[TheForge] Ping Bruce (or any other chemists): Phosphate deposits in pickle

[Bruce Freeman]

Mike,
I'm away from home so my usual sources are not available, but, yes,
that sounds like it could be iron phosphate.  I know that aluminum
phosphate is a rock (feldspar, IIRC), so it's likely that one or more
of the possible iron phosphates are also rocks.
I'm on a slow link here (cell phone modem) so I don't care to take the
time to look things up on line.  Ask me again next week and I'll see
what I can find out for you.
Bruce

On Fri, Apr 23, 2010 at 2:41 AM, Mike Spencer <mspencer at tallships.ca> wrote:
>
> When I leave a tray of used phosphoric acid pickle sit around for a
> prolonged time, I get a bunch hard, brittle, rocky deposit adhering to
> the tray.  Stuff is white when rinsed off, insoluble or only very
> slightly soluble in cold water and HCl.  What is it?
>
> Only stuff in the mix should be phosphoric acid, water and, of course,
> iron.  So is this iron phosphate?  The HBoC&P doesn't mention acid
> solubility of iron phosphate but intuitively, I would expect it to be
> HCl soluble.
>
> It doesn't form in my container of new, undiluted phosphoric acid but
> does form in a stored gas can of used acid.
>
> Brain dump on chemistry of H2PO4, Fe, H2O welcome.
>
> - Mike
>
> --
> Michael Spencer                  Nova Scotia, Canada       .~.
>                                                           /V\
> mspencer at tallships.ca                                     /( )\
> http://home.tallships.ca/mspencer/                        ^^-^^
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-- 
Bruce
NJ