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

[Mike Spencer]

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/                        ^^-^^