Sustainable method to extract potassium from K-feldspar using limestone flotation tailings

This study explores the potential use of limestone flotation tailings (LFT) for recovering potash values from K-feldspar (K2O, 11.4 wt.%). High-temperature leaching tests of potassium-enriched feldspar powder using various mineral acids reveal that a maximum of 18%–23% of potassium can be extracted under optimal conditions (specifically, with an acid concentration of 4M, at 90°C, for 60 min, using a particle size of <100 μm). In contrast, chlorination roasting employing LFT and NaCl as roasting additives, followed by water leaching, shows a significantly higher potassium recovery rate of 97%. The optimal conditions for this maximum recovery include a roasting temperature of 900°C, a roasting time of 40 min, and a K-feldspar to LFT and NaCl ratio of 1:0.5:0.75. The extraction value decreases to 50%–60% with only NaCl as an additive and drops to less than 10% when only LFT is used. This suggests that to effectively replace the K ions from the core of the crystal structure, all three ions (Na⁺, Ca²⁺, and Cl⁻) are necessary. The roasting temperature must exceed the melting point of the NaCl additive, which plays a crucial role in the extraction process. During roasting, the formation of water-soluble potassium phases (sylvite, KCl) and water-insoluble silicate phases (anorthite and nepheline) indicates the breakdown of the complex feldspar crystal structure. Various physicochemical characterizations of the samples were conducted to support the experimental results, using wet chemical analysis, inductively coupled plasma optical emission spectrometry, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray diffraction techniques.