Browsing by Subject "ion exchange"

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  • Kareinen, Timo; Nissinen, Ari; Ilvesniemi, Hannu (The Society of Forestry in Finland - The Finnish Forest Research Institute, 1998)
    In this study we analyze how the ion concentrations in forest soil solution are determined by hydrological and biogeochemical processes. A dynamic model ACIDIC was developed, including processes common to dynamic soil acidification models. The model treats up to eight interacting layers and simulates soil hydrology, transpiration, root water and nutrient uptake, cation exchange, dissolution and reactions of Al hydroxides in solution, and the formation of carbonic acid and its dissociation products. It includes also a possibility to a simultaneous use of preferential and matrix flow paths, enabling the throughfall water to enter the deeper soil layers in macropores without first reacting with the upper layers. Three different combinations of routing the throughfall water via macro- and micropores through the soil profile is presented. The large vertical gradient in the observed total charge was simulated succesfully. According to the simulations, gradient is mostly caused by differences in the intensity of water uptake, sulfate adsorption and organic anion retention at the various depths. The temporal variations in Ca and Mg concentrations were simulated fairly well in all soil layers. For H+, Al and K there were much more variation in the observed than in the simulated concentrations. Flow in macropores is a possible explanation for the apparent disequilibrium of the cation exchange for H+ and K, as the solution H+ and K concentrations have great vertical gradients in soil. The amount of exchangeable H+ increased in the O and E horizons and decreased in the Bs1 and Bs2 horizons, the net change in whole soil profile being a decrease. A large part of the decrease of the exchangeable H+ in the illuvial B horizon was caused by sulfate adsorption. The model produces soil water amounts and solution ion concentrations which are comparable to the measured values, and it can be used in both hydrological and chemical studies of soils.
  • Puhakka, Eini; Ritala, Mikko; Lehto, Jukka (2020)
    Potassium cobalt hexacyanoferrate(II) [K2CoFe(CN)(6)] is an extremely selective ion exchanger for cesium ions. To examine the atomic level background for the selectivity a computational structural study using DFT modelling was carried out for K2CoFe(CN)(6) and for products where Cs has replaced K in the elemental cube cages closest to the surface. In the K-form compound the potassium ions are not in the center of the Co-Fe-CN elementary cube cages closest to the surface but locate about 140 pm from the cube center towards the surface. When cesium ions are exchanged to these potassium ions they locate much deeper from the surface, being only about 70 pm upwards from the cube center. 'Ibis apparently leads to much stronger bonding of cesium compared to potassium. Once taken up into the outermost cube cages on the surface of the crystallites cesium ions are not able to penetrate further since they are much larger than the electron window between the cubes. Furthermore, they are not able to return to the solution phase either leading to a practically irreversible sorption.
  • Leskinen, Anumaija; Gautier, Celine; Räty, Antti; Kekki, Tommi; Laporte, Elodie; Giuliani, Margaux; Bubendorff, Jacques; Laurila, Julia Pauliina; Kurhela, Kristian Otto Aleksi; Fichet, Pascal; Salminen-Paatero, Susanna (2021)
    This paper reports the results obtained in a Nordic Nuclear Safety Research project during the second intercomparison exercise for the determination of difficult to measure radionuclides in decommissioning waste. Eight laboratories participated by carrying out radiochemical analysis of H-3, C-14, Cl-36, Ca-41, Fe-55 and Ni-63 in an activated concrete. In addition, gamma emitters, namely Eu-152 and Co-60, were analysed. The assigned values were derived from the submitted results according to ISO 13,528 standard and the performance assessments were determined using z scores. The measured results were compared with activation calculation result showing varying degree of comparability.
  • Zhang, Wenzhong; Hietala, Sami; Khryashchev, Leonid; Hatanpää, Timo; Doshi, Bhairavi; Koivula, Risto (2018)
    The lanthanides (Ln) are an essential part of many advanced technologies. Our societal transformation toward renewable energy drives their ever-growing demand. The similar chemical properties of the Ln pose fundamental difficulties in separating them from each other, yet high purity elements are crucial for specific applications. Here, we propose an intralanthanide separation method utilizing a group of titanium(IV) butyl phosphate coordination polymers as solid-phase extractants. These materials are characterized, and they contain layered structures directed by the hydrophobic interaction of the alkyl chains. The selective Ln uptake results from the transmetalation reaction (framework metal cation exchange), where the titanium(IV) serves as sacrificial coordination centers. The “tetrad effect” is observed from a dilute Ln3+ mixture. However, smaller Ln3+ ions are preferentially extracted in competitive binary separation models between adjacent Ln pairs. The intralanthanide ion-exchange selectivity arises synergistically from the coordination and steric strain preferences, both of which follow the reversed Ln contraction order. A one-step aqueous separation of neodymium (Nd) and dysprosium (Dy) is quantitatively achievable by simply controlling the solution pH in a batch mode, translating into a separation factor of greater than 2000 and 99.1% molar purity of Dy in the solid phase. Coordination polymers provide a versatile platform for further exploring selective Ln separation processes via the transmetalation process.
  • Lehto, Jukka; Koivula, Risto; Leinonen, Heikki; Tusa, Esko; Harjula, Risto (2019)
    This paper describes the processes used at the Fukushima Daiichi plant, Japan, to purify the waste effluents generated in the cooling of damaged reactors. These include primary cesium removal with the Kurion zeolite system and the SARRY system utilizing silicotitanate to remove radiocesium from water recirculated to reactors for cooling. Another process is the ALPS system to purify the retentates of the reverse osmosis plant to further purify the water from radionuclides after primary cesium separation. In ALPS, a major role is played by the transition metal hexacyanoferrate product CsTreat and sodium titanate SrTreat in the removal of radiocesium and radiostrontium, respectively. The performance of these four exchangers (zeolite, silicotitanate, hexacyanoferrate, and sodium titanate) is critically analyzed with respect to processing capacities and the decontamination factors obtained in the processes. Furthermore, general information on preparation, structure and ion exchange of these ion-exchanger categories is given with additional information on their use in nuclear waste effluent treatment processes. Finally, the importance of selectivity and associated factors are discussed.