Iron ores, Chapter

The negative sign of AG° implies that although Fe203 does not spontaneously decompose, it can be converted to iron by reaction with carbon monoxide. This is in fact the reaction used in the blast furnace when iron ore consisting mainly of Fe203 is reduced to iron (Chapter 20). 

The difficulty in recognizing redox reactions is illustrated by two of the reactions that occur during the extraction of iron from iron ores, a process that we describe in detail in Chapter 20 ... 

Chapter 26 Fluid-Particle Reactors Design Iron ore Coke... 

By convention, rocks are divided into three groups magmatic (volcanic or extrusive and plutonic or intrusive), metamorphic and sedimentary rocks. Iron ores being the source of iron as a metal, are also rocks and are common in all three groups. Most rocks contain iron oxide minerals of varying nature and abundance. This chapter collects information about their occurrence (Tab. 15.1), properties and formation. 

Fuel uses are a potential application which would require substantial volumes of methanol. As mentioned earlier they are reviewed in the following chapter. A fuel related potential use of methanol is as a replacement for water used to carry coal in pipelines. Methanol is being considered for this use because it would eliminate a demand for water, which is often scarce in areas where coal is mined, and methanol could be burned as a fuel with the coal at its destination. Methanol has also been touted as a good feedstock for gases used in the direct reduction of iron ore. If this use of methanol is realized, it will not be before the mid to late 1980 s. Other potential new uses for methanol include a feedstock for ethylene and propylene production (9) and a feedstock for gasoline production (10). 

In this chapter, we have attempted to relate current ideas on the roles of microorganisms to the genesis of two very different types of iron deposits — one very ancient (Precambrian BIF s) and one modem (ferromanganese nodules and crusts) one comprising the most extensive resource of iron ore on land, and the other comprising the most extensive mineral deposit in the oceans. We can conclude that organisms were almost certainly involved, directly or indirectly, in the formation of both types of deposits, but exactly how and to what extent they are involved remain unanswered questions even for modem deposits. 

Lime, CaO, is added to molten iron ore during the manufacture of pig iron. It lowers the melting point of the mixture. The metallurgy of iron is discussed in more detail in Chapter 22. 

The true flotation technique is described in Chapter 34. This technique is of tremendous importance industrially. Two examples are the removal of industrial grade diamonds from the surrounding granite and the concentration of taconite iron ore to an economically high percentage of iron. This can become quite involved. The surface of the solid particle must be made attractive to the gas bubble. This may require an activator on the surface to hold the collector that will then attract the gas bubble. Much chemistry is involved. 

Nuclear reactions of this type do not naturally occur on the earth today. The temperature is simply too low. As a result we have, for the most part, a collection of stable elements existing as chemical compounds, atoms joined together by chemical bonds while retaining their identity even in the combined state. SUicon exists all around us as sand and soil in a combined form, silicon dioxide most metals exist as a part of a chemical compound, such as iron ore. We are learning more about the structure and properties of these compounds in this chapter. 

In any case, three major uses of quicklime are listed. The calcium oxide combines with various oxides to rid iron ore of its silicon, aluminum, and phosphorus impurities, as shown in Equation (13.22) in Figure 13.11. It is a major component (with sodium carbonate from the Solvay process) for the glass industry. (More on this in Chapter 15 when we discuss silicates.) Finally, it is used to make calcium carbide that in turn is used to produce acetylene [Equation (13.23b) in Figure 13.11]. 

One last word about nonspontaneity— nonspontaneous process is not impossible. For example, the extraction of iron metal from iron ore is a nonspontaneous process it does not happen if the iron ore is left to itself, but that does not mean it is impossible. As we will see later in this chapter, a nonspontaneous process can be made spontaneous by coupling it to another process that is spontaneous or by supplying energy from an external source. Iron can be separated from its ore if external energy is supplied, usually by means of another reaction (that is itself highly spontaneous). 

We listed many examples early in this chapter, and they can be quite different in practice, from the msting of iron to the toasting of dough to the roasting of ore. The reactant A could be a gas or a liquid, and the film could be a sohd or liquid. The migration of A through the reacted film could be diffusion of A dissolved in C or permeation of A through a porous film of C. We describe this by a diffusion coefficient D s, but the value of D/ s and the mechanism by which transport occurs will not be discussed here. 

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