Evolution of mineral phases and microstructure of high efficiency Si–Ca–K–Mg fertilizer prepared by water-insoluble K-feldspar

Abstract: Potassium feldspar (K-feldspar) was decomposed with limestone and dolomite as additives to prepare alkaline mineral silicon-calcium-potassium-magnesium fertilizer (abbreviated as Si–Ca–K–Mg fertilizer) via high temperature calcination route. The effects of calcination temperature on the mineral composition, extraction ratios of available effective elements, and the microstructure of powder particles of Si–Ca–K–Mg fertilizer were studied in detail. The results show that the high-efficiency potassium extraction ratio (83%) and silicon extraction ratio (96%) are obtained in the fertilizer calcined at 1250 °C. The reason is that most of the K-feldspar is decomposed into nanoscale kalsilite crystalline grains, which are easily soluble in weak acids. In addition, part of the kalsilite and most leucite melt into amorphous substances. Above 1300 °C, the extraction ratios of potassium and silicon, including calcium and magnesium, are all close to 100%, because the fertilizer particles are basically in an amorphous state. Furthermore, the elements in the Si–Ca–K–Mg fertilizer can be directly absorbed by the crops in the acidic soil. Therefore, this work can promote the comprehensive development of water-insoluble K-feldspar resources and enhance the sustainable use of soil. [Figure not available: see fulltext.].