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Radio pollutant removal is one of several priority restoration strategies for the environment. This study assessed the effect of low molecular weight organic acid on the lability and mechanisms for release of (137)Cs from contaminated soils. The amount of (137)Cs radioactivity released from contaminated soils reacting with 0.02 M low molecular weight organic acids (LMWOAs) specifically acetic, succinic, oxalic, tartaric, and citric acid over 48 h were 265, 370, 760, 850, and 1002 Bq kg(-1), respectively. The kinetic results indicate that (137)Cs exhibits a two-step parabolic diffusion equation and a good linear relationship, indicating that the parabolic diffusion equation describes the data quite well, as shown by low p and high r(2) values. The fast stage, which was found to occur within a short period of time (0.083-3 h), corresponds to the interaction of LMWOAs with the surface of clay minerals; meanwhile, during the slow stage, which occurs over a much longer time period (3-24 h), desorption primarily is attributed to inter-particle or intra-particle diffusion. After a fifth renewal of the LMWOAs, the total levels of (137)Cs radioactivity released by acetic, succinic, oxalic, tartaric, and citric acid were equivalent to 390, 520, 3949, 2061, and 4422 Bq kg(-1) soil, respectively. H(+) can protonate the hydroxyl groups and oxygen atoms at the broken edges or surfaces of the minerals, thereby weakening Fe-O and Al-O bonds. After protonation of H(+), organic ligands can attack the OH and OH(2) groups in the minerals easily, to form complexes with surface structure cations, such as Al and Fe. The amounts of (137)Cs released from contaminated soil treated with LMWOAs were substantially increased, indicating that the LMWOAs excreted by the roots of plants play a critical role in (137)Cs release., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Abstract: The dynamics of Cs and Sr sorption by soils, especially in the subtropics and tropics, as influenced by soil components are not fully understood. The rates and capacities of Cs and Sr sorption by selected subtropical and tropical soils in Taiwan were investigated to facilitate our understanding of the transformation and dynamics of Cs and Sr in soils developed under highly weathering intensity. The Langmuir isotherms and kinetic rates of Cs and Sr sorption on the Ap1 and Bt1 horizons of the Long-Tan (Lt) and the A and Bt1 horizons of the Kuan-Shan (Kt), Mao-Lin (Tml) and Chi-Lo (Cl) soils were selected for this study. Air-dried soil (<2mm) samples were reacted with of 7.5×10−5 to 1.88×10−3 M of CsCl (pH 4.0) or 1.14×10−4 to 2.85×10−3 M of SrCl2 (pH 4.0) solutions at 25°C. The sorption maximum capacity (q m) of Cs by the Ap1 and Bt1 horizons of the Lt soil (62.24 and 70.70mmolCskg−1 soil) were significantly (p <0.05) higher than those by the A and Bt1 horizons of the Kt and Cl soils (26.46 and 27.49mmolCskg−1 soil in Kt soil and 34.83 and 29.96mmolCskg−1 soil in Cl soil, respectively), however, the sorption maximum capacity values of the Lt and Tml soils did not show significant differences. The amounts of pyrophosphate extractable Fe (Fep) were correlated significantly with the Cs and Sr sorption capacities (for Cs sorption, r 2 =0.97, p <1.0×10−4; for Sr sorption, r 2 =0.82, p <2.0×10−3). The partition coefficient of radiocesium sorbed on soil showed the following order: Cl soil≫Kt soil>Tml soil>Lt soil. It was due to clay minerals. The second-order kinetic model was applied to the Cs and Sr sorption data. The rate constant of Cs or Sr sorption on the four soils was substantiality increased with increasing temperature. This is attributable to the availability of more energy for bond breaking and bond formation brought about by the higher temperatures. The rate constant of Cs sorption at 308K was 1.39–2.09 times higher than that at 278K in the four soils. The activation energy of Cs and Sr sorbed by the four soils ranged from 7.2 to 16.7kJmol−1 and from 15.2 to 22.4kJmol−1, respectively. Therefore, the limiting step of the Cs+ or Sr2+ sorption on the soils was diffusion-controlled processes. The reactive components, which are significantly correlated with the Langmuir sorption maxima of Cs and Sr by these soils, substantially influenced their kinetic rates of Cs and Sr sorption. The data indicate that among components of the subtropical and tropical soils studied, short-range ordered sesquioxides especially Al- and Fe-oxides complexed with organics play important roles in influencing their capacity and dynamics of Cs and Sr sorption. [Copyright &y& Elsevier]

Abstract: 137Cs is one of the major artificial radionuclides found in environments; but the mechanisms behind fertilizer-induced 137Cs desorption from soil remain unknown. This study aimed to investigate the kinetics and mechanisms underlying the various cations and anions that cause Cs release from soil under acidic conditions. NH4H2PO4 (1M), 0.5M (NH4)2SO4, 1M NH4Cl, 1M KCl or 1M NaCl solutions were added to 137Cs-contaminated soil. The power function model well described the short term 137Cs desorption with the solutions. The rate coefficients for 137Cs release from soil in NH4H2PO4, (NH4)2SO4, NH4Cl, and KCl solutions were 7.7, 7.3, 6.8, and 6.1 times higher than the rate observed in a NaCl solution, respectively. The NH4H2PO4 and (NH4)2SO4 solutions induced significantly greater 137Cs release from the contaminated soil than the NH4Cl, KCl and NaCl solutions. After four times repeated extractions with the fertilizer solutions, the total amount of 137Cs extracted by (NH4)2SO4 and NH4Cl solutions reached equilibrium, while that extracted using an NH4H2PO4 solution continued to increase. The combined effect of phosphate and protons was the major mechanism behind 137Cs release from contaminated soils, when an NH4H2PO4 solution was used. [Copyright &y& Elsevier]