Morphological, Microstructural, and In Situ Chemical Characteristics of Siderite Produced by Iron-Reducing Bacteria

Dissimilatory iron-reducing bacteria (DIRB) oxidize organic matter or hydrogen and reduce ferric iron to form Fe(II)-bearing minerals, such as magnetite and siderite. However, compared with magnetite, which was extensively studied, the mineralization process and mechanisms of siderite remain unclear. Here, with the combination of advanced electron microscopy and synchrotron-based scanning transmission X-ray microscopy (STXM) approaches, we studied in detail the morphological, structural, and chemical features of biogenic siderite via a growth experiment with Shewanella oneidensis MR-4. Results showed that along with the growth of cells, Fe(II) ions were increasingly released into solution and reacted with CO32- to form micrometer-sized siderite minerals with spindle, rod, peanut, dumbbell, and sphere shapes. They are composed of many single-crystal siderite plates that are fanned out from the center of the particles. Additionally, STXM revealed Fh and organic molecules inside siderite. This suggests that the siderite crystals might assemble around a Fh-organic molecule core and then continue to grow radially. This study illustrates the biomineralization and assembly of siderite by a successive multistep growth process induced by DIRB, also provides evidences that the distinctive shapes and the presence of organic molecules inside might be morphological and chemical features for biogenic siderite.

Gamma-ray shielding parameters of Li2B4O7 glasses: undoped and doped with magnetite, siderite and Zinc-Borate minerals cases

Designing new shielding materials and calculating their shielding parameters are important task to keep living in safe from hazardous effects of radiation. In this study, the lithium borate glasses with chemical formula (Li2B4O7)(100−x)Yx (x = 0, 10, 20, 30 and 40 wt % and Y = magnetite, siderite and zinc-borate) were fabricated via melt quenching technique. X-ray diffraction method was employed to confirm amorphous structure of fabricated glass samples. The glass sample’s shielding parameters such as mass attenuation coefficient, effective atomic number, and half value layer were measured experimentally by the narrow beam transmission method for 81, 276, 302, 356, and 383 keV of incident photon energies. Also, WinXCom software was used to calculate theoretical shielding parameters from 1 keV to 105 MeV photon energy. Moreover, Geometric Progression (G–P) method was used to calculate exposure buildup factor (EBF) values for incident photon energy 0.015 MeV–15 MeV up to penetration depths of 40 mfp (mean free path). Among the obtained results, while Li2B4O7 glass with magnetite 40 % has the highest mass attenuation and effective atomic number, it has the lowest half value layer and exposure buildup factor. The results show that the fabricated glass systems could be considered as a good candidate for radiation safety.

Timing of the Brunhes-Matuyama transition constrained by U-series disequilibrium

U-series disequilibrium measurements carried out on thermogenic travertine samples from a 12.6 m-long core and a 10 m-thick section from southeastern Morocco yielded finite ages ranging from 500 ka to the present-day, as well as two clusters determined to be older than 500 ka. The calculation of initial ²³⁴U/²³⁸U activity ratios in all samples younger than 500 ka shows high, reasonably constant values, with an average of 5.172 ± 0.520 (one standard deviation). Assuming that this value prevailed for periods older than 500 ka, we derived ages of up to approximately 1.2 Ma using the initial ²³⁴U excess decay. Our results indicate that the two older clusters have ages of 776 ± 14 ka for samples from between 8 and 10.1 m and 1173 ± 22 ka for deeper samples respectively. The palaeomagnetic record of the core shows normal polarity inclinations from the surface to around 9 m followed by reverse polarity inclination and antipodal declinations. The inversion is attributed to the Brunhes-Matuyama transition. ²³⁴U excess ages for the interval corresponding to the part of the core where the polarity inversion occurred are in the range of 735 ± 51 to 794 ± 54 ka, with an arithmetic mean value of 776 ± 14 ka for the B-M transition. This age is in good agreement with that determined previously using other dating methods.

Responses of magnetic properties to heavy metal pollution recorded by lacustrine sediments from the Lugu Lake, Southwest China

Environmental magnetism, which is rapid, sensitive, economical, and non-destructive, has been used to assess heavy metal pollution in lake sediments based on the relationships between magnetic properties and heavy metal concentrations. We conducted a systematic environmental magnetic and heavy metal study of the sediments of the core LGS from Lugu Lake in Southwest China. The results show that the concentration-related magnetic parameters (χ, χ_ARM, and SIRM) in the core LGS showed an increasing trend from bottom to top. The results of rock magnetism indicated that the dominant magnetic particles were magnetite. Two sources of magnetic minerals can be distinguished by the correlations of χ vs. χ_fd% and χ vs. χ_ARM/χ: the surrounding catchment and anthropogenic activities. In addition, Pearson correlation analysis and principal component analysis showed that the concentration-dependent magnetic parameters have significant correlations with heavy metal (Al, Ti, Fe, Cr, Ni, Cu, Zn, and Cd) concentrations as well as the Tomlinson pollution load index (PLI), indicating that there are essential linkages of sources, deposition, and migration between magnetic particles and heavy metals. Based on previously reported ¹³⁷Cs and ²¹⁰Pb data, the historical trends of heavy metal pollution in Lugu Lake were successfully reconstructed, and the causes of heavy metal pollution were mainly agricultural practices and atmospheric metal depositions from anthropogenic sources. The significant correlations between magnetic parameters, heavy metals, and the PLI indicate that magnetic parameters can potentially be used as an index of heavy metal pollution in lacustrine deposits.

The properties of the nano-minerals and hazardous elements: Potential environmental impacts of Brazilian coal waste fire

Brazilian coal area (South Brazil) impacted the environment by means of a large number of coal waste piles emplaced over the old mine sites and the adjacent areas of the Criciúma, Urussanga, and Siderópolis cities. The area studied here was abandoned and after almost 30 years (smokeless visual) some companies use the actual minerals derived from burning coal cleaning rejects (BCCRs) complied in the mentioned area for industry tiles or refractory bricks. Mineralogical and geochemical similarities between the BCCRs and non-anthropogenic geological environments are outlined here. Although no visible flames were observed, this study revealed that auto-combustion existed in the studied area for many years. The presence of amorphous phases, mullite, hematite and other Fe-minerals formed by high temperature was found. There is also pyrite, Fe-sulphates (eg. jarosite) and unburnt coal present, which are useful for comparison purposes. Bad disposal of coal-dump wastes represents significant environmental concerns due to their potential influence on atmosphere, river sediments, soils and as well as on the surface and groundwater in the surroundings of these areas. The present study using advanced analytical techniques were performed to provide an improved understanding of the complex processes related with sulphide-rich coal waste oxidation, spontaneous combustion and mineral formation. It is reporting huge numbers of rare minerals with alunite, montmorillonite, szomolnokite, halotrichite, coquimbite and copiapite at the BCCRs. The data showed the presence of abundant amorphous Si-Al-Fe-Ti as (oxy-)hydroxides and Fe-hydro/oxides with goethite and hematite with various degrees of crystallinity, containing hazardous elements, such as Cu, Cr, Hf, Hg, Mo, Ni, Se, Pb, Th, U, Zr, and others. By Principal Component Analysis (PCA), the mineralogical composition was related with the range of elemental concentration of each sample. Most of the nano-minerals and ultra-fine particles found in the burned coal-dump wastes are the same as those commonly associated with coal cleaning rejects, in which oxidation of sulphides plays an important role to environment and human health.

Magnetic characterization of oil sands at Osmington Mills and Mupe Bay, Wessex Basin, UK

This study combines magnetic experimentation and geochemical analysis on oil sands from Osmington Mills and Mupe Bay, Wessex Basin, UK to investigate the possibility of a relationship between hydrocarbons and magnetic mineralogy. Removal of hydrocarbons by chemical extraction was conducted to allow comparison of (1) oil sands and (2) cleaned sands. Detailed magnetic analysis including low-temperature and high-temperature experimentation revealed that all but one sample was dominated by siderite, identified by the Néel transition at 37–38 K as well as containing large grains of multidomain magnetite (Verwey transition 110 K) and hematite (Morin transition 250 K). Scanning electron microscopy and energy dispersive x-ray analysis confirmed the presence of iron oxides, in particular framboids 500 nm–45 µm in diameter, probably magnetite. Hysteresis parameters showed distinct grouping of oil sands compared to their clean counterparts and a negative linear regression in log space was observed (R2=0.7) between the percentage of extractable organic matter and magnetic susceptibility. These results suggest a relationship exists between magnetic minerals and the alteration of oil due to biodegradation, which is not yet fully understood. Possible mechanisms are suggested to be due to anaerobic bacteria or the transportation of the oil as it migrates through the host rock.