Bottom-blown oxygen converter
The Bottom-blown Oxygen Converter or BBOCTM is a smelting furnace developed by the staff at Britannia Refined Metals Limited (“BRM”), a British subsidiary of MIM Holdings Limited (which is now part of the Glencore Xstrata group of companies). The furnace is currently marketed by Xstrata Technology. It is a sealed, flat-bottomed furnace mounted on a tilting frame that is used in the recovery of precious metals. A key feature is the use of a shrouded lance to inject oxygen through the bottom of the furnace, directly into the precious metals contained in the furnace, to oxidize base metals or other impurities as part of their removal as slag.
Ores mined for their base metal content often contain precious metals, usually gold and silver. These have to be removed from the base metals as part of the refining processes used to purify the metals. In the case of copper electrolytic refining, the gold and silver fall to the bottom of the electrolytic refining cell as “slimes” that are subsequently treated to recover gold and silver as by-products. In the case of lead refining, silver and other precious metals are typically removed using the Parkes process, in which zinc is added to the impure lead bullion to collect the silver, gold and other precious metals.
The BRM lead refinery at Northfleet in England uses the Parkes process followed by liquation and a vacuum induction retort to recover precious metals. The product of this process is a feed for the BBOC consisting of a mixture of lead, silver (60–75%), zinc (2–3%) and copper (2–3%), with trace amounts of gold. Prior to the development of the BBOC, BRM used cupellation in a 15 tonne (“t”) reverberatory cupellation furnace to recover the precious metals from this mixture. Three of these furnaces were used to produce 450 t of silver per year.
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