Thermodynamics of Reactions Among Al2O3, CaO, SiO2 and Fe2O3 During Roasting Processes

The thermodynamic of the chemical reactions among Al 2 O 3 , CaO, SiO 2 and Fe 2 O 3 in the roasting processes was investigated in this chapter.The chemical reactions are classified into SiO 2 -Al 2 O 3 system, Fe 2 O 3 -Al 2 O 3 system, SiO 2 -Fe 2 O 3 system, CaO-Al 2 O 3 system, SiO 2 -CaO system, SiO 2 -calcium aluminates system, CaO-Fe 2 O 3 system, Al 2 O 3 -calcium ferrites system and Al 2 O 3 -CaO-SiO 2 -Fe 2 O 3 system.When the roasting temperature is over 1100K,oxide and SiO 2 could not generate iron silicate; 12CaO•7Al 2 O 3 is preferentially formed in CaO-Al 2 O 3 system when one mole Al 2 O 3 reacts with CaO; 2CaO•SiO 2 is preferentially formed in SiO 2 -CaO system; except for CaO•2Al 2 O 3 and CaO•Al 2 O 3 , the other calcium aluminates can transform into calcium silicate by reacting with SiO 2 in SiO 2 -calcium aluminates system; 2CaO•Fe 2 O 3 is preferentially formed in CaO-Fe 2 O 3 system; alumina is unable to form 3CaO•Al 2 O 3 with calcium ferrites(2CaO•Fe 2 O 3 and CaO•Fe 2 O 3 ), but able to form 12CaO•7Al 2 O 3 with 2CaO•Fe 2 O 3 ; when CaO, Fe 2 O 3 , Al 2 O 3 ,SiO 2 coexist, they are more likely to form ternary compound 2CaO•Al 2 O 3 •SiO 2 and 4CaO•Al 2 O 3 •Fe 2 O 3 .2. Binary compounds 2.1 Fe 2 O 3 -Al 2 O 3 -CaCO 3 system Fe 2 O 3 and Al 2 O 3 can all react with limestone during roasting to generate corresponding aluminates and ferrites.In Fe 2 O 3 -Al 2 O 3 -CaO system, the reaction Fe 2 O 3 and Al 2 O 3 with CaCO 3 coexist, and the reactions equations are as followed: Reactions A, J/mol B, J/K.mol Temperature, K CaCO 3 +Al 2 O 3 =CaO•Al 2 O 3 +CO 2 161088.3-244.1 298~1200 CaCO 3 +Fe 2 O 3 =CaO•Fe 2 O 3 +CO 2 151677.8-220.9 298~1200 Table 1.The   T G of Fe 2 O 3 -Al 2 O 3 -CaCO 3 system   T GA B T , J/mol; 2 CO P =30Pa, i.e., the partial pressure of CO 2 in the air www.intechopen.