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Abstract
The dissolution behaviour of 3.5–12.5 at% Cr substituted haematites in a citric acid-EDTA-ascorbic acid (CEA) reductive-complexing formulation with and without alkaline permanganate (AP) oxidative pre-treatment is presented. In the direct treatment, with increasing Cr content of the oxide, employing CEA formulations containing increased concentrations of ascorbic acid could either completely or significantly solubilise the oxide. In the 3.5–10 at% Cr in the oxide, the concentrations of reducing agent employed in the CEA formulation to achieve a solubility of >40% in iron have been demarcated. The AP pre-treatment resulted in a release of only <4% of Cr from the oxide irrespective of the Cr content of the oxide and the concentrations of the permanganate. Nevertheless, such a pre-treatment was found to improve the percentage dissolution of the oxide significantly in the subsequent treatment with the reductive-complexing formulation. With AP pre-treatment, CEA formulations containing a lower concentration of the reducing agent dissolved as much oxide as the one by CEA formulations containing a higher concentration of the reducing agent in the direct treatment. Both with and without pre-treatment methods of dissolution yielded a preferential solubilization of Fe over Cr.