Fine analysis of the component effect on the microstructure of LiCl solution

Lithium resources are abundant in Chinese salt lakes, but the high Mg/Li ratio in such aqueous natural sources has brought difficulties to the separation and purification of lithium. Crystallization processes are highly affected by the solution microstructure, which, in turn, depends on its composition. Synchrotron X-ray scattering, Raman spectroscopy, and molecular dynamics simulation methods were used to study the microstructure of aqueous LiCl solutions with different concentrations. In the reduced structure function, F(Q), the double peak around the scattering vector Q = 2.5 A-1 becomes a single peak, which indicates the addition of LiCl changes the tetrahedral hydrogen bond structure in the aqueous solution. The deconvolution fitting of the Raman spectra show that the DDAA-type (double donor -double acceptor) hydrogen bonds tend to be transformed into DA-type (single donor-single acceptor) hydrogen bonds, confirming that the addition of LiCl breaks the tetrahedral hydrogen bond structure. This hydrogen-bond transformation was confirmed by pair distribution function analysis from molecular dynamics simulations of aqueous KCl solutions. In addition, considering the large number of magnesium ions coexisting with LiCl in the Salt Lake, the microstructure of mixed LiCl-MgCl2 solution was also stud-ied. According to the X-ray scattering results, the peak in the reduced pair distribution function G(r) near r = 3.25 A shifted from 3.25 A to 3.10 A with increased Mg/Li ratio. This change is likely to result from the Cl-O and OAO interactions in the mixed aqueous solution. The deconvolution fitting results of Raman spectra show that the DDAA type hydrogen bond increases with the Mg/Li ratio, while the DA + DDA type hydrogen bond decreases. The molecular dynamics results showed that chlorine ions have a higher ten-dency to form contact ion pairs with Mg2+ than Li+. We propose this to be one of the processes retarding the separation of pure LiCl crystal from mixed LiCl-MgCl2 systems.(c) 2023 Elsevier B.V. All rights reserved.

Automated summary

Lithium resources are abundant in Chinese salt lakes, but the high Mg/Li ratio in these natural sources has made it difficult to separate and purify lithium. This study used synchrotron X-ray scattering, Raman spectroscopy, and molecular dynamics simulation methods to investigate the microstructure of aqueous LiCl solutions with different concentrations. The results revealed the disruption of the tetrahedral hydrogen bond structure in the aqueous solution due to the addition of LiCl and the enhanced interactions between chlorine and oxygen atoms.