Commonly-used ore of Mn is pyrolusite whose main composition is MnO2. With rapidly growing demand for Mn products, low grade Mn ores and secondary Mn sources impossible to be processed by conventional metallurgical methods have become important Mn sources.
In recent years, various hydrometallurgical methods based on various reductants have been developed for the recovery of Mn from these sources. In other words, the reductive acid leaching of low-grade Mn ores in sulfuric or hydrochloric acid solutions with reductants such as hydrogen peroxide, oxalic acid, glucose, corncob, aqueous methanol, ferrous sulfate, pyrite and sulphur was the main focus. However, these leaching techniques have some drawbacks. For example, oxidants and reductants are expensive and sulfur dioxide may be harmful to the environment, and organic reductants are effective but expensive, and their consumption is too much.
Pak Yong Song, a section head at the Faculty of Metal Engineering, has conducted an experiment to enhance the leaching rate of Mn in the preparation of Mn sulfate by the direct reductive leaching method using sawdust as a reductant and spent electrolyte as leaching solution, and confirmed its effectiveness.
He has examined the effects of experimental parameters such as the amount of concentrated sulfuric acid (95%), the amount of reductant, leaching temperature and leaching time.
The results show the following.
First, in order to enhance the leaching rate of Mn, the amount of concentrated sulfuric acid (95%) has to be 2.5mL, the amount of reductant 0.75g, the leaching temperature 85℃ and the leaching time 6h for 10g of pyrolusite powder. In this case, the leaching rate of Mn reaches 98.25%. Second, suitable solid/liquid ratio by spent electrolyte is needed to reduce the viscosity of the solution and provide suitable conditions for filtration.