At present, in the iron and steel industry, the main use of calcium metal (intermediate alloy containing calcium) is to process into calcium particles, special high-temperature magnesium oxide and then made into calcium iron wire or pure calcium wire, and ultimately used for steel refining outside the furnace, its role is desulfurization, deoxidation, increase the fluidity of molten steel, promote the rapid floatation of inclusions in molten steel. Usually used in the production of high-quality steel; used as dehydrating agent, anhydrous alcohol; in the petroleum industry, used as a desulfurizing agent, in the metallurgical industry, used to deoxidize or desulfurize. However, calcium compounds are widely used, especially in the construction industry.
Let's start with marble. Marble is a very valuable building material; it is named because it is abundant in Dali County of Yunnan Province, and it is also produced elsewhere, but also called "marble". Marble is a kind of limestone. The chemical composition of limestone is calcium carbonate. Limestone is mostly bluish gray, hard and crisp. In nature, often a large area of strata is composed of limestone. Limestone is used to repair reservoirs, paving roads, and building bridges. Like the famous "red flag canal" in Nanlin County, it is made of limestone produced locally.
Limestone is mixed with coke in lime kilns and burned to make quicklime (Figure 40). The chemical composition of quicklime is calcium oxide. Quick lime is a white stone. It's interesting. It reacts violently with water, turning it into a white powder, hydrated lime, and releasing a lot of heat (Fig. 41). On construction sites, you can often see people adding water to lime. At this point, if you put an egg in it, it is enough to cook it. Hydrated lime is composed of calcium hydroxide and soluble in water. Lime water, a solution of calcium hydroxide and a lime water brush on the wall, is not very white at first, but will become more and more white after a while. It's an interesting cycle: ripe lime reacts with carbon dioxide in the air and becomes calcium carbonate again; in lime kilns, however, limestone (calcium carbonate) is used to burn quicklime. When burning, limestone releases carbon dioxide and becomes calcium oxide.
Calcium sulfate is also an important compound of calcium, commonly known as gypsum, slightly soluble in water. In industry, plaster is used to mold gold, silver, aluminum, magnesium, copper and other non-ferrous alloys. Gypsum is also used for making gypsum figures. Natural gypsum, however, is not a dense snow-white solid, but rather a paraffin-like appearance, it is a crystalline water. When gypsum is burned, it becomes mature gypsum.
Natural water, such as river, lake and river water, often contains some soluble calcium compounds, such as calcium bicarbonate. This kind of water is called hard water. Hard water gives people a lot of trouble, with it boiled water, the original dissolved in the water of calcium bicarbonate heated will be converted into insoluble calcium carbonate, precipitation, into pot scale. If the boiler scale in the factory is too thick, it will not only waste fuel, but even cause explosion due to uneven heating. Washing clothes with it, calcium bicarbonate and soap will act as a chemical precipitation of calcium stearate, waste of soap. In order to overcome these shortcomings of hard water, people often need to soften hard water, such as adding soda (sodium carbonate), can make calcium bicarbonate into calcium carbonate precipitation, filter out. Some also use boiling to soften hard water.