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Zinc removal (from wastewater) w/sulfide

I need to remove Zn to very low levels and cannot do it with pH alone. In the past I have use NaHS but I cannot find the pH vs. solubility curves to determine pH required.

Can anyone help?

Tim Hone
chemicals - Farmington Hills, Michigan
2003

You may want to try adding a small amount of trimercapto-s-triazine (Degussa TMT15) prior to filtering in your process, it's very effective in precipitating ionic elements such as zinc to extremely low or non detectable levels.

Jim Sivertsen
- Alden, N.Y.
2003

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You first need to determine whether the zinc is soluble or insoluble by analysis before and after 0.2 micron filtration. We have seen a lot of instances where the zinc was already insoluble, but fine suspended solids were passing through the treatment system. If this is the case, you need better settling and/or polishing filtration.

In cases where the zinc is soluble and there is ammonia or a weak chelator present, but no EDTA or NTA, an IX polishing system will work well and can get to < 0.2 mg/L.

Lyle Kirman
consultant - Cleveland Heights, Ohio
2003

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I had very good luck removing Zn to 0.3 - 0.5 mg/l using a combination of sodium sulfide and ferrous sulfate ⇦ this on eBay or Amazon [affil links] at pH 9.2.
The pH is critical to optimum removal - since the sodium sulfide is very alkaline, it should be added after the waste mixture has been brought to about 8.8 with sodium hydroxide.

Dave Wichern
Consultant - The Bronx, New York
2003