The Formation of Chemical and Isotopic Composition of Surface Water of Open Water Bodies in the Bodrak River Basin (North-Western Slope of the Crimean Mountains)

Water Resources - The major factors governing the formation of the chemical and isotopic compositions of surface water in open water bodies (ponds) in the Bodrak River basin have been studied by...     

Thermodynamics of arsenates,selenites, and sulfates in the oxidation zone of sulfide ores. X. thermal stability and dehydration features of synthetic analogs of the cobaltomenite–ahlfeldite solid solution series

The aim of this study is the experimental investigation of the synthetic analogs of cobaltomenite, CoSeO₃ ? 2H₂O, ahlfeldite, NiSeO₃ ? 2H₂O, members of the cobaltomenite–ahlfeldite solid solution series (Ni _x Co_1–x )SeO₃ ? 2H₂O, and singularities of their dehydration and dissociation. The intermediate members of the cobaltomenite (CoSeO₃ ? 2H₂O)–ahlfeldite (NiSeO₃ ? 2H₂O) series have been synthesized and studied with a combination of X-ray diffraction, scanning electron microscopy, and the simultaneous application of thermogravimetry (TG) and differential scanning calorimetry (DSC) within the temperature range from 25 to 640°C. The complete solid solution series corresponds to the monoclinic space group P2₁/n. Unit-cell dimensions decrease in all crystallographic directions as the amount of Ni increases. The angle β increases from 98.82(1) (cobaltomenite) to 99.05(1)° (ahlfeldite). It has been established that CoSeO₃ ? 2H₂O and NiSeO₃ ? 2H₂O dehydrate at 120–340°C through two stages apparently corresponding, to the formation of intermediate hydrated species CoSeO₃ ? H₂O and NiSeO₃ ? 1/3H₂O. The reaction enthalpies for each dehydration stage of CoSeO₃ ? 2H₂O and NiSeO₃ ? 2H₂O have been determined. Changes of the unit-cell dimensions and dehydration temperatures are rationalized in terms of the Co and Ni site occupancy in the structure of the cobaltomenite–ahlfeldite solid-solution series members.     

The thermodynamics of arsenates,selenites, and sulfates in the oxidation zone of sulfide ores. XI. Solubility of synthetic chalcomenite analog and zinc selenite at 25°C

The aim of this study is the synthesis of CuSeO₃·2H₂O (chalcomenite analog), ZnSeO₃·2H₂O, and ZnSeO₃·H₂O and the investigation of their solubility in water. CuSeO₃·2H₂O has been synthesized from solutions of Cu nitrate and Na selenite, while Zn selenites were synthesized from solutions of Zn nitrate and Na selenite. The samples obtained have been examined with X-ray diffraction and infrared and Raman spectroscopy. The solubility has been determined using the isothermal saturation method in ampoules at 25°C. The solubility has been calculated using the Geochemist’s Workbench (GMB 9.0) software package. Solubility products have been calculated for CuSeO₃·2H₂O (10^–10.63), ZnSeO₃·2H₂O (10^–8.35), and ZnSeO₃·H₂O (10^–7.96). The database used comprises thermodynamic characteristics of 46 elements, 47 base particles, 48 redox pairs, 551 particles in solution, and 624 solid phases. The Eh–pH diagrams of the Zn–Se–H₂O and Cu–Se–H₂O systems were plotted for the average contents of these elements in underground water in oxidation zones of sulfide deposits.     

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

Mineralogy and Petrology - Contemporary mineralogy and geochemistry are concerned with understanding and deciphering processes that occur near the surface of the Earth. These processes are...     

Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide Ores: Part VII. Solubility of synthetic analogs of erythrite and annabergite at 25°C

Understanding the mechanisms of arsenic’s behavior under near-surface conditions is one of the actual problems of contemporary mineralogy and geochemistry and is important for solving environmental problems. The aim of this study is to synthesize analogs of erythrite and annabergite and to investigate their solubility in water. These phases have been synthesized by the boiling-dry of aqueous solutions of cobalt and nickel nitrates mixed with sodium hydroarsenate alkalized with NaOH. The samples obtained have been identified with electron microprobe, X-ray diffraction, and IR spectroscopy. Solubility has been determined by the isothermal saturation method in ampoules at 25°C. The solubility has been calculated using the Geochemist’s Workbench (GMB 7.0) software package. The measured solubilities of erythrite and annabergite are 10^?35.76 and 10^?36.43, respectively. Eh-pH diagrams were calculated and plotted using the GMB 7.0 software package. The database comprises the thermodynamic parameters of 46 elements, 47 main particles, 48 redox pairs, 552 particles in solution, 624 solid phases, and 10 gases. The Eh-pH diagrams of the Ni-As-H₂O and Co-As-H₂O systems were plotted for the average contents of these elements in the acidic waters in the oxidation zones of sulfide deposits. The formation of erythrite and annabergite under near-surface conditions is discussed.     

Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores: VI. Solubility of synthetic analogs of ahlfeldite and cobaltomenite at 25°C

The understanding of the mechanisms of the selenium behavior under near-surface conditions is an urgent problem of modern mineralogy and geochemistry, and is very important for solving environmental problems. The objective of this study is to synthesize analogs of ahlfeldite and cobaltomenite and to estimate their solubility in water. These analogs have been synthesized by mixing aqueous solutions of cobalt and nickel nitrates, respectively, and sodium selenite acidified with a solution of nitric acid. The obtained samples have been identified by X-ray diffraction and IR spectroscopy. The solubility has been determined by the isothermal saturation method in ampoules at 25°C, while the solubility products have been calculated using the Geochemist’s Workbench (GMB 7.0) software package. The solubility products of ahlfeldite and cobaltomenite are 10^?9.20 and 10^?9.44, respectively. The Eh-pH diagrams were calculated and plotted with the GMB 7.0 software package. The Eh-pH diagrams of the Ni-Se-H₂O and Co-Se-H₂O systems have been calculated for the average contents of these elements in underground water and their contents in acidic water of the oxidation zone of sulfide deposits. The formation of ahlfeldite and cobaltomenite under near-surface conditions is discussed.     

Thermal behavior of ferric selenite hydrates (Fe2(SeO3)3·3H2O,Fe2(SeO3)3·5H2O) and the water content in the natural ferric selenite mandarinoite

Any progress in our understanding of low-temperature mineral assemblages and of quantitative physico-chemical modeling of stability conditions of mineral phases, especially those containing toxic elements like selenium, strongly depends on the knowledge of structural and thermodynamic properties of coexisting mineral phases. Interrelation of crystal chemistry/structure and thermodynamic properties of selenium-containing minerals is not systematically studied so far and thus any essential generalization might be difficult, inaccurate or even impossible and erroneous. Disagreement even exists regarding the crystal chemistry of some natural and synthetic selenium-containing phases. Hence, a systematic study was performed by synthesizing ferric selenite hydrates and subsequent thermal analysis to examine the thermal stability of synthetic analogues of the natural hydrous ferric selenite mandarinoite and its dehydration and dissociation to unravel controversial issues regarding the crystal chemistry. Dehydration of synthesized analogues of mandarinoite starts at 56–87?°C and ends at 226–237?°C. The dehydration happens in two stages and two possible schemes of dehydration exist: (a) mandarinoite loses three molecules of water in the first stage of the dehydration (up to 180?°C) and the remaining two molecules of water will be lost in the second stage (>180?°C) or (b) four molecules of water will be lost in the first stage up to 180?°C and the last molecule of water will be lost at a temperature above 180?°C. Based on XRD measurements and thermal analyses we were able to deduce Fe₂(SeO₃)₃·(6-x)H₂O (x?=?0.0–1.0) as formula of the hydrous ferric selenite mandarinoite. The total amount of water apparently affects the crystallinity, and possibly the stability of crystals: the less the x value, the higher crystallinity could be expected.     

Thermodynamics of arsenates,selenites, and sulfates in the oxidation zone of sulfide ores: IV. Eh-pH diagrams of the Me-Se-H<Subscript>2</Subscript>O systems (Me = Co,Ni, Fe,Cu, Zn,Pb) at 25°C

The behavior of selenium at the Earth’s surface and nearby at low temperatures and pressures is controlled by variations of the redox potential and the acidity of solutions. These parameters determine the migration of selenium and its precipitation as various solid phases. Understanding the mechanism of selenium’s behavior under surface conditions, which is important for solving environmental problems, is an urgent task of contemporary mineralogy and geochemistry. The activities of components in natural waters beyond the zones of natural (oxidation zones) and man-made contamination with selenium (a _ΣSe = 10⁻⁹, a _ΣFe = 10⁻⁵, a _ΣCu = 10⁻⁷, a _ΣZn = 5 × 10⁻⁷, a _ΣCo = 10⁻⁸, a _ΣNi = 6 × 10⁻⁸, a _ΣPb = 10⁻⁸) and in waters formed in the oxidation zone (a _ΣSe = 10⁻⁵–10⁻⁴, a _ΣFe = 10⁻², a _ΣCu = 10⁻², a _ΣZn = 5 × 10⁻², a _ΣCo = 10⁻³, a _ΣNi = 10⁻², a _ΣPb = 10⁻⁴) have been estimated. Eh-pH diagrams were calculated and plotted using the Geochemist’s Workbench (GMB 7.0) software package. The database comprises the thermodynamic parameters of 46 elements, 47 main particles, 48 redox pairs, 551 particles in solution, 624 solid phases, and 10 gases. The Eh-pH diagrams of the Me-Se-H₂O systems (Me = Co, Ni, Fe, Cu, Zn, Pb) were plotted for the average contents of these elements in underground water and for their contents in oxidation zones of sulfide deposits. The formation of Co, Ni, Fe, Cu, Zn, and Pb selenites and selenates at the surface is discussed.     

Thermodynamics of arsenates,selenites, and sulfates in the oxidation zone of sulfide ores: Part III: Eh-pH diagrams of the Me-As-H<Subscript>2</Subscript>O systems (Me = Co,Ni, Fe,Cu, Zn,Pb) at 25°C

The behavior of arsenic at the Earth’s surface and nearby at low temperatures and pressures depends mainly on the redox potential and the acidity-alkalinity of the crystallization media. These parameters determine the migration of arsenic compounds and their precipitation as various solid phases. Understanding the mechanism of arsenic’s behavior under surface conditions, which is important for solving environmental problems, is an urgent task of contemporary mineralogy and geochemistry. The activities of the components in natural waters beyond the zones of natural (oxidation zones) and man-made contamination with arsenic (a _ΣAs = 3 × 10⁻⁸, a _ΣFe = 10⁻⁵, a _ΣCu = 10⁻⁷, a _ΣZn = 5 × 10⁻⁷, a _ΣCo = 10⁻⁸, a _ΣNi = 6 × 10⁻⁸, a _ΣPb = 10⁻⁸) and in waters formed in the oxidation zone (a _ΣSe = 10⁻³, a _ΣFe = 10⁻², a _ΣCu = 10⁻², a _ΣZn = 5 × 10⁻², a _ΣCo = 10⁻³, a _ΣNi = 10⁻², a _ΣPb = 10⁻⁴) have been estimated. Eh-pH diagrams were calculated and plotted using the Geochemist’s Workbench (GMB 7.0) software package. The database comprises the thermodynamic parameters of 46 elements, 47 main particles, 48 redox pairs, 551 particles in solution, 624 solid phases, and 10 gases. The Eh-pH diagrams of the Me-As-H₂O systems (Me = Co, Ni, Fe, Cu, Zn, Pb) were plotted for the average contents of these elements in the underground water and for their higher contents in the oxidation zones of sulfide deposits. The formation of Co, Ni, Fe, Cu, Zn, and Pb arsenates at the surface is discussed.