Lepidolite is an important hard-rock lithium resource commonly associated with valuable rare alkali metals such as Rb and Cs, but its stable layered aluminosilicate structure and structural fluorine limit direct extraction. In this study, steam-assisted defluorination of lepidolite concentrate from Yichun, Jiangxi Province, was investigated by varying roasting temperature, roasting time, steam flow rate, and particle size. Thermodynamic calculations, kinetic fitting, XRD, SEM–EDS, and BET analyses were used to evaluate the defluorination behavior and structural changes. The results showed that particle size and roasting temperature were the dominant factors. Under the optimized conditions of −74 + 38 μm, 880 °C, 25 min, and 1.5 g/min steam flow, the defluorination efficiency reached 96.13%. Thermodynamic calculations based on LiF and AlF₃ as simplified models of Li-F and Al-F bonds indicated that direct hydrolytic defluorination was unfavorable. However, when SiO₂ participated in the reaction, aluminosilicate reconstruction substantially reduced the Gibbs free energy, thereby facilitating fluorine release. Kinetic fitting showed that the process followed the A3 random nucleation model, with an apparent activation energy of 257.73 ± 40.13 kJ/mol, indicating that new-phase nucleation, growth, and structural reconstruction jointly controlled defluorination. Structural characterization further confirmed that steam roasting destroyed the characteristic lepidolite structure, promoted F migration and removal, and induced aluminosilicate reconstruction, while excessive temperature caused pore shrinkage and structural densification. These findings provide a basis for improving the subsequent extraction of Li, Rb, and Cs from lepidolite.
To address the limitations of conventional techniques for preparing spherical Ti-6Al-4V powder in particle-size control—particularly the inefficient utilization of the large amount of coarse powder generated—this study combined hydrogenation-dehydrogenation (HDH) processing with radio-frequency plasma spheroidization to achieve controllable preparation of fine spherical Ti-6Al-4V powder. The influence of hydrogen content in the plasma (H2/Ar = 6–15%) on hydrogen-decrepitation fragmentation behavior was systematically investigated. The results revealed a non-monotonic dependence of decrepitation efficiency on hydrogen concentration, with an optimal H2/Ar ratio of 12%, at which the D50 of the starting powder decreases from 61 μm to 21 μm. Excessive hydrogen reduces refinement efficiency due to hydride desorption saturation and intensified evaporation of ultrafine fragments. Phase characterization demonstrated the progressive transformation from TiH2 to TiH1.23, α'-Ti, and finally β-Ti with increasing hydrogen content, driven by accelerated heating and cooling rates in the rich hydrogen plasma. Comparative experiments on powders with different particle sizes and morphologies show that decrepitation efficiency is strongly governed by the initial structural integrity, where low-strength, crack-containing hydride powders exhibit markedly higher fracture probabilities. Plasma powder interaction model analysis further confirmed that reducing characteristic strength and increasing hydrogen-release-induced internal stress are key to enhancing fragmentation. These findings provide mechanistic insight and practical process guidance for precise particle size control in the fabrication of Ti-6Al-4V powders for metal injection molding.
Powder wetting and liquid penetration dynamics are critical in wet granulation, particularly for formulations containing poorly wettable drugs such as ibuprofen. So that, it is necessary to understand water-powder interactions if an optimized granulation process is required. In the present study we investigate the capillary wetting of a simplified model formulation composed of 60wt% of ibuprofen (a hydrophobic drug), 3wt% of polyvinylpyrrolidone (a binder) and different ratios of two common excipients, lactose and microcrystalline cellulose (MCC). In particular, we focus on the effects produced by three specific ratios of lactose to MCC, 50:50, 70:30, and 90:10.In order to quantify the effects of lactose:MCC ratios, drop penetration experiments using water and polydimethylsiloxane were performed on porous powder beds. The results are analyzed through a previously developed capillary imbibition model that was adapted to address the specific complexities introduced by the formulations. The main modification is the definition of the strength of interaction parameter, β, which captures microscopic wetting effects and structural changes (e.g., swelling). Thereby, our model gives microscopic information by using macroscopic measurements without requiring detailed knowledge of internal porous properties.It was observed that water failed to penetrate pure ibuprofen, whereas the addition of excipients enabled liquid penetration. The parameter β showed that MCC content plays an important role in penetration dynamics, with increasing MCC proportions leading to higher water penetration rates. The same trend was qualitatively observed in highly compacted tablets, but penetration times are considerably enlarged so, dissolution effects cannot be discharged.The proposed capillary imbibition model and the parameter β effectively characterize liquid-powder interactions using simple macroscopic experiments. This approach enables penetration times to be tuned to the residence times of granulation process, providing a cost-effective tool for formulation design and optimization. Consequently, it can significantly reduce the need for the extensive trial-and-error studies that are traditionally used during formulation screening.
