Potassium recovery from muscovite using NaCl-roasting followed by H2SO4-leaching

Abstract

The present study aims at the recovery of potassium from muscovite mica (which contains K2O; similar to 10 wt%) using NaCl-roasting coupled with H2SO4-leaching process. The preliminary acid leaching studies applying different mineral acids resulted in a potassium recovery of 8%-18%. The optimum leaching conditions for the maximum recovery were 4 mol/L H2SO4, 60 min leaching time and liquid-solid ratio 4 mL/g at 90 degrees C. However, the roasting of muscovite with additive NaCl (muscovite: NaCl mass ratio of 1:1.00, 900 degrees C, 45 min) followed by H2SO4-leaching (95 degrees C, 60 min) extracted potassium to the tune of 98%. Under similar roasting conditions, the H2O-leaching process extracted only 60% of potassium. The effects of various roasting and leaching parameters such as temperature, time, NaCl concentration, acid concentration, liquid-solid ratio on potassium extraction were evaluated. The appearance of the sylvite (KCl) mineral phase in the NaCl-roasted muscovite and its disappearance in the acid/water leached residue confirmed the physical and chemical distortions of the muscovite crystal structure. The possible mechanism of potassium release from the complex muscovite structure was elucidated based on available literature substantiated by characterizations using X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-rays spectroscopy (SEM-EDX).