New Improved Counter-Current Multi-Stage Centrifugal Extractor for Solvent Extraction Proces

STUDIA UNIVERSITATIS BABES-BOLYAI, PHYSICA, SPECIAL ISSUE, 2003

NEW IMPROVED COUNTER-CURRENT MULTI-STAGE CENTRIFUGAL EXTRACTOR FOR SOLVENT EXTRACTION PROCES

Gheorghe Ionita 1, Asashi Kitamoto2, Dumitru Mirica1, Croitoru Cornelia1, Ioan Stefanescu1 and Retegan Teodora1

1-National Institute for Cryogenics and Isotopic Separation Rm-Valcea, P.O. Box 10, Romania, E-mail: [email protected] 2-Tokyo Institute of Technology, O-Okayama, Meguro- ku, Tokyo, 152 Japan

ABSTRACT. Total actinide recovery, lanthanide/actinide separation and the selective partitioning of actinide from high level waste (HLW) are nowadays of a major interest. Actinide partitioning with a view to safe disposing of HLW or utilization in many other applications of recovered elements involves an extraction process usually by means mixer-settler, pulse column or centrifugal contactor. This last, presents some doubtless advantages and responds to the above mentioned goals. A new type of counter-current multistage centrifugal extractor has been designed and performed. Similar apparatus still not found from other published paper yet. The counter-current multi-stage centrifugal extractor was a cylinder made of stainless steel with an effective length of 346 mm, the effective diameter of 100 mm and a volume of 1.5 liters, having horizontal position as working position. The new internal structure and geometry of the new advanced centrifugal extractor (Fig.1) consists in nine cells (units): five rotation units(R), two mixing units (M), two propelling units (P) and two final plates (S) assures the counter-current running of the two phases. The central shaft (CS) having the rotation cells fixed on it is connected by an intermediary connection to an electric motor of high rotation speed The new designed extractor has been tested at 500-2800 rot/min for a ratio of the aqueous/organic phase =1. The results showed that the performances have been generally good and the design demand was reached. New designed counter-current multistage centrifugal extractor may be a promising idea to increase extraction rate of radionuclides and metals from liquid effluents.

Introduction. The separation by extraction of transuranium elements and long- lived nuclides (99Tc, 129I etc) from high level radioactive waste is the key point in radioactive waste management as integrant part of partitioning- transmutation concept. What kind of extraction process can realize such fine partitioning of the high level waste with small radioisotopes inventory, with high recovery and with negligibly secondary wastes. In conventional extractors are needed to improve the separation factor to level of commercial importance. A more compact size, high GH. IONITA, A. KITAMOTO, D. MIRICA, C. CROITORU, I. STEFANESCU and T. RETEGAN throughput and high extraction efficiency as well as the minimization of solvent radiolysis and rapidly achieve steady state operation are necessary. Some strong advantages which determine an major interest for this type of extractor. At present time, the most countries with nuclear fuel processing programs are involved to some degree with centrifugal extractor development.

Counter-Current Multistage Centrifugal Extractor. A new type of centrifugal extractor having a counter-current flowing of phases, an horizontal working position and special inner geometry have been designed and tested. Similar apparatus has not been found in the published papers yet. The counter-current multistage centrifugal extractor is a stainless steel cylinder with a 1.55 l capacity, having more settling and mixing cells set on the central shaft. This can be rotated up to 2800 rpm by means an electric motor connected at central shaft by special connection piece.In the mixing zone, the two phases are mixed.The TBP extracts (in the same time) the radionuclides or metal of interest.In the settling zone the two phaseses are separated. A special geometry of the cells at the both ends of extractor assures the evacuations of organic and aqueous phase. The conceptual layout of advanced counter-current multistage centrifugal extractor is showed bellow.

Inlet of Heavy Inlet of Light Liquid Liquid

R R R R R R R

CS S M P M P S 2 @ 2 Outlet of Light Outlet 2 of Heavy Liquid Liquid 2 Fig.1 Conceptual layout of advanced counter-current multi-stage centrifugal extractor.

Experimental and Results. Preliminary tests concerning the mechanical behaviour showed a good balance and stability. Than the preliminary tests of the hydrodinamics of the two phases show the countercurrent flowing and a good separation of organic and aqueous phases. However some disturbing phenomena (remixing of phases, emulsion formation etc) could be avoided only in extreme operation conditions. In order to improve the separation performances and to avoid such phenomena a new inner geometry of settling and mixing zone has been proposed and performed. The hydrodynamic properties of two phases and NEW IMPROVED COUNTER-CURRENT MULTI-STAGE CENTRIFUGAL EXTRACTOR separation performances of new improved centrifugal extractor were studied for a wide range of operation parameters: 500-2800 rotations per minute, 5-35 sec., residence time, 0.1- 5.0 organic/aqueous flow rate ratio. The influence of the operation parameters on separation performances and on the formation of third phase are presented and discussed in order to select the optimal operation parameters. A separation level for organic and aqueous phases upper of 93% and also a good efficiency for mixing zones

(fig.1) have been obtained for whole range of operation parameters. The disturbing phenomena could be partially avoided.The operating stability of the multi-stage centrifugal extractor is quite good and is very well showed in the figure 2. Some GH. IONITA, A. KITAMOTO, D. MIRICA, C. CROITORU, I. STEFANESCU and T. RETEGAN studies concerning the extension of number of stages and specific aspect for each application are still necessary. Conclusion

The new type of counter-current centrifugal extractor showed satisfied results, it meet the design demand and by its advantages it could be a promising equipment for solvent extraction in chemical and nuclear industry.

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