Quantitative Effects of Desorption Intensity on Structural Stability and Readsorption Performance of Lithium/Aluminum Layered Double Hydroxides in Cyclic Li+ Extraction from Brines with Ultrahigh Mg/Li Ratio

Lithium/aluminum layered double hydroxides (Li/Al-LDHs) have shown great advantages in extracting lithium from low-grade brines without elution dissolution. However, their structures are sensitive and prone to damage in the desorption process. In this study, the quantitative influence of desorption intensity on the structure and readsorption capacity of Li/Al-LDHs was thoroughly investigated with hierarchical desorption conditions obtained by modulating the desorption temperature, eluent consumption, or lithium concentration of the desorption solution. It was found that the experimental readsorption capacity did not continuously improve with the lithium content in Li/Al-LDHs declining with the strengthening desorption. Various measurements were applied to trace the structural transformation of Li/Al-LDHs during the desorption processes, and the generation of gibbsite appeared in Li/Al-LDHs with the structural damages from excessive desorption, resulting in the lowering of the experimental readsorption capacity and poor extraction efficiency of Li+ from brines. The reference intensity ratio quantitative method calculations revealed that the mass fractions of gibbsite in Li/Al-LDHs suffered different excessive desorption, and the results were in agreement with the experimental readsorption capacities for Li+ from the Qarhan Salt Lake brine. In addition, the relationships between the desorption intensity and the Li/Al molar ratio in Li/Al-LDH compositions, as well as the readsorption performance, were systematically investigated to provide a feasible desorption method for the cyclic extraction of Li+. Under the developed conditions, the cyclic extraction of Li+ was nondestructive for Li/Al-LDHs and exhibited stable adsorption capacity during continuous adsorption–desorption cyclic experiments.