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

On 11/03/13 00:02, Dave Sage wrote:

> Perhaps someone with some knowledge on public works and sewage treatment can
> clarify this for me.
>
> I guess it must be the copper in the ferric chloride etchant that we dispose
> of that is the problem - is that correct? Is there actually copper per se
> any more after the reaction of etching?
>
> I'm pretty sure somewhere in the sewage treatment process, after gross
> solids are removed, the water in the sewage system is sent to settling
> ponds. While in the ponds ferric chloride is added to act as a flocculent
> i.e. an agent that causes solids to gather together in clumps for easy
> removal. If this is the case, would it make any difference if there were
> some ferric chloride in the system to begin with (from flushing etchant down
> the drain)?

The ferric chloride i got was in a 60Lt bottle labelled "Profloc F", and they
said it was used in sewer treatment. I've got lots left since i figured out how
to keep regenerating the current tank etchant as copper chloride.

Copper chloride is very toxic to plants, as i found out when emptying a load on
the back lawn. If you put it in a spray bottle, it'll make a wonderful weed
killer. The grass recovers after a few weeks.

I don't know how toxic it is for the sewer system, but a different copper
compound is commonly used for unblocking sewers.

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