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InterviewSolution
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What isthesignificanceof leachingin theextractionofaluminium ? |
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Answer» Solution :Bauxineis the principleore of aluminium. It usually contains silica `(SiO_2) `, ironoxide` (Fe_2O_3) `andtitanium oxide `(TiO_2) `as impurities. These impurities can beremovedbytheprocessof LEACHING. Duringleaching, thepowdered bauxine oreis heatedwithaconcentrated(45%) solution ofNaOHat 473 - 523 Kand35 - 36 barpressurewhen aluminadissolves as sodium meta- aluminate and silica`(SiO_2) `as sodiumsilicateleaving` Fe_2O_3, TiO_2 `and other impurities behind. ` underset ("Alumina")(Al_2O_3(s)) +2 NaOH (AQ)+3 H _2 O(l)overset ( 473 - 523K) underset (35 - 36" bar pressure") tounderset ("Sodium meta-aluminate")(2NA[Al(OH)_4](aq) ` ` underset ("Silica")(SiO_(2)(l)) + 2 NaOH (aq) underset (473 - 523K) tounderset ("Sodiumsilicate")(Na_2SiO_3(aq)) +H_ 2 O(l) ` Theimpuritiesare filtered off andthe solution of sodiummeta- aluminateis neutralizedbypassing` CO_ 2` when hydratedaluminaseparatesoutwhilesodiumsilicateremainsinthesolution. ` ""2Na[Al(OH)_4](aq) +2CO _2(g)toAl_2 O _3. x H_2O(s) downarrow+2 NaHCO_3(aq) ` Thehydratedalumina thusobtainedisfiltered, driedandheatedto give backpure alumina. ` "" Al _2O_ 3 . xH _2 O (s)overset ( 1473 K) toAl_2 O _3(s)+xH_2O (g)` Thus,the significanceof leachingintheextractionofaluminiumis topreparepurealuminafro thebauxiteore. |
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