In situ synchrotron XRD analysis of the kinetics of spodumene phase transitions

Influence of calcination temperatures on lithium deportment by screening hard rock lithium

Calcination of spodumene is a pre-treatment stage in preparation for sulfation roasting and leaching in lithium recovery. During calcination, α-spodumene (less reactive, monoclinic crystal structure) is converted to β-spodumene (more reactive, tetragonal crystal structure). A third, metastable γ-phase has been identified at lower temperatures than full conversion to the β-phase. It has been previously observed that calcination greatly alters the physical properties of the various minerals in pegmatite ores, impacting comminution energy and liberation. Thus, this work investigates the relationships between calcination temperatures and the physical behaviour of hard rock lithium ores. The results showed that the increase in calcination temperature resulted in a higher lithium deportment in the finest size fraction (-0.6 mm) and thus a higher lithium grade and recovery. The samples calcined at 813.15 K and 1223.15 K did not show a significant increase in lithium grades in the finest size fraction. This work shows the incremental change in the physical properties of various minerals in the ore with increasing calcination temperature.

Novel extraction route of lithium from α-spodumene by dry chlorination

Processing spodumene for lithium is challenging as it requires a high temperature transformation of the natural α-monoclinic form to β-tetragonal form, usually followed by acid baking and digestion. This three-step extraction process requires significant heat energy, acid, process complexity and residence time, leading to both operating and capital costs. An approach which helps to eliminate this challenge will therefore be a milestone in processing spodumene. This study, thus, investigates a direct chlorination of α-spodumene using calcium chloride followed by water leaching of the residue to recover lithium, which reduces the energy requirement and number of unit operations. HSC Chemistry software was used to simulate the process using both phases (α and β) of the mineral up to 1100 °C prior to experimental investigation. The α-form was the only polymorph identified in residues after leaching, suggesting that the extraction is directly from the α-phase. However, an initial formation of a metastable β-form followed by a fast synthesis of lithium chloride from it is also suspected. Under optimal conditions of calcium chloride/spodumene molar ratio of 2.0, and 1000 °C treatment for 60 minutes, almost 90 percent lithium chloride was extracted and 85 percent was recovered to the leach solution with the remainder exiting with the off-gas. An apparent activation energy of about 122 ± 6 kJ mol⁻¹ was obtained at temperatures ranging from 800 to 950 °C during the process.

Processing spodumene for lithium is challenging as it requires a high temperature transformation of the natural α-monoclinic form to β-tetragonal form, usually followed by acid baking and digestion.

Multi-Technique Analytical Approach to Quantitative Analysis of Spodumene

The aim of this study was to establish the capability of X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) methods to determine different spodumene forms (α-, β- and γ-spodumene) occurring during heat treatment of lithium spodumene. It is essential to correctly identify and quantify the presence of different forms of spodumene after heat treatment to ensure optimum lithium extraction. A sample from the Haapaluoma lithium-pegmatite (western Finland) was used for this study. An experimental programme was initiated to model the progression of the mineral transformation at different stages through heat treatment. The specimen was broken down and split into five portions. One of the splits was analysed unheated with XRD, FTIR, XRF and ICP; the other four splits were analysed with XRD and FTIR after heat treatment at different temperatures from 850 to 1100 °C. In this study, we show that both laboratory-based XRD and portable FTIR methods are effective in identifying and quantifying α-, β- and ϒ-spodumene as well as impurities. The accuracy of the quantification of the minerals with XRD was established by using a mass balance calculation and was compared with the actual chemistry of the sample measured with ICP analysis. Fully quantitative XRD analysis of heat-treated spodumene is considered a challenge due to peak overlaps between the β-, and ϒ-spodumene forms, particularly when gangue minerals and amorphous content are present. The novelty of this study consists of the use of the XRD technique complemented by the Rietveld method to fully quantify the different forms of spodumene from one another: α-, β- and ϒ-spodumene, along with the gangue minerals and the amorphous content. It is also shown that reproducible systematic changes occur in the FTIR spectra that track the spodumene transformation during heat treatment. With more samples and cross-validation between the XRD results, the FTIR methodology could be developed further to provide semi-quantitative information on the different spodumene forms in the future. This would permit the use of a fast, cost-effective and portable technique for quality control of the spodumene forms, which would open opportunities across the Li value chain.

Physico-Chemical Characteristics of Spodumene Concentrate and Its Thermal Transformations

Spodumene concentrate from the Pilbara region in Western Australia was characterized by X-ray diffraction (XRD), Scanning Electron Microscope Energy Dispersive Spectroscopy (SEM-EDS) and Mineral Liberation Analysis (MLA) to identify and quantify major minerals in the concentrate. Particle diameters ranged from 10 to 200 microns and the degree of liberation of major minerals was found to be more than 90%. The thermal behavior of spodumene and the concentration of its polymorphs were studied by heat treatments in the range of 900 to 1050 °C. All three polymorphs of the mineral (α, γ and β) were identified. Full transformation of the α-phase was achieved at 975 °C and 1000 °C after 240 and 60 min treatments, respectively. SEM images of thermally treated concentrate revealed fracturing of spodumene grains, producing minor cracks initially which became more prominent with increasing temperature. Material disintegration, melting and agglomeration with gangue minerals were also observed at higher temperatures. The metastable γ-phase achieved a peak concentration of 23% after 120 min at 975 °C. We suggest 1050 °C to be the threshold temperature for the process where even a short residence time causes appreciable transformation, however, 1000 °C may be the ideal temperature for processing the concentrate due to the degree of material disintegration and α-phase transformation observed. The application of a first-order kinetic model yields kinetic parameters which fit the experimental data well. The resultant apparent activation energies of 655 and 731 kJ mol⁻¹ obtained for α- and γ-decay, respectively, confirm the strong temperature dependence for the spodumene polymorph transformations.

Two-Step Reaction Mechanism of Roasting Spodumene with Potassium Sulfate

The conventional process of lithium extraction from α-spodumene (LiAlSi₂O₆) is energy-intensive and associated with high byproduct management cost. Here, we investigate an alternative process route that uses potassium sulfate (K₂SO₄) to extract lithium while producing leucite (KAlSi₂O₆), 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.

Literature Review and Thermodynamic Modelling of Roasting Processes for Lithium Extraction from Spodumene

This review adds to the public domain literature on the extraction of lithium from mineral ores. The focus is on the pyrometallurgical pre-treatment of spodumene. Information on the phase transformation from α to β, the heat treatment methods as well as the behavior of various compounds in the roasting processes are evaluated. Insight into the chemical thermodynamics of the baking process is evaluated using HSC Chemistry software up to 1200 °C. It was observed that the alkaline, sulfation, chlorination (using Cl2 and CaCl2), carbonizing (to form Li2CO3) and fluorination processes were feasible either throughout or at a point within the temperature range considered. Chlorination using KCl and carbonizing to form Li2O are the processes found to be nonspontaneous throughout the temperatures considered.

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

Heat-treatment of spodumene concentrate at 1323 K (1050 °C) for 30 min in a rotary kiln yielded a successful decrepitation. Particle size decreased from 2 cm to less than 425 µm for 80% of the initial mass. X-ray analysis of both fractions did not reveal the presence of α-spodumene or γ-spodumene. The coarse fraction was ground to less than 425 µm with minimal mechanical energy and mixed with the finer fraction to perform lithium extraction. The lithium extraction efficiency reached 98 wt% without the need for flotation. Some aspects of the thermodynamic behavior of the spodumene system were assessed. Results show that metastable γ-spodumene may hinder the formation of β-spodumene at lower heat treatment temperatures. Some heat-treated samples presented non-negligible γ-spodumene content and lithium extraction efficiency decreases as the γ content increases. Finally, the assumed irreversibility of the transformations was studied by analyzing heat-treated samples following long controlled-storage periods. The results show that concentrate composition is not static over the studied time. This suggests that the β formation is not as irreversible as claimed. It is recommended to avoid long periods between heat-treatment and extraction to avoid the slow conversion of β-spodumene to other allotropes, which are less susceptible to lithium extraction.

Effects of coupling agent on antioxidant properties and structure of PP/cotton stalk lignin composites

In this paper, the effects of coupling agent and lignin extracted from waste cotton stalks in Xinjiang on thermal-oxygen aging properties of polypropylene (PP) composites were studied. The melt index test and indoor thermal oxygen aging test was carried out on the samples treated with coupling agent. The mechanical properties, surface micromorphology, rheological properties and element composition of the materials before and after 30 days of aging were studied. The results showed that the titanate coupling agent was the best for improving the melt index and mechanical properties of PP/cotton stalk lignin composites. After the 30-day thermal oxygen aging test, the samples with 2% lignin had the best impact strength and retention rate of fracture elongation, reaching 68.9% and 77.3% respectively. The sample with 3% lignin content had the smoothen surface, no crack appeared. After aging, the increase of C=O was the least, and the crystal peak area decreased less.