Recovering Battery-Grade LiOH·H2O from Spent Lithium-Containing Sagger Crucible by Thermal Dehydration and BaSO4-Driven Double Decomposition

This study develops and validates an integrated hydrometallurgical process to recover battery-grade lithium hydroxide monohydrate from spent aluminosilicate sagger crucibles. Lithium was first leached as Li2SO4 from the crucibles using sulfuric acid; the Li2SO4·H2O present in the leachate was then thermally decomposed at 300 °C to Li2SO4 + H2O, as confirmed by TGA-guided selection and XRD. Subsequent conversion to LiOH proceeded via double decomposition with Ba(OH)2. Guided by HSC-based equilibrium simulations and an Eh–pH analysis of the Li–Ba–S–H2O system, reaction conditions were optimized over 60–80 °C and [OH−]/[Li+] = 1–3. The optimum was identified at 70 °C and [OH−]/[Li+] = 1, delivering a conversion efficiency of 98.78% and a Li recovery of 98.86%. Two-end-point acid titration indicated a LiOH content of 90.29 wt.% in solution with minimal Li2CO3 formation, consistent with processing under vacuum–Ar to suppress CO2 uptake. The crystallized product obtained by evaporation at ≥90 °C for 24 h was confirmed as LiOH·H2O (with LiOH) by XRD, while the solid by-product was single-phase BaSO4. ICP-OES measured a final LiOH·H2O purity of 99.8%.