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A Comparison of Synthetic and Animal Bone Derived Apatite for Sequestering Uranium and Strontium in Soil and Groundwater

Robert C. Moore1, Charles Sanchez2, Fred Salas3, Andrew Tofe4, and Gregory R. Choppin5

Abstract: Apatite, Ca10(PO4)6(OH)2, is a strong sorbent for actinides, strontium, and heavy metals. Apatite may be synthetically produced, obtained from apatite ores, or made from animal bones. In this work, we compare reaction kinetics and Kd values for the reactions of synthetic
hydroxyapatite, cow-bone derived apatite, and fishbone derived apatite with strontium and uranium. Two methods were used for preparing apatite from fish bone: heat treatment to 700/C and reaction with hydrogen peroxide. The apatites prepared by these two methods were compared for their effectiveness for sorption of strontium and uranium. The results indicate that U is taken up by apatite almost 3 times faster than Sr by all forms of apatite. For Sr, Kd values ranged from128 to 307. For U, Kd values ranged from 2420 to 9240. Heat-treated apatite was more effective for strontium and uranium sorption than apatite treatment with hydrogen peroxide. The animal derived apatite that was heat-treated exhibited similar sorption characteristics as synthetic apatite.

It is well documented that apatite strongly sorbs uranium (Arey et al., 1999), strontium (Laxic and Vukovic, 1991), and other metals (Gauglitz et al., 1992). Apatite is an ideal material for long-term containment of contaminants because of its high sorption capacity for actinides and
Heavy metals, low water solubility (Ksp>10-40), high stability under reducing and oxidizing conditions, availability, and low cost. Apatite can be produced synthetically by calcium and phosphate precipitation reactions or high temperature solid state processes (LeGeros, 1991), obtained from apatite ores, or derived from animal bones by heat treatment (Joschek et al., 2000) or treatment with hydrogen peroxide (Erts et al., 1994) to remove the organic fraction of the bone. Heat treatment has the added advantage of producing a more crystalline apatite. Although a significant amount of data on sorption exists in the literature, a comparison of the sorption properties of animal derived apatite and synthetic apatite has not been reported. In this work, we compare reaction kinetics and Kd values for the reactions of synthetic hydroxyapatite and cow bone and fish bone derived apatites with U and Sr. Experiments were performed by placing .3 g of apatite in 30 ml of a 1 x10-6m Sr or 2.6 x 10-5m U solution containing .1m KNO3 as the background electrolyte. The pH of each solution was set to 8.0 and the solutions agitated. Samples were collected at different times and analyzed by liquid scintillation counting (LSC). All cow bone apatite was provided by Xmax Corporation and was heat-treated at either 500, 700 or 900/C. Fishbone apatite was treated by either heat treatment at 700/C or by reaction with hydrogen peroxide. For hydrogen peroxide treated fish bone, the fish bone was placed in a 30% solution of hydrogen peroxide for 7 days. The solution was changed daily. All apatite was sized to between 60-80 mesh.

The results for Sr and U sorption are given graphically in Figures 1 and 2, respectively. The results indicate Sr uptake by apatite takes approximately 50 to 100 hours of contact time to reach equilibrium. For U, the kinetics are much faster with equilibrium being reached in approximately 24 hours. For the cow bone apatite, heat treatment at 500, 700, or 900/C made little difference in Sr or U sorption. Fishbone that was heat treated at 700/C gave similar sorption behavior as cow bone apatite processed by heat treatment. Fish bone treated by reaction with hydrogen peroxide did not uptake as much U as heat treated or synthetic apatite. Analysis of the fishbone apatite indicated 15% organics remained after hydrogen peroxide treatment where as less that 1% remained in the fish bone after heat treatment. Wudnehand Breese (1999) have reported that fish bone apatite is less effective than synthetic apatite for removing lead from water. However, the authors do not indicate how the fish bone in their experiments was processed to remove organic components from the bone. Hydrogen peroxide treatment for longer periods of time may produce apatite with better sorption properties. Kd values (defined as ratio of conc. in solid, in moles of Sr or U per mole of apatite, to the conc. in sol., in mol/L) were calculated for the most and least effective apatite sorbent in each case for Sr and U. For Sr, a value of 307 was determined for synthetic hydroxyapatite and a value of 128 was determined for cow bone apatite treated to 700/C. For U, a value of 9240 was calculated for synthetic and 500/C cow bone apatite and a value of 2420 was calculated for fish bone treated with hydrogen peroxide. The results indicated heat treatment of cow bone and fish bone produces apatite that has similar sorption behavior as synthetic apatite. However, synthetic apatite is approximately 100 times the cost of animal bone apatite. Therefore, animal bone apatite is much more economical to use. More work on hydrogen peroxide treatment of animal bones is needed.

In all reversibility experiments less than 1% of the Sr or U was released back into solution. This work was performed under a Cooperative Research and Development Agreement between Sandia National Laboratories and Xmax Corporation.

References
Arey, J. S., J. C. Seaman, et al. (1999). “Immobilization of Uraniumin Contaminated Sediments by Hydroxyapatite Addition.” Environmental Science and Technology 33:337-342.

Erts, D., L.J. Gatheercole, and E.D.T. Atkins (1994) “Scanning Probe Microscopy of Intrafibrillar Crystallites in Calcified Collagen” Journal of Materials Science-Materials in Medicine 5(4) pp. 200-206

Gauglitz, R., M. Holterdorf, et al. (1992). “Immobilization of Heavy Metals by Hydroxylapatite.” Radiochimica Acta 58(59):253-257.
Joschek, S., B. Nies, R. Krotz, and A. Gopferich, (2000) “Chemical and Physicochemical Characterization of Porous Hydroxyapatite Ceramics Made of Natural Bone.” Biomaterials 21 pp. 1645-1658

Laxic, S. and Z. Vukovic (1991). “Ion-Exchange of Strontium on Synthetic Hydroxyapatite.” Journal of Radioanalytical and Nuclear Chemistry-Articles 149(1):161-168.

LeGeros, R.Z, (1991) Calcium Phosphates in Oral Biology and Medicine Karger Press: Basel Wudneh, A and T. Breese, (1999) “Feasibility of Using Natural Fish bone Apatite as a Substitute for Hydroxyapatite in Remediating Aqueous Heavy Metals.” Journal of Hazardous
Materials B69 pp. 187-196
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1 Sandia National Laboratories, Albuquerque, NM (505)844-1281 FAX (505)844-2348 email: [email protected] (corresponding author).

2 Resident Dirctor, Yuma Agricultural Center, The University of Arizona, Tucson, AZ (520)782-3836.

3 Xmax Corporation, Lakewood, CO, (1-800-426-7836).

4 Sandia National Laboratories, Albuquerque, NM (505)844-2910.

5 Professor, Florida State University, Tallahassee, FL (850)644-3875 FAX (850)644-8281 email: [email protected]


Z Lebensm Unters Forsch. 1992 Apr;194(4):377-80.

[Thorium amd uranium in food of animal origin]

[Article in German]

Frindik O.

Bundesforschungsanstalt fur Ernahrung, Zentrallaboratorium fur Isotopentechnik, Karlsruhe, Bundesrepublik Deutschland.

The thorium and uranium contents (alpha-activities of the natural isotopes Th-228, Th-230, Th-232, U-234, and U-238) in several samples of the meat of domestic animals, venison, and cold-blooded animals are reported. The activity of thorium and of uranium was surprisingly constant in lean meat of all the animals tested. The average activity of the main isotope of thorium was 1-2 mBq Th-232/kg fresh meat (FM) and of uranium 21-34 mBq U-238/kg FM. The lowest and highest values observed were 0.4 and 2.7 mBq Th-232/kg FM, and 9 and 41 mBq U-238/kg FM, respectively. In some internal organs distinctly higher values were obtained: 8.6 mBq Th-232/kg in cattle bones, and 51 mBq U-238/kg in hog kidneys. The highest content of U-238, 84 mBq/kg, was observed in cuttlefish (whole animal). In lean meat, the activity of the daughter isotope Th-228 was on average (by factor) two to four times higher than that of the parent isotope Th-232. In cattle bones, and in fish samples including bones, the factor was 20 and 26, respectively. The activity of the isotope Th-230 ranged between Th-232 and Th-228. In all samples investigated, the daughter isotope U-234 showed an excess activity of 19 +/- 7% as compared to the parent isotope U-238. The above nuclides were determined alpha-spectrometrically using Th-229 for thorium, and U-232 for uranium as internal standard.

PMID: 1598792

Half lives of:
Thorium 230 – 80,000 years 4.6-4.7 Alpha
Uranium 238 -4.46 billion years 4.1-4.2 Alpha
Uranium 234 – 250,000 years 4.7-4.8 Alpha

Radiobiologiia. 1990 Jul-Aug;30(4):502-5.

[The microlocalization of natural uranium in bone tissue]

[Article in Russian]

Egorova ES.

The author experimentally confirms the presence of a large share of uranium within the organic matrix of bone tissue and its uniform distribution within the bone mineral. It was shown in the powder-typed stratum bone cuts that the bone uranium is uniformly distributed within the bone mineral. The same is with the organic fraction of bone where uranium is uniformly distributed as well. This conclusion simplifies the calculation of the dose rate of irradiation of bone cells and red bone marrow cells with alpha-particles from the incorporated uranium, the event that these cells are plunged into a "cloud" of alpha-particles being proposed.

PMID: 2217742

Nuclear researchers use various forms of "apatite" to sequester (or grab-up, absorb) heavy metals and metals like radio-active uranium and strontium 90 (first study). Cow bones and fish bones can be used. The first study showed that "For the cow bone apatite, heat treatment at 500, 700, or 900/C made little difference in Sr or U sorption."

The next few studies show that uranium is deposited in bones, both in the organic matrix (with proteins) and in the bone mineral (which makes up cow-bone apatite).

Feeding offal contaminated with uranium, heavy metals "bone meal" would have allowed concentrated amounts of these metals to bio-accumulate in the feed and consequently the animals consuming it.

Rightly so, only a small fraction of the uranium that they consumed would be absorbed into their systems, but what would be absorbed would have been absorbed via the small intestine, as Dr. Paquet's paper here showed that uranium was only "absorbed", in this model, via the small intestine and not the mouth, stomach or large intestine. The distal ileum which makes up a specified risk material (SRM), is part of the small intestine.

Int. J. Radiat. Biol. 2005 Jun;81(6):473-82
Absorption of uranium through the entire gastrointestinal tract of the rat.

Dublineau I, Grison S, Baudelin C, Dudoignon N, Souidi M, Marquette C, Paquet F, Aigueperse J, Gourmelon P.

Institut de Radioprotection et de Surete Nucleaire, Direction de la RadioProtection de l'Homme, Service de Radiobiologie et d'Epidemiologie, Laboratoire de Radiotoxicologie experimentale, Fontenay-aux-Roses Cedex, France. [email protected]

The aim was to determine the gastrointestinal segments preferentially implicated in the absorption of uranium. The apparent permeability to uranium (233U) was measured ex vivo in Ussing chambers to assess uranium passage in the various parts of the small and large intestines. The transepithelial electrical parameters (potential difference, short-circuit current, transepithelial resistance and tissue conductance) were also recorded for each segment. Determination of in vivo uranium absorption after in-situ deposition of 233U in digestive segments (buccal cavity, ileum and proximal colon) and measurements of uranium in peripheral blood were then made to validate the ex vivo results. In addition, autoradiography was performed to localize the presence of uranium in the digestive segments. The in vivo experiments indicated that uranium absorption from the digestive tract was restricted to the small intestine (with no absorption from the buccal cavity, stomach or large intestine). The apparent permeability to uranium measured with ex vivo techniques was similar in the various parts of small intestine. In addition, the experiments demonstrated the existence of a transcellular pathway for uranium in the small intestine. The study indicates that uranium absorption from the gastrointestinal tract takes place exclusively in the small intestine, probably via a transcellular pathway.

PMID: 16249162
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