Synthesis of zeolites from halloysite

Abstract

In this study a halloysite which is one of the kaolin group minerals was used as sources of alumina and silica in the synthesis of several zeolites. The reactivity of alumina was determined by chemical dissolution method. The reactivity of alumina was varied upon calcination temperature. The reactivity of silica showed no discernible change in the range of 550 to 1050℃. IR spectra of halloysites indicated that $AlO_4$ peak near $800cm^{-1}$ became intense in the range of 550 to 850℃ and reduced at higher temperature. IR spectra of acid leached halloysite indicated that $AlO_4$ peak reduced in the range of 550 to 850℃ and that at higher temperatures the spectra showed no change. The results suggested that the acid leachable alumina in halloysite is a reactive species for the formation of zeolite and that the alumina is tetrahedrally coordinated. The effective $SiO_2/Al_2O_3$ mole ratio of halloysite to be transformed into zeolites could be determined by chemical dissolution method and the ratio could be controlled by calcining temperature followed by adding reactive alumina compound and/or by mixing the low temperature calcined halloysite and high temperature calcined halloysite. The faujasite type zeolities and the attrition resistant zeolite 4A could be easily synthesized from halloysite with controlling the effective $SiO_2/Al_2O_3$ mole ratio.