When the former is used it is roasted with calcium sulphate or alkali waste to form a matte which is then blown in a Bessemer converter or heated in a reverberatory furnace with a siliceous flux with the object of forming a rich nickel sulphide.
The process adopted for the Canadian ores, which are poor in copper and nickel, consists in a preliminary roasting in heaps and smelting in a blast furnace in order to obtain a matte, which is then further smelted with a siliceous flux for a rich matte.
This rich matte is then mixed with coke and salt-cake and melted down in an open hearth furnace.
For a wet method of extraction of the matte see Christofle and Bouilhet, French Patent 111591 (1876).
The roasted ore is then smelted to a mixture of copper and iron sulphides, known as copper " matte " or " coarse-metal," which contains little or no arsenic, antimony or silica.