CHANGES IN PHYSICO-CHEMICAL PROPERTIES OF CLINOPTILOLITE TUFF BY CHEMICAL TREATMENT (1)

EFFECT OF ACID SOLUTION TREATMENT

Abstract

The effect of acid treatment on some physico-chemical properties of clinoptilolite tuff from Futatsui, Akita Pref., was investigated by means of a powder method of X-ray diffraction, chemical analyses and measurement of gas adsorption.
Aluminium was dissolved by acid treatment and consequently the ratio of silica to alumina increased as follows: 10.2-33.2 for the specimens treated with 0.01-5N-HCl solu. at 97-98°C, 11.2-18.7 for the specimens treated with 0.1-6N-H₂SO₄ solu. at 97-98°C and 10.3-14.1 for the specimens treated with 0.24-2.4N-HF solu. at room temperature.
When aluminium dissolution ratios after treatments with HCl or H₂SO₄ solu. are below 12.% the intensities of X-ray diffraction 132 in clinoptilolite were not virturally changed. However they decreased gradually with the increase of aluminium removal at above 12%. When the aluminium dissolution ratios were 14, 25, 35, 52 and 71% after HCl treatment, the intensity of X-ray peak 132 of clinoptilolite decreased to 95, 86, 74, 59 and 33% respectively compared with that of original clinoptilolite tuff. Thus the progressive removal of aluminium from the frameworks resulted in the gradual collapse of clinoptilolite structure.
Na⁺ and K⁺ were exchanged with H⁺ by the acid treatments, and a little Ca⁺⁺ was exchanged but the exchange of Mg⁺⁺ was not detected, hence H-riched clinoptilolite was obtained.
The apparent diameter of small aperture in clinoptilolite was enlarged by the acid treatments and the amount adsorbed of C₃H₈ increased according to the enlargement of the diameter of small pore. However the amount of CH₄ and CO₂ decreased with the decrease of zeolite content by acid treatments, because they adsorb on both large and small pores in clinoptilolite.