Hydrothermal reaction of K-feldspar powder in NaOH-Ca(OH)2 mixed medium

The hydrothermal reactions between K-feldspar powder and NaOH-Ca (OH)(2) mixed alkaline medium at 240 degrees C were investigated. The effects of Na ratio (x(Na), Na2O/(Na2O + CaO) in mole) on the phase and composition change in solid products were explored in detail. Results showed that increase in x(Na) led to the orderly formation of compounds following the sequence of CaO-SiO2-H2O -> Na2O-CaO-SiO2-H2O -> Na2O-Al2O3-SiO2-H2O, and K+ was accessible into solution after reaction. The new products after reaction was tobermorite, pectorite, nepheline hydrate, analcime, and hydroxycancrinite, depending on different x(Na). The hydrothermal reaction was deduced to be a coupled dissolution and reprecipitation process, which was governed by the chemical equilibrium with the change in solution chemistry.