Table of contents
This section describes the metallurgy of the transition metal elements. More importantly, it discusses the methods in which transition metal elements (Groups 3-12) are extracted from their metal ores. It concludes with a brief description of steel production using the concepts of equilibrium, thermodynamics, & kinetics.
Transition metal elements, unlike metals of groups 1,2, & Al of group 3, are obtained from a process of extractive metallurgy.
The table above shows some examples of transition metals & their corresponding ores in which they naturally occur.
Processes of Extraction
Concentration (removing the impurities)
Ores mined from the earth’s crust will contain impurities. In fact the desired metal contained in the mineral ore will constitute a small % of the mined material. These impurities are known as gangue (i.e sand,& gravel)
Ore is crushed and heated to a high temp using a strong blast of hot air. The process converts the ores to their oxides which can then be reduced. Eg: The natural occurring ores of zinc are ZnS (sphalerite) & ZnCO3 (smithsonite). When roasted, smithsonite decomposes to to ZnO(s) & CO2(g). The strong blast of hot air involved in roasting supplies O2(g) to the sphalerite, thus, becoming oxidized as a result. The oxidation produces ZnO(s) & SO2(g).
ZnCO3(s) + (heat) → ZnO(s) + CO2(g)
2 ZnS(s) + 3 O2(g) + (heat) → 2 ZnO(s) + 2 SO2(g)
C(s) & CO(g) are often used as reducing agents in simultaneous reactions. Oxides of Cr, V, & Mn are reduced using Al. During the reduction process the metal oxide is heated to a temperature above its boiling point in order to vaporize it & condense as a liquid.
Eg: The ZnO(s) that is produced in the roasting process is combined with C(s)/CO(g) & heated @ a temperature of 1100 oC allowing for reduction & vaporization to occur.
ZnO(s) +C(s) + (heat)→ Zn(g) + CO(g)
ZnO(s) + CO(g)+ (heat) → Zn(g) + CO2(g)
Pyrometallurgy is the processes of roasting an ore @ a high temperature & then reducing its oxide product. Its characteristics include:
The impurities contained in the metal product of the roasting/reduction process are removed.
Eg: The Zn(l) produced in the reduction process often contains impurities of Cd & Pb. Though fractional distillation of Zn(l) will work in the refining process, a more commonly used and efficient method is electrolysis. The ZnO(s) produced from roasting is dissolved in H2SO4(aq) & then Zn(s) powder is added allowing the impurities to be displaced. The solution is then electrolyzed & Zn2+ is reduced to its pure metallic Zn(s) as a result.
Hydrometallurgy is the process of extraction & refining that involves the use of water & aqueous solutions. It is carreid out at moderate temps & is generally carried out in 3 steps:
A rod containing the desired pure metal & impurities is passed through a series of heating coils and cooled again. The process isolates the impurities that concentrate in the molten zones, leaving the portions behind them somewhat more pure. This process is repeated until impurities are moved to the end of the rod and cut off, resulting in an almost completely pure metal rod.
In commercial production sometimes it is important to leave metals in their oxide or naturally occurring ore form in order to produce a metal alloy.
Eg 1: Iron Alloys of Cr,V, & Mn:
Eg 2: Titanium Production(The Kroll Process):
The Kroll process described above is slow & proposes a health/safety risk due to the high- temp. vacuum distillation
Eg 3: Alternative Means of Titanium Production:
The electrolysis of TiO2 pellets:
Eg 4: Copper Production:
Relating Thermodynamics to Extractive Metallurgy
To establish the conditions under which a reducing agent will completely reduce an oxide of a transition metal to its desired pure metal we must look @ the tendencies of the metal & reducing agent to undergo oxidization. This is due to the fact that both the oxide & reducing agent are competing for Oxygen atoms. The ability of a metal & reducing agent to undergo oxidization is represented by the change in Gibbs Free Energy related to Temperature. For the reducing agent to be sufficient in the reduction of the transition metal, the reaction must be spontaneous. Many times, the ore must be heated to a high temperature make the overall reaction spontaneous.
Eg 2: For reaction that occurs with the reduction of Mg oxide using Carbon ( 2MgO(s) + 2 C(s) → 2 Mg(g) + 2 CO(g)), spontaneity only occurs for temps exceeding 1700 oC. Since the temperature is extremely high it is not used in the production of pure Mg metal.
Iron Metallurgy & Steel Production
The figure above illustrates the reactions that take place in the different regions of the blast furnace. Iron ore, coke, & limestone are added to the top of the blast furnace. The bottom of the furnace has a blast of hot air & is the region where the highest temperatures are attained. The varying temperature regions of the blast furnace allow for reduction, slag formation, formation of reducing agents, & extraction of pig iron.
Fe2O3(s) + 3CO(g) → 2 Fe(l) + 3CO2(g)
The primary components of the blast furnace are:
Many methods of extractive metallurgy may be applied to get a pure metal from its naturally occurring ore. First ores must be concentrated and separated from their earthly impurities. Concentration of ores may be achieved by froth flotation in which an ore is contained in a froth that floats at the top of a water vat. After the ore has been concentrated it must be roasted to a high temperature allowing for the desired metal to be oxidized. Once the metal is oxidized it is reduced by a reducing agent. Reduction may require the metal oxide to be heated at a high temperature. The metal must be further refined to remove all of the impurities that it may contain. Refining a metal can be accomplished by electrolysis or zone refining. Certain ores such as those of copper and titanium require special treatment before they can be refined. The extraction of iron ore is particularly important for commercial uses because of the mass production of its alloy, steel.
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