Crystal Transition Behavior and its Effect on Lithium Extraction during Spodumene Transformation Roasting AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY22030021

Chinese Library Classification Number:TF826.3

Citation Information:

With the wide application of new energy batteries，the demand for lithium resources is increasing year by year. Spodumene，as an important lithium resource in China，is the main source of lithium. At present，lithium extraction from spodumene is mainly by sulfuric acid roasting，and the extraction rate can reach more than 90%，but this process requires the transformation of α-spodumene into β-spodumene by high temperature roasting. Moreover，the high-temperature roasting transformation of spodumene is an indispensable part of lithium extraction from spodumene. However，the composition of spodumene in different areas is complex and changeable，so it is necessary to systematically explore the crystal type change of spodumene before and after roasting to obtain the theoretical optimal conditions of spodumene roasting transformation. At the same time，from the perspective of crystal structure，the crystal type transition behavior and lattice parameter change of α-spodumene calcining to β-spodumene can be studied and analyzed，and the essential reason of β-spodumene being easier to extract lithium than α-spodumene can be analyzed from the perspective of bond energy. The types，occurrence states，crystal structures and molecular structures of spodumene single minerals were systematically analyzed by chemical element analysis，X-ray diffraction （XRD），scanning electron microscopy （SEM），infrared spectroscopy （IR），Crystal Maker Demo and Materials Studio. The effects of roasting temperature，time and particle size on the roasting process were discussed，and the optimal process conditions for the roasting transformation of spodumene single mineral were determined. At the same time，it was proved that β-spodumene after roasting was easier to extract lithium. The results showed that the calcination transition of spodumene was greatly affected by temperature. When the temperature reached 950 ℃，the crystal transformation took place and β-spodumene was formed. When the temperature reached 1000 ℃，α-spodumene no longer existed，and XRD analysis results showed that the characteristic peak of β-spodumene did not enhance.When the roasting time was 60 min，XRD analysis showed that spodumene had been completely transformed into β-spodumene，and the characteristic peak intensity of β-spodumene did not increase with the extension of roasting time. When the size of spodumene was -0.075 mm+0.048 mm，the phenomenon of inadequate heat transfer caused by the large size of spodumene could be avoided，so that the spodumene could be completely transformed. Through mineral analysis of roasted spodumene，the optimal roasting conditions of spodumene single mineral were determined as follows： roasting temperature was 1000 ℃，leaching time was 60 min，particle size was -0.075 mm+0.048 mm. By comparing the lithium leaching rate of spodumene sulfated roasting before and after the transformation，the importance of the transformation of α-spodumene roasting was clarified. The crystal structure of spodumene before and after the transformation was analyzed，and it was found that the cell parameters of α-spodumene changed from monoclinic to tetragonal β-spodumene. The cell parameters a，b and c changed from 9.47，8.40 and 5.23 nm to 7.53，7.53 and 9.16 nm，respectively. The cell volume increased from 390.14 to 519.84 nm³ with volume expansion of 133.25%. At the same time，in α-spodumene crystal cell，silicon atom formed ［SiO₄］ tetrahedron with oxygen atom，and Al^Ⅵ，which was in sixth coordination，formed ［AlO₆］ octahedron with oxygen atom besides silicon oxygen backbone. In β-spodumene cells，Si⁴⁺ in the tetrahedron ［SiO₄］ was substituted by Al^Ⅳ in a quaternized coordination，and entered complex anions. In order to meet the requirement of electric price equilibrium，the void in the structure was filled by Li⁺. Due to the ratio of the type of cation entering the anion gap to the ion radius （R_f） and anion radius （R_p），the volume of the tetrahedral coordination polyhedron with aluminum in β-spodumene was only 1/4 of that of AlO₆ octahedron in α-spodumene，which made the activity range of Li in β-spodumene crystal cell larger. From the change of cell structure，it could be seen that the volume of β-spodumene cell expanded，and the volume of coordination polyhedron in β-spodumene cell was smaller than that in α-spodumene cell，so the range of activity of Li⁺ in the cell was larger，and it was easier to detach. The average length of each chemical bond could be measured by Materials Studio8.0. As the electrostatic attraction between anion and anion could be calculated by Coulomb's law in the mineral structure，Li–O ions in the crystal cell could be analyzed and calculated. It could be seen that during the roasting and transformation of α-lithium pyroxene into β-lithium pyroxene，the bond valence of ［LiO₆］ octahedron decreased from 1.6218 to 1.304，and the electrostatic attraction between Li⁺–O²⁻ decreased from 6.24×10⁻⁸ to 4.16×10⁻⁸ N. At the same time，the analysis of the Li–O structure in the crystalline cell showed that the stable ［LiO₆］ octahedron in α-spodumene was transformed into the unstable ［LiO₄］ tetrahedron，and the Li in β-spodumene was easier to free from the binding of O ions. Therefore，the calcination of α-spodumene into β-spodumene was the key step of lithium extraction from spodumene.