Recovery of lithium from a zinnwaldite-bearing concentrate derived from tailings using commonly available flue-gas...

Natural gypsum and flue-gas desulfurization (FGD) gypsum were investigated as sulfate additives for lithium recovery from a zinnwaldite-bearing concentrate obtained from the Cinovec tailings repository. The performance of the gypsum materials during calcination followed by water leaching was compared with that of laboratory-grade calcium sulfate at an equivalent calcium dosage. For all additives, the principal operating window was centred at approximately 950 °C with an annealing time of 60-90 min, where high lithium recoveries of ca. 93-96% were obtained. Raising the temperature to 1000 °C did not improve recovery and, in some cases, even decreased it. Relative to natural gypsum, FGD gypsum showed a more homogeneous morphology, higher Ca and S contents, and lower levels of silicate impurities. Nevertheless, the differences in process performance between the two industrial gypsum sources were modest. Milling the concentrate prior to calcination increased lithium recovery from 81.7% to 98.6%, whereas intensive milling of the calcined clinker decreased the apparent recovery from 97.8% to 87.2%, most likely because ultrafine particles hindered filtration and retained Li-bearing solution. These results indicate that FGD gypsum is a practical alternative to reagent-grade calcium sulfate for gypsum-assisted lithium recovery from zinnwaldite. More importantly, the comparable performance of FGD gypsum, natural gypsum and laboratory-grade CaSO₄ shows that the gypsum-assisted route is not restricted to model reagents but can tolerate technically realistic sulfate sources. Beyond demonstrating the practical impact, this study elucidates the complex solid-state reaction pathways and kinetic boundaries that govern lithium mobilization when utilizing industrial by-products. By mapping these phase transformations, this work advances the fundamental chemical understanding necessary to recover critical materials from secondary waste streams.