Leaching Process of Potassium Feldspar by Sub-Molten Salt at Low Temperature

Potassium feldspar crude ore came from Lingshou County, Hebei Province, which mainly contained K₂O (w=13.71%), Al₂O₃ (w=21.51%) and SiO₂ (w=61.02%) based on the mineralogical characteristics analysis by inductively coupled plasma optical emission spectrometry (ICP-OES) and X-ray fluorescence (XRF). To recover valuable elements including K, Al, Si from potassium feldspar crude ore for preparation of high quality products, KOH sub-molten salt method was adopted to decompose potassium feldspar crude ore at low temperature under atmospheric conditions. The effects of leaching temperature, alkali-to-ore mass ratio, stirring rate and leaching time on the leaching rates of K, Al, Si from potassium feldspar crude ore were investigated, respectively. Both thermodynamic analysis and experimental results demonstrated that the concentrated alkali solution (w_KOH=89.66%) at sub-molten salt state had a high chemical reaction activity, which could decompose potassium feldspar crude ore at a relatively low temperature, such as 230 ℃. With alkali-to-ore mass ratio of 3∶1, stirring rate of 500 r/min, leaching time of 150 min, the leaching rates of K, Al, Si from potassium feldspar crude ore at 230 ℃ were 98.3%, 96.9% and 94.3%, respectively. X-ray diffraction (XRD) spectra of products also demonstrated that potassium feldspar crude ore almost completely decomposed. The unreacted shrinking core model with the surface chemical reaction control was used to predict the leaching kinetics of potassium feldspar crude ore by KOH sub-molten salt at the temperature range of 220−250 ℃. Based on the experimental data of leaching kinetics, the apparent activation energy of K, Al, Si were calculated as 84.2, 79.1, 78.3 kJ/mol, respectively.