Question

How is the technique of complex formation useful in the extraction of metals? Explain with an example.

Answer 1

The technique of complex formation is widely used in the extraction of metals, especially for metals that are difficult to extract by traditional methods like roasting or reduction. Complex formation helps to increase the solubility of metal ions, making it easier to separate and purify the metal from its ore. This technique is particularly valuable when extracting metals from low-grade ores or when selective separation of metals is needed.

• Increased Solubility of Metal Ions: When a metal forms a complex with a suitable ligand, the resulting complex is often more soluble in a given solvent than the free metal ion. This allows the metal to be extracted more efficiently.
• Selective Extraction: By choosing a ligand that selectively binds to the desired metal, it is possible to separate that metal from other metals or impurities in the ore. This enhances the purity and yield of the extracted metal.
• Enhanced Metal Recovery: Once the metal is dissolved as a complex, it can be recovered either by displacement or reduction. The metal is then extracted from the solution in its elemental form.
• Example: Cyanide Process for Gold Extraction a classic example of complex formation in metal extraction is the cyanide process for extracting gold from its ores. Gold, which is often found in low concentrations in ores, reacts with cyanide ions (CN⁻) to form a soluble gold cyanide complex. Steps Involved in Gold Extraction Using Cyanide Complex Formation:
  1. Formation of the Gold Cyanide Complex: Gold metal reacts with cyanide ions (CN⁻) in the presence of oxygen to form a soluble gold cyanide complex. The reaction is as follows:
     \[\ce{Au + 2CN^- -> [Au(CN)2]^-}\] 
     The formation of the [Au(CN)₂]⁻ complex significantly increases the solubility of gold, making it dissolve in the cyanide solution.
  2. Separation from the Ore: The old cyanide complex dissolves in water, allowing gold to be separated from the solid ore. The solution containing the [Au(CN)₂]⁻ complex can then be treated to recover the gold.
  3. Recovery of Gold: To recover the gold, the cyanide complex is reduced using a reducing agent, such as zinc powder, which displaces gold from the complex and restores it to its metallic form:
     \[\ce{[Au(CN)2]^- + Zn -> Au + Zn(CN)^-_2}\]
     The metallic gold is then separated, purified, and refined.