Thermal and infrared spectrum analyses of natural and synthetic andersonites

Abstract

NATURAL HISTORY MUSEUM, NATIONAL MUSEUM IN PRAGUE, 115 79 PRAGUE, t~. S. S. R. NUCLEAR RESEARCH INSTITUTE, 250 68 I~E2 NEAR PRAGUE, t~. S. S. R.The thermal decompositions of natural and synthetic andersonites were studied. Two partly overlapping dehydration steps and three partly overlapping decarbonation steps were observed. The second dehydration and the first decarbonation steps also partly overlap. During decarbonation, the gradual formation of sodium diuranate and monoclinic and hexagonal phases in the NazU2OT-CaUO4_ x system was proved. The results were correlated with measured infrared spectra using site and factor group analysis and X-ray structure analysis. The chemical formula inferred for natural andersonite, NazCa[UO2(CO3)3] ~_ 5.6H20, agrees with that proposed for its synthetic analogue.Andersonite has been found in several deposits and also synthetized by several authors. Infrared spectra of both natural and synthetic specimens and luminescence spectra of the mineral have been published.A thermal analysis of synthetic anders0nite has been described. According to the crystal structure of synthetic andersonite [1], only five water molecules in the formula were found in the final Fourier map. The possible statistical distribution of the remainder in a structure channel is presumed. On the basis of our preliminary conclusions [2, 3], the formula Na2Ca[UO2(CO3)3]. _ 5.6H20 was proposed for synthetic andersonite [1], In this paper, attention is especially paid to the content of molecular water in natural andersonite and for comparison in synthetic andersonite, using combined TG and DTA and IR spectroscopy. A complex contribution to the crystal chemistry of andersonite will be published elsewhere [4]. The paper forms part of the scientific reassessment of secondary uranium minerals from the collections of the National Museum in Prague.

A note on the molecular water content in uranyl carbonate mineral andersonite

“…The structure refinement (R 1 = 0.028 for 1860 observed unique reflections) of the synthetics presented in that paper provided a localization of additional O site within the channel that belongs to the molecular H 2 O, leading to the structure formula Na 2 Ca[(UO 2 )(CO 3 ) 3 ](H 2 O) 5.333 . Thermal analysis of the natural specimen published by Čejka and Urbanec (1988) nevertheless confirmed the results of the previous thermal studies by Coda et al (1981) and Čejka (1969).…”

“…on synthetic and natural andersonite, provided largely different H 2 O contents in the structure, ranging from 5 (Kubatko et al 2005), through 5.6 (Čejka andUrbanec 1988) and5.4-5.8 (Coda et al 1981) to 6 (Alwan and Williams 1980;Vochten et al 1994;Kubatko et al 2005). However, various methods of thermal analysis applied to well-defined synthetic and natural samples of andersonite proved that in every case the H 2 O content was lower than six, varying from 5.4 to 5.8, or given as an average of ~ 5.6 H 2 O (Urbanec and Čejka 1979; Čejka et al 1987;Čejka and Urbanec 1988).…”

“…However, various methods of thermal analysis applied to well-defined synthetic and natural samples of andersonite proved that in every case the H 2 O content was lower than six, varying from 5.4 to 5.8, or given as an average of ~ 5.6 H 2 O (Urbanec and Čejka 1979; Čejka et al 1987;Čejka and Urbanec 1988). The sharp bands in the infrared spectra of andersonite (Čejka et al 1987;Čejka and Urbanec 1988), occurring at 3545-3565 cm -1 , may be connected with certain portion (~ 0.4-0.8 H 2 O) of molecular H 2 O, which is relatively weakly bonded in the channels of the structure. Likewise, such bands were also observed in the Raman spectra (Frost et al 2004).…”

Raman spectroscopic study of the uranyl carbonate mineral voglite

“…Further vibrational spectroscopy determines parameters at the chemical bond level as opposed to the lattice or unit cell parameters. Often infrared spectroscopy has been applied to the study of the uranyl carbonates 2,13,14,22,23 and yet very little work based upon Raman spectroscopy has been forthcoming .…”

Raman spectroscopic study of the multi‐anion uranyl mineral schroeckingerite

“…Further, vibrational spectroscopy determines the parameters at the chemical-bond level as opposed to the lattice. Often, IR spectroscopy has been applied to the study of the uranyl carbonates 2,15,16,19,30 and yet very little work based on Raman spectroscopy has been forthcoming.…”