Membrane-based solvent extraction for selective removal and recovery of metals

A membrane-based solvent extraction process was developed for selective removal and recovery of metals from aqueous solutions. The process utilizes microporous membranes as an interface between an aqueous solution and organic solvents containing liquid ion exchangers. Metal ions are transported from the aqueous solution to the organic phase at the interface created in the pores of membrane. The organic solvent, which is loaded with metal ions in the extraction module, is regenerated in contact with the stripping solution in the stripping module. One important feature of this process is the stability of the membrane system, which results from using an aqueous—organic separator to remove aqueous solution from the organic circulating line. This process was evaluated for enrichment of copper using solvents containing LIX 64N. The process is applicable to selective recovery of metals from ore leachates or metal-containing wastewater.     

Hot particles analysis originating from failed and damaged fuels

The increase of activities of fission products and transmutation products in the primary coolant of a nuclear power plant indicates the presence of fuel rod failures. The measurement of the activity concentration of the primary coolant was able to detect fuel failures in the reactor core. Microanalytical methods for examining individual hot particles have been developed and applied to fuel failure detection under normal operation conditions as well as during the severe fuel damage that occurred in the cleaning tank incident at Unit 2 of NPP Paks in April 2003. Several faulty fuel rods can be detected simultaneously by the characterization of individual hot particles originating from the primary water. The analysis of particles originating from the damaged fuels provides information relating to the dissolution process of the fuel debris.     

Lightfastness of Polymeric Color Filters with Metal-Containing Dyes and Heterocyclic Azo Dyes as Absorbing Agents

Color filters containing in the cellulose acetobutyrate matrix a combination of a metal-containing organic dye and an azo dye derived from thiophene or furan were prepared, and their lightfastness was studied.     

Determination of uranium,plutonium and selected fission products in the coolant of the KS-150 reactor

The method of monitoring of U, Pu and some fission products (^103,106Ru,^134,137Cs and^141,144Ce) in gaseous CO₂ coolant is described. The method is based on the retention of the radionuclides studied by membrane filters built in by-pass of the burst-cartridge detection (BCD) system. The purpose of the present study was the determination of U, Pu in CO₂ and the verification of the possibility of the indirect monitoring of U and Pu contents in the coolant, using the gamma-spectrometric determination of selected fission products retained by the filter. For calibration of the proposed method after decomposition of the filters, uranium was determined spectrophotometrically using Arsenazo III, plutonium was determined radiometrically after its separation by extraction with 2-thenoyltrifluoracetone and the fission products were determined by gamma-spectrometry. From the results obtained it follows that a correlation exists between the U and Pu content in the coolant and the activity of certain fission products retained on the filter.     

Biomimetic membranes with aqueous nano channels but without proteins: impedance of impregnated cellulose ester filters

Earlier we have shown that many important properties of ionic aqueous channels in biological membranes can be imitated using simple biomimetic membranes. These membranes are composed of mixed cellulose ester-based filters, impregnated with isopropyl myristate or other esters of fatty acids, and can be used for high-throughput drug screening. If the membrane separates two aqueous solutions, combination of relatively hydrophilic polymer support with immobilized carboxylic groups results in the formation of thin aqueous layers covering inner surface of the pores, while the pore volume is filled by lipid-like substances. Because of these aqueous layers biomimetic membranes even without proteins have a cation/anion ion selectivity and specific (per unit of thickness) electrical properties, which are similar to typical properties of biological membranes. Here we describe frequency-dependent impedance of the isopropyl myristate-impregnated biomimetic membranes in the 4-electrode arrangement and present the results as Bode and Nyquist diagrams. When the membranes are placed in deionized water, it is possible to observe three different dispersion processes in the frequency range 0.1 Hz to 30 kHz. Only one dispersion is observed in 5 mM KH(2)PO(4) solution. It is suggested that these three dispersion features are determined by (a) conductivity in aqueous structures/channels, formed near the internal walls of the filter pores at high frequencies, (b) dielectric properties of the whole membrane at medium frequencies, determined by polymer support, aqueous layers and impregnating oil, and, finally, (c) by the processes in hydrated liquid crystal structures formed in pores by impregnating oil in contact with water at low frequencies.     

Hydrophilic membrane-based humidity control.

A dehumidification system for low gravity plant growth experiments requires the generation of no free-liquid condensate and the recovery of water for reuse. In the systems discussed in this paper, the membrane is a barrier between the humid air phase and a liquid-coolant water phase. The coolant water temperature combined with a transmembrane pressure differential establishes a water flux from the humid air into the coolant water. Building on the work of others, we directly compared different hydrophilic membranes for humidity control. In a direct comparison of the hydrophilic membranes, hollow fiber cellulose ester membranes were superior to metal and ceramic membranes in the categories of condensation flux per surface area, ease of start-up, and stability. However, cellulose ester membranes were inferior to metal membranes in one significant category, durability. Dehumidification systems using mixed cellulose ester membranes failed after operational times of only hours to days. We propose that the ratio of fluid surface area to membrane material area (approximately = membrane porosity) controls the relative performances among membranes. In addition, we clarified design equations for operational parameters such as the transmembrane pressure differential. This technology has several potential benefits related to earth environmental issues including the minimization of airborne pathogen release and higher energy efficiency in air conditioning equipment. Utilizing these study results, we designed, constructed, and flew on the space shuttle missions a membrane-based dehumidification system for a plant growth chamber.     

Synthesis of Polymers by Using Divalent Metal Salts of Mono(hydroxyethyl)phthalate: Metal-Containing Unsaturated Polyesters with Pendent Methacrylate Groups

Syntheses of novel metal-containing unsaturated polyesters having pendent methacrylate groups obtained by use of divalent metal salts of mono(hydroxyethyl)phthalate-maleic anhydride (MA)-glycidyl methacrylate (GMA) reactions were investigated. The yields were generally high. The metal-containing polyesters obtained were slightly yellow-brown solids, and the molecular weights ranged from 1546 to 2174, depending on the mole ratio of feed. Among them, the polyesters obtained at a feed mole ratio of metal salt:MA:GMA of 1:8:8 were miscible with methyl methacrylate (MMA), giving homogeneous solutions suitable for copolymerization, and the polyesters could be easily cross-linked with MMA to give cured resins. The metal-containing cured polyester resins showed excellent physical properties. Resistance of the resins to chemical attack and boiling water and thermal behavior are also discussed.     

Analysis of actinides in the primary coolant of a WWER-440 type reactor

A simple and effective method has been developed for the determination of the transuranium isotopes in primary coolant samples of WWER-440 type reactors. Membrane filters containing undissolved particles from about one liter coolant were destroyed by mineral acids, then americium-curium isotopes and neptunium-plutonium isotopes were coprecipitated sequentially with NdF₃ based on their different redox behavior. Alpha-spectra were determined by silicon semiconductor detectors connected to multichannel analyzers. Activity ratios measured in a reactor unit with a failed fuel element were compared with calculated values of the same type of reactor under similar conditions. Parameters of the defective fuel (burnup, original enrichment) could be estimated.     

Solid phase extraction of trace amount of mercury from natural waters on silver and gold nanoparticles

Silver (Ag) and gold (Au) nanoparticles impregnated in nylon membrane filters have been proposed as a new solid phase for preconcentration of mercury from natural waters. Water samples were treated with KMnO₄ to convert all mercury species to inorganic Hg²⁺ and this was followed by the reduction of Hg²⁺ with NaBH₄ to elemental Hg⁰. The determination of Hg was carried out by thermal evaporation of mercury from membrane filters using Zeeman mercury analyzer RA–915+ (Lumex, Russia). This process does not involve any additional sample treatment and sharply reduces risk of samples contamination. The limit of detection (LOD) was found to be 0.04 ng (absolute mass). Relative LOD was 0.4 ng L⁻¹ for 100 mL of water. The method was validated through the analysis of CRM NRCC Tort–2 (Lobster hepatopancreas) and the found value (0.30 ± 0.07 μg g⁻¹) was in good agreement with the certified value (0.27 ± 0.06 μg g⁻¹). High efficiency of Hg accumulation from aqueous phase to membrane filters can be attributed to a large surface area of nanoparticles.     

Effect of Contamination and Cleaning of a Microfiltration Membrane in Filtration of an Aqueous Extract of Dog-Rose

The main factors responsible for decrease in the filtration flux (membrane throughput) in removal of pectin substances from an aqueous extract from dog-rose fruits and reasons for membrane contamination were studied. The method for membrane cleaning with distilled water and additional cleaning agents, aqueous solutions of NaOH and HNO₃, was optimized.     

Plurality of radiation-chemical steady states during the radiolysis of water coolant in nuclear reactor

A computational study has been performed on the radiolysis of an aqueous solution that has the chemical composition and irradiation parameters typical of the primary coolant of pressurized water reactors. In this work, in contrast to previous studies on this subject, it has been taken into account that temporary fluctuations of the reactor radiation parameters, such as the composition of reactor n, γ]-radiation and the absorbed dose rate in the coolant, may occur in an actual real reactor during irradiation. The feasibility of spontaneous switching of the radiation-chemical system from one steady state with low concentrations of oxidizing products of radiolysis to another state with high concentrations resulting from a spike of the reactor radiation dose rate against the background of constant dose rate before and after the spike has been shown. The event triggering the switch is an increase in the concentration of oxygen and HO₂ (O₂^–) radicals during the spike, after which the positive feedback does not allow the system to return back to the initial steady state. In practice, this effect can be caused by phenomena associated with local irregularities in the reactor core: the composition and dose rate of reactor radiation, the presence of steam–gas bubbles due to local subcooled nucleate boiling of the coolant in the core, and the perturbation of the water radiolysis mechanism at the surface of fuel rods because of an increased contribution of heterogeneous reactions etc.     

Effect of the degradation of ion-exchange resins on the quality of high-purity water prepared by ion-exchange deionization

In the course of water deionization on ion-exchange filters of mixed action, charged with a mixture of KU-2×8 ch.s. cation exchanger and AV-17×8 ch.s. anion exchanger, which are ion-exchange resins of nuclear class, the water being treated is contaminated with soluble organic substances originating from degradation of the resins. Their concentration can reach 20 µg L–1, gradually decreasing to 5–6 µg L–1. Procedures were suggested for determining soluble organic substances washed out from the ion-exchange filters, including gravimetric determination of their sum in aqueous extracts from the organic ion exchangers, spectrophotometric determination in water being purified on the ion exchangers, and preconcentration of electrically charged forms of soluble organic substances by electroosmosis.     

Selective separation of water–alcohol binary mixture through poly(maleimide-co-acrylonitrile) membrane

Separation of various alcohols and water through a membrane was carried out by means of a hydrogen-bonding interaction. A membrane obtained from poly(maleimide-co-acrylonitrile) was effective for a selective separation of water from aqueous alcohol solution by pervaporation technique. Spectroscopic analyses verified that this high selectivity was attributed to the hydrogen-bonding interaction between water and maleimide units in the membrane.     

Permselectivity, solubility and diffusivity of propyl propionate/water mixtures in poly(ether block amide) membranes

This work is concerned with the separation of propyl propionate/water mixtures by pervaporation using PEBA membranes, which is relevant to aroma compound recovery from dilute aqueous solutions. The solubility and diffusivity pertinent to the permselectivity were investigated. The effects of feed concentration and the operating temperature on the separation performance were studied. Under the experimental conditions tested, the permeate concentration was much higher than the solubility limit, and upon phase separation substantially pure propyl propionate could be achieved. The diffusivity of propyl propionate through the membrane from its dilute aqueous solutions was affected by the solution concentration exponentially. It was shown that the permselectivity of the membrane for propyl propionate/water separation was mainly derived from its sorption selectivity due to the organophilicity of the membrane. The diffusivity of pure propyl propionate in the membrane was about 28 times higher than pure water diffusivity.     

Speciation and analysis of corrosion products in the primary coolant of pressurized water reactors

The procedure involves separate sampling and determination of the insoluble, cationic and anionic species of corrosion products (Fe, Ni, Cr, Mn, Co, Zn, Cu) in the primary coolant of pressurized water reactors (PWRs) with concentrations in the range 0–2000 mg l^?1 boron and 0–5 mg l^?1 lithium. Samples of coolant (0.2–1 l) are passed through packs consisting of one 0.45-μm filter paper, one cation-exchange membrane (Whatman SA-2) and one anion-exchange membrane (Whatman SB-2). The membranes are examined by wavelength-dispersive x-ray spectrometry. Selection of the ion-exchange membranes and the influence of the boron and lithium concentrations (and pH) on retention of soluble species are discussed. With sample volumes of 0.5 l, the detection limits are between 0.05 and 0.3 μg l^?1 for undissolved species and from 0.03 to 0.14 μg l^?1 for ions. Data collected during a PWR shutdown procedure are summarized.     

Selective separation of water–ethanol mixture through synthetic polymer membranes having carboxylic acid as a functional group

Separation of water–ethanol mixture through a membrane was carried out by pervaporation using a membrane which provided a hydrogen-bonding interaction. A membrane obtained from poly(acrylic acid-co-acrylonitrile) was effective for a selective separation of water from aqueous ethanol solution by pervaporation technique. Spectroscopic and flux analyses verified that this high selectivity toward water was attributed to the hydrogen-bonding interaction between water and acrylic acid (carboxylic acid) unit in the membrane. On the other hand, a membrane from poly(acrylic acid-co-styrene) preferentially permeated ethanol in the low water feed concentration region.     

乙二醇基冷却液污染对质子交换膜燃料电池电堆的影响及恢复措施

冷却液作为燃料电池冷却系统的热传导介质,对于燃料电池电堆的热管理非常重要。在实际应用中经常会发生冷却液泄漏进入电堆内部的情况。本文通过模拟燃料电池发动机正常工作过程中冷却液泄漏的不同情况,研究了乙二醇基冷却液泄漏污染对燃料电池电堆的性能影响。针对阴极侧乙二醇基冷却液污染后难以恢复的问题,本文提出了一种冷却液污染的恢复策略。整个污染恢复策略分为污染物氧化和污染物冲洗两个阶段,通过对比冷却液污染前和污染恢复后的性能,证实了这种冷却液污染恢复策略的有效性。     

Determination of dissolved and particle-bound PCB congeners at ultra-trace concentrations in water

Adsorption of 10 PCB congeners in aqueous solutions on glass-fibre filters taken from different boxes but of the same type were not significantly different. The standard deviations using filters from the same box were below 10% at concentration levels of 4.1?ng?L^?1. At this level, the adsorption of dissolved PCB at the filters was in the range of 5–20% depending on the congener. This led to a procedure for determination of dissolved and particle-bound congener in authentic landfill leachate, which included correction for adsorption losses. The procedure was based on filtration through glass-fibre filters, followed by trapping of the PCB in the eluate on solid-phase extraction (SPE) disks. After separate supercritical fluid (SFE) extractions, with carbon dioxide, of the filters as well as of the SPE disks, the extracts were analysed on a two-column capillary GC-ECD system. Corrections for congener adsorption on glass-fibre filters were made, from which corrected distribution constants between particle-bound and dissolved PCB congener in the water phase could be obtained for authentic landfill leachate. These values (10⁴–10⁵) agreed well with those obtained by others.     

Gravitational effects on transmembrane flux: the rayleigh—taylor convective instability

Using a cell with horizontally mounted membranes, volume flux was measured as a function of gravitational geometry. Water was placed on one side of the membrane. The opposite side of the membrane was exposed to either aqueous glucose solutions, with densities greater than water; or aqueous ethanol, less dense than water; or ethanol—glucose—water solutions. In all cases, the osmotic pressure gradient generated volume flux from water to the solution. No mechanical stirring was used.Experiments were performed first with water above the membrane and the solution below it. They were then repeated with water below and the solution above the membrane. In all cases, volume flux was significantly larger when the denser liquid was above the membrane.Mach—Zehnder interferograms were obtained for the interface region of the water—membrane—0.1 M glucose system, Results show directly that boundary layers are substantially larger and more uniform with the lower-density liquid above the membrane than with the opposite geometry.These experimental findings are interpreted in terms of a convective gravitational instability that reduces boundary layer dimensions and increases volume flux. Following Rayleigh—Tavlor analysis of fluid gravitational stability, a concentration-gradient Rayleigh Number is developed and used in a mathematical model for gravitationally sensitive volume flux.