Engineering Compounds for the Recovery of Critical Elements from Slags: Melt Characteristics of Li₅AlO₄, LiAlO₂, and LiAl₅O₈

Abstract

Engineered artificial minerals (EnAMs) are the core of a new concept of designing scavenger compounds for the recovery of critical elements from slags. It requires a fundamental understanding of solidification from complex oxide melts. Ion diffusivity and viscosity play vital roles in this process. In the melt, phase separations and ion transport give rise to gradients/ increments in composition and, with it, to ion diffusivity, temperature, and viscosity. Due to this complexity, solidification phenomena are yet not well understood. If the melt is understood as increments of simple composition on a microscopic level, then the properties of these are more easily accessible from models and experiments. Here, we obtain these data for three stoichiometric lithium aluminum oxides. LiAlO 2 is a promising EnAM for the recovery of lithium from lithium-ion battery pyrometallurgical processing. It is obtained through the addition of aluminum to the recycling slag melt. The high temperature properties spanning from below to above the liquidus temperature of three stoichiometric Li−Al−Oxides: Li 5 AlO 4 , LiAlO 2 , and LiAl 5 O 8 are determined using molecular dynamic simulations. The compounds are also synthesized via the sol−gel route. The Li + ion exhibits the largest diffusivity. They are quite mobile already below the liquidus temperature, i.e., for LiAlO 2 at T = 1700 K, the diffusion coefficient of the lithium ion equals D = 3.0 × 10 −9 m 2 s −1 . The other ions Al 3+ and O 2− do not move considerably at that temperature. The diffusivity of Li + is largest in the lithium-rich compound Li 5 AlO 4 with D = 32 × 10 −9 m 2 s −1 at 2500 K. The lower the viscosity, the higher the lithium content. The Li 5 AlO 4 exhibits a viscosity of η = 2.2 mPa s at 1328 K which matches well with the experimentally determined 2.5 mPa s at this temperature. The viscosity of LiAlO 2 at 1800 K is more than two times higher. These data sets can help to describe the melts on a microscopic level and understand how the melt properties will change due to gradients in the Li/Al concentration.

Experimental and Simulation Studies on the Mn Oxidation State Evolution of a Li2O-MnOx-CaO-SiO2 Slag Analogue

“…If the combustion wasn't fully obtained, about 5 g ammonium nitrate and 10 mL ultra-pure water were added to the cooled beaker followed by another ignition procedure. The total amount of substances was set to 75 mmol requiring two to three ignition steps compared to 25 mmol total amount of substances using only one combustion step [24]. The sol-gel combustion was prepared four times to result in 28.84 g powder.…”

“…Starting from the mean square displacement function of the ions at different temperatures the diffusion coefficients of the individual ions in the two phases are calculated. It was previously shown that Li + ions are most mobile [24], this was found here as well in the lithium manganate phase with e.g. diffusion coefficients of 0.45 × 10 −9 m 2 •s −1 at 1700 K and 20.28 × 10 −9 m 2 •s −1 at 2100 K. The manganese cations and the oxygen anions have quite similar diffusion coefficients with 0.7 × 10 −11 m 2 •s −1 for Mn 3+ and 0.3 × 10 −11 m 2 •s −1 for O 2− at 1700 K as well as 3.77 × 10 −9 m 2 •s −1 for Mn 3+ and 4.99 × 10 −9 m 2 •s −1 for O 2− at 2100 K (Figure 11 left).…”

“…With respect to the lithium EnAM, lithium aluminates have been studied with MD simulations and experimentally. Individual diffusivities depend on the Li:Al ratio and strongly decrease viscosity [24]. The effect of Mn has been less explored.…”

“…These gradients can be described incrementally from systems with reduced complexity. This has been done for LiAlO 2 and for the thermodynamically predicted compounds sharing its precipitation zone which are LiAl 5 O 8 spinel and Li 5 AlO 4 [24] and a recent review paper describes this approach [25]. In this work the system Li 2 O-MnO x -SiO 2 -CaO is studied.…”