Indi an Journ al of Chemical Technology Vol. 9, Janu ary 2002, pp. 25-3 1 Studies on electrolytically generated vanadous complexes used in decontamination formulations J Manjanna" & G Venkateswaranb* "Department of Industri al Chemistry, Ku vempu University, Shimoga 577 451, Indi a bApplied Chemistry Di vision, BARC, Trombay, Mumbai 400 085, India Received 27 September 2000; revised 10 November 2001; accepted 15 November 2001 The low oxidati on state metal io n, V 2+ bein g a strong reducing agent can be formul ated/complex ed with suitable che lating agents to obtain a significant dissolution (reductive) of iron ox ides, commonly found on the primary system surfaces (iron base alloys) of water-cooled nuclear reactors. The relative strength of the complexes of V 2+ (as formate) with different chelating agents, L suc h as picolinic acid, EDTA and c itric acid is studied by measurements of redox potenti al and UV-Yisible spectra. The decay kinetics of the reducti o n of water by V(Il)-picolinate (as a typical case) (V 2+ to V 3 + conversion) under deaerated condition was estimated using redox potential values and decay was found to follow two stages of first order kinetics with a faster initial stage (k 1=3.45xL0-3 min-1) and a slower second stage (k 2 =3 .84x l0-4 min -1). The cation and anion exchange resin behaviour of the complexes/formulations in their different oxidation states with their derived species is reported and the V(IIl)-picolinate is shown to exist as an anionic species in formate medium. The use of V(JI)-EDTA and V(Il)-citrate for dissolution has an advantage as their oxidation (to V([II) stage) at higher concentration ca. >7mM has not res ulted in any precipitation/crystallization unlike in the case of V(Il)-picolinate. The chemical decontamination of primary coolant circuit in water-cooled nuclear power reactors involves the di ssolution of corrosion films (Ni, Crsubstituted as well as simple iron oxides) accumulated on the structural surfaces 1-6 • The Cr-containing iron oxides are not easily amenable for dissolution in conventional organic acid based formulations like citric acid-EDT A-ascorbic acid (CEA) mixture 5·6 . However, low ox idation state metal ions (LOMI) such as V2+ and Cr2+ in presence of suitable chelating agents are known to be very strong reducing agents (rapid kinetics) towards the dissolution of such oxide matrices 1.2 _ Normally V(II) based LOMI formulations involving V(II)-picolinate is employed for such purposes 1• Use of V(II) picolinate complex is limited to concentration levels below 7 mM . Above thi s concentration level , V(III) picolinate (which is generated either during reductive dissolution of corrosion films accumulated on structural surfaces or sometimes by air oxidation due to system leaks) precipitates/crystallizes. The use of EDT A and citric acid as complexing agents can overcome such sol ubility problems. The electrochemical method of preparing V(II) enables the generation of composition *For correspondence (E-mail: gvenk@magn um.barc.ernet.in) specific formulations, which is an important consideration towards base material compatibility aspects in real system applications. The relati ve stabilities of electrochemically prepared V(Il)picolinate, V(Il)-EDT A and V(II)-citrate complexes/ formulations as derived from the redox and UVVisible spectra are reported in thi s paper. The behaviour of these complexes in their different oxidation states on the conventional ion-exchange resin is studied, and the derived species getting sorbed is reported. The detailed studies on the dissolution of Cr-substituted oxides in these formulations are published elesewhere5 . Experimental Procedure Electrochemical Assembly A flat bottomed closed vessel of 500 mL capacity with five vents of IC joints-for free flow N 2 gas, for Pt-SCE assembly and a provision for re-circulation was used as shown in Fig. 1. A 2 mm thick Pt rod of about I em height dipping inside the Hg and the other end of which was fused to a glass tube served as cathode contact to power supply. The cylindrical Pt gauze anode (- 25 wires ca. -0.5 mm gauze/em) of I em diameter and 3 em height attached to a 1 mm thick Pt wire served as the anode. A sintered glass disc 26 INDIAN J. CHEM . T EC HNOL., JANUARY 2002 Table 1- The op timi zed parameters for th e elec trochemica l generati o n o f V(ll ) formate Catholyte. NaY0 3 pH 2.8 Anolyte. HCOOH Curre nt 80 mA Voltage 40 Time (mi n) v 4mM 2.0M II mM 2.6 M 22 mM 3.5 M 70 44mM 4.0M 90 60 60 Table 2-Co mposition of VIII ) based formu lati ons (i n mM ) containing sto ichi ometric amou nt of L for the dissolu tion of 20 at. % Cr-substituted he matite/mag neti te* Fig . 1- Elec trochemi ca l assembly for the preparation. and o n-line estim ati o n o f V(ll ) formate. [I. Mag netic stirrer-c um hot plate; 2. Cathode compartment; 3. Anode compartment; 4. Peri staltic pump; 5. SCE with lu gg in probe; 6. Pt foil electrode; 7. Assembly for o n-line titration of e lectrolysis product: 8 & 9. Voltammeters for Solution potential and Cathode potenti al measurements respectively; I 0. Power supply Unit] (2.5 em diameter of G3 porosity) separated the anode and cathode compartments. The bottom of anode compartment was kept at - 2 em (approximately the focal point) from the convex surface of mercury held in the glass container down below so as to allow maximum current between the cathode and anode. A saturated calomel electrode (SCE) mounted at the top portion of a lug-in probe holding saturated KCl whose bottom tip was close to the surface of Hg was used as reference electrode. The Pt electrode (foil-type) was also held close to the lug-in probe (SCE) for cathode potential and solution potential measurement. Electrolysis The electrolysis was carried out after charging required amounts of catholyte and anolyte. In cathode compartment a known amount of aqueous Na V03 in formic acid media (pH-2 .8) was placed, while in the anode compartment only formic acid of appropriate concentration was taken . Before starting the electrolysis the solutions (both anolyte and catholyte) were kept for deoxygenation ca.-30 min using high purity N2 gas (scrubbed through V2 + trap generated by Zn-amalgam in HCl) and N2 bubbling was continued throughout the electrolysis . The concentration of formic acid (anolyte), cell-current, cell-voltage and time required for completion of electrolysis (Table 1) to obtain V 2+ (as V 11 (HCOO)z) in the concentration range of 4-44 mM were optimized/standardized from the initial experiments. The optimization was done by number of initial trial experiments based on the IV'' -formate J pH 3.0±0.3 I Pic I pH 4.0±0 .3 !EDTAI pH 3.6±0. 3 !C it! pH 2.6±0 .3 IHCOOHI 4 93 31 31 8 II 114 38 38 39 22 147 49 49 43 *equi val ent to 22 mM iron and -5.5 mM Cr (from Fe 24 C r06 0J) in 200 mL formu lation (ref. 5) F e .~ 6 Cr 0 . J O .J stoichiometric amount of formate ions required as well as the reduction potentials re ported in the 7 literature for the reduction of vanadium species . Estimation of V(ll)-formate The electro-generation of Y 2+ species was confirmed by online redox potential (- -0.580Y v/s. SCE) measurements. During electrol ys is, the so lution was kept circulating from the vessel through a burette using a peristaltic pump. This arrangement helped in titrating the solution periodically against standard KMn04 solution to estimate the extent of V 2+ generation. The oxidation of Y 2+ by permanganate can be represented as, 5Y 2++3Mn0 4- +24H+ (10% HzS04) 5 2 ---7 5V + +3Mn + +12Hz0 The electrolysis proceeded with the accompanying colour changes viz. yellow, blue, green and purple for V(V), V(IV) , V(lll) and V(ll) respectively during electrolysis. Estimation free formic acid The total formic acid content was estimated at the . end of the electrolysis by passing the sample through the strong acid cation exchange resin . The eluate was titrated against standard NaOH solution using phenolphthalein indicator. The free formic acid was calculated from the total formic acid by subtracting 2 two times the V + concentration and the sodium 27 MANJANNA & VENKATESWARAN: ELECTRO LYTICALLY GENERATED YANADOUS COMPLEXES Table 3-A bsorption maxima, Arnax (in nm) of the vanadou s formulation s at different ox idation sta tes Chelating age nt 100 Vanadium species V(J l) V( IIl ) V(JV) V(V) Formic ac id 570 430 382 215 Picolinic ac id 510 370 36 1 325 EDTA 440 240 244 232 C itric ac id 550 370 242 230 .... ·· 6 ········ 80 0 0 ··· .... ·6 o· 9··· concentration from the initial sodium metavenadate used for the preparation of V 2+ (Table 2). 1 Formulation/complexation of V • species o o 6 v 2 After confirmation and estimation of V + species, the electrolysis was stopped and the Hg (cathode) was removed carefully (through the outlet provided with the flask). The V2+ (as formate) thus generated was then made to complex with different chelating agents viz. picolinic acid (H 3 Pic), EDT A (disodi um salt, Na 2EDTA) and citric acid (C 6 H 80 7 ). The EDTA and citric acid were added directly into the cell containing V(ll) formate. However, the picolinic acid required to complex with V 2+ was neutralized (in order to provide the li gand in readily complexable form) with NaOH separately in a deaerated aqueous medium before its addition. In all the cases, stoichiometrically excess (w.r.t V2+) amounts of chelating agent, L viz. H3Pic, Na2EDT A and C 6 H80 7 were added. Table 3 shows the composition of V(II) based formulations which have been employed in the di ssolution studies of Crsubstituted iron oxides 5 . The amount of chelating agent provided in each case is stoichiometrically 2 equival ent to that required for complexation with V + species as well as Fe and Cr from the oxide ca. 20 metal atom% Cr-substituted hematite/magnetite (as a typical case). Dissolution behaviour Fig. 2 shows the typical dissolution profi les of Crsubstituted hematite/magnetite in V (II)- EDT A and CEA (c itric acid-EDTA-ascorbic ac id) formulations . The details of ex periment, and the determination of dissolution rate coefficients using general kinetic equati on applicable for polydispersed particles are reported 5 ·8 ·9 . It is observed that the Cr substitution in hexagonal lattice (a-Fe 20 3 ) has hindered the di ssoluti on to a greater extent than that observed when Cr is substituted in cubic lattice (Fe 30 4). Using CEA , the complete disso lution of simple iron oxides viz., a -Fe2 0 3 and up to 10% Cr-substituted magnetite 20 o o- 5% csh/ 22 VE 20% csh/ 22 VE 20% csm/22 VE 20% csm/ 44 CEA ~ 0 ~-L 50 100 150 200 250 300 350 400 Dissolution time (min) Fig. 2-Typical dissolution profiles obtained for cs h/csm in YE and CEA fo rmulati o n. [csh/csm: C r- substituted hemati te/ magnetite; VE: V(II)-EDTA formulation, 22 mM ; CEA : II mM c itric ac id + 44 mM Na 2E DT A + 44 mM ascorb ic acid (p H 2.8) mi xture] can be obtained to the reductive mechani sm of internally generated (during the course of di ssolution ) Fe(II)-EDT A. However, when Cr is substituted to the 8 extent of > 10 at%, there was no dissolution even on employing higher concentrations of CEA . As shown in Fig. 2, vanadous formulation , V(II)-EDT A has resulted higher dis solution when compared to CEA, and there is a higher dissolution in the case of csm. Thi s observation documents the advantage of employing vanadous formulations over conventional formulations like CEA in dissolving Cr-substituted iron oxides encountered on the structural surfaces of water-cooled nuclear reactors. Ion -exchange behaviour During thi s particular study , the L was added 2 equivalent to the stoichiometric complexation of V + alone and no extra L (free L) was provided . The V(II)-L ( formic acid, picol inic acid, EDT A and citric acid) were passed through strong acid cation and/or anion exchange resin (polystyrene based gel type resin). The resin bed was regenerated (by S%H2S04 or NaOH) freshly and deoxygenated by circulating deaerated water before passing the V(II)-L. For thi s purpose, a closed loop was set up from electrolytic INDIAN J. C H EM . T EC HNO L.. JANUA RY 2002 28 Results and Discussions Electrochemical generation of V1+ 40 -40 Ul u Ul u <ll -60 ~ > -80 E \ 3,- 100 ~ -120 0 c.. -8- 140 0 C0 \ -20 ~\ 0 20 ] " 0"' c.. c: -40 .S! :; - o- - o-o-o- J -160 ~ .::> - o- o.._o ..c ~ >E 0 . . . . .. . . . . 0 ~ C/l 20 "i - - · - - - ~ 40 - 60 0 - ~ - -60 C/l 80 Elec trolys is time (min) 100 0 u C/) -100 >s -200 .s -::: -300 .~ 20 V(/1)-Formulations V(II)-Formate ----<>- V(II)-Picolinate - v - - V(II)-EDT A ----<>- Then V 3+ from Eq . (3) was reduced to V2+ as (4) V(II)-Citrate Time: 0-360 =>de-aerated condition 360-540 =>aerated -400 t:: ;; C/) (2) .. . (3) .9 -500 0 (1 ) Y0 2+ directl y goes to y l+ irreversibl y as V0 2+ + 2H + + 2e- ----j Y 2+ + HzO ----<>- c ~ o n io ni zation Na+ + Y0 3Y0 2+ + H2 0 chemical process V0 2 + + H20 , E0 =1.00Y Al so, V 2+ thu s generated reduces Y0 2+ to V2+ eas ily and in the process gets oxidized to V 3+ as 20.-~ ~ aV 0 3 -~ V03- + 2H+ YOz+ + 2 H+ + eN Fig. 3- Yari ati o n of cathode/so luti o n pote ntial w ith time d uring th e electroge ne ratio n of II mM V 2+ (as fo rm ate) from aqueo us sod ium metavanadate in formi c acid buffer (p H 2 .8). ,......., u.l The vanadous ion, V2+ was prepared as V(II ) fo rmate by th e elec trochemi cal red ucti on over the surface of Hg, using deoxygenated aqueous so lu tion containing req uired amounts of sod iu m metavanadate (NaV0 3 ) and for mic acid at p H 2.8. The cel l parameters such as cu tTent, vo ltage and du ration of electrolys is are shown in Table 1. Du ring electrolys is, the step-wi se reductio n of V0 2 + to Y 2 + can be represented 7· 10 by the fo ll owi ng equatio ns (V versus SHE). -600 -700 0 100 200 300 400 500 600 Time (min) Fig. 4--Va riation of solution potential for V(II)-L as a function of time in deaerated followed by aerated condition at 353 ± 5 K. cell and resin column with the help of peristaltic pump. Uniform flow rate, 5 mL/min was maintained in each case. The oxidized forms of V(II)-L viz., V(III)/ (IV)/ (Y)-L were obtained on controlled air oxidation of V(II)-L for which the conversions were monitored by redox potential measurements. Due to H+ consumption during electrolysis, the initial pH (2 .8) of catholyte was increased slightly to pH 3.0 at the end of electrolysis. In anode compartment the decomposition of water resulted in the liberation of 0 2 during electrolysis and in order to improve the conductivity of the so lution, an appropriate amount of formic acid was placed. Whenever the formic acid was not sufficient (during the initial experiments), a black precipitate of vanadic oxide, which is the hydrolysis product of vanadium was noticed. Monitoring the solution potential on Pt electrode helped in following the reduction process during electrolysis. The yellowish orange V0 2+ turns to sky blue colour of V0 2+ which before going to the purplish violet colour of V2+ goes through a dark blackish green stage showing the fo rmation of V 3+ also in the solution according to the Eq. (3). The variation of cathode potential and solution potential during the time of electrolysis in a typical case of II mM is shown in Fig. 3. The electrolytic generation of V(II)-picolinate and its application in the decontamination of BWR 10 surfaces has been presented previously • During the 29 MANJANNA & YENKATESWARAN: ELECTROLYTIC ALLY GENERATED VANADOUS COMPLEXES same study, £ 112 was found to be - l. 32V (vs . SCE) and the potential corresponding to the limiting diffusion current is -1.4 to - l. 6V using DC polarogram. In the present case also a cell of -40V yielded a cathode potential of -l.55Y in the later stage of electrol ysi s. Also, the V 2+ could be generated with the desired conditions in the concentration range of 4 to 44 mM. During the course of electrolys is, the cathode potential (Fig. 2) was found to decrease in the first phase (lasting - 10 min), there was a sli ght increase and thereafter it decreased slowly reaching a plateau valu e of - -1.55Y. The increase of cathode potential in the mid -way of electro lys is indicates th e formation of V3+ during the process of reducing V0 2+ by V2+ according to Eq. (2) . On providin g chelating agents, L viz. picolinic aci d, EDT A and citri c acid into the V (IT) formate soluti on showed a negati ve shift in soluti on potential (Fig. 4) . This is a clear indication of complex formation between V(II) and L. Relatively more potenti al shift was observed (Fig. 4, at t=O) in case of EDT A and pi colinic acid when compared to citric aci d, indicating their better complexing ability. This observation is in corroboration with the UV- Visible spectra, which showed a blue shift as the ligand was changed successively from formic acid to citric acid to picolinic acid , and to EDT A (Fig. 5). The choice of L was based on the various dissolution studies reported in the literature 1-4 • Stability of V(Il)-formulations Solution potential measurements using a Pt electrode again st SCE were employed to assess the stability of V(ll)-L (L= picolinic acid, EDT A or citric acid). Yanadous ion is very easily oxidized by exposing the solution to air (4V 2+ +0 2 +4H+ ~ 4V 3+ +2H 20). The extent of oxidation was assessed when a typical concentration (ca. II mM) of the formulation was kept stirred magnetically at 353 ± 5 K for about 6 h under deoxygenated condition using high purity nitrogen gas. Fig. 4 shows the variation in the redox potential with time of V(II)-L under deaerated and aerated conditions . The initial negative shift (t=O) of redox potential upon adding different L to V(II)(as formate) under deaerated conditions was in the order: picolinate : : : EDT A > citrate > formate showing the chelating ability of the complexes as formate< citrate <EDTA < picolinate. The V(II)-L (L= picolinate, EDTA and citrate) formulations upon storage under deaerated conditions (Fig. 4) showed a positive 0.10 Fonnulations A: V(II)-fonnate 0.08 V(ll) ---> 570 V(II D 43 0 B: V(II)-picolinate ---> 510 370 C : V(li)-EDTA 240 0 : V(ll)-citrate ···> 440 ·--> 550 370 0.06 i!".. -e ] < 0.04 0.02 200 300 400 500 600 700 800 Wavelength (run) Fig. 5-UV-Visible absorp ti on spectra of V(ll ) based formulation s/complexes (A, C and 0 are 4 mM wh ile B is I mM ). potential shift of- 25 m V in 6 h duration suggesting the reduction of water by the reaction V2+-L + H+ ~ V 3+-L + Y2 H2 thereby contributing to the oxidation of V(II ). Converting the potential values into concentrations using the Nernst equation, the decay of [V(ll)] with time was computed. Fig. 6 shows the decay kinetics in a typical case of V(II)-picolinate when the soluti on was kept stirred under deaerated condition at 353±5 K. A two-stage first order kinetics with a fast initial 1 stage showing a rate constant k 1=3.45xJ0-3 min- and 4 1 a slow second stage having a k2=3.84x l0- min- is observed. The lower rate constant in the second stage is probably due to V 3+ build-up in solution resisting the further decay of V(TI) . Since the potential shift observed in case of other two chelating agents is of same magnitude (< 30 m V) the rate constants for their decay are expected to be the same. However, when Nrbubbling was stopped. all the formulations got oxidized V(III)-L in< 5 min. The further air oxidation leading to V(IV) state took- 15 min in case of EDTA and citrate. While picolinate and formate took - 90 min and 150 min respectively . This observation is of importance with respect to dissolution of oxides in INDI AN J. C HEM . TECHNOL., JANU ARY 2002 30 serious concern durin g the large scale application such as reactor system decontamin ation as it can hinder the dissolution by fo rming a protective layer (of fine crystals) on the underl ying ox ide surface at the oxide-solution interface. Also, it may req uire lot of washings to bring the system to norm alcy for operation . In this regard, however, the other two formulations, V(II)-EDT A and V(II)-citrate will be of ad vantageous when it is requ ired to use hi gher concentration of formulati ons as they do not pose any such type of prec ipitation or crystallization ca. in the concentration range of 4 to 44 mM prepared in thi s study . these formulations as the V(III)-L (EDTA and citrate) can also serve as internally generated reducing agents for further di sso luti on unlike V(III)-picolinate whose ox idation appears to be kinetically hindered . In no case, V(V) state was reached even after a suffici ent expos ure to ai r - 6 h. In the case of V(II)-picolinate when th e co ncentratio n was > 7 mM , th e air oxidation over a period of time ca. >5 h resulted in precipitation as brick-red crystals due to poor so lubility of V(III)-picolinate. Although, its effect is insignificant on th e di sso lution of iron based ox ides in a lab scale studi es, it will be of 9.0 ~ 7.8 Cll (.) k, = 3.45 x 10 ., min·' (/) tll .2 c: ~ ~ E §:6 .0 C. • k, = 3.84 x 10 4 min·' 5.0 0 100 200 300 400 500 600 Time (m in) Fig. 6-Decay kinetic of V(l l)-picolinate in water under deaerated conditi ons at 353 ± 5 K. UV- Visible spectra The UV-Yisible spectra of pure V(ll)-formate showed a Amax at 570nm. When di fferent chelating agents viz. citri c acid, picolinic acid and EDT A were added, the maxima shifted to 550, 510 and 440 nm res pectively (Fig. 5). The shift in Amax towards blue region suggests the relative strength of complexes in the order as V(l[)-formate < citrate < picolinate < EDT A. This is in corroboration with the inferences obtained from initial shift in redox potential measurements (Fig. 4). Fig. 5 shows the absorption maxima values for V(III)-L also since a small fraction (-10%) of V(II)-L got oxidized to V(ll[) state during spectral measurements. The Amax values of vanadium species at different oxidation states are also shown in 7 Table 3. The reported stability constants , log K of V(II)-EDTA and V(II)-picolinate of 12.7 and 12.8 respectively lend support to the conclu sion reached in this study from the spectral data are in agreement with the above observations. Though , the stability constant value of V(II)-citrate is not available, and V0 2+citrate is reported to have a log K of 8.8, from th e present study it is ex pected that citric acid forms relatively weaker complex with V(II). Tab le 4- Ion-exchange ( IX ) behav iou r of vanado us based formulations and the ir ox idi zed forms on polystyrene based strong acid cation and an ion exc hange resin o.s +2 +3 +4 +5 Metal ion species y2+ Likely metal ion species in the complexed form with different che latin g agents Picolinic acid 2 EDTA C itric acid 2 anion [V0 2+-H . 1citf v v v [VO/ -H. 1citf· X v v v v 2 [V +(pich]" [Y +-EDTAf [Y +- H.1citf y3+ vo 2+ [V 3+(pic) 2(HCOOH [Y0 2\ pich]" [V 3+-E DTAr [Y 3+- H.1citr YO/ [Y0 2+(pic) 3f [V0 2+E DTA f [Y0 2+E DTA] 3 - IX behaviour cation Here (V) and (x) sy mbol s indicate the removal and non-removal by resi n respecti vely o.s : oxidation state MANJ ANN A & YENKATESW ARAN: ELECTROLYTICALLY GENERATED V ANADOUS COMPLEXES Ion-exchange behaviour The decontamination is generally followed by the removal of all the chemical constituents of the decontaminating formulations. Passing the dissolved species (aqueous) through cation and/or anion exchange resin normally does this exercise. The V 2+ species after reducing the ferric oxides (corrosion products) can go to higher oxidation state of +3 and +4 and sometimes to even +5 due to the increase in dissolved oxygen content in the system. Hence, the ion exchange behaviour of these complexes of vanadium with citric acid, EDT A and picolinic acid becomes important when spent decontamination solution is treated by synthetic organic ion exchange resin as a part of waste solid ification . Thus in thi s study, all these formulations at different oxidation states of vanadium (higher ox idation states were obtained by air oxidation of V 2+ formulations) were passed through strong cation and strong anion exchange resin independently. It was found that the 2 anion resin picked up all these species, while the V +, 2 3 V + and V0 + excepting V0 2+-citrate complexes were dissociating on the cation exchanger. The fact that, the V(III)-picolinate which is usually referred to as V(pich (neutral complex), gets sorbed on the anion exchanger shows that it is existing as anionic complex in formate medium and may be represented as [V(pich(HCOO)zr. Existence of vanadium species in different oxidation states with different chelating agents and their sorption behaviour on the cation/ anion exchanger is shown in Table 4. Thus the ion exchange behaviour of V(ll) formulations is highly encouraging for their application in nuclear reactors as a decontamination formulation. Conclusions The relative complexing ability of chelating agents with V 2+ (as formate) under deoxygenated condition 31 follows the order can be shown as V(ll)-formate < V(II)-citrate < V(II)-picolinate :=:: V(II)-EDTA . Their stability in aqueous medium under deoxygenated condition followed two-stage decay kinetics. The Ion exchange behaviour of the vanadium complexes viz. V(H)-picolinate, V(II)-EDTA and V(II)-citrate and their oxidized species shows that they can be picked up both on anion and cation exchange resin column. The ex istence of V(III)-picolinate as an anionic species is shown by this study. Acknowledgements This study forms part of the Ph .D Thesis of J.M. Authors wish to thank Dr. N. M. Gupta, Head, Applied Chemistry Division, BARC and Drs . B. S. Sherigara and P. V. Nayak from Kuvempu University for their keen interest and encouragement during thi s study. References l 2 3 4 5 6 7 8 9 10 Swan T , Segal M G, Williams W J & Pick M E, EPRI-NP 5522M, U.S .A., 1987. Jonhson Jr A B, Griggs B, Kustas F & Shaw R A, Water Chemistry of Nuclear Reactor Systems 2 (BNES, London, U.K). 1980. Regazzoni A E & Matijevic E, Corrosion, 40(5) ( 1984) 257. Segal M G & Sellers R M , J Chem Soc Faraday Trans I , 78 (1982) 1149. Manjanna J & Yenkateswaran G. Hydrom etallurgy, 6 1 (2001) 45. Joseph S, Venkateswaran G & Moorthy P N, J Nuc/ Sci Techno!, 36(9) ( 1999) 798 . Martell A E & Smith R M, Critical Stability Tables. Vols 1-6 (Plenum Press, New York), 1975. Manjanna J & Venkateswaran G, Hydrometallurgy, 60 (2001) 155. Manjanna J, Yenkateswaran G, Sherigara B S & Nayak P V, Powerplant Chemistry, 3(2) (200 l) 80. Yenkateswaran G, Gokhale A S & Moorthy P N, National Symposium on £/ectrochemislly in Nuclear Technology, IGCAR, Kalpakkam, India, 1998.