INDUSTRIES.
The improvements in recent years in the sul phide smelting have consisted in the adoption of mechanical roasters, the arrangement of the furnaces so that the product can be trans ferred from one department to another with minimum loss of heat and with the least pos sible handling, and the enlargement of the smelt ing units; for example, some reverberatory smelting furnaces now have a hearth measure ment of 25 X 146 feet, and a smelting capacity of over 1,000 tons daily. Blast furnaces may now be built of unlimited length, the largest measuring 56 inches by 87 feet at the tuyeres with a daily capacity of 3,000 tons of charge; converters holding over 100 tons of matte have been built, but the most economical size seems to be of a capacity of about 80 tons. Other eco nomical practices are the handling of slag, ashes, and other waste products in sluice boxes by water; the handling of materials generally by machinery; and the saving of waste heat from smelting furnaces; all the modern appli ances for handling materials, water, steam, electricity and compressed air are called upon to assist in the operation of modern plants. Fuel oil and pulverized coal have been applied to reverberatory furnaces with great success in recent years. Developments looked for in the near future are the substitution of electric fur naces for the blast furnaces and an extension of the hydro-metallurgical processes.
The industry is prosecuted on a gigantic scale in the United States; the amount of capi tal invested is enormous, the average cost of a sulphide smelting establishment being $1,000 for each ton of ore treated daily. The largest plant constructed to date (1919) is the Anaconda Reduction Works at Anaconda, Mont., having a daily capacity of 18,000 tons of ore and produc ing about 15 per cent of the world's output of copper. A brief description of this smelter will give a general idea of the operation of a modern copper sulphide smelting plant, and the immense size of the plant. The copper ores,
delivered on the °high line by the Butte, Ana conda and Pacific Railway, are first enriched by mechanical concentration. In this process the useless part of the ore is separated from the valuable portion by making use of differences in specific gravity, the useless part being sluiced to the dump and the 3 per cent of copper in the ore becoming 8 per cent in the concentrated product.
The fine portion of this product is roasted, to remove 80 per cent of its sulphur, and is then smelted in reverberatory furnaces. The coarser portion goes to the blast furnaces, in which the burning off of 60 per cent of the sulphur and the melting of the charge are done in one operation. The reverberatories and blast furnaces produce matte the copper content of which ranges from 40 to 50 per cent), and make slag as a waste product which is sluiced to the dump. The matte is treated in converters, which deliver an impure copper. The last stage is reached in the refining furnaces, which turn out the commer cially pure metal; and this is shipped to the company's electrolytic plants at Great Falls, Mont., and Perth Amboy, N. J., where the silver and the small amount of gold are separated. The metals are then marketed.
The zinc ore is increased from an assay of 12 per cent zinc to 32 per cent by mechanical concentration. The metallurgical treatment of this concentrate is conducted at the company's plant in Great Falls, except as noted under the subject of roasting.
Hofman, H. 0.,