José González-García

Influence of chloride ion on electrochemical degradation of phenol in alkaline medium using bismuth doped and pure PbO2 anodes

Electrochemical method at laboratory scale for the treatment of biorefractory solutions with high phenol content--1000 ppm is described. Total degradation of phenol was obtained at alkaline pH when NaCl was present using Bi-doped and pure lead dioxide electrodes. A filter press cell of 63 cm2 geometric area was used for this purpose. Measurements of chemical oxygen demand (COD), phenol, carbon monoxide, carbon dioxide, and volatile organic compounds (VOCs) have been used to characterise the electrochemical process for phenol elimination. It is worth noting that in the absence of NaCl, the charge efficiency of COD removal was independent of the current density in the range studied (50-100 mA cm(-2)) Moreover, when NaCl was present, the current efficiency for COD and phenol removal increase as the chloride concentration increases. Chloroform was the only halocompound detected at the end of reaction. For both electrodes, Bi-doped and pure lead dioxide, the chloroform concentration at the end of the electrolysis decreases, working at low current densities and for low chloride concentrations.

Current topics on sonoelectrochemistry

Sonoelectrochemistry is undergoing a reemerging activity in the last years with an increasing number of papers appearing in a wide range of peer review journals. Applied studies which cover environmental treatments, synthesis or characterization of nanostructures, polymeric materials synthesis, analytical procedures, films preparations, membrane preparations among other interesting applications have been reviewed. The revised fundamental analyses trying to elucidate the mechanism of the interactions between the ultrasound and electrical fields, are focused on test electrochemical processes, on the use of unconventional solvents and combination with other techniques. After the review of the achievements and faults of sonoelectrochemistry, future research lines are suggested.

Electrochemical Treatment of Industrial Wastewater Containing Phenols

The use of phenolic resins for manufacturing different textile products in a company, our case example, generates wastewater with high phenol concentration (30-400 ppm) and chemical oxygen demand (COD) between 3,000 and 15,000 ppm. Moreover, the effluent also contains high chloride concentrations ranging between 4000 and 7000 ppm, Ca 2+ ions with a concentration of ca. 2000 ppm, and suspended solids. A study at the laboratory scale of the anodic electrochemical treatment of this industrial effluent has been carried out. The influence of variables such as current density, pH, and charge passed on phenol degradation and COD reduction was studied. As anodes, PbO 2 /Ti or Bi-PhO 2 /Pt/Ti or Pt/Ti were used. As the separator, a 117 Nafion cation exchange membrane was employed. The results showed that the final COD value was lower than 1000 ppm. After electrochemical treatment the final concentration of phenol was lower than 1 ppm, and the COD decrease was 70-80%. Unidentified aliphatic carboxylic acids and alcohols were the main products of oxidation. For electrolyses carried out at alkaline pH, the only halocompound detected in the anolyte, gas, and aqueous phases, was chloroform regardless the electric charge passed, the current density employed, and the anode used.

Simulation of the spatial distribution of the acoustic pressure in sonochemical reactors with numerical methods: a review

Numerical methods for the calculation of the acoustic field inside sonoreactors have rapidly emerged in the last 15 years. This paper summarizes some of the most important works on this topic presented in the past, along with the diverse numerical works that have been published since then, reviewing the state of the art from a qualitative point of view. In this sense, we illustrate and discuss some of the models recently developed by the scientific community to deal with some of the complex events that take place in a sonochemical reactor such as the vibration of the reactor walls and the nonlinear phenomena inherent to the presence of ultrasonic cavitation. In addition, we point out some of the upcoming challenges that must be addressed in order to develop a reliable tool for the proper designing of efficient sonoreactors and the scale-up of sonochemical processes.

FEM simulation of a sono-reactor accounting for vibrations of the boundaries

The chemical effects of acoustic cavitation are obtained in sono-reactors built-up from a vessel and an ultrasonic source. In this paper, simulations of an existing sono-reactor are carried out, using a linear acoustics model, accounting for the vibrations of the solid walls. The available frequency range of the generator (19-21 kHz) is systematically scanned. Global quantities are plotted as a function of frequency in order to obtain response curves, exhibiting several resonance peaks. In absence of the precise knowledge of the bubbles size distribution and spatial location, the attenuation coefficient of the wave is taken as a variable, but spatially uniform parameter, and its influence is studied. The concepts of acoustic energy, intensity, active power, and source impedance are recalled, along with the general balance equation for acoustic energy, which is used as a convergence check of the simulations. It is shown that the interface between the liquid and the solid walls cannot be correctly represented by the simple approximations of either infinitely soft, or infinitely hard boundaries. Moreover, the liquid-solid coupling allows the cooling jacket to receive a noticeable part of the input power, although it is not in direct contact with the sonotrode. It may therefore undergo cavitation and this feature opens the perspective to design sono-reactors which avoid direct contact between the working liquid and the sonotrode. Besides, the possibility to shift the main pressure antinode far from the sonotrode area by exciting a resonance of the system is examined.

Electrochemical degradation of perchloroethylene in aqueous media: an approach to different strategies.

An approaching study to the electrochemical degradation of perchloroethylene (PCE) in water has been carried out using controlled current density degradation electrolyses. The different electrochemical strategies to degrade perchloroethylene in aqueous media (i.e. cathodic, anodic and dual treatments) have been checked using divided and undivided configurations. The influence of the initial concentration, pH and current density on the general behavior of the system has been studied, and special attention was paid to the nature of the byproducts formed and to the analysis of the closed mass balance at the end of the reaction. Results from several analytical techniques have been compared. Undivided configuration provides the best results in these experimental conditions, with degradation percentages higher than 50% and with only 6% of the initial perchloroethylene concentration remaining in the system.

Sonoelectrochemical treatment of water polluted with trichloroacetic acid: From sonovoltammetry to pre-pilot plant scale

The sonoelectrochemical treatment of aqueous solutions of trichloroacetic acid (TCAA) has been scaled-up from the voltammetric analysis to pre-pilot stage. The degradation in absence of ultrasound field has yield to a poor performance which has been improved in presence of ultrasound. The sonovoltametry study has provided the range of potentials and/or current densities to be used with the lowest current efficiency penalty. Sonoelectrolyses at batch scale (carried out with a horn-transducer 24 kHz positioned at about 3 cm from the surface of the electrode) achieved little improvement in the degradation. However, when a specifically designed sonoelectrochemical reactor (not optimized) was used during the scale-up, the presence of ultrasound field provided better results (fractional conversion 97%, degradation efficiency 26%, selectivity 0.92 and current efficiency 8%) at lower ultrasonic intensities and volumetric flow.

Effects of ultrasound on the electrodeposition of lead dioxide on glassy carbon electrodes

The electrodeposition of lead dioxide from lead(II) nitrate in an acid medium has been used as a test reaction to study the effects of an ultrasound field. The different behaviours found between platinum and glassy carbon electrodes have been compared by means of cyclic voltammetry and simple potential steps. The current–time response for a platinum electrode is not affected by the presence or absence of ultrasound; in contrast, significant changes have been observed in the characteristic regions of these curves (induction time t0) with the glassy carbon electrode. Scanning electron microscopy (SEM) has been employed to follow changes in the surface topography after the electrodes had been exposed to ultrasound. Results indicate that neither pits nor structural modifications that may increase the electrode surface occur with the device used. It is concluded that the activation of glassy carbon electrodes by the action of an ultrasound field for electrodeposition of lead dioxide is associated with the surface functionalization caused by the reaction of OH radicals (derived from aqueous sonolysis) with the carbon surface.

Lead electrowinning in a fluoborate medium. Use of hydrogen diffusion anodes

The results of an investigation of the electrowinning of lead employing a fluoboric acid bath are reported. The electrodeposition lead . reaction was studied by voltammetric methods and scanning electron microscopy SEM microphotographs of the electrodeposited lead were taken. The effects of current density, temperature, catholyte flow and H q concentration were investigated on a laboratory scale to . optimise operating conditions. Finally, the substitution of the traditionally used Dimensionally Stable Anode DSA by a Hydrogen . . Diffusion Electrode HDE was made in order to decrease the energy consumption EC of the overall process. q 2000 Elsevier Science S.A. All rights reserved.

Early stages of lead dioxide electrodeposition on rough titanium

The electrodeposition of lead dioxide onto rough titanium surfaces has been studied using both voltammetric and chronoamperometric techniques. The behaviour of the system is a function of the upper potential limit and also of the surface topography, and can be explained bearing in mind the competence between the (inactivation) of the support and the electrodeposition process. The influence of an ultrasonic field in the process has also been analyzed.