Study Of The Phase Equilibria Of CaO-SiO₂-La₂O₃-Nb₂O₅ Slag At Different Atmospheres

Niobium and rare earth are indispensable metal materials in modern industry and advanced fields.China has huge reserves of niobium and rare earth resources.However,due to the variety of mineral phases,fine grain size and low niobium grade,it is extremely difficult to smelt the niobium and rare earth resources.Most of the niobium and rare earth resources are still stay in tailing.CaO-SiO2-La2O3-Nb2O5 slag system is the basic slag system involved in the process of comprehensive utilization of niobium and rare earth resources.However,due to the lack of thermodynamic data such as phase equilibrium relation of the related slag systems,there is no thermodynamic data can be refered to in the research of smelting and melting separation processes,which seriously hinders the utilization of niobium and rare earth resources.This paper choose the CaO-SiO2-La2O3-Nb2O5 slag system as the research object,and determines the composition range of the experimental slag by referring to the composition of crude niobium concentrate ore and niobium riched slag.Based on the metallurgical physics and chemistry knowledge,the phase equilibrium relationship of CSNL slag system under air atmosphere and reductive atmosphere at 1200℃ was studied through high temperature equilibrium experiment,and the pseudo-quaternary phase diagram of slag under different atmosphere conditions was drawn.Under the current experiment condition,the conclusions are as follows:(1)Within the composition range of slag system,the high temperature equilibrium phases are liquid phase,CaO·Nb2O5,CaO-SiO2,La2O3·Nb2O5,SiO2,2CaO·Nb2O5。(2)Within the composition range of slag system,under both air and reducing atmosphere,the increase of niobium content promote the equilibrium phase coexistence of CaO·Nb2O5 and La2O3-Nb2O5,inhibite the equilibrium phase coexistence of CaO·SiO2 and SiO2.(3)Within the composition range of slag system,as the basicity of slags is between 0.98 and 1.17,the increase of niobium content will not cause the change of equilibrium phase,the main precipitated phase are CaO·Nb2O5,CaO·SiO2 and La2O3·Nb2O5,when the content of niobium reduce to 6.57%,the La2O3-Nb2O5 phase disappears.(4)According to the high temperature equilibrium phase composition,the phase equilibrium coexistence relationship of CaO-SiO2-La2O3-Nb2O5 slag was drawn.(5)Confirmed the CN-S,CN-LN,CN-CS and CS-S primary crystal zone intersection and the single variable points in the CaO-SiO2-La2O3-Nb2O5 diagram,then divided the primary crystal zone of each phase.(6)The pseudo quaternary phase diagrams of CaO-SiO2-La2O3-Nb2O5 slag under different atmosphere were drawn.Comparing to the air atmosphere,the primary crystal zone intersection of CN-LN moves to the LN and that of CN-S moves to CN under reducing atmosphere.