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

Abstract

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. Response to Reviewers:Following the advice of the editor, the paper was reviewed by a native speaker of English, which has made several changes, including the title.

Electroprecipitation of Magnesium and Calcium Compounds for Weathering Protection of Ornamental Rocks

“…In both cases, there is an evolution in the electrical behavior of the material to be treated. Both in the desalination process and in the consolidation process, as the treatment progresses, the intensity that flows through the material tends to decrease (either because the ionic content inside the material decreases ,,, or because some percolating paths are blocked due to the precipitation of some compounds , ), while the resistance exerted by the material against current flow increases. The evolution of both parameters allows assessing the progress of each treatment, so that an increase in resistance during the consolidation process indicates that the precipitation of certain compounds in some of the pores of the material is taking place.…”

“…This stone was selected due to its high accessible porosity to water (13.24%), which makes it sensitive to salt weathering, as can be seen on-site, and its chemical composition composed mainly by SiO 2 (91.51%) and Al 2 O 3 (6.96%). ,, Furthermore, the low content of other chemical elements will facilitate the subsequent identification of the different chemical compounds formed from the precursors chosen for this study.…”

“…In the case of water, efforts are focused on hindering moisture penetration into the structure, as stated in refs and , by (I) reducing the sorptivity of the material, i.e., construction of subsoil drains around the monument, wall cutting to the insertion of impermeable materials against capillary flux, and injection of chemical barriers or water repellents; , (II) increasing the evaporation rate using different systems such as the installation of wall base ventilation systems, , thermal methods, and restoration of plaster by ones with high porosity and high water vapor transport; and (III) moving the moisture flow using systems based on active and passive electro-osmosis. , In many cases it is necessary to apply more than one intervention strategy, for example electro-osmosis and drying plaster. In the case of soluble salts, the main strategy is to reduce, as far as possible, the ion content from porous building materials by the application of different desalination techniques such as immersion baths in water for small size pieces, , application of poultices on the affected surface made with different materials, , use of crystallization modifiers into the pores, , and application of electrokinetic techniques. − …”

Effect of electrokinetic treatment time on energy consumption and salt ions removal from clayey soils

“…In addition to enhance salt ions transport in soil, the applied electric field produces H + and OH − ions at the anode and cathode, respectively. A higher transfer number of H + and OH − ions in soils limits the electromigration of targeted ions [28]. However, in the case of inorganic contaminants, the acidic environment promotes their solubility and facilitates their removal by electroosmosis and electromigration [29].…”

Experimental and mechanistic research on modifying the mechanic properties of the high water backfill material by electrochemical treatment

“…In recent years, the electrochemical method has been successfully applied to many fields of geotechnical engineering, such as the electrochemical consolidation of weak rock [10][11][12] , the electrochemical desalination of rock or soil [14][15][16][17][18][19][20] , the drainage and consolidation of soil by electro-osmosis [21][22][23][24][25][26][27] , and the acceleration of methane desorption in lump anthracite by the electrochemical treatment [28][29][30] . Meanwhile, the electrochemical treatment was used to accelerate the hydration reaction rate to enhance the strength and deformation characteristics of fly-ash-cemented filling materials 31 .…”