To synergistically recover alumina and alkali from red mud(RM),the structural stability and conversion mechanism of hydroandradite(HA)from hydrogarnet(HG)were investigated via the First-principles,XRF,XRD,PSD and SEM ...To synergistically recover alumina and alkali from red mud(RM),the structural stability and conversion mechanism of hydroandradite(HA)from hydrogarnet(HG)were investigated via the First-principles,XRF,XRD,PSD and SEM methods,and a novel hydrothermal process based on the conversion principle was finally proposed.The crystal structure simulation shows that the HA with varied silicon saturation coefficients is more stable than HG,and the HA with a high iron substitution coefficient is more difficult to be converted from HG.The(110)plane of Fe_(2)O_(3) is easier to combine with HG to form HA,and the binding energy is 81.93 kJ/mol.The effects of raw material ratio,solution concentration and hydrothermal parameters on the conversion from HG to HA were revealed,and the optimal conditions for the alumina recovery were obtained.The recovery efficiencies of alumina and Na_(2)O from the RM are 63.06%and 97.34%,respectively,and the Na_(2)O content in the treated RM is only 0.13%.展开更多
The effect of lime on the pre-desilication and digestion of gibbsitic bauxite in synthetic sodium aluminate liquor at different tem- peratures was investigated. The bauxite is comprised of gibbsite, aluminogoethite, h...The effect of lime on the pre-desilication and digestion of gibbsitic bauxite in synthetic sodium aluminate liquor at different tem- peratures was investigated. The bauxite is comprised of gibbsite, aluminogoethite, hematite, kaolin, quartz, and minor boehmite. Lime in- creases the desilication efficiency of the bauxite during the pre-desilication process by promoting the conversion of sodalite and cancrinite to hydrogamet. Desilication reactions during the digestion process promoted by lime result in the loss of A1203 entering the red mud, but the amount of aluminogoethite-to-hematite conversion promoted by lime leads to the increase of aluminogoethific A1203 entering the digested liquor. The alumina digestion rate at 245~C is higher than that at 145 C due to the more pronounced conversion of aluminogoethite to hema- tite. The soda consumption during the digestion process decreases due to lime addition, especially at higher temperatures.展开更多
AIM: To investigate the clinical features of Crohn's disease(CD) and intestinal tuberculosis(ITB) with a scoring system that we have developed.METHODS: A total of 25 CD and 40 ITB patients were prospectively enrol...AIM: To investigate the clinical features of Crohn's disease(CD) and intestinal tuberculosis(ITB) with a scoring system that we have developed.METHODS: A total of 25 CD and 40 ITB patients were prospectively enrolled from August 2011 to July 2012.Their characteristics and clinical features were recorded. Laboratory, endoscopic, histologic and radiographic features were determined. The features with a high specificity were selected to establish a scoring system. The features supporting CD scored +1, and those supporting ITB scored-1; each patient received a final total score. A receiver operating characteristic(ROC) curve was used to determine the best cut-off value for distinguishing CD from ITB.RESULTS: Based on a high specificity of differentiating between CD and ITB, 12 features, including longitudinal ulcers, nodular hyperplasia, cobblestone-like mucosa, intestinal diseases, intestinal fistula, the target sign, the comb sign, night sweats, the purified protein derivative test, the interferon-γ release assay(T-SPOT.TB), ring ulcers and ulcer scars, were selected for the scoring system. The results showed that the average total score of the CD group was 3.12 ± 1.740, the average total score of the ITB group was-2.58 ± 0.984, the best cutoff value for the ROC curve was-0.5, and the diagnostic area under the curve was 0.997, which was statistically significant(P < 0.001). The patients whose total scores were higher than-0.5 were diagnosed with CD; otherwise, patients were diagnosed with ITB. Overall, the diagnostic accuracy rate and misdiagnosis rate of this scoring system were 97% and 3%, respectively. CONCLUSION: Some clinical features are valuable for CD and ITB diagnosis. The described scoring system is key to differentiating between CD and ITB.展开更多
A new chemical pre-desilication process of kaolinite in diasporic bauxite in alkali solution at atmospheric pressure was proposed.The dissolution kinetics and mechanism were studied by chemical analysis,XRD and SEM.Th...A new chemical pre-desilication process of kaolinite in diasporic bauxite in alkali solution at atmospheric pressure was proposed.The dissolution kinetics and mechanism were studied by chemical analysis,XRD and SEM.The kinetic results of dissolution process show that the kaolinite is symbiotic with diaspore but without cladding.The dissolution ratio of kaolinite is close to 100%at 100℃for 90 min.The dissolution kinetic equation is 1-(1-α)^1/3=7.88×10^6 exp[-64434/(RT)]t.With the low L/S(L/S=10:1),the dissolution ratio of kaolinite decreases to 55%.This is due to the formation of lamellar hydroxyl-sodalite(OH-SOD)which is deposited on the surface of kaolinite and hinders the further dissolution of kaolinite.Under the optimum conditions,the A/S(mass ratio of Al2 O3 to SiO2)of dissolved residues is increased to 8.55,while the A/S of the bauxite is only 4.97.展开更多
The mineral transition, microstructure and self-pulverization as well as the Al2O3 leaching performance of calcium aluminate clinkers with different P additions in CaO-Al2O3-SiO2 system during high-temperature sinteri...The mineral transition, microstructure and self-pulverization as well as the Al2O3 leaching performance of calcium aluminate clinkers with different P additions in CaO-Al2O3-SiO2 system during high-temperature sintering were systematically studied by XRF, XRD, SEM-EDS and DSC-TG technologies. The clinkers sintered at 1350 °C mainly contain 12CaO·7Al2O3, CaO·Al2O3,β-2CaO·SiO2 and γ-2CaO·SiO2. The content of β-2CaO·SiO2 increases while the content of γ-2CaO·SiO2 decreases as the P addition increases. The self-pulverization property of clinkers deteriorates with increasing P addition. P distributes evenly in the clinkers, and inhibits the transformation of β-2CaO·SiO2 to γ-2CaO·SiO2. The cell volumes of 12CaO·7Al2O3 and CaO·Al2O3 decrease and increase respectively as the P addition increases, and P decreases their formation temperatures. The Al2O3 leaching rate of calcium aluminate clinkers decreases obviously with increasing P addition, which decreases form 95.01% to 83.84% as the P addition increases from 0 to 0.85%.展开更多
The formation kinetics and mechanism of tricalcium aluminate hydrate and calcium oxalate in dilute sodium aluminate solution and sodium oxalate solution were studied respectively based on the lime causticization, and ...The formation kinetics and mechanism of tricalcium aluminate hydrate and calcium oxalate in dilute sodium aluminate solution and sodium oxalate solution were studied respectively based on the lime causticization, and the optimal conditions for removing the oxalate in dilute sodium aluminate solution as well as the mechanism were finally obtained.The formation processes of tricalcium aluminate hydrate and calcium oxalate are mainly controlled by the chemical reaction and the inner diffusion respectively,and the corresponding reaction rate equations as well as the apparent activation energy were calculated. The hydrocalumite with a spatially interleaved structure will form in dilute sodium aluminate solution with sodium oxalate, greatly removing the oxalate impurity by absorption. Calcium oxalate can be converted to tricalcium aluminate hydrate with the increasing reaction time. The oxalate causticization efficiency and the alumina loss rate can be over 90% and below 31% respectively when reacted at 50℃ with a stirring rate of 200 r/min.展开更多
The sintering characteristics at 1350℃ and leaching property at 80℃ of calcium aluminate clinkers in the CaO-Al2O3-SiO2 （C-A-S） system with different additions of FeO and Fe2O3 were investigated. FeO inhibits the ...The sintering characteristics at 1350℃ and leaching property at 80℃ of calcium aluminate clinkers in the CaO-Al2O3-SiO2 （C-A-S） system with different additions of FeO and Fe2O3 were investigated. FeO inhibits the conversion of β-Ca2SiO4 to γ-Ca2SiO4 and makes the clinker not pulverizable. FeO and Fe2O3 inhibit the formation of CaAl2O4, but promote the formation of Ca12Al14O33. The interplanar spacing at （2 1 1） crystal face of Ca12 Al14O33 in the clinker increases with the increase of FeO addition, which indicates that FeO forms solid solutions in Ca12Al14O33. The clinkers with Fe2O3 addition form a new phase Ca2Fe2O5, and the amount of Ca2Fe2o5 increases with the in crease of Fe2O3 addition. Both FeO and Fe2O3 do not affect the Al2O3 leaching rate of calcium aluminate clinker in sodium carbonate solution, but they increase the molar ratio of caustic Na2O to Al2O3 in the leached liquor.展开更多
The mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al2O3-Na2O system during the hightemperature sintering process were systematically investigated using DSC-TG,XRD,SEM-EDS,FTIR,and Ra...The mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al2O3-Na2O system during the hightemperature sintering process were systematically investigated using DSC-TG,XRD,SEM-EDS,FTIR,and Raman spectra,and the crystal structure of Na4Ca3(AlO2)10 was also simulated by Material Studio software.The results indicated that the minerals formed during the sintering process included Na4Ca3(AlO2)10,CaO·Al2O3,and 12 CaO·7 Al2O3,and the content of Na4Ca3(AlO2)10 could reach 92 wt%when sintered at 1200°C for 30 min.The main formation stage of Na4Ca3(AlO2)10 occurred at temperatures from 970 to 1100°C,and the content could reach82 wt%when the reaction temperature increased to 1100°C.The crystal system of Na4Ca3(AlO2)10 was tetragonal,and the cells preferred to grow along crystal planes(110)and(210).The formation of Na4Ca3(AlO2)10 was an exothermic reaction that followed a secondary reaction model,and its activation energy was 223.97 kJ/mol.展开更多
Various characterization methods, including scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller surface-area measurements, thermogravimetry–d...Various characterization methods, including scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller surface-area measurements, thermogravimetry–differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy, were used to study the mineral structure and surface characteristics of high-iron hydrargillite. Gibbsite, goethite, and hematite were found to be the main mineral components of hydrargillite, whereas the goethite and hematite were closely clad to the surface of the multilayer gibbsite crystals. Compared with the synthetic gibbsite, the hydrargillite contained more structural micropores generated by the mineral evolution during the mineralization process. The gibbsite in hydrargillite contained less crystal water compared with the synthetic gibbsite, and it was a typical polymorphic structure. The isomorphous substitution of Al and Fe was observed in goethite. The dissolution-controlling step of hydrargillite was the ionic diffusion speed because of the goethite and hematite that closely covered and encapsulated the gibbsite crystals.展开更多
The precipitation characteristics and mechanism of vanadium carbides during isothermal transformation at 650℃ in aV-microalloyed medium-carbon steel were investigated through scanning electron microscopy and transmis...The precipitation characteristics and mechanism of vanadium carbides during isothermal transformation at 650℃ in aV-microalloyed medium-carbon steel were investigated through scanning electron microscopy and transmission electronmicroscopy as well as dilatometry test. Five morphologies of vanadium carbides were found to precipitate at differentnucleation sites during the transformation. Two kinds of interphase precipitation form simultaneously in both pro-eutectoidand pearlitic ferrites. The linear arrays of fine interphase precipitates are parallel to the γ/α interface, and the fine needles ofinterphase precipitates are perpendicular to the 7/ct interface. The vanadium carbides of long or short fibers, coarse particlesand fine particles form in both pro-eutectoid and pearlitic ferrites, displaying different precipitation distributions andorientation relationships with ferrite. The precipitation mechanisms of vanadium carbide precipitates with different modeswere proposed, and the precipitation sequence of various vanadium carbide precipitates was finally ascertained.展开更多
The effects of Ti-and Mg-bearing minerals on the crystal structure,morphology,particle size distribution,and formation mechanism of efficient desilication product of hydroandradite(HA)during hydrothermal conversion in...The effects of Ti-and Mg-bearing minerals on the crystal structure,morphology,particle size distribution,and formation mechanism of efficient desilication product of hydroandradite(HA)during hydrothermal conversion in a synthetic sodium aluminate solution were investigated via X-ray diffractometer,scanning electron microscope and particle size analyzer.During HA formation,anatase,rutile,and periclase dissolved in sodium aluminate solution engage in ion substitution reactions between Ti4+and Si4+,and between Mg^(2+)and Ca^(2+),respectively.However,dissolved hydromagnesite cannot enter into the HA.The content of HA after the hydrothermal reactions changes slightly with the increase of anatase and periclase contents,but it notably decreases with increased quantities of rutile and hydromagnesite.Ti-bearing minerals reduce the particle size and enhance the specific surface area of HA,whereas Mg-bearing minerals exert the opposite effect.The morphology of HA with Ti-and Mg-bearing minerals changes from spherical particles to flocculent structure and hexagonal plate-like particles.展开更多
基金the financial support from the National Key R&D Program of China(No.2022YFC2904405)the National Natural Science Foundation of China(Nos.22078055,51774079)。
文摘To synergistically recover alumina and alkali from red mud(RM),the structural stability and conversion mechanism of hydroandradite(HA)from hydrogarnet(HG)were investigated via the First-principles,XRF,XRD,PSD and SEM methods,and a novel hydrothermal process based on the conversion principle was finally proposed.The crystal structure simulation shows that the HA with varied silicon saturation coefficients is more stable than HG,and the HA with a high iron substitution coefficient is more difficult to be converted from HG.The(110)plane of Fe_(2)O_(3) is easier to combine with HG to form HA,and the binding energy is 81.93 kJ/mol.The effects of raw material ratio,solution concentration and hydrothermal parameters on the conversion from HG to HA were revealed,and the optimal conditions for the alumina recovery were obtained.The recovery efficiencies of alumina and Na_(2)O from the RM are 63.06%and 97.34%,respectively,and the Na_(2)O content in the treated RM is only 0.13%.
基金the financial supports from the National Key R&D Program of China(No.2022YFC2904401)the National Natural Science Foundation of China(Nos.22078055,52074083,51774079)the Fundamental Research Funds for the Central Universities,China(No.N2225002)。
基金the National Natural Science Foundation of China(Nos.51104041 and 51174054)
文摘The effect of lime on the pre-desilication and digestion of gibbsitic bauxite in synthetic sodium aluminate liquor at different tem- peratures was investigated. The bauxite is comprised of gibbsite, aluminogoethite, hematite, kaolin, quartz, and minor boehmite. Lime in- creases the desilication efficiency of the bauxite during the pre-desilication process by promoting the conversion of sodalite and cancrinite to hydrogamet. Desilication reactions during the digestion process promoted by lime result in the loss of A1203 entering the red mud, but the amount of aluminogoethite-to-hematite conversion promoted by lime leads to the increase of aluminogoethific A1203 entering the digested liquor. The alumina digestion rate at 245~C is higher than that at 145 C due to the more pronounced conversion of aluminogoethite to hema- tite. The soda consumption during the digestion process decreases due to lime addition, especially at higher temperatures.
文摘AIM: To investigate the clinical features of Crohn's disease(CD) and intestinal tuberculosis(ITB) with a scoring system that we have developed.METHODS: A total of 25 CD and 40 ITB patients were prospectively enrolled from August 2011 to July 2012.Their characteristics and clinical features were recorded. Laboratory, endoscopic, histologic and radiographic features were determined. The features with a high specificity were selected to establish a scoring system. The features supporting CD scored +1, and those supporting ITB scored-1; each patient received a final total score. A receiver operating characteristic(ROC) curve was used to determine the best cut-off value for distinguishing CD from ITB.RESULTS: Based on a high specificity of differentiating between CD and ITB, 12 features, including longitudinal ulcers, nodular hyperplasia, cobblestone-like mucosa, intestinal diseases, intestinal fistula, the target sign, the comb sign, night sweats, the purified protein derivative test, the interferon-γ release assay(T-SPOT.TB), ring ulcers and ulcer scars, were selected for the scoring system. The results showed that the average total score of the CD group was 3.12 ± 1.740, the average total score of the ITB group was-2.58 ± 0.984, the best cutoff value for the ROC curve was-0.5, and the diagnostic area under the curve was 0.997, which was statistically significant(P < 0.001). The patients whose total scores were higher than-0.5 were diagnosed with CD; otherwise, patients were diagnosed with ITB. Overall, the diagnostic accuracy rate and misdiagnosis rate of this scoring system were 97% and 3%, respectively. CONCLUSION: Some clinical features are valuable for CD and ITB diagnosis. The described scoring system is key to differentiating between CD and ITB.
基金Project(2018YFC1901903) supported by the National Key Research and Development Program of ChinaProjects(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A new chemical pre-desilication process of kaolinite in diasporic bauxite in alkali solution at atmospheric pressure was proposed.The dissolution kinetics and mechanism were studied by chemical analysis,XRD and SEM.The kinetic results of dissolution process show that the kaolinite is symbiotic with diaspore but without cladding.The dissolution ratio of kaolinite is close to 100%at 100℃for 90 min.The dissolution kinetic equation is 1-(1-α)^1/3=7.88×10^6 exp[-64434/(RT)]t.With the low L/S(L/S=10:1),the dissolution ratio of kaolinite decreases to 55%.This is due to the formation of lamellar hydroxyl-sodalite(OH-SOD)which is deposited on the surface of kaolinite and hinders the further dissolution of kaolinite.Under the optimum conditions,the A/S(mass ratio of Al2 O3 to SiO2)of dissolved residues is increased to 8.55,while the A/S of the bauxite is only 4.97.
基金Projects(51674075,51774079) supported by the National Natural Science Foundation of China
文摘The mineral transition, microstructure and self-pulverization as well as the Al2O3 leaching performance of calcium aluminate clinkers with different P additions in CaO-Al2O3-SiO2 system during high-temperature sintering were systematically studied by XRF, XRD, SEM-EDS and DSC-TG technologies. The clinkers sintered at 1350 °C mainly contain 12CaO·7Al2O3, CaO·Al2O3,β-2CaO·SiO2 and γ-2CaO·SiO2. The content of β-2CaO·SiO2 increases while the content of γ-2CaO·SiO2 decreases as the P addition increases. The self-pulverization property of clinkers deteriorates with increasing P addition. P distributes evenly in the clinkers, and inhibits the transformation of β-2CaO·SiO2 to γ-2CaO·SiO2. The cell volumes of 12CaO·7Al2O3 and CaO·Al2O3 decrease and increase respectively as the P addition increases, and P decreases their formation temperatures. The Al2O3 leaching rate of calcium aluminate clinkers decreases obviously with increasing P addition, which decreases form 95.01% to 83.84% as the P addition increases from 0 to 0.85%.
基金Project(2018YFC1901903)supported by the National Key R&D Program of ChinaProjects(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 formation kinetics and mechanism of tricalcium aluminate hydrate and calcium oxalate in dilute sodium aluminate solution and sodium oxalate solution were studied respectively based on the lime causticization, and the optimal conditions for removing the oxalate in dilute sodium aluminate solution as well as the mechanism were finally obtained.The formation processes of tricalcium aluminate hydrate and calcium oxalate are mainly controlled by the chemical reaction and the inner diffusion respectively,and the corresponding reaction rate equations as well as the apparent activation energy were calculated. The hydrocalumite with a spatially interleaved structure will form in dilute sodium aluminate solution with sodium oxalate, greatly removing the oxalate impurity by absorption. Calcium oxalate can be converted to tricalcium aluminate hydrate with the increasing reaction time. The oxalate causticization efficiency and the alumina loss rate can be over 90% and below 31% respectively when reacted at 50℃ with a stirring rate of 200 r/min.
基金Item Sponsored by National Natural Science Foundation of China(51174054,51104041,51374065)
文摘The sintering characteristics at 1350℃ and leaching property at 80℃ of calcium aluminate clinkers in the CaO-Al2O3-SiO2 （C-A-S） system with different additions of FeO and Fe2O3 were investigated. FeO inhibits the conversion of β-Ca2SiO4 to γ-Ca2SiO4 and makes the clinker not pulverizable. FeO and Fe2O3 inhibit the formation of CaAl2O4, but promote the formation of Ca12Al14O33. The interplanar spacing at （2 1 1） crystal face of Ca12 Al14O33 in the clinker increases with the increase of FeO addition, which indicates that FeO forms solid solutions in Ca12Al14O33. The clinkers with Fe2O3 addition form a new phase Ca2Fe2O5, and the amount of Ca2Fe2o5 increases with the in crease of Fe2O3 addition. Both FeO and Fe2O3 do not affect the Al2O3 leaching rate of calcium aluminate clinker in sodium carbonate solution, but they increase the molar ratio of caustic Na2O to Al2O3 in the leached liquor.
基金financially supported by the National Key R&D Program of China(No.2018YFC1901903)the National Nature Science Foundation of China(Nos.51674075 and 51774079)the Fundamental Research Funds for the Central Universities,China(No.N182508026)。
文摘The mineral transition and formation mechanism of calcium aluminate compounds in CaO-Al2O3-Na2O system during the hightemperature sintering process were systematically investigated using DSC-TG,XRD,SEM-EDS,FTIR,and Raman spectra,and the crystal structure of Na4Ca3(AlO2)10 was also simulated by Material Studio software.The results indicated that the minerals formed during the sintering process included Na4Ca3(AlO2)10,CaO·Al2O3,and 12 CaO·7 Al2O3,and the content of Na4Ca3(AlO2)10 could reach 92 wt%when sintered at 1200°C for 30 min.The main formation stage of Na4Ca3(AlO2)10 occurred at temperatures from 970 to 1100°C,and the content could reach82 wt%when the reaction temperature increased to 1100°C.The crystal system of Na4Ca3(AlO2)10 was tetragonal,and the cells preferred to grow along crystal planes(110)and(210).The formation of Na4Ca3(AlO2)10 was an exothermic reaction that followed a secondary reaction model,and its activation energy was 223.97 kJ/mol.
基金financially supported by the National Natural Science Foundation of China (No.51104041)
文摘Various characterization methods, including scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer–Emmett–Teller surface-area measurements, thermogravimetry–differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy, were used to study the mineral structure and surface characteristics of high-iron hydrargillite. Gibbsite, goethite, and hematite were found to be the main mineral components of hydrargillite, whereas the goethite and hematite were closely clad to the surface of the multilayer gibbsite crystals. Compared with the synthetic gibbsite, the hydrargillite contained more structural micropores generated by the mineral evolution during the mineralization process. The gibbsite in hydrargillite contained less crystal water compared with the synthetic gibbsite, and it was a typical polymorphic structure. The isomorphous substitution of Al and Fe was observed in goethite. The dissolution-controlling step of hydrargillite was the ionic diffusion speed because of the goethite and hematite that closely covered and encapsulated the gibbsite crystals.
文摘The precipitation characteristics and mechanism of vanadium carbides during isothermal transformation at 650℃ in aV-microalloyed medium-carbon steel were investigated through scanning electron microscopy and transmission electronmicroscopy as well as dilatometry test. Five morphologies of vanadium carbides were found to precipitate at differentnucleation sites during the transformation. Two kinds of interphase precipitation form simultaneously in both pro-eutectoidand pearlitic ferrites. The linear arrays of fine interphase precipitates are parallel to the γ/α interface, and the fine needles ofinterphase precipitates are perpendicular to the 7/ct interface. The vanadium carbides of long or short fibers, coarse particlesand fine particles form in both pro-eutectoid and pearlitic ferrites, displaying different precipitation distributions andorientation relationships with ferrite. The precipitation mechanisms of vanadium carbide precipitates with different modeswere proposed, and the precipitation sequence of various vanadium carbide precipitates was finally ascertained.
基金financial supports from the National Key R&D Program of China (No.2022YFC2904401)the National Natural Science Foundation of China (Nos.22078055,51774079)the Fundamental Research Funds for the Central Universities,China (No.N2225002)。
文摘The effects of Ti-and Mg-bearing minerals on the crystal structure,morphology,particle size distribution,and formation mechanism of efficient desilication product of hydroandradite(HA)during hydrothermal conversion in a synthetic sodium aluminate solution were investigated via X-ray diffractometer,scanning electron microscope and particle size analyzer.During HA formation,anatase,rutile,and periclase dissolved in sodium aluminate solution engage in ion substitution reactions between Ti4+and Si4+,and between Mg^(2+)and Ca^(2+),respectively.However,dissolved hydromagnesite cannot enter into the HA.The content of HA after the hydrothermal reactions changes slightly with the increase of anatase and periclase contents,but it notably decreases with increased quantities of rutile and hydromagnesite.Ti-bearing minerals reduce the particle size and enhance the specific surface area of HA,whereas Mg-bearing minerals exert the opposite effect.The morphology of HA with Ti-and Mg-bearing minerals changes from spherical particles to flocculent structure and hexagonal plate-like particles.
