Acid resistance of zeolites in HNO
3 solution were studied at 25°C by means of X-ray powder diffraction. The structure of zeolite A (Si/Al=1.0) and X (Si/Al=1.25) began to collapse by treatment with 0.1 M HNO
3 and that of mordenite (Si/Al=5) began to collapse by treatment with 1 M HNO
3.
Thermal transformations of Na, Cs and Sr type clinoptilolites were studied by means of differential thermal analysis (DTA), thermogravimetric analysis (TGA) and X-ray powder diffraction. Their structures collapsed above about 900°C and did not recrystallize until 1, 400°C.
Leachabilities of Cs and Sr from the calcined clinoptilolite and mordenite saturated with Cs and Sr decreased as the calcining temperature rose. Especially, the leaching rates of Cs from clinoptilolite and mordenite calcined at 1, 200°C for 3 hr were under 10
-9 g/cm
2·day. This value was under 1/10 of the leaching rates from zeolites calcined at 1, 100°C. The leaching rates of Sr from clinoptilolite and mordenite calcined at 1, 100°C for 3 hr were about 10
-9 g/cm
2·day. The surface area of calcined zeolites used in this calculation was measured by N
2 gas adsorption method.
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