Concentrate lumps (tan) and coke (dark grey) drop through the shaft into the reaction zone, where blast-air oxygen (bubbles) burns coke to CO and reduces PbO back to metallic lead: PbO + CO → Pb + CO₂. Each lump resolves to either a molten-lead droplet (joins the bullion pool at the bottom) or a slag droplet (joins the layer above it), with the split set by the extraction efficiency below — not a fixed animation:
r (Pb extraction) = min(98, 46 + (T−1100)·0.13 + O₂·0.15 + coke·0.9) [%]
Pb→slag = max(0.4, 13 − r·0.09 + O₂·0.025 − coke·0.15) [% of slag]
bullion yield = grade · r / 100 [% of charge]
Too little oxygen or reductant leaves lead locked in the slag as unreduced PbO; too much oxygen re-oxidizes metal that already reduced, and excess coke does little once the reduction potential is already saturated — so the extraction curve has diminishing returns, same as a real reverberatory or blast-furnace lead smelter.
- Bullion — the bright silver layer at the furnace bottom; its share of the bath grows with extraction efficiency.
- Slag — the amber layer above it; darkens and thickens when Pb loss is high.