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?