SORPTION OF CESIUM BY HEXACYANOFERRATE COMPOSITES FROM NEUTRAL AND ACIDIC MEDIA

ABSTRACT

Silica-supported copper, cobalt, nickel and zinc hexacyanoferrate(II) composites were prepared by a modified procedure and sorption of cesium by these materials from neutral and acidic media was studied. Distribution coefficient (K_d) values in the range of 10³ to 10⁵ mL/g and capacity values in the range of 1.1 to 2.5 meq/g were obtained in neutral media. A considerable increase in K_d values and capacities was observed for cobalt composites as compared to those for the corresponding unsupported material. High K_d values (10⁴ to 10⁵) were also exhibited in nitric acid media by copper, cobalt and nickel composites but only in the presence of low concentration of hydrazine. The underlying mechanism of the sorption of trace cesium by these composites was found to be true ion exchange. Of all the composites studied, nickel-based materials were found to be most attrition-resistant in agitated test solutions. The behaviour of composites observed in this work is explained from a knowledge of known crystal structure and surface properties of pure compounds.     

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).     

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.     

THE SORPTION OF COBALT FROM AQUEOUS SOLUTIONS BY POTASSIUM NICKEL HEXACYANOFERRATE COMPLEX

ABSTRACT

The inorganic complex, potassium nickel hexacyanoferrate, KNiFC, was used for the separation of cobalt from diluted nitric acid aqueous solutions using the batch technique. The effect of hydrogen ion concentration on the distribution coefficient of cobalt has been studied in the pH range 2–5.5. The effect of particle size and temperature on the sorption isotherm and rate of uptake of cobalt were investigated. The increase of temperature was found to enhance the sorption equilibrium and rate of uptake. The diffusivity of cobalt ions into different particle sizes of KNiFC was calculated. The effect of the presence of cesium ions on the rate of uptake of cobalt is presented.     

Leaching and electrochemical recovery of copper,lead and tin from scrap printed circuit boards

The recovery of copper, lead and tin from scrap printed circuit boards (PCBs) has been achieved using a combination of leaching, electrochemical ion exchange and electrodeposition. A simple aqueous nitric acid stripping solution, with the concentration range of 1–6 mol dm^?3, has demonstrated the potential for selective extraction of copper and lead from the PCBs. Precipitation of tin as H₂SnO₃ (metastannic acid) occurred at acid concentrations above 4 mol dm^?3. Preliminary galvanostatic electrolysis from simulated leaching solutions has investigated the feasibility of electrodeposition of copper and lead at different concentrations of HNO₃. Cathodic lead deposition, particularly at high electrolyte conditions, resulted in poor current efficiency. This was mainly due to dentritic metal formation and subsequent re‐dissolution. An alternative method investigated for recovering the metal values was the simultaneous electrodeposition of copper at the cathode and lead dioxide at the anode. Electrohydrolysis for acid and base regeneration from the spent nitric acid electrolyte has also been investigated. © 2002 Society of Chemical Industry     

EXTRACTION OF Ce(III) AND Eu(III) BY NITROBENZENE SOLUTIONS OF BIS-1,2-DICARBOLLYLCOBALTATE IN THE PRESENCE OF 18-CROWN-6

ABSTRACT

The extraction of Ce(III) and Eu(III) by nitrobenzene solutions of bis-l,2-dicarbollylcobaltate anions in the presence of 18-crown-6 from aqueous solutions of nitric acid has been investigated. Distribution ratios, the protonization and exchange extraction constants for the investigated systems has been determined. The calculated values of distribution ratios D have been compared with experimental ones.     

Hollow-Fiber Membrane Extraction of Copper from Aqueous Nitrate Media by LIX® Reagents: Comparison of Extraction Efficiency and Fractional Resistances

Abstract

Extraction of copper from nitrate/nitric acid aqueous solutions was studied using a HF Membrane Module and four LIX reagents (LIX® 860N-I, LIX® 984N, LIX® 84-I, and LIX® 65N) containing different active compounds (ketoximes and/or salicylaldoximes). Kinetic experiments varying the flow rates of both phases, aqueous and organic, and the extractant concentration were carried out to compare the extraction rate and efficiency from nitrate-aqueous media. A mathematical model based on the “aqueous extraction mechanism” in which the chemical reaction takes place in an aqueous-reaction zone was applied to determine the individual resistances of the copper mass-transfer process. It was found that the fractional resistance due to chemical reaction in the aqueous reaction zone, which varied from 92.5% to 95.8% in the order LIX® 860N-I < LIX® 984N < LIX® 84-I < LIX® 65N, controlled the total rate of the hollow-fiber copper extraction from nitrate aqueous media.     

Development of Steam Reforming for the Solidification of the Cesium and Strontium Separations Product from Advanced Aqueous Reprocessing of Spent Nuclear Fuel

Abstract

Steam reforming is one option currently being investigated for stabilization of the cesium/strontium strip products from spent fuel reprocessing solvent extraction processes because it can potentially destroy the nitrates and organics present in these aqueous, nitrate‐bearing solutions, while converting the cesium and strontium into leach resistant aluminosilicate minerals, such as pollucite. To produce pollucite and other mineral analogs of the alkaline metals, the feeds must be mixed with aluminosilicate compounds and thermally sintered or calcined to activate solid‐state crystal formation. Scoping tests completed indicated that the cesium/strontium in these organic and acid solutions can be converted into aluminosilicate materials using steam reforming.     

RECOVERY OF URANIUM FROM ACID MEDIA BY MACROPOROUS BIFUNCTIONAL PHOSPHINIC ACID RESIN

ABSTRACT

The extraction of uranium from various acid media such as nitric acid, sulphuric acid, hydrochloric acid, phosphoric acid and perchloric acid by a macroporous bifunctional phosphinic acid resin (MPBPA) has been studied. The distribution coefficients for the extraction of uranium by the MPBPA resin are compared with the corresponding values reported in literature for the conventional sulphonic acid resin. The results clearly indicate the suitability of the MPBPA resin to recover uranium from different types of acid solutions of widely ranging acidities.     

Evaluation of Elution Parameters for Cesium Ion Exchange Resins

Abstract

Cesium ion exchange is one of the planned processes for treating and disposing of waste at the U.S. Department of Energy Hanford Site. Radioactive supernatant liquids from the waste tanks will undergo ultrafiltration, followed by cesium ion exchange using a regenerable organic ion exchange resin. Two resins, SuperLig^®644 and a resorcinol‐formaldehyde resin, are being evaluated for cesium removal and cesium elution characteristics. The main purpose of this study is to optimize the cesium elution to provide a resin that, after undergoing elution, would meet the U.S. Department of Energy/Office of River Protection Project‐Waste Treatment Plant processing and resin disposal criteria. Columns of each resin type were loaded to greater or equal to 90% breakthrough with a Hanford waste stimulant and eluted with nitric acid. The temperature, flow rate, and nitric acid concentration were varied to determine the optimal elution conditions. Temperature and eluant flow rate were the most important elution parameters. As would be predicted based upon kinetic consideration alone, decreasing the eluant flow rate and increasing the temperature provided the optimal elution conditions. Varying the nitric acid concentration did not have a significant effect on the elution completion; however, elutions performed using both high acid concentration (1 M) and elevated temperature (45°C) resulted in resin degradation, causing gas generation and resin bed disruption.     

EXTRACTION OF ACTINIDES BY BIFUNCTIONAL PHOSPHINIC ACID RESIN

ABSTRACT

The extraction of U(VI), Am( III), Pu( IV), Np( IV) and ThIV) by bifunctional phosphinic acid resin of various cross linkages is reported as function of nitric acid concentration. From the comparison of the distribution coefficient values it is suggested that the recovery of these actinide elements from waste solutions as we II as their mutual separations is possible by using phosphinic acid resin.     

Alternatives to Nitric Acid Stripping in the Caustic‐Side Solvent Extraction (CSSX) Process for Cesium Removal from Alkaline High‐Level Waste

Effective alternatives to nitric acid stripping in the Caustic‐Side Solvent Extraction (CSSX) solvent have been demonstrated in this work. The CSSX solvent employs calix[4]arene‐bis(tert‐octylbenzo‐18‐crown‐6) (BOBCalixC6) as the cesium extractant in a modified alkane diluent for decontamination of alkaline high‐level wastes, such as those found at the Savannah River and Hanford sites. Results reported in this paper support the idea that replacement of the nitrate anion by a much more hydrophilic anion like borate can substantially lower cesium distribution ratios on stripping. Without any other change in the CSSX flowsheet, however, the use of a boric acid stripping solution in place of the 1 mM nitric acid solution used in the CSSX process marginally, though perhaps still usefully, improves stripping. The less‐than‐expected improvement was explained by the carryover of nitrate from scrubbing into stripping. Accordingly, more effective stripping is obtained after a scrub of the solvent with 0.1 M sodium hydroxide. Functional alternatives to boric acid include sodium bicarbonate or cesium hydroxide as strip solutions. Profound stripping improvement is achieved when trioctylamine, one of the components of the CSSX solvent, is replaced with a commercial guanidine reagent (LIX^® 79). The more basic guanidine affords greater latitude in the selection of aqueous conditions in that it becomes protonated even at mildly alkaline pH values. Under process‐relevant conditions, cesium distribution ratios on stripping are approximately 100‐fold lower compared with the current CSSX performance. The tolerance to surfactants is good, and the extraction properties of the solvent remain unchanged over three successive extract‐scrub‐strip cycles. From the point of view of compatibility with downstream processing, boric acid represents an attractive stripping agent, as it is also a potentially ideal feed for borosilicate vitrification of the separated ¹³⁷Cs product stream. The possibilities for use of these results toward a dramatically better next‐generation CSSX process, possibly one employing the more soluble cesium extractant calix[4]arene‐bis(2‐ethylhexylbenzo‐18‐crown‐6) (BEHBCalixC6) are discussed.     

Separation of La(III), Eu(III), and Ho(III) with Sorbents Impregnated by Mixtures of Acidic Phosphoryl Podands and Amines in Nitric Acid Solutions

ABSTRACT

The possibility of separation of La(III), Eu(III), and Ho(III) as respective individual representatives of light, medium, and heavy rare earth elements was studied using sorbents impregnated by mixtures of acidic phosphoryl podands derived from diethylene glycol and octyl, dioctyl, and trioctyl amines from nitric acid solutions of various concentrations. The influence of the phosphoryl podands structure, their percentage content, and proportion in a sorbent and the nature of an acid on the efficiency of separation of La(III), Eu(III), Ho(III) was studied. It is shown that the greater is the concentration of HNO₃, the smaller are the separation factors of REEs, and remarkably so. The most efficient separation is achieved with the concentration of HNO₃ not over 0.04 mol/L. The optimal conditions of separation of La(III), Eu(III), and Ho(III) with the developed sorbent were found. Repeated use of the sorbent for the separation of La(III), Eu(III), and Ho(III) after its regeneration with 0.04 mol/L HNO₃ was estimated. It was found that the efficiency of separation of REEs with the sorbents impregnated by a mixture of 1,5-bis(2-oxyethoxyphosphoryl-4-ethylphenoxy)-3-oxapentane and trioctylamine (TOA) exceeds markedly that made of a mixture of di-(2-ethylhexyl)phosphoric acid (DEHPA) and TOA.     

Reactivity of Metal Oxide Sorbents for Removal of Sulfur Compounds from Coal Gases at High Temperature and Pressure

Abstract

Hot-gas desulfurization for the integrated gasification combined cycle (IGCC) process has been investigated to effectively remove hydrogen sulfide with various metal oxide sorbents at high temperatures and pressures. Metal oxide sorbents such as zinc titanate oxide, zinc ferrite oxide, copper oxide, manganese oxide, and calcium oxide were found to be promising sorbents in comparison with other removal methods such as membrane separation and reactive membrane separation. The removal reaction of H₂S from coal gas mixtures with zinc titanate oxide sorbents was conducted in a batch reactor. The main objectives of this research are to formulate promising metal oxide sorbents for removal of hydrogen sulfide from coal gas mixtures, to compare reactivity of a formulated sorbent with a sorbent supplied by the Research Triangle Institute at high temperatures and pressures, and to determine effects of concentrations of moisture contained in coal gas mixtures, and to determine effects of concentrations of moisture contained in coal gas mixtures on equilibrium absorption of H₂S into metal oxide sorbents. Promising durable metal oxide sorbents with high-sulfur-absorbing capacity were formulated by mixing active metal oxide powders with inert metal oxide powders and calcining these powder mixtures.     

Sorption of palladium on carbon adsorbents from nitric acid solutions

Sorption recovery of palladium from nitric acid solutions on carbon adsorbents BAU, LKAU-7, ABG and UC has been investigated using model solutions with concentrations 8 × 10⁻⁴–8 × 10⁻³ mol/l for palladium and 1, 2 and 5 mol/l for nitric acid. The recovery degrees of Pd(II) depend on the concentration of palladium in contacting solutions as well as on the type of sorbent used. On average, they reach 60%–100% with the maximum in 1 M HNO₃ The palladium desorption by 10% thiocarbamide solution in 1M H₂SO₄ proceeds completely for the sorbent LKAU-7. The use of thiocarbamide solutions in 0.1 M NaOH increases the desorption of palladium from the sorbents BAU and UC up to 80%–85%     

Recovery of purified radiocesium from acidic solution using ammonium molybdophosphate and resorcinol formaldehyde polycondensate resin

Separation of Cs⁺ from acidic solution was investigated using ammonium molybdo- phosphate (AMP) based sorbents. Four sorbents including two AMP powders and two composites prepared by coating of AMP powder on polymethylmethacrylate (PMMA) beads were used in this study. Equilibrium sorption isotherms for Cs⁺ on AMP sorbents were determined. The effect of H⁺ concentration on Cs⁺ uptake by AMP–PMMA beads was examined. Two column runs were carried out to establish the Cs⁺ separation performance of AMP–PMMA beads from 1.0 M nitric acid having Cs⁺ concentration equivalent to 10 Ci of ¹³⁷Cs per litre. Recovery of Cs⁺ from loaded AMP–PMMA column was carried out by dissolution of AMP using NaOH solution. The feasibility of ion exchange purification of the recovered Cs⁺ solution was examined using resorcinol formaldehyde polycondensate resin (RFPR). The Cs⁺ sorption isotherm on RFPR from Cs-bearing dissolved AMP solution was determined. Purification of Cs⁺ from dissolved AMP solution was studied in two column runs using RFPR in loading-elution cycles. The results of these studies are useful in formulating a scheme for the recovery of purified ¹³⁷Cs product from high level waste for large-scale utilization as a radiation source in industrial irradiators.     

The Mechanical Properties and Chemical Resistance of Short Glass-Fiber-Reinforced Epoxy Composites

ABSTRACT

Epoxy–short glass fiber composites were prepared by directly blending two-pack system of Araldite (CY-230) and hardner (HY-951) with short glass fibers. The short glass fiber content was varied from 2% to 10% by weight of the total matrix. These composites were then characterized for morphology using scanning electron microscopy, mechanical properties, that is, tensile and flexural properties and resistance toward various chemicals. The epoxy-glass fiber composites showed improved tensile and flexural properties but increased dispersion among the properties with increasing fiber content. Several reasons to explain these effects in terms of reinforcing mechanisms were discussed. These composites were stable in most chemicals but were completely destroyed in concentrated sulfuric acid, nitric acid, and pyridine.     

POLYNITROGEN REAGENTS,IN METAL SEPARATION. PART 5 THE EXTRACTION OF URANIUM(VI) FROM SULPHURIC,NITRIC AND HYDROCHLORIC ACID MEDIA WITH ALKYLDIAMHONIUM EXTRACTANTS.

ABSTRACT

A variety of a1kyldiammonium extractants (tertiary and quaternary) were used to extract uranium(VI) from sulphuric, nitric and hydrochloric acid media. The performance of these extractants was compared with that of Aliquat-336 and Alamine-336. Extractions from dilute uranium(VI) solutions were carried out in order to simulate conditions employed in the local mining industry     

The Radiation Chemistry of the Cs-7SB Modifier used in Cs and Sr Solvent Extraction

Abstract

The compound 1-(2,2,3,3,-tetrafluoropropoxy)-3-(4-sec-butylphenoxy)-2-propanol, also called Cs-7SB, is used as a solvent modifier in formulations containing calixarenes and crown ethers for cesium and strontium extraction from nuclear waste solutions. The compound solvates complexes of both metals and decreases in its concentration result in lowered extraction efficiency for both. The use of Cs-7SB in nuclear-solvent extraction ensures that it will be exposed to high-radiation doses, and thus its radiation-chemical robustness is a matter of interest in the design of extraction systems employing it. The behavior of the compound in irradiated solution, both in the presence and absence of a nitric acid aqueous phase was investigated here using steady state- and pulsed-radiolysis techniques. The rate constants for the aqueous reactions of Cs-7SB with ^?H, ^?OH, ^?NO₃, and ^?NO₂ radicals are reported. UPLC-UV-MS results were used to identify major products of the radiolysis of Cs-7SB in contact with nitric acid, and revealed the production of hydroxylated nitro-derivatives. Reaction mechanisms are proposed and it was concluded that the aryl-ether configuration of this molecule makes it especially susceptible to nitration in the presence of radiolytically-produced nitrous acid. Fluoride yields are also given under various conditions.     

EXTRACTION OF PLUTONIUM (III) BY TBP IN PRESENCE OF URANIUM

ABSTRACT

The distribution ratio (D) values for the extraction of plutonium (III) from nitric acid medium into 30% TBP in n-dodecane saturated with uranium(VI) (0% to 80%) were determined. For a fixed saturation of TBP with uranium, the D values for Pu(III) were found to increase with increase in nitric acid concentration (1M to 5M). At a fixed nitric acid concentration, the D values were found to decrease with increase in loading of TBP with uranium. The D values for the extraction of Pu(III) using 20% TBP in n-dodecane and 30% TBP in n-paraffin at 80% uranium saturation were also determined The distribution data was least squares analysed against concentration of HNO₃ as well as percentage saturation of TBP with uranium and the coefficients obtained are reported. For all these extraction systems, D values for U(VI) were also determined.