Polyelectrolyte for electroplating effluent
How metal-finishing effluent is treated, where the metals drop out, and why an anionic flocculant finishes the job.
What the effluent carries
Plating and metal-finishing units discharge rinse water carrying dissolved metals such as nickel, zinc, copper and chromium, along with acids, alkalis and, in some processes, cyanide.
Separate streams first
Chromium and cyanide streams are usually treated on their own before they join the rest. Hexavalent chromium is reduced to the trivalent form under acidic conditions; cyanide is destroyed by alkaline oxidation. Mixing them untreated can create hazards and makes both harder to remove.
Precipitating the metals
Once combined, the effluent is raised to an alkaline pH, typically with lime or caustic soda, so that the metals come out as hydroxides. The right pH differs from metal to metal, so mixed-metal streams are usually run at a compromise value found by testing.
Where the flocculant comes in
Metal hydroxides form as fine, light particles that settle slowly and carry over from the clarifier. A small dose of an anionic polyacrylamide such as Sunfloc Anionic HQ gathers them into large flocs that settle quickly and leave a clear overflow.
Dewatering the sludge
Metal hydroxide sludge is mostly inorganic and usually responds to the same anionic grade on a filter press. Press the sludge as dry as you can, since it often has to be handled as hazardous waste and disposal is charged by weight.
Find the dose by jar test
Raise a sample to your treatment pH, add the coagulant if one is used, then compare a few Sunfloc doses side by side. Send us a sample and we will run the jar test for you.
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Send us a one-litre sample or describe your process. We test it in our lab free of charge and recommend a grade and starting dose, and quote within 1 business hour.