I ndian Journal of Chemical Technology Vol. 1 0, March 2003, pp. 1 37- 1 42

Articles

Determination of some metal ions in aquatic environs by atomic absorption spectrometry after concentration with modified silica

A A Hanna*", Kh S Abou-EI -Sherbin i", E E l zahany & M A Hamedh

"I norganic Chemistry Department, National Research Centre, Dokki. Cairo. Egypt hNational I nstitute of Oceanography and Fisheries. Suez. Egypt

Received I April 2002; revised received 2 Decelllber 2002; accepled 1 0 jWll/arv 2003

N-propylsalicy la ld imine based on porous s i l ica, as ion exchanger, is used for the separation and preconcentration of Fe'+, Co2+, N i2+ and Zn2+ from surface water samples col lected from eleven locations at N i l e river, Mediterranean and Red seas and Mansoura city tap water. The effects of pH, t ime of stirring, concentration of e lut ing acids and some common ionic species on the separation and preconcentration of the investigated metal ions in synthetic aqueous solutions are studied. The results indicate that the opt imum condit ions for separation are pH = 9.0-9.5 and t ime of stirring = 30 min. HCI is better elu­ent for the investigated metal ions than HNO, except for Fe3+. C itrate and EDTA show severe i nterference on the recovery of the metal ions, therefore, the water samples are previollsly oxidized to d igest organic matter prior to the application process.

The synthesis of chemical ly-modified porous si l ica with N-propylsal icyaldi mine ( l E I I ) as chelating agent was described elsewhere ' . The nature of bonding of I E I I with some metal ions was investigated by ele­mental analysis, electronic and i nfrared spectra, ther­mal analysis and electrical properties2

. Thi s confirmed that the uptake behaviour of I E I I towards these metal ions is due to complexation.

According to the importance of metals to the aquatic environs, it may be divided i nto three groups (i) l ight metals such as sodium, potass ium and cal­cium which are normal ly mobile cations in aqueous solution; ( i i ) transi t ional metals such as i ron, copper, cobalt and manganese which may be tox ic in high concentrations and ( i i i ) heavy metals and metal loids such as mercury, l ead, cadmium, t in , selenium and arsenic which are generally not required for metabol ic activi ties and are tox ic to the cel l at qui te low con­centrations

) .

Due to the i nterest on water quality, many studies have been performed on the water sources to esti mate the levels of heavy metals4.<.I. The metal-uptake be­haviour of I E I I was studied in different media4. The factors control l ing and i nfluencing the metal uptake capacity such as pH of the metal ion solu ti on and st ir­ring time were determined to evaluate and compare

* For correspondence (E-mai l : adli-hanna @ yahoo.com: Fax: 002102/337(93 1 )

the performance towards extraction o f CdC I I ) . Cr( I I I ,VI) , Cu( I I) , MnC I I ,V I I ) and Pb( l l ) ions. I n con­tinuation, the present paper is aimed to study the up­take behaviour of l E I I towards FeJ+, C02+, Ni2+ and Zn2+ to ascertain the opt imum conditions for the sepa­ration, preconcentration and determination of these metal ions in aquatic environs.

Experimental Procedure

Synthesis

The ion exchanger I E I I was prepared as previ­ously described ' . Porous s i l ica was prepared by ac id

leaching of s ieved boros i l icate glass « 70 , .. 1In, 8/Si = 6: 1 ) obtained by sol gel technique, then grafted with 3-aminopropyltrimethoxysi lane and the obtained product was retluxed wi th salicylaldehyde.

Complexes of IE 1 1 wi th the i nvestigated metal ions were prepared by adding 1 00 mg of the ion ex­changer to 25 mL of 0. 1 M of the metal chlorides so­l ution and pH value was adjusted to be below 5.5 (ex­cept fbr Fe where the pH < 3) with 5% NaOH and 2% HCI and sti rred for 24 h, then the M-I E 1 1 complexes were fi l tered, washed with double dist i l led water and dried at 80°C.

Method

For the investigation of the effect of pH on the separation of the i nvestigated metal ions, 0.02 g of

Articles

l E I I was added to 25 m L of 1 0 )1g/mL of Fe.1+, C02+

and Zn2+ (as ch lorides) . The p H values of the sol u­t ions were adj usted in the range 3- 1 1 using 2 M

aOH and 0. 1 M HC! . Then the sol ut ions were st i rred at constant rate for 30 min, fi l tered and the concentra­t ions of the i nvest igated ions i n the fi l t rates were de­termi ned by atomic absorpt ion spectrometry (AAS) . The di sr ibut ion coeffic ient (Ke !) i s determi ned us ing the eq uat ion :

where Ci ex is the metal concentrat ion 1 11 the ion ex­changer (sol id phase) and Csol is the metal ion con­centration i n the solu t ion phase.

A rter adjus t ing the pH of the solu t ion at 9.0-9.5 to g ive max i mum K", effect of s t i rr ing t i mc and weight of ion exchanger was stud ied to obta in opti mum t ime of s t i rri ng and weight of ion exchanger for precon­centrat ion and separat ion of thc i nvestigated metal ions. The opti mum condi t ions (pH = 9.0-9.5, t ime of st i rri ng = JO mi n and weight of I E I I = 1 00 mg) were appl ied duri ng the study of the i n terferi ng effects of d i fferent foreign ions on the effic iency of separat ion and the effect of concentration of the e luent aci ds ( 1 0 mL of HCI or H NO,) on the recovery .

Application

Surface water samples were col lected from eleven locat ions i n N i le ri ver. M ed i terranean and Red seas, Egypt . A l l samples were fi l tered and acid i fi ed w i th concentrated H N O.1 to p H � 2 and preserved i n poly­ethy lene vessels at temperature 1 5-20°e.

For preconcentrat ion and separat ion of metal ions, 0.5 g of K2S20R and 5 m L of 98% H 2S04 were added to I L of the water sample and heated for 2 h at 95°C to d igest a l l organ ic matter wh ich may be pres­ent . A rter coo l i ng to room temperature, 1 00 mg of I E I I was added to the sample and the pH va lue was adjusted to 9.0-9.5 and st i rred for 30 min then fi l tered. To the fi l trate another 50 mg of the ion exchanger was added and pH value was aga i n contro l led . The sample was st i rred agai n for 30 min and fi l tered. Both res i ­dues were gathered a n d the col lected metal ions were released by 1 0 mL 2M H NO.1, to g i ve a concentration factor of I OO-fo ld .

Equipmellts I n frared reflectance spectra were recorded on a

1 ]8

I nd ian J . Chcm. Techno / . . March 20m

Bruker rFS 48 FfI R spectrometer us ing a gold bal l as reference. The sample in the form of f i ne powder was flattened on a sta in less s teel sheet wi th a drop of acetone which was a l lowed to vapourize then the reflec tance spectrum was measured i n a dry CO2-free a i r atmosphere . Th i s measurement was performcd i n the Phys i ka l i sch Techn ische Bundesansta l t B h · G A I . ,. F 1+ C

'+ N " + raunsc welg, ermany. na YSls 0 c· , 0- , l -and Zn2+ was pcrformed by the Perk i n-E lmer 2380 flame atomic absorpt ion spectrophotometer. For pH measurements a H A N N A p H-meter with an expan­

ded scale was used with accuracy ±0.0 1 log un i t . I t was fi rst standardi zed w i th 0.05 M potass ium hydrogen phthal ate of pH 4.0 I and pH tablet 9 .2 a t 2S°e.

Results and DisclIssion

Effect of pH

Fig . I represents the e ffect of p H on the uptake be­haviour of Fe.1+, C02+ and Zn2+ on l E I I . The d istr i bu­tion coeffic ient of Fe�+, C02+, N i2+ and Zn2+ on l E I I i ncreases w i th p H and reaches max i mu lll at pH = 9 .0-9.5 then decreases except for Fe.1+, N i2+ and Zn"+

showed sorpt ion on [ E l l at relat i vely low pH values d C

'+ N " + compare to 0- and 1 - .

The decrease i n the d istr ibut ion coeffic ient at pH > \ 0 i s attributed to the hydro lys is of the s i l ica based ion exchangers 10 whereas the stab i l i ty of the d istr i bu­t ion coeffic ient of N i2+ may be attr ibuted to the re la­t ive strength of i ts complex wi th l E I I as i nd icated from the rel at i ve ly h igh activation energy of substrate pyrolys is2. Log K" at pH = 9.0-9.5 was 4.86, 4.79, 5 .09 and 4.59 respect ive ly .

'0 � 8'

....J 3

9 pH

10 1 1

• Co • Fe • Ni " Zn

1 2 1 3

Fig. I -Effect of pH on the d i str ibut ion coeffic ien t of Fe( I I I ). Co( l I ) , N i(ll) and Zn( I 1 ) on I E- t I

Hanna el [Ii. : Determi nation of some metal ions in aquatic environs by atomic absorption spectrometry Articles

Effect of time of stirring

Fig. 2 represents the effect of time of st irring on the recovery of the investigated metal ions at pH = 9.0-9.5 using lE I I . In general, the recovery (%) increases with t ime of sti rring up to 30 min, then it becomes independent on the time of stirri ng. The ion exchanger shows fast k inetics of equi l ibration as 30 min of stirring was enough to reach maximum values of recovery.

Effect (�f cOll.cell.tration of eluent acids

Fig. 3 (a & b) shows the effect of concentration of eluting acids on the recovery after separation at pH =

9.0-9.5 and weight = 1 00 mg. The results show that HCI exhibit better leaching efficiency of the investi­gated metal ions from the ion exchanger than HN03

100 . � . f

'-'1'

;F- 95 �'I' c:- � Q) > �/ 1 0 90 u Q) et:

85 -.. - Zn

80 10 20 30 40 50 60 tirne, min

Fig. 2-Effect of t ime of st irring on the recovery of Fe( l l ) , Co( l l ) . N i ( l l ) and Zn( l I ) separated on 20 mg IE I I at pH=9.0-9.5

except in case of Fe·h where the recovery was appar­ently lower with HCI . Thi s may be attributed to the formation of anionic chloro-complex with Fe3+ which may be bonded to the protonated i mine nitrogen of the substrate suggested previously to be present at pH ::; 4' . However, molar concentration of the Hel and HN03 was sufficient to obtain maximum recov­ery but the laller is recommended for appl ication due to low recovery in case of iron.

Effect of interfering species

The effect of some common ionic species on the recovery was studied in Table I . Acetate, oxalate, n itrate, sulfate, phosphate, NH4 +, Mg2+ and Ca"+ ions were found to have no interfering effect on the recov­ery of C02+, Ni2+, Fe3+ and Zn2+. Ci trate and EDTA show severe interfering effect on the recovery of the investigated metal ions due to the formation of com-

plexes with the metal ions of higher stabi l i ty than those with l E I I . Consequently, the organic matter present in the natural water samples (wh ich may has the same effect) should firstly be digested prior to the appl ication process.

80

;F-e:- 60 <ll > 0 u <ll 100 et:

80

0.0

e __ -e---- e I

�--:===--=== .. � .. -

b

�. •

-.- Fe j -·- Co j

0.5 1.0 1 .5 Concentration, mole/l

2.0

Fig. 3-Effect of HCI (a) and HNO, (b) concentration on the recovery of Fe( I I/ ) . Co( l l ). N i ( l l ) and Zn( l l ) separated on 20 mg at pH=9.0-9.5 and t ime of stirring=30 min

Table I -Effect of some common ion ic species on the separat ion of Fe ( I I I ) . Co(l l ). N i ( l I ) and Zn ( I I ) on I E I I

Ionic species Recover,l %

Fe Co N i Z n

Acetate 94.3 97.9 97.4 99.9

Oxalate 99.9 96.4 92.5 99.6

Ci trate 75.4 63.8 39.6 96.3

EDTA 56.6 70.3 1 6 .9 80.6

N itrate 99.9 98.4 99.9 99.2

Sulphate 99.9 97.0 92.7 99.9

Phosphate 99.9 98.8 99.9 99.5

N H4 99.9 98. 1 99.8 98.8

Mg 98. 1 97.0 98.7 99.9

Ca 98. 1 98.3 99.9 98.9

1 39

.j:::.. o

Table 2-Multi-elements analysis of natural water samples usi ng AAS for determi nation of Fe 1., Co" . N il. and Zn" in �lg dill'" (;; ppb) aftcr pr<!concentration w ith ion ts

exchange separation by l E I , ! . Ion exchange conditions: pH == 9.0-9.5, weight of l E I I == I Y) mg. stirring t ime == 30 min at 25°C, X ± - � for == 5, where X is the average. I is ... '. , n

the student factor and equals 2.57 for P == 0.05 and s is the standard deviation

Location Fe Co N i Zn Found Reported Found Reported Found Reported Found Reported

1 - Mansoura 233.98±5.98 427, 80.09, 83.9R NO 1 .57, 1 .38 5 .08±0. 1 6 4.57,4.29, 1 4.58 26.38±0.9 1

(river water) 3607,220.09.220. 1 s

2- Faraskor 53. 1 5±2. 1 8 47.4-1 NO 3 1 7 1 .62±0.06 7.77 1 1 . 8 1 ±0.52

(river water) 1 607

3- Oamietta bridge 97.20±3.26 3 1 7 , 1 66.78 ND 257,5.88 4.4 1 ±0. 1 4 1 1 .87, 1 4 . 1 8 1 3 .72±0.46

(breakish water) 847. 64.88

4- Gerbi 1 60.07±4.25 377, 1 209, 93.88 N O 3.58 5 .6 1 ±0. 1 8 1 87,9.09.9. 1 8 2 1 .96±0.72

(brackish water) 247.40.09,33.68

5- Ras-Elbar 1 1 8.64±4.27 N O 3.26±0. 1 1 8.70±0.33

(brackish water)

6- Ras-Elbar 65.75±3.49 657,0.69, 28.68 N O 3 .27.5.58 2 .9±0.07 1 5 .87.O.39, I U8 23 .28±0.75

(brackish water) 267.3.09,26.78

7 - Damietta port 37.34±2. 1 7 N O 1 .3 3±0.05 1 0.70±0.57

(brackish water)

8- Port Said 9 1 .7±3.25 27.27, 0.49 N O 1 .57 1 .4 1 ±0.05 1 . 57. 1 .39 I 1 . 1 1 ±0.6 1

(seawater) 1 5.87.4.09

9- Suez Gulf 4.39±0.25 3.98-26.495 N O 0.42- 1 .44; N O 0.44- 1 .8 1 j 1 .80±0.05

(seawater) 6.92-25.8 1 s

1 0- Elmanzalah 52.67±3.2 1 N O 9.57 1 .49±0.06 2 1 7.4.09 8.0:HO.29

(brackish water) 1 1 27,90.09 5207.580.09

1 1 - Mansoura city 32.83± 1 .42 22.57.209.300 1 ) N O 0.057 2.73±0.07 1 .47,2.09 1 3 .75±0.49 (tap water) 1 757.2009.5000 I J

N O == not detected

> "1 .-;:;. ;" [Jl

g, '" '-n g-:3 -l ('; g. c

:s:: g. I" X �

Hanna el ({/. : Determination of some metal ions i n aquatic environs by atomic absorption spectrometry A rticles

Cl) u c ro U .!l! Qi a::

Wave number, em" 1500 1000

Fig. 4-I R retlectance spectra of I E I I and i ts complexes with Fe( l l l ). Co( l l ). N i ( l l ) and Zn( l I )

IR spectra

Fig. 4 shows the I R reflectance spectra of I E I I and its complexes with Fe.l+, C02+, Ni2+ and Zn2+. The 8(O-H);11 plal1e and 8 (N-H);11 plal1e (from the enamine tau to mer) vibration bands previously I observed at 1 276 cm' l and at 1 492 cm, l respectively I I , in the spectrum of the l E I I were not detected in the spec­trum of the investigated complexes. This i ndicates that the complexation takes place through proton dis­placement from these groups. Furthermore, the band

due to v(C-N) obtained in l E I I at 1 408 cm, l was shifted to 5- 1 0 cm, l lower in case of M-IE I I com­plexes.

Application

The results of chemical analysis of different sam­ples of water; river N i le (Mansoura, Faraskor, behind Damietta Bridge, Gerbi and Ras Elbar effluent, 1 -5 respectively), sea water (Ras Elbar, Damietta Port, Port Said and Suez Gulf, 6-9 respectively), lake water (EI-Manazalah, 1 0) and tap water (Mansoura city, I I ) are shown in Table 2 in comparison with the reported values.

The minimum values of Fe3+, C02+, Ni2+ were found in the gulf of Suez (sample 9) . These values are in agreement with those recorded in the Gulf of Suez with the APDC/M I Bk systems.

I t can be concluded from the results that the con­centrations of heavy metal ions i ncrease obviously in the region beginning from Damietta bridge to the river effluent at Ras Elbar. The nearby locations (Faraskor, Gerbi, Ras-Elbar and Damietta Port) showed higher concentrations of the investigated metal ions. This may be attributed to the heavy load

of wastes and effluents draining into th is area, par­ticularly from developing industries and agriculture besides the domestic wastes. The effect of such loads is highly prominent at the outpour of the river Nile near Damietta' 2 . However, these results lie within the permissible levels and are in agreement with those reported previousl/ ·6. 1 3 .

Comparing the results obtained from the present study with those reported earl ier8.'J, the observed dif­ference may be due to the sampling date. This was explained by Lashein et 01.6.7, as due to the low flood of river Ni le i n previous t imes (before 1 995) , where both Faraskor and High Dams were closed, and con­sequently to the relatively higher pollution of the river. In 1 998-200 I , the flood was moderate to high, hence allowing the opening of both dams in front of the high stream which washes the river body and en­hanced the reclamation and the quality of water as well .

Conclusion

The optimum conditions for the concentration of F 3+ C 2+ N·2+ d Z 2+ .

h .

II d 'fi d e' , 0 , I an n uSing c emlca y-mo I Ie porous silica with N-propylsal icylaldi mine are pH = 9 .0-9.5 , time of sti rring=30 min and eluent acid 2M HN03. Ci trate and EDT A cause strong interference therefore digestion of organic matter should be per­formed prior to the separation process with the ion exchanger.

In general, the estimated levels of the investigated metal ions in Jan 2002 is lower than those reported in 1 990's . In region near Damietta, the concentration of the studied metal ions is relatively high, whereas those found i n Suez gulf was low.

The ion exchanger IE I I can be used in the separa­tion and preconcentration of Fe

3+, C02+, Ni2+ and Zn2+

with high distribution coefficient at optimum condi­tions with no interference from common ionic species.

References

I Abou-EI-Sherbini Kh S, Kenawy I M M, Issa R M & EI­morsi R ( under publication).

2 Abou-EI-Sherbini Kh S, Khal i l M Sh & EI-Ayaan U. JMS & T, 1 0 (2002).

3 Clarck R B, Marine PolIU/io/l (Oxford. Uni versity Press), 1993.

4 Abou-EI-Sherbin i Kh S. Hamed M A. Kenawy I M M , Issa R M & E lmorsi R. TalWl/a. 52/2 (2002) 289.

5 Abou-EI-Sherbin i Kh S & Hamed M. £g),pliclll J Aquaric

Bioi Fish, 4 (2000) 37.

1 4 1

A rticles

6 Lashein R. M.Sc. Thesis. Mansoura Un iversity, Egypt, 2000. 7 Kenawy I M, Hafez M A A & Lashien R. A/wl Sci, 1 6

(2000) 493. 8 EI-Defrawy M, Kenawy I & E I-Said Kh, BIII/ Fac Sci Mal/­

SOIlr({ Ulliversity, Egypt, 1 9 ( 1 992) 1 93. 9 Kenawy I M & Hafez M A, A/wlusis. 24 ( 1 996) 275.

10 Sohrin Y. I wamoto S, Akiyama S. Fuj i ta T, Kugi i T. Obata H. Nakayama E. Goda S, Fujishima Y, Hasegawa H, Ueda K & Matsui M. Alia/ Chilli Acta. 363 ( 1 998) I I .

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I I Parikah V M , A bsorptiOlI Spectroscopv 0/ Org{{lIic Mole­

cules (Assison-Wesley Publ ishing Company. London), 1 974.

1 2 Aggour Y A M. M.Sc. Thesis. Facu l ty o r Science. Mansoura Un iversity, Egypt, 1 9S5.

1 3 Fi field F W & Hai nes P. Ellvirolllllellt{{/ AII{{/vrical Chelllis­

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