Raman spectroscopic characterization of the copper, cobalt, and nickel selenites: Synthetic analogs of chalcomenite, cobaltomenite, and ahlfeldite

<p>Raman spectroscopy has been used to study synthetic analogs of the minerals chalcomenite, cobaltomenite, and ahlfeldite occurring in nature. The results obtained are compared with the spectra of these minerals. In general, the majority of vibrational bands of synthetic species are in good agreement with natural chalcomenite, cobaltomenite, and ahlfeldite. The noticeable discrepancies are found for the bands assigned to the deformation mode of selenite groups. A better signal-to-noise ratio realized with synthetic species aids in comprehensive analysis of the spectra, especially in the region of water bands.</p

Mixed Uranyl Sulfate–Selenates: Evolution of Structural Topology and Complexity vs Chemical Composition

Phase formation in the aqueous system of uranyl nitrate, potassium hydroxide, and variable amounts of sulfuric and selenic acids has been investigated. Four different types of crystalline phases with variable S and Se contents were isolated and characterized using single-crystal X-ray diffraction (XRD) and IR spectroscopy. Topological analysis and information-based complexity calculations demonstrated the following: (a) the absence of a continuous solid solution in the system, (b) the absence of isotypic sulfate and selenate phases, and (c) the discovery of two layered topologies unprecedented among inorganic oxysalts

A Calorimetric and Thermodynamic Investigation of the Synthetic Analogue of Mandarinoite, Fe₂(SeO₃)₃·5H₂O

Thermophysical and thermochemical calorimetric investigations were carried out on the synthetic analogue of mandarinoite. The low-temperature heat capacity of Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O ( cr ) was measured using adiabatic calorimetry between 5.3 and 324.8 K, and the third-law entropy was determined. Using these C p , m o ( T ) data, the third law entropy at T = 298.15 K, S m o , is calculated as 520.1 &#177; 1.1 J∙K&#8722;1∙mol&#8722;1. Smoothed C p , m o ( T ) values between T &#8594; 0 K and 320 K are presented, along with values for S m o and the functions [ H m o ( T ) &#8722; H m o ( 0 ) ] and [ &#934; m o ( T ) &#8722; &#934; m o ( 0 ) ] . The enthalpy of formation of Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O ( cr ) was determined by solution calorimetry with HF solution as the solvent, giving &#916; f H m o ( 298 &nbsp; K , &nbsp; Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O , &nbsp; cr ) = &#8722;3124.6 &#177; 5.3 kJ/mol. The standard Gibbs energy of formation for Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O ( cr ) at T = 298 K can be calculated on the basis on &#916; f H m o ( 298 &nbsp; K ) and &#916; f S m o ( 298 &nbsp; K ) : &#916; f G m o ( 298 &nbsp; K , &nbsp; Fe 2 ( SeO 3 ) 3 &#183; 5 H 2 O , &nbsp; cr ) = &#8722;2600.8 &#177; 5.4 kJ/mol. The value of &#916;fGm for Fe2(SeO3)3&#183;5H2O(cr) was used to calculate the Eh&#8315;pH diagram of the Fe&#8315;Se&#8315;H2O system. This diagram has been constructed for the average contents of these elements in acidic waters of the oxidation zones of sulfide deposits. The behaviors of selenium and iron in the surface environment have been quantitatively explained by variations of the redox potential and the acidity-basicity of the mineral-forming medium. These parameters precisely determine the migration ability of selenium compounds and its precipitation in the form of solid phases