The Boliden Lead Process

5 - Original lead smelting at Boliden - Ronnskar smelter. 

Coke was also added to the furnace as fines at one per cent of the concentrate input to assist in reducing the lead level of slag, which contained around 4.1 per cent Pb as well as zinc. Carbon was also added from the electrodes and represented around 1.3 per cent of the concentrate input. 

Gas from the furnace contained copious fumes and dusts at around 40 per cent of concentrate feed, and around eight per cent SO2. Dust and fume collected from gas cleaning was returned to the electric furnace and represented a significant recycling load. 

Bullion was tapped continuously via a siphon from the centre of the furnace and slag was tapped intermittently from one end. Lead bullion contained around three per cent S, which was transferred to either of two small batch operated Pierce Smith converters, blown with air to remove sulfur. Slag from the converters and dusts collected from converter gases were also returned to the electric furnace. A copper matte was periodically recovered from the converters and the bullion was sent to the lead refinery. 

Capacity of the electric furnace was around 55 000 t/a of lead bullion and electrical energy consumption was around 900 kWh per tonne of lead bulhon produced. 

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