Earth's Composition and Element Distribution

Elemental Abundance

• The abundance of an element varies in different regions of the Earth, influenced by their physical and chemical properties.
• Dense Group 8B(8) to 8B(10) metals are abundant in the Earth's core.
• The Earth's crust predominantly contains nonmetals, metalloids, and light active metals.

Earth's Compositional Phases

• Gravity and convection during Earth's cooling process led to separation of materials by density, forming different layers.
• The core is primarily composed of iron (Fe).
• The mantle and crust comprise the outer silicate phase, containing oxygen combined with silicon, aluminum, magnesium, and some iron.
• The sulfide phase, of intermediate density, consists mostly of iron sulfide with traces of other elements.

Distribution of Elements

• Elements' distribution in Earth's layers depends on their chemical affinity for the three phases: silicate, iron, and sulfide.
• Elements with low or high electronegativity tend to form ionic compounds and are concentrated in the silicate phase, including active metals and nonmetals.
• Metals with intermediate electronegativity dissolve in the iron phase.
• Lower-melting transition metals and many elements in Groups 11 to 16 concentrate in the sulfide phase.

Sources of Elements

• Oxygen (O2), nitrogen (N2), and noble gases (excluding helium) are obtained from the atmosphere.
• Some elements like sulfur, carbon in coal, and unreactive metals occur naturally in their uncombined state.
• Most elements exist in ores, which are natural compounds or mixtures requiring extraction.

Metallurgy

• Metallurgy deals with the extraction and utilization of metals.
• Pyrometallurgy utilizes heat to extract metals.
• Electrometallurgy involves electrochemical processes.
• Hydrometallurgy relies on aqueous solution chemistry.
• Extracting a pure element from its ore involves various stages starting with mining.
• Mineral refers to the element of interest within the ore, while gangue is the non-valuable portion.

Pretreating the Ore

• Magnetic attraction separates magnetic minerals from gangue.
• Density separation utilizes differences in density, as seen in panning for gold.
• Flotation uses oil-detergent mixtures to create a slurry that, when mixed with air, produces a mineral-rich froth.
• Leaching involves forming a water-soluble complex ion.

Converting Minerals to Compounds

• Roasting uses high-temperature heating in excess of air to convert minerals to oxides for easier reduction.
• Roasting is crucial for purifying metals, removing volatile impurities and moisture.

Converting Minerals to Metal

• Chemical redox methods, often involving reduction, are used to convert minerals to the desired metal.
• Smelting involves heating an oxide with a reducing agent, like carbon, to obtain the metal.
• Less active metal oxides are reduced with hydrogen instead of carbon.
• More active metals can be used as reducing agents.
• Electrochemical redox methods provide an alternative for metal extraction.

Leaching Gold

• Cyanide leaching is the widely used hydrometallurgical process for extracting gold from ores and concentrates.
• Despite its hazards, cyanide leaching remains the most economical method for gold extraction.

Common Mineral Sources

• Gibbsite (in bauxite) for aluminum: Al(OH)3
• Barite for barium: BaSO4
• Beryl for beryllium: Be3Al2Si6O18
• Limestone for calcium: CaCO3
• Hematite for iron: Fe2O3
• Cinnabar for mercury: HgS
• Halite for sodium: NaCl
• Galena for lead: PbS
• Cassiterite for tin: SnO2
• Sphalerite for zinc: ZnS