A spectroscopic and computational study of Al(III) complexes in cryolite melts: Effect of cation nature

Abstract

Graphical abstractHighlights► We investigate Li, Na and K cryolite melts by Raman spectroscopy and dft. ► A slight red shift of main Raman peaks is observed in the row Li+, Na+, K+. ► A decrease of the half-widths of peaks is observed in the same row. ► Fluoroaluminates and their complexation kinetics play an important role.

Existence of Al2F7− in molten MF–AlF3 (M = K, Cs) systems as determined by Raman spectroscopy and structural simulation

“…The ionic structures of the molten systems of alkali metal fluorides and aluminum fluoride have attracted significant interest from the research community. At present, the existence of AlF 6 3 − , AlF 5 2 − , and AlF 4 − complex ions have been proven by Raman spectroscopy [9][10][11][12][13][14] . It is acknowledged that the equilibria among the Al-F complex ions in molten systems exist as AlF 6 3 − = AlF 5 2 − + F − and AlF 5 2 − = AlF 4 − + F − .…”

“…Simulation technology does not require physical experiments; thus, it is excellent for studying the ionic structures of molten salts. Molecular dynamic simulation and quantum chemical calculation are two conventional simulation techniques used to study the ionic structure of alkali metal fluorides and aluminum fluoride mixtures [14,[19][20][21] . The molecular dynamic results from the study by Bu čko and Šimko [22,23] showed that Al 2 F 7…”

“…− was present in the Li 3 AlF 6 system but not in the Na 3 AlF 6 , K 3 AlF 6 , and Rb 3 AlF 6 systems. However, Nazmutdinov et al [14] studied the molten Li/Na/KF-AlF 3 systems using Raman spectroscopy combined with quantum chemical calculations and reported that Al 2 F 7…”

Quantitative analysis on the microstructure of molten binary KF‐AlF3 system by in situ Raman spectroscopy assisted with first principles method

“…Raman spectra of molten fluoroaluminates were reinvestigated to certify the existence of [AlF 5 ] 2− clusters. [6] Lacassagne [7] observed 23 [8] In recent years, the molten binary MF-AlF 3 system has been extensively studied, [9][10][11] but the species in the melts is still a debatable issue. Since 1999, in situ high temperature 27 Al nuclear magnetic resonance (NMR) spectroscopy has been conjuncted with in situ high-temperature Raman spectroscopy to explore the structure of the molten NaF-AlF 3 system.…”

Aluminium phosphate behaviour in Na3AlF6–Al2O3 melts: a new insight from in situ high temperature NMR measurements

“…The structure of cryolitic melts has been widely studied using different techniques such as cryoscopy, 2 molecular dynamics calculations 3 or Raman spectroscopy. [4][5][6][7] More recently, high temperature NMR spectroscopy has proven to be a powerful tool to determine in situ the structure of molten cryolitic systems. [8][9][10][11][12] Phosphorus is an important impurity element in electrolytic aluminium production, which comes from natural raw materials (primary and secondary alumina, and aluminium fluoride) and from fresh and recycled electrolyte.…”