Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

----- Original Message -----
From: "pcb.easy" <rpdavidson@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Sunday, April 15, 2007 9:18 PM
Subject: [Homebrew_PCBs] Disposing of Chemicals


>I design my own boards using positive acting pre-sensitized boards.
>
> My developer solution is made of 1/2 teaspoon Sodium Hydroxide in
> 300ml water.
>
> My etch solution is made up of 1 part 31% Hydrochloric acid (HCl),
> and 2 parts 3% Hydrogen Peroxide (H2O2).
>
> The above chemical solutions work very well for me, and are extremely
> fast. I'm not looking to find a better way. I am looking to reduce
> the waste that goes to the hazard waste facility.
>
> I'm not a chemist, didn't even take high school chemistry. Anyway
> here is an experiment I did with the above chemicals, to try and
> reduce the amount of waste.
>
> Safety first, wear chemical goggles, gloves, apron, and work in a
> well ventilated area
>
> Hydrochloric acid (HCl) is very acidic, PH1. Sodium Hydroxide (NaOH)
> is very alkaline, PH14. When you mix an acid with an alkaline and
> adjust the solution to PH7 they become table salt and water.
> HCl + NaOH = NaCl + H2O2
>
> It takes a lot of Sodium Hydroxide to move from PH1 to PH2, but it
> takes very little to move from PH6 to PH7. And if the solution is
> very alkaline it takes a lot of Hydrochloric acid to move from PH14
> to PH13, and very little to move from PH8 to PH7.
>
> I mixed the spent etchant and developer together and started to
> neutralize the mixture. At about PH6 what I believe to be copper
> chloride started to precipitate out of solution. After the solution
> had set for about 12 hours, a blue sludge had formed at the bottom of
> the container and what I believe to be saltwater solution was at the
> top.
>
> I siphoned off most of the water being careful not to disturb the
> sludge.
>
> I tested the PH of the water that had been removed from the sludge
> container and it is still approximately PH7, and is crystal clear.
>
> I have reduced the 3 liters of chemicals down to less than 250ml of
> sludge.
>
> Am I on the right track?
> Is the blue sludge copper hydroxide?
> Can the sludge be reduced even more by drying?
> If so how can it be safely dried?
> Is there an issue storing copper hydroxide in powder form?

I think it's more likely to be cupric hydrate. You'll need to heat it to
form the hydroxide.

Leon