Process Optimization of Potassium Release from K-Feldspar by Combining Calcination and Hydrothermal Method

An optimized process of the hydrothermal treatment of potassium feldspar (K-feldspar) and lime to obtain a potash alternative is reported. The optimization did not change a two-key-step process and only modified the first step, in which K-feldspar was calcined together with calcium carbonate. However, this modified treatment greatly improved the dissolution of K-feldspar, and the released K+Al+Si content was increased by 43 %. Phase analysis showed that new phases (i. e., leucite, larnite, and portlandite) appeared, and the structure of K-feldspar was destroyed during calcination. After the hydrothermal reaction (i. e., the second step), many new mineral phases were generated: butschliite, calcite, hibschite, tobermorite, and alpha-dicalcium silicate hydrate. Therefore, the optimized product showed better physicochemical properties. In addition, the activity of lime was investigated to evaluate its effect on the hydrothermal dissolution of K-feldspar. The optimized hydrothermal product, as a potential commodity, was evaluated from technological and environmental points of view.