Enhancing the efficiency of electrochemical desalination of stones: a proton pump approach

Soluble salts are among the most harmful alteration agents affecting the building materials. In recent years, several researches have been devoted to counteract alterations induced by soluble salts using electrokinetic techniques. However, the applicability of these techniques for conservation purposes remains limited due to adverse side effects, such as the extreme pH values occurring near the electrodes, which can affect the stone to be treated. The decrease in efficiency of the treatment caused by the dominant transport of H+ and OH− groups is also an undesired effect. The reduced duration of these treatments due to the drying of the material in contact with the anode also limits their practical use. To overcome these problems, a new electrokinetic design that includes a so called proton pump is presented in this report. This design is based on placing two electrodes in the anodic compartment in order to modulate the net amount of H+ produced. The design was applied to desalinate sandstone samples contaminated with several soluble salts. The application of this new approach allowed us to establish an additional electroosmotic process at the anode, which was able to increase the duration of the treatment. Moreover, the new setup provided improved pH buffer ability due to the generation of OH− in the anodic compartment, which increased the effectiveness of the treatment by hindering the entrance of H+ in the porous structure.