India n Journa l o r C hem ical Tec hno logy

Vol. 9 . Scptcmber 2002. pp. -120-42:1

I "" • I - .

Articles

C7 , )

Synthesis and analytical application of lead selecti ve thorium iodate cation exchanger

" I M Jithal Kunhikri shnan1& J anardanal * . r Depart ment o f C he ,;, istry. S ree Naraya na Post Grad uate Co llege. Ka nn ur 670 0071 India

Rl'ce i l'l'd 17 Jlliv 2001; r l' l' ised r l'cl' il'ed II March 2002; (IccepIl'd 22 Mav 2002

L A new inorganic ion exchanger thorium iodate was synthesized and characterized by studying the properties like ion exchange capacity, pH titra tion curves, distribution coefficients for various metal ions, effect of hydrated ionic radii, temperature, electrolyte concentration, etc. on the ion exchange capacity. The empirical formula pro­posed for the ion exchanger is Th01.I10 S.nH20. Important binary as well as ternary separations were carried out. The synthetic utility of the exchanger is revealed from the separation studies. The separation performed on the ion exchanger column is very important for the environmentalists, since the mixtures analysed are Cu2+-Pb"+, Ni2+_Pb2+, Cd2+_Pb2+ and Hg2+_Pb2+. -,

.,I

I norgani c ion exchangers have estab l ished 1-3 their pl ace in analyti ca l chemistry due to their resistance to heat and radi ati on and their differenti al selectivity for metal ions. A large number of such material s have been sy nthes ized earlier, most of whi ch are the hy­drous ox ides and th e heteropolyacid-salts of the tetra and pentavalent metals. These compounds have show n great promise in anal yt ical chemistry because of their separation potenti al of metal ions4

. Every sy nthet ic inorgani c ion exchanger (SII E) has specific se lecti vity towards one or two metallic species. They are also highl y stable to a wide range of pH and up to hi gh temperature. However, their rea l analyti cal ap­pli cation in various fields are still lacking.

Two component ion exchange materials have been fo und to be more stable possess ing better ion exchange characteri stics , parti cul arly the zirconium based arsenite, vanadate of cerium (l V)S.6, selenite of

. . 7 I bl 8 d ~ I . ZI rconIum , arsenate, mo y ( ate , vana ate, se enlte, tungustate lO of antimony (III ) have been prepared earli er and their analyti ca l applicati on have been studied appropriately. I n order to explore the analyti cal potential of such materi als further a new material namely thorium iodate has been prepared and its ion exchange properties were studied. It is found to possess high thermal stability and selecti­vity fo r lead which makes it important for the environmentali sts.

Experimental Procedure

Reagents and chemicals Thorium nitrate [Th (N03)~. 5 H 20] and potass ium

iodate (KJ03) were obtained from Loba-chemi (In­di a) . All other reagents and chemicals were of ana­lyti cal grade.

Apparatus A pH meter model mkVr from Systronics Ltd . was

used for pH measurements.

Reagent solution

Decimol ar soiutions of thorium nitrate and potas­sium iodate were prepared in deminerali sed water (DMW).

Synthesis of thorium( IV)iodate Thorium iodate was prepared by adding 500 mL of

0. 1 M potassium iodate solution to O. I M 500 mL thorium nitrate with constant stirring. Dilute ni tri c ac id and dilute sodium hydrox ide were used to main­tain the pH at 1.0. On standing for 24 h the precipitate settled and it was filtered, washed fi rst with dilute HN0 3 (pH- I), then with demineral ised water and dried at room temperature. The white amorphous solid thus obtained was then converted into H+ fo rm by treating with 1.0 lv1 HN03 for 24 h with occasional shaking and intermittent change of the acid .

Kunhi kr isllllan & Janardanan : SYl1thesis of lead sei.::c ti ve thoriu lll iodate cati ol1 exchanger Articles

/011 excha11ge capacity (i.e.c) The ion exchangc capac ilY or the sample was de­

tcrm i ned by the co l umn opcrat ion. The ion exc hangcr ( 1.0 g) in the H+ form was placcd in the column with glass woo l support. Sodium chlor idc ( 1.0 M) was uscd as thc elucnt and 200 mL of thc clua tc from thc co lumn were detcrm incd ti tri mctri caly wi th sta ndard NaOH . The cxc hange r cou ld be regenerated thri ce wi thout any appreciable loss or exchangc capac i ty. The ion cxchange capacilics in meq g-t (el ry bas is) 1'01'

vari ous mctal ions are reported in Tab le I .

Th ermal stability Scvcra l 1.0 g porti ons o r th e sampl e wcrc hcaled al

vari ous tcmperaturcs in air-oven 1'01' three hours and thci r ion cxchangc capac ity was determ ined by the usua l co lum n process ancr coo li ng them to the room temperature. The rcsul ts arc given ill th e Tah le I .

pH titratio11 IJH titrati ons \\'ere perrormcd by batch process us­

ing the ll1eth ,ld o r Tnpp and Pepperll . 500 mg por­tion, or the c\ehanger in till' Ir rmlll "'crc pl aced in

'I al>,' 1,,11' (h;11l~L' L'II':I' JI~ "I' th"riulll i"d:ltc r,)r \ ;1I111U, IllL'I,tI illil "lUll"'" a III I 1.·1I1pnalurL· clll"l"1 "11 i.l·.l".

I"n C\L'h;IIl~L 'I L' lllpcr;tlUI'C d~

L"l'acil~ IllL<I I eJllp

I_iel

:\a( I

K( 'j

\ tgC'1

Ca( '1,

[.:l aCI

II 10

(tin ) ~

(l.X"

1.2 )

1.-13

1.)0,'

I.X()

3.0l)

,0 -;()

I (H)

1-;0

2()()

':5()

7 .~. ~ :I /

~ly' 2 -

I

o · ,'-0.5 1.5 2.5

~1 ' lTlo l s orO !! ion added

Fig. I - p H tilration curve

( ~,I ,

I.l'.\..

1.23

t.2()

I .()()

(l.X')

0.52

O.3X

-..-- Senes ' Ba(OH.,)/BaCI}

-.- Series2 NaOH/NaCI

.1.5 1.5

each of thc several 250 mL conical flasks foll owed by the equimolar soluti on o r mClal chl orides and their hydroxides in different vo lume rati os , the rinal vo l­umc bcing 50 mL to maintain constant ionic strength . The pH or the diffe rent so luti ons "/ere recordcd artcr cqu ili brium and pl otted agai nst the mill ieq uivalcnt s o r the OH - ions added. The result s arc shown in Fi g. I.

Distributio11 studies 100 mg porti on 01' the exc hanger in thc H+ rorm

were shaken fo r few hours in 20 mL So lu lion or dif­fe rent metal ions. Thc initial metal ion co nccnt rati on was ri xed below ]C'ln or the total ion cxc hange capa­city o r thc sam ple taken . The meta l ions in the solu­tion bcrore and after cquili briu l11 werc detcrmined by EDTA' 2 titration and the di stribution coclTicienl s (K,, )

were calculated us ing the foll ow ing fo rmul a K" = 1(/­F)IF I (VIM ) (mUg) where I is the ini tial vo lume or EDTA used, F is thc rinal vo lu me or EDTA u<;ed. V is the total vol umc of the so lut ion (mL) and M is the mass o r the cxchan ger (g ). The K" values for the metal io ns are gi"cn in Table 2.

Errcct or th e elect ro l) te conccnlrati on on ion ex­change capacity \\'a<; de termined by equilihrati ng meta ! ion:-- in dirrc rent conce ntratill n:-- ()~- electro lyte, sueh as I I. '0, and 1'\ H INO,. The rl':--ul t.., arc gl\l'n in Tahle :\.

COlli pm it i Oil

The exchanger (100 mg) grounci to rine PO\\dt'T. \\ as di,,<;olved in 10 mL or C(\ncd I leI. Thorium \\ a' eo.,t imated gravimetrica ll y as Thori,t l11 and iodate gra­, 'inl': tricall y as Ag l ' ,''. The molar compo\ il ion or the material was found to be I : I ror thori um and iodate

Tahle ':- Di , tribulioll coc llicien l ( I\d ) of Illetal iOlb ,)n thoriulll ioelate

Cations

Zn2+

Mg~ t­

Ca 2+

j :!+

CUC+

Coc+

Cel Cf

SnC+

Hgc+

Pb2+

Bi.l+

Takcn a,

Sulphale

Sulphate

Chlori de

Sulphale

Chloride

ilrate

N itrate

Chloride

Chloride

Nit rate

Nitrate

Kd ( Ill l/g)

':.<)7

50.':

20. 10

0.00

25.5X

130.30

27. 10

833.33

15.55

t4X7

mus

42 1

Articles

Separations achieved For separati o n studi es of binary and ternary mi x­

ture: 5 g of the exchanger in the H+ form was taken in a glass column (30 cm x 1. 1 cm di ameter). The rate of flow in a ll separati ons was 2-3 dro ps per min ute. T he

Table 3- Effect of electro ly te concentration on distribution coeffic ient

Electro ly te

HNO, O.IM

O.OIM

O.OOIM

O.IM

O.OI M

O.OOIM

Pb2+

1205

13 15

1396

1093

11 85

1295

Meta l ions Bi .1+

112

123

128

102

11 8

137

S '+ n-

7 12

8 10

823

698

780

825

Indian 1. Chcm. Technol. . September 2002

separations were achieved by passing a suitable so l­vent through the column as e luen t and the metal ions in the effluent were determi ned quan ti tati vel y by EDT A ti trations. The sa l ient features o f separati on are given in Tab les 4 & 5.

Results and Discussion Thori um iodate was o btained in the fo rm of w hite

amorphous solid . It was stable in water, alcohol , ace­tic ac id, I .OM H2S04 , 1.0 M HN03, J .OM HC I and in aqueous solutions of LiC I, NaCI , KCI , MgCl 2, CaCl2

and SaCl2. The maximum ion exchange capac ity was found to be 1.23 meg/g. The chemical composit ion was fo und to be I : I (Th: I0 3) with a variation of

±0.01 % for success ive determination . The empirical fo rm ul a of thorium iodate is proposed 14 as Th02.

h Os· nH20.

Table 4- Separatioll of binary mixtures 011 thorium iodate co lumn

Sample Mixture with eluellts M etal iOIl ill mg % Error Loaded Recovered

Cu2+(0.02M HNO, ) 1.60 1.60 0.00

Pb2+(0. IM HN03+O.I NH4NO,) 0.86 0.85 -1.16

2 Ni2+(O.M. W) 2.50 2A5 -2 .00

Pb2+(0.1 M HN03+O.1 M NH4N03 ) 0.86 0.87 +1.1 6

Cd2+(0.02M HNO, ) 5.00 4.98 -OAO

Pb2+(0. 1 M HNO,+O. I M NH4NO, ) 0.86 0.85 -1.16

4 Hg2+(0.0 I M HNO, ) 13.00 13.00 0.00

Pb2+(0.1 M HNO,+O.I M NH4N03) 0.86 0.85 - 1.16

Table 5-Separation of ternary mixtures on thorium iodate column

Sample Mi xtures with eluellts Metal iOIl in mg % Error Loaded Recovered

Zn2+(OMW) 8.00 8.00 0.00

Hg2+(0.02M HNO, ) 13.00 13.20 + 1.50

Pb2+(0.1 M HNO,+O.I M NH4NO,) 0.86 0.85 -1.10

2 Ni2+(OMW) 2.50 2.50 0.00

Cu2+(0.02M HNO, ) 1.60 1.56 -2.50

Pb2+(0. 1 M HN03+O. 1 M NH4NO,) 0.86 0.88 +2.30

3 Cu2+(OMW) 1.60 1.6 1 +0.62

C02+(0.02M HNO,) 5.00 4.95 -1.00

Pb2+(0. 1 M HNO,+O. I M NH4N03) 0.86 0.85 - 1. 16

4 Hg2+(0.0 1M HNO.1) 13.00 13.00 0.00

Cd2+(0.02M HNO,) 5.00 4.98 -OAO

Pb2+(0. 1 M HNO,+O.I MNH4N03) 0.86 0.85 -1.1 6

5 Ni2+(OMW) 2.50 2.50 0.00

Cd2+(0.02M HN03) 9.00 8.80 -2 .20

Pb2+(0.1 M HNO,+O. I M NH4NO,) 0.86 0. 87 + 1. 16

422

Kunhikri shnan & lanardanan: Sy nthes is o f lead se lective thorium iodate ca ti on exc hanger Articles

The effect of size and charge of the metal ion on the capacity of the exchanger was studied for all the alkali and alkaline earth metal ions. The order of the exchange capacities on thorium iodate is as follows:

The ion exchange capacity increases with decrease in hydrated ionic radii . This trend in the exchange capacities revealed that the ion exchange capacity de­creases with increase in temperature and little ex­change persi sts even at 250°C.

The distribution studies of eleven metal ions have revealed that thorium iodate shows affinity for the metal ion in the order,

Pb2+ > Sn2+ > Bi 3+ > C02+ > Mg2+ > Cd2+ > Cu2+ > Ca2+ > Hg2+ > Zn2+ > Ni2+

The effect of electrolyte (HN03, NH4N03) con­centration on the distribution coefficient of some metal ions was also studied. The sorption of cation on ion exchanger was found to decrease with increase in electrolyte concentration .

The pH titration studies reveal that the material be­haves as a mono functional acid for Na+ ions showing the theoretical i.e.c at equilibrium -1.8 meq/g. Simi­larly the monofunctional behaviour of Ba2+ ions showing its theoretical i.e.c at equilibrium -3.00 meq/g.

Binary separation of Cu2+_Pb2+, Ni 2+_Pb2+, Cd2+_ Pb2+ and Hg2+_Pb2+ were achieved on a column of tho­rium iodate in addition to important ternary separa-

tions like Zn2+_H a2+_Pb2+ Ni 2+_Cu2+_Pb2+ Cu2+-Co"+-b' ,

Pb2+, Hg2+_C02+_Pb2+ and Ni"+-Cd2+-Pb2+. The eluents used are HNO] and NH4NO, . The recovery range is from 97-100% with a variation of 1% for repetitive determination. The importance of the exchanger is revealed from the binary and ternary separati ons car­ried out successfully on the exchanger column and also quite helpful for the environmentalists as the in­dustrial effluent waste often consists of such mixture combinations.

References I Al1lphlett C B, Inorganic Ion Exchangers (Elsevier Amster­

dam), 1964. 2 C learfield A (Ed) Inorganic Ion Exchange Malerial (C RC

Press Inc., Boca Raton, Florida), 1982. 3 Qureshi M & Varshney K G (Ed), Inorganic Ion Exchangers

in Chelllical Analysis (C RC Press, Inc ., Boca Raton. Fl or­ida), 1991.

4 Abe M, Kotaoka T & Suzuki T , Nelli Developmenl In Ion Exchange Pro. In[ COI(/ Ion Exchange, IC IE' 91 (Tokyo, l apan), Oct 2-4, 1991.

5 l anardanan C, Nair S M K & Savaria C P, Analv:;I, 11 3 ( 1988) 1141.

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7 lanardanan C, Nair S M K & Savaria C P, J Indian Chelll Soc, (1989) 912 .

8 lanardanan C & Nair S M K, Analyst, 115 (1990) 85 . 9 l anardanan C & Nair S M K, J Indian Chem Soc, (1992) 48.

10 l anardanan C & Nair S M K, Indian J Chelll , 35 ( 1996) 74. II Topp N E & Pepper K W, J Chelll Soc, (1949) 3299. 12 Reilley C N, Schmid R W & Sadek F S, J G elll Edllc. 36

( 1959) 555. 13 Voge l A I, A Text Book of Qllantitative Inorgallic Analysis

11/ Edn (Longman ELBS), 196 1, a :540, b:572 14 Albert G, Constantino U & Zimba L, J II10rg Nllci Chelll , 34

( 1972) 3549.