Acid-free extraction of manganese from pyrolusite tailings by in situ redox interaction with waste copperas

Pyrolusite tailings (PTs) is a solid waste discharged from the mining of high grade pyrolusite, and is also regraded as an important secondary resource of manganese. However, its extraction requires an expensive reductant used for the reduction of Mn(IV) to low valence. In this paper, an innovative process using in situ redox interaction of PTs with waste copperas (as reductant and sulfating agent) followed by water leaching for efficient manganese extraction was proposed. The in situ redox interaction mechanism was investigated systematically. At lower temperatures (< 500 degrees C), Fe(II) was the main reductant by direct solid-to-solid reaction. In the temperature range of 500-650 degrees C, the Mn(IV) in PTs was reduced to Mn(II) due to the synergistic effect of Fe(II) and SO2, and then Mn(II) was sulfated into water-soluble MnSO4. The reduction of Fe(III) into Fe(II) by SO2 occurred i.e. the Fe (II)Fe(III) redox cycle. And the generated FeSO4 continued to react with PTs, indicating that the Fe(II)Fe(III) redox cycle facilitated the extraction of manganese. Furthermore, high roasting temperatures caused MnSO4 to decompose into insoluble Mn2O3, inhibiting the extraction.

Automated summary

In this study, an innovative process using in situ redox interaction of pyrolusite tailings with waste copperas was proposed for efficient manganese extraction. The mechanism of the in situ redox interaction was systematically investigated, and it was found that at lower temperatures, Fe(II) was the main reductant while at higher temperatures, the Fe(II)Fe(III) redox cycle facilitated the extraction of manganese. However, high roasting temperatures inhibited the extraction by causing decomposition of manganese sulfate.