Distribution Of Molybdenum Research Articles

Effect of Mo Content on the Structural, Mechanical, and Tribological Properties of New Zr-Nb-Mo Alloys Obtained by Combining Powder Metallurgy and Vacuum Arc Melting Methods.

Considering the high demand for innovative solutions in medicine, a major increase in interest in biomaterials research has been noticed, with the most significant advancements in metals and their alloys. Titanium-based alloys are one of the most recognised in the scientific community but do not represent the only way to achieve optimal results. Zirconium alloys for medical applications are a novelty with significant research potential based on their outstanding properties, which may be of value for medicine. The aim of the present study was to obtain new biomedical Zr-Nb-Mo alloys with varying ratios of their respective elements-Zr and Mo-using combined powder metallurgy (PM) and arc melting (VAM) methods. The obtained samples underwent microstructure analysis using an optical microscope (OM) and a scanning electron microscope (SEM). The study of element distribution was conducted with energy dispersive spectroscopy (EDS), whereas the phase composition was determined using X-ray diffraction (XRD). Mechanical properties were examined with a Micro Combi Tester MCT3, whereas tribological properties were assessed with a TRN Tribometer, and Ringer's solution was used as a lubricant. Additionally, the wear tracks of the studied samples were observed using the SEM. The research results indicated that increased Mo content conduced to microstructure refinement and homogeneity. Furthermore, the higher content of this element contributed to the growth of the HVIT, HIT, and EIT parameters, together with the improvement in the tribological performance of the alloys. XRD analysis revealed that the obtained samples were multiphase, and raising the Mo addition promoted the formation of new phases, including a ternary phase-Zr0.9Nb0.66Mo1.44 (Fd3¯m). The chemical composition study showed uneven distribution of niobium and areas of uneven mutual distribution of zirconium and molybdenum.

Differential accumulation of metals in the lacustrine and fluvial Alpine bullheads (Cottus poecilopus) and recovery of fish from metal contamination after a flash flood

The spatiotemporal distribution and transport of mercury, zinc, molybdenum, rubidium, and strontium from alpine terrestrial ecosystems to alpine lake and mountain stream populations of Cottus poecilopus were investigated. Metals were measured for 66 wild fish collected from different lakes and Javorinka stream across. Mercury was measured in the pectoral fins, other elements in the skull. Bullheads contained more metals in the alpine lakes than in the mountain stream. In particular, mercury and zinc concentrations in lake bullheads were 6 and 2.5 times higher, respectively, than those of stream-dwelling fish. New data were generated on metal bioaccumulation in fish of understudied West Carpathian alpine lake environments. In July 2018, a major flood occurred in the area of the Javorinka. Already then, the mercury content in bullheads increased significantly. Bioaccumulation of mercury in fish occurred very quickly after the flood and was also significant in the following 2019. Then, the concentrations of mercury quickly decreased up to 70% in 2021–2022. Average concentrations of molybdenum and rubidium in bullheads in the stream rapidly declined in the year following the flood disturbance, but within less than 2 years, the metal levels stabilized at about the same level as in 2017 prior the flood. Strontium concentrations in fish dropped rapidly immediately after the flood, increased in the following years, and dropped again after 4 years, suggesting that many more factors are influencing strontium bioaccumulation in fish that are comparable in magnitude to the flood. The most serious warning seems to be the absence of biogenic zinc. The average concentration in the Alpine bullheads population in the stream has declined by 70% in less than 5 years and is steadily declining. An important result of this study is the demonstration that disturbance by a single factor (heavy rainfall and flooding) has a clear and timely effect on average metal concentrations in the fish population.Graphical abstract

The use of LA-ICP-MS as an auxiliary tool to assess the pulmonary toxicity of molybdenum(IV) sulfide (MoS2) nano- and microparticles.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) has considerable applicative potential for both qualitative and quantitative analyses of elemental spatial distribution and concentration. It provides high resolutions at pg-level detection limits. These qualities make it very useful for analyzing biological samples. The present study responds to the growing demand for adequate analytical methods which would allow to assess the distribution of nanostructured molybdenum(IV) disulfide (MoS2) in organs. It was also motivated by an apparent lack of literature on the biological effects of MoS2 in living organisms. The study was aimed at using LA-ICP-MS for comparing micro- and nanosized MoS2 ditribution in selected rat tissue samples (lung, liver, brain and spleen tissues) after the intratracheal instillation (7 administrations) of MoS2 nano- and microparticles vs. controls. The experimental study, approved by the Ethics Committee for Animal Experiments was performed using albino Wistar rats. This was performed at 2-week intervals at a dose of 5 mg/kg b.w., followed by an analysis after 90 days of exposure. The MoS2 levels in control tissues were determined with the laser ablation system at optimized operating conditions. The parameter optimization process for the LA system was conducted using The National Institute of Standards and Technology (NIST) glass standard reference materials. Instrument parameters were optimized. The study found that molybdenum (Mo) levels in the lungs of microparticle-exposed rats were higher compared to nanoparticle-exposed rats. The opposite results were found for liver and spleen tissues. Brain Mo concentrations were below the detection limit. The LA-ICP-MS technique may be used as an important tool for visualizing the distribution of Mo on the surface of soft samples through quantitative and qualitative elemental mapping. Int J Occup Med Environ Health. 2024;37(1):18-33.

A study of Physicochemical Parameters, Heavy Metals and Algae in the Euphrates River, Iraq

For many individuals, heavy metal persistence and toxicity are severe problems. Most of these heavy metals collect in wastewater from effluents discharged by various industries. The efficient re-use of these particles as catalysts is another new development in research that complements the success of hazardous metal particle removal. Five locations along the Euphrates River in western Iraq’s Anbar Governorate were the subject of the research (Husaibah Al-Sharqiah, Al-Karābilah, Barwana, Al-Garma, Al-Forat sub district) and for four seasons (Summer, Autumn, Winter, and Spring) from November 2021 to November 2022 in order to examine how the physical and chemical characteristics of the water in the Euphrates River vary over space and time in these areas. Based on these locations of garbage, contaminants, and heavy metal components that may flow into the river without environmental management, sampling locations on the Euphrates River were chosen. In order to better understand the distribution of heavy metals (HMs: Arsenic (As), Antimony (Sb), Selenium (Se), Molybdenum (Mo), Cyanide (CN-), and Chromium (Cr) in river sediments, five locations in western Iraq were chosen for the research. The PH, electrical conductivity (EC), algaes, and sediments (Nitrate (NO3), sulfate (SO4), and HMs content) were all measured in the river’s edge water. A qualitative research was also carried out at various times of year and locations. 104 different kinds of algae were found, and some of them dominated all the research locations. In each station near the beginning of the estuary, the quantitative research revealed a rise in the number of algae species indicative of pollution, confirming that these sites are impacted by the pollutants from untreated sewage discharged into the Euphrates River in those locations. The average concentrations of HMs and compounds in the sediments were as follows: SO4> NO3>Mo>Cn>Cr>Sb>Se>As. According to the investigation, the HMs polluted cities in the following ways: Sediment concentrations are greater in Husaibah Al-Sharqiah, Al-Karbilah, Barwana, Al-Garma, and Al-Forat subdistrict cities.

Spatial distribution of molybdenum in catchment sediments in the Sino-Mongolian border region

The Sino-Mongolian border region is an important exploration hotspot in the Asia-Pacific margin and hosts one of the three major porphyry Cu-Au-Mo mineralization belts in the world. Variations in the concentration and spatial distribution of Mo in the region can indirectly reflect the distribution of other minerals, such as copper; therefore, Mo has been widely used as a pathfinder element for geochemical prospecting for porphyry Cu deposits. However, comprehensive and integrated analytical studies of single elements (e.g., Mo) in the Sino-Mongolian border region are lacking. Therefore, this study collected 10,453 catchment sediment samples from the study region and analyzed 69 elements. The concentration of Mo in these samples ranged from 0.10 to 84.96 mg/kg, with a median and mean of 0.84 mg/kg (considered the geochemical background value) and 0.97 mg/kg, respectively. The factors influencing the Mo concentration and spatial distribution along the Sino-Mongolian border region were investigated in terms of geological background, climate, precipitation, mineral distribution, and exploitation history. Influenced by climate and precipitation, Mo in catchment sediments is solubilized and easily transported under the oxidizing effect of hypergenesis. Mo concentrations were low in forested areas along the Altai Mountains in the west and Da Hinggan Ling Mountains in the east. Sixteen high-concentration Mo areas (geochemical province/domain, > 1.07 mg/kg, > Q75%) that contained 46 Mo geochemical anomalies (> 1.24 mg/kg, > Q85%) were circumscribed in this study. These anomalous areas were mainly related to the widespread distribution of minerals, coal-forming strata, and black shale deposits in the region. Compared to previous studies, this study identified more concentrated geochemical anomaly areas with a wider distribution in the Sino-Mongolian border region and provided higher quality geochemical data to promote further mineral exploration and support environmental change studies in this area.

Distribution of molybdenum in soft tissues and blood of rats after intratracheal instillation of molybdenum(IV) sulfide nano- and microparticles

There is still little literature data on the toxicity and safety of the commonly used molybdenum (Mo) disulfide which is present in the working as well as living environments. Thus, an experiment was carried out involving rats, with single and repeated intratracheal exposure (in the latter case, 7 administrations at 2-week intervals with the analysis performed after 90 days) to lower (1.5 mg Mo kg−1 b.w.) and higher (5 mg Mo kg−1 b.w.) doses of molybdenum(IV) sulfide nanoparticles (MoS2-NPs) and microparticles (MoS2-MPs). The analysis of Mo concentrations in the tail and heart blood as well as in soft tissues (lung, liver, spleen, brain), after mineralization and bioimaging, was meant to facilitate an assessment of its accumulation and potential effects on the body following short- and long-term exposure. The multi-compartment model with an exponential curve of Mo concentration over time with different half-lives for the distribution and elimination phases of MoS2-MPs and MoS2-NPs was observed. After 24 h of exposure, a slight increase in Mo concentration in blood was observed. Next, Mo concentration indicated a decrease in blood concentration from 24 h to day 14 (the Mo concentration before the second administration), below the pre-exposure concentration. The next phase was linear, less abrupt and practically flat, but with an increasing trend towards the end of the experiment. Significantly higher Mo concentrations in MoS2-NPs and MoS2-MPs was found in the lungs of repeatedly exposed rats compared to those exposed to a single dose. The analysis of Mo content in the liver and the spleen tissue showed a slightly higher concentration for MoS2-NPs compared to MoS2-MPs. The results for the brain were below the calculated detection limit. Results were consistent with results obtained by bioimaging technique.

Distribution of Uranium and Molybdenum in River Sediment near Molybdenite Mining Region: A Case Study in SW China

This work aims to understand the distribution and migration mechanisms of U and Mo between surface sediment and water in acid mine drainage (AMD) regions near a molybdenum mining region. A series of river sediment and water samples near the Jinduicheng mining area, one of the largest deposits of molybdenite ore in Asia, were collected and analyzed. Our results indicate that: (1) The pH value of river water samples increases with distance from upstream to downstream, while the pH has poor correlation with Mo and U; (2) The content of Mo and U in the sediment are significantly higher than the background value, which suggests potential pollution; (3) The content of Mo and U in the water and sediments in the lower reaches of the Wenyu river is significantly linearly related with the distance from the mining area, suggesting that AMD is a potential source; (4) BCR analysis shows that Mo in river sediments mainly existed as the residual, while U mainly existed as the non-residual; (5) The distribution coefficient Kd(Mo) exceeds Kd(U), indicating that Mo is enriched in sediments while U is more prone to porewater.

Quantitative characterization and magnetic separation of copper pyrometallurgical tailing for molybdenum and copper pre-concentration and cleaning of environmentally hazardous elements

The comprehensive and harmless utilization of copper slag flotation tailing (CSFT) is the key to a waste-free and sustainable copper industry. Here, the mineralogy and molybdenum micro-dissemination in CSFT were quantified and characterized, and the feasibility of the comprehensive recovery of Mo, Cu and Fe resources from CSFT and hazardous elements fractionation behavior by magnetic separation was discussed. To investigate the occurrence and abundance of Mo in each phase, CSFT was classified into four types of phases, including magnetite/hematite (27.26%), silicate associations (43.37%), and metallic sulphides and oxides. Molybdenum distribution is closely related to magnetite/hematite-Fe and S. The magnetic separation results indicated that Mo and Cu were enhanced in magnetic products by 34–41 and 15–21%, respectively. Cleaner non-magnetic residues were found to decrease significantly by 37–44, 58–60, and 11–19% for Cu, As, and Cr, respectively. Mineral fractionation was observed instead of chemical changes during magnetic separation. Despite a weak separation effect on magnetic and non-magnetic phases due to their close bonds and fine-disseminated minerals, the Fe-silicate associations without magnetic phases were well separated into non-magnetic residues. The enrichment of Ca, Mg and separation of an iron-silicate component in non-magnetic residues enhanced the cementitious property and allowed the development of more pathways of reutilization.

The Au[sbnd]Ag (Zn, Pb, Mo, Cu) Sulfuro Vein, La Paloma district, Deseado Massif, Argentina: Geochemical characterization and new insights into the 4D evolution of ore shoots

Unravelling the 3D architecture of ore shoots and its evolution through time, thereby moving towards a 4D understanding of mineralization processes, requires an interdisciplinary approach based on the capability of carrying out extensive trenching and drilling as well as effectively integrating structural and geochemical analyses. Such conditions are offered in La Paloma district of the Deseado Massif, Argentina. Here, eight epithermal AuAg veins are hosted in Middle Jurassic volcanic rocks (Bajo Pobre Formation). The AuAg (Zn, Pb, Mo and Cu) Sulfuro Vein, representing the main ore body in the district, is a 750 m long, N to NW striking structure extending 230 m at depth. The geometry and distribution of ore shoots within the Sulfuro Vein are controlled by: (i) lithological and structural features, (ii) metal concentration, (iii) temperature of the fluids at the time of ore deposition, and (iv) remobilization processes. The highest values of Au, Ag, Cu, Mo, Pb, Zn and Sb are concentrated at depths between 50 and 100 m.a.s.l., while high Mo values occur also at greater depths in the southern segment of the vein. Molybdenum distribution in shallower sectors of the vein is controlled by its remobilization by later infill stages. The Au, Ag and Cu ore shoots are widely distributed in the southern and central segments of the vein, as are the areas of greater vein thickness. These ore shoots exhibit a sub-horizontal geometry consistent with dominant extensional faulting during mineralization. In the northern segment of the vein, the Au, Ag and Cu ore shoots are discontinuous and small, and show gentle to moderate plunges probably associated with variable fault kinematics and depletion of the fluid in these metals. Ore-shoots of Mo, Pb and Zn display high values along the longitudinal section and sub-horizontal geometry in the central and northern sectors of the vein, with high-grade Mo ore shoots decreasing to the north. The fact that Pb and Zn high grades extend up to the tip of the northern vein segment suggests that these metals continued to precipitate at lower temperatures, favoured by the permeability of the volcaniclastic units. All of the ore shoots exhibit steeper plunges towards the southern termination of the vein. Here, upward fluid flow may have been enhanced by the dilation associated with oblique-slip along the N-S striking segment of the steeply dipping Sulfuro Vein. The geochemical distribution of metals shows a slight vertical zonation and a distinct lateral zonation, which suggest hydrothermal fluids flowed northward from deeper zones in the southern sector of the vein.

РАСПРЕДЕЛЕНИЕ ХРОМА И МОЛИБДЕНА В ДИФФУЗИОННОМ СЛОЕ СТАЛИ 35Х2Н3 ПРИ СОВМЕСТНОМ ТЕРМОДИФФУЗИОННОМ НАСЫЩЕНИИ

Known methods of chemical-thermal treatment of structural parts, such as carburizing, nitriding, diffusion metallization technologies, make it possible to obtain a unique combination of surface and core properties of the product. The positive experience of using methods of multi-element diffusion saturation opens up prospects for the development of methods for complex saturation. The article describes the technology of thermal diffusion saturation of steel X35CrNi2-3 with chromium and molybdenum at a temperature of 1000 °C. A technique for analyzing the obtained coating is presented, based on the possibilities of X-ray spectral microanalysis (XMS) of the diffusion layer on transverse microsections of the obtained samples. The elemental composition of the diffusion layer was monitored using a JEOL JSM-6460 LV universal scanning (scanning) electron microscope. The microstructure was studied on an optical metallographic microscope Axio Observer D1.m. X-ray phase analysis was carried out on a Rigaku Ultima IV diffractometer. The hardness measurement was carried out on an FM-800 microhardness tester at a load of 100 g. Data were obtained on the qualitative and quantitative distribution of chromium and molybdenum in the surface layer of steel. It is shown that the resulting thermal diffusion coating consists mainly of a substitutional solid solution based on Cr–Fe–Mo with a bcc lattice and chromium and molybdenum carbides. The depth of the outer coating on the sample was about 20 μm, the depth of the diffusion layer in the base metal was about 25 μm. The absence of a decarburized area in the surface layer of the base metal was noted. The average diffusion coefficients of chromium and molybdenum in the α-phase of chromium were determined DCr = 6.6·10–15 m2/s and DMo = 4.35·10–16 m2/s respectively; in the γ-phase of iron DCr = 2.95·10–15 m2/s, DMo = 2.48·10–16 m2/s respectively. The microhardness of the outer surface layer was 1400–1980 H, the diffusion layer in the base metal was 1000–600 HV, and the base metal was about 540–510 HV.

Reconciling evidence of oxidative weathering and atmospheric anoxia on Archean Earth.

Evidence continues to emerge for the production and low-level accumulation of molecular oxygen (O2) at Earth’s surface before the Great Oxidation Event. Quantifying this early O2 has proven difficult. Here, we use the distribution and isotopic composition of molybdenum in the ancient sedimentary record to quantify Archean Mo cycling, which allows us to calculate lower limits for atmospheric O2 partial pressures (PO2) and O2 production fluxes during the Archean. We consider two end-member scenarios. First, if O2 was evenly distributed throughout the atmosphere, then PO2 > 10–6.9 present atmospheric level was required for large periods of time during the Archean eon. Alternatively, if O2 accumulation was instead spatially restricted (e.g., occurring only near the sites of O2 production), then O2 production fluxes >0.01 Tmol O2/year were required. Archean O2 levels were vanishingly low according to our calculations but substantially above those predicted for an abiotic Earth system.

INVESTIGATION OF THE INFLUENCE OF PREHEATING ON THE STRUCTURE AND PROPERTIES TRANSITION ZONE BETWEEN HARDFACED WEAR-RESISTANT ALLOY AND 55NICRMOV5 STEEL

The results of the experimental studies hardfacing of the 55NiCrMoV5 die steel of the three types of wear and heat-resistant alloys with preheating are presented. The effect of the preheating on the structure hardfaced alloys as well as on the heat affected zone formation of the base metal is estimated. It is revealed that the use of preheating under the considered conditions of surfacing causes the formation of a structural heterogeneity of the heat-affected zone of the base metal, which manifests itself as a variable distribution of chromium and molybdenum.

Processing of Copper-Containing Molybdenite Concentrates by Roasting with Sodium Salts to Produce Technical Molybdenum Trioxide

The paper discusses methods of processing copper-containing molybdenite concentrates. A process flow diagram based on roasting with sodium chloride (or carbonate) and subsequent water leaching is presented. The chemistry of sulfide interaction with salt additives is described. The effect of the roasting temperature on copper and molybdenum distribution among the process products was studied. It was found that during roasting, 75 to 80% of molybdenum is converted from the sulfide into trioxide form, while copper predominantly forms water-soluble compounds and, thus, enables extraction by water leaching. It was established that the cake obtained as a result of water leaching meets the requirements for raw materials used for ferromolybdenum smelting.

Electrophoretic deposition and characterization of chitosan-molybdenum composite coatings

In this paper, the effect of the electric field on the properties of a new chitosan-molybdenum (Chit-Mo) composite coating obtained by electrophoretic deposition (EPD) was investigated. The composite coatings obtained showed different morphologies depending on the conditions used during the deposition process. Chemical composition results and microstructure analysis showed homogeneous distribution of molybdenum in a chitosan matrix. Corrosion test results showed that the Chit-Mo composite coatings can increase corrosion resistance of 1020 steel in NaCl medium (3.5 %). The coatings obtained at 5 V, pH 5.5, and using a low concentration of reagents (suspension 1: chitosan 0.5 g/L and 1 mM sodium molybdate) reached an inhibition efficiency of up to 76.7 %. Therefore, the results obtained in this work prove the achievement of a new class of chitosan-based composite materials with potential application in the protection of metal structures against corrosion.

Network distribution of molybdenum among pure titanium powders for enhanced wear properties

A homogeneous network distribution of molybdenum particles among pure titanium particles was successfully produced by powder metallurgy. The Ti–xMo mixtures were consolidated by uniaxial hot pressing under a 10−4 mbar vacuum atmosphere at 950 °C for 30 min. The distribution of the molybdenum particles in the structure was investigated by optical and scanning electron microscopy in polished and etched conditions. The dry sliding wear properties of the Ti–xMo compacts and the Ti6Al4V alloy was carried out using a ball on disc test using a 250 m distance, 150 rpm and 20 N load. 100Cr6 steel was selected as the counterface material during the wear tests. The results showed that titanium alloy with a content of 10 wt.% Mo has the highest wear resistance within the Ti–xMo alloys. In addition, Ti–10Mo alloys showed an intensive wear resistance compared to the Ti6Al4V alloy.

The fluxes and distribution of molybdenum in a mountainous fir forest in two hydrological years

<p>The distribution, stocks and fluxes of Mo were examined in a mountainous fir forest in Greece in two hydrological years. In both years, the fluxes of Mo in throughfall were lower than those in bulk deposition implying Mo retention and probably uptake by tree canopies. The Mo concentration was appreciable in soil solution but its fluxes were lower than those in throughfall. The Mo fluxes in both bulk and throughfall deposition were higher than those in litterfall, a finding that stresses the importance of the hydrological cycle for this metal. The Mo concentration in the older twigs in the standing trees were higher than the current year ones most probably due to the existence of dry deposition. The concentrations of total Mo in soils reflected the nature of the sedimentary rocks underlying the soil and increased with depth following the clay concentration gradient. The available (oxalate extractable) Mo in soils ranged from 3% to 14% of the total Mo. In terms of the stocks of Mo, the soil had by far the highest values in both total and available Mo. The needs of the fir plants for Mo uptake are covered by the available Mo in the mineral soil layers, whereas the Mo content in the organic horizon may not be adequate for this purpose.</p>

Laser Surface Treatment of Sintered Stainless Steels for Wear Resistance Enhancement

In the present study, sintered austenitic stainless steel type 316L was laser surface alloyed with Inconel 625 powder by the fibre optic laser. The Inconel 625 spheroidal powder of grain size 60-150 μm was introduced by the coaxial feeding head directly to the liquid metal, during laser surface alloying. The process parameters were selected to melt and fully dissolve alloying powder into the alloyed surface. As a result of laser alloying, the porosity of sintered stainless steel was eliminated, a uniform distribution of nickel and molybdenum in the entire alloyed zone was obtained. The alloyed surface shows fully austenitic microstructure of 17%Cr, 18%Ni, 3%Mo. The superficial hardness, microhardness and surface wear resistance were significantly improved in respect to an untreated substrate material. The presented technique of laser surface alloying can be easily applied for sintered austenitic stainless steel components where selected component surfaces require an improved surface performance.

Concentrations, variations and distribution of molybdenum (Mo) in catchment outlet sediments of China: Conclusions from the China geochemical baselines project

The concentrations, variations and distribution of molybdenum (Mo) in catchment outlet sediments from China were studied in this contribution based on the results of recently-finished, continental-scale, China Geochemical Baselines (CGB) project. The data from CGB were combined with other published data-sets with the purpose of understanding the spatial distribution of Mo in China and, in addition, relating the observed geochemical features to natural and/or anthropogenic processes. This geochemical mapping with a density of ca. 3000 km2 per site involves catchment sediments in two horizons at each site: a top sample (TOS) at a depth of 0–25 cm and a bottom sample (BOS) at a depth greater than 100 cm. In total, 3382 TOS and 3380 BOS samples were collected. The analytical results show that the concentrations of Mo in the catchment outlet sediments of China range from 0.07 to 57.86 μg/g for the TOS and 0.09–32.43 μg/g for the BOS. The median and mean values of the TOS data are 0.73 and 1.01 μg/g respectively, and those of the BOS data are 0.71 and 0.94 μg/g. The variations of both the TOS and BOS are high at this continental scale. The Mo concentrations vary greatly from one geological and/or geographic unit to another. For instance, from the Cathaysia Block with the TOS and BOS median values of 1.22 and 1.46 μg/g to the North China craton with those of approximately 0.61 and 0.58 μg/g. Various processes govern the spatial distribution of Mo in the catchment sediments of China but regional-scale natural sources (e.g. lithologies) predominate. Sedimentary sandstones and carbonate rocks, alluvium in plain terrain and aeolian materials (e.g. loess) account for the extensive low concentrations (<0.5 μg/g) at such regions as the Songpan-Ganzi orogen and Songliao Basin; whereas shales, basalts and granitoids like granodiorite, plagiogranite and granite porphyry are taken to be responsible for the high concentrations (>1.2 μg/g) in the Yangtze and Cathaysia blocks. Simultaneously, some local mineralized areas can be also identified at this scale because the sampled sites just happened to fall on sediments derived from mineralized rocks or anthropogenic addition by mining activities. Furthermore, the TOS share the similar patterns with the BOS indicating relatively stable inheritance and no apparent extensive secondary enrichment or depletion in the catchment sediments of China. The CGB demonstrates that a series of baseline levels of Mo are needed at different regions and scales and ultra-low density mapping can still deliver robust geochemical patterns.

The influence of hydrothermal activity during the origin of Co-rich manganese crusts of the N-W Pacific

The distribution of cobalt, vanadium, cadmium and molybdenum in the mineral fractions of the Co-rich manganese crusts (CMC) from Zubov and Govorov Guyots is considered. It is shown that the concentrations of cobalt in the ferrous fraction, and vanadium, cadmium in the manganese fraction indicate the ability of the CMC to record the rejuvenated volcanism in the N-W Pacific.

Distribution and Chemical Speciation of Molybdenum in River and Pond Sediments Affected by Mining Activity in Erdenet City, Mongolia

Rivers and ponds near the Erdenet mine, one of the world’s largest copper-molybdenum mines, exhibit high concentrations of molybdenum (Mo). This study evaluates the distribution and chemical speciation of Mo in surface sediments from ponds and rivers in Erdenet city to elucidate the mobility and solubility of Mo in the surface aquatic environments in the area. The waters and sediments were collected in two shallow ponds connected to the tailing pond and from three rivers flowing through Erdenet city. The distribution and chemical speciation of Mo in the sediments were examined using five-step sequential extraction and X-ray absorption fine structure (XAFS) analyses. The XAFS spectra of the sediments showed that large amounts of Mo in the sediments are molybdate or polymeric molybdate, weakly adsorbed onto ferrihydrite. Sequential extraction consistently showed a large amount of Mo distributed in the labile fractions. Results suggest that the surface sediments from ponds and rivers play a role as secondary contamination sources of Mo rather than as sinks of Mo in the area.