Sulfate Melts Research Articles

Partitioning of elements between silicate melt and immiscible fluoride, chloride, carbonate, phosphate and sulfate melts, with implications to the origin of natrocarbonatite

Liquid–liquid partitioning of 42 elements between synthetic silicate melts and immiscible fluoride, chloride, carbonate, phosphate and sulfate liquids was studied at temperatures of 650–1100°C, pressures 72–100MPa, with 0–11wt.% H2O. One series of experiments was performed in a rotating internally-heated autoclave where separation of the immiscible liquids was assisted by centrifugal forces. An analogous series of experiments was done in static rapid-quench cold-seal pressure vessels. The experimentally determined liquid–liquid distribution coefficients (D’s) vary over several orders of magnitude, as a result of variable Coulombic interactions between cations and anions. For alkaline, alkaline earth and rare earth elements ther is a strong and systematic dependence of the liquid/liquid D values on the ionic potential Z/r for all the examined systems. In contrast, highly charged cations (e.g., HFSE) show no systematic relationships between the D’s and Z/r.New experimental constraints on the carbonate/silicate liquid–liquid D values presented here confirm that rare metals such as Nb, Zr, REE, Th and U concentrate in silicate liquids, and therefore carbonatites that carry economical rare metal mineralization are not likely to have formed by liquid immiscibility. The comparison between experimentally-determined carbonate–silicate liquid–liquid D values and bulk-rock natrocarbonatite vs. nephelinite compositions at the Oldoinyo Lengai in Tanzania reveals significant discrepancies for Cs, Rb, Ba, Be, Zn, heavy REE, Ti, Mo and W, thus rendering a simple, one-stage immiscibility model for Oldoinyo Lengai questionable.

Inclusions of silicate and sulfate melts in chrome diposide from the Inagli deposit, Yakutia, Russia

Melt inclusions were studied in chrome diopside from the Inagli deposit of gemstones in the Inagli massif of alkaline ultrabasic rocks of potassic affinity in the northwestern Aldan shield, Yakutia, Russia. The chrome diopside is highly transparent and has an intense green color. Its Cr2O3 content varies from 0.13 to 0.75 wt %. Primary and primary-secondary polyphase inclusions in chrome diopside are dominated by crystal phases (80–90 vol %) and contain aqueous solution and a gas phase. Using electron microprobe analysis and Raman spectroscopy, the following crystalline phases were identified. Silicate minerals are represented by potassium feldspar, pectolite [NaCa2Si3O8(OH)], and phlogopite. The most abundant minerals in the majority of inclusions are sulfates: glaserite (aphthitalite) [K3Na(SO4)2], glauberite [Na2Ca(SO4)2], aluminum sulfate, anhydrite (CaSO4), gypsum (CaSO4 × 2H2O), barite (BaSO4), bloedite [Na2Mg(SO4)2 × 4H2O], thenardite (NaSO4), polyhalite [K2Ca2Mg(SO4)4 × 2H2O], arcanite (K2SO4), and celestite (SrSO4). In addition, apatite was detected in some inclusions. Chlorides are probably present among small crystalline phases, because some analyses of aggregates of silicate and sulfate minerals showed up to 0.19–10.3 wt % Cl. Hydrogen was identified in the gas phase of polyphase inclusions by Raman spectroscopy. The composition of melt from which the chrome diopside crystallized was calculated on the basis of the investigation of silicate melt inclusions. This melt contains 53.5 wt % SiO2, considerable amounts of CaO (16.3 wt %), K2O (7.9 wt %), Na2O (3.5 wt %), and SO3 (1.4 wt %) and moderate amounts of Al2O3 (7.5 wt %), MgO (5.8 wt %), FeO (1.1 wt %), and H2O (0.75 wt %). The content of Cr2O3 in the melt was 0.13 wt %. Many inclusions were homogenized at 770–850°C, when all of the crystals and the gas phase were dissolved. The material of inclusions heated up to the homogenization temperature became heterogeneous even during very fast quenching (two seconds) producing numerous small crystals. This fact implies that most of the inclusions contained a salt (rather than silicate) melt of sulfate-dominated composition. Such inclusions were formed from salt globules (with a density of about 2.5 g/cm3) occurring as an emulsion in the denser (2.6 g/cm3) silicate melt from which the chrome diopside crystallized.

Modeling of Equilibria in Complex Cryolite Melts

In the fully ionized sodium sulfate melt, the solubility of an oxide (at a given melt basicity) is well described by considering a single equilibrium to form a specific simple acidic or basic solute. In this case, the dominant solutes are identified by a simple log–log interpretation describing the dependence of the solute concentration on an acid-base parameter \(\log a_{\rm Na_2 O}\). However, in fused cryolite (Na3AlF6) solutions, the solvent itself and the solutes of oxides involve anionic complexes (alumino-fluorides and oxy-fluorides). Therefore, a single simple equilibrium does not suffice to model the complex solution. Rather, as for a high temperature multi-component gas phase containing many complex volatile species, every possible equilibrium must be individually satisfied and coupled to a mass balance. Examples will be given for each limiting type of solution behavior.

An Experimental Study of the Sulfur Content in Basaltic Melts Saturated with Immiscible Sulfide or Sulfate Liquids at 1300 C and 1{middle dot}0 GPa

The sulfur content in basaltic melts coexisting with either sulfide or sulfate melts was determined experimentally. The experimental conditions were in the range of 1300–1355°C and 1·0–1·6 GPa, conditions appropriate for the melting of the upper mantle above subduction zones. Under these conditions, both sulfide and sulfate were present as immiscible liquids, as inferred from the round geometries of the quenched sulfide and sulfate phases. The measured S content in basaltic melts saturated with sulfate liquids ([S] = 1·5 ± 0·2 wt %) was 10 times higher than the S content in basaltic melts saturated with sulfide liquids ([S] = 0·14 ± 0·02 wt %). In our experiments, sulfate liquids were stable at fO2 as low as ΔFMQ = +1·85 [ΔFMQ = log (fO2)sample – log (fO2)FMQ, where FMQ is the fayalite–magnetite–quartz oxygen buffer], and evidence from other sources indicates that sulfates will be stable at lower fO2 in melts with lower activities of silica. Because chalcophile and highly siderophile elements, such as Cu, Ni, Au, and Pd, are partitioned preferentially into sulfide phases, melting of sufficiently oxidized sources, in which sulfides are not stable, would favor incorporation of these elements into the silicate melt produced. Such melts would have a higher potential to generate ore deposits. This study shows that the high sulfur contents of such oxidized basalts also means that relatively small amounts of such magmas can provide significant amounts of sulfur to exsolving volatile phases and account for the bulk of the sulfur expelled in some volcanic eruptions, such the 1991 eruption of Mount Pinatubo.

High-temperature oxidation and hot corrosion behaviors of the NiCr–CrAl coating on a nickel-based superalloy

The hot-section components in commercial aerogas turbines were typically made of nickel-based superalloys and were protected by coatings. Two kinds of diffusion aluminide coatings, including simple aluminide coating and NiCr–CrAl coating, were prepared on a nickel-based cast superalloy by LP-VCD and pack cementation techniques, respectively. The isothermal oxidation behavior of the cast alloy and the coatings at 1000 and 1100 °C and their hot corrosion behaviors in the presence of 75 wt.% Na 2SO 4+K 2SO 4 film at 900 °C were studied using TGA, scanning electron microscopy (SEM)/energy-dispersive spectrometry (EDS), X-ray diffraction (XRD) and electron probe microanalysis (EPMA), respectively. The results showed that NiCr–CrAl coating, not only held a very excellent oxidation resistance due to the α-Al 2O 3 formation on the coating surface during the isothermal process at 1000 and 1100 °C, but also possessed excellent hot corrosion resistance in sulphate melt. Internal oxidation and nitridation were found in the cast alloy during the oxidation process. Moreover, the cast alloy suffered from catastrophic hot corrosion, resulting in the serious internal oxidation and sulfidation. The oxidation resistance of the simple aluminide coating was superior to the cast alloy; the simple aluminide coating was damaged completely and lost its protective effect after the hot corrosion test. In addition, the mechanisms for oxidation and corrosion of the cast alloy and the coatings are discussed simultaneously.

Influence of Moisture on the Hot Corrosion of Metals in Nitrate and Sulfate Melts

Influence of Moisture on the Hot Corrosion of Metals in Nitrate and Sulfate Melts

Evaluation of Cupric/Cuprous Red-OX Equilibria and the Basicity of Alkali Sulfate Melts

Binary and ternary alkali sulfate melts containing small amounts of cuprous and cupric ions have been equilibrated at 1073 K with an Ar, SO2, O2 gas mixture of controlled composition in order to determine the applicability of the (Cu2+)/(Cu+) red-ox ratio as a relative indicator of melt basicity in sulfate systems. It was found that all of the results for the red-ox ratio, from the present work on sodium sulfate based systems as well as those from a previous study on lithium sulfate based systems, can be rationalized in terms of a logarithmic relationship with a simple compositional parameter. This is indicative of melt basicity and incorporates the ionic radii of the alkali metals and the mole fractions of the corresponding sulfates.log(Cu2+)/(Cu+)=1.44+1.9log{Σ(i)x(i)}

Evaluation of Cupric/Cuprous Red-OX Equilibria and the Basicity of Alkali Sulfate Melts

Evaluation of Cupric/Cuprous Red-OX Equilibria and the Basicity of Alkali Sulfate Melts

The Interactions between Ta-Nb Ferroalloys and Sulfate-carbonate Melts

Abstract The reactions of pure metals Ta, Nb, V, Fe, Si, etc. and Ta-Nb-containing ferroalloys with sodium (calcium) sulfate (carbonate) melts are characterized by large exothermic effects and formation of solid, liquid and gaseous products. The liquid phases formed reduce diffusion restrictions and result in catastrophically large rates of metal oxidation.

Thermodynamic equilibrium study of trace element mobilisation under pulverised fuel combustion conditions

The thermodynamic equilibrium distributions of the trace elements lead, arsenic, zinc, copper, nickel, chromium, manganese and boron have been examined using the factwin computational software and associated databases. It is found that the facility for simulation of these elements in a comprehensive model of the oxide melt formed by the major coal mineral elements and (in the early stages of combustion) in an extended sulphide melt model enhances the value of the predictions over those for earlier restricted fact melt models. This is emphasised by comparison with the limitations of predictions for strontium, barium and vanadium, for which no solution models are available in factwin. The influence of sulphur and chlorine concentration variations on the mobilities of the elements varies, and can differ markedly between oxidising and reducing conditions. The predictions are extensively compared with published partitioning results calculated from experimental observations on large combustors. Given the uncertainties involved in both observations and predictions, the degree of agreement is considered satisfactory. The condensation sequence from the equilibrium gas phase at 1300 K has been predicted on cooling, in isolation, by 10 K steps. An alkali sulphate-based melt is predicted to form, and the majority of the other elements are predicted to form sulphates, implying development of a complex sulphate melt, which cannot at present be modelled.

Prilling of aluminum sulfate hydrates

A prilling technique was used to produce droplets of aluminum sulfate hydrates in the size range of 2–2.5 mm. Production of spherical particles of aluminum sulfate hydrates by using a prilling technique has never been studied, nor carried out. The effects of the orifice geometry and hydrostatic head on drop formation were measured. The flow rates of hydrated aluminum sulfate melt through bores of 0.08 and 0.11 cm were measured for liquid heads of 10–100 cm. It was found that the break-up of a liquid jet produced particles in the size range 2.0–2.5 mm with a 0.8 mm orifice. The modified Meister and Scheele correlation, which is the first application on a high viscous fluid in air system, was found to be satisfactory for estimating the particle size obtained by the jet break-up mechanism. © 2000 Society of Chemical Industry

Physical and Chemical Properties of a Highly Viscous Aluminum Sulfate Melt

The physical and chemical properties of the commercial aluminum sulfate melt that do not exist in the literature were measured in this study. The aluminum content of commercial aluminum sulfate hydrate varies between 16 and 17% Al2O3. The viscosity of this product is in the range 160−260 cP, density is in the range 1.705−1.735 g/cm3, and the surface tension is predicted to be 105 dyn/cm. These properties change sharply with temperature and concentration.

Oxidation-reduction equilibrium of Cu2+/Cu+ in binary alkaline sulfate melts

Oxidation-reduction equilibria for a Cu2+/Cu+ couple in binary alkaline sulfate melts, Li2SO4 + R2SO4 (R = Na, K, Rb, Cs), were determined at temperatures of 973, 1023, and 1073 K by equilibrating these melts with gas mixtures of Ar + O2 + SO2. RedOx equilibria are well interpreted by the average ionic radii of alkaline metals: r(average) = X(Li2SO4) r(Li) + X(R2SO4) r(R), wherer andX denote, respectively, mole fraction and the ionic radii of alkaline metal. The oxygen anion activities would increase with an increase in R2SO4 mole fractions of binary sulfates Li2SO4 + R2SO4.

A Molecular Dynamics Investigation of the Structures and Mixed Alkali Effect in Sulfate Glasses

A molecular dynamics stimulation of alkali sulfate-zinc sulfate melts and glasses is presented. Oxygen coordinations of Zn2+, Na+, and K+ cations have been found to be nearly six, eight, and twelve respectively. The radial distribution function has been calculated and compared with the same reported from experimental X-ray diffraction work. Several important aspects of a modified random close packing model described earlier to account for the behavior of sulfate glasses have been confirmed by the present molecular dynamics simulation. Diffusion coefficients of various ions have been evaluated from mean squared displacement data and occurrence of the mixed alkali effect has been noted. A surprising spatial correlation of dissimilar alkali ions has been observed and it is suggested that it provides support for a structural origin of mixed alkali effect in ionic glasses.

Solubilities of Cr2 O 3 and SiO2 in Na2 SO 4 ‐ K 2 SO 4 ‐ Fe2 ( SO 4 ) 3 at 963 K

By the use of a reference electrode to indicate the acidity of a fused ternary sulfate melt at 963 K, the solubilities of the oxides and have been determined experimentally as a function of melt acidity. Compared to a previous determination in pure at 1200 K, the solubility of as the basic chromate solute at 963 K is a factor of six higher. Likewise, the acidity‐independent solubility of is a factor of 3 higher at the lower temperature.

Corrosion Kinetics and Strength Degradation of Sintered δ‐Silicon Carbide in Potassium Sulfate Melts

Pressureless sintered α‐SiC ceramics containing carbon and boron as sintering aids and hot‐pressed SiC containing aluminum nitride as a sintering aid were corroded in K2SO4 melts at 1080° to 1150°C. SiC ceramics were oxidized and dissolved into K2SO4 melts. Since the corrosion of SiC ceramics in K2SO4 melts proceeded autocatalytically, a reaction product such as K2S1.44 was suspected to promote the corrosion reaction. The corrosion resistance of SiC containing AlN in K2SO4 melt was superior to that of SiC containing boron and carbon. Apparent activation energies for the corrosion of SiC ceramics were 309 to 331 kJ mol‐1. The fracture strength of the specimens corroded by K2SO4 melt degraded to 40% to 70% of the original values up to a 20% weight loss and then was almost constant up to 45% weight loss.

Effects of Chromate and Vanadate Anions on the Hot Corrosion of Preoxidized Ni by a Thin Fused Na2 SO 4 Film at 900°C

The effects of chromate and vanadate anions on the hot corrosion of preoxidized Ni by a thin fused film in an gas atmosphere at 900°C were investigated by use of a sodium sensor and an oxygen probe. The chromate anion suppressed the sulfidation of Ni probably by precipitating solid from the melt. However, the corrosion rate during self‐sustained hot corrosion was faster than for a pure sodium sulfate melt, probably due to the fast counterdiffusion of species. The vanadate anion rapidly attacked the protective oxide and enhanced the sulfidation of Ni causing a self‐sustained hot corrosion of Ni.

溶融硫酸塩による金属材料の電気化学的高温腐食

溶融硫酸塩による金属材料の電気化学的高温腐食

Thermogravimetric investigation of reactions between vanadium(v) compounds and pyrosulphate in alkali metal sulphate melts

The interactions between sulphate, pyrosulphate, vanadium pentoxide, metavanadate and orthovanadate have been studied thermogravimetrically and were shown to be strongly dependent on the alkali metal present, the smaller and more polarising cations causing decomposition of pyrosulphate (to SO 3) at lower temperatures. Sulphate and vanadium pentoxide were found to have a stabilising effect on pyrosulphate, thought to be due to the formation of vanado-sulphato polymers, an explanation which received support from infrared spectroscopy. The physical nature of the melts (i.e. whether viscous or mobile, and the formation of solid crusts on liquid melts) influenced the rates of weight loss. The results enabled the behaviour of the contact catalyst for sulphuric acid manufacture to be more completely understood.

Corrosion reactions in molten sulphates

The redox potential in sulphate melts is controlled by the partial pressures of oxygen and SO3 in equilibrium with the melt. The rate for the reduction of oxygen is limited by the solubility. Higher rates are observed for the reduction of SO3 which is identified as the principal oxidizing species. Equilibrium potentials for reversible metal-metal ion couples for the principal components of superalloys are negative relative to the redox potential for the melt. The anodic oxidation of the metal therefore proceeds irreversibly in conjunction with the cathodic reduction of SO3 An oxide layer is formed on the surface of the metal when the metal ion concentration at the surface, combined with the oxide ion concentration in the melt, which is related to the partial pressure of SO3, exceeds the solubility limit for the oxide. The corrosion behaviour will depend on the mass transport processes through this oxide layer. Temperature gradients through the molten sulphate, and oxide ion concentration gradients established as a consequence of the corrosion reaction, may influence the morphology of the corrosion product. The gradient between the oxygen chemical potential at the outer surface of the molten sulphate, defined by the oxygen partial pressure in the gas and the oxygen chemical potential at the metal/metal oxide interface, defined by the dissociation equilibrium for the metal oxide, combined with the transport of SO3 through the molten sulphate, increases the sulphur chemical potential at the metal surface and leads to the formation of the metal sulphide. Stress in the protective oxide layer caused by the growth of the sulphide phase at the interface between the metal and the oxide will eventually fracture the oxide and cause accelerated corrosion.