scholarly journals Rare elements — setting markers of the formation of the manganese and iron ore deposits of Kalahari and Postmasburg areas (South Africa). Communication 1. Kalahari manganese field

2019 ◽  
pp. 364-386
Author(s):  
I. M. Varentsov ◽  
V. N. Kuleshov
Keyword(s):  
Regional Metamorphism ◽  
Water Layer ◽  
Ore Deposits ◽  
Oxide Surface ◽  
Manganese Ores ◽  
Rare Elements ◽  
Wide Range ◽  
Iron Ore Deposits ◽  
Transvaal Supergroup ◽  
High Concentrations

In manganese ores of the Hotazel Formation (Transvaal supergroup) of the Lower Proterozoic, associated with banded ferrous silicites, high concentrations of a number of rare elements (B, Ge, W, Mo, Cr, Ni, Zn, Cd, Pb, Ag, Bi, As, Sb, Te, Se) were determined. High boron contents in oxide-carbonate ores (manganese lutites) are considered as a consequence of the concentration by chemsorbtion of this element on Mn-carbonates. It is proposed that as a result of hydrothermal transformations, a wide range of ore-forming (mainly Fe, Mn) and rare elements (including REE) was removed from the underlying andesite-basaltic hyaloclastite Ongeluk Formation In manganese ores and ferruginous silicites, typical values of cerium (Ce/Ce* 0.28–1.72) and europium (Eu/Eu* 0.57–16.31) anomalies were established, which may indicate that the initial sediments accumulated in the marginal shallow sea basin with a pronounced oxide surface water layer and close to anoxide conditions near the bottom. Metalliferous (Mn, Fe) sediments of a shallow water basin at different stages of lithogenesis were enriched with europium (positive Eu/Eu*), subjected to metasomatosis (with redistribution of manganese and the formation of manganese carbonates) and, subsequently, regional metamorphism (up to the stage of sericitic green schists).

scholarly journals Rare elements — setting markers of the formation of the manganese and iron ore deposits of Kalahari and Postmasburg areas (South Africa). Communication 2. Iron- and manganese ore of Postmasburg area

2019 ◽  
pp. 466-485
Author(s):  
I. M. Varentsov ◽  
V. N. Kuleshov
Keyword(s):  
South Africa ◽  
Hydrothermal Activity ◽  
Ore Deposits ◽  
Manganese Ore ◽  
Iron Ores ◽  
Ore Formation ◽  
Rare Elements ◽  
Iron Ore Deposits ◽  
Marine Basin ◽  
Iron And Manganese

In the world resources of manganese and iron ores, a significant place belongs to the Postmasburg ore field (South Africa), enclosed in rocks of the Transvaal Supegroup. Ore deposits have the nature of karst residual accumulations. A number of elements (B, Cr, Ni, Zn, Ge, As, Se, Mo, Ag, Cd, Sb, Te, W, Pb, REE) form a characteristic association that sheds light on the geochemistry of the ore formation processes. Of these, the most representative elements are: Mo, As, Ag and REE. Molybdenum is distinguished by the chemisorption incorporation nature of accumulation in the ores under consideration, often with the formation of epic growths of ferri molybdate-type minerals. Arsenic leached from substrate rocks and accumulated in karstic Mn-Fe- and Fe-ores reflects the total effect of the dominant iron oxide minerals on its mobility. The behavior of silver is controlled by the processes of hypergenic change of Archean-Early Proterozoic carbonate rocks and banded iron ores (BIF). Comparison of the distribution of REE in karst Fe-, Mn-Fe- and Mn-ores and in banded iron ores shows that they are characterized by similar values of cerium (C/Ce*) and europium (Eu/Eu*) anomalies, but differ in the fractionation of heavy and light REE (typical values: Ce/Ce* = 0.7‒1.0; Eu/Eu* = 0.8‒1.1). Strip iron ores and associated manganese ore deposits accumulated in the marginal anoxide-disoxide marine basin, which was limited to continental land. Anoxide and disoxide conditions were the result of intense hydrothermal activity.

An Investigation on the Performance of an Oxidation Catalyst Using Two-dimensional Simulation with Detailed Reaction Mechanism

2020 ◽  
Vol 0 (0) ◽  
Author(s):  
Sreeharsh Nair ◽  
Mayank Mittal
Keyword(s):  
Single Channel ◽  
Catalytic Converter ◽  
Oxidation Catalyst ◽  
Low Temperature Combustion ◽  
Wide Range ◽  
Detailed Reaction Mechanism ◽  
Temperature Combustion ◽  
High Concentrations ◽  
Dimensional Simulation ◽  
Surface Reaction Kinetics

AbstractThe advent of stricter emission standards has increased the importance of aftertreatment devices and the role of numerical simulations in the evolution of better catalytic converters in order to satisfy these emission regulations. In this paper, a 2-D numerical simulation of a single channel of the monolith catalytic converter is presented by using detailed surface reaction kinetics aiming to investigate the chemical behaviour inside the converter. The model has been developed to study the conversion of carbon monoxide (CO) in the presence of propene (C3H6) for low-temperature combustion (LTC) engine application. The inhibition effect of C3H6 over a wide range of CO inlet concentrations is investigated. Considering both low and high levels of CO concentration at the inlet, the 2-D model predicted better results than their corresponding 1-D counterparts when compared with the experimental data from literature. It was also observed that C3H6 inhibition at high temperatures was significant, particularly for high concentrations of CO compared to low concentrations of CO at the inlet.

scholarly journals Mineral Physicochemistry Underlying Feature-Based Extraction of Mineral Abundance and Composition from Shortwave, Mid and Thermal Infrared Reflectance Spectra

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 347
Author(s):  
Carsten Laukamp ◽  
Andrew Rodger ◽  
Monica LeGras ◽  
Heta Lampinen ◽  
Ian C. Lau ◽  
...  
Keyword(s):  
Mineral Exploration ◽  
Relevant Information ◽  
Ore Deposits ◽  
Reflectance Spectra ◽  
Full Potential ◽  
Infrared Reflectance ◽  
Vibrational Modes ◽  
Diagnostic Features ◽  
Wide Range ◽  
Mineral Assemblages

Reflectance spectroscopy allows cost-effective and rapid mineral characterisation, addressing mineral exploration and mining challenges. Shortwave (SWIR), mid (MIR) and thermal (TIR) infrared reflectance spectra are collected in a wide range of environments and scales, with instrumentation ranging from spaceborne, airborne, field and drill core sensors to IR microscopy. However, interpretation of reflectance spectra is, due to the abundance of potential vibrational modes in mineral assemblages, non-trivial and requires a thorough understanding of the potential factors contributing to the reflectance spectra. In order to close the gap between understanding mineral-diagnostic absorption features and efficient interpretation of reflectance spectra, an up-to-date overview of major vibrational modes of rock-forming minerals in the SWIR, MIR and TIR is provided. A series of scripts are proposed that allow the extraction of the relative intensity or wavelength position of single absorption and other mineral-diagnostic features. Binary discrimination diagrams can assist in rapidly evaluating mineral assemblages, and relative abundance and chemical composition of key vector minerals, in hydrothermal ore deposits. The aim of this contribution is to make geologically relevant information more easily extractable from reflectance spectra, enabling the mineral resources and geoscience communities to realise the full potential of hyperspectral sensing technologies.

Application of the EYTEX™ System to the Evaluation of Cosmetic Products and their Ingredients

1992 ◽  
Vol 20 (1) ◽  
pp. 146-163
Author(s):  
Francis H. Kruszewski ◽  
Laura H. Hearn ◽  
Kyle T. Smith ◽  
Janice J. Teal ◽  
Virginia C. Gordon ◽  
...  
Keyword(s):  
Double Blind ◽  
Eye Irritation ◽  
Ocular Irritation ◽  
Rabbit Eye ◽  
Wide Range ◽  
High Concentrations ◽  
Alkaline Membrane ◽  
Positive Agreement

465 cosmetic product formulations and raw ingredients were evaluated with the EYTEX™ system to determine the potential of this in vitro alternative for identifying eye irritation potential. The EYTEX™ system is a non-animal, biochemical procedure developed by Ropak Laboratories, Irvine, CA, that was designed to approximate the Draize rabbit eye irritation assay for the evaluation of ocular irritation. Avon Products Inc. provided all the test samples, which included over 30 different product types and represented a wide range of eye irritancy. All the EYTEX™ protocols available at the time of this study were used. Samples were evaluated double-blind with both the membrane partition assay (MPA) and the rapid membrane assay (RMA). When appropriate, the standard assay (STD) and the alkaline membrane assay (AMA) were used, as well as specific, documented protocol modifications. EYTEX™ results were correlated with rabbit eye irritation data which was obtained from the historical records of Avon Products Inc. A positive agreement of EYTEX™ results with the in vivo assay was demonstrated by an overall concordance of 80%. The assay error was 20%, of which 18% was due to an overestimation of sample irritancy (false positives) and 2% was attributed to underestimation (false negatives). Overestimation error in this study was due in part to the inability of the protocols to accurately classify test samples with very low irritation potential. Underestimation of sample irritancy was generally associated with ethoxylated materials and high concentrations of specific types of surfactants. 100% sensitivity and 85% predictability were described by the data, indicating the efficiency of EYTEX™ in identifying known irritants. A specificity rate of 39% showed the EYTEX™ assay to be weak in discerning non-irritants. However, the EYTEX™ protocols used in this study were not designed to identify non-irritants. A compatibility rate of 99% proved the effectiveness of the EYTEX™ assay in accommodating a diversity of product types. The EYTEX™ system protocols, when used appropriately, can provide a conservative means of assessing the irritant potential of most cosmetic formulations and their ingredients.

scholarly journals Oxygen Is Instrumental for Biological Signaling: An Overview

Oxygen ◽  
2021 ◽  
Vol 1 (1) ◽  
pp. 3-15
Author(s):  
John T. Hancock
Keyword(s):  
Oxidative Stress ◽  
Superoxide Anion ◽  
Nitrosative Stress ◽  
Redox Status ◽  
Complex Interplay ◽  
Wide Range ◽  
Form Part ◽  
High Concentrations ◽  
And Control ◽  
Signaling Components

Control of cellular function is extremely complex, being reliant on a wide range of components. Several of these are small oxygen-based molecules. Although reactive compounds containing oxygen are usually harmful to cells when accumulated to relatively high concentrations, they are also instrumental in the control of the activity of a myriad of proteins, and control both the upregulation and downregulation of gene expression. The formation of one oxygen-based molecule, such as the superoxide anion, can lead to a cascade of downstream generation of others, such as hydrogen peroxide (H2O2) and the hydroxyl radical (∙OH), each with their own reactivity and effect. Nitrogen-based signaling molecules also contain oxygen, and include nitric oxide (NO) and peroxynitrite, both instrumental among the suite of cell signaling components. These molecules do not act alone, but form part of a complex interplay of reactions, including with several sulfur-based compounds, such as glutathione and hydrogen sulfide (H2S). Overaccumulation of oxygen-based reactive compounds may alter the redox status of the cell and lead to programmed cell death, in processes referred to as oxidative stress, or nitrosative stress (for nitrogen-based molecules). Here, an overview of the main oxygen-based molecules involved, and the ramifications of their production, is given.

The Pilot Knob Iron Ore Deposits in Southeast Missouri: A High-To-Low Temperature Magmatic-Hydrothermal Continuum

2021 ◽  
pp. 103973
Author(s):  
Bolorchimeg N. Tunnell ◽  
Marek Locmelis ◽  
Cheryl Seeger ◽  
Ryan Mathur ◽  
István Dunkl ◽  
...  
Keyword(s):  
Low Temperature ◽  
Iron Ore ◽  
Ore Deposits ◽  
Southeast Missouri ◽  
Iron Ore Deposits
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