A case study targeting K fertilizer chemical synthesis with complete valorization of extraction by-products as an option

Abstract

Here, we demonstrate processing techniques for KNO₃ preparation through green chemical reaction engineering of abundant rock-forming minerals to achieve materials sustainability. In this study, chemical reactions at both low and high temperatures were conducted to investigate the extraction of potassium from kalsilite, KAlSiO₄ for use as a K-fertilizer material and simultaneous transformation of kalsilite to materials such as aluminosilicate gel at low temperatures or muscovite at high temperatures; both these materials have many uses. In the low temperature range of 30 to 80 °C, the optimal conditions to extract potassium from KAlSiO₄ and to obtain aluminosilicate gel were found to be as follows: by using the n(HNO₃)/n(KAlSiO₄) ratio of 1.1, solid to water (S/L) ratio of 1 : 10, a reaction time of 3 h and a temperature of 40 °C. In the high temperature range of 210 to 250 °C, both potassium extraction and crystallization of muscovite were achieved at 250 °C. The mechanisms of K extractions and the simultaneous crystallization of muscovite at higher temperatures were determined by using different characterization techniques such as X-ray diffraction, SEM/TEM, Fourier transform infrared spectroscopy (FTIR), and magic-angle-spinning nuclear magnetic resonance spectroscopy (MAS NMR). Results from the above characterization tools demonstrated that kalsilite can be converted to muscovite by dissolution and recrystallization under hydrothermal conditions at 250 °C while releasing K into solution simultaneously. Three comprehensive utilization routes of potassium-rich rocks for KNO₃ preparation were proposed. Our current results suggest that molecular engineering of abundant natural minerals may lead to materials sustainability through a green chemical approach where reactions are conducted in a closed system to prevent pollution and recover all the components as resources.