Cesium, strontium, europium(III) and plutonium(IV) complexes with humic acid in solution and on montmorillonite surface

Abstract

The effect of Aldrich humic acid (HA) on the mobility of ~37Cs, 85Sr, ~SZEu and 239pu radionuclides was studied in Ca-montmorillonite suspensions. Verified 2-sites-2-species (2s2s) models correspond to an intensive interaction of all elements with humificated surface, what is in a remarkable contrast with the weak complexation of cesium and even strontium in solutions -the neutral ligand interaction constants 13 (1/mol) are log 13<-9.9 and 7.56+0.21 for Cs and Sr, respectively. The result for europium complexation in solution, log 13= 12.49-2-_0.18 is in a good agreement with literature data. For plutonium(IV) not only a high proton competitive constant in solution was obtained, log 13=(-0.67+ 0.32)+3pH, but also a strong chemisorption, which at high concentrations ofhumic acid (above 0.05 g/I) indicates the formation of bridge humate complexes of plutonium on the humificated surface. Logarithms of heterogeneous interaction constants (~10, I/g) of the elements with surface humic acid are 4.47+0.23, 4.39+0.08, and 6.40+0.33 for Cs, Sr, and Eu(III), respectively, and the logarithm of the proton competitive constant (~24, I/g) for Pu(IV) -3.80+0.72. Distribution coefficients of humic acid and metal humates between 0.01 g HA/1 solution and montmorillonite were derived as log Ka(AH ) =-1.04_+0.11, log Ka(EuA ) = 1.56_+0.11 and log Ka(PUA ) = 2.25+0.04, while the values for Cs and Sr were obtained with very high uncertainty. Speciation of the elements on montmorillonite surface is illustrated as a function of equilibrium concentration of humic acid in solution and ofpH.*

Sorption of curium by silica colloids: Effect of humic acid

“…Owing to the high alpha activity of Am(III) and Cm(III) the number of such studies on their sorption by mineral oxides is limited [10,11]. Instead, extensive studies have been carried out using lanthanides as analogue of trivalent actinides [12][13][14][15][16]. The mechanism of the sorption process of metal ions by the mineral oxides is explained in terms of the surface complexation models [17,18].…”

Assessment of 137Cs and 239,240Pu Distribution in Forest Soils of the Opole Anomaly

“…In forest soils, both soluble and insoluble plutonium compounds remain in top layers (Bunzl 1998;Druteikienė 1999;Lujanienė 2002). The main reason of plutonium compounds retention in organic soil horizons are associations between humic substances and Pu ions (Fujikawa 1999;Macášek 1999;Sokolik 2003). It was found that besides organic matter Pu was also bound with Fe/Mn oxides (e.g., Komosa 2002).…”

“…Though organic soil horizons do not contain enough clay minerals to immobilize cesium, many authors (Beli et al 1994;Takenaka et al 1998;Nakamaru et al 2007;El Samad et al 2007;El-Reefy et al 2006;Zhiyanski et al 2008;Wacławek et al 2004;Dołhańczuk-Śródka et al 2006aDołhańczuk-Śródka et al , 2006bDołhańczuk-Śródka et al , 2006c reported the highest 137 Cs activities just in upper horizons, rich in organic matter. A reason of Cs + retention in organic horizons could be explained by formation of certain complexes between cesium ions and humic acids (Macášek 1999). There is a hypothesis which suggested that organic matter modifies the adsorption properties of clay minerals in soil (El-Reefy 2006).…”

Luminescence from γ-irradiated humic acid

“…An increase in the molecular weight and a release of CO 2 were found when HAs from soil and peat in aqueous media were irradiated with g-rays in the dose range 10-100 kGy [8]. The effect of HS on the g-irradiated pollutants, herbicides and pesticides was extensively studied [1,10,11]. The secondary electromagnetic ultraweak radiation-radiochemiluminescence (RCL)-following g-radiolysis of the HA-alkaline solution was detected recently.…”