Electrorefining of Copper and Metal Properties

Electrorefining of Copper

• Tough pitch copper (99.2-99.6% Cu) can be refined to 99.98% purity using electrolysis.
• Anodes are thick plates of tough pitch copper.
• Cathodes are thin plates of pure copper coated with graphite.
• Refining tank is a wooden vat lined with lead sheets.
• Electrolyte is 15% CuSO₄ solution and 5-10% sulphuric acid.
• Copper ions are discharged at the cathode, forming pure copper.
• Sulphate ions react with copper at the anode, forming copper sulphate.
• Impurities like Zn, Fe, Ni, Se, Te, and Pb go into solution as sulphates and don't deposit on the cathode.
• Gold and silver create insoluble deposits (anode mud/slime).
• Precious metals (Ag, Au, Pt) are recovered from the anode mud.

Mechanical Properties of Metals

• Metals have various physical and mechanical properties important in engineering.
• Hardness is the resistance to wear, penetration, and scratching. Sodium and potassium are soft, while iron and tungsten are hard.
• Ductility is the ability to be stretched into wires without breaking. Gold, silver, and platinum are highly ductile.
• Malleability is the ability to be hammered into shapes without cracking or rolled to thin sheets. Gold, silver, platinum, aluminium, and copper are malleable.
• Toughness is a combination of strength and elasticity.
• Brittleness is the tendency to break easily.
• Tensile strength is the maximum stress a material can withstand before breaking.
• Weldability is the ability of a material to fuse together.
• Machinability is the ease with which a material can be shaped.
• Tenacity refers to strength and persistence.

Other Refining Methods

• Poling: Uses wood to oxidize impurities, making the metal purer.
• Aluminothermic: Uses a mixture of aluminium and metal oxide (thermite) to reduce the metal oxide. Magnesium wire involved.
• Carbon reduction: Used for metals with high atomic weights, involves high temps. Oxides are converted to metal using a reducing agent (e.g., carbon), typically in blast furnaces, mixing ore, coke, and flux (like limestone).

Chemical Processes

• Calcination: Heating ore in limited air, removes moisture and decomposes some compounds.
• Roasting: Heating ore in air, mainly for sulphide ores to form oxides.
• Reduction: A process of converting metal oxides into the free metal (usually using carbon or another reducing agent). Done in blast furnaces, reverberatory furnaces, or other heating systems.

Various Steels and Alloys

• Different types of steel and alloys have various properties and uses.
• Mild steel is soft, tough, easy to weld, and used for wires and sheets.
• Medium carbon steel is harder than mild steel, heat-treatable, and used for various structures.
• High carbon steel is hard, tough, and resistant to wear, with a keen cutting edge.
• Brass is an alloy of copper and zinc, used for many applications. The composition greatly determines the strengths and weaknesses.
• Bronze is an alloy of copper and tin, with specific strength and corrosion resistance.
• Solders are alloys used for joining metals.
• Duralumin is an alloy of aluminum, copper, magnesium, and manganese, it's corrosion-resistant, strong, and lightweight.
• Wood's Metal is a low-melting fusible alloy, used in safety devices and other applications.