Hello Sav,
I will first suggest you not use any acids or heavy chemicals on your tiles as this will damage them, possibly for the life of the floor.
Here is something I found on quite a few websites that talk about vitrified tiles:
Research Products notes, "It is important to clean water scrub and rinse to remove all residues and alkalinity." Leaving leftover soap or residue on your tiles can cause new stains and leave sticky areas.
I also found this faq question from the Sogo Vitrified Tile Website (
http://www.sogovitrified.com/)
How does one clean the tiles/maintain/get rid of stains?On a regular basis you can sweep the floors to remove any tracked in dirt and keep an anti-dust mat by the exterior doors to minimize abrasive dirt, like grit and sand, being brought in by people's shoes.
Other than that, just use a neutral PH detergent or standard tile care product to mop or sponge tiles as required.
It is possible the tiles have been scratched or the stain is permanent.
You may want to contact a professional or manufacturer of the tiles as it's possible the chemical has leached out the color from the tiles?
Mrs. Clean