Identifying the differences between clays used in the brick industry by various methods: Iron extraction and NMR spectroscopy.

This study focused on identifying the differences in a clay quarry that is used in brick production to understand the variation between samples based on two kinds of clays: the first kind was suitable for brick production, but the second one did not show good production efficiency. Various samples were characterized by physical and chemical methods. In addition, free iron extraction by a CBD method and calcination at various temperatures were performed. The clay samples were then structurally characterized by XRD, FTIR and 27 Al NMR spectroscopy and thermally characterized using dilatometry. Finally, these results were correlated to the SEM investigation. These results revealed variations in the Si/Al molar ratio (1.4 to 3.3) due to the mineralogy variation within the quarry. Indeed, the non-secondary phase and clay phase contents differed according to the location in the quarry. NMR analysis also revealed that some iron atoms were located in a kaolinite structure, whereas other iron phases, in goethite form, interacted with clay minerals only on the surface of, e.g., kaolinite and muscovite and were not in their structures. From the thermal characterization, the influence of this structural iron in the kaolinite was also evidenced by an increase in the total shrinkage. In conclusion, this work determined the structural differences and their impact on brick production. [ABSTRACT FROM AUTHOR]