Public Abstract

DE-SC0024392: Uptake mechanisms of REE in sedimentary phosphorite mineral Sponsor: Department of Energy

Award Status: Active

Institution: Boise State University, Boise, ID
UEI: HYWTVM5HNFM3
DUNS: 072995848

Most Recent Award Date: 08/02/2025
Number of Support Periods: 3
PM: Wilk, Philip

Current Budget Period: 09/01/2025 - 08/31/2026
Current Project Period: 09/01/2023 - 08/31/2026
PI: Kohn, Matthew

Supplement Budget Period: N/A

Public Abstract

Phosphorites are sedimentary phosphate deposits that are mined in the US for fertilizer. Rare-earth elements (REE) are moderately enriched in phosphorites and in principle could satisfy US and global needs for REE, if these REE could be economically extracted. However, we do not know where REE reside in the nanocrystals of the main phosphorite mineral, carbonate fluorapatite, or how they are taken up and transported at the nanoscale. Diverse models for REE enrichment include lattice (volume) diffusion through crystallites, adsorption onto crystallite surfaces, recrystallization and coarsening, and addition of other REE-rich phases. These processes may differentially enrich different REE (light-, middle-, heavy-) or to differentially distribute them into crystallite interiors vs. onto crystallite surfaces. If so, mining could exploit these differences to preferentially extract the most economic REE (e.g., there are fewer sources for heavy REE than light REE). An understanding of rates of REE movement could also identify whether targeting of deposits with higher or lower burial temperatures will benefit extraction of light-, middle-, or heavy-REE. Here, we propose using novel atom probe tomography (APT) to investigate natural and experimental uptake of REE in modern and fossil teeth to identify the physical locations of REE in crystallites and on crystallite surfaces. Distributions are predicted to be characteristic of uptake mechanisms, and will provide insight into the partitioning of light-, middle-, and heavy-REE within crystallites and on crystallite surfaces. APT is ideal because it simultaneously identifies the spatial locations of each atom and what element it is, so we can look at distributions of light-, middle-, and heavy-REE at the atom to nanocrystallite scale. Vertebrate fossils provide an ideal foundation for understanding REE uptake processes because: 1. They are common components of natural phosphorite deposits. 2. They share the same overall nanocrystallite structure of other phosphorite components. 3. Most importantly, they are virtually devoid of REE prior to deposition. REE uptake must occur post-deposition, so the patterns of REE distributions through these materials elucidate uptake mechanisms. Our research will consist of 4 research tasks: 1. Identify and sample optimal natural materials. A PhD student at Boise State (PhD1) will characterize REE concentrations and patterns of uptake at the 10s of μm to mm scale. 2. Determine REE diffusivities in bioapatite between 50 and 90 °C. PhD1 will conduct REE uptake experiments into modern and fossil tooth enamel to determine temperature-dependencies of REE diffusion. Room temperature results show that lower temperature experiments are not feasible (diffusion is too slow). In both tasks 1 and 2, PhD1 will identify ideal locations in natural and experimental materials for sampling for APT. APT sample tips will be prepared at a collaborative facility and sent to University at Buffalo. 3. Three-dimensional nanoscale imaging of REE. A PhD student at University at Buffalo (PhD2) will use in-house APT to map the distributions of atoms in materials provided through tasks 1 and 2. These data will determine the location and homogeneous/inhomogeneous distributions of heavy-, middle-, and light- REE. 4. Correlative APT-S/TEM microscopy to identify REE adsorption. PhD2 will combine S/TEM imaging of APT samples with APT analysis to directly correlate crystallite structure and chemistry. Results will identify distributions and transport mechanisms and rates of REE, and inform extraction methods of targeted unconventional sources (phosphorites). Thus, our work will help fulfill DOE’s strategic goals to “enable recovery of currently unrecoverable minerals” and “Foster scientific innovation that will ensure supply chains independent of resources and processing from foreign adversaries”.

Phosphorites are sedimentary phosphate deposits that are mined in the US for fertilizer. Rare-earth elements (REE) are moderately enriched in phosphorites and in principle could satisfy US and global needs for REE, if these REE could be economically extracted. However, we do not know where REE reside in the nanocrystals of the main phosphorite mineral, carbonate fluorapatite, or how they are taken up and transported at the nanoscale. Diverse models for REE enrichment include lattice (volume) diffusion through crystallites, adsorption onto crystallite surfaces, recrystallization and coarsening, and addition of other REE-rich phases. These processes may differentially enrich different REE (light-, middle-, heavy-) or to differentially distribute them into crystallite interiors vs. onto crystallite surfaces. If so, mining could exploit these differences to preferentially extract the most economic REE (e.g., there are fewer sources for heavy REE than light REE). An understanding of rates of REE movement could also identify whether targeting of deposits with higher or lower burial temperatures will benefit extraction of light-, middle-, or heavy-REE. Here, we propose using novel atom probe tomography (APT) to investigate natural and experimental uptake of REE in modern and fossil teeth to identify the physical locations of REE in crystallites and on crystallite surfaces. Distributions are predicted to be characteristic of uptake mechanisms, and will provide insight into the partitioning of light-, middle-, and heavy-REE within crystallites and on crystallite surfaces. APT is ideal because it simultaneously identifies the spatial locations of each atom and what element it is, so we can look at distributions of light-, middle-, and heavy-REE at the atom to nanocrystallite scale. Vertebrate fossils provide an ideal foundation for understanding REE uptake processes because: 1. They are common components of natural phosphorite deposits. 2. They share the same overall nanocrystallite structure of other phosphorite components. 3. Most importantly, they are virtually devoid of REE prior to deposition. REE uptake must occur post-deposition, so the patterns of REE distributions through these materials elucidate uptake mechanisms.

Our research will consist of 4 research tasks:

1. Identify and sample optimal natural materials. A PhD student at Boise State (PhD1) will characterize REE concentrations and patterns of uptake at the 10s of μm to mm scale.

2. Determine REE diffusivities in bioapatite between 50 and 90 °C. PhD1 will conduct REE uptake experiments into modern and fossil tooth enamel to determine temperature-dependencies of REE diffusion. Room temperature results show that lower temperature experiments are not feasible (diffusion is too slow). In both tasks 1 and 2, PhD1 will identify ideal locations in natural and experimental materials for sampling for APT. APT sample tips will be prepared at a collaborative facility and sent to University at Buffalo.

3. Three-dimensional nanoscale imaging of REE. A PhD student at University at Buffalo (PhD2) will use in-house APT to map the distributions of atoms in materials provided through tasks 1 and 2. These data will determine the location and homogeneous/inhomogeneous distributions of heavy-, middle-, and light- REE.

4. Correlative APT-S/TEM microscopy to identify REE adsorption. PhD2 will combine S/TEM imaging of APT samples with APT analysis to directly correlate crystallite structure and chemistry. Results will identify distributions and transport mechanisms and rates of REE, and inform extraction methods of targeted unconventional sources (phosphorites). Thus, our work will help fulfill DOE’s strategic goals to “enable recovery of currently unrecoverable minerals” and “Foster scientific innovation that will ensure supply chains independent of resources and processing from foreign adversaries”.