| In the modern industry,aluminum is produced by the Hall-Heroult process extensively.In that process,Al2O3 is taken as solute,NaF-AlF3 molten salt as solvent,and certain amount of additives are also added.In the process of aluminum electrolysis,the value of Cryolite Ratio(CR)and alumina concentration are important parameters.Accurate and rapid determination of CR and alumina concentration not only contribute to the smooth production,but also improve the production efficiency and energy saving.Meantime,due to the existence of potassium and lithium in the alumina from Chinese domestic plants,the enrichment of potassium and lithium salts existed in the aluminum electrolysis cells that have used this kind of alumina as raw material for a long time,which may lead to the error increment in the conventional CR determining technique.In recent years,with the technical progress of Raman spectroscopy,it has been widely used in the field of aluminum elctrolyte analysis and is expected to open up new trails in the determination of aluminum electrolyte composition.Based on the above analysis,the Raman spectra of the MF-AIF3(M=Na,K,Li)electrolyte systems with different values of molar ratio of MF to AIF3 and the NaF-AlF3 electrolyte system with different contents of KF,LiF or Al2O3 were measured by Raman spectroscopy.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 and other related parameters of aluminum electrolyte by Raman spectroscopy.First,the NaF-AlF3 system was studied.The results show that the intensity and area ratio of v2,Vs to vi bands of AlF63-decrease with the increase of the value of CR in NaF-AlF3 system when the value of CR is greater than 2.1.The linear equations between these parameters and the value of CR were obtained.Then,the corresponding studies on the KF-AIF3 system and the LiF-AlF3 system were carried out.The results show that there were differences of Raman shift of the correspond bands for different alkali metal cation.However,as the molar ratio of KF or LiF to NaF increases,the intensity ratio of the area ratio to the characteristic peaks of v2,V5 to v1 tend to decrease.The linearequations of these Raman parameters and molar ratio of MF to AIF3 were obtained.Further,the Raman spectra of MF-NaF-AlF3(M=K,Li)system with different molar ratios of(MF+NaF)to AlF3 were investigated.The experimental results show that with the increase of MF content,the intensity ratio and the area ratio of v2 to v1 characteristic peak tend to increase.The linear equations of the intensity ratio and the area ratio of v2 characteristic peak to vi characteristic peak of AlF63-in Raman spectra and MF content were obtained.Finally,the Raman spectra of NaF-AlF3-Al2O3 system with different compositions were studied.The experimental results show that the CR and Al2O3 concentration have some influence on the form of Al-O-F ionic groups in NaF-AlF3-Al2O3 system.For lower CR and Al2O3,the dominant species is Al2OF62-,and for higher CR and Al2O3,the dominant species is Al2O2F42-.The intensity ratio and the area ratio of each characteristic peak of AlF63-to the characteristic peak of Al-O-F complex in the Raman spectra of NaF-AlF3-Al2O3 system were increased with the increase of Al2O3 concentration.The linear equations of intensity ratio and area ratio of each characteristic peak of AlF63-to Al-O-F characteristic peak in Raman spectra and Al2O3 content were obtained. |
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