Spectroscopic investigations on structural incorporation pathways of FeIII into zeolite frameworks in cement-relevant environments

Abstract FeIII-containing aluminosilicate zeolites are present in cement-relevant and natural environments. Although FeIII is known to occur in framework tetrahedral sites where it substitutes isomorphically AlIIIO4 or in extra-framework octahedral sites as free Fe(H2O)63+, the structural incorporation process of FeIII into different sites is little known. We aim to discern feasible pathways of FeIII incorporation using hydrothermal synthesis methods and synchrotron-based spectroscopic analyses. Results showed that introducing either Fe3+ or Fe2O3·xH2O initially during zeolite nucleation did not lead to FeIII incorporation into the zeolites but only Fe2O3·xH2O prevailed in both cases. However, Fe(NO3)3, FeCl3, and Fe2O3·xH2O affected the kind of zeolite formed. A feasible pathway to incorporate tetrahedral FeIII in the zeolite framework was to introduce firstly FeIII in the cage of faujasite-Y followed by a phase transformation to chabazite. This study facilitates understanding of FeIII uptake in zeolites and of FeIII functional sites that can contribute to immobilization of contaminants.