Determination Of Cryolite Ratio In NaF-AlF₃-CaF₂-KF/LiF/Al₂O₃ System By Raman Spectroscopy

Aluminum electrolyte is a vital part in the aluminum electrolytic process.From the dissolution of alumina to the precipitation of aluminum liquid at the cathode,the electrolytic process is all done in the aluminum electrolyte.The change of the aluminum electrolyte affects the entire electrolytic process directly.Therefore,in order to make electrolytic process smoothly operated,it is important to ensure the stability of the parameters of the aluminum electrolyte.Among the parameters of the aluminum electrolyte,Cryolite Ratio(CR)is a very important one.Furthermore,there are impurities,such as lithium and potassium in bauxite in China.As a result,lithium and potassium elements enrichment in the electrolyte will occur in the aluminum electrolyte using the alumina produced by them,which makes it difficult to determine the value of CR.In recent years,the continuous research on aluminum electrolytes by Raman spectroscopy has provided a new direction for the determination of aluminum electrolyte parameters.In the present study,Raman spectra of the NaF-AlF3-CaF2-KF/LiF/Al2O3 electrolyte systems with different value of CR,alumina and additive contents were measured.The relationship between different papameters of Raman bands and the composition of the electrolyte was discussed in order to establish the connection between them.The present study has laid the foundation for the further determination of the value of CR of the aluminum electrolyte by Raman spectroscopy.Firstly,NaF-AlF3-LiF,NaF-AlF3-KF and NaF-AlF3-CaF2 systems were studied,and the result showed that there were differences of Raman shift of the correspond bands among different alkali metal cations.When the content of additives was constant,as the value of CR of the system increased,the intensity ratio of v1 characteristic peak of Al3F145-to v1 characteristic peak of AlF63-in Raman spectra tended to decrease and the equations of the intensity ratio and the value of CR were obtained.Secondly,NaF-AlF3-CaF2-LiF and NaF-AlF3-CaF2-KF systems were investigated.The results showed that when the content of the additives was constant,the intensity of the peaks of v5 peak to v1 peak of AlF63-was decrease with the increase of the value of CR.The equations of the intensity ratio and the value of CR were obtained.Finally,NaF-AlF3-4wt%LiF-Al2O3 system was studied,and it was found that when the content of Al2O3 was constant,as the value of CR of the system increased,the Raman shift,width at half maximum of v1 characteristic peak of Al3F145-to v1 characteristic peak of AlF63-,and the intensity ratio of them had a tendency to decrease.Then,NaF-AlF3-4wt%KF-Al2O3 and NaF-AlF3-4wt%CaF2-Al2O3 systems were studied.The results showed that with the addition of Al2O3,the Raman characteristic peaks of each system showed blue shifted.When the content of Al2O3 was constant,as the value of CR of the system increased,the intensity ratio of v1 characteristic peak of Al3F145-to v1 characteristic peak of AlF63-decreased.In the solidif1ed sample,O element still existed as Al2O3,and the content of Al2O3 had no obvious relationship with the characteristic peak parameters of the Raman spectra in these systems.