Indian Journal of Chern stryVol. 28A, August 1989,pp. 693-695

Studies on in rganic ion-exchangers: Part 3-Preparation, properties and ap-plications of cerium{IV) vanadate

C 1anardanan, S M K Nair* & C P Savariar

Department of Chemistry, University of Calicut 673 635 A

Rece ved 7 March 1988; revised 2 September 1988; rerevised and accepted 28 November 1988

Cerium(IV vanadate has been prepared by different methods by changing volume ratio, molarityand pH. Its io -exchange capacity, chemical composition (Ce:V::l:4), chemical stability, distribution co-efficients for 1 metal ions, and change in its capacity with ionic radii of incoming ion have been stud-ied. The utilit of cerium(IV) vanadate as an ion-exchanger has been tested by achieving some import-ant binary and ternary separations such as Hg2 + - Cd2 +, Zn2+ - Hg2+, Zn2 + - Pb2+ ,Zn2+ - Hg2+ - Cd2+, Zn2+ - Pb2+ - Cd2+ and Mg2+ - Pb2+ - Cd2+.

Inorganic ion-exc angers, possessing high selecti-vities for certain ins, or groups of ionsl-4, can beutilised for chro atographic separations of ele-ments. Most invest gations with insoluble acid saltsof quadrivalent etals as ion-exchangers havebeen carried out zirconium and titanium phos-phates of various ypes'. Vanadates of U, Th, TI,Nb, Zr and Ti hav been also studied extensively".These materials a e reported to behave as cationexchangers with r latively high capacity and showselectivity for- alka ine earth metal ions. However,no information exi ts on the use of 'cerium(IV) va-n~date as ion exch nger.

This paper rep rts the results of our studies onthe synthesis and on exchange behaviour of ceri-um(IV) vanadate. he material possesses requisiteexchange capacity and mechanical strength to beused in columns fo metal ion separations.

Materials and Met odsCeric ammoniu nitrate and sodium vanadate

(Loba Chemicals) ere used as such. All the otherreagents used were of AR grade.

Synthesis of the ion-exchangerCerium(IV) vanadate was prepared by adding 1

litre of 0.05 M sodium vanadate dissolved in 0.1M NaOH to 500 ml of 0.05 M eerie ammoniumnitrate with constant stirring under the conditionsgiven in Table 1. The pH was adjusted by addingeither dilute HN03 or NaOH. On standing for 24h, the precipitate settled. It was filtered, washedfirst with dilute nitric acid at the same pH as thatat which the precipitation was made and then withdemineralised water and dried at room tempera-ture. The material was then converted into theH + -form by treatment with 0.5 M HN03 for 24 hwith occasional shaking and intermittent changingof the acid. Beads of orange red crystals of ceri-um(IV) vanadate were obtained. The product wasdried at 40°C in an oven.

Determination of ion-exchange capacityThe ion-exchange capacity of the various sam-

ples of cerium{IV) vanadate was determined bycolumn operation. The ion exchanger in the hy-drogen form was placed in the column with a glass

Table I-Conditions of preparation and properties of cerium(IV) vanadate

Sample Molarity of reagents Mixing pH Colour in lon-exchangeratios H+-form capacity

Ce V (Ce:V) (meq/g)

I 0.1 0.1 1:1 Orange yellow 0.43

2 0.1 0.1 1:2 Orange yellow 0.40

3 0.05 0.05 1:2 Orange yellow 0;86crystals

4 0.05 0.05 1:2 1.55 Yellow 0.53

5 O.OS 0.05 t:2 2 Yellow 0.58

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INDIAN J CHEM, SEe. A, AUGUST 1989

wool support. Sodium chloride (1.0 M) was usedas the eluent, and 250 ml of eluate was collectedin every case. The hydrogen ions eluted from thecolumn were determined titrimetrically with stand-ard NaOH. One gram of the exchanger was usedin each case to determine tlie capacity. The ex-changer could be regenerated twice without anyappreciable loss of exchange capacity.

Chemical analysis100 mgof the exchanger, ground to fine pow-

der, was dissolved in 10 ml cone. H2S04; ceri-um(IV) was estimated volumetrically?" with ferrousammonium sulphate, and vanadium as silver va-nadate gravimetrically", The Ce:V value wasfound to be 1:4 with a variation of ± 0.01 % forsuccessive determinations. The empirical formulaof the combined oxide" can, therefore, be writtenas Ce022V205nH20.

Results and DiscussionThermal stability

Thermoanalytical investigation throws somelight on the' empirical formula and theoretical ex-change capacity of the sample. The mass loss upto110°C, determined thermogravimetrically, is10.72% ± 0.01 %, and this can be related to theloss of water from the exchanger.

The number of moles of water lost per formulaweight of the exchanger was calculated by themethod of Alberti et at'. If 'n' is the number ofwater molecules per mole of the 'mixed oxide', ncomes out to be equal to 4 from the equation1800n/(535.90 + 18n) = 10.72. So, the formula ofthe sample can be suggested as Ce022V20s4H20.Cation exchange capacity calculated on the basisof one proton per formula weight is 1000/607.90= 1.6 meq/g. The experimental value is 0.86 meq/g; the departure from the theoretical value may bedue to the hydrolysis of the salt.

The effect of size, charge and the ionic radiiThe effect of size and charge of the incoming

ion on the capacity of the exchanger was studied.For the alkali and alkaline earth metal ions the se-quence shown by cerium(IV) vanadate is as fol-lows:Na+(0.86» K+(O.62» Li+(0.30)Mg2+(0.75) > Ca2+(0.68) > Sr2+(0.55)

The exchange capacities are given in parenthesis.Usually the ion exchange capacities are in the or-der of the hydrated ionic radii. In the present casethe sequence is not followed. This may 'be due tothe decisive role of the solubility products of the

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corresponding vanadates of th metal ion in theadsorption processv'".

Usually, at low aqueous co centrations and atordinary temperature the exte t of exchange in-creases with increasing valency of the ingoing ion,i.e., Ca(lI) > Na(I)1c. Cerium(IV) vanadate does notshow this sequence. Such irre arities are not un-common with inorganic ion exchangers II.

Distribution coefficientsThe distribution studies were carried out for 10

metal ions by a batch process in the usual man-ner'? by equilibrating the meta ion solution withthe exchanger beads for 6 h at room temperature(30 ± 1°C). The Kd values for etal ions were cal-culated using the expression,

=(/-F) ~«, F 0.5

Where 1 is the volume of EDT consumed by theoriginal solution and F is the volume of EDTAconsumed at equilibrium. The otal volume of thesolution was 25 ml and the a ount of exchangerused was 0.5 g. The concentr ions of metal ionswere found out by EDTA t tration?". The Kdvalues are given in Table 2.

SeparationsFor separation studies, 5 g f the exchanger in

the H +-forrn was taken in. a glass column (30em x 0.69 cm dia.). The rate 0 flow in all separ-ations was 0.5 ml/min. The s paration of metalions was tried in cases where t e separation factorwas greater than 5. The el ents were, water,HN03, HCI and NH4N03•

In all separations the metal ion concentrationwas 0.005 M. For binary separ tion 10 ml each ofthe metal ion solutions were sed. Details of the

Table 2-Distribution coefficients of s me metal ions on ceri-um(IV) vanadate ion-e changer

Cation Taken as K; (ml/g)

Zn(II) Sulphate 6.54Mg(II) Sulphate 6.20Pb(II) Nitrate 25.60Co(II) Nitrate 8.37Ca(II) Chloride 5.00Ni(II) Sulphate 4.62Cu(II) Chloride 5.66Cd(lI) Carbonate 227.03Hg«H)' ; .Chloride 30.77Bi{nJI); : Nitrate C mplete uptake

J NARDANAN et al: STUDIES ON INORGANIC ION EXCHANGERS

Table 3-Binary and t rnary separations on cerium(IV) va-nadate (sample 3) col ns (exchanger used in columns 5 g)

Separation Amount of cation (mg)

13.009.007.006.700.688.000.394.802.240.392'()72.240.492.072.27

(b) 0.01 MHNo.,

(d) 0.05 M HNo.,(f) o.or M NH.No.,

Loaded Recovered

Eluents:

g'+(a)d2+(c)

Zn2+(c)

~

Ig2+(a)il2+(b+e) .b1+(b+g)n1+(b+f)g2+(a)d2+(d)n1+(b+f)b1+(c+g)d1+(d)gZ+(b+f)

b2+(c+g)d2+(d)

(a) 0.02 MH I

(c) 0.02 MH Io,(e) o.ot MN 4No.,

(g) 0.5 M NH NO.1

12.609.006.50

6.700.687.300.364.602.240.370.192.200.44

0.192.25

three important bin ry separations carried out aregiven in Tahle 3. Tlte recovery ranged from 95 to100%. All the separations were carried out in neu-tral medium. In add tion to the binary separations,a few ternary sepa at ions have also been made(Table 3). Five mlach of the metal ion solution

were mixed and passed through the column. Allseparations were carried out in neutral medium.

The distribution studies with ten metal ions(Table 2) reveal that cerium(IV) shows greatest af-finity for Cd(II). It may be assumed that in addi-tion to the ion exchange reaction, adsorption andion-sieve properties of the exchanger are responsi-ble for the high uptake of the element.

The studies on the ion exchange properties ofcerium(IV) vanadate have shown that this reagentis suitable for binary separations like Hg2 + -Cd2 + ,

Zn2+ -Hg2+ and ternary separations such as Zn2+-Hg~+ -Cd2 +, Zn2 + -Pb2 + -Cd2 + and Mg2+-Pb2+-Cd2 + with fairly high efficiency.

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