copper alloys in sodium cyanide solution

[ytse]

Does anyone has corrosion data of copper alloys in very dilute sodium cyanide solution (<20 ppm)?
From all the literature I've seen, copper alloys are not suitable for sodium cyanide solution, however there is no information on such low concentrations.
My specific problem is whether backflow preventers with copper alloy (bronze/brass) internals will be suitable for service in water with about 10 - 20 ppm of sodium cyanide solution.

 

[metengr]

I would not recommend the use of brass or bronze alloys for this specific application. My reasoning is the risk crevice corrosion on the brass or bronze alloy even in a dilute aqueous sodium cyanide solution. Any type of crevice will significantly increase the concentration of harmful cyanide ions that could attack the brass or bronze alloy, over time. If your water temperature is above ambient, this will further increase the rate of corrosion. I reviewed a couple of corrosion sources, and the consensus I have reached is that copper base alloys are not suitable for use in aqueous sodium cyanide solutions. I would remain conservative, and apply this to an aqueous solution containing any measurable level of sodium cyanide.