text: In the 1990s, the Niihama copper refinery, owned by Sumitomo Metal Mining Company Limited (“Sumitomo”), treated copper anode slimes generated in-house, together with anode slimes from Sumitomo’s Toyo refinery and lead refinery slime from the Harima Imperial Smelting Process smelter. A total of 1200 tonnes per year (“t/y”) of anode slimes and 400 t/y of lead refinery slimes were treated using a process flow sheet that included a chloridizing step to remove separate the lead as lead chloride (PbCl) and a reverberatory-type doré furnace. It produced about 200 t of silver, 22 t of gold, 1.5 t of palladium, 300 kilograms (“kg”) of platinum and 40 kg of rhodium, as well as 60 t of selenium, 50 t of bismuth, 900 kg of tellurium and 150 t of antimony alloy annually.
  The gold production doubled during the decade to 1996, as its concentration in anode slimes and the quantity of anode slimes increased. To enable this, Sumitomo decided in 1990 to upgrade the refinery, and as part of that upgrade, installed a 3.5 t-capacity BBOC to replace its reverberatory doré furnace in October 1992.
  Sumitomo reported that, while the old oil-fired reverberatory furnace had served it well for many years, it had the following drawbacks:	
  * its operation was labor-intensive
  * it had a low fuel efficiency
  * there was a high waste gas volume
  * the reaction rate was low.
  Sumitomo investigated both the TBRC and BBOC furnaces before making a selection. It chose the BBOC over the TBRC technology because of the ease of control of the bath temperature, its high oxygen efficiency and its simple maintenance.
  Sumitomo found that the impurity contents of BBOC doré anodes was high when the furnace was first commissioned. This was because it was important to determine the endpoint of the oxidation reactions to maximize the quality of the anodes. Sumitomo found that this could be determined by measuring the oxygen content of the off-gas using oxygen sensors based on stabilized zirconia with an Fe/FeO reference electrode.
  Sumitomo subsequently adapted the BBOC to allow the chloridizing step to be undertaken in the furnace, thus eliminating the need for a separate chloridizing furnace for lead chloride production. This was done in February 1994 and was reported to be “giving very good results.”