Mineral nucleation and growth are key processes affecting the mobility of critical plant nutrients and contaminants in soils. Mineral precipitation often occurs via amorphous intermediates whose chemical composition and short-range structure determine the nature and nutrient/contaminant content of the crystalline end-products. Determining the mechanisms of nutrient/contaminant incorporation in amorphous intermediates is thus important to our understanding of carbon, nutrient, and contaminant cycling in the environment and in the rhizosphere in particular. But this determination is also extremely challenging due to the lack of long-range structure of amorphous phases and the presence of microorganisms that can control their composition, short-range structure, and lifetime. Consequently, our understanding of the molecular-scale mechanisms of inorganic nutrient/contaminant retention by minerals in biogeochemical systems remains limited. The long-term vision of this research is therefore to develop a quantitative understanding of nutrient and contaminant incorporation in amorphous intermediates and crystalline end-products that leads to accurate predictions of the bioavailability of nutrients and the fate of contaminants in biogeochemical systems.
Retention of ionic inorganic nutrients (e.g., K+, NO3−, PO43−) and contaminants (e.g., 137Cs+, 90Sr2+, Cd2+) in carbonate precipitates formed in aqueous conditions and at bacterial cell surfaces will be used as a model system due to the ubiquitous presence of carbonates in soils. A combination of state-of-the-art experimental capabilities and molecular simulations will be deployed to overcome current limitations and identify the mechanisms that control nutrient/contaminant incorporation into amorphous intermediates during carbonate nucleation and growth in biogeochemical systems. Specifically, this research will investigate how the extent and mechanisms of incorporation, the lifetime of amorphous intermediates, and the nature of crystalline end-products are affected by (1) nutrient/contaminant ionic charge, radius, and geometry, (2) the interplay between nutrient/contaminant concentration and water content, and (3) microbially-induced carbonate precipitation.