IadilUl Joumal of QaemlstrJVol. 21A, April 1982, pp. 398401

Synthesis & Ion Exchange Properties of Amine Tin(IV) Hexacyano-ferrate(II) & Its Use in the Separation of Cadmium(II) from Zinc(II),

Manganese(II), Magnesium(II) & Aluminium(III)

K. G. VARSHNEY·, ASIF A. KHAN & s. S. VARSHNEYtChemistry Section, Z. H. College of Engineering & Technology, Aligarh Muslim University, Aligarh 202001

Received 27 June 1981; revised and accepted 16 November 1981

A new type of Inorganic Ion exchanger, amine Sn(lV) heucyanoferrate(lI), with seven different amines hasbeen prepared. Different samples of the exchanger have been prepared to study the Ion exchange capacities fordifferent metals at different temperatures, Based on pH titrations, e1utiODcurves, m and thermogravimetric studies,a tentative formula of the compound bas been proposed. The utility of this material bas been tested by achieving someImportant binary metal separations such as CcP+ _Zn2+ and Cu2+ -AP+.

METAL hexacyanoferrates(II) have been usedas scavengers for the removal of alkalimetals from sea water, milk and urinev".

Ammonium hexacyanocobaltferrate(Il) was reportedto have an extra affinity" for Cs and was found to beuseful for the analysis of mcs. A further improve-ment in its performance was achieved" using ahigh molecular weight amine instead of NHt ionsin its preparation. In continuation of the earlierwork1-8 from our laboratories on Sn(Il) and Sn(IV)hexacyanoferrates(II) and amine Sn(ll) hexacy-anoferrate(Il) as ion exchangers, we have nowprepared amine Sn(IV) hexacyanoferrate(II). Someimportant binary metal separations, such as Cdll+from Zn2+, Mn2+, Mg2+ and AP+ and Cu2+ fromAI3+ have been achieved using this ion exchanger.

Materials and MethodsStannic chloride (p.p.H. Polskie Odczynniki

chemiezene giiwice, Poland) and potassium hexa-cyanoferrate (II) (BDH, England) were used. Otherreagents and chemicals were of AR grade. Ferro-cyanic acid was obtained by passing a solution ofK4Fe(CN), over a bed of Amberlite IR-120 resinin H+ form.

pH-metric and IR studies were carried out usingElico digital model LI-120 pH meter and Perkin-Elmer model 137 spectrophotometer respectively,TGA studies were made on a thermo-balance designedby FCI (Sindri). For X-ray studies, a Philips X-rayunit with Ni-filtered Cu-Ka. radiations was used.SEM studies were made on a Cambridge StereoscanElectron Microscope attached with an X-ray Micro-probe Analyser.

Synthesis - K4Fe(CN)e solution (100 ml, 0.1M)was passed through a resin column in H+ form witha very slow rate. The column was washed with

tDepartment of Chemistry, Hindu College, Moradabad244001.

398

distilled water so that the effluent, bluish-green incolour, was approximately 275 ml in volume. Anexcess of the selected amine (-5 ml) was added tothis solution to prepare the amine hydrogen salt[A2H2Fe(CN)6]. Hydrazine sulphate was takenas solid (1 g). This solution was poured into aO.1M stannic chloride solution drop wise, stirringrapidly. Cone, HCl was added to maintain thepH around 1. The precipitate thus formed waskept at room temperature for 24 hr before filteringin vacuo. The precipitate was washed several timeswith demineralized water (DMW) until the pH ofwashing became 5-6. The material was finally driedin an oven at 50°C and cracked into small granulesby immersing it in DMW. It was converted intothe H+ form by putting it in I-2M HN03• Theexcess acid was washed out and the material wasagain dried in air at 50°C. Different samples wereprepared by varying the volume of the SnClt solu-tion. Ion exchange capacity (i.e.c.) of differentsamples was determined by the column process using1.0M KN03 solution. The results are summarizedin Table 1. On the basis of its better exchangecapacity, lower solubility and higher yield as com-pared to other samples prepared, sample S-2 wasselected for a detailed study.

Results and DiscussionThe composition of the exchanger was deter-

mined by the same procedure as adopted earlier'for amine Snell) hexacyanoferrate (II). The amountsof tin and iron, determined by the standardmethods'v-", were found to be 33% and 18% res-pectively in the substance.

As the material was a cation exchanger, its i.e.c.was found using 1.0 to 2.0M solutions of metalions (alkali and alkaline earth metal ions), by thecolumn process as usual", Since the concentrationof the eluant was found to affect the elution beha-viour of the material, KNOa solutions (200 ml) of

VARSHNEY et al. : AMINE TIN(IV) HEXACYANOFERRATE(II) ION EXCHANGER

T.4BLE 1 - SYNTHESIS ION EXCHANGE CAPACITIESIl

AND 01'DIFFERENT AMINE BASED Sn(lV) HExACYANOFERRATES(II)

Sample No. Volume of Amine added i.e.c, 10O.lM SnCI. meq/g (dry)

(ml)

s-i SO Aniline 1.86 8S-2 200 Do 1.70S-3 100 Do 1.60 :r~S-4 300 Do 1.20 6S-S SO Ethyl amine 1.6SS-6 200 Do 1.62S-7 SO Diethanolamine 1.20S-8 200 Do 1.08

4S-9 SO Hydrazine sulphate 1.14S-10 200 Do 0.91S-l1 50 Methyl amine 1.30S-12 200 Do 1.23

Z- .•. 40- kOH .• KCI system

S-13 sa Dimethyl amine 1.05 ___ No');! + Noel system

S-14 200 Do 1.00 ~ Li OH + LiCI s~stem

S-15 50 Ethanolamine 0.72S-16 200 Do 0.58

varying concentrations (0.1 to 2.5M) were passedthrough the column bed of 0.5 g material. Themaximum i.e.c. was obtained with an eluant con-centration of ,....2.0M. Also, approximately 130 mlof the eluant were enough for the complete elutionof H+ ions from the column. The ion exchangecapacity (meq/g) of sample S-2 for different metalions (hydrated radii, A in parentheses) is asfollows: Li+ (3.40), 1.01; Na+ (2.76), 1.15; K+(2.32), 1.70; Rb+ (2.28), 1.06; Cs+ (2.28), 1.20;Mg2+ (3.10), 0.52; Ca2+ (2.00), 1.10; Sr2+ (1.80),0.90; and Ba2+ (1.50),0.86. On heating 1.0 g of theexchanger at various temperatures for 1 hr thei.e.c. was observed to decrease. It became 0.30meq/g on heating the substance upto 150°C, 0.08meq/g on heating it upto 200°C and almost zerobeyond this temperature.

Solutions of LiOH, NaOH and KOH containingdifferent amounts of OH- were taken and the ex-changer (500 mg) was added to each solution. Thecommon ion effect was nullified by adding respec-tively metal salts (LiCI, NaCI and KCI), keeping thetotal volume 50 ml. After allowing the solutions tostand for 24 hr for the attainment of equilibrium,the pH was recorded and plotted against the OH-added (Fig. 1).

Distribution studies - The distribution coefficients(Kd) of 14 metal ions for sample S-2 were determinedas usual" by the batch process in DMW and IO-2MHN03 solutions. The metal ions were determinedin the solution volurnetrically= using EDT A. Thefollowing formula was used for determining Kdvalues,

I-FF

vX M ml g-l

where I= initial concentration of the metal in solu-tion, F = final concentration of the metal afterequilibrium, V = total volume of the solution (ml)and M = weight of the exchanger (g). The Kdvalues obtained are shown in Table 2.

o , 2 3 ~ 5

meq of OH-jons addedFig. 1 - pH titration curves for sample S-2.

TABLE2 - DISTRIBUTIONCoEFFICIENTSOF SOME METAL IONSON SAMPLES-2

Kd (mlJg) inMetal ions

DMW IO-'M HNO.

BaH 85.0 40.0Sr'+ 85.0 14.0CaH 175 x 10' 0.0Zn2+ 5S.0 46.0MnH 0.0 0.0MgH 25.0 0.0Cd'+ 43.8 x 10' 1.09 x 10'AJ3+ 60.0 0.0Hg2+ 6.00 x 10' 5.62 X 101

Cu2+ 43.8 X 10' 1.01 X 10'La3+ 3.62 X 10' 3.62 X 10"Pr3+ 68.0 68.0Th'+ 7.00 x 10' 2.38 x 10'Bis+ 16.5 x 10' 9.7S x lO'

Separations achieved - Table 3 shows the binaryseparations achieved using 1 g columns of this ex-changer, with all the details of amounts of the metalions loaded and recovered alongwith the % errorin each case.

Different samples of the amine Sn(IV) hexacyano-ferrate(II) exchanger (Table I) show reproduciblestoichiometry, water content and ion exchange capa-city. The i.e.c. appears to depend on the nature ofthe amine used in the preparation of the exchanger.It varies in the following order : aniline > ethylamine> methyl amine> diethylamine> hydrazinesulphate> dimethylamine > ethanolamine. Thesame order was observed in the case of amine Sn(Il)hexacyanoferrate (II) exchanger prepared earlier'.

On the basis of chemical analysis, TGA and IRstudies the following formula may be tentativelyproposed for the compound :

rSn(OH)t.A2' H2Fe(CN).]n.H20, A= C,H6NHt

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-INDIAN J. CHBM .• VOL. 21A. APRIL 1982

TARL!! 3 - QUANTITATIVI! SEPARATION OF METAL IONS ONCoLUMNS OF SAMPLE S-2

Separation Metal Amount Amount Eluant Errorachieved ion loaded recovered ('Y.)

eluted «.Ig) (v.g)

Znh'-Cdl+ Znl+ 305.5 299.0 0.02M NH.NO~ -2.1CdH 241.9 247.6 4M HNO. in +2.4

2MNH.NO.

MnI+-Cd1+ Mn2+ 264.0 269.5 0.02M NH.NO. +2.0&Cdl+ 241.9 247.6 4M HNO. in +2.4

2M NH.NO.

Mgl+_Cdl+ Mgt+ 100.8 105.6 0.02M NH.NO. +4.7Cd2+ 241.9 245.3 4MHNO.in -1.4

2M NH.NO.

Al'+_CdI+ AP+ 94.5 102.6 0.02M NH.NO. +8.6Cd2+ 241.9 247.6 4M HNO. in +2.4

2MNH,NO.

AJI+-CUI+ Al'+ 94.5 89.1 O.02M NH. NO. -5.5Cu"+ 137.2 145.8 4MHNO,in +6.3

2MNH.NO.

40

~~2C 20'"~ --------

10,, ,

I'

~i,I

100 l~O )00 400

Temperoture C °c )

Fig. 2 - Thermogram for Sn (IV) aniline hexacyanoferrate(ll)in H+ form.

The stoichiometry of A2HaFe(CN). has earlier beenestablished8• The number of external water mole-cules, n, was determined from the thermogram of thesample S-2 (Fig. 2) using Alberti's formula,

I8n = . x (M + 18n).100

where x = % weight loss in exchanger, n = numberof external water molecules and M = molecularweight of the exchanger without water molecules.

If it is assumed that all external water is removedat 200°C, which corresponds to a weight loss of_14%, the value of n comes out to be 5.3. Afurther loss in weight upto 41O"C may be accountedfor by the loss of internal water molecules andcyanogen which comes offia at 237°C. Beyond41O"C the weight of the exchanger becomes constantupto 6OO"C. A loss in weight between 600° and700"C may be due to the removal of C as CO2,

Above this temperature only the oxides of tin and

400

iron are left as indicated by the grey colour of theresidue.

The pH titration curves (Fig. 1) indicate that thecompound exhibits two end points with a combinedexchange capacity of ..•..6 meqJg corresponding to a4 meq/mol of the exchanger. The first end pointcorresponds to an i.e.c. of ..•..2 meq/g (..•..Imeq/mol).It is probably due to the release of one H+ from theH2Fe(CN)e site. During the second end pointthe remaining H+ ion of this site and two moreH+ ions from a more basic site, Sn(OH)4, might bereleased, giving a total ion exchange capacity of 4meq/mol.

The IR spectra of the first four samples (SvlS-2, S-3 and S-4) dried at 5O"Cshow peaks at -500:-600, •..•..800, -980, -1400, ..•..1610, -2100 and.....3000cm-l. Some of these confirm the presenceof SnO (..•..500), M-C stretching in Fe(CN):--(600), water molecules (..•..1610 and 3000 cm-l)and ferrocyanide group (..•..2100 crrr-') The rest areobserved due to the presence of N-H rocking mode(-725 cm=), CH rocking mode (,....980 cm-I) andO-H bending mode (-1640 em-I). The OH bandsat -3000 cm-1 are indicative of strongly hydrogenbonded OH or extremely strongly coordinated H20.The IR spectra obtained for the samples driedat different temperatures i.e. at 100°, 150°, 200'"and 400" show a gradual decrease in the intensitiesof peaks at 2100 cm-! and 1610em-I. This is becauseof the loss of CN- and H20 molecules on heating.The intensity of the peak at 3000 em'? is also affect-ed because of the condensation of the exchangermolecule which is accompanied by the removal ofstrongly coordinated H20 molecules.

The X-ray studies show that the material is essen-tially amorphous in nature, and this finding is sup-ported by the SEM studies.

The aniline Sn(IV) hexacyanoferrate (II) is foundto be highly selective for Cd2+ and Cu2+ (Table 2).The selectivity for metal ions decreases considerablyin acid solutions, which is obvious. On this basissome metal ion separations were tried and actuallyachieved as summarized in Table 3. Amine Sn(IV)hexacyanoferrate(II), therefore, seems to have higherseparation potential than the Sn(II) salt preparedearlier.

AcknowledgementThe authors thank Prof. M. Qureshi for research

facilities and Dr (Mrs) G. K. Sandhu of G. N. D.University (Amritsar) for TGA work. The X-rayand SEM studies were carried out at the HatfieldPolytechnic Hertfordshire (U.K.) for which DrD. V. Nowell is thanked. The financial assistancefrom the UGC and CSIR, New Delhi is gratefullyacknowledged.

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