Structure Of Calcium Aluminate Minerals And Chracteristics Of Clinkers Doped With Na₂O

The energy consumption of the lime sintering process is lower than that of the soda-lime sintering process.Because the lime sintering process avoides the energy consumption of the vaporaiton of water in the sintering raw materials.However,the consumption of calcium and the clinker convertion ratio of the lime sintering process are higher than that of the soda-lime sintering process.The Al2O3 leaching rate of the lime sintering process clinker is low.The disadvantages prohibit the development of the lime sintering process.In this paper,analytical reagents were used as raw materials of sintering.The analytical methods include XRD,SEM,EDS,TG-DSC,FT-IR,Raman and Material Studio simulation.The minerals formation kinetics and conversion mechanism,the microstructure characteristics of clinkers,the simulation of calcium aluminate crystal structures and the Al2O3 leaching rate of clinkers were studied.The results are as follows:The formation mechanism and microstructure of caliucm aluminates of CaO-Al2O3 system clinkers were studied when the molar ratio of CaO to Al2O3 is 0.60～1.70.The complete crystal structure of 12CaO·7Al2O3 and structure with Ca vacancy were also analysized.The calcium aluminates include 3CaO·Al2O3、5CaO·3Al2O3、12CaO·7Al2O3、CaO·Al2O3、CaO·2Al2O3 and CaO·6Al2O3.3CaO·Al2O3 and 5CaO·3Al2O3 are formed at the initial reaction stage of materials with different CaO contents.The formula of mayenite transforms to 12CaO·7Al2O3 from 11.3CaO·7Al2O3 with the extension of sintering time.The O-Al plays a major role in the stability of 12CaO·7Al2O3 crystal structure and structural stability decreases because of the vacancy of Ca atom.The calcium aluminates present as a layered distribution.The calcium aluminates of outer layer contain more CaO which are 12CaO·7Al2O3 and 3CaO·Al2O3,and Al2O3 is in the core.The phase compositions of Na2O-CaO-Al2O3 system clinkers were analysized when the molar ratio of CaO to Al2O3 is 0.30～0.60 and that of Na2O to Al2O3 is 0.10～0.50.The formation dynamic and crystal structure characteristics of 2Na2O·3CaO·5Al2O3,the microstructure and leaching efficiency of sintered clinkers were also studied.The mainly formation period of 2Na2O·3CaO·5Al2O3 is between 860℃ and 1000℃.The formation process conforms to the second-order reaction model.The activation energy of the reaction is 223.97 kJ mol-1 and the pre-exponential factor is 3.42×106.The characteristic Raman bands of 2Na2O·3CaO·5Al2O3 are 524 cm-1,789 cm-1,1590 cm-1 and 2712 cm-1 and the characteristic Infrared absorption wavelength are 662 cm-1,704 cm-1,772 cm-1 and 930 cm-1.The grains of 2Na2O 3Ca0·5Al2O3 is much higher than those of 12CaO·7Al2O3 and CaO Al2O3.The leaching rate of Al2O3 can be above 90%when 2Na2O·3CaO· 5Al2O3 was leached in 40℃ for 10 min.The transformation of calcium aluminates doped by Na2O and the microstructure of sintered clinkers are studied when Na2Cv3 and Na2O·Al2O3 as the carrier of Na2O.The crystal structure of 12CaO·7Al2O3 doped with Na2O was also studied.CaO·Al2O3 transforms to 12CaO·7Al2O3 and 2Na2O·3Ca0·5Al2O3 because of the doping of Na2CO3 and Na2O·Al2O3.The crystallinity of 12CaO·7Al2O3 and 2Na2O·3CaO·5Al2O3 decrease while that of CaO Al2O3 increases with the increasing amount of Na2O doping.Na2O were mainly doped in 12CaO·7Al2O3 and the structural stability decreases because of the doping of Na2O.The Al2O3 leaching efficiency of 2Na2O·3CaO.5Al2O3 is better than that of 12Ca0 7Al2O3 and CaO·Al2O3.The mineral compositions and formation mechanism,the microstructure features and the Al2O3 leaching efficiency of Na2O-CaO-Al2O3-SiO2 system clinkers were studied when 12Ca0 7Al2O3 and 2Na2O·3CaO·5Al2O3 are the target Al-containing minerals in clinkers,respectively.The minerals mainly include 12CaO·7Al2O3,CaO·Al2O3,2CaO·Al2O3·SiO2,β-2CaO·SiO2,y-2CaO·SiO2 when 12CaO·7Al2O3 is the target Al-containing phase.Some 2Na2O·3CaO·5Al2O3 and Na2O·Al2O3 also exist in the clinkers.The reaction velocity of the materials is accelerated by the doping of Na2O.CaO·2Al2O3 and 2CaO·Al2O3·SiO2 transforms into 12CaO·7Al2O3 and 2Na2O·3CaO·5Al2O3.The leaching rate of clinkers sintered at 1350℃ for 1h can be 88.17%when the mass ratio of Al2O3 to SiO2 is 1.6,the molar ratio of CaO to Al2O3 is 0.88 and that of Na2O to Al2O3 is 0.24.The phases mainly include 2Na2O·3CaO·5Al2O3,2CaO·Al203 Si02 and β-2CaO·SiO2 when 2Na2O·3CaO·5Al2O3 is the target Al-containing phase.The clinkers also contain some 12CaO·7Al2O3,the content of which increases with the increasing sintering temperature.The Al2O3 leaching rate of clinkers sintered at 1150～一1350℃ for 1h are about 75%when the mass ratio of Al2O3 to SiO2 is 2.0,the molar ratio of CaO to Al2O3 is 0.60.The mineral compositions and leaching efficiency of clinkers sintered with desilicification ash,CaCO3 and Na2CO3 were studied.The phases mainly include 12CaO·7Al2O3,β-2Cao·SiO2,γ-2CaO·SiO2 and 2CaO·Al2O3 SiO2 when 12CaO·7Al2O3 is the target Al-containing mineral.The increasing CaO content promotes the transformation of 2CaO·Al2O3·SiO2 to 12Ca0·7Al2O3.The leaching rate of clinkers sintered at 1350℃ for 1h can be 93.29%when the mass ratio of Al2O3 to SiO2 is 2.2,the molar ratio of CaO to Al2O3 is 1.40 and that of Na2O to Al2O3 is 0.10.The clinkers also have a good self-decomposition property.