Thermodynamic and Raman spectroscopic speciation to define the operating conditions of an innovative cleaning treatment for carbonated stones based on the use of ion exchangers—A case study

Thermodynamic and Raman spectroscopic speciation was used to define the operating conditions for an innovative cleaning treatment of the decayed carbonate-based stones using ion exchange technology. The conditioning process of the Lewatit OC1071 anion exchanger with EDTA (Y) was monitored by ionic chromatography. Characterisation of the initial (R–Cl) and the final (R2–H2Y) forms of the ion exchanger was carried out by dispersive Raman microprobe spectroscopy. The subtraction spectrum obtained between the chloride and the EDTA forms of the ion exchanger shows Raman bands at 1403, 1324, 1223, 1122, 932, 908, 591, 431 and 350 cm−1, which agree with bands showed in the spectrum of the standard solution of the H2Y2− species. Therefore, this seems to be the EDTA species which takes part in the cleaning treatment performed by using resin poultices on black crusted limestone samples from an historical building.