Speciation and reduction of U(VI) in acidic chloride brines under hydrothermal conditions: From transport to deposition of uranium in unconformity-related deposits

Abstract : Circulations of acidic chloride brines are associated with unconformity-related uranium (URU) deposits. The spectacular high grade combined with the large tonnage of these deposits is at the origin of the key questions concerning the geological processes responsible for U transport and precipitation. The aim of this work is to performed experimental studies of U6+ speciation and its reduction to U4+ subsequently precipitation to UO2 under hydrothermal condition. About U transport, the study of U6+ speciation in acidic brines at high temperature is performed by Raman spectroscopy and XAS, showing the coexistence of several uranyl chloride complexes UO2Cln2-n (n=0-5). From this study, complexation constants are proposed. The strong capability of chloride to complex uranyl is at the origin of the transport of U6+ at high concentration in acidic chloride brines. Concerning U precipitation, the reactivity of four potential reductants under conditions relevant for URU deposits genesis is investigated: H2, CH4, Fe2+ and the C-graphite. The kinetics of reduction reaction is measured as a function of temperature, salinity, pH and concentration of reductant. H2, CH4, and the C-graphite are very efficient while Fe2+ is not able to reduce U6+ in same conditions. These mobile and efficient gaseous reductant could be at the origin of the extremely focus and massive character of ore in URU deposits. Finally, first partition coefficients UO2/fluid of trace elements are obtained. This last part opens-up new perspectives on (i) REE signatures interpretation for a given type of U deposit (ii) and reconstruction of mineralizing fluids composition
Document type :
Theses
Complete list of metadatas

https://hal.univ-lorraine.fr/tel-01751347
Contributor : Thèses Ul <>
Submitted on : Thursday, March 29, 2018 - 1:17:21 PM
Last modification on : Friday, April 5, 2019 - 8:21:42 PM

File

DDOC_T_2014_0278_DARGENT.pdf
Files produced by the author(s)

Identifiers

  • HAL Id : tel-01751347, version 1

Citation

Maxime Dargent. Speciation and reduction of U(VI) in acidic chloride brines under hydrothermal conditions: From transport to deposition of uranium in unconformity-related deposits. Earth Sciences. Université de Lorraine, 2014. English. ⟨NNT : 2014LORR0278⟩. ⟨tel-01751347⟩

Share

Metrics

Record views

26

Files downloads

43