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Analysing why sodium cyanide solution is contaminated

July 25, 2008

Hi! Again,this is Diana Fe.As a laboratory analyst for an electroplating company, I also analyze pre-treatment and post-treatment solutions. one of our process uses 10 g/L sodium cyanide solution as a pre-treatment and post treatment step. One time, a few hours after renewal of the solutions, we noticed that the bottom part of the solutions turned red to maroon in color. We suspected that it was contaminated since the solution normally is colorless. But we are now confused what could be the reason of the contamination when the tanks of both solutions are located about 10-15 meters from each other.The person who renewed the solution said that during renewal, he only poured the NaCN pellets to the tank with clean water without mixing. When we analyze the solutions,we found out that the concentrations are only 5 g/L total NaCN which is way below the expected 10 g/L. We are currently considering the possibility that the pellets added were KCN and not NaCN since the same analysis shows 6.5 g/L KCN. Also our storage of the two chemicals are next to each other. Is the possibility of KCN correct? Is the analysis procedure for total NaCN and KCN really the same?

Looking forward for your immediate responses.Thank you very much.

Diana Fe Espinosa
plating shop employee - Cebu City, Philippines

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If you are using AgNO3 as a titrant, KI for endpoint indicator, you are analysing for FREE CYANIDE only. The procedure do not distinguished between Potassium or Sodium salt. If you have AA, analyze for metal ions. I.e Nickel, copper, iron or whatever metal salt you use for plating.
Metal ions forms double salts and complex compound. They use a lot of free cyanide.

another contaminant could be acid salts( i.e. citric --)

Cyanide salts left on open containers for a long period of time decompose. Your source might not what they say they are.

In my experiences of using cyanide for washout, activation, cleaning, etc. addition of caustic soda [affil links] at 2 oz oer gallon helps to prolong its use.

Good Luck

Hamilton M.Solidum
- Mays Landing, New Jersey
August 20, 2008