Partitioning Behavior Of Elements Research Articles

Crystal–melt partitioning of noble gases (helium, neon, argon, krypton, and xenon) for olivine and clinopyroxene

Mineral–melt partition coefficients of all noble gases ( min/melt D i ) have been obtained for olivine (ol) and clinopyroxene (cpx) by UV laser ablation (213 nm) of individual crystals grown from melts at 0.1 GPa mixed noble gas pressure. Experimental techniques were developed to grow crystals virtually free of melt and fluid inclusions since both have been found to cause profound problems in previous work. This is a particularly important issue for the analysis of noble gases in crystals that have very low partition coefficients relative to coexisting melt and fluid phases. The preferred partitioning values obtained for the ol–melt system for He, Ne, Ar, Kr, and Xe are 0.00017(13), 0.00007(7), 0.0011(6), 0.00026(16), and 0.0006 ( - 6 ) ( + 9 ) , respectively. The respective cpx–melt partition coefficients are 0.0002(2), 0.00041(35), 0.0011(7), 0.0002(2), and 0.0002 ( - 2 ) ( + 3 ) . The data confirm the incompatible behaviour of noble gases for both olivine and clinopyroxene but unlike other trace elements these values show little variation for a wide range of atomic radius. The lack of dependence of partitioning on atomic radius is, however, consistent with the partitioning behaviour of other trace elements which have been found to exhibit progressively lower dependence of min/melt D i on radius as the charge decreases. As all noble gases appear to exhibit similar min/melt D i values we deduce that noble gases are not significantly fractionated from each other by olivine and clinopyroxene during melting and fractional crystallisation. Although incompatible, the partitioning values for noble gases also suggest that significant amounts of primordial noble gases may well have been retained in the mantle despite intensive melting processes. The implication of our data is that high primordial/radiogenic noble gas ratios ( 3He/ 4He, 22Ne/ 21Ne, and 36Ar/ 40Ar) characteristic of plume basalt sources can be achieved by recycling a previously melted (depleted) mantle source rather than reflecting an isolated, non-degassed primordial mantle region.

Environmental impact of a coal combustion-desulphurisation plant: Abatement capacity of desulphurisation process and environmental characterisation of combustion by-products

The fate of trace elements in a combustion power plant equipped with a wet limestone flue gas desulphurisation (FGD) installation was studied in order to evaluate its emission abatement capacity. With this aim representative samples of feed coal, boiler slag, fly ash, limestone, FGD gypsum and FGD process water and wastewater were analysed for major and trace elements using the following techniques: inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-atomic emission spectrometry (ICP-AES), ion chromatography (IC), ion selective electrode (ISE) and atomic absorption spectroscopy (AAS). Mass balances were established allowing to determine the element partitioning behaviour. It was found that, together with S, Hg, Cl, F, Se and As were those elements entering in the FGD plant primarily as gaseous species. The abatement capacity of the FGD plant for such elements offered values ranged from 96% to 100% for As, Cl, F, S and Se, and about 60% for Hg. The environmental characterisation of combustion by-products (boiler slag, fly ash and FGD gypsum) were also established according to the Council Decision 2003/33/EC on waste disposal. To this end, water leaching tests (EN-12457-4) were performed, analysing the elements with environmental concern by means of the aforementioned techniques. According to the leaching behaviour of combustion by-products studied, these could be disposed of in landfills for non-hazardous wastes.

Element partitioning between transition‐zone minerals and ultramafic melt under hydrous conditions

Element partitioning between wadsleyite, garnet, and hydrous ultramafic melt has been determined at 16 GPa and 1600°C using a Kawai‐type multi‐anvil high‐pressure apparatus. Element partitioning between olivine and hydrous ultramafic melt was also studied at 5 GPa and 1500°C in order to compare element partitioning behavior between wadsleyite and olivine. Major and trace elements analyses of the quenched melt and coexisting wadsleyite, garnet, and olivine were made with an EPMA and LA‐ICP‐MS, respectively. The experimental results demonstrate that LIL (Rb, Sr, Ba) and HFS (Ti, Zr, Nb, Hf, Ta, Th, U) elements are preferably incorporated into wadsleyite relative to olivine, suggesting that the concentration of these elements in the hydrous transition zone could be greater than that in upper mantle. Our results contribute to understand magmatism and chemical differentiation in the Earth's interior.

06/01495 Partitioning behaviour of trace elements in a stoker-fired combustion unit: An example using bituminous coals from the Greymouth coalfield (Cretaceous), New Zealand: Li, Z. et al. International Journal of Coal Geology, 2005, 63, (1–2), 98–116

06/01495 Partitioning behaviour of trace elements in a stoker-fired combustion unit: An example using bituminous coals from the Greymouth coalfield (Cretaceous), New Zealand: Li, Z. et al. International Journal of Coal Geology, 2005, 63, (1–2), 98–116

Partitioning behavior of trace elements during pilot-scale fluidized bed combustion of high ash content lignite

This study describes the partitioning of 20 trace elements (As, B, Ba, Cd, Co, Cr, Cu, Hg, Li, Mn, Mo, Ni, P, Pb, Sb, Se, Sn, Tl, V, Zn) and eight major and minor elements (Al, Ca, Fe, K, Mg, Na, Si, Ti) during the combustion of high ash content lignite. The experiments were carried out in the 0.3 MW t Middle East Technical University (METU) atmospheric bubbling fluidized bed combustor (ABFBC) test rig with and without limestone addition. Inert bed material utilized in the experiments was bed ash obtained previously from the combustion of the same lignite without limestone addition in the same test rig. Concentrations of trace elements in coal, limestone, bottom ash, cyclone ash and filter ash were determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). Partitioning of major and minor elements are influenced by the ash split between the bottom ash and fly ash and that the major proportion of most of the trace elements (As, Ba, Cr, Hg, Li, Mo, Ni, Sn, V, Zn) are recovered in fly ash. Limestone addition shifts the partitioning of Ba, Cr, Mo, Ni, Sn, V, Zn from bottom ash to fly ash.

The influence of carbon on trace element partitioning behavior

Carbon has been proposed as a potential light element in planetary cores, included in models of planetary core formation, and found in meteoritic samples and minerals. To better understand the effect of C on the partitioning behavior of elements, solid/liquid partition coefficients ( D = (solid metal)/(liquid metal)) were determined for 17 elements (As, Au, Co, Cr, Cu, Ga, Ge, Ir, Ni, Os, Pd, Pt, Re, Ru, Sb, Sn, and W) over a range of C contents in the Fe–Ni–C system at 1 atm. The partition coefficients for the majority of the elements increased as the C content of the liquid increased, an effect analogous to that of S for many of the elements. In contrast, three of the elements, Cr, Re, and W, were found to have anthracophile (C-loving) preferences, partitioning more strongly into the metallic liquid as the C content increased, resulting in decreases to their partition coefficients. For half of the elements examined, the prediction that partitioning in the Fe–Ni–S and Fe–Ni–C systems could be parameterized using a single set of variables was not supported. The effects of S and C on elemental partitioning behavior can be quite different; consequently, the presence of different non-metals can result in different fractionation patterns, and that uniqueness offers the opportunity to gain insight into the evolution of planetary bodies.

Partitioning of minerals and elements during preparation of Taixi coal, China

Mineralogy, sulfur and 40 other element contents were determined on eight samples of the Taixi coal and its preparation products from the Rujigou mining district, China. INAA, ICP-AES, CV-AAS, GAAS, XRD, SEM/EDX, conventional chemical and maceral analysis were carried out on the samples. This study is focused on the partitioning behavior of the minerals and elements during the coal cleaning, and the main factors influencing the partitioning behavior of elements were also discussed. The clay minerals (kaolinite, illite, montmorillonite and chlorite), quartz and, to a lesser extent, carbonate minerals (calcite, dolomite and siderite) dominate the mineralogy of Taixi coal. There is also minor amounts of pyrite and trace amounts of gypsum and feldspar. The quartz is dominantly epigenetic in origin, and clay minerals were modified by the thermal metamorphism. They are easily liberated from the coal by cleaning. However, although the majority of carbonate minerals are also mainly epigenetic in origin, its degree of removal is relatively low, especially with respect to dolomite and siderite, which are often finely dispersed in coal macerals, so that they are mostly retained in cleaned coal. Most of the elements studied could be removed effectively during the cleaning processes, especially for the elements predominantly hosted in coarse, epigenetic minerals. Compared with other sized cleaned coals, the coarse-grained cleaned coal is cleanest and has a relatively low potential of environmental risk. The majority of the potentially hazardous elements are notably enriched in the coal waste so that the waste is not feasible to be used as fuel. The partitioning of elements during the coal cleaning processes is essentially controlled by some factors such as the modes of occurrence of elements, maceral type, grain size and textural relation of minerals, and types of cleaning technique used.

The temporal evolution of the nanostructures of model Ni–Al–Cr and Ni–Al–Cr–Re superalloys

The temporal evolution of γ'(L1 2 )-precipitates in Ni-5.2 Al-14.2 Cr at.% and Ni-9.5 Al-8.6 Cr-2.0 Re at.% alloys are studied utilizing three-dimensional atom-probe microscopy. For the times investigated (0.0833 to 1024 h), these alloys exhibit a high number density (10 2 2 -10 2 4 m - 3 ) of spheroidal y'-precipitates, 0.45-30 nm in radius. For the Ni 5.2 Al-14.2 Cr at.% alloy, nucleation, growth, and coarsening of the y'-precipitates is observed during the isothermal transformation at 873 K. Precipitate coalescence is present, and its influence on the power-law dependencies of the number density and mean radius during coarsening is discussed and compared to classical models. For Ni-9.5 Al-8.6 Cr-2.0 Re at.%, phase separation occurs during the initial quench leading to a highly interconnected '-nanostructure. The temporal evolution of the elemental partitioning behavior at 1073 K between the γ-matrix and y'-precipitates is studied in detail.

Partitioning behaviour of trace elements in a stoker-fired combustion unit: An example using bituminous coals from the Greymouth coalfield (Cretaceous), New Zealand

In order to understand trace element behaviour during combustion of coals from the Greymouth coalfield, combustion tests were performed on three seam composite samples. The major and trace elements from sub-samples of feed coal, bottom ash, fly ash, and flue gas were analysed by different techniques including inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma-atomic emission spectrometry (ICP-AES), wavelength dispersive X-ray fluorescence (WD-XRF), and scanning electron microscopy with energy-dispersive X-ray analyser (SEM-EDXA). To help better understand trace element partitioning in combustion ash, float–sink and sequential leaching experiments were also employed to determine the association of trace elements with mineral matter or organic matter. Instrumental Neutron Activation Analysis (INAA) was also employed to determine trace element content in float and sink fractions of fly ash as well as in three major phases in the bottom ash. The partitioning behaviour of trace elements, including some that are environmentally sensitive, was also investigated through the use of float–sink tests and direct determination of trace elements in different combustion ash types and phases. Mass balance and partitioning of major and trace elements have been studied to determine the fate of trace elements after combustion. The partitioning of trace elements, especially hazardous air pollutants (HAPs), in different combustion ashes can be summarised as follows: 1. Most trace elements, especially As, Ba, Co, Cr, Mn, Ni, are partitioned in the glassy and refractory bottom ash fractions. 2. A significant proportion of trace elements of As, Se, and Pb are partitioned into fly ash fractions. 3. Some volatile elements (e.g. > 90% of S and Hg and up to 64% of Cl) and, to a lesser extent, B (up to 44%) and Cd (up to 50%) are partitioned in the flue gas fraction. 4. Although the low ash yield of Greymouth coal seams have the advantage of generating less solid combustion ash, one of the accompanying consequences is that resultant trace elements tend to be enriched in the ash to a greater magnitude than other more clastic sediment influenced coals.

Trace element partitioning and substitution mechanisms in calcium perovskites

We have determined the partition coefficients of a large number of trace elements between CaTiO3 perovskite and anhydrous silicate melts at atmospheric pressure and 3 GPa. Determination of the concentration limits of Henry’s law behaviour in the CaO-Al2O3–SiO2–TiO2 system reveals that the incorporation of rare earth elements (REE) and tetravalent large ion lithophile elements (LILE4+ such as U and Th) at the Ca-site of CaTiO3 perovskite occurs with charge compensation through Ca-vacancy formation rather than by coupled substitution of Al for Ti. When melt composition is varied, we find that partition coefficients for REE and Th are strong functions of the CaO content of the melt. The observed trends are in excellent agreement with those predicted from the Ca-vacancy model. Given that they adopt the same crystal structure and have similar trace element partitioning behaviour, CaTiO3 perovskite and the deep mantle phase CaSiO3 perovskite can be considered analogous to one another. When the analogy is pursued in detail, we find that partitioning into both phases follows the composition-dependence predicted by the Ca-vacancy model. Thus, substitution of REE, U4+ and Th into CaSiO3 in the lower mantle also occurs with Ca-vacancy formation to balance charge. Furthermore when 2+, 3+ and 4+ partition coefficients for both phases are plotted as functions of CaO melt content, the trends for CaSiO3 and CaTiO3 appear to be continuous. This surprising result means that partitioning into Ca-perovskite is independent of pressure and temperature and also of whether or not the host is CaSiO3 or CaTiO3. One implication is that CaSiO3 crystallising from a peridotitic magma ocean may have partition coefficients for Th and U up to about 400. Crystallisation and sequestration of as little as 0.25 volume% of this phase in the lower mantle early in earth history would make a significant contribution to current mantle heat production.

04/02036 Trace elements in circulating fluidized bed combustion of coal: Zhang, J. et al. Ranshao Kexue Yu Jishu, 2003, 9, (1), 64–67. (In Chinese)

For the better understanding of the partitioning behaviors of trace elements and their emissions with or without additive during circulating fluidized bed (CFB) combustion of coal, the coal was burned in a small CFB combustor. Coal samples, including CFB ash, magnetic ash in CFB ash, ash from chimney after dust remover and spraying water from chimney, were collected and analyzed using ICP-AES, AFS, INAA,ICS and CV-AAS. The experimental result shows that the trace elements (As, Sb, Pb, Cu, Be, Zn) are enriched substantially in the fine particles of CFB ash, and Pb, As, Sb, Se, Th, Ni, Cr are enriched in the magnetic ash in CFB ash.In the ash from chimney after dust remover, Zn, As, P, Ni, Cr, Mo, Be, Pb, Th, Hg, F are enriched while Nb, Rb, Zr are obvious deficient. With sulphur capture additive, the contents of As, Se, Sb, Zn in the fine particles of CFB ash decrease, and the contents of As, Se, Li, Be, Mo, Cr, Co, Ni in the ash from chimney after dust remover and the contents of Cu, Zn, Cr, Pb, Co, Ni, F, and Se in the spraying water from chimney decrease. Additive can control the emission of some potentially hazardous trace elements.

Trace element diffusion and element partitioning between garnet and andesite melt using synchrotron X-ray fluorescence microanalysis (-SRXRF)

Synchrotron radiation X-ray fluorescence microanalysis (μ-SRXRF) was applied to products of experimental geochemistry to determine (1) trace element diffusivities in andesite melts and (2) trace element partitioning behaviour between garnet and melt. To achieve sufficient spatial resolution, non-focusing and focusing glass capillaries reduced the incoming synchrotron beam down to sizes of 20 and 2.7 μm, respectively. (1) Diffusion couples of trace element-doped and undoped andesite melts were prepared in internally heated pressure vessels. A special sample setup allowed the pencil-shaped synchrotron beam to irradiate volume elements showing identical diffusion behaviour. Eighteen trace elements were measured simultaneously and quickly, resulting in diffusion profiles well suited for evaluating diffusion coefficients. (2) Garnet and andesitic melt were synthesized and equilibrated in a piston cylinder apparatus. The garnets were exceptionally large due to specially designed dehydration-melting experiments with monazite as a trace element source. Coexisting garnets and melt were analyzed with μ-SRXRF, and new distribution coefficients for Sr (0.126), Y (5.27), Zr (0.533), La (0.014), Ce (0.020), Nd (0.245), Sm (1.21), Eu (1.18), Gd (5.29), Yb (52.5), and Lu (76) were determined. However, the general use of μ-SRXRF for experimental partitioning studies is limited due to the relatively poor spatial resolution caused by the penetrating character of the synchrotron beam and due to limited count rates at high energies.

Trace-element partitioning between vacancy-rich eclogitic clinopyroxene and silicate melt

We investigated experimentally trace-element partitioning between clinopyroxene and anhydrous silicate melt at conditions relevant to near-solidus melting of quartz eclogite in the upper mantle. Partitioning experiments were carried out at 3.0 GPa and 1335–1365 °C on a synthetic mixture similar to a low-degree melt of a quartz eclogite. Clinopyroxene is Al2O3-rich (~17 wt%), cation deficient (~3.92 cations per six O atoms), and coexists with andesitic melt (~57 wt% SiO2), quartz, and traces of rutile. The clinopyroxene cation deficiency indicates a large proportion of vacant M2 sites in form of the Ca-Eskola (CaEs) component (Ca0.5□0.5AlSi2O6). Clinopyroxene-melt partition coefficients ( D -values) were determined for Sr, Y, Zr, Nb, REE, Th, and U by SIMS, and for Sc, V, Cr, Mn, Co, Ni, K, and major elements by electron microprobe analysis. Compared to previous studies of clinopyroxene with >10 wt% Al2O3, partition coefficients in vacancy-rich aluminous clinopyroxene for elements substituting into the M2 site are elevated for monovalent cations ( D Na ~ 1.0, D K = 0.027), and reduced for trivalent cations, particularly for LREE ( D La = 0.029). D Th and D U range from 0.0017 to 0.0037, much lower than previously assumed for clinopyroxene pertaining to partial melting of eclogite in the upper mantle, and D U/ D Th is apparently >1. Observed partitioning behavior of elements substituting into M2 is attributable to the low average charge (1.53–1.57) of the site. This low average charge increases the number of configurations available to charge balance 1+ cations and vacancies, and decreases the number of configurations available to charge balance cations with high valences. Stablization of low-valence species suggests that these vacancy-rich clinopyroxenes may be substantial hosts of noble gases in the mantle. Partition coefficients for cations substituting into the M1 site show relatively little effect from the high vacancy concentrations of M2, but partitioning systematics may be obscured by strong crystal field stabilization of some cations in the M1 site, notably Ni2+ and Cr3+. Application of the measured D -values of this study to partial-melting calculations results in small increases in the Sm/Yb of liquids produced by modest extents of melting of quartz eclogite. Significant enrichments in (230Th)/(238U) activity ratios (>1.21) are expected for decompression melting of quartz eclogite at upwelling rates below 5 cm/year, but enrichments would be small (<1.11) above 10 cm/year.

Experimental Constraints on the Sulfide- and Chromite-Silicate Melt Partitioning Behavior of Rhenium and Platinum-Group Elements

We investigate the origin of high platinum-group element (PGE) abundances associated with chromite-rich rocks by determining the relative partitioning of these elements between chromite- and sulfide-silicate liquids. Chromites were crystallized in the presence of immiscible sulfide and silicate melts in experiments at 1 GPa, producing a few, relatively large (20–50 μ ) crystals, which were analyzed by laser ablation ICP-MS. Our results show that the PGE inventory of chromite and silicate melt produced in experiments is dominated by sulfide and/or alloy micronuggets and that the intrinsic PGE content of these phases is low (sub-ppm), despite high concentrations in coexisting sulfide liquid (i.e., up to alloy saturation). Lower bounds on minimum sulfide-silicate melt PGE partition coefficients (D PGE ) calculated from this data are 0.4 to 10 × 10 4 , which are similar to values determined in previous studies, confirming the extreme fractionation of these elements into the sulfide phase. Rhenium, which was added to experiments in order to constrain Re-Os fractionation, is highly concentrated in sulfide liquid, present at low but uniform levels in silicate melt, and undetectable in chromite. Calculated sulfide-silicate melt D Re are 3.3 to 5.2 × 10 4 , and experiments yielded lower bounds for D Os /D Re of 3, indicating that sulfide-silicate melt equilibrium can fractionate Re from Os. Minimum sulfide melt-chromite partition coefficients are 1,000 or more, indicating that coexisting sulfide melt will be the dominant host for the PGE. Using this partitioning data, we have calculated the mass balance for Ir in chromite-sulfide mixtures and show that for rocks with greater than 200 ppm sulfur, less than 24 percent of the Ir will be in chromite, illustrating that chromite is not the significant PGE host even in low sulfur chromitites. In an experiment saturated in Ir-Re alloy, we measured a maximum iridium concentration in run-product chromites of 150 ppb, which, when combined with an estimate of the Ir activity in the coexisting alloy, yields a maximum Ir solubility of ∼210 ppb. We have found examples of chromitites with Ir contents exceeding this value, indicating that these samples have accumulated an additional PGE-bearing phase. Such results support the notion that interstitial sulfide liquid, or accessory minerals included at the magmatic stage (i.e., laurite, alloys), are most likely to be the dominant primary hosts for PGE in chromite-rich rocks.

Topaz–albite granites and rare-metal mineralization in the Limu District, Guangxi Province, southeast China

The topaz–albite granites of the Limu district are ultra-acidic, peraluminous, Li–F–Na-rich and Sn–Ta–Nb-mineralized. A distinct vertical zonation is developed in the granite stocks. There is an upward, systematic transition from leucocratic microcline-albite granite, through albite-microcline granite, topaz–albite granite, pegmatite stockscheider and layered pegmatite–aplite dikes, to K-feldspar–quartz veins and lepidolite–fluorite stringers in the country rocks. Snow-ball textures, homogeneous distribution of rock-forming and accessory minerals, disseminated mineralization, and melt inclusions in quartz, topaz, and albite are typical features indicative of their crystallization from the late stage Li–F–Na-rich and Sn–Ta–Nb-bearing residual granitic melts at a higher intrusion level. A comparison with rare-metal-bearing pegmatite, ongonite, topaz rhyolite and obsidian glass from other regions shows the worldwide existence of these specialized residual melts. Their emplacement and crystallization in a variety of geological environments result in the formation of a series of chemically similar rocks with different petrographic textures and mineral associations. The topaz–albite granites and associated mineralization in the Limu district provide a good example of highly evolved magmatic fractionation in the F-rich granite system and fluid/melt partitioning behavior of rare-metal elements during magmatic-hydrothermal evolution.

Trace-element partitioning between immiscible lunar melts: An example from naturally occurring lunar melt inclusions

Evidence for liquid immiscibility on the Moon has been documented in melt inclusions in minerals that crystallized from mare basalts, within mesostasis in mare basalts and in at least one sample of a lunar plutonic rock. This study focuses on trace-element partitioning between immiscible melt pairs occurring as inclusions in plagioclase. These inclusions are blade-like in shape and range in length from 2 to 150 μm. They consist of two coexisting glasses separated by a sharp meniscus. The colorless, low-index glass (felsite) is spherical and immersed in a dark-brown, high-index glass (high-Fe basalt). The Fe-rich basaltic component of the inclusion is quartz + hypersthene normative with low Mg/(Mg + Fe) and variable SiO2 content (between 34 and 45 wt%). The felsic component has a SiO2 content between 72 and 82 wt% and variable K2O (4.4 to 8.5 wt%) In most cases, the partitioning behavior of the trace elements agrees with behavior either predicted or measured in experimental and natural systems. The high charge density elements preferentially partition into the basaltic component. High P2O5 and a wider solvus increase the D basalt/felsite for these elements. In contrast to many experimental studies and in agreement with studies of natural silicate liquid immiscibility, the D basalt/felsite for Ba indicates a preference for the felsic component. This difference in Ba behavior between experimental and natural samples has been attributed to differences in melt polymerization and compensation for charge unbalance within the polymerized melt structure. The apparent differences in D basalt/felsite for Sr and divalent Eu between the Apollo 11 high-Ti basalts and Apollo 12 low-Ti basalts may be a result of either subtle differences in bulk composition or the extent of plagioclase plating on inclusion walls. Based on our partitioning data from melt inclusions and the chemical characteristics of lunar felsites, the latter cannot be a product of simple fractional crystallization. Silicate liquid immiscibility can account for fractionation of Ba/ La, K/U, and Ba/U in the lunar felsites and the limited variation in Zr/La. However, it cannot account for the REE pattern of the lunar felsites or the fractionation of U/La. These characteristics must be attributed to whitlockite crystallization prior to the onset of liquid immiscibility.

Rare-earth elements in chlorapatite [Ca10(PO4)6Cl2]: Uptake, site preference, and degradation of monoclinic structure

Differences in the inter- and intracrystalline partitioning behavior of rare earth elements (REE) between chlorapatite (ClAp), fluorapatite (FAp), and hydroxylapatite (OHAp) are directly or indirectly related to substitution mechanism and spatial accommodation. The substitution of REE for Ca is charge compensated by Na in ClAp, Na and Si in FAp, and Si in OHAp. Twinned crystals of REE-substituted ClAp [La-ClAp, Nd-ClAp, Sm-ClAp, Dy-ClAp; Ca 10–2y Na y REE y (PO 4 ) 6 Cl 2 , with y = 0.05–0.09; space group P 2 1 / b ] have been grown from SiO 2 -bearing, H 2 O- and Na-rich phosphate-chloride melts, and their hexagonal ( P 6 3 / m ) subcell structures refined at room temperature with single-crystal X-ray intensities to R = 0.020–0.023. The crystal/melt partition coefficients for La, Nd, Sm, and Dy are 0.073, 0.128, 0.122, and 0.101. Thus, uptake of REE is up to two orders of magnitude lower in ClAp than in REE-substituted FAp and OHAp crystallized under equivalent conditions, but remains peaked at Nd. REE site occupancy ratios [(REE-Ca2)/(REE-Ca1)] obtained from direct refinement of electron densities are 0.71, 1.11, 0.21, and 0.09 for La-, Nd-, Sm-, and Dy-ClAp, respectively, and are consistent with relative change in Ca-O bond distances and sizes of Ca polyhedra. Thus, La, Sm, and Dy favor the Ca1 position of ClAp, not Ca2, as in FAp and OHAp; this unusual site preference is attributed to the large increase in size (6–8%) and distortion of the Ca2O 6 X polyhedron on substitution of Cl for (F,OH). The slight preference of Nd for Ca2 and the peaking of REE uptake at Nd are attributed to a 4 f crystal-field contribution, which is revealed by an anomalous decrease in the Ca2-O1 bond length and volume of the Ca2O 6 X polyhedron in Nd-ClAp, Nd-Fap, and Nd-OHAp. The P 2 1 / b structure of La-ClAp has been refined by detwinning the diffraction pattern, confirming that this monoclinic superstructure largely represents ordering of Cl atoms displaced along [001]. The P 2 1 / b structure of Dy-OHAp has been refined similarly. The intensity of superstructure reflections decreases abruptly with increasing substitution of REE for Ca, showing that REE cations interfere with ordering of Cl atoms(and OH − groups) during the P 6 3 / m → P 2 1 / b transition.

Partitioning behaviour of some toxic trace elements during coal combustion—the influence of events occurring during the deposition stage

The distribution of trace elements in a sub-bituminous coal seam and a peat dome both located in the Waikato/Hauraki region of the central North Island of New Zealand is controlled by the presence or absence of inorganic layers. One of these is a volcanic ash fall layer (tephra) containing high titanium and low calcium levels compared to inorganic phases in other regions of the seam. When coal samples taken from the centre of the seam and including the tephra derived parting were combusted in an underfeed stoker, the partitioning behaviour of the toxic class II volatile boron was found to be significantly different than for samples of coal from other parts of the seam not including the tephra derived parting. Reasons for the different behaviour are identified.

Crystallization of magmatic iron meteorites: The effects of phosphorus and liquid immiscibility

Abstract— Magmatic iron meteorites are commonly thought to have formed by fractional crystallization of the metallic cores of asteroid‐sized bodies. As fractional crystallization proceeds, light elements such as P and S become enriched in the molten portion of the core. The light element content of the metallic liquid influences the partitioning behavior of trace elements and may cause liquid immiscibility to occur. The elemental trends observed in magmatic iron meteorites may have been affected by both of these processes.We have examined experimentally the effect of P on the solid‐metal‐liquid‐metal partitioning behavior of Ag and Pd, Re and Os, two element pairs used to date iron meteorite processes. Phosphorus has no effect on the partition coefficient of either Ag or Pd, which are incompatible and identical within experimental error. Compatible Re and Os also have identical partitioning behavior, within experimental error, and show increasing compatibility in the solid metal with increasing P content of the metallic liquid. Including the effects of both S and P on the partitioning behavior of Re and Os, simple fractional crystallization calculations can reproduce the large variation of Re and Os concentrations observed in four magmatic iron meteorite groups but have difficulty matching the later crystallizing portions of the trends.We have also conducted experiments with three phases—solid metal and two immiscible metallic liquids—to determine the location of the liquid immiscibility field near conditions thought to be relevant to magmatic iron meteorites. Our results show a significantly smaller liquid immiscibility field as compared to the previously published Fe‐P‐S phase diagram. Our revised phase diagram suggests that liquid immiscibility was encountered during the crystallization of asteroidal cores, but much later during the crystallization process than predicted by the previously published diagram.

Partitioning behavior of trace elements during pilot-scale combustion of pulverized coal and coal–water slurry fuel

Release pathways for inorganic hazardous air pollutants (IHAPs) from a pilot-scale, down-fired combustor (DFC) when firing pulverized coal (PC) and coal–water slurry fuel (CWSF) were identified and quantified to demonstrate the effect of fuel form on IHAP partitioning, enrichment and emissions. The baghouse capturing efficiency for each element was calculated to determine the effectiveness of IHAP emission control. Most of the IHAPs were enriched in the fly ash and depleted in the bottom ash. Mercury was found to be enriched in the flue gas, and preferentially emitted in the vapor phase. When firing CWSF, more IHAPs were partitioned in the bottom ash than when firing PC. Significant reduction of Hg emissions during CWSF combustion was also observed.