Eduardo Expósito

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.

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.

Electrochemical wastewater treatment directly powered by photovoltaic panels: electrooxidation of a dye-containing wastewater.

Electrochemical technologies have proved to be useful for the treatment of wastewater, but to enhance their green characteristics it seems interesting to use a green electric energy such as that provided by photovoltaic (PV) cells, which are actually under active research to decrease the economic cost of solar kW. The aim of this work is to demonstrate the feasibility and utility of using an electrooxidation system directly powered by a photovoltaic array for the treatment of a wastewater. The experimental system used was an industrial electrochemical filter press reactor and a 40-module PV array. The influence on the degradation of a dye-containing solution (Remazol RB 133) of different experimental parameters such as the PV array and electrochemical reactor configurations has been studied. It has been demonstrated that the electrical configuration of the PV array has a strong influence on the optimal use of the electric energy generated. The optimum PV array configuration changes with the intensity of the solar irradiation, the conductivity of the solution, and the concentration of pollutant in the wastewater. A useful and effective methodology to adjust the EO-PV system operation conditions to the wastewater treatment is proposed.

Mineral Iron Oxides as Iron Source in Electro-Fenton and Photoelectro-Fenton Mineralization Processes

Several low-soluble mineral iron oxides have been studied as an iron source for the production of hydroxyl radicals via H 2 O 2 decomposition in the presence of ferrous ions (Fentons reaction). In particular, this study focuses on electro-Fenton and photoelectro-Fenton processes, using aniline as a model pollutant. The aim of this work is to spread the use of iron minerals as catalyst in the different electrochemical wastewater treatments. Among all the iron oxides tested, magnetite (Fe 3 O 4 ) and wustite (FeO) show the more promising results. The main advantages of these minerals are that they produce lower concentrations of iron in solution, ease of recycling the iron catalyst, and their ability to self-regulate the concentration of iron ions in solution. Wustite and magnetite behave purely as a source of iron ions in the electro-Fenton process. But, magnetite exhibits a heterogeneous photocatalytic effect when used as an iron source in the photoelectro-Fenton process. This new magnetite-photoelectro-Fenton process significantly improves the pollutant removal yield (16.7% more after 5 h of mineralization) compared to the conventional photoelectro-Fenton process. This effect is observed for two different wavelengths in the UV range, 254 and 360 nm.

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.

Use of thiobacillus ferrooxidans in a coupled microbiological-electrochemical system for wastewater detoxification

We have developed a mixed system, electrochemical-microbiological, that can be used for detoxifying organic compounds present in wastewater. In this system, organic matter oxidation takes place at the anode of an electrochemical reactor while ferric iron reduction takes place at the cathode. We have used a growing culture of Thiobacillus ferrooxidans to regenerate the ferric ions consumed. The culture is used as the catholyte (solution in the cathode compartment) of the system and is therefore permanently subjected to an electric field. We have verified that, under our working conditions, the culture is able to oxidize ferrous ions for long periods of time (up to 15 days) depending on the intensity of the applied current. We have checked the performance of this system in methanol oxidation. Our results show that it decreases the energy cost by 35% when com- pared with the pure electrochemical system traditionally used. Copyright 1999 John Wiley & Sons, Inc.

Influence of an ultrasonic field on lead electrodeposition on copper using a fluoroboric bath

The influence of three different types of stirring: mechanical, ultrasonic and a combination of both, on the mass transport coefficient and on the characteristics of the deposit of lead on copper electrodes has been studied. The results obtained show that ultrasounds always provide higher mass transport rates than mechanical stirring. The best deposition characteristics are obtained at 35°C using a combination of ultrasound and mechanical stirring. Normally, ultrasounds increase the quality of the deposit by decreasing the number and size of dendrites. However, the sonication time has a strong influence on the adherence of the deposits. Thus, for long sonication times, part of the lead deposit detaches itself from the surface, giving deposits of very poor quality. A preliminary study of lead deposition on three-dimensional copper foam electrodes was made and similar results were obtained. With mechanical stirring, the interior of the foam was not coated with lead while when combined stirring was used, better results were obtained. However, for long sonication times the mechanical stability of copper foams is strongly decreased and the electrode is destroyed.

A new electrochemical method for consolidation of porous rocks

This work shows the preliminary results of a newly developed electrochemical method to seal the porous system of a building stone. The method is based on the use of porous rock as separator in a divided electrochemical reactor, where anolyte and catholyte compositions are selected in such a way that anions in catholyte and cations in anolyte can precipitate as a very insoluble salt. In our experiments, the insoluble salt chosen was barium phosphate. The results obtained show that barium phosphate precipitates in a small area near the catholyte side of the material. The area closer to the surface is where the maximum damage takes place. Accepting that the pore sealing is only produced in this region, the theoretical diminution of accessible porosity in this area should be approximately 25%.

Electrosynthesis of L-Cysteine on a Dispersed Pb/Carbon Black Electrode

The electrosynthesis of L-cysteine (RSH) in aqueous medium has been investigated using Pb particles dispersed on carbon as a cathode for L-cystine electroreduction. Pb particles were synthesized in a water-in-oil microemulsion and later dispersed on carbon Vulcan XC-72. The electrochemical characterization of the Pb/C catalyst was carried out by cyclic voltammetry and scanning electrochemical microscopy (SECM). In particular, an approach of the substrate generation/tip collection mode of the SECM has been used for imaging the RSH generation. Different 20 wt % Pb/C-supported cathodes have been fabricated and morphologically characterized. These cathodes were tested for RSH electrosynthesis and compared with a conventional bulk Pb cathode. After a 100% theoretical charge, our three-dimensional 20 wt % Pb/C cathode exhibits a 30% higher RSH yield and current efficiency than the other cathodes. This performance improvement is related to the increase in the available geometric area of this electrode. We demonstrate the feasibility of using Pb/C particles as a catalyst in a type of cathode for RSH electrosynthesis. Moreover, our Pb/C electrodes show a broad scope because they can be applied to other electrosyntheses of valuable organic compounds where bulk Pb is the conventional cathode at present.