Efficiency and sustainable leaching process of manganese from pyrolusite-pyrite mixture in sulfuric acid systems enhanced by microwave heating

Abstract Recently, with the decrease in the quality of manganese resources, the efficient use of low-quality manganese ore resources has attracted widespread attention. At present, pyrite is often used as reducing agent to recover Mn(IV) in industrialization. However, the passivation of pyrite in the leaching reaction process will lead to a decreased reaction efficiency. Hence, in this study, microwave heating was applied in the reduction system in order to remove the inhibition of the passivation layer and accelerate the dissolution of pyrite, indicating an improvement in the corresponding Mn(IV) reduction efficiency. The results show that the leaching rate assisted by microwave heating was 95.07%, approximately 20% higher than that of conventional heating (75.08%), and the amount of sulfuric acid and pyrite was reduced by 14% and 20%, respectively. XPS analysis shows that there was an obvious sulfur elemental peak at 164.3 eV under traditional heating conditions, but it was absent when microwave heating was applied, and the elemental sulfur under conventional heating is 11.63%, which is higher than that under microwave heating (4.80%). Through scanning electron microscopy, it was noted that there are a large number of voids on the mineral surface under microwave heating, which can increase the solid-liquid contact area, effectively reducing the formation of the sulfur passivation layer and accelerating the dissolution of Mn (IV). In addition, the measurement of the dielectric constant of the solution mixture shows that the dielectric constant of the solution with mineral addition was increased from 36.533 (F/M) to 37.717 (F/M) and the loss tangent angle was increased from 8.61 × 10⁻³ to 9.21 × 10⁻³. It can be inferred that microwaves act directly on the mineral itself through the solution. Thus, the application of pyrite and microwave heating in the recovery of Mn(IV) is expected to effectively reduce the use of sulfuric acid, and achieve green, environmentally friendly and efficient leaching of manganese