Hydrothermal decomposition of K-feldspar in KOH-NaOH-H2O medium

The hydrothermal decomposition of K-feldspar in mixed alkaline solutions containing NaOH and KOH at a concentration of 8.5 M was studied. As the mole fraction of KOH (chi(KOH) = KOH/(KOH + NaOH) in mole) in the mixed alkaline solution decreased, metastable kalsilite, kalsilite and hydroxyl-cancrinite crystallized progressively at 240 degrees C. The metastable kalsilite disappeared when reaction temperature increased from 240 degrees C to 280 degrees C, while the crystallization zone of kalsilite was extended from chi(KOH) = 0.8-03 to chi(KOH) = 1.0-0.4, and the crystallization zone of hydroxyl-cancrinite was enlarged from chi(KOH) = 0 to chi(KOH) = 0.2-0. The K-feldspar dissolved under the action of OH- and released K+, Al(OH)(4)(-) and H2SiO42-. The kalsilite or hydroxyl-cancrinite was precipitated from solution. (C) 2015 Elsevier B.V. All rights reserved.