Alejandro Medel

Universitat of Barcelona · Departament de Química Física, Facultat de Química


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    ABSTRACT: During the crude oil refining process, NaOH solutions are used to remove H2S, H2Saq, and sulfur compounds from different hydrocarbon streams. The residues obtained are called “spent caustics”. These residues can be mixed with those obtained in other processes, adding to its chemical composition naphthenic acids and phenolic compounds, resulting in one of the most dangerous industrial residues. In this study, the use of electrochemical technology (ET), using BDD with Ti as substrate (Ti/BDD), is evaluated in electrolysis of spent caustic mixtures, obtained through individual samples from different refineries. In this way, the Ti/BDD’s capability of carrying out the electrochemical destruction of spent caustics in an acidic medium is evaluated having as key process a chemical pre-treatment phase. The potential production of ●OHs, as main reactive oxygen species electrogenerated over Ti/BDD surface, was evaluated in HCl and H2SO4 through fluorescence spectroscopy, demonstrating the reaction medium’s influence on its production. The results show that the hydrocarbon industry spent caustics can be mineralized to CO2 and water, driving the use of ET and of the Ti/BDD to solve a real problem, whose potential and negative impact on the environment and on human health is and has been environmental agencies’ main focus.
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    ABSTRACT: This research evaluated two electrokinetic remediation systems (EKR) for separating phenanthrene from bentonite and its electrochemical destruction by using a Boron Doped Diamond (BDD) electrode. The effect of the electrochemical potential for the oxidation of phenanthrene in liquid phase with BDD was analyzed by Normal Pulse Voltammetry and Hydroxyl Radical (●OH) analysis using the Spin Trapping Technique. The results showed that 70% of phenanthrene was removed from bentonite through EKR by applying 20 mA for 4 h in alkaline conditions, and that phenanthrene in solution was 100% degraded with BDD by applying 2.3 V vs Hg|Hg2SO4, for 2.5 h. These results demonstrate the potential application of the electrochemical technology in treating soils contaminated with highly toxic compounds, such as Polyaromatic Hydrocarbons (PAHs) and their final destruction using the EKR-BDD process.
    Environmental engineering and management journal 08/2014; · 1.26 Impact Factor
  • Alejandro Medel
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    ABSTRACT: In electrochemical processes, multiple oxidation-reduction reactions can occur at the electrode surface. The subsequent reaction products are dependent on the operating parameters and the electrocatalytic properties of the materials used. Electrochemical production of ●OH from water oxidation has been widely reported for various materials like DSA electrodes and doped diamonds such as BDD. In contrast, as far as we know the comparative generation of ●OH by electrochemical reduction at different cathode materials has not been reported yet. The present study has assessed the different production of ●OH by electrochemical reduction of O2 and H2O2 in an acidic medium at four conventional cathode materials (Pt, Ti, C-sp2, and AISI 304 stainless steel). The possible ●OH production was analyzed using UV-Vis Spectroscopy, Electron Spin Resonance Spectroscopy (ESR), Reverse Phase High Performance Liquid Chromatography (RP-HPLC) with a photodiode array detector, and RP-HPLC coupled to a fluorescence detector. The results showed that production of ●OH depends on the nature of the material under investigation. From greatest to least, the output of ●OH as a function of the material was: PtC-sp2stainless steel Ti. These results reveal the potential impact of the counter electrode in electro-oxidation treatments if either O2 or H2O2 are present.
    The 64th Annual Meeting of the International Society of Electrochemistry; 09/2013
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    ABSTRACT: C-sp 2 (graphite) impurities are undesirable in syn-thetic diamond electrodes (C-sp 3), because they can affect the electrochemical response. In this work, we demonstrate that C-sp 3 surfaces can be activated successfully by applying an anodic current density corresponding to sufficiently high po-tential where the hydroxyl radicals (● OH) are generated. The effectiveness of this activation process was verified by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and cyclic voltammetry.
    Electrocatalysis 09/2013;
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    ABSTRACT: Electrochemical incineration using boron-doped diamond electrodes was applied to samples obtained from a refinery and compared to the photo-electro-Fenton process in order to selectively eliminate the phenol and phenolic compounds from a complex matrix. Due to the complex chemical composition of the sample, a pretreatment to the sample in order to isolate the phenolic compounds was applied. The effects of the pretreatment and of pH on the degradation of the phenolic compounds were evaluated. The results indicate that the use of a boron-doped diamond electrode in an electrochemical incineration process mineralizes 99.5% of the phenolic sample content. Working in acidic medium (pH = 1), and applying 2 A at 298 K under constant stirring for 2 hours, also results in the incineration of the reaction intermediates reflected by 97% removal of TOC. In contrast, the photo-electro-Fenton process results in 99.9% oxidation of phenolic compounds with only a 25.69% removal of TOC.
    International Journal of Photoenergy 01/2012; 2012. · 2.66 Impact Factor
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    Alejandro Medel-Reyes
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    ABSTRACT: Characterization of different tailings from the mining district of Guanajuato, México were carried out, including a tailing from an abandoned dam 20 years ago, a dam in operation and another coming from the mixture of different companies. The three tail¬ings presented alkaline conditions, normal salinity, aerobic environment with oxida¬tive tendency, low humidity, very low capacity of cationic exchange, and absence of organic matter. These conditions restrict the metal mobility. The mineralogical analysis showed that the tailings contained mainly quartz, calcite and magnetite. Leaching tests indicated that metals cannot be leached in percentages higher than 0.1%, and so these tailings do not represent an environmental risk. The low leaching of metals in the studied tailings was consistent with the miner¬alogical and physicochemical prevailing conditions, the low acid drainage generation potential and the high degree of stability observed in the tests of metals fractionation.
    Rev. Int. Contam. Ambie. 01/2012; 28:49-59.

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