Studies on the Recovery of Uranium from Phosphoric Acid Medium by D2EHPA/n-Dodecane Supported Liquid Membrane

Abstract

Present studies deal with the application of supported liquid membrane (SLM) technique for the separation of uranium (VI) from phosphoric acid medium using Di-2 ethyl hexyl phosphoric acid (D2EHPA)/n-dodecane as a carrier and ammonium carbonate as a receiving phase. The studies involve the investigation of process controlling parameters like feed acidity of phosphoric acid, carrier concentration, stripping agents, and the effect of thickness and the pore size of the membrane. The transport of uranium decreases with increase in the concentration of phosphoric acid in feed solution whereas it increases with increase in carrier concentration in supported liquid membrane. More than 90% uranium (VI) is recovered in 360 minutes using 0.5 M D2EHPA/dodecane as carrier and 0.5 M ammonium carbonate as stripping phase from the 0.001 M H₃PO₄ feed. Lower concentration of phosphoric acid and higher carrier concentration is found to be the most suitable condition for maximum transport of uranium (VI) from its lean sources like commercial phosphoric acid and analytical wastes generated from the analysis of uranium by Volumetric (Davis-Gray) method.     

Gravity Filtration with Accretion of Slurry at Constant Rate

Abstract

The separation of liquid from solid in many industrial effluents may be described by a physical theory developed originally to describe one-dimensional movement of water in a swelling soil. The theory makes use of measured hydraulic conductivity-liquid content, and liquid content-liquid potential relations. Both these functions have been found to be well defined, as required for their use in the theory.

The process of gravity filtration is explored in terms of this theory for vertical columns of effluent, to the top of which additional effluent is applied continuously at a constant rate, and from the bottom of which the liquid phase escapes through a membrane which prevents escape of the solid phase. The physics of the process is discussed, and illustrative calculations and experimental data are presented for one aspect of the process for which a quasianalytical solution is possible. The calculations are simplified using the flux-concentration relation of Philip.

The approach permits reliable calculation of the liquid-solid profile and the filtration rate for the process.     

Nanofiltration of Bleaching Pulp and Paper Effluents in Tubular Polymeric Membranes

Abstract

A systematic investigation of the nanofiltration (NF) of alkaline bleaching effluent (E₁) from the pulp and paper industry is carried out through a first assessment of NF of model systems, namely, solutions of salts—NaCl and Na₂SO₄—and organic solutes—glucose, saccharose, and raffinose—which develop membrane–solute(s) interactions similar to those developed by the bleaching effluent. The ampholytic polymer of the membrane active layer, under controlled feed conditions, develops a surface charge distribution which determines the membrane performance. The verification of the effects of the anion valence and the feed concentration on the salts rejections, in accordance with the Donnan exclusion principle, is an important feature of this work. For the bleaching effluent, the NF performance is strongly dependent on the pH due to the influence of this parameter on the membrane surface charge. The contribution of this work toward the optimization of the NF operating conditions would allow for future scale-up of this separation process for E₁ effluent purification and water recovery in the pulp and paper industry.     

Treatment of Liming Effluent from Tannery using Membrane Separation Processes

Abstract

A treatment method of liming effluent of a tannery is tested using hybrid membrane separation processes. The effluent after gravity settling and alum coagulation is subjected to ultrafiltration followed by nanofiltration. The optimum alum dose is obtained by analyzing the effluent using various concentrations of alum. The membrane separation processes are conducted in a continuous cross flow mode. The effects of operating conditions e.g., transmembrane pressure difference, and cross flow velocity (Reynolds number) on the permeate flux are analyzed. Effects of change in hydrodynamic conditions in various flow regimes, e.g., laminar, laminar with turbulent promoter, and turbulent flow on flux improvement have been studied. A resistance‐in‐series model for flux decline during the filtration process is proposed. COD, BOD, TDS, TS, pH, Ca²⁺ concentration, Cl^? concentration and conductivity are measured before and after each operation. The potential of the dried sludge as organic fertilizer is also explored.     

Improved U/Pu Separation in Pulsed Columns by Optimized Pulsation Conditions and Use of Two Consecutive Extraction Columns

Abstract

The separation of plutonium from uranium in the PUREX process was investigated in a pulsed column facility. The separation efficiency can be improved by optimization of the pulse conditions.

A further essential improvement was achieved by use of two consecutive electroreduction pulse columns. With this equipment excellent decontamination factors for Pu up to 500000 were measured and so the specification of the final uranium product was met in only one step. The required separation of the uranium from the plutonium product was achieved by a scrub part integrated in the first electroreduction column.     

SEPARATION OF IONIC SPECIES UNDER SUPERCRITICAL WATER CONDITIONS

ABSTRACT

The unique characteristics of supercritical water (SCW) offer potentially attractive processing options that can be explored for reaction and separation purposes. While supercritical water oxidation (SCWO) can achieve high organic conversion efficiencies, low and relative solubilities of inorganic species in SCW may be further utilized for in situ separation of potential by-products from the SCWO process effluent.

This paper describes a novel method for separating ionic species under SCW conditions. The concept is based on relative solubilities of different ionic species in SCW. Laboratory-scale demonstration tests were conducted with a Nylon monomer manufacturing process wastewater containing sodium hydroxide, sodium borate, carboxylic acids, and water. The process achieved (1) effective destruction (>99%) of organic components in the wastewater; (2) selective precipitation of sodium (>99.5%) as carbonates produced from oxidation of the organic components; and (3) efficient recovery of boron (>90%) as boric acid in the reactor effluent. The sodium removal efficiency is governed by the solubilities of sodium carbonates in SCW and, therefore, can be directly improved by increasing process temperature. As a result of the temperature increase, both organic destruction and boron recovery efficiencies may be enhanced.

This method of selective separation of ionic species in SCW has potential for a wide range of processing applications.     

Application of Extraction Chromatography to Nuclear Fuel Reprocessing

Abstract

The potentialities of applying extraction chromatography to the reprocessing of reactor fuels on an industrial scale have been investigated. The stationary phase was undiluted (100%) tri-n-butyl phosphate (TBP) and the mobile phases were nitric acid or nitrate salt solutions with or without reducing agents for plutonium.

Several extraction chromatographic processes for the recovery of nuclear grade uranium and plutonium are described. The flowsheets are based on a systematic determination of the distribution coefficients of relevant metal species (particularly those of uranium, neptunium, plutonium, americium, ruthenium, zirconium and niobium) in the chromatographic systems employed.

The Purochromex process developed for the recovery of uranium and plutonium from light-water reactor fuels and the Eurochromex process developed for the separation of highly enriched uranium from irradiated U/A1 alloy, U/Zr alloy and uranyl sulfate fuels have successfully been hot-tested on a laboratory scale and cold-tested on an “industrial scale.”

Some complementary studies related to the separation processes. such as radiation degradation of the stationary phase and the removal of tributyl phosphate from product and waste streams, are also described.     

Selective Cesium Removal from a Sodium Nitrate Aqueous Medium by Nanofiltration—Complexation

Abstract

In aqueous medium, selective complexation increases the ionic separation by nanofiltration. Within the context of the nuclear effluent treatment, the nanofiltration-complexation association is applied to sodium/cesium separation. Resorcinarene, a water-soluble ligand of cesium, is associated to the FILMTEC NF 70 membrane. Effects of pH, transmembrane pressure, ligand concentration, and ionic strength on salts retention and filtration fluxes are described. Finally, cesium complexation constants with resorcinarene are determined by using the nanofiltration-complexation process.     

Extraction of Uranium from Seawater Using Magnetic Adsorbents

Abstract

A new process for the extraction of uranium from seawater was developed. In the process, uranium adsorption is effected using powdered magnetic adsorbents; the adsorbents are then separated from seawater using magnetic separation technology. This process is superior to a column method using a granulated hydrous titanium oxide adsorber bed in the following ways: (1) a higher rate of adsorption is realized because smaller particles are used in the uranium adsorption; and (2) blocking, which is inevitable in an adsorber bed, is eliminated.

The composite hydrous titanium-iron oxide as a magnetic adsorbent having high uranium adsorption capacity and magnetization can be prepared by adding urea to a mixed solution of titanium sulfate and ferrous sulfate. Adsorption and desorption of uranium and the removal of the adsorbent using a small-scale uranium extraction plant (about 15 m³/d) is reported, and the feasibility of uranium extraction from seawater by this process is demonstrated.     

Partitioning of Actinides from High Level Waste of PUREX Origin Using Octylphenyl-N,N'-diisobutylcarbamoylmethyl Phosphine Oxide (CMPO)-Based Supported Liquid Membrane

Abstract

The present studies deal with the application of the supported liquid membrane (SLM) technique for partitioning of actinides from high level waste of PUREX origin. The process uses a solution of octylphenyl-N,N'-diisobutylcarbamoylmethyl phosphine oxide (CMPO) in n-dodecane as a carrier with a polytetrafluoroethylene support and a mixture of citric acid, formic acid, and hydrazine hydrate as the receiving phase. The studies involve the investigation of such parameters as carrier concentration in SLM, acidity of the feed, and the feed composition. The studies indicated good transport of actinides like neptunium, americium, and plutonium across the membrane from nitric acid medium. A high concentration of uranium in the feed retards the transport of americium, suggesting the need for prior removal of uranium from the waste. The separation of actinides from uranium-lean simulated samples as well as actual high level waste has been found to be feasible using the above technique.     

Affinity Dialysis–A Method of Continuous,Rapid Metal Ion Separation Using Dialysis Membranes and Selective,Water-Soluble Polymers as Extractants

Abstract

A membrane process utilizing dialysis and selective complexation by water-soluble polymers has been developed. This process, termed affinity dialysis, has been shown to selectively extract and concentrate both cations and anions in a manner similar to ion exchange or solvent extraction. The selective removal of calcium from sodium with selectivity of about 30, removal of chromate ion from dilute streams, and separation of transition metal ions such as Cu/Fe and Cu/Zn have all been successfully demonstrated. Effects of different polymers, polymer concentration, temperature, and flow rates have been studied. The effect of increased polymer concentration is to increase product concentration if appropriate changes in feed, polymer solution, and strip flow rates are made. A continuous polymer solution recycle and regeneration system has been constructed and operated with Cu/Zn and chromate/chloride feed streams. Removal of over 95% of the desired ion in one pass and concentration factors of product over effluent in excess of 100 have been achieved at feed flow rates of 24 gal/d. Product concentrations of greater than 3% from as little as 400 ppm feed have been demonstrated in a continuous process. In addition, the degree of polymer loss to the effluent stream has been shown to be less than 0.01%/d for a typical system. Metal removal from typical feeds is about 0.9 g/m² per 1000 ppm metal in the feed. It is expected that this technique may be useful in the separation of organic and biological materials, as well as for ionic species     

Separation of Uranium Isotopes by the Chemical Exchange Method

Abstract

The basic chemical process and technology for producing 3-5% enriched uranium has been established, through advances which allowed increases in the electron-exchange and adsorption-desorption reaction rates, effective uranium adsorption band formation and maintenance, reduction of the mobile-phase dispersion, and reduction in the height of the separation unit, which is largely determined by the diffusion coefficient, the electron exchange reaction rate of uranium ions, and the non-uniform flow pattern in the adsorption band. Physical theory and experimental results show the attainment of a specific separation power of approximately 500 SWU/m³·yr for the process, and the possibility of an enrichment cost of $41/SWU in its commercial-scale application as calculated with depreciation terms of 15 years for equipment and 45 years for buildings and interest payments at 8% on investment capital. Inherent advantages of the process, in addition to low enrichment cost, are simple, stable operation and facilitation of the nuclear fuel cycle, with efficient separation of uranium-235 from the other uranium isotopes of spent nuclear fuel and elimination of the need for UF₆ conversion.     

Studies on Concentration of Simulated Ammonium-diuranate Filtered Effluent Solution by Forward Osmosis Using Indigenously Developed Cellulosic Osmosis Membranes

In this study, we discuss the preparations of cellulosic membranes from cellulose acetate (CA), cellulose triacetate (CTA) and cellulose acetate blend (CAB) [blending of CA and CTA] systems and their potential for concentration of simulated ammonium-diuranate (ADU) effluent solution (only uranium and ammonium nitrate) by FO. The membranes are prepared using casting solution of polymers in mixed solvent systems with gelling in ice-cold water followed by annealing in 80°C hot water. Prepared membranes are characterized in terms of separation performance (tested under brackish water reverse osmosis test condition), water contact angle and surface average roughness. The performance of the membranes are evaluated in terms of volume reduction factor using solution of 40,000 ppm of NH₄NO₃ and 20 ppm uranium as feed and 320000ppm of NH₄NO₃ as draw solution. It is found that the volume reduction factor increases in the order of CTA<CAB<CA membranes. The effect of different draw solutions on volume reduction for the same system using CA membrane is also evaluated. Almost no leaching of uranium is found to the draw solution side for all the membranes. Possibility of using the FO process in a simpler way (as membrane pouch) to concentrate this simulated ADU filtered solution has been ascertained.     

Treatment of Leather Plant Effluent by Membrane Separation Processes

Abstract

A scheme is proposed for the treatment of the leather plant effluent using membrane based separation processes. The effluent coming out from the various upstream units of the leather plant (except chrome tanning) are combined and a two step pressure driven membrane processes involving nanofiltration (NF) and reverse osmosis (RO) are adopted after a pretreatment consisting of gravity settling, coagulation, and cloth filtration. The entire membrane separation scheme is validated by conducting experiments under a continuous cross flow mode. A detailed parametric study for cross flow experiments is investigated to observe the effects of the operating conditions, i.e., the transmembrane pressure drop and the cross flow velocity on the permeate flux and quality for both NF and RO. Using a combination of osmotic pressure and solution diffusion model for both NF and RO, the effective osmotic pressure coefficient, solute diffusivity, and the solute permeability through the membrane are obtained by optimizing the experimental permeate flux and concentration (in terms of total dissolved solids) values for this complex industrial effluent. The BOD and COD values of the finally treated effluent are well within the permissible limits (in India).     

Extraction Behavior of Uranium(VI) with Polyurethane Foam

Abstract

The extraction of uranium(VI) from aqueous solution with polyether-based polyurethane (PU) foam was studied. The effects of the kinds and concentrations of nitrate salts, uranium(VI) concentration, temperature, nitric acid concentration, pH, the content of poly(ethylene oxide) in the polyurethane foam, and the ratio of PU foam weight and solution volume on the extraction of uranium(VI) were investigated. The interferences of fluoride and carbonate ions on the extraction of uranium(VI) were also examined, and methods to overcome both interferences were suggested. It was found that no uranium was extracted in the absence of a nitrate salting-out agent, and the extraction behaviors of uranium(VI) with polyurethane foam could be explained in terms of an etherlike solvent extraction mechanism. In addition, the percentage extraction of a multiple stage was also estimated theoretically.     

Zirconium and Hafnium Separation,Part 3. Ligand‐Enhanced Separation of Zirconium and Hafnium from Aqueous Solution using Nanofiltration

Abstract

Membrane filtration equipment was used to evaluate zirconium and hafnium separation efficiency by a membrane separation process. High rejection of Zr and Hf species in aqueous solution were obtained with nanofiltration and ultrafiltration membranes. This high rejection could be explained by the formation of high molecular weight polynuclear species. Enhanced transportation across the nanofiltration and ultrafiltration membranes was observed when aminocarboxylic ligands, like EDTA, were introduced in the solution. This enhancement could be explained by a depolymerization process of the polynuclear complexes induced by the ligands. The rejection of Zr and Hf was markedly influenced by the counter anions and the EDTA/metal ratio. By using Zr and Hf oxynitrates instead of oxychlorides a difference of rejection of up to 20% was observed for Zr and Hf indicating that the membrane separation process could be an alternative process for Zr and Hf separation.     

Numerical Simulation of Uranium Extraction from Nitric Acid Medium Using Hollow-Fiber Contactor

ABSTRACT

A two-dimensional axisymmetric computational fluid dynamics (CFD) model is presented to simulate uranium extraction from nitric acid medium using tri-n-butyl phosphate in n-dodecane in a hollow-fiber membrane contactor operated in non-dispersive solvent extraction mode. CFD model solves continuity and momentum-transport equations for the feed and shell sides and species transport equations for the feed side, shell side, as well as the membrane. Complex boundary conditions of flux continuity and concentration jump are implemented in the CFD model. The estimates of percentage of uranium extraction obtained from CFD simulations for different parametric conditions are compared with the experimental results, and a good agreement is observed. The validated CFD model is used to gain detailed insights into the hydrodynamics and mass transfer.

Abbreviations CFD: Computational fluid dynamics; NDSX: Non-dispersive solvent extraction; TBP: Tri n-butyl phosphate     

Pseudo-Emulsion Based Hollow Fiber Strip Dispersion Technique (PEHFSD): Optimization,Modelling and Application of PEHFSD for Recovery of U(VI) from Process Effluent

Abstract

Pseudo emulsion based hollow fiber strip dispersion technique (PEHFSD) is the first of its kind ever explored in radioactive environment for the extraction of uranium from acidic process streams. Permeation of U(VI) was investigated as a function of various experimental variables such as hydrodynamic conditions (flow rates of pseudo-emulsion and feed phase), concentration of U(VI) in the feed phase, concentration of tri-n-butylphosphate (TBP), HNO₃ concentration in feed phase, O/A ratio and 0.01 M HNO₃ as stripping agent in pseudo-emulsion phase. The mass transfer coefficient was calculated from the experimental results and a model has been presented for determining mass transfer characteristics. PEHFSD has been demonstrated for separation/recovery of uranium from oxalate supernatant waste generated during plutonium precipitation by oxalic acid. PEHFSD and HFSLM (hollow fiber supported liquid membrane) performance has been compared in order to analyze the efficiency of the technique.     

Evaluation of Proposed Flowsheet Changes for the Highly Enriched Uranium Blenddown Program

Abstract

At the Savannah River Site, highly enriched uranium (HEU) is dissolved, purified, and blended with natural uranium to make low enriched uranium solutions sufficiently pure for conversion to power reactor fuel. The process to dissolve and purify aluminum-clad HEU fuel at SRS is well-established. However, for the dissolution and recovery of metal scrap, flowsheet changes were proposed. This study evaluates the proposed changes. Specifically, solvent extraction modeling calculations were performed which indicated that one solvent extraction cycle would be sufficient to purify the metal scrap solution by removing boron, which is added as a neutron poison. In addition, stability constants from the literature and Savannah River National Laboratory corrosion studies were documented to demonstrate that boron complexation of fluoride in nitric acid solutions, at the levels anticipated, is sufficient to prevent excessive corrosion in stainless steel vessels. Downstream from the purification process, limitations on the boron concentration in waste evaporators were recommended to prevent formation of boron-containing solids.     

EXTRACTIVE SEPARATION OF URANIUM AND ZIRCONIUM SULFATES BY AMINES

ABSTRACT

This paper describes an amine extraction process for zirconium and uranium separation. The behaviour of an extraction system containing uranium (VI) sulfate, zirconium (IV) sulfate, 0.2 and 0.5 M sulfuric acid (as the original aqueous phase), tertiary amine tri-n-lauryl- amine or primary amine Primene JMT in benzene (as the original organic phase) is discussed on the basis of equilibrium data.

The measured dependences show that the degree of extraction of zirconium at the sulfuric acid concentration of 0.5 M and above is only slightly affected by a presence of uranium in solution. From this surprising behaviour it follows that zirconium may be employed for the displacement of uranium from the organic phase. This effect is more pronounced with the primary amine Primene JMT than with TLA.