Seawater Concentrations Research Articles

اختبار أداء محطة تحلية مياه البحر بالزويتينة

The present study is applied on the seawater multi-stage flash (MSF) desalination plant that is currently under operation in E-Zuetina operations plant located in Libya. The plant contains 21 evaporator stages at capacity of 10025 (ton/day). The presented operating data has been collected during a visit of the plant, a mathematical model for multistage flash (MSF) desalination plants was developed. The model was based on basic principles of physics and chemistry that describe the stages occurring in the desalination process. The input plant parameters that are known to affect the operation of the MSF desalination plant and its performance were taken into account in the construction of the model. These parameters included make-up flow, brine recycle flow, seawater flow, seawater temperature, seawater concentration, steam temperature and the plant load. For each stage, the developed model was used for predicting the temperatures and pressure of the brine, distillate, cooling brine, and the flow rates of brine outlet and distillate production. The developed model was evaluated with the MSF plant vendor simulation results and its actual operating data. The evaluation indicated that model predictions matched well with the vendor simulation results and the plant operating data. The developed model is sufficiently accurate and model predictions can be relied upon. Therefore, it may be recommended for determining optimum set point of a running MSF desalination plant at different loads to maximize the water production or minimize energy consumption. It can also be used to calculate controller set points for different loads of the plant. Keywords:E-Zuetina MSF Desalination Plant, case study, stage model, brine heater.

Constraining global transport of perfluoroalkyl acids on sea spray aerosol using field measurements.

Perfluoroalkyl acids (PFAAs) are highly persistent anthropogenic pollutants that have been detected in the global oceans. Our previous laboratory studies demonstrated that PFAAs in seawater are remobilized to the air in sea spray aerosols (SSAs). Here, we conducted field experiments along a north-south transect of the Atlantic Ocean to study the enrichment of PFAAs in SSA. We show that in some cases PFAAs were enriched >100,000 times in the SSA relative to seawater concentrations. On the basis of the results of the field experiments, we estimate that the secondary emission of certain PFAAs from the global oceans via SSA emission is comparable to or greater than estimates for the other known global sources of PFAAs to the atmosphere from manufacturing emissions and precursor degradation.

Organophosphate esters (OPEs) in corals of the South China Sea: Occurrence, distribution, and bioaccumulation

Organophosphate esters (OPEs) have garnered significant attention in recent years. In view of the enormous ecosystem services value and severe degradation of coral reefs in the South China Sea, this study investigated the occurrence, distribution, and bioaccumulation of 11 OPEs in five coral regions: Daya Bay (DY), Weizhou Island (WZ), Sanya Luhuitou (LHT), Xisha (XS) Islands, and Nansha (NS) Islands. Although OPEs were detected at a high rate, their concentration in South China Sea seawater (1.56 ± 0.89 ng L−1) remained relatively low compared to global levels. All OPEs were identified in coral tissues, with Luhuitou (575 ± 242 ng g−1 dw) showing the highest pollution levels, attributed to intense human activities. Coral mucus, acting as a defense against environmental stresses, accumulated higher ∑11OPEs (414 ± 461 ng g−1 dw) than coral tissues (412 ± 197 ng g−1 dw) (nonparametric test, p < 0.05), and their compositional characteristics varied greatly. In the case of harsh aquatic environments, corals increase mucus secretion and then accumulate organic pollutants. Tissue-mucus partitioning varied among coral species. Most OPEs were found to be bioaccumulative (BAFs >5000 L kg−1) in a few coral tissue samples besides Triphenyl phosphate (TPHP). Mucus' role in the bioaccumulation of OPEs in coral shouldn't be ignored.

Zn-doped CeO2 nanorod based dispersive solid phase micro-extraction of lead in water, black pepper, lentils and tea samples

In this work, pristine CeO2 and Zn-doped CeO2 nanorods were prepared through facile hydrothermal process and characterized. The Zn- doped CeO2 was first used for dispersive solid phase micro extraction (d-SPµE) of lead in water and food. The conditions affecting d-SPµE of lead were optimized. They were pH, adsorption/elution contact time, eluent type/volume/concentration, interfering ion effects and sample volume. The sample pH, eluent concentration/volume and sample volume were 3, 2 mol L−1 HCl/1 mL and 60 mL, respectively. The adsorption/desorption kinetics of the developed d-SPµE were very fast, and the extraction time was only 30 s (30 s for adsorption and without vortexing for elution). The preconcentration factor (PF) and limit of detection (LOD) of the d-SPµE for lead were 60 and 2.0 µg L−1, respectively. The RSD% (n=5) of the extraction method was found to be ≤ 3.0%. The high tolerable interfering ion concentrations were obtained. The sorbent could be used for 46 times. The method was confirmed with analyses of NW-TMDA 54.6 Lake water, SPS-WW1 Batch 114 Wastewater and NIST 1573a Tomato Leaves certificate reference materials. The trace lead concentrations in wastewater, dam water, river water, sea water, tea, lentils, and black pepper were determined by d-SPµE-FAAS.

Ocean acidification significantly alters the trace element content of the kelp, Saccharina latissima

Seaweeds are ecosystem engineers that can serve as habitat, sequester carbon, buffer ecosystems against acidification, and, in an aquaculture setting, represent an important food source. One health issue regarding the consumption of seaweeds and specifically, kelp, is the accumulation of some trace elements of concern within tissues. As atmospheric CO2 concentrations rise, and global oceans acidify, the concentrations of elements in seawater and kelp may change. Here, we cultivated the sugar kelp, Saccharina latissima under ambient (~400 μatm) and elevated pCO2 (600–2400 μatm) conditions and examined the accumulation of trace elements using x-ray powder diffraction, sub-micron resolution x-ray imaging, and inductively coupled plasma mass spectrometry. Exposure of S. latissima to higher concentrations of pCO2 and lower pH caused a significant increase (p < 0.05) in the iodine and arsenic content of kelp along with increased subcellular heterogeneity of these two elements as well as bromine. The iodine-to‑calcium and bromine-to‑calcium ratios of kelp also increased significantly under high CO2/low pH (p < 0.05). In contrast, high CO2/low pH significantly reduced levels of copper and cadmium in kelp tissue (p < 0.05) and there were significant inverse correlations between concentrations of pCO2 and concentrations of cadmium and copper in kelp (p < 0.05). Changes in copper and cadmium levels in kelp were counter to expected changes in their free ionic concentrations in seawater, suggesting that the influence of low pH on algal physiology was an important control on the elemental content of kelp. Collectively, these findings reveal the complex effects of ocean acidification on the elemental composition of seaweeds and indicate that the elemental content of seaweeds used as food must be carefully monitored as climate change accelerates this century.

1.44 Ga Oxygenation Event: Evidence From the Southern Margin of North China

AbstractPrevious studies suggest that the atmospheric and shallow seawater oxygen levels during the mid‐Proterozoic may have remained persistently unbalanced due to the low atmospheric oxygen levels and that, under these conditions, the oxygen concentrations of shallow seawater would largely reflect local oxygenation caused by primary productivity. As a result, in a microbialite‐rich setting, it may be difficult to differentiate oxygenation caused by local primary productivity from overall oxygenation of the surface environment. To address this issue, we conducted an integrative study of the ∼1.44 Ga stromatolitic carbonates of the Fengjiawan Formation in the Xiong’er Basin, southern North China, using techniques of sedimentology, mineralogy and geochemistry. The results show that the Fengjiawan Formation is dominated by water‐column precipitated carbonate mud (now dolomitized), pointing to moderately oxidized marine conditions. A significant and stable negative Cerium (Ce) anomaly (as low as 0.42) is identified in a long interval (&gt;50 m in thickness) of this formation. This Ce anomaly is lower than the minimum values both recorded in the Great Oxidation Event (GOE; minimum 0.76) and in the Neoproterozoic Oxygenation Event (NOE; minimum 0.52), suggesting a significant oxygenation process rather than an oxygen oasis. Some intervals in this formation show I/(Ca + Mg) values higher than the Precambrian background value of 0.5 μmol/mol, providing a further support for shallow seawater oxygenation. This study, together with the enhanced oxygenation identified in the time‐equivalent Tieling Formation, indicates a multi‐basin oxygenation event in North China at ∼1.44 Ga.

Analysis of the Effect of Distillation Parameters on Freshwater Yield in Seawater Dispenser

The purpose of this study is to analyze the process of condensation that occurs in the condenser in the seawater distillation dispenser system. In the seawater dispenser system, it has been tested using the default system from the existing dispenser. The test results from the seawater distillation dispenser can change seawater with a seawater content of 20% to 0%. Initial testing was carried out only to see whether the built-in dispenser system with the addition of a 1-level condenser system could work well or not. Therefore, it is necessary to analyze the condensation process that occurs in the condenser to see how efficiently the condenser works. The method used is by testing directly on the seawater distillation dispenser system. The test was carried out in 3 stages, each of which used a volume of 400 mL of seawater. The capacity refers to the volume available in the sea-water distillation dispenser reactor. The results obtained from the tests carried out are in the form of the time required for the freshwater production process, the amount of fresh water produced and the condenser temperature that occurs. This research is important to see the performance of the distillation dispenser system. In previous tests it has not been seen how efficient the system has been made. by testing the seawater distillation dispenser system, you can see how efficient the tool is and how the operating parameters occur. Fresh water production in stage 1 condenser starts to appear at 350 seconds (6 minutes first). The maximum production of fresh water is 24.6 mL (6.15%) of the total 400 ml. The average condenser temperature is above 80°C.

Recovery of phosphate from aqueous solution by modified biochar with concentrated seawater and its potential application as fertilizer

Concentrated seawater as a byproduct of seawater desalination, its resource utilization potential has attracted widespread attention because of its rich inorganic salt resources. Concentrated seawater-modified biochar for phosphate recovery is undoubtedly a promising and sustainable option for resource utilization and eutrophication control. In this study, peanut shells as a carbon source, and modified biochar composites were successfully synthesized by co-precipitation with concentrated seawater for phosphate removal from aqueous solution. Meanwhile, the potential of phosphorus-enriched modified biochar as a soil slow-release fertilizer was evaluated. A series of characterization results showed that magnesium/calcium in the form of Mg(OH)2 and CaCO3 were successfully loaded onto the modified biochar composites. Furthermore, the pseudo-second-order kinetic model and Langmuir model can describe the adsorption process more accurately. According to the Langmuir model calculations, the theoretical maximum adsorption of phosphate by modified biochar composite was 173.09 mg/g, which can be compared with those of many Ca/Mg biochar composites. The primary sorption mechanism is electrostatic adsorption, ligand exchange and chemical precipitation interactions between phosphate and modified biochar composites. In addition, it was shown that the phosphorus-rich modified biochar embodied significant effects in improving the germination rate as well as the growth of plants, and had great potential as a slow-release fertilizer for agricultural soils.

Chinese yam-derived aerogel as a versatile platform for efficient freshwater production and pollution remediation

Water scarcity and pollution have become major obstacles to sustainable global development. The development of a versatile platform that can simultaneously produce clean water and remediate pollutants from water is highly desirable but still difficult to realize. Herein, to address this challenge, we have developed a CY@PPy@Ag aerogel with excellent photothermal and photocatalytic capabilities through a freeze-drying process, followed by polypyrrole coating and Ag deposition. The excellent characteristics, including broad-spectrum light absorption (97.2%), localization of converted heat, rapid water transport, and porous open microchannels, enabled it to act as an advanced solar evaporator for efficient and continuous steam generation without salt crystallization. Moreover, the high evaporation rate (1.51 kg m−2 h−1) was maintained even in high concentrations of brine and real seawater. Taking advantage of its enhanced photocatalytic performance, organic dyes in water could be rapidly and completely decomposed by the CY@PPy@Ag aerogel under solar irradiation, and this photodegradation process was significantly accelerated with the help of NaBH4. This work is expected to provide a one-stone-two-birds strategy to simultaneously achieve clean water harvesting and pollution remediation, which holds great promise in the fields of solar energy harvesting, wastewater treatment, and seawater desalination.

Simultaneous determination of seawater trimethylamine and methanol by purge and trap gas chromatography using dual nitrogen-phosphorus detector and flame-ionization detector

Compounds containing one carbon atom or no carbon-carbon bond (C1 compounds), such as trimethylamine and methanol, are important climate relevant gases in the atmosphere and play key roles in global warming. The ocean is a significant source or sink of such compounds, while the concentrations of trimethylamine and methanol in seawater remain largely unconstrained due to the analytical challenges involved. Therefore, it is necessary to establish a continuous, rapid and sensitive method for the determination of these compounds with high polarity, volatility or solubility at low seawater concentrations. Here we developed a purge and trap system, coupled to a gas chromatography equipped with dual nitrogen phosphorus detector (NPD) and flame ionization detector (FID) for the simultaneous online analysis of trimethylamine and methanol at nanomolar range using a small sample volume (~ 10 mL). The dual detection of trimethylamine and methanol with NPD or FID was achieved by installing a capillary flow splitter between the capillary column and detectors. After modification and optimization of the setup and conditions, excellent linearity (R2 &amp;gt; 0.99) and repeatability (&amp;lt; 6%) were obtained for both compounds; the detection limits for trimethylamine and methanol were 0.3 nM and 17.6 nM, respectively. Using this method, water samples collected from coastal and open ocean were analyzed; trimethylamine and methanol concentrations ranged from 0.6 to 18.8 nM and 26.0 to 256.2 nM, respectively. Collectively, this method allowed for online, rapid, sensitive and simultaneous quantification of trace trimethylamine and methanol concentrations with low-cost instrumentation and small sample volume, which makes it promising for further application in volatile compounds analysis in marine environments.

Same volume, larger output: 3D trapezoidal multi-interface solar evaporator for concentrated seawater desalination and wastewater treatment

With the scarcity of freshwater resources, solar desalination of seawater is a promising strategy for freshwater production. Compared to 2D evaporators with limited evaporation area, 3D evaporators can increase the evaporation area. However, traditional 3D evaporators cannot fully utilize the internal space of the evaporator for evaporation. In this study, a 3D trapezoidal multi-interface evaporator (Evap1), which composed of superhydrophilic sponges and superhydrophobic sponges arranged by alternate permutation for making full use of the inside structure of the evaporator to expand the actual evaporation area and achieve effective thermal management, were developed. The selective water transport channels and heat transfer channels were constructed by alternate permutation of hydrophilic and hydrophobic sponges in Evap1, while the top trapezoidal structure prevented heat from accumulating on the top surface of Evap1, which can enhance the efficiency of photothermal conversion. The Evap1 exhibited excellent evaporation rate of 3.6 kg m−2 h−1 under 1 sun illumination, and the evaporation rate was almost unchanged in brine with 20 wt% concentration for 8 h working. In addition, the Evap1 can achieve efficiently purificaiton of waste water containing dye, and the potential practical application of Evap1 was further proved by repeated and outdoor evaporation experiments.

Hydrogeochemical conditions of submarine and terrestrial karst sulfur springs in the Northern Adriatic

Submarine springs near Izola, in the Northern Adriatic Sea, appear in funnel-shaped depressions and smell strongly of sulfur. Along the Mediterranean coast there are many submarine karst springs containing brackish or fresh water, but submarine sulfur springs are not particularly common. Three submarine sulfur springs and one terrestrial sulfur spring were investigated to better understand the water properties, water–rock interaction within the aquifer, and to explore the origin of the spring water. Groundwater and seawater samples were also collected for comparison. Based on the geological setting, physicochemical parameters, hydrogeochemical data, and stable isotope data (δ18O, δ2H, δ13CDIC, δ34SSO4, δ18OSO4), we can affirm that (1) the large concentration of seawater in the submarine springs samples is due to sampling challenges; (2) springs recharge from precipitation where confined karst aquifers outcrop; (3) deep water circulation is indicated; (4) redox conditions can provide a suitable environment for bacterial reduction of the marine or organic sulfate to the odorous H2S; (5) geological data suggests that the coals beneath the alveolinic-nummulitic limestones are the source of sulfur. A multi-parameter and interdisciplinary approach has proven important in assessing submarine sulfur springs affected by seawater input.

Chlorella vulgaris in biodesalination: a sustainable future from seawater to freshwater

Demand for freshwater is increasing rapid due to population growth and climate change. A potential solution to this problem is the use of biodesalination, which involves the removal of salt from seawater and brackish water using biological agents. In this study, we investigated the feasibility of using Chlorella vulgaris, a green microalga, to remove salt from seawater to produce fresh water. The effects of salinity, light intensity, and nutrient concentration on the growth and salt removal efficiency of C.vulgaris were examined. Our results showed that C. vulgaris was able to grow and remove salt from seawater under salinities of approximately 24ppt and nutrient concentrations of 50%. The highest salt removal efficiency was achieved at a desalination setup involving C. vulgaris and seawater concentration of 1:5 ratio. We also evaluated the economic feasibility of biodesalination using C. vulgaris by estimating the production costs and comparing them with those of conventional desalination technologies. Our results showed that biodesalination using C.vulgaris is potentially a cost-effective and sustainable alternative to conventional desalination technologies. In conclusion, our study demonstrated the potential of C. vulgaris for the biodesalination of seawater, which could contribute to meeting the growing demand for fresh water.

Early Triassic (Griesbachian) spheroids in Beibei, Chongqing, Southwestern China: Characteristics, cause and implications for palaeo‐oceanic conditions

Following the latest Permian mass extinction (LPME), abundant unusual sedimentary features and fabrics were widely distributed in Early Triassic carbonate platforms. As a unique type of carbonate grain, spheroids from the Lower Triassic are infrequently reported, yet differ significantly from giant ooids and oncoids. Griesbachian micritic spheroids are well preserved in the Lower Triassic Feixianguan Formation at the Baimiaozi (BMZ) outcrop in Beibei, Chongqing, southwestern China. These spheroids (diameter: 3.9–10.8 mm) were in a marl layer interbedded with massive oolites. They were deposited in the wave troughs of ripple marks comprising micritic clots, sparry calcite, clay minerals, organic matter and pyrite. A microbial spheroid origin is implied based on the coccoidal microbes (coccoid‐like microspherules and bacterial clump‐like microspherules), numerous pyrite framboids (indications suggest the presence of many sulphate‐reducing bacteria and the high iron content in seawater can promote nitrogen‐fixing cyanobacteria proliferation) and microbial‐derived microspherules. The dark‐coloured matrix between the spheroids primarily included microcrystalline calcite, clay minerals, organic matter and metazoan fossils. The spherical and ellipsoidal shapes of the spheroids suggested rapid accretion and lithification. As a unique carbonate depositional mode, Greisbachian spheroids may have been recorded for a palaeo‐ocean with dysoxic and calcium carbonate supersaturation shortly after the LPME.

Adsorbents for the Uranium Capture from Seawater for a Clean Energy Source and Environmental Safety: A Review.

On the global level, uranium is considered the main nuclear energy source, and its removal from terrestrial ores is enough to last until the end of the current century. Therefore, a major focus is attracted toward the capture of uranium from a sustainable source (seawater). Uranium recovery from seawater has been reported over the last few decades, and recently many efforts have been devoted to the preparation of such adsorbents with higher selectivity and adsorption capacity. The purpose of this review is to report the advancement in adsorbent preparation and modification of porous materials. It also discusses challenges such as adsorbent selectivity, low uranium concentration in seawater, contact time, biofouling, and the solution to the problems necessary to ensure a better adsorption performance of the adsorbent.

The Growth and Hemocyte Analysis of the Shrimp (Litopenaeus vannamei) Induced by Different Concentration of Artificial Seawater and Water Extract Of Sea Grapes (Caulerpa lentillifera)

The Growth and Hemocyte Analysis of the Shrimp (Litopenaeus vannamei) Induced by Different Concentration of Artificial Seawater and Water Extract Of Sea Grapes (Caulerpa lentillifera)

Introducing the halophyte Salicornia europaea to investigate combined impact of salt and tidal submergence conditions.

Tolerance mechanisms to single abiotic stress events are being investigated in different plant species, but how plants deal with multiple stress factors occurring simultaneously is still poorly understood. Here, we introduce Salicornia europaea as a species with an extraordinary tolerance level to both flooding and high salt concentrations. Plants exposed to 0.5MNaCl (mimicking sea water concentrations) grew larger than plants not exposed to salt. Adding more salt reduced growth, but concentrations up to 2.5MNaCl were not lethal. Regular tidal flooding with salt water (0.5MNaCl) did not affect growth or chlorophyll fluorescence, whereas continuous flooding stopped growth while plants survived. Quantitative polymerase chain reaction (qPCR) analysis of plants exposed to 1% oxygen in air revealed induction of selected hypoxia responsive genes, but these genes were not induced during tidal flooding, suggesting that S. europaea did not experience hypoxic stress. Indeed, plants were able to transport oxygen into waterlogged soil. Interestingly, sequential exposure to salt and hypoxic air changed the expression of several but not all genes as compared to their expression upon hypoxia only, demonstrating the potential to use S . europaea to investigate signalling-crosstalk between tolerance reactions to multiple environmental perturbations.

Thermochemical modeling and performance evaluation of freeze desalination systems

Freeze desalination (FD) is a method in which saline water is cooled below its freezing point and freshwater is separated from the brine in the form of ice crystals. FD is relatively insensitive to the salinity of the feed solution, making it suitable for desalination of high concentration brines such as the brine rejected from the seawater desalination plants. The design of the FD system and the thermochemical behavior of the brine upon freezing are critical factors in the energy performance of this method. To date, thermochemical properties of the concentrated seawater during cooling, such as the threshold of formation of ice and salt-hydrates and their corresponding cooling load of formation, are not well known. Likewise, the optimal configuration of the FD system to achieve the maximum energy efficiency has not been investigated. This work provides comprehensive data about the cooling load of freezing of concentrated brine rejected from seawater desalination plants along with the threshold of formation of ice and salt-hydrates backed-up by validation. Furthermore, the optimal configuration of the FD system is identified and the effects of the compressor isentropic efficiency and effectiveness of the system's heat exchangers on the work consumption of the FD system were investigated.

Effect of maintenance environment on the mechanical property and pore structure of cement paste mixed by seawater

This study aims to examine the effects of macroscopic mechanical properties and pore structure of cement paste mixed with seawater and explore the relationship between pore structure and macroscopic properties. The changeable law of mechanical properties and pore microstructure of hardened cement paste under seawater mixing is methodically investigated based on the compressive and flexural strengths using X-ray diffraction (XRD), scanning electron microscopy (SEM), and mercury intrusion porosimetry (MIP) tests. The relationship between the fractal dimension of the pore structure of cementitious materials and the concentration of chloride ions in simulated seawater, the curing age, and the fly ash dose was obtained based on the thermodynamic fractal model. The obtained results reveal that with the increase in chloride ion concentration of the simulated seawater, the compressive and flexural strengths of the samples substantially grow in the pre-maintenance period, and the strength of the samples tends to stabilize at the age of 28 days. For the case of the chloride ion concentration of 1.3%, the compressive strength of the cement slurry exhibits a growth of 24.08%, 24.83%, and 28.81% compared to the control cement sample after curing at 5 °C, 20 °C, and 50 °C for 3 days, respectively. Additionally, the flexural strengths in order are 41.86%, 46.57%, and 38.89% higher than those of the control group. The interaction of Cl- with C3A, C4AF, or AFm in seawater mixed at high-temperature to generate Friedel's salt stimulated the volcanic ash reaction of fly ash, promoted the generation of C-S-H gels, and improved the internal pore structure of cementitious materials. The results indicate that at 50 °C curing, the most probable pore diameter of cement paste with 1.3% chloride ion concentration is 39.51% less than that of the control cement sample, and its harmless pores are 23% higher than that of the control group. At 5 °C curing, the total specific pore volume of cement paste with 1.3% chloride ion concentration is 30.18% less than that of the control cement sample, and the total specific pore volume is 22.9% less than the control group for the fly ash content of 25%. The obtained results reveal that there exists a fairly low correlation between the fractal dimension of the pore surface area of the cement paste and porosity, compressive strength, and flexural strength. However, the achieved correlation with the mean pore diameter, median pore diameter, and pore surface area is good, which are all above 75%. The fractal dimension fitting curve of high-temperature curing possesses a range of singular points.

Interactions of Perrhenate (Re(VII)O4−) with Fe(II)-Bearing Minerals

Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re concentrations in anoxic marine sediments range from 2 to 184 ppb, which is attributed to reduction of the highly soluble perrhenate ion (Re(VII)O4−) to insoluble Re(IV) species. Anoxic sediments typically contain Fe(II) and sulfide species, which could potentially reduce Re(VII) to Re(IV). In this study, we examined the interactions of KReO4 with magnetite (Fe3O4), siderite (FeCO3), vivianite (Fe3(PO4)2•8H2O), green rust (mixed Fe(II)/Fe(III) layered double hydroxide), mackinawite (FeS), and chemically reduced nontronite (NAu-1) using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the valence state and speciation of Re. Uptake of Re by green rust was rapid, with ~50% associated with the solids within 2 days. In contrast, there was &lt;10% uptake by the other Fe(II) phases over 48 days. Reduction of Re(VII) to Re(IV) was only observed in the presence of green rust, producing clusters of bidentate-coordinated Re(IV)O6 octahedra.. These results suggest that except for green rust, the potential for other Fe(II)-bearing minerals to act as reductants for ReO4− in sedimentary environments requires further investigation.