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Question

What is meant by leaching?


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Solution

  1. Leaching is a method used in the concentration of ore.
  2. It involves dissolving the ore in a suitable solvent in which the impurities remain insoluble.
  3. For example - Bauxite which is an ore of Aluminium is treated with concentrated NaOH at a temperature ranging from 473-523K forming a compound of Aluminium while other impurities (Fe2O3,TiO2) remain insoluble. Al2O3.2H2O(s)+2NaOH(aq)+H2O(l)473-523K2Na[Al(OH)4](aq)BauxiteSodiumhydroxideSodiumaluminate
  4. Silica (SiO2) which is one of the impurities forms Sodium Silicate and dissolves in the Sodium hydroxide solution.SiO2(s)+2NaOH(aq)473-523KNa2SiO3(aq)+H2O(l)SilicaSodiumhydroxideSodiumsilicate
  5. Sodium aluminate solution is then treated with CO2 forming hydrated Alumina. 2Na[Al(OH)4](aq)+2CO2(g)Al2O3.xH2O(s)+2NaHCO3(aq)SodiumaluminateHydratedaluminaSodiumbicarbonate
  6. Hydrated Alumina is washed, purified and undergoes heating to form pure Alumina.
  7. This process is used to extract pure Alumina from Bauxite ore. Hence, Leaching is a concentration process.

Al2O3.xH2O(s)Al2O3(s)+xH2O(l)HydratedAluminaAlumina


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