18.2 Occurrence and Preparation of the Representative Metals

Representative metals occur naturally in minerals and ores. Extracting these metals involves various metallurgical processes, including pyrometallurgy, hydrometallurgy, and electrometallurgy. These methods are crucial for obtaining pure metals from their natural sources.

Electrolytic isolation is used for reactive metals like sodium and aluminum, while chemical reduction is employed for metals like magnesium, zinc, and tin. Each method has specific steps and reactions tailored to the properties of the metal being extracted.

Occurrence and Extraction of Representative Metals

Representative metals in minerals

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• Representative metals naturally occur as minerals and ores
  • Minerals are inorganic solids with a specific chemical composition and crystalline structure that form naturally (halite, magnesite)
  • Ores are rocks or sediments that contain valuable minerals, typically metals, in high enough concentrations to be economically extracted (bauxite, galena)
• Common minerals and ores of representative metals include
  • Sodium found in halite (NaCl) and trona (Na3(CO3)(HCO3)·2H2O)
  • Magnesium found in dolomite (CaMg(CO3)2) and magnesite (MgCO3)
  • Aluminum found in bauxite (###Al2O3·nH2O_0###)
  • Potassium found in sylvite (KCl) and carnallite (KMgCl3·6H2O)
  • Calcium found in limestone (CaCO3) and gypsum (CaSO4·2H2O)
  • Tin found in cassiterite (SnO2)
  • Lead found in galena (PbS)

Metallurgy: Extraction and Purification of Metals

• Metallurgy encompasses various processes for extracting and purifying metals from their ores
• Pyrometallurgy involves high-temperature processes such as smelting to extract metals from their ores
• Hydrometallurgy uses aqueous solutions to extract and recover metals from ores or concentrates
• Electrometallurgy employs electrochemistry for metal extraction and refining

Electrolytic isolation of reactive metals

• Electrolytic processes use electrical energy to drive nonspontaneous chemical reactions that decompose molten salts or solutions to produce pure metals (sodium, aluminum)
• These processes involve redox reactions, where the metal ions are reduced at the cathode
• Extraction of sodium by the Downs process involves
  1. Electrolyzing a molten mixture of NaCl and CaCl2
  2. Producing liquid sodium metal at the cathode and chlorine gas at the anode according to the reaction $\text{NaCl} \xrightarrow{\text{electrolysis}} \text{Na} + \frac{1}{2}\text{Cl}_2$
• Extraction of aluminum by the ###Hall-Héroult_process_0### involves
  1. Using molten cryolite (Na3AlF6) as a solvent for alumina (Al2O3)
  2. Reducing aluminum ions to liquid aluminum metal at the cathode via electrolysis
  3. Producing oxygen at the anode which reacts with the carbon anode to form CO2 according to the overall reaction $\text{Al}_2\text{O}_3 \xrightarrow{\text{electrolysis}} 2\text{Al} + \frac{3}{2}\text{O}_2$

Chemical reduction for metal production

• Chemical reduction methods use a more reactive metal or compound to reduce the metal compound to its elemental form (magnesium, zinc, tin)
• Magnesium production by the Pidgeon process involves
  • Reducing magnesium oxide (MgO) with ferrosilicon (FeSi) at high temperatures according to the reaction $\text{MgO} + \text{FeSi} \xrightarrow{\Delta} \text{Mg} + \text{Fe} + \text{SiO}_2$
  • Condensing and collecting the magnesium vapor produced
• Zinc production by roasting and reduction involves
  1. Roasting zinc sulfide (ZnS) in air to form zinc oxide (ZnO) according to the reaction $2\text{ZnS} + 3\text{O}_2 \xrightarrow{\Delta} 2\text{ZnO} + 2\text{SO}_2$
  2. Reducing zinc oxide with carbon monoxide (CO) in a blast furnace according to the reaction $\text{ZnO} + \text{CO} \xrightarrow{\Delta} \text{Zn} + \text{CO}_2$
• Tin production by carbothermic reduction involves
  • Reducing cassiterite (SnO2) with carbon in a blast furnace according to the reaction $\text{SnO}_2 + 2\text{C} \xrightarrow{\Delta} \text{Sn} + 2\text{CO}$
  • Collecting molten tin at the bottom of the furnace