Inge Rörig-Dalgaard

Utilization of electromigration in civil and environmental engineering—Processes, transport rates and matrix changes

Electromigration (movement of ions in an applied electric field) is utilized for supply or extraction of ions from various porous materials within both civil and environmental engineering. In civil engineering, most research has been conducted on the removal of chlorides from concrete to hinder reinforcement corrosion while in environmental engineering remediation of heavy metal polluted soil is the issue most studied. Never the less, experiments have been conducted with utilization for several other materials and purposes within both engineering fields. Even though there are many topics of common interest in the use of electromigration for the two fields, there is no tradition for collaboration. The present paper is a review with the aim of pointing out areas of shared interest. Focus is laid on the purposes of the different processes, transport rates of various ions in different materials and on changes in the matrix itself. Desorption and dissolution of the target elements into ionic form is a key issue to most of the processes, and can be the limiting step. The removal rate is generally below 1 cm day− 1, but it can be much less than 1 mm day− 1 when desorption is slow and insufficient. Matrix changes occurs under the action of the applied electric field and it includes both physico-chemical and hydrological changes. Some of the solid phases is weathered and new can be formed. Increased fundamental understanding of the effects and side effects, when applying the electric field to a porous material, can lead to improvement of the known technologies and possibly to new applications.

Desalination for preservation of murals by electromigration and regulated climate

The presence of salts is a threat against the preservation of cultural heritage, e.g. murals. The volume change from dissolved salt (ions) to precipitated salts results in crystallization pressure. This crystallization pressure can result in deterioration when the crystallization occurs underneath the surface, resulting in deterioration of the overlying material. The crystallization occurs most often in the evaporation zone, close to the surface, e.g. between the brick masonry and the lime layer with paintings. In the present investigation it was aimed to improve the electromigration (ion transport in an applied electric field) desalination efficiency of a wall section with murals by regulation of the surrounding climate. The idea was to obtain a relative humidity (RH) above the polluting salts deliquesce point (NaCl ~ 76%) to ensure the presence of dissolved salt (ions). A humidifier was used to create high relative humidity and the actual RH was followed with a hygrograph. After two weeks of treatment with an applied electric DC field and regulated climate, the average chloride content for all brick and mortar samples was decreased from 0.6 wt% to 0.1 wt% and for all the brick samples from 0.53 wt% to 0.06wt% on average. The present experiment clearly showed the necessity of a relative humidity around the polluting salts deliquesce point in order to dissolute the salts before they can be transported in an applied electric DC field. Significant desalination was obtained in all the positions within the same range as seen in previous experiments with capillary saturated single bricks.

High accuracy calibration of a dynamic vapor sorption instrument and determination of the equilibrium humidities using single salts

We present a procedure for accurately calibrating a dynamic vapor sorption (DVS) instrument using single salts. The procedure accounts for and tailors distinct calibration tests according to the fundamental properties of each salt. Especially relevant properties influencing the calibration are the heat of solution, heat of condensation, and the kinetics connected to the salt phase transition, as these influence the microclimate surrounding the salts during calibration. All these issues were dealt with to obtain precise calibration results. The DVS instrument comprises two control modes to generate and measure the relative humidity (RH). Both control modes were separately examined and combined to overcome the shortcomings of each of the two control modes and thereby obtain the most accurate results. Repeated calibration testing with the single salts (LiCl, MgCl2, Mg(NO3)2, NaCl, and KNO3) enables five discrete sorption isotherm measurements within the range of 11%-93%RH. The equilibrium RH of the solution for LiCl, MgCl2, Mg(NO3)2, NaCl, and KNO3 was determined with a standard deviation of 0.06%-0.15% (0.45% for KNO3) RH. By comparing the measured calibration values with the well-known equilibrium RH of each salt solution, the presented methods results are both accurate with significant agreement and precise with small variation.