Carbonate Ores Research Articles

A Step towards CO2 Sequestration through Mineral Carbonation: Using Ammonium-Based Lixiviants for the Dissolution of Calcium from Iron-Making Blast Furnace Slag

In recent years, technical processes for the sequestration of CO2 through industrial waste mineral carbonation have been explored and developed. There is a large portfolio of carbon capture, utilisation, and storage (CCUS) techniques that have been employed in laboratories and at pilot scale. These include geological storage, ocean storage, and mineralisation by carbonate ores. In view of this, the main purpose of this research was to investigate and explore chemical variables, particularly ammonium salts as lixiviants for calcium mineral extraction from iron-making slag. The slag in use was acquired from a steel mill in the Vaal Triangle Region in Gauteng, South Africa. The experimental test work was conducted using different ammonium lixiviants, namely, NH4NO3, NH4Cl, and CH3COONH4, to understand the influence of anion type as well as possible differences in mechanisms of interactions. Lixiviant concentration as well as reaction time were varied in this research study. The three selected ammonium-based lixiviants showed different extents of calcium extraction owing to differences in the anion groups. NH4NO3, NH4Cl, and CH3COONH4 were found to be capable of dissolving 50% to 80% of the calcium from the selected slag for different molar concentrations. Anion type and leaching time also had significant influences on the leaching of calcium from the slag. Rapid pH degradation resulted in better calcium extraction capabilities. This work has shown that the selected ammonium salts have the potential to be lixiviants for calcium dissolution from iron-making blast furnace slags. These lixiviants would, therefore, be important to consider during calcium mineral carbonation for CO2 sequestration.

Anatomy and genesis of the world’s largest carbonate-hosted Zn-Pb deposit: New insights from ore characteristics, Zn-Pb-C-O isotopes, and trace element constraints of the Huoshaoyun deposit, Karakorum Range, Xinjiang

The Huoshaoyun deposit in the Karakorum area of NW China is the world’s largest zinc-lead carbonate ore deposit. Here we investigate the genesis of the mineralization based on multiproxy investigations. The deposit contains zinc-lead carbonate and sulfide minerals, with smithsonite (Smt), cerussite (Cer), and sulfides accounting for 85%, 10%, and 5% of the total lead and zinc resources, respectively. Three ore-forming stages, involving Smt, Cer, and sulfides ores were summarized. The Smt mineralization is characterized by veined, massive, and stratified Smt forming horizontal sedimentary layered ore and vertical feeder veins similar to the SEDEX-type deposits. The sulfide and Cer veins display typical hydrothermal characteristics and are superimposed on the massive Smt ores. The Smt ores show high Li, Be, Cr, Y, Ba, Nd, Yb, and Zr contents, whereas the Cer veins have extremely high Sr contents (up to 3814–9174 ppm) and low Zr contents (less than 0.01 ppm). Galena and sphalerite show higher Cd concentrations compared to Smt and Cer ores.The Smt ores differ with different spatial locations, with Smt ores formed at the vent have δ66Zn values of +0.15‰ to +0.21‰, the massive Smt formed close to the vent show a value of +0.13‰, and those formed away from the vent show a value of 0.05‰, all values being close to 0. The sulfides have δ66Zn values of −0.09‰ to +0.04‰. The C-O isotopes of Smt ores are similar to both altered and unaltered host limestone, suggesting that the limestone was a potential source for carbon and oxygen. Quartz with veined Smt shows magmatic signatures with δ18OVSMOW of +1.14‰ to +2.23‰, high Pb (115–401 ppm) and Zn concentrations (390–997 ppm), whereas quartz associated with sulfide has meteoric fluid signature with the lowest δ18OVSMOW (−14‰ to −10.7‰), low Pb (11.6–49.0 ppm) and Zn (18.1–72.8 ppm) concentrations. The temperature of equilibration computed based on oxygen isotope fractionation between Smt and coeval quartz indicate a dual source with that of quartz derived from an aqueous fluid, whereas the source for Smt might involve CO2 or HCO3−.We trace multiple metallogenic stages for this deposit including exhalation, hydrothermal deposition, and fault-controlled sulfide vein formation. The largest orebody (III-1) preserves a 16 Mt reserve of Zn and was formed by crust-mantle interaction at ca. 195 Ma in the early development of the Linjitang post-arc rift system. Fluid convection, zinc enrichment driven by granitic magma, volcanic activity, and karst alteration induced by acid rain in a lagoonal environment promoted ore enrichment.

Genesis of the sediment-hosted Qukuleke Au deposit in the East Kunlun Orogenic Belt, NW China: Constraints from geology, apatite U–Pb age, and C–O–S–Pb isotopes

Genetic classification of sediment-hosted Au deposits is often disputed in many orogenic belts around the world. The marine sediment-hosted Qukuleke Au deposit (>5 t Au) is an example of this, which has been attributed to orogenic or intrusion-related type. This paper addresses its metallogeny through detailed geologic and petrographic studies, together with apatite U–Pb dating and C–O–S–Pb isotopes.The hydrothermal paragenesis at Qukuleke is divided into three stages (I to III): Stage I (pre-ore) sheeted quartz veins; Stage II (main ore) pervasive sericite ± carbonate ± apatite ± pyrite ± arsenopyrite alteration associated with quartz–calcite ± stibnite veins; Stage III (post-ore) barren calcite veins. LA-ICP–MS hydrothermal apatite U–Pb dating on Stage II disseminated Au ore yielded 208.1 ± 6.5 Ma, coeval with the Late Triassic post-collisional intrusions from the periphery of Qukuleke deposit. Carbon–oxygen isotopes of Au–Sb ore-related hydrothermal calcite show that the hydrothermal fluids were derived from the marine carbonate ore host with considerable magmatic input. Lead–sulfur isotopes of the Au–Sb ore-related are consistent with those of coeval intrusions around the deposit, but different from those of the local sedimentary strata. Our age and geochemical data suggest the presence of a magma source that supplied the hydrothermal fluids, sulfur and metals for the mineralization. Combining the low sulfide content and the Au–As–W–Sb–Mo assemblage characteristics, the Qukuleke is best classified as a sediment-hosted intrusion-related Au deposit. Considering also the discovery of the large coeval Qukukekedong Au deposit nearby, we propose that Late Triassic intrusion-related Au system is a high-potential exploration target in the western EKOB.

Phosphate-associated sulfate in Lingula shells represents a potential archive for seawater sulfate composition

The marine sulfur cycle is highly sensitive to redox environments at the Earth's surface. Fluctuations in atmospheric pO2 level or marine redox environments are commonly associated with changes in seawater sulfate concentration, sulfate sulfur (S) and oxygen (O) isotopes. Thus, the marine S cycle through the Earth's ancient past provides a first-order constraint on the redox evolution of the Earth's surface. Reconstructions of the marine S cycle have been approached through analyses of various sulfate-bearing geological materials, such as sedimentary barite, evaporitic sulfate (e.g., gypsum), carbonate associated sulfate (CAS), and phosphate-associated sulfate (PAS) in phosphatic ores. These geological materials have their own pros and cons. In this study, we focus on PAS in Lingula brachiopods, which possess phosphatic shells and have a long evolutionary history since Cambrian times. Biogenic phosphate typically has a higher sulfate concentration than carbonate and phosphate ores, and is less vulnerable to diagenetic alteration. Here, we analyzed modern Lingula shells from the South China Sea and fossil Lingula shells collected from the Late Devonian Xiejingsi Formation of South China. Living and fossil Lingula shells have similar P/S ratios (PO43−/SO42−) of ∼76, and S and O isotopes of PAS (δ34SPAS and δ18OPAS) in each group show limited variations. For living Lingula shells, the mean values of δ34SPAS and δ18OPAS are +15.0 ± 1.5‰ and + 9.8 ± 0.4‰, respectively, which are ∼6‰ lower and comparable to those of modern seawater sulfate compositions (δ34SSW and δ18OSW-SO4), probably due to vital effects. For fossil Lingula shells, δ18OPAS (14.1 ± 0.9‰) is identical to coeval evaporite. The range of δ34SPAS is encompassed by the values of both coeval evaporite and CAS, but the mean value of δ34SPAS (29.5 ± 0.9‰) is higher. Thus, fossil Lingula shells show a good potential for reconstructing δ34SSW and δ18OSW-SO4 values.

Synergistic denitrification and Mn cycle driven by sulfur autotrophy significantly enhanced nitrogen removal

Due to the low C/N and high NO3−-N content in tailwater of wastewater treatment plants, the need for further denitrification treatment attracted wide attention. To achieve deep denitrification of tailwater with low C/N and high NO3−-N, a novel sulfur-manganese carbonate ore denitrification (SMCD) biological reactor was constructed. The denitrification performance of SMCD reactor was significantly higher than that of sulfur denitrification and manganese carbonate ore denitrification reactors. Across the study, the removal efficiencies of TN and NO3−-N were above 90%, and without NO2−-N accumulation in the SMCD reactor. Quantitative results of functional genes showed that SMCD reactor were conducive to realize complete denitrification. Besides, manganese autotrophic denitrification (MAD) process occurred in the SMCD reactor. By analyzing the nitrogen as well as SO42- and Mn(Ⅱ) concentrations along the height, it was found that the conversion between Mn(II) and Mn(IV) was stable during Stage Ⅲ (C/N=1). The microbiota in the SMCD reactor was distinctly different from that in the controls. Thiobacillus, Thermomonas, and an unclassified member in family cvE6 were the dominant members of SMCD reactor. Besides, Thermomonas, Dokdonella, and Simplicispira were identified as potential Mn oxidizers. The SMCD reactor exhibited a significant synergistic denitrification effect by coupling sulfur autotrophic denitrification and MAD process, which provided an effective solution for the deep denitrification of low C/N tailwater.

Dynamic deep-water oxygenation of marginal seas in the aftermath of the Sturtian Snowball Earth: Insights from redox-hydrological reconstructions of the Nanhua basin (South China)

The Cryogenian interglacial period, separated by the Sturtian and Marinoan icehouses, witnessed early radiations of eukaryotic algae and the first emergence of putative metazoans. To date, the detailed oceanic redox state in the aftermath of the Sturtian glaciation remains obscure, limiting our understanding of the causal linkage, if any, between environmental changes and biological evolution during this critical interval. In order to gain further insights into the marine redox framework following the Sturtian Snowball glaciation, here we present high-resolution geochemical results of an integrated study on the basal Datangpo Formation from the Daotuo area (South China), and also provide a systematically compiled dataset of counterparts in other profiles from the Nanhua Basin. The basal Datangpo Formation is characterized by black shales intercalated with Mn carbonate ore layers in the lower (Member I), and only black shales in the upper (Member II). The Member I black shales have relatively high abundances of Mo and Re, and display a MoEF-UEF pattern typical of Mn-oxide shuttle, indicating that the Nanhua basin was redox-stratified with the oxic-euxinic chemocline fluctuating above the deep-basin floor. Multiple lines of evidence, including positive PAAS-normalized Ce anomalies, negative δ13Ccarb values, and marked authigenic enrichments of manganophile elements (Co, Ni, Cu), imply that the Mn carbonate ore beds were generated through the diagenetic transformation of Mn oxides originally deposited under oxic bottom waters. Therefore, these Mn ore layers hosted by the Member I black shales reflect episodic benthic oxygenation. By contrast, the Nanhua basin was more stagnant during deposition of Member II black shales, as supported by their rather low Mo/TOC ratios, as well as the relatively lower abundances of Mo and Re compared to Member I black shales. Moreover, the Mo isotope data of the basal Datangpo Formation indicate that the global ocean remained pervasively anoxic. Taken together, this study reveals a more holistic redox landscape in the wake of the Sturtian Snowball Earth—that is, extensive anoxia in the global ocean with episodic deep-water oxygenation in the marginal seas such as the Nanhua Basin. These epicratonic seas with dynamic redox variations might promote the ecological revolution during the interglacial period immediately after the Sturtian glaciation.

Understanding adsorption mechanism of a novel “Y” structure carboxylate-hydroxamate surfactant towards rhodochrosite

High consumption and low selectivity of traditional collectors limit the efficient flotation recovery of rhodochrosite particles from finely disseminated complex ores. Herein, a novel “Y” structure multi-functional surfactant, 2-decanoylamino-4-hydroxycarbamoyl-butyric acid (DHBA) was developed for flotation recovery of rhodochrosite. The micro-flotation results showed that DHBA exhibited an excellent collecting ability for rhodochrosite than common collector octanohydroxamic acid (OHA) (the recovery reached 85.7% for 7 × 10–5 mol·L–1 DHBA, while only 27.9% for OHA). Meanwhile, DHBA can selectively separated rhodochrosite from quartz at neutral pH and low collector dosages. The experimental analysis combined with the density functional theory calculations revealed that DHBA was lattice matched to the rhodochrosite via the oxygen atoms of carboxyl and hydroxamate groups chelating with two Mn atoms, conferring strong adsorption affinity of DHBA. In addition, intermolecular hydrogen bonds coexist through the amide groups, promoting the collectors' self-assembly on the rhodochrosite surface, improving surface hydrophobicity. This research provides a feasible collector design protocol for the separation and enrichment of manganese carbonate ore.

Geochemistry of Cryogenian Datangpo manganese deposits in the southeastern Yangtze Platform of South China: implications for the origin of metallogenesis and depositional environment

ABSTRACT Sedimentary manganese (Mn) deposits in the southeastern Yangtze Platform of China have been newly discovered with considerable potential for resource exploration. Such deposits formed due to dynamic changes in the global environment, including the break-up of the supercontinent Rodinia, Snowball Earth glaciation, and the Neoproterozoic Oxygenation Event. The Mn-bearing sequences are hosted in the basal Datangpo Formation and are interbedded with black carbonaceous shale in a series of graben sub-basins in the Nanhua Rift Basin. We investigated the origin of these Mn deposits by analysing the major and trace elements, total organic carbon, and stable carbon and oxygen isotopes. Positive Eu anomalies were observed, indicating that the Mn was derived from a hydrothermal system. Redox-related elements, including Ce, Mo, U, V, S, and P, indicated that the depositional environment of the Mn layers was oxidative and that Mn2+ was initially oxidized to Mn oxides. However, the host rock (i.e. black carbonaceous shale) was deposited under dysoxic – anoxic and even sulfidic water conditions. The alternating distribution of Mn ore and host rock suggested alternating redox conditions in the sub-basins. A negative correlation between the Mn content and δ 13Ccarb values (−10‰–−7‰) and a deficiency of sulphide minerals indicate that the diagenetic degradation of organic matter (δ 13Corg from − 34‰ to − 31.9‰) took place through Mn oxide reduction rather than microbial sulphate reduction and can contribute to a considerable source of bicarbonates. The approximately homogeneous δ 13Ccarb depletion and their apparent discrepancy with δ 13Corg indicate that the post-depositional genesis of the Mn carbonate ore occurred in a relatively open early diagenetic pore water system with a considerable contribution from seawater-derived carbon sources.

Study on condition prediction and influencing factors of manganese carbonate recovery by high gradient pulse magnetic separation

Manganese carbonate ore belongs to weakly magnetic minerals, and its co-associated minerals are mainly non-magnetic minerals, which can be separated from gangue minerals at high magnetic field intensity. However, manganese grade and recovery of magnetic separation concentrate of manganese carbonate ore are low in actual production. Therefore, the influences of manganese carbonate particle size, magnetic field intensity, volume susceptibility, pulse stroke, pH, and other factors were studied. The optimal test conditions for manganese carbonate ore recovery by high-gradient magnetic separation were predicted through the calculation results. The results show that the particle radius of manganese carbonate is 0.020 mm, the pulse impulse time is 200 r/min, and the magnetic field intensity is 0.9 T. The optimum condition test was carried out with Qianbei manganese carbonate ore as the material. The test results show that the optimum conditions are the particle radius of 0.074-0.019 mm, pulse impulse time of 200 r/min, and magnetic field intensity of 1.2 T. The reason for the deviation is that the actual ore has a fine distribution particle size, many associative bodies, complex composition, and serious agglomeration, resulting in variable particle volume susceptibility. The capture yield increases with the increase of magnetic field intensity and volume susceptibility but decreases with the increase of pulse. The lower the surface potential of manganese carbonate, the higher the recovery of manganese carbonate. The grade of manganese concentrate was 19.06% and the recovery was 76.85%. Mixed manganese concentrate with a grade of 18.04% and recovery of 87.14% was obtained by adding drugs and changing the grinding method.

Removal and Resource Utilization of High Concentration Flue Gas Sulfur Dioxide Using Manganese Carbonate Ore

The removal of high concentration flue gas sulfur dioxide (SO2) using manganese carbonate ore desulfurization (MCO-FGD) is a promising route that combines economic benefits and pollution control. However, the problems of intermediate oxidation and by-product control have plagued the industrial application of the MCO-FGD technique for a long time. Based on the fact that there is symbiosis of manganese and iron in natural manganese ore, in this study, small amounts of Fe(III) and MnO2 were introduced into the MCO-FGD reaction system to enhance the oxidation of SO2 to SO4− and suppress the manganous dithionate (MnS2O6) by-product generation. The results suggested that the addition of Fe(III) led to the generation of potent oxidant Mn(III) in the reaction system, which accelerated the generation of SO3−• radicals and, thus, enhanced the oxidation of SO2. Under the optimum reaction conditions, the 2.0% of inlet SO2 could be removed to 62 ppm, obtaining 90.1% manganese leaching efficiency, and the concentration of MnS2O6 in the desulfurized liquid was kept below 2.5 g/L after a six-stage desulfurization. The results are of great importance for the sustainable development of the manganese metallurgical industry, which provides theoretical and technical support for the recycling of sulfur and manganese. The influences of different operational conditions on SO2 removal, the catalytic mechanism, and manganese leaching were studied to provide theoretical and technical support for resourceful MCO-FGD technology.

Carboniferous–Triassic tectonic and thermal evolution of the middle crust section of the Dervio–Olgiasca Zone (Southern Alps)

AbstractA well‐preserved remnant of the middle crust of the former Adriatic passive margin is exposed in the Southern Alps (Italy). The Dervio–Olgiasca Zone is located south of the Insubric Line along the northern part of Como Lake and, because of the lack of Alpine overprint, provides favourable conditions to investigate the pre‐Alpine (rift‐related) history. We reconstruct the P–T–t–d evolution of the Adria middle crust through petrological (petrography, mineral chemistry, thermobarometry and thermodynamic modelling) and geochronological (Lu/Hf in garnet and U–Pb in monazite) data from pegmatites and host micaschists. These data allow reconstruction of a complex tectono‐thermal evolution of the future proximal Adriatic margin at the onset of Alpine rifting. The amphibolite‐facies Carboniferous metamorphic basement (7.6–10 kbar and 610–660°C at 318–312 Ma) was affected by pervasive extensional deformation (5.1–7.6 kbar and 580–660°C) in the Middle‐ to Late‐Permian (257.5 ± 3.8 Ma). Pegmatite intruded at 249.8 ± 1.1 Ma in an extensional phase that re‐equilibrated rocks of the basement at 3.5–4.5 kbar and 560–600°C. During the Middle‐ to Late‐Triassic (241–235 Ma), the basement experienced static thermal recrystallization (T = 689 ± 41°C and ~5.0 kbar). This Late‐Anisian to Early‐Carnian thermal event was simultaneous with the emersion of carbonate platforms, volcanism and ore deposition in the future proximal Adriatic margin. The subsequent cooling of the middle crust was synchronous with large‐scale extensional detachments developed in the upper crust (e.g., the Lugano‐Val Grande Fault), which controlled the formation of the Monte Generoso Basin. This study reveals that the local post‐Carboniferous thinning and heating events recorded in the Adriatic middle crust were interconnected to other processes occurring at different crustal levels that were, in turn, induced by crustal stretching in the early stages of the Alpine rifting.

Direct smelting process of copper carbonate ore using SiO2 as fluxing agent in electric arc furnace

ABSTRACT The demand for copper, especially from the transportation sector, continues to increase. However, the supply of copper still depends on the primary process production, namely processing or extracting copper from its ore. In addition to copper sulfide ores, copper oxide and carbonate ores are alternative raw materials for copper production, especially in countries with abundant copper reserves, such as Indonesia. This study aims to analyse the effect of SiO2 flux addition in the direct smelting process of mixed oxide and carbonate-type copper ore. This study used an electric arc furnace to carry out the smelting process. The addition of SiO2 varied between 0 and 8 wt% with an interval of 2 wt%. As a result, a direct smelting product was successfully made with a Cu content of 87.01 wt% and Cu recovery of 92.6% when using 4 wt% SiO2. The slag’s main compounds were SiO2, Fe2SiO4, FeSiO3, and Fe3O4.

Mechanistic insight of hydrophobic agglomeration of rhodochrosite fines Co-enhanced by Oleic-Kerosene emulsion and static magnetic field

Efficient enrichment of fine rhodochrosite is key to purifying manganese carbonate ore and reducing the discharge of electrolytic manganese slag at the source. Enhancing the agglomeration of rhodochrosite fines is important for efficient flotation separation. In this study, we investigated the agglomeration mechanism of rhodochrosite fines co-enhanced by oleic-kerosene emulsion and static magnetic field using agglomerate and surface properties analysis, electrical conductivity and atomic force microscopy measurements, and extended Derjaguin, Landau, Verwey, and Overbeek theoretical calculations. The results showed that the agglomerate size and regularity degree increased with increasing shearing time, achieving the maximum values of the average size at 20 min with magnetic field and at 40 min without magnetic field. Larger-sized and tighter agglomerates can be formed in a shorter time by the Lorentz force in magnetic field. As magnetic field was applied, the surface electronegativity of rhodochrosite in emulsion solution was stronger and positively correlated with magnetic field intensity. In addition, due to the higher solubility of oleic acid, the adsorption capacity and net heat of emulsion increased, resulting in a stronger hydrophobicity of rhodochrosite with a shorter hydrophobization time. Interestingly, almost no attraction existed between particles with magnetic field in aqueous solution, while a larger attraction existed without magnetic field in emulsion solution, and the attraction and action distance both increased markedly with increasing magnetic field intensity. However, the magnetic attraction was much smaller than hydrophobic attraction. As a result, agglomeration of rhodochrosite fines could be enhanced by stronger hydrophobic attraction under the synergy effect of magnetic field and oleic-kerosene emulsion. This research will be conducive to in-depth insight into the enhancement mechanisms of rhodochrosite agglomeration and will provide a basis for flotation regulation.

Effects of Surfactin, a Promising Carbonate Ore Collector, on the Physicochemical Properties of Magnesite Surface

Effects of Surfactin, a Promising Carbonate Ore Collector, on the Physicochemical Properties of Magnesite Surface

Episodic ventilation of euxinic bottom waters triggers the formation of black shale-hosted Mn carbonate deposits

Many manganese (Mn) carbonate deposits over geologic history are often closely associated with black shales. However, the mechanism(s) by which the Mn entered the sediments remains controversial because on one hand oxygenated waters are required for primary Mn(IV) oxide formation but on the other hand black shales generally form under reducing conditions. China hosts some of the world’s largest black shale-hosted Mn deposits, for example, the Carboniferous Ortokarnash and Malkantu Mn deposits in the Malkansu region, offering a good opportunity to revisit the genesis of black shale-hosted Mn carbonate deposits. Here, we present the first coupled, systematic paleoredox and hydrographic reconstruction of those deposits with the aim of elucidating the redox-state of the depositional basin at the time of their initial deposition. The Mn ore beds in this region are hosted within laminated, organic-rich mudstones (i.e., black shales) reflective of a relatively deep-water depositional environment. The Mn ores are comprised of the Mn(II) carbonate minerals (rhodochrosite and Ca-rhodochrosite), with minor alabandite, pyrite, and monazite. Multiple independent lines of evidence, including positive shale-normalized Ce anomalies (average 3.0), negative δ13CVPDB values (average −11.55 ‰), and negative δ98MoNIST+0.25 values (average −1.07 ‰), indicate that the Mn(II) carbonate ores were formed during diagenesis via the coupled oxidation of organic matter and reduction of Mn(IV) oxides originally deposited from an oxygenated water column. However, in apparent contradiction, highly reactive iron to total iron (FeHR/FeT; average 0.66) and pyrite iron to highly reactive iron (FePy/FeHR; average 0.71) ratios, combined with a high abundance of small framboidal pyrites (mean diameter ∼5 μm) with narrow size ranges (standard deviations <2 μm), suggest that the associated black shales were deposited in euxinic (H2S-bearing) bottom waters. Euxinia resulted from sluggish water mass circulation, with sedimentary Mo/TOC ratios indicating a relatively strong hydrologic restriction. During this stage, dissolved Mn(II) would have accumulated in euxinic waters but not become permanently fixed into sediments, as indicated by higher degrees of enrichment for Mo over U and lower Mo isotope values than coeval seawater recorded in the black shales. These reveal an active Mn(IV) oxide shuttle across a redox-stratified water column. Combined, the Mn ore intervals document sharp benthic oxygenation of euxinic bottom waters, a process that might be induced by the periodic incursions of oxic seawater associated with eustatic sea level rises. This model is supported by the Mo isotopic characteristics of the Mn carbonate ores, which indicate original Mn oxide precipitation from an overlying water with Mo isotopic composition close to coeval open seawater (minimum δ98MoNIST+0.25 of 1.9 ‰). In contrast to the generalized “bathtub ring” model envisaging that the black shale-hosted Mn deposits were formed at shallow basin margins, our results highlight that they were more likely formed by in-situ ventilation of anoxic (especially euxinic) deep waters of basin center settings. In this regard, we suggest that the ventilation model better explains the close association of Mn carbonate ores with black shales, and has profound implications for understanding the paleoredox framework of otherwise Mn-rich black shale successions.

Reaction kinetics of direct reduction of mineral iron carbonate with hydrogen: Determination of the kinetic triplet

Direct reduction of mineral iron carbonate with hydrogen is a CO2-lean technology for the production of elemental iron from iron carbonate ore. In this study, the reaction mechanism and reaction kinetics were investigated by thermogravimetric analysis and in a fixed-bed tubular reactor. The degree of metallization increases with increasing temperature from 773 to 1023 K. At 1023 K, the degree of metallization is 93 wt%, with the remaining iron species being wüstite. The reduction proceeds via two reaction pathways: calcination of iron carbonate to wüstite with consecutive reduction of wüstite to elemental iron and direct reduction of iron carbonate to elemental iron. The reaction steps occur simultaneously. During the first hour of reaction, which corresponds to the heat-up phase, calcination of iron carbonate to wüstite adopts the dominant reaction path. Then wüstite reduction and direct iron carbonate reduction with hydrogen to elemental iron, become dominant, facilitated by the increasing porosity of the ore due to the release of CO2. Towards the end of the reduction process the remaining wüstite is reduced to elemental iron. The kinetic triplet – solid phase reaction kinetic model, activation energy and frequency factor – was determined for each reaction step. The reaction kinetics can be described by a combination of an Avrami-Erofeyev model (A3 model for iron carbonate calcination to wüstite), and reaction-order models (F2 model for the reduction of iron carbonate to elemental iron and F3 model for the reduction of wüstite to elemental iron).

From Fossil to Active Hydrothermal Outflow in the Back‐Arc of the Central Apennines (Zannone Island, Italy)

AbstractPost‐orogenic back‐arc magmatism is accompanied by hydrothermal ore deposits and mineralizations derived from mantle and crustal sources. We investigate Zannone Island (ZI), back‐arc Tyrrhenian basin, Italy, to define the source(s) of mineralizing hydrothermal fluids and their relationships with the regional petrological‐tectonic setting. On ZI, early Miocene thrusting was overprinted by late Miocene post‐orogenic extension and related hydrothermal alteration. Since active submarine hydrothermal outflow is reported close to the island, Zannone provides an ideal site to determine the P‐T‐X evolution of the long‐lived hydrothermal system. We combined field work with microstructural analyses on syn‐tectonic quartz veins and carbonate mineralizations, X‐ray diffraction analysis, microthermometry and element mapping of fluid inclusions (FIs), C, O, and clumped isotopes, and analyses of noble gases (He‐Ne‐Ar) and CO2 content in FIs. Our results document the evolution of a fluid system of magmatic origin with increasing mixing of meteoric fluids. Magmatic fluids were responsible for quartz veins precipitation at ∼125 to 150 MPa and ∼300°C–350°C. With the onset of extensional faulting, magmatic fluids progressively interacted with carbonate rocks and mixed with meteoric fluids, leading to (a) host rock alteration with associated carbonate and minor ore mineral precipitation, (b) progressive fluid neutralization, (c) cooling of the hydrothermal system (from ∼320°C to ∼86°C), and (d) embrittlement and fracturing of the host rocks. Both quartz and carbonate mineralizations show noble gases values lower than those from the adjacent active volcanic areas and submarine hydrothermal systems, indicating that the fossil‐to‐active hydrothermal history is associated with the emplacement of multiple magmatic intrusions.

Determination of optimal technological modes for obtaining manganese alloys from poor carbonate and oxide ores in a jet-emulsion unit

The paper presents the results of development and research of a new resource-saving technology for processing poor oxide and carbonate manganese ores in a unit of jet-emulsion type. The basic principles of creating a jet unit and the technology of processing pulverized manganese ores are considered. For the preliminary reduction of manganese from higher oxides or carbonates decomposition, as well as the removal of moisture from the ore, it is proposed to use a reducing gas, which is a product of the implementation of manganese reduction technology in jet-emulsion unit. Thus, the authors propose to close the process, that is, to create a consistent flow of substance and energy passing through the main jet-emulsion unit and the preparatory unit of the fluidized bed. The main task of calculating the proposed technology is to determine the consumption of crude ore in the fluidized bed unit in order to obtain a given yield of the intermediate product and at the same time to ensure the possibility of complete conversion of high oxides or carbonates of crude ore into lower oxides by reducing gas produced in the main unit. To solve this problem, an optimization task was set and implemented. The first stage is selection of composition and consumption of the reducing gas and determination of consumption of the initial manganese ore, which provides the output of a given amount of the intermediate product. The second stage is solution of the optimization problem for output and composition of the gas, which should ensure the recovery process in the second unit. The paper presents the results of calculating the processing technology in the jet-emulsion unit for oxide ore of the Selezen’skoe and carbonate ore of the Usinskoe deposits. A comparative analysis of two options for processing manganese ores by the proposed technology and by the technology without preliminary recovery and roasting was carried out. The proposed technology of processing manganese ores in a closed-cycle jet-emulsion unit allows one to significantly reduce the specific costs of materials, increase productivity, and significantly reduce the energy intensity of the process compared to the technology of processing poor manganese ores without preliminary reduction or roasting.

Insights into the low-temperature NH3-SCR of NO performance and mechanism over manganese tailings-derived catalyst

Manganese carbonate ore is ascertained as the most abundant manganese ore in China, while its mining and beneficiation generated a large amount of manganese tailings which is regarded as a hazardous waste. Owing to great catalytic performance of manganese oxides, it is double-benefit to employ manganese tailings as catalyst to eliminate harmful nitrogen oxides from flue gas. In this study, the effects of calcination temperature on the low-temperature denitration performance and physicochemical properties of manganese tailings were systematically investigated via XRF, XRD, XPS, H2-TPR, NH3-TPD and DRIFTS, aiming at exploring the effective utilization of manganese tailings. The results revealed the best catalytic activity can be obtained at a calcination temperature of 500 °C with over 95 % NO conversion attained in the denitration temperature range of 75–225 °C. Lower calcination temperature led to the incomplete decomposition of MnCO3, while higher calcination temperature led to the decrease in specific surface area, surface acidity and oxidation performance. The denitration reaction was followed by Eley-Rideal pathway, in which the absorbed NH3 species was reacted with the gaseous NO and NO2. Based on the results in this study, the effective utilization of manganese tailings for NO emission reduction could promise for wide applications.

Prereduction Behavior of Manganese Ores With Solid Carbon and in CO/CO2 Gas Atmosphere

The prereduction reactions in the submerged arc furnace (SAF) are highly decisive of the total carbon, and energy consumption of the ferromanganese process. Therefore, understanding the dependency of prereduction behavior on ore characteristics and furnace conditions is of paramount importance. Prereduction behavior of Comilog, Nchwaning and UMK ores with solid carbon was studied in an open 75 kVA induction furnace set up simulating the conditions of an industrial SAF. In addition, the ores were thermogravimetrically studied with non-isothermal heating to 1000 °C in a flowing 70/30 CO/CO2 atmosphere. Gasification of carbon according to Boudouard reaction was considered significant for carbonate ores in induction furnace setup. UMK had a greater extent of prereduction compared to Nchwaning which is low in carbonates and Comilog which is known to have a higher CO reactivity at similar CO contents. TGA rate curves shows that prereduction of UMK ore occurred with two major distinctive steps. The first one was a combination of prereduction reactions and decomposition of carbonates with a peak temperature of 700 °C, and the second peak was the decomposition of calcite at 900 °C. The O/Mn ratio for UMK shows that prereduction is already completed prior to the second decomposition peak at 900 °C. In addition to prereduction reactions, Nchwaning is also characterized by an endothermic step which is decomposition of carbonates at 900 °C. Comilog ore produced the most fines followed by Nchwaning and lastly UMK on decrepitation.