Lake Superior Paper - The Constitution of Mattes Produced in Copper-Smelting

The term a matte " is applied to smelting-products so extremely diverse in composition and physical properties that it appears impossible to devise any generic formula to represent, chemically, the manner in which the varied proportions of the almost unlimited possible constituents combine with each other. Mattes produced in copper-smelting, in distinction from those produced in smelting-operations in which the recovery of cop per is secondary to that of other metals, cover a narrower range in composition. The copper-content of such mattes vary from 20 to 80 per cent., and even this range is much smaller in general practice since it is found advantageous, when possible, to produce mattes with about 50 per cent. of copper in the first operation. Further, it is unusual that arsenic or antimony occurs in copper-ores in sufficient proportions to form arsenides or antimonides in such quantities that they will separate out from the furnace-products, as is common in lead-smelting. Generally, the mattes produced in copper-smelting are composed mainly of copper (usually greater than 35 per cent.), iron and sulphur, the remaining elements being usually in proportions sufficiently small to allow of their treatment as impuritiee, rather than as essential constituents of the mattes. In modern practice of smelting copper-ores in blast-furnaces the tendency is to approach pyritic smelting as nearly as possible, the furnaces being low and the air supplied being largely in excess of that required for complete combustion of the carbonaceous fuel. Hence, the atmosphere of the blast-furnace thus used is usually oxidizing or nearly neutral, and, as a consequence, the reduction of metallic iron that was a necessary evil of former practice is of unusual occurrence in operations where the main object is the recovery of copper. Hearth-accre-