The use of RbCl disks for the infrared spectroscopy detection of hydrated and dehydrated halloysite in mixtures with kaolinite

Abstract A simple IR spectroscopy method for detecting hydrated and dehydrated halloysite in artificial mixtures with kaolinite is described. The method is based on the exclusive ability of RbCl among the alkali halides to form a complex with halloysite but not with kaolinite. This complex absorbs at 3500 cm−1 when hydrated halloysite or admixed halloysite is examined in RbCl disks, the limit of detection being 15% in the kaolin admixture. Heating the clay powders or corresponding RbCl disks at 110°C affects the 3500 cm−1 frequency. The development of this absorption band together with a decrease in the intensity ratio of the 3690/3620 cm−1 frequencies is proportional to increasing amounts of halloysite in the kaolin admixtures. This method has an analytical applicability and is relatively rapid.