Synthesis and ion exchange properties of zirconogermanates
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.639
Synthesisandionexchangeproperties ofzirconogermanates Ryan George and Joseph A. Hriljac1 1
School of Chemistry, University of Birmingham, Edgbaston, Birmingham, B15 2TT, U.K.
Abstract
Pure and Nb-doped zirconium germanate materials of composition K2-xZr1-xNbxGe3O9.H2O where x = 0, 0.1, 0.2 and 0.25 with the structure of the mineral umbite have been successfully synthesised. The parent material displays negligible ion exchange of K+ for Cs+ but the doped materials shows much improved exchange. Synchrotron X-ray diffraction shows substantial peak splitting which varies with increasing niobium content. Preliminary Rietveld refinements suggest a two phase model with a caesium and potassium rich doped umbite phase.
INTRODUCTION: The synthesis of novel ion exchange materials for uses in nuclear waste management and environmental remediation is a key area of research. Much effort is being placed in designing materials with high selectivity and ion exchange capacity, especially in relation to caesium and strontium. The established methodology for the removal of these radionuclides in the UK involves the use of a natural zeolite material clinoptilolite [1], but future waste streams and POCO activities may be better tackled with other systems. One family of materials which have been widely investigated are mixed octahedral and tetrahedral framework metal silicates, due to potentially interesting ion exchange properties and better chemical and radiation stability than aluminosilicate zeolites. Altering the composition of these metal silicates by substituting in different metal ions affects the properties, making it a great tool for modification of the product [2]. Materials have been synthesised with a range of metals such as Zr [3], Sn [4] and Ti [5] in the silicate framework. This allows for fine tuning of the materials properties by either total substitution or partial doping into the structure. It has been of great interest to
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introduce a wide range of different metal atoms into the framework in order to develop materials that can be of use industrially as cation-exchangers. One of these types of materials, a natural zirconosilicate mineral umbite (K2ZrSi3O9.H2O) has been synthesised with both Sn and Ti as the octahedral component, for which the ion exchange properties have been explored in the literature [6]. The successful synthesis of a zirconogermanate derivative (K2ZrGe3O9.H2O), figure 1, has been reported [7]. However the material exhibits poor ion exchange properties, with minimal Cs+ and Sr2+ uptake. This can be improved with 30% Nb5+ for Zr4+ shown to increase Cs+ uptake relative to the parent material [8]. This work further explores niobium doping into the umbite structure and the
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