Using Fuller's earth is a very common and harmless way to treat marble and limestone that has been damaged/corroded by atmostpheric pollutants such as PM2.5/PM10 carbon particles (Soot) , Oxides of sulphur and nitrogen and Acid rain. Such a treatment has been tried on Taj Mahal in India as well as Delphi in Greece.

I know that fuller's earth usually contains Ion Complexes of Si, Al, and Mg. I would like to know what is the action of these ion complexes on the surface in removing the soot particles from limestone and marble.

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    $\begingroup$ No chemical reaction but simple mechanical abrasion and adsorbent. It is a good adsorbent of oil (recall face cleaning with so called Multani matti (=Fuller's earth) in the South Asia. $\endgroup$ – M. Farooq Jun 21 at 6:10
  • $\begingroup$ @M.Farooq I read somewhere that the OH- ions from the Aluminium Hydrosilicate (the main constituent of fullers earth) can attract the carbon particles and other adsorbed compounds from the surface $\endgroup$ – pyramiskyma Jun 22 at 0:30
  • $\begingroup$ Yes, this is a good adsorbent but we cannot pin point what is causing what? The question to consider are, what is the surface chage on Fuller's earth? What is the surface charge of carbon particles. $\endgroup$ – M. Farooq Jun 22 at 0:48

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