Purification of Radioactive Wastes by Low Temperature Evaporation (Membrane Distillation)

Abstract

A method of radioactive waste concentration by membrane distillation is presented. Water flow through a hydrophobic membrane results from the temperature gradient between membrane surfaces which are in contact with two waste streams, warm and cold. A transport of water from the warm to the cold stream occurs and radionuclides and other impurities are concentrated in the warm stream (retentate).     

Teaching a new technology,eutectic freeze crystallization,by means of a solved problem

A solved design problem of how to deal quantitatively with crystallization problems below the eutectic temperature is presented. This problem serves as an excellent pedagogic complement to undergraduate students of chemical engineering since it is solved by means of a solubility diagram. It also promises novelty and environmental improvement to students, exposing them to eutectic freeze crystallization (EFC) technology, which is gaining momentum to be implemented in waste water treatment. By means of mass balances together with the solubility diagram, the proposed problem involving two crystallizers and a recycle stream is solved, and in so doing teaches students about the possible application of EFC in the treatment of brines.     

A review on membrane distillation in process engineering: design and exergy equations,materials and wetting problems

One of the problems that most afflicts humanity is the lack of clean water. Water stress, which is the pressure on the quantity and quality of water resources, exists in many places throughout the World. Desalination represents a valid solution to the scarcity of fresh water and several technologies are already well applied and successful (such as reverse osmosis), producing about 100 million m³·d⁻¹ of fresh water. Further advances in the field of desalination can be provided by innovative processes such as membrane distillation. The latter is of particular interest for the treatment of waste currents from conventional desalination processes (for example the retentate of reverse osmosis) as it allows to desalt highly concentrated currents as it is not limited by concentration polarization phenomena. New perspectives have enhanced research activities and allowed a deeper understanding of mass and heat transport phenomena, membrane wetting, polarization phenomena and have encouraged the use of materials particularly suitable for membrane distillation applications. This work summarizes recent developments in the field of membrane distillation, studies for module length optimization, commercial membrane modules developed, recent patents and advancement of membrane material.     

A novel scraped cooled wall crystallizer: Recovery of sodium carbonate and ice from an industrial aqueous solution by eutectic freeze crystallization

A novel scraped cooled wall crystallizer (SCWC-2) with 130 l capacity and total heat transfer area of 2.94 m² m⁻³ crystallizer volume was specifically designed for eutectic freeze crystallization (EFC). It has been successfully tested for the recovery of Na₂CO₃ from an industrial solution. Compared with earlier designs this new crystallizer shows a high improvement in gravitational separation and ice scaling removal. High heat transfer fluxes between the heat exchanger and the solution (up to 10.5 kW m⁻²) were obtained and as a consequence high production rates were achieved.     

Conductivite et viscosite des systemes composes du melange eutectique NH4NO3LiNO3NH4Cl et d'eau

The conductivity, the specific mass and the viscosity of mixtures of water and the eutectic system NH₄NO₃LiNO₃NH₄Cl have beem measured at concentrations ranging from dilute aqueous solutions to the pure molten salt. The conductivity reaches a maximum value at a molar fraction of water (X_H2O) of 0.835. The viscosity of the mixtures raises strongly from X_H2O = 0.2 to X_H2O = 0, the Walden product remains approximately constant from X_H2O 1 to X_H2O = 0.2. The results are discussed, the water content at the conductivity maximum is sufficient to ensure the primary hydration of all the ions of the solution.     

Solubility of Na2SO4, Na2CO3 and their mixture in supercritical water

The solubility of many salts in water decreases dramatically with temperature in the vicinity of the critical point of pure water. Examples of these salts are sulfates of sodium, potassium, lithium and sodium carbonate. These salts are usually produced during supercritical water oxidation (SCWO) and contribute to fouling. The solubility of Na₂CO₃ and Na₂SO₄ has been determined in pure form and in the presence of each other, for the temperature range relevant to SCWO. The experimental procedure was to pass the salt solution through a tube at constant temperature. After a brief initiation period during which no salt sticks to the tube, the salt above the solubility limit deposited on the tube surface. The solution leaving the section was thus at the solubility limit. A rapid decrease in the salt solubility was observed just above the pseudo-critical temperature. For supercritical conditions, the solubility of each salt in the form of a mixture was quite close to the solubility of pure salt. At the highest fluid density considered (480 kg/m³) the presence of Na₂CO₃ reduces the solubility of Na₂SO₄, as might be expected from the “common-ion effect”.     

Calculation of composition in LaB6-TiB2 and LaB6-ZrB2 eutectics by means of pseudopotential method

A method of aprioristic pseudo-potential and an internal energy of individual components of composite materials are introduced that allows prediction of eutectic composition for the eutectic invariant point of LaB₆-TiB₂ and LaB₆-ZrB₂ system. The numerical predictions agreed well with the experimental data for eutectic composition. We determined the crystal lattice parameters and demonstrated the insolubility of the constituent phases of LaB₆-TiB₂ and LaB₆-ZrB₂ eutectic systems. The experimental results validated the predictions for the lattice constants of the constituent phases. The transferability of these potentials by including kinetic energy components has been discussed.     

Synthesis of highly efficient,structurally improved Li4SiO4 sorbents for high-temperature CO2 capture

Li₄SiO₄ sorbents for high-temperature CO₂ removal have drawn extensive attention owing to their potential application in carbon capture and storage (CCS). The major challenge in the application lies in the poor CO₂ capture performance under realistic conditions of low CO₂ concentrations, owing to the dense structure and poor porosity. In this work, Li₄SiO₄ sorbents were prepared with porous micromorphologies and large contact areas using a variety of organometallic Li-precursors, achieving fast CO₂ sorption kinetics, high capacity and excellent cyclic stability at a low CO₂ concentration (15?vol%). It was found that a high conversion of ~?74% was maintained for pure Li₄SiO₄ even after 100 sorption/desorption cycles. Moreover, by doping with Na₂CO₃ to reduce the CO₂ diffusion resistance, the conversion of the sorbent was further enhanced to 93.2%. The enhancement mechanism of alkali carbonate have been proven here to be ascribed to the formation of the eutectic melt of Li/Na carbonates, the existence and function of which has been confirmed in this study.     

Reverse Osmosis Separation of Metal Ions in Acid Mine-Water

Abstract

Cellulose acetate membranes obtained from Osmonics Inc. were characterized in terms of pure water permeability constant, solute transport parameter, and mass transfer coefficient with the reference system of aqueous sodium chloride solution. Reverse osmosis separation behavior of Ca, Mg, Zn, Mn, Cu, Al, and Fe as nitrate, chloride, and sulfate salts was studied. The effect of the addition of sodium sulfate to Mg(ClO₄)₂ and Mn(NO₃)₂ solutions on solute separation was also investigated. Acid mine-water obtained from New Brunswick was subjected to reverse osmosis, and separation of metal ions in the range of 95 to 99 % was obtained along with the recovery of product water of suitable quality for use in recycle operations.     

Processing,microstructure and performance of Al2O3/Er3Al5O12/ZrO2 ternary eutectic ceramics prepared by laser floating zone melting with ultra-high temperature gradient

Directionally solidified Al₂O₃/Er₃Al₅O₁₂(EAG)/ZrO₂ ternary eutectic/off-eutectic composite ceramics with high density, homogeneous microstructures, well-oriented growth have been prepared by laser floating zone melting at different solidification rates from 4 to 400 µm/s. Uniform and stable melting zone is obtained by optimizing temperature field distribution to keep continuous and stable eutectic growth and prevent from cracks and defects. The as-solidified composite ceramic exhibits complexly irregular eutectic structure, in which the eutectic spacing is rapidly refined but dotted ZrO₂ number inside Al₂O₃ phase is decreased as increasing the solidification rate. The formation mechanism of ZrO₂ distributed inside Al₂O₃ matrix is revealed by examining the depression of solid/liquid interface. Furthermore, after heat exposure 1500 °C for 200 h, the eutectic microstructure only shows tiny coarsening, which indicates it has excellent microstructural stability. As increasing the ZrO₂ content, the fracture toughness can be improved up to 3.5 MPa m^1/2 at 20.6 mol% ZrO₂.     

反渗透工艺浓盐水回配应用

每台反渗透装置可生产除盐水60t／h,但需排出浓盐水20t／h。为了减少废水排放,对设备进行了改造,将1／2浓盐水回刚到反渗透装置的给水中。改造后反渗透工艺运行稳定,出水指标达到国家标准,可节约地下水20t／h,达到r竹能减排与环保增效的目的。     

Improvement of electrochemical stability of LiMn2O4 by CeO2 coating for lithium-ion batteries

CeO₂-coated LiMn₂O₄ spinel cathode was synthesized using two-step synthesis method. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The results of the electrochemical performances on CeO₂-coated electrode are compared to those of electrodes based on LiMn₂O₄ spinel without CeO₂ coating. CeO₂-coated LiMn₂O₄ cathode improved the cycling stability of the electrode. The capacity retention of 2 wt% CeO₂-coated LiMn₂O₄ was more than 82% after 150 cycles between 3.0 and 4.4 V at room temperature and 82% after 40 cycles at elevated temperature of 60 °C. The amounts of dissolved manganese-ions in CeO₂-coated LiMn₂O₄ significantly are smaller than pristine LiMn₂O₄ systems especially at elevated temperatures. Surface-modified LiMn₂O₄ can suppress the dissolution reaction of manganese-ions at elevated temperature and clearly improve the cyclability of the spinel LiMn₂O₄ cathode materials.     

Thermodynamic properties of F-22(CHClF2) hydrate for use in desalting

In this study are reported the pressure-temperature phase diagrams of F-22 in both pure water and aqueous NaCl solutions in the region where the hydrate forms. From these data we have determined the hydrate decomposition conditions and the invariant points including the eutectic. These are the necessary thermo-dynamic data for evaluating F-22 as an agent for use in the hydrate process for desalination of sea water. Other thermal, mechanical, and economic properties of pure F-22 are well known, e.g. duPont data (1). Kinetic data on the rate of formation of the hydrate in a stirred reactor will be reported at a later date.     

Microstructure and cytotoxicity of Al2O3-ZrO2 eutectic bioceramics with high mechanical properties prepared by laser floating zone melting

Developing new generation of strong, tough and stable bioceramics used in dental filed has been highly desired for attaining the clinical requirement of secure and reliable therapy. In this paper, a novel Al₂O₃-ZrO₂ eutectic bioceramics with nearly fully density and extremely aesthetic luster was in-situ prepared by innovative laser floating zone melting (LFZM) method. The influence of solidification rates on microstructure evolution, mechanical properties and cytotoxicity was investigated. The eutectic bioceramics displayed a special three dimensional interpenetrating microstructure evolving with increasing the solidification rate. The eutectic colony structure occurred when solidification rate overpassed 8?µm/s, and lamellar spacing was below 1?µm when solidification rate exceeded 30?µm/s. The eutectic bioceramics solidified at 100?µm/s exhibited optimal mechanical properties with an average hardness of 16.53?GPa, fracture toughness of 6.5?MPa?m^1/2 and flexural strength of 1.37?GPa. The cytotoxicity of Al₂O₃-ZrO₂ eutectic bioceramics was evaluated by MTT methods according to ISO 10993-5 standard. Non-cytotoxic behavior was detected for the eutectic bioceramics, indicating this eutectic bioceramic could be used as promising dental restoration material.     

Structure of porous cellulose acetate membranes and a method for improving their performance in reverse osmosis

Experimental data support the hypothesis that the surface layer of the asymmetric Loeb-Sourirajan type porous cellulose acetate membranes has a heterogeneous microporous structure. A general method is proposed for improving the performance of the above membranes in reverse osmosis, by which product rates are increased without decreasing solute separation. The method consists in pumping pure water past the back side of the membrane under just enough pressure for a sufficiently prolonged period of time; after such pretreatment, the membrane is used in the reverse osmosis experiments in the normal manner with the surface layer facing the feed solution. Back-pressure treatment at 400 psig for 85 hr on preshrunk and normally pressure-treated membranes increases the product rate by over 20% without decreasing solute separation in reverse osmosis experiments at 600 psig with the use of 0.5 wt-% NaCl–H₂O feed solutions; with a different sequence of back-pressure treatment, similar results have been obtained in reverse osmosis experiments at 1500 psig also. The compaction effect of a normal membrane and that of a back pressure treated membrane are the same during continuous reverse osmosis operation under 600 psig; the effects of back-pressure treatment on a normal membrane and a compacted membrane are also the same. The pure water permeability data obtained in cyclic experiments show that the smaller pores on the surface layer are opened more than the bigger ones during the back side operation. The probable structural changes taking place in the film during back-pressure treatment are discussed.     

二氧化氯三相催化氧化法处理反渗透浓水试验研究

针对炼化企业污水回用装置反渗透单元浓水CODCr浓度高、难生化降解以及含盐量高等特点,利用ClO2三相催化氧化法处理反渗透浓水.试验结果表明:在催化剂存在条件下,催化剂的最佳活性组成为CuO/NiO/La2O3/CeO2,活性组分的最佳物质的量之比为3∶1∶2∶2;在反渗透浓水进水量为50 L/h、进水CODCr的质量...     

反渗透技术在废水处理中应用的研究进展

反渗透技术是一种高效、易操作的液体分离技术,同传统的废水处理方法相比具有处理效果好,可实现废水的循环利用和对有用物质回收等优点。文章简要介绍了反渗透技术的基本原理,重点介绍了反渗透技术在垃圾渗滤液、矿区污水、钢铁工业废水、电厂废水处理中的应用研究进展状况。并讨论了反渗透膜技术的预处理、反渗透膜污染及清洗和反渗透技术的发展前景。     

REVERSE OSMOSIS CONCENTRATION OF FLAVOR COMPONENTS IN APPLE JUICE-AND GRAPE JUICE-WATERS

Several flavor components including alcohols, aldehydes and esters were identified and quantitatively estimated, by gas chromatography, in membrane permeated apple juice- and grape juice-waters collected by reverse osmosis treatment of natural juices using cellulose acetate membranes. The flavor components present in the juice-waters so collected were then concentrated by reverse osmosis treatment of the latter at 5°C and 68.95 x 10² kPa gauge pressure (1000 psig) using aromatic polyamide membranes. It is shown that the concentrations of each flavor component in the concentrate and the permeate solutions obtained in the latter treatment are predictable from only a single set of experimental reverse osmosis data with a reference NaCl-H₂O feed solution for each membrane. This prediction technique is described, and its utility in reverse osmosis process design is illustrated.     

Fabrication of B4C from Na2B4O7 + Mg + C by SHS method

This paper deals with the formation of boron carbide (B₄C) powders from Na₂B₄O₇ + Mg + C system by self-propagating high-temperature synthesis (SHS) method. B₄C without impurities could be obtained after the acid enrichment and distilled water washing. The reaction mechanism of SHS of B₄C was proposed: the synthesis of B₄C is a process involving the decomposition of Na₂B₄O₇ into the intermediate phase B₂O₃, which reacts with Mg and carbon to form B₄C.     

The hydrolysis of halocarbon refrigerants in freeze desalination processes Part 1. Solubility and hydrolysis rates of Freon 114 (CClF2CClF2)

The solubility and rate of hydrolysis of Freon 114 (CClF₂ CCLF₂) have been measured over a range of conditions relating to secondary refrigerant freeze desalination technology. In this paper, results are presented for the solubility of gaseous Freon 114 between 0 and 50°C as a function of pressure in pure and saline water. The solubility of liquid Freon 114 has been calculated from vapor pressure data and Henry's law extrapolations. The magnitude of the calculated heat of solution is consistent with corresponding results for other fluorocarbon refrigerants. Semiempirical relations are also presented for solubility trends of fluorocarbon refrigerants as a function of molecular parameters of molar volume and polarizability. The very slow rates of hydrolysis of Freon 114 with and without catalysts have been followed with an ion selective membrane electrode which responds to fluoride ion activity. The significance of the results to the economics of refrigerant loss in freeze desalination plants is discussed. On the basis of the measured hydrolysis rates and estimated residence times based on feed flow for a typical plant, it is concluded that economic losses resulting from hydrolysis of Freon 114 would amount to less than 0.001¢ (U.S.) per 1000 gallons.