Short answer: PAC stands for Poly Aluminium Chloride. It is a pre-hydrolysed aluminium coagulant used to remove turbidity, colour and suspended solids from drinking water, process water and industrial effluent. It is also used in paper making. Compared with alum it usually works over a wider pH range, forms flocs faster and produces less sludge.
PAC chemical full form and formula
The full form of PAC is Poly Aluminium Chloride (also written polyaluminium chloride). It is not a single fixed molecule but a family of partly neutralised aluminium chlorides. Its general formula is written as [Al₂(OH)ₙCl₆₋ₙ]ₘ. The share of hydroxide in the molecule is called basicity; together with the aluminium oxide (Al₂O₃) content, basicity is the main way PAC grades are compared.
How PAC works
Suspended particles in water carry a negative charge and repel each other. PAC releases highly charged polymeric aluminium species that neutralise this charge. The particles then join into micro-flocs, which grow and settle. Because PAC is already partly “pre-polymerised”, it reacts faster than alum and consumes less of the water’s alkalinity. For the full process, see our guide on coagulants vs flocculants.
Uses of poly aluminium chloride
- Drinking water treatment: removing turbidity and colour before filtration.
- Effluent treatment (ETP): clarifying wastewater from paper, textile, dyeing, sugar and food plants. See our ETP chemicals guide.
- Paper making: as a fixing agent and a partial alternative to alum in sizing systems. See alum in paper making.
- Process and cooling water: clarifying river or canal water before use.
PAC vs alum
| Point | PAC | Alum (aluminium sulphate) |
|---|---|---|
| Effective pH range | Wider | Narrower |
| Floc formation | Faster, denser flocs | Slower |
| Alkalinity consumed | Lower | Higher; pH often needs correcting |
| Sludge | Usually less | Usually more |
| Cost per kg | Higher | Lower |
PAC costs more per kilogram, but because the dose and sludge are often lower, the cost per cubic metre treated can be similar or better. A jar test on your own water is the reliable way to compare.
PAC liquid vs PAC powder
PAC is sold as a liquid and as a powder. Liquid is easy to dose straight from the tank and suits plants close to the supplier. Powder has a higher active content per kilogram, is cheaper to transport and stores longer, but must be dissolved before dosing. Both are available from Mittal Trading Company as PAC liquid and powder.
Handling and storage
- PAC solutions are acidic: use gloves and eye protection and follow the supplier’s safety data sheet.
- Store powder in a dry, covered place and keep bags sealed, since it absorbs moisture. See our monsoon storage tips.
- Use plastic or other acid-resistant tanks and pipes for PAC solutions.
Frequently asked questions
What is the full form of PAC in water treatment?
PAC means Poly Aluminium Chloride, an aluminium-based coagulant.
Is PAC a coagulant or flocculant?
PAC is a coagulant. A polymer flocculant is often added after it to build bigger flocs.
How much PAC should I dose?
It depends on the turbidity, pH and type of water, so the dose must be set by a jar test on your own sample.
Looking for PAC? Mittal Trading Company has supplied water treatment and paper chemicals since 1988 to customers in India, Nepal and Bangladesh. Ask for a quotation or call +91-9927022000.