Indian Journal of ChemistryVol. 28A, April 1989, pp. 346-348

Studies on zirconium tungstateion exchanger

B Sarkar & S Basu*Department of Chemistry, The University of Burdwan,

Burdwan 713104

Received 22 February 1988; revised 9 May 1988;accepted 28 June 1988

Granular zirconium tungstate as an ion exchangersuitable for column operation has been prepared. Theproperties, composition and ion exchange behaviour ofthe material are reported. Distribution coefficients ofseveral cations have been measured and a few separ-ations of analytical importance achieved.

In recent years, synthetic inorganic ion exchangersare gaining increasing interest due to their high sta-bility toward thermal and radiation doses. Amongthese materials, insoluble salts of polybasic acidsand polyvalent metals have been studied exten-sively I.". Preparations of both poorly crystalline andamorphous compounds have been reported amongwhich zirconium phosphate.' is the most widelystudied. Besides, compounds like antimonate, mo-lybdate and silicate salts of zirconium'>, analogouscompounds like titanium- and thorium-' phos-phates have also been reported. However, only alittle attention has been paid jo zirconium tung-state". Presently we have synthesised a granular var-iety of zirconium tungstate suitable for column op-eration. The exchange capacities and distributioncoefficients of several cations on this exchangerhave been evaluated and from the results of suchmeasurements, useful separations of some binarymixtures of cations have been achieved.

Zirconium oxychloride (Riedel, AR) and sodiumtungstate (Loba, GR) were used as such. All otherchemicals used were of AR grade.

A digital pH meter (Sambros 335 type) was usedfor pH measurements. Spectrophotometric mea-surements were carried out using a double-beamspectrophotometer (Shimadzu, UV-190). Shimadzuatomic absorption spectrometer (model 646) withMVU-J was used for the determination of Hg2 ".

Granular and stable form of zirconium tungstatesuitable for column operation was prepared as fol-lows. To a solution of 0.1 M zirconium oxychloride(50 ml) in 2 N HCI kept at 40°C, 0.1 M sodiumtungstate solution (100 ml) was added dropwiscwith constant stirring. After the addition was com-

346

plete, fine white precipitate appeared and the reac-tion mixture was diluted to one litre and kept over-night. The precipitate was filtered and washedseveral times with distilled water, filtered and againwashed with hot water until chloride-free and pH offinal washings was around 4.The white solid wasdried at room temperature over silica gel.

A weighed quantity of the solid material so pre-pared was fused with caustic soda, poured into hotwater and filtered. The precipitate was dissolved in4 NHCI and analysed for zirconium by alizarin redmethod 10. The filtrate was analysed for tungstate bythiocyanate!" method. The exchanger was found tocontain Zr = 10.3% and W= 40.7% i.e. the ratioZr:W= 1:2.

The exchanger was chemically stable in all miner-alacids upto 4 M concentration in cold but on heat-ing the solution it slowly dissolved. Hot and concen-trated alkali partially attacked the exchanger. Thesolid was stable in solutions of NaCI, KCI, NH4C1,CaCl2, MgCI2 etc. and also in ethanol or benzene.

To find the volume of eluent necessary to eluteH+ completely from the column, the titre of alkaliwas plotted against successive volume of eluent. Theresults showed that the amount of H + liberated waspractically negligible at very large volume ( - 100ml) of eluent. For batch operations, concentrationsand the time required for equilibration were also de-termined to find optimum concentration and timenecessary for equilibration. The equilibration timewas found to be 16 hr and a constant capacity wasattained with a concentration of NaCi > 2 M.

The ion exchange capacity of the exchanger wasdetermined by equilibrating a definite amount of thesolid with 2 M NaCi solution and titrating the libe-rated acid with standard sodium hydroxide solution.Similar values for several other cations were deter-mined.

A definite amount of the exchanger was equili-brated with a solution containing varying propor-tions of NaCi and NaOH, concentration of Na + be-ing always kept at 0.1 N. pH of the resulting solu-tions were plotted against the meq of base added/gof the exchanger. Only one break was observed inthe pH titration curve indicating that the exchangerhad only monofunctional acid group.

Distribution coefficients (Ko) of several cationswere determined by equilibrating the exchanger ( -0.5 g) with solutions of (50 ml each) cations for 16 hrat room temperatures with intermittent shaking.The K[) values were calculated as usual.

The ferric ions were determined spectrophoto-metrically!" and mercury by atomic absorption spec-troscopy". All other cations were determined bytitrations with standard EDTA solutions'<!',

Separation of binary mixture was carried out oncolumns containing zirconium tungstate (10 g; 50-

Table I-Ion exchange capacity of zirconium tungstate atpH 6.0-6.5

Metal ion Hydrated Ion exchangeradius capacity

(A) (meq/g)

Na" 2.76 0.185K+ 2.32 0.296NH: 0.246Mg2+ 7.00 0.173Ca2+ 6.30 0.251Ba2+ 5.90 0.308

NOTES

Table 2-Distribution coefficients of metal ions on zirconiumtungstate at 30 ± 2°C

Metal ion Taken as Kd values at pH5.5-6.5 (ml/g)

16.5627.6320.4018.5021.98

22.2216.8615.879.80

45.0(at pH 2)

*N.A.(atpH2)

Mg2+Ca'+Cu2+

Zn2+

Ni2+

C02+

Cd2+Mn2+

Aj3+

*N.A. = No adsorption

SulphateChlorideSulphateSulphateChlorideSulphateSulphateSulphateChlorideChloride

Chloride

5 - O.1(M)NaC~----1(M)HC~~1(M)NaCI-

Fe3+

3 5 O.1(M)NaCI q 1(M)HCI+1(M)NaCl---->

3

0

.1(M)NaCI-l(M)HCI+l(M)NaCI-> , 05

--:E 3<! EI-

0<!wI-~ 0 5 o.1(M)NaCI ,"'(M)HCI+l(M)NaCI-

M 0 W'0 ::;:

M'0 :i0

5 .l( M)NaCI--»- 1(M)HCI+~M)NaCI..•..0E

:J

'"0 E> ~ 00>..

0

Water + 1(M)NoCI+1(M)HCI-5

5 35Effluent collected (rnt )

Fig. l+-Scparation of Co(II)-Fe(III). Mn(II)-Fc(IIlJ. Nif l l i-Fctl l l ). Cut l l l-Fcl l l l ). Zn(If)-Fc(lll) ami AlIlll)-h:(IlI) on a zirconiumtungstate column [Int. diam .. 1.5 em and now rate, (l.n ml mini

347

INDIAN J CHEM, SEC A, APRIL 1989

100 mesh size) inserted in a glass column (int. di-am. = 1.5 em) with a glass-wool support. The flowrate was maintained at 0.6 ml/min. The column wasloaded with an amount of cation representing lessthan 20% of the breakthrough capacity of the metalion.

Initially, liberation of H+ is rapid since the ex-changer is totally in H+ form but as the elution pro-ceeds partial replacement of H + by sodium ion de-creases the rate of liberation of H + and at very largevolumes ( - 100 rnl) of the eluent, the amount of H +liberated is so small that column capacity can safelybe calculated upto this point. The ion exchangecapacities in the pH range of 6-6.5 for univalent ions(Table 1) follows the order Na + < NH: < K +. Theorder for bivalent ions is Mg2+ <Ba2+ Asthe hydrated ionic radius decreases, the exchangecapacity increases. Distribution coefficient data(Table 2) show that Hg2 + has the least affinity to-ward the exchanger in the triad Zn2+, Cd2+ andHg2+. Similarly Fe3 + gets strongly adsorbed on thismaterial in comparison to the ions like Mn2+, NF+,Co2+, Cu2+, Cd2+ or Zn2+. From these results se-parations of several binary mixtures have been per-formed successfully. In these systems, weakly ad-sorbed components were eluted with a dilute solu-tion of sodium chloride (0.1 M) which howevercould not remove Fe3 + ion from the column (Fig. 1).Adsorption of aluminium was small than even bywashing with demineralised water it was completelyremoved from the column. In all cases, Fe3 + waseluted with 1 M HCI + 1 M NaCl. Separation trendin the binary mixtures of mercury is exactly oppo-site. Since Hg2 + ions are only weakly adsorbed,washing with very dil. NaCI (0.001 M) removed itcompletely (Fig. 2) from the column, its countercomponent being eluted by using stronger concen-tration of the same eluent. The method has been ap-plied for the separation and estimation of iron pre-sent in very small amount in pyrolurite ( - 1%) andaluminium-bronze (2.2%).

The overall separation process is quantitative,rapid and very simple thus establishing its use as asuccessful ion exchanger. Application of the ex-

348

E~c(I-oUJ

~<'>'0..,

•

Effluent collected (ml ).

Fig. 2-Separation of Hg(II)-Zn(II), Hg(Il)-Cd(II) on a zirconiumtungstable column [Int. diam., 1.5 em; and flow rate, 0.6 ml/min 1

changer to other common ore and alloys are inprogress.

The authors are grateful to Dr A.K. Das for AASmeasurements.

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