α→γ→β-phase transformation of spodumene with hybrid microwave and conventional furnaces

摘要

Spodumene is the most important lithium containing hard rock mineral. In order to extract lithium from spodumene by leaching, the crystal structure of spodumene must be converted from the natural monodinic a-form to the tetragonal (3-form. The heat treatment was carried out by a domestic microwave furnace (700 W) with silicon carbide susceptor and by a conventional resistance heated furnace. In the microwave furnace the phase transformation of spodumene began after 110 s of heating and samples were converted almost completely to (3-spodumene after 170 s. Partial melting of gangue minerals was observed in samples after 170 s of heating. Heating in microwave furnace for 170 s corresponded with the heating of approximately 480-600 s at temperature of 1100 °C in the conventional furnace. In addition to a- and p-forms an intermediate phase, hexagonal y-spodumene, was identified from samples heated with both furnaces. The conversion of spodumene samples was verified with x-ray diffraction (XRD) and with field emission scanning electron microscope (FESEM).