Apr 18 – 23, 2010
Casino Conference Centre
UTC timezone

The study of the speciation of uranyl-sulphate complexes by UV-VIS absorption spectra decomposition

Apr 22, 2010, 12:00 PM
1h 30m
Gallery (Casino Conference Centre)


Casino Conference Centre

Reitenbergerova 4/95, Marianske Lazne, Czech Republic
Board: SEP.P07
Poster Separation Methods, Speciation Poster Session - Separation Methods, Speciation


barbora Drtinova (CTU Prague)


Uranyl-sulphate complexes are the most significant U(VI) species in acid solutions containing sulphate ions. The study of their properties is of practical significance for characterisation of solutions used in underground uranium ore leaching and following remediation of leaching sites. At low pH values, the speciation of U(VI) mainly depends on its total concentration [UVI] and sulphate ions concentration [SO42–]. As absorption UV-VIS spectra of UO2(NO3)2 + Na2SO4 solutions were found significantly depend upon the ratio  = [SO42–] / [UVI], the spectrophotometric method for closer study of U(VI) - SO42– complexes speciation was used. Studied solutions were of constant uranium concentration [UVI] = 5•10–2 mol•L–1. Required values of the  ratio were adjusted by proper additions of Na2SO4 solution and varied from  = 0 up to  = 20. Constant pH value pH = 2 was maintained by the additions of either HNO3 or NaOH solution of negligible volume. Absorption spectra were recorded using UV/VIS spectrophotometer CARRY 100 within the wave-length range 190 – 900 nm. The following U(VI) species were considered under conditions given: UO22+, UO2SO4 (aq), UO2(SO4)22– and UO2(SO4)34–. As the most pronounced effects of the  ratio value changes on the spectra revealed at wave-length between 380 and 500 nm, these parts of spectra were used as a database for the identification of individual U(VI) species and for determination of their individual spectra by deconvolution of the experimental spectrum. Proposed simple deconvolution method needs to estimate relative amounts of individual species, preliminary. Stability constants from NEA database and SIT method of activity coefficients calculation at high ionic strength were used for this purpose. The spectrum of UO2(NO3)2 solution without Na2SO4 ( = 0, pH = 2) was considered to be individual spectrum of pure UO22+ specie. Absorbance data following from it and calculated relative amounts of all four species for each  value were taken as the basic set of input data for deconvolution. Then, the absorbance of each of the three remaining species (UO2SO4 (aq), UO2(SO4)22–, UO2(SO4)34–) at given wave length can be find by solving the system of three linear equations involving experimental data from three spectra of different  ratio. The disagreement of spectra calculated from different triplets of experimental spectra can be caused either by experimental errors, or by incorrect estimation of relative amounts of individual species. Thus, presented method can be helpful even for estimation of accuracy of stability constants and SIT activity coefficients used in speciation calculations.

Primary author

Karel Stamberg (CTU Prague)


Alois Motl (CTU Prague) Dusan Vopalka (CTU Prague) barbora Drtinova (CTU Prague)

Presentation materials