The impact of mineralogy in the U(VI)-Ca-PO4 system on the environmental availability of uranium

Authors: Sowder A.G.¹; Clark S.B.²; Fjeld R.A.³

Source: Journal of Radioanalytical and Nuclear Chemistry, Volume 248, Number 3, June 2001 , pp. 517-524(8)

Publisher: Springer

Abstract:

Kinetic dissolution studies were conducted on four prominent U-Ca-PO_4 minerals (metaschoepite, becquerelite, chernikovite and metaautunite). Synthetic samples were contacted with four extractants (acetic acid, deionized water, EDTA and sodium bicarbonate) at room temperature at two concentrations, 100 mM and 1 mM. Dissolution progress was monitored by periodic sampling for dissolved U, and dissolution rates were obtained from fits to a three term exponential model. Significant variations were observed in the rate and extent of dissolution among the minerals examined. The uranyl phosphates chernikovite and metaautunite proved resistant to dissolution in non-carbonate systems, with dissolution half-times of days to weeks in 100 mM systems and weeks to years in 1 mM systems. In contrast, the uranyl oxide hydrates schoepite and becquerelite were solubilized over much shorter time scales. While 100 mM bicarbonate was successful in dissolving U in all forms, dissolution rates varied among the four minerals. Overall, EDTA was the least sensitive to a 100 to 1 mM drop in its concentration in its solubilization of all four mineral phases, underscoring the importance of organic complexation for the environmental mobility of uranium.

Language: English

Document Type: Regular paper

Affiliations: 1: Savannah River Ecology Laboratory, The University of Georgia, Aiken, South Carolina 29802, USA, present address: 938 Westminster St., NW; Washington, D.C. 20001, E-mail: honest.abe@juno.com; 2: Department of Chemistry, Washington State University, Pullman, Washington 99164, USA 3: Department of Environmental Engineering and Science, Clemson University, Clemson, South Carolina 29634, USA

Publication date: 2001-06-01

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• In this Subject: Physical & Theoretical Chemistry
• By this author: Sowder A.G. ;  Clark S.B. ;  Fjeld R.A.

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