The corrosion of kaolinite by iron minerals and the effects on geopolymerization

Iron-rich aluminosilicates with disordered structure (laterites) due to the corrosion of kaolinite by iron minerals were investigated as solid precursors for geopolymerization. The particle size distribution, B.E.T surface area, thermal activation, and chemical and mineralogical compositions were used to evaluate the reactivity of iron-rich laterites (35 wt.% of Fe2O3-FeO). The raw materials in the temperature range between 25 and 500 °C showed geopolymerization behaviour similar to that of metakaolin. At temperatures higher than 500 °C, the coarsening of particles and the decrease of B.E.T surface area correspond to an initial sintering of laterites explaining the poor polycondensation/geopolymerization and the decrease of strength of the final products. The increase of the temperature of calcination of raw laterites between 25 and 500 °C corresponds to a reduction of the setting time of geopolymer products. However, this variation of temperature did not significantly affect the flexural strength that remained between ~ 4 and ~ 6 MPa, confirming the possibility to produce sustainable matrices, with more energy saving, using highly corroded laterites.