Introduction
When selecting a coagulant for water and wastewater treatment, two of the most common choices are Poly Aluminium Chloride (PAC) and Ferric Chloride (FeCl3). Both are metal-based coagulants, but they differ significantly in performance, cost, and application suitability. This guide compares them across key criteria to help you make an informed decision.
Chemical Properties
PAC is an inorganic polymer with the formula [Al2(OH)nCl6-n]m, pre-hydrolyzed for immediate coagulation. Ferric Chloride is a simple iron salt (FeCl3) that forms iron hydroxide flocs upon hydrolysis.
Performance Comparison
| Parameter | PAC 30% | Ferric Chloride |
|---|---|---|
| Effective pH range | 5.0-9.0 | 4.0-11.0 |
| Optimal pH | 6.5-7.5 | 5.0-7.0 |
| Typical dosage | 100-500 mg/L | 200-800 mg/L |
| Sludge volume | Lower | Higher (Fe(OH)3 is denser) |
| Color in treated water | Clear | May impart yellowish tint |
| Corrosivity | Low (pH 3.5-4.5) | High (pH <2) |
| Cold water performance | Excellent | Moderate to poor |
| Residual metal | Al <0.05 mg/L | Fe may stain surfaces |
| Phosphorus removal | Moderate | Excellent |
| Sulfide/odor removal | Poor | Excellent |
When to Choose PAC
- Drinking water treatment — low residual aluminium, no color in finished water
- Textile wastewater — superior dye removal (90-99%)
- Cold climates — effective below 5C where FeCl3 underperforms
- Low-alkalinity water — PAC consumes less alkalinity
- When you want less sludge — PAC produces 30-50% less sludge
When to Choose Ferric Chloride
- Phosphorus removal in municipal WWTP
- Hydrogen sulfide (H2S) and odor control
- Wide pH range applications (4.0-11.0)
- When iron-based coagulant is specifically required
Cost Comparison
While FeCl3 has a lower unit price per ton, PAC’s lower dosage requirement (50-70% less) and reduced sludge disposal costs often make it more economical on a total cost of ownership basis. For textile, paper, and drinking water applications, PAC is generally the more cost-effective choice.
Conclusion
For most industrial water treatment applications — particularly drinking water, textile effluent, and POME — PAC 30% offers superior performance, lower total cost, and simpler handling. Ferric Chloride remains the better choice for phosphorus removal and odor control applications.
Contact Hydrochemix Chemicals at jingshuicc@gmail.com for PAC 30% product specifications and a free sample for bench testing.