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Haematite, an ore ofiron, firstconcentratedand thencalcined. Thecalcinedore isthen heated in ablastfurnace inpresence ofcoke thelimestone and atthesame timea blastof hot air(pre heated to1000 K ) isintroduced intothe furnace throughtuyeres.Two products(X) and(Y) are obtained. Now answer thefollowingquestions. (a) Whatmethodis used forconcentrationof haematite ore? (b) Whathappensduringcalcination ? (c )Identiythe twoproductsand mention their uses. |
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Answer» Solution :(a) Sincehaematite`(Fe_2O _ 3 ) `isanoxideore, it isconcentrated bygravityseparationprocess in which the crushedore iswashed in astreamof waterwhen lighersand and clayparticlesare washed awaywhilethe heavierore particlessettledown. (b) Duringcalcination, theimpuritiesof sulphur, phosphorus andarsenicescape as theirvolatile oxides. ` S_8 +8 O_ 2 to8 SO _ 2uparrow, P _ 4+5 O _ 2 toP _ 4O _(10) uparrow ,2 As+5 O _ 2toAs_ 2O_5uparrow ` (c)The variousreactionstakingplacein theblastfurnace are : `CaCO_ 3` decomposes to formCaOand`CO_ 2`. The CaO thus formed actsas aflux andcombines withsilica(present as an IMPURITY ) to formfusiblecalcium silicateslag (N). ` underset("Limestone")(CaCO_3) (s)overset(1123K)toCaO(s) +CO_ 2 (g)` `CaO(s)+SiO_ 2tounderset("Calciumsilicate (slag)") underset (N) (CaSiO_ 3 ) ` Calciumsilicateslag is usedas a buildingmaterialsuchascement. `C (s)+CO_ 2(g) to2CO(g) ` Both COandcokereduce`Fe_2 O _ 3`toFemetal(X). `Fe_2O_ 3 (s) +CO(g) overset (773 -873 K )to2Fe O (s) +CO _ 2(g) ` ` FeO (s)+C(s)overset( gt 1073K )tounderset ("Iron metal (M)")(Fe(s//l)) +CO(g) ` `Fe_ 2O_ 3(s)+3 C (s) overset ( 1073K ) tounderset("Iron metal (M)")( 2 Fe (s//l)) +3 CO(g) ` The ironthusobtainedfromthefurnacecontainsabout 4% carbonand manyimpurities(e.g., S, P, Si, MN) insmaller amount. This is calledpig iron and iscast intoavariety of shapes. |
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