Metal Extraction and Processing: From Ore to Finished Product

Posted on Dec 11, 2024 in Chemistry

Metal Extraction and Processing

10. Factors Determining Profitable Ore Extraction

Profitability in ore extraction depends on several key factors:

  • Location: Depth, land consistency, ease of transport, etc.
  • Extraction Method: Quarrying, mining, etc.
  • Gangue and Ore Quality: A minimum concentration of 40-50% is often required, with low sulfur content.
  • Socioeconomic Factors: Current supply and demand.

Role of Limestone and Coke in Cast Iron Production

Coke, produced by coal combustion, provides the heat for reduction reactions (deoxygenation) and melts the ore. Limestone (dolomite) lowers the melting point of the gangue, creating a fluid slag that separates from the iron.

Blast Furnace Process

  1. Preparation: Close cleaning gates, open slag and iron exits, and air nozzles.
  2. Fuel Loading: Add fuel and ignite.
  3. Heating: Gradually introduce coke in thirds, ensuring the fusion zone is filled.
  4. Continuous Operation: Add remaining components (coke, limestone) and continuously remove iron and slag.

13. Steel Production Procedures

Blowing Procedures

Oxygen Furnace (LD)
  • Bottom lined with basic refractory bricks.
  • Produces high-quality steel.
  • Batch production of up to 300 tons.
Operation
  • Furnace tilted for charging.
  • Liquid iron, fluxes, and/or scrap added.
  • Carbon and alloying elements added.
Converters (Bessemer and Thomas)
  • Similar to LD, but uses oxygen-nitrogen mix. Largely obsolete due to nitrogen’s effect on steel brittleness.
  • Bessemer converter used for low sulfur/phosphorus ores; Thomas converter (with dolomite lining and lime addition) removes phosphorus and sulfur.

Open-Hearth Processes

Martin-Siemens Oven
  • Mixes iron with scrap steel (lower carbon content) on an acid (for sulfur/phosphorus removal) or basic tray.
  • Scrap steel and limestone added, followed by molten iron.
  • Regular sampling for process control.

Electrical Procedures

Electric Oven
  • Firebrick lining.
  • Capacity up to 100 tons.
  • Primarily uses selected scrap steel and alloying materials (Ni, Cr, Mo, etc.).
Operation
  1. Scrap and flux (lime) added.
  2. Graphite electrodes melt the metal with electric arcs.
  3. Slag removed, carbon added, and mass heated.
  4. Ferroalloys (ferrosilicon, ferromanganese), silica, and lime added for sulfur removal.
  5. Molten steel poured into a ladle for casting.

14. Foundry Classification by Carbon Percentage

Cast iron contains 2-5% carbon and is generally brittle and hard, but resists compression well. Classifications include white, gray, malleable, and ductile.

  • White Cast Iron: Carbon combined with iron as cementite. Brittle, tough, hard to machine. Used in high-abrasion parts.
  • Gray Cast Iron: Carbon in graphite sheets. Brittle, machinable, malleable, absorbs vibrations well. Used for complex shapes.
  • Malleable Cast Iron: Treated white cast iron with improved malleability and ductility. Used in parts not subject to high mechanical forces.
  • Ductile Iron: Gray iron with added magnesium and nickel, creating nodular graphite. Similar properties to malleable iron, but with higher strength and ductility.

15. Casting/Molding Process

Casting involves pouring molten material into molds. Ideal for lower melting point materials like cast iron. Operations include:

  1. Metal Melting: Furnaces or converters, transferred in ladles or torpedo cars.
  2. Model Preparation: Usually wooden, considers material contraction and design limitations.
  3. Mold Preparation: Based on the model, includes a trough (inlet) and riser (gas outlet).
  4. Casting Methods:
    • Direct casting: Mold filled from the top.
    • Siphon/bottom pouring: Improved removal of impurities, but potential for solidification in troughs.
    • Side pouring: A compromise between the two methods.
    • Continuous casting: Molten metal poured into a moving mold, minimizing waste.
  5. Finishing: Mold removal, cleaning, deburring, heat treatment to remove internal stresses.

16. Deformation Processes

Deformation processes shape material through hot or cold deformation:

  • Forging: Plastic deformation (hot or cold) without melting.
  • Rolling: Compressing metal (hot or cold).
  • Hot Stamping: Mechanized forging for larger pieces.
  • Cold Stamping: Deforming rolled sheet metal (folding, punching, pressing, stretching, shearing).

17. Chip Removal Processes

Uses machine tools (planer, shaper, lathe, drill, mill, grinder) for precise part manufacturing.

18. Treatments for Improved Mechanical Properties

Thermal and thermochemical treatments enhance mechanical properties:

  • Hardening: Heating (900°C) and quenching in liquid. Increases hardness and strength, but also brittleness.
  • Tempering: Similar to hardening, but lower temperature (700°C). Reduces brittleness.
  • Annealing: Heating (1100°C) and slow cooling. Softens material.
  • Cementation: Heating steel in contact with carbon. Increases surface hardness.