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J3 B. A. R. C.-933 3 GOVERNMENT OF INDIA ATOMIC ENERGY COMMISSION SEPARATION OF TRIBUTYL PHOSPHATE FROM DEGRADED SOLVBNTS USING SOLVBNT EXTRACTION TECHNIQUE by S. V. Kumar, M N. Nadktrni. A. Ranunujtm, M. VeoktteMD, V. Gopalakrishnan and J. A. Kazi Fuel Reprocessing Division BHABHA ATOMtC RESEARCH CENTRE BOMBAY, INDIA 1977 B.A.R.C.-933 GOVERNMENT OF INDIA «n ATOMIC ENERGY COMMISSION SEPARATION OF TRIBUTYL PHOSPHATE FROM DEGRADED SOLVENTS USING SOLVENT EXTRACTION TECHNIQUE by 8, V,1 Kumar, M. N. Nadkaxni, A. Ramaxrajam, M. V«nkateian» V. Gopaiakrlahnan and X. A. Kasl Fual Reprocessing Dlrlalon BHABHA ATOMIC RESEARCH CENTRE BOMBAY, INDIA 1977 INIS Subject C*f ggrr i B12, B16 DmtcxjylkorBt PUREX PROCESS SOLVENT EXTRACTION MIXER-SETTLERS ACTIVATED CARBON CHARCOAJL THORtUM NITRATES TBP ABSTRACT A solvent extraction method is described for' the recovery of Tributyl Phosphate (TBP) from degraded process solvents. The method involves the separation of TBP and shall solT(SST) from 30% TBP/SSP mixture by thorium nitrate extraction leading to the formation of a heavy phase (Third phase) which contains osssntially TBP. The equilibrium experiments revsaled that by utilizing Thorium feeds of concentrations above 525 g/L. in water at 111 ratio, a 30% TBP/SST mixture can be effectively separated into TBP and SST fractions with light SST phase having about 3% TBP, Using single stage mixer settler experiments, the feasibility of continuous separation of the three phases was assessed. Since there is a tendency for the degraded products of the diluent to seek the TBP phase, additional treatment steps would be necessary for their removal if the TBP is to be reused. Activated charcoal was investigated for this purpose. If purification of the TBP is not envisaged the volume of the organic waste generated la processing .plants could be reduced by separating the diluent and TBP and only the TBP could be sent as concentrated waste. SEPARATION OF TRIBUTYL PHOSPHATE FROM DEGRADED SOLVENTS USING SOLVENT EXTRACTION TECHNIQUE by S. V. Kumar, M. N. Nadkarni, A. Ramanujam, M. Venkatesan, V. Gopalakrishnan and J. A. Kazi 1. INTRODUCTION Among the aqueous processes used for treating the irradiated fuel elements, Purex process using Tributyl Phosphate (TBP) in a diluent as extractant has been widely employed on an industrial scale. In addition, TBP is also used for recovery/refining of uranium from the ores and for its Reparation from rare earth elements. In spite of many merits of TBP as a solvent, it is vulnerable to Uhemical and radiation damage* ' , Even though Its radiation and chemical stability can be considered to be reasonably good, when compared to most of the other organic solvents, however, during protracted use even' moderate radiation and chemical damages can lead to a gradual deterioration in the process performance. The radiolysis of TBP and the diluent leads to the formation of various coznpounds like Dibutyl Phosphate (DBF), Monobutyl Phosphate (MBP), nltroparaffins, carbonyl compounds etc. '. Polymerisation of some of these products has also been reported' '. In the purex process, the presence Of DBP in TBF increases the extraction of uranium, plutonium, zirconium and Ruthenium by this solvent and makes complete stripping of these elements epttrpmely difficult* '. The presence of DBP affects the Zirconium decontamination seriously^ '. Under intense radiation.fields TBP It DBF undergo further damage to form MBP and phosphoric acid in extreme 4ases leading to precipitate formation -2- In process equipments^10). Traces of TBP present la aqueous product streams might find their way into product evaporatfars where the thermal decomposition leads jto the formation of a heavy organic phase and solid degradation products which could Accumulate Pu, Zr and U and cause problem in subsequent cycles1 ' .In some proceasea especially in ore refining plants'13' extraneous matter like compressor oil, lubri- cants etc. find their way into process streams and tend to accumulate in TBP streams affecting its characteristics. In order to mitigate these problems, the solvent is generally washed with sodium carbonate and sodium hydroxide solutions before recycling in the purex process. This step removes DBP and MBF but does not improve the diluent quality . In addition, solvent clean up by iiorpii.on techniques using fresh A12°3 *14^' ZrO2 *15*' TiUaU*16*, activated charcoal*17', macro retl- cular anion exchangers* ' etc.•' have been reported. Liquid scrubbing using ethanoiamines.haye be|en investigated^(19 )'. Improvements in the extraction properties ol TBP have bean reported when the degradation products are esterifled with, dis,sa methane . Various distillation tech- niques have been tested successfully for the purification Of used TBP solvent* ' '. In spit* <jf these efforts, the solvent quality deteriorates over protracted use and has to b* discarded periodically. Depending upon the capacity of the processing pUnts the annual Inventory of TBP is generally of the order of several tons. Hence, it will be worthwhile to explore the possibility of recovering the TBP from spent solvents with a view to either purify it or to reduce the volume of the degraded TBP ao that the wast* volume can be smaller. -3- The Eurowat Process^ ' developed by the Eurochemic Centre enviaagea the ultimate dlaposal of the degraded TBP by formation of a third phase by acid saturation using concentrated phsophoric acid or dissolution of T BP by anhydroua phosporlc acid. The author* report that on loading the TBP in a diluent with concentrated phosphoric ac'd, a third phase ia formed 'Which contains essentially all the TBP and the degraded products. When anhydrous phosphoric acid is used only two phases are formed as the anhy- drous phosphoric acid dissolves the! TBP, and degraded products leaving a diluent phase which la free from ; mpurities. It has however been reported^ - that TBP separated even from pure'TBP/OK by this method has high metal retention properties, particularly for Zlrcor'um and Plutonium. Acid equilibration technique leading to third phase formation has been utilized for ! (22) the development of analytics^ methods for TBP eatimationv ' and other (23) applications . Third phase formation is A commonly encountered phenomenon when mineral acids or tetravelent metal nitrates like Pu, Th, Zr etc. are extracted in TBF systems especially wtien their concentrations is organic phase are very high^24). This is generally attributed to the limited solubility of the TBP complexes of these tetraWtrates In the diluents used^25\ When the limiting solubility of the solute is reached in the TBP diluent mixture, the organic phase splits into two distinct immiscible layers, one having a high TBP and metal nitrata content and the other being mostly the diluent used. This limiting concentration of metal nitrate beyond which the third phase formation occurs is dependent on the acidity, temperature, the nature and concentration tetravalent element, the type of the diluent and thf concen- tration of TBP employed* \ This mode of separation of TBP from diluent haa been examined several year* ago' \ when aorae compound* tike Th(NO3)4, 2rO(NO3)2, FeClj and CaCl2 were studied far this purpose. The main object of theaa studies has been to produca a diluent frea from radio- activity and from phosphorus contamination such that tfc can be reused la . fuel reprocessing or stored in a solid matrix"6' 6'. A TBP recovery method from the degraded solvent employing metal nitrate saturation technique could be advantageous since the diluent and the TBP could be separated using a solvent extraction method by properly choosing the metal nitrates which could be subsequently stripped from the organic phase. The main disadvantages of this technique would be the carry over of the degraded impurities with TBP phase and small losses of TBF to diluent phase. However, this method of separation of TBP could be employed in combination with methods like distillation or solid sorpHon on activated charcoal etc. for purification of TBP. This report deals with the separation of TBP and shell solT (SST) from the TBP/SST mixture by thorium nitrate extraction leading to third phase formation. The report also includes a summary of efforts made to purify a chemically degraded process solvent. 2. SEPARATION OF TBP fROM TBP/SST MIXTURES BY Th(NOj)4 LOADING Extensive data are available on tha formation of third phase during the extraction of Thorium ay TBP dissolved la aliphatic diluents*27'28* which has alao beam review** by Kerteat24). The extraction capacity -5- of TBP for Thorium nltrata la •ufficlantly high such that at high con- eaatratlons, Th(NO3)4 can ba loadad into TflP from water and alao can a* atrippad with waiter by adopting auitabte roluma ration. To atart with, equilibrium axpsrimanta wara conducted tc arrlra at idaal ..onditiona for maximum aeparation of TBP and S8T by Thorium nitrate loading, «nd baaed on tha reaulta, an extraction achama waa propoaad and tested In a laboratory single ataga mixer aattlar unit with fresh 30% TBP in SST and a chemically dagradad solvent, 2.1 Experimental 2.1.1 Reagent a (a) Thorium Nitrate obtained from Indian Raro Earth a Ltd. waa used in all the experiments. V (b) Tributyl Phosphate (from Morsanto Chemicals, USA) diluted with shell nolT (ShelliNetherland) was us«d In all tha experiments. (c) Pure Plutonium (IV) stock conditioned with H2O2 in 8 M HNOj was used for tha Plutonium retention tests performed for degraded TBP solution*. (d) Activated charcoal from BO H (UK) was used la tha purification experiments. 2.1.2 Equilibrium experiments t Tha extractions wara carried out la aeparatbig funnels by taking appropriate volumes of aqueous feed solution and tha organic extractant and manually shaking for S minutes. Tha three layers ware separated aad after cantrlfugatlon wara analysed, 1.1.3 Analytical Procedurea t Tha samples wan analysed for Acidity, Sfcaalty, Thorium content aad also TBP coatent ia tha two organic layers, (a) Estimation of free add was carried eut by flrat ccmplaxiag Thoritur.

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