When buying powdered PAC, many buyers assume that a higher Al₂O₃ percentage automatically means better performance. However, the relationship between Al₂O₃ content, basicity, and treatment efficiency is more nuanced.
This document explains what PAC grade specifications actually represent, how they influence performance and costs, and what to evaluate beyond the Al₂O₃ value.
Need help selecting a PAC grade for your application? Contact our technical team for free recommendations and samples.
What Does Al₂O₃ Content Indicate?
Al₂O₃ content, expressed as a weight percentage, measures the equivalent amount of aluminum oxide in the product. It is a standard indicator of active aluminum concentration in polyaluminum chloride (PAC), allowing comparison across different water contents and formulations.
Higher Al₂O₃ means:
More active aluminum per kilogram of product
Lower weight-based dosage required to deliver the same amount of aluminum to water
Reduced transport and storage costs per unit of treatment capacity
But Al₂O₃ alone does not determine treatment effectiveness. Basicity ratio - the percentage of hydroxyl (OH) relative to aluminum - is equally or more important for coagulation performance in real-world applications.
Three Common Powdered PAC Grades
| Specification | 28% PAC | 30% PAC | 31% PAC |
|---|---|---|---|
| Al₂O₃ content | 28% min | 30% min | 31% min |
| Typical basicity range | 60–75% | 65–80% | 70–85% |
| Active Al per kg | Lower | Moderate | Higher |
| Required dosage (by weight) | Slightly higher | Moderate | Lower |
| Cost per kg | Lower | Moderate | Higher |
| Cost per unit Al₂O₃ | Similar | Similar | Similar |
Why Basicity Matters as Much as Al₂O₃ Content
Basicity is defined as the molar ratio of OH to Al in the PAC molecule, shown as a percentage. A basicity of 70% means 70% of aluminum coordination sites are occupied by OH groups, with the remainder occupied by Cl.
Higher basicity means:
More pre-polymerized aluminum species in the product
Faster hydrolysis and charge neutralization when added to water
Better performance in cold water (below 10°C)
More stable coagulation across varying water conditions
Lower residual aluminum in treated effluent
In most coagulation applications, a 28% PAC product with 80% basicity will outperform a 31% PAC product with only 60% basicity - even though the latter has higher Al₂O₃. Buyers who focus only on Al₂O₃ without checking basicity often end up disappointed with the real-world results of higher-nominal-grade products.
Recommended basicity range for most applications: 60–85%
Which Grade Should You Choose?
28% PAC is suitable for:
High-volume, cost-sensitive applications where Al₂O₃ cost per unit is the main driver
Moderate water quality with stable influent conditions
Facilities that can run regular jar tests and adjust dosage to compensate for slightly lower basicity
30% PAC - the most commonly used grade - offers:
A balance between Al₂O₃ content and basicity
Reliable performance in most municipal and industrial water treatment applications
Wide availability from multiple suppliers
31% PAC is preferred for:
Applications where dosage volume is limited (small storage or feed systems)
High-performance needs with low residual aluminum (drinking water)
Cold climates where higher basicity helps maintain stable performance in cold water
Buyers who prioritize consistent performance over the lowest unit price
Beyond Grade: Other Factors When Buying PAC
While Al₂O₃ and basicity are the two most important parameters, a complete product evaluation should also include:
Heavy metal content. PAC for drinking water must meet NSF/ANSI 60 or local equivalent standards for heavy metals including arsenic, lead, mercury, and cadmium. Request Certificates of Analysis (COA) for each batch showing heavy metal levels.
pH of 1% solution. Should be between 3.5 and 5.0. Values outside this range may indicate instability or impurities.
Insoluble matter content. Low-quality PAC may contain undissolved particles that clog feed lines and reduce effective Al₂O₃ delivery. Quality products have insoluble matter below 0.2%.
Batch consistency. Ask suppliers for production history across multiple batches and their corresponding COAs. Consistent specifications across batches indicate reliable manufacturing quality control.
Cost Analysis: Is a Higher Grade More Economical?
The economics of PAC grade selection depend on delivered cost per unit of Al₂O₃ - not cost per kilogram of product.
Example comparison for equivalent treatment:
28% PAC at $X/kg requires dosage D to achieve target Al₂O₃
31% PAC at $1.1X/kg requires 0.9D to deliver the same Al₂O₃
If the 10% price increase is proportional to the 10% higher Al₂O₃ content, the economics are identical. In practice, premium pricing for higher grades varies by supplier and market - comparing cost per kilogram of Al₂O₃ (not cost per kg of product) is the correct economic comparison.
Additionally, if the higher basicity in a 31% product reduces the effective dosage needed beyond what Al₂O₃ content alone would predict, the higher-grade product may be more economical even at a higher unit price.
Related cost guide: PAC vs. Alum: Which Coagulant Performs Better?
Frequently Asked Questions
Can I replace 30% PAC with 28% PAC without changing my dosing system?
Yes, but recalibration is required. To deliver the same amount of Al₂O₃ to water, increase the dosage proportionally - approximately 7% more 28% PAC by weight compared to 30% PAC. Run jar tests after switching to confirm the adjusted optimal dosage.
Does PAC grade affect sludge production?
At the same Al₂O₃ dosage, sludge production is similar across grades. However, if a higher-grade product with higher basicity achieves the same treatment results at a lower Al₂O₃ dosage, sludge production may decrease slightly.
How can I verify that a supplier's PAC meets the claimed grade?
Request COAs for the batches you receive, and periodically send samples to an independent laboratory for verification. Key parameters to validate include Al₂O₃ content, basicity, pH of 1% solution, insoluble matter, and heavy metals. Our products come with complete COA documentation for every batch.
Conclusion
Selecting a PAC grade is not simply about picking the highest Al₂O₃ content. Basicity, heavy metal levels, batch consistency, and total cost per unit of Al₂O₃ are equally important for making the right choice for your application.
For most industrial and municipal applications, 30% PAC with 65–80% basicity offers the best balance of performance and cost. For drinking water or cold-climate applications, higher-basicity 31% PAC provides the performance margin needed for demanding conditions.
Contact our technical team today for free grade recommendations, samples across our full PAC product range, and batch COA documents. We respond within 24 hours.
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