The precipitation performance and kinetics of gibbsite from sodium aluminate solution with different sodium oxalate concentrations as well as the corresponding influence mechanism of oxalate during the seed precipitat...The precipitation performance and kinetics of gibbsite from sodium aluminate solution with different sodium oxalate concentrations as well as the corresponding influence mechanism of oxalate during the seed precipitation process were systematically investigated by physicochemical properties test,using SEM and Raman spectra.As the concentration of sodium oxalate increases,both the precipitation rate and particle size of gibbsite decrease.The presence of sodium oxalate not only increases the viscosity of sodium aluminate solution,but also promotes the transformation of Al(OH)4^? to Al2O(OH)6^2?.The overall reaction rate constant decreases and the apparent activation energy of gibbsite increases with the increasing sodium oxalate concentration,the rate controlling step of which is chemical reaction.The needle-like sodium oxalate precipitates on the gibbsite crystals and covers the active Al(OH)3 seed sites,which leads to the lower precipitation rate and the finer particle size of gibbsite during the seed precipitation process.展开更多
The phase transition,morphology,stability and pulverization performance of dicalcium silicate(C_(2)S)with different Na_(2)O additions during the high-temperature sintering process were studied using XRD,SEM-EDS,FT-IR,...The phase transition,morphology,stability and pulverization performance of dicalcium silicate(C_(2)S)with different Na_(2)O additions during the high-temperature sintering process were studied using XRD,SEM-EDS,FT-IR,and Raman spectra methods.When the CaO to SiO_(2) molar ratio is 2.0 and the Na_(2)O to SiO_(2) molar ratio is below 0.20,the crystalline calcium silicate compounds includeγ-C_(2)S andβ-C_(2)S.As the Na_(2)O addition increases,the proportion,crystallinity and grain size ofβ-C_(2)S in the sintered products increase,those parameters ofγ-C_(2)S decrease,and the content of amorphous phase increases.Na_(2)O mainly forms solid solutions inβ-C_(2)S and inhibits the transition ofβ-C_(2)S toγ-C_(2)S,resulting in the sintered products unpulverized.The stability of sintered products in alkali solution decreases significantly with the increasing Na_(2)O additions,and theβ-C_(2)S solid solution with Na_(2)O is less stable thanγ-C_(2)S.The mechanism that Na_(2)O affects the transition of C_(2)S as well as its stability was also discussed,which can give actual guidance for the treatment of low-grade alumina-containing resources by the sintering process.展开更多
The crystal structure,formation kinetics and micro-morphology of CaO·SiO2 during high-temperature sintering process were studied in low-calcium system by XRD,FT-IR,Raman and SEM-EDS methods.When the molar ratio o...The crystal structure,formation kinetics and micro-morphology of CaO·SiO2 during high-temperature sintering process were studied in low-calcium system by XRD,FT-IR,Raman and SEM-EDS methods.When the molar ratio of CaCO3 to SiO2 is 1.0,β-2CaO·SiO2 forms firstly during the heating process,and then CaO·SiO2 is generated by the transformation reaction of pre-formed 2CaO·SiO2 with SiO2.3CaO·SiO2 and 3CaO·2SiO2 do not form either in the heating or sintering process.Rising the sintering temperature and prolonging the holding time promote the phase transition of 2CaO·SiO2 to CaO·SiO2,resulting in the sintered products a small blue shift and broadening in Raman spectra.The content of CS can reach 97.4%when sintered at 1400℃ for 1 h.The formation kinetics of CaO·SiO2 follows the second-order chemical reaction model,and the corresponding apparent activation energy and pre-exponential factor are 505.82 kJ/mol and 2.16×10^14 s^−1 respectively.展开更多
基金Project (2022YFC2904405) supported by the National Key Research and Development Program of ChinaProjects (22078055,52074083) supported by the National Natural Science Foundation of China。
基金Projects(51774079,51674075)supported by the National Natural Science Foundation of ChinaProject(N182508026)supported by the Fundamental Research Funds for the Central Universities,China。
文摘The precipitation performance and kinetics of gibbsite from sodium aluminate solution with different sodium oxalate concentrations as well as the corresponding influence mechanism of oxalate during the seed precipitation process were systematically investigated by physicochemical properties test,using SEM and Raman spectra.As the concentration of sodium oxalate increases,both the precipitation rate and particle size of gibbsite decrease.The presence of sodium oxalate not only increases the viscosity of sodium aluminate solution,but also promotes the transformation of Al(OH)4^? to Al2O(OH)6^2?.The overall reaction rate constant decreases and the apparent activation energy of gibbsite increases with the increasing sodium oxalate concentration,the rate controlling step of which is chemical reaction.The needle-like sodium oxalate precipitates on the gibbsite crystals and covers the active Al(OH)3 seed sites,which leads to the lower precipitation rate and the finer particle size of gibbsite during the seed precipitation process.
基金Project(2018YFC1901903)supported by the National Key R&D Program of ChinaProjects(22078055,52074083,51674075)supported by the National Natural Science Foundation of China。
文摘The phase transition,morphology,stability and pulverization performance of dicalcium silicate(C_(2)S)with different Na_(2)O additions during the high-temperature sintering process were studied using XRD,SEM-EDS,FT-IR,and Raman spectra methods.When the CaO to SiO_(2) molar ratio is 2.0 and the Na_(2)O to SiO_(2) molar ratio is below 0.20,the crystalline calcium silicate compounds includeγ-C_(2)S andβ-C_(2)S.As the Na_(2)O addition increases,the proportion,crystallinity and grain size ofβ-C_(2)S in the sintered products increase,those parameters ofγ-C_(2)S decrease,and the content of amorphous phase increases.Na_(2)O mainly forms solid solutions inβ-C_(2)S and inhibits the transition ofβ-C_(2)S toγ-C_(2)S,resulting in the sintered products unpulverized.The stability of sintered products in alkali solution decreases significantly with the increasing Na_(2)O additions,and theβ-C_(2)S solid solution with Na_(2)O is less stable thanγ-C_(2)S.The mechanism that Na_(2)O affects the transition of C_(2)S as well as its stability was also discussed,which can give actual guidance for the treatment of low-grade alumina-containing resources by the sintering process.
基金Projects(51674075,51774079)supported by the National Natural Science Foundation of ChinaProject(2018YFC1901903)supported by the National Key R&D Program of ChinaProject(N182508026)supported by the Fundamental Research Funds for the Central Universities of China。
文摘The crystal structure,formation kinetics and micro-morphology of CaO·SiO2 during high-temperature sintering process were studied in low-calcium system by XRD,FT-IR,Raman and SEM-EDS methods.When the molar ratio of CaCO3 to SiO2 is 1.0,β-2CaO·SiO2 forms firstly during the heating process,and then CaO·SiO2 is generated by the transformation reaction of pre-formed 2CaO·SiO2 with SiO2.3CaO·SiO2 and 3CaO·2SiO2 do not form either in the heating or sintering process.Rising the sintering temperature and prolonging the holding time promote the phase transition of 2CaO·SiO2 to CaO·SiO2,resulting in the sintered products a small blue shift and broadening in Raman spectra.The content of CS can reach 97.4%when sintered at 1400℃ for 1 h.The formation kinetics of CaO·SiO2 follows the second-order chemical reaction model,and the corresponding apparent activation energy and pre-exponential factor are 505.82 kJ/mol and 2.16×10^14 s^−1 respectively.
