Fig. 2: Structure of the starting ligands and the grafted mesoporous silicas. (a) Ac-phos ligand and SBA-15-Ac-phos; (b) Prop-phos ligand and SBA-15-Prop-phos<\/figcaption><\/figure>\nFunctionalisation of silica surfaces by phosphonate groups<\/h3>\n Silica SBA-15 grafted with phosphonate ligands, allowing the recovery of actinides contained in an aqueous effluent, were synthesised according to the procedures reported by Fryxell.7<\/sup> The ligand Ac-phos and Prop-phos, which has amide and phosphonic acid functions, were used. All ligands are linked to the silicon atom by an alkyl chain containing three carbon atoms and the amide function. The structure of the grafted mesoporous silicas and the corresponding ligands (before their grafting) is shown in Fig. 2. The silica surface\u2019s functionalisation considerably reduces its specific surface from about 700m2<\/sup>\/g to 300m2<\/sup>\/g.<\/p>\nSorption of actinides by functionalised silica<\/h3>\n Initially, sorption experiments were carried out to test the adsorption capacity of thorium by a silica functionalised with phosphonate groups. These tests were continued with solutions containing plutonium, which presents a specific activity much higher than that of thorium, in particular plutonium 238, to study the silica porosity\u2019s closure by the irradiation damage caused by the alpha disintegrations of plutonium. The obtained results presented in Fig. 3 show a comparable efficiency of these ligands for Pu or Th radionuclides.<\/p>\nFig. 3: Adsorption isotherms of Th on SBA-15-Pro-phos and SBA-15-Ac-phos compared with the adsorption of 238Pu \/239Pu (relative errors of the data were about \u00b15%). The tests were carried out at pH~0.3<\/figcaption><\/figure>\nSelf-irradiation and structural changes<\/h3>\n As discussed previously, particle irradiations (ions, electrons) induce the collapse of silicas\u2019 mesoporosity. Ballistic interactions with 0.5 MeV Au ions are very efficient for that. Under the reported operating conditions, the mesoporous silica is completely densified for a damage of about 1dpa. The objective of the Automact project is to assess whether the self-irradiation caused by the alpha decays of plutonium can induce the same collapse. Actinide test sorption showed that mesoporous silicas can adsorb about 10wt.% of plutonium. This Pu loading makes it possible to obtain radiation damage of 1 dpa in approximately one year for samples doped with isotope 238<\/sup>Pu. This is why the SBA15-Pro-phos-238<\/sup>Pu sample was chosen to study the evolution of mesoporosity under self-irradiation. This sample was charaterised as small-angle X-ray scattering technique (SAXS), which is accessible on the SOLEIL synchrotron\u2019s MARS beamline located in France.<\/p>\nFig. 4 : Comparison of SAXS patterns for SBA-15-Prop-phos, SBA-15-Prop-phos + Th, SBA15-Prop-phos + 238Pu, SBA-15-Propphos + 239Pu measured on the MARS beamline at the SOLEIL synchrotron (except for sample SBA-15-Prop-phos+Th) in October 2022; and detail view on the peak (100)<\/figcaption><\/figure>\nThe first analysis took place in October 2022 and showed a little shift in the position of the (100) peak which can be attributed to a densification of the porous silica network (Fig. 4). This result has to be confirmed; two experiments are scheduled for March 2023 and in the autumn of 2023.<\/p>\n
Concluding remarks<\/h3>\n This study has gone some way towards enhancing the potential application of the process of closing porosity by self-irradiation, and developing the \u2018separation\/conditioning\u2019 strategy for the decontamination of radioactive effluents. As a first step, the functionalised porous support of the silica would be used to capture the radionuclides, and in the second step, it would act as a conditioning matrix. The results that will be obtained in 2023 will make it possible to clarify the validity of this concept and determine the kinetics of closure of the porosity. At the same time, we believe that the high plutonium capture capacity (10wt.%) of the studied materials (SBA15-AcPhos\/PropPhos) will be valuable in solving the difficulty of continuous decontamination processes for radioactive effluents.<\/p>\n
References<\/h4>\n 1\u00a0\u00a0\u00a0 Zur Loye, H.-C., T. Besmann, J. Amoroso, K. Brinkman, A. Grandjean, C. H. Henager, S. Hu, S. T. Misture, S. R. Phillpot, N. B. Shustova, H. Wang, R. J. Koch, G. Morrison and E. Dolgopolova, Chem. Mater<\/em>. 30, 4475-4488 (2018)<\/p>\n2\u00a0\u00a0\u00a0 Makowski, P., X. Deschanels, A. Grandjean, D. Meyer, G. Toquer and F. Goettmann, New J. Chem<\/em>. 36, 531-541 (2012)<\/p>\n3\u00a0\u00a0\u00a0 Lin, J., G. Toquer, C. Grygiel, S. Dourdain, Y. Guari, C. Rey, J. Causse and X. Deschanels, Microporous Mesoporous Mater<\/em>. 328, 111454 (2021)<\/p>\n4\u00a0\u00a0\u00a0 Lou, Y., S. Dourdain, C. Rey, Y. Serruys, D. Simeone, N. Mollard and X. Deschanels, Microporous Mesoporous Mater<\/em>. 251, 146-154 (2017)<\/p>\n5\u00a0\u00a0\u00a0 Lou, Y., G. Toquer, S. Dourdain, C. Rey, C. Grygiel, D. Simeone and X. Deschanels, Nucl. Instrum. Methods Phys. Res<\/em>. B 365, 336-341 (2015)<\/p>\n6\u00a0\u00a0\u00a0 Project-ANR-18-CE05-0016, AUTOMACT: Solid fixation and auto-conditioning of actinideelements coming from contaminated liquid outflows (2018) https:\/\/anr.fr\/Project-ANR-18-CE05-0016<\/p>\n
7\u00a0\u00a0\u00a0 Fryxell, G. E., Y. Lin, S. Fiskum, J. C. Birnbaum, H. Wu, K. Kemner and S. Kelly, Environ. Sci. Technol<\/em>. 39, 1324-1331 (2005)<\/p>\nPlease note, this article will also appear in the thirteenth edition of our\u00a0quarterly publication<\/a>.<\/em><\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"A study considering a new strategy for the treatment of radioactive effluents based on the use of mesoporous silicas is under way. <\/p>\n","protected":false},"author":18,"featured_media":30072,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[24204],"tags":[529,24407,24477],"acf":[],"yoast_head":"\n
Can mesoporous silicas be used for the treatment of radioactive effluent?<\/title>\n \n \n \n \n \n \n \n \n \n \n \n \n\t \n\t \n\t \n \n \n \n \n \n\t \n\t \n\t \n