The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Suggestions on Wastewater treatment with Ni and Cu problems

June 2, 2011

We are struggling to meet discharge consent with Ni and Cu we usually "lime" our tanks up to >12 then use Ferric acid to treat we then press solids and discharge.

We have problems with meeting the consent due to a few problematic waste streams, any suggestions on possible answers to our problem (is the Ni or Cu in the right oxidation state?, is the effluent undergoing secondary reactions with solids in discharge tanks using cation exchange?

I have suggested using a oxidizing agent like Peroxide or KMnO4 but have done lab checks and neither work.

I have now started to use MgO but am not sure under the circumstances to which I should treat out tanks. NOTE Our tanks cannot go below pH 4.

Gavin Powell
Employee - Cardiff, Wales

---

A pH of 12 is way too high. Try 10 - 10.5.

MgO will not bring the pH high enough to precipitate Ni.

If ammonia or other complexing agents are present, try a pH of 8.5 - 9 in conjunction with sodium sulfide, DTC, or other sulfur based precipitant.

I doubt very much whether adding oxidizing agents will solve your trouble, though it cannot hurt to try.

Dave Wichern
Consultant - The Bronx, New York
June 10, 2011

---

You will first need to determine if the metals are soluble or insoluble by analyzing before and after a 0.2 micron filter. If insoluble, then a polishing filter is needed. If soluble, then a precipitant that is used for chelated metals may be required.

Lyle Kirman
consultant - Cleveland Heights, Ohio
June 13, 2011