Transformation of meta-stable Al to kaolinite: Molecular structure and reaction pathways from solid-state NMR.
EMSL Project ID
30212
Abstract
Disposal of environmental pollutants and radioactive waste relies on our ability to understand the complex chemistry of rock-water interactions. Reactions such as sorption of metal ions and the dissolution and precipitation of silicate minerals can control the fate and transport of environmental contaminates. To predict these molecular-scale processes and subsequently assess the safe disposal of waste forms, we need experimental data coupled with accurate simulations to identify reaction pathways. However, there are few rate data on bulk and surface-enhanced precipitation reactions and even fewer studies that derive uptake mechanisms. We propose to quantify the precipitation kinetics and reaction pathways involved in the transformation of Al-precursor phases to kaolinite by coupling solution chemistry with solid-state NMR techniques. Our previous work on tetrahedrally coordinated-Al ([4]Al) precursor phases (Houston et al, 2008) suggests that the interfacial energies for the nucleation of [4]Al are much lower than the interfacial energy for the heterogeneous nucleation of kaolinite, an octahedrally coordinated ([6]Al) aluminosilicate. These data are profound because it indicates that Al solubility and thus toxicity is not initially controlled by kaolinite.
Critical towards understanding the precipitation of precursor and stable phases from the bulk or at a surface substrate, is the discrimination between meta-stable [4]Al, precipitated [6]Al in kaolinite, and framework nuclei from the substrate. Therefore, we propose a multitude of NMR techniques including high-field 27Al, 27Al MQMAS, and 17O MQMAS NMR to monitor the progression from meta-stable to stable Al-assemblages and derive reaction mechanisms.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2008-10-01
End Date
2011-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members