Separation of Manganese from Iron in the $$\hbox {SO}_{2}$$ Reductive Leaching Iron-Rich Pyrolusite Ore: Leaching Mechanism and Kinetics

Manganese (Mn) extraction from iron-rich pyrolusite ore with cheap sulphur dioxide is considered to be the most promising method with advantages of rapid leaching rate and high leaching efficiency. Nevertheless, co-dissolution of iron (Fe) with manganese has limited the development of its commercial practice. In this work, the separation kinetics and mechanism were investigated during the leaching process of high-iron pyrolusite ore in order to achieve high separation efficiency of manganese from iron. Firstly, the thermochemical analysis has been carried out to determine the feasibility of Mn/Fe separation. Secondly, the leaching behaviour and relative extraction of manganese and iron in the presence of \(\hbox {SO}_{2}\) gas/aqueous \(\hbox {SO}_{2}\) were investigated. Then, the effects of different variables containing reaction temperature, \(\hbox {SO}_{2}\) concentration and sulphuric acid concentration on the separation efficiency were studied systematically. Lastly, the leaching kinetics was analysed and the separation mechanism was put forward. The results show that the iron leaching occurs in two stages. The separation efficiency depends on both the content of poor-crystalline iron oxide in the raw ore and the leaching conditions. In the first stage, the reactant diffusion was the rate-limiting step for the dissolution of both manganese and poor-crystalline iron oxide with activation energy of 10.48 kJ/mol and 20.18 kJ/mol, respectively. The iron dissolution of well-crystalline iron was controlled by reactant diffusion (25–\(45\,^{\circ }\hbox {C}\)) and chemical reaction (45–\(65\,^{\circ }\hbox {C}\)) with activation energy of 18.14 kJ/mol and 41.73 kJ/mol, respectively.