Multi-stage dealumination for characteristic engineering of mordenite-clinoptilolite natural zeolite

Porous materials have been applied for various applications, mainly as adsorbent and catalyst. One of them is zeolite, particularly in a synthetic form which has excellent performance but has some drawbacks of high cost, complex processing, and waste production. Meanwhile, natural zeolite is available in abundant amount and has low-cost provisioning, so it has prospective room for developed. Some of the common types of natural zeolites are mordenite and clinoptilolite; one of the availabilities is located in Gunungkidul, Yogyakarta, Indonesia. The typical modification of zeolite is dealumination which was also applied to the natural zeolite. Dealumination was carried out to improve the natural zeolite properties, particularly Si/Al ratio. The various types of dealumination process were conducted in variable of acid concentration (0 to 12 N HCl), volume ratio (1:1, 1:2, 1:4), soaking time studies (1, 2, 4, 24 hours), agitation (stirring and no stirring), and multi-stage dealumination (1 to 10 stages). XPS analysis determined the Si/Al ratio, then supported by XRD and BET to explore the other characteristics transformation of crystal structure and specific surface area. In the single stage dealumination, the highest Si/Al ratio of 16.2 was produced at 12 N HCl, 1:4 volume ratio, 24 hours soaking time and stirring action. Meanwhile, the multi-stage dealumination has the evidence to improve the Si/Al ratio sequentially than others variable in single stage dealumination; the highest Si/Al ratio attained over than 120 at the most upper stage of dealumination. Moreover, dealumination treatment also increases the specific surface area over than 220m ² /g, but the multi-stage variable was not affected much. The multi-stage dealumination effect provides prospective application of mordenite-clinoptilolite natural zeolite, particularly in the high Si/Al ratio, as hydrophobic surface porous adsorbent or catalyst.