Modes of occurrence of Fe in kaolin from Yunnan China

Iron as the main contaminating element in kaolin gives an undesirable reddish color to this white clay, therefore analyzing the modes of occurrence of Fe in kaolin has important guidance for their removal. In this paper, the modes of occurrence of Fe were investigated on a very special kaolin from Yunnan China, which contains kaolinite and halloysite at the same time. Attempts were made to study the Fe species by correlating the XRD, microscopic investigations and XPS spectral information of the clay samples. Mineralogical characterization revealed that halloysite or kaolinite as the main mineral phases associated to illite, quartz and gibbsite as ancillary mineral in the Yunnan kaolin samples. Apart from the main mineral phases, goethite, magnetite and hematite are the three major iron impurities in this kaolin. Microscopic investigations (SEM/EDX and TEM/EDS) confirmed the both existence of pseudo-hexagonal kaolinite and tubular halloysite. The relationship between the mineral and iron impurities was also pointed out under microscope, the results showed that the iron impurity materials exist as free iron forms, and they tend to be present alone or adsorbed on the surface of kaolinite instead of halloysite. XPS characterization gives the specific content of the iron impurity, and the relative ratios of goethite, magnetite and hematite are 55.7%, 32.9% and 11.4%, respectively. This work is of great theoretical significance and guidance for removal of Fe from kaolin which has the kaolinite and halloysite minerals at the same time.