Rhonda Sinders, age 12, of Indianapolis, Indiana, for her question.:
How do they produce iron?
Our man made plastics are actually synthesized, or chemically remodeled, from simpler substances, most of them extracted from hydrocarbons in coal and petroleum. The basic raw materials are provided by nature. The same thing applies to the story of iron. The ore that provides the basic ingredient for making iron and steel is produced by the patient earth. Our part of the project is to find it and process it to make our mighty bridges and tall towers, our pounding hammers and whirling wheels and all those other sturdy objects.
Iron is spread thinly almost everywhere, in rocks and gravels, sands and clays and many other minerals. The total amount makes up about five per cent of the earth's crust. It is, of course, a metallic element that tends to oxidize in moist air and form compounds of rusty iron oxides. It has been there since the earth's crust formed. And here and there through the ages, it has been modeled and remodeled by crustal activities. We find it in sedimentary rocks, in fire formed lavas and also in remade metamorphic minerals.
But in nature, we never find this metallic element alone. It is always in a chemical compound with oxygen, nitrogen, silicon, sulphur or other elements. The job of separating it is complex and costly and most of it is spread too sparsely to make this worthwhile. But in at least 40 countries there are mineral deposits that contain a very high concentration of iron. These are the valuable ores that we mine and process to make objects of iron and steel.
In North America, the most commonly used ores are the iron oxides hematite, magnetite and siderite and also pyrite which is a compound of iron and sulphur. Our major deposits are around the Great Lakes, in the western and also the eastern mountains. The mines may be open surface pits, or shafts and tunnels dug down to reach deposits buried deep in the ground. The job calls for drills and mighty shovels, crushers and trucks and usually streams to toe the ore to gigantic processing mills.
In these common ores, the iron content is from 50 to 70 per cent. The rocky chunks are loaded into skyscraper blast furnaces, along with lumpy limestone and cindery coke. To treat seven tons of ore, a furnace requires three tons of coke, a ton of limestone, four tons of b7~sting air and streams of water. When the hefty ingredients are heated to about 3,000 degrees Fahrenheit, chemical reactions in the furnace separate the unwanted ingredients and melt the iron. The molten iron sinks to the bottom and is drained off to cool in heat resistant containers.
It is estimated that our rich iron ore deposits may meet our needs for several centuries. But our needs are accelerating and the supplies will dwindle. Modern industry already is using taconite and other low grade ores with iron contents of 25 to 40 per cent. However, the iron is extracted by new and elaborate processes that are even more costly than the faithful blast furnace.