INVESTIGATION INTO OPTIMAL CONDITIONS FOR CROSS -FLOW FILTRATION OF HIGH-LEVEL NUCLEAR WASTE

ABSTRACT

The Savannah River Site has 23 Type III high-level radioactive waste tanks, each with a storage capacity of 1.3 million gallons. These tanks contain nearly 9 million gallons of precipitated salt. To immobilize the waste, the salt is dissolved through water addition, followed by precipitation of the radionuclides through the addition of sodium tetraphenylborate. This precipitate is then concentrated and washed to remove sodium through cross-flow filtration. This waste pretreatment process started radioactive operation in late 1995. During the normal plant operation, the cross-flow filtration system (consisting of two 216-square-foot filter elements) maintains a constant filtrate production rate. This Objective is achieved by allowing the operating pressure to increase to maintain a constant filtrate production rate. A maximum pressure differential limit of 40 psig has been imposed on this system. When this maximum is approached, a high-energy backpulse of filtrate removes foulant from the surface of the filter, thereby restoring the filter flux.

This laboratory work examined two key aspects of the anticipated facility operating conditions: the efficacy of using pressure differential to control filtrate production rates and the risk posed to filter performance associated with pore plugging of the filter immediately following the backpulse. Tests used simulated tetraphenylborate precipitate and a bench-scale cross-flow filtration unit consisting of two parallel filter units each 4 feet in length. Tests used slurries containing between 1 and 10 wt % tetraphenylborate to cover the anticipated range of operation. Data collected included both initial flux-decline measurements and steady-state filtrate production measurements. Analysis of these data indicates, for the more dilute slurries, pressure was an effective tool in controlling filtrate flux. However, as the slurry became more concentrated, the ability to manipulate filtrate flux by pressure greatly diminished. Analysis of the initial filtrate decline data using first- principle models indicates that the primary mechanism for decreasing filter flux involved development of a surface cake. Given the operating constraints of the facility, these results provide guidance for future filtration operation.     

UNIVERSAL SOLVENT EXTRACTION (UNEX) FLOWSHEET TESTING FOR THE REMOVAL OF CESIUM,STRONTIUM, AND ACTINIDE ELEMENTS FROM RADIOACTIVE,ACIDIC DISSOLVED CALCINE WASTE

ABSTRACT

The presence of long-lived radionuclides presents a challenge to the management of radioactive wastes. Separation of the radionuclides from the waste solutions has the potential of significantly decreasing the costs associated with the immobilization and disposal of the radioactive waste by minimizing waste volumes. Typically, several separate processes are required for the separation of cesium, strontium, and actinides from radioactive wastes. A novel solvent extraction process, the Universal Extraction (UNEX) process, has been developed for the simultaneous separation of cesium, strontium, and the actinides from radioactive acidic waste solutions. The UNEX process solvent consists of chlorinated cobalt dicarbollide for the extraction of ¹³⁷Cs, polyethylene glycol for the extraction of ⁹⁰Sr, and diphenyl-N,N-di-n-butylcarbamoylmethyl phosphine oxide for the extraction of the actinides and lanthanides. A non-nitroaromatic polar diluent, phenyltrifluoromethyl sulfone, is used for this process. A UNEX flowsheet consisting of a single solvent extraction cycle has been developed as a part of a collaborative effort between the Khlopin Radium Institute (KRI) and the Idaho National Engineering and Environmental Laboratory (INEEL). This flowsheet has been demonstrated with actual dissolved radioactive calcine waste at the INEEL using 24 stages of 2-cm diameter centrifugal contactors installed in a shielded hot cell facility. For the major radionuclides, 99.99% of the ¹³⁷Cs, 99.73% of the ⁹⁰Sr, and >99.9% of the actinides in the initial dissolved calcine feed were extracted and recovered in the high activity fraction. For the stable matrix elements, 12% of the Mo, 0.7% of the Zr, and 2% of the Fe were extracted and recovered in the strip product. The minor components Ba and Pb were quantitatively extracted and recovered in the strip product; 23% of the Mn was also present in this fraction. Very little Al, Ca, Cr, Na, and Ni were extracted into the UNEX solvent.     

Correlation of Filtrate Flow Rate for Irradiated and Unirradiated Tetraphenylborate Slurries

Abstract

The filtrate flow rates obtained during the cross-flow filtration of slurries are dependent on the properties of the slurry particles. Tetraphenylborate is used to precipitate radioactive cesium from supernate salt solutions at the Savannah River Site. These slurries are then processed by a sequence of filtration steps. However, prior to the last filtration step, the slurries are exposed to significant doses of irradiation that appear to dramatically change the properties of these particles. A concomitant decrease in filter performance has been observed. An empirical model has been developed to predict the impact of irradiation on filtration. This model also predicts the dependency of performance on axial velocity and pressure drop.     

PARTITIONING OF MERCURY FROM ACTINIDES IN THE TRUEX PROCESS

A mercury complexant, L-cysteine hydrochloride, was tested for use in separating Hg(II) from actinides during transuranic extraction (TRUEX) processing of wastes at the Idaho National Engineering and Environmental Laboratory (INEEL). Mercury, americium, plutonium, and uranyl distributions for the TRUEX solvent were characterized over a nitric acid concentration range of 0.01 to 2 M with and without cysteine. The applicability of cysteine was evaluated for selective Hg(II) complexation in an INEEL sodium-bearing waste simulant. A test was also conducted to evaluate the applicability of cysteine to separate Hg(II) from Sr in the strontium extraction (SREX) process with Sr Resin used as a stand-in for the SREX process solvent. In all cases, the use of L-cysteine HCl retained Hg in the aqueous phase while causing no or little perturbation in the actinide and Sr distribution behavior.     

The cross-flow filtration of an unstable β-lactam antibiotic fermentation broth

A ceramic cross-flow filter has been evaluated in a recycle loop connected to a bioreactor containing a viscous Streptomyces sp. broth. Because of the instability of the antibiotics formed, it would be advantageous to extract them continuously as they are produced. The performance of the filter, under conditions of high viscosity and suspended solids, has been calculated. Resistance to filtrate flux, distribution of the antibiotic and sterilisability within the system were also examined. An initial flux at a cross-flow velocity of 4 ms^?1 gave readings of 162 litres m^?2 h^?1, which dropped to 131 litres m^?1 h^?1 on subsequent runs because of ‘bedding-in’. Fluxes were improved by an increase of cross-flow velocity and, for short periods, by applying pressure. They were reduced by anti-foam agents and the gradual build-up of particle polarisation layers. Loop sterilisation and removal of the antibiotic in the filtrate stream were excellent.     

膜过滤优化大观霉素提炼工艺

利用膜技术优化大观霉素提炼生产工艺,对金属膜过滤和板框分离进行了对比实验,对滤液的收率和质量进行了考察。结果表明,采用膜过滤,原液质量得到提高,可以省去原液复滤,过滤收率提高8%。     

Ultrafilter Conditions for High‐Level Waste Sludge Processing

Abstract

Optimal filtration conditions were evaluated for the ultrafiltration process planned for pretreating high‐level waste (HLW) sludge in the Hanford Waste Treatment Plant. This sludge must be filtered in the pretreatment process to remove sodium and, consequently, reduce the number of canisters for storage. The evaluation, which was based on Hanford HLW slurry test data, was performed to identify the optimal pressure drop and crossflow velocity for filtration at both high and low solids loading. Results from this analysis indicate that the actual filtration rate achieved is relatively insensitive to these conditions under anticipated operating conditions. The maximum filter flux was obtained by adjusting the system control valve pressure to between 400 kPa and 650 kPa while the filter feed concentration increased from 5 wt% to 20 wt%. However, operating the system with a constant control‐valve pressure drop of 500 kPa resulted in a reduction of less than 1% in the average filter flux. Also, allowing the control valve pressure to swing as much as ±20% resulted in less than a 5% decrease in filter flux. This analysis indicates that a back pressure setting of 500 kPa±100 kPa will give effectively optimal results for the system of interest.     

Integrated pore blockage-cake filtration model for crossflow filtration

Crossflow filtration is to be a key process in the treatment and disposal of approximately 60,000 metric tons of high-level radioactive waste stored at the Hanford Site in Richland, Washington. Pacific Northwest National Laboratory is assessing filter performance with waste simulant materials that mimic the chemical and physical properties of Hanford tank waste. Prior simulant studies indicated that waste filtration performance may be limited by pore and cake fouling. To limit the shutdown of waste treatment operations, the pre-treatment facility plans to recover filter flux losses from cake formation and filter fouling by frequently backpulsing the filter elements. The objective of the current paper is to develop a simple model of flux decline resulting from cake and pore fouling and potential flux recovery through backpulsing of the filters for Hanford waste filtration operations. To this end, a model capable of characterizing the decline in waste simulant filter flux as a function of both irreversible pore blockage and reversible cake formation is proposed. This model is used to characterize the filtration behavior of Hanford waste simulants in both continuous and backpulsed operations. The model is then used to infer the optimal backpulse frequency under specific operating conditions.     

Laboratory‐Scale Column Testing Using Crystalline Silicotitanate (IONSIV™ IE‐911) for Removing Cesium from Acidic Tank Waste Simulant. 1: Cesium Exchange Capacity of a 15‐cm3 Column and Dynamic Stability of the Exchange Media*

Abstract

Bench‐scale column tests were performed using a commercial form of crystalline silicotitanate (CST) for removing radio‐cesium from a surrogate acidic tank solution representative of liquid waste stored at the Idaho National Engineering and Environmental Laboratory (INEEL). An engineered form of CST ion exchanger, known as IONSIV? IE‐911 (UOP, Mt. Laurel, NJ, USA), was tested in 15 cm³ columns at a flow rate of 5 bed volumes per hour. These experiments showed the ion exchange material to have reasonable selectivity and capacity for removing cesium from the complex chemical matrix of the solution. However, previous testing indicated that partial neutralization of the feed stream was necessary to increase the stability of the ion exchange media. Thus, in these studies, CST degradation was determined as a function of throughput in order to better assess the stability characteristics of the exchanger for potential future waste treatment applications. Results of these tests indicate that the degradation of the CST reaches a maximum very soon after the acidic feed is introduced to the column and then rapidly declines. Total dissolution of bed material did not exceed 3% under the experimental regime used.     

Evaluation of the SREX Solvent Extraction Process for the Removal Of 90Sr and Hazardous Metals from Acidic Nuclear Waste Solutions Containing High Concentrations of Interfering Alkali Metal Ions

Abstract

The SREX process, which was developed at Argonne National Laboratories, has been evaluated for its effectiveness for the decontamination of radioactive liquid waste at the Idaho Chemical Processing Plant located at the Idaho National Engineering Laboratory. The extraction solvent consists of 0.15 M 4′,4′,(5′)-di-(t-butyl-dicyclohexo)-18-crown-6 in either 1.2 M TBP/Isopar L®. Suppressed extraction due to matrix interferences limits D_Sr values to the range of 3-4 in batch extraction experiments. The SREX solvent has been shown to be effective in the removal of non-radioactive Pb from liquid wastes, in addition to the extraction of ⁹⁰Sr. The information from this study has been used to develop a proposed flowsheet for the treatment of liquid waste in centrifugal contactors.     

WASTE TREATMENT AT THE RADIOCHEMICAL ENGINEERING DEVELOPMENT CENTER

ABSTRACT

At the Radiochemical Engineering Development Center (REDC), irradiated targets are processed for the recovery of valuable radioisotopes, principally transuranium nuclides. A system was recently installed for treating the various liquid alkaline waste streams for removal of excess radioactive contaminants at REDC. Radionuclides that are removed will be stored as solids, and thus the future discharge of radionuclides to liquid-low level waste tank storage will be greatly reduced. The treatment system is of modular design and is installed in a hot cell at REDC, where preliminary testing is in progress. The module incorporates the following: (1) a resorcinol-formaldehyde resin column for cesium removal, (2) a cross-flow filtration unit for removal of rare earths and actinides as hydroxide, and (3) a waste solidification unit. Process flowsheets for operation of the module, key features of the module design, and its computer-assisted control system are presented. Good operability of the cross-flow filter system is mandatory to the successful treatment of REDC wastes. Results of tests to date on the operation of the filter in its slurry collection mode and its slurry washing mode are presented. These tests include the effects of entrained organic solvent in the waste stream to the filter.     

Ultrafiltration behavior in the treatment of agro-industry effluent: Pilot scale studies

This pilot-scale study deals with highly polluting agro-industry's wastewater, palm oil mill effluent (POME). Ceramic ultrafiltration membrane was applied to treat this effluent. UF separation behavior of POME is reported. The effects of transmembrane pressure and crossflow velocity on permeate flux, limiting flux and percentage rejection for suspended solids and dissolved organic matters were investigated. The limiting flux obtained was further applied to determine critical flux and deposit resistance, R_c, using the possible theoretical link of critical flux and limiting flux. The verified values of critical flux are useful in the operation of ultrafiltration to minimized membrane fouling; thus, longer lifespan of the membrane can be expected. Both transmembrane pressure and crossflow velocity show their significant effects to the permeate flux, whereas only the crossflow velocity influences the rejection of dissolved organic matters in terms of COD and BOD.     

Adsorption behavior and effectiveness of poly(N,N‐dimethylacrylamide‐co‐Ca 2‐acrylamido‐2‐methylpropanesulfonate) as cement fluid loss additive in the presence of acetone‐formaldehyde‐sulfite dispersant

A copolymer of N,N‐dimethylacrylamide and Calcium 2‐acrylamido‐2‐methylpropanesulfonate was synthesized by free‐radical copolymerization. Its performance as anionic fluid loss additive (FLA) was studied by measuring static filtration properties of oil well cement slurries at 27°C and 70 bar pressure, respectively. It was found that cement filter cake permeability and API fluid loss decrease with increasing FLA dosage. Filtrate analysis revealed a linear correlation between fluid loss and the amount of FLA adsorbed on the cement surface. FLA adsorption on cement was determined by total organic carbon (TOC) analysis in cement filtrate and confirmed by ζ‐potential measurement. According to environmental scanning electron microscopy (ESEM) investigations, FLA does not alter the filter cake structure. In the presence of an anionic acetone–formaldehyde–sulfite (AFS) polycondensate dispersant, fluid loss control from FLA decreased and cement filter cake permeability increased because AFS reduces the amount of FLA adsorbed. In comparison to FLA, AFS shows stronger adsorption on the cement surface and succeeds in the competition with FLA. The different adsorption behavior of the two polymers is the reason for limited compatibility of this admixture com bination. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4341–4347, 2006     

Effect of Acid Cleaning and Calcination on Rheological Properties of Concentrated Aqueous Suspensions of Silicon Nitride Powder

The powder characteristics of two types of Si₃N₄ (referred to as FD1 and FD2), as well as the rheological properties of their aqueous suspensions, were studied in this paper. There are distinctive differences in size distribution, soluble counterions, and surface groups. Highly concentrated aqueous slurries could not be prepared from these two as-received powders. Acid cleaning and calcination improved the solids loading of their aqueous slurries, but the improvement varied with the powder. For the as-received FD1 powder, poor dispersibility was caused by high-valence counterions, which can be eliminated through acid-cleaning. However, for the as-received FD2 powder, it was the surface group of amine structures and carbon-hydrogen bonding that limited the dispersibility. The calcination of FD2 can remove the amine structure and carbon-hydrogen bonding and improve the slurry's rheological properties almost perfectly. For acid-cleaned and calcined FD1, and calcined FD2, the solids loading of their aqueous suspensions reached 50 vol% with a viscosity below 300 mPa·s.     

采用超高分子量聚乙烯过滤介质强化过滤过程的研究

采用颗粒烧结法制备的超高分子量聚乙烯过滤介质,对用途广泛、难过滤的一种无机盐醋酸钙物料做了动态强化过滤过程研究。在对3种超高分子量聚乙烯过滤介质表征的基础上,考察了不同操作压力、旋转速度、固含量、操作温度等对过滤过程的影响。研究表明,过滤通量随着过滤介质孔径增大、压力增大、温度升高、固含量降低均有所增加,截留效果较好,滤液浊度都在30.0 NTU以下,实现了有效的过滤分离,可供技术工程化应用研究参考。     

Pretreatment of seawater: Results of pilot trials in Singapore

In this paper, performance ofdifferent pretreatment systems used in the seawaterreverse osmosis desalination process is presented. The different pretreatment techniques analyzed included conventional media-filtration technique and non-conventional membrane filtration techniques. For the membrane filtration techniques, two ultrafiltration and one microfiltration pilot plants were used in the experimental study. During the experiments, the silt density index (SDI) of the filtrate samples was regularly measured to quantify the performance of pretreatment systems in rejecting colloidal particles. Measurements of other important parameters included filtrate flux, transmembrane pressure, total suspended solids, colloidal silica, total organic carbon, etc. According to the experimental findings, the quality of the filtrate produced by the conventional media-filtration technique was inferior and highly inconsistent. SDI of filtrate varied from 2.8 to 3.8 and spikes as high as 6.3 were frequently observed. Membrane pretreatment produced filtrate of a better quality. SDI ofthe filtrate produced was consistently below 3.0, a prerequisite for proper operation of a RO desalination plant. The ease of operation of the membrane pretreatment processes was also noted. Together with improved maintenance procedures such as filtrate backwashing and air scouring, complete flux and pressure recoveries were achievable with minimal use of chemicals during the experiments.     

The use of dean vortices for crossflow microfiltration: basic principles and further investigation

The effect of Dean vortices on the filtration flux and efficiency of crossflow microfiltration processes in sinusoidal curved and helically coiled tubular membranes was investigated by several research groups. Experimental results are presented showing an enhanced filtrate flux and efficiency of the filtration process. CFD simulations were performed, revealing two important effects of secondary flow: an increased wall shear stress causing a reduced particle deposition and an enhanced mass transfer between the boundary layer and the bulk phase.     

A preliminary study into the local solids fluxes in a downer reactor

A non-isokinetic sampling method was used to study the effects of gas velocity, solids circulation rate and axial and radial positions on the local solids flux in a gas–solids downer fluidized bed. The radial profiles of solids flux are highly dependent on the axial position. The local solids flux is also dependent on the overall solids circulation rate but not dependent on the gas velocity. The solids flux profiles in the downer were also found to be quite different from those reported in the riser.     

Engineering aspects and applications of crossflow microfiltration

Crossflow microfiltration (CMF) is a pressure driven membrane process for the separation of suspended microparticles, bacteria and emulsion droplets. The fluid to be filtered flows in parallel to the membrane surface and restricts the formation of a filter cake. This contribution explains the basic process characteristics and the combination of the crossflow technique with other membrane cleaning methods (periodic backflushing, chemical cleaning). Special attention is paid to the influence of different process parameters on the flux through the membrane. The principle of plant design and different operation modes are described. Engineering aspects such as hydrodynamics, energy requirement and selection of construction materials are discussed in some detail.     

水泥及其复合体系固化放射性核废物研究现状

水泥优良的物理化学性能使其在放射性废物固化领域应用广泛。介绍了水泥固化的机理和对水泥固化体的基本性能要求,并综述了硅酸盐水泥、碱激发胶凝材料、硫铝酸盐水泥和磷酸镁水泥在放射性废物固化领域的研究进展。对水泥基固化材料的发展具有一定的借鉴意义。