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How can you separate alumina from bauxite ore associated with silica ? Give equations. |
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Answer» Solution :Bauxite, a principal ore of aluminium contains silica, iron oxide and titanium oxide as impurities. The ore is digested with a concentrated solution of NaOH at 473-523 K and 35 - 36 bar pressure.`Al_2O_3` is leached out as sodium aluminate and silica as sodium silicate while impurities are left behind. `RAl_2O_3(s)+ 2NaOH(AQ) + 3H_2O to 2Na[Al(OH)_4](aq)` The aluminate in the solution is neutralised by passing `CO_2` gas and hydrated `Al_2O_3` is precipitated. `2Na[Al(OH)_4] (aq) + CO_2(g) to Al_2O_3.xH_2O + 2NaHCO_3(aq)` he sodium silicate remains in the solution while hydrated ALUMINA is filtered and dried. The hydrated alumina thus precipitated is filtered, dried and HEATED to give back pure alumina. `underset("Hydrated alumina")(Al_2O_3.x H_2O) overset(1473 K)tounderset("Alumina")(Al_2O_3(s)) + xH_2O` |
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