Study Of Theory And Experiments On Preparing Strontium By Vacuum Carbothermic Reduction

Sr and its compounds are widely used in the electronic, chemical, optical andmedical field, Traditional methods of preparing metal strontium have molten saltelectrolysis and vacuum thermoreduction. The molten salt electrolysis has lots ofdisadvantages that include raw material high cost, environmental pollution, volatile losslarge and equipments serious corrosion. The vacuum thermoreduction hasaluminothermic reduction and silicothermic reduction, the two methods consume a largeamount of Al and Si or Si-Fe, engender a lot of solid state slag, economical, resourceand environmental poor. This paper put forward the new method of preparing strontiumby Vacuum Carbothermic Reduction, thermodynamics and kinetics of the new methodwere studied systematically. It obtained metallic strontium by Vacuum CarbothermicReduction experiment. The technology, economy, resources and environment benefit ofthis method were calculated and analyzed. Prospect of this method was indicated.①Thermodynamic, kinetics analysis and experimental study on direct thermaldecomposition of SrCO3and vacuum thermal decomposition of SrCO3with carbonwere implemented. The results show, the initial decomposition temperature decreasewith the system pressure decrease, the initial decomposition temperature of vacuumthermal decomposition of SrCO3with carbon average decrease about200K comparedwith direct thermal decomposition of SrCO3when the pressure is1~100Pa. It provedthat the chemical reaction is the rate-determining step of the overall reaction process.The activation energies of the direct thermal decomposition of SrCO3and vacuumthermal decomposition of SrCO3with carbon are142.76kJ/mol and124.82kJ/molseparately when they are decomposed in the973~1123K. So carbon is helpful todecrease the activation energy, the reaction of vacuum thermal decomposition of SrCO3with carbon is more rapid and thorough.②Thermodynamic on vacuum carbothermic reduction producing metallicstrontium was calculated and analyzed. The results show, the critical reactiontemperature of is up to2279K at standard state. The Gibbs free energy and criticalreaction temperature decrease with the system pressure decrease under the condition ofvacuum, the critical reaction temperature is only1423K when system pressure is10Pa.③The reaction mechanism and kinetics on vacuum carbothermic reductionproducing metallic strontium was studied. The results show, the activation energies are 315.00kJ/mol~384.46kJ/mol under the control of gasification diffusion, the activationenergy is163.39kJ/mol under the control of the boudouard reaction of carbon, theactivation energy is212.29kJ/mol under the control of chemical reaction. The activationenergy under the control of gasification diffusion is maximum, so the gasificationdiffusion is the rate-determining step of the overall reduction process.④The experiment on vacuum carbothermic reduction producing metallicstrontium was studied. The results show, it get metallic strontium when system pressureis10Pa and reaction temperature is1473K. Reduction rate and reduction efficiencyincrease with C/SrO molar ratio increase, the system pressure decrease, the temperatureincrease. The experimental results are in excellent agreement with the thermodynamic,kinetics analysis. The vacuum carbothermic reduction producing metallic strontium canbe realized in engineering.⑤The technology, economy, resources and environment benefit of vacuumcarbothermic reduction producing metallic strontium were calculated and analyzed. Theresults show, reducing agent cost of carbothermic reduction producing metallicstrontium is only2.93%of aluminothermic reduction and6.85%of silicothermicreduction. Theory reduction rate of strontium of carbothermic reduction producingmetallic strontium increase44%and45%separately compared with aluminothermicreduction and silicothermic reduction, resource utilization rate was higher. The slag ofcarbothermic reduction producing metallic strontium was nothing theoretically.