Molybdenum in natural waters: A review of occurrence, distributions and controls
TL;DR: The 2011 WHO Guidelines for Drinking-Water Quality (fourth edition) advised a health-based value of 70μg/L for Mo but this is no longer promulgated as a formal guideline value as WHO consider such concentrations to be rarely found in drinking water as discussed by the authors.
About: This article is published in Applied Geochemistry.The article was published on 2017-09-01 and is currently open access. It has received 196 citations till now. The article focuses on the topics: Waste disposal & Anoxic waters.
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TL;DR: The elevated mobilization potential, e.g., through competition and ligand induced desorption, is the reason for faster Cd release from soil into groundwater than other heavy metals.
464 citations
01 Dec 2011
TL;DR: In this article, the effect of igneous crustal rock weathering on the aquatic δ 98 / 95 Mo signal was investigated by comparing stream water and bedrock Mo isotope data to results of bulk rock leach experiments.
Abstract: River waters have been shown to be systematically enriched in the heavy molybdenum (Mo) isotopes when compared to typical granites and basalts, which generally possess Mo isotopic compositions ( δ 98 / 95 Mo) of around 0 ‰ . This inconsistency has been used to argue against weathering of crustal rocks as the cause for heavy riverine δ 98 / 95 Mo signatures. Incongruent dissolution of primary bedrock, however, may be an important process by which the anomalous Mo signatures of the river dissolved load are produced. This study therefore investigates the effect of igneous crustal rock weathering on the aquatic δ 98 / 95 Mo signal by comparing stream water and bedrock Mo isotope data to results of bulk rock leach experiments. For this purpose, stream water and bedrock (orthogneiss, granite, basalt), as well as soil and vegetation samples were collected in a small catchment in the French Massif Central. In accordance with the results of earlier studies on riverine Mo, both streams are isotopically heavier ( δ 98 / 95 Mo = 0.5–1.1 ‰ ) than the typical granites and basalts. The excellent agreement of these data with those of Mo released during experimental leaching of the basalt bedrock (0.6–1.0 ‰ ) identifies a predominance of basalt weathering over the stream water Mo geochemistry, while other processes (i.e. soil formation, secondary mineral precipitation and adsorption) are subordinate in this catchment. Given that the basalt bulk rock δ 98 / 95 Mo reflects a value typical for crustal magmatic rocks (ca. 0.1 ‰ ), Mo isotope fractionation during the incongruent dissolution of basalt can explain the observed isotopically heavy aquatic Mo signatures. Laser ablation analyses demonstrate that the volumetrically minor magmatic sulfides can be highly enriched in Mo and mass balance calculations identify the sulfide melt inclusions as the principal Mo source for the leach solutions. These data suggest that the magmatic sulfides possess a distinctly heavier δ 98 / 95 Mo signature than the coexisting silicate melt. In this case, Mo would behave like Fe by showing a detectable isotope fractionation at magmatic temperatures. Incongruent crustal bedrock weathering may thus cause a preferential release of heavy Mo isotopes. This effect, however, is highly dependent on the primary bedrock mineralogy. Consequently, the average continental runoff may have been significantly affected by incongruent weathering during periods when the Earth system was exceptionally far from steady state, e.g., large glaciations with enhanced physical weathering or large subaerial basalt eruptions such as the Deccan and the Siberian plateau.
68 citations
TL;DR: In this paper, a facile co-precipitation method, followed by thermal postsynthetic treatment in N2/air, was developed to synthesize molybdenum-doped α-Mn2O3 materials.
Abstract: The development of efficient and noble-metal-free electrocatalysts for the challenging oxygen evolution reaction (OER) is crucial for sustainable energy solutions. In this work, a facile co-precipitation method, followed by thermal postsynthetic treatment in N2/air, was developed to synthesize molybdenum-doped α-Mn2O3 materials (Mn2O3:1.72%Mo, Mn2O3:2.64%Mo, Mn2O3:32.23%Mo, and Mn2O3:49.67%Mo) as low-cost water-oxidizing electrocatalysts. Powder X-ray diffraction (PXRD), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) investigations showed the presence of strong distortions in the molybdenum-doped α-Mn2O3 host lattice (Mn2O3:2.64%Mo) and an average oxidation state of Mn2.8+. Several test assays demonstrated that these structural features significantly promote the OER activity. Mn2O3:2.64%Mo was found to exhibit very good activity among the series in cerium ammonium nitrate (CAN)-assisted water oxidation with a maximum turnover frequency (TOF) of 585 μmol O2 m–2 h–1, which is a 15-fold improvement of the pure α-Mn2O3 activity and higher than the value of the previously reported benchmark Mn-based catalyst, birnessite. The optimized catalyst (Mn2O3:2.64%Mo) excelled through a low onset potential (300 mV) and a promising overpotential of 570 mV for OER at a current density of 10 mA cm–2, which is only 20 mV above that of the noble metal benchmark RuO2 electrode and competitive with that of the most active Mn-based OER catalysts reported to date. Electrochemical impedance spectroscopy (EIS) studies demonstrated that the catalytically active surface area of Mn2O3:2.64%Mo is much higher than that of α-Mn2O3 for the OER at the applied potential. In addition, stability during 30 h without degradation was achieved, which exceeds that of a wide range of current noble-metal-free electrocatalysts. Our study provides a facile and effective approach for the preparation of economical and high-performance manganese-based electrocatalysts for water oxidation.
61 citations
TL;DR: In this paper, the composition and stability of colloidal FeMoS4 precipitates formed at mildly basic pH and H2S(aq) > 10-5 M were determined.
Abstract: Relative to continental crust, sediments underlying sulfidic marine waters are molybdenum-rich, a property preserved in the rock record and useful for characterizing paleoenvironments. The enrichment mechanism is not agreed upon but is attributed at least partly to deposition of Fe–Mo–S compounds, which are as yet uncharacterized. Here, we determine the composition and stability of colloidal Fe–Mo–S precipitates formed at mildly basic pH and H2S(aq) > 10–5 M. The first product consists simply of FeMoS4, with Ksp = 10–14.95. Within hours, FeMoS4 irreversibly transforms by internal self-reduction to a Mo(IV) product of similar composition. The reduced product is insoluble in 1 M HCl but soluble in concentrated HNO3, implying that it would be recovered with pyrite in a common assay of sediments. X-ray absorption fine structure data show that Mo(IV) in the colloids is coordinated by a split first shell of about five sulfur atoms at average distances of 2.31 and 2.46 A and in its second shell by an iron atom a...
47 citations
TL;DR: In this paper, the second highest energy consuming step in aluminum anodization and a step with significant environmental impacts has been critical reviewed in this systematic review, focusing on the need to reduce both the energy input in the anodic oxide process and environmental implications.
Abstract: Increasing demands for environmental accountability and energy efficiency in industrial practice necessitates significant modification(s) of existing technologies and development of new ones to meet the stringent sustainability demands of the future. Generally, development of required new technologies and appropriate modifications of existing ones need to be premised on in-depth appreciation of existing technologies, their limitations, and desired ideal products or processes. In the light of these, published literature mostly in the past 30 years on the sealing process; the second highest energy consuming step in aluminum anodization and a step with significant environmental impacts has been critical reviewed in this systematic review. Emphasis have been placed on the need to reduce both the energy input in the anodization process and environmental implications. The implications of the nano-porous structure of the anodic oxide on mass transport and chemical reactivity of relevant species during the sealing process is highlighted with a focus on exploiting these peculiarities, in improving the quality of sealed products. In addition, perspective is provided on plausible approaches and important factors to be considered in developing sealing procedures that can minimize the energy input and environmental impact of the sealing step, and ensure a more sustainable aluminum anodization process/industry.
45 citations
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TL;DR: PHREEQC as discussed by the authors is a C program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations.
Abstract: PHREEQC version 2 is a computer program written in the C programming language that is designed to perform a wide variety of low-temperature aqueous geochemical calculations. PHREEQC is based on an ion-association aqueous model and has capabilities for (1) speciation and saturation-index calculations; (2) batch-reaction and onedimensional (1D) transport calculations involving reversible reactions, which include aqueous, mineral, gas, solidsolution, surface-complexation, and ion-exchange equilibria, and irreversible reactions, which include specified mole transfers of reactants, kinetically controlled reactions, mixing of solutions, and temperature changes; and (3) inverse modeling, which finds sets of mineral and gas mole transfers that account for differences in composition between waters, within specified compositional uncertainty limits. New features in PHREEQC version 2 relative to version 1 include capabilities to simulate dispersion (or diffusion) and stagnant zones in 1D-transport calculations, to model kinetic reactions with user-defined rate expressions, to model the formation or dissolution of ideal, multicomponent or nonideal, binary solid solutions, to model fixed-volume gas phases in addition to fixed-pressure gas phases, to allow the number of surface or exchange sites to vary with the dissolution or precipitation of minerals or kinetic reactants, to include isotope mole balances in inverse modeling calculations, to automatically use multiple sets of convergence parameters, to print user-defined quantities to the primary output file and (or) to a file suitable for importation into a spreadsheet, and to define solution compositions in a format more compatible with spreadsheet programs. This report presents the equations that are the basis for chemical equilibrium, kinetic, transport, and inverse modeling calculations in PHREEQC; describes the input for the program; and presents examples that demonstrate most of the program's capabilities.
7,654 citations
TL;DR: The scale of the problem in terms of population exposed to high As concentrations is greatest in the Bengal Basin with more than 40 million people drinking water containing ‘excessive’ As as mentioned in this paper.
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TL;DR: In this paper, a new calculation of the crustal composition is based on the proportions of upper crust (UC) to felsic lower crust (FLC) to mafic lower-crust (MLC) of about 1.6:0.4.
5,317 citations
TL;DR: In this article, a table of element abundances in the continental crust, calculated on the basis of a 1:1 mixture of granite and basalt abundances, is presented.
2,460 citations