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How can you separate alumina from silica in a bauxite ore associated with silica? Give equations, if any.

6.13 How can you separate alumina from silica in a bauxite ore associated with silica? Give equations, if any.

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M manish

The separation of alumina carried out in the following steps-

  1. The powdered ore is treated with the concentrated NaOH solution at 473K-523K and 35-36 bar pressure.
    \\Al_{2}O_{3}+2NaOH(aq)+3H_{2}O\rightarrow 2Na[Al(OH)_{4}](aq)\\ SiO_{2}+NaOH\rightarrow Na_{2}SiO_{3}+H_{2}O
  2. The CO_{2} gas is passed through the resulting solution to neutralise the aluminate, which results in ppt. of hydrated alumina.
    2Na[Al(OH)_{2}](aq)+CO_{2}\rightarrow Al_{2}O_{3}+2NaHCO_{3}(aq)
     The obtained hydrated alumina is filtered, dried and heated to get pure alumina.
    Al_{2}O_{3}.xH_{2}O\rightarrow Al_{2}O_{3}+x.H_{2}O

 

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