The sulphur dioxide gas produced in the furnace is extracted by centrifugal fans and discharged through ducting to the acid plant, an essential part of every copper smelter.
Here it is processed and converted to sulphuric acid being used in smelting and ore processes, any remaining acid being sold off as a by product.
Meanwhile in the converter furnace, the molten copper is being subjected to an injection of oxygenated compressed air. The oxygen reacts with the sulphide ore, producing copper sulphate whilst converting the copper ions to blister copper of over 98% purity.
The converter furnace is tilted and the blister copper poured is into a crucible which is transported by overhead crane and tipped into an anode furnace. The molten copper is now tapped and run into 3' x 3' moulds from which the copper anodes are formed.
These anodes are now transported to the tank shop where they are subjected to electrolytic refining. This process consists of suspending an anode in a tank containing copper sulphate and a plate of pure copper effectively acting as a cathode. A current is passed through the solution and the copper ions are stripped from the anode and deposited on the cathode, the impurities falling through the solution to the bottom of the tank.
Among these impurities are noble metals such as gold, platinum and silver which are periodically removed along with the sludge from the bottom of the tank. The tank shop houses several hundred such tanks that in a continuous process refine the copper anodes to cathode copper to 99.99% purity.
The cathode copper is now ready for transportation to the various copper extrusion and alloying specialist facilities.