Effect of the Local Atomic Ordering on the Stability of β-Spodumene

Abstract

This study focuses on the relative energetic stability of β-spodumene configurations with different atomic ordering, evaluated using electronic structure methods based on static periodic density functional theory. We found that β-spodumene configurations with a framework containing exclusively Al-O-Si linkages are energetically the most stable, consistent with the aluminum avoidance principle. A correlation between the interstitial sites occupied by lithium and the stability of the configuration was established: highly stable configurations contain greater proportions of lithium associated with the edges of AlO4 tetrahedrons. The identified low-energy configurations have a band gap of ∼4.8 eV, and similar electronic band structures and densities of states. Both the PBE and PBEsol functionals predict small differences in the relative stabilities of the different configurations of β-spodumene. However, only PBEsol is able to reproduce the experimentally observed stability differences between α-spodumene and β-spodumene. β-Spodumene is the preferred polymorph at high temperatures, with the PBEsol inversion temperature from α- to β-spodumene predicted to occur at 1070 K.

Phase Transitions in the α–γ–β Spodumene Thermodynamic System and Impact of γ-Spodumene on the Efficiency of Lithium Extraction by Acid Leaching

“…Implementing Konar's data [15] into the calculations results in an allotropic phase transition from α-spodumene to β-spodumene at 1162 K (889 °C). This is in agreement with our experimental results since it validates that β-spodumene is the only stable allotrope at 1323 K (1050 Moreover, the beginning of this allotropic transition temperature of 1162 K (889 °C) is higher than the previous calculations presented by Roy [8], who predicts a transition at 1023 ± 50 K (750 ± 50 °C), while being in agreement with the work of Moore [21], who calculates a transition at 1073 ± 80 K (800 ± 80 °C).…”

Physico-Chemical Characteristics of Spodumene Concentrate and Its Thermal Transformations

“…β-spodumene, another polymorph of the mineral consists of two separate tetrahedron structures which are joined in a three-dimensional form with their central parts hosting aluminum or silicon [ 7 ]. Lithium in this phase is located between the cavity of five-member rings, formed by the individual tetrahedron.…”

“…The zeolite-like channels which are parallel to the a and b axis are comparatively larger and account for the tremendous ion-exchange capacity of β-spodumene during roasting [ 8 ]. It has the space group P4 3 2 1 2 with cell parameters a = b = 7.534 Å and c = 9.158 Å [ 7 ]. An intermediary metastable γ-phase which transforms to the β-phase upon continuous heating has also been identified.…”

Two-Step Reaction Mechanism of Roasting Spodumene with Potassium Sulfate

“…Alpha spodumene (α-LiAlSi 2 O 6 ), a monoclinic lithium aluminum silicate mineral that belongs to the pyroxene group, is the main hard rock source of lithium. , The spodumene crystal structure is compact and consists of SiO 4 tetrahedra chains, running along the c axis, which are interconnected by chains of edge-sharing AlO 6 octahedra and irregularly shaped polyhedra of six-fold coordinated lithium ions (Figure a).…”

“…The conventional process of extracting lithium from spodumene involves calcination of α-spodumene to obtain β-spodumene that is subsequently roasted with sulfuric acid at 250 ° C and water-leached. , Tetragonal β-spodumene has a more open structure that is dominated by interlocking five-membered rings of (Si, Al) tetrahedra with lithium atoms in interstitial positions (Figure b). All the five-membered rings run approximately parallel to either (010) or (100), thus creating zeolite-like channels that allow an effective ion exchange between lithium ions and hydrogen ions during acid roasting. , Lithium extraction efficiency above 95% is achieved in this process . However, the conventional spodumene process suffers from high energy and byproduct management cost (HAlSi 2 O 6 and Na 2 SO 4 ) ,…”