Solvent-Polymeric Membranes for Separation of Li+ From Other Alkali Metal and Alkaline Earth Ions

Lithium may be recovered from the Dead Sea brines by a process which combines membrane separation with ion-exchange. Solvent-polymeric membranes based on alkyl-arylphosphates cause selective permeation of lithium ions with Br⁻₃ as counter ions. Addition of the derivatives of neutral “crown” ethers did not improve their performance and an adverse effect, due to the decrease in the fluidity of the membrane system, was observed. Incorporation of ionizable “crown” ethers compatible with the system may, however, be advantageous; pH gradients could act as a driving force for transport of lithium in such systems. Membranes prepared with (2-ethylhexyl)-diphenyl phosphate (Santicizer 141) gave the best results from the point of view of selectivity of Li⁺ transport vs. Mg²⁺ and Ca²⁺. Maintenance of ca. 10⁻³ M concentrations of Br₂ in the end-brine solutions gives optimal membrane performance. No significant change in membrane permeability and selectivity occurred during six months of their operation. Lithium ions in the product solution of the membrane separation process may be further separated from the residual Mg²⁺ and Ca²⁺ ions and concentrated up to 1 M by ion exchange processes. Lithium may be precipitated from such solutions, free from alkaline earth ions, as Li₂CO₃.     

Investigation of an Ozone Membrane Contactor System

Ozone mass transfer rates were determined for nine expanded porous Teflon membranes that had different pore size, thickness, and pore volume, a nonporous Teflon membrane, and a PVDF membrane. The mass transfer coefficient was 7.6 ± 0.5 × 10^?5 m/s at Re of 2000 for all membranes tested even though pore sizes ranged from 0.07 to 6 μm and thickness from 0.076 to 0.25 mm. Mass transfer increased with liquid side Reynolds number. Therefore, it is likely that ozone mass transfer is liquid phase controlling and not membrane limited. For a hypothetical case of 4000 m³/d and 2 mg/L ozone transferred, plate and frame membrane and hollow fiber contactors are approximately one and two orders of magnitude smaller, respectively, than fine-bubble diffusers.     

Catalytic Formation of C−N Bonds: ICS Symposium Honoring Wolf Prize Laureates Stephen L. Buchwald and John F. Hartwig: May 29, 2019, Technion-Israel Institute of Technology,Haifa, Israel

This report covers two exciting events in the scientific landscape of the State of Israel: the traditional Wolf Prize Symposium of the ICS and the Wolf Prize Ceremony in the Knesset. The symposium, dedicated to the science of Stephen L. Buchwald and John F. Hartwig, highlighted the catalytic formation of C−N bonds. In a general sense, the two Wolf Prize laureates may be considered as molecular architects who produced efficient molecular-scale machines that make important molecules for the benefit of humanity. After receiving the Wolf Prize from Israel's President, Buchwald commented, “There are many who believe that support for research should focus exclusively on endeavors that have specific practical applications in mind. With this mindset, our work would have never been possible. Time and time again experience shows that it is exceedingly difficult to predict which scientific discoveries will lead to major advances. So often, it is the scientist following his or her own intellectual curiosity whose work leads to a breakthrough. I believe that basic curiosity-driven research and societal and economic progress are inextricably linked.” And Hartwig comments, “We all know the principles of science know no boundaries, but maybe less appreciated, or taken for granted, is that the assembly of research teams in many places knows no boundaries. If we recognize and nurture talent in people from all corners and all backgrounds we can address and maybe solve today's most important problems in health, energy, and environmental sustainability that are urgently facing us.”     

Development of Saturable Absorbers for Laser Passive Q‐Switching near 1.5 μm Based on Transparent Ceramic Co2+:MgAl2O4

We describe the development of a reasonable cost Co²⁺:MgAl₂O₄ transparent ceramic plates fabrication technology that allows the producing of parts functioning as passive laser Q‐switches in the 1.3–1.7 μm domain. The main relevant material characteristics were measured. The absorption band, positioned between 1.2 and 1.7 μm, is typical of the ⁴A₂ (⁴F) → ⁴T₁ (⁴F) transition of Co²⁺ substituting Mg²⁺ ions in their T_d symmetry sites. The measured ground‐state absorption cross section σ_gs = 2.9 × 10^?19 cm², saturation contrast γ = 0.12, and depleted ground‐state recovery time τ₂ = 110–430 ns render such parts suitable for the intended application. The radiative lifetime was estimated as . The spin‐orbit splitting constant was estimated as ξ_SL??150 cm^?1 for the ⁴F parent ground state, and ξ_SL ? –575 cm^?1 for the ⁴P parent excited state. Obtained specimens had a transmission of ~80% (t = 2 mm, λ = 600 nm) and included some opaque, white spots. Further improvement of host optical transmission and resistance to laser damage are necessary.     

Amyloidogenic Properties of Peptides Derived from the VHL Tumor Suppressor Protein

The von Hippel-Lindau tumor suppressor protein (pVHL) is involved in maintaining cellular oxygen homeostasis through the regulated degradation of HIF-α. The intrinsically disordered nature of pVHL makes it prone to aggregation that impairs its function, and this is further aggravated in mutant versions of the protein, thus promoting tumor development. By using in silico analysis, we predicted six peptide fragments from pVHL to be amyloidogenic. This was verified for two of the peptides by biophysical approaches, which demonstrated self-assembly and formation of β-sheet-rich aggregates, which, under transmission electron microscopy, atomic force microscopy, and X-ray diffraction, displayed typical fibrillar amyloid characteristics. These motifs may serve as proxies for exploring the nature of pVHL aggregation.     

Plutonium recycling in hydride fueled PWR cores

The classic approach to the recycling of Pu in PWR is to use mixed U-oxide Pu-oxide (MOX) fuel. The mono-recycling of plutonium in PWR transmutes less than 30% of the loaded plutonium, providing only a limited reduction in the long-term radiotoxicity and in the inventory of TRU to be stored in the repository. The primary objective of this study is to assess the feasibility of plutonium recycling in PWR in the form of plutonium hydride, PuH₂, mixed with uranium and zirconium hydride, ZrH_1.6, referred to as PUZH, that is loaded uniformly in each fuel rod. The assessment is performed by comparing the performance of the PUZH fueled core to that of the MOX fueled core. Performance characteristics examined are transmutation effectiveness, proliferation resistance of the discharged fuel and fuel cycle economics. The PUZH loaded core is found superior to the MOX fueled core in terms of the transmutation effectiveness and proliferation resistance. For the reference cycle duration and reference fuel rod diameter and pitch, the percentage of the plutonium loaded that is transmuted in one recycle is 53% for PUZH versus 29% for MOX fuel. That is, the net amount of plutonium transmuted in the first recycle is 55% higher in cores using PUZH than in cores using MOX fuel. Relative to the discharged MOX, the discharged PUZH fuel has smaller fissile plutonium fraction - 45% versus 60%, 15% smaller minor actinides (MA) inventory and more than double spontaneous fission neutron source intensity and decay heat per gram of discharged TRU. Relative to the MOX fuel assembly, the radioactivity of the PUZH fuel assembly is 26% smaller and the decay heat and the neutron yield are only 3% larger. The net effect is that the handling of the discharged PUZH fuel assembly will be comparable in difficulty to that of the discharged MOX assembly while the proliferation resistance of the TRU of the discharged PUZH fuel is enhanced.     

Uranium-zirconium hydride fuel properties

Properties of the two-phase hydride U_0.3ZrH_1.6 pertinent to performance as a nuclear fuel for LWRs are reviewed. Much of the available data come from the Space Nuclear Auxiliary Power (SNAP) program of 4 decades ago and from the more restricted data base prepared for the TRIGA research reactors some 3 decades back. Transport, mechanical, thermal and chemical properties are summarized. A principal difference between oxide and hydride fuels is the high thermal conductivity of the latter. This feature greatly decreases the temperature drop over the fuel during operation, thereby reducing the release of fission gases to the fraction due only to recoil. However, very unusual early swelling due to void formation around the uranium particles has been observed in hydride fuels. Avoidance of this source of swelling limits the maximum fuel temperature to ∼650 °C (the design limit recommended by the fuel developer is 750 °C). To satisfy this temperature limitation, the fuel-cladding gap needs to be bonded with a liquid metal instead of helium. Because the former has a thermal conductivity ∼100 times larger than the latter, there is no restriction on gap thickness as there is in helium-bonded fuel rods. This opens the possibility of initial gap sizes large enough to significantly delay the onset of pellet-cladding mechanical interaction (PCMI). The large fission-product swelling rate of hydride fuel (3× that of oxide fuel) requires an initial radial fuel-cladding gap of ∼300 m if PCMI is to be avoided. The liquid-metal bond permits operation of the fuel at current LWR linear-heat-generation rates without exceeding any design constraint. The behavior of hydrogen in the fuel is the source of phenomena during operation that are absent in oxide fuels. Because of the large heat of transport (thermal diffusivity) of H in ZrH_x, redistribution of hydrogen in the temperature gradient in the fuel pellet changes the initial H/Zr ratio of 1.6 to ∼1.45 at the center and ∼1.70 at the periphery. Because the density of the hydride decreases with increasing H/Zr ratio, the result of H redistribution is to subject the interior of the pellet to a tensile stress while the outside of the pellet is placed in compression. The resulting stress at the pellet periphery is sufficient to overcome the tensile stress due to thermal expansion in the temperature gradient and to prevent radial cracking that is a characteristic of oxide fuel. Several mechanisms for reduction of the H/Zr ratio during irradiation are identified. The first is transfer of impurity oxygen in the fuel from Zr to rare-earth oxide fission products. The second is the formation of metal hydrides by these same fission products. The third is by loss to the plenum as H₂.The review of the fabrication method for the hydride fuel suggests that its production, even on a large scale, may be significantly higher than the cost of oxide fuel fabrication.     

Exact and efficient computation of moments of free-form surface and trivariate based geometry

Two schemes for computing moments of free-form objects are developed and analyzed. In the first scheme, we assume that the boundary of the analyzed object is represented using parametric surfaces. In the second scheme, we represent the boundary of the object as a constant set of a trivariate function. These schemes rely on a pre-computation step which allows fast re-evaluation of the moments when the analyzed object is modified. Both schemes take advantage of a representation that is based on the B-spline blending functions.     

Solid-state NMR studies of the prion protein H1 fragment

Conformational changes in the prion protein (PrP) seem to be responsible for prion diseases. We have used conformation-dependent chemical-shift measurements and rotational-resonance distance measurements to analyze the conformation of solid-state peptides lacking long-range order, corresponding to a region of PrP designated H1. This region is predicted to undergo a transformation of secondary structure in generating the infectious form of the protein. Solid-state NMR spectra of specifically 13C-enriched samples of H1, residues 109-122 (MKHMAGAAAAGAVV) of Syrian hamster PrP, have been acquired under cross-polarization and magic-angle spinning conditions. Samples lyophilized from 50% acetonitrile/50% water show chemical shifts characteristic of a beta-sheet conformation in the region corresponding to residues 112-121, whereas samples lyophilized from hexafluoroisopropanol display shifts indicative of alpha-helical secondary structure in the region corresponding to residues 113-117. Complete conversion to the helical conformation was not observed and conversion from alpha-helix back to beta-sheet, as inferred from the solid-state NMR spectra, occurred when samples were exposed to water. Rotational-resonance experiments were performed on seven doubly 13C-labeled H1 samples dried from water. Measured distances suggest that the peptide is in an extended, possibly beta-strand, conformation. These results are consistent with the experimental observation that PrP can exist in different conformational states and with structural predictions based on biological data and theoretical modeling that suggest that H1 may play a key role in the conformational transition involved in the development of prion diseases.