Although the world is using up iron ores at the rate of over 150,000,000 tons a year, the supply keeps increasing from new discoveries and better preparation of lean ores. The principal countries of the globe are well supplied, each with enough in sight to last many years. The United States is especially well provided, not only within its own borders but in adjacent countries. We now have probably 10,000,000,000 tons which we may call the reserve, and our present yearly consumption of some 50,000,000 tons can be increased considerably without fear of exhaustion.
The minerals which constitute the main ores of iron are shown in Table IV. Magnetite and siderite are minerals forming only minor ore deposits as at present available. Hematite is our present chief mineral. The deposits of the hydrous oxides are especially large and have more promise for future usefulness.
In preparing iron ores for the blast furnace, we use drying, washing, and magnetic concentration, calcining, nodulizing, sintering, and briquetting.
Fig. 16 indicates with what seriousness the large companies are beginning to work lower-grade deposits. This particular plant is for washing some 20,000 tons of iron ore each day. It is a carefully designed and costly plant. The fines which are blown out of the furnace and collected in dust catchers and washers are just as good as new ore, if they are agglomerated; the working up of these fines with fresh fine ore is a rapidly developing phase of the smelting.