Characterisation of Bauxites by X-ray Fluorescence Method

摘要

X-ray fluorescence has been the common tool for analysis of various silicate, fly ash and other minerals containing Al_2O_3. The ceramic and chemical industries use bauxite in the solid form while in alumina refinery industry; the bauxite is digested with caustic soda converting in to liquid form as Na-aluminate. Al_2O_3 present in free form as gibbsite, diaspore, goethite or brucite, can be converted to the liquid form with NaOH at steam temperature or higher but not the Al_2O_3 present in kaolinite and some other minerals, which are invariably present as impurities in bauxite. The former type of Al_2O_3 is termed as reactive. SiO_2 can be present similarly in reactive or non-reactive forms. Wet chemical and auto-analyser methods are considered suitable as liquid of Na-aluminate can be analysed unlike in XRF where only solids can be analysed. In order to simulate the plant conditions where reactive Al_2O_3, SiO_2 and liquid Na-aluminate from bauxite, are in the process, XRF is often not considered suitable and it is not procured. The authors have experienced analysis in 3 methods for bauxite from mines, feed bauxile to alumina refinery plant, reactive Al_2O_3 and SiO_2 as well as the mud, which are described here. Bauxites with the present chemical compositions have been rarely exploited elsewhere for production of alumina and consequently, XRF analysis of this bauxite may be considered also rare type and interesting from industry point of view. While gibbsite is the main crystalline phase in this bauxite, Jamaican bauxite, for example, contains goethite as the main crystalline phase. XRF analysis with hematite/goethite ratio of 0 to 80 in bauxite has been reported.