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.     

A Review of Information on Ferrocyanide Solids for Removal of Cesium from Solutions

Abstract

Ferrocyanide solids have important applications to the removal of radioactive cesium from nuclear waste solutions. These materials are prepared by mixing soluble ferrocyanides and salts of divalent transition metals or other divalent cations. The simple precipitations most commonly give very fine particles or slimes of variable compositions. Special preparation procedures have been developed to control the compositions or to prepare granular solids suitable for column operation. The removal of cesium from solutions has been measured for many different ferrocyanide solids. Some of these solids show an exchange of K⁺, Na⁺, or NH₄ ⁺ for cesium, but many show sorptions of cesium without a true ion exchange. The performance for cesium removal is described by measurements of the distribution coefficients for cesium with large excesses of ferrocyanides, the capacity for cesium with excess cesium in solution, and the rates of cesium removal. The chemical and physical stability, the solubility, and the elution or recovery requirements for ferrocyanide solids are important to practical applications. These properties are reviewed along with several of the proposed applications.     

CESIUM REMOVAL FROM HIGH-pH,HIGH-SALT WASTEWATER USING CRYSTALLINE SILICOTITANATE SORBENT

ABSTRACT

Treatment and disposal options for Department of Energy (DOE) underground storage tank waste at Hanford, Savannah River, Idaho National Engineering and Environmental Laboratory (INEEL), and Oak Ridge National Laboratory (ORNL) are limited by high gamma radiation fields that are produced by high concentrations of cesium in the waste. Treatment methods are needed to remove the cesium from the liquid waste and thus concentrate the cesium into high-activity, remote-handled waste forms. The treated liquids could then be processed and disposed of by more cost-effective means with less radiation exposure to workers.

A full-scale demonstration of one cesium removal technology has been conducted at ORNL. This demonstration utilizes a modular, mobile ion-exchange system and existing facilities for the off-gas system, secondary containment, and utilities. The ion-exchange material, crystalline silicotitanate (CST), was chosen on the basis of its effectiveness in laboratory tests. The CST, which was developed through a Cooperative Research and Development Agreement between DOE and private industry, has several advantages over current organic ion-exchange technologies. These advantages include (1) the ability to remove cesium in the presence of high concentrations of potassium, (2) a high affinity for cesium in both alkaline and acidic conditions, (3) physical stability over wide alkaline and acidic ranges, and (4) the elimination of large volumes of secondary waste required for regeneration of organic ion exchangers. Approximately 116,000 L of supernate was processed during the demonstration with ～1,142 Ci of¹³⁷CS removed from the supernate and loaded onto 265L (70 gal) of sorbent. The supernate processed had a high salt content, about 4 M NaNO₃, and a pH of 12 to 13. This paper discusses the results of the full-scale demonstration and compares these results with data from the laboratory tests.     

Full-Scale Testing of a Caustic Side Solvent Extraction System to Remove Cesium from Savannah River Site Radioactive Waste

Abstract

Savannah River Site (SRS) personnel have completed construction and assembly of the Modular Caustic Side Solvent Extraction Unit (MCU) facility. Following assembly, they conducted testing to evaluate the ability of the process to remove non-radioactive cesium and to separate the aqueous and organic phases. They conducted tests at salt solution flow rates of 3.5, 6.0, and 8.5 gpm.

During testing, the MCU Facility collected samples and submitted them to Savannah River National Laboratory (SRNL) personnel for analysis of cesium, Isopar® L, and modifier [1-(2,2,3,3-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol]. SRNL personnel analyzed the aqueous samples for cesium by Inductively-Coupled Plasma Mass Spectroscopy (ICP-MS) and the solvent samples for cesium using a Parr Bomb digestion followed by ICP-MS. They analyzed aqueous samples for Isopar® L and modifier by gas chromatography (GC).

The conclusions from the cesium analyses follow.

• The cesium in the feed samples measured 15.8 mg/L, in agreement with expectations.

• The decontamination factor measured 181–1580 at a salt solution flow rate of 3.5 gpm, 211–252 at a salt solution flow rate of 6.0 gpm, and 275–878 at a salt solution flow rate of 8.5 gpm.

• The concentration factor measured 11.0–11.1 at 3.5 gpm salt solution flow rate, 12.8–13.2 at 6.0 gpm salt solution flow rate, and 12.0–13.2 at 8.5 gpm salt solution flow rate.

• The organic carryover from the final extraction contactor (#7) varied between 22 and 710 mg/L Isopar® L. The organic carryover was less at the lowest flow rate.

• The organic carryover from the final strip contactor (#7) varied between 80 and 180 mg/L Isopar® L.

• The organic carryover in the Decontaminated Salt Solution Hold Tank (DSSHT) and the Strip Effluent Hold Tank (SEHT) was less than 10 mg/L Isopar® L, indicating good recovery of the solvent by the coalescers and decanters.

     

Effects of pH and Inorganic Salts on the Adsorption of Phenol from Aqueous Systems on Activated Decolorizing Charcoal

Abstract

An experimental investigation of the effects of pH and three inorganic salts (KCl, KI, and NaCl) on the adsorption isotherms of phenol (from a dilute aqueous solution) on activated charcoal was conducted. Each salt was studied at three different concentrations, i.e., 0.1, 0.001, and 0.005 M. The effect of pH (in the pH range 3 to 11) in the presence of KI, KCl, and NaCl was also investigated. The concentration of phenol in the aqueous systems studied ranged from 10 to 200 ppm. The temperature effect was also studied, and the resulting experimental equilibrium isotherms at 30, 40, and 55°C are well represented by Freundlich, Langmuir, and Redlich—Paterson isotherms. The relevant parameters for these isotherms are presented.     

Axial Dispersion during Hanford Saltcake Washing

Abstract

This paper describes laboratory‐scale testing conducted to evaluate Selective Dissolution of cesium from non‐radioactive Hanford tank 241‐S‐112 salt cake simulant containing the primary chemicals found in the actual tank. A modified axial dispersion model with increasing axial dispersion was developed to predict cesium removal. The model recognizes that water dissolves the salt cake during washing, which causes an increase in the axial dispersion during the wash. This model was subsequently compared with on‐line cesium measurements from the retrieval of tank 241‐S‐112. The model had remarkably good agreement with both the lab‐scale and full‐scale data.     

Distillation of Ethanol-Water Solutions in the Presence of Potassium Acetate

Abstract

Complete separation of ethanol-water mixtures through salt addition has been demonstrated in a continuously operated single sieve-plate-column including salt recycling. The effect of salt concentration as well as reflux ratio on the separation are outlined based on experimental data. The results clearly indicate that distillation in the presence of salts is an economical alternative to more conventional processes.     

SRS Low‐Curie Process Modeling and Experiments

Abstract

Engineers at SRS are evaluating the Low‐Curie Salt Process which is aimed at initially withdrawing the interstitial liquor followed by dissolution of the salt cake. Partitioning of the cesium is predominantly within the interstitial liquor; consequently a separation based on activity can be effected. Laboratory experiments using simulants from SRS tanks have been performed along with thermodynamic simulations. Results indicate that insoluble layers such as Al(OH)₃ and/or cancrinite may form and hinder the dissolution processes. The effectiveness of the Low‐Curie Salt Process may be reduced based on layer formation and the distribution of the interstitial liquor within the waste.     

Fundamental Chemistry of Cesium Extraction from Acidic Media by HCCD in FS‐13

Abstract

We previously published a model for cesium extraction from acidic media by the protonated form of the hexachlorinated derivative of the chloro‐protected cobalt bis(dicarbollide), HCCD, dissolved in trifluoromethylphenyl sulfone, FS‐13. The model indicated that Cs extraction proceeds through a series of ion‐paired and/or dissociated extraction equilibria. Additional Cs distribution ratio data has been obtained and the model refined and simplified. It is demonstrated that the equilibrium exclusively involving the exchange of proton for cesium by formation of ion‐paired CsCCD models the Cs distribution data very well, particularly for the concentrations of HCCD greater than ～0.0005 M (0.5 mM). Finally, activity corrections for the aqueous phase to the Cs distribution data results in good agreement to the theoretical value of ?1 for slope (log‐log) analysis of the data over a wide range of HNO₃ and HCCD concentrations.     

Modeling Ion-Exchange for Cesium Removal from Alkaline Radioactive Waste Solutions

Abstract

The performance of spherical Resorcinol-Formaldehyde ion-exchange resin for treatment of radioactive waste solutions is investigated through computer modeling. Results show that ion-exchange is an efficient method for cesium removal from highly alkaline radioactive waste solutions. On average, two 1300 liter columns operating in series are able to treat 690,000 liters of waste with an initial cesium concentration of 0.09 mM in 11 days achieving a decontamination factor of over 50,000. The study investigated the sensitivity of ion-exchange column performance to variations in flow, temperature, and column dimensions. Modeling results can be used to optimize the design of the ion exchange system.     

ION EXCHANGE SELECTIVITY OF A RESORCINOL-FQRMALDEHYDE POLYCONDENSATE RESIN FOR CESIUM IN RELATION TO OTHER ALKALI METAL IONS

ABSTRACT

Ion exchange isotherms for the ion-pairs Li⁺ -Cs⁺, Na⁺ -Cs⁺ and K⁺ -Cs⁺ have been measured for a cesium selective resorcinol—formaldehyde polycondensate resin synthesized in the laboratory- The equilibrium data have been used to calculate the thermodynami c equilibrium constants as well as standard free energies of ion ex change and thus arrive at a selectivity series for the above ions- The high selectivity towards cesium as compared to other alkali metal ions has been discussed in the 1ight of existing theories and models of ion ex change phenomena.     

Demineralization of Protein Hydrolysates from Enzymatic Hydrolysis of Leather Shavings Using Membrane Diafiltration

ABSTRACT

Pressure-driven membrane separations operated in the diafiltration mode appear promising as an efficient demineralization method of waste protein hydrolysates from leather production. The conclusion drawn from our experimental results is that nanofiltration membranes should be used rather then ultrafiltration ones as they show complete passage of the salts with high retention of the protein hydrolysates. In addition to the classical membrane separation operating parameters, which are crossflow fluid velocity, transmembrane pressure difference, and temperature,the required residual salt concentration as well as acceptable protein losses affect the effectiveness of the process.     

Studies on the Extraction—Simultaneous Back-Extraction of Alkali Metal Picrates Using 1,3 Bis-Benzo-Crown-6-Calix[4] Arene in Hollow-Fiber Contactors

Abstract

An extraction and simultaneous back-extraction process with two hollow-fiber membrane contactors is evaluated for the continuous recovery of alkali metals and 1,3 bis-benzo-crown-6-calix[4]arene. The results show that this configuration operates as a “liquid membrane” (permeable only with alkali picrate) and order of the recovery yields is in agreement with the Donnan equilibrium. It is higher for the rubidium (75.8%) than for the cesium (68.1%) while it is only 11% for the potassium. This is a case where the high affinity of cesium picrate for the 1,3 bis-benzo-crown-6-calix[4]arene cannot be neglected and, as a consequence, its release in the back-extraction aqueous phase is more difficult. The effect of the alkali metal and the initial concentration on the system behavior shows that the concentration gradient controls the mass transfer. The kinetics are similar for the cesium and the rubidium whereas the mass-transfer resistance increases for the potassium. A high mass transfer in the first module can slow down the global-transport kinetics.     

Experimental measurement and thermodynamic modeling of cyclopentane hydrates with NaCl,KCl, CaCl2, or NaCl‐KCl present

Consistent phase equilibrium data for cyclopentane hydrates in presence of salts are vitally important to many industries, with particular interest to the field of hydrate‐based water separation via cyclopentane hydrate crystallization such as desalination. However, there are very little experimental equilibrium data, and no thermodynamic prediction tools. Hence, we set up a method to generate a great deal of much needed equilibrium data for cyclopentane hydrates in diverse saline solutions with a wide range of salt concentrations. Our method does furnish verified, reliable and accurate equilibrium data. Plus, three thermodynamic approaches are developed to predict equilibrium, and provide tools for simulations, by considering the kind of salt and concentrations. All three models are in very good accordance with experimental data. One method, using a new correlation between occupancy factor and water activity, might be the best way to obtain consistent, quick, and accurate dissociation temperatures of cyclopentane hydrate in brine. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2207–2218, 2018     

Adsorption and diffusion of cesium ions in zirconium(IV) iodomolybdate exchanger

Tetravalent metal acid (TMA) salt zirconium(IV) iodomolybdate ion exchanger was chemically synthesized under different conditions and subjected into batch reactor for cesium removal investigation. The properties of synthesized exchangers were characterized using X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Data revealed that the prepared beads are amorphous in nature and thermally stable up to 350 °C. The influences of contact time, pH, ionic strength, and organic acids were investigated. Results illustrated that cesium uptake reached equilibrium within 2 h and it is strongly dependent on ionic strength and nearly independent of pH values. Speciation of cesium ions and their ability to form ternary complexes less adhered to the applied exchangers predominate their adsorption behavior. The prepared exchangers had a good ion-exchange capacity ranged from 7.94 to 9.62 mmol g⁻¹.     

Ion-Exchange Selectivities of Periderm and Cuticular Membranes toward Alkali Cations

Abstract

The ion-exchange selectivities of lithium, sodium, potassium, and cesium on isolated potato periderm (solanum tuberosum) and pear fruit cuticular membranes were investigated; the general order of preference both for cation selectivities and ion-exchange capacities was lithium > sodium > potassium > cesium. The potato periderm and pear fruit cuticular membranes exhibited a behavior typical of ion-exchange resins of the weak acid type. At constant pH7, the ion-exchange capacities of periderm and cuticular membranes increased with hydrated ionic radius, and also with increasing pH and neutral salt concentration, and decreased with crystal ionic radius. Counterion selectivities also exhibited the same behavior. The ion-exchange properties are discussed in terms of the structure and function of potato periderm and pear fruit cuticular membranes.     

Extraction of Cesium by a Calix[4]arene‐Crown‐6 Ether Bearing a Pendant Amine Group

Abstract

The goal of this work was to evaluate the role of the amino group of 5‐aminomethylcalix[4]arene‐[bis‐4‐(2‐ethylhexyl)benzo‐crown‐6] (AMBEHB) in the extraction of cesium from acidic and basic mixtures of sodium nitrate and other concentrated salts. The extraction of cesium from nitrate media was measured as a function of extractant concentration, nitrate concentration, cesium concentration, and pH over the range 1–13. The initial studies showed a moderate decrease in the extraction of cesium in acidic media, which indicated the binding of cesium by the calixarene‐crown was weakened by the protonation of the amine group. The results also indicated that a 1∶1∶1 Cs‐ligand‐nitrate complex is formed in the organic phase. To further evaluate AMBEHB, the empirical data were mathematically modeled to determine the formation constants of the complexes formed in the organic phase. The resulting formation constants showed that the attachment of the amine group to the calixarene‐crown molecule reduced the binding stability for the cesium ion upon contact with an acidic solution. This supports the hypothesis of charge repulsion as the basis for more efficient stripping of cesium via pH‐switching.     

Electrical Aspects of Adsorbing Colloid Flotation II. Theory of Rate Processes

Abstract

The kinetic and equilibrium factors affecting the rate of precipitate flotation are analyzed by means of the Gouy-Chapman model. Kinetic effects are found to be extremely rapid, and the rate of precipitate flotation is due to equilibrium considerations. Removal efficiency as a function of inert salt concentration goes through a maximum at about 10^?5 M for films 300 Å thick. Removal efficiency increases with increasing zeta potential of the film surface and with increasing charge on the precipitate particles.     

EXTRACTION OF CESIUM NITRATE FROM CONCENTRATED SODIUM NITRATE SOLUTIONS WITH 21-CROWN-7 ETHERS: SELECnVITY AND EQUILIBRIUM MODELING

ABSTRACT

The extraction of cesium nitrate from a high concentration of sodium nitrate by a family of 21-crown-7 ethers in 1,2-dichloroethane has been investigated. Dibenzo-21-crown-7 (DB21C7) and bis[4(5),4′(5′)-rm-butylbenzo]-21-crown-7 (BtBB21C7) ethers have higher selectivity for cesium but lower extraction efficiency than dicyclohexano-21-crown-7 (DC21C7) ether. As measured by the distribution coefficient ratio D_cs/D_Na, the cesium selectivity averaged 78 and 93 for DB21C7 and BtBB21C7, respectively. However, in the case of DC21C7, the cesium selectivity was lower and decreased approximately three-fold from 10 to 3 as cesiüm loading increased. Alkyl substitution on the benzo group has only a small effect on the extraction behavior. It was shown by use of the equilibrium modeling program SXLSQI that the extraction of sodium and cesium could be adequately modeled by augmenting the previously determined cesium nitrate equilibrium model with a 1:1 Na⁺:crown organic-phase complex. No evidence for a mixed-metal species was found. In accord with our previous study, cesium nitrate extraction entails formation of a 1:1 Cs⁺:crown complex, but a minor 1:2 complex also forms in the case of DC21C7. Although the sodium and cesium made possible by the U. S. Department of Energy Postgraduate Research Program administered by the Oak Ridge Associated Universities.     

Diffusion coefficients of aqueous cesium fluoride at 40°C

Diaphragm cell technique has been employed to determine diffusion coefficient for cesium fluoride at 40°C in the concentration range varying from 0.01 to 0.1 M. The data were analysed in the light of the theory of Onsager and Fuoss (O-F), J. chem. Phys.2, 599 (1932)[20]. The results indicate that the O-F theory is inadequate to explain the behaviour of this salt at 45°C. The results are also discussed with other 1:1 type salts of cesium.