Microwave-assisted extraction of potassium from K-feldspar in the presence of NaOH and CaO at low temperature

A creative approach for the hydrothermal decomposition of K-feldspar for the extraction of potassium (K) in mixed alkaline solutions containing NaOH and CaO pretreated by microwave was studied. Under the same processing conditions, a systematic comparison of microwave pretreatment and traditional hydrothermal reaction showed that K⁺ dissolution efficiency was 95% when the mixture was pretreated by microwave. In the test range, the optimum conditions for dissolution of K-feldspar were found to be K-feldspar/H₂O of 50 g/L, NaOH concentration of 5.625 mol/L, CaO/NaOH mass ratio of 1:3, reaction temperature of 200 °C and time of 3 h. The changes of K-feldspar before and after reactions were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). SEM analysis indicates perfectly that microwave heating is volumetric and inside-out compared to conventional heating being outside-in. Analysis of XRD spectra results showed that the mechanism of potassium extraction was ion exchange. The anorthite or hydroxyl-cancrinite was precipitated from solution.