EXTRACTION OF LITHIUM DIRECTLY FROM α-SPODUMENE CONCENTRATE

Fadhil Al-Mawali

The demand for lithium is increasing, mostly due to the growth of lithium-ion battery production. Much of this lithium is produced from spodumene (LiAlSi2O6) mined from lithium pegmatites, by a process which has not changed significantly since the 1950s. Spodumene is concentrated by dense media separation and/or froth flotation. This concentrate is calcined at around 1100°C in a rotary kiln to convert the refractory α-spodumene into the more reactive and less dense polymorph β-spodumene. The calcined product is subsequently treated with concentrated sulphuric acid at 250°C and leached in water, dissolving the lithium as lithium sulphate. This leaching process typically extracts approximately 95% of the lithium. It also dissolves other elements, primarily aluminium and silicon but also iron, magnesium, calcium, sodium and potassium. The conventional lithium extraction process has several intrinsic limitations. Firstly, it is quite energy intensive due to the calcination stage. Finer grained spodumene concentrates are unsuitable for these rotary kiln-based processes, due to the risk of dust formation and melting, forming a glassy material that the lithium can’t be extracted from. The use of sulphuric acid is also inherently problematic both from occupational and environmental health and safety perspectives. The residue from the water leach consists of hydrogen aluminosilicate and sodium sulphate, both of which have no significant commercial value. Additional costs are required for their disposal or conversion to a valuable byproduct. Significant promise has been demonstrated with processes utilising alkaline reagents in hydro- and pyrometallurgical systems. The calcination pre-treatment stage can be omitted with these processes; the fine grained spodumene problem becomes negligible; the lithium forms as a more desirable lithium hydroxide product; the use of less problematic reagents reduces costs from mitigating environmental damage and occupational health and safety risks; and the residue may contain commercially valuable materials. This study investigates several parameters of alkaline roast leach systems to develop a more economically efficient process for the extraction of lithium from spodumene concentrate. The parameters investigated in this study are varied combinations of alkaline reagents (NaOH, KOH and Ca(OH)2), roasting durations (15 to 240 minutes), roasting temperatures (300 to 1000°C), reagent dosages (0.10 to 3.2g per gram of spodumene), single and two-stage leaching of roast products, varied acid concentrations in leaching (0.50, 1.0 and 2.0 M) and varied acid types in leaching (H2SO4 and HCl). Reagent dosage and roasting temperature were found to be the most influential parameters on lithium extraction. Through detailed investigations of these two parameters, as well as others, several sets of relatively mild conditions were found to result in lithium extraction >90 ±5%. Lithium extraction of approximately 99% is also achieved when the spodumene concentrate is roasted at 600°C with 2.4g NaOH per gram of spodumene for 1 hour, then leached with water at 50°C for 2 hours and leached again with 1.0 M H2SO4 for 24 hours at 25°C. The conditions and resulting lithium extraction of this study demonstrate the significant promise of an alkaline roast leach alternative for lithium extraction from spodumene. Because of the significant importance of lithium and it’s continued projected growth, even the smallest improvements could lead to significant economics and environmental benefits.

EXTRACTION OF LITHIUM DIRECTLY FROM α-SPODUMENE CONCENTRATE

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