Synthesis, characterization, and thermodynamics of arsenates forming in the Ca-Fe(III)-As(V)-NO3 system: Implications for the stability of Ca-Fe arsenates
-
Dogan Paktunc
,
Juraj Majzlan
Abstract
Arseniosiderite and yukonite are among the important arsenate minerals occurring as secondary alteration products in relation to the oxidation of arsenopyrite and arsenian pyrite and as discrete grains in some gold ores, mine tailings, and contaminated soils. Characteristics of these Ca-Fe arsenate species are not well known and our understanding of the conditions promoting their formation and dissolution is limited. Long- and short-range structural characteristics and thermodynamic properties of the Ca-Fe arsenates forming in the Ca-Fe(III)-As(V)-NO3 system were determined to better predict the mineralogical transformations taking place in neutralized sludge and tailings environments, and their influence on arsenic mobilization. Yukonite and arseniosiderite readily form from solutions with highly variable compositions at a wide pH range from slightly acidic to alkaline conditions. Calcium concentrations corresponding to molar Ca/(Ca+Fe+As) ratios as low as 0.1 appear to be adequate for their formation. Our experimental results confirm observations in natural settings and mine tailings where scorodite is progressively replaced by yukonite and arseniosiderite. The initial amorphous precipitates made of small oligomeric units of edge-sharing FeO6 octahedra with bridging arsenate evolve to yukonite through the establishment of corner linkages between the FeO6 chains. Yukonite represents a nanocrystalline precursor and Ca-deficient variety of arseniosiderite. Formation of arseniosiderite is kinetically controlled with faster development of crystallinity at neutral to slightly acidic pH and slower kinetics under alkaline conditions. Calorimetric measurements provided an enthalpy of formation value of -1950.3 ± 3.1 kJ/mol and standard entropy of 237.4 ± 4.4 J/(mol·K) for arseniosiderite [with composition Ca0.663Fe1.093(AsO4)(OH)1.605·0.827H2O], the corresponding Gibbs free energy of formation is -1733 ± 3.4 kJ/mol. A rough estimate of the thermodynamic properties of yukonite is also provided. Arseniosiderite is a stable arsenate between pH 3.5 and 7.5 in solutions saturated with respect to soluble Ca minerals such as calcite, gypsum, anorthite, or Ca-montmorillonite. Arsenic release from mine wastes and contaminated soils can be effectively controlled by arseniosiderite and the conditions promoting its formation such as lime-treatment leading to gypsum saturation in ferric arsenate solutions would prove to be desirable for stabilizing arsenic in the form of arseniosiderite in mine wastes.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Data, ideas, and the nature of scientific progress
- Beyond the equilibrium paradigm: How consideration of kinetics enhances metamorphic interpretation
- Magmatic volatiles (H, C, N, F, S, Cl) in the lunar mantle, crust, and regolith: Abundances, distributions, processes, and reservoirs
- The mafic component of the lunar crust: Constraints on the crustal abundance of mantle and intrusive rock, and the mineralogy of lunar anorthosites
- Degassing pathways of Cl-, F-, H-, and S-bearing magmas near the lunar surface: Implications for the composition and Cl isotopic values of lunar apatite
- Uranium scavenging during mineral replacement reactions
- New structure of high-pressure body-centered orthorhombic Fe2SiO4
- Spectroscopic study of ordering in non-stoichiometric magnesium aluminate spinel
- High-pressure behavior of cuprospinel CuFe2O4: Influence of the Jahn-Teller effect on the spinel structure
- Field and model constraints on silicic melt segregation by compaction/hindered settling: The role of water and its effect on latent heat release
- Formation of rhyolite at the Okataina Volcanic Complex, New Zealand: New insights from analysis of quartz clusters in plutonic lithics
- Experimental investigation of F, Cl, and OH partitioning between apatite and Fe-rich basaltic melt at 1.0–1.2 GPa and 950–1000 °C
- Synthesis, characterization, and thermodynamics of arsenates forming in the Ca-Fe(III)-As(V)-NO3 system: Implications for the stability of Ca-Fe arsenates
- High-pressure phases of cordierite from single-crystal X-ray diffraction to 15 GPa
- Planar microstructures in zircon from paleo-seismic zones
- Ultra-deep subduction of Yematan eclogite in the North Qaidam UHP belt, NW China: Evidence from phengite exsolution in omphacite
- Elastic wave velocity anomalies of anorthite in a subducting plate: In situ experiments
- Current limitations of molecular dynamic simulations as probes of thermo-physical behavior of silicate melts
- Three-component mixed-layer illite/smectite/kaolinite (I/S/K) minerals in hydromorphic soils, south China
- Melting curve of NaCl to 20 GPa from electrical measurements of capacitive current
- Grain size measurement from two-dimensional micro-X-ray diffraction: Laboratory application of a radial integration technique
- Decrease of hydrogen incorporation in forsterite from CO2-H2O-rich kimberlitic liquid
- Provenance determination of sapphires and rubies using laser-induced breakdown spectroscopy and multivariate analysis
- Structural insights and elasticity of single-crystal antigorite from high-pressure Raman and Brillouin spectroscopy measured in the (010) plane
- Magnetic anisotropy in natural amphibole crystals
- Resolving oxygen isotopic disturbance in zircon: A case study from the low δ18O Scourie dikes, NW Scotland
- Accurate determination of Fe3+/ΣFe of andesitic glass by Mössbauer spectroscopy
- Recoil-free fractions of iron in aluminous bridgmanite from temperature-dependent Mössbauer spectra
- Chemical interactions between a sedimentary diapir and surrounding magma: Evidence from the Phepane Dome and Bushveld Complex, South Africa
- The crystal structures of Mg2Fe2C4O13, with tetrahedrally coordinated carbon, and Fe13O19, synthesized at deep mantle conditions
- New Mineral Names
- Book Review: Geodynamics, Third edition.
Articles in the same Issue
- Data, ideas, and the nature of scientific progress
- Beyond the equilibrium paradigm: How consideration of kinetics enhances metamorphic interpretation
- Magmatic volatiles (H, C, N, F, S, Cl) in the lunar mantle, crust, and regolith: Abundances, distributions, processes, and reservoirs
- The mafic component of the lunar crust: Constraints on the crustal abundance of mantle and intrusive rock, and the mineralogy of lunar anorthosites
- Degassing pathways of Cl-, F-, H-, and S-bearing magmas near the lunar surface: Implications for the composition and Cl isotopic values of lunar apatite
- Uranium scavenging during mineral replacement reactions
- New structure of high-pressure body-centered orthorhombic Fe2SiO4
- Spectroscopic study of ordering in non-stoichiometric magnesium aluminate spinel
- High-pressure behavior of cuprospinel CuFe2O4: Influence of the Jahn-Teller effect on the spinel structure
- Field and model constraints on silicic melt segregation by compaction/hindered settling: The role of water and its effect on latent heat release
- Formation of rhyolite at the Okataina Volcanic Complex, New Zealand: New insights from analysis of quartz clusters in plutonic lithics
- Experimental investigation of F, Cl, and OH partitioning between apatite and Fe-rich basaltic melt at 1.0–1.2 GPa and 950–1000 °C
- Synthesis, characterization, and thermodynamics of arsenates forming in the Ca-Fe(III)-As(V)-NO3 system: Implications for the stability of Ca-Fe arsenates
- High-pressure phases of cordierite from single-crystal X-ray diffraction to 15 GPa
- Planar microstructures in zircon from paleo-seismic zones
- Ultra-deep subduction of Yematan eclogite in the North Qaidam UHP belt, NW China: Evidence from phengite exsolution in omphacite
- Elastic wave velocity anomalies of anorthite in a subducting plate: In situ experiments
- Current limitations of molecular dynamic simulations as probes of thermo-physical behavior of silicate melts
- Three-component mixed-layer illite/smectite/kaolinite (I/S/K) minerals in hydromorphic soils, south China
- Melting curve of NaCl to 20 GPa from electrical measurements of capacitive current
- Grain size measurement from two-dimensional micro-X-ray diffraction: Laboratory application of a radial integration technique
- Decrease of hydrogen incorporation in forsterite from CO2-H2O-rich kimberlitic liquid
- Provenance determination of sapphires and rubies using laser-induced breakdown spectroscopy and multivariate analysis
- Structural insights and elasticity of single-crystal antigorite from high-pressure Raman and Brillouin spectroscopy measured in the (010) plane
- Magnetic anisotropy in natural amphibole crystals
- Resolving oxygen isotopic disturbance in zircon: A case study from the low δ18O Scourie dikes, NW Scotland
- Accurate determination of Fe3+/ΣFe of andesitic glass by Mössbauer spectroscopy
- Recoil-free fractions of iron in aluminous bridgmanite from temperature-dependent Mössbauer spectra
- Chemical interactions between a sedimentary diapir and surrounding magma: Evidence from the Phepane Dome and Bushveld Complex, South Africa
- The crystal structures of Mg2Fe2C4O13, with tetrahedrally coordinated carbon, and Fe13O19, synthesized at deep mantle conditions
- New Mineral Names
- Book Review: Geodynamics, Third edition.
