In mining, water is both a processing medium and a cost. The slurry leaving a flotation or grinding circuit must be thickened, the water recycled, and the tailings stacked or stored safely — and anionic polyacrylamide (PAM, CAS 9003-05-8) is the reagent that makes it all possible. This article explains how PAM is used in tailings thickening and dewatering, and how to get the best performance from it.
1. The Job: Thickeners, Clarifiers and Tailings
Mineral processing produces large volumes of dilute slurry. The thickener settles the solids so that:
- process water is recovered and recycled to the plant;
- the underflow is dense enough for the next stage (filtration, or direct tailings disposal);
- the overflow is clear enough to discharge or reuse.
Without flocculants, fine mineral particles settle far too slowly — a thickener would need a huge footprint. Anionic PAM dramatically accelerates settling by bridging particles into large, fast-settling flocs.
2. Why Anionic PAM for Mining
- High molecular weight: the longest chains give the strongest bridging — exactly what fast settling needs.
- Alkaline circuits: flotation and thickening often run at pH 8-11, where anionic PAM performs best.
- Fine particle bridging: clay and ultrafine minerals are bridged effectively at moderate doses.
- Cost: anionic PAM is the most economical flocculant per ton of solids treated.
3. Key Applications
3.1 Tailings thickening and dewatering
Anionic PAM is dosed into the feed well of the thickener to form large flocs that settle quickly and compact well. The dense underflow feeds filter presses, centrifuges or paste plants, and in high-density (paste) tailings systems, flocculant selection and dose directly control the underflow density you can achieve.
3.2 Process water clarification
Overflow clarity from thickeners and clarifiers is controlled by flocculant dose. Clear water reduces reagent losses, improves flotation performance and helps meet discharge limits.
3.3 Filtration aid
PAM conditions concentrate slurry before vacuum or pressure filtration, improving filter throughput and cake moisture.
3.4 Coal washing
Anionic PAM clarifies coal washing water and dewaters fine coal refuse, keeping the washing circuit closed.
4. Dosing Practice
- Make-up: dissolve PAM powder at 0.05-0.2% in clean water with gentle agitation for 30-60 minutes; never use fast stirring, which shears the polymer chains and destroys flocculation power.
- Dose: typically 10-50 g per ton of solids for tailings thickening (confirm by cylinder settling tests); too high a dose re-stabilizes particles and can actually slow settling.
- Injection point: dose into the feed well with proper mixing; the flocs must not be sheared by excessive turbulence after formation.
- Combination: in difficult (clay-rich) tailings, an inorganic coagulant or cationic polyamine may be dosed first, then anionic PAM as the flocculant.
5. Troubleshooting
| Symptom | Likely cause | Fix |
|---|---|---|
| Slow settling in thickener | Underdose or poor floc formation | Increase dose; check make-up and mixing |
| Turbid overflow | Underdose or floc breakage | Increase dose; reduce shear after dosing |
| Underflow too dilute | Flocculant overdose or wrong grade | Reduce dose; try higher molecular weight |
| Performance varies with ore | Ore type changed | Re-optimize dose and grade for current ore |
6. FAQ
What dose of PAM is typical for tailings thickening?
Typically 10-50 g/t of dry solids, depending on ore type, particle size and target underflow density. Always confirm by settling tests.
Anionic or nonionic PAM for tailings?
Anionic high-molecular-weight PAM is the standard choice for most sulfide and oxide tailings; nonionic is used in some special circuits.
Why is my PAM not dissolving?
Usually too-high concentration, fast stirring, cold water or hard water. Prepare at 0.05-0.2% with slow gentle agitation in clean water.
Can PAM improve paste tailings density?
Yes — flocculant selection and dose are key controls in high-density tailings systems; the right anionic PAM can significantly raise achievable underflow density.
PolyblueChem supplies anionic polyacrylamide (PAM, CAS 9003-05-8) for mining and tailings applications, with COA and MSDS. See also our PAM guide and related reagent guides. Contact our team for grade selection and dosing support.
Polyacrylamide for Tailings: Grades and Specifications
| Parameter | Typical range |
|---|---|
| Charge type | Anionic (most common for tailings), cationic, nonionic |
| Molecular weight | Medium to very high (by grade) |
| Solid content | Powder (about 90%+) or emulsion |
| Dissolution time | Usually 30 – 60 min at the working strength |
| Working solution | About 0.1 – 0.5% (then dosed into the slurry) |
Typical Dosage in Mining
| Application | Typical dose (starting point) |
|---|---|
| Tailings thickening | About 10 – 50 g per tonne of solids |
| Concentrate dewatering / filtration | About 20 – 80 g per tonne of solids |
| Slurry / CCD circuits | Set by jar or plant test |
Dose is ore- and circuit-specific; the same polymer seldom works the same way in two plants. Screen the charge type and molecular weight on your own slurry (jar test or in-plant trial) before committing to a grade – the floc size, settling rate and underflow density are the deciding factors.
Frequently Asked Questions about PAM in Mining
Which PAM is used for tailings thickening?
Anionic, high-molecular-weight grades are the most common, but the right choice depends on the slurry – test it.
How much PAM is needed?
As a starting point, about 10-50 g/t for thickening and 20-80 g/t for dewatering, but the real dose is set by a plant test.
How is PAM made up and dosed?
It is dissolved to about 0.1-0.5% in clean water (30-60 min), then dosed into the slurry with good mixing but without shearing the flocs.
Handling and Make-up
- Make-up water. Use clean, low-hardness water to avoid the polymer locking up before it reaches the slurry.
- Dissolution. Add powder slowly to stirred water; avoid lumps and over-shearing.
- Dosing point. Coat the flocs gently – high shear breaks them and wastes polymer.
- Packaging. 25 kg bags and 750-1000 kg jumbo bags; keep dry and store away from heat.
PAM is not a commodity in the way a coagulant is: two polymers with the same nominal charge can behave very differently on the same slurry. Treat grade selection as a test, and standardise on the grade once it works.