A.P. Pazdnikov

A.S. Skobtsov

B.V. Soldatov

M.V. Logunov

Sergey I. Rovny

Y.A. Voroshilov

Comptes Rendus Chimie

Full paper / MémoireResearch and application of inorganic selective sorbentsat Mayak PAM.V. Logunov *, A.S. Skobtsov, B.V. Soldatov, A.P. Pazdnikov,Y.A. Voroshilov, Sergey I. RovnyMayak Production Association, Ermolaev Str, 18, Ozyorsk, Chelyabinsk Region, Russia, 456784Received 1 December 2003; accepted after revision 11 May 2004Available online 5 November 2004AbstractThis work has been performed in order to identify selective inorganic sorbents for caesium and strontium. Thin-layer sorbentswith nickel ferrocyanide embedded in an inert matrix were found to be the best for caesium. Sorbents including non-stoichiometric manganese dioxide were selected for strontium. Bench tests have been carried out on the purification of desaltedwater of SNF storage-pool from 137Cs, and on the purification of contaminated natural water from 90Sr. The facility forsynthesizing the ferrocyanide sorbent with the registered mark ‘Seleks-CFN’ has been brought into operation. The sorbentISM-S seems promising for 90Sr decontamination. To cite this article: M.V. Logunov et al., C. R. Chimie 7 (2004).© 2004 Published by Elsevier SAS on behalf of Académie des sciences.RésuméRecherches et applications sur l’utilisation de sorbants spécifiques à Mayak. Des sorbants sélectifs du césium et dustrontium ont été identifiés. Pour le césium, le meilleur s’avère être le ferrocyanure de nickel, s’il est utilisé sous forme de couchemince. Pour le strontium, on a sélectionné des composés non stœchiométriques de dioxyde de manganèse. On a mené des testsvisant à épurer en césium l’eau des piscines d’entreposage des combustibles nucléaires usagés, et en strontium des eauxcontaminées. Une installation industrielle permettant de préparer le sorbant à base de ferrocyanure de marque « Seleks-CFN » aété réalisée. Le sorbant ISM-S semble prometteur pour la décontamination en strontium. Pour citer cet article : M.V. Logunovet al., C. R. Chimie 7 (2004).© 2004 Published by Elsevier SAS on behalf of Académie des sciences.Keywords: Decontamination; Caesium; StrontiumMots clés : Décontamination ; Césium ; Strontium* Corresponding author.E-mail address: cpl@po-mayak.ru (M.V. Logunov).C. R. Chimie 7 (2004) 1185–1190http://france.elsevier.com/direct/CRAS2C/1631-0748/$ - see front matter © 2004 Published by Elsevier SAS on behalf of Académie des sciences.doi:10.1016/j.crci.2004.05.0061. IntroductionThe use of selective inorganic sorbents is one of themost up-to-date methods of radiochemical waste de-contamination for aqueous low-level waste (LLW).Those of ‘Mayak PA’, coming from drainage system aswell as water from spent-fuel assembly storage pool,are mainly contaminated with 137Cs. Water of storagereservoirs of the ‘Techa River Cascade’ is mainly con-taminated with 90Sr [1]. Such multicomponent con-taminated LLW predetermined the possibility of effec-tive application of selective inorganic sorbents.Mass distribution coefficients of 137Cs for somesynthetic and natural materials were measured in orderto define the most prospective type of Cs selectivesorbents [2]. The results of experiments are given inTable 1. Full-scale dynamic laboratory tests were alsoconducted on real desalted water from the spent-fuelassembly storage pool in order to select the best sor-bent among those offering the more perspectives: fer-rocyanides, phosphates, and zeolites. Filtration rate intop–down direction was supported with about 20 col-umn volumes per hour. Results of the experiments aregiven in Fig. 1. The effective filtration cycle with a137Cs purification factor ≥ 10 was 30 thousand columnvolumes for zeolite CBF-10, and about 60 thousandcolumn volumes for zirconium phosphate (T-3A). Theeffective filtration cycle on nickel ferrocyanides (NZAand T-35) was about 90 thousand column volumes.Thin-layer sorbent demonstrates better hydrolytic sta-bility than composite sorbent.This paper concerns experimental tests on 137Cs and90Sr removal from some aqueous LLW.2. Experimental results2.1. 137Cs decontaminationThe data obtained allowed us to perform experi-mental industrial tests of the process of LLW decon-tamination from 137Cs with water from the specialdrainage system of Mayak PA radiochemical facility,which annual water flow reaches 400 thousands m3 [3].Composition of water used in experimental industrialtests was as follows: not stable; pH value in the rangefrom 7.7 to 8.2, water hardness from 4.65 to10.2 mg equiv l–1, calcium concentration from 46 to117 mg l–1, magnesium from 29 to 53 mg l–1, sodiumfrom 117 to 155 mg l–1, nitrite ion from 624 to1232 mg l–1, 137Cs activity was (7.03–13.4) × 103 Bq l–1.Single synthesis of a large batch (about 8 m3) of ferrocya-nide sorbent NZS, which is a close analogue to NZA, wasperformed. Water purification unit was installed for purifi-cation of special drainage water on the basis of two filtersand the existing manifold pipelines. Filters F-1 andF-2 contained 3.85 m3 of NZS sorbent with size fractionfrom 0.2 to 0.3 mm per each filter. In F-2 NZS, sorbent wasmixed with 0.77 m3 of spent resin KU-2×8 to make acomposition with improved hydrodynamic properties. Ex-perimental sorption filters were operated at water flow rateequal to 25–30 m3 h–1 or 7–8 column volumes per hour perTable 1Values of 137Cs distribution factors depending on the composition of the initial solutionSorbent Caesium distribution factors (ml g–1) from the solutionWater 0.1 M NaNO3 1 M NaNO3 0.05 M Ca(NO3)2Vermiculite (Covdor) 4900 ± 1600 770 ± 180 80 ± 16 2500 ± 800Clinoptilolite (Dzegvi) 5900 ± 400 9700 ± 600 200 ± 10 8600 ± 1600Nickel ferrocyanide (NZA) a 4000 ± 900 3300 ± 300 2800 ± 600 5200 ± 2100Nickel ferrocyanide (Seleks-CFN) a 2800 ± 400 7400 ± 500 26 000 ± 2400 24 200 ± 5200Nickel ferrocyanide (T-35) b 5700 ± 1300 8200 ± 1400 15 700 ± 3000 8600 ± 2000Titanium ferrocyanide (KNTZ) b 2500 ± 900 5500 ± 1400 4400 ± 1100 16 300 ± 4800Iron ferrocyanide (FS-10) b 890 ± 160 2200 ± 300 10 700 ± 600 4000 ± 400Zr phosphate (T-3A) 3900 ± 400 1900 ± 300 460 ± 30 4400 ± 1600CFB-10 c 3600 ± 1000 450 ± 20 82 ± 46 4600 ± 300CMP c 2200 ± 500 440 ± 30 70 ± 12 1700 ± 300Sulfonic cation resin KU-2×8 8100 ± 800 180 ± 20 18 ± 5 16 ± 3a Thin-layer ferrocyanides.b Composite ferrocyanides.c Zeolites.1186 M.V. Logunov et al. / C. R. Chimie 7 (2004) 1185–1190each filter. The results of experimental industrial testing aregiven in Table 2. Data prove that in the process ofapplication of sorption filters at selective caesium ex-traction units (with a purification factor ≥ 10), about85 m3 of special drainage water was decontaminated.The best results were achieved using filter F-2 withadded KU-2×8. About 1.96 TBq of 137Cs were ex-tracted from LLW in total. 137Cs concentration in theFig. 1. Result curves for sorption of 137Cs on inorganic sorbents.Table 2Results of experimental-industrial tests of drainage water decontamination from 137Cs with NZS sorbentOperationstageFilters Filtrate volume Average 137Csactivity in thefiltrates (Bq l–1)Waterdecontaminationfactor from 137CsAmountof extracted137Cs (GBq)Radiation background(µSv s–1)m3 ColumnvolumeOver resin Nearapparatus1 F-1 3266 848 347 15 15.9 0.60 0.30F-2 3266 848 151 35 16.6 0.14 0.302 F-1 17 470 4537 296 77 392.2 4.00 0.30F-2 17 470 4537 128 178 392.2 6.00 0.503 F-1 8649 2246 825 45 316.0 8.00 0.80F-2 8649 2246 181 206 321.5 10.0 1.004 F-1 14 011 3639 3922 4.2 175.8 – –F-2 15 931 4138 403 37 256.4 18.0 1.605 F-2 11 740 3049 507 10.1 54.4 – –Total result F-1 43 396 11 272 1576 14.2 899.9 8.00 0.80F-2 57 056 14 820 292 64 1041.1 18.0 1.601187M.V. Logunov et al. / C. R. Chimie 7 (2004) 1185–1190filtrates exceeded only slightly the admissible level fordischarged industrial water during the major part of thetest. An additional purification factor was obtained onroutine ion-exchange treatment. Thus, discharged wa-ter was practically not contaminated with 137Cs.Experimental-industrial facility Seleks-CFN for thesynthesis of ferrocyanide sorbent of NZS-type with anoutput up to 12 t/year was built up at Mayak PA withconsideration of successful results of experimental in-dustrial tests of synthesis and water purification pro-cess. Seleks-CFN sorbent synthesis is based on satura-tion of granular silica gel or other porous material,loaded into sorption column, with nickel and ferrocya-nide ions. Water solutions of nickel ammoniate orpotassium ferrocyanide are used. A sparingly solublecompound, nickel-potassium ferrocyanide, forms as aresult of such a treatment in silica gel pores.Seleks-CFN facility was commissioned in 1999 andit works in periodic mode when it is necessary. About1420 kg of Seleks-CFN sorbent were synthesized inthe course of the facility operation. The effective pH ofcontaminated water for Seleks-CFN sorbent is in therange 2–12. Statistic exchange capacity for caesium isup to 30 mg g–1. Half-exchange time is 2.1 min.A process technology and a prototype of the indus-trial facility for decontamination of desalted water ofspent-fuel assembly (SFA) storage pool were devel-oped using this sorbent. A pilot sorption facility withsorbent volume of 65 l was mounted on the slottedcovering of the pool. The column itself was placed atthe depth about 3 m, which provided sufficient radia-tion shielding. In order to decontaminate the maximumvolume of water in the storage pool, water was takenfor treatment and purified water was discharged fromthe column in the opposite loci of the storage pool.Sorption column was used with bottom up flow ratefrom 2.5 m3 h–1 to 6.0 m3 h–1. The results of theexperiment are presented in Table 3. They show that22 885 m3 of water were filtered through the sorbentduring the experiment, which is equal to about253 thousand column volumes. High water purifica-tion efficiency and column hydrodynamic characteris-tics were stable during the whole filtration cycle. Ac-tivity of the initial water decreased 5 times for 137Cs.Preliminary calculation show that 2.07TBq of 137Cswere deposited in the column. The data show thatMayak PA developed an effective process of SFAstorage-pool water decontamination from 137Cs.2.2. 90Sr decontaminationThe most advanced oxy-hydrate sorbents whosecomposition is based on non-stoichiometric manga-nese dioxide were studied for purification of non-saline natural waters from 90Sr in static and dynamicconditions. The following sorbent types were used:ISM-S with composition (Na, K)xMnOy, wherex = 0.25 to 0.3 and y = 1.9 to 2.1, as well as ISM-SP,which is the same sorbent, fixed in a matrix of inertmedium (perchlorovinyl). Method was developed andsorbents were synthesized in Russia in the city of Permunder the leadership of Professor V. Volkhin [4]. TheTable 3Results of experimental/industrial tests of water treatment process in the storage pool using Seleks-CFN sorbentOperation stage Filtrated watervolume, m3Radionuclide activityin initial water (Bq l–1)Radionuclide activityin filtrate, (Bq l–1)Water decontaminationfactor from 137Cs137Cs 134Cs 137Cs1 3706 1.49 × 105 1.73 × 103 2.53 × 103 592 3601 1.49 × 105 1.40 × 103 5.0 × 103 309.93 × 104 1.20 × 103 3.33 × 103 303 2990 1.12 × 105 1.07 × 103 3.27 × 103 344 2423 8.80 × 104 – 1.20 × 103 735 2901 7.47 × 104 600 < 100 > 7006 2687 5.30 × 104 313 387 1404.67 × 104 400 213 2207 1239 5.90 × 104 667 333 1808 2370 5.49 × 104 733 667 825.70 × 104 667 333 1709 968 3.0 × 104 333 467 64Total 22 8851188 M.V. Logunov et al. / C. R. Chimie 7 (2004) 1185–1190peculiar feature of these sorbents in comparison withwell-known natural and synthetic samples on the basisof manganese oxy-hydrate is their ability for reversiblesorption of strontium.It was defined experimentally that the pH rangefrom 6 to 10 with maximum at pH 6.9 is optimal for90Sr sorption with ISM-S sorbent. Radionuclide des-orption is possible in acid medium up to pH 1 to 2 [4].The results of laboratory investigations allowed us toperform experimental industrial tests.Three 3.5-l sorption columns (I to III) filled with thesorbent ISM-SP were used. One additional columnwas filled with a layer of quartz sand for mechanicfiltration of the contaminated water (pH ~ 8, totalbeta-activity about 3.3 kBq l–1, 90Sr activity around1.6 kBq l–1, water hardness –4.5 to 5.4 mg equiv l–1)before being directed toward the sorption columns.Contaminated water went top–down with a flow rate of30 to 35 column volume h–1 trough two concatenatedcolumns. Desorption was obtained with a 0.3-mol l–1solution of HNO3 and regeneration with a 0.2 mol l–1solution of NaOH. Output curves of strontium arepresented in Fig. 2 depending of the columns engagedin the process. Optimum results were obtained forcolumns III–I. This shows that column performancesare different depending on packaging. Over 7 m3(~2000 column volumes) of radioactive contaminatednatural water were decontaminated in the course of thethird test cycle (engaging columns III–I) to the admis-sible level water discharge.The obtained results make it possible to concludethat the ISM-SP (ISM-S) sorbent is quite prospectivefor the decontamination of natural waters from Sr andit can serve as a basis for development of a respectiveprocess technology with a mode sorption–desorption–regeneration. Thus, Mayak PA experts have consider-able experience in the use of inorganic selective sor-bents for applied tasks of radiochemistry.3. Conclusions1. Thin-layer ferrocyanide sorbents are the mosteffective for low-level waste 137Cs decontamination.2. ‘Mayak’ PA is experienced in synthesis of thinlayer ferrocyanide sorbents; purification techniques forFig. 2. Output curves of 90Sr depending of columns engaging in the process.1189M.V. Logunov et al. / C. R. Chimie 7 (2004) 1185–1190special drainage saline water and spent-fuel storage-pool non-saline water are used at the experimentalindustrial scale.3. For 90Sr decontamination of natural contami-nated water, sorbents based on non-stoichiometricmanganese dioxide were tested and recommended foruse.References[1] Y.V. Glagolenko, E.G. Dzekun, E.G. Drozhko, G.M. Medvedev,S.I. Rovny, A.P. Suslov, Radiat. Saf. Probl. 2 (1996) 7.[2] Y.A. Voroshilov, Y.V. Glagolenko, D.N. Kolupaev,K.K. Korchenkin, M.V. Logunov, A.P. Pazdnikov, E.R. Sabi-tov, A.S. Skobtsov, Radiat. Saf. Probl. 1 (2001) 32.[3] A.I. Bardov, Y.A. Voroshilov, N.P. Zemlina, M.V. Logunov,N.N. Prokofyev, B.V. Soldatov, Radiochemistry 41 (1999) 451.[4] Y.A. Voroshilov, M.V. Logunov, N.N. Prokofyev, N.P. Zem-lina, Radiochemistry 45 (2003) 62.1190 M.V. Logunov et al. / C. R. Chimie 7 (2004) 1185–1190

Research and application of inorganic selective sorbents at Mayak PA

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Research and application of inorganic selective sorbents at Mayak PA

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