Zirconium Molybdate Research Articles

Industrial-Scale Production of 99mTc Generators for Clinical Use Based on Zirconium Molybdate Gel

This paper is a narration of gel generator technology development and adoption in Iran including production of 99Mo by neutron activation of molybdenum [98Mo(n,γ)99Mo] in the research reactor of Tehran. The indigenous design and development of units for the manufacturing of gel generators included the setting up of shielded plant facilities with pneumatic-driven as well as manual controls and special gadgets, process adaptation to automation in the shielded facility, regulatory clearances and commencement of operations for periodic production of gel generators, demonstration of clinical utility, and adaptation of the generator design. Molybdenum-99 is being converted to zirconium molybdate gel under controlled conditions, and the resulting gel is dried at three steps, which include 2 h at 100°C, 2 h at 90°C, and 5 h at 70°C in order to reduce the time period between the end of reactor irradiation and completion of the processing of gel generators. The produced sodium pertechnetate solution from these gel-type 99Mo/99mTc generators fulfills all requirements of U.S. pharmacopeia. All the generators provide high-yield and pure elutions as well as sterile and pyrogen-free pertechnetate solution. In addition, it shows favorable-quality features to prepare various 99mTc complexes.

Subsolidus phase equilibrium in Cs2MoO4-Al2(MoO4)3-Zr(MoO4)2 system and crystal structure of new ternary molybdate Cs(AlZr0.5)(MoO4)3

The subsolidus area of Cs2MoO4-Al2(MoO4)3-Zr(MoO4)2 system was studied by X-ray powder diffraction. Two new molybdates with component molar ratios of 1: 1: 1 (S1) and 5:1:2 (S2) were synthesized for the first time. The crystallographic parameters of the 5:1:2 compound were determined. Solution- melt crystallization and spontaneous nucleation yielded crystals of new 1:1:1 cesium aluminum zirconium molybdate Cs(AlZr0.5)(MoO4)3. Its formula unit and crystal structure were refined by X-ray diffraction (1592 reflections, R=0.0249). Trigonal crystals: a=12.9441(2) A, c=12.0457(4) A, V=1747.86(7) A3, Z = 6, space group R \( \bar 3 \). The three-dimensional combined framework of this structure is formed by MoO4 tetrahedrons linked through common vertices to (Al,Zr)O6 octahedrons. Cesium atoms occupy large cavities of the framework. Crystallographic position M(1) is occupied by randomly distributed Al3+ and Zr4+ cations.

Influence of drying conditions of zirconium molybdate gel on performance of 99mTc gel generator

99mTc can be produced from 99Mo/ 99mTc gel generators. These gels are part of the generator and the 99Mo/ 99mTc gel generator performance is directly related with gel structure. In this work a series of zirconium molybdate gels have been synthesized and dried under different conditions and characterized using thermal analysis (TGA, DTA), SEM, XRD and porosity measurements. It is found that the water content of the gel determines the structure porosity which allows the diffusion of the 99mTcO 4 − ions inside the gel and was directly connected with performance of the 99Mo/ 99mTc gel generators. Drying conditions of the gel is as an important factor that influence water content and physical–chemical properties of this gel and must be carefully studied to optimize the properties of the gel generators.

Synthesis and ionic conductivity of silver magnesium zirconium molybdates

The silver magnesium zirconium molybdate Ag4Mg2Zr(MoO4), undoped and aliovalently doped with yttrium and aluminum, has been characterized by impedance spectroscopy, X-ray diffraction, and IR spectroscopy. The materials studied possess relatively high ionic conductivity at temperatures above 550 K. Partial yttrium substitution on the zirconium site ensures an increase in ionic conductivity almost throughout the temperature range studied.

Lead cation exchange and alumina columns for concentration of 99mTc-pertechnetate

Large columns containing aluminum oxide (Al2O3) or gel (e.g. zirconium molybdate) are needed to prepare 98Mo(n,γ)99Mo→99mTc column chromatographic generators that results in large elution volumes containing relatively high 99Mo impurity and low concentrations of 99mTc. The decrease in radioactive concentration or specific volume concentration of 99mTc places a limitation on some pharmaceutical kits (DTPA, MIBI, ECD, etc.) or clinical procedures. We report on the post elution concentration of 99mTc using in house prepared lead cation-exchange and alumina columns. Using these columns high bolus volumes (10–60 mL 0.02M sodium sulfate) of 99mTc can conveniently be concentrated in 1 mL of physiological saline. This approach also works very effectively to prepare high specific volume solutions of 99mTc-pertechnetate from a fission based 99Mo/99mTc generator in the second week of its normal working life.

Phase equilibrium in the Cs2MoO4-Bi2(MoO4)3-Zn(MoO4)2 system and the crystal structure of new triple molybdate Cs5BiZr(MoO4)6

The subsolidus region of the Cs2MoO4-Bi2(MoO4)3-Zr(MoO4) system was studied by X-ray powder diffraction. Quasi-binary sections were elucidated, and triangulation performed. Triple molybdates with the component ratios 5: 1: 2 (S1) and 2: 1: 4 (S2) were prepared for the first time. Crystals of cesium bismuth zirconium molybdate of the 5: 1: 2 stoichiometry (Cs5BiZr(MoO4)6) were grown from fluxed melts with spontaneous nucleation. The composition and crystal structure of this triple molybdate were refined using X-ray diffraction data (collected on X8 APEX automated diffractometer, MoKα radiation, 2348 F(hkl), R = 0.0226). The trigonal unit cell parameters were as follows: a = b = 10.9569(2), c = 39.804(4) A, V = 4138.4(4) A3, Z = 6, space group R\( \bar 3 \)c. The mixed-metal three-dimensional framework in this structure is built of Mo tetrahedra and two sorts of (Bi,Zr)O6 octahedra. Large interstices accommodate two sorts of cesium atoms. The Bi3+ and Zr4+ cation distributions over two positions were refined during structure solution.

99Mo/99mTc generators performances prepared from zirconium molybate gels

99mTc may be produced from 99Mo/99mTc zirconium molybdate gel generators. These gels are part of the generator matrix and their chemical and physical characteristics directly influence the generator performances. In this work zirconium molybdate gels were synthesized under different preparation conditions and characterized by TGA, IR and INAA. Our goal was to investigate and correlate generator performance with the physical-chemical properties of the gel. The two factors studied were the molybdate solution pH and the preparation conditions of the zirconyl salt solutions. Several polymolybdate and zirconium species can be formed in solution which can inhibit or favor the zirconium molybdate gel formation or the insoluble polymolybdate-rich and zirconium oxy-hydroxide phases. The 99Mo/99mTc gel generator performance is directly correlated with gel structures. More regular network gels present lower generator performances compared to gels with more flexible random framework. The physico-chemical properties of the gels as well as their behavior as technetium-99m generators are presented and discussed.

Determination of Mo, W and Zr in molybdates and tungstates of zirconium and titanium

Molybdate and tungstate of zirconium and titanium gels, used as matrices of 99Mo/99mTc and 188W/188Re generators, were synthesized under different conditions, in order to establish their performance and to choose the most appropriate gel to produce commercially. This type of generators demands a high content of Mo or W (>25%) in the matrices, since they use 99Mo and 188W of low specific activities. Therefore, it is of vital importance, to know the concentration of W and Mo in these gels, to determine their viability as matrices of the 99Mo/99mTc and 188W/188Re generators. There are different analytical methods to determine Mo and W, however, the presence of Zr and Ti in these gels, in many occasions, interfere in the analysis, imposing the previous separation of both metals before their determination. Therefore, the preparation time of the sample, the cost and the generation of chemical waste of these analyses are increasing. In order to eliminate these difficulties, the concentration of Mo, W and Zr of approximately 43 gels of molybdate and tungstate of zirconium and titanium, were evaluated by NAA without preparation of the samples. The results of this study reveal that the conditions of preparation of the gels influence directly their Mo and W content. In general, the titanium molybdate gels possess, on the average, a larger content of Mo (37%) than the zirconium molybdate gels (30%), while the titanium tungstenate gels contain only 8.5%.

Nucleation and crystal growth of zirconium molybdate hydrate in nitric acid

Zirconium molybdate hydrate can precipitate in nitric acid media during the process of spent nuclear fuel recycling. The precipitates can occur either in the nitric acid dissolution solution or in the waste fission product solution, and can lead to the formation of fouling layers. If such layers are left to grow, they can generate dysfunctions requiring heavy mechanical intervention and lead to production losses. In order to reduce the fouling risk as much as possible, nucleation and crystal growth data of zirconium molybdate hydrate in nitric acid are used to propose a fouling mechanism. Two parameters, supersaturation ratio and temperature, are used with the classical theory of primary nucleation to describe the stability of the supersaturated solutions within an observation time scale of approximately one hour. A quartz crystal microbalance is used to measure zirconium molybdate hydrate crystal growth kinetics on an initial crystal deposit. The collected data allocated four zones delimited by supersaturation ratios and temperatures, each zone describing a specific behaviour of zirconium and molybdenum solutions in nitric acid. As a result, a fouling scenario is proposed and the data is used to greatly limit its growth.

Adsorption of some radionuclides from their aqueous solutions using zirconium molybdate ion exchanger

Zirconium molybdate ion exchanger prepared from equimolar amounts of sodium molybdate and zirconyl chloride was used as an effective sorbent for the absorption of some radionuclides from their aqueous solutions. The zirconium molybdate sorbent was characterized by IR spectra and X-ray diffraction. The adsorption behavior of zirconium molybdate toward Cs(I) (134Cs), Co(II) (60Co), Zn(II) (65Zn), and Eu(III) (152, 154Eu) ions in aqueous solutions was studied in relation to the contact time, composition of aqueous solutions, and temperature. The separation factors of the radionuclides in sorption on zirconium molybdate were determined. The efficiency of the recovery and separation of the radionuclides on zirconium molybdate was assessed.

Chromatographic separation of sodium, cobalt and europium on the particles of zirconium molybdate and zirconium silicate ion exchangers

Zirconium molybdate and zirconium silicate were prepared by application of the precipitation and sol–gel routes, respectively. The produced ion exchange powders were physically characterized using X-ray diffraction, infrared and differential thermal analysis. The obtained data revealed that they are thermally and chemically stable, having unique microstructure properties that permit their use in chromatographic separation of Na +, Co 2+, and Eu 3+ from liquid waste streams. Distribution coefficient studies have been conducted in parallel with the loading-elution column operations; both ion exchangers showed the same order of selectivity towards the aforementioned ions and the K d values decreased in the order; Eu 3+ > Co 2+ > Na +. The capacities of the used exchangers differed with drying temperature; zirconium-silicate possessed higher capacities than corresponding molybdate one. 22Na, 60Co and 152+154Eu were separated from each other on the loaded columns using 0.1 M HNO 3 and 1 M HNO 3.

Pressure-induced amorphization of cubic ZrMo 2O 8 studied in situ by X-ray absorption spectroscopy and diffraction

A combination of in situ high-pressure X-ray diffraction and Mo K-edge XANES was used to examine the changes in local structure that occur as the negative thermal expansion material cubic zirconium molybdate becomes amorphous on compression and, hence, provide insight into the mechanism of amorphization. Amorphization started at ∼1.7 and by 4.1 GPa the sample was glass like by diffraction. The XANES data shows that the pressure induced amorphization at 4.1 GPa does not involve a complete change of molybdenum coordination from tetrahedral, in the starting phase, to approximately octahedral as would be expected if the amorphous material were a metastable intermediate well advanced along the pathway towards decomposition into a mixture of MoO 3 and ZrO 2. Recrystallization of the amorphous material at 600 °C and 4.1 GPa produced a sample that was not a simple mixture of known MoO 3 and ZrO 2 polymorphs nor a known polymorph of ZrMo 2O 8.

Synthesis, Structure and Thermal Contraction of a New Low‐Temperature Polymorph of ZrMo2O8.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis, Structure and Thermal Contraction of a New Low-Temperature Polymorph of ZrMo2O8

We report the synthesis and characterization of a new negative thermal expansion polymorph of zirconium molybdate, LT-ZrMo2O8, and suggest a possible topotactic mechanism for its formation from a precursor phase. The successful identification of this phase sheds new light on the pathway by which cubic ZrMo2O8 can be synthesized and allows one to quantify this process using in situ diffraction experiments for the first time.

Effect of Zr:Mo ratio on 99mTc generator performance based on zirconium molybdate gels

Zirconium molybdate gels have shown to be viable alternatives for preparation of 99mTc generators using 99Mo produced by neutron activation. The aim of this work was to investigate the effect of the Zr:Mo molar ratio on the gel chemical structure and correlate it with the elution efficiency. A series of gels were prepared at Zr:Mo molar ratios from 0.5:1 to 2.3:1 and characterized by TGA, IR, XRD and UV. It was found that the variation of Zr:Mo ratio produces different polymolybdate arrangements on the octahedral units around to the zirconia which is mainly influenced by the water content. When the matrix molybdenum concentration was increased a lesser amount of water was found and the elution efficiencies were increased. However high elution efficiencies produce higher 99Mo breakthrough values. The gel formulation appears thus to be a compromise between the elution efficiency and the molybdenum breakthrough. The chemical–physical properties of these gels are presented and discussed.

Removal of cesium and strontium from acid solution using a composite of zirconium molybdate and zirconium tungstate

A composite mixture of zirconium molybdate and zirconium tungstate was prepared and studied for the sorption of cesium and strontium as a function of nitric acid, metal ion concentration, time and temperature. The distribution coefficient (Kd) of 7000 ml/g (~90% sorption) and 70 ml/g (~20% sorption) was obtained for the sorption of cesium and strontium in 0.1M nitric acid, respectively. Experimental sorption capacity, b for cesium was found to be 50 mg/g from 0.1M HNO3 and 30 mg/g for strontium from 0.001M nitric acid. The sorption of strontium on the sorbent was accompanied by the absorption of heat but the sorption of Cs+ results in the liberation of heat. Column studies were conducted by following a breakthrough (BT) curve of cesium and strontium up to C/C0=1 and the results are reported.

The formation of hydrated zirconium molybdate in simulated spent nuclear fuel reprocessing solutions

Hydrated zirconium molybdate (ZMh) is known to precipitate from solutions of dissolved spent nuclear fuel, particularly from the waste fission product solution after the uranium and plutonium have been extracted during reprocessing. Its precipitation can cause major problems during waste treatment, and therefore a complete understanding of its chemical behaviour, especially with regard to its role in the nuclear fuel cycle, is desirable. We have used a number of complementary analytical techniques to elucidate the hitherto incompletely understood chemistry of formation of ZMh in synthetic fuel reprocessing solutions. We have demonstrated that ZMh formation was governed by multi-step surface reactions and does not involve the formation of colloids or particulates in solution. The first step in the deposition of ZMh onto surfaces is the formation of an amorphous film with a Zr ∶ Mo ratio close to unity. It is followed by the formation, growth and nucleation of ZMh particles of varying degrees of crystallinity with a Zr ∶ Mo ratio close to 0.5. The X-ray diffraction pattern of deposited ZMh particles is in agreement with the reported crystallographic data. The structural features of the film and ZMh were also examined at the nanometer scale.

Post-elution concentration of 99TcmO4- by a single anion exchanger column: II. Preparation and evaluation of jumbo alumina column chromatographic generator for 99Tcm.

We report on the preparation and evaluation of a large size (jumbo) alumina column (approximately 40 g, 90 x 20 mm) chromatographic generator and post-elution concentration of 99Tcm using a single column of a weak anion exchanger. The generator was eluted with approximately 40 ml of a modified single salt buffer solution of 1:1 v/v 0.025 M or 0.05 M NH4OAc:0.7 M AcOH. This eluate was then passed through a small column of DEAE cellulose, a common weak anion exchanger, to trap 99TcmO4-, which was recovered by elution in 6 ml of normal saline. This amounts to a 5- to 7-fold increase in radioactive concentration (RAC) of 99Tcm, when compared to the RAC on direct elution with normal saline from the same jumbo alumina column generator. The overall yield of 99Tcm was in the range of 70-90%. 99Mo breakthrough was 10(-3)-10(-4)%, radiochemical purity was > 98%, and chemical purity, in terms of Al and Mo content, < 10 ppm each. The compatibility of pertechnetate obtained by this method for preparing 99Tcm labelled formulations such as Tc-MDP and 99Tcm-ethyl cysteinate dimer was found to be satisfactory. These promising results open up the feasibility of using (n, gamma) 99Mo adsorbed on a large (40-60 g) alumina column as a relatively more user-friendly source of 99Tcm in comparison to methyl ethyl ketone extraction, and as a producer-friendly process in comparison to the zirconium molybdate gel method.

High-pressure structures of alpha- and delta-ZrMo2O8.

In situ high-pressure synchrotron X-ray powder diffraction studies of trigonal alpha-ZrMo(2)O(8), zirconium molybdate, have been performed from ambient conditions to 1.9 GPa, over the alpha-delta phase transition at 1.06-1.11 GPa. The monoclinic structure of delta-ZrMo(2)O(8), stable between 1.1 and 2.5 GPa at 298 K, has been solved by direct methods and refined using the Rietveld method. Significant distortions of the ZrO(6) and MoO(4) polyhedral elements are observed for delta-ZrMo(2)O(8), as compared to the ambient conditions of the alpha-phase, while the packing of anions becomes more symmetric at high pressure.

Thermal Decomposition of Several Layered Zirconium Salts

The thermal decomposition of zirconium molybdate, tungstate and arsenate were investigated. The total mass losses of the investigated materials were 12.5, 11 and 8.5%, respectively. Despite having different crystal dimensions and structure the thermal decomposition of the samples takes place in a similar way. During heating two main endothermic processes with mass loss were observed. At the end of the thermal decomposition, oxides of the original materials were observed. The mentioned mass losses originate partly from the crystal water loss of the materials. The calculated crystal water content in the original molecule was 1.3 and 1 mole/molecule unit, respectively. Furthermore, for zirconium arsenate, a sublimation process was recorded above 960 K.