quarry tiles

[Sarahhump]

Hi, i've been restoring some quarry tiles in two rooms. some are red with decoative border the other room is red with white triangle inbetween. i have been using acid to remove the cement and scrubbing with cif or floor cleaner inbetween. i have also been using a scraper to get rid of the cement. The majority of the floor is clear of debris now but the tiles are still stained (whitish ingrained stain) and dull. what is the best thing i can use to clean them at this stage?
Thanks

 

[Sarahhump]

Can i use a sander on the tiles? Was wondering if i bought a specific buffer or sandpaper could i use this to ge rid of the surface layer of dirt etc?