Indian Journal of Chemical Technology Vol. 9. May 2002. pp. 245-250

Articles

Sorption aided process for the removal and recovery of Zinc (II) using salicylaldoxime immobilised silica gel

Mitali Sarkar* & Pradip Kumar Datta

Department of Chemi stry, Uni vers ity of Kalyani , Kalyani 74 1 235

Received 27 Apri/ 200 1; revised received 3 January 2002; accepted 6 March 2002

Salicylaldoxime immobilised silica gel was used as an effective solid phase surface, for the preconcentration, removal or recovery of zinc ion from aqueous phase. The efficiency was tested by the equilibrium sorption study both in batch and column operations. The efficiency increases with the shaking period, agitation speed, adsorbent dose, temperature and flow rate but is independent on the volume of the solution. Maximum adsorption was found to occur at pH 5.5. Alkali metal, alkaline earth metal and ammonium salts do not influence the adsorption process. Heavy metal ions viz. Cu(II), Ni(II), Co(II) and Fe(III) get adsorbed by the said process but at much different pH values. Complexing ligands like EDT A and cyanide markedly decrease the adsorption of Zn(II) by the said procedure. The adsorption data fits well the Langmuir adsorption isotherm model. The negative free energy change indicates that the process is favourable as well as spontaneous. The merit of the process lies with its high preconcentration factor.

It is known that many metals are normally present in natural water systems. The constituents in natural water exhibit properties that may be class ified as either conservati ve or non-conservati ve. The fo rmer relates to concentration of species that remains at relati vely constant ratio to each other throughout the system. Thi s applies mostly to the more abundant lighter elements such as sodium, potass ium and calcium. The non-conservative behaviour is shown by most other metals such as iron, copper, zinc, lead, mercury which show concentration variation depending on variables such as position, time, temperature and most importantly bio logical activity 1. These conservative metals are generally most reactive and are normally present in concentration much above the tox ic level that is li kely to cause serious health hazards. Zinc is one such non-conservative metal.

Zinc finds wide applications in various industrial processes . Due to its remarkable res istant to atmospheric corrosion, zinc is largely used to protect iron from rusting, in the process called gal vanization. Zinc is widely used fo r the manufacturing of zinc white and several useful alloys such as brass, German sil ver, deltametal, for the preparation of gold and sil ver in the cyanide method, for the desil verization of lead in Parkes process and as the anode materi al in ga lvanic cell s. Lithographic plates are al so made of ZlllC.

*For correspondence (E-mail: mitali @klyuni v.ernet.in)

Zinc tox1c1ty from excess ive ingest ion IS uncommon but gas tro intestinal distress and diarrhoea has been known fo llowing ingestion of beverages standing in galvanized cans or from use of ga lvanized utensils . With regard to industri al exposure, metal fume fever resulting from inhalati on of freshly formed fumes of zinc presents the most signi ficant effec t.

It is necessary to determine the load of zinc ongmating from any industri al ac ti vity. Preconcentration of trace metal from vari ous samples is an important step prior to its determination. Among the various methods avail able viz. co-precipitation, electrodeposition, liquid-liquid extraction, solid-liquid extraction and filter paper impregnated with chelati ng agent solid phase extraction has gained rap id acceptance. Many workers have used the adsorption technique for the removal and preconcentration of metal ions from solutions. Of particular interests are those that involve inorganic solid surfaces modi fied with chelating groups and so have the advantage of selectivity. Preconcentration of metals by sorption on

. b 2 I I I . act1 ve car on , porous or natura po ymers· , Ion exchange resins4 and waste materi als such as tl y ash 5, rice husk ash6 and waste Fe(III )/Cr(III ) hydrox ide7• blast furnace slag8 are found effec tive. Applicati on of chelating polymeric resins fo r separation and concentration of trace metals from ocean, ri ver and natural water systems is reviewed by Kantipull/. Silica based chelating res ins, on the other hand, are

Sarkar & Datta: Sorption Aided Recovery of Zinc(! I) Using Salicylaldoximc lmmobili sed Silica Gel Articles

most commonly used since immobili sation reactions on si lica are relatively simple. Moreover, silica has good mechanical strength and does not swell and can undergo heat treatment 10. The use of chemically bonded silica gel 11 -26 has also been reported. Furthermore, the preconcentration of metal s using modified silica gel columns includes the use of surfactants27 or polymer as coating material on Ci s-bonded silica28, the formation of new stationary phases with a cationic polyelectrolyte with ferron29 as counterion and ion-pair formati on between a metal complex and a long chain quarternary ammonium salt and subseq uent sorption of thi s ion pair on the silica oe]30 c .

In thi s communication, salicylaldoxime immobilised silica gel has been used for removal and preconcentration of zinc from aqueous samples.

Experimental Procedure All chemical s were of analytical reagent grade.

Silica gel H 4267 of parti cle size 60 ~un , specific , - 1 . 0

surface area 420 m-g and pore SIZe 120A was obtained from Sigma. Stock solution of zinc (5 mgmL- 1) was prepared by dissolving zinc chloride in doubly di still ed water. pl-1 of the ex perimental solution in the range 3.5-6.0 was maintained by acetate buffer by mixing acetic acid and sodium acetate. pl-1 below 3.5 was maintained by HCI while pH above 6.0 was maintained by NaOH solution.

Instruments The absorbance spectra of the solution were

registered with a Shimadzu UV-VIS Spectrophotometer. The IR spectra of sorbent was registered with an automatic Perkin-Elmer IR photometer. Samples being prepared as thin films between KBr windows. Atomic absorption measurement of Zn2+ ion was recorded on an atomic absorption spectrophotometer (Perkin-Elmer) equipped with a standard burner with an air-acetylene flame at the wavelength 213 .9 nm. Standard hollow cathode lamp was used as a line source. A Systronics pl-1 meter with glass electrode was used pH measurements. The column was a glass tube (160x6mm) with a coarse sintered glass disc and a tap at the bottom.

Preparation of sa/icy/aldoxime immobilised silica gel; the synthetic solid phase

Silica gel was refluxed with HCI (6.0 moldm-3) for about 3 h to remove contaminating metal such as iron. It was then washed with deioni sed water and dried

246

under reduced pressure at 150°C. The dried silica gel was refluxed with sal icylaldox ime ( I O%w/w) in ethanol for 4 h. The so lid thus obta ined was filtered and dri ed under vacuum.

AdsOIJJtion Procedure Batch experiments were performed to obtain rate

and equilibrium data. The flask containing 20mL of zinc(!!) solution (20-200mg.dm-3) 1 aintained at the required pl-1 was shaken with 1.0 g of immobi li sed silica gel in a mechanical shaker unt il equilibrium is attained . The remaining zinc(ll) in the supernatant was determined by atomic absorpt ion spectroscopy. The amount of zinc(ll) adsorbed by immobili sed silica gel was determined by the equati on:

{Jc = (X-Y)IZ

where, X is the initial amount of zinc(ll ) added ().lg), Y the amount of zinc (ll ) remained in supernatant ().lg), Z the mass of adso rbent (g) and q., th e amount of z inc(lf)(~tg ) adso rbed per gram o f adsorbent.

Column experiment was performed fo r elution or the adsorbed metal. Zinc(II) so luti on at a definit e pl-1 (between 2.0 to 8.0) was perco la ted at a defin it e fl ow rate of 5.0 mL.min -1• After washing th e column with about 20 mL of deionsed water. an eluting solution of definite compo siti on was passed throu gh at a fl ow rate of 3.0 mL. rn in -1• The metal ion concentrati on in the eluate, after dilutin g to th e desi red volume, was determined by AAS. Wet di ges tion of th e sampl es with HNO" and H2S04 was performed prior to estimating zinc co ncentration by AAS following the standard procedu re31 .

Results and discussion

Characterization of the immobilised silica gel (adsorbent)

IR spectrum of immobili sed silica gel show characteristic peaks of salicylaldox ime suggesting that the lignad was immobili sed as such without any structur11l change with the silica gel. In another ex periment ethanol was passed through the column packed with a weighed quantity of sorbent to remove all the li gand immobili secl with sili ca ge l. The eluate gave identical absorption band of sa licy laldoxime. Quantitative determination showed that the amount of salicylaldoxime immobili secl with sil ica gel was 27+2 mgg·1 of silica ge l.

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12o.oo T - ------ - -----.

_...-..

~ c 60.00 0

0. L 0 VI

'U 0

c 40.00

Sarkar & Datta : Sorption Aided Recove ry o f Z inc(! I) Using S:~ Ii c y l :~ l dox i mc lm mobilisecl S il ica Ge l Articles

80.00

-1 Zn

70.00 ,...... ~ c 0

~ '-- 60.00 0 rn -o 0

c Q) 50.00 ~ Q)

o_

0 . 0

Dose (g)

Fig. 3 - Effect o f dose on adso rpti on.

80.00 Znn----------~~a~

~ 60.00

c 0

:g_ '--0 40.00 rn -o 0

+' c Q)

~ 20.00 Q)

o_

.............., 298K

..........._. 308K ~318K

Sh.time (min)

Fig. 5 - Effec t of te mperature on adsorpti on.

metals, alkaline earth metals and ammonium salts do not get adsorbed on the said adsorbent. Among the heavy metal ions viz., Cu(IJ) , Ni(lf) , Co(IJ) and Fe(lll ) although adsorb similarly on the adsorbent , but at much different pH of the solution.

Ads01ption isotherms The ability of immobili sed sili ca ge l to ex tract

zinc( ll ) from aqueous solution at pH 5.5 was evalu ated by measuring sorption iso therm (Fig. 6). The shape of the curve gives an indication that the adsorption is fa vourable33. The L-type nature of the curve obtained in the prese nt system indicates the strong tendency fo r monolayer adsorption. With an L-type isotherm the adsorpti on sites are grad uall y fi lied and the subsequent adsorption becomes diffi cult so

248

120.00

• ~ ..... im mobi lised .....,..._.__. untreated (--r------.

~ 80.00

c 0

:g_

j '--0 j rn -o I 0 40.00 I ....-c I Q) ~ I Q) I o_

I I

pH

Fig . 4 - EITect of pH on adsorption.

3000.00 Zn ________________ _

:::----1 2000.00

Cl1

Cl1 ::J

,; 1000.00

80. 0

c. (mg.dm -J) r: _ .. , . . ..

Fig. 6 - Adsorpti on iso therm plot.

that adsorp tion tends to be limited. Data trea tment revealed th at the sorpti on conformed to the Langmuir iso therm model, which is va lid for monolaye r adsorpti on onto the surface cont aining a finite number of identi cal sites and is represented as,

C,/q" = 1/Qb + C,IQ

where, C c (mgdnf3) and {/e (mgg-t) are corresponding co ncentrati on and amount of zinc(lf) adsorbed at equilibrium. Q and b are Langmuir constants and related to the adsorption capac ity and energy of adsorpti on respectively . Plot of C01(jc versus Ce (Fig.7) yields Q (2.61 0 mgg-1) and b (0. 1542 dm-·' 1--!g-1) from the slope and intercept through linear regress ion. The hi gher va lue of regress ion coefficient (0.9950) indicates the validity of Langmuir mode l. The

Articles

adsorption capacity of the synthetic sorbent thus corresponds to 4.0. 10-2 mmolg-1.

Evaluation of equilibrium and thermodynamic constants

Application of the present sorbent for recovery of Zn(H) from large volumes of water demands the process to be favourab le thermodynamically . The

standard free energy change (L'>.G 0 ) of the process was calculated from the equilibrium constant (Kc) usmg fo llowing the equations,

K, = CAJCc

where, Cc and CAc are the equilibrium concentration (mgdm-3) of Zn(ll) in solution and on the adsorbent respectively, R the uni versal gas constant and Tis the abso lute temperature.

The negative value of L'>.G 0 (-1.89-kCal) calculated at 298 K indicates the feas ibility of the process as well as its spontaneous nature.

,., I

E

0.04 -::r- ------------

r Zn

0.03

Fig. 7 - Lang muir adsorpti o n isotherm plot.

Ind ian J. C hem. Techno!. , May 200 1

Column experiment Effect of flow rate and volume of th e sample

solution - The effect o f fl ow rate of the so lu ti on through the column on th e adsorption behaviour of zinc(II ) soluti o n was s tudi ed over the range 1- 10 mL min· '. The adsorpti on was quantita tive and reproducibl e regardless of any change in the fl ow rate up to 9.0 mL min-' . Again when the vo lu me o f the samp le so luti on was varied for a fixed amoun t of adsorbent and fi xed a mount of zinc( II ) no change in the percentage adso rpti on was observed upro a vo lume of 1000 mL. In the present stud y, 20 mL o f zinc (Il ) so luti on was take n and th e flow rate •va. maintain ed a t 5 mLmin -1•

Desorption or elution of zinc( II)-The e lution o f adso rbed z inc(ll) over the immob ili sed s ilica ge l so rbed with z inc(II ) was pe rformed for the pu rpose of recovery or preconcentra tion of zinc(ll) io ns fro m aqueous sampl es. Th e adsorben t was subjected to inte racti o n with differe nt co ncentrat ions of HN03 or HC I0 4. The e lut ion was found e ffec tive w ith e ith er H N03 (2 .4 mo ldm-

3) or

HC I04 (3.0 . 10- ' mo ldm-3

) and about 96 .09'£ of the added z inc(ll ) was recovered in a small vol ume . Solution contain ing Zn(l l) ( 1000 cm3, I mg per 50 cm3) at pH 5.5 was passed throu gh th e packed co lumn of the adsorbe nt and the adso rbed Zn (l l) was subsequently recovered in 25 c m3 of the chosen acid . The metal io n concentrati on in th e el uate was measured following AAS 31.

Utility of the proposed 1nethod with industrial sample

The industria! effluents contain large number of diverse ions, whi ch may influence the effecti veness of the adsorbent as well as the process. The remova l and recovery of Zn(ll ) \'ia the preconcentration proced ure were made from the effluent co ll ected from a typi cal

Tab le I - Preconcentration and recovery o f Z n(ll ) from aqueous phase

Sample Co mpositiun Z n(ll ) Standard Preconccntrat ion Certified Fo und Dev iati on fac to r

NBS SRM - 17 1 Mn :0 .45. 1.05 % 1.00% 0 .64 40 (n* =7)

Si:O.II S. Ni :0 .0009.

Al: 2.98. Pb:O.OOJ3. fc:O. OOJ H

Mi lk sampl e ~7 ~ t gg ' 1 )J+O.OI~tgg·' 0.5 1 40 In "' =·/!

(* n indicates the number of repl ica ti ons)

249

Sarka r & Datta: Sorption Aided Recovery of Zinc( II ) Using Salicy laldox ime lmmobi lised Si lica Gel Articles

electroplating industry, and the powdered milk sample (Table. I). The data indicates hi gh degree of removal and recovery of zinc fro m the samples.

Conclusion The present in vesti gation shows that

sa li cy laldox ime immobili sed silica gel can be employed as an effecti ve adsorbent for removal of zinc(Il ) from water and wastewater. The removal was fo und to depend on time of contact, initi al concentration, agitation speed, temperature and pH of the med ium. The equili brium data fit s well the Langmu ir adsorption isotherm model. The recovery of zinc( II ) fro m the sa li cy laldox ime immobili sed silica gel (96%) is comparable with solvent extraction34

(96%) and ion exchange35 (99% ).

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