Flash calcination of fine spodumene concentrate in the Calix reactor

A spodumene concentrate containing 6.0% Li2O with a size range of 90% passing 200 μm was calcined in a Calix reactor, a new type of flash calcination reactor, between 1050°C and 1120°C converting up to 88% of the α-spodumene to β-/γ-spodumene. In this reactor, powdered material falls through a heated, vertical shaft. Rapid conversion of α-spodumene to β-/γ-spodumene was achieved using this new furnace, though multiple passes, up to four were needed to achieve good conversion percentages. When two different size fractions, -106 μm and +106 μm were treated under the same conditions (one pass, 1100°C) there was minimal difference in the extent of conversion. Calcination led to an increase in surface area, a decrease in density, and a change in particle size distribution. The unit-cell expansion that occurs during the phase change from α- to β-/γ-spodumene resulted in an increase in the top-size of the particles, but the stresses from uneven expansion caused cracking and fragmentation of the spodumene which increased the amount of fines present. In the intermediate stages of conversion, this resulted in an increase in surface area as the particles become covered in cracks. Acid baking/water leaching of the calcined samples was performed using a standard set of conditions: 180% stoichiometric acid requirement, 250°C for 1 h followed by 2 h of leaching in water at 50°C. Lithium extractions correlated closely with the extent of spodumene conversion of the calcined samples as measured by chemical and XRD methods. Preliminary results showed that separation of α- from β-/γ-spodumene is possible by gravity-separation, which presents an opportunity to further optimise the technology by separating the converted material, though more work is needed to develop this into an effective separation process.