Your observation that potassium cyanide is not necessary is correct, but more importantly mixing potassium cyanide with acid could potentially be very dangerous. Using potassium cyanide as a neutralizing agent would release hydrogen cyanide, a toxic gas used with deadly effect by the Nazis in death camps. The amounts released by neutralizing residual acid would be minimal but the plating community should be made aware of the potential. C.M.
The comment above was in response to my December 2004 column. Specifically, the question was related to the use of potassium cyanide in a caustic bath meant for neutralizing a previous acidic process step. My opinion was that it was not necessary to accomplish the neutralization step, however, CM went on to point out the dangers of potassium cyanide.
Although workers routinely deal with the dangers of cyanide with plating in general and copper or zinc plating in particular, it is an important enough subject to remind everyone about it. The safety of yourself and your fellow workers cannot be emphasized enough in dealing with this chemical.
Any alkaline (i.e., sodium or potassium) cyanide product can be used with the correct safety precautions. But when mixed with an acid, it will create the very lethal hydrogen cyanide gas. Not only does that represent an inhalation problem but can eventually be absorbed through the skin. Even though safety is stressed in plating shops, it can never be over emphasized when dealing with sodium or potassium cyanide. One of the worst examples of this is the tragedy that killed five workers in Indiana in 1988. A worker mistakenly used hydrochloric acid when cleaning out a cyanide zinc plating tank. He quickly passed out and four of his co-workers coming to his aid were also killed. That should demonstrate the danger of misuse of this chemical. Additional reading on this tragedy can be found at the Products Finishing web site. Follow the link under editor picks.