Reconstruction of MgAl-layered double hydroxides to LiAl-layered double hydroxides for scalable lithium extraction from salt lake brine

Abstract

MgAl-layered double hydroxides (MgAl-LDHs) attract interest for lithium extraction due to their wide availability, high stability, and environmental friendliness. LiAl-layered double hydroxides (LiAl-LDHs) can be obtained by lithiation of MgAl-LDHs, yielding the facile preparation of adsorbents with high selectivity. Herein we synthesized porous MgAl-LDHs by a sol-gel method. MgAl-LDHs can be converted into LiAl-LDHs via dissolution and recrystallization process in LiOH solution. The structure of MgAl-LDHs dissolves, and Mg2+ exchange with Li+ in the solution to generate LiAl-LDHs. Mg2+ enter the solution. MgAl-LDHs and LiAl-LDHs were characterized using X-ray powder diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), N2 adsorption-desorption isotherms and X-ray photoelectron spectroscopy (XPS). The granulation of MgAl-LDHs and LiAl-LDHs was facilitated by chemical/physical cross-linking of sodium alginate using CaCl2 solutions. The performance of lithium extraction was investigated using synthetic brines, and real salt lake brines. The results showed that MgAl-LDHs and LiAl-LDHs adsorbents registered an adsorption capacity of 9.7 and 6.4 mg/g, respectively, at pH = 6 in 300 mg/L of Li+ solutions. The kinetic analysis revealed that granulated MgAl-LDHs and LiAl-LDHs exhibited pseudo-second-order adsorption behavior attributed to the redox behavior. In the brine of East Taigener Salt Lake, the granulated MgAl-LDHs and LiAl-LDHs achieved an adsorption capacity of 15.5 and 9.1 mg/g, respectively. The granulated LiAl-LDHs and MgAl-LDHs are promising for scalable lithium extraction from salt-lake brines.