Section 3: The Process Of Making Iron

SECTION 3 : THE PROCESS OF MAKING IRON Iron is the fourth most abundant element on earth. In nature, iron occurs in compound form, including hematite (Fe2 O3 ), magnetite (Fe3 O4 ), pyrite (FeS2 ), and siderite (FeCO3 ). Apart from being very reactive, namely quickly oxidizing to form rust in humid air, pure iron is soft and ductile. The iron making process is carried out in two stages. 1. Iron Smelting Iron smelting is carried out in a tool called a blast furnace with a height of 40 m and a width of 14 m and is made of bricks that are highly heat resistant. There are three types of materials included in this furnace, namely iron ore contaminated with sand (usually hematite), limestone (CaCO3 ) to bind dirt (flux), and carbon (coke) as a reducing agent. Reaction: 2 FeO3 + 3 C 4 Fe + 3 CO2 The reaction temperature is very high and the furnace pressure is around 1 – 3 atm gauge, so the iron melts and is called pig iron.Molten iron is generally processed directly to make steel, but some is also flowed into molds to make cast iron which contains 3 – 4% carbon and a small amount of other impurities, such as Mn, Si, P. Iron which contains carbon very low (0.005 – 0.2%) is called wrought iron.Limestone functions as a flux, namely to bind acidic impurities, such as SiO2 to form slag. The slag formation reaction is as follows. First the limestone decomposes to form calcium oxide (CaO) and carbon dioxide (CO2 ). Reaction: CaCO3 (s) CaO(s) + CO2 (g) Calcium oxide then reacts with sand to form calcium silicate, the main component in slag. Reaction: CaO(s) + SiO2 (s) CaSiO3 (l) This slag floats on top of the molten iron and must be issued within a certain time interval. 2. Iron-Steel Remelting The steel making process is divided into So several stages are as follows. a. Reducing the carbon content in pig iron from 3 – 4% to 0 – 1.5%, namely by oxidizing it with oxygen. b. Removes Si, Mn, and P as well as other impurities through slag formation. c. Add metal aliases, such as Cr, Ni, Mn, V, Mo, and W according to the type of steel desired. The technology for processing pig iron into steel cheaply and quickly was introduced by Henry Bessemer (1856), but is no longer used. William Siemens in 1860 developed an open herth furnace, and now the furnace that is widely used is the oxygen furnace. Various types of substances are added to steel processing which are useful as "scavangers" (impurity binders), especially to bind oxygen and nitrogen. The most important scavengers are aluminum, ferrosilicon, ferromanganese, and ferrotitan. This substance reacts with dissolved nitrogen or oxygen to form oxides which are then separated into slag. Steel can be classified into three groups, namely:    Carbon steel, consisting of iron and carbon. Stainless steel (stainless steel), has a low carbon content and contains about 14% chromium. Aliase steel, namely special steel that contains certain elements according to the desired properties. To prevent rust on steel, you can do it in various ways, namely:     Adding other metals. Use a protective layer. Using sacrificial metal. Cathodically protects.