Research On Phase Transformation Law And Alumina Leaching Properties During Sintering Process Of Calcium Sulphoaluminate Clinker

As the main component of calcium aluminate clinker which contains S element,calcium sulphoaluminate（3CaO·3Al₂O₃·CaSO₄）has excellent leaching performance,and its C/A ratio（the molar ratio of CaO to Al2O3）can reach 1.33.In contrast with traditional lime sintering process,the amount of lime addition can be significantly reduced and the leaching property of alumina can be improved in the clinker.In this paper,analytical reagents were used as raw materials,the effects of raw material mixture ratio,sintering condition and Na₂O doping on phase transformation,microstructure,pulverization and alumina leaching property of CaO-Al₂O₃-SiO₂-SO₃ system were studied by XRD,SEM-EDS,TG-DSC,FTIR and particle size analysis.The main results are as follows:1)The best raw material mixture ratio is C/A=1.0 and A/S=2.0（the mass fraction ratio of Al₂O₃ to SiO₂）when the sintering temperature is 1350℃for 2h.The main phases of clinker are 3CaO·3Al2O3·CaSO4 andβ-2CaO·SiO2,and its leaching rate of alumina is 87.42%.When the C/A=1.0 and A/S=2.0,the best sintering condition is as followed:sintering temperature is 1250℃and sintering duration is 30min.The minerals in the clinker mainly include 3CaO·3Al₂O₃·CaSO₄ andβ-2CaO·SiO₂,and its leaching rate of alumina is86.41%.2)In order to achieve the goal of high leaching rate under low calcium ratio,the alumina leaching rate of clinker can be significantly improved by doping with Na₂O in the CaO-Al2O3-SiO2-SO3 system when C/A ratio is 0.8.When the addition of Na2O is less than 4%,sodium will promote the phase transformation to CaO·Al₂O₃,2CaO·SiO₂ and Na₂SO₄ from 3CaO·3Al₂O₃·CaSO₄,CaO·2Al₂O₃ and 2CaO·Al₂O₃·SiO₂.When the amount of Na2O doping is between 4%and 12%,the addition of Na2O will promote the phase transformation to 2Na₂O·3CaO·5Al₂O₃,12CaO·7Al₂O₃ and Na₂SO₄ from CaO·Al₂O₃,3CaO·3Al₂O₃·CaSO₄,CaO·2Al₂O₃ and 2CaO·Al₂O₃·SiO₂.When the amount of Na₂O doping is 12%,3CaO·3Al₂O₃·CaSO₄ disappears and the S element exists in the form of Na₂SO_4.With the increasing of C/A ratio,12CaO·7Al₂O₃ increases while the amount of 3CaO·3Al₂O₃·CaSO₄ and 2Na₂O·3CaO·5Al₂O₃ decrease when the amount of Na2O is 8%and A/S ratio is 2.0.When the C/A ratio is 1.4,3CaO·3Al2O3·CaSO4disappears.3)The phase composition of the clinker does not change with the increasing of sintering temperature and holding time when the amount of Na₂O is 8%,A/S=2.0,C/A=0.7 and 0.8.The amount of 3CaO·3Al₂O₃·CaSO₄ and 2Na₂O·3CaO·5Al₂O₃ increase while 12CaO·7Al2O3 decreases gradually.The leaching rate of alumina is 93.68%when C/A=0.8 and the sintering temperature is 1250℃for 30min.