Effect of mechanical and thermal treatment on the crystalline phases of spodumene/NaF mixture

M.R. ESQUIVEL; G.D.ROSALES; M.H.RODRIGUEZ; A.C.J. RESENTERA

Ciudad de Antofagasta

Jornada; 7 th IWLiMe 2020 International Workshop on Lithium Industrial Minerals and Energy; 2020

Universidad de Antofagasta

The mechanical activation was used in mineral processing improvingyields in calcination, leaching and dissolution processes. The mechanicalgrinding added energy to the reacting systems, increasing their reactive surfaceand generating deformations and defects in the crystalline network of solids. Thus,regions of high reactivity were generated that facilitate the development of chemicalprocesses. [1] Rosales et al. studied the fluorination process of the mineral spodumenein its β phase with NaF.The reaction starts at 540°C generating LiF, nepheline and albite according to Eq(1). [2]2β-LiAlSi2O6+ 2NaF →2LiF + NaAlSi3O8 + NaAlSiO4                       (1)The present work proposes the study of the effect of mechanicalactivation on the α-spodumene/NaF mixture and its subsequent thermal treatment.The α-spodumene (3.01% Li2O), fromthe province of San Luis Argentine, was mixed with NaF (Alkemit, ≥99%) with a1:2 molar ratio. The operating variablesstudied were ball mass/sample mass ratio (9 - 64), mechanical activation time(15-600 min), and calcination temperature (400-700 °C).The reactants andcalcined materials were characterized by X-ray fluorescence (XRF), X-raydiffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry(EDS), differential scanning calorimetry (DSC) and flame photometry (FP). Figure 1 shows the comparative XRD of theeffect of milling as a function of time. The diffractograms presented in Figure 1 showthat there are no changes in the composition of the phases present in themixture. The increase in the milling time generates a marked decrease in theintensity/background ratio for the peaks of the present phases. Also, there wasa widening of the peaks, which suggests both a decrease in the crystallite sizeand an increase in the strain. These effects are greater for the NaF phasebecause it is softer than the mineral. Based on these results, samples with grindingtimes of 600 min were selected for the thermal treatment study. The Figure 2 showsthe effect of heating rate in the initial reaction temperature (a) and theeffect of roasting temperature in the crystalline phases of the mixture (b). From Figure 2a it can be seen that the heating rate affects the α-spodumene/NaFinitial reaction temperature TR, obtaining a minimum TRof 480 °C and a maximum of 530 °C. These results are relevant since there areno pyrometallurgical processes of the mineral α-spodumene reported in the literature that registersuch a low starting reaction temperature.The diffractograms presented in Figure 2b show the ocurrence of newphases in the α-spodumene / NaFreactive mixture at 600°C, corresponding to the compounds, LiF, albite andnepheline. These results coincide with those reported by Rosales et al.according to Eq (1). [2] Keywords:MechanicalActivation, Thermal treatment, α-spodumene,LiF.  References: [1] G. Mucsi. A review on mechanical activation and mechanical alloying instirred media mill, Chemical EngineeringResearch and Design, 148 (2019). https://doi.org/10.1016/j.cherd.2019.06.029[2] G. Rosales, A. Resentera, J. Gonzalez, R. Wuilloud, M.Rodriguez. Efficient extraction of lithiumfrom β-spodumene by direct roasting with NaF and leaching, Chemical Engineering Research and Design, 150 (2019). https://doi.org/10.1016/j.cherd.2019.08.009