Investigation of Electrokinetic Decontamination of Concrete

Abstract

Experiments have been conducted to investigate the capabilities of electrokinetic decontamination of conceret. Batch equilibration studies have determined that the loading of cesium and strontium on concrete may be decreased using electrolyte solutions containing competing cations, while solubilization of uranium and cobalt, that precipitate at high pH, will require lixiviants containing complexing agents. Dynamic electrokinetic experiments showed greater mobility of cesium than strontium, while some positive results were obtained for the transport of cobalt through concrete using EDTA and for uranium using carbonate.

     

Electrochemical Analysis of Ion-Exchange Membranes with Respect to a Possible Use in Electrodialytic Decontamination of Soil Polluted with Heavy Metals †

Abstract

Transport numbers in different metal chloride solutions were estimated using the emf method for two ion-exchange membranes: Ionics CR67 HMR412 (cation-exchange membrane) and Ionics AR204 SXRA 7639 (anion-exchange membrane). The cation-exchange membrane was found to work nearly ideally for NaCl and CaCl₂ solutions even at high concentrations, whereas deviation from ideality was seen for ZnCl₂ and CuCl₂ solutions. The anion-exchange membrane showed transport numbers for the anion around 0.95 for NaCl, CaCl₂ and ZnCl₂ solutions for the concentration range investigated. Electrodialytic desalting experiments taken as a simplified simulation of the electrokinetic decontamination method showed that it was possible to remove all ions in the simulated soil volume, with a sharp increase in the potential difference over the soil volume as a result, and that it was possible to control the metal content in the different solutions in the electrodialytic decontamination method.

     

Caustic Recycle from Hanford Tank Waste Using NaSICON Ceramic Membranes

Abstract

A sodium (Na) Super Ion Conductor (NaSICON), has been studied at Pacific Northwest National Laboratory (PNNL) to investigate its ability to separate sodium from radioactively contaminated sodium salt solutions for treating U.S. Department of Energy (DOE) tank wastes. Ceramatec Inc. developed and fabricated a membrane disk containing a proprietary NAS-GY material formulation that was electrochemically tested in a bench-scale apparatus with both a simulant and a radioactive tank-waste solution to determine the membrane performance when removing sodium from DOE tank wastes.

Implementing this sodium separation process can result in significant cost savings by reducing the disposal volume of low-activity wastes and by producing a 19 M NaOH feedstock product for recycle into waste treatment processes such as sludge leaching, regenerating ion exchange resins, inhibiting corrosion in carbon-steel tanks, or retrieving tank wastes.

In actual waste tests, average sodium transport rates of 10.3 kg/day/m² were achieved at average sodium transport efficiencies of 99%. The membrane was found to be highly selective to sodium ions resulting in no detectable cation transport except Na and a small quantity (0.04% to 0.06%) of ¹³⁷Cs. An average decontamination factor of 2000 was observed with respect to ¹³⁷Cs. As expected, Gibbsite precipitation was observed as OH^? ions were depleted from the tank waste.     

Studies of Ion Transport through a Liquid Membrane by Using Crown Ethers

Abstract

Studies on ion transport through a liquid membrane system composed of two extraction processes have been carried out. Kinetic models based on extraction processes with consideration of the controlled parameters were developed for mediated ion transport through liquid membranes, especially those using crown ethers as the ion carrier. A study of the concentration change in the receiving or source phase envisages the determination of the equilibrium constant by a kinetic method corresponding to the chemical reaction at the interface as well as the maximum initial flux through the membrane. The equilibrium constant values determined by the kinetic process were checked by the solvent extraction method.     

Separation of Organic Dyes from Wastewater by Using Colloidal Gas Aphrons

Abstract

Auxiliary chemicals used in the preparation of water-based dyes have been reported to pose problems in conventional wastewater treatment processes. The dye manufacturing industries have to find alternate wastewater treatment processes to remove dyes from their waste effluents. This paper investigates a novel method of separation of dyes by flotation using colloidal gas aphrons (CGAs). The results indicate that this is an effective method for the separation of synthetic dyes from wastewater. The mechanism of removal has been shown to be ion coupling of the oppositely charged species of the surfactant forming the CGA and the dye and flotation of the ion-dye complex on the surface of CGA microbubbles.     

Application of Single-Ion Activity Coefficients to Determine the Solvent Extraction Mechanism for Components of High-Level Nuclear Waste

Abstract

The TRUEX solvent extraction process is being developed to remove and concentrate transuranic (TRU) elements from high-level and TRU radioactive wastes that are currently stored at U.S. Department of Energy sites. Phosphoric acid is one of the chemical species of concern in the application of solvent extraction processes for removal of actinides, for instance at the Hanford site, where bismuth phosphate was used to recover plutonium.

The mechanism of phosphoric acid extraction with TRUEX-NPH solvent at 25°C was determined from phosphoric acid distribution ratios, which were measured by using a phosphoric acid radiotracer and a variety of aqueous phases containing different concentrations of nitric acid and nitrate. A model was developed for predicting phosphoric acid distribution ratios as a function of the thermodynamic activities of nitrate ion, and hydrogen ion. The Generic TRUEX Model (GTM) was used to calculate these activities based on the Bromley method. The derived model supports extraction by CMIO and TBP in TRUEX-NPH solvent of a phosphoric acid-nitric acid complex and a CMPO-phosphoric acid complex.     

Comprehensive modeling of chloride ion and water ingress into concrete considering thermal and carbonation state for real climate

This article presents a comprehensive modeling of temperature, carbonation, water and chloride ions transport in cover concrete using the transport model “TransChlor”. The TransChlor transport model employs weather data and chloride ion concentrations present on the concrete surface to predict the temporal and spatial evolution of the presence of chloride ion concentrations in the cover concrete pores. The main features of the TransChlor model are presented and validated.The TransChlor model has been calibrated using experimental data on liquid water movement in concrete of different permeabilities under realistic microclimatic conditions. Chloride ion transport is validated by means of experimental results obtained from a newly developed chloride ion optical fiber based sensor.     

Selective Metal Ion Sorption and Transport Using Polymer Inclusion Membranes Containing Dicyclohexano-18-crown-6

Abstract

A novel polymer material composed of cellulose triacetate as support, o-ni-trophenyl octyl ether as plasticizer (solvent), and dicyclohexano-18-crown-6 as carrier was investigated as a solid extractant for metal ion sorption and as a membrane material for ion transport. Selective extraction and transport of Pb(II), Ga(III), and Fe(III) were observed. The influence of the source solution counterion on sorption and transport processes was investigated. The transport mechanism is discussed in terms of diffusion coefficients (D) and extraction constants (K ₁). A diffusion-limited transport model has been found to accurately describe metal ion transport by dicyclohexano-18-crown-6 in these systems. The membranes are easy to prepare in the laboratory, and they may be useful in separation and concentration procedures.     

Quantitative Description of Ion Transport in Donnan Ion Exchange Membrane Systems

Abstract

Presented are simplified mass transfer techniques describing the transfer of ions in continuous ion selective membrane systems in which the resistance to ion transport through the membrane is Small in relation to the resistance to ion transport in the solution phase. Methods are developed through the application of the transfer unit concept to the Donnan equilibrium. This equilibrium describes the equilibrium ion concentration on either side of an ion selective membrane. Data from one cation selection system is presented as evidence of the validity of these methods. Further techniques are shown that will allow the determination of ion transport given only equipment parameters and solution diffusivities. Supporting data are shewn.     

A Funtadamental Study on Particle Transport Through Rotary Dryers for Flight Design and System Optimisation

ABSTRACT

A model for particle transport in a flighted horizontal rotary dryer is developed in this paper. Mathematical principles applied to the current study are in the areas of differential calculus and analytical geomentry. In contrast to the conventional approaches which are either based on mpirical/semi-empirical correlations or obtained from the investieation of single particle trajectories, this paper develops rigorous mathematical analysis of the transport of bulk solids. A variety of important issues in rotary drying, such as axial flowrate of solids, retention time distribution and solid holdup are addressed and treated by using non-traditional methods. Since the model takes dimension, number and geometry of flights into account, it possesses the following two haracteristics : (1) it is not only useful in the study of rotary drying dynamics, but lso applicable to other processes employing flighted rotating cylinders (such as granulation drumsand crushers) and (2) based on the model, an optimal drum configuration can be designed by using optimisation techniques. The model can be incorporated within a distributed arameter dryer model developed previously to form a more rigorous integrated dynamic model. A heoretical foundation for optimal flight design by using the current model is explained.

A pilot scale perspex rotary dryer equipped with a video camera has been constructed and used for model validation. Raw sugar was handled in the experiments. Particle transport was observed and measured by using a flow visualisation technique supplemented with traditional sampling methods. A significant model quality improvement has been observed through a comparative study between the newly developed model and conventional ones.     

Decontamination of radioactive concrete using electrokinetic technology

The experimental results of the electrokinetic decontamination with 0.01 M of nitric acid were that the cesium ions were removed by up to 52% from the concrete after 15 days, also the cobalt ions were only removed by up to 0.7%. The concrete should be washed with H₂SO₄ as a pretreatment before electrokintic decontamination to lower its pH below 4.0. The removal efficiencies of ⁶⁰Co and ¹³⁷Cs by nitric acid were increased by 3.1 and 2.5% more than those by acetic acid. The larger the particle size of the concrete, the more the removal efficiencies of ⁶⁰Co and ¹³⁷Cs were increased. Also, the removal efficiencies of ⁶⁰Co and ¹³⁷Cs by the application of an electric current of 20 mA/cm² were increased by 1.6 and 3.9% more than those by the application of 10 mA/cm². The removal efficiencies of ⁶⁰Co and ¹³⁷Cs from the radioactive concrete of 1,940 Bq/kg were 99.8 and 92.3% by electrokinetic decontamination after pretreatment by the application of an electric current of 20 mA/cm² for 25 days.     

Fluid Mechanics–Foam Flotation Interactions

Abstract

Foam flotation methods have been used for years for ore concentration and show considerable promise for the removal of a variety of pollutants from wastewaters. However, scant attention has been given to the critical interaction in these processes of surface chemistry and fluid mechanics. A numerical model of an air bubble with an attached floc particle rising in a Stokes flow regime through a liquid pool at the bottom of a batch foam flotation column was developed. This model computed the viscous forces acting to separate the bubble and particle, and these forces were compared with those given by previous investigators. This research demonstrates that, while previous methods have correctly estimated the magnitudes of the viscous forces, they have failed to correctly estimate the directions. Based on the results of this work, a much simpler model for describing the interaction of fluid mechanics and surface chemistry in particle attachment to bubbles in foam flotation columns is suggested.     

Sorption of 239Np and 235U Fission Products by Zeolite Y,Mexican Natural Erionite,and Bentonite

Abstract

Zeolite Y, erionite, and bentonite have been used in this work to remove ²³⁹Np and ²³⁵U fission products from aqueous solutions at various pH values. It was found that the sorption of fission products by aluminosilicates takes place by different mechanisms, mainly ion exchange, precipitation, and electrostatic surface interaction. The radio nuclides content was determined by γ-spectrometry, and x-ray diffraction was used to learn whether the solids maintained their crystallinity at different pH values.     

General Survey of Adsorptive Bubble Separation Processes

Abstract

In this article we present a general survey of adsorptive bubble separation processes. These separation methods involve the use of selective adsorption at gas-liquid interfaces, the interfaces being generated by gas bubbles in aqueous media. A variety of processes based on this mechanism have been developed, and these methods are described in this review. The underlying concepts in this field are then explored so that the similarities between the methods can be seen. Engineering applications, as well as our own work on analytical applications, are presented. Suggestions are also made as to future potentialities for these adsorptive bubble separation processes. Finally, to place these methods in proper perspective, the techniques are compared to such widely used processes as ion exchange and liquid-liquid extraction.     

Cyclic Separation Processes

Abstract

This review covers cyclic separation methods used for adsorption, ion exchange, and chromatographic separation processes where the cyclic parameter is a thermodynamic variable which changes the equilibrium distribution coefficients of the solutes. The cyclic methods reviewed include heatless or pressure-swing adsorption, parametric pumping, and cycling zone adsorption. These cyclic techniques have been studied as a possible preparative chromatographic separation method or for continuous production from adsorption or ion exchange columns.     

An Electrokinetic Study on the Oil Flotation of Oxidized Coal

Abstract

The objective of this investigation was to study the electrokinetic behavior of oxidized coals and of hydrocarbon emulsion droplets of flotation reagents to indicate the feasibility of separating the oxidized coals from ash materials and pyrite by an oil flotation process. The effects of surfactants and hydrolyzed metal ions were also included. The electrokinetic behavior of the oxidized coals and the hydrocarbon emulsion droplets were studied by an electrophoresis technique. Generally the isoelectric point (IEP) of the coals decreased with increasing degree of oxidation.

A model of selective flotation of oxidized coal is postulated on the basis of the electrokinetic results. This model simply states that in the presence of a suitable amount of collector and frother, the optimal selective flotation of oxidized coal will occur at the IEP of the oxidized coal. To achieve this condition at the coal surface, it is necessary to adsorb heavy metal hydroxide ions prior to flotation and to absorb hydrocarbon oil droplets containing positively charged organic functional groups during flotation. Oxidized coal becomes more hydrophobic at its IEP because most of its surface is relatively non-polarizable. In contrast, pyrite and ash minerals have relatively polarizable surfaces and remain in suspension even when they are at an IEP.     

Manganese Removal from Water by a Precipitate Flotation Technique

Abstract

Microgas dispersions were used to remove manganese from dilute aqueous solution by a precipitate flotation technique. Manganese in its coagulated oxide form is difficult to remove from water by other methods, such as filtration. Flotation processes appear to be more suited to continuous manganese dioxide removal than other conventional methods. Taking advantage of the tendency for manganese dioxide to coagulate, manganese removals as high as 98% were observed for continuous flotation when the metal was present in only trace quantites (2 to 5 mg/L).     

Electrical Aspects of Adsorbing Colloid Flotation. Y. Nonideal Flocs and Salts

Abstract

Three methods are developed for the calculation of adsorption isotherms in precipitate and adsorbing colloid flotation. The Gouy-Chapman model is used in all three, with corrections for the effective volumes of the ions in the ionic atmosphere and of the floc particles. The theories all predict a weak dependence of adsorption isotherm on temperature and a stronger dependence on ionic strength; increasing either variable decreases the surface adsorption. The effects of film surface potential, floc zeta potential, ion and floc effective volumes, and floc-floc screening are examined.     

Analysis of Fluidized Beds for the Simultaneous Aerosol Separation and Heat Recovery

Abstract

A mathematical model is developed to describe the performance of fluidized beds for the simultaneous heat recovery and aerosol separation. This new concept is analyzed in light of the various transport processes taking place within the bed. A two-phase model is developed for the system in which heat and aerosol particles are transferred from the bubble phase to the emulsion phase. In addition to aerosol separation via diffusion, interception, impaction and electrostatic precipitation, thermophoretic collection is also analyzed. The results indicate that high thermal and separation efficiencies can be obtained.     

Ion Exchange in Selected Low Rank Coals. Part II: Kinetics

ABSTRACT

The kinetics of ion exchange in a subbituminous coal have been investigated. The rate determining step in the exchange processes was determined to be intraparticle diffusion for particle sizes of 9,500 × 4,000 μm, 425 × 250 μm and 180 × 125 μm. The kinetics of exchange for the 180 × 125 μm particles was very rapid and approached film diffusion control. A relatively simple mathematical model developed by Helfferich (1) describe adequately ion exchange kinetics. The model was effective in predicting the extent of exchange as a function of time and the time required to reach complete exchange. Interdiffusion coefficients at 298 K obtained from the model for exchange of H for Na ⁺, Mg²⁺and Ca²⁺ranged from 2.0 × 10^10?6to 2.6 × 10^?8cm²/s with the values decreasing in the order:

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