On Fri, 31 Oct 2003 10:33:47 -0800, Grant Erwin wrote:
Question: can I neutralize HCl with TSP? I know that TSP in solution
is basic. I'm just wondering what happens when you mix TSP with HCl -
obviously, you'd get Na+ ions, H+ ions, PO3-- ions, and Cl- ions.
Sort of like a mix of phosphoric and hydrochloric acids, except for
the sodium. I can't figure it out, my college chem days are long over.

What you get is salt, NaCl. This salt residue will hide in every pore,
crack, and crevice of the part, promoting corrosion. You get the same
thing if you try to neutralize with lye or baking soda. So do *not* try
to neutralize the HCl. Just rinse the part off with plenty of hot water
(chlorides are soluble in hot water). The hotter the water, the better,
because solubility increases with temperature, and the hot water will
evaporate off the part faster, so the part doesn't stay wet long.

Note that the metal will be *extremely* clean at this point, and will
flash rust if you don't immediately oil it or otherwise protect it from
contact with oxygen. That's why the galvanizing guys normally do
the HCl dip and rinse immediately before galvanizing.

Note too that you don't have to worry about the rinse water going
down the drain. You need to use lots of it, and it will dilute any HCl
it washes off the part to harmless levels.

Final question: assuming #2 does NOT work, and further assuming it's
bad news to dump TSP into the sewer, is there any easy cheap way to
neutralize the TSP and make it less environmentally harmful? My
neighbor, no dummy, suggests using it as fertilizer. Does that make
any sense?

Sure, it *is* fertilizer. If you only have a few gallons of the stuff, dumping
it down the sewer isn't a problem either. The environmental concern was
when *everyone* was doing it (laundry detergents with TSP), and the result
was algae blooms downstream of the sewage treatment plant. But a few
gallons is nothing.

For *these* chemicals, dilution is the solution to pollution. That's not true
for some chemicals, or industrial quantities of most chemicals, but it is
fine for disposing of the small amounts of acids and bases used around
the home shop.

Gary