Understanding the Geological Wealth: An Exploration into the Occurrence of Metals in Nature and the Significance of Ores

• Most elements, especially metals, occur in nature in a combined state with other elements. All these compounds of metals are known as minerals. But out of them, only a few are viable sources of that metal. Such sources are called ores 

Extraction of Metals: Mining, Ores Enrichment, and Reactivity Dynamics

• Mining: The process of extracting metal ores buried deep underground is called Mining. The metal ores are found in the earth’s crust in varying abundance. 
  • The extraction of metals from ores is what allows us to use the minerals in the ground. The ores are very different from the finished metals that we see in buildings and bridges. 
• Ores consist of the desired metal compound and the impurities and earthly substances called Gangue.
  • Metals of high reactivity – Na, K, Mg, Al.
  • Metals of medium reactivity – Fe, Zn, Pb, Sn.
  • Metals of low reactivity – Cu, Ag, Hg
• Enrichment of Ores: It means the removal of impurities or gangue from ore through various physical and chemical processes. 
• The technique used for a particular ore depends on the difference in the properties of the ore and the gangue.

Extraction of Metals with Low Reactivity Series: A Mechanistic Insight into Crude Metal Production from Low Reactivity Metal Sulphide Ores

• By self-reduction- when the sulphide ores of less electropositive metals like Hg, Pb, Cu etc., are heated in air, a part of the ore gets converted to oxide, which then reacts with the remaining sulphide ore to give the crude metal and sulphur dioxide. 
  • In this process, no external reducing agent is used.
    • 2HgS(Cinnabar) + 3O2(g) + heat → 2HgO(crude metal) + 2SO2(g)
    • 2HgO(s) + heat → 2Hg(l) + O2(g)
    • Cu2S(Copper pyrite) + 3O2(g) + heat→2Cu2O(s) + 2SO2(g)
    • 2Cu2O(s) + Cu2S(s) + heat → 6Cu(crude metal) + SO2(g)

Extraction of Metals in the Middle of Reactivity Series: Calcination, Smelting and Aluminothermic reaction

• Calcination: Calcination is a process in which ore is heated in the absence of air, or air might be supplied in limited quantities. 
  • Roasting involves heating of ore lower than its melting point in the presence of air or oxygen. 
  • Calcination involves the thermal decomposition of carbonate ores.
• Smelting: It involves heating the roasted or calcined ore (metal oxide) to a high temperature with a suitable reducing agent. 
  • The crude metal is obtained in its molten state.
    • Fe2O3 + 3C(coke) → 2Fe + 3CO2
• Aluminothermic Reaction: it is also known as the Goldschmidt reaction and is a highly exothermic reaction in which metal oxides, usually of Fe and Cr, are heated to a high temperature with aluminium.
  • Fe2O3+ 2Al → Al2O3 + 2Fe + Heat
  • Cr2O3 + 2Al → Al2O3 + 2Cr + Heat
• Cr2O3 + 2Al → Al2O3 + 2Cr + Heat

Extraction of Metals Towards the Top of the Reactivity Series:

• The metals high up in the reactivity series are very reactive. They cannot be obtained from their compounds by heating with carbon. 
  • Example: carbon cannot reduce the oxides of sodium, magnesium, calcium, aluminium, etc., to the respective metals.
• This is because these metals have more affinity for oxygen than carbon. These metals are obtained by electrolytic reduction. 
  • Example: Sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides.
• The metals are deposited at the cathode (the negatively charged electrode), whereas chlorine is liberated at the anode (the positively charged electrode).
• The reactions are:
  • At cathode Na+ + e– → Na
  • At anode 2Cl– → Cl2 + 2e–
• Similarly, aluminium is obtained by the electrolytic reduction of aluminium oxide.

Refining of Metals:

• It is the process of removing impurities or gangue from crude metal. 
• It is the last step in metallurgy and is based on the difference between the properties of metal and gangue.
• Purifying Metals: Electrolytic Refining for Revealing the Purity of Copper, Zinc, and Precious Metals

Extraction of metals is a fundamental process that unveils the treasures hidden within the Earth’s crust. 

• • Metals like copper, zinc, nickel, silver, tin, gold etc., are refined electrolytically.
    • Anode: Impure or crude metal
    • Cathode: A thin strip of pure metal
  • Electrolyte: It is the aqueous solution of metal salt
    • From anode (oxidation): Metal ions are released into the solution from anode.
    • At cathode (reduction): The equivalent amount of metal from the solution is deposited at the cathode.
  • Impurities deposit at the bottom of the anode.

Corrosion:

• Gradual deterioration of a material, usually a metal, by the action of moisture, air or chemicals in the surrounding environment.

Rusting:

• During the corrosion of iron, iron metal is oxidised by the oxygen of air in the presence of water (moisture) to form hydrated iron (III) oxide called rust.

4Fe(s)+3O2 (from air)+xH2O(moisture)→2Fe2O3. xH2O(rust)

4Fe(s)+3O2 (from air)+xH2O(moisture)→2Fe2O3. xH2O(rust)

Oxidative Interactions of Copper with Atmospheric Gases: Formation of Green Copper Carbonate and Hydroxide

• Copper metal when exposed to air turns green in colour due to corrosion. 
• When a copper vessel is exposed to air in the rainy season, the metal reacts with gases and moisture and atmospheric gases to form a mixture of copper carbonate and copper hydroxide. 
  • This gives a green colour to the surface of copper metal.

Cu(s)+H2O(moisture)+CO2(from air)→CuCO3.Cu(OH)2(green)

 The Mechanism Behind Silver Corrosion in the Presence of Hydrogen Sulphide

• When placed in air the Silver object turns black.This is due to the presence of Hydrogen sulphide in the air, the Silver object reacts with the Hydrogen sulphide present in the air. 
• This whole process is actually known as corrosion which is basically the degradation or the destruction of the article when present in the excess moisture and air. 
• In the case of Silver element, corrosion is known as Silver tarnishing. 
  • And so after this corrosion, the black substance formed is known as Silver sulphide.

 Ag(s) + H2S(from air) →Ag2S(black) + H2(g)

Advanced Strategies for Corrosion Prevention in Metals: From Coatings to Sacrificial Protection

• Coating with paints or oil or grease: The application of paint or oil or grease on metal surfaces keeps out air and moisture.
• Alloying: Alloyed metal is more resistant to corrosion. Example: stainless steel.
• Galvanization: This is a process of coating molten zinc on iron articles. Zinc forms a protective layer and prevents corrosion. 
• Electroplating: It is a method of coating one metal with another by the use of an electric current. 
  • This method not only lends protection but also enhances the metallic appearance. 
  • Examples: silver plating, and nickel plating.

• Sacrificial Protection: Magnesium is more reactive than iron. When it is coated on articles made of iron or steel, it acts as the cathode undergoes a reaction (sacrifice) instead of iron and protects the articles.

Exploring the Unique Physical Properties of Nonmetals: An In-Depth Analysis

• Nonmetals are those elements which do not exhibit the properties of metals.