Study On Thermal Decomposition Characteristics Of Sodium Pyroxenite And Solid Phase Synthesis Of Sodium Pyroxene

In the process of sintering, physical and chemical properties of complex silicateand aluminosilicate gangue will change, which has great influences on the generation ofcomplex calcium ferrite in Bayan-obo sintered ore. A typical kind of sodium pyroxenitein Bayan-obo iron ore is selected as the research object in this experiment. Theendothermic peak and the change of quality is definited by means of thermal analysis inthe rising process. And then the samples are sintered at the peak temperatures. The mainingredients of sodium pyroxenite and the resultants are definited by means of X-raydiffraction analysis. The experiment ascertains the change law of physical and chemicalproperties of sodium pyroxenite such as thermal decomposition, softening, meltingtemperatures and the corresponding resultants, which provides basic data for exploringthe formation mechanism of complex calcium ferrite （SFCA） in baogang specialsintered ore. It shows: at room temperature, natural sodium pyroxenite contains not onlythe main mineral NaFeSi₂O₆, but also a certain amount of impurity BaSO4, etc; the mainmineral composition is also NaFeSi₂O₆sintered at555℃; CaF2comes from complexcompounds containing fluorine at993℃. NaFeSi₂O₆in the sodium pyroxenite reactswith CaF2, accompanying with evolution of NaF gas; the melting temperature is1194¹300℃.Because the components of natural sodium pyroxenite rock （its main component isNaFeSi₂O₆） are complex, it will make the problem become more complicated to studyon the formation mechanism of SFCA in Bayan-obo sinter if it is directly used as theexperimental raw material. Consequently, solid phase synthetic reaction of sodiumpyroxene NaFeSi₂O₆is studied in the laboratory using pure reagents: Na₂CO₃, NaOH,Fe₂O₃, Fe（OH）₃, SiO₂and H₂SiO₃as raw materials in order to obtain pure sodiumpyroxene, which will provide the experimental material of pure （or relative pure）sodium pyroxene for further research on the formation mechanism of SFCA in thesintering process of Bayan-obo special ore. The possible solid phase reactions forNa₂O·Fe₂O₃-SiO₂system, Na₂CO₃-Fe₂O₃-SiO₂system, Na₂CO₃-Fe（OH）₃-H₂SiO₃system, Na₂CO₃-Fe₂O₃-H₂SiO₃system and NaOH-Fe（OH）₃-H₂SiO₃system have beenstudied by means of thermal analysis （TG-DSC/DTA） and X-ray diffraction （XRD） insintering process; the system and the influencing factors of sodium pyroxene NaFeSi₂O₆synthetic reaction also have been studied. The results show that: Na₂CO₃-Fe₂O₃-SiO₂ system, Na₂CO₃-Fe（OH）₃-H₂SiO₃system and Na₂CO₃-Fe₂O₃-H₂SiO₃system cansynthetize sodium pyroxene NaFeSi₂O₆; Na₂O·Fe₂O₃-SiO₂system is hard to largelysynthesize sodium pyroxene NaFeSi₂O₆due to the existence of the displacementresponse; while NaOH-Fe（OH）₃-H₂SiO₃system can’t synthesize sodium pyroxeneNaFeSi₂O₆. Na₂CO₃-Fe（OH）₃-H₂SiO₃system is the best solid phase synthesis system,and the optimum synthesis temperature should be controlled at900℃or so. ForNa₂CO₃-Fe（OH）₃-H₂SiO₃system, the main influencing factors of sodium pyroxenesynthesis is temperature; appropriately increasing sintering temperature is beneficial forsynthesis of sodium pyroxene NaFeSi₂O₆, but it will melt and decompose at highertemperatures. Extending holding time or increasing sintering times can promotesynthesis of sodium pyroxene NaFeSi₂O₆. But when the sample is sintered more thancertain time and times, increasing sintering times or extending holding time have noobvious influence on the purity of sodium pyroxene.