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

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.

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 ⇦this on eBay or Amazon [affil links] 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 :-)