Refining α-Spodumene with Potassium Sulfate Compared to the Conventional Sulfuric Acid Process

Abstract

The conventional process of extracting lithium by decrepitating the concentrates of α-spodumene and then baking β-spodumene with concentrated sulfuric acid is the most economic to operate but nonsustainable because of its feedstock, energy, and waste byproduct intensity. Directly extracting lithium from α-spodumene by roasting it with potassium sulfate (K₂SO₄) followed by leaching it with water offers a more sustainable alternative. We optimized the potassium sulfate process (PSP) at a ratio of K₂SO₄ to spodumene concentrate of 0.6:1 (w/w), 1050 °C, and 30 min roasting time, achieving a lithium extraction efficiency of 96.3 ± 1.4% (w/w), in comparison to 96.66 ± 0.37% (w/w) for the conventional process, for the same feedstock of spodumene concentrate. While the purification of the leach liquor from PSP is more complex, requiring the addition of aluminum sulfate to recover potassium as potash alum, its byproducts have high economic value. Both processes display a similar energy demand, based on 200 kt y^–1 of the spodumene concentrate feed. The use of aluminum sulfate increases the overall cost of PSP by $12.8 million, but sales of potassium alum elevate the revenue by $45.8 million. We reveal that the key advantage of PSP lies in its capability of leveraging the byproducts (leucite and potash alum), while the sulfuric acid process (SAP) may incur disposal cost for its hydrogen aluminosilicate (HAS) byproduct. For PSP to breakeven with SAP, leucite must be converted to a fertilizer and sold at a price of $102.6 t^–1 if HAS requires no disposal cost. With the process development focused on the byproduct value, the proposed PSP provides an efficient, more sustainable, and potential near zero-waste alternative to the conventional refining of the lithium chemicals from spodumene.