Thursday, September 12, 2013

Chemical Method ( Leaching )

             In this process the ore is washed with some suitable reagent ( solvent ) So the main metal passes into its salt solution. This solution is separated and subjected to further treatment like precipitation. It is then treated further to recover the metal. This is chemical process.
Example :   Aluminium Extraction ;
   Bauxite ore is treated with NaOH, The Al2O3  goes into the solution to form sodium meta-aluminate. The Sodium meta aluminate contain undissolved impurities like SiO2 , Fe2O3 , Fe(OH)3    
  etc. Which are then filtered off.
                                   Al2O3 + 2NaOH        →  2NaAlO2  +  H2O
                                                                     (In solution Form)
The filtrate on dilution, and stirring gives a precipitate of aluminium hydroxide, which is filtered and ignited to get pure alumina.
                                  NaAlO2  + 2 H2O      →    Al(OH)3    +   NaOH     
                                    2  Al(OH)3         Δ→    Al2O3      +   3 H2O

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