Mechanical activation of β-spodumene

In situsynchrotron XRD analysis of the kinetics of spodumene phase transitions

“…18 However, it has also been suggested that inversion may be possible at temperatures as low as 520 1C. 19 It is known the g phase transforms into the b phase with an increase in temperature and/or pressure, [19][20][21] with first-principles calculations confirming the stability of the b phase over g. 22 For design and optimisation of calcination processes, it is desirable to understand the kinetics of the conversion of a-spodumene to the band g-forms in which Li is more mobile and amenable to extraction by ion exchange. The ato b-transformation is known to be reconstructive and irreversible, 13 requiring relatively high temperatures of the order of 900 1C to attain appreciable rates.…”

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

“…6−9 Heat treatment of mechanically activated αor βspodumene between 973 and 1173 K at atmospheric pressure results in a γ-spodumene polymorph, which is metastable after further heating to above 1173 K, forming β-spodumene. 2, 10,11 The crystal structure of α-spodumene has been well characterized by means of X-ray diffraction studies, 12 IR spectroscopy, 13 Raman spectroscopy, 7,14 and a combination of vibrational spectroscopy and ab initio molecular dynamics simulations. 15 α-Spodumene has a monoclinic unit cell with a space group C2/c and cell parameters of a = 9.463 Å, b = 8.392 Å, c = 5.218 Å, and α = γ = 90°and β = 110.05°.…”

“…Thus, in practice, β-spodumene is the active phase for lithium extraction under acidic conditions. Heat treatment of α-spodumene at atmospheric pressures above 973 K induces a phase transition to the β-spodumene polymorph. − The phase change from α- to β-spodumene is of a reconstructive nature, occurring irreversibly with a change in the crystallographic features. − Heat treatment of mechanically activated α- or β-spodumene between 973 and 1173 K at atmospheric pressure results in a γ-spodumene polymorph, which is metastable after further heating to above 1173 K, forming β-spodumene. ,, …”

Real-Time and In Situ Monitoring of Mechanochemical Reactions: A New Playground for All Chemists

“…This can be related to the, until recently, largely impassable difficulty to directly monitor physical and chemical transformations taking place under violent impact of rapidly moving grinding media, made of steel, ceramic (e.g., zirconia, alumina), or tungsten carbide. As pointed out by Drebuschak and co-workers, “It is a challenge to understand the processes taking place in a powder sample during its grinding in a mill, or compacting, since one can neither measure local temperature, pressure, shear stresses, nor follow the changes in the diffraction patterns or vibrational spectra in situ.” As a result, kinetics and mechanisms of reactions by milling have been investigated largely by ex situ (stepwise) approaches, wherein milling is periodically interrupted and the reaction mixture analyzed by suitable solid-state techniques, including powder X-ray diffraction (PXRD), Raman or infrared spectroscopy, surface area measurements, thermal analysis, or solid-state nuclear magnetic resonance (ssNMR) spectroscopy . It is, however, becoming increasingly clear that mechanistic ex situ analysis is limited due to the often not realized possibility that chemical or structural transformations may continue even after mechanical treatment , or that reactivity of mechanically activated samples may be changed or promoted by the surrounding atmosphere .…”