Combined Extraction of Cesium and Strontium from Alkaline Nitrate Solutions

Abstract

The combined extraction of cesium and strontium from caustic wastes can be achieved by adding a crown ether and a carboxylic acid to the Caustic‐Side Solvent Extraction (CSSX) solvent. The ligand 4,4′(5′)‐di(tert‐butyl)cyclohexano‐18‐crown‐6 and one of four different carboxylic acids were combined with the components of the CSSX solvent optimized for the extraction of cesium, allowing for the simultaneous extraction of cesium and strontium from alkaline nitrate media simulating alkaline high level wastes present at the U.S. Department of Energy Savannah River Site. Extraction and stripping experiments were conducted independently and exhibited adequate results for mimicking waste simulant processing through batch contacts. The promising results of these batch tests showed that the system could reasonably be tested on actual waste.     

Immobilization of strontium and cesium by aluminosilicate ceramics derived from metakaolin geopolymer-zeolite A composites via 1100 °C heating treatment

In this work, K-based metakaolin geopolymer-zeolite A composites doped with strontium and cesium radionuclides have been subjected to 1100 °C to prepare aluminosilicate ceramic waste forms. Serial analysis of mineral characterization, physical properties and leaching resistance have been adopted to investigate the immobilization performance of aluminosilicate ceramic waste forms for strontium and cesium radionuclides. Compared to geopolymer-zeolite A composites, the obtained ceramic waste forms exhibit preferable mechanical property and leaching resistance (in deionized water, brine solutions and silicate solutions). The compressive strengths of aluminosilicate ceramic waste forms (Sr/Cs-loaded matrix) are both above 80 MPa, which are far higher than that of geopolymer-zeolite composites solidification matrices. Owing to the viscous sintering under 1100 °C heating treatment, even compact and dense ceramic waste forms have been successfully synthesized, accompanied by the main crystalline phase transformation in monoliths from zeolite A to leucite. Cs-leucite and Sr-feldspar also have been detected by XRD and TEM analyses, which are conducive to capturing strontium and cesium radionuclides in ceramic monoliths. All findings have proven that the ceramics waste forms derived from metakaolin geopolymer-zeolite A composites could be an ideal option for nuclear wastes immobilization.     

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.

     

γ‐Radiation Effects on the Performance of HCCD‐PEG for Cs and Sr Extraction

Abstract

Cobalt dicarbollide and polyethylene glycol in phenyltrifluoromethyl sulfone (HCCD/PEG in FS‐13) is currently under consideration for use in the process‐scale selective extraction of fission product cesium and strontium from acidic radioactive solutions. While the Cs and Sr solvent extraction efficiency of this formulation has been previously characterized, this solvent will be exposed to high radiation doses during use, and has not been adequately investigated for radiation stability. Here, HCCD/PEG was γ‐irradiated to various absorbed doses, to a maximum of 432 kGy, using ⁶⁰Co. Irradiations were performed for the neat organic phase, and also for the organic phase in contact with 1 M‐nitric acid mixed by air sparging. Post‐irradiation solvent extraction measurements showed that Cs distribution ratios were unaffected; however, strontium distribution ratios decreased with the absorbed dose under both conditions. The decrease in the extraction efficiency for strontium was greater when in contact with the aqueous phase. The stripping performance was not affected. A mechanism, based on reaction with the products of direct diluent radiolysis, is proposed to explain the decreases in the strontium extraction efficiency.     

The Use of 24-Crown-8's in the Solvent Extraction of CsNO3 and Sr(NO3)2

Abstract

The feasibility of a solvent extraction process for removing strontium and cesium from acidic high activity nuclear waste is shown. Both strontium and cesium can be extracted from an aqueous HNO₃ phase containing the metal nitrates into an organic phase containing kerosene or CCl₄ as a diluent and complexing agents dissolved in the diluent. The most promising results obtained thus far have required the use of a mixture of three metal complexing agents: tributyl phosphate, di-2-ethylhexyl phosphoric acid, and 4,4′(5′)-di-tert-butylbenzo-24-crown-8. The highest distribution coefficients obtained (organic/aqueous) were 1.45 ± 0.05 for Cs⁺ and 200 for Sr²⁺. The extraction is reversible and is strongly dependent on the pH of the aqueous phase. The metal can be removed from the organic phase by lowering the pH to 1, while raising the pH above 3 causes the metal to return to the organic phase. The utility of this extraction technique for nuclear processing will depend on the radiation stability of the complexing agents and the degree of selectivity obtained when extracting strontium and cesium from mixed fission products.     

Effects of Li Substitution on the Microstructure and Thermal Expansion Behavior of Pollucite Derived from Geopolymer

The purpose of this work was to study the role of lithium in cesium‐based geopolymers and the thermal evolution during heat treatment together with thermal expansion behavior of the resulting geopolymer ceramic. A series of lithium‐substituted cesium‐based geopolymers, Cs_(1?x)Li_xGP (where x = 0, 0.1, 0.2, and 0.3), were prepared. All the geopolymer samples were heated at 1300°C for 2 h and thermal evolution on heating was studied by a variety of techniques. Phase composition, microstructure evolution, and thermal expansion behaviors of the ceramics derived from the geopolymers were characterized. All the geopolymer specimens exhibited similar thermal evolutionary trends. With increases in lithium content, overall mass loss increased gradually due to the higher hydration energy of Li⁺ than Cs⁺. Thermal shrinkage of these specimens can be divided into four stages, i.e., structural resilience, dehydration, dehydroxylation, and sintering, according to the dilatometer results. The introduction of Li results in two‐step sintering behavior for the lithium‐substituted cesium‐based geopolymers. The average thermal expansion coefficient (CTE) of Cs_(1?x)Li_xGP ceramics decreased from 4.80 × 10^?6 K^?1 (x = 0) to 3.61 × 10^?6 K^?1 (x = 0.3) with increase in lithium substitution. The reason can be attributed to the presence of spodumene after thermal treatment, which has a relatively low thermal expansion coefficient compared with pollucite. Meanwhile, molten spodumene could serve as a buffer phase between pollucite crystals also conducive to the decline of CTE of this system.     

Polyfunctional microspherical materials for long-term disposal of liquid radioactive wastes

The possibility of immobilizing liquid radioactive wastes into polyfunctional microspherical materials of the block and powdered types is demonstrated. These materials are intended for reprocessing radioactive wastes of different compositions and make it possible to perform a multistage process of conditioning radioactive wastes under relatively mild conditions (at temperatures below 1000°C) with the conversion of water-soluble cesium and strontium compounds into water-insoluble mineral forms in the course of solid-phase transformations. Owing to the aluminosilicate composition of microspherical components of energy ashes (cenospheres), the cenospheres can serve as precursors of aluminosilicate granitoid minerals. Different techniques are proposed and conditions are experimentally determined for transforming precursors into final mineral-like materials of the predicted structure types chosen in the framework of the geoecological approach. The framework structures of aluminosilicates and phosphates thus formed can fix cesium and strontium in the crystal lattice and ensure the geochemical equilibrium between the matrix and incorporating granitoid rocks under conditions of long-term disposal.     

水热离子交换时间对铯离子改型白榴石的影响

为实现对白榴石热膨胀系数的有效调控,利用铯离子对白榴石粉体进行改型。将白榴石粉体在浓度为0.3 mol/L的硫酸铯溶液中进行水热离子交换处理。利用X射线衍射仪（XRD）和扫描电子显微镜（SEM）对180 ℃下不同离子交换时间得到样品的物相和形貌进行了分析和观察。结果表明:铯离子进入白榴石晶格后,使部分白榴石转变生成了铯榴石,并且随着保温时间的延长,产物铯榴石晶体会逐渐由四方晶系过渡为立方晶系。当保温时间超过10 h时,两相间内应力增加会导致铯榴石从白榴石颗粒表面脱落,所以保温时间应该控制在2~10 h。利用JMA方程对合成铯榴石生长动力学过程进行拟合分析,从Avrami指数n小于0.5可知,整个反应主要由扩散控制。     

Effects of Na+ substitution Cs+ on the microstructure and thermal expansion behavior of ceramic derived from geopolymer

As part of a series of studies, effects of Na⁺ substitution on the thermal evolution of cesium‐based geopolymers on heating were studied. A series of sodium‐substituted cesium‐based geopolymers, Cs_(1?x)Na_xGPs (where x=0, 0.1, 0.2, 0.3, and 0.4), were prepared and treated at 1300°C for 2 hours to obtain the corresponding ceramic products. The thermal evolution process was disclosed by virtue of a variety of technical, including TG‐DTA, thermal shrinkage, XRD analysis, SEM, and TEM investigation. The results indicated that unheated Cs_(1?x)Na_xGPs was not completely amorphous after the substitution of Na⁺ and the crystallinity of Cs_(1?x)Na_xGPs gradually increased with the rise of sodium content. Meanwhile, the average particle sizes of Cs_(1?x)Na_xGPs also increased evidently with increases in sodium substitution. The final product after heat treatment mainly consisted of pollucite (CsAlSi₂O₆) and amorphous glass phase. The particle size of pollucite grain gradually decreased as more Cs⁺ were replaced maybe owing to the role of Na⁺ in the nucleation process of pollucite. Two forms of Na⁺ present in the final products: A small portion was present in the pollucite grains due to Na⁺ partial occupied the crystallographic sites of Cs⁺; and the rest were present in the amorphous glass phase among the pollucite grains. The average coefficient of thermal expansion (CTE) of resulting Cs_(1?x)Na_xGPs ceramics increased from 4.80×10^‐6 K^?1 (x=0) to 7.26×10^?6 K^?1 (x=0.4) with increases in sodium substitution, which could be due to the amorphous glass phase had a relatively higher CTE than that of pollucite.     

Preparation and Evaluation of Fullers Earth Beads for Removal of Cesium from Waste Streams

Abstract

Fullers earth beads and cylinders were prepared using chitosan and sodium silicate as binders, respectively, for removal of cesium ion from aqueous solutions. The cost of the adsorbent is expected to be significantly lower as the raw materials are low cost materials and readily available. The adsorbents were characterized by SEM, EDS, and x‐ray microanalysis. Adsorption capacity of the beads was evaluated under both batch and dynamic conditions. The adsorption capacity for Fullers earth beads was found to be 26.3 mg/g of adsorbent at 293 K when the liquid phase concentration of cesium was 1000 mg/L. The adsorption capacity of Fullers earth cylinder was found to be higher than that of beads, however, it was concluded that the alkaline nature of the cylinder precipitated out cesium increasing its capacity. The capacity of Fullers earth beads decreased by almost 62% when 1 mol/L NaCl and 2.25 mmol/L of strontium were present in the solution. The Freundlich, the Langmuir isotherm equations, and a modified Polanyi's equation were used to correlate the data. The isosteric heats of adsorption suggested the heterogeneity of the surface and multilayer coverage. The first order reversible kinetic model adequately described the dynamic system during the adsorption process. The adsorption (k₁) and desorption (k₂) rate constants were evaluated from the dynamic model.     

Waste Remediation Using in Situ Magnetically Assisted Chemical Separation

Abstract

The magnetically assisted chemical separation process (MACS) combines the selective and efficient separation afforded by chemical sorption with the magnetic recovery of ferromagnetic particles. This process is being developed for treating the underground storage tanks at Hanford. These waste streams contain cesium, strontium, and transuranics (TRU) that must be removed before this waste can be disposed of as grout. The separation process uses magnetic particles coated with either 1) a selective ion exchange material or an organic extractant-containing solvent (for cesium and strontium removal) or 2) solvents for selective separation of TRU elements (e.g., TRUEX process). These coatings, by their chemical nature, selectively separate the contaminants onto the particles, which can then be recovered from the tank using a magnet. Once the particles are removed, the contaminants can either be left on the loaded particles and added to the glass feed slurry or stripped into a small volume of solution so that the extracting particles can be reused. The status of the chemistry and separation process is discussed in this paper.     

XRD Analysis of the Role of Cesium in Sodium‐Based Geopolymer

The purpose of this work was to study the role of cesium in sodium‐based geopolymer and its thermal stability for nuclear waste management. A series of mixed sodium and cesium geopolymer samples (Na_1?x Cs _x )₂O·Al₂O₃·SiO₂·12H₂O (referred to as (Na_{1? x} Cs _x )‐GP, where x = 0, 0.08, 0.15, 0.42, 1) have been prepared. All geopolymer samples were heated at 1100°C for 24 h. Pollucite (CsAlSi₂O₆) and feldspathoid (CsAlSiO₄) were crystallized from Cs‐GP. Nepheline (NaAlSiO₄) and a small amount of crystallized silica were obtained from Na‐GP. The other geopolymers (Na_{1? x} Cs _x )‐GP (x = 0.08, 0.15, 0.42) led to pollucite and nepheline main phases. Amorphous silica phase was observed in all the geopolymer samples with various amounts. Phase quantification and scanning electron microscope revealed that higher Cs concentrations in Na‐GP tend to decrease the amorphous phase while improving pollucite and nepheline phase quantification. The amorphous geopolymers have also been studied by pair distribution function analysis. Tetrahedral chains formed by T–O bonding (with T = Si, Al) were shown to be more tighten around Cs⁺ than around Na⁺. It led to shorter Cs–T bond than Na–T bond matching the higher solvation property of Na⁺. Furthermore, thermal study analysis pointed out the fact that geopolymer samples (Na_{1? x} Cs _x )‐GP, can be considered as solid solutions.     

THE EXTRACTION OF CESIUM AND STRONTIUM FROM ACIDIC HIGH ACTIVITY NUCLEAR WASTE USING A PUREX PROCESS COMPATIBLE ORGANIC EXTRACTANT

Purex process compatible organic systems which selectively and reversibly extract cesium and strontium from synthetic mixed fission product solutions containing3M HNO₃, have been developed. This advance makes the development of continuous solvent extraction processes for their recovery more likely.

The matrix solution from the Purex process consists of tributyl phosphate (TBP) and kerosene. For cesium and strontium recovery a macrocyclic polyether (crown compound) has been developed for each element. When used in conjunction with a liquid cation exchanger in the matrix solution, the crown compounds will extract either alkali metals or alkaline earths from the synthetic mixed fission product solution. The organic cation exchangers used in this research were didodecylnaphthalene sulfonic acid (DNS) and dinonylnaphthalene sulfonic acid (NNS). As was expected both zirconium and ruthenium also tend to be extracted due to the TBP in the matrix solution and to their complex chemistry.

The most favorable cesium and strontium complexing solutions have been tested for radiation stability to 10⁷ rad using a 0.4 × 10⁷ rad/hr ⁶⁰ Co source. The distribution coefficients dropped somewhat but remained above unity.

For cesium the comp1exing organic solution is 5vol% (0.10M) NNS, 27vol% TBP and 68vol% kerosene containing 0.05M bis 4,4′,(5′) [l-hydroxy 2-ethylhexyl]benzo 18-crown-6 (Crown XVII). with an aqueous phase containing 0.006M Cs^+l in contact with an equal volume of extractant, the Dorg/aq = 1.6 at a temperature of 25?35°C.

For strontium the complexing organic solution is 5vol% (0.10M) NNS, 27vol% TBP and 68vol% kerosene containing 0.02M bis 4,4′(5′) (l-hydroxyheptyl)cyclohexo 18-crown-6 (Crown XVI). with an aqueous phase containing 0.003M Sr⁺² in contact with an equal volume of extractant, the Dorg/aq 1.98 at a temperature of 25?35°C.     

Strontium and Actinide Separations from High Level Nuclear Waste Solutions Using Monosodium Titanate 2. Actual Waste Testing

Abstract

Pretreatment processes at the Savannah River Site will separate ⁹⁰Sr, alpha‐emitting and radionuclides (i.e., actinides) and ¹³⁷Cs prior to disposal of the high‐level nuclear waste. Separation of ⁹⁰Sr and alpha‐emitting radionuclides occurs by ion exchange/adsorption using an inorganic material, monosodium titanate (MST). Previously reported testing with simulants indicates that the MST exhibits high selectivity for strontium and actinides in high ionic strength and strongly alkaline salt solutions. This paper provides a summary of data acquired to measure the performance of MST to remove strontium and actinides from actual waste solutions. These tests evaluated the effects of ionic strength, mixing, elevated alpha activities, and multiple contacts of the waste with MST. Tests also provided confirmation that MST performs well at much larger laboratory scales (300 – 700 times larger) and exhibits little affinity for desorption of strontium and plutonium during washing.     

THE REMOVAL OF STRONTIUM AND CESIUM FROM SIMULATED HANFORD GROUNDWATER USING INORGANIC ION EXCHANGE MATERIALS

ABSTRACT

A number of inorganic ion exchange materials that are commercially available or under development were evaluated for the removal of strontium and cesium from a simulated groundwater found in the Hanford waste storage area using a groundwater simulant spiked with either 89Sr or 137 Cs. The most promising materials for strontium were found to be a sodium titanosilicate from Texas A&M University closely followed by two titanium silicate pharmacosiderites obtained from AlliedSignal. The most promising materials for the selective removal of cesium from the simulant was again the sodium titanosilicate followed by an alumina-pillared montmorillonite clay obtained from Laporte Industries Ltd. The ion exchange kinetics were shown to be very rapid for both the titanosilicate and the pharmacosiderite, whilst the alumina-pillared montmorillonite had slower kinetics more comparable to those of the zeolite AW500.     

Application of Equilibrium Density Gradient Sedimentation to the Separation and Purification of Proteinpolysaccharides

Abstract

Mixtures of proteinpolysaccharides can be effectively separated by equilibrium sedimentation of solutions containing high concentrations of salts such as cesium chloride.

The method is most effective when the buoyant densities of the constituent molecules differ widely. Degradation of the proteinpolysaccharide macromoleculcs is minimized because degradative enzymes readily sediment away from the denser carbohydrate-containing substances. The macromolccules are subjected to conditions no more severe than exposure to high salt concentrations. The recovery of material is always quantitative and all components are subjected to identical treatments. By sedimenting dilute solutions of proteinpolysaccharides to equilibrium in cesium salt density gradients, separation and concentration can often be effected in a single step.

The method is less suitable when the constituent proteinpolysaccharides are polydisperse or of small molecular weight. In the case of very complex mixtures of proteinpolysaccharides, i.e., extracts from arterial tissue, the method may be useful for preliminary separations only.

The method is time-consuming and can be expensive with regard to materials and equipment. However, as most laboratories possess high-speed preparative centrifuges and cesium salts can be recovered after use, these problems are not insurmountable.     

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 Absorption from Acidic Solutions Using Ammonium Molybdophosphate on a Polyacrylonitrile Support (AMP-PAN)

Abstract

Recent effort at the Idaho Chemical Processing Plant (ICPP) have included evaluation of cesium removal technologies as applied to ICPP acidic radioactive waste streams. Ammonium molybdophosphate (AMP) immobilized on a polyacrylonitrile support (AMP-PAN) has been studied as an ion exchange agent for cesium removal from acidic waste solutions. Capacities, distribution coefficients, elutability, and kinetics of cesium extraction have been evaluated. Exchange breakthrough curves using small columns have been determined from 1M HNO₃ and simulated waste solutions. The theoretical capacity of AMP is 213 g Cs/Kg AMP. The average experimental capacity in batch contacts with various acidic solutions was 150 g Cs/kg AMP. The measured cesium distribution coefficients from actual waste solutions were 3287 mL/g for dissolved zirconia calcines, and 2679 mL/g for sodium-bearing waste. The cesium in the dissolved alumina calcines was analyzed for; however, the concentration was below analytical detectable limits resulting in inconclusive results. The reaction kinetics are very rapid (2-10 minutes). Cesium absorption appears to be independent of acid concentration over the range tested (0.1 M to 5 M HNO₃).     

SYNTHESIS,SORPTION AND KINETIC CHARACTERISTICS OF SILICA-HEXACYANOFERRATE COMPOSITES

ABSTRACT

The precipitation behaviour of the compounds in the system, divalent metal-hexacyanoferrate(II)-sodium silicate, has been investigated. Under suitable conditions, copper, cobalt and nickel-based composite sorbents have been prepared. These sorbents were very effective in removing cesium from neutral solutions. In regard to exchange capacities, copper hexacyanoferrate (Cu-Hcf) composites exhibited highest values and these values were found to be independent of silica content. Similarly, rates of cesium uptake also were higher and these rates were not affected by granulation of copper-based materials. There was little decrease in the rates in hydrazine containing nitric acid solutions. Several cycles of batchwise sorption and desorption operations were performed with Cu-Hcf composites and quantitative recovery of cesium from loaded sorbents was achieved using nitric acid     

Hydrothermal Reaction and Dissolution Studies of CsAISi5Or12 in Water and Brines

The alteration of CsAlSi₅O₁₂, a possible host for ¹³⁷Cs in tailored nuclear waste ceramics, was studied under simulated nuclear waste repository conditions of 100°, 200°, and 300°C with a confining pressure of 30 MPa. The cesium radiophase was found to be quite stable in water or 3N CaCl₂, or 3N MgCl₂ but not in 3N NaCl or 3N KCI or a bittern brine. The acid resistance of CsAlSi₅O₁₂ can be deduced from its stability in hydrothermal MgCl₂ brine. Possible reaction mechanisms include the formations of pollucite and quartz in deionized water and the formation of Na or K feldspars and quartz in the presence of NaCl or KCl brines, respectively. A comparison of the various cesium aluminosilicates indicates that pollucite (CsAlSi₂O₆) is the best candidate for cesium-137 immobilization.