Simulated Waste Streams Research Articles

Exploring the insights and benefits of biomass-derived sulfuric acid activated carbon for selective recovery of gold from simulated waste streams

The surging affluent in society, concomitant with increasing global demand for electrical and electronic devices, has led to a sharp rise in e-waste generation. E-wastes contain significant amounts of precious metals, such as gold, which can be recovered and reused, thus reducing the environmental impact of mining new metals. Selective recovery using sustainable and cost-effective materials and methods is therefore vital. This study undertook a detailed evaluation of low-cost biomass-derived activated carbon (AC) for selective recovery of Au from simulated e-waste streams. Utilizing high-performance synthesized H2SO4-AC, the adsorption mechanisms were explicated through a combination of characterization techniques, i.e., FE-SEM, BET, TGA, XRD, FTIR, XPS, and DFT simulations to conceptualize the atomic and molecular level interactions. Optimization of coordination geometries between model H2SO4-AC and anionic complexes revealed the most stable coordination for AuCl4- (binding energy, Eb = -4064.15 eV). The Au selectivity was further enhanced by reduction of Au(III) to Au(0), as determined by XRD and XPS. The adsorption reaction was relatively fast (∼5h), and maximum Au uptake reached 1679.74 ± 37.66 mg/g (among highest), achieved through adsorption isotherm experiments. Furthermore, a mixture of 0.5 M thiourea/1 M HCl could effectively elute the loaded Au and regenerate the spent AC. This study presents radical attempts to examine in detail, the synergistic effects of H2SO4 activation on biomass-derived ACs for selective recovery of Au from complex mixtures. The paper therefore describes a novel approach for the selective recovery of Au from e-wastes using multifunctional biomass-derived H2SO4-AC.

Steam recovery from flue gas by organosilica membranes for simultaneous harvesting of water and energy

Steam recovery from the spent gases from flues could be a key step in addressing the water shortage issue while additionally benefiting energy saving. Herein, we propose a system that uses organosilica membranes consisting of a developed layered structure to recover steam and latent heat from waste. Proof-of-concept testing is conducted in a running incinerator plant. The proposed system eliminates the need for a water supply while simultaneously recovering latent heat from the waste stream. First, the long-term stability of an organosilica membrane is confirmed over the course of six months on a laboratory-scale under a simulated waste stream. Second, steam recovery is demonstrated in a running waste incinerator plant (bench-scale), which confirms the steady operation of this steam recovery system with a steam recovery rate comparable to that recorded in the laboratory-scale test. Third, process simulation reveals that this system enables water-self-reliance with energy recovery that approximates 70% of waste combustion energy.

Three-dimensional fluorinated pyrazinium-based cationic organic polymers with high charge density for enhanced ReO4− removal

Ultrafast separation of hazardous and radioactive anions from strongly alkaline nuclear wastewater is urgently needed for both the public health and environment, but also extremely challenging. Herein, we report a 3D fluorinated pyrazinium-based cationic organic polymer (TBPM-Fpz) with high charge density for ultrafast and selective removal of ReO4−. Using fluorinated pyrazine as the linker and rigid tetraphenylmethane as the building block, a high charge density and relatively hydrophobic diamond-like topology skeleton of TBPM-Fpz was constructed, which is beneficial to improve the affinity for ReO4− and promote thorough exposure of active sites. Batch sorption experiments revealed that TBPM-Fpz is a rare example that can integrate ultrafast sorption kinetics (equilibrium within 3 min), high capacity (833.01 mg g−1), and excellent selectivity towards ReO4− (92.34% in 1000 times excess of SO42−) in one adsorbent. In addition, TBPM-Fpz achieve high ReO4− removal efficiency in simulated Savannah River Site High-Level Waste stream (95.32%, solid-to-liquid ratio: 40:1) and simulated Hanford Low Activity Waste wastewater (89.76%, solid-to-liquid ratio: 1:1). Experimental and computational results indicate that the superior performance is attributed to fluorination that increases charge density and decrease the steric hindrance. This study shows the enormous potential of fluorinated cationic organic polymer for enhanced ReO4− removal from strongly alkaline wastewater, providing valuable insights into designing high-performance cationic organic polymers for alkaline nuclear waste treatment.

Influence of coexisting EDTA, citrate, and chloride ions on the recovery of copper and cobalt from simulated wastewater using fluidized-bed homogeneous granulation process

Copper and cobalt from industrial operations build up in the environment, posing a substantial health risk. This study examined how ethylenediaminetetraacetic acid (EDTA), citrate, and chloride ions affected the fluidized bed homogeneous granulation process' (FBHGP) ability to recover both individual and combination of copper and cobalt ions from simulated waste streams. A 99% copper removal and 95% granulation efficiency were attained in copper-based solutions. The soluble copper still present in the solution caused a 4% variation in the removal and granulation efficiencies. There were 99% removal and 99% granulation efficiencies in cobalt-based solutions. When EDTA was present in a copper-based solution, 95% removal and 86% granulation were reached, and for cobalt-based solutions, 95% and 91% were the removal and granulation efficiency, respectively. The presence of citrate in the copper-based solution obtained the removal of 83% and granulation efficiency of 54% at 0.1 MR of citrate to copper. No copper phosphate precipitate was formed when the MR was greater than 0.1. There were 96% removal and 92% granulation efficiency when citrate was present in cobalt-based solutions. The presence of chloride ions in copper solution achieved a 99% removal and 91% granulation efficiency, while in cobalt solutions, 99% removal and 98% granulation efficiency were attained. Solutions with combined copper and cobalt with chloride ions achieved 99% removal and 95% granulation efficiency for copper and 99% removal and 95% granulation efficiency for cobalt. The granule sizes decreased as the MR of the complexing agents to metal, and the concentration of chloride ions increased. The peaks on the XRD pattern exactly matched the peaks of cobalt phosphate hydrate (Co3(PO4)2·8 H2O). FBHGP has effectively recovered copper and cobalt from the waste streams of simulated metals.

Enhancement of Dye Separation Performance of Eco-Friendly Cellulose Acetate-Based Membranes

Many reasons have caused a worldwide water stress problem. Thus, the recycling of wastewater streams has been extensively studied. In this work, eco-friendly mixed matrix membranes (MMMs) were fabricated, characterized, and tested for the removal of two separate dyes from simulated waste streams. The environmentally friendly nano activated carbon (NAC) was extracted from water hyacinth to be impregnated as a membrane nano-filler to enhance the neat membrane performance. The extracted NAC was further studied and characterized. Cellulose acetate (CA)-based membranes were obtained by phase inversion and electrospinning mechanisms. All four synthesized blank and MMMs were characterized via scanning electron microscope (SEM) and contact angle to study their structure and hydrophilic nature, respectively. However, the membrane with optimum performance was further characterized using Fourier transfer infrared (FTIR) and X-ray diffraction (XRD). The four prepared cast and electro-spun, blank, and mixed matrix CA-based membranes showed an acceptable performance in the removal and selectivity of methylene blue (MB) dye over Congo red (CR) dye with a removal percentage ranging from 31 to 70% depending on the membrane used. It was found that the CA/NAC hybrid nanofiber membrane possessed the highest removal efficiency for MB, where the dye concentration declined from 10 to 2.92 mg/L. In contrast, the cast blank CA membrane showed the least removal percentage among the synthesized membranes with only 30% removal. As a result, this paper suggests the use of the CA/NAC hybrid membrane as an alternative and cost-effective solution for MB dye removal.

A highly selective superphane for ReO4− recognition and extraction

Highly selective anion recognition and extraction is challenging and yet critical for removal of pollutants from the environment and the effective recovery of valuable chemicals from low-content (at sub-ppm or ppb level) sources. In this paper, we detail the gram-scale synthesis of a superphane 2 , an anion receptor that selectively binds ReO 4 − . Superphane 2 can extract perrhenate from solid mixtures containing traces of ReO 4 − anion (as low as 200 ppb) and aqueous media with near 100% selectivity over large excesses of competing anions. Meanwhile, up to 99.99% of ReO 4 − can be separated from complex simulated aqueous waste streams containing ppm-level perrhenate via either liquid-liquid extraction or simple column adsorption. Importantly, after extraction or adsorption, superphane 2 can be recycled and reused by simple treatment with aqueous NaHCO 3 . • A superphane for highly selective recognition of ReO 4 − is synthesized in gram scale • Over 99.99% of ReO 4 − can be separated from complex simulated waste streams • Rapid removal of ppb-level ReO 4 − is achieved via extraction or column adsorption • The superphane for ReO 4 − extraction/adsorption can be recycled and reused Extraction of low concentrations of rhenium anions from waste streams is important industrially. Zhou et al. present the facile and gram-scale synthesis of a superphane via dynamic imine chemistry coupled with NaBH 4 reduction, which can separate perrhenate from low-content mixtures and simulated Hanford waste streams with exceptionally high efficiency and selectivity, along with good recyclability and reusability.

Task-Specific Tailored Cationic Polymeric Network with High Base-Resistance for Unprecedented 99TcO4 - Cleanup from Alkaline Nuclear Waste.

Direct removal of 99TcO4– from alkaline nuclear waste is desirable because of the nuclear waste management and environmental protection relevant to nuclear energy but is yet to be achieved given that combined features of decent base-resistance and high uptake selectivity toward anions with low charge density have not been integrated into a single anion-exchange material. Herein, we proposed a strategy overcoming these challenges by rationally modifying the imidazolium unit of a cationic polymeric network (SCU-CPN-4) with bulky alkyl groups avoiding its ring-opening reaction induced by OH– because of the steric hindrance effect. This significantly improves not only the base-resistance but also the affinity toward TcO4– as a result of enhanced hydrophobicity, compared to other existing anion-exchange materials. More importantly, SCU-CPN-4 exhibits record high uptake selectivity, fast sorption kinetics, sufficient robustness, and promising reusability for removing 99TcO4– from the simulated high-level waste stream at the U.S. Savannah River Site, a typical alkaline nuclear waste, in both batch experiment and dynamic column separation test for the first time.

Defect Engineering on a Ti4O7 Electrode by Ce3+ Doping for the Efficient Electrooxidation of Perfluorooctanesulfonate.

Defect engineering in an electrocatalyst, such as doping, has the potential to significantly enhance its catalytic activity and stability. Herein, we report the use of a defect engineering strategy to enhance the electrochemical reactivity of Ti4O7 through Ce3+ doping (1-3 at. %), resulting in the significantly accelerated interfacial charge transfer and yielding a 37-129% increase in the anodic production of the hydroxyl radical (OH•). The Ce3+-doped Ti4O7 electrodes, [(Ti1-xCex)4O7], also exhibited a more stable electrocatalytic activity than the pristine Ti4O7 electrode so as to facilitate the long-term operation. Furthermore, (Ti1-xCex)4O7 electrodes were also shown to effectively mineralize perfluorooctanesulfonate (PFOS) in electrooxidation processes in both a trace-concentration river water sample and a simulated preconcentration waste stream sample. A 3 at. % dopant amount of Ce3+ resulted in a PFOS oxidation rate 2.4× greater than that of the pristine Ti4O7 electrode. X-ray photoelectron spectroscopy results suggest that Ce3+ doping created surficial oxygen vacancies that may be responsible for the enhanced electrochemical reactivity and stability of the (Ti1-xCex)4O7 electrodes. Results of this study provide insights into the defect engineering strategy for boosting the electrochemical performance of the Ti4O7 electrode with a robust reactivity and stability.

Implementation of Ion Exchange Processes for Carbon Dioxide Mineralization Using Industrial Waste Streams

Sequestration of CO2 within stable mineral carbonates (e.g., CaCO3) represents an attractive emission reduction strategy because it offers a leakage-free alternative to geological storage of CO2 in an environmentally benign form. However, the pH of aqueous streams equilibrated with gaseous streams containing CO2 (pH < 4) are typically lower than that which is required for carbonate precipitation (pH > 8). Traditionally, alkalinity is provided by a stoichiometric reagent (e.g., NaOH) which renders these processes environmentally hazardous and economically unfeasible. This work investigates the use of regenerable ion-exchange materials to induce alkalinity in CO2-saturated aqueous solutions such that the pH shift required for mineralization occurs without the need for stoichiometric reagents. Na+-H+ exchange isotherms (at [H+] = 10−8–10−1 M) and rates were measured for 13X and 4A zeolites and TP-207 and TP-260 organic exchange resins in batch equilibrium and fixed-bed exchange experiments, respectively. At solutions equilibrated with CO2 at 1.0 atm (pH = 3.9), H+ exchange capacities for the materials were similar (1.7–2.4 mmol H+/g material) and resulted in pH increases from 3.9 to greater than 8.0. Multi-component mixtures using Ca2+ and Mg2+ cations (at 10−3–10−1 M) in CO2-saturated water were used to probe competitive ion exchange. The presence of divalent cations in solution inhibited H+ exchange, reducing capacities to as low as 0.2 mmol H+/g for both resins and zeolites. Dynamic H+ exchange capacities in fixed-bed ion exchange columns were similar to equilibrium values for resins (∼1.5 mmol/g) and zeolites (∼0.8 mmol/g) using inlet solutions that were equilibrated with gaseous streams of CO2 at 1.0 atm. However, exchange kinetics were limited by intraparticle diffusion as indicated by the increased rate parameters with increasing inlet flow rates (20–160 cm3 min−1). Experimental calcite precipitation from mixing the alkaline CO32−-rich water solution obtained from the ion-exchange column with a simulated liquid waste stream solution achieved thermodynamic maximum yields. The results from these studies indicate that ion exchange processes can be used as an alternative to the addition of stoichiometric bases to induce alkalinity for the precipitation of CaCO3, thereby opening a pathway toward sustainable and economic mineralization processes.

Kinetics of Co-Mingled 99Tc and Cr Removal during Mineral Transformation of Ferrous Hydroxide

Four simulated waste streams relevant to the vitrification of Hanford nuclear waste were studied to evaluate the removal kinetics of technetium-99 (Tc) and co-mingled Cr(VI) during treatment with solid ferrous hydroxide (Fe(OH)2(s)). Simulants treated with Fe(OH)2(s) were reacted for 24 h and sub-sampled periodically to monitor Tc and Cr removal. Solution sample analysis during the reaction was coupled with solid phase characterization, for example, X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD), to establish influence of the solid phase product on Tc and Cr removal rates. Based on these results, the majority of Tc and Cr removal occurs within the first 5 min of simulant contact with Fe(OH)2(s). However, the order in which Tc and Cr are completely removed from each simulant depends on the simulant chemistry, the preferred reduction pathway, and the solid phase product, for example, magnetite (Fe3O4) versus goethite (α-FeOOH). Low pH and low Cr concentrations favor rapid Tc removal, with XRD and XAS confirming that Fe3O4 readily incorporates reduced Tc(IV) into its structure. High pH, high Cr concentrations, and the presence of other co-mingled constituents favor heterogeneous removal of Tc early in the reaction (<1 h) with removal rates often faster than those determined for Cr. At reaction times of >1 h, Tc removal slows as homogeneous removal of Cr begins to dominate, concurrent with an increase in the formation of FeOOH as the solid phase reaction product. These results suggest that for complex, high pH waste streams, Tc removal within the first hour after Fe(OH)2(s) treatment is necessary for complete Tc reduction and improved mineral immobilization.

Uranium recovery and purification from simulated waste streams containing high uranium concentrations with dispersion liquid membranes

The suitability of dispersion liquid membranes (DLMs) to recover and purify uranium from simulated waste streams containing nitric acid, high uranium concentrations and radionuclide contaminants with tributyl phosphate (TBP) and ammonium carbonate ((NH4)2CO3) as stripping solution was investigated. The radionuclide surrogates were not extracted and complete uranium recovery was obtained from 15 g U L−1 solutions using a 1:4 ratio of 30% TBP in kerosene and 0.75 M (NH4)2CO3 dispersion. In addition, all the uranium in the stripping solution was precipitated. Consequently, DLM proved to be a promising solvent extraction contacting method for uranium recovery and purification.

Measuring space radiation shielding effectiveness

Passive radiation shielding is one strategy to mitigate the problem of space radiation exposure. While space vehicles are constructed largely of aluminum, polyethylene has been demonstrated to have superior shielding characteristics for both galactic cosmic rays and solar particle events due to the high hydrogen content. A method to calculate the shielding effectiveness of a material relative to reference material from Bragg peak measurements performed using energetic heavy charged particles is described. Using accelerated alpha particles at the National Aeronautics and Space Administration Space Radiation Laboratory at Brookhaven National Laboratory, the method is applied to sample tiles from the Heat Melt Compactor, which were created by melting material from a simulated astronaut waste stream, consisting of materials such as trash and unconsumed food. The shielding effectiveness calculated from measurements of the Heat Melt Compactor sample tiles is about 10% less than the shielding effectiveness of polyethylene. Shielding material produced from the astronaut waste stream in the form of Heat Melt Compactor tiles is therefore found to be an attractive solution for protection against space radiation.

Swirl Flow Bioreactor coupled with Cu-alginate beads: A system for the eradication of Coliform and Escherichia coli from biological effluents.

It is estimated that approximately 1.1 billion people globally drink unsafe water. We previously reported both a novel copper-alginate bead, which quickly reduces pathogen loading in waste streams and the incorporation of these beads into a novel swirl flow bioreactor (SFB), of low capital and running costs and of simple construction from commercially available plumbing pipes and fittings. The purpose of the present study was to trial this system for pathogen reduction in waste streams from an operating Dewats system in Hinjewadi, Pune, India and in both simulated and real waste streams in Seattle, Washington, USA. The trials in India, showed a complete inactivation of coliforms in the discharged effluent (Mean Log removal Value (MLRV) = 3.51), accompanied by a total inactivation of E. coli with a MLRV of 1.95. The secondary clarifier effluent also showed a 4.38 MLRV in viable coliforms during treatment. However, the system was slightly less effective in reducing E. coli viability, with a MLRV of 1.80. The trials in Seattle also demonstrated the efficacy of the system in the reduction of viable bacteria, with a LRV of 5.67 observed of viable Raoultella terrigena cells (100%).

Pollucite and feldspar formation in sintered bentonite for nuclear waste immobilization

Future reprocessing of nuclear fuel may produce a waste stream consisting of alkali and alkaline earth fission products that can be converted into stable aluminosilicate minerals after sintering in bentonite. Precise knowledge of the mineral composition of the host phases is required for ultimate disposal. As determined by several analytical techniques, stable pollucite and celsian phases formed after sintering of bentonite and a simulated waste at 1200 °C. This relatively low temperature was likely a result of several impurities in the bentonite and simulated waste stream. While most of the waste metal ions were enriched in the crystalline phases, trace amounts remained in a silica-rich glassy region with other impurities.

Studies on a synthetic sitinakite-type silicotitanate cation exchanger. Part 2. Effect of alkaline earth and alkali metals on the uptake of Cs and Sr radioisotopes

A commercially available synthetic silicotitanate (IONSIV ® IE-911), with a sitinakite-like structure, is a candidate material for the remediation of aqueous nuclear waste streams. These streams often vary in both cation composition and cation concentration. Commonly Na, K, Mg, Ca and Ba are present, and sodium is the most prevalent with barium present at much lower concentrations. Batch experiments to measure distribution coefficients (K d) have been carried out to monitor the effect of these cations on the removal of the fission products Cs and Sr from simulated aqueous waste streams relevant to their remediation prior to release to the environment.

Effect of Gallium Oxide on Phase Assemblage in Apatite and Whitlockite Hosts for Waste Immobilization

AbstractTo immobilize halide and actinide ions present in specific ILW waste a process has been developed that uses mineral phases as the host material. The mechanism of substitution of gallium into these phases will have a large effect on the phase assemblage. This will inevitably affect the total amount of halide that can be immobilized in to total phase mixture.The full simulated waste stream composition containing varying concentrations (1–40 wt.%) of gallium oxide was studied. Also nominal compositions for gallium doped fluorapatites (Ca10-1.5xGax)F2(PO4)6 (x = 0, 0.25, 0.5, 0.75, 1.0) and gallium doped whitlockites Ca9Gay(PO4)6+y (x = 0.2, 0.4, 0.6, 0.8, 1.0) were prepared at 750–1050 °C.These were studied by powder x-ray diffraction (XRD) to determine the phase assemblage and solid solution limits of gallium in the apatite and whitlockite phases. It was found that a complete solid solution was formed between whitlockite, Ca3(PO4)2, and Ca9Gay(PO4)6+y. In the nominal apatite compositions it was found that gallium did not substitute into the apatite structure but was instead partitioned over Ca9Gay(PO4)6+y, gallium phosphate, and unreacted gallium oxide. At higher temperatures gallium suppressed the formation of the apatite phase and was largely partitioned into the Ca9Gay(PO4)6+y phase whereas at lower temperature the majority was present as unreacted Ga2O3. In the full DCHP compositions it was found that gallium is likely to be partitioned over a number of phases including apatite, cationdoped whitlockite and gallium phosphate.

Removal of Pertechnetate from Simulated Nuclear Waste Streams Using Supported Zerovalent Iron

The application of nanoparticles of predominantly zerovalent iron (nanoiron), either unsupported or supported, to the separation and reduction of pertechnetate anions (TcO4-) from complex waste mixtures was investigated as an alternative approach to current waste-processing schemes. Although applicable to pertechnetate-containing waste streams in general, the research discussed here was directed at two specific potential applications at the U.S. Department of Energy's Hanford Site: (1) the direct removal of pertechnetate from highly alkaline solutions, typical of those found in Hanford tank waste, and (2) the removal of dilute pertechnetate from near-neutral solutions, typical of the eluate streams from commercial organic ion-exchange resins that may be used to remediate Hanford tank wastes. It was envisioned that both applications would involve the subsequent encapsulation of the loaded sorbent material into a separate waste form. A high surface area (>200 m2/g) base-stable, nanocrystalline zirconia was used as a support for nanoiron for tests with highly alkaline solutions, while a silica gel support was used for tests with near-neutral solutions. It was shown that after 24 h of contact time, the high surface area zirconia supported nanoiron sorbent removed about 50% (Kd = 370 L/kg) of the pertechnetate from a pH 14 tank waste simulant containing 0.51 mM TcO4- and large concentrations of Na+, OH-, NO3-, and CO32- for a phase ratio of 360 L simulant per kg of sorbent. It was also shown that after 18 h of contact time, the silica-supported nanoiron removed >95% pertechnetate from a neutral pH eluate simulant containing 0.076 mM TcO4- for a phase ratio of 290 L/kg. It was determined that in all cases, nanoiron reduced the Tc(VII) to Tc(IV), or possibly to Tc(V), through a redox reaction. Finally, it was demonstrated that a mixture of 20 mass % of the solid reaction products obtained from contacting zirconia-supported nanoiron with an alkaline waste solution containing Re(VII), a surrogate for Tc(VII), with 80 mass % alkali borosilicate based frit heat-treated at 700 °C for 4 h sintered into an easily handled glass composite waste form.

Anomalous transient leaching behavior of metals solidified/stabilized by pozzolanic fly ash

This study presents observations on the transient leaching behavior of chromium, cadmium, and aluminum that were solidified/stabilized by pozzolanic fly ash. These three metals were selected since they were present in a simulated waste stream generated by an evaporator during plutonium purification and also because the minimum solubility of these metals occurs at significantly different pHs. The transient pH behavior of the toxicity characteristic leaching procedure (TCLP) leachate showed a monotonic increase for all cases, but the equilibrium value was affected by process conditions. The transient leachate concentration behavior showed curves with one or two local maxima for some cases and curves with a monotonic increase for other cases. Data from the leaching experiments was compared to the solubility curves for the hydroxides of each metal since it was assumed that the highly alkaline conditions inside the fly ash waste would cause the metals to precipitate as hydroxides after initially dissolving in the acidic leaching solution. It was found that of the three metals, only cadmium followed the solubility curve for pure hydroxide solutions or for fly ash systems currently reported in the literature.

A comparison of large-scale electron beam and bench-scale 60Co irradiations of simulated aqueous waste streams

The effectiveness of using high energy electron beam irradiation for the removal of toxic organic chemicals from water and wastewater has been demonstrated by commercial-scale experiments conducted at the Electron Beam Research Facility (EBRF) located in Miami, Florida and elsewhere. The EBRF treats various waste and water streams up to 450 l min −1 (120 gal min −1) with doses up to 8 kilogray (kGy). Many experiments have been conducted by injecting toxic organic compounds into various plant feed streams and measuring the concentrations of compound(s) before and after exposure to the electron beam at various doses. Extensive experimentation has also been performed by dissolving selected chemicals in 22,700 l (6000 gal) tank trucks of potable water to simulate contaminated groundwater, and pumping the resulting solutions through the electron beam. These large-scale experiments, although necessary to demonstrate the commercial viability of the process, require a great deal of time and effort. This paper compares the results of large-scale electron beam irradiations to those obtained from bench-scale irradiations using gamma rays generated by a 60Co source. Dose constants from exponential contaminant removal models are found to depend on the source of radiation and initial contaminant concentration. Possible reasons for observed differences such as a dose rate effect are discussed. Models for estimating electron beam dose constants from bench-scale gamma experiments are presented. Data used to compare the removal of organic compounds using gamma irradiation and electron beam irradiation are taken from the literature and a series of experiments designed to examine the effects of pH, the presence of turbidity, and initial concentration on the removal of various organic compounds (benzene, toluene, phenol, PCE, TCE and chloroform) from simulated groundwater.

Enhanced selectivity for actinides over lanthanides with CMPO ligands secured to a C(3)-symmetric triphenoxymethane platform.

A ligand system containing three preorganized carbamoylmethylphosphine oxide (CMPO) moieties anchored onto a rigid C(3)-symmetric triphenoxymethane platform has been developed for facile metal complexation and subsequent extraction from aqueous acidic nuclear waste streams. Intended to mimic the 3:1 CMPO-actinide stoichiometry of the extracted species in the TRUEX nuclear waste treatment process, the CMPO arms on this ligand are oriented such that all three CMPO moieties can cooperatively bind a metal ion. Extractions of simulated nuclear waste streams (10(-4) M metal in 1 M nitric acid) with solutions of this ligand in methylene chloride (10(-3) M) reveal a high affinity for the actinide thorium and a very low, but constant, affinity for the lanthanides across the series. Thorium and five lanthanide (lanthanum, cerium, neodymium, europium, and ytterbium) nitrate complexes of this ligand have been synthesized and fully characterized by X-ray crystallography, (1)H and (31)P NMR spectra, and FT-ICR-MS to elucidate the mechanism of this unique actinide selectivity. All six oxygen donors from the three CMPO arms of the ligand and one or two nitrate counterions coordinate these metals to afford 2+ cationic complexes in every case. Because of the large size of the ligand, both the thorium and lanthanide complexes present similarly charged and sized surfaces to the extraction solvents, but the thorium complex is extracted quantitatively over the lanthanide complexes. A possible rationale for this extraction behavior difference is presented and further illustrated by the extraction properties of this ligand system for the alkali metals (lithium, sodium, potassium, rubidium, and cesium) as picrate salts and by the solid- and solution-state structures of its lithium picrate complex.