The Evaluation of Clay Suitability for Geopolymer Technology

In the last 20 years, laboratory work on geopolymer technology has been confronted with the necessity to determine whether a certain clay material has the properties necessary to form genuine geopolymer when thermally treated and alkalized. The assessment of the properties of clay source materials and of the ability of the materials to form geopolymer 3D netting mainly involves the study of the aluminum transformation level during the thermal treatment of the clay. The presented study combines several classical analytical methods (chemical and mineralogical analyses, the calculation of the Hinckley index (HI) based on X-ray diffraction analyses, and the measurement of particle size distribution) for eleven samples of kaolin and kaolinitic clay of various origins and coming from different locations. The results of these methods have been compared with those of 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) in solid state. Based on them, the mentioned methods could be combined for an estimation of the aluminum-ion behavior during the thermal treatment of the clay. HI calculations have shown favorable agreement in 63% of the kaolin samples studied, especially for high purity kaolin without significant impurities in the form of feldspars and/or quartz. The main aim of this work is not to replace the precise MAS–NMR analysis, but to offer an alternative evaluation method when MAS–NMR is not available.