Electroplating and metal finishing generate wastewater loaded with heavy metals (chromium, nickel, copper, zinc), suspended solids, and oils. Polyacrylamide is the standard flocculant for metal finishing wastewater treatment — it removes suspended solids and helps precipitate dissolved metals. We supply PAM to plating shops and metal finishing facilities across Asia and the Middle East.
Metal Finishing Wastewater Treatment
| Process | Main Contaminants | pH Range | PAM Type |
|---|---|---|---|
| Chromium plating | Cr(VI), Cr(III), suspended solids | 1-3 (acidic) | NPAM |
| Nickel plating | Ni²⁺, suspended solids | 3-5 (acidic) | NPAM or APAM |
| Zinc plating | Zn²⁺, suspended solids | 3-6 (acidic) | APAM |
| Copper plating | Cu²⁺, suspended solids | 4-7 (acidic to neutral) | APAM |
| Anodizing (aluminum) | Al³⁺, sulfate, suspended solids | 2-4 (acidic) | NPAM |
| Passivation rinse | Cr(VI), suspended solids | 1-3 (acidic) | NPAM |
Metal Finishing Wastewater Treatment Process
The standard treatment sequence for metal finishing wastewater:
- pH adjustment — raise pH to 8-10 with lime or caustic soda. This precipitates dissolved metals as hydroxides.
- Coagulation — add ferric chloride or aluminum sulfate to destabilize colloidal particles
- Flocculation — add PAM to bridge precipitated metal hydroxides and suspended solids into large, fast-settling flocs
- Settling — allow flocs to settle in a clarifier (1-2 hours residence time)
- Sludge dewatering — filter or press the settled sludge to reduce volume
- Discharge — clarified water meets discharge standards (typically <2 mg/L total metals, <50 mg/L TSS)
PAM is critical in step 3. Without PAM, metal hydroxide precipitates remain colloidal and pass through the clarifier. With PAM, they flocculate into large, dense particles that settle quickly and completely.
Our CPAM with 40-60% charge density is engineered for exactly this use case, with batch-level quality control from our Zhengzhou facility.
PAM Selection for Metal Finishing
Metal finishing wastewater is typically acidic (pH 1-6). At this pH, ionic PAM (APAM, CPAM) loses effectiveness because surface charges collapse. NPAM (nonionic polyacrylamide) is the standard choice because it works through pure polymer bridging, independent of pH.
However, after pH adjustment to 8-10, APAM can also work. Some facilities use APAM post-pH adjustment to save cost (APAM is cheaper than NPAM). The choice depends on your treatment sequence and cost priorities.
Typical dosage: 3-8 ppm NPAM or APAM depending on metal concentration and suspended solids. Higher metal concentration = higher dosage needed.
Heavy Metal Removal Efficiency
PAM does not directly remove dissolved metals — it removes the metal hydroxide precipitates formed during pH adjustment. Removal efficiency depends on:
- pH adjustment — must be high enough (8-10) to precipitate all metals
- Coagulant dose — must be sufficient to destabilize colloids
- PAM dose — must be sufficient to bridge all precipitates
- Settling time — longer settling = better removal (diminishing returns after 2 hours)
Typical removal rates with proper treatment:
- Chromium: 95-99%
- Nickel: 90-98%
- Copper: 95-99%
- Zinc: 90-97%
- Lead: 98-99%
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Sludge Disposal
Metal finishing sludge contains concentrated heavy metals and must be disposed of as hazardous waste. Proper dewatering reduces sludge volume and disposal cost.
After settling, the sludge is typically 5-15% solids. CPAM at 4-8 kg/ton dry solids can condition the sludge for filter press or centrifuge dewatering, achieving 25-40% solids. This reduces sludge volume by 60-70% and disposal cost proportionally.
Our Metal Finishing PAM
We produce both NPAM and APAM for metal finishing applications:
- NPAM for acidic wastewater: 8-12M MW, 0% ionic charge
- APAM for pH-adjusted wastewater: 10-15M MW, 20-35% hydrolysis
- CPAM for sludge dewatering: 10-15M MW, 40-60% charge density
All grades: solid content ≥92%, dissolution time ≤90 minutes, residual monomer ≤0.05%. ISO 9001, ISO 14001, ISO 45001 certified.
Ready to Optimize Your Metal Finishing Treatment?
Send us your wastewater analysis (pH, metal concentrations, TSS, flow rate) and we will recommend the right PAM grade and dosage. Free samples available for jar testing.
WhatsApp: +86 150-0381-8598 | Request a quote
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Our factory in Zhengzhou produces 100,000 tons/year of PAM across 18+ grades. MOQ 500kg, delivery 7-10 days standard. Contact us for pricing and free sample:
- WhatsApp: +86 150-0381-8598
- Email: info@chinapolyacrylamide.com