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• Metallurgy is a branch of science that deals with the extraction of pure metals from their respective ores.

Definitions

• Minerals are compounds of various metals found in nature, associated with earthly impurities.
• Ores are naturally occurring minerals from which metals can be extracted profitably and conventionally.
• Flux refers to a substance added to the ore to remove the matrix, resulting in the formation of fusible compound slag.
• Gangue/Matrix describes rocky impurities, including silica, mud, etc., associated with ore.

Steps Involved in Metallurgy

• Concentration of Ore/Ore Enrichment/Ore Dressing refines naturally occurring minerals to increase the concentration of the desired metal compound(s).
• Conversion of Ore into Oxide involves turning metal compounds in the ore into their corresponding oxides.
• Extraction of Metal from Oxide obtains the crude form of the desired metal element.
• Refining of Metal purifies the metal by removing the remaining impurities.

Concentration of Ore

• Ore enrichment/Ore dressing involves the removal of earthly impurities from the ore.
• Magnetic Separation Method removes non-magnetic impurities from a magnetic substance or vice versa; it concentrates iron ore.
• Froth Floatation method enriches sulphide ores by exploiting differences in the wettability of the ore and the gangue.
• The principle of the froth floatation method is based on the ore's preference for oil.
• Hot air blown through the ore-oil mix creates a foam or froth on the water's surface, allowing it to be skimmed off for processing so the ore comes to the surface of water in the form of oil.
• Gravity Separation (Hydrolytic Method) is based on the density of the particles.
• In the gravity separation method, ore is poured over a vibrating slope table, and a jet of water flows over it.
• Denser ore particles settle while lighter impurities flow away with the running water in the gravity separation method.
• Chemical Method employs a chemical substance to concentrate the ore, for example, the use of NaOH for bauxite.
• After concentration, the ore is then said to be free of earthly impurities in the chemical method.

Conversion of Concentrated Ore into Oxide

• After concentrating the ore, it is converted into an oxide, because oxides can be easily reduced to obtain the metal, in most circumstances.
• Roasting involves heating the concentrated ore in the presence of excess air at high temperature with conversion to metal happening later. Roasting is generally used for sulphide ores.
• Calcination involves heating of ore in the absence of air or in a limited supply of air at a temperature below its melting point and is usually carried out for carbonate ores.

Extraction of Metal from its Oxides

• Some elements are extracted from their oxides by electrolytic reduction, specifically for highly reactive and electropositive metals with a strong affinity for oxygen and high oxide stability.
• Certain metals are extracted from their oxides through the use of a reducing agent, used for less reactive metals with less affinity for oxygen, and correspondingly less stable oxides.

Extraction of Aluminium from Bauxite Ore

• Aluminium is extracted from Bauxite ore with the formula Al₂O₃·2H₂O.

Concentration of Bauxite Ore

• A chemical method, specifically the Bayer's process, concentrates Bauxite ores.
• Concentrated NaOH is used to concentrate bauxite ore because bauxite is amphoteric and reacts with NaOH, while impurities like Fe₂O₃ and SiO₂ do not react.

Electrolytic Reactions

• Electrolytic reactions involve the ionization of the alumina and cryolite mixture, leading to the formation of aluminum and oxide ions.

Give Reasons

• Graphite rods act as the anode in Hall-Heroult process and are replaced periodically due to oxidation by oxygen gas which forms carbon monoxide and carbon dioxide.
• Coke powder is sprinkled over the electrolytic mixture in the Hall-Heroult process to prevent heat loss by radiation and burning of the graphite anode due to escaping oxygen.

State The Alloy Use

• Medals - Bronze

• Surgical instruments - Stainless steel

• Electrical fuse - Solder

• Electrical fitting - Brass

• Aircraft - Duralumin

• Cryolite dissolves Al₂O₃ in a molten state.

• NTF (Not To Forget): Cryolite is the solvent for molten Al₂O₃.

• Cryolite and fluorspar lower the melting point of Al₂O₃ from 2050°C to 950°C. They also increase the mixutre’s mobility.

• Cryolite increases the mixture's conductivity.

Important ores

• Aluminium - Bauxite (Al₂O₃·2H₂O) and Cryolite (Na₃AlF₆)

• Zinc - Zinc blende/Zinc Sulphide (ZnS) and Calamine (Zinc Carbonate)

• Haematite (Fe₂O₃) and Magnetite (Fe₃O₄), are both iron ores.

• In alloys, solder containing Tin lowers the materials melting point.

• Zinc in brass imparts hardness.

• Nickel and chromium impart luster to the alloy stainles steel and carbon enhances hardness.

• In Duralumin or Magnesium lightness is imparted to the alloy due to aluminu, with magnesium adding more strength.

• A monovalent metal present in cryolite is Na or Sodium; the trivalent is Al (Aluminium).

• A divalent metal present in fluorospar is calcium.

• A chemical used to concentrate Bauxite ore is a concentrated NauOH (Sodium Hydroxide) solution.

• Main impurities present in Bauxite ore include Iron Oxide and Silicon Dioxide.

• The soluble salt formed when Bauxite ore reacts with concentrated Sodium Hydroxide is sodium aluminate, (NaAlO₂).

• The process used for the enrichment of sulphide ores is Froth Floatation.

• The temperature required to convert aluminum hydroxide to aluminum oxide is eleven hundred degrees Celcius.

• Processes and steps to extract aluminum from aluminum oxide: Hall-Heroult.

• The process used to concentrate bauxite ore: Bayer's Process.

• A key value of Sodium Hydroxide’s role in Bauxite extraction is the amphoteric nature of the Bauxite ore.

• The primary metal and composition is:

  • Brass incorporates Copper and Zinc while adding more hardness to copper.
  • Bronze alloy incorporates Copper, and Zinc in addition to tin.
  • Solder alloy incorporates lead and tin, and is used to lower the melting point of an alloy.
  • Duralumin incorporates alluminium , manganese and copper.
  • Stainless steel: It has iron, nickel, chromium and carbon, which increase the material’s strength.

• An alloy in which one of the metallic components includes mercury is known as an amalgam. A specific type of amalgam, with the formula NaHg, is called "Sodium Amalgam," while another amalgam type, with the formula ZnHg, is identified as "Zinc Amalgam”.

• The alloy form of Zinc blend is Zinc Sulphide.