Smectite-, silica- and zeolites-bearing raw materials (Hliník nad Hronom bentonite, Slovakia) - A new approach using integrated petrographic and mineralogical studies

Abstract This paper presents the results of detailed petrographic and mineralogical studies of commercial bentonite from the Hlinik nad Hronom deposit in Slovakia. The X-ray diffraction, optical microscopy, field emission scanning electron microscopy (FESEM), thermal analysis, infrared spectroscopy and chemical analyses revealed that the main component of the studied commercial bentonite is montmorillonite (47%) followed by opal-C/CT (20%), clinoptilolite (15%), biotite (3%), potassium feldspar and plagioclases (12%), and quartz (3%). Both the optical microscopy and FESEM studies demonstrated that the precursor of bentonite was ignimbrite composed of compressed, strongly deformed pumice fragments, which were moulded around pyroclastic grains such as biotite, plagioclase, quartz and fragments of volcanic rocks. The pumice fragments were locally cemented by microcrystals of potassium feldspars and subsequently replaced by montmorillonite, and opal-C/CT, less commonly by clinoptilolite. The specific surface area of the studied bentonite is about 50 m2/g. Although bentonite from the Hlinik nad Hronom deposit is recognized as a medium-quality raw material due to relatively low content of smectite, it can be valuable as a substance which integrates the properties of smectite-, silica- and zeolite-bearing raw materials.