The Evaluation of Clay Suitability for Geopolymer Technology

Tomáš Hanzlíček,Helena Štěpánková,Kateřina Uličná,Ivana Perná,Václav Římal

doi:10.3390/min10100852

Tomáš Hanzlíček, Helena Štěpánková + Show 3 more

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https://doi.org/10.3390/min10100852

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Abstract

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.

Highlights

The trend in the recognition of clay suitability for geopolymer technology is closely associated with the use of many different local sources of clay materials
The kaolin lattice ordering was calculated on the basis of X-ray diffraction (XRD) patterns, and these results were compared with magic angle spinning nuclear magnetic resonance (MAS NMR) analysis of the Al3+ shift of kaolin thermally treated at 750 ◦ C
As the geopolymer technology is spread worldwide among the laboratories and scientific organizations working with very different types of kaolin and kaolinitic clay, the evaluation of a local material based on the recognition of the above-mentioned qualities would greatly facilitate their research

Summary

Introduction

The trend in the recognition of clay suitability for geopolymer technology is closely associated with the use of many different local sources of clay materials. It is well known that clay should be transformed (activated) in the sense of changing its aluminum-ion coordination [1,2,3] This activation involves thermal treatment, during which dehydroxylation is followed by a destruction of the double-layer clay lattice (e.g., kaolin, dickite, and nacrite). The origin and nature of kaolin and kaolinitic clay deposits fundamentally influence their affinity to form geopolymer-matrix precursors [7,8]. It has been confirmed [2,9,10,11] that only four- and five-coordinated aluminum ions are in a state in which subsequent alkalization results in a stable polycondensed system. Geopolymers are predominantly amorphous materials, whose properties mainly depend on the clay material used and its thermal activation, on the alkaline activator utilized

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