Heavy Metal Wastewater Treatment and Resource Utilization

Heavy metal wastewater refers to the wastewater containing heavy metals (such as cadmium, nickel, mercury, zinc, etc.) discharged from industrial production processes such as mining and metallurgy, machinery manufacturing, chemical engineering, electronics, and instrumentation. This type of wastewater is one of the most serious industrial wastewater that causes environmental pollution and poses the greatest harm to humans. Its water quality and quantity are related to the production process. Heavy metals in wastewater generally cannot be decomposed or destroyed, and can only be relocated and transformed into their physical and chemical forms. Heavy metal pollution in water bodies has become one of the most serious environmental problems in the world today.

At present, the commonly used technologies for treating heavy metal wastewater include chemical precipitation, solvent extraction, membrane separation, and adsorption. Except for adsorption methods, none of these methods can treat heavy metals to meet emission standards, and they can also bring many negative impacts. Chemical precipitation method can generate a large amount of sludge, which can easily cause secondary pollution; The operation steps of extraction method are complex, and solvent loss occurs during multiple extraction and back extraction processes, resulting in high energy consumption of this method; During the operation of membrane separation method, at least 30% of the inflow volume of concentrated water is generated, which needs further treatment. In addition, the membrane material is highly susceptible to contamination and requires frequent cleaning, which increases operating costs.

Adsorption method mainly utilizes the exchange effect of adsorbents on heavy metal ions to achieve adsorption and separation of heavy metal ions. The key to adsorption method is to use adsorption materials with high selectivity and high adsorption capacity for heavy metals, which can ensure high concentration ratio, produce less concentrated water, and achieve high processing accuracy, making them more suitable for end of pipe inspection.

The special adsorbent prepared by our company contains functional groups that can strongly coordinate with heavy metals, even stronger than commonly used chelating agents such as citric acid and EDTA. Therefore, it has superior removal ability for both ionic and complexed heavy metals in solution. Our technical team has developed an application process with this material as the core. The effluent is directly discharged to meet the standard (Ni treated to 0.1ppm), and after adsorption saturation, it is treated with a solvent. The adsorbent is regenerated and recyclable, and the material has a long service life. The process concentration ratio is high, and the resulting desorption solution is processed appropriately to recover the metals. The method developed by our company can not only solve the problem of wastewater discharge, but also selectively recover various heavy metals, achieving the resource utilization of heavy metals.

Case 1: The water quality of the effluent from the secondary sedimentation tank of a certain enterprise in Jiangsu Province is shown in the table below. The treatment requirement is that the nickel ion concentration should be less than 0.1mg/L.

Our company uses special adsorbents for treatment, and the nickel content in the effluent is 0.05mg/L, which meets the discharge standard and customer requirements. The specific process flow is as follows, and the desorption solution can be further processed to recover metallic nickel.

Process flowchart

Case 2: The electroplating waste acid generated by a certain enterprise in Jiangsu during the production process contains a large amount of zinc ions and iron ions. The water quality is shown in the table below, and the treatment requirements are zinc iron separation:

After our company's resin adsorption treatment, this type of waste acid produces a ferrous acid solution with a zinc content of less than 100mg/L and a zinc removal rate of 90%, which meets customer requirements; The iron containing acid solution in the desorption solution is reused in production together with the effluent. The high iron and low zinc acid solution is returned to the wastewater for adsorption, and the metals in the high zinc and low iron acid solution are further processed and recovered.

Process flowchart

Case 3: Production wastewater from a certain enterprise in Anhui Province. The water quality is shown in the table below, and the treatment requirements are chromium ions below 0.5mg/L:

After treatment with a special adsorbent, our company achieved a chromium content of 0.3mg/L in the effluent, which meets the discharge standards and customer requirements. The specific process flow is as follows, and the desorption solution can be further processed to recover metallic chromium.

Process flowchart

Comparison chart of effects