**2.2 Cathode modification**

222 Electrochemical Cells – New Advances in Fundamental Researches and Applications

IrO2-Ta2O5, and two cathode materials carbon felt (CF) and titanium plate (Ti), plus a variation of its position respect to the soil matrix. These experiments are described in the

Results correspond to two independent experimental sets, so far methodology for each one

For this set of experiments soil was collected at 50 cm depth in an undisturbed site of Guanajuato, México. Applying the ASTM D4318-10 methodology soil was characterized for liquid (LL) and plastic (PL) limits, the water content difference between LL and PL provides the plasticity index (PI), which is an indicator of soil response, because greater PI values correspond to a soil which is more plastic and compressible and so far it exhibits greater volume changes using LL and PI values on the plasticity chart (Helwany, 2007), can be obtained a fast classification of soil type, providing an insight on the possible soil response, before any electrical perturbation is applied. Also, textural classification was done following the USCS-P13-B-2 procedure. This soil was artificially polluted by mixing it with a phenanthrene solution, let stand overnight, and room temperature dried. Later on, it was characterized for sorbed phenanthrene, which resulted in 12 mg Kg-1. For experiments

This set of experiments considered electrodes made from 100 ppi (pores per inch) reticulated vitreous carbon (RVC), impregnated with TiO2 by a sol-gel method. Impregnating solution was prepared dissolving metallic Ti in concentrated HCl; later on it was precipitated with NH4OH, obtained product was filtered and washed before dispersing it into a 10% ethanol solution; in this solution RVC pieces were immersed for 24 hours; after that, they were dried and subjected to a 3 hours calcination, this procedure pursues formation of the anatase phase in the deposit; confirmation of anatase presence was done by Raman spectroscopy and some micrographs were obtained with a Leica S8APO stereomicroscope. The

Electrokinetic experiments were run for 24 hours, a 25 mA cm-2 electrical current density was imposed with an electrophoresis power supply FR500-125 BIOELEC. Electrode arrangement considered keeping constant a bare RVC cathode, and switching the anode from bare RVC to RVC-TiO2, recorded parameters correspond to: pH and electric conductivity measured with a Multipurpose Lab Interphase Vernier Software;

In order to quantify residual phenanthrene concentrations, at the end of each experiment, soil sample was cut in slices, room temperature dried, and phenanthrene was Soxhlet extracted with ethylic ether. After that, the solvent was evaporated and phenanthrene was solubilized in 5 mL of HPLC grade acetonitrile, this sample was centrifuged and injected into an inverse phase Hypersil chromatographic column C-18 ODS (100 mmx4.6 mm, and 3 mm particle size); detection was done using a mobile phase made of a mixture CH3CN/H2O/CH3OH in proportions 30:15:55 % v/v; using a flow rate of 0.4 mL min-1 and

electrochemical cell was a rectangular one (14 cm length, 10 cm width, 9 cm high).

electroosmotic flow was registered with an illuminated multitester MUL-270 Steren.

following paragraphs.

**2.1 Anode modification** 

will be discussed in an independent section.

polluted soil was rewetted with deionized water.

254 nm detection wavelength.

**2. Methodology** 

Soil sample corresponds to a hydrocarbon polluted weathered soil, for which a physical characterization is done by using the ASTM D4318 as well as the USCS-P13-B-2 procedure, by which it was established soil type and textural composition. Since this soil has hydrocarbon pollutants, its concentration was determined as oil and grease by the Soxhlet technique. According to published results (Murillo-Rivera et al, 2009), 0.1M NaOH solution is an electrolyte that works fine for hydrocarbon polluted soils, so this one was chosen as the electrolyte for soil wetting, and wells replenishment.

Experimental cell was a rectangular one (10 cm length, 2 cm width, 4 cm high), a current density of 20 mA cm-2 was imposed with a PDC-GP 4303DU Power Source, in a galvanostatic mode during 4 hours.

Considering that a DSA anode provides oxidant species at higher rates, then for this hydrocarbon polluted soil electroremediation it was chosen an electrode arrangement, considering a modified DSA made of a titanium plate covered with an iridium-tantalum film (TiIrO2-Ta2O5), and two types of cathode: carbon felt (CF) and a titanium plate (Ti). Also, in these set of experiments it was considered two electrode positions: in the first one, a physical barrier of filter paper was included between soil and electrode, while in the second one the electrode was set in direct contact with soil sample.

Registered experimental parameters were: applied electrical current, developed electrical potential, with these it was possible to calculate cell resistance and energy consumption. At the end of each experiment soil was cut in 3 sections (anode, middle, cathode), hydrocarbon removal was estimated from soil residual concentrations, which were extracted by the Soxhlet technique, and later analyzed by UV-Vis (XLS, Perkin-Elmer) gas chromatography coupled to mass spectroscopy (CG-EM, Agilent GC 19091-413).
