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Erschienen in:
20.03.2020 | Original Paper: Sol-gel and hybrid materials for energy, environment and building applications
Evolution of mineral phases and microstructure of high efficiency Si–Ca–K–Mg fertilizer prepared by water-insoluble K-feldspar
Erschienen in: Journal of Sol-Gel Science and Technology | Ausgabe 1/2020
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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.
Evolution of mineral phases during calcination of potassium feldspar and release of effective elements in Si–Ca–K–Mg fertilizer under acidic environment. First of all, this graphical abstract provides a good description of the evolution of mineral phases during the high-temperature calcination of K-feldspar ore. As shown in the figure, limestone and dolomite are selected as additives and calcined with microcline (major mineral in K-feldspar ore) at high temperatures. At high temperatures, limestone is thermally decomposed into calcium oxide, and dolomite is thermally decomposed into calcium oxide and magnesium oxide. Calcium oxide reacts with microcline, destroying the stable silicate skeleton in the microcline. Thus, the microcline is converted into leucite and silica. With the increase of calcium oxide content, leucite will be further decomposed into kalsilite. At the same time, reactions occur between silica, calcium oxide, and magnesium oxide. In addition, the figure also describes the release performance of effective elements in Si–Ca–K–Mg fertilizer under acid soil environment. Microcline will not be dissolved in weakly acidic environment. Leucite is difficult to be dissolved in weak acids. However, kalsilite is easily dissolved by weak acids. Therefore, kalsilite is the main mineral source of available potassium. Other silicate minerals formed in fertilizers can release silicon, calcium, and magnesium. Therefore, this graphical abstract provides a good description of the main points of this article.
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