Dissolution of pure and substituted goethites controlled by the surface reaction under conditions of abrasive stripping voltammetry

Pure goethites and Al-, Cr-, and Mn-goethites, as synthetic and natural products, were used to establish the conditions for electrochemical reductive dissolution following surface reaction kinetics. In diluted perchloric acid and at reaction rate coefficients of the order of 10(-4)s(-1), the gamma parameters in the kinetic equation J/N-0 = k(N/N-0)(gamma) (where J is the reaction rate and N and N-0 are actual and total molar amounts of a solid reactant) were in the range expected for the shape-preserving dissolution of the particles with a certain size and reactivity distribution function. The same range of gamma was found using the dissolution of goethites by a chemical reaction via oxalate-ferrous ion surface complexation. The importance of the charge transfer coefficient to describe the iron oxide reactivities was highlighted as it is sensitive to the synthetic route and also to the substitution of iron.