I've just got hold of a nice little PCB etching kit, which uses ferric chloride as the etchant. I know it's re-usable for at least a few etches (though the kit doesn't actually specify an estimated re-use count) but after that I'll need to dispose of the used chemical.
I've read the accompanying safety sheet thoroughly, which states that I should use add sodium carbonate to form ferric oxide, which can then be disposed of. It's not very clear about the details though.
It seems to indicate that a 1:1 mixture of Na2CO3 and FeCl3 should be achieved, but (from what I can tell) the Na2CO3 is usually sold as a powder. How do I measure a 1:1 mixture between the two?
As a side question, I see a lot of people here using boiling water with their ferric chloride etchant, but the instructions for this kit state 21°C – 24°C is the optimal temperature. Are they just trying to cover their asses in case someone gets boiling hot corrosive liquid on themselves, or am I missing something?
Best Answer
Washing soda is the harmless of the two reagents, so it doesn't matter if your mixture contains some excess, unreacted soda.
Soda is cheap enough that you don't have to worry about optimizing your use to the absolute stoichiometric ratio.
You can use baking soda also (bicarbonate).