Polyaluminium Ferric Chloride (PAFC): The Complete Water Treatment Coagulant Guide
Coagulation is the cornerstone of nearly every modern water and wastewater treatment process, and the choice of coagulant directly determines effluent quality, operating cost, and sludge management efficiency. Among the growing family of inorganic polymer coagulants, polyaluminium ferric chloride—commonly abbreviated as PAFC—has emerged as a high-performance solution that bridges the gap between conventional aluminum salts and iron salts. This guide explores the chemistry, specifications, applications, and practical optimization of the PAFC coagulant, helping water treatment professionals make informed decisions for their facilities.
What Is Polyaluminium Ferric Chloride (PAFC)?
Polyaluminium ferric chloride (PAFC) is an inorganic polymer coagulant that combines the hydroxylated complexes of both aluminum and iron into a single, multinuclear molecular structure. Often described as an iron-modified form of polyaluminium chloride, PAFC integrates ferric iron (Fe3+) into the polynuclear aluminum framework, producing a coagulant that inherits the strengths of both metal systems while mitigating their individual weaknesses.
The general chemical formula of PAFC can be expressed as [Al2(OH)nCl6-n]m·[Fe2(OH)nCl6-n]m, reflecting its dual-metal composition. In appearance, solid poly aluminum iron chloride is typically a reddish-brown or yellowish-brown powder, distinguishing it from the white or pale-yellow PAC. The liquid form presents as a reddish-brown solution with a density above 1.19 g/cm3.
PAFC was developed to solve a persistent challenge in water treatment: aluminum-based coagulants such as PAC deliver excellent charge neutralization and broad pH adaptability, yet they often produce relatively light flocs that settle slowly—particularly in cold, low-turbidity water. Iron-based coagulants, by contrast, form dense, rapidly settling flocs but tend to lower the pH aggressively and carry a risk of color residuals. By fusing the two, PAFC water treatment achieves faster sedimentation, denser floc formation, and superior performance under challenging conditions such as low temperature, high turbidity, and complex industrial matrices.
PAFC Chemistry: Dual Coagulation Mechanism
The Aluminum-Iron Synergy
The effectiveness of the PAFC coagulant stems from its dual coagulation mechanism. Aluminum hydroxyl species in the polymer are responsible for strong charge neutralization. These highly charged multinuclear complexes (such as Al13 and Al30 species) rapidly destabilize colloidal particles in raw water, causing them to aggregate. This is the same mechanism that makes polyaluminium chloride so effective across a wide range of conditions.
The ferric component contributes a complementary mechanism. Iron hydroxide precipitates—Fe(OH)3—form over a broader pH range than aluminum hydroxide and remain as stable solids rather than redissolving at elevated alkalinity. This produces dense, heavy flocs with strong adsorption and bridging capacity. The iron fraction also enhances the coagulant’s ability to capture heavy metals, dyes, and suspended organic matter through sweep flocculation and enmeshment.
Coagulation and Flocculation Pathways
In practice, PAFC acts through three simultaneous pathways: (1) charge neutralization driven by aluminum species, (2) adsorption and bridging provided by the extended polymer chain, and (3) sweep flocculation and rapid sedimentation driven by the dense iron hydroxide precipitates. The result is faster floc growth, a wider effective pH range (approximately 4–11), and improved adaptability to temperature fluctuations compared with single-metal coagulants.
Because iron hydroxide maintains stability at higher pH values, PAFC performs notably well in alkaline wastewater streams—such as those from paper mills, glass processing, and textile dyeing—where standard aluminum coagulants may become less effective. This broad-spectrum performance is a key reason operators increasingly select PAFC for variable or hard-to-treat water sources.
PAFC Specifications and Quality Standards
Polyaluminium ferric chloride is manufactured to strict quality parameters that define its coagulation performance, stability, and suitability for potable water applications. The table below summarizes typical specifications for both solid and liquid PAFC products, aligned with common industry standards such as China’s GB/T 15892 series.
| Parameter | Solid PAFC | Liquid PAFC |
|---|---|---|
| Al2O3 content | ≥ 27.0% (typical 28–30%) | ≥ 10.0% |
| Fe2O3 content | 1.0% – 5.0% | 1.0% – 3.0% |
| Basicity (%) | 30 – 95% | 30 – 95% |
| pH (1% aqueous solution) | 3.5 – 5.0 | 3.5 – 5.0 |
| Water-insoluble matter | ≤ 1.0% | ≤ 0.3% |
| Density (20°C) | — | ≥ 1.19 g/cm3 |
| Heavy metals (as Pb) | ≤ 0.003% | ≤ 0.0015% |
| Arsenic (As) | ≤ 0.0005% | ≤ 0.0003% |
For drinking water applications, the permissible levels of heavy metals—including lead, arsenic, cadmium, and mercury—are tightly controlled to ensure the treated water meets national sanitary standards. Buyers sourcing PAFC for potable water treatment should always request a full heavy-metal analysis certificate from the manufacturer. Basicity (the degree of hydroxylation) is another critical indicator: a higher basicity generally means stronger polymerization, larger floc size, and better adaptability, though extremely high basicity can reduce storage stability.
PAFC vs PAC: Comparison and Selection
Because polyaluminium ferric chloride is closely related to polyaluminium chloride, the most common question operators face is when to choose one over the other. The comparison table below highlights the key differences to guide selection.
| Feature | PAC (Polyaluminium Chloride) | PAFC (Polyaluminium Ferric Chloride) |
|---|---|---|
| Composition | Pure aluminum-based polymer | Aluminum + iron composite polymer |
| Appearance (solid) | White, pale yellow, or yellow | Reddish-brown or yellowish-brown |
| Primary mechanism | Charge neutralization (strong) | Charge neutralization + dense sweep flocculation |
| Floc density & settling speed | Moderate; slower in cold water | Dense flocs; faster sedimentation |
| Effective pH range | Approximately 5 – 9 | Approximately 4 – 11 |
| Low-temperature performance | Reduced efficiency below 10°C | Stable; maintains performance in cold water |
| Heavy metal removal | Moderate | Superior (e.g., Cr6+, Pb, Cd) |
| Color & organic removal | Strong | Strong; enhanced for dyes and humic substances |
| Residual metal in effluent | Residual aluminum risk | Lower residual; combined Al/Fe |
| Corrosivity | Low to moderate | Moderate (iron component slightly higher) |
| Cost | Economical | Slightly higher; offset by lower dosage needs |
When to Choose PAFC Over PAC
For plants handling low-temperature, low-turbidity source water, PAFC is generally the superior choice because the iron fraction sustains floc formation when aluminum-only coagulants struggle. PAFC is also preferred for high-turbidity water, where dense iron-bearing flocs settle more rapidly and reduce clarifier load. When treating industrial effluents rich in heavy metals, dyes, or high alkalinity—such as electroplating wastewater, textile dyeing, and paper-making—the broader pH tolerance and enhanced sweep flocculation of poly aluminum iron chloride deliver measurably better results.
Conversely, when raw water is moderate in turbidity and temperature, cost-sensitive, and color removal is the primary goal, standard PAC remains a proven and economical option. Many facilities also combine PAFC with an organic polymer such as PAM to further enlarge and strengthen flocs, achieving both rapid sedimentation and high clarity in a single treatment train.
PAFC Applications in Water Treatment
The versatility of the PAFC coagulant makes it suitable for a broad spectrum of water treatment scenarios, from potable water purification to complex industrial effluent processing.
Drinking Water Purification
In municipal water treatment plants, PAFC effectively removes turbidity, suspended solids, natural organic matter, and micro-pollutants from surface water and groundwater. Its ability to form dense flocs at low temperatures makes it particularly valuable during winter months when conventional coagulants underperform. When produced to drinking-water-grade standards, PAFC yields treated water that complies with national sanitary standards for residual aluminum and iron.
Municipal and Industrial Wastewater
For domestic sewage and industrial wastewater, PAFC rapidly destabilizes colloidal organic matter and phosphorus, supporting efficient primary clarification and chemical phosphorus removal. Its broad pH tolerance and strong sweep-flocculation action make it effective for paper-making, printing and dyeing, tannery, food processing, and chemical manufacturing effluents. The coagulant also excels at removing heavy metals—including chromium, lead, and nickel—from electroplating and mining wastewater.
Specialized Industrial Applications
Beyond mainstream water treatment, PAFC is used in cooling water conditioning, oily wastewater emulsion breaking, sludge dewatering conditioning, and the treatment of high-alkalinity process streams such as those found in glass and ceramic manufacturing. In these demanding environments, the iron component’s stability at elevated pH proves especially advantageous.
PAFC Dosage and Treatment Optimization
Preparing the PAFC Solution
Solid PAFC should be dissolved in clean water at a ratio of approximately 1:5 (solid to water) with continuous stirring until fully dissolved. The resulting stock solution is then diluted to a working concentration of 2–3% (for precise dosing) or 5–10% (for conventional application) before being fed into the treatment system. Liquid PAFC can be dosed directly or diluted as needed. All dosing equipment, pipes, and pumps should be constructed from corrosion-resistant materials such as stainless steel, PVC, or HDPE, because the iron chloride component is mildly corrosive.
Determining Optimal Dosage
The recommended effective dosage of PAFC typically falls in the range of 10–30 mg/L for drinking water and 20–100 mg/L for industrial wastewater, though actual requirements vary significantly with raw water quality, turbidity, pH, and temperature. Because water characteristics differ from site to site, operators should always conduct jar tests to identify the optimal dosage and pH conditions before full-scale deployment. Jar testing allows precise comparison of settling velocity, supernatant clarity, and floc characteristics across a range of doses.
Operational Best Practices
To maximize PAFC performance, maintain the raw water pH within the coagulant’s effective range and adjust with acid or alkali only when necessary. Rapid mixing (1–3 minutes at high velocity) ensures uniform dispersion and effective charge neutralization, followed by slower flocculation mixing (10–30 minutes) to allow floc growth. When paired with a PAM flocculant, introduce the polymer after PAFC coagulation to build larger, more shear-resistant flocs. Regularly monitor residual aluminum and iron in the effluent, and perform routine calibration of dosing pumps to prevent over- or under-dosing.
How to Choose Quality PAFC
Selecting a high-quality polyaluminium ferric chloride product is essential for consistent treatment performance and regulatory compliance. Consider the following factors when evaluating suppliers:
- Active content: Verify that Al2O3 and Fe2O3 contents meet or exceed stated specifications through independent testing.
- Basicity: Choose a basicity appropriate for your water conditions—higher basicity suits high-turbidity and high-organic water, while moderate basicity offers broader stability.
- Heavy-metal compliance: For potable water, demand a certificate confirming arsenic, lead, cadmium, and mercury levels within drinking-water limits.
- Solubility and insolubles: Low water-insoluble matter (
- Manufacturer credentials: Prefer suppliers with ISO 9001 quality management certification, documented production consistency, and technical support for dosage optimization.
- Appearance and uniformity: Consistent reddish-brown coloration and particle uniformity in solid products indicate stable production quality.
Requesting samples for jar testing before committing to bulk purchases is a best practice that protects both treatment performance and budget. A reliable supplier should provide full technical data sheets, application guidance, and responsive after-sales support.
FAQ
What is the difference between PAFC and PAC?
The primary difference is composition: PAC is a pure aluminum-based polymer, while PAFC is a composite of aluminum and iron. PAFC produces denser flocs that settle faster, performs better in cold and low-turbidity water, removes heavy metals more effectively, and tolerates a broader pH range. PAC is typically more economical and excels at color removal in moderate conditions.
Is PAFC safe for drinking water treatment?
Yes. When manufactured to drinking-water-grade standards and certified for low heavy-metal content, PAFC is safe for potable water treatment. Treated water can meet national sanitary standards for residual aluminum and iron. Always source PAFC from certified suppliers and request full heavy-metal analysis documentation.
What is the typical PAFC dosage for water treatment?
For drinking water, the effective dosage generally ranges from 10 to 30 mg/L. For industrial and municipal wastewater, dosages typically range from 20 to 100 mg/L depending on pollutant load, turbidity, and pH. Always conduct jar tests to determine the precise optimal dose for your specific water source.
How should PAFC be stored?
Solid PAFC should be stored in a cool, dry, well-ventilated area, protected from moisture and direct sunlight, in sealed original packaging. Under proper conditions, solid PAFC retains a shelf life of approximately 12 months. Liquid PAFC should be stored in corrosion-resistant tanks and used within 6 months to avoid sedimentation and reduced activity.
Can PAFC be used with other coagulants or flocculants?
Yes. PAFC is frequently combined with organic polymers such as PAM to enhance floc size, strength, and settling speed. It can also be used alongside PAC or other inorganic coagulants in dual-coagulant strategies. When combining products, determine the optimal dosing sequence and ratios through jar testing.
Why does PAFC perform better in cold water than PAC?
The iron hydroxide component in PAFC forms dense precipitates that maintain their coagulation and settling performance at low temperatures, whereas aluminum-only coagulants like PAC experience reduced hydrolysis and slower floc formation in cold water. This makes PAFC particularly effective for winter operations and cold-region water treatment.
What is the effective pH range of PAFC?
PAFC is effective across a broad pH range of approximately 4 to 11. The iron fraction remains stable and active at higher pH values where aluminum hydroxide may redissolve, giving PAFC an advantage in treating alkaline industrial wastewater such as that from glass, paper, and textile processing.
What color is PAFC and why?
Solid PAFC is typically reddish-brown or yellowish-brown, and the liquid form is a reddish-brown solution. The coloration comes from the ferric iron (Fe3+) component integrated into the polymer structure, which distinguishes PAFC visually from the white or pale-yellow PAC.
Polyaluminium ferric chloride represents a significant advancement in inorganic polymer coagulant technology, delivering the charge-neutralization power of aluminum with the dense, fast-settling flocs of iron. Whether treating drinking water, municipal sewage, or complex industrial effluents, the PAFC coagulant offers versatility, efficiency, and reliability across challenging conditions. By understanding its chemistry, specifications, and optimization principles, water treatment professionals can leverage PAFC water treatment to achieve cleaner effluent, lower operating costs, and more resilient plant performance.