Simultaneous removal of As(III) and Cu(II) by biochar modified siderite: The key roles of ROS and mineral conversion.

Abstract(Mg, Fe)CO3 is an important deep carbon carrier and plays a vital role in our understanding of lower‐mantle carbon reservoirs. The electrical conductivity (EC) of FeCO3 was measured at 126−2000 K up to 83 GPa in diamond‐anvil cells using a standard four‐probe van der Pauw method. Moreover, the EC of FeCO3 increases by ∼6 orders of magnitude from 300 to 1500 K at 10−20 GPa, indicating a strong effect of high temperature. The EC of Fe0.65Mg0.35CO3 was measured up to 60 GPa at 300 K, the EC values of (Mg, Fe)CO3 are proportional to iron content and increase by 2–3 orders of magnitude at 300 K across the spin crossover. The EC values of (Mg, Fe)CO3 and FeCO3 + Fe3O4 ± C mixtures surpass that of bridgmanite, ferropericlase and davemaoite by ∼1–4 orders of magnitude at depths of 800–2,000 km. This result sheds insights into the genesis of local geomagnetic heterogeneities in the mid‐lower mantle.

Abstract The high‐pressure behavior of deep carbonate dictates the state and dynamics of oxidized carbon in the Earth's mantle, playing a vital role in the global carbon cycle and potentially influencing long‐term climate change. Optical absorption and Raman spectroscopic measurements were carried out on two natural carbonate samples in diamond‐anvil cells up to 60 GPa. Mg‐substitution in high‐spin siderite FeCO3 increases the crystal field absorption band position by approximately 1000 cm–1 but such an effect is marginal at >40 GPa when entering the low‐spin state. The crystal field absorption band of dolomite cannot be recognized upon compression to 45.8 GPa at room temperature but, in contrast, the high‐pressure polymorph of dolomite exhibits a strong absorption band at frequencies higher than (Mg,Fe)CO3 in the low‐spin state by 2000–2500 cm–1. Additionally, these carbonate minerals show more complicated features for the absorption edge, decreasing with pressure and undergoing a dramatic change through the spin crossover. The optical and vibrational properties of carbonate minerals are highly correlated with iron content and spin transition, indicating that iron is preferentially partitioned into low‐spin carbonates. These results shed new light on how carbonate minerals evolve in the mantle, which is crucial to decode the deep carbon cycle.

During grinding with forged steel media, sulphides such as pyrite undergo surface changes due to the occurrence of oxidation–reduction reactions, which affect its depression during the concentration process. For this reason, in this work, the surface modification of pyrite during grinding was studied; FTIR, ICP-OES, XRD and SEM-EDS were used for the materials’ characterisation. It was found that the pyrite obtained during grinding showed magnetic susceptibility due to the absorption and superficial formation of magnetite Fe3O4, Fe–O bonds identified by FTIR at 598 cm−1, and of other species, such as oxy-hydroxy-sulphates at 696 cm−1 and goethite α-FeOOH at 875 cm−1. This caused the reversal of the zeta potential magnitude (ζ) from positive to negative at pH 8.3 and 30 min of grinding. The ζ of the pyrite throughout the studied pH ranges was, overall, positive, i.e., +5 mV. However, at pH 10.5 and 15 min of grinding, the ζ turned negative. This was associated with the formation of Fe–CO3 (−2) bonds in the siderite, which were identified with the absorption bands corresponding to 756, 1448 and 1493 cm−1.

Carbonate minerals as a dominant carbon host can be transported to the Earth’s deep interior via subduction of the oceanic lithosphere, and their physicochemical behavior potentially has a significant influence on the compositional heterogeneity and physical properties in the deep mantle. In this study, we measured the electrical conductivity of natural siderite at 1–3 GPa and 100–700°C using a complex impedance analyzer in a large volume multi-anvil high-pressure apparatus. A sharp increase in conductivity was observed at ∼400°C under various pressures, and subsequently, the electrical conductivity keeps anomalously high values in the whole temperature range owing to a small quantity of interconnected highly conductive phases (graphite and magnetite) produced from the low degree decarbonation of siderite. The change in electrical conductivity and activation enthalpy suggest that the conduction mechanisms before and after low degree decarbonation of siderite are the small polaron (electron hopping in Fe2+–Fe3+) and highly conductive phases, respectively. Our results indicate the incipient decarbonation temperatures at 1–3 GPa are considerably lower than the decomposition boundary of siderite determined by phase equilibrium experiments, implying the initial decarbonation reaction of Fe-bearing carbonates in the subducting oceanic crust occurs at a shallower depth. The 30 vol.% of siderite is required to enhance the electrical conductivity of (Mg, Fe)CO3 solid solutions. Magnetite and graphite generated from the decarbonation reaction of the siderite component of Fe-bearing carbonate make a significant contribution to the high conductivity anomaly observed in the slab-mantle wedge interface.

Ferromagnesite (Mg,Fe)CO3, also referred to as magnesiosiderite at high iron concentration, is a solid solution of magnesite (MgCO3) and siderite (FeCO3). Ferromagnesite is believed to enter the Earth's lower mantle via subduction and is considered a major carbon carrier in the Earth's lower mantle, playing a key role in the Earth's deep carbon cycle. Experiments have shown that ferromagnesite undergoes a pressure-induced spin crossover, accompanied by volume and elastic anomalies, in the lower-mantle pressure range. In this work, we investigate thermal properties of (Mg,Fe)CO3 using first-principles calculations. We show that nearly all thermal properties of ferromagnesite are drastically altered by iron spin crossover, including anomalous reduction of volume, anomalous softening of bulk modulus, and anomalous increases of thermal expansion, heat capacity, and Guneisen parameter. Remarkably, the anomaly of heat capacity remains prominent (up to 40%) at high temperature without smearing out, which suggests that iron spin crossover may significantly affect the thermal properties of subducting slabs and the Earth's deep carbon cycle.

The decomposition of Mn-substituted siderite during coaling enhanced the transformation of NO before catalyst bed: Effect of Mn substitution

Magnetic and optical properties of synthesized ZnO–ZnFe2O4 nanocomposites via calcined Zn–Fe layered double hydroxide

Abstract —Experimental modeling of decarbonation reactions with the formation of Mg,Fe-garnets and CO2 fluid during mantle–crust interactions was carried out in a wide range of the upper-mantle pressures and temperatures. Experimental studies were performed in the MgCO3–Al2O3–SiO2 and (Mg,Fe)CO3–Al2O3–SiO2 systems in the pressure range 3.0–7.5 GPa and temperature range 950–1450 °C (t = 10– 60 h), using a multianvil high-pressure apparatus of the “split-sphere” type (BARS). Experiments were carried out with a specially designed high-pressure buffered cell with a hematite container that prevents the diffusion of hydrogen into a Pt-capsule with a sample. It has been experimentally established that in the MgCO3–Al2O3–SiO2 system decarbonation occurs by the schematic reaction MgCO3 + SiO2 + Al2O3 → Mg3Al2Si3O12 + CO2 at 1100 ± 20 °C (3.0 GPa), 1150 ± 20 °C (6.3 GPa), and 1400 ± 20 °C (7.5 GPa) and in the (Mg,Fe)CO3–Al2O3– SiO2 system, by the reaction (Mg,Fe)CO3 + SiO2 + Al2O3 → (Mg,Fe)3Al2Si3O12 + CO2 at 1000 ± 20 °C (3.0 GPa), 1150 ± 20 °C (6.3 GPa), and 1400 ± 20 °C (7.5 GPa). Based on Raman spectroscopic characterization of the synthesized garnets, the position of the main modes R, υ2, and υ1 in the pyrope has been determined to be 364, 562, and 924–925 cm-1, respectively, and that in pyrope-almandine, 350–351, 556–558, and 918–919 cm-1. The effectiveness of the hematite container was demonstrated by means of mass spectrometry analysis. It has been found that the fluid composition corresponded to pure CO2 in all experiments. The P,T-positions of decarbonation curves leading to the formation of a CO2 fluid in assemblage with pyrope and pyrope-almandine have been experimentally reconstructed and compared with the previous calculation and experimental data. It has been established that the experimentally reproduced reaction lines with the formation of pyrope + CO2 or pyrope-almandine + CO2 assemblages are shifted to lower temperatures by 50–150 °C relative to the calculated ones. When considering the obtained results with regard to the stability of natural carbonates of various compositions in subduction settings, it has been found that at depths of ~90–190 km Mg,Fe-carbonates react with oxides in the temperature range 1000–1250 °C, and at depths of ~225 km, at 1400 °C.

Mössbauer and EPR study of ferrihydrite and siderite biotransformations by a syntrophic culture of alkaliphilic bacteria

Pyroxene control of H2 production and carbon storage during water-peridotite-CO2 hydrothermal reactions

Acceleration of hydrogen production during water-olivine-CO2 reactions via high-temperature-facilitated Fe(II) release

Enhanced hydrogen production with carbon storage by olivine alteration in CO2-rich hydrothermal environments

Adsorption of atoms of Co, Mn, Fe on the calcite surface in ultra-high vacuum and the interaction of the formed adsorption systems with the water have been studied by means of X-ray photoelectron spectroscopy. It is shown that Mn and Fe form solid solutions CaCO3/Mn(Fe)CO3 on the calcite surface, whereas Co preferentially forms CoO and Co3O4. Upon interaction with water the surface compounds formed by Mn and Fe do not undergo notable changes, unlike the Co oxides which partially transform into soluble hydroxylated complexes.

Рассмотрена карбонатная жильная минерализация в породах Сафьяновского медно-колчеданного месторождения (Средний Урал), представленная кальцитом, железистыми разностями магнезита и доломита, сидеритом, арагонитом. Кальцитовая, доломитовая и рассеянная сидеритовая минерализация сосредоточена в кварц-плагиоклаз-карбонат-хлоритовых породах надрудной зоны. Сидерит-магнезитовая прожилковая минерализация развита в околорудных метасоматитах на контакте с массивной медно-цинковой рудой в ассоциации с баритом, каолинитом и гидрослюдой. Рассеянная и прожилковая магнезитовая минерализация встречается в кварц-каолинит-серицит-хлоритовых подрудных метасоматитах. Жильный арагонит обнаружен в околорудных метасоматитах на глубине 240 м, новообразованный кальцит – в гидротермально-измененных известняках на глубине 275 м. Карбонаты отличаются по содержанию и распределению РЗЭ, С-О изотопии, по интенсивности ЭПР спектра Mn2+ в карбонатах. В целом зональность распределения карбонатов в околорудных породах Сафьяновского месторождения соответствует зональности уральского типа, отмеченной на некоторых колчеданных месторождениях Южного Урала, в околорудной части карбонаты представлены более железистыми разностями по сравненю с надрудной частью. Исследования показали, что карбонатная минерализация на Сафьяновском месторождении является естественным продолжением пострудных преобразований вмещающих пород и их тектонического разрушения при релаксации внутренних напряжений.

Adsorption of Co, Mn, and Fe atoms on the surface of calcite in ultrahigh vacuum and the interaction of the generated adsorption systems with water were studied by X-ray photoelectron spectroscopy. It is demonstrated that Mn and Fe atoms form CaCO3/Mn(Fe)CO3 solid solutions on calcite surface, whereas the dominant compounds of adsorbed Co atoms are CoО and Co3О4. When interacting with water, the Mn and Fe surface compounds are not appreciably modified, whereas the Co compounds are partly transformed into soluble hydroxylated complexes.

Perovskite-type oxides of LaFe(1+x)O(3+δ) (x = 0.0, 0.2, 0.5 and 0.7) were synthesized by citrate sol–gel method to ensure the formation of nanosized perovskites. The physicochemical properties of these LaFe(1+x)O(3+δ) materials were characterized by thermal gravimetric/differential analyses, Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron and transmission electron microscopies, ultraviolet-visible spectroscopy, Brunauer Emmett Teller nitrogen absorption, electrical conductivity measurements and magnetic studies. Catalytic performances of the prepared materials were evaluated for the carbon monoxide oxidation. Trace of FeCO3 and Fe2O3 phases were detected over the perovskites of LaFe(1+x)O(3+δ) with excess iron (x > 0) using the XRD and FT-IR studies. The SEM results demonstrate the formation of non-spongy particles. The magnetic measurements show a charge ordering transition at ~230 K for LaFe1.2O(3+δ) perovskite. The weak long range charge ordering of Fe2+/Fe3+ destroys over an increase in the content of the phases other than LaFeO3 perovskite. The best σox/σRed and the lowest Ec is accounted for the more suitable path for catching and giving of the gas phase oxygen over LaFe1.2O(3+δ) nanoperovskite; meaning most favorable redox properties. The light off temperature of the CO oxidation in terms of reducibility studies is decreased about 70°C over crystalline LaFe1.2O(3+δ) catalyst.

In this paper, a novel quadri-metal layered double hydroxide Mg–Al–Cu–Fe–CO3 (LDH) was synthesized by a co-precipitation method. Part of the synthesized LDH was subjected to calcination (CLDH) using thermal treatment under a temperature of $$550\,^{\circ }\hbox {C}$$ . The application of the synthesized material (LDH) as well as its derived product (CLDH) as adsorbents for the anionic dye Acid Red 66 (AR66) was investigated. The characterization of LDH and CLDH was done using several methods, such as X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analyses, $$\hbox {N}_{2}$$ adsorption desorption isotherms (BET), scanning electron microscopy, X-ray fluorescence spectrometry analysis XRF and zeta potential measurement. In addition to the kinetic and the equilibrium studies, the influences of different factors, the initial pH, the mass of adsorbent, the contact time, the ionic strength and the temperature were explored. The results revealed that the novel layered double hydroxide Mg–Cu–Al–Fe-LDH was an efficient adsorbent for AR66. The thermal treatment of LDH increased significantly the capacity of adsorption of anionic dye, from 125 to 920 mg g $$^{-1}$$ in natural conditions (natural pH, room temperature), due to the increase in pore size and also the memory effect of the CLDH after adsorption. The capacity of adsorption was susceptible to a further increase in acidic conditions or by addition of salts suggesting a positive impact of acid medium and competing anions on the adsorption mechanism. Kinetic data were accurately fitted by a pseudo-second-order model. Adsorption isotherms were well described by the Sips and Toth models. The thermodynamic study revealed that the adsorption of AR66 on both LDH and CLDH was spontaneous and endothermic.

Simultaneous ex-situ CO2 mineral sequestration and hydrogen production from olivine-bearing mine tailings

Geologic carbon storage (GCS) involves capture and purification of CO2 at industrial emission sources, compression into a supercritical state, and subsequent injection into geologic formations. This process reverses the flow of carbon to the atmosphere with the intention of returning the carbon to long-term geologic storage. Models suggest that most of the injected CO2 will be "trapped" in the subsurface by physical means, but the most risk-free and permanent form of carbon storage is as carbonate minerals (Ca,Mg,Fe)CO3. The transformation of CO2 to carbonate minerals requires supply of the necessary divalent cations by dissolution of silicate minerals. Available data suggest that rates of transformation are highly uncertain and difficult to predict by standard approaches. Here we show that the chemical kinetic observations and experimental results, when they can be reduced to a single cation-release time scale that describes the fractional rate at which cations are released to solution by mineral dissolution, show sufficiently systematic behavior as a function of pH, fluid flow rate, and time that the rates of mineralization can be estimated with reasonable certainty. The rate of mineralization depends on both the abundance (determined by the reservoir rock mineralogy) and the rate at which cations are released from silicate minerals by dissolution into pore fluid that has been acidified with dissolved CO2. Laboratory-measured rates and field observations give values spanning 8 to 10 orders of magnitude, but when they are evaluated in the context of a reservoir-scale reactive transport simulation, this range becomes much smaller. The reservoir scale simulations provide limits on the applicable conditions under which silicate mineral dissolution and subsequent carbonate mineral precipitation are likely to occur (pH 4.5 to 6, fluid flow velocity less than 5 m/year, and 50-100 years or more after the start of injection). These constraints lead to estimates of 200 to 2000 years for conversion of 60-90% of injected CO2 when the reservoir rock has a sufficient volume fraction of divalent cation-bearing silicate minerals and confirms that when reservoir rock mineralogy is not favorable the fraction of CO2 converted to carbonate minerals is minimal over 104 years. A sufficient amount of reactive minerals is typically about 20% by volume. Our approach may allow for rapid evaluation of mineralization potential of subsurface storage reservoirs and illustrates how reservoir scale modeling can be integrated with other observations to address key issues relating to engineering of geologic systems.