Electrochemical impedance spectroscopy has become a mature and well-understood technique. It is now possible to acquire, validate, and quantitatively interpret the experimental impedances. This chapter has been addressed to understanding the fundamental processes of diffusion and faradaic reaction at electrodes. However, the most difficult problem in EIS is modeling the electrode processes, which is where most of the problems and errors arise. There is an almost infinite variety of different reactions and interfaces that can be studied (corrosion, coatings, conducting polymers, batteries and fuel cells, semiconductors, electrocatalytic reactions, chemical reactions coupled with faradaic processes, etc.) and the main effort is now being applied to understanding and analyzing these processes. These applications will be the subject of a second review in a forthcoming volume in this series.

Electrochemical Impedance Spectroscopy and its Applications

Arsenic toxicity, health hazards and removal techniques from water : an overview

Nitrate contamination in surface and ground waters is one of this century’s major engineering challenges due to negative environmental impacts and the risk to human health in drinking water. Electrochemical reduction is a promising water treatment technology to manage nitrate in drinking water. This critical review describes the fundamental principles necessary to understand electrochemical reduction technologies and how to apply them. The focus is on electrochemical nitrate reduction mechanisms and pathways that form undesirable products (nitrite, ammonium) or the more desirable product (dinitrogen). Factors influencing the conversion rates and selectivity of electrochemical nitrate reduction, such as electrode material and operating parameters, are also described. Finally, the applicability for treating drinking water matrices using electrochemical processes is analyzed, including existing implementation of commercial treatment systems. Overall, this critical review contributes to the understanding of the potential applications and constraints of electrochemical reduction to manage nitrate in drinking waters and highlights directions for future research required for implementation.

Electrocatalytic reduction of nitrate: Fundamentals to full-scale water treatment applications

Electrochemical approaches to environmental problems in the process industry

Three-dimensional electrochemical process for wastewater treatment: A general review

A new process for removal of sulphur dioxide from waste gases is proposed consisting of both electrochemical and catalytic sulphur dioxide oxidation. In the catalytic step a part of the sulphur dioxide is oxidized by oxygen on copper producing sulphuric acid and copper sulphate. The other part is oxidized electrochemically on graphite. The cathodic reaction of this electrolysis is used for recovering the copper dissolved in the catalytic step. The basic reactions of this process have been studied experimentally in detail. It has been shown that sulphur dioxide can be electrochemically oxidized on carbon electrodes to sulphuric acid with high current efficiency. The reaction rate of the electrochemical copper deposition is increased by dissolved sulphur dioxide in the electrolyte. The catalytic oxidation of sulphur dioxide on copper has been investigated for different sulphur dioxide concentrations and temperatures. The ratio of the reaction products, sulphuric acid and copper sulphate, varies over a wide range depending on the experimental conditions.

Fundamental studies on a new concept of flue gas desulphurization

This paper deals with the use of iron felt as a reducing agent for the removal of mercury from aqueous dilute solutions containing chloride ions. The kinetic behavior of the mercuric ion reduction was analyzed and its diffusion coefficient was determined with the use of a rotating disk electrode. Experimental results of the removal of mercury from aqueous sodium chloride solutions containing 100 ppm mercury by contact with iron felt are reported. The mercury concentration was decreased to values lower than 0·1 ppm. The recovery of metallic mercury by chemical attack of the residual iron felt was also analyzed.

Removal and recovery of mercury from chloride solutions by contact deposition on iron felt

The performance of a batch undivided electrochemical reactor with a rotating cylinder electrode of expanded metal sheets for the removal of tin from synthetic sulfate solution is studied. The effect of the cathode potential, initial tin concentration, number of sheets forming the cathode and cathodic side reactions on the figures of merit of the reactor is analysed. For a cathode potential of −0.65 V vs SCE at 500 rpm, the tin concentration decreased from 393 to 94 mg l−1 after 30 min of electrolysis with a specific energy consumption of 3.93 kWh kg−1 and a normalized space velocity of 1.27 h−1. The change in concentration was higher when the potential was more negative because of the turbulence-promoting action of the hydrogen evolution. The results suggest that the applied potential must represent a compromise between the increase in space time yield or normalized space velocity and the increase in the specific energy consumption.

Electrochemical Removal of Tin from Dilute Aqueous Sulfate Solutions using a Rotating Cylinder Electrode of Expanded Metal

Evaluation of the hydrodynamic behaviour of turbulence promoters in parallel plate electrochemical reactors by means of the dispersion model

This paper analyses the effect of side reactions, such as the reduction of oxygen or Fe(III), on copper deposition from dilute acid sulfate solutions. Fundamental studies with a rotating disc electrode were performed to determine the potential regions where the reactions take place and also to calculate kinetic parameters under the conditions of the experiments. Applied studies carried out in a through-flow electrochemical reactor with a packed bed cathode formed by a stack of nets are reported. The experimental data are compared with theoretical results, according to the continuous model, to corroborate its reliability for the case of simultaneous electrochemical reactions. It was found that the agreement between the mathematical treatment and the experimental data is similar to the case of a single reaction in the electrode. Taking into account the side reactions, criteria for the selection of bed thickness parallel to the current flow are discussed.

Jose Maria Bisang

Papers

Fundamental studies on a new concept of flue gas desulphurization

Removal and recovery of mercury from chloride solutions by contact deposition on iron felt

Electrochemical Removal of Tin from Dilute Aqueous Sulfate Solutions using a Rotating Cylinder Electrode of Expanded Metal

Evaluation of the hydrodynamic behaviour of turbulence promoters in parallel plate electrochemical reactors by means of the dispersion model

Theoretical and experimental studies of the effect of side reactions in copper deposition from dilute solutions on packed-bed electrodes