Acidic dissolution of magnetite in mixtures of oxalic and sulfuric acid

• Dissolution of magnetite in sulfuric acid can be greatly enhanced with oxalic acid.
• The Kabai model was the best in describing the dissolution.
• The reaction rate coefficient was 4.1 · 10− 5–5.6 · 10− 4 s− 1 for different acid ratios.
• The solid specific constant of the Kabai model changes during dissolution.

Thermodynamic and kinetic dissolution experiments were performed at different temperatures and different oxalic and sulfuric acid ratios by using synthetic magnetite powder. The Kabai model was the most appropriate one for describing the dissolution kinetics of magnetite in mixtures of sulfuric and oxalic acid. The reaction rate constant, k, at 35 °C was found to vary between 4.1 · 10− 5 and 5.6 · 10− 4 s− 1 for the different acid ratios. The solid specific constant of the Kabai model, a, was also found to vary in the different acid systems, suggesting that changes in the solid take place during dissolution in different media. Increasing the oxalic acid content in the solution phase yielded higher solubilities, as well as accelerated kinetics. Whereas kinetics was significantly improved when increasing the oxalic acid fraction from 50 to 70, solubility no longer increased markedly.