CaO FeO Research Articles

Thermodynamic Modeling of Iron and Zinc Reduction from B2O3–CaO–Fe2O3–ZnO Melt by СО–СО2 and Н2–Н2О Mixtures

Thermodynamic Modeling of Iron and Zinc Reduction from B2O3–CaO–Fe2O3–ZnO Melt by СО–СО2 and Н2–Н2О Mixtures

Crystal-chemical variations of spinel, clinopyroxene, and plagioclase in MORB basaltic melt induced by continuous cooling

In this study we present the compositional changes of clinopyroxene (cpx), plagioclase (plg), spinel (sp), and glass experimentally solidified from an Icelandic MORB melt. The starting material was cooled at Patm and fO2 of air, in the thermal range of cooling (ΔTc) between 1300 °C (superliquidus) to 800 °C (solidus) with rates (ΔT/Δt) of 1, 7, 60, 180, 1800, and 9000 °C/h. The run products obtained at 1, 7 and 60 °C/h are holocrystalline, whilst between 60 and 180 °C/h plg disappears, and texture of cpx + sp. shifts from faceted to dendritic.As cooling rate increases, we observe that Fe2O3 decreases and Al2O3 increases in sp. and Al2O3 + Fe2O3 increase and CaO + MgO decrease in cpx. These measured variations mirror changes induced by cooling rate in cation (atoms per formula unit, a.p.f.u.) and molecular abundances of these two crystalline phases. Plg composition shows clear linear trends versus cooling rate. The chemistry of sp., cpx and, to a minor extent, plg solidified from this basaltic liquid is thus strictly related to the cooling rate condition and is similar to those observed in previous investigations on alkaline and evolved basaltic systems. In particular, cpx is the only mineral phase profusely present at all the cooling rates, showing the greatest chemical variations in terms of oxides, cations, and components. The intra-crystalline glass (≤ 50 μm from crystal rims) obtained at 180–1800 °C/h shows compositional variations related to the surrounding crystal growth, evidencing strong supersaturation phenomena (such as dendritic texture) due to the establishment of a diffusion-controlled growth regime. Chemical attributes of mineral phases are also quantitatively related with the maximum (Gmax) and average (GCSD) growth rates of sp., cpx, and plg.When compared with the starting melt composition, the chemistry of cpx suggests the attainment of near-equilibrium crystallization conditions at cooling rate ≤ 60 °C/h, whereas disequilibrium effects are found at cooling rate > 60 °C/h. In contrast, plg is in disequilibrium with the initial melt chemistry in all experiments. By using thermometric models, the calculated crystallization of plg takes place at temperatures much lower than those of cpx, when the crystal content is high and the diffusion of cations in the melt is slow due to the higher (residual) melt viscosity. Under such conditions and due to the effect of cooling, the system cannot return to homogeneous concentrations and, consequently, plg more effectively records the disequilibrium partitioning of cations between the growing crystal surface.The data-set reported here captures the entire (superliquidus to solidus) and intrinsic (heterogeneous site-free silicate liquid) solidification behavior from an actual MORB melt from very rapid to extremely sluggish cooling rate. Finally, all analytical relationships found in this work enable careful reconstruction of the solidification conditions of MORB melts, providing novel geo-speedometers for them at high fO2.

Thermodynamic Modeling of Nickel and Iron Reduction from B2O3–CaO–Fe2O3–NiO Melt by СО–СО2 and Н2–Н2О Mixtures

Thermodynamic Modeling of Nickel and Iron Reduction from B2O3–CaO–Fe2O3–NiO Melt by СО–СО2 and Н2–Н2О Mixtures

Synthesis and study of ferri-diopside ceramic pigments

The article reports the mineralogical composition, structural features and changes in color parameters of iron-containing diopside pigments. The source of SiO2 in these pigments was SiO2nH2O with a particle size in the range of 2–7 m, which is much more reactive than conventionally used quartz sand. A series of ceramic pigments on the basis of stoichiometric diopside in the system CaO–Fe2O3–MgO–SiO2 was synthesized via solid-state high temperature sintering at 1000, 1100 and 12000C. The resulting ceramic pigments were examined by powder X-ray diffraction, infrared spectroscopy, electron microscopy, electron paramagnetic resonance and Mössbauer spectroscopy. The color characteristics were measured using spectrophotometry method. It was found that multiphase ceramic pigments were obtained under the synthesis conditions, which contain diopside, wollastonite, cristobalite, akermanite and periclase in various proportions. The synthesized ceramic pigments are brown and beige in color, depending on the content of Fe2O3 additive, firing temperature and phase composition. The synthesized pigments can be used for staining of ceramic glazes.

Syngas production from biomass chemical looping gasification with Fe2O3–CaO oxygen carrier

Syngas production from biomass chemical looping gasification with Fe2O3–CaO oxygen carrier

TiB2 embedded borosilicate coatings with improved wear resistance

ABSTRACT State-of-the-art abrasion resistance of glass ceramic coatings (GCCs) is set by dense, low closed porosity, defect- and micro-stress-free microstructure since GCCs have low fracture toughness. Titanium diboride (TiB2) is a ceramic material with relatively high strength and durability as characterized by the high melting point, hardness, and wear resistance. In this study, the effect of mill additive TiB2 hard ceramic particles (HCP) on GCCs was investigated. The precursor glass ceramic system of SiO2–Na2O–B2O3–CaO–Fe2O3 was selected. The wear resistance of the GCCs was tested simultaneously by Taber Abraser and by a tribometer. B2O3, which is formed by the oxidation of TiB2, fills the pores and the microcracks on the surface, thus reducing the stress areas and increasing the wear resistance. Increasing the TiB2 HCP addition yielded a decrease in mass loss of about 81%, wear rate of about 82% and increase in the coefficient of friction of 15%.

MSW incineration bottom ash (MIBA) as a substitute to conventional materials in geotechnical applications: A characterization study from India and comparison with literature

The study characterizes Delhi municipal solid waste incineration (MSWI) bottom ash (MIBA) collected from three incineration plants over a period of 1.5 years in different seasons (monsoon, winter, summer). Physicochemical characteristics such as chemical composition, visual composition, grain-size distribution, specific gravity and loss on ignition as well as geotechnical characteristics i.e., compaction behaviour, permeability, compressibility and shear strength were ascertained on soil-sized fraction of Delhi MIBA (SSF-DBA) and the material was assessed for suitability of geotechnical reuse. Furthermore, the results were compared with three locally available granular materials i.e., Badarpur sand, Yamuna sand and coal bottom ash. Present work is the first detailed characterization on MIBA from a lower-income nation which also attempts to evaluate the differences (or similarities) with MIBA from higher-income nations through a comprehensive compilation of global experimental data.The study reveals higher SiO2, lower CaO and lower Fe2O3 content of SSF-DBA in comparison to higher-income nations. Additionally, greater percentage of fines and lower compacted unit weight has been observed for Indian MIBA. While permeability and compression index of SSF-DBA are similar to the results reported from other countries, angle of shearing resistance lies in a narrow range of 40-46° in comparison to the wide range of values (24-59°) reported in literature. The influence of different seasons on properties of SSF-DBA was only attributable to MSWI plant’s combustion efficiency as more unburnt organics resulted in lower stiffness and reduced shearing resistance of SSF-DBA. Mechanical behaviour of SSF-DBA compares favourably with other granular materials.

Thermodynamic modeling of iron and zinc reduction from B<sub>2</sub>O<sub>3</sub> ‒ CaO ‒ Fe<sub>2</sub>O<sub>3</sub> ‒ ZnО melt by СО ‒ CO<sub>2</sub> and H<sub>2</sub> ‒ Н<sub>2</sub>О mixtures

The paper presents the thermodynamic modeling results of zinc and iron reduction from B2O3 ‒ CaO ‒ Fe2O3 ‒ ZnО melts by CO ‒ CO2 and H2 ‒ H2O mixtures containing 0 – 60 % CO2 (H2O) at 1273 – 1673 K using a technique describing the reduction of metals from an oxide melt by gas in bubbling processes, under conditions that provide an approximation to real systems. Its originality is equilibrium determination for each individual portion of gas supplied into the working fluid. The reducible metals oxides content in each calculation cycle is taken from the previous data. During the calculations, changes in the content of zinc (СZnO ) and iron (СFe2O3 , СFe3O4 and СFeO ) oxides in the melt and the degree of their reduction were estimated. When using CO or H2 as a reducing agent, this process proceeds in three stages. In the first stage, Fe2O3 is reduced to Fe3O4 and FeO. CFe2O3 values decrease to almost zero, while CFe3O4 and CFeO increase simultaneously. By the end of the stage, СFe3O4 reaches its maximum value. At the second stage, the Fe3O4 → FeO transition occurs, when СFeO values reach its maximum. At these stages, there is a slight increase in the CZnO . At the third stage, the values CFeO and CZnO decrease, and iron and zinc are reduced. An increase in temperature dramatically reduces the gas consumption for zinc reduction by 2 – 3 times, and the replacement of CO with H2 reduces it by less than 20 %. In the presence of oxidizing agents (CO or H2O), only zinc is reduced. The process ends when the final content of zinc oxide in the melt corresponds to the equilibrium with the initial gas composition. The higher the temperature, the less CZnO is. The obtained data are useful for the development of technologies for the selective recovery of metals.

A model involving amphibolite lower crust melting and subsequent melt extraction for leucogranite generation

Abstract In the southern Tibetan Plateau, leucogranites are dominantly distributed in the Himalayan orogenic belt with minor occurrences in the southern Lhasa subterrane. In this paper, we report the first Miocene Anglonggangri leucogranites in the northern Lhasa subterrane. This finding provides important constraints on both leucogranite petrogenesis and the tectono-magmatic evolution of the Lhasa terrane. The Anglonggangri leucogranites include biotite-muscovite granite and slightly younger garnet-muscovite granite and pegmatite. Zircon U-Pb and muscovite 40Ar-39Ar dating of these leucogranites yields Miocene ages of 11.1–10.2 Ma. The biotite-muscovite and garnet-muscovite granites are characterized by high SiO2 (72.3–74.4 wt.%) and Al2O3 contents (14.4–15.4 wt.%) and are peraluminous. The biotite-muscovite granite displays geochemical signatures with high Sr/Y (29.2–81.0) and (La/Yb)N (37.5–98.9) ratios, low Y (4.30–7.22 ppm) and Yb contents (0.26–0.47 ppm), low to moderate initial (87Sr/86Sr)i ratios (0.7085–0.7192), and moderate εNd(t) values (−10.17 to −6.94). Furthermore, they also exhibit radiogenic Pb isotope and variable zircon εHf(t) values (−9.6 to +4.4) with Proterozoic Nd (1.1–1.4 Ga) and Hf model ages (0.8–1.7 Ga). By comparison, the garnet-muscovite granite has lower CaO, MgO, TiO2, and total FeO contents and is enriched in Rb (380–466 ppm) and depleted in Sr (24.1–38.5 ppm) and Ba (30.7–58.6 ppm) and further characterized by a significant rare earth element (REE) tetrad effect and non-charge and radius-controlled (CHARAC) trace element behaviors. The garnet-muscovite granite shows a negative Eu anomaly and positive correlations among Sr and Eu, Sr and Ba, and Th and light rare earth elements (LREEs). Pegmatite comprising Nb-Ta oxides and cassiterite occurs in the garnet-muscovite granite. Geochronological and geochemical characteristics of the Anglonggangri leucogranites indicate that the magma of the biotite-muscovite granite was derived from partial melting of amphibolite lower crust contaminated with Proterozoic-Archean upper crustal materials. The garnet-muscovite granite was generated through melt extraction from the biotite-muscovite granite crystal mush. These results confirm that partial melting of the amphibolite lower crust not only occurred in the southern and central Lhasa subterranes but also in the northern Lhasa subterrane.

Viscosity and Electrical Conductivity of B2O3–CaO–FeO Melts

Viscosity and Electrical Conductivity of B2O3–CaO–FeO Melts

Features of the material composition and possible technologies of pyrite cinders processing

Relevance of research is determined by the need to study for subsequent rational processing of technogenic mineral raw materials – pyrite cinders formed during firing pyritic concentrates for the production of sulfuric acid. Topical issues here are the determination of their chemical and mineral composition, morphology of particles, which predetermine possible technologies of their processing. Purpose of research – study of the material composition of pyrite cinders of the dumps of the Kirovgrad coppersmelting plant, features identification of the composition of different-age dumps. Methods of research. In the selected samples of pyrite cinders, their chemical composition was determined, the morphology of particles was studied by photographing them using the Philips XL-30 electron microscope equipped with an energy dispersive spectrometer (EDS), and possible processing technologies were analyzed. Results. It was found that pyrite cinder of the old dump (no. 1) is characterized by low SO3 contents and low values of losses when firing relative to dump no. 2, which is determined by the oxidation of residual pyrite, as well as CaO and higher Fe2 O3 contents. The study of the morphology of pyrite cinders microparticles showed that they have an irregular shape, globule shape and spherical size from 40 μm to 2 mm. Some known technologies of purple ore processing are considered. Conclusion. The morphology of pyrite cinders particles and their chemical composition were determined as a result of the research. Taking into account the research results and morphostructural characteristics of cinders material, in particular, it is obvious that a number of technologies can be chosen for their complex processing; at the same time this determines further directions of their research, for example, the study of valuable impurity elements in them and their behavior in the process of changing the material of the dumps.

Addition of V2O5 and V2O3 to the CaO–FeO–Fe2O3–MgO–SiO2 database for vanadium distribution and viscosity calculations

Vanadium oxides were added to the existing GTOx database because of its important role in the ferro-titanium metallurgy as well as in petroleum coke gasification. The CaO–FeO–Fe2O3–MgO–SiO2 system is a part of GTOx database and is chosen because of the existence of experimentally determined vanadium distributions between vanadium ferroalloys and metallurgical slags. The CaO–FeO–Fe2O3–MgO–SiO2–V2O3–V2O5 system including all binary and ternary sub-systems was thermodynamically assessed using all available experimental data. Vanadium was introduced into the thermodynamic description of solid solution phases such as MeO, Spinel, Corundum and Ca2SiO4-α using available experimental information. Particular attention was given to the phase Spinel which forms the wide completely miscible solid solution Fe3O4–FeV2O4–MgV2O4–MgFe2O4. The thermodynamic description of the metallic vanadium containing systems was taken from the SGTE alloy database. With the knowledge about the complex behavior of vanadium in slags as well as in liquid metal alloys it is possible to calculate the vanadium distribution ratios (V)/[V] between iron melts and slags in a wide range of temperatures and compositions, corroborating the validity of the model under reducing conditions. The additionally developed viscosity model shows good agreement between the calculated and experimental values in vanadium-containing slags.

Dephosphorisation of hot metal containing moderate amounts of chromium with CaO–FeO x –Cr2O3–CaF2 slag

ABSTRACT With the extensive use of low-grade Cr-containing ore, the dephosphorisation issue of hot metal containing moderate amounts (0.2%-1%) of chromium is gaining more and more attention. To achieve dephosphorisation and chromium retention, a series of experiments on the dephosphorisation of hot metal containing moderate amounts of chromium were carried out at 1723 K. In the experiments, the crystallisation performance of the slag with various CaO/Fe2O3 ratio and Cr2O3 content, as well as the transfer of phosphorus and chromium between slag and hot metal at 1723 K were investigated. The results show that the dephosphorisation process goes through four stages: melting and precipitation, dissolution of refractory, continual oxidation, and phase transition. With the increase of CaO/Fe2O3 ratio, the chromium loss decreases while the dephosphorisation ratio first increases and then decreases. The addition of Cr2O3 promotes the precipitation of Fe(Cr,Al)2O4, which inhibits the dephosphorisation and chromium loss.

A Thermodynamic Model for the Subsolidus Evolution and Melting of Peridotite

Abstract We present a structural update to the thermodynamic model for calculating peridotite phase relations and melt compositions at 0·01 to 60 kbar and from 600 °C to the peridotite liquidus in the system K2O–Na2O–CaO–FeO–MgO–Al2O3–SiO2–TiO2–Fe2O3–Cr2O3 (KNCFMASTOCr), based on the model of Holland et al., 2018 [Melting of Peridotites through to Granites: A Simple Thermodynamic Model in the System KNCFMASHTOCr. Journal of Petrology 59, 881–900]. The new model is better able to predict the phase relations and melting of ultramafic rocks, in particular the abundance of orthopyroxene in the residue and the concentration of silica in the melt. In addition, improvements in modelling Cr-spinels mean that the model is now able to reproduce Cr-content of garnet and spinel above and below the solidus without modification to the knorringite free energy. Model calculations indicate that, for peridotite composition KR4003, the spinel to garnet transition intersects the solidus at 22·1–24·8 kbar and orthopyroxene disappears from the solidus at 29·1 kbar. Below the solidus, the model is able to reproduce the abundances and compositions of phases in experimental studies and natural samples spanning a range of compositions, allowing it to be used for investigating subsolidus equilibration during mantle cooling and pressurisation/decompression. The liquid model provides a good fit to experimental data and is able to replicate the position of the solidus and the composition of both melt and residue at and above the solidus for a range of peridotite compositions. The model may, therefore, be used to investigate fractional mantle melting and basalt generation in modern geodynamic regimes, and also to explore equilibrium mantle melting in the early Earth. The model can also be used to explore liquid and residue compositions for melting of non-pyrolitic mantle, for which there is a paucity of experimental data. We demonstrate the scope of the model using two case studies investigating the subsolidus evolution and melting of a silica-rich cratonic peridotite from the Kaapvaal craton.

The phases of the Moon: Modelling crystallisation of the lunar magma ocean through equilibrium thermodynamics

Despite some 50 years of intense research on samples returned from the Apollo missions and lunar meteorites, along with remote-sensing and Earth-based observations, many questions regarding the formation and evolution of the Moon persist. These include the detailed compositional and density structure of the lunar mantle and the source and petrogenesis of the diverse suite of extrusive and intrusive igneous rocks. There is broad agreement that the primary internal structure of the Moon reflects crystallisation of a lunar magma ocean (LMO), and that an inverted density gradient within the mantle cumulates led to some reorganisation of layers by partial convective overturn. Experimental studies have provided invaluable constraints on crystallisation of the LMO, but are limited by the relatively small number of experiments that can practically be undertaken. Here we use recently-developed thermodynamic models for minerals and melt in the K2O–Na2O–CaO–FeO–MgO–Al2O3–SiO2–TiO2–Cr2O3 system to model crystallisation of a full-moon LMO based on two existing end-member bulk compositions—Taylor Whole-Moon (TWM), and Lunar Primitive Upper Mantle, LPUM—on which many experimental studies have been based. We follow several recent studies in considering equilibrium crystallisation of the first 50 vol.% and fractional crystallisation thereafter. Our results match well with experimental studies, and provide detailed constraints on the major oxide composition, mineralogy and density structure based on the two starting compositions that, while exhibiting some similarities, show important differences. The more fertile TWM composition contains significant quantities of garnet in the deep mantle, whereas the LPUM composition has none. By contrast, prior to any gravitational overturn, the uppermost mantle cumulates for TWM are strongly silica-undersaturated and contain abundant aluminous spinel, whereas those for LPUM are silica-saturated. For both starting compositions, with the exception of TiO2 and Na2O, our modelled compositions of the final dregs of fractionated melt show a reasonable match with existing estimates on the composition of urKREEP. Modelled partial melts of the upper-mantle cumulates at low to moderate melt fractions have major oxide compositions that match well with low- and intermediate-Ti lunar basalts. The correspondence is particularly good for picritic (green) glasses that likely represent melts derived from deeper levels within the upper mantle. The wide spread in TiO2 concentrations in lunar basalts and basaltic glasses is consistent with density-driven reorganisation involving ilmenite. Our simulations provide thermodynamically-robust estimates of the compositional, mineralogical and density structure of the lunar interior that are unprecedented in their detail, and which provide the foundation for several lines of future research addressing the origin and secular evolution of the Moon.

Fluxes for the Slag Melting of Metallic Radioactive Wastes to Return Fissionable Materials to a Nuclear Fuel Cycle

The possibility of flux fabrication for processing metallurgical radioactive wastes by melting the components into a slag agglomerate aimed at returning fissionable materials to a nuclear fuel cycle is shown. The proposed compositions contain no components used in nonferrous and ferrous metallurgy, namely, silica, fluorides, and boron compounds. Fluxes based on the systems Al2O3–MnO, Al2O3–MnO–Na2O, Al2O3–MnO–CaO, and Al2O3–MgO–CaO–Fe2O3 are synthesized by cold crucible induction melting. Their thermochemical properties and phase compositions are studied.

Immobilisation of heavy metals in hazardous waste incineration residue using SiO2–Al2O3–Fe2O3–CaO glass-ceramic

Hazardous waste incineration residue (HWIR) is categorised as hazardous waste due to the presence of heavy metals such as Zn, Cu, and Cr. Based on the abundant components of silica, aluminium oxide, iron oxide, and calcium oxide in a HWIR from an environmental protection corporation in China, a 100% HWIR was used to prepare SiO2–Al2O3–Fe2O3–CaO glass-ceramic samples. The results showed that Zn, Cu, and Cr present in the glass-ceramic samples were effectively immobilised through the melting–sintering process. Among the four parameters of heat treatment, crystallisation temperature played the most significant role. The glass-ceramic that was formed under optimal conditions contained haematite, pseudobrookite, and anorthite, and exhibited a superior compressive strength, volume density, and water absorption of 204.84 MPa, 2.80 g/cm3, and 1.20%, respectively. Compared with the raw HWIR sample, the leaching concentrations of Zn, Cu, and Cr from the prepared glass-ceramic samples decreased significantly, and their immobilisation efficiencies exceeded 99%. Physical encapsulation in the glass-ceramic samples along with ion exchange in the amorphous glassy matrix and iron-rich crystalline phases were the main immobilisation mechanisms of Zn, Cu, and Cr.

Effect of various components on the distribution of phosphorus in CaO–FeO–MgO–SiO2–MnO–TiO2–V2O5–P2O5 slag based on IMCT

ABSTRACT A thermodynamic calculation model of phosphorus distribution ratio between CaO–FeO–MgO–SiO2–MnO–TiO2–V2O5–P2O5 slags and molten metal has been developed based on the ion and molecule coexistence theory (IMCT). The calculated phosphorus distribution ratio shows a good agreement with the measured ones by the data of industrial trial, which proves the reliability of this model. Therefore, the model is used to study the effects of TiO2, V2O5, slag basicity, FeO, MgO and MnO on phosphorus distribution. The results illustrate that the effects on phosphorus distribution from V2O5 and TiO2 are non-negligible and they are almost the same, slag basicity and FeO have the most significant effects on phosphorus distribution, while MgO and MnO have the least.

Effect of Temperature on Dephosphorization of Hot Metal in Double‐Slag Converter Steelmaking Process by High‐Temperature Laboratorial Experiments

The influence of temperature on the dephosphorization of hot metal at the low temperature range of 1300–1450 °C with the slag of the low basicity (CaO/SiO2) of about 1.8 is investigated using high‐temperature laboratorial experiments. The results show that with increasing temperature, the phosphorus contents in hot metal decrease first and then increase. The phosphorus can be removed from the initial content of 0.246% to the final content of 0.066% with the highest dephosphorization ratio of 73.2% at 1375 °C. The P2O5 content in slag increases first and then decreases. When the actual dephosphorization temperature is 1350–1375 °C being about 60 °C higher than the conversion temperature of decarbonization and dephosphorization, a very high LP of about 25 can be obtained. Moreover, the dephosphorization slag at the temperature from 1300 to 1400 °C is mainly comprised of three mineralogical phases: phosphorus‐rich, metal oxide (RO), and CaO–FeO–SiO2 phases. When the temperature is increased to 1425 and 1450 °C, the dephosphorization slag is mainly comprised of liquid slag containing Ca3(PO4)2 and RO phase.

The fate of calcareous pelites in collisional orogens

AbstractAlthough calcareous pelites are important constituents of sediments involved in orogenic processes, their prograde metamorphism is significantly less studied than that of pure pelites with negligible amounts of modal calcite. This paper presents mineral equilibria modelling in the system MnO–Na2O–K2O–CaO–FeO–MgO–Al2O3–SiO2–TiO2–H2O–CO2, with the aim of constraining the prograde evolution of calcareous pelites in collisional orogenic settings. A suite of model bulk‐rock compositions is used to investigate the influence of different proportions of calcite in the protolith on (a) the equilibrium assemblages at different pressure, temperature and fluid composition (P–T–X(CO2)) conditions; (b) the melt fertility and (c) the fluid evolution and the main decarbonation reactions occurring during prograde metamorphism of calcareous pelites. In spite of being purely theoretical, the reliability of the modelling is tested by comparing the predicted assemblages with those observed in a wide set of natural samples from the Himalayan metamorphic core. Comparison between the predicted and the modelled assemblages demonstrates that even a small amount of calcite in the calcareous pelitic protoliths has a strong influence on the final mineral assemblages and compositions, with potential effects on their melt productivity. Specifically, it appears that up to ~800°C, the melt productivity of calcic metapelites remains low, and melt production occurs gradationally because it is mostly controlled by continuous biotite dehydration melting reactions, rather than by muscovite breakdown. Moreover, the study demonstrates that calcareous pelites could be non‐negligible CO2‐source rocks in orogenic settings, and that in such contexts, an internal buffered behaviour is likely for most of them.