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Technical guidance: 15271938854VX. Project name: Mercury removal from wastewater in a chlor-alkali chemical enterprise. Process selected: Sulfidation precipitation + fiber filter + two-stage activated carbon + ion exchange for mercury removal. Principle of the process: Thiourea utilizes selective functional group chelation to adsorb mercury from high-salinity water. Project background: Against the backdrop of rapid development in modern industry, the chlor-alkali industry, as an industry based on basic raw materials, is widely used in daily production and life. However, the issue of wastewater treatment generated during its production process has become a key challenge for environmental protection, especially the problem of mercury pollution. Given the high toxicity and persistence of mercury, it not only affects human health but also poses a potential threat to the ecological environment. As environmental regulations become increasingly comprehensive and stringent, governments around the world have set stricter standards for mercury emissions. Therefore, chlor-alkali chemical enterprises must strictly comply with relevant laws and regulations during production, and adopt scientific and reasonable wastewater treatment techniques to ensure that emissions meet environmental protection standards. To address the mercury pollution in chlor-alkali chemical wastewater, the treatment methods that enterprises can adopt include physical adsorption, chemical precipitation, ion exchange, biological treatment, and electrochemical methods. Each method has its own characteristics and scope of application; for example, although physical adsorption is simple to operate, it has a limited adsorption capacity and high costs ； Although chemical precipitation can effectively treat high-concentration mercury, it is less effective for low-concentration levels ； The ion exchange method is highly efficient and exhibits good selectivity, making it suitable for treating low-concentration mercury-containing wastewater; however, the selectivity of common resins may be limited ； Biological treatment is environmentally friendly, but it is slow and requires stringent conditions ； Electrochemical treatment is highly efficient, but it is energy-intensive and requires substantial equipment investment. How to find a balance among numerous processes? A large chlor-alkali chemical company adopted the sulfidation precipitation method to treat mercury in wastewater. Although this method can effectively remove high concentrations of mercury, its effectiveness is still insufficient to meet new environmental standards. To improve this situation, the company decided to collaborate with Kirin to introduce ion exchange technology as a supplementary measure. Through this innovative combined process, not only is the efficiency of mercury removal improved, but the stability of the effluent quality is also ensured, meeting environmental protection requirements. Project Overview: This mercury removal project for the chlor-alkali industry handles a water flow rate of 3.6 tons per hour. The initial mercury content in the resin is between 50–100 ppb, with a pH value of 6.9±0.5. To address the issues associated with the traditional sulfidation precipitation and activated carbon filtration methods used by this company – such as their poor effectiveness, the tendency of mercury to volatilize and remain in the water, resulting in unstable treatment outcomes – as well as the fact that nearly 20% salinity in the water makes it difficult for mercury sulfide precipitates to settle, Kehaisi developed an efficient and reliable solution that takes into account the owner’s requirements and the actual conditions of the project, while also ensuring a balance between operating costs and ease of maintenance. This solution combines sodium sulfide precipitation, activated carbon filtration, and mercury-removing resin technologies to create a complete treatment process that ensures the mercury content in the treated water is well below the **specified emission standards. Specifically, this treatment process first removes most of the mercury using the sodium sulfide precipitation method, and then employs activated carbon filtration to further purify the water by removing any existing organic substances and other impurities, thereby providing cleaner water for the subsequent mercury removal steps. Immediately thereafter, advanced treatment is carried out using a mercury-removal resin containing thiourea selective functional groups. Unlike ordinary mercury-removing resins, the CH-95 special chelating resin used in this approach is designed specifically for the removal of mercury and precious metals from industrial wastewater. It features a macroporous structure with polyethylene isothiourea functional groups, which grants it excellent selectivity for mercury. Even in high-salt environments, other heavy metals such as sodium, alkaline earth metals, iron, and copper do not interfere with its efficient adsorption of mercury. Through its unique chelation mechanism, it effectively adsorbs residual mercury ions; the system operates in two stages in series, ensuring that the mercury content in the effluent remains below 0.4 μg/l, which is below the environmental emission standards. Tulsimer®CH-95 is a specialized mercury-removal chelating resin. It is a high-performance chelating resin designed for the recovery and removal of mercury and precious metals from industrial wastewater. This resin features a unique polyethylene isothiourea functional group structure and large-pore characteristics, which enable it to adsorb mercury ions efficiently and accurately, maintaining excellent selectivity and adsorption capacity even in complex wastewater environments. The following are the main advantages of Tulsimer CH-95 resin: High processing precision: it can reduce mercury content to below 0.1 ppb, meeting strict environmental standards. High-capacity adsorption: Each liter of resin can absorb up to 150 grams of mercury, providing an efficient solution for pollution control. Excellent selectivity: Even in wastewater containing various metal ions such as sodium, calcium, magnesium, iron, and copper, it can selectively adsorb mercury preferentially, ensuring the effective removal of the target pollutant. Adaptation to high-salt environments: It is particularly suitable for the removal of mercury from wastewater with high salinity, such as in the wastewater treatment process during PVC production, offering unparalleled advantages. Long-term stability: Designed with a service life of 3–5 years, it requires no frequent regeneration or replacement during this period, significantly reducing maintenance costs and operational complexity while ensuring the long-term stable operation of the system. By using the Tulsimer CH-95 heavy-metal mercury removal resin, it is possible to not only improve the efficiency of mercury removal and reduce environmental pollution, but also effectively lower operating costs, thereby achieving both economic benefits and environmental protection.