Oxalic Acid and Marble
Date: December 2007
How is Oxalic Acid H2C2O4 used to polish CaCO3. How can a
strong acid produce a shine when the acid should be dissolving CaC03?
Polishing, in this case, usually means dissolving a small top layer
and leaving behind a smooth surface.
Greg (Roberto Gregorius)
Strong acids, at low concentration, polish reactive surfaces BY DISSOLVING
the solid. With mechanical rubbing the acid preferentially dissolves the
"high" spots thus leveling the peaks and valleys. Oxalic acid used to polish
marble by also forming the complex salt Ca(C2O4). The key to using aggressive
polishing agents like oxalic acid is LOW CONCENTRATION. You don't want the
reaction to dissolve much of the solid surface, only the "peaks" that are
exposed by rubbing.
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Update: June 2012