Synthesis of Zeolite from Granitic Soil Produced in Tochigi Prefecture, Japan

We investigated the synthesis of zeolites from soil composed mainly of quartz and feldspar, commonly found in Japan, via hydrothermal treatment up to 473 K using 1 M to 10 M sodium hydroxide solution as a solvent. When a high concentration of 10 M NaOH was used, cancrinite was obtained with a yield of approximately 50 wt% after 24 hours of hydrothermal treatment at 473 K. When mechanochemical mixing was applied as a pretreatment, analcime was formed under hydrothermal treatment at temperatures ranging from 423 K to 473 K for 24 hours. At even lower temperatures, sodalite and phillipsite were produced after 72 hours of hydrothermal treatment. The formation conditions of sodalite and phillipsite were examined in relation to sodium hydroxide concentration and temperature. The zeolites synthesized from soil treated with sodium hydroxide were those typically formed under high sodium concentration conditions. We also demonstrated that the filtrate obtained after cancrinite synthesis can be regarded as a sodium hydroxide solution of silica and used as a raw material to synthesize mordenite hydrothermally at 443 K, which forms under low sodium concentration conditions.