Two-Step Reaction Mechanism of Roasting Spodumene with Potassium Sulfate

Abstract

The conventional process of lithium extraction from α-spodumene (LiAlSi 2 O 6 ) is energy-intensive and associated with high byproduct management cost. Here, we investigate an alternative process route that uses potassium sulfate (K 2 SO 4 ) to extract lithium while producing leucite (KAlSi 2 O 6 ), a slow release fertilizer. Presenting the first-ever in situ record of the reaction of α-spodumene with potassium sulfate, we use synchrotron X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to document the reaction sequence during prograde heating. From 780 °C, we observe a broad endothermic DSC peak, abnormal expansion of the α-spodumene structure, and an increase in α-(Li, K)-spodumene peak intensity during heating with potassium sulfate, indicative of the exchange between lithium and potassium in the spodumene structure. When 11 ± 1% K occupancy in the M2 site of α-(Li, K)-spodumene is reached, the mechanism changes from ion exchange to a reconstructive transformation of α-(Li, K)-spodumene into leucite, evidenced by a decrease in α-spodumene and potassium sulfate abundance concurring with formation of leucite over a narrow temperature range between 850 and 890 °C. The increasing background intensity in synchrotron XRD above 870 °C suggests that a lithium sulfate-bearing melt starts to form once >90% of α-spodumene has been converted during the reaction. This fundamental understanding of the reaction between α-spodumene and potassium sulfate will enable future development of lithium extraction routes using additives to significantly decrease energy intensity and to produce marketable byproducts from α-spodumene.

A review of lithium extraction from natural resources

“…2.1.5. Salt roasting method In addition to leaching using acids and alkalis, salt roasting methods have also been reported, as shown in Table 1 [49][50][51][52][53][54][55][56][57][58]. The main flow is shown in Fig.…”

The COOL process – a holistic approach towards Lithium recycling

“…The exact mechanism has not been elucidated yet and is matter of forthcoming investigations. However, from the literature, lithiumpotassium solid ion exchange is known for spodumene treated with K 2 SO 4 [29]. In the case of carbonates, however, a side reaction with the silicate is to be expected and will be evaluated in the following section.…”

Direct Preparation of Water-Soluble Lithium Salts from α-Spodumene by Roasting with Different Sulfates

“…A large excess of K 2 SO 4 was required to form lithium sulfate due to the reversible reaction. Ncube et al proposed that the reaction of α-spodumene with K 2 SO 4 proceeded in two steps by using synchrotron XRD and TGA-DSC: (1) ion-exchange producing α-(Li, K)-spodumene between 780 and 850 °C and (2) reconstructive transformation of α-(Li, K)-spodumene into leucite (KAlSi 2 O 6 ) and lithium-bearing sulfate species between 850 and 890 °C …”