GAC to remove contaminants from the water. It is not affected by pH and does not require adjustment of chemical additives, reducing chemical and labor costs. However, MeBT is highly selective for heavy metals and transition metals, so it does not bind non-target metals. This further extends its service life, reduces the frequent replacement of filter media, and ultimately lowers user costs. Once carbon is saturated, it can be removed by removing the metal with a solvent. In addition, MRT-100 is simple and efficient. Conclusion With the national emphasis on environmental protection, the metal processing industry must strictly follow the existing regulations and national standards on waste water discharge, and actively transition to a green production and environment-friendly direction to prepare for the long-term development of the company.