Phase transformation mechanism of spodumene during its calcination

Ethyl xanthate (EX) is a widely used collector in the flotation of sulfide minerals. However, it also has the disadvantages of low selectivity and harm to human health. Screening and/or designing more selective and green collectors is a hot topic in mineral processing field. In this work, 1-Hydroxyethylidene-1, 1-diphosphonic acid (HEDP), a cheap green reagent widely used in water treatment, was for the first time, applied in the flotation separation of chalcopyrite from pyrite. In addition, a comparative test of the traditional EX collector was also carried out. Flotation results of single mineral and binary mineral mixture showed that HEDP possessed a better selectivity for the separation of chalcopyrite from pyrite than EX. Zeta potential measurement results indicated that HEDP exhibited a stronger adsorption on chalcopyrite and a weaker interaction with pyrite. Hence, HEDP is a promising collector that possesses the potential to replace EX in future chalcopyrite flotation practice. This contribution provides a detailed in-situ account of transformation reactions during calcination of a typical high-grade a-spodumene (a-LiAISi(2)O(6)) concentrate; a. pre-treatment step required to refine spodumene into commercial lithium chemicals. We observe four reaction pathways during the transition of spodUmene, employing in-situ high-temperature powder XRD measurements using both cathode-tube and 'synchrotron radiation. At a relatively slow heating rate of 8 degrees C Min(-1), we observe a close relationship between the development of y-spodumene, with an onset temperature of 842 degrees C, and 'reduction of the amorphous background, in the collected. XRD spectra. This demonstrates that, initially y-spodumene recrystallises from amorphous spodumene. At the fast initial heating rate of 100 degrees C min(-1), y-spodumene first appears at a high& temperature of 1025 C. This mineral subsequently transforms into j3-spodumene at high temperatures along the reaction pathways denoted as pathway (1) amorphous spodumene y-spodumene-beta-spodumene and (3) crystalline a-spodumene y-spodumenc-q3-spodumene. The stability of. y-spodumene strongly depends on the mechanical treatment of the sample, and the heating rate of the calcination process, suggesting high and low activation energies for pathways (3) and (1), respectively. In another, experiment, we observe rising peaksofd-quartz, a minor gangue mineral in the spodumene' concentrate, that reflect the substitution of Li+ and AI' foi SO+ above 875 C. This phase ultimately transforms to 73-spodumene at 975 degrees C. The same experiment demonstrates the spectrum of i3-spodumene Contirilioirsly increasing in-magnitude, atioite 975 degrees C; with decreasing 'abundance of a!spciduniene, indicating 'a direct conversion of a- to)3-spodumene. Thus, the two other reaction corridors comprise: (2) crystalline a-spodumene-q-quartz-q-spodumene; (4) crystalline a-spoduMene,)g-spodumene. Heating of a finely ground sample results in faster and more-complete conversion 'of a-spodumerte compared to a coarser specimen. Our experiments establish the characteristic temperatures of phase transformations during spodumene calcination and reveal the influence of amorphous material and thermal history on reaction sequences. Approaches that integrate the optimisation of grinding and heating thus beaithe potential to reduce the energy requirements of the calcination process, including the extraction of lithium from y-spodumene formed at a lower temperature.