Chemistry of Copper Etchant Solutions
October 19, 2011 1:43 AM Subscribe
What copper salt is left behind in this neutralized etchant solution? Also, how can I safely dispose of spent etchant in general?
posted by [expletive deleted] to Science & Nature (3 answers total) 2 users marked this as a favorite
I've been experimenting with etching copper lately, and I have a growing amount of depleted ferric chloride etchant to dispose of. As an experiment, I neutralized the used etchant with baking soda, hoping to precipitate out the metal ions as carbonate and hydroxide so I could dispose of them as dry waste.
I filtered out the resultant brown sludge, and was left with a bright blue solution. I left the solution a little longer and it turned cloudy yellow-green with precipitate. I filtered the solution again and was left with completely transparent blue solution. Evaporating the water left a white solid at the top and a blue/green solid at the bottom. I'm curious what this could be.
It's my understanding that copper carbonate or hydroxide would not be soluble enough to be responsible for the colour of the solution, which would suggest that the resulting salts would be sodium chloride and copper (I)?(II)? chloride, but that would just be a guess.
Finally, how should I dispose of the spent etchant in general? I'm not willing to just put a neutralized solution down the drain because of the copper content. If there is somewhere I could take it (in Vancouver BC) that would dispose of it properly, that would be an option. A method of precipitating out the metal that actually eliminates the copper and leaves behind something non-toxic would also be most welcome.