THERMODYNAMIC ANALYSIS OF THE REACTIONS OF IRON-OXIDES - DISSOLUTION OXALIC-ACID

The mechanism of dissolution of pure iron oxides by means of organic a cids comprises two different chemical pathways: (a) non-reductive diss olution and (b) reductive dissolution. In this paper, the thermodynami c analysis of these pathways for the iron oxides-oxalic acid system is presented. In low acid solutions (pH higher than 3) the only thermody namically stable complex ions of bivalent and trivalent iron are [Fe2(C2O4)(2)](2-) and [Fe3+(C2O4)(3)](3-). Uncomplexed Fe2+ ion can be id entified only in high acid solutions, while uncomplexed Fe3+ ion is no t likely to build-up in oxalic acid solutions. In the pH range 1-2 the [Fe3+(C2O4)(2)](-) and [Fe3+C2O4](+) ions are stable, while at pH les s than 1, the [Fe3+HC2O4](2+) is the only ion existing. Copyright (C) 1996 Canadian Institute of Mining and Metallurgy. Published by Elsevie r Science Ltd.