Coal-based power generation produces over 750Mt of coal ash per year globally, but under 50% of world production is utilised. Large amounts of fly ash are either stored temporarily in stockpiles, ...disposed of in ash landfills or lagooned. Coal ash is viewed as a major potential source of release of many environmentally sensitive elements to the environment. This paper encompasses over 90 publications on coal fly ash and demonstrates that a large number of elements are tightly bound to fly ash and may not be easily released to the environment, regardless of the nature of the ash. This review provides an extensive look at the extent to which major and trace elements are leached from coal fly ash. It also gives an insight into the factors underlying the leachability of elements and addresses the causes of the mobility. The mode of occurrence of a given element in the parent coal was found to play an important role in the leaching behaviour of fly ash. The amount of calcium in fly ash exerts a dominant influence on the pH of the ash–water system. The mobility of most elements contained in ash is markedly pH sensitive. The alkalinity of fly ash attenuates the release of a large number of elements of concern such as Cd, Co, Cu, Hg, Ni, Pb, Sn or Zn among others, but at the same time, it enhances the release of oxyanionic species such as As, B, Cr, Mo, Sb, Se, V and W. The precipitation of secondary phases such as ettringite may capture and bind several pollutants such ash As, B, Cr, Sb, Se and V.
► The mode of occurrence of elements in coal determines their solubility in fly ash. ► Most elements contained in fly ash display a pH-dependent solubility. ► Most trace elements in fly ash are poorly leached in pH 7–10 region. ► Oxyanionic-forming species are the main concern in alkaline fly ash. ► Absorption and precipitation processes attenuate the release of pollutants.
Earth's continental crust is dominantly made of buoyant, felsic igneous material (granitoids), that was ultimately extracted from the mantle as a result of Earth's differentiation. Since felsic melts ...are not in chemical equilibrium with the mantle, they can originate either from melting of older crustal lithologies, or from differentiation of a primitive mantle melt; only the latter case will contribute to crustal growth. To understand the mechanisms of continental crust growth and differentiation through time, it is therefore necessary to unravel the respective contribution of these two different mechanisms in the genesis of granitoid suites. In modern Earth, granitoids are chiefly generated in convergent plate boundaries (subduction and collision). This paper examines the granitic suites in a late-collision environment, the Variscan French Massif Central (FMC), and compares them with the suites found in an oceanic arc. We therefore describe, and compare, two end-members sites of granite generation.
In the FMC, several main types of granites are described. Muscovite and Cordierite bearing Peraluminous Granites (resp. MPG and CPG) contain large amounts of inherited zircons, and their chemistry demonstrates that their sources were older crustal material (resp. metasediments and metaigneous). On the other hand, Potassic Calc-alkaline Granites (KCG), associated to potassic diorites (vaugnerites) do not contain inherited zircons, and ultimately derive from the vaugnerites. The vaugnerites in turn form by partial melting of a mantle contaminated by the regional crust. Therefore, although they are isotopically similar to the crust, the KCG are net contributors to crustal growth. Thus we conclude that although late-orogenic settings are dominated by crustal melting and recycling, they may be sites of net crustal growth, even though this is not visible from isotopes only. In contrast, arc granitoids are purely or almost purely mantle derived. However, the preservation potential of arcs is much smaller than the preservation of late-orogenic domains, such that at the scale of a whole orogenic belt, late-orogenic magmatism is probably as important as arc magmatism.
Finally, we speculate that the situation may have been similar in the Archaean, or even more skewed towards late-orogenic sites (or similar environments, dominated by melting of an altered mafic protocrust), owing to the hotter mantle and less stable subductions during that period.
•We describe the different granite types in a late collision environment, the Variscan French Massif Central (FMC).•Most granitoids are crustal melts Some granites are mantle-derived, but have isotopic properties controlled by small amounts of crustal recycling to the mantle.•Late-collision sites are significant for crustal growth; although less efficient than subductions, they are better preserved.•Sites similar to late collision may be a realistic alternative to supra-subduction arcs for Archaean crustal growth.
Accurate determination of major elements using limited standard samples is always a big challenge in laser-induced breakdown spectroscopy (LIBS). Based on a simple calculation process, we propose a ...new one-point calibration method called single-sample calibration LIBS (SSC-LIBS) to build the calibration and improve the accuracy of determination of major elements. In this work, several major elements (Fe, Cu, Zn, Ni, Cr, Nb, and Mo) in three sets of matrix-matched certified samples were determined without sample preparation. The results showed that compared with multipoint calibration LIBS (MPC-LIBS), the R2, RMSECV, and ARE of Cu elements were improved from 0.40 to 0.97, 3.55 wt% to 0.76 wt%, and 5.19% to 1.05%, respectively, while the ARSD decreased from 16.22% to 1.15%. Furthermore, the AREs in the concentration ranges of 1–10, 10–20, 30–40, 50–60, 60–70, and 80–100 wt% were 5.16%, 2.55%, 1.75%, 1.69%, 1.05%, and 0.44%, respectively, with almost all less than 5%, as calculated by SSC-LIBS. These results demonstrated that SSC-LIBS can improve the accuracy and stability of detecting major elements using only one standard sample, which can greatly promote the application of LIBS.
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•Accurate determination of major elements is always a big challenge in LIBS.•Single-sample calibration LIBS (SSC-LIBS) was proposed to achieve the accurate determination of major elements.•The method uses only one standard sample for quantitative analysis.•The analytical performance of SSC-LIBS was compared with multi-point calibration LIBS.
We report new experimental data on the composition of magmatic amphiboles synthesised from a variety of granite (sensu lato) bulk compositions at near-solidus temperatures and pressures of ...0.8–10 kbar. The total aluminium content (Al
tot
) of the synthetic calcic amphiboles varies systematically with pressure (
P
), although the relationship is nonlinear at low pressures (<2.5 kbar). At higher pressures, the relationship resembles that of other experimental studies, which suggests of a general relationship between Al
tot
and P that is relatively insensitive to bulk composition. We have developed a new Al-in-hornblende geobarometer that is applicable to granitic rocks with the low-variance mineral assemblage: amphibole + plagioclase (An
15–80
) + biotite + quartz + alkali feldspar + ilmenite/titanite + magnetite + apatite. Amphibole analyses should be taken from the rims of grains, in contact with plagioclase and in apparent textural equilibrium with the rest of the mineral assemblage at temperatures close to the haplogranite solidus (725 ± 75 °C), as determined from amphibole–plagioclase thermometry. Mean amphibole rim compositions that meet these criteria can then be used to calculate
P
(in kbar) from Al
tot
(in atoms per formula unit, apfu) according to the expression:
P
kbar
=
0.5
+
0.331
8
×
Al
tot
+
0.995
4
×
Al
tot
2
This expression recovers equilibration pressures of our calibrant dataset, comprising both new and published experimental and natural data, to within ±16 % relative uncertainty. An uncertainty of 10 % relative for a typical Al
tot
value of 1.5 apfu translates to an uncertainty in pressure estimate of 0.5 kbar, or 15 % relative. Thus the accuracy of the barometer expression is comparable to the precision with which near-solidus amphibole rim composition can be characterised.
Here we describe an internal standard-independent calibration strategy for LA-ICP-MS analysis of anhydrous minerals and glasses. Based on the normalization of the sum of all metal oxides to 100 wt.%, ...the
ablation yield correction factor (AYCF) was used to correct the matrix-dependent absolute amount of materials ablated during each run.
A
Y
C
F
=
100
∑
j
=
1
N
(
c
p
s
sam
j
×
l
j
)
,
l
j
=
C
rm
j
/
c
p
s
rm
j
, where cps
sam
j
and cps
rm
j
are net count rates of analyte element
j of the sample and reference material for calibration,
C
rm
j
is concentration of element
j in the reference material,
N is the number of elements that can be determined by LA-ICP-MS. When multiple reference materials were used for calibration,
l value can be calculated with regression statistics according to the used reference materials.
Applying an AYCF and using the USGS reference glasses BCR-2G, BHVO-2G and BIR-1G as reference materials for external calibration, analyses of MPI-DING reference glasses generally agree with recommended values within 5% for major elements (relative standard deviation (RSD)
=
0.3–3.9% except for P
2O
5,
n
=
11), and 5–10% for trace elements. Analyses of anhydrous silicate minerals (clinopyroxene, orthopyroxene, olivine, plagioclase and garnet) and spinel generally agree with the results of electron microprobe analysis within 0.2–7% for SiO
2, Fe
2O
3, MgO and CaO. RSD are generally <
5% for elements with concentrations >
0.1 wt.%. The results indicate that, by applying an AYCF and using USGS reference glasses as multiple reference materials for calibration, elements of these anhydrous minerals can be precisely analyzed
in situ by LA-ICP-MS without applying internal standardization. The different element fractionations between the NIST glasses and those glasses with natural compositions indicate that NIST SRM 610 is a less than ideal reference material for external calibration of analyses of natural silicates.
Forty years of TTG research Moyen, Jean-François; Martin, Hervé
Lithos,
09/2012, Volume:
148
Journal Article
Peer reviewed
TTGs (tonalite–trondhjemite–granodiorite) are one of the archetypical lithologies of Archaean cratons. Since their original description in the 1970s, they have been the subject of many studies and ...discussions relating to Archaean geology. In this paper, we review the ideas, concepts and arguments brought forward in these 40years, and try to address some open questions — both old and new.
The late 1960s and the 1970s mark the appearance of “grey gneisses” (TTG) in the scientific literature. During this period, most work was focused on the identification and description of this suite, and the recognition that it is a typical Archaean lithology. TTGs were already recognised as generated by melting of mafic rocks. This was corroborated during the next decade, when detailed geochemical TTG studies allowed us to constrain their petrogenesis (melting of garnet-bearing metamafic rocks), and to conclude that they must have been generated by Archaean geodynamic processes distinct from their modern counterparts. However, the geodynamic debate raged for the following 30years, as many distinct tectonic scenarios can be imagined, all resulting in the melting of mafic rocks in the garnet stability field. The 1990s were dominated by experimental petrology work. A wealth of independent studies demonstrated that melting of amphibolites as well as of mafic eclogites can give rise to TTG liquids; whether amphibolitic or eclogitic conditions are more likely is still an ongoing debate. From 1990s onwards, one of the key questions became the comparison with modern adakites. As originally defined these arc lavas are reasonably close equivalents to Archaean TTGs.
Pending issues largely revolve around definitions, as the name TTG has now been applied to most Archaean plutonic rocks, whether sodic or potassic, irrespective of their HREE contents. This leads to a large range of petrogenetic and tectonic scenarios; a fair number of which may well have operated concurrently, but are applicable only to some of the rocks lumped together in the ever-broadening TTG “bin”.
In Earth and planetary sciences, the chemical composition of chondritic meteorites provides an essential reference to constrain the composition and differentiation history of planetary reservoirs. ...Yet, for many trace elements, and in particular for volatile trace elements the composition of chondrites is not well constrained. Here we present new compositional data for carbonaceous chondrites with an emphasis on the origin of the volatile element depletion pattern. Our database includes 25 carbonaceous chondrites from 6 different groups (CI, CM, CR, CV, CO, CK), two ungrouped carbonaceous chondrites and Murchison powder samples heated up to 1000 °C in O2 or Ar gas streams, respectively. A total of 51 major and trace elements were analyzed by sector field inductively coupled plasma mass spectrometry (SF-ICP-MS), using chondrite-matched calibration solutions. Our results confirm that parent body alteration and terrestrial weathering only have minor effects on the bulk chondrite compositions. Thermal metamorphism can lead to the loss of some volatile elements, as best observed in the heating experiments and two thermally overprinted chondrites Y-980115 (CI) and EET 96026 (CV4/5 or CK4/5). The effects of aqueous alteration and terrestrial weathering on the Antarctic samples are difficult to discriminate. Both processes may redistribute fluid mobile elements such as K, Na, Rb, U and the light rare earth elements (LREE) within the meteorite. In hot desert finds, the typical weathering effects are enrichments of Sr, Ba and U and a depletion of S.
In general, moderately volatile elements with 50% condensation temperatures (TC) ranging from 1250 K to 800 K show an increasing depletion, whereas 11 moderately volatile elements with 50% TC between 800 K and 500 K are unfractionated from each other in most samples. Their extent of depletion is characteristic for the different chondrite groups. Because of this well-defined “hockey stick” pattern, we propose to divide the moderately volatile elements into two subgroups, the ‘slope volatile elements’ and the unfractionated ‘plateau volatile elements’ with lower TC. Notably, the abundances of plateau volatile elements exhibit a co-variation with the matrix abundances of the respective host meteorites. Carbonaceous chondrite matrices are likely mixes of: (i) CI-like material and (ii) chondrule-related matrix. Chondrule-related matrix is expected to be depleted in volatile elements relative to CI and likely formed contemporaneously with chondrules, leading to chondrule-matrix complementarity. The addition of CI-like material only changed the absolute elemental concentrations of bulk matrix and bulk chondrite, while refractory and main component element ratios such as Mg/Si remain unaffected. Such a model can also account for the co-existence of low temperature CI-like material and high temperature chondrule and chondrule-related matrix. However, elevated volatile element abundances observed in chondrules still provide a challenge for the model as proposed here.
This work examines the global distribution of Archaean and modern igneous rock's compositions, without relying on preconceptions about the link between rock compositions and tectonic sites (in ...contrast with “geotectonic” diagrams). Rather, Archaean and modern geochemical patterns are interpreted and compared in terms of source and melting conditions.
Mafic rocks on the modern Earth show a clear chemical separation between arc and non-arc rocks. This points to the first order difference between wet (arc) and dry (mid-ocean ridges and hotspots) mantle melting. Dry melts are further separated in depleted (MORB) and enriched (OIB) sources. This three-fold pattern is a clear image of the ridge/subduction/plume system that dominates modern tectonics. In contrast, Archaean mafic and ultramafic rocks are clustered in an intermediate position, between the three main modern types. This suggests that the Archaean mantle had lesser amounts of clearly depleted or enriched portions; that true subductions were rare; and that the distinction between oceanic plateaus and ridges may have been less significant.
Modern granitic rocks dominantly belong to two groups: arc-related granitoids, petrologically connected to arc basalts; and collision granitoids, related to felsic sources. In contrast, the Archaean record is dominated by the TTG suite that derives from an alkali-rich mafic source (i.e. altered basalt). The geochemical diversity of the TTG suite points to a great range of melting depths, from ca. 5 to >20kbar. This reveals the absence of large sedimentary accumulations, again the paucity of modern-like arc situations, and the importance played by reworking of an earlier basaltic shell, in a range of settings (including some proto-subduction mechanisms). Nonetheless, granitoids in each individual region show a progressive transition towards more modern-looking associations of arc-like and peraluminous granites.
Collectively, the geochemical evidence suggests an Archaean Earth with somewhat different tectonic systems. In particular, the familiar distinction between collision, arcs, ridges and hotspots seems to blur in the Archaean. Rather, the large-scale geochemical pattern reveals a long-lived, altered and periodically resurfaced basaltic crust. This protocrust is reworked, through a range of processes occurring at various depths that correspond to a progressive stabilization of burial systems and the establishment of true subductions. A punctuated onset of global plate tectonics is unlikely to have occurred, but rather short-term episodes of proto-subduction in the late Archaean evolved over time into longer-term, more stable style of plate tectonics as mantle temperature decayed.
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•Archaean mafic rocks fill the gap between modern arc, MORB and OIB.•Archaean granitoids reflect a different balance of sources, and no true arc granites.•Archaean tectonic style involved progressively maturing subduction.
The majority of arc magmas are highly evolved due to differentiation within the lithosphere or crust. Some studies have suggested a relationship between crustal thickness and magmatic ...differentiation, but the exact nature of this relationship is unclear. Here, we examine the interplay of crustal thickness and magmatic differentiation using a global geochemical dataset compiled from active volcanic arcs and elevation as a proxy for crustal thickness. With increasing crustal thickness, average arc magma compositions become more silicic (andesitic) and enriched in incompatible elements, indicating that on average, arc magmas in thick crust are more evolved, which can be easily explained by the longer transit and cooling times of magmas traversing thick arc lithosphere and crust. As crustal thickness increases, arc magmas show higher degrees of iron depletion at a given MgO content, indicating that arc magmas saturate earlier in magnetite when traversing thick crust. This suggests that differentiation within thick crust occurs under more oxidizing conditions and that the origin of oxidation is due to intracrustal processes (contamination or recharge) or the role of thick crust in modulating melting degree in the mantle wedge. We also show that although arc magmas are on average more silicic in thick crust, the most silicic magmas (>70 wt.% SiO2) are paradoxically found in thin crust settings, where average compositions are low in silica (basaltic). We suggest that extreme residual magmas, such as those exceeding 70 wt.% SiO2, are preferentially extracted from shallow crustal magma bodies than from deep-seated magma bodies, the latter more commonly found in regions of thick crust. We suggest that this may be because the convective lifespan of crustal magma bodies is limited by conductive cooling through the overlying crustal lid and that magma bodies in thick crust cool more slowly than in thin crust. When the crust is thin, cooling is rapid, preventing residual magmas from being extracted; in the rare case that residual magmas can be extracted, they represent the very last melt fractions, which are highly silicic. When the crust is thick, cooling is slow, so intermediate melt fractions can readily segregate and erupt to the surface, where they cool and crystallize before highly silicic residual melts can be generated.
•Arc lavas tend towards more evolved compositions with increasing crustal thickness.•Lavas become more calc-alkaline, or Fe-depleted, with increasing elevation.•Crustal thickness effects composition by modifying relative melt cooling and segregation times.•Relative cooling and segregation times determine composition of erupted melts.•Intermediate compositions may preferentially form in thickened and reprocessed crust.
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