BUYER'S GUIDE
PAC Specifications Explained: What Al2O3 and Basicity Really Mean
Two PAC quotations can describe the same 25 kg bag and still differ by a third in what you actually get. The gap sits in two numbers - Al2O3 content and basicity - and in whether the supplier is willing to put them on a per-batch certificate of analysis. Here is how to read a PAC specification properly.
You are buying aluminium oxide, not bags
A 25 kg bag of PAC at Al2O3 28% contains 7.0 kg of active coagulant. At 29% it contains 7.25 kg. The rest is chloride, water of crystallisation, sodium and insolubles - mass you pay to produce, pack, freight and store without buying any coagulation.
That is why the only fair price comparison in this business is cost per kilogram of Al2O3 delivered to your plant, not price per tonne on the quotation.
| Parameter | What it means | Commercial range | Why you should care |
|---|---|---|---|
| Al2O3 content | Active coagulant in the product | 28% industrial, 29% drinking water; liquid 10% | Sets the dose and the true cost |
| Basicity (OH/Al) | Degree of pre-hydrolysis - how polymerised the aluminium already is | 40 - 90% | Floc speed, alkalinity demand, pH drop |
| pH (1% solution) | Acidity of the product as supplied | 3.5 - 5.0 | Pump, tank and pipe material; corrosion |
| Water-insoluble matter | Residue that will not dissolve | 0.6% drinking water, 1.5% industrial, solid | Line blockage, sludge volume, filter load |
| Heavy metals | As, Pb, Cd, Hg, Cr(VI) | Tight individual limits in drinking-water grade | Admission to potable treatment |
| Appearance | White, light yellow, yellow | Indicator of the production route | White product usually comes from a low-iron route |
Basicity: the number most buyers skip
Basicity expresses how much of the aluminium has already been neutralised by hydroxyl groups. The scale runs from aluminium chloride at one end, with no hydroxyl attached, to aluminium hydroxide at the other, where every aluminium carries its full hydroxyl complement. It decides how the product behaves in the plant, and it is the parameter most often missing from a quotation.
Low basicity, roughly 40 - 60%, behaves closer to a conventional aluminium salt. It is more acidic, it consumes more alkalinity per milligram of Al2O3, and it is more forgiving when the raw water pH swings around. High basicity, roughly 70 - 85%, carries more pre-formed polymer: floc appears faster, flocs are denser, and less alkalinity is consumed per milligram dosed. That is why the municipal band usually sits there.
Above about 85% you are close to the stability limit of the product. Solutions can throw a precipitate in storage, and dilution with hard water is less forgiving. Higher basicity is not automatically better - it is a trade-off between speed, alkalinity demand and shelf stability.
pH and insolubles: the two boring numbers that cause most complaints
PAC solution is acidic, pH 3.5 - 5.0 for a 1% solution. That is normal, and it dictates materials: HDPE, polypropylene, FRP and rubber-lined steel are fine; carbon steel and aluminium are not. If a 1% solution of your stored product reads above pH 5, the batch has started to hydrolyse in the tank and should be re-tested before use.
Water-insoluble matter is the fraction that never dissolves. At a 100 mg/L dose, 1.5% insolubles puts about 1.5 mg/L of inert solids into the clarifier, which is tolerable. The same product in a 5% make-up tank leaves a sediment layer that finds its way into dosing pumps and strainers. On a small plant with narrow dosing lines, insolubles cause more downtime than coagulation problems do.
Drinking-water grade is a different specification, not a marketing label
The active chemistry is identical. What changes is the impurity envelope and the paperwork. Drinking-water grade in China is released against GB 15892-2020, which caps water-insoluble matter at 0.6% for solid product and sets individual limits for arsenic, lead, cadmium, mercury and hexavalent chromium. Industrial product is released against GB/T 22627-2022, which does not carry the same heavy-metal suite.
Across borders the scheme changes again: NSF/ANSI 60 in the United States and Canada, EN 883 plus national approval schemes in the EU, and separate registration in most Gulf and Southeast Asian markets. A batch released to GB 15892-2020 is not automatically accepted under NSF/ANSI 60. If the treated water is going into a distribution network, the specification has to match the rules of that market, not the price list.
What a complete COA contains
A certificate of analysis is only useful if it can be tied to the material in your store. A complete sheet carries the following:
- Batch number and production date, so the certificate traces back to a reactor campaign
- Al2O3 content, with the test method or standard reference
- Basicity, as a percentage
- pH of a 1% solution
- Water-insoluble matter
- Heavy metals - As, Pb, Cd, Hg, Cr(VI) - for drinking-water grade
- Appearance, and density where relevant for liquid product
- The standard the batch was released against
Comparing two quotations like-for-like
Divide the price per tonne by the Al2O3 content as a decimal. That single step removes most of the confusion in this market.
| Offer | Price per tonne | Al2O3 | Cost per tonne of Al2O3 |
|---|---|---|---|
| Supplier A, solid | USD 340 | 28% | USD 1,214 |
| Supplier B, solid | USD 350 | 29% | USD 1,207 |
Three adjustments that finish the comparison
In the example above, the offer that looks 3% more expensive per tonne is the cheaper coagulant per unit of active. Reverse the numbers and the conclusion flips. Neither supplier is misrepresenting anything - they are quoting different products.
Add freight and handling per tonne, because a 25 kg bagged product and a 1,000 kg jumbo bag do not cost the same to move and unpack. Check basicity, because two products at the same Al2O3 can need different doses in your water. Then check insolubles, because they cost you in strainers, filter runs and sludge, not on the invoice.
What we put on paper
We produce two solid grades, Al2O3 28% industrial to GB/T 22627-2022 and 29% drinking water to GB 15892-2020, plus liquid at 10% for drinking-water duty. Each batch is tested before dispatch and ships with a certificate of analysis; the safety data sheet and technical data sheet go with the first order, and third-party inspection can be arranged when a letter of credit or a buyer's quality department requires it.
Send us your water data and we will run a jar test and return a grade, a starting dose and the certificate format we would ship against. That is a more useful document than any catalogue. See the full PAC grade list or send a quotation request.
Frequently asked questions
Is a higher Al2O3 content always better?
It is not a better molecule, it is a more concentrated delivery of the same one. Higher content means less mass to freight and store per unit of active. Performance differences between two products usually come from basicity and impurities, not from the last percentage point of Al2O3.
Can I use industrial grade PAC for drinking water if the plant has filtration?
No. Filtration removes particles, not dissolved arsenic, lead or chromium. The heavy-metal limits apply to what goes into the water, and a plant cannot compensate downstream for an out-of-spec coagulant.
Why is white PAC more expensive than yellow?
Colour follows the raw material route. White product is typically made from a refined aluminium source with low iron; yellow and brown product comes from a lower-grade route. The white route gives lower iron, lower insolubles and a lighter colour, which is why drinking-water grades are usually white.
Does basicity change the dose I need?
Indirectly. Basicity changes how much alkalinity the product consumes and where the pH settles after dosing, and both shift the effective dose. Two products at the same Al2O3 but different basicity can need measurably different doses in the same water - which is why a jar test beats a specification sheet on its own.