La-doped MgFe-Layered Double Hydroxides and their sorption properties towards Tungsten Oxyanions (WO42-) at alkaline pH's

The present study focuses on the tungsten recovery from alkaline solutions using for the first time La-doped MgFe-LDH type sorbents (pH  ≥ 13). A small-scale synthesis procedure was optimized, and further upscaled (20x) to produce up to 200g batches with reproducibility degree close to 100 %. The chemical composition, structural and textural characteristics of the as-synthesized materials were investigated by ICP-OES, X-ray Diffraction, N₂ physisorption and IR spectroscopy techniques. The materials were applied for sorption of WO₄^2- anions in aqueous media under relevant conditions. Parameters influencing the sorption process, such as the LDH composition, pH of the sorption media, adsorption capacity, kinetics and desorption solution composition were thoroughly investigated. Multi-cycling tests in different desorption solutions combined with IR and XRD characterization of the La-MgFe-LDH solids in different steps of the process, allowed us to elucidate the WO₄^2- recovery mechanism. Further, the La-doping in the LDH structure increases the sorption capacity and assures the material stability throughout the WO₄^2- recovery process in high pH media. The alkaline stability was demonstrated by powder post characterization by X-ray Diffraction as well as performing alkaline stability test and follow up of any leaching elements by ICP-OES in alkaline solutions. The results indicate that the as-developed La-MgFe-LDH are suitable candidates for WO₄^2- recovery from aqueous solutions, including highly alkaline solutions compatible with the current hydrometallurgical processes.