Impurities iron ore

A sample of an impure iron ore is believed to be approximately 55% w/w Fe. The amount of Fe in the sample is to be determined gravimetrically by isolating it as Fe203. How many grams of sample should be taken to ensure that approximately 1 g of Fe203 will be isolated ... 

O Historically, the extraction of a metal from its ore was known as reduction. One way to reduce iron ore on an industrial scale is to use a huge reaction vessel, 30 m to 40 m high, called a blast furnace. The reactants in a blast furnace are an impure iron ore, such as Fe203, mixed with limestone, CaC03, and coke, C, which is made from coal. The solid mixture is fed into the top of the blast furnace. A blast of very hot air, at about 900°C, is blown in near the bottom of the furnace. The following reactions occur. 

An iron ore sample contains Fe203 plus other impurities. A 752-g sample of impure iron ore is heated with excess carbon, producing 453 g of pure iron by the following reaction ... 

What is the mass percent of Fe203 in the impure iron ore sample Assume that Fe203 is the only source of iron and that the reaction is 100% efficient. 

Methods exist to make impure iron direcdy from ore, ie, to make DRI without first reducing the ore in the blast furnace to make pig iron which has to be purified in a second step. These processes, generally referred to as direct-reduction processes, are employed where natural gas is readily available for the reduction (see also Ironbydirectreduction). Carbonization of iron ore to make iron carbide as an alternative source of iron units is in its infancy as of the mid-1990s but may grow. 

Smelting iron ores produces large amounts of sulfur dioxide, which is catalytically oxidized to sulfur trioxide for sulfuric acid production. This process is declining due to pollution control measures and the presence of some impurities in the product acid. 

The calcium oxide formed reacts with impurities in the iron ore to form a glassy material called slag. The main reaction is with Si02 to form calcium silicate, CaSi03 ... 

Since the reactions (15), (16), and (17) require successively higher temperatures, the blast furnace temperature is kept highest near the bottom of the furnace. Near the bottom, the temperature, is sufficiently high that the impure iron—saturated with carbon—collects there as a molten liquid. The slag, which is mainly calcium silicate, CaSi03, removes any sand in the ore through reaction with limestone, CaC03. 

The production of steel begins when iron ore is fed into a blast furnace (Fig. 16.39). The furnace, which is approximately 40 m high, is continuously replenished from the top with a mixture of ore, coke, and limestone. Each kilogram of iron produced requires about 1.75 kg of ore, 0.75 kg of coke, and 0.25 kg of limestone. The limestone, which is primarily calcium carbonate, undergoes thermal decomposition to calcium oxide (lime) and carbon dioxide. The calcium oxide, which contains the Lewis base O2", helps to remove the acidic (nonmetal oxide) and amphoteric impurities from the ore ... 

The iron formed in a blast furnace, called pig iron, contains impurities that make the metal brittle. These include phosphorus and silicon from silicate and phosphate minerals that contaminated the original ore, as well as carbon and sulfur from the coke. This iron is refined in a converter furnace. Here, a stream of O2 gas blows through molten impure iron. Oxygen reacts with the nonmetal impurities, converting them to oxides. As in the blast furnace, CaO is added to convert Si02 into liquid calcium silicate, in which the other oxides dissolve. The molten iron is analyzed at intervals until its impurities have been reduced to satisfactory levels. Then the liquid metal, now in the form called steel, is poured from the converter and allowed to solidify. 

Sulfides Metal ion(s) + sulfur ion Galena (composed of lead sulfide), a metal ore, from which lead and also silver (which occurs in galena as an impurity, are extracted Pyrite (composed of iron sulfide), an iron ore... 

Detecting known substances, and determining their quantity, is also important. In synthetic research, it is essential to know the relative proportions of various reaction products. In manufacturing, it is important to detect any impurities in the product and to determine whether they are present in a significant amount. Analytical characterization is critical in pharmaceutical products, for instance. Products for practical uses—paint or adhesives, for example—will typically consist of several components. For proper and reliable performance it is important to measure the amounts of each of the components as part of a manufacturing quality control system. Manufacturers also commonly need to analyze the raw materials they receive, measuring the amounts of various substances in them to be sure that the material meets their requirements. Before it can be correctly processed into steel, iron ore must be analyzed to determine how much of other components need to be added to produce a metal alloy of the desired composition and properties. 

Iron ore Ores of different grades are available in restricted quantities. Different ores have varying percentages of iron and different types and amounts of impurities. The proportion of each ore that occurs in the final hot metal is assumed to be fixed by its composition. For example, the amount of fine ore must be limited because too much can disrupt the flow of gas through the furnace and limit production. 

Table 5.1 summarizes the uses of lime. Lime is used as a basic flux in the manufacture of steel. Silicon dioxide is a common impurity in iron ore that cannot be melted unless it combines with another substance first to convert it to a more fluid lava called slag. Silicon dioxide is a Lewis acid and therefore it reacts with the Lewis base lime. The molten silicate slag is less dense than the molten iron and collects at the top of the reactor, where it can be drawn off. Over 100 lb of lime must be used to manufacture a ton of steel. 

Valuation of Iron Ores.—The value of the ore depends npon two conditions —first, the quantity of iron it oontains, and, second, the amount of impurities Or matrix. The character and properties of the impurities, and the extent to which they will interfere with the quality of the iron when manufactured, must also be considered. To ascertain these points, the ore must be subjected to testing or assaying. There-are two methods of assaying, termed respectively the wot and dry. 

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