Mineral systems and the thermodynamics of selenites and selenates in the oxidation zone of sulfide ores – a review

Charykova, M. V.; Кривовичев, В. Г.

doi:10.1007/s00710-016-0463-1

Cited by 20 publications

(14 citation statements)

References 60 publications

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“…Eh-pH diagrams of Me-Se-H 2 O systems (where Me = Co, Ni, Fe, Cu, Pb, Zn, Cd, Hg, Ag, Bi, As, Sb, Al and Ca) have been constructed for the average contents of these elements in acidic waters of the oxidation zones of sulfide deposits [51]. It should be noted that Eh-pH diagrams of Me-Se-H 2 O systems (where Me = Co, Ni, Fe, Cu, Pb, Zn, Al and Ca) have been discussed in detail previously [8] and therefore we present here only their brief description.…”

Section: Resultsmentioning

confidence: 99%

“…The composition, solubility, and the thermal behavior of iron selenite were discussed earlier [8]. Figure 4 presents Eh-pH diagrams of the Fe-Se-H 2 O system, which contains wide stability fields of native selenium, hematite and ferroselite, and small fields corresponding to the crystallization of oxides (magnetite, wüstite).…”

Section: Thermodynamic System Fe-se-h 2 Omentioning

confidence: 98%

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The Thermodynamics of Selenium Minerals in Near-Surface Environments

2017

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Selenium compounds are relatively rare as minerals; there are presently only 118 known mineral species. This work is intended to codify and systematize the data of mineral systems and the thermodynamics of selenium minerals, which are unstable (selenides) or formed in near-surface environments (selenites), where the behavior of selenium is controlled by variations of the redox potential and the acidity of solutions at low temperatures and pressures. These parameters determine the migration of selenium and its precipitation as various solid phases. All selenium minerals are divided into four groups-native selenium, oxide, selenides, and oxysalts-anhydrous selenites (I) and hydrous selenites and selenates (II). Within each of the groups, minerals are codified according to the minimum number of independent elements necessary to define the composition of the mineral system. Eh-pH diagrams were calculated and plotted using the Geochemist's Workbench (GMB 9.0) software package. The Eh-pH diagrams of the Me-Se-H 2 O systems (where Me = Co, Ni, Fe, Cu, Pb, Zn, Cd, Hg, Ag, Bi, As, Sb, Al and Ca) were plotted for the average contents of these elements in acidic waters in the oxidation zones of sulfide deposits. The possibility of the formation of Zn, Cd, Ag and Hg selenites under natural oxidation conditions in near surface environments is discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Thermodynamic System Fe-se-h 2 Omentioning

confidence: 98%

The Thermodynamics of Selenium Minerals in Near-Surface Environments

2017

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“…Analogously, the crystal structures of synthetic uranyl chromates [67,68] and molybdates [69], which are isotypic to that one of demesmaekerite, were obtained at hydrothermal conditions (above 120 • C) or solid state reactions (at 300 • C). Nevertheless, based on laboratory [91,92] and field observations, namely of the mineral association from Zálesí (Czech Republic) [8], it is clear that demesmaekerite and piretite (and several other unnamed or poorly identified U-Se phases) formed as a result of supergene alteration processes, which exclude hydrothermal activity. These observations are supported by the radioanalytical dating of demesmaekerite.…”

Section: Discussionmentioning

confidence: 99%

Crystal Chemistry and Structural Complexity of Natural and Synthetic Uranyl Selenites

et al. 2019

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Comparison of the natural and synthetic phases allows an overview to be made and even an understanding of the crystal growth processes and mechanisms of the particular crystal structure formation. Thus, in this work, we review the crystal chemistry of the family of uranyl selenite compounds, paying special attention to the pathways of synthesis and topological analysis of the known crystal structures. Comparison of the isotypic natural and synthetic uranyl-bearing compounds suggests that uranyl selenite mineral formation requires heating, which most likely can be attributed to the radioactive decay. Structural complexity studies revealed that the majority of synthetic compounds have the topological symmetry of uranyl selenite building blocks equal to the structural symmetry, which means that the highest symmetry of uranyl complexes is preserved regardless of the interstitial filling of the structures. Whereas the real symmetry of U-Se complexes in the structures of minerals is lower than their topological symmetry, which means that interstitial cations and H 2 O molecules significantly affect the structural architecture of natural compounds. At the same time, structural complexity parameters for the whole structure are usually higher for the minerals than those for the synthetic compounds of a similar or close organization, which probably indicates the preferred existence of such natural-born architectures. In addition, the reexamination of the crystal structures of two uranyl selenite minerals guilleminite and demesmaekerite is reported. As a result of the single crystal X-ray diffraction analysis of demesmaekerite, Pb 2 Cu 5 [(UO 2 ) 2 (SeO 3 ) 6 (OH) 6 ](H 2 O) 2 , the H atoms positions belonging to the interstitial H 2 O molecules were assigned. The refinement of the guilleminite crystal structure allowed the determination of an additional site arranged within the void of the interlayer space and occupied by an H 2 O molecule, which suggests the formula of guilleminite to be written as Ba 3 . occurrence is limited to just a few localities. First, these are Musonoi and Shinkolobwe mines in DR Congo [6], two of the minerals were only found in the Repete mine (San Juan County, Utah, USA) [5], and a few more occurrences in Europe could be mentioned (small uranium deposit Zálesí in the Czech Republic, Liauzun in France, and La Creusaz U prospect in Switzerland) [8]. Nevertheless, apart from mineralogy, uranyl selenites are of great interest from the geochemical and radiochemical points of view. It is known that fission products contain 53 g per ton [9] of long-lived 79 Se isotope with a half-life of 1.1 × 10 6 years [10] after three years of nuclear fuel irradiation in the reactor. Thus, an understanding of the processes of mineral formation in nature and their synthetic analogs in laboratories can help in the processing of nuclear wastes. Crystal chemical and structural investigations are key points in such a material's scientific studies due to the essential knowledge of how the variation in the chemical composi...

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“…Hydrous selenite minerals are found, as a rule, in the oxidation zone of sulfide and selenide ores [1,2]. Our understanding of low-temperature mineral assemblages strongly depends on our knowledge of the thermodynamic stability of the constituting mineral phases.…”

Section: Introductionmentioning

confidence: 99%

“…The analysis of the thermodynamic parameters (solubility product or Gibbs energy of formation) for calculation of mineral equilibria involving selenites [1][2][3]5,[9][10][11] showed that these parameters frequently raise questions and need specification.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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Thermophysical and thermochemical calorimetric investigations were carried out on the synthetic analogue of mandarinoite. The low-temperature heat capacity of Fe2(SeO3)3∙5H2O(cr) was measured using adiabatic calorimetry between 5.3 and 324.8 K, and the third-law entropy was determined. Using these Cp,mo(T) data, the third law entropy at T = 298.15 K, Smo, is calculated as 520.1 ± 1.1 J∙K–1∙mol–1. Smoothed Cp,moT values between T → 0 K and 320 K are presented, along with values for Smo and the functions [HmoT-Hmo0] and [ΦmoT-Φmo0]. The enthalpy of formation of Fe2(SeO3)3∙5H2O(cr) was determined by solution calorimetry with HF solution as the solvent, giving ΔfHmo(298 К, Fe2(SeO3)3∙5H2O, cr) = –3124.6 ± 5.3 kJ/mol. The standard Gibbs energy of formation for Fe2(SeO3)3∙5H2O(cr) at T = 298 K can be calculated on the basis on ΔfHmo(298 К) and ΔfSmo(298 К): ΔfGmo(298 К, Fe2(SeO3)3∙5H2O, cr) = ‒2600.8 ± 5.4 kJ/mol. The value of ΔfGm for Fe2(SeO3)3·5H2O(cr) was used to calculate the Eh–pH diagram of the Fe–Se–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.

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Mineral systems and the thermodynamics of selenites and selenates in the oxidation zone of sulfide ores – a review

Cited by 20 publications

References 60 publications

The Thermodynamics of Selenium Minerals in Near-Surface Environments

The Thermodynamics of Selenium Minerals in Near-Surface Environments

Crystal Chemistry and Structural Complexity of Natural and Synthetic Uranyl Selenites

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

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