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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

CO 2 zonal injection rate allocation and plume extent evaluation through wellbore temperature analysis

Temperature analysis during a pause in injection operations, known as warmback analysis, has been used in the petroleum industry for evaluating the injection conformance and estimating the location of the flooded front in applications, such as waterflooding oil reservoirs. Here in this work, methods are introduced to extend the application of temperature warmback analysis to estimate the zonal CO 2 injection rate and zonal CO 2 plume extent during geologic CO 2 storage in a saline aquifer. First, novel analytical solutions are developed to model transient temperature in the aquifer during the injection and subsequent shut-in periods considering two-phase flow (gaseous CO 2 and aqueous brine) conditions in the aquifer. The solution involves a discretization of the aquifer into regions; the energy and mass conservation equations for the regions are solved simultaneously considering appropriate boundary conditions at the interfaces. Two solutions techniques are presented: multi-region and three-region solutions. Inverse models are developed accordingly to evaluate the injection profile and estimate the extent of the plume front in the reservoir during the injection period. The multi-region solution results in an inversion approach that requires regression analysis. However, the three-region formulation results in a simple graphical technique for inverse modeling. The analytical solutions are validated against a thermally coupled reservoir simulation tool using different synthetic cases for CO 2 injection in deep saline aquifers. The results of the developed solutions provide a good match with numerical results during forward and inverse modeling.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Synergistic Effects of the Electric Field Induced by Imidazolium Rotation and Hydrogen Bonding in Electrocatalysis of CO 2

The roles of the ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF₄]), and water in controlling the mechanism, energetics, and electrocatalytic activity of CO₂ reduction to CO on silver in non-aqueous electrolytes were investigated. The first electron transfer occurs to CO₂ at reduced overpotentials when it is trapped between the planes of [EMIM]⁺ ring and electrode surface due to cation re-orientation as determined from voltammetry, in-situ surface-enhanced Raman spectroscopy, and density functional theory calculations. Within this interface, water up to 0.5 M does not induce significant faradaic activity, opposing the notion of it as a free proton source. Instead, water acts as a hydrogen bond donor and the proton is sourced from [EMIM]⁺. Furthermore, this study demonstrates that alcohols with varying acidity tune the hydrogen bonding network in the interfacial microenvironment to lower the energetics required for CO₂ reduction. Here, the hydrogen bonding suppresses the formation of inactive carboxylate species, thus preserving the catalytic activity of [EMIM]⁺. The ability to tune the hydrogen bonding network opens new avenues for advancing IL-mediated electrocatalytic reactions in non-aqueous electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

ZnTiN 2 as an Electron-Selective, Protective Layer on Si Photocathodes

Photoelectrochemical production of fuels requires photoelectrodes that efficiently convert sunlight to electrochemical energy by producing photovoltage and photocurrent and maintain this ability over time under a variety of pH, illumination, and applied bias conditions. Work in the photovoltaic community has demonstrated that interfaces with high charge carrier selectivity provide high photovoltages. This offers a co-design opportunity to create semiconductor photoelectrodes with contact layers that are both carrier-selective and offer protection from degradation in aqueous solutions. In this work, we explored the ternary nitride ZnTiN 2 as an electronselective, protective layer for Si-based photocathodes. We demonstrated that ZnTiN 2 formed a heterojunction with p-type Si that facilitated electron movement toward the ZnTiN 2 surface for light-driven reduction reactions. Across a variety of electrolyte conditions, ZnTiN 2 /Si produced an open circuit voltage of ca. 400 mV vs the solution potential, while bare Si produced 220−480 mV vs the solution potential depending on conditions. ZnTiN 2 was also shown to protect Si over 72 h at open circuit in the dark in 0.1 M KHCO 3 aqueous solution at pH 10.5, with a 2.4% loss in open circuit voltage compared to a 17% loss for unprotected Si. A protective effect was also observed under illumination during methyl viologen reduction at pH 3.5 for 21 h, with a 2.5% loss in open circuit voltage observed for ZnTiN 2 /Si compared to a 25% loss in open circuit voltage for unprotected Si under the same conditions. Elemental characterization revealed the presence of oxides on the surface of ZnTiN 2 that are consistent with the Pourbaix diagram after photoelectrochemical operation; these oxides appeared to support durability without hindering charge carrier extraction to drive electrochemical work. This work highlights the promise of ZnTiN 2 for durable photoelectrochemical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Impact of solvent forces and broken symmetry on the assembly of designed proteins at a liquid-solid interface

The era of protein design has enabled the creation of hybrid protein-inorganic interfaces, leading to both surface-directed self-assembly of de novo protein architectures and protein-directed formation of inorganic materials. However, the resulting patterns of protein assembly are often unexpected, implying that essential interactions are not accounted for in current design platforms. Here, we use high-speed atomic force microscopy (AFM) analyzed through machine learning to follow the assembly of protein nanorods in aqueous electrolytes on two types of mica exhibiting disparate symmetry elements, which are imprinted on the overlying hydration structure. Using Monte Carlo simulations, we reproduce the observed phases and show that an observed smectic phase, previously thought to be unstable for non-interacting rods in two dimensions, emerges when crystal symmetry introduces a directional bias. The findings demonstrate the importance of incorporating solvent forces as modulated by the hydration structure inherent to interfacial systems when designing protein assemblies at liquid-crystal interfaces. Coupling physics-based simulations that can account for these factors to de novo protein design algorithms can lead to improved design platforms for bio-inspired, hybrid materials.

bioinspired materials↗
DOE OSTI2024

Controlling saturation to improve per- and polyfluoroalkyl substance (PFAS) removal in biochar-amended stormwater bioretention systems

Black carbon-amended bioretention systems are an increasingly popular strategy for the removal of organic contaminants, including poly- and perfluoroalkyl substances (PFASs) and other trace organic contaminants (TOrCs), from urban stormwater. Many PFASs preferentially accumulate at the air–water interface, but detention time requirements for stormwater bioretention systems typically result in full saturation of the bioretention systems, effectively removing their air–water interfaces. This study assessed the effect of bioretention system saturation on removal of PFASs, metals, and hydrophilic TOrCs. A field-aged mixture of 40% v/v sand, 30% v/v zeolite, and 30% v/v biochar was packed into columns which were operated with hydraulic controls to remain unsaturated or fully saturated throughout the duration of the experiment. Twenty-four storm events sized to a 95th percentile storm at a California, United States military site were simulated using synthetic stormwater fortified with aqueous film forming foam-derived PFASs, TOrCs, and metals to mimic real-world conditions. Unsaturated conditions outperformed saturated conditions for removal of all PFASs analyzed. A simulated inadvertent system perturbation (i.e. flooding event) in the unsaturated columns did not result in significantly greater mobilization of PFAS mass, suggesting that more sorption to the biochar occurred as a result of the transient retention of PFASs at the air–water interface reducing kinetic sorption limitations. Overall, maintaining unsaturated conditions in a biofilter may extend the sorptive filter lifetime for PFASs by up to 83%. The results have implications for bioretention system application and design for PFAS removal in contaminated catchment areas.

13 HYDRO ENERGY↗
NASA NTRSDate not supplied

AMMPER: Agent-based Model for Microbial Populations Exposed to Radiation

Exposure of microbial populations to galactic cosmic radiation (GCR) in the deep-space radiation environment may lead to intracellular damage that compromises the ability of cells to repair and replicate. While simulation programs of deep-space radiation do exist, they focus primarily on single-cell damage, rather than population-wide effects. In this work, a new application and graphical user interface, Agent-Based Model for Microbial Populations Exposed to Radiation (AMMPER) is presented, which simulates the effects of proton-based GCR on Saccharomyces cerevisiae population growth. AMMPER consists of a 50x50x50 µm simulation space, analogous to an aqueous culture medium with non-limiting nutrient and pH buffering, in a microwell plate or microfluidic culture card. This model utilizes Relativistic Ion Tracks (RITRACKS) to create detailed track structures of the radiation traversals. AMMPER then calculates the radiation dose present at each cell, and subsequently determines the damage (chromosomal aberrations, oxidative stress, etc.) and resulting loss of cell viability from both primary and secondary radiative effects. Through implementing cell replication, repair, damage, and death, the effect of radiation exposure on the population growth can be determined. With AMMPER, long-duration effects of the deep space environment on entire populations can be determined and used to assess the feasibility of sustaining life in space.

Amrita Singh↗
NASA NTRS2004

Method for determining the three-dimensional structure of a protein

Microcapsules prepared by encapsulating an aqueous solution of a protein, drug or other bioactive substance inside a semi-permeable membrane by are disclosed. The microcapsules are formed by interfacial coacervation under conditions where the shear forces are limited to 0-100 dynes/cm.sup.2 at the interface. By placing the microcapsules in a high osmotic dewatering solution, the protein solution is gradually made saturated and then supersaturated, and the controlled nucleation and crystallization of the protein is achieved. The crystal-filled microcapsules prepared by this method can be conveniently harvested and stored while keeping the encapsulated crystals in essentially pristine condition due to the rugged, protective membrane. Because the membrane components themselves are x-ray transparent, large crystal-containing microcapsules can be individually selected, mounted in x-ray capillary tubes and subjected to high energy x-ray diffraction studies to determine the 3-D structure of the protein molecules. Certain embodiments of the microcapsules of the invention have composite polymeric outer membranes which are somewhat elastic, water insoluble, permeable only to water, salts, and low molecular weight molecules and are structurally stable in fluid shear forces typically encountered in the human vascular system.

Morrison, Dennis R.↗
DOE OSTI2025

Elucidating the Interfacial Barriers in Lanthanide Back-Extraction: From Water to Oil and Back Again

Recovery of critical rare earth elements from complex mixtures has long been realized via solvent extraction, where ions in an aqueous phase are separated into an organic phase using amphiphilic ligands. While a great deal of effort has been placed on understanding this forward reaction, substantial knowledge gaps in the back-extraction process remain. This includes the mechanism of interfacial dissociation and transport back into a highly acidic aqueous phase for further processing. In this work, we connect back-extraction kinetics made in realistic solvent extraction systems to salient interfacial chemistry and structure that represent bottlenecks in the back-extraction of lanthanide ions. We show that the interface between the two liquid phases varies dramatically based on the composition of both phases. Water stretching signals are shown to report on the population of lingering interfacial complexes and are thus used as a reporter of competitive adsorption from excess free ligands in solution for limited interfacial vacancies. We show that excess free ligands, often used to improve forward extractions, set up interfacial blockades inhibiting back-extraction both kinetically and thermodynamically. In conclusion, this insight opens up avenues to tune interfacial properties to facilitate a more dynamic, exchangeable interface to speed up back-extractions while using less energy intensive chemical swings.

Interfaces↗
NASA NTRS2016

The Antarctic Analogy for Ancient Lakes at Gale Crater, Mars

In place of the dual choice of “warm and wet” versus “cold and dry” Mars, we reconcile in this paper the notion of a cold Mars with the notion of wet Mars. Both the geological evidences at Gale's for the presence of liquid water during the Hesperian (Grotzinger et al., Science, 350 (6257), 2015) and the failure of climate models make Mars warm (Wordsworth, Review of Earth and Planetary Science, 44, 1-31, 2016) suggested that an alternative scenario could be envisioned. The lake Untersee, Antarctica is an inspiring example of how an aqueous environment can survive for an extended period of the time in a place where the day average temperatures never, ever, each 273K. The key process which maintains a liquid, potentially habitable, environment under the ice is the subaqueous melting of a glacial dam in contact with the lake which provides a constant latent heat flux into the lake (McKay et al, in preparation) Our calculations showed that for certain range of pressures, temperatures and ice optical properties, a large body of water at Gale's will not freeze solid even if the surface temperatures are at all times well below freezing. The rather high sublimation rates of ice at Mars', the sunlight penetrating the ice and the geothermal flux contribute to stabilize the solid/liquid interface at a certain depth. We found that for a mean annual temperature of 245K ice thicknesses range from 3-10 meters which are comparable values to the range of those for the Antarctic lakes (2-7m). Thus, the ice potentially gets thin enough to let sediments penetrate the ice (Rivera-Hernandez et al., in preparation) and geological features associated with aqueous environments may still be possible with a perennially-covered lake, on cold, but wet planet. The Antarctic lakes model is engaging as it relaxes the requirement for a long-lived active hydrological cycle.

The lake Untersee↗
DOE OSTI2020

Aqueous Ni-rich-cathode dispersions processed with phosphoric acid for lithium-ion batteries with ultra-thick electrodes

Lithium-ion battery (LIB) production can benefit both economically and environmentally from aqueous processing. Although these electrodes have the potential to surpass electrodes conventionally processed with N -methyl-2-pyrrolidone (NMP) in terms of performance, significant issues still exist with respect to ultra-thick cathodes ($\gg$4 mAh/cm 2 areal capacities). A major concern for these types of electrodes with high-nickel active material stems from lithium leaching from active material, which drives the pH of the dispersion in excess of 12 and subsequently corrodes the current collector interface. As this corrosion reaction proceeds, hydrogen generation at the interface creates bubbles which cause severe cracking in the dried electrode surface. When areal loadings are increased, this effect becomes more pronounced and is detrimental to both mechanical and electrochemical properties of these electrodes. In this work, a technique for mitigating corrosion at the current collector by adjusting the pH of the dispersion with the addition of phosphoric acid is investigated. Phosphoric acid was added in 0.5 wt% increments between 0.0 and 1.5 wt%, and effects on rheology, adhesion, corrosion, and electrochemical performance were investigated. A technique is reported for producing aqueous processed cathodes with areal loadings of 6–8 mAh/cm 2 with reduced surface cracking and superior high-rate discharge capacity (i.e. high-power performance) for this class of cathode loadings.

25 ENERGY STORAGE↗
DOE OSTI2025

Electroplated Polymer‐Modified Carbon Fiber for Performance‐Enhancing Composite Interfaces

Carbon fiber composite performance relies on the fiber-matrix interface for effective load transfer. To enhance interfacial properties between the fiber and matrix, often carbon fiber surfaces are oxidatively and covalently modified to incorporate chemical functional groups. By contrast, here, noncovalent electrodeposition of functional polyelectrolyte is applied onto conducting carbon fibers from aqueous solutions. A natural polymer, chitosan (CS), is electro-deposited onto the fiber surface, which undergoes multi-scale physical interactions. The bound CS layer with abundant amine functionalities reacts with epoxy moieties within the matrix to improve the interfacial properties. The scalable and energy-efficient electrodeposition eliminates traditional functionalization and sizing requirements of carbon fiber while delivering significantly higher mechanical performance with enhanced consistency. For continuous fiber reinforced composites, compared to conventional fibers, apparent interlaminar shear strength increases by 27%, reaching ≈86 MPa. The short fiber composites with only 2–11 wt.% fibers exhibit ≈20% increase in tensile strength with a peak performance of 120 MPa. Unlike traditionally treated and sized carbon fiber, this approach delivers coated fibers with long shelf-life and allows recovery of both CS in electrolyte form and carbon fiber by continuous electrochemical processing of the modified fibers with inverse polarity; thus, it promotes overall fiber recyclability.

36 MATERIALS SCIENCE↗
NASA NTRS2002

Microencapsulated Bioactive Agents and Method of Making

Microcapsules prepared by encapsulating an aqueous solution of a protein, drug or other bioactive substance inside a semi-permeable membrane by are disclosed. The microcapsules are formed by interfacial coacervation under conditions where the shear forces are limited to 0- 100 dynes per sq cm at the interface. By placing the microcapsules in a high osmotic watering solution, the protein solution is gradually made saturated and then supersaturated, and the controlled nucleation and crystallization of the protein is achieved. The crystal-filled microcapsules prepared by this method can be conveniently harvested and stored while keeping the encapsulated crystals in essentially pristine condition due to the rugged, protective membrane. Because the membrane components themselves are x-ray transparent, large crystal-containing microcapsules can be individually selected. mounted in x-ray capillary tubes and subjected to high energy x-ray diffraction studies to determine the 3-D structure of the protein molecules. Certain embodiments of the microcapsules of the invention have composite polymeric outer membranes which are somewhat elastic, water insoluble, permeable only to water, salts, and low molecular weight molecules and are structurally stable in fluid shear forces typically encountered in the human vascular system.

Dennis R Morrison↗
NASA NTRS2004

X-Ray Crystallography Reagent

Microcapsules prepared by encapsulating an aqueous solution of a protein, drug or other bioactive substance inside a semi-permeable membrane by are disclosed. The microcapsules are formed by interfacial coacervation under conditions where the shear forces are limited to 0-100 dynes per square centimeter at the interface. By placing the microcapsules in a high osmotic dewatering solution. the protein solution is gradually made saturated and then supersaturated. and the controlled nucleation and crystallization of the protein is achieved. The crystal-filled microcapsules prepared by this method can be conveniently harvested and stored while keeping the encapsulated crystals in essentially pristine condition due to the rugged. protective membrane. Because the membrane components themselves are x-ray transparent, large crystal-containing microcapsules can be individually selected, mounted in x-ray capillary tubes and subjected to high energy x-ray diffraction studies to determine the 3-D smucture of the protein molecules. Certain embodiments of the microcapsules of the invention have composite polymeric outer membranes which are somewhat elastic, water insoluble, permeable only to water, salts, and low molecular weight molecules and are structurally stable in fluid shear forces typically encountered in the human vascular system.

Dennis R Morrison↗
DOE OSTI2024

Phase Behavior of Charged Star Block Copolymers at Fluids Interface

The phase behavior of block copolymers (BCPs) at the water-oil interface is influenced by the segmental interaction parameter (χ) and chain architecture. We synthesized a series of star block copolymers (s-BCPs) having polystyrene (PS) as core and poly(2-vinylpyridine) (P2VP) as corona. The interaction parameters of block-block (χ PS-P2VP ) and block-solvent (χ P2VP-solvent ) were varied by adjusting the pH of the aqueous solution. Lowering pH increased the fraction of quaternized-P2VP (Q-P2VP) with enhanced hydrophilicity. By transferring the equilibrated interfacial assemblies, morphologies ranging from bicontinuous films at pH of 7 and 3.1 to nanoporous and nanotubular structure at pH of 0.65 were observed. The nanoporous films formed hexagonally packed pores in s-BCP matrix, while nanotubes comprised Q-P2VP as corona and PS as core. Control over pore size, d-spacing between pores, and nanotube diameters was achieved by varying polymer concentration, molecular weight, volume fraction and arm number of s-BCPs. Large-scale nanoporous films were obtained by freeze-drying emulsions. Remarkably, the morphologies of linear BCPs were inverted, forming hexagonal-packed rigid spherical micelles with Q-P2VP as core and PS as corona in multilayer. Here, this work provides insights of phase behaviors of BCP at fluids interface and offer a facile approach to prepare nanoporous film with well-controlled pore structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Kraft black liquor concentration with graphene oxide membranes: Process simulations and technoeconomic analysis

Abstract Black liquor (BL) dewatering by multi‐effect evaporation in the kraft papermaking process is highly energy‐intensive. It was previously shown that graphene oxide (GO) nanofiltration membranes can remove lignin, other organics, and inorganic salts from BL while exhibiting stability in caustic BL conditions. Here, we design and simulate several candidate dewatering processes and evaluate their technoeconomic characteristics. All processes concentrate BL from 15 to 30 wt% solutes while producing aqueous permeate. Two process options were analyzed—option A including “last‐mile” permeate treatment to reduce solutes to 0.2 wt%, and option B excluding this treatment and producing a 3–4 wt% solutes stream. These processes were simulated in custom‐built ASPEN Plus flowsheets interfaced with Microsoft Excel and MATLAB. All processes deliver large (>40%) energy savings. Detailed technoeconomic analysis showed that option A processes are profitable in mills equipped with condensing turbines, but unprofitable with only purchased fuel savings. Option B processes are profitable in both situations, but require the caustic permeate to be utilized in other kraft process units. They are also profitable with electricity generation when operated at smaller scales matching the requirements of other process units. Monte‐Carlo sensitivity analysis shows that Option A can yield median 20‐year NPVs up to ~$10MM and Option B up to ~$25MM. Overall, GO membrane‐based BL dewatering is economically promising, assuming successful slipstream piloting and scale‐up campaigns. It would have immediate sustainability benefits from large energy savings, and broader implications for biorefinery processes due to the ability to fractionate biomass feedstock components under harsh conditions.

Wang, Zhongzhen↗
DOE OSTI2024

Electrically Powered High-Salinity Brine Separation Using Dimethyl Ether

Dewatering highly saline aqueous streams, from mining and geothermal leachates to industrial wastewater, is essential for effective resource recovery and safe disposal. Membraneless water extraction (MWE) uses a low-polarity solvent to separate water from concentrated aqueous solutions. In this study, we design a new MWE that uses dimethyl ether (DME) to selectively extract water from high-salinity brines, leveraging the volatility of DME to achieve rapid solvent recovery. By separating water and dissolved salts at a liquid–liquid interface, MWE minimizes the deleterious effects of scaling on vulnerable membrane and heat exchanger surfaces, reducing the need for extensive pretreatment and expensive materials. We begin by developing a computational framework for a multistage counterflow liquid–liquid contactor, which extracts water into DME, coupled with a multistage solvent regenerator that uses vapor compression to efficiently separate the desalinated water from the DME extractant. Excess Gibbs free energy and equation of state frameworks are used to model fluid phase equilibria in water–DME–sodium chloride (NaCl) mixtures, with interaction parameters estimated from experimental data. Incorporating equilibrium calculations into a system-scale computational model, we examine the performance of MWE using DME for the first time. Our analysis demonstrates that MWE can concentrate seawater desalination brine (>1.0 mol NaCl kg –1 ) to zero-liquid discharge salinities, with an energy consumption of under 50 kW h per m 3 of water extracted with a solvent recovery ratio greater than 99.9%. We highlight the importance of staging the vapor compression process to simultaneously minimize energy consumption while enabling brine concentration and product water solvent contamination. Finally, the thermodynamic framework developed here allows for the robust evaluation of new MWE solvents and systems for critical brine concentration and fractional precipitation applications.

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

MBX: A many-body energy and force calculator for data-driven many-body simulations

Many-Body eXpansion (MBX) is a C++ library that implements many-body potential energy functions (PEFs) within the “many-body energy” (MB-nrg) formalism. MB-nrg PEFs integrate an underlying polarizable model with explicit machine-learned representations of many-body interactions to achieve chemical accuracy from the gas to the condensed phases. MBX can be employed either as a stand-alone package or as an energy/force engine that can be integrated with generic software for molecular dynamics and Monte Carlo simulations. MBX is parallelized internally using Open Multi-Processing and can utilize Message Passing Interface when available in interfaced molecular simulation software. In this study, MBX enables classical and quantum molecular simulations with MB-nrg PEFs, as well as hybrid simulations that combine conventional force fields and MB-nrg PEFs, for diverse systems ranging from small gas-phase clusters to aqueous solutions and molecular fluids to biomolecular systems and metal-organic frameworks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Pb Sorption at the Barite (001)–Water Interface

Sorption of ions at the mineral-water interface is an important factor that determines the fate of toxic metals in the environment. Here, we use barite as a model substrate to understand the interaction of toxic-metal lead (Pb) with ionic crystals. The coverage and location of Pb sorbed to the (001) surface was measured as a function of aqueous Pb concentration ([Pb] aq ) using in situ specular resonant anomalous X-ray reflectivity (RAXR) to determine the sorption capacity and process. In this work, the results show that Pb sorption occurs via incorporation (primarily within the top barite layer similar to 3 angstrom in depth) and adsorption (mostly as an inner-sphere complex at similar to 2 angstrom in height) simultaneously. Both the incorporated and adsorbed Pb coverages increase with increasing [Pb] aq up to [Pb] aq similar to 200 mu M, above which the adsorbed fraction increases more rapidly than the incorporated fraction. This enhanced adsorption has a height distribution that is further extended (>= 15 angstrom from the surface) than that observed in lower [Pb] aq . This change in distribution is interpreted as arising from additional sorption of outer-sphere species or Pb-bearing phases precipitated on the surface. Desorption experiments in Pb-free solutions show that the incorporated fraction is more resistant to removal than the adsorbed fraction, consistent with the speciation-dependent stabilities premised in the classical sorption models.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗