Luís A.M. Ruotolo

Removal of toxic metals from aqueous effluents by electrodeposition in a spouted bed electrochemical reactor

This work investigates the removal of metal ions from synthetic aqueous effluents using a spouted bed electrochemical reactor whose cathode was composed of 1.0 mm copper particles. Using a Box–Behnken factorial design, the effects of current (I), electrode thickness (L), draught distance (d) and support electrolyte concentration (Cs) on current efficiency (CE), space–time yield (Y) and energy consumption (EC) were analysed. The results were statistically analysed and the effect of each variable was evaluated using the surface response methodology. The results showed that Cs is the most important variable to consider in the process optimization. A current of 8.0 A can be applied in order to obtain high Y and CE with an acceptable EC. Electrode thicknesses greater than 1.3 cm are not recommended because the irregular potential distribution leads to a Y drop owing to the low CE observed for this condition. The draught distance does not have statistical significance; therefore, the particle circulation rate is not important in this kind of electrochemical reactor.

Electrochemical Removal of Copper Ions from Aqueous Solutions Using a Modulated Current Method

The use of porous electrodes to remove toxic metals from industrial effluents has been recognized over the years due to its high mass transfer rates resulting in high current efficiencies (CE) and low energy consumption (EC), even at very low metal concentrations. This work addresses the effects of flow velocity and electric current on current efficiency and energy consumption of copper electrodeposition using reticulated vitreous carbon, aiming to optimize the CE and EC by using a modulated current method. First, it was found that a flow velocity of 0.246 m s−1 maximizes the mass transfer coefficient (km). Applying this flow velocity and a modulated current, the electrodeposition process was investigated and compared with that carried out under galvanostatic mode. The results showed that using a current control there is a reduction of average EC due to the improvement of the average CE, but the operational time also increases when compared to that obtained using the galvanostatic mode.

Mass transfer study on the electrochemical removal of copper ions from synthetic effluents using reticulated vitreous carbon

Porous electrodes have been successfully used for metal electrodeposition from diluted aqueous solution due to their high porosity and specific surface area, which lead to high mass transfer rates. This work studies the mass transfer of copper electrodeposition on reticulated vitreous carbon in a flow reactor without membrane. The flow configuration, otherwise the filter-press electrochemical reactors, was designed in order to minimize the pressure drop. The mass transfer coefficient was determined by voltammetric and galvanostatic electrodeposition. In the voltammetric experiments a Luggin capillary was used to measure the current–potential curves and to determine the limiting current (and, consequently, the mass transfer coefficient). In the galvanostatic experiments the concentration–time curves were obtained and considering a limiting current kinetics model, the mass transfer coefficient (k m) was determined for different flow velocities. The results showed that both methods give similar values of k m, thus the voltammetric method can be recommended because it is faster and simpler. Finally, the reactor performance was compared with others from literature, and it was observed that the proposed reactor design has high Sherwood numbers similar to other reactor configurations using membranes and reticulated vitreous carbon electrodes.

Charge and Potential Balancing for Optimized Capacitive Deionization Using Lignin‐Derived, Low‐Cost Activated Carbon Electrodes

Lignin-derived carbon is introduced as a promising electrode material for water desalination by using capacitive deionization (CDI). Lignin is a low-cost precursor that is obtained from the cellulose and ethanol industries, and we used carbonization and subsequent KOH activation to obtain highly porous carbon. CDI cells with a pair of lignin-derived carbon electrodes presented an initially high salt adsorption capacity but rapidly lost their beneficial desalination performance. To capitalize on the high porosity of lignin-derived carbon and to stabilize the CDI performance, we then used asymmetric electrode configurations. By using electrodes of the same material but with different thicknesses, the desalination performance was stabilized through reduction of the potential at the positive electrode. To enhance the desalination capacity further, we used cell configurations with different materials for the positive and negative electrodes. The best performance was achieved by a cell with lignin-derived carbon as a negative electrode and commercial activated carbon as a positive electrode. Thereby, a maximum desalination capacity of 18.5 mg g-1 was obtained with charge efficiency over 80 % and excellent performance retention over 100 cycles. The improvements were related to the difference in the potential of zero charge between the electrodes. Our work shows that an asymmetric cell configuration is a powerful tool to adapt otherwise inappropriate CDI electrode materials.

Development of Three-Dimensional Electrodes of PbO2 Electrodeposited on Reticulated Vitreous Carbon for Organic Eletrooxidation

The application of electrochemical technology for the degradation of organic pollutants often faces two main problems, related to the anode material and mass transport limitations. Although PbO2 electrode is inexpensive and provides satisfactory electrooxidation kinetics, in the form of plane electrodes it is unable to resolve the mass transfer problem that arises at low concentrations of organics. In this work, an electrochemical flow reactor was developed for the preparation of three-dimensional electrodes consisting of PbO2 films electrodeposited onto reticulated vitreous carbon. The electrodes were characterized in terms of the substrate coating, morphology, structure, and electrocatalytic activity in the decoloration reaction of Reactive Blue 19 dye. The results showed that it was possible to deposit a uniform film of PbO 2 on the surface of the substrate after optimization of the current density and deposition time (0.7 mA cm -2 for 30 min). Comparison of the plane and three-dimensional electrodes revealed that the turbulence generated by the porous matrix significantly accelerated the dye decoloration kinetics, increasing 3.3-fold the first order kinetic constant (from 0.010 min -1 for VC/PbO2 to 0.033 min -1 for RVC/PbO2).

ELETRORRECUPERAÇÃO DE COBRE UTILIZANDO REATOR ELETROQUÍMICO DE LEITO DE JORRO

In this work, copper electrowinning using a three-dimensional spouted-bed electrode (SBE) was studied in order to investigate the effects of current density (i), concentration of supporting electrolyte (Cs), pH, electrolyte temperature, and bed thickness on the process current efficiency (EC), energy consumption (CE) and space-time yield (Y). The results indicated that the SBE may be successfully used for the electrowinning of copper when the copper ion concentration is high and the pH is between 1 and 2. In this case, 100% CE, 2.7 kWh kg-1 EC and 118 kg L-1 h-1 Y can be achieved. It was verified that an increase in the electrolyte temperature caused a decrease in the electrodeposition rate (from 3.97 g L-1h-1 to 1.17 g L-1 h-1), indicating that, despite the solution conductivity enhancement, temperature promoted the increase in the anodic dissolution kinetics. The results also showed that EC depends on the applied current density, whereby greater EC values can be obtained using high current densities. Finally, the copper particles were analyzed by scanning electron microscopy and it was confirmed that a smooth, uniform and compact electrodeposit can be obtained without using any chemical additives.

Modificação do polímero condutor polianilina para uso como trocador catiônico

This article reports the use of polyaniline (PAni), chemically and electrochemically synthesized, for copper removal from aqueous solutions. PAni films were electrodeposited on reticulated vitreous carbon (RVC). In all cases, p-toluenesulfonate anion (PTS-) was used as the dopant to obtain cation exchange properties. RVC/PAni showed no expressive copper removal due to the small amount of polymer in the film. Chemically synthesized PAni-PTS- was obtained in its reduced form (leucoesmeraldine). PAni degraded at neutral pH but remained stable at low pH, showing a very high ion-exchange capacity, which is superior to those observed for commercial resins.

PREPARAÇÃO E CARACTERIZAÇÃO DE FILMES DE PbO2 DEPOSITADOS SOBRE ANODOS TRIDIMENSIONAIS PARA DEGRADAÇÃO DE POLUENTES ORGÂNICOS

RESUMO Neste trabalho foi estudado em uma primeira etapa a tecnica de eletrodeposicao do PbO2 sobre o substrato de CVR com porosidade de 45 ppi, verificando o efeito da densidade de corrente e do tempo de eletrodeposicao sobre a qualidade e uniformidade do deposito obtido. Em uma segunda etapa estudou-se a obtencao de um eletrodo com maior area superficial, variando-se a porosidade do substrato de CVR em 45, 60 e 80 ppi. Os eletrodos foram analisados quanto a sua capacidade de degradar o corante AR 19 em um reator de fluxo. Os filmes de PbO2 formados aplicando-se as maiores densidades de corrente apresentaram um deposito mais espesso nas extremidades do eletrodo, porem no centro do eletrodo ainda haviam areas em que era possivel observar que nao houve eletrodeposicao. Observou-se que em densidades de correntes menores ocorreu um deposito mais uniforme e que a densidade de corrente a ser aplicada no processo de eletrodeposicao do filme de PbO2 deve ser otimizada para cada substrato com diferentes porosidades. O eletrodo CVR/PbO2 de 60 ppi preparado aplicando-se 3,5 mA cm -2 apresentou os melhores resultados de recobrimento, area superficial eletroativa e atividade eletrocatalitica, sendo o escolhido como o eletrodo de trabalho para degradar compostos orgânicos poluentes.

Synthesis and Characterization of ZrO2 Coatings on Micro End Mills With Sol–Gel Processing

The objective of this paper is to develop a coating method for placing ultrathin zirconia films, fabricated using sol–gel methods, onto micro end mills. Sol–gel synthesis is investigated because of its potential as a low energy and inexpensive method for depositing a variety of wear resistant and chemically stable oxide coatings that could potentially extend tool life. Two sol–gel based deposition methods are investigated: dip-coating and electrophoretic deposition (EPD). The coatings are deposited on 300-μm-diameter micro end mills. Initial results suggest that sol–gel coating methods can produce the required coverage and conformity in the cutting zone. However, preliminary findings show that the coating is removed in the cutting zone after a short time of machining (6 s). The tool pretreatment and extent of sintering, which affect surface adhesion coating mechanical properties, require further study and optimization.