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Laboratory actinide partitioning: Whitlockite/liquid and influence of actinide concentration levels

Benjamin, T. M. and Jones, J. H. and Heuser, W. R. and Burnett, D. S. (1983) Laboratory actinide partitioning: Whitlockite/liquid and influence of actinide concentration levels. Geochimica et Cosmochimica Acta, 47 (10). pp. 1695-1705. ISSN 0016-7037. doi:10.1016/0016-7037(83)90019-4.

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Fission and alpha track radiography techniques have been used to measure partition coefficients (D) at trace (ppm) concentration levels for the actinide elements Th, U, and Pu between synthetic whitlockite and coexisting “haplobasaltic” silicate liquid at 1 bar pressure and 1250°C at oxygen fugacities from 10^(−8.5) and 10^(−0.7) bars. Pu is much more readily incorporated into crystalline phases than is U or Th under reducing conditions (fO_2 = 10^(−8.5)), because Pu is primarily trivalent, whereas U and Th are tetravalent. Definitive valence state assignments cannot be made, but our best estimates of corrected partition coefficients for Pu^(+3), Pu^(+4), Th^(+4), U^(+4), and U^(+6) are, for whitlockite 3.6/<⩽0.6/1.2/0.5/⩽0.002. The effect of changing pressure and liquidus temperature is relatively small, which probably reflects a weak temperature dependence for D (whitlockite) but possibly could be due to cancellation of opposing temperature and pressure effects. Comparison of experiments at trace U levels with those containing percent concentrations of UO_2 indicate that Si is involved in the substitution of U in whitlockite with U + 2Si ⇄ Ca + 2P being the most likely mechanism. D_u is lower. 0.3 vs 0.5. at percent levels compared to 20 ppm. This is best explained by the effect of U on melt structure or by a decrease in the fraction of tetravalent U at high U concentrations.

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Burnett, D. S.0000-0001-9521-8675
Additional Information:© 1983 Pergamon Press Ltd. Received 6 August 1982, Accepted 27 June 1983. This research was supported by NASA grant NSG 7202. We thank M. T. Murrell for helpful discussions. The manuscript profited greatly from reviews by E. Dowty and L. Haskin.
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Issue or Number:10
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Official Citation:T.M. Benjamin, J.H. Jones, W.R. Heuser, D.S. Burnett, Laboratory actinide partitioning: Whitlockite/liquid and influence of actinide concentration levels, Geochimica et Cosmochimica Acta, Volume 47, Issue 10, October 1983, Pages 1695-1705, ISSN 0016-7037, (
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ID Code:57001
Deposited On:27 Apr 2015 19:27
Last Modified:10 Nov 2021 21:06

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