Sustainable Treatment of Spodumene: Extraction of Lithium from Spodumene Through Roasting with Potassium Sulfate

Lithium can be extracted from α-spodumene (LiAlSi2O6) by roasting with potassium sulfate (K2SO4) followed by water leaching, removing the need for acid baking from the conventional sulfuric acid process. We optimised the potassium sulfate process at a K2SO4:α-SC 7.6 ratio of 0.6:1 (w/w), 1050 oC and 30 min roasting time, achieving high lithium extraction efficiency (96.3 ± 2 % (w/w)); SC 7.6 is a commercial spodumene concentrate from Talison Lithium with the nominal Li2O content of 7.6 %. Upon water-leaching the roast product obtained under optimum conditions, lithium sulfate and potassium lithium sulfate dissolve completely, producing a solid leucite residue. The potassium sulfate process is more selective than the sulfuric acid process, extracting 0.05 % Al and 2.3 ± 0.4 % Fe from the concentrate, compared to 5.0 ± 0.6 % Al and 11.3 ± 2.2 % Fe, respectively. The purification of the leach liquor from the potassium sulfate process is more complex, requiring the addition of aluminium sulfate to recover potassium as potash alum (KAl(SO4)2∙12H2O). Based on 200 kt y-1 of spodumene concentrate feed, we estimate the operating profit of the potassium sulfate and sulfuric acid processes for producing lithium hydroxide monohydrate, as US$368 million and US$386 million, respectively. Because of its potassium content, leucite could be converted into a slow-release fertiliser through drying, grinding and granulation. Potash alum, which constitutes another valuable potassium sulfate process by-product, finds its application in water purification, leather tanning, fireproof textiles, baking powder, medical drugs, and cosmetics. With process development focussed on by-product value, the proposed potassium sulfate process provides an efficient, sustainable, potential zero-waste alternative to the conventional refining of lithium chemicals from spodumene.