Cationic polyacrylamide (Hydrex 6311) is a high-performance flocculant and coagulant produced by Veolia Water Technologies under its Hydrex 6000 series. This series includes advanced polymers designed for solid–liquid separation, sludge dewatering, and wastewater clarification across a wide range of industrial and municipal processes. Hydrex 6311, in particular, is a cationic polyacrylamide (CPAM) characterized by strong positive charge density and high molecular weight, making it highly effective in destabilizing negatively charged particles, colloids, and organic matter suspended in water. Through mechanisms such as charge neutralization and polymer bridging, Hydrex 6311 enhances the formation of large, dense flocs that settle or filter rapidly, leading to cleaner water and more efficient sludge handling.

1. Application in municipal and industrial wastewater treatment

Hydrex 6311 is extensively used in municipal wastewater treatment plants for primary clarification, secondary clarification, and sludge dewatering. During primary treatment, it functions as a coagulant or coagulant aid, improving the removal of suspended solids, fats, oils, and greases. When added to raw or pretreated sewage, the cationic polymer neutralizes the negative surface charge of fine colloidal particles, enabling them to agglomerate into larger flocs that settle quickly in clarifiers.

In biological (secondary) treatment systems, Hydrex 6311 improves the settling properties of activated sludge. Many biological sludges contain fine or filamentous microorganisms that do not settle easily, leading to turbid effluent and sludge bulking. The addition of a controlled dosage of Hydrex 6311 enhances floc compactness and reduces effluent turbidity. It also assists in controlling sludge blanket height and improves the efficiency of secondary clarifiers, resulting in better effluent quality with lower total suspended solids (TSS) and biochemical oxygen demand (BOD).

One of the most important uses of Hydrex 6311 in wastewater systems is in sludge thickening and dewatering. Sludge from biological and chemical treatment processes often contains a high proportion of water (95–99%). By promoting flocculation and water release, Hydrex 6311 enables the formation of drier, more compact sludge cakes when used in centrifuges, belt presses, or screw presses. This significantly reduces sludge volume, transportation costs, and disposal expenses. The product’s high molecular weight and optimized cationic charge make it especially effective for organic-rich sludges, such as those from municipal wastewater, food processing, or dairy plants.

Hydrex 6311 also helps to minimize polymer consumption compared with lower-molecular-weight flocculants, thanks to its superior bridging efficiency. It can be used alone or in combination with inorganic coagulants such as ferric chloride or polyaluminum chloride (PAC) to achieve optimal clarification performance and improved sludge settling.

2. Application in the paper and pulp industry

In the paper and pulp sector, Hydrex 6311 acts as a multifunctional polymer used for retention, drainage, and pitch control. During the papermaking process, fine fibers and mineral fillers can be lost with white water, reducing paper yield and consistency. By adding cationic polyacrylamide to the wet end, these fine particles are captured and retained in the paper sheet, improving retention efficiency and product quality.

The cationic charge of Hydrex 6311 also neutralizes anionic trash—dissolved or colloidal anionic substances such as lignin derivatives, resin acids, and dispersants—that would otherwise interfere with additives like dyes and cationic starch. As a fixative, the polymer stabilizes the charge balance in the wet end system and minimizes the formation of deposits or pitch. Additionally, by improving drainage on the forming wire, Hydrex 6311 enhances machine speed, reduces drying energy, and stabilizes paper machine operation. Its use leads to cleaner systems, reduced downtime, and more consistent paper properties.

3. Application in oilfield and petrochemical water treatment

Hydrex 6311 is used widely in oilfield wastewater and produced water treatment, where emulsified oil, solids, and organics must be separated before discharge or reuse. The cationic polymer destabilizes negatively charged oil droplets and suspended solids, promoting their aggregation and facilitating phase separation. This makes Hydrex 6311 an efficient flocculant for oil–water separation and clarification of produced water in both onshore and offshore facilities.

In refineries and petrochemical plants, Hydrex 6311 helps treat process effluents containing emulsified hydrocarbons, polymers, and fine solids. Its high molecular weight enables it to capture small colloidal particles and enhance clarification in dissolved air flotation (DAF) units and gravity separators. The polymer’s chemical stability allows it to perform under varying pH, salinity, and temperature conditions typical of oilfield operations.

4. Application in mining and mineral processing

In the mining industry, Hydrex 6311 plays a critical role in tailings dewatering, thickening, and water recovery. Mineral processing generates vast quantities of fine suspended solids that are difficult to settle. By adding Hydrex 6311 to tailings or concentrate slurries, particles aggregate into large flocs that settle more rapidly, leading to higher underflow density and clearer overflow water.

In thickener applications, the polymer reduces overflow turbidity and improves water recycling efficiency. This recovered water can be reused in ore processing circuits, reducing fresh water consumption and environmental impact. In filtration and dewatering stages, Hydrex 6311 enhances filtration rate and cake dryness, contributing to improved operational efficiency and lower disposal costs. Its compatibility with anionic and nonionic polymers allows for customized programs depending on the specific mineral type and slurry chemistry.

5. Application in textile, food, and chemical industries

Hydrex 6311 is also widely applied in textile wastewater treatment, where it helps remove dyes, surfactants, and organic colorants. The polymer destabilizes dye molecules and colloidal matter, promoting rapid color removal through coagulation and flocculation. In the food and beverage industry, it assists in clarifying process water, removing organic particles like proteins and starch, and improving wastewater quality before discharge or reuse.

In chemical manufacturing, Hydrex 6311 serves as a coagulant for separating fine solids and organic residues from process effluents. It helps clarify process streams, enabling efficient recycling and compliance with discharge standards. Because of its high cationic activity, it is particularly effective for effluents with high organic load and strong anionic content.

6. Performance characteristics and advantages

Hydrex 6311 provides several important advantages over inorganic coagulants and lower-grade polymers:

• High molecular weight promotes efficient bridging of fine particles, forming dense flocs.

• Strong cationic charge density enables rapid neutralization of negatively charged particles.

• Fast floc formation improves sedimentation, flotation, and filtration efficiency.

• Low sludge generation compared with metal salts, reducing disposal costs.

• Wide pH adaptability (typically effective between pH 4–9).

• Compatibility with other treatment agents like PAC, alum, and anionic polyacrylamides.

• Environmental friendliness, as it contains no heavy metals or harmful residues.

7. Handling and dosage

Hydrex 6311 is typically supplied as a powder or emulsion polymer with active content ranging from 20 to 50%. It should be diluted in clean water to form a 0.1–0.5% working solution prior to use. Proper mixing is critical to ensure uniform distribution. Typical dosage ranges from 1–10 mg/L for water clarification and 2–8 kg per ton of dry solids for sludge dewatering, depending on system characteristics.

Prepared solutions should be used within 24 hours to prevent hydrolysis and viscosity loss. The polymer should be stored in a cool, dry area, away from direct sunlight and strong oxidizing agents.

Conclusion

Cationic polyacrylamide (Hydrex 6311) is an advanced, high-molecular-weight flocculant optimized for efficient solid–liquid separation in municipal, industrial, and process water systems. Its strong cationic charge, rapid flocculation performance, and wide compatibility make it an indispensable chemical for wastewater clarification, sludge dewatering, papermaking, oilfield water treatment, and mineral processing. By reducing turbidity, improving sludge dryness, and enhancing water reuse, Hydrex 6311 supports cleaner production, cost reduction, and sustainable water management. Its proven efficiency and versatility make it one of the most reliable solutions for modern water treatment operations worldwide.