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• First colorimetric and chemical characterisation performed on the chromatic evolution Portuguese azulejos (glazed tiles) comprising a timespan of ca. 250 years. • The methodology followed a non-invasive approach that can and will be replicated on other sets of tiles. • While basic pigments remained the same, their chemical composition changed over time and the colour palette exhibited different hues in specific chronologies. • A modified Naples yellow pigment with zinc was characteristic of 17th-century Portuguese azulejos. • The mixture of Naples yellow with cobalt blue to obtain olive green is also characteristic of Portuguese azulejos , but rarely mentioned in the literature for coeval maiolica/faience productions. This work provides an overview of the pigments used by Portuguese azulejo painters through the study of 34 glazed tiles belonging to the National Azulejo Museum in Lisbon, Portugal. The tiles are dated from the late 16th century to the early 19th century, with most samples attributed to the 17th and 18th centuries. Building on a previous study where the chemical composition of the 17th-century colour palette was characterised [1] , we used a non-invasive methodology to further identify compositional differences among groups of colours spanning a wider timeframe. Blue, white, yellow, orange, purple, green and brown decorations were analysed by EDXRF to obtain qualitative and (in some samples) quantitative information on their chemical composition. µ-Raman spectroscopy was used to identify the main colouring agents. Finally, colorimetric measurements of the different hues of each colour were performed to address the relation between colour and chemical composition. Our results show that greens could be obtained through a copper-based pigment or by mixing lead-antimonate with cobalt-blue pigment. Although cobalt is the colouring agent of all blue decorations, compositional differences suggest the use of different types of raw materials or the addition of specific reagents to modify the hue. On the other hand, yellow hues ranging from lemon yellow to orange were manufactured by adding zinc, tin, or iron oxide to a lead antimonate base. Finally, a manganese ore was used to make the purple pigment. Overall, we noted that while the basic pigments remained the same, the colour palette was progressively widened during the 18th century. This was done by using more pure pigments (i.e., with less iron), by changing the ratio in pigment mixtures (i.e., blue and yellow), or by overlapping colour layers for artistic effects. Finally, the results of the chemical and colorimetric analyses are always influenced by the concentration of the pigment in the glaze, its thickness and the overlapping of pigments used by azulejo painters to expand the shades available for the final artistic composition. [ABSTRACT FROM AUTHOR]

• Mn ore was pre-reduced using CO/CO 2 , H 2 /H 2 O, or H 2 atmospheres. • H 2 -only atmosphere had the lowest oxygen partial pressure. • Fe-oxide metallization was accelerated in hydrogen-containing atmospheres. • Carbonate decomposition was accelerated in the absence of CO/CO 2. • Higher Mn oxides were reduced to lower states in H 2 -containing atmospheres. Hydrogen (H 2), a relatively underexplored reductant in ferromanganese (FeMn) production, offers an attractive avenue for mitigating gaseous carbon (C) emissions. The reduction behaviour of South African Nchwaning manganese (Mn) ore using gaseous CO/CO 2 , H 2 /H 2 O, and H 2 atmospheres was investigated experimentally in the temperature variation of 700, 800, and 900 °C. The effect of different gas compositions and temperatures was studied using a vertical thermogravimetric (TG) tube furnace. During pre-reduction, two parallel reactions occurred, namely the reduction of higher Mn- and iron (Fe) -oxides, and the decomposition of carbonates. After each test, decrepitation, chemical composition, phase transformation, and porosity were characterised. Using the rate of mass loss, a kinetic model was obtained to predict kinetic constants. The oxidation state of the higher Mn- and Fe-oxides was lowered during CO/CO 2 and H 2 /H 2 O pre-reduction. Only during pure H 2 pre-reduction was Fe2+ reduced to its metallic state, Fe0. The majority of carbonates decomposed in the presence of the CO/CO 2 atmosphere at 900 °C, whereas in the presence of H 2 in the reducing atmosphere carbonates decomposed at a higher rate and lower temperatures. Additionally, the extent and rate of mass loss were expedited by increasing the temperature, employing H 2 -containing atmospheres, and lowering the oxygen partial pressure (pO 2) of the H 2 -containing atmospheres. No significant trends were observed in ore decrepitation and porosity across various atmospheres and temperatures, except for decrepitation in the water vapour-containing atmosphere. The utilisation of a pure H 2 atmosphere has a significant ability for pre-reducing Mn ores with carbonate content by expediting carbonate decomposition and promoting Fe-oxide metallisation, thereby enhancing the efficiency of ore treatment in metallurgical applications. [ABSTRACT FROM AUTHOR]

Iron and manganese are considered to be strategic national mineral resources. Ferromanganese ore, which is characterised by low-grade, fine particle size, and complex associated relationships, represents the primary source of manganese resources. Given the urgent demand for ferromanganese resources in China, it is of significant importance to carry out basic research and cutting-edge technology exploration around co-associated ferromanganese ores in order to realize the efficient separation and utilization of these resources, with the aim of reducing the country's dependence on imports. This study reports on the physicochemical properties of ferromanganese ore and conventional separation methods, including mechanical beneficiation, leaching technology, roasting technology, and pyrometallurgical smelting. This paper presents a review of the various technical principles, parameter optimization and mechanism characteristics associated with the extraction and separation of iron and manganese from ferromanganese. This review offers guidance for the selection and development of ferromanganese or other complex refractory iron and manganese ore resources. In light of the aforementioned considerations, a novel approach to the treatment of ferromanganese via microwave fluidization roasting is proposed in the paper. [ABSTRACT FROM AUTHOR]

During the interglacial period of the Cryogenian glaciation, the extensive "Datangpo-type" manganese ores were deposited in the Nanhua Basin. However, there has been significant controversy over the precipitation mechanism of manganese for decades. Based on iron and nitrogen isotope data from the manganese ores of the Datangpo Formation in Chongqing (South China), combined with previous research, we propose that the manganese ores of the Datangpo Formation precipitated directly in an anoxic bottom-water environment in the form of rhodochrosite. The δ56Fe values in the Bijiashan manganese ore (δ56Fe = −0.19 ± 0.13 ‰) are close to those of modern marine hydrothermal iron, and there is a strong positive correlation between the δ56Fe value and iron concentration (R2 = 0.81), indicating that the precipitation of manganese ore could be mainly affected by hydrothermal input. After comprehensively comparing the δ56Fe values of the whole rock and pyrite in the manganese ore of the Datangpo Formation, we believe that iron from hydrothermal sources directly and quantitatively combined with sulfides to form pyrite. Additionally, the bottom seawater of the basin was mainly anoxic. The nitrogen isotope composition indicates the presence of a stable nitrate reservoir in the ocean at that time, and manganese ore deposition may have been influenced by the input of high-salinity water from the open ocean. Due to the supply of NO 3 - from the open ocean to the graben basin, the δ15N in manganese ore is significantly higher than that in black shale. The input from the open ocean led to an increase in alkalinity in the bottom water of the basin, which favored the precipitation of rhodochrosite. Considering that the oxidation potential required for manganese oxidation precipitation is higher than that required for iron oxidation precipitation, it is most reasonable to conclude that under alkaline anoxic conditions in the bottom water layer, Mn2+ directly precipitated in the form of rhodochrosite. • The iron isotopes in Mn ores indicate extensive hydrothermal activity. • Fe2+ aq was directly precipitated as sulfide during the precipitation of Mn ores. • Nitrogen isotopes prove that Mn ores precipitate with open ocean water input. • The "Datangpo-type" manganese ore may be directly precipitated as rhodochrosite. [ABSTRACT FROM AUTHOR]

• Mn-based oxides are suitable oxygen carriers for chemical looping combustion (CLC) • CLC of waste-derived fuels is effective for carbon capture and storage • The type of Mn-based OC impacts ash species behavior and system operation • Ash species can combine with Mn-based OCs to form new oxygen carrier phases Chemical looping combustion (CLC) is an innovative technology suitable for converting waste-derived fuels into heat and power. The process inherently produces pure CO 2 , which is highly favorable for carbon capture and storage and could be instrumental for achieving negative emissions. CLC operates by utilizing solid oxygen carriers (OCs) to transfer heat and oxygen between two reactors. The OC play a crucial role in achieving an efficient combustion. Manganese-based OCs are particularly interesting, due to their ability to release gaseous oxygen. However, ash components from solid fuels could alter their oxygen transfer capacity, and cause problems related to corrosion and agglomeration. The objective of this work is to obtain in-depth insights about Mn-based OCs for CLC of waste-derived fuels. This is achieved by investigating phase transitions during CLC of solid fuels when utilizing two manganese-based OCs: manganese oxide and a representative manganese ore. For this purpose, thermodynamic modeling is employed, and a specific focus is given to K, Na, Cu, Zn, and Pb, due to their important role in corrosion and/or agglomeration. Thermodynamic databases are expanded by calculating properties from first-principles. It is shown that Mn-based OCs are suitable for effectively converting waste-derived fuels while limiting corrosion. Furthermore, the iron in manganese ores is found to have positive implications for oxygen-transfer reactions. In terms of alkali release to the gas phase, manganese ore seems to be a more promising material compared to manganese oxide. The pathways for the heavy metals Zn, Cu, and Pb were, meanwhile, independent of the OC type. [ABSTRACT FROM AUTHOR]

Silver-bearing manganese ore (Mn-Ag ore) is an important resource for the extraction of the precious metal Ag. However, the efficient and economical utilization of low-grade Mn-Ag ore poses challenges due to its polymetallic co-occurrence, complex associated mineral structures, and lower Ag grade compared to an industrial Ag grade of 80 g/t. In contrast, the Ag grade of commercially viable concentrate, achieved through physicochemical beneficiation, generally exceeds 1000 g/t. This work briefly discusses the metallogeny and resource characteristics and the processing technologies of Mn-Ag ore to produce high grade Ag concentrates. Based on the metallogeny characteristics of Mn-Ag deposits, this work delves into the challenges and difficulties in the physical separation of Ag and Mn. By regulating the differences in the chemical properties of Mn and Ag constituents, chemical beneficiation processes, including unit operations of pyrometallurgy and hydrometallurgy, result in favorable Ag and Mn enrichment and separation. The chemical principles, technical parameters, Mn-Ag separation efficiency, and advantages and disadvantages of chemical beneficiation (blast furnace smelting, chlorination roasting, one-step leaching, and two-step leaching) were systematically summarized and discussed. This work can provide theoretical and technical guidance for the effective treatment of low-grade Mn-Ag ores. [Display omitted] • Diverse processes for pyro- and hydro- separation of Ag and Mn are reviewed. • Metallurgical properties of Mn-Ag ores and the characteristics of silver resources are introduced. • Separation methods based on the differences in reduction, volatility, fusibility and selective solubility are highlighted. • Advantages and disadvantages of separation methods for Ag and Mn are discussed. [ABSTRACT FROM AUTHOR]

This research focuses on the cheap synthesis of manganese ferrite nanoparticles. Sintering of a mixture of ferric oxide powder (Fe2O3) and low-grade manganese ore is achieved by a simple pyrometallurgical synthesis method at temperatures of 1000 °C, 1100 °C, and 1200 °C. In this process, controlling the particle size proved successful, which is essential to increasing the application of the material. Results have shown that at 1200 °C, the developed phase was a manganese ferrite with a high-intensity peak, which was well confirmed by the XRD diffractogram. As expected, an increase in temperature significantly increased particle size. Through thermal analysis, a minor gain in weight was found at 792 °C, which indicates the formation of phases. The FTIR spectra showed characteristic ferrite stretching vibrations at 1636 cm-1 and other peaks below 1000 cm-1. TEM analysis and microstructural examination confirmed the simultaneous nucleation and growth of nanoparticles with tiny surface pores, indicating optimal magnetic properties and a high melting point. The material showed low coercivity and rapid switching of magnetic states, which is useful for different applications. [Display omitted] • Manganese ferrite was synthesized by mixing ferric oxide powder with low grade Mn-Ore powder. The samples were heat treated at different sintering temperatures in Nabertherm furnace. The method is cheap and not time consuming. • Different characterization techniques like, XRD, FTIR, SEM, EDX, TGA, DSC, TEM, SAED, and magnetic analysis were used to characterize the samples. • Manganese ferrite phase was successfully achieved, which was confirmed from XRD analysis. High intensity Mn-ferrite peak was recorded for the sample sintered at 1200 °C for 2.5 hours. • The prepared nanoparticles possess homogeneity in magnetic properties and can be utilized in applications where consistent and rapidly switching magnetic states are required. [ABSTRACT FROM AUTHOR]

• Mercury is readily released into the environment during the Manganese mining and manganese ore smelting factories. • The concentrations of Hg and MeHg showed obvious seasonal variation in river water, the bed retention sediments and the fluvial bank sediments. • The content of Hg mainly associated with crystalline Fe–Mn oxyhydroxides in sediments. Manganese (Mn) ores contain substantial concentrations of mercury (Hg), and mining and smelting of Mn ores can bring Hg into the surrounding aquatic environment through atmospheric deposition, leaching of electrolytic Mn residue and Mn gangue dump. However, limited is known that how these processes influence the environmental behaviors of Hg in waterbody. Therefore, the seasonal distribution and existing form of Hg in water and sediment in one Mn ore area in Xiushan County, Chongqing were investigated. Our results showed that the mean Hg and methylmercury (MeHg) concentrations in water (n =35) were 5.8 ± 4.6 ng/L and 0.22 ± 0.14 ng/L, respectively. The mean Hg concentrations in retained riverbed and fluvial bank sediment (n =35) were 0.74 ± 0.26 mg/kg and 0.63 ± 0.27 mg/kg, respectively (the mean MeHg concentrations were 0.64 ± 0.40 µg/kg and 0.51 ± 0.30 µg/kg, respectively). It indicated that the mining and smelting of Mn ores were the main sources of anthropogenic Hg, and Mn may inhibit Hg methylation in rivers in Mn ore areas. Mercury in the bound to iron/ Mn (Fe/Mn) oxides of low crystallinity fraction (Hg-OX) accounted for 4.01% and 5.25% of the total Hg concentrations in the retained riverbed and fluvial bank sediment, respectively. The amount of Hg bound to Fe/Mn oxides in sediment increased significantly due to the manganese mining activities in the investigated area. Therefore, it could be hypothesized that high Hg concentrations in river sediment in Mn mining areas are closely related to high Mn concentration in sediment. [Display omitted] [ABSTRACT FROM AUTHOR]

Unlike modern Mn(IV)-dominated manganese nodules, ancient manganese deposits primarily contain Mn(II) (manganous) mineral phases. The general assumption is that these manganous minerals formed post-depositionally from a Mn(IV) precursor phase during diagenesis and metamorphism. However, recent studies have shown that aqueous Mn(II) may combine with either CO 3 2– (aq) or H 4 SiO 4(aq) to nucleate and precipitate as primary manganous phases within anoxic waters. These findings thus make it difficult to assess what comprised the primary mineral assemblage of ancient Mn deposits, which in turn, has implications for understanding the redox fabric of the past marine water column. Here, we investigate the paragenesis and oxidation state of various Mn minerals (oxides, carbonates, and silicates) from the late Devonian Xialei and middle to late Permian Zunyi manganese deposits in South China. Through characterization of the micro-scale distribution, composition, and speciation of different Mn-bearing mineral phases, we provide evidence to support an oxidative mechanism during Mn cycling at the time of deposition. We document the presence of a residual oxide phase (hausmannite; Mn 3 O 4) that represents a primary to early formed Mn(III)-bearing oxide preserved in Mn(II)-carbonate nodules. Additionally, we observe spherulitic textures comprised of mixed-valence Mn(II,III,IV)-silicates enclosed in diagenetic Mn(II)-carbonate laminations. Our results allow for the construction of a paragenetic model for these deposits beginning with the reduction of a primary Mn(IV) phase and the subsequent precipitation of intermediate Mn(III)-oxide or -silicate mineral phases. Following continued exposure to reducing conditions during early diagenesis, Mn(III)-oxides were then replaced by Mn(II)-carbonates. Similarly, Mn(III)-silicates were transformed into various Mn(II)-silicates during late-stage diagenesis and metamorphism. This model suggests that the accumulation of various divalent Mn mineral phases in ancient sediments may, therefore, be indicative of deposition under a water column with a sufficient oxidizing potential to induce Mn(II) oxidation. [ABSTRACT FROM AUTHOR]

• Manganese ore showed higher nitrogen removal in constructed wetlands (CWs). • Manganese ore enhanced ammonia oxidation and nitrate reduction in CWs. • Zeolite and manganese ore selected for distinct bacterial communities in CWs. • Stochastic processes dominated microbial community assembly in CWs. • Manganese ore-based CWs had more keystone microbes and complex interactions. A limited understanding of microbial interactions and community assembly mechanisms in constructed wetlands (CWs), particularly with different substrates, has hampered the establishment of ecological connections between micro-level interactions and macro-level wetland performance. In this study, CWs with distinct substrates (zeolite, CW_A; manganese ore, CW_B) were constructed to investigate the nutrient removal efficiency, microbial interactions, metabolic mechanisms, and ecological assembly for treating rural sewage with a low carbon-to-nitrogen ratio. CW_B showed higher removal of ammonia nitrogen and total nitrogen by about 1.75–6.75 % and 3.42–5.18 %, respectively, compared to CW_A. Candidatus_Competibacter (denitrifying glycogen-accumulating bacteria) was the dominant microbial genus in CW_A, whereas unclassified_f_Blastocatellaceae (involved in carbon and nitrogen transformation) dominated in CW_B. The null model revealed that stochastic processes (drift) dominated community assembly in both CWs; however, deterministic selection accounted for a higher proportion in CW_B. Compared to those in CW_A, the interactions between microbes in CW_B were more complex, with more key microbes involved in carbon, nitrogen, and phosphorus conversion; the synergistic cooperation of functional bacteria facilitated simultaneous nitrification-denitrification. Manganese ores favour biofilm formation, increase the activity of the electron transport system, and enhance ammonia oxidation and nitrate reduction. These results elucidated the ecological patterns exhibited by microbes under different substrate conditions thereby contributing to our understanding of how substrates shape distinct microcosms in CW systems. This study provides valuable insights for guiding the future construction and management of CWs. [Display omitted] [ABSTRACT FROM AUTHOR]

Due to the low C/N and high NO 3 −-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 NO 3 −-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 NO 3 −-N were above 90 %, and without NO 2 −-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 SO 4 2- 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. [Display omitted] • SMCD reactor was an efficient carbon self-sufficient system. • MnCO 3 acted as alkaline buffer and provided inorganic carbon source. • Synergistic effects of SAD and MAD process enhanced nitrogen removal. • Mn cycle was formed in SMCD reactor. • Thermomonas , Dokdonella , and Simplicispira were potential Mn oxidizers. [ABSTRACT FROM AUTHOR]

• Seed-induced by iron-rich manganese electrolytic residue as seeding was applied to iron removal. • The iron removal efficiency was 99.97% and the manganese loss efficiency was 1.5%. • The iron-rich manganese residue generation was reduced by 64.45%. • This study provides technical support for the emission reduction of EMR at source. Enhanced removal of iron from iron-rich manganese ore leaching solution has become a bottleneck limiting the development of the electrolytic manganese industry. Herein, iron-rich electrolytic manganese residue (IREMR) as a seeding to enhance iron removal. The results showed that the iron removal efficiency was 99.97 % with only manganese loss of 1.5 % whenadding 1 g/L IREMR. Compared with the traditional conditions of electrolytic metal manganese enterprise, it demonstrated several environmental advantages: lower manganese loss (from 16 % to 1.5 %), less IREMR produced (64.45 %), faster filtration speed (from 0.0013 to 0.1966 mL/s.cm2). Based on multiphase equilibria modelling and strengthening mechanism analysis, enhanced iron removal by seed-induced can reduce the formation of ammonium-alum complex salts and prevent the formation of Fe(OH) 3 colloid. In addition, IREMR as seeding applied in the iron removal process can accelerate the formation of goethite and hematite to shorten the nucleation cycle. This strategy is important for source reduction and resource utilization of electrolytic manganese residue. [ABSTRACT FROM AUTHOR]

Considering the synergistic carbon/pollution reduction and resource utilization, this study proposes recycling of manganese desulfurization slag to prepare low-temperature NH 3 −SCR catalyst based on solid-state ion-exchange. The desulfurization slag was hydrothermally treated to be support under mild conditions, with the parent manganese oxide ore serving as active component. Hydrothermal treatment with a desulfurization slag to NaOH mass ratio of 1.0, at 100 °C for 10 h were actually cost-effective conditions for DS recycling. The catalyst with 13.6 wt% of Mn and activated at 450 °C for 2 h in air (MO3/DSH−450 −2) performed the best, with a NO conversion of 86.9% at 150 °C and 10000 h−1, and up to 92.6% at 175 °C. Hydrothermal treatment of DS, SSIE and calcination activation resulting in a rich surface acidity and lattice oxygen of MO3/DSH, coupled with better chemical state distribution of active metal sites, promoting the NH 3 −SCR activity. The scale-up produced MO3/DSH−G maintained 90.4% NOx conversion at 175 °C, showing good robustness, flexibility, and better sulfur/water resistance. The development of MO3/DSH catalyst may make full use of natural manganese ore, is a typical coupling strategy for carbon-pollutant synergistic emission reduction and resource fully utilize. [Display omitted] • DS and its parent MO were used to prepare low-temperature NH 3 −SCR catalyst. • MO/DSH catalyst enabled theoretically 100% utilization of natural manganese ore. • MO3/DSH− 450 − 2 performed 86.9% NO conversion at 150 °C and up to 92.6% at 175 °C. • Scale-up produced MO3/DSH−g kept good catalytic activity and water/sulfur resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Enhanced reduction and compressive strength of nickel–chromium-manganese reduced pellets was realized. • Thermodynamics analysis of the main metallic oxides was studied. • Phase transformation and microstructure evolution of reduced pellets were clarified. • The mechanism of reduction and consolidation strengthening for the reduced pellets was disclosed. For increasing the reduction degree and compressive strength of nickel–chromium-manganese bearing reduced pellets, the manganese ore and calcium oxide were applied as additives to improve the reduction and consolidation characteristic. The thermodynamics analysis and systematic process mineralogy were also conducted to further determine the related strengthening mechanism. The results showed that compared with no manganese ore and natural basicity, the compressive strength, reduction degree of pellets, iron and nickel for the reduced pellets can reach from 58 N per pellet, 56.21 %, 71.29 % and 91.45 % to 489 N per pellet, 69.58 %, 88.21 % and 98.55 % respectively with 5 % manganese ore and 0.30 binary basicity. MnO and CaO can improve the reduction of iron oxides. Meanwhile, during the reduction process, the low-melting-point phases can generate in the prereduced pellets, which can act as binding phases to wet and tighten the solid particles around through surface tension. The enhanced ways can accelerate the reduction of multi-metal bearing phases, growth of α (Fe, Ni) and solid phase reaction of adjacent particles, resulting in an improvement of reduction degree and compressive strength for the nickel–chromium-manganese bearing reduced pellets. [ABSTRACT FROM AUTHOR]

Datangpo-type manganese ores which originated in the Cryogenian Datangpo Formation, are overlaid and underlaid by Nantuo diamicite and Tiesi'ao silistones, respectively. A thorough understanding of the manganese mineralization process is currently limited by the continued uncertainty regarding the metallogenic redox condition of the Mn-bearing rock series. This study employed statistical analysis of pyrite framboid sizes and iron isotope (δ56Fe) to determine the redox conditions and constrain the mineralization process of Datangpo-type manganese ores in South China, considering the Gaolou in Chongqing, Yanglizhang in Guizhou, and Minle and Zhenxing in Hunan as examples. The results showed that Tiesi'ao siltstones mainly developed relatively larger diameter (7.29–7.68 μm) framboidal pyrites, whereas mudstones in the Datangpo Formation developed relatively smaller diameter (2.63–5.56 μm) framboidal pyrites. Furthermore, manganese ores produce non-framboidal pyrites. In three profiles, framboidal pyrite concentrations were found to be negatively correlated with Mn contents. These characteristics suggested that siltstones, mudstones, and manganese ores were deposited in oxic-anoxic, dysoxic-euxinic, and oxic-dysoxic conditions, respectively. The δ56Fe of whole rocks (δ56Fe WR) exhibited a range from −0.73 ‰ to +0.48 ‰ (average of −0.32 ‰), whereas pyrite (δ56Fe Py) varied from +0.03 ‰ to +0.83 ‰ (average of +0.36 ‰). Furthermore, δ56Fe Py in manganese ore (average = +0.27 ‰) were lighter than those in mudstone (average = +0.49 ‰). The results of this study demonstrated that oxidation deposition played a role in pyrite formation, with manganese ores exhibiting more oxic conditions compared to mudstones. The findings of this study suggested that idiomorphic pyrite formation was similar to that of manganese ore, in which Mn precipitated in the form of manganese (hydro)oxides under oxic seawater, and then converted into rhodochrosite under anoxic sulfidic diagenetic conditions, with the involvement of microbes. This research has the potential to enhance comprehension regarding redox conditions and the regulation of sedimentary manganese ores via redox transformation. • Pyrite framboids were studied to reflect the sedimentary redox conditions. • Manganese ores deposited under more oxic conditions than siltstones and mudstones. • Iron isotopes reveal that the pyrite formation underwent oxidation deposition. • Manganese precipitated as (hydro)oxides from seawater. • The (hydro)oxides converted into rhodochrosite during diagenesis. [ABSTRACT FROM AUTHOR]

The origin process of manganese ores remains unsolved worldwide. Exploring the origins of stromatolites that contain manganese may be a key to deciphering the sedimentary environments and metallogenic processes of these deposits. However, only a few manganese stromatolites have been discovered and described until now. Microbialites are well developed in the manganese deposits, located near the top of the Ediacaran Doushantuo Formation in Chengkou area of Chongqing, northern Yangtze Craton, but has not been explicitly studied; and whether they are true stromatolites or Epiphyton microbialites remains controversial. Based on field and core observations and thin section microscopy, the characteristics of five types of manganese stromatolites and their growth modes are described in detail in this study. The results show that these stromatolites grew in a biostrome in shoal and lagoon environments and were syngenetic with oncolites and oolites on a carbonate ramp behind the shoal. Manganese stromatolites can be categorized into three forms: (1) stratiform; (2) columnar, which includes branched and columnar types; and (3) stratiform-columnar, which is a transitional type. Based on a criterion that the diameter is less than or greater than 1 mm, columnar stromatolites are further divided into micro-columnar (< 1 mm) and columnar (> 1 mm) columns, which display synchronous growth and are similar to Pseudogymnosolenaceae. Their shapes are mainly controlled by water depths and hydrodynamic strengths. The greater the water depth, the more columnar the columns tend to be. Excessively strong hydrodynamic conditions decrease the growth rate of stromatolites, and they even stopped growth due to wave damage. Furthermore, pillared laminar textures (not Epiphyton), which consist of dendritic, micro-branched and micro-columnar stromatolites, are a common feature of the larger stratiform, stratiform-columnar and columnar stromatolites. The alternations of laminae with different internal textures record subtle fluctuations in water depths and hydrodynamic strengths, which indicate that stromatolite growth is controlled by tidal cycles at the lamina level. Therefore, it is possible that the vertical evolution of the stromatolites could reveal the changing characteristics of both local and regional sedimentary environments, i.e., stromatolite shape changes from columnar to stratiform can represent the onset of shallower environments with weak hydrodynamic conditions. In addition, as important reef builders in shallow carbonate ramps, microstromatolites accelerate the development from ramp to platform. Indicators of microbial control on stromatolite shapes and manganese sedimentation processes include the fabric of stromatolite laminae, organic rhodochrosite with a micritic texture that is usually clotted, spherical, tubular, fibrous or dendritic, which suggests that the laminae resulted from microbially induced in situ precipitation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coupled of MnO x and corncob achieved high NO 3 − removal of low C/N tailwaters. • MnO x enhanced HD by improving the bioavailability of organics. • Abundant functional bacteria ensured the high efficiency of the MnO x system. • Supplement with MnO x and corncob increased nitrogen and carbon metabolism key genes. The key limiting factor in advanced nitrogen removal of carbon-poor municipal tailwaters is deficient electron donor. Corncob, a low-cost external carbon source, can enhance heterotrophic denitrification by releasing organics sustainably. But its practical application is usually restricted to low bioavailability of organics and the risk of secondary pollution. Manganese oxides (MnO x) can regulate the organics released from corncob by altering the structure and bioavailability of organics. Herein, coupling Mn Ore (MnO 2 content ∼35 %) with corncob as substrate for microorganisms, quite high nitrate removal (98.4 ± 1.2 %) and less residual organics (COD < 10 mg/L) were observed. Organics characterization showed that original organics released from corncob were mainly humic substants (B/C = 0.4 ± 0.05, MW = 1.5 ∼ 350 kDa), and could be oxidized by MnO x into small molecular organics with high bioavailability (B/C = 0.72 ± 0.08, MW = 1.5 ∼ 35 kDa). Mn oxidation state analysis revealed that Mn(III/IV) in MnO x played an important role in organics transformation. The addition of corncob and redox transition of Mn enriched various functional denitrifying bacteria and dissimilatory lignocellulose -degrading bacteria, thereby upregulating functional genes encoding vital enzymes involved in nitrogen/carbon transformation. Overall, a Mn cycle-driven mixotrophic denitrification process was achieved, low molecular organics formed via MnO x oxidation accelerated heterotrophic denitrification rate, the Mn(II) produced from Mn(IV) reduction drive autotrophic denitrification. This finding could guide the low-cost technologies development for deep nitrogen removal from carbon-poor waters. [ABSTRACT FROM AUTHOR]

Manganese ore and CaO were applied as additives to improve the consolidation characteristic of fired nickel‑chromium iron ore pellets. The thermodynamics analysis and systematic process mineralogy were also conducted to further determine the related strengthening mechanism. The results showed that compared with no manganese ore and natural basicity, the compressive strength and porosity of fired pellets varied from 231 N per pellet and 32.45% to 1509 N per pellet and 17.21%, respectively with 6% manganese ore and 0.30 binary basicity. Meanwhile, the low-melting-point phases can generate and amount from 2.18% to 16.24% in the fired pellets, which can act as binding phases to wet the surface of skeleton phases, tighten the solid particles around through surface tension and accelerate recrystallization of hematite and solid phase reaction of adjacent particles, resulting in an improvement of solid phase consolidation and compressive strength for the fired nickel‑chromium‑manganese iron ore pellets. [Display omitted] • The compressive strength of fired nickel-chromium‑manganese iron ore pellets was increased. • Thermodynamics analysis on the raw materials of fired pellets was studied. • Phase transformation and microstructure evolution of fired pellets were clarified. • The mechanism of consolidation strengthening for the fired pellets was disclosed. [ABSTRACT FROM AUTHOR]

A new understanding of the reduction mechanisms of ferruginous manganese ores for ferromanganese alloy smelting was reported, and this new understanding was used to produce excellent ferromanganese alloys. To fulfill this objective, the effects of the operating variables on smelting ferromanganese alloys were initially investigated. The formation mechanisms and reduction reaction behaviors of olivine (Ca x Fe y Mn 2-x-y)SiO 4 , spinel (Ca x Fe y Mn 1-y-x)Al 2 O 4 , gehlenite (Ca x Mn 2-x)SiAl 2 O 7 and wüstite Mn x Fe y Ca 1-x-y O systems were systematically discussed to understand the phase transformation and reconstruction of manganese ore at high temperatures. The spinel (Ca x Fe y Mn 1-y-x)Al 2 O 4 that originated from (Fe y Mn 1-y)Al 2 O 4 was converted to CaAl 2 O 4 and then further reduced to ferromanganese alloys. A similar expression was applied to describe how the reduction mechanism of olivine (Ca x Fe y Mn 2-x-y)SiO 4 that originated from (Fe y Mn 2-y)SiO 4 was converted to Ca 2 SiO 4. In addition, the importance of the formation of gehlenite (Ca x Mn 2-x)SiAl 2 O 7 and wüstite Mn x Fe y Ca 1-x-y O phases in smelting ferromanganese alloys was discussed and clarified in detail. Based on the findings, recommendations are provided for the theoretical basis and technical support of smelting ferromanganese alloys. Unlabelled Image • New understanding on reduction mechanisms of Fe Mn ores was successfully clarified. • Crystal structure modification of Fe Mn ores by CaO addition for facilitating smelting. • Formation mechanism of (FeO) x (MnO) 1-x , Fe y Mn 2-y SiO 4 and Fe y Mn 1-y Al 2 O 4 is clarified. • Interface stepwise reaction between FeSiO 4 , FeAl 2 O 4 and flux systematically is discussed. • Formation mechanisms of gehlenite systems and wüstite systems were systemically clarified. [ABSTRACT FROM AUTHOR]

Mill scale scrap, which contains vast amounts of valuable metals, is a solid waste produced in the iron and steel industry. Conventional mill scale scrap treatment methods for metal extraction are characterized by high energy consumption and low value addition. In this study, co-treatment of mill scale scrap and manganese ore via the oxidization roasting-magnetic separation process was investigated for the synchronous preparation of higher-value materials and recovery of valuable metals. Thermodynamic and magnetism analyses indicated that a higher temperature (>1100 °C) and a MnO 2 /Fe 2 O 3 molar ratio of 0.75–1 are essential for the preparation of manganese ferrite. The experimental validation revealed that soft magnetic manganese ferrite powders with a purity of 97.5 wt% were obtained when the test was conducted at 1300 °C for 120 min, followed by a two-stage grinding and magnetic separation process; the corresponding yield and the Mn and Fe recoveries were 78.99 wt%, 86.14 wt%, and 84.60 wt%, respectively. During the oxidization process, [Fe2+]O was initially oxidized to the anti-form spinel-type structure of [Fe3+][Fe2+Fe3+]O 4 , and thereafter, it reacted with the decomposition product of [Mn3+][Mn2+Mn3+]O 4 to form a hybrid spinel-type structure [Me2+ x Me3+ l-x ][Me2+ 1-x Me3+ 1+x ]O 4 (Me refers to Mn and Fe) via the Mn2+/Fe2+/Mn3+/Fe3+ ions exchange at the tetrahedral and octahedral sites. Moreover, the as-purified ferrite can be used as an ingredient for the preparation of high-performance MnZn ferrite. Image 1 • A sustainable treatment of mill scale scrap and manganese ore is presented. • Valuable metals in the scrap and manganese ores are synchronously recovered. • The formation mechanism of manganese ferrite is discussed. • Oxidization roasting and magnetic separation regimes are systematically studied. • Mn and MnZn ferrites with good electromagnetic performance from scrap are obtained. [ABSTRACT FROM AUTHOR]

Low grade iron-bearing manganese ore is a potential solid waste resource. In this study, an innovative technology of suspension reductive roasting and magnetic separation (SRMS) was used to treat the iron-bearing manganese ore for comprehensive recovery of iron and manganese. The phase transformation of minerals in roasting process was systematically investigated by X-ray diffraction analyzer (XRD) and high-resolution transmission electronic microscope (HRTEM). The results show under the optimum conditions of reduction temperature 680 °C, reduction time 30 min, CO concentration 20% and particle size −0.9 mm, iron concentrate with iron grade 67.38% and iron recovery 87.14% and manganese concentrate with manganese grade 30.51% and manganese recovery 87.02% were obtained respectively. Magnetite converted from hematite was enriched in the concentrate of magnetic separation, while manganosite transformed from pyrolusite and braunite was enriched in the tailings of magnetic separation. SRMS can achieve full component utilization of iron-bearing manganese without residues. Unlabelled Image • Suspension reductive roasting and magnetic separation (SRMS) was proposed. • The SRMS technology was beneficial to phase selective transformation. • High-quality products of manganese-rich and iron-rich were obtained. • SRMS can achieve full component utilization of iron-bearing manganese. [ABSTRACT FROM AUTHOR]

Extraction of nano materials form natural ores is considered as an interesting point of research. The present work focuses on preparation of nano Mn 3 O 4 from two different sources, namely; manganese ore and pure chemicals. Mn 3 O 4 leached from manganese ore or that prepared from pure chemicals were utilized for preparation of LiMn 2 O 4 spinel by solid state method. The prepared oxide and spinel materials were investigated by XRF, XRD, TEM, SEM, BET and particle size distribution. The results revealed that the percentage of Mn 3 O 4 reached 82% for that leached from manganese ore and 99.1% for that prepared from pure chemicals. Both of them exhibited needle-like particles with comparable size of several nanometers; at least in one dimension. The analysis of manganese oxide leached from manganese ore exhibited Mn 3 O 4 , iron oxide and some impurities while that prepared from pure chemical displayed only pure Mn 3 O 4. LiMn 2 O 4 spinel and excess manganese oxide were detected in the sample prepared using pure Mn 3 O 4 while only LiMn 2 O 4 spinel phase was detected in the sample prepared using oxide leached form manganese ore. The particle size of LiMn 2 O 4 prepared from pure Mn 3 O 4 (50 nm - <1 μm) was smaller than that prepared from oxide leached from manganese ore (100 nm - 2 μm). Consequently, the surface area of LiMn 2 O 4 prepared from pure Mn 3 O 4 was higher than (9.32 m2/g) that prepared form leached Mn 3 O 4 (2.34 m2/g). [ABSTRACT FROM AUTHOR]

In this study, it is aimed to investigate neutron self-shielding effect in application of k 0 -NAA standardization method to determine Mn contents in manganese ores. Because the neutron self-shielding correction factors are significant factors in application of k 0 -NAA method for large samples. To estimate these, several Mn-ore samples and Au monitor were irradiated separately in a 37 GBq 241Am–Be neutron source irradiation unit and then they were measured by using a 78.5% relative efficient HPGe detector. In this study, the sigmoid function approaches for calculation of G th and Ge factors were applied for the right cylinder sample geometry at known elemental compositions in samples, determined by EDXRF technique with a 25 mm2 Silicon Drift Detector (SDD). The present results indicate that k 0 -NAA method is applicable successfully to determine Mn contents in Mn-ore samples providing that G th and G e factors are estimated accurately even if a low-flux isotopic neutron source is used. [ABSTRACT FROM AUTHOR]

During the industrial-scale smelting process of manganese ore, blast may occur due to the high moisture content of the ore, and drying pretreatment of the manganese ore is needed in the aspects of safety. In the present paper, microwave drying experiments were conducted under different particle size distributions and different microwave power conditions to explore the basic theory of microwave drying characteristics and kinetics of manganese ore, and the experimental data were fitted and analyzed by using thin-layer drying dynamics model. Results indicated that with the increase of the particle size and the microwave power of the manganese ore, the microwave drying rate increased, and accompanied with a promoting on the drying efficiency. For describing the microwave drying process of manganese ore, diffusion approach model was adopted among the commonly used thin-layer drying kinetic models. Based on Fick's second law, it can be seen that the surface diffusion coefficient increased from 4.27 × 10−13 m2/s to 8.24 × 10−8 m2/s with the increase of particle size from a particle size range of 0.012–0.095 mm to a particle size range of 4.2–5.0 mm. Clearly, the particle size has a significant influence on microwave drying efficiency. [ABSTRACT FROM AUTHOR]

The present study focuses on the leaching of MnO 2 form manganese ore by acid leaching method using glucose as a reducing agent. The leached MnO 2 was used to prepare nano La x Ca 1-x MnO 3 and La x Sr 1-x MnO 3 (x = 0.1, 0.3, 0.5 and 1) perovskites by mechanical activation method in the presence of La 2 O 3 , CaO or SrO. The leached MnO 2 and synthesized perovskite powders were investigated by x-ray diffraction technique (XRD) and transmission electron microscope (TEM).The prepared La x Ca 1-x MnO 3 and La x Sr 1-x MnO 3 perovskites were subjected for sintering up to 1350 and 1400 °C, respectively. The physical, electrical and magnetic properties as well as microstructure of sintered perovskites were investigated. The results showed that MnO 2 was successfully leached and utilized for preparation of nano La x Ca 1-x MnO 3 and La x Sr 1-x MnO 3 perovskites after milling for 8 h. La x Ca (1-x) MnO 3 was sintered at 1350 °C while La x Sr (1-x) MnO 3 was sintered 1400 °C. The doping with Ca and Sr led to decreasing the electrical resistivity, while they led improving the magnetic property until specific limit (x = 0.5) after which magnetic property was decreased again with increasing their amounts. The highest magnetization was obtained for La 0.5 Ca 0.5 MnO 3 and La 0.5 Sr 0.5 MnO 3. In all cases, their values were higher than that of pure LaMnO 3. [ABSTRACT FROM AUTHOR]

Low-grade refractory rhodochrosite ores are difficult to be utilized by traditional beneficiation process owing to their complex characteristics. In this study, preconcentration-neutral suspension roasting-magnetic separation process was firstly proposed, and the thermodynamics, kinetics, phase and microstructure evolution of mineral reaction during rhodochrosite roasting were systematically studied. The results show the raw ore was preconcentrated by high intensity magnetic separation. The suspension roasting was carried out under optimum conditions. After magnetic separation, the magnetic separation concentrate with 24.30% manganese grade and 59.61% manganese recovery was obtained. Manganese ore was transformed from MnCO 3 to MnO during roasting. The thermal decomposition reaction of manganese ore conformed to random nucleation and subsequent growth model. The original minerals was destroyed due to the cracks caused by the decomposition of carbonate in rhodochrosite ore, which was conducive to the full dissociation of useful minerals and gangue mineral, and further improve the separation and enrichment effect. Unlabelled Image • Preconcentration-neutral suspension roasting-magnetic separation were proposed. • This process performs stable production, with high-quality roasted product. • Manganese ore was transformed from MnCO 3 to MnO. • Thermal decomposition reaction conformed to random nucleation and growth model. [ABSTRACT FROM AUTHOR]

• Mn grade and recovery in Mn-Fe ore are upgrade to 54.35% and 90.05%, respectively. • Phase transformation of solid-state reaction of Mn-Fe ore is clarified. • The formation of Mn x Fe 1−x O and FeO·Al 2 O 3 result in poor separation efficiency of Mn and Fe. • Reduction behaviors of Mn x Fe 1−x O and FeO·Al 2 O 3 is studied. Carbothermal reduction followed by magnetic separation has been recognized as an effective recovery strategy to achieve separation of Mn and Fe from ferruginous manganese ores (Fe-Mn ores). However, it is difficult to improve the recovery of manganese more than 85% by changing carbothermic roasting reduction and magnetic separation. This work clarified the underlying reason for the poor separation with the magnetic separation process and proposed a promising process for the recovery of Fe and Mn from Fe-Mn ore. The effect of operating variables on recovery and separation of Mn and Fe from Fe-Mn ore is initially investigated during the carbothermic reduction roasting process followed by magnetic separation to reveal the underlying reason for the poor separation from Fe-Mn ores. Then, the stepwise reduction behaviors of the MnO-Fe 2 O 3 and MnO-Fe 2 O 3 -Al 2 O 3 systems were investigated to clarify that the formation of composite oxide Mn 1−x Fe x O (0 < x < 0.497) and hercynite (FeO·Al 2 O 3) directly caused the poor separation of Fe and Mn from high-alumina Fe-Mn ores. Then, the stepwise reduction roasting behaviors of Mn 1−x Fe x O and FeO·Al 2 O 3 were investigated by XRD, SEM-EDS and XPS analysis. After adjusting the experimental parameters, iron-rich products with a Fe recovery of 94.31% and a grade of 85.21% and manganese-rich product with a Mn recovery of 90.05% and a grade of 54.35% are obtained. The mass ratio of Mn/Fe increased to 8.5 in the manganese-rich product. [ABSTRACT FROM AUTHOR]

Manganese ferrite spinel (Mn x Fe 3-x O 4) has been synthesized by multi-step roasting and magnetic separation from ferruginous manganese ore (Fe Mn ore). In the current work, during the carbothermic reduction process, the reduction behavior of Fe Mn ore at the high temperature was investigated. Then, the reduced Fe Mn ore was separated by two-step magnetic separation. The morphologies and properties of the obtained Fe x Mn 1-x O products with various x-values by two-step magnetic separation were characterized by XRD and SEM-EDS analysis to further understand the formation mechanism of Fe x Mn 1-x O from Fe Mn ore. In the end, the intermediates were magnetized in an oxidizing roasting step. Based on the experimental results and the thermodynamic calculations, the high temperature (above 950 °C) and long reduction time were conducted to promote the formation of Mn x Fe 3-x O 4. The formation mechanism of spinel-type Mn x Fe 3-x O 4 was also described in this paper. The morphology and the property evolution of manganese ferrite (Mn x Fe 3-x O 4) synthesized by multi-step roasting and magnetic separation were investigated in air atmosphere. The synthesized Fe x Mn 3-x O 4 product with saturation magnetization was achieved when the intermediates were roasted at 1000 °C for 90 min in air. These findings can provide theoretical support for the reasonable utilization of Fe Mn ore by multi-step roasting and magnetic separation. Unlabelled Image • MnFe 2 O 4 was synthesized by multi-step roasting and magnetic separation. • The reduction behavior of Fe x Mn 1-x O compound was analyzed. • Oxidation behavior of synthetic MnFe 2 O 4 in air atmosphere was studied. • Morphologies and phase transformation of Fe and Mn in Fe Mn ore was clarified. [ABSTRACT FROM AUTHOR]

Rhodochrosite and calcite have similar physicochemical characteristics and floatability, making it difficult for conventional flotation collectors to effectively separate the two minerals. In this paper, a novel 3-tetradecylamine propyl amidoxime (TPA) collector with selective and excellent collection capability for rhodochrosite has been investigated. The micro-flotation experiments showed that the flotation performance of TPA is superior to that of the commonly used sodium oleate (NaOL) collector, and the separation of rhodochrosite and calcite can be achieved under neutral conditions. At a slurry pH of 7 and a dosage of 2.0 × 10−4 mol/L, TPA provided a recovery of 88.5% for rhodochrosite and only 15.0% for calcite. The mechanism of interaction between TPA and minerals was examined by contact angle, Zeta potential tests and Fourier transform infrared (FTIR) analysis, which indicated that TPA selectively adsorbed on the surface of rhodochrosite rather than calcite. Finally, the adsorption behavior of TPA molecules on the surface of rhodochrosite was confirmed by Density functional theory (DFT) calculation to be through electrostatic interaction. This paper provides a novel collector for the flotation separation of rhodochrosite from calcite with excellent collecting ability and selectivity, which is significant for the efficient utilization of manganese ore resources. [Display omitted] • A amidoxime collector TPA was prepared and introduced in rhodochrosite flotation. • The adsorption mechanism of TPA on the surface of pure rhodochrosite was studied. • TPA has better flotation performance and selectivity than NaoL for rhodochrosite. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2-Decanoylamino-4-hydroxycarbamoyl-butyric acid (DHBA) is designed. • "Y" structure surfactant DHBA is used as rhodochrosite flotation collector. • DHBA exhibits excellent collecting ability to rhodochrosite at a low dosage. • DHBA achieved a selective flotation separation of rhodochrosite from quartz at pH 7. • Both carboxyl and hydroxamic groups of DHBA chemisorbed on rhodochrosite surface. 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. [ABSTRACT FROM AUTHOR]

A coupled system comprised of a biofilm electrode reactor (BER) and a manganese ore substrate microbial fuel cell-constructed wetland (MFC-CW) system was used to remove co-exposed antibiotic and Zn (II), as well as simultaneously reduce copies of antibiotic resistance genes (ARGs) in the current study. In this system, BER primarily reduced the concentrations of antibiotics and Zn (II), and the effluent was used as the input to the MFC-CW, thereby providing electricity to BER. Co-exposure to a high concentration of Zn (II) decreased the relative abundances (RAs) of ARGs in the BER effluent, whereas the remaining sub-lethal concentration of Zn (II) increased the RAs of ARGs in the MFC-CW effluent. Even though the absolute copies of ARGs in the effluents increased during co-exposure, the total number of target ARG copies in the effluent of MFC-CW was significantly lower than that of BER. Moreover, BER pre-treatment eliminated most of Zn (II), which improved the electrical power generation characteristic of the MFC-CW unit. Correspondingly, the bacterial community and the ARGs hosts were analyzed to demonstrate the mechanism. In conclusion, the coupled system demonstrates significant potential to reduce antibiotics, Zn (II) and environmental risks posed by ARGs. [Display omitted] • Zn (II) reduced total relative abundances of ARGs and intI in the BER effluent. • Sub-lethal concentration of Zn (II) enriched ARGs in the MFC-CW effluent. • The total copies of the target ARGs in the MFC-CW effluent were reduced. • BER reduced the toxic damage of Zn (II) to the MFC-CW anode community. [ABSTRACT FROM AUTHOR]

Manganese ore substrate up-flow microbial fuel cell constructed wetland (UCW-MFC(Mn)) as an innovative wastewater treatment technology for purifying antibiotics and electricity generation with few antibiotic resistance genes (ARGs) generation has attracted attention. However, antibiotic purifying effects should be further enhanced. In this study, a biofilm electrode reactor (BER) that needs direct current driving was powered by a Mn ore anode (UCW-MFC(Mn)) to form a coupled system without requiring direct-current source. Removal efficiencies of sulfadiazine (SDZ), ciprofloxacin (CIP) and the corresponding ARGs in the coupled system were compared with composite (BER was powered by direct-current source) and anaerobic systems (both of BER and UCW-MFC were in open circuit mode). The result showed that higher antibiotic removal efficiency (94% for SDZ and 99.1% for CIP) in the coupled system was achieved than the anaerobic system (88.5% for SDZ and 98.2% for CIP). Moreover, electrical stimulation reduced antibiotic selective pressure and horizontal gene transfer potential in BER, and UCW-MFC further reduced ARG abundances by strengthening the electro-adsorption of ARG hosts determined by Network analysis. Bacterial community diversity continuously decreased in BER while it increased in UCW-MFC, indicating that BER mitigated the toxicity of antibiotic. Degree of modularity, some functional bacteria (antibiotic degrading bacteria, fermentative bacteria and EAB), and P450 enzyme related to antibiotic and xenobiotics biodegradation genes were enriched in electric field existing UCW-MFC, accounting for the higher degradation efficiency. In conclusion, this study provided an effective strategy for removing antibiotics and ARGs in wastewater by operating a BER-UCW-MFC coupled system. [Display omitted] • BER decreased antibiotic selective pressure and horizontal gene transfer potential. • Electric field strengthened antibiotic and resistance gene removal in the coupled system. • UCW-MFC has higher adsorption ability for antibiotic resistance gene than BER. • Cooperation between fermentative and electrochemically active bacteria was observed. • The bacterial community composition and function was impacted by electric field. [ABSTRACT FROM AUTHOR]

• Chemical-Looping Combustion (CLC) operational experience is more than 11,000 h. • Ideally, no gas active separation is needed in CLC as carbon capture is inherent. • CLC has a unique potential for reducing cost and energy penalty of carbon capture. • A large number of oxygen-carrier materials suitable for CLC have been identified. • CLC can be used with most fuels, including biomass which gives negative emissions. A key for chemical-looping combustion (CLC) is the oxygen carrier. The ultimate test is obviously the actual operation, which reveals if it turns to dust, agglomerates or loses its reactivity or oxygen carrier capacity. The CLC process has been operated in 46 smaller chemical-looping combustors, for a total of more than 11,000 h. The operation involves both manufactured oxygen carriers, with 70% of the total time of operation, and less costly materials, i.e. natural ores or waste materials. Among manufactured materials, the most popular materials are based on NiO with 29% of the operational time, Fe 2 O 3 with 16% and CuO with 13%. Among the monometallic oxides there are also Mn 3 O 4 with 1%, and CoO with 2%. The manufactured materials also include a number of combined oxides with 11% of operation, mostly calcium manganites and other combined manganese oxides. Finally, the natural ores and waste materials include ilmenite, FeTiO 3 with 13%, iron ore/waste with 9% and manganese ore with 6%. In the last years a shift towards more focus on CuO, combined oxides and natural ores has been seen. The operational experience shows a large variation in performance depending on pilot design, operational conditions, solids inventory, oxygen carrier and fuel. However, there is at present no experience of the process at commercial or semi-commercial scale, although oxygen-carrier materials have been successfully used in commercial fluidized-bed boilers for Oxygen-Carrier Aided Combustion (OCAC) during more than 12,000 h of operation. The paper discusses strategies for upscaling as well as the use of biomass for negative emissions. A key question is how scaling-up will affect the performance, which again will determine the costs for purification of CO 2 through e.g. oxy-polishing. Unfortunately, the conditions in the small-scale pilots do not allow for any safe conclusions with respect to performance in full scale. Nevertheless, the experiences from pilot operation shows that the process works and can be expected to work in the large scale and gives important information, for instance on the usefulness of various oxygen-carriers. Because further research is not likely to improve our understanding of the performance that can be achieved in full scale, there is little sense in waiting with the scale-up. A major difficulty with the scaling-up of a novel process is in the risk. First-of-its-kind large-scale projects include risks of technical mistakes and unforeseen obstacles, leading to added costs or, in the worst case, failure. One way of addressing these risks is to focus on the heart of the process and build it with maximum flexibility for future use. A concept for maximum flexibility is the Multipurpose Dual Fluidized Bed (MDFB). Another is to find a suitable existing plant, e.g. a dual fluidized-bed thermal gasifier. With present emissions the global CO 2 budget associated with a maximum temperature of 2 °C may be spent in around 20–25 years, whereas the CO 2 budget for 1.5 °C is may be exhausted in 10 years. Thus, the need for both CO 2 neutral fuels and negative emissions will become increasingly urgent as we are nearing or transgressing the maximum amount of CO 2 that can be emitted without compromising the global climate agreement in Paris saying we must keep "well below" 2 °C and aim for a maximum of 1.5 °C. Thus, biomass may turn out to be a key fuel for Carbon Capture and Storage (CCS), because CO 2 -free power does not necessarily need CCS, but negative emissions will definitely need Bio-CCS. [ABSTRACT FROM AUTHOR]

Manganese is a strategically important metal that is widely used in industrial applications such as steel, catalysts, and batteries. Manganese generally presents as manganese dioxide (MnO 2) in most of the ores. As MnO 2 is stable in acid or alkaline oxidizing conditions, manganese extraction must be performed under reducing conditions to convert the insoluble Mn(IV) to soluble Mn(II) in aqueous medium. In this regard, two processes are followed viz. reduction roasting followed by leaching and reductive leaching. The major disadvantage of the reduction roasting process is the intensive energy consumption, high investment and operating costs as well as the occasional release of harmful gases. The hydrometallurgical reductive leaching method possesses the advantages of energy conservation and one-step leaching process. The reducing agents used for leaching are either pure inorganic or organic chemicals or sometimes new kinds of reducing agents such as agricultural and biomass wastes. The present review summarizes the process developed for extraction and recovery of manganese from ores using different kinds of reducing agents. The parameters affecting the leaching of manganese and reactions involved are reviewed and discussed. • Reductive leaching of Mn from ores were comprehensively reviewed. • Reducing agents were categorized and explained according to their nature. • Chemistry and mechanism of reduction was discussed for each reducing agents. • The optimum conditions for Mn recovery were summarized. • The economic feasibility of reductive leaching should be further investigated. [ABSTRACT FROM AUTHOR]

• Mn ores are cheap and promising oxygen carriers for chemical-looping combustion. • Effect of precalcination on e.g. reactivity was investigated for 4 Mn ores. • Calcination was associated with significant mass losses and chemical transformations. Manganese ores have been identified as promising oxygen carriers for chemical-looping processes with solid fuels, including combustion and gasification systems. Such Mn-based minerals are readily available globally and could thus be a cheap alternative to other naturally occurring oxygen carriers, such as ilmenite. These ores are usually highly heterogeneous, with varying phase composition, both on the inter-particle as well as intra-particle level. Further, manganese ores contain Mn in many forms and states, including combined or mixed oxides. The content of Fe, Al, Si, Mg and Ca can be high, but also vary significantly. Thus, it can be expected that there will be transformations of the chemical and physical structures during heating from room temperature to operational conditions. In fact, natural materials are often calcined in air prior to use in CLC systems, to avoid agglomeration and defluidization. In this work the effect of heat treatment is investigated for four different manganese ores that have widely different compositions. The mass losses during heat-up in a batch, fluidized-bed reactor and a thermogravimetric analyzer (TGA) were measured. In addition, the change in reactivity over 21 redox cycles with both methane and a syngas (CO/H 2) was investigated for both heat treated and fresh ores. During the batch experiments, the defluidization tendency of the ores was investigated as well. The ores were characterized with X-ray diffraction (XRD) and ICP-SFMS. It was found that there was a release of CO 2 and O 2 from the ores during heat up in the batch experiment, likely originating from carbonates and thermodynamic unstable manganese oxides respectively. Also, significant mass losses were observed for the untreated ores in the TGA, and in addition to the release of CO 2 and O 2 , a release of H 2 O was observed at lower temperatures. Reactivity was similar between heat treated and untreated ores, especially when considering the mass loss during heat-up. Still, the reactivity varied significantly among the different ores tested. Defluidization was observed only for one of the ores, when a blend of manganese ore and quartz sand was used as bed material during testing with syngas. However, no defluidization was observed during heat-up. In summary, depending upon the ore used, significant mass losses can be expected, which may need to be accounted for during operation with solid fuels. [ABSTRACT FROM AUTHOR]

• Manganese ore morphology development impacts reduction reaction progress. • Reduction quickly transforms minerals to manganosite, alloy and glass phase. • Glass phase basicity levels are much lower than bulk ore basicity levels. • Matrix glass phase formation lowers manganese ore reduction rates at 1300 °C. Manganese ores differ extensively in their mineralogical and bulk chemical composition. Consequently these ores follow different mineralogical morphology development paths as the reduction reaction proceeds in the production furnace. Mineralogical factors such as composition and distribution of initial liquid silicate formed at specific temperatures, as well as iron and manganese metallisation patterns, are significant determining factors in the relative importance of different parallel reduction reaction mechanisms in each ore type. Applied mineralogy techniques were used to identify and analyse matrix liquid silicate phase formation in manganese ore reacted at 1300 °C with Carbon Black reductant. The study includes three South African ores from the Kalahari Manganese Field, the ores represent both the Wessels-type and Mamatwan-type mineralogy. FactSage computational thermodynamic calculations were made to explain liquid silicate phase formation and its evolution with increased reaction time. Matrix silicate phase liquidus temperatures and pseudo-ternary phase diagrams in the MnO-FeO-SiO 2 -CaO-MgO-Al 2 O 3 composition system were calculated. Matrix liquid silicate formed at the relatively low reaction temperature of 1300 °C within all three ores, although different quantities of liquid silicate formed along differing composition paths set by ore mineralogy. [ABSTRACT FROM AUTHOR]

Abstract In chemical looping combustion (CLC), a necessary oxygen polishing step exerted an additional cost to the technology due to an extra demand of pure O 2. However, the additional cost can be lowered if the oxygen carriers can produce gaseous oxygen, i.e. has a chemical looping with oxygen uncoupling (CLOU) property. A CLC + CLOU scheme is proposed in the study. Production of gaseous O 2 using a manganese ore and the Cu-modified manganese ore as oxygen carriers were investigated. The reaction kinetics of the two oxygen carriers were studied by thermogravimetric analysis (TGA). Multiple O 2 uptake and release cycles were carried out to demonstrate the good stability of the oxygen carriers. Continuous tests with both oxygen carriers were carried out in a dual fluidized bed. Results showed that both oxygen carriers could be fluidized well in the continuous run and a stream of O 2 could be obtained stably. The Cu-modified manganese ore showed higher oxidation rate and oxygen transport capacity than the original manganese ore. Both materials have advantage economically and could be promising for O 2 production in the CLC + CLOU scheme. [ABSTRACT FROM AUTHOR]

Iron ore tailings (FeT) and manganese ore tailings (MnT), which are abundant and inexpensive materials that contain many trace elements, were employed for the remediation of As-contaminated soil to mitigate As accumulation in rice under greenhouse conditions. Prior to the experiments, the toxicities of both amendments were assessed with the toxicity characteristic leaching procedure (TCLP) and horizontal vibration method (HVM). Based on the assessment results, both amendments were pretreated until no As was present in the leaching solution. After application of both amendments to the soil, the soil pH increased significantly (p < 0.05). The ranges of As concentrations in husk and brown rice samples were 0.13–1.54 mg kg−1 and 0.06–0.42 mg kg−1, respectively. The lowest concentrations of As (0.06±0.02 mg kg−1) in rice grains were observed with MnT treatment, which was related to the structure and composition of MnT. There was a significant negative relationship (p < 0.05) between Mn and As in rice plants, while there was a significant positive relationship (p < 0.05) between Fe and As in rice plants as well as the ratio of Fe/Mn and As in rice plants. In conclusion, MnT could potentially be useful as an amendment to remediate As-contaminated soil and control As uptake by rice plants. [ABSTRACT FROM AUTHOR]

Iron ore tailings (FeT) and manganese ore tailings (MnT), which are abundant and inexpensive materials that contain many trace elements, were employed for the remediation of As-contaminated soil to mitigate As accumulation in rice under greenhouse conditions. Prior to the experiments, the toxicities of both amendments were assessed with the toxicity characteristic leaching procedure (TCLP) and horizontal vibration method (HVM). Based on the assessment results, both amendments were pretreated until no As was present in the leaching solution. After application of both amendments to the soil, the soil pH increased significantly (p < 0.05). The ranges of As concentrations in husk and brown rice samples were 0.13-1.54 mg kg-1 and 0.06-0.42 mg kg-1, respectively. The lowest concentrations of As (0.06±0.02 mg kg-1) in rice grains were observed with MnT treatment, which was related to the structure and composition of MnT. There was a significant negative relationship (p < 0.05) between Mn and As in rice plants, while there was a significant positive relationship (p < 0.05) between Fe and As in rice plants as well as the ratio of Fe/Mn and As in rice plants. In conclusion, MnT could potentially be useful as an amendment to remediate As-contaminated soil and control As uptake by rice plants. [ABSTRACT FROM AUTHOR]

Abstract Polycrystalline perovskite-type manganite La 0.65 Ca 0.35 Mn 1-x Ni x O 3 were prepared by sol-gel method. X-ray diffraction measurement showed that all samples have a single phase. Rietveld's refinement result of X-ray diffraction indicates that our samples have an orthorhombic structure with pnma space group. Magnetization measurements versus temperature in a magnetic applied field of 0.1 T showed that Ni-doping leads to a paramagnetic to ferromagnetic transition with a Curie temperature decreasing from 272 K to 194 K. When x = 0.05, the Tc of the sample was adjusted to near room temperature. The maximum magnetic entropy change - ΔS M corresponding to a 3 T magnetic field variation was found to be 4.76 J/kg K and about 69.59 J/kg of relative cooling power for La 0.65 Ca 0.35 Mn 0.95 Ni 0.05 O 3. Besides, Arrott plots showed that our sample exhibit a second-order on the phase transition of the manganite. Highlights • The traditional sol-gel method was improved by using citric acid as complexant, shortening the preparation period and reducing the sintering temperature. • Doping at the Mn site severely affects the Curie temperature of the sample. Our results show the sample La 0.65 Ca 0.35 Mn 0.95 Ni 0.05 O 3 exhibited a magnetic entropy change -ΔS M 4.76 J/kg K and a RCP 69.59 J/kg under a 3.0 T magnetic field near Tc. • In theory, the parameters such as magnetic entropy change and relative refrigeration capacity of the prepared products are simulated, and the experimental results are compared with the theoretical predictions. • The sample we obtained can be used as candidates for potential applications for magnetic refrigeration. [ABSTRACT FROM AUTHOR]

Highlights • Characteristics of manganese ore resources and Mn alloy products consumption are summarized. • Diverse processes for extracting and separating Mn and Fe from Fe-Mn ores are reviewed. • Enlarging magnetism, solubility or fusibility difference is critical to extract and separate Fe and Mn. • Selecting reductants and leaching agents is important for extraction and separation of Fe and Mn. Abstract There are abundant ferruginous manganese ores (abbr. Fe-Mn ores) in many parts of the world. For example, almost half of the manganese ore resources in India are ferruginous and more than 73% of the manganese ores in China belong to Fe-Mn ores with a low Mn/Fe mass ratio (<3). With the depletion of high grade manganese ore resources, the Fe-Mn ores are becoming important substitution resources for extracting manganese. In general, the production of Mn alloy from manganese ores requires that the Mn grade is more than 30% and the Mn/Fe mass ratio is greater than 5. During the production of electrolytic manganese or manganese chemical products, the issue of co-leaching of Mn and Fe complicates the purification procedure for the MnSO 4 solution if Fe-Mn ores are used as raw materials. Numerous approaches are reported to realize the selective extraction and separation of Mn and Fe from the Fe-Mn ores. The extraction and separation technologies cover physical beneficiation, chemical beneficiation (hydrometallurgy and pyrometallurgy) and physico-chemical combined processes. This present work reviews the technical principles, parameters and recovery efficiencies of diverse processes on the aspect of selective extraction and separation of Mn and Fe from Fe-Mn ores. This review can provide guidance for selecting appropriate methods to exploit Fe-Mn ores or other secondary resources containing Fe and Mn oxides. The authors also put forward a new route to produce manganese ferrite materials using Fe-Mn ores as the raw materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • BPA oxidation in bioelectro-activation of PMS system was enhanced by the FMO. • Both Mn and Fe in the natural FMO are the reactive sites. • Radical and non-radical reactions are responsible for BPA degradation. • The FMO/MFC/PMS system could be applied in natural water. Abstract The natural Fe-bearing manganese ore (FMO) and bioelectricity supplied by a single-chamber microbial fuel cell (MFC) were employed to construct the peroxymonosulfate (PMS) activation system (FMO/MFC/PMS) for the degradation of bisphenol A (BPA). The FMO was characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results show that ε-MnO 2 and α-Fe 2 O 3 were the active components of the natural FMO and they could greatly facilitate the bioelectro-activation of PMS for the oxidation of BPA. When FMO dosage, PMS concentration and current density were set as 0.5 g L−1, 10 mM and 100 mA m−2, respectively, 97.8% of BPA degradation could be achieved at natural pH of BPA solution after 80 min reaction and about 80% of TOC could be removed when the reaction time was prolonged to 120 min. Based on the electron paramagnetic resonance result, scavenging tests, fluorescence spectra experiment and X-ray photoelectron spectroscopy analysis, both radical oxidation (sulfate and hydroxyl radical) and non-radical reactions (such as singlet oxygen and direct electron transfer) were considered to be responsible for BPA removal. The FMO exhibited good stability and could be recycled at least 3 runs without any additional special treatment. 10 mM of Cl− and HCO 3 − could suppress the degradation of BPA while 10 mM of NO 3 − showed negligible effects on BPA removal. The FMO/MFC/PMS process could be applied in natural water without the decrease of BPA removal. [ABSTRACT FROM AUTHOR]

Abstract Oxygen carrier aided combustion (OCAC) is a combustion concept which utilises oxygen carriers as bed material in existing fluidised bed boilers. In this study, a manganese ore was used in a 12 MW th CFB boiler. During the experimental session with the manganese ore, the boiler was operated with wood chips as fuel for more than a week without replacement of the bed material. Bed samples were extracted each day in order to investigate interactions between the manganese ore and the wood ash components. The samples were examined with SEM/EDX to follow the chemical distribution of ash elements in the bed particles. Physical properties such as density, size distribution and attrition resistance were followed as well. The impact on the reactivity of the oxygen-carrier bed particles was examined in a batch fluidised bed reactor at laboratory scale with gaseous fuels. Elemental composition analysis of the samples showed that common ash elements such as silicon, calcium, potassium, magnesium and sulphur had been accumulated in the manganese ore. Silicon, calcium and potassium were found throughout the particles as well as in formed surface layers. Sulphur was only found at the surface of the particles. The reactivity of the oxygen-carrying particles was affected during operation and showed a continuous decrease with increasing residence time in the boiler. The decrease in reactivity could be coupled to the layers of ash formed. Thus, this is an important issue when developing novel combustion concepts, such as OCAC and chemical-looping combustion (CLC), for biomass fuels. Highlights • A manganese ore was used as active bed material in a 12 MW th biomass CFB boiler. • Silicon, calcium, potassium, magnesium and sulphur were accumulating in the bed. • Sulphur and potassium coexisted in a surface layer around some of the particles. • The fuel reactivity of the particles decreased continuously during the operation. [ABSTRACT FROM AUTHOR]

The use of manganese ore as oxygen carrier has recently gained interest, primarily due to the combination of low cost and moderate to high reactivity. The possibility of an oxygen uncoupling reaction enhancing reactivity may be an additional advantage. In this paper, six manganese ores (Gloria, Tshipi, Gui Zhou, Metmin, Sibelco Calcined and SinAus) were evaluated with respect to their ability to release oxygen with a devolatilized wood fuel (char) using a small batch fluidized bed reactor. The char was used in order to establish the rate of the oxygen release i.e. oxygen uncoupling. The manganese ore samples were heat treated for 24 h at 950 °C and sieved to a size fraction of 125–180 µm prior to experiments. The oxygen release was evaluated at four temperatures (850, 900, 950 and 1000 °C). Moreover, comparisons were made with the reactivity of these ores with gaseous fuels made in previous works. All six investigated ores showed a small O 2 release (CLOU effect), which increased with temperature. Still, the oxygen uncoupling effect is likely not the dominating reaction when using gaseous fuels, as the overall oxygen transfer via CLOU is considerably smaller compared to the oxygen transfer when gaseous components react directly with the particle. For example, at 1000 °C the Gloria ore had the highest mass-based reduction rate, dω/dt, was 0.047 wt%/s for methane and 0.36 wt%/s for syngas, which should be compared with the much lower dω/dt of 0.0073 wt%/s for char, which is a measure of the CLOU effect. The best performing ores were Gloria and Tshipi, which showed the highest uncoupling capacity and rate of oxygen release. It is interesting to note that these two ores had significantly higher Ca and Mg fractions compared to the other four ores with lower reactivity. This suggests that combined Mn-Ca phases may be active for the oxygen release reaction. The ores were analyzed with XRD and SEM-EDX to establish which phases were present in the ores. It was found that the bulk of the ores are very heterogeneous, while the individual particles are much more homogeneous in composition. [ABSTRACT FROM AUTHOR]

Abstract The detailed investigation on the specific heat in manganites of Pr 0.6 Sr 0.4− x Ag x MnO 3 (x = 0.05 and x = 0.1) has been reported. The experimental conditions were: the temperature range 1.8–330 K and applied magnetic fields of 0, 1, 2 and 3 T. Specific heat results confirmed two phase transitions, a structural one at T str = 43 K for both samples and a paramagnetic–ferromagnetic one near T PM–FM = 288 K and 284 K for the x = 0.05 and x = 0.1 sample, respectively. For the more doped sample the magnetic field causes the shift of the PM–FM transition temperature towards higher temperatures. A thorough analysis of particular contributions to the specific heat was presented. The indirect magnetocaloric effect was deduced for the more doped sample (x = 0.1). Under an applied magnetic field of 3 T magnetic entropy changes and adiabatic temperature exhibits a maximum. The absolute Δ S max reaches the value of 1.74 J/mol K, resulting in adiabatic cooling of Δ T ad = 0.95 K. Such result confirms presented samples as promising candidates for the magnetic cooling technology at room temperature. Highlights • Heat transport investigations towards magnetic cooling applications. • Praseodymium based manganites exhibit good magnetocaloric properties. • Applying magnetic field induces glass-like fraction. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) is a type of carbon capture technology that employs metal oxide particles in a redox reaction to transport oxygen to the fuel. As opposed to first-generation carbon capture concepts, CLC does not include a gas separation step and thus offers the advantage of having no thermodynamic energy penalty in the capture process. Manganese-containing oxygen carriers have been shown to offer a good compromise of gas conversion performance, availability, and cost. On the other hand, previously tested manganese materials have often been challenged with high attrition in continuous CLC. By sintering the ore prior to its use as oxygen carrier, the structure of the particles can be reinforced to increase their durability in the process. In this study, a sintered manganese ore was tested for 56 h in two pilot units of different size. The oxygen carrier worked well in the process, was easily fluidized, and did not exhibit any tendency towards agglomeration. Compared to other manganese materials tested in the same units, a higher lifetime based on fines production was reached, while gas conversion performance was similar. Different biomass fuels, mainly biochar of different sizes and black wood pellets, were employed in the study. A clear correlation between gas conversion and the fuel volatile content was detected; this is consistent with results reported in previous studies. The highest gas conversion reached in both units was ∼93.5% using wood char. The highest carbon capture efficiency, 99% and 100% in the 10- and 100-kW unit, respectively, was reached with black pellets. To compare the tested material with the state-of-the-art oxygen carrier ilmenite, some tests were conducted with a bituminous coal that had been used in the same pilot with ilmenite. The results indicate a higher conversion performance for the tested manganese material. [ABSTRACT FROM AUTHOR]

The striking effect of Ti-doping on the magnetic properties of La 0.5 Ca 0.5 MnO 3 nanoparticles have been investigated by different methods. The half doped manganites are at the boundary between the ferromagnetic metallic and antiferromagnetic insulating phases. There is a delicate balance between ferromagnetic double exchange and antiferromagnetic superexchange interactions. In half doped La 0.5 Ca 0.5 MnO 3 charge ordered antiferromagnetic state is destabilized below a critical size followed by development of ferromagnetism. We have seen that slight disturbance in magnetic exchange interactions by Ti-substitution (>5%) drastically changes the fraction of ferromagnetic clusters. The ferromagnetic Mn 3+ —O—Mn 4+ interaction is suppressed by Mn 3+ —O—Ti 4+ type of interactions. For more than 10% Ti doping the surface ferromagnetic character of the nanoparticles is largely weighed down. This suppression of ferromagnetic component by diamagnetic Ti-doping eventually leads to phase separated states with lower magnetization value. [ABSTRACT FROM AUTHOR]

• Four alkalis are compared for the interaction with a Mn ore oxygen carrier in CLC. • Potassium salts result in earlier onset of defluidization than sodium. • Carbonate alkalis (Na and K) derived defluidization is more permanent than chloride. • Sodium retention in the oxygen carrier is double that for potassium. Chemical looping combustion (CLC) is a novel technology for heat and power generation with inherent CO 2 capture. Using biomass in CLC (bio-CLC), negative CO 2 emissions can be attained. Biomass usually contains high content of alkalis (mainly K and Na) which can be problematic in the process, such as potential alkali-bed interaction, and this is the focus of current work. This work uses charcoal with and without the impregnation with alkali chlorides, KCl and NaCl. The results are compared to previous data from samples impregnated with K 2 CO 3 and Na 2 CO 3. A low-alkali braunite manganese ore is used as bed material to study the oxygen carrier interaction with the alkalis in cyclic experiments at 950 °C in a quartz batch fluidized-bed reactor. As compared to charcoal without alkali impregnation, the impregnation with KCl, NaCl, K 2 CO 3 , and Na 2 CO 3 can improve the rate of gasification by a factor of 4, 3, 10, 8, respectively. Partial-defluidization of the braunite particles was found with all the alkali-fuels, although the extent differed, e.g., K 2 CO 3 and KCl resulted in earlier onset of defluidization than Na 2 CO 3 and NaCl. Further, indications of partial defluidization were earlier and more permanent with the carbonates than the chlorides. Partial agglomeration with soft agglomerates of the bed was observed, while hard agglomerations were never seen. Accumulation of K, Na, Si, and Ca was found in the agglomerates after cycles with K 2 CO 3 -charcoal and Na 2 CO 3 -charcoal, while little K and Na was detected in the bridges between particles after the KCl and NaCl cycles. A significant fraction of the alkali added was found in the oxygen carrier, with 80% or more being retained for the Na salts, and around 40% for the K salts. There was no clear difference between chlorides and carbonates with respect to retention. The fresh and used braunite have very similar reactivity with CH 4 and H 2 , whereas some decrease in reactivity is noticed with CO. [ABSTRACT FROM AUTHOR]