The alteration of uraninite to Clarkeite
- Univ. of New Mexico, Albuquerque, NM (United States)
The oxidative alteration of uraninite by alkali-bearing, hydrothermal (200-400{degrees}C) solutions in granitic rocks produces the rare mineral clarkeite. The general formula for Na-clarkeite is {l_brace}(Na,K){sub 6-y-z}(M{sup 2+}{sub p}M{sup 3+}{sub q}M{sup 4+}{sub r}){sub y}({open_square}{sub 1+z-x}Pb{sub x}){r_brace}[(UO{sub 2}){sub 7-x}O{sub 10}]{center_dot}nH{sub 2}O z = p+2q+3r. The terms in square brackets designate the sheet structure; the other elements and vacancies ({open_square}) occur in interlayer sites. Clarkeite can accommodate Ca, Sr, Ba, Y, Th, and lanthanides. Thus, clarkeite is a potential actinide and fission product host. The replacement of uraninite by clarkeite occurs in the solid state and results in the loss of one-half of the uranium from uraninite. As U decays to Pb, the radiogenic Pb enters interlayer vacancies in clarkeite. This destabilizes the structure and clarkeite eventually decomposes to woelsendorfite, (Pb,Ca){sub 2}U{sub 2}O{sub 7}{center_dot}2H{sub 2}O, or curite, Pb{sub 3}U{sub 8}O{sub 27}{center_dot}3H{sub 2}O.
- OSTI ID:
- 62240
- Report Number(s):
- CONF-921101--Vol.294
- Country of Publication:
- United States
- Language:
- English
Similar Records
Geochemical alteration of pyrochlore group minerals: Betafite subgroup
Uraninite-water interactions in an oxidizing environment