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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Rechargeable Seawater Battery and Its Electrochemical Mechanism

Here in this paper, we explore the electrochemical mechanism of a novel rechargeable seawater battery system that uses seawater as the cathode material. Sodium is harvested from seawater while charging the battery, and the harvested sodium is discharged with oxygen dissolved in the seawater, functioning as oxidants to produce electricity. The seawater provides both anode (Na metal) and cathode (O 2 ) materials for the proposed battery. Based on the discharge voltage (~2.9 V) with participation of O 2 and the charge voltage (~4.1 V) with Cl 2 evolution during the first cycle, a voltage efficiency of about 73% is obtained. If the seawater battery is constructed using hard carbon as the anode and a Na super ion conductor as the solid electrolyte, a strong cycle performance of 84% is observed after 40 cycles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Energy considerations associated with increased adoption of seawater desalination in the United States

Due in part to increased water demand and uncertainty around the availability of existing freshwater resources, there is interest in expanding the use of seawater desalination in the U.S. In order for greater adoption to occur, existing barriers need to be mitigated. One of these barriers is the energy consumption of seawater desalination. This paper reviews the existing energy requirements for membrane and thermal-based seawater desalination systems to produce potable water. Through literature review, it identifies the commercially-available option with the lowest energy intensity and the thermodynamic minimum energy requirement for each unit operation of the system. The paper then estimates the energy requirements to expand seawater desalination capacity to meet the potable water needs of water-stressed regions in the U.S. The results show that supplying 10% of the potable water demand for these regions located within 250 miles of a coastline using the lowest energy-intensity seawater desalination system commercially available would require <0.1% of 2018 U.S. electricity consumption. This increases to approximately 0.5% if all public water for these same regions is supplied via desalinated seawater. Furthermore, these estimates of the energy implications of broader adoption provide an initial comparison to current U.S. electricity consumption.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

High salinity seawater boiling point elevation: Experimental verification

Boiling point elevation (BPE) for high salinity solutions is a crucial parameter that significantly affects the overall thermal efficiency of desalination, water treatment, and many other industrial processing systems, especially when minimum or zero liquid discharge is a key requirement. This paper addresses the discrepancies among the empirical correlations reported in the literature that were commonly used to determine BPE for seawater solutions. An evaluation of the experimental data with low solution concentration reveals that the data cannot be extrapolated to determine the BPE at high concentration (X > 140 ppt or g/kg). Besides, disparities are established within different equations used to determine the BPE for high salinity seawater. As a result of the minimal availability of experimental data of BPE for X > 140 ppt and the need to eliminate the discrepancies, an experimental setup was built, which can produce reliable and repeatable BPE data for any solution concentration. Boiling points were obtained experimentally for seawater solutions with a wide range of salinity (X between 20 and 280 ppt) and brine solution temperature (t b between 20 and 80°C). The experimental results of boiling point elevations for seawater are further compared with the experimental data and analytical results reported in the literature. The newly obtained experimental results show that the minimum and maximum BPE values for the brine solutions tested are 0.175°C at t b = 80°C and X = 20 ppt, and 11.6°C at t b = 80°C and X = 280 ppt, respectively. Furthermore, the measured BPE data for seawater concentration over 80 ppt are fitted and presented using an appropriate fitting model. The new correlation can accurately predict the BPE for high salinity seawater brines and thus should be very helpful in the design of high-energy-efficient evaporation systems.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2018

Numerical simulation of seawater intrusion to coastal aquifers and brine water/freshwater interaction in south coast of Laizhou Bay, China

Seawater intrusion and brine water/freshwater interaction have significantly affected agriculture, industry and public water supply at Laizhou Bay, Shandong Province, China. A two-dimensional SEAWAT model is developed to simulate the seawater intrusion to coastal aquifers and brine water/fresh water interaction in the south of Laizhou Bay. This model is applied to predict the seawater intrusion and brine water/freshwater interface development in the coming years. The model profile is perpendicular to the coastal line with two interfaces, freshwater-saline water interface near the shore and inland brine water-saline water-seawater interface. The hydrogeological parameters in the SEAWAT-2000 model are calibrated by the head and salinity measurements. The precipitation infiltration coefficient, boundary conditions and thicknesses of aquifers are studied in a sensitivity analysis. The predicted results indicate that equivalent freshwater head in shallow freshwater-saline water area will decline 2.0 m by the end of the forecasting period, caused by groundwater over-pumping for farmland irrigation. The groundwater head in the brine-saline water area will also decrease about 1.8 m by the end of forecasting period, caused by excessive brine mining. Salinity decreases below 105 g/L in the brine area, but increases in other areas and contaminates fresh groundwater resources.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Investigation of MO x (M = Cr, Mn, Re, and Mo) coated stainless-steel electrodes for oxygen evolution reaction in natural seawater electrolysis

Seawater electrolysis is considered a potential strategy for large-scale of affordable H 2 production. However, poor durability of the anode for oxygen evolution reaction (OER) in natural seawater is a remaining concern due to chloride-induced reaction. Herein, the effect of various MO x (M = Mn, Cr, Re, and Mo) coated stainless steel (SS) electrodes on OER in direct natural seawater electrolysis was comprehensively studied. It is found that the Mo-coated SS electrode is superior to all others in terms of durability, followed by Re-coated SS, while the Cr and Mn-coated SS electrodes show the poorest durability. Additionally, the durability and activity of the Mo/SS electrode can be boosted remarkably in 1 M KOH/seawater compared to the natural seawater, resulting in an overpotential at 10 mA cm −2 decrease from 830 to 399 mV. Meanwhile, no degradation is observed at 1000 mA cm −2 for 100 h in 1 M KOH seawater, which is among the best stability, based on the literature review. Moreover, the improved durability and activity with Mo coating were extended to the Inconel 718 substrate, and around 40 % improvement in durability and 25 mV overpotential decrease at 10 mA cm −2 are observed, which indicates that Mo coating can be considered as a universal approach to improve the anode durability and activity. The improved performance with Mo coating may be attributed to the continuous Mo oxide layer formation or in situ generated MoO 4 2− in the OER process. In conclusion, this work provides a holistic strategy to enhance the anode durability and activity under harsh conditions, offering valuable insights for designing corrosion-resistant electrodes in direct seawater electrolysis.

Direct seawater electrolysis↗
DOE OSTI2025

Impact of inland boundary conditions on seawater intrusion modeling in stratified coastal aquifers under sea-level rise

This study systematically examines the impact of inland boundary conditions on seawater intrusion modeling in general stratified coastal aquifers under sea-level rise (SLR). We derived analytical solutions for seawater wedge toe positions in stratified aquifers with general head boundary (GHB) conditions and compiled solutions for constant head boundary (CHB), constant flux boundary (CFB), and GHB conditions in both homogeneous and stratified aquifers. Additionally, we introduced the concept of equivalent boundary conditions and developed equations to ensure consistent steady-state toe positions across different boundary types. Unlike previous studies focusing on specific layering configurations, we conducted a comprehensive sensitivity analysis of seawater intrusion in general stratified aquifers using transmissivity centroid elevation (TCE). Our results show that SLR generally exacerbates seawater intrusion, with unconfined aquifers exhibiting higher sensitivity across all boundary conditions. Among boundary types, CHB conditions were the most sensitive to SLR, CFB the least, and GHB showed an intermediate response depending on its distance from the model boundary. Furthermore, seawater intrusion increases with the TCE of the stratified aquifer under SLR, suggesting that high-permeability or preferential flow layers near the surface amplify the impact of SLR. These findings emphasize the importance of selecting appropriate boundary conditions when evaluating SLR-driven seawater intrusion in stratified coastal aquifers.

Boundary condition↗
DOE OSTI2018

Enhancement of the Extraction of Uranium from Seawater

Due to the limited uranium resources available for recovery through mining and ore processing and to the environmental problems associated with these operations, the future of nuclear power depends, to a large extent, on the feasibility of recovery of uranium from the ocean. While the amounts of uranium in the ocean are sufficient to fulfill the nuclear industry for many thousands of years, recovery of uranium from the ocean is hampered by its low concentration (3.3 parts per billion) and the presence of many other solutes in seawater at comparable or much higher concentrations. Thus, the only hope for economically viable recovery of uranium from the ocean lies in the development of adsorbents with high capacity and high selectivity for uranium as present in the seawater environment (pH 8.1, U(VI) oxidation state, anionic carbonate complexes). Moreover, it is quite unlikely that economically viable recovery of uranium could be achieved if the adsorbent could be used only once. Thus it is essential to develop adsorbents that can be used through multiple cycles of uranium adsorption followed by elution of the uranium to regenerate the adsorbent without significant degradation of their capacity and selectivity for uranium. Adsorbents used in the large majority of studies aimed at recovery of uranium from seawater are based on the use of radiation grafting to produce polymeric supports, in particular polyethylene, with attached amidoxime groups. This configuration has been concluded to offer the best candidate for use in recovery based on studies which were performed in the early 1980’s. Substantial progress has been made in improving the amidoxime-based adsorbents. The basic approach undertaken by the authors of the proposal, on the other hand, has been to test ligands which have not been included in the scoping studies of the 1980’s or have been developed since then. So far, 18 such ligands have been tested, of which three, including B2MP (an organic phosphate), DAOx (an organic oxalate), and Br-PADAP (an azo compound) have been selected for further investigation. In addition, Winged Nylon 6 has been identified as a promising polymeric support in view of its large surface area and high chemical stability. Furthermore, improved grafting techniques intended to achieve high grafting density under “green chemistry” conditions, i.e., in aqueous media, have been developed. These techniques include the use of surfactants to enhance the solubility of ligands in water and the use of a homopolymerization inhibitor to promote grafting rather than homopolymerization. Furthermore, unlike amidoxime-based adsorbents, which require a chemical treatment step following the radiation grafting to convert a nitrile group to amidoxime, the adsorbents developed by the authors do not require an additional step after grafting. Highly effective regeneration has been demonstrated for the phosphate-grafted polymeric adsorbent over at least 21 adsorption/elution cycles without significant loss of capacity. The currently proposed study is intended to build upon the progress made so far in developing alternative systems for removal of uranium from seawater. It will focus on the following objectives: Continued searches will be conducted for high-capacity, high-selectivity ligands based on systematic characterization of structural features favorable to uranium adsorption. (For instance, phosphates have been found to be much more effective than the corresponding phosphonates). At the same time, development and testing of the three ligands selected so far will continue, focusing on issues such as high grafting densities and effective regeneration. Testing will be conducted in non-spiked sweater (3.3 µg/L U) and lightly spiked seawater (up to 10 µg/L U). The authors have recently been able to refurbish an ICP-MS spectrometer for this purpose. Improved grafting techniques will be developed and refined for specific ligands. These techniques will include the use of surfactants to allow grafting of ligands with low solubility in water, the use of homopolymerization inhibitors, modifying the chemical structure of ligands to introduce C=C bonds, investigating possible modification of the surface of the polymeric support, and mechanistic analysis of the effects of grafting conditions, in particular accumulated dose and dose rate. Improvements in the characterization of adsorbents before and after contact with seawater will be implemented using techniques such as XPS, SEM-EDS, and zeta potential measurements to investigate the mechanism of uranium adsorption. Effective techniques of multi-cycle regeneration of promising adsorbents without degradation of their performance will be developed and refined through testing of mild, preferably near-neutral eluant solutions. The kinetics of adsorption and desorption of uranium will be investigated. This study is of great operational value and it will also greatly contribute to improved understanding of adsorption/desorption mechanism on promising adsorbents.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRSDate not supplied

Predicting the Seawater Chemistry of an Ocean World Using Machine Learning on Isotopic Measurements of Volatile CO2

Introduction: Given the long time intervals required for data transmission to and from ocean worlds targets, low bandwidth for data transmission, time required for data processing and analysis, and potentially extreme radiation environments (e.g., Europa), it is clear that ocean worlds missions will need more autonomous flight instruments and software in order to achieve established science goals. Protracted time intervals for data analysis (e.g., Europa Lander) strongly motivates the development of rapid, consistent and streamlined methods for interpreting data from flight mass spectrometers to e.g., determine how mass spectra from a plume or surface liquid/ice relates to the surface/subsurface. Since mass spectrometry also has the potential to correctly identify biosignatures[1], it is imperative that such methods for interpreting data are consistent and accurate. We used 848 isotope ratio mass spectra from laboratory analyses of CO2 that interacted with ocean worlds-relevant seawaters as a ‘training’ dataset for ‘unsupervised’ machine learning. In unsupervised learning, characteristics of the data are not labeled or linked, and any similarities found only result from the neural network. CO2 isotopologues analyzed for this dataset mimic the remote measurements of CO2 by a flight mass spectrometer, and are detailed in Theiling [2]. From this dataset, we used measured features of the spectra, such as retention time, intensity, and (isotopologue) mass ratios as inputs for our autoencoder neural network. Our neural network was trained to find similarities in these and other spectral features for seawaters of a particular composition and amount of initial CO2. Successful training then created an output of these similarities for various seawaters, which included MgSO4, Na2SO4, NaCl, MgCl2, KCl, and NaHCO3, and combinations of these salts. We then applied dimensionality reduction techniques such as Principal Component Analysis (PCA), T-Distributed Stochastic Neighbor Embedding (TSNE), and Uniform Manifold Approximation and Projection (UMAP) to demonstrate latent data features as a two-dimensional projection in a unitless, high-dimensional space. In this projection, a data point represents the combined effect of spectral features such as intensity, retention time, and isotope ratio. Our initial UMAP demonstrates data clustering (organization of the data by the neural network) based on the amount of CO2 that had initially interacted with each seawater. Further training using more ‘supervised’ learning techniques demonstrate strong clustering of preliminary data based on initial CO2 concentration, seawater chemical composition, and ionic strength (salinity). Our preliminary work therefore suggests that machine learning has the potential to identify compositional variants of an ocean world seawater based on mass spectra from volatile CO2 measurements. Acknowledgments: This work was funded through a Strategic Task Group at NASA Goddard Space Flight Center. The training dataset was collected through funding from the Oklahoma Space Grant Consortium. References: [1] Pappalardo, R. et al. (2013) Astrobiology, 13, 740–773. [2] Theiling (2020) Icarus, 114216.

Europa↗
DOE OSTI2016

A Higher Fidelity Cost Analysis of Wind and Uranium from Seawater Acquisition symbiotic Infrastructure

The vastness of the worlds oceans makes the low concentration of naturally existing uranium, 3.3 ppb, appealing as a recoverable natural resource. Although ample uranium is available currently through conventional means, uranium from seawater is a widely studied topic due to the long term security it can assure the nuclear fuel cycle. It is important to mention that seawater uranium is not meant to act as a direct competitor to terrestrial uranium, but instead create a cost ceiling that provides economic stability and potential savings. Additionally, seawater uranium could circumvent some of the environmental impacts associated with recovery of any land based resource. The system currently studied by a nation-wide consortium of national lab and university partners involves the passive recovery of uranium using polymer based adsorbents. High Density Polyethylene fibers undergo a radiation induced graft co-polymerization process involving amidoxime, to attract uranium, and a polar co-monomer to increase hydrophilicity. After further chemical conditioning adsorbent fibers are braided into 60 meter strands for marine deployment. Braids are moored to the ocean floor for the duration of their soaking campaign. After sufficient seawater exposure they are winched up so the adsorbed uranium may be eluted off the braids. This deployment and elution process is repeated multiple times before the adsorbent's ultimate disposal, where its lifetime is dictated by the degradation it suffers with each re-cycle. Previous economic analyses have identified the adsorbent production and mooring as the most expensive components of the recovery process. Therefore, a later publication by Picard et al. proposed an alternative deployment method in an effort to reduce seawater uranium production cost. The Wind and Uranium from Seawater Acquisition symbiotic Infrastructure (WUSABI) couples uranium recovery with off shore wind to reduce mooring capital cost. The uranium harvesting structure attached to the underwater base of the wind turbine supports elution tanks and an adsorbent pulley system. This allows for a nearly autonomous mooring and elution procedure as adsorbent is in constant motion, reaching the elution tanks at the end of its soaking campaign. Although the original publication did include a short economic section, further analysis was carried out to provide a higher fidelity production cost estimate for uranium recovered by this system. Sufficient detail was provided regarding the capital and operating costs of the novel uranium harvesting units. The adsorbent production and uranium elution and purification steps however were estimated by simpler methods, for example applying a previously reported cost for producing a unit mass of adsorbent. This methodology, although satisfactory for the zeroth-order approximation desired in the original publication, overlooks many of the complexities and feedbacks embedded in the full cost model, which are necessary to provide a more accurate estimate. Perhaps more importantly, given the constant updates regarding adsorbent synthesis and performance this value quickly become outdated. Syncing an improved estimate for the WUSABI harvesting units with the existing economic analysis for adsorbent production and elution, which evolves in tandem with the technology, provides a more robust production cost estimate that will remain current over time. In addition to the updates and higher level of detail provided in this independent analysis, consistency in methodology allows for accurate comparison of uranium production costs across recovery methods. (authors)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

Declining carbohydrate content of Sitka-spruce treesdying from seawater exposure

Abstract Increasing sea levels associated with climate change threaten the survival of coastal forests, yet the mechanisms by which seawater exposure causes tree death remain poorly understood. Despite the potentially crucial role of nonstructural carbohydrate (NSC) reserves in tree survival, their dynamics in the process of death under seawater exposure are unknown. Here we monitored progressive tree mortality and associated NSC storage in Sitka-spruce (Picea sitchensis) trees dying under ecosystem-scale increases in seawater exposure in western Washington, USA. All trees exposed to seawater, because of monthly tidal intrusion, experienced declining crown foliage during the sampling period, and individuals with a lower percentage of live foliated crown (PLFC) died faster. Tree PLFC was strongly correlated with subsurface salinity and needle ion contents. Total NSC concentrations in trees declined remarkably with crown decline, and reached extremely low levels at tree death (2.4% and 1.6% in leaves and branches, respectively, and 0.4% in stems and roots). Starch in all tissues was almost completely consumed, while sugars remained at a homeostatic level in foliage. The decreasing NSC with closer proximity to death and near zero starch at death are evidences that carbon starvation occurred during Sitka-spruce mortality during seawater exposure. Our results highlight the importance of carbon storage as an indicator of tree mortality risks under seawater exposure.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Development of Novel Sorbents for Uranium Extraction from Seawater

As the uranium resource in terrestrial ores is limited, it is difficult to ensure a long-term sustainable nuclear energy technology. The oceans contain approximately 4.5 billion tons of uranium, which is one thousand times the amount of uranium in terrestrial ores. Development of technologies to recover the uranium from seawater would greatly improve the uranium resource availability, sustaining the fuel supply for nuclear energy. Several methods have been previously evaluated including solvent extraction, ion exchange, flotation, biomass collection, and adsorption; however, none have been found to be suitable for reasons such as cost effectiveness, long term stability, and selectivity. Recent research has focused on the amidoxime functional group as a promising candidate for uranium sorption. Polymer beads and fibers have been functionalized with amidoxime functional groups, and uranium adsorption capacities as high as 1.5 g U/kg adsorbent have recently been reported with these types of materials. As uranium concentration in seawater is only ~3 ppb, great improvements to uranium collection systems must be made in order to make uranium extraction from seawater economically feasible. This proposed research intends to develop transformative technologies for economic uranium extraction from seawater. The Lin group will design advanced porous supports by taking advantage of recent breakthroughs in nanoscience and nanotechnology and incorporate high densities of well-designed chelators into such nanoporous supports to allow selective and efficient binding of uranyl ions from seawater. Several classes of nanoporous materials, including mesoporous silica nanoparticles (MSNs), mesoporous carbon nanoparticles (MCNs), meta-organic frameworks (MOFs), and covalent-organic frameworks (COFs), will be synthesized. Selective uranium-binding liagnds such as amidoxime will be incorporated into the nanoporous materials to afford a new generation of sorbent materials that will be evaluated for their uranium extraction efficiency. The initial testing of these materials for uranium binding will be carried out in the Lin group, but more detailed sorption studies will be carried out by Dr. Taylor-Pashow of Savannah River National Laboratory in order to obtain quantitative uranyl sorption selectivity and kinetics data for the proposed materials. The proposed nanostructured sorbent materials are expected to have higher binding capacities, enhanced extraction kinetics, optimal stripping efficiency for uranyl ions, and enhanced mechanical and chemical stabilities. This transformative research will significantly impact uranium extraction from seawater as well as benefit DOE’s efforts on environmental remediation by developing new materials and providing knowledge for enriching and sequestering ultralow concentrations of other metals.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Functionalized Porous Organic Polymers as Uranium Nano-Traps for Efficient Recovery of Uranium from Seawater

The long-term use of nuclear power for energy applications relies on the secure and economical supply of nuclear fuel. Among various natural sources of uranium for use in nuclear reactors, seawater is highly appealing given that the oceans contain about 4.5 billion tons of dissolved uranium, almost 1000 times that estimated for mineral reserves. Nonetheless, the concentration of uranium in seawater is extremely low (3-3.3 mg L -1 or 3-3.3 ppb); this, coupled with the presence of a relatively high concentration of other metal ions, makes uranium recovery from seawater a challenge that requires the development of efficient and effective separation processes. Various adsorbent technologies based upon synthetic organic polymers, biopolymers, inorganic materials, mesoporous silica materials, porous carbon-based adsorbents, and ionic liquids have been widely developed for the extraction of uranium from seawater. However, these benchmark sorbent materials suffer from a number of drawbacks such as low adsorption capacity (typically 0.1~3.2 mg-U g -1 adsorbent), poor selectivity, and slow kinetics. Given the extreme complexity and vast volume of seawater, as well as the very low concentration of uranium present, to attain this ambitious task demands the design of adsorbents with high affinity and fast kinetics. The main objective of this project is to develop functional porous organic polymers (POPs) as a new type of adsorbent for mining uranium from seawater. This class of porous materials has quickly moved to the forefront of materials research due to their high internal surface areas, exceptional water/chemical stability, facile chemical tunability, and extraordinary capability to selectively adsorb large quantities of guest species The potential to deploy POPs in uranium extraction is related to the ease with which their internal surfaces can be decorated with high densities of strong binding sites. Beyond introducing postsynthetic modification, the specific functionalities also can be used as building units to be incorporated into porous frameworks. Our approach to fulfill this task involves the custom-design of POP-based uranium “nano-traps” via a “crystal engineering” guided design followed by stepwise post-synthetic modification. Furthermore, to increase the density of chelating groups and to enhance their affinity towards uranyl ions, judiciously designed chelating systems were constructed into porous organic polymers. Moreover, to improve the accessibility of the chelating groups and thereby the utilization efficiency, we assembled the chelating groups into highly crystalline materials where they are aligned in periodic arrays on the open channels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Production of Uranium from Seawater Using a Novel Polymer Adsorbent – Process Development and Cost Analysis (Final Scientific/Technical Report SBIR Phase II)

Research in developing techniques for extracting uranium from seawater is of considerable current interest. One reason which drives scientists to develop techniques of sequestering uranium from ocean is the prediction that the land-based uranium reserves would be depleted by the end of this century based on the current production rate. Uranium exists in seawater at a very low concentration (about 3 ppb) and as highly stable uranyl tris-carbonato complexes, primarily in the form Ca 2 [UO 2 (CO 3 ) 3 ]. Because of the enormous volume of seawater, the total amount of uranium in ocean is estimated to be a thousand times greater than the land-based uranium resources. As early as 1964, the idea of extracting uranium from seawater was discussed by Davies et al. in a Nature paper. In the past decades, many different materials were tested to evaluate their ability for sequestering uranium from seawater. Among them, amidoxime and carboxylate containing polymer fiber adsorbents appear most promising because of their high uranium adsorption capacity and stability in seawater. The carboxylate groups are necessary to make the polymer adsorbent hydrophilic whereas the amidoxime groups provide strong coordination sites for uranyl ions. Moreover, according to theoretical analysis, the adsorbability of uranium may involve synergistic effects of both amidoxime and carboxyl groups in the fiber adsorbent.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1987

The evaporation path of seawater and the coprecipitation of Br- and K+ with halite

Brines and salt were sampled at the Morton Bahamas solar salt production facility on Great Inagua Island in the Bahamas. The brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies. At Inagua, calcium carbonate begins to precipitate at a brine concentration factor of 1.8 times that of seawater. Gypsum begins to precipitate at a brine concentration of 3.8 times seawater, and halite at a concentration factor of 10.6. Three of the most concentrated brines from Inagua (40 times seawater) were evaporated further in the laboratory. Magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater, and potassium-bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater. The distribution of coefficients of Br- and K+ between brines and halite were determined by combining analytical data for the Inagua brines with measurements of the Br- and K+ content of halites from Inagua and of halite which had precipitated from Inagua brines during storage. The observed average value of DBr- is 0.032, in good agreement with some of the previous measurements. The measured values of DK+ are highly variable (0.001 to 0.021); DK+ for halite precipitated early in the halite facies is in the vicinity of 0.015.

NASA Discipline Exobiology↗
DOE OSTI2019

Simulating seawater intrusion in a complex coastal karst aquifer using an improved variable-density flow and solute transport–conduit flow process model

VDFST-CFP (variable-density flow and solute transport–conduit flow process) is a density-dependent discrete-continuum numerical model for simulating seawater intrusion in a dual-permeability coastal karst aquifer. A previous study (Xu and Hu 2017) simulates variable-density flow only in a single conduit, and studies the parameter sensitivities only in the horizontal case (2D domain as horizontal section) by the VDFST-CFP model. This paper focuses on the density-dependent vertical case (2D domain as vertical section) with two major improvements: 1) when implementing double-conduit networks in the domain, simulated intruded plumes in the porous medium are extended in the double-conduit scenario, compared to the single-conduit system; 2) by quantifying micro-textures on the conduit wall by the Goudar-Sonnad equation and considering macro-structures as local head loss. Sensitivity analysis shows that medium hydraulic conductivity, conduit diameter and effective porosity are important parameters for simulating seawater intrusion in the discrete-continuum system. On the other hand, rougher micro-structures and additional macro-structure components on the conduit wall would reduce the distance of seawater intrusion to the conduit system, but, rarely affect salinity distribution in the matrix. Compared to the equivalent mean roughness height, the new method (with more detailed description of structure) simulates seawater intrusion slightly landward in the conduit system. Here, the macro-structure measured by local head loss is more reasonable but needs further study on conduit flow. Xu and Hu (2017) Development of a discrete-continuum VDFST-CFP numerical model for simulating seawater intrusion to a coastal karst aquifer with a conduit system.

58 GEOSCIENCES↗
DOE OSTI2018

Seawater desalination by over-potential membrane capacitive deionization: Opportunities and hurdles

The salt removal capacity ( SRC ) of the carbon electrodes in membrane capacitive deionization (MCDI) is limited by the applied potential (<1.6 V). Thus, enhancement of the SRC is essential before applying MCDI to seawater desalination. This study aims at developing a novel MCDI system for seawater desalination by applying over-potential (OP) to enhance ion-adsorption capacity and kinetics, and by reversing the polarity (RP) of electrodes to improve ion-desorption kinetics (hereafter named OP-MCDI-RP) for seawater desalination. At 2.4 V, the OP-MCDI system with mesoporous carbon demonstrated a SRC value of 64.7 mg g –1 when desalting 0.5 M NaCl solution, while the OP-CDI system could only remove 8.2 mg g –1 under identical conditions. Similarly, an OP-MCDI cell using carbon aerogel demonstrated a greater SRC value of 43.4 mg g –1 in comparison with 12.5 mg g –1 achieved in OP-CDI. These results indicate that the OP-MCDI system can directly desalt high salinity water regardless of the electrode material. In contrast to the OP-MCDI system, the OP-MCDI-RP system yields a higher regeneration efficiency by applying a reversed low-voltage. It is shown that, under appropriate operating conditions, the OP-MCDI-RP system reduced the electrical conductivity of a seawater sample of 37 practical salinity units by 99.9%, suggesting that the OP-MCDI-RP system can be employed for seawater desalination. In conclusion, due to the dramatic increase in energy demand and insufficient long-term stability caused by high potential and high salt concentration, however, the OP-MCDI-RP process should be further investigated for potential practical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Investigation of oxygen evolution reaction with 316 and 304 stainless-steel mesh electrodes in natural seawater electrolysis

Here, two commercially available stainless steel mesh substrates (316 SS and 304 SS) were evaluated as electrodes for oxygen evolution reaction (OER) in natural seawater electrolysis. The results show the 304 SS is less stable against corrosion under neutral (pH of 8.5) and low alkaline (0.1 M NaOH, pH of 12.8) seawater electrolytes because of the direct metal dissolution and chlorine evolution reaction (CER), and the 316 SS is superior to 304 SS in terms of electrocatalytic activity and resistance to corrosion under the same media. The performance of 304 SS is comparable to 316 SS under the high alkaline (1 M NaOH, pH of 13.7) seawater electrolyte, where the CER and metal dissolution are suppressed by OER. The overpotential for 304 and 316 SS is around 430 mV at 10 mA cm -2 , and the Tafel slopes are below 50 mV dec -1 under the high alkaline (1 M NaOH) seawater electrolyte, showing promising performance. The poor resistance to corrosion of 304 SS is attributed to the low Mo content, and it is supposed that the stability of both 304 and 316 SS can be improved further with the addition of Mo content. This work expands on promising substrates for natural seawater electrolysis, with cost and performance advantages.

Stainless-steel mesh↗
DOE OSTI2011

Measurement of volume resistivity/conductivity of metallic alloy in inhibited seawater by optical interferometry techniques

Optical interferometry techniques were used for the first time to measure the volume resistivity/conductivity of carbon steel samples in seawater with different concentrations of a corrosion inhibitor. In this investigation, the real-time holographic interferometry was carried out to measure the thickness of anodic dissolved layer or the total thickness, U{sub total}, of formed oxide layer of carbon steel samples during the alternating current (ac) impedance of the samples in blank seawater and in 5-20 ppm TROS C-70 inhibited seawater, respectively. In addition, a mathematical model was derived in order to correlate between the ac impedance (resistance) and the surface (orthogonal) displacement of the surface of the samples in solutions. In other words, a proportionality constant [resistivity ({rho}) or conductivity ({sigma})= 1/{rho}] between the determined ac impedance [by electrochemical impedance spectroscopy (EIS) technique] and the orthogonal displacement (by the optical interferometry techniques) was obtained. The value of the resistivity of the carbon steel sample in the blank seawater was found similar to the value of the resistivity of the carbon steel sample air, around 1 x 10{sup -5}{Omega} cm. On the contrary, the measured values of the resistivity of the carbon steel samples were 1.85 x 10{sup 7}, 3.35 x 10{sup 7}, and 1.7 x 10{sup 7}{Omega} cm in 5, 10, and 20 ppm TROS C-70 inhibited seawater solutions, respectively. Furthermore, the determined value range of {rho} of the formed oxide layers, from 1.7 x 10{sup 7} to 3.35 x 10{sup 7}{Omega} cm, is found in a reasonable agreement with the one found in literature for the Fe oxide-hydroxides, i.e., goethite ({alpha}-FeOOH) and for the lepidocrocite ({gamma}-FeOOH), 1 x 10{sup 9}{Omega} cm. The {rho} value of the Fe oxide-hydroxides, 1 x 10{sup 9}{Omega} cm, was found slightly higher than the {rho} value range of the formed oxide layer of the present study. This is because the former value was determined by a dc method rather than by an electromagnetic method, i.e., holographic interferometry with applications of EIS, i.e., ac method. As a result, erroneous measurements were recorded due to the introduction of heat to Fe oxide-hydroxides.

36 MATERIALS SCIENCE↗