Efficient leaching of potassium from K-feldspar in KOH-Ca(OH)2 solution via one-step hydrothermal process

Abstract

Potassium, as an essential element for crop growth, plays an important role in the agricultural field. Extraction of potassium from insoluble potassium salts can greatly alleviate the supply–demand contradiction of potassium fertilizer. However, the current methods have the problems of long process flow and high energy consumption. There is an issue of high Na⁺ content in the leachate after high-temperature roasting and alkaline leaching, making it difficult to separate potassium and sodium. In this study, using KOH and CaO as additives, the decomposition of K-feldspar was promoted by hydrothermal method, and the potassium was converted into soluble component and the silicon components into hydrated dicalcium silicate, which has application value in fields such as construction, ceramics, and carbonization. The results showed that under the reaction conditions of 210 °C, reaction time of 10 h, initial KOH concentration of 3.5 g/L, calcium to silicon molar ratio of 2.6, and liquid–solid ratio of 20 mL/g, the leaching ratios of potassium, aluminum, and sodium reached 93.63 %, 32.94 %, and 97.04 %, respectively; And cyclic leaching can enrich ions in the solution, reducing the difficulty of subsequent leaching solution treatment. The mechanism of hydrothermal leaching for potassium was further revealed through thermodynamic calculations and transformation of solid products. The Ca²⁺/K⁺ exchange mechanism and OH^– structure destruction mechanism occur simultaneously, effectively promoting the leaching of potassium from K-feldspar.