The Exploratory Study Of Thiostannate Ion-exchange Materials

To date,with the increasing depletion of conventional fossil fuels,the development of nuclear energy as a new type of efficient and clean energy is of vital significance.The radioactive liquid wastes problem caused by nuclear power plants poses severe threat to public health.The disposal of the high level wastes(HLW)is required.137Cs+ and 90Sr2+ ions are the most hazardous and long-lived byproducts in the HLW.Ion-exchange method is one of the most efficient options of removing the 137Cs+ and 90Sr2+ ions in aqueous HLW.As a kind of promising ion-exchange material,metal chalcogenides have attracted much attention for its unique performance such as rapid kinetic,high ion-exchange capacity,wide pH resistance and high selectivity.Thus it is desirable to explore the chalcogenido ion-exchange materials that are capable of the removal of Cs+ and Sr2+ ions from the HLW.On the other hand,rare earth elements(REEs)are the strategic resources with wide applications in fluorescence,permanent magnet,catalyst and superconductivity.However,the leakage of REEs in mining and utilization process may result in wastefulness of resources and harm to human health.Thus it is necessary to develop an ion-exchange material that could be utilized in recovering the REEs from the aqueous environment.As we know,the crystalline chalcogenido compound hasn’t been exploited as an ion-exchanger for REEs adsorption until now.This thesis is focused on the syntheses and characterizations of chalcogenido ion-exchangers based on tin and explore their ion-exchange properties for Cs+,Sr22+ and Ln3+ions.The major outcomes of this thesis are as follows.1.A two-dimensional microporous thiostannate,namely[Me2NH2]4/3[Me3NH]2/3Sn3S7·1.25H2O(FJSM-SnS)has been synthesized and structural characterized.The existence of in-situ generated[Me3NH]+ cations in the structure was confirmed by the characterization techniques such as single crystal X-ray diffraction,TGA-MS,MS and EA.Significantly,the crystalline FJSM-SnS material with high purity could be obtained in a large scale through a one-step solvothermal synthesis with high atom utilization rate from low cost starting materials.Another attempt was made in the introduction of Mn and Cu into the system of thiostannates,and three compounds,i.e.2D-MnSnS3(1,2-DACH),2D-K2Cu2Sn2S6·xH2O and 3D-K4Cu8Sn3S12·xH2O have been obtained.2.The organic[Me2NH2]+ and[Me3NH]+ cations in FJSM-SnS could be exchanged by Cs+ and Sr2+.The structure of Cs+-exchanged FJSM-SnS with the formula of Cs2Sn3S7·4.5H2O(FJSM-SnS-Cs)was confirm to further understand the ion-exchange mechanism.After systematic studies of Cs+ and Sr2+ ion-exchange performance including kinetics,isothermal models,pH dependent distribution coefficients(Kd),simulated groundwater environment,and ion-exchange chromatography column experiments,we found that FJSM-SnS was a highly efficient ion-exchange material for Cs+ and Sr2+.The ion-exchange for Cs+ and Sr2+ could reach a balance in 5 minutes.The maximum ion-exchange capacity for Cs+ was 408.91 ± 29.1 mg/g and that for Sr2+ was 65.19 ± 4.8 mg/g,respectively.In the pH = 0.7～12.7 range,the[Sn3S7]n2n-framework could maintain its flexible structure.In the simulated groundwater,the distribution coefficient(Kd)of FJSM-SnS could keep high value.In the application of ion-exchange column,the removal rates of Cs+ could maintain at 96.1%～98.82%,while that of Sr2+ could maintain at 100%.This study revealed a tin-based ion-exchange material for the removal of Cs+ and Sr2+ The ion-exchange process was highly efficient,and the low-cost synthesis could be easily scaled up,both of which are beneficial for its potential application in HLW disposal.3.We have also investigated the Ln3+ enrichment properties of FJSM-SnS.The material showed rapid kinetic(<5min),high ion-exchange capacity(Eu3+,139.82 ± 3.42 mg g-1 and Tb3+,147.05 ± 4.53 mg g-1),and high selectivity against Al3+ and Fe3+.The recovery rates for Ln3+ could reach～99%in the ion-exchange column experiments,which suggested that the FJSM-SnS is a promising ion-exchange material for Ln3+.