Alkali-hydrothermal modification of air-classified Korean natural zeolite and their ammonium adsorption behaviors

Abstract

Korean natural zeolite in which clinoptilolite and mordenite coexisted with feldspar and illite as impurities, was treated with 1.0, 3.0, and 5.0 M NaOH solutions at 100, 150, and 200°C under autogeneous pressure for 17 hours either with or without an air classification as pretreatment. Phillipsite, analcime, and hydroxycancrinite were identified as reaction products depending on the reaction temperature and NaOH concentration. The air classification of the starting material prior to alkali-hydrothermal treatment effectively reduced the amount of feldspar, which hardly reacted to zeolite in the hydrothermal reaction. The ammonium adsorption behavior of the treated and untreated samples were ..