NEW FORMULATIONS FOR IRON-OXIDES DISSOLUTION

The dissolution of Fe-59-labelled synthetic goethite, alpha-FeOOH, has been studied in solutions of mineral (HCl, HNO3, H2SO4) and organic acids, belonging to the families of carboxylic and diphosphonic acids, alone, or in the presence of reducing agents. The data have been interpreted with a first-order rate law, although the shrinking core dissolution rate law has been shown to apply generally. The effect of several reducing agents on the rate of dissolution of alpha-FeOOH by inorganic and organic acids has been measured. Very high accelerations of the dissolution process were exhibited by ascorbic acid, sodium dithionite and sodium formaldehydesulfoxylate. In particular, the mixture of 1-hydroxyethane-1,1-diphosphonic acid and sodium formaldehydesulfoxylate proved to be extremely effective for alpha-FeOOH dissolution even at room temperature.