128 A Tribute to Rodney C. Ewing: Celebrating a Half-Century of Transformative Contributions to Geoscience, Mineralogy, and Material Science

Honoring Prof. Rodney C. Ewing (1946–2024), this session celebrates over 50 years of groundbreaking contributions to mineralogy, geoscience, and materials science, from atomic-scale processes to field-scale applications.

Monday, 20 October 2025
1:30 PM - 5:30 PM
HBGCC, 217A

Immobilization of Strontium by Apatite at Hydrothermal Conditions

Paper number: 128-6
Program: Technical Sessions
Time: 2:55 PM – 3:10 PM

Authors

Abstract

Regarded as a high-level radioactive waste (HLW), 90Sr is commonly a fission by-product due to the many processes used to generate nuclear energy. Furthermore, the danger of 90Sr lies within the strontium ability to replace calcium within calcium phosphate systems (e.g., bones). The replacement of calcium with radioactive strontium has the potential to cause fatal complications like radiation burns and red-blood cell depletion. This experiment focuses on the uptake of strontium using apatite (Ca10(PO4)6(OH)2), derived from a conversion of brushite to apatite, which is meant to aid model in the immobilization of 90Sr within nuclear wastes. The experimental setup started with the synthesis of brushite (CaHPO4·2H2O), a precursor to apatite. After the brushite was synthesized, approximately 200 mg was placed into 5 separate autoclaves containing 1, 5, 10, 15, and 20 ppm of strontium doped fluid and placed into a laboratory oven at various temperatures (40, 80, 120, 160, and 200°C) for 5 days to ensure the proper time for the complete transformation. 40 experiments were conducted. Once completed both the solid and liquid portion of the experiment are then separated. The samples were characterized and analyzed using ICP-OES, XRD, optical microscopy, and SEM. Using the ICP-OES we determined the available Sr concentrations within the fluid and solid portions of the samples, which revealed that solid samples of temperatures at 120°C and above contained vastly more Sr concentrations than that of 40 and 80°C. The data gathered from the XRD, SEM, and optical microscopy aided in characterizing the solid samples and determining their crystal morphology and mineralogy. The lower temperatures (40 and 80°C) displayed little to no conversion, being in the states of brushite to monetite. The higher temperatures (120°C and above) on the other hand, revealed full conversion to apatite. Partitioning data for 40 and 80°C experiments resulted lower by a factor of 3 compared to those conducted at 120, 160, and 200°C. Calculated yield of extraction resulted on an average of 51% for all experiments, where some experiments resulted as low as 20% and others no greater than 66%. This new data suggests that moderate 90Sr immobilization was achieved at our experimental conditions, when T³120°C.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413064

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