Nonionic polyacrylamide (NPAM)
The least-used of the three polyacrylamide families and the right answer in a narrow set of cases: acidic streams, very high ionic strength, and duties where charge has already been dealt with and only bridging is left to do.
Nonionic polyacrylamide is a homopolymer of acrylamide with a molecular weight of 8–15 million and a charge density below about 5 mol%. With almost no ionic character, it flocculates purely by hydrogen bonding and physical bridging rather than by charge interaction.
That makes it insensitive to pH and to dissolved salts, which is precisely where it wins: acidic process streams below pH 4, brines and high-TDS water where an ionic polymer would coil up and lose its bridging reach, and coal and mineral duties where the particle surface already carries what it needs.
Where nonionic is the correct choice
| Situation | Why anionic and cationic fail | Typical dose |
|---|---|---|
| Acidic streams below pH 4 | Anionic carboxyl groups protonate and lose charge; the polymer coils and stops bridging | 1–3 mg/L |
| High TDS, brine, seawater | Dissolved salts screen the charge on ionic polymers and collapse the chain | 1–4 mg/L |
| Coal washery and fine coal recovery | Hydrophobic coal surface bridges better than it bonds ionically | 10–40 g/t solids |
| Mineral processing at extreme pH | Charge behaviour is unpredictable at pH extremes; nonionic is not | 5–30 g/t solids |
| Behind a high-dose cationic first stage | Charge is already neutralised; only bridging remains | 0.5–2 mg/L |
| Paper mill retention aid systems | Where added charge would disturb the wet-end chemistry | 0.3–1.5 mg/L |
Specification
| Parameter | Value |
|---|---|
| Active polymer | 88–92% |
| Molecular weight | 8–15 million |
| Charge density | < 5 mol% |
| Residual acrylamide monomer | ≤ 0.05% |
| Appearance | White granular powder |
| Dissolution time | 40–60 min at 0.3–0.5% w/v |
| pH, 0.5% solution | 6.0–8.0 |
| Shelf life sealed | 12–24 months |
| Solution life | 24–48 hours |
Frequently asked questions
When should I use nonionic instead of anionic polymer?
Three cases. Acidic streams below about pH 4, where the carboxyl groups on an anionic polymer protonate and the chain coils up. High-TDS or brine streams, where dissolved salts screen the charge and collapse an ionic polymer. And duties where charge has already been fully neutralised by a high-dose cationic first stage and only bridging remains. Outside those, anionic is normally better.
Does nonionic polymer work without a coagulant?
On some mineral and coal duties, yes — the particles bridge physically without needing charge neutralisation first. On colloidal organic streams, no. If the particles are stable because of surface charge, a polymer with no charge cannot destabilise them, and a coagulant is still required.
Is nonionic polymer more expensive?
Usually slightly cheaper than an equivalent-molecular-weight anionic grade, since it is a simple homopolymer with no comonomer. It is less widely stocked, so lead time rather than price is the more common constraint on an African supply line.