Abstract
To make potassium from K-bearing rocks accessible to agriculture, processing on biotite syenite powder under mild alkaline hydrothermal conditions was carried out, in which two types of KAlSiO4 were obtained successfully. The dissolution-precipitation process of silicate rocks is a significant process in lithospheric evolution. Its effective utilization will be of importance for realizing the comprehensiveness of aluminosilicate minerals in nature. Two kinds of KAlSiO4 were precipitated in sequence during the dissolution process of biotite syenite. The crystal structures of two kinds of KAlSiO4 were compared by Rietveld structure refinements. The kinetics model derived from geochemical research was adopted to describe the dissolution behavior. The reaction order and apparent activation energy at the temperature range of 240–300 °C were 2.992 and 97.41 kJ/mol, respectively. The higher dissolution reaction rate of K-feldspar mainly relies on the alkaline solution, which gives rise to higher reaction order. During the dissolution-precipitation process of K-feldspar, two types of KAlSiO4 with different crystal structure were precipitated. This study provides novel green chemical routes for the comprehensive utilization of potassium-rich silicates.
Highlights
The continuous growth of the world population causes a lack of crops production
We found that the intermediate phase was well-matched with the megakalsilite (ICDD-PDF No 00-054-1123 (2020)) of P63 [35], which is similar to the crystal structure of MZnPO4 (M = Na, K, Rb, Cs) as described in the report of Andratschke [36], so the intermediate product was abbreviated as MEK
Two kinds of KAlSiO4 obtained here are easier to be decomposed in the acid soil, which can supply potassium nutrition to plants but can ameliorate the soil with the porous structure
Summary
The global demand for potassium will appear as a rising tendency in the coming several decades [1]. The potassium salt is obtained mainly from water-soluble potassium salt resources [2]. The use of water-insoluble potassium resources, such as potassium feldspar, nepheline, and muscovite, is a guarantee for Chinese agriculture sustainable development [3]. Feldspars consisting of a group of minerals are fairly common in igneous rocks such as granites, gneisses and schists, as well as metamorphic and some sedimentary rocks, constituting 60% of both the continental and the oceanic crusts of our planet [2]. Thereby, K-feldspar was suggested as a source of potassium for agriculture in the beginning of the twentieth century [3,4]
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