Desarrollo de un nuevo tratamiento para la conservación de piedras con alto contenido en carbonatos utilizando la Tecnología de Resinas de Intercambio Iónico

Abstract

Atmospheric contamination is the main cause of erosion of stone in urban monuments. Gas emissions produce a gradual acidification in the environment, reducing the resistance of all types of stone. Stones with high CaCO₃ content (limestone, carbonated marble and sandstone) are those most affected by acid rain. Numerous studies into the influence of calcium oxalate on calcareous stones conclude that this compound, produced naturally from certain lichens, can act as protection against acid. Calcium oxalate is more stable than calcium carbonate against changes in pH. The treatment proposed in this study consists of the artificially induced conversion of calcium carbonate present in calcareous stones into calcium oxalate using ionic exchange technology. Resin in oxalate form is placed in contact with the stone through an ion conducting solution, producing the formation of a crystalline micro-layer of calcium oxalate over the surface of the stone. The results have been evaluated with FT-Raman spectroscope. The crystals formed initially are CaC₂O₄·2H₂O (weddellite) which evolves partially into the species CaC₂O 4·H₂O (whewellite) according to atmospheric conditions of humidity and temperature.