The roasting of the sulphide nickel ore

The Sudbury ore is first roasted to remove part of the sulphur. The roasting may be conducted in heaps when the agricultural work in the surrounding country is of so little value that there is no risk of compensating damages for the injury to vegetation by the escaping noxious sulphurous fumes. In Norway one plant had to abandon heap roasting, and even smelting could not be conducted in the summer months on account of injury to neighbouring forests. In heap roasting, the ore, crushed to a convenient size, is piled on a bed of brushwood, 5 to 15 feet high, so as to allow a circulation of air. One pile may contain a few thousand tons, and after the brushwood has started the combustion, the heap may burn from six to twenty weeks. Roasting in reverberatory furnaces is more costly, and the same remark applies to special roasting furnaces. In exceptional cases there may be a market for products like sulphite liquor, and sulphuric acid, which can be manufactured from the flue gases up the roasting furnaces. The roasting is not allowed to oxidize fully the ore; enough sulphur is allowed to remain so that it can combine with the nickel, copper, and some of the iron in the first smelting to form a crude sulphide matte.