Electrochemical Dissolution of Goethite by Abrasive Stripping Voltammetry

Abstract

Abrasive stripping voltammetry was applied to the investigation of the reductive dissolution of some iron(III) oxides and hydroxy-oxides, particularly goethite (α-FeOOH), in acid media. The electrode reaction directly involves the solid phase, and the reaction pathway depends on the phase composition and particle shape. This can be used for a qualitative and quantitative characterization of goethite. The results of a quantitative analysis of a mixture of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) are compared with those of IR and Moessbauer spectroscopic examination. The effects of the particle appearance (shape, crystal intergrowth) on the results of the voltammetric and chronoamperometric measurements are discussed.Direct analysis of powdered solids by electrochemical methods complements nicely conventional phase analysis methods such as powder X-ray analysis, IR spectroscopy and, for iron compounds, Moessbauer spectroscopy. In fact, each of the methods places some specific requirements on the phase crystallinity and particle size and the procedures are instrumentally demanding and time consuming and so that the possibility of resorting to alternative analytical methods is very appealing.A method which does not place very high demands on instrumentation, is well suited to routine phase analysis, and moreover, can be used on a micro scale, has been suggested by Scholz and coworkers 1,2 . The method is based on voltammetric measurement with a carbon electrode to which analyte particles are fixed by rubbing against sample, the authors named the technique "abrasive stripping voltammetry" (henceforth AbrSV). The method is useful for the analysis and characterization of metal alloys 1 , minerals 2 , various inorganic binary mixtures 3 , pigments 4 , for the study of high-temperature superconductors 5 , for the calculation of thermodynamic constants of low soluble compounds 6,7 , etc. (a survey of applications has been presented in ref. 8 ). Since electrode processes can generally involve higher order electrochemical reactions, diffusion, adsorption, and chemical reactions of the substance in the surroundings of the electrode, the overall reaction pathway is very complex 8 and interpretation of the voltammograms requires prior understanding of the conversion mechanism of the substance on the electrode and/or in its surroundings. 950Grygar, Subrt, Bohacek:

V(V) species in supported catalysts: Analysis and performance in oxidative dehydrogenation of ethane

“…The identification of the number of components of VMP curves is very valuable information but the number of VMP peaks is not necessarily equal to the number of species. More peaks for nominally the same redox process of a single solid were found for anisotropic crystals, such as goethite a-FeOOH [53], and similar peak splitting is obvious here in the reduction/ion insertion reaction of both V 2 O 5 phases, shcherbinaite (Figs. 1 and 2) and layered V 2 O 5 ( Fig.…”

Electrochemical Analysis of Solids. A Review

“…Both I p and Q can hence only be used for quantitative analysis, provided calibration curves have been constructed. The requirement for calibration plots is especially essential in differential pulse voltammetry and other alternating current techniques if the voltammetric peaks are overlapped 103,104 and if the peak assignment is not clear 105 . The problem of calibration curves was avoided 106 by the method of "internal standard" in analysis of Ag 2 O admixture in AgO, which was in fact normalisation of the minor Ag 2 O signal to the sum of signals of major (matrix) AgO and AgO formed from Ag 2 O by oxidation.…”

Cadmium Yellow Detection and Quantification by Voltammetry of Immobilized Microparticles

“…A similar calibration was used in the evaluation of voltammograms obtained for the study of amalgams [14]. It was also possible to quantify concentrations of different minerals within a mixture, by making a calibration plot with mixtures of know amounts of welldefined minerals [10,15]. Also, small quantities of iron oxides could be detected by a semi-quantitative method with a standard addition method with pyrolusite (b-MnO 2 ) as internal standard [16], or with pyrolusite and birnessite (K 0.2 5 MnO 2 ) [18].…”