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Organometallic precipitants for metal finishing wastewater treatment Q&A's


Q. Dear Sir,

I'm studying the treatment of heavy metals in waste water effluent and from my research I found out that one way of recovering these metals is by organometallic precipitation. My problem is what modern and specific type of an organometallic compound is used for the precipitation of these metals such as nickel, chromium, zinc, and etc.

Also, provide me also the reaction taking place.

Thank you in advance.

Juber Celino [last name deleted for privacy by Editor]
- Baguio City, Philippines

Q. [Same question cut & pasted by]

Jorge André
- Uppsala, Sweden


A. That is a good question, students. I've employed these agents a number of times in combination with DTC (dithiocarbamate), but I don't know exactly what they are. Unfortunately, although I know several vendors of the product, they all claim the material as proprietary. A patent search might help though. Good luck.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey


Q. Dear Ted Mooney,

I was browsing the past letters from the archives and when I opened a letter entitled "Tin Plating Waste Treatment" where you mentioned about using a combination of a proprietary organo-metallic precipitant and DTC where its an effective way in the removal of metals. Can you give or advise me then what proprietary organometallic precipitant for nickel and chrome.

Thanks in advance.

Yours truly,

Juber Celino [returning]
- Baguio City

"Heavy Metals: Advances in Industrial and Hazardous Wastes Treatment"
from Abe Books

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A. Hello again Juber. To put this into context for readers who did not review that earlier letter--

Conventional hydroxide precipitation is used for electroplating wastes, but the solubility of such hydroxides (sometimes in the presence of complexors and chelates) may be too high for discharge. Therefore it is sometimes necessary to take the treated, clarified waste, and subject it to a secondary treatment with a stronger precipitating agent like calcium polysulfide or DTC (sodium diethyl dithiocarbamate).

The problem that can arise in such a case is that there is so very little metal in the solution that when it is precipitated by the DTC it does not want to agglomerate into settleable particles, but acts almost like a colloid. The usual inorganic co-precipitants like ferric chloride sometimes seem to not help much, and neither do polyelectrolytes; but the suppliers offer a special proprietary organic co-precipitant that allows the DTC-precipitated material to settle for clarification.

I am not a chemist and don't know the basis for these organic co-precipitants, but in my experience they do work. The one I have used was offered by Hubbard-Hall. You add a quantity of the proprietary co-precipitant to the waste water, and mix it; then when the DTC hits it, the precipitate settles much better. Sorry, but that's all I really know :-)

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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