| Alumina extracting from low-grade alumina-containing resources in the lime sinter process has the advantages of dry sintering,clinker self-pulverization and abundant lime resources.However,high lime dosage,high amounts of leached residues and poor alumina leaching property of calcium aluminate clinker inhibit its application and development.Therefore,reducing lime dosage and improving alumina leaching property are always the fundamental development direction in the lime sinter process.The expansion-shrinkage property,melting temperature,mineral formation and transition mechanism,microstructure,crystal structure,pulverization and alumina leaching property of the low-lime dosage calcium aluminate clinker were systematically studied using analytical reagent.It also provides the basic research for the application and development in the lime sinter process to extract alumina from low-grade alumina-containing resources.The sintering behavior of calcium aluminate clinker was systematically studied when the molar ratio of CaO to Al2O3(C/A)is 1.0 and the mass ratio of Al2O3 to SiO2(A/S)is 3.0 in the CaO-Al2O3-SiO2 system.The results show that the calcium aluminate clinker shows a expansion process at first and then starts to shrink,and the melting temperature is 1392?.Ca2Si04(C2S),Ca2Al2Si07(C2AS)and CaAl2O4(CA)are formed at 985°C,1045°C and 1339? respectively.CaAl4O7,CA,Ca12Al14O33(C12A7),Ca3Al2O6(C3A),Ca3SiO5(C3S),C2S and C2AS can generate in the initial stage of reactions.The formation of C2S accelerates the diffusion of CaO and Al2O3,which promotes the process C3A and C12A7 react with Al2O3 to form CA,while C2AS reacts with CaO,C3A or C12A7 to form C2S and CA.When sintering temperature is higher than the melting temperature,increasing sintering temperature could promote the formation of C2AS and C12A7 in the initial stage of reactions and prevent the transition of C12A7 to CA.It also prevents the transition of ?-C2S to ?-C2S,and then deteriorates the pulverization and alumina leaching property of calcium aluminate clinker.The calcium aluminate clinker contains CA and ?-C2S as well as some C12A7 with good pulverization and alumina leaching property at 1350?.The mineral transition,crystal structure,pulverization and alumina leaching property of the calcium aluminate clinkers were studied at 1350°C when the A/S is 3.0 and the C/A are 0.9-1.4 in the CaO-Al2O3-SiO2 system.Increasing lime dosage could increase the melting temperature of calcium aluminate clinker.It also promotes the process C2AS reacts with CaO to form C2S,CA and C12A7,while CA reacts with CaO to form C12A7.The pulverization and alumina leaching property of calcium aluminate clinker increase at first and then decrease.The calcium aluminate clinker contains CA,C12A7 and ?-C2S as well as some C2AS when the C/A is lower than 1.0.C2AS is in the matrix of CA and C12A7.The calcium aluminate clinker contains CA,C12A7 and ?-C2S when the C/A are 1.0-1.4.The unit cell volume of CA and C12A7 is larger with good reaction activity in sodium carbonate solution.The transition mechanism of C2AS,and crystal structure,pulverization and alumina leaching property of calcium aluminate clinker were studied at 1350-1500 °C in the Ca2Al2SiO7-CaO system.Ca2+ replaces the Si4+ lattice position of C2AS to form calcium aluminate gradually,and then the separated Si4+ reacts with CaO to form calcium silicate.C3A,C12A7,CA and C2S can generate in the initial stage of reactions.Controlling sintering temperature at 1350? or higher than 1500? also could promote the transition process C2AS reacts with CaO to form C2S and CA,and then increase the pulverization and alumina leaching property of calcium aluminate clinker.The main minerals are CA,C12A7 and ?-C2S as well as some ?-C2S and C2AS at 1350? when the C/A is 1.0,The unit cell volume of CA and C12A7 is smaller with poor reaction activity in sodium carbonate solution.The transition mechanism of A16Si2013(A3S2),and crystal structure,pulverization and alumina leaching property of calcium aluminate clinker were studied at 1350-1500? in the Al6Si2O13-CaO system.Ca2+ replaces the Si4+ lattice position of Al6Si2O13 to form C2AS and calcium aluminate gradually,and then the separated Si4+ reacts with CaO to form calcium silicate.C2AS,C3A,C12A7,CA and C2S can generate in the initial stage of reactions.Controlling sintering temperature between 1350°C and 1500°C could promote the transition process A3S2 reacts with CaO to form C2S and CA,and then increase the pulverization and alumina leaching property of calcium aluminate clinker.The main minerals are CA,C12A7 and ?-C2S as well as some ?-C2S and C2AS at 135O? when the C/A is 1.0.The unit cell volume of CA and C12A7 is smaller with poor reaction activity in sodium carbonate solution.The effects of MgO dosage on mineral transition,crystal structure,pulverization and alumina leaching property of calcium aluminate clinker were studied in the CaO-Al2O3-SiO2 system.C12A7,CA,C2AS,Ca20Al26Mg3Si3O68(C20A13M3S3),C2S and C3S can generate in the initial stage of reactions.Increasing sintering temperature or MgO dosage also could promote the formation of C20A13M3S3 and C2AS.It prevents the transition of C12A7 to CA.It also prevents the transition of ?-C2S to y-C2S and then deteriorates the pulverization and alumina leaching property of calcium aluminate clinker.The main minerals are C20A13M3 S3 and y-C2S as well as some CA,C12A7 and/?-C2S at 1350? when the MgO dosage is 2.0%and the C/A is 1.0. |
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