Al-doped spinel LiMn2O4 anchored on diatomaceous earth for selective lithium adsorption under simulated brine conditions

Abstract

Lithium (Li), a crucial element for next-generation energy storage technologies, is driving the need to explore the major global Li reserves, i.e., brines. In this investigation, an aluminium-doped lithium manganese oxide (LMO) composite supported by diatomaceous earth (ALMO/DE) was developed, delithiated (acid pickled) to produce HAMO/DE (the desired adsorbent), and was further utilized for Li⁺ recovery against high background Na⁺ ionic strength solutions. The synthesis conditions were optimized for maximum Li uptake, which resulted in the best performing adsorbent at Li/Mn = 0.5 by weight, an Al doping of 5%, DE = 5 mmol, and a calcination time of 12 h (at 650 °C). The as-synthesised HAMO/DE showed an equilibrium adsorption capacity of 3.5 mg Li g⁻¹ for LiCl buffered solution (initial Li concentration = 10 mg L⁻¹; contact time = 24 h; pH = 12.0) and a maximum uptake capacity of 27.4 mg Li g⁻¹ at an initial Li concentration >150 mg L⁻¹. SEM–EDX and XRD confirmed a porous DE-supported Al-stabilized Li–Mn spinel with a preserved Fdm structure and topotactic Li⁺ exchange. FTIR and XPS revealed enhanced lattice oxygen stability, suppressed Mn²⁺ formation, and dominant lattice-bound Li in Al-doped composites, enabling selective and durable Li⁺ recovery. Furthermore, the equilibrium and kinetic studies showed that the adsorption process was monolayer and homogenous chemisorption following Langmuir isotherm and pseudo-second-order kinetic models. The HAMO/DE exhibited a high adsorption selectivity towards 10 mg L⁻¹ Li⁺ concentration in the presence of high Na⁺ concentration (0.2 g L⁻¹–10 g L⁻¹), with a separation factor (α_Li/Na) ranging between ∼1767 and ∼27. Overall, the HAMO/DE emerged as a stable and highly selective adsorbent for Li extraction from brines and other Na⁺ rich media/wastewater streams and can be utilized to selectively concentrate and recover Li in an engineered system.