Aluminum crustal abundance

The extraction of metals fundamentally relies on their availability in nature. Three terms are important while one refers to availability. One is the crustal abundance and the other two are the terms resources and reserves. The average crustal abundance of the most abundant metals, aluminum, iron and magnesium, are 8.1%, 5.0% and 2.1% respectively. Among the rare metals titanium is the most abundant, constituting 0.53% of the Earth s crust No metal can be economically extracted from a source in which its concentration is the same... 

Figure 1 The average and range of concentrations of the elements in the deep ocean from 2000 m to the bottom plotted against their average abundance in the Earth s crust. (Crustal abundances from Taylor (1964) Seawater concentrations from various references.) The dotted line shows a 1 1 slope plotted through the average concentration of aluminum. Elements that plot above this line are enriched in sea water relative to aluminum and their abundance in the crust.

Continued growth in the production of aluminum is unlikely to be hampered by a shortage of mineral since the earth s crust consists of about 8% aluminum, chiefly as aluminosilicates. Even though aluminum is the most abundant metallic crustal element, bauxite ores suitable for aluminum recovery only occur in more limited areas where natural leaching processes have concentrated the aluminum-containing minerals. Since the free metal is chemically reactive it is never found in nature in this form. 

Wet-chemical analyses of aqueous extracts of aerosol samples have established the presence of anions such as sulfate, nitrate, and the halides, and of cations such as ammonium and the ions of the alkali and alkaline earth elements. Table 7-13 shows selected data to illustrate the abundances of important inorganic components in the urban, continental, arctic, and marine aerosols. Included for comparison are the concentrations of silicon, aluminum, and iron, which are the major elements of crustal origin. They occur in oxidized form, such as in aluminosilicates, which are practically insoluble. Taken together, the elements listed in Table 7-13 account for 90% of all inorganic constituents of the atmospheric aerosol. 

Also included in Table 1 is an estimate of the average oceanic residence times for these elements. A shorter residence time indicates a more rapid removal from the oceans. Another way to estimate the relative reactivity of elements with crustal sources is to compare their sea water concentrations with their abundance in the Earth s crust. This is presented in Table 2 (with a normalization to aluminum) and is shown graphically in Figure 1. If variations in the composition of continental materials and differences in the solubility of the elements from these materials are not too great, then to a first approximation the... 

As the twelfth most abundant element in the earth s crust (0.106% in crustal rocks), manganese is found in over 250 different minerals of which some 10-15 are of commercial importance. In primary hydrothermal deposits the metal occurs as silicates, but as it is readily depleted from igneous and metamorphic rocks by weathering, particularly under acid conditions, it is normally found in commercially useful ores as oxides or carbonates, deposited, as are iron and aluminum, under alkaline conditions [9]. 

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