Influence of the synthesis route of lithium adsorbent Li/Al LDHs on physicochemical properties and extraction properties

Lithium can be extracted from brines using a process commonly called Direct Lithium Extraction (DLE) using a lithium selective adsorbent as solid support. For that purpose, Li/Al layered double hydroxide (Li/Al LDH) are efficient materials for trapping Li⁺ in the vacant octahedral sites and chloride ions in their interlayer space. This article presents two distinct synthesis routes of Li/Al LDH materials, hydrothermal and coprecipitation, their characterizations and their Li extraction properties in synthetic brine. Indeed, the synthesis route impacts the physicochemical properties of the adsorbent and hence the Li⁺ extraction performances. A link between the structural and morphological properties of the adsorbents and the extraction properties was established. The material obtained by the coprecipitation method appears more effective for extracting lithium, as it is made up of grains of small particles with a greater pore volume and a larger exchange surface. This morphological property leads directly to a fast extraction kinetics, which is an essential point for a viable DLE process. This article also shows a close link between the LiCl content in the materials and the maximum achievable extraction capacity. The two active materials studied here have in fact the same maximum capacities due to an identical LiCl content in their crystalline structure, meaning that all sorption sites can be reached under optimal extraction conditions. It is therefore crucial to understand the influence of synthesis method on the extraction performance to optimize the process.