Systematic study on synthesis and characterization of lithium manganese oxides for direct lithium extraction from natural brines

Lithium recovery from natural sources such as continental brines is an alternative to reaching high lithium demands. However, the current evaporitic technology is recognized for its techno-economic disadvantages and negative environmental impacts. Lithium manganese oxides were synthesized, characterized, and evaluated in this work regarding their capacity for selective lithium recovery from natural brine through adsorption. Two synthetic methodologies were assessed, a solid-state synthesis and a hydrothermal method, and the conditions of formulations were modified to prepare 13 different lithium manganese oxides with very high lithium recovery capacity. The formulated sub-micrometer sized particles showed diameters ranging from 149 nm to particles of about 1500 nm. Several lithium manganese oxide ion sieves were obtained from different Li:Mn ratios of precursors: LiMn₂O₄, Li_1.33Mn_1.67O₄, and Li_1.6Mn_1.6O₄. Lithium adsorption capacity showed significant differences depending on the chemical structure, but especially on the particle size of the adsorbent, with some influence of the mesoporosity. The maximum lithium recovery capacity was 35.4 mg_Li/g_HMO when Li_1.6Mn_1.6O₄ of 317 nm or 166 nm was used. The cyclability showed a high dependence on particle size. The general trend is that the adsorption capacity is more significant when particle size is smaller. All lithium-ion sieves showed high lithium selectivity in complex media, such as natural brine. Mn was not detected in neither the lithium deprived brine, nor in the HCl recovery solution, which was attributed to the room temperature and the neutral pH of the adsorption tests, as compared with previous studies.