A submerged-arc furnace reduces manganese ore with carbon (coke) in three burden zones: a preheat zone near the charge surface, a reduction zone around the electrode tips where MnO is stripped of oxygen, and a molten pool at the hearth where metal separates from slag and is periodically tapped. The core reaction is:
MnO(s) + C(s) → Mn(l) + CO(g)
On an Ellingham diagram the MnO line sits below the FeO line — manganese binds oxygen more strongly than iron does — so carbothermic reduction of MnO needs a noticeably higher temperature (and more excess carbon) to go to completion than the equivalent iron-oxide reduction. This simulation reproduces that: recovery barely moves until the furnace is well past ~1250 °C, then climbs steeply with both temperature and reductant potential.
recovery = min(96%, 38% + 0.16·(T−1100) + 0.18·reductant)
alloy grade = 45% + 0.8·ore_grade + 0.08·recovery
sp. energy = max(2.1, 5.8 − 0.004·(T−1100) − 0.012·reductant) [MWh/t]
- Temperature and reductant potential both drive the reduction reaction forward — more heat and more available carbon push MnO → Mn further to completion.
- Ore grade sets the ceiling on alloy purity: a lean charge can never produce a rich alloy, no matter how efficient the reduction.
- Once alloy grade exceeds 70% Mn the furnace is producing standard high-carbon ferromanganese; below that the tap is an under-reduced, Mn-depleted alloy that has to be re-melted.
- Running hotter/harder lowers specific energy per tonne up to a point — the furnace is using its electrical energy more efficiently once the reaction is no longer starved of heat.