Caustic Bath for Pre-copper Plating
Can you help me come up with the amounts of caustic potash and potassium cyanide that you need to makeup a caustic bath to use to neutralize acids from parts prior to copper plating them.
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Question:
Can you help me come up with the amounts of caustic potash and potassium cyanide that you need to makeup a caustic bath to use to neutralize acids from parts prior to copper plating them?
Answer:
It is difficult to answer this question without knowing more about your process. What are the parts? What is the base material? What type of copper plating process are they going into? Even at that, I am not sure I see the necessity of the potassium cyanide in the neutralization tank. The sodium hydroxide alone should take care of that. I guess that amount could be estimated by essentially titrating the rinse tank just prior to the neutralization tank with a known concentration of sodium hydroxide to a pH of seven (neutral). You could then estimate the amount of sodium hydroxide to add to the tank based on an estimated carry-over from the rinse tank, expected sodium hydroxide concentration and expected tank life between additions.
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Follow Up Question:
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. The amounts released by neutralizing residual acid would be minimal but the plating community should be made aware of the potential.
Answer:
My opinion was that it was not necessary to accomplish the neutralization step. 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.
