Thermodynamics of the α-FeOOH (goethite)-ScOOH solid solution

Copiapite-group minerals are common products of weathering of sulfides, especially pyrite and pyrrhotite. They have a general formula AFe3+4(SO4)6(OH)2·20H2O and all crystallize in the triclinic crystal system (space group P). In this work, we have determined the thermodynamic properties of copiapite (A = Fe2+), ferricopiapite (A = 2/3Fe3+), magnesiocopiapite (A = Mg), and aluminocopiapite (A = 2/3Al). Enthalpies of formation were calculated from enthalpies of dissolution in 5 mol/dm3 HCl (measured by acid-solution calorimetry) and entropies from low-temperature heat capacity data (measured by relaxation calorimetry). Differential scanning calorimetry was used in a restricted temperature range to verify the accuracy of the heat capacity measurements. We also present calculated molar volumes and densities for the copiapite-group phases. The calculated Gibbs free energies of formation are (all values in kJ/mol) −10,322.6 ± 11.8 (A = Mg), −9862.7 ± 12.4 (A = 2/3Fe3+), −10,177.4 ± 10.9 (A = 2/3Al), and −9949.0 ± 12.1 (A = Fe2+). They correspond to solubility products (log Ksp) of −21.24 (A = Mg), −18.55 (A = 2/3Fe3+), −18.17 (A = 2/3Al), and −19.66 (A = Fe2+). They all relate to the dissolution reaction AxFe3+4(SO4)6(OH)2·20H2O + 2H+ → xA + 4Fe3+ + 6SO42− + 22H2O. Using an extended Pitzer model for highly concentrated ferric iron-sulfate solutions, positions of solubility curves for several ferric sulfates were calculated. The shape of the solubility envelope was reproduced, but the position of the curves was not matched. It seems that there is a considerable way to go before a satisfactory thermodynamic model can be constructed for this particular system.

The Raman spectra of the end member pyroxenes CaZnSi2O6 and Zn2Si2O6 are calculated by quantum mechanical modeling and compared with the experimental ones measured in synthetic (CaxZn1−x)ZnSi2O6 pyroxenes with x = 0, 0.2, 0.3, 0.5, 0.7, 1. The calculated spectra correctly predict the intensity and peak positions of the spectra recorded on the end members. The model provides also useful hints for the mode assignment at the intermediate compositions. The experimental peak positions are compared in (CaxM2+1−x)M2+Si2O6 pyroxenes, with M2+ = Mg, Co, Zn, Fe2+. These pyroxenes share a common charge and different mass and ionic radius; the relative contributions of the mass and ionic radius in the experimental spectrum are discussed in four of the most intense peaks. We found that the positions of the strongest peaks are related to the average bond distances of the polyhedra which most affect a given mode. Ca–Zn pyroxenes provide an exception, whereas the CaZnSi2O6 end member fits quite well in the bond-distance/peak positions relations found in other pyroxenes, and the same does not occur as Zn exchanges for Ca. Peak broadening occurs in Zn pyroxenes in intermediate compositions; it is related to the presence of polyhedral local configurations around Zn and Ca atoms in the M2 polyhedron. The broadening is higher in the ~ 1010 cm−1 peak (ν19), which, among the strongest peaks, shows the highest difference in the Raman wavenumber between end members. The different behaviours of Zn pyroxenes with respect to Mg, Co, and Fe2+ ones are likely related to the partially covalent bonding in the M2 cavity shown by Zn pyroxenes.

The mixing enthalpies of liquid binary iron‐nickel, nickel‐chromium and iron‐chromium alloys were measured by levitation alloying calorimetry. The mixing enthalpy of iron‐nickel alloys is asymmetric and was described by an equation according to the modified quasichemical solution model. Liquid nickel‐chromium alloys were determined to conform to a regular solution model whereas the system iron‐chromium behaves ideally. Based upon the analytical descriptions obtained for the binary systems an isoenthalpy diagram for liquid ternary iron‐nickel‐chromium alloys was calculated. Mixing enthalpy measurements of the concentration section Fe35Ni65 ‐ Cr are in agreement with the model calculation. Iron rich alloys of the system tend to almost ideal behaviour whereas nickel rich alloys are characterized by negative mixing enthalpies up to ‐5 kJ/mol.

Reactivity of As and U co-occurring in Mine Wastes in northeastern Arizona

Thermodynamics of the goethite-diaspore solid solution

Enthalpies of l-proline dissolution in aqueous solution of N,N-dimethylformamide at 293.15–308.15 K

This study assessed arsenic (As) contamination and the characteristics of secondary minerals in mine drainage using integrated acid–base accounting (ABA) and toxicity characterisation leaching procedure (TCLP), aqueous and solid-phase media monitoring, as well as a textural and mineralogical analysis of tailings material at the Obuasi mine in Ghana. The neutralisation potential and maximum potential acidity from an ABA test; As and pH in TCLP leachate and mine drainage, particle size, trace and major elements in tailings, were analyzed using the relevant methodologies. The ABA results which indicated a high tendency for acid generation were interpreted using a four data point model developed for the purpose. The model allows an additional 40 kg CaCO3/ton amendment value to take care of any delayed acidification. Arsenic leaching simulations are described by the equation: [As] \(= {\text{A }}\left( {\frac{\text{NP}}{\text{MPA}}} \right)^{2} - \;{\text{B}}\left( {\frac{\text{NP}}{\text{MPA}}} \right)\; + \;{\text{C}}\). With the y-axis set to zero, pH simulation equations are defined by pH = K\(\left( {\frac{\text{NP}}{\text{MPA}}} \right)\), where the K and pH values ranging from 82 to 100 and 4.1 to 9.0 respectively, represent limits within which natural attenuation of As in drainage can be sustained. Expressing the pH equation above in the form, pH = (ln |R2| − lnK), the simulation equations defined the range 2.2–4.6 which conformed to pH range for which secondary minerals such as jarosite, schwertmannite and ferrihydrite, could occur as buffering agents in mine drainage. Also, molar value plot for Fe2O3 against Al2O3 indicate the precipitation of goethite and alunite into tailings, while increased fines and As enrichment in older tailings confirmed As attenuation. Such information is relevant for front-end planning for As impact remediation in mine drainage.

Various model equations are available for representing the excess Gibbs energy properties (osmotic and activity coefficients) of aqueous and other liquid mixed-electrolyte solutions. Scatchard’s neutral-electrolyte model is among the simplest of these equations for ternary systems and contains terms that represent both symmetrical and asymmetrical deviations from ideal mixing behavior when two single-electrolyte solutions are mixed in different proportions at constant ionic strengths. The usual form of this model allows from zero to six mixing parameters. In this report we present an analytical method for transforming the mixing parameters of neutral-electrolyte-type models with larger numbers of mixing parameters directly to those of models with fewer mixing parameters, without recourse to the source data used for evaluation of the original model parameters. The equations for this parameter conversion are based on an extension to ternary systems of the methodology of Rard and Wijesinghe (J. Chem. Thermodyn. 35:439–473, 2003) and Wijesinghe and Rard (J. Chem. Thermodyn. 37:1196–1218, 2005) that was applied by them to binary systems. It was found that the use of this approach with a constant ionic-strength cutoff of I≤6.2 mol⋅kg−1 (the NaCl solubility limit) yielded parameters for the NaCl+SrCl2+H2O and NaCl+MgCl2+H2O systems that predicted osmotic coefficients φ in excellent agreement with those calculated using the same sets of parameters whose values were evaluated directly from the source data by least-squares, with root-mean-square differences of RMSE(φ)=0.00006 to 0.00062 for the first system and RMSE(φ)=0.00014 to 0.00042 for the second. If, however, the directly evaluated parameters were based on experimental data where the ionic strength cutoff varied with the ionic-strength fraction, i.e., because they were constrained by isopiestic ionic strengths (MgCl2+MgSO4+H2O) or solubility/oversaturation ionic strengths (NaCl+SrCl2+H2O and NaCl+MgCl2+H2O), then parameters converted by this approach assuming a constant ionic-strength cutoff yield RMSE(φ) differences about an order of magnitude larger than the previous case. This indicates that for an accurate conversion of model parameters when the source model is constrained with variable ionic strength cutoffs, an extension of the parameter conversion method described herein will be required. However, when the source model parameters are evaluated at a constant ionic strength cuttoff, such as when source isopiestic data are restricted to ionic strengths at or below the solubility limit of the less soluble component, or are Emf measurements that are commonly made at constant ionic strengths, then our method yields accurate converted models.

Exploring applicability of end member mixing approach for predicting environmental reactivity of dissolved organic matter

Standard enthalpies and heat capacities of solution of 2,4-dimethyl- and 2,4-diethylglycolurils in water at temperatures from (278.15 to 313.15)K

Mechanistic insights on the catalytic ozonation of trimethoprim in aqueous phase using geopolymer catalysts produced from mining waste

The NASA Curiosity rover has investigated a diverse stratigraphic record at Gale crater, Mars, ranging from poorly-sorted conglomerates to cross-bedded sandstones and thinly-laminated mudstones. This stratigraphic record is indicative of deposition in multiple paleoenvironments (fluvial, lacustrine and aeolian), within which variable degrees of mineral sorting, chemical weathering and post-depositional aqueous alteration occurred. This study delineates the geochemical effects of these different sedimentary processes using major element data from the Chemistry and Camera (ChemCam) instrument suite and mineralogical data provided by the Chemistry and Mineralogy (CheMin) instrument suite to identify source region characteristics, mineral sorting regimes, variations in chemical weathering, and the impact of diagenesis on the geochemistry of the host rock. Delineating the different geochemical effects of these sedimentary processes on the lithified units will better constrain our understanding of the geological record and paleoenvironmental conditions in Gale crater, along with the extent of geochemical variation in the surrounding Martian crust. Here, I show that four previously identified compositional endmembers (subalkaline basalt, trachybasalt, trachyte and rhyolite), and one new endmember (silica-rich basalt) contributed to Gale crater’s stratigraphic groups. The previously identified endmembers’ influence extends throughout Gale crater’s stratigraphic record beyond where they were initially identified. The silica-rich basalt source region is the main contributor to the lower Mt Sharp Group, including the Vera Rubin Ridge, whose hardness likely results from a later diagenetic event precipitating additional hematite in sedimentary pore spaces. This thesis further supports that Martian fluviolacustrine deposits are more enriched in felsic material relative to mafic material with distance from the sediment source. Meanwhile, aeolian deposits become preferentially enriched in mafic materials. Geochemically identifying the ancient aeolian mineral sorting trend has also constrained the prevailing wind direction at the time of deposition as SW-NE, which is the reverse of the current prevailing wind direction within Gale crater today.

Simulation of thermodynamic mixing properties of garnet solid solutions at high temperatures and pressures

The Koktokay No. 3 pegmatite, Altai, northwestern China, is a spodumene-subtype granitic pegmatite. In this study, we report textural and chemical features of tourmaline from the altered country-rock, the contact zone, and the pegmatite. The tourmaline ill the altered country-rock, Ca- and Fe-rich dravite, shows an obvious chemical heterogeneity within individual grains. Tourmaline in the contact zone consists of two generations: zoned Ca- and Fe-rich dravite and in interstitial foitite-schorl solid solution. Tourmaline from the altered country-rock and the contact zone reflects interaction between the country rock (metagabbro) and the pegmatite-forming melt or fluids derived from it. The chemical variation of these tourmalines depends on various contributions of components from the country rock and the pegmatite. The tourmaline in the outer zones (zones I to IV) of the pegmatite is elbaite-schorl solid solution with all intermediate composition between the end members; it is generally homogeneous within individual grains. In the inner zones (zones V, VI, and VIII), the tourmaline is dominantly elbaite with rare rossmanite in zone V. Elbaite is either abruptly zoned within individual grains, or has a replacement texture. Chemically, elbaite in the inner zones has a higher proportion of X-site vacancy than elbaite-schorl in the outer zones. Chemical trends of tourmaline compositions in the spodumene-subtype Koktokay No. 3 pegmatite are generally similar to those in other pegmatite subtypes (lepidolite, petalite, and elbaite subtype). Systematic variations in the internal textures of tourmaline from the outer zones to the inner zones suggest that exsolution of fluids occurred between zone IV and zone V. The outer zones crystallized from a volatile-unsaturated pegmatite-forming magma, whereas the inner zones crystallized from a hydrothermal system. This evolution process is consistent with the London model of internal evolution of granitic pegmatites.

An examination of the volcanics of the Crescent formation on the Olympic Peninsula was undertaken for this study, in order to determine variations between exhalative deposits of ophiolitic and fore-arc origins. Information gathered during the investigation suggests that deposits related to early fore-arc formation are most closely related to deposits of deep ocean origins with time, arc volcanics trend from basic to intermediate composition and their related ore deposits from black smoker type mineralization toward Beshi type massive sulfides. Massive, sulfide terrains examined in the Crescent volcanics appear to be midway between these two end members, with elements of both types. Detailed geology and geochemistry of the deposits leads to the conclusion that similar ore bodies might be found in recent fore-arc chains and may constitute a greater potential resource for ocean mining then their ophiolitic counterparts. INTRODUCTION Since the time of Hutton and the concept of uniformitarianism, it has been the job of the geologist to relate ancient even to corresponding recent geological process. Though the use of this technique is an excellent tool for explaining the strata accumulated on continents in past eras, our lack of data on recent oceanic events limits it's utility. Using information taken from continentally accreted ophiolites, discovery has recently been made of actively forming exhalative deposits in oceanic spreading centers. This reverse uniformitarianism (The key to the present, may be found in the past.) may serve as a general tool for mineral exploration in oceanic environments. Using this concept, a basic fore-arc volcanic terrain of Eocene age was chosen for detailed study, with hopes of initiating exploration for recent ore deposits of like origin. Geologic mapping and geochemical sampling were conducted to determine the physiochemical parameters of these exhalative systems and their relation to deposits formed in deep ocean and more developed arc settings. The data gathered was used to construct an exploration model with postulated grades and tonnages for recent exhalatives. Given the correctness of the model, it may be possible to locate minable resources in arc terrains such as the Aleutian Islands. GENERAL GEOLOGY The Crescent Formation is a pile of basic forearc volcanics accumulated on the continental margin during the Eocene. Lower Crescent extrusives are composed of interbedded pillow basalts, basaltic andesites, quartz keratophyres and related tuffs, tuff breccias and mixed organic /chemical sediments. Locally, small stocks of gabbroic intrusives occur near erruptive centers, associated with diabasic dike and sill complexes. with time, the erruptives trend toward more intermediated composition and the upper member is composed of mixed basaltic andesite and andesite, many flows of which are Subaerially errupted. Unlike similar terrains, i.e. Japan, the Crescent contains few centers of andesite and rhyolite composition. Cowan (1982) inferred that the arc may have been uprooted during large scale tectonic activity on the San Juan and Leech River Faults during the oligiocene.