Extraction of Rare Earth Elements from Idaho-Sourced Soil Through Phytomining: A Case Study in Central Idaho, USA
Abstract
:1. Introduction
2. Materials and Methods
2.1. Soil Preparation
2.2. Seed Preparation
2.3. Experimental Design, Growing, and Treatments
2.4. Plant Harvesting
2.5. Pyrolysis and Elemental Analysis
2.6. Statistical Analysis
2.7. Life Cycle Assessment
2.7.1. Goal and Scope Definition
2.7.2. Life Cycle Inventory
2.7.3. Life Cycle Impact Assessment
- The greenhouse climate control system and grow lights used 24,200 kWh and 64,500 kWh, respectively, for a total of 88,700 kWh of electricity consumed during controlled-environment cultivation.
- A diesel tractor is used to fertilize, sow seeds, and harvest P. arundinaceae biomass in the field study.
- A growth period of six weeks is enough for P. arundinacea to hyperaccumulate REEs optimally.
- P. arundinacea biomass is 90% water by weight and oven drying it for 24 h at 95 °C removes all possible moisture content.
- Biomass is pyrolyzed directly after drying (no grinding).
- Dried biomass weight is reduced by 50% when converted to bio-ore.
- Nitrogen gas pumped through the pyrolysis reaction chamber remains unchanged after it is emitted into the atmosphere.
- Emissions from pyrolysis of biomass at 350 °C have the following chemical contents: 69% CO2, 25% CO, 2.5% H2, 1% CH4, and 2.5% other mixed hydrocarbon gases [38].
- All GHG emissions produced are emitted directly into the atmosphere.
- All electricity used was supplied by Western Electricity Coordinating Council (WECC) Northwest. Emission factors from this provider are as follows: 602.1 lb/MWh CO2, 0.056 lb/MWh CH4, and 0.008 lb/MWh N2O [39].
- Energy used to power the biomass drying and pyrolysis processes was considered, but energy used to power the facility itself (e.g., lighting, heating) was not considered.
- Transport between the field and biomass processing and pyrolysis facilities was not considered.
2.7.4. Interpretation
2.8. Techno-Economic Assessment
3. Results
3.1. Growing Success and Bio-Ore Mass Production
3.2. Hyperaccumulation Ability
3.3. Life Cycle Assessment and Techno-Economic Analysis Results
4. Discussion
5. Conclusions
Supplementary Materials
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Study | Objective | Elements | Plant Species | Substrate Type | Treatment | |
---|---|---|---|---|---|---|
1 | 2 | |||||
[19] | ✗ | ✓ | La, Ce, Pr, Nd | Dicropteris dichotoma | Soil from REE ore deposit | Histidine, citric acid, malic acid |
[20] | ✗ | ✓ | Al, Fe, K, Ca, Mg, Mn Ni, Zn, Cr, Pb, Co, Cu, Cd | Plantago almogravensis | Podzol | - |
[21] | ✗ | ✓ | Lanthanides (Atomic # 57-71) | Achillea millefolium, Artemisia vulgaris, Papaver rhoeas, Taraxacum officinale, Tripleurospermum inodorum | Roadside-sourced soil | - |
[22] | ✗ | ✓ | Cd, Ce, La, Nd, Sr, Y | Trifolium pratense, Helianthus annuus | Phosphogypsum compost mix | Bacillus cereus |
[23] | ✗ | ✓ | Lanthanides | Dicranopteris dichotoma | Soil from rare earth mines | - |
[24] | ✗ | ✓ | Lanthanides | Phytolacca americana | Soil with REE mine tailings | Manure and sawdust mixture, biochar |
[25] | ✗ | ✓ | Cu, Pb, Cr, Zn, Cd, Ni | Ludwigia stolonifera, Sphaeranthus gomphrenoides, Leersia hexandra, Commelina benghalensis, Sphaeranthus kirkii, Typha capensis, Cyperus articulantus, Fuirena umbellate, Agave sisalana, Cyperus exaltatus, Crinum papilosum, Hoslundia opposita, Pluchea dioscoridis, Hygrophylla auricultata, Ipomoea batata | Heavy metal contaminated soil | - |
[26] | ✗ | ✓ | Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu | Phytolacca americana, P. acinose, P. clavigera, P. bogotensis, P. isosandra | Murashige and Skoog medium, quarter-strength Hoagland nutrient solution | H2SO4, REE tri-chloride salt |
[27] | ✗ | ✓ | La, Y, Nd, Dy, Ce, Tb | Salix myrsinfolia, S. shwerinii | Hydroponically grown | REE-enriched tap water |
[28] | ✓ | ✓ | As, Cd, Cu, Ni, Pb, Zn | Helianthus annuus | Soil with various heavy metal concentrations | none |
[29] | ✗ | ✓ | Sc, Y, La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu | Dicranopterus dichotoma, D. linearis, Melastoma malabathricum, Cyperus difformis, C. kyllingia. C. distans, C. rotundus | Soil from a former mining area | - |
[30] | ✓ | ✓ | As, Cu, Mo, Ni, Zn, Re | Arundo donax, Tamarix ramosissima, Salsola kali, Cynodon dactylon, Chenopodium album, Atriplex leucoclada, Zygophyllum fabago | Soil with mine tailings | - |
[31] | ✗ | ✓ | La, Ce, Nd, Sm, Eu, Tb, Yb, Lu, Sc | Citrus limonia | Commercial substrate | Superphosphate fertilizer |
[32] | ✓ | ✓ | Lanthanides, Ge | Lupinus albus, Brassica napus, Zea mays | Soil containing trace REEs and Ge | Fertilizer, lime |
This study | ✓ | ✓ | Ce, La, Nd, Y, Pr | P. arundinaceae, S. nigrum, P. americana, B. juncea | REE-rich Idaho-sourced soil | Fertilizer, biochar, citric acid |
Objective | Evaluate REE Uptake Across Plant Species and Soil/Water Treatments |
---|---|
Species | Phalaris arundinacea, Solanum nigrum, Phytolacca americana, Brassica juncea |
Experimental units | 72 pots total, 18 per species, 3 replications of each species–soil–water combination |
Soil treatment | Non-treated vs. fertilizer vs. biochar |
Water treatment | Non-treated vs. citric acid |
Greenhouse conditions | 18–32 °C controlled temperature, 16:8 h light:dark cycle with minimum 308 µmol/m2/s light intensity |
Duration | 6 weeks from germination to harvest |
Sample processing | Biomass washed, dried, pyrolyzed, and acid-digested |
Sample analysis | Via ICP-MS |
Elements analyzed | REEs including Ce, La, Nd, Pr, Y |
Postanalysis evaluation | Life cycle analysis and techno-economic analysis |
Parameters | Values | Parameters | Values |
---|---|---|---|
pH | 7.6 | Calcium (meq/100 g) | 12.4 |
Sand % | 47.3 | Magnesium (meq/100 g) | 3.4 |
Silt % | 39.5 | Sulfate-S (µg/g) | 3.0 |
Clay % | 13.2 | Zinc (µg/g) | 1.3 |
Salts (mmhos/cm) | 0.6 | Iron (µg/g) | 9.2 |
Chlorides (µg/g) | 7.0 | Manganese (µg/g) | 1.5 |
Sodium (meq/100 g) | 0.2 | Copper (µg/g) | 0.1 |
CEC (meq/100 g) | 16.3 | Boron (µg/g) | 0.2 |
Excess lime (%) | 3.2 | Cerium (µg/g) | 2889 |
Organic matter (%) | 2.8 | Lanthanum (µg/g) | 2071 |
Organic N (lb/Acre) | 55.0 | Neodymium (µg/g) | 1690 |
Ammonium-N (µg/g) | 2.6 | Praseodymium (µg/g) | 435 |
Nitrate-N (µg/g) | 5.0 | Yttrium (µg/g) | 808 |
Phosphorus (µg/g) | 5.0 | Total mixed target REEs (µg/g) | 7893 |
Potassium (µg/g) | 97.0 |
Plant Species | Success Rate (out of 18) | Treatment # | Soil Treatment | Water Treatment | Avg Bio-ore Mass (g) | Ce | La | Nd | Pr | Y | Total Target REE | Total Mixed REE | Target REE BF |
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Phalaris arundinacea (reed canary grass) | 22% (4) | 1 | Non-treated | Non-treated | 0.3 | 2820 | 74 | 1567 | 420 | 1895 | 6676 | 9121 | 0.79 |
2 | 1% CA | - | - | - | - | - | - | - | - | - | |||
3 | Fertilizer | Non-treated | 4.5 | 14,930 | 392 | 7236 | 1858 | 11,623 | 36,041 | 47,830 | 4.72 | ||
4 | 1% CA | 4.2 | 15,977 | 391 | 7800 | 2009 | 13,726 | 39,904 | 52,910 | 4.77 | |||
5 | Biochar | Non-treated | 1.6 | 11,170 | 245 | 6460 | 1564 | 9100 | 29,138 | 41,513 | 4.40 | ||
Average | 2.7 | 11,224 | 276 | 5766 | 1463 | 9086 | 27,940 | 37,844 | 3.67 | ||||
Solanum nigrum (black nightshade) | 61% (11) | 1 | Non-treated | Non-treated | 0.5 | 11,950 | 282 | 5245 | 1428 | 6020 | 24,924 | 32,309 | 2.6 |
2 | 1% CA | - | - | - | - | - | - | - | - | - | |||
3 | Fertilizer | Non-treated | 3.6 | 2653 | 84 | 1390 | 367 | 2890 | 7384 | 9349 | 1.00 | ||
4 | 1% CA | 6.0 | 3362 | 78 | 1569 | 419 | 2521 | 7948 | 10,204 | 1.32 | |||
5 | Biochar | Non-treated | 6.4 | 5017 | 104 | 2577 | 668 | 3322 | 11,690 | 16,072 | 1.20 | ||
Average | 4.1 | 5746 | 137 | 2695 | 721 | 3688 | 12,987 | 16,984 | 1.53 | ||||
Phytolacca americana (pokeweed) | 50% (9) | 1 | Non-treated | Non-treated | 0.4 | 1731 | 30 | 1060 | 276 | 1467 | 4562 | 6165 | 0.53 |
2 | 1% CA | 7.4 | 1702 | 68 | 994 | 251 | 1579 | 4594 | 6163 | 0.61 | |||
3 | Fertilizer | Non-treated | 1.1 | 507 | 0 | 277 | 76 | 769 | 1625 | 2072 | 0.19 | ||
4 | 1% CA | 7.1 | 1523 | 540 | 738 | 210 | 1487 | 4500 | 5429 | 0.60 | |||
5 | Biochar | Non-treated | 0.8 | 1644 | 70 | 922 | 235 | 1091 | 3962 | 5382 | 0.57 | ||
Average | 3.4 | 1421 | 142 | 798 | 210 | 1279 | 3849 | 5042 | 0.5 | ||||
Brassica juncea (brown mustard) | 61% (11) | 1 | Non-treated | Non-treated | 3.5 | 266 | 6 | 142 | 37 | 270 | 720 | 950 | 0.08 |
2 | 1% CA | - | - | - | - | - | - | - | - | - | |||
3 | Fertilizer | Non-treated | 8.9 | 566 | 28 | 318 | 76 | 675 | 1666 | 2200 | 0.29 | ||
4 | 1% CA | 10.9 | 1099 | 28 | 553 | 147 | 980 | 2808 | 3629 | 0.51 | |||
5 | Biochar | Non-treated | 3.7 | 288 | 64 | 163 | 41 | 284 | 840 | 1108 | 0.16 | ||
Average | 6.8 | 555 | 32 | 294 | 75 | 552 | 1508 | 1972 | 0.26 |
Impact Category | Unit | Greenhouse Study | Field Study |
---|---|---|---|
Global warming | kg CO2 eq. | 69.11 | 14.28 × 102 |
Smog | kg O3 eq. | 1.41 × 10−2 | 6.48 |
Respiratory effects | kg PM2.5 eq. | 8.89 × 10−5 | 4.10 × 10−2 |
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Richardson, K.; Mirkouei, A.; Duellman, K.; Aylward, A.; Zirker, D.; Schwarz, E.; Sun, Y. Extraction of Rare Earth Elements from Idaho-Sourced Soil Through Phytomining: A Case Study in Central Idaho, USA. Sustainability 2025, 17, 5118. https://doi.org/10.3390/su17115118
Richardson K, Mirkouei A, Duellman K, Aylward A, Zirker D, Schwarz E, Sun Y. Extraction of Rare Earth Elements from Idaho-Sourced Soil Through Phytomining: A Case Study in Central Idaho, USA. Sustainability. 2025; 17(11):5118. https://doi.org/10.3390/su17115118
Chicago/Turabian StyleRichardson, Kathryn, Amin Mirkouei, Kasia Duellman, Anthony Aylward, David Zirker, Eliezer Schwarz, and Ying Sun. 2025. "Extraction of Rare Earth Elements from Idaho-Sourced Soil Through Phytomining: A Case Study in Central Idaho, USA" Sustainability 17, no. 11: 5118. https://doi.org/10.3390/su17115118
APA StyleRichardson, K., Mirkouei, A., Duellman, K., Aylward, A., Zirker, D., Schwarz, E., & Sun, Y. (2025). Extraction of Rare Earth Elements from Idaho-Sourced Soil Through Phytomining: A Case Study in Central Idaho, USA. Sustainability, 17(11), 5118. https://doi.org/10.3390/su17115118