Jiangsu Hengfeng Fine Chemical Co., Ltd.

HENGFENG Floc Application Process of Flocculant (PAM) in Heavy Metal-Contaminated Soil Leaching Remediation 1. Pretreatment: Wastewater pH Adjustment and Homogenization Purpose Citric acid is acidic (pH ≈ 2-3), while polyacrylamide (PAM), especially HENGFENG Floc non-ionic or HENGFENG Floc anionic types, exhibits optimal flocculation performance under neutral to weakly alkaline conditions. Meanwhile, pH adjustment can disrupt part of the heavy metal-citric acid complexes, releasing free heavy metal ions (e.g., Co²⁺) or forming hydroxide/carbonate micro-precipitates, thereby creating favorable conditions for subsequent flocculation. Operation Add quicklime (CaO) or sodium hydroxide (NaOH) into the leachate storage tank to adjust the pH to 7.0-8.5, with real-time monitoring via an online pH meter. Simultaneously, start the agitator at a rotational speed of 150-200 r/min to homogenize the wastewater, preventing local pH fluctuations from affecting flocculation efficiency. 2. PAM Selection and Dissolution Preparation Selection Basis The wastewater in this case contains negatively charged soil colloids (due to the negative charge on the surface of soil clay minerals) and heavy metal complexes (mostly negatively charged or neutral). Therefore, anionic PAM (with a molecular weight of 8-12 million Da) is preferred. The carboxyl groups (-COO⁻) on its molecular chains can promote agglomeration through "charge neutralization" (adsorbing negative charges on the surface of soil colloids) and "bridging effect" (connecting multiple micro-particles). Compared with HENGFENG Floc  non-ionic PAM, it has higher flocculation efficiency, and its cost is lower than that of HENGFENG Floc cationic PAM. Dissolution Preparation Dissolution Water: Use deionized water or clarified tap water (to avoid precipitation caused by the reaction of Ca²⁺ and Mg²⁺ in hard water with PAM). Concentration Control: Mix HENGFENG Floc PAM powder with water at a mass ratio of 0.1%-0.3%, i.e., add 1-3 g of HENGFENG Floc PAM to 1 L of water. Dissolution Method: First add water into the stirring tank, then slowly sprinkle PAM powder (to prevent caking). Control the stirring speed at 80-100 r/min and the stirring time at 30-60 minutes until the solution becomes transparent and viscous (with no visible particles to the naked eye). If dissolution is insufficient, undissolved PAM particles will form "fish eyes" in the wastewater, which will instead reduce flocculation efficiency. 3. PAM Dosing and Reaction (Flocculation Reaction Tank) Dosing Method Adopt "metering pump dripping" to slowly inject the prepared PAM solution into the flocculation reaction tank at a final dosage of 1-5 mg/L (i.e., 1-5 mg of effective PAM component per liter of leachate). The dosing port is installed in front of the stirring impeller to ensure rapid mixing with the wastewater. Reaction Control (Two Stages) Rapid Mixing Stage: Control the stirring speed at 200-300 r/min for 1-2 minutes. The purpose is to achieve instant and uniform contact between the PAM solution and the wastewater, enabling PAM molecules to quickly adsorb onto the surface of colloidal particles. Slow Flocculation Stage: Reduce the rotational speed to 50-80 r/min and maintain it for 10-15 minutes. This stage is critical for "bridging and agglomeration". Slow stirring can avoid damaging the flocs being formed, allowing small particles to gradually aggregate into large flocs (visible "alum flowers") with a particle size of ≥ 100 μm. Meanwhile, the flocs can adsorb cobalt complexes or free Co²⁺ in the wastewater. 4. Solid-Liquid Separation (Sedimentation Tank / Clarification Tank) Process Selection Due to the high density of the flocs (containing heavy metal precipitates), vertical flow sedimentation tanks or inclined tube sedimentation tanks are adopted, as they occupy less area and have higher separation efficiency. Operating Parameters Control the hydraulic retention time (HRT) of the sedimentation tank at 1-2 hours and the upward flow velocity at 1.5-2.5 mm/s. This ensures that the flocs have sufficient time to settle to the bottom of the tank, forming "sludge" (containing heavy metal precipitates, soil colloids, and PAM flocs), while the upper layer becomes clarified liquid. Key Function Through this step, the removal rate of suspended solids (SS) in the wastewater can reach over 90%. At the same time, heavy metals such as cobalt settle along with the flocs, significantly reducing the heavy metal concentration in the clarified liquid and laying a foundation for subsequent up-to-standard discharge or advanced treatment. 5. Subsequent Treatment: Disposal of Sludge and Clarified Liquid Sludge Treatment The heavy metal-containing sludge at the bottom of the sedimentation tank (with a moisture content of approximately 80%-90%) is transported to a plate-and-frame filter press via a sludge pump for dewatering, forming sludge cakes with a moisture content of ≤ 60%. These sludge cakes must be managed as hazardous waste and sent to qualified institutions for solidification/stabilization treatment or cobalt recovery (e.g., through pyrometallurgical smelting or hydrometallurgical leaching). Clarified Liquid Treatment The upper clarified liquid needs to be tested for pH, chemical oxygen demand (COD, caused by residual citric acid), and heavy metal concentrations (e.g., Co, As, Cu). If it meets the standards (e.g., cobalt concentration < 0.01 mg/L, in line with the Environmental Quality Standards for Surface Water (GB 3838-2002)), it can be directly discharged. If it fails to meet the standards, further advanced treatment using ion exchange resins or membrane separation technology is required to ensure the complete removal of pollutants.

HENGFENG Anionic polyacrylamide emulsion is widely used in the alumina separation process. It serves as a flocculant to promote the settling of solid - liquid mixtures, improve separation efficiency, and enhance product quality. The following is a detailed introduction:     · Role in the alumina separation process: In the alumina production process, especially in the Bayer process, after bauxite is dissolved in caustic soda solution at high temperature and pressure, a large - amount of solid - liquid mixture containing red mud and aluminum - sodium solution is formed1. Anionic polyacrylamide emulsion can adsorb and bridge the fine - grained solid particles in the slurry. By adding an appropriate amount of anionic polyacrylamide emulsion to the primary thickener, the red mud particles can be aggregated into larger flocs, accelerating their sedimentation rate. This helps to obtain clear overflow liquid, reduce the loss of aluminum - sodium solution, and improve the efficiency of subsequent filtration and other operations. In addition, in the counter - current decantation process for red mud washing, anionic polyacrylamide emulsion is also used to promote the settlement of residual red mud particles, so as to recover more alumina from the solution and improve the utilization rate of resources.   · Product characteristics required: · High molecular weight: Usually, anionic polyacrylamide emulsion with a high molecular weight is required. High - molecular - weight polymers can form longer molecular chains, which are more conducive to adsorbing and bridging between particles, and can form larger flocs. · Adjustable hydrolysis degree: According to different bauxite qualities and process requirements, the hydrolysis degree of anionic polyacrylamide can be adjusted. Generally, the hydrolysis degree is in the range of 6% - 45%. A suitable hydrolysis degree can ensure that the product has a good charge - density, so as to better adsorb particles with opposite charges or neutral particles through electrostatic interaction. · Good water - solubility: It can be quickly and evenly dissolved in water to form a uniform solution, so as to be effectively mixed with the alumina - containing slurry. It is usually required to be dissolved in low - hardness water, and the dissolution time is generally within 1 hour.   · Usage : · Dispersion: Efficient dispersion is very important during use. Otherwise, agglomeration and “fish eyes” will occur, and the dissolution time will be prolonged. · Water quality: Use low - hardness water, and avoid using tanks or pools that may affect water quality. · Temperature: Appropriate heating can accelerate the dissolution rate, but the water temperature should not exceed 50℃. · Stirring: Stirring can accelerate dissolution, but strong stirring will break the molecular chain of the dispersant and cause degradation. A ship - shaped agitator with a rotation speed of 200 - 500 rpm is the best. · Concentration preparation: Usually, the product is mixed into a 0.05% - 0.5% (w/w) solution for standby. · Dosage adjustment: The optimal dosage should be adjusted according to specific application conditions to achieve the best flocculation effect and economic benefits.

Application of Cationic Polymers in Municipal Sludge Dewatering - Thailand     A municipal wastewater treatment plant in Bangkok, Thailand, had been facing challenges in sludge dewatering. The plant's existing flocculants resulted in poor cake dryness and unstable dewatering performance, especially when the influent water quality fluctuated during the rainy season. This not only increased operating costs, but also brought difficulties to sludge treatment and disposal. Solution:   Hengfeng Chemical provided cationic polyacrylamide, which has a high charge density and optimized molecular weight, tailored to the characteristics of Thai municipal sludge. Our technical support team conducted a comprehensive on-site evaluation, including beaker tests and pilot tests, to optimize dosing parameters and ensure seamless integration with the plant's existing filter press system.   Results: Sludge dewatering efficiency increased by more than 35% Significantly improved sludge cake dryness, reducing transportation and landfill costs Reduce chemical consumption and improve cost-effectiveness Maintain stable performance under different wastewater qualities Make dewatering equipment run more smoothly, reduce blockage and maintenance requirements   The customer is very satisfied with the efficiency improvement and cost savings, and has adopted Hengfeng's cationic polyacrylamide as its long-term sludge treatment solution. This case shows that Hengfeng Chemical can provide targeted solutions for complex municipal challenges in Southeast Asia and other regions.