Electrokinetic Treatment of Mercury - Polluted Soil Facilitated By Ethylenediaminetetraacetic Acid Coupled with a Reactor with a Permeable Reactive Barrier of Carbon to Recover Mercury (II) from Water
Authors: Trejo Diana Irene , Mora Oscar , Sepúlveda Selene , Bustos Erika 
Published: February 2020

Electroremediation or electrokinetic treatment (EKT) has been successfully applied in a variety of polluted soils; this technology refers to the application of an electric field or direct current through a pair of electrodes (anode and cathode). These electrodes are inserted in the soil, where an electrolyte improves the conductive properties of the electric field [1-2]. Enhancing solutions can be added to the soil to improve the efficacy of the treatments [3-4]. The most common enhancing solutions are ethylenediaminetetraacetic acid (EDTA) [5-6], which is a compound with four carboxylic and two associated amino groups, which can act as electron pair donors or Lewis bases. EDTA, in an aqueous solution, forms an octahedral complex with mostly divalent metal cations (M2+). A very strong mercury-EDTA ([Hg-EDTA]2-) complex is formed, with a log b of 21.8 [7]. Considering the negative charge of this complex, most mercury moves towards the anode side, where it can be recovered.

In this study, a soil sample polluted with mercury was treated with electrokinetic treatment (EKT). Seventy-two h was necessary to remove most of the mercury present in soil from the cathode to the anode with a removal percentage of 76.30%. During this period, we measured the interfacial potential and current. We analyzed the physicochemical properties before and after EKT where physical properties such as color, soil particle, real density, porosity and fraction of organic matter did not change; chemical properties such as pH and electric conductivity changed due to the electric field applied to the soil and the addition of EDTA as a facilitating agent. Finally, the remaining solution obtained from the EKT was treated in a reactor with a permeable reactive barrier (PRB) of carbon, where close to 99 % of Hg2+ was recovered from water after 2h (Figure 1), which is a good alternative than PRB of iron, where 84.47% of the Hg2+ was recovered from water.

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Figure 1