Study on the preparation of mineral silicon-potassium fertilizer by hydrothermal leaching of kaolinite to generate potassium aluminosilicate under the “calcification-potash alkali” system

Kaolinite is a typical silicate mineral found in bauxite, which tends to combine with sodium aluminosilicate hydrate (red mud) as the equilibrium solid phase in the Bayer process. This combination leads to increased losses of alumina and alkali, resulting in environmental pollution. Kaolinite and other aluminum and silica mineral phases are considered harmful impurities in alumina production. Their removal complicates the treatment process, increases production costs, and does not fundamentally address the issue of red mud accumulation and emissions. This study proposes a “calcification-potash alkali”(CPA) process, wherein potash is utilized instead of sodium alkali to simulate the hydrothermal leaching of kaolinite, the primary silicon-containing mineral phase in bauxite, during the Bayer process. The transformation product is Kaliophilite(KAlSiO₄), which can be used to prepare mineral-based silicon‑potassium fertilizers. This paper investigates the dissolution behavior and mechanism of kaolinite during the leaching process. Leaching experiments and analyses (FTIR, XRD, XRF, XPS, and SEM-EDS) reveal that potassium oxide concentration and alkali leaching temperature are the main factors influencing kaolinite transformation. The optimal dissolution conditions are a temperature of 200 °C, a calcium-to‑silicon ratio of 0.2, a K₂O concentration of 160 g/L, and a reaction time of 60 min. Under these conditions, the kaolinite reaction rate reaches 98.9 %, yielding potassium aluminosilicate. Furthermore, the heavy metal content and other indices met relevant standards, allowing for its incorporation into organic matter and the preparation of mineral silica‑potassium fertilizers to partially replace industrial fertilizers in agriculture, offering significant cost advantages and promising market prospects. This process transforms the silicon-containing mineral phase in bauxite from waste into a valuable resource, offering a new reference for the utilization of medium- and low-grade bauxite as well as the treatment of red mud.