Assessment of electrophoresis and electroosmosis in construction materials: effect of enhancing electrolytes and heavy metals contamination

Abstract

Electrokinetic effects are those that take place by application of an electric field to porous materials, with the zeta potential as the key parameter. Specifically, in the case of contaminated construction materials, the generation of an electroosmotic flux, with the corresponding dragging due to water transport, is a crucial mechanism to succeed in the treatment of decontamination. Therefore, it is of great interest trying to optimize the treatment by the addition of specific electrolytes enhancing the electrokinetic phenomena. Most of the data of zeta potential found in literature for construction materials are based in micro-electrophoresis measurements, which are quite far of the real conditions of application of the remediation treatments. In this paper, electrophoretic and electroosmotic experiments, with monolithic and powdered material respectively, have been carried out for mortar, brick and granite clean and contaminated with Cs, Sr, Co, Cd, Cu and Pb. The electrolytes tested have been distilled water (DW), Na 2 -EDTA, oxalic acid, acetic acid and citric acid. The zeta potential values have been determined through the two different techniques and the results compared and critically analysed.

Electrokinetic decontamination of heavy metals in construction materials: contribution of the different parameters to the global efficiency

“…As expected, provided the conditions of the experiments are continually changing, the zeta potential values change correspondingly and are timedependent, in agreement with [11]. A comprehensive study on the zeta potential determination through electrophoresis and electroosmosis experiments, including these materials and solutions, is given in [20]. In [20], the differential curves of the zeta potential are given and it can be seen that for these experiments the shape of the curves is quite different depending on the material and on the dissolution used: Mortar exhibits smaller values than brick, being the higher absolute value, for mortar, that corresponding to distilled water being a positive value; so, with flux towards the anode [20].…”

“…8, it can be seen that the zeta potential value strongly influences the decontamination percentage: increasing the negative absolute value of the zeta potential increases the decontamination percentage. It has to be pointed out, on one hand, that the actual values of f are corresponding to electroosmotic measurements on monolithic materials, as zeta potentials determined by electrophoresis in diluted suspensions of the same powdered material give different values [20]. Maintaining constant the rest of parameters, changing the value of zeta potential from -3 to ?3 mV implies a change from almost a 60% of decontamination to a 10% of remediated material.…”

“…In the case of pH, apart from the fact of the effect of the anion associated to the acid that goes through the specimen [20], the more acidic the solution, the more easiness to make the heavy metals soluble. The same effect operates for the pH of the material.…”

“…A comprehensive study on the zeta potential determination through electrophoresis and electroosmosis experiments, including these materials and solutions, is given in [20]. In [20], the differential curves of the zeta potential are given and it can be seen that for these experiments the shape of the curves is quite different depending on the material and on the dissolution used: Mortar exhibits smaller values than brick, being the higher absolute value, for mortar, that corresponding to distilled water being a positive value; so, with flux towards the anode [20]. The enhancing solutions behave differently, obtaining negative values of the zeta potential for all of them, with the maximum absolute value for Na 2 -EDTA.…”

Granite desalination using electromigration. Influence of type of granite and saline contaminant

“…Desalination by electromigration is a non-destructive method for extracting salts that has been relatively well studied in applications such as soil remediation [9,10], chloride removal from reinforced cement and concrete [11][12][13] and brick desalination [14,15]. Regarding granites, only a previous work has been published, but related to metal decontamination [16]. The application of this method to granite with the aim to desalinate has not been scientifically studied to date, so our research into electromigration to desalinate granite represents an innovative contribution to the field of heritage conservation.…”