The spontaneous precipitation in the systems U02(N03)2-
-MOH-HaP04--H20 and U02(N03)2-MNOa-H3P04- H20 (M =
= Li, Na, K, Rb, Cs) is examined. The formation of alkaline-
uranyl(2+) phosphates polyhydrates is detected: M[U02P04] ·
· n H20 (n = 4 for M = Li, n = 3 for M = Na, K, Rb and n = 2.5
for M =Cs).
The X-ray powder patterns of these compounds are determined
and compared with that of H30[U02P04] · 3 H20. A close structural
relation within this series is observed. The size of the alkaline
ionic species in the particular compound affects the content of
crystalline water in the unit cell

B. Kojić-Prodić

M. Marković

N. Pavković

English

Hrčak - Portal of scientific journals of Croatia

CROATICA CHEMICA ACTA CCA-1345 CCACAA 55 (4) 405-412 (1982) YU ISSN 0011-1643 UDC 546.791 Originai Scientific Paper Identification and Characterization of Alkaline Uranyl(2 +) Phosphates N . Pavkov ic, M. Markovic, and B. Kojic-Prodic Department of Physicai Chemistry, Facuity of Science, University of Zagreb, P .O.B. 163, 41001 Zagreb, Croatia, Yugosiavia and Ruder Boskovic Institute, P .O.B. 1016, 41001 Zagreb Croatia, Yugostavia Received March 29, 1982 The spontaneous precipitation in the systems U02(N03)2--MOH-HaP04--H20 and U02(N03)2-MNOa-H3P04- H20 (M = = Li, Na, K, Rb, Cs) is examined. The formation of alkaline--uranyl(2+) phosphates polyhydrates is detected: M[U02P04] · · n H20 (n = 4 for M = Li, n = 3 for M = Na, K, Rb and n = 2.5 for M =Cs). The X-ray powder patterns of these compounds are determined and compared with that of H30 [U02P04] · 3 H20. A close struc-tural relation within this series is observed. The size of the alkaline ionic species in the particular compound affects the content of crystalline water in the unit cell. INTRODUCTION In the precipitation system U02(N03)z - H 3P04 - H 20 the stable solid phases HU02P04 • 4 H20 1 (tetragonal polymorph type I according to Moroz et al.2) and (U02h (P04)z · 8 H 20 1 were found. K [U02P04] • 3 H20 precipitates in the system U02(N03)z - KOH - H3P04 - H20 at high concentrations of KOH3• The spontaneous precipitation and identification of other alkaline uranyl(2 +) phosphates has not been systematically examined. The formation of compounds with general formula M [U02P04] • n H20 (M = Li, Na, K, Rb, Cs) was described4-6• The number of crystalline water molecules for the particular compound has not been uniquely defined in the literature7- 14 . The formation of alkaline-uranyl(2 +) phosphate hydrates is described in this paper; compounds are identified by chemical and TG analyses, and X-ray powder patterns. EXPERIMENTAL Stock solutions were prepared by dissolving the following p.a. chemicals in triply distilled water: uranyl(2 +)nitrate hexahydrate, phosphoric acid, alkaline hydroxides and alkaline nitrates (Merck, Darmstadt). Standardization of solutions was performed according to classical analytical methods. The precipitation systems were prepared by the mixing15 of uranyl(2 + )nitrate solution with an equal volume of alkaline-phosphate solution (the mixture of H3P04 with MOH or MN03) and aged 1 day at a temperature of 298 K, pH was measured with the electrode GK 2302 C, using a Radiometer Mo 26 pH-meter. The morphology of the precipitates was examined in white, polarized and UV light under an Ortho-406 N. PAVKOVIC ET AL. plan microscope (Leitz, Wetzlar) and by electron microscopy (Elmiskop I, Siemens). Turbidity measurements were performed on the Zeiss tyndallometer in connection with Pulfrich photometer. For the chosen systems the initial concentrations of reactants were: [U02(N03h] = = 1 · 10-2 mol dm-3, [H3P04] = 8 · 10-3 mol dm-3 ; the solution of alkaline nitrate was added to the phosphoric acid solution. The concentrations of alkaline nitrates were: [LiN03] = 3.0 mol dm-3 ; [NaN03] = 1.4 mol dm-3 ; [MN03] = 0.2 mol dm-3 (M = K, Rb, Cs). After the mixing, the precipitation systems were kept in a water bath at 298 K for 24 hours. The precipitates were separated, washed with triply distilled water, and dried at 293 K for 24 hours. Selected precipitates were characterized by means of chemical and thermogravimetric analyses, X-ray powder diffraction pat-terns and IR spectra. After dissolution in nitric acid solid phase was chemically analysed for uranium, phosphorus and alkaline metal. Uranium was precipitated with (NH4)2HP04, heated at 1373 K and weighed as U203P20116• Phosphorus was deter-mined gravimetrically by precipitation with ammonium molybdate17 and spectro-photometrically as a phosphovanadatomolybdato complex17• Alkaline metals were determined by atomic absorption spectroscopy (Li, Rb), flame photometry (Na, K) and gravimetrically as chloroplatinates (Rb, Cs)18• Water was determined by thermo-gravimetric analysis (Cahn RG recording electromicrobalance, sensitivity 10-6 g, heating rate 4 K in minute, heating to 1050 K) . X-ray diffraction patterns were recorded on a Philips X-ray diffractometer with proportional counter, using graphite monochromated CuKa radiation. X-ray patterns were calibrated with an internal standard, graphite, with a unit cell a = 2.463 A, c = 6.714 A (J, = 1.54178 A) 19 • Relative intensities, Ire!, are given as a peak height. IR spectra were carried out on Mo-221 spectrophotometer (Perkin--Elmer) by the standard KBr platelets technique. RESULTS The precipitation of alkaline-uranyl(2 +) phosphates at 1 · 10-.:i < < [U02(N03)z] = [H3P04] < 1 · 10-2 mol dm-3 and 1 · 10-5 < [MOH] < 1 · 10-1 mol dm-3 was examined. Figure 1 shows dependence of turbidity and pH ([U02(N03)2] = [H3P04] = 1 · 10-3 mol dm-3) on the concentration of MOH; the presented curves for all alkaline hydroxides are of the same shape. In the region of low MOH concentration precipitates (U02)3(P04) 2 • 8 H20 which does not exhibit fluorescence, pH keeps the constant value. At higher concentrations of CsOH, RbOH and KOH (different values for particular hydroxide -Figure 1) the fluorescent precipitates of M [U02P04] · n H20 (M = Cs, Rb, K) are formed in the very narrow range. Increasing the concentration of MOH successively, a significant increase of pH and the formation of stable colloids were observed. Similar properties of particles, morphology and fluorescence, prevent an identification of pure solid phase of M [U02P04] · n H 20 or its mixture with HU02P04 • 4 H20. Uranates precipitate in all systems at pH> 9.5. In the concentration range with stable colloidal particles the turbidity does not exhibit a significant dependence on time. It is obvious that U02(N03)2 - H3P04 - MOH - H20 system was not suitable for the isolation of alkaline-uranyl(2 +) phosphates. However, the system with [U02(N03)z] = [H3P04] and with MN03 (instead of MOH) is suitable, giving crystalline precipitates. At low concentrations of MN03 (and MOH - Figure 1) 12 10 pH 8 6 4 2 w :J _J <t 0.10 > u Ci:: .,_ w ~ 0 _J _J <t 0.00 0 z >-.,_ ~ ALKALINE URANYL(2 + ) PHOSPHATES 1 day J 298K [U02 {N0 3}z] = -3 -3 1·10 mol dm [H 3POJ uranates -3 3 = 1 ·JO mol dm-colloids precipitate ',/ '----v---"'--~-,~~-M[UOzPOJn Hp ( U02 )3 ( POJ2 ·8H20 K Rb Cs 2 3 4 - log ( [MOH] / mol dm-3 ) 407 Figure 1. Turbidity and pH versus [MOH] (M ~ Li, Na, K, Rb, Cs) . Arrows show concentrations of CsOH, RbOH and KOH where precipitate their alkaline-uranyl(2 + )phosphate. 408 N. PAVKOVIC ET AL. only (U02h(P04)2 · 8 H20 precipitates. At higher concentrations, a mixture appears of alkaline-uranyl(2 +)phosphate and (U02h(P04)i · 8 H20 or alkaline--uranyl(2 +)phosphate and HU02P04 • 4 H20 . At constant and equal concen-trations of uranyl(2 +)nitrate and phosphoric acid precipitates pure M [U02P04] · n H20 at different concentration of particular alkaline nitrate: CsN03 < RbN03 < KN03 < NaN03 « LiN03. The mm1mum molar ratio (MRM) of alkaline nitrate and uranyl(2 +)nitrate, where M [U02P04] · n H20 precipitates only, is constant for each alkaline nitrate: MRcs = 1.0, MRRb = 1.5, MRK = 2.0, MRNa = 30 and MRLi = 70. Results of chemical and TG analyses for all alkaline-uranyl(2 +) phosphates are listed in Table I. The TGA curves TABLE I Anaiyticai Data of M[U02P04] · n H20 O/o U O/o p M[U02P04] · n H20 exp. calc. exp. calc. Li[U02P04] · 4 H20 53.83 ± 0.13 53.61 7.01 ± 0,01 6.98 Na[U02P04] · 3 H20 53.60 ± 0.32 53.85 7.05 ± 0.11 7.01 K[U02P04] · 3 H20 51.85 ± 0.20 51.95 6.76 ± 0.12 6.76 Rb[U02P04] · 3 H20 47.08 ± 0.44 47.18 6.27 ± 0.19 6.14 Cs[U02P04] · 2.5 H20 44.00 ± 1.10 43.84 5.73 ± 0.03 5.70 M[U02P04] · n H20 O/o M O/o H20 exp. calc. exp. calc. Li[U02P04] · 4 H20 1.55 ± 0.10 1.56 16.36 ± 0.37 16.22 Na[U02P04] · 3 H20 5.15 ± 0.10 5.20 12.46 ± 0.33 12.23 K[U02P04] · 3 H20 8.50 ± 0.10 8.53 11.67 ± 0.21 11.80 Rb[U02P04] · 3 H20 16.65 ± 0.20 16.94 10.82 ± 0.27 10.71 Cs[U02P04] · 2.5 H20 24.04 ± 0.62 24.48 8.29 ± 0.57 8.30 give evidence of a water loss as follows: in Li [U02P04] • 4 H20 - 1.5 mole-cules up to 305 K, 1.5 molecule's up to 460 K and 1 molecule up to 1000 K ; in Na [U02P04] · 3 H20, K [U02P04] · 3 H20 and Rb [U02P04] · 3 H20 - 2.2 ± 0.3 molecules up to 460 K and 0.8 ± 0.3 molecule up to 1000 K; in Cs [U02P04] · · 2.5 H20 - 2 molecules up to 460 K and 0.5 molecule up to 1000 K. The IR spectra of these compounds were recorded in the range 600-3600 cm-1, characteristical vibrations of uranyl(2 +) and phosphate groups are in accord with literature13• The X-ray powder patterns are separated in two groups: A (Table II) and B (Table III). ALKALINE URANYL(2 + ) PHOSPHATES 409 TABLE II X-ray Powder Patterns for Compounds of Group A. HaO[U02P04] · 3 H20 Na[U02P04] · 3 H20 K[U02P04] · 3 H20 Cs[U02P04]1 • 2.5 H20 d/A Ire! d/A Ire! d/A Ire! d/A Ire! 8.76 100 8.85 100 8.95 100 8.90 100 5.47 26 5.48 44 5.52 20 5.55 26 4.95 18 4.95 36 4.95 18 4.99 20 4.82 4 4.46 18 4.46 25 4.45 25 4.37 15 4.39 23 4.36 27 4.31 18 4.33 42 4.33 18 3.98 8 3.71 59 3.72 80 3.77 55 3.76 100 3.51 24 3.51 50 3.51 26 3.53 32 3.25 30 3.26 55 3.26 28 3.27 53 3.15 5 3.16 21 3.09 2 3.08 3 3.09 4 3.12 5 2.95 15 2.94 30 2.95 15 2.98 20 2.76 9 2.73 3 2.73 9 2.74 20 2.73 17 2.69 20 2.69 39 2.55 8 2.54 20 2.56 8 2.57 5 2.51 3 2.52 6 2.54 5 2.48 6 2.47 14 2.48 7 2.48 5 2.38 9 2.37 18 2.39 9 2.40 9 2.25 4 2.26 12 2.26 6 2.27 9 2.23 15 2.23 11 2.21 10 2.21 22 2.21 11 2.21 21 2.19 10 2.19 12 2.15 10 2.16 14 2.16 25 2.13 12 2.13 10 2.11 11 2.09 7 2.09 12 2.06 8 2.06 17 2.07 9 2.07 9 2.01 8 2.00 14 2.03 8 2.02 8 1.896 3 1.895 8 1.896 5 1.900 3 1.856 3 1.859 6 1.871 3 1.823 6 1.822 11 1.837 6 1.834 7 1.794 3 1.795 8 1.782 10 1.785 7 1.775 7 1.775 14 1.752 7 1.749 10 1.752 5 1.760 7 1.717 3 1.715 8 1.717 4 1.720 5 1.676 2 1.665 4 1.679 11 1.651 10 1.652 13 1.665 8 1.646 6 1.627 6 1.630 6 1.617 6 1.615 13 1.596 2 1.600 4 1.595 5 1.584 3 1.582 7 1.589 8 1.577 10 1.566 8 1.564 13 1.568 6 1.570 8 1.562 3 1.556 6 1.542 3 1.468 2 1.465 6 1.476 5 1.450 3 1.444 4 410 N. PAVKOVIC ET AL. TABLE III X-ray Powder Patterns for Compounds of Group B . Li[U02P04] · 4 H20 Rb[U02P04] · 3 H20 d/A I rel d/A I rel 9.25 100 9.25 100 5.61 13 5.58 15 5.00 8 4.96 6 4.58 83 4.60 60 4.40 12 4.36 13 3.83 83 3.84 90 3.53 12 3.50 12 3.29 17 3.26 15 3.11 1 3.04 19 2.98 10 2.95 8 2.80 31 2.80 60 2.59 7 2.59 6 2.57 8 2.50 1 2.47 3 2.41 7 2.38 7 2.28 92 2.30 38 2.23 7 2.26 1 2.20 7 2.18 12 2.18 37 2.17 22 2. 15 7 2.09 7 2.08 23 2.02 1 1.910 3 1.911 6 1.890 1 1.860 3 1.842 5 1.845 12 1.821 19 1.831 18 1.794 5 1.780 2 1.760 5 1.730 1 1.741 1 1.710 14 1.715 26 1.705 14 1.643 2 1.635 2 1.630 7 1.617 3 1.620 13 1.613 2 1.591 2 1.588 8 1.575 1 1.516 7 1.525 6 1.481 8 1.490 6 1.470 4 1.458 12 DISCUSSION A number of crystalline water molecules established for Li and Na compounds are in agreement with the literature1- 11 • K compound is defined with 2, 3 and 3.5 molecules of water. The formation of various hydrates can be caused by different conditions under which the samples were kept. Our analytical data correspond to three water molecules3,12,9• The appearance of Rb compound monohydrate is described py Muraveva et al.9, whereas our analytical data correspond to trihydrate. However, dehydratation of Na, K, ALKALINE URANYL(2 + ) PHOSPHATES 411 Rb and Cs uranyl(2 +) phosphate hydrates starts at room temperature, these low hydrates were detected by TG and chemical analyses. The X-ray powder patterns of the series with general formula M [U02P04] • · n H20 (M = H30 , Li, Na, K, Rb and Cs) are compared. They can be clas-sified in two groups; the patterns of H30 , Na, K , and Cs compounds form one group (Table II group - A) whereas those of Li and Rb form another group (Table III - group B). The X-ray powder pattern of tetragonal polymorph of HU02P04 • 4 H20 with space group P 4/n c c (type I according to Moroz et al.2) was previously reported1• The X-ray structure analysis of this polymorph20 revealed its cor-rect structural formula - H30 [U02P04] • 3 H20. Its X-ray powder pattern is similar to those of alkaline-uranyl(2 +) phosphates with an analogous for-mula; d - values and relative intensities are listed in Table II for comparison. The crystal structure of H30 [U02P04] · 3 H20 explains by itself relations between the X-ray powder patterns of these compounds. uo22+ is coordinated with four oxygen atoms from four P04 tetrahedra. None of the four water molecules is involved in coordination; they form a continuously hydrogen bonded network containing H3Q+ species2,21• Thus the structure is composed of [U02P04] - and water layers containing H30 +. In the network of four water molecules there is enough space to accomodate the Li ion (ri = 0.68 A)22 • Thus lithium uranyl(2 +)phosphate crystallized as a tetrahydrate. In the holes of this water layer there is no space available for Na (ri = 0.97 A)22 and K (ri = = 1.33 A).22 However , three molecules of crystalline water leave enough space to accommodate these ions. In the lattice of the Cs compound (ri = 1.67 A)22 the water content is reduced to 2.5 molecules. The unit cell is slightly decreased. Therefore, the d - values of the Cs compound are lower than those of Na and K compounds (Table II) . The Rb compound (ri = 1.47 A)22 with three crystalline water m olecules exhibits the X-ray powder pattern which is very close to one of the Li compound with four water molecules (Table III). The octahedral coordination around uranium is maintained in all the structures but the size of the alkaline ionic species in particular compound affects the content of crystalline water in the unit cell. An accomodation of the particular ion in the water layer has been already explained. These structural relations give an explanation for similar X-ray powder patterns of all the mentioned compounds in both groups, A and B (Tables II and III); d - values show a better agreement within each group. Acknowledgement. - The authors wish to thank Professor M. Branica for valuable suggestions at the initial stage of this work. Support of this research by the Self-Management Council for Scientific Research of S. R. Croatia is gratefully acknowledged. REFERENCES 1. N. Pav k o vi c, B. Ko j i c - P r od i c, and M. Markov i c, submitted for publication (1982) . 2. I. Kh. Moroz, A. A. Va 1 u e v a, G. A. S id o re n k o, L. G. Z h i 1 t s o v a, and L. N. Karp ova, Geokhimiya U.S.S.R. 2 (1973) 210. 3. N. Pav k o vi c, M. Marko v i c, and B. Ko j i c - Pr o d i c, Croat. Chem. Acta 55 (1982) 393. 4. V. G. Chu k h 1 ants e v and S. I. Step a n o v, Zh. N eorg. Khim. 1 (1956) 478. 412 N. PA VKOVIC ET AL. 5. V. Ve s e 1 y, V. P e k a re k, and M. Ab b r en t, J. Inorg. Nucl. Chem. 27 (1965) 1159. 6. F. G. Garcia and R. R. Di a z: Ann. de la Real. Soc. Espan. de Fiz. y Quim. (Madrid) 55 B (1959) 399. 7. I. A. Mura v e v a, 0. G. Ne m k ova, R. P. Cher k as ova, and A. S. 0 r 1 ova, Issledovaniya v Oblasti Khimii Urana, Izd. Mosk. Univ. Moscow, 1961, p. 240. 8. I. A. Mura v e v a, 0. G. Ne m k ova, and Yu. V. 0r1 ova, Issledovaniya v Oblasti Khimii Urana, Izd. Mosk. Univ. Moscow, 1961, p. 248. 9. I. A. Mura v e v a, K. B. Z ab ore n k o, O. G. Ne m k ova, and Khan D e Pi n, Radiokhim. 6 (1964) 124. 10. V. Pekarek and V. Ve s e 1 y, J. Inorg. Nucl. Chem. 27 (1965) 1151. 11. A. I. Moskvin, A. M. Shelyakina, and P. S. Perminov, Zh. Neorg. Khim. 12 (1967) 3319. 12. A. I. Kry u k ova, I. A. K or shun o v, Z. V. K hr i p kin a, G. N. K a-z ants e v, and 0. V. Skiba, Radiokhim. 3 (1977) 314. 13. L. V. Kobets, T. A. Kolevich, and D. S. Umreiko, Zh. Neorg. Khim. 23 (1978) 909. 14. M. V. Nik an o vi ch, D. S. Um re i k o, and A. N. Se v ch en k o, Zh. Prikl. Spektrosk. 32 (1980) 658. 15. B. Tezak, E. Mat i j e vi c, and K. Sch u 1 t z, J. Phys. Colloid Chem. 55 (1951) 1557. 16. Analiticheskaya Khimiya Elementov - Uran, Izd. Akad. Nauk ·S.S.S.R. Moscow, 1962, p. 62. 17. Vogel's Textbook of Quantitative Inorganic Analysis, 4th ed., Longman Inc. New York, 1978, pp. 499, 756. 18. Standard Methods of Chemical Analysis, Volume I, 6th ed., D. Van Nostrand Company, Inc. New York, 1962, p . 36. 19. Selected Powder Diffraction Data for Minerals, Joint Committee on Powder Dif-fraction Standards, Swathmore, 1974. 20. B. Mo r o s i n, Acta Cryst. B 34 (1978) 3732. 21. A . T. Ho we and M. G. S h i 1 ton, J. Solid State Chem. 28 (1979) 345. 22. L . Pa u 1 in g, The Nature of Chemical Bond, 3rd. ed., Ithaca, Cornell Univ. Press. New York, 1960. SAZETAK Identifikacija i karakterizacija alkalijskih uranil(2 +) fosfata N. Pavkovic, M. Markovic i B. Kojic-Prodic Spontani talofoi procesi ispitani su u sistemima U02(N03)2-MOH-H3P04-H20 i U02(NOal2-HsP04-MNOa-H20 (M = Li, Na, K, Rb, Cs). Utvrdeno je nastajanje alkalijskih uranil(2 +) fosfata polihidrata, opce formule M[U02P04] · n H 20 (n = 4 za M = Li, n = 3 za M = Na, K, Rb i n = 2.5 za M = Cs) . Navedeni su meduplosni razmaci i intenziteti svih alkalijskih uranil(2+) fos-fata dobiveni rendgenskom difrakcijom na praskastim uzorcima, te su usporedeni s pripadnim vrijednostima dobivenim za HaO[U02P04] · 3 H 20. Utvrdena je izrazita slicnost izmedu njihovih struktura. Ovisno o velicinama iona razlicitih alkalijskih metala mijenja se broj kristalnih voda u jedinienoj celiji pojedinog spoja. 

Identification and Characterization of Alkaline Uranyl(2 +) Phosphates

Abstract

Similar works

Full text

Available Versions

Hrčak - Portal of scientific journals of Croatia

HRČAK - Portal of Croatian Scientific and Professional Journals