Refining

After a further, slight fire-refining, the copper is cast into shapes known as anodes. These are shipped to an electrolytic refinery for the purification of the copper to commercial specifications, and for the recovery of the precious metals which the copper has gathered to itself in the converter.

In the electrolytic plant, the copper anodes are located in tanks containing copper sulphate. Thin sheets of pure copper are also placed in the tanks to work as cathodes. Electric current is passed through the system of anode-electrolyte-cathode, and the copper is taken from the anodes to build up on the cathodes in a form which is highly purified.

The cathodes eventually are removed and melted down for casting into many commercial shapes. Any precious metals in the copper anodes fall to the bottom of the tank with the last of the impurities and become contained in a deposit which is muddy, from whence they are recovered and refined in a separate process.

The smelting of complex, nickel-copper sulphide ores and the refining of their contained metals involves a much more complicated suite of processes. Nevertheless, the same, principal ideas which are outlined previously for the smelting of copper are to be followed.

In the case of the lead which is derived from galena (lead sulphide) ores, a lead concentrate is roasted in a sintering machine, then fed to a blast furnace along with coke, which acts as a fuel and as an agent of reduction, and many fluxes. The actual reduction to metallic lead is carried out completely in this furnace, which produces an impure lead bullion. The bullion is refined electrolytically and the precious metals contained are recovered in a very similar way as in refining copper.

The treatment of zinc concentrates follows the pattern of roasting to a form in which all of the sulphur has been driven off, and the resulting calcine consists of zinc oxides and sulphates, iron oxides and sulphates and many gangue minerals.

The calcine is leached with sulphuric acid to dissolve the zinc as a sulphate. The leach solution is purified chemically so that a pure zinc sulphate solution may be fed to an electrolytic tank for its final reduction to the pure metal.