Complexation of Radionuclides with Humic Substance: The Metal Concentration Effect

http://www.radiochimacta.deInternational audienceThe influence of humic acids (HA) on the retention of thorium (IV) onto the surface of silica colloids is investigated. Thorium is considered as an analogue of tetravalent actinides (U, Np, Pu), except for the fact that it has no f electrons. Silica (SiO2) is chosen as a model surface because it is a component of many minerals and because of its weak HA sorption properties. Retention experiments are performed by batch procedure at constant ionic strength (I = 0.1M NaClO4), at various pH (2 to 9) and HA concentrations (1–100 mg/L). The sorption of Th(IV) onto colloidal amorphous silica is characterised using a surface complexation model. The ternary system (i.e. HA-Th-Silica) clearly shows the influence of HA on Th(IV) retention. This can lead to a strong reduction of the amount of Th(IV) sorbed onto silica in the presence of HA compared to silica colloids without HA, due to a predominant part of thorium present in solution as humic complexes. In a pH range where no organic coating onto silica occurs, there is a competitive reaction between Th(IV) sorption onto the silica surface and onto HA reactive functional groups. In this case, Schubert's method is applied to obtain a global interaction constant for the Th(IV)-HA system. The large interaction constant values indicate a strong affinity of HA for Th(IV)

Section: Extent Of Th-ha Complexationmentioning

confidence: 99%

On the study of Th(IV)-humic acid interactions by competition sorption studies with silica and determination of global interaction constants

Reiller¹,

Moulin²,

Casanova³

et al. 2003

“…A large amount of literature data [2,15] is available on the interaction of trivalent metal ions M(III) with various types of humic substances at pH = 5 in 0.1 M NaClO 4 . However, the comparison between both Eu/PMA and M(III)/HS systems is difficult as (i) various models are used to describe the experimental results and (ii) the interpretation of experimental data differs from one study to another.…”

Section: Comparison Of the Eu/pma And M(iii)/hs Systemsmentioning

confidence: 99%

“…The interaction of Eu with PMA is studied at pH = 5 for comparison with the large number of studies carried out with Eu and humic substances at this pH [15]. Note that Eu is considered as an analogue of trivalent metal actinides, Cm 3+ and Am 3+ .…”

Section: Introductionmentioning

confidence: 99%

Complexation and luminescence spectroscopic studies of europium(III) with polymaleic acid

Montavon¹,

Markai²,

Billard³

et al. 2002

Eu / Polycarboxylic acid / Complexation / Laser spectroscopySummary. The complexation behavior of europium(III) with polymaleic acid (PMA) was studied at pH 5 in 0.1 M NaClO 4 by anion exchange (AE). The concentration range investigated was from 10 −9 M to 10 −4 M for the europium ion and from 1 to 50 mg/l for the polymer. The quantitative description of experimental data showed the formation of a 1 : 1 Eu : PMA complex and the existence of at least two distinct interaction environments ("sites") of Eu with the polymer chain whose proportions varied with the ratio between total Eu and PMA concentrations. The existence of different sites was further demonstrated by Time Resolved Laser-induced Fluorescence Spectroscopy (TRLFS) measuring the lifetimes and emission spectra of EuPMA complexes. By using empirical relationships, environments implying 1 : 2 and 1 : 1 Eu : COO − coordination could be deduced. The results show similarities with published data obtained for fulvic and Aldrich humic acids as far as complexation properties at pH = 5 are concerned.

“…The models agree in the view that pH and ionic strength are main factors which influence the complexation reaction of metal cations with humic acids. The influence of varying the metal ion concentration is discussed controversially [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Complexation behaviour of neptunium with humic acid

Seibert¹,

Mansel²,

Marquardt³

et al. 2001

The complexation of Np(V) with humic acid (HA) was studied under environmental conditions (pH ≥ 6, concentration of HA 1-150 mg/L) over a wide range of metal ion concentrations (10 −14 to 10 −4 mol/L). The experimental methods used for the determination of the complexation constants were continuous electrophoretic ion focusing, anion exchange, and ultrafiltration in combination with radiometric measurements, and, as a direct speciation method, UV/Visspectroscopy. The interaction between Np(V) and humic acid has been described with the charge neutralization model including a correction for different loading capacities (LC) which makes possible the comparison of results obtained at various experimental conditions. Furthermore, the degree of deprotonation has also been used to calculate the complexation constants. The complexation constants calculated for Np(V) with the LC-concept vary with the metal ion concentration in the range between 10 −14 and 10 −4 mol/L. At metal concentrations below 10 −11 mol/L, a complexation constant log β LC = 5.0 ± 0.3 was obtained. In the concentration range 10 −7 to 5 × 10 −4 mol/L, the log β LC values decrease continuously to 3.7 ± 0.4 (10 −5 -5 × 10 −4 mol/L). The latter is in agreement with direct measurements (UV/Vis-spectroscopy) at this concentration and data from the literature.