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Heavy metal removal from industrial effluent

We are working(lab scale) with an effluent for removing heavy metals. We tried with lime slurry and the supernatant obtained is tried with caustic again.We could precipitate rest of the HMetals with caustic but the flocculation happening is not satisfactory. We tried with a small amount of anionic polyelectrolyte also but not an interesting result.Initial pH was 1.9 and is raise to 4 with lime and again raised to around 11 using caustic. Could you please suggest a suitable solution.

Thank you,

Moosa Shaharban
Research & Development Officer - United Arab Emirates
June 16, 2009

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First of two simultaneous responses --

What heavy metal are you trying to remove?

A pH of 11 is a bit high, unless you are dealing with high levels of Ni or Cd. Try 9.5 - 10.

Also, try a different flocculant. There are many, and often you may have luck trying a different product.

Dave Wichern
Consultant - The Bronx, New York
June 18, 2009

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Second of two simultaneous responses --

It is important to use a polymer that works well in your pH range, or little flocculation or pin floc will be formed.

Most anionic polymers have an optimum pH range that is much lower than the pH of 11. Most often, a pH of 9.2-9.5 is best for multiple heavy metals with an anionic polymer.

If this doesn't work, add some calcium or iron in addition to the polymer to help form a better, more stable floc.

Lyle Kirman
consultant - Cleveland Heights, Ohio
June 19, 2009