Production of Potassium Sulfate through Valorization of Zero Liquid Discharge Mining Waste from Lithium Clays

Fertilizers are essential for global food security, enabling the agricultural sector to meet the increasing demand for food driven by a growing population. This study focuses on fertilizer production from repurposed mining waste generated from a lithium clay extraction process. Specifically, the waste derived from lithium clay extraction contains potassium sulfate (K2SO4), a premium fertilizer. Through the application of straightforward crystallization techniques and metathesis reactions, guided by solubility and phase diagrams, K2SO4 with over 90% purity was successfully isolated. Analytical techniques, including inductively coupled plasma mass spectrometry (ICP-MS), microwave plasma atomic emission spectroscopy (MP-AES), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA), were utilized at various steps of the process to characterize the composition, structural properties, and thermal behavior of the materials. These characterization methods coupled with life cycle assessment (LCA) and technoeconomic analysis indicate that a two-step crystallization method with KCl metathesis is more viable than a three-step crystallization method involving an intermediate 3K2SO4–Na2SO4 step. This research provides valuable insight into the chemical properties and compositions of the products and identifies the pathways and impacts for the conversion of mining waste into high-value agricultural fertilizers.