Iron-bearing kaolinite in Venezuelan laterites: I. Infrared spectroscopy and chemical dissolution evidence

Abstract

Abstract Fe substitution for Al in kaolinite (from Venezuelan laterites) is proved by infrared spectroscopy and chemical techniques. The location of Fe in the octahedral sheet is characterized by two absorption bands, at 865–875 and 3607 cm −1 , assigned as δ Al-OH-Fe and v OH respectively. The detection of the 865 cm −1 band requires the use of CsCl for the preparation of the disks heated to 270°C so that the clay delaminates as a result of a kaolinite-CsCl-H 2 O complex formation. The 3607 cm −1 absorption is detected when KI disks are prepared. These two characteristic frequencies persist after either thermal decomposition or selective chemical dissolution of free iron and aluminium hydroxides. Selective chemical dissolutions by consecutive treatments for; (1) the removal of free iron oxides, (2) gibbsite removal and (3) extractions of Fe and Al from kaolinite, give additional evidence about the occurrence of this solid solution.