Indian Journal of Chemical Technology Vol. 8, July 2001, pp. 286-292

Sorption recovery of metal ions from aqueous solution using humus-boehmite complex

Beena T Abraham & T S Anirudhan*

Department of Chemistry, University of Kerala, Kariavattom, Trivandrurn 695 581, India

Received 25 November 2000; Accepted 12 February 2001

Humic acid (HA) was immobilized on boehmite (AlOOH) by batch equilibration. Removal _of Pb(II), Hg(II) ~nd Cd(II) from aqueous solution was studied using the batch equilibrium method. Experiments were earned out as a functi_on of pH and concentration of metal ions. It was shown that the maximum adsorption of 96.7 % for Pb(II) occurred at an optimum (lH of 5.5 whereas the maximum adsorption of 91.7% for Hg(II) and 80.8% for Cd(II) was observed at pH 6.0. T_he adsorptwn of metal ion proceeds predominently by the cation-exchange mechanism. Adsorption isothermal data co~ld be mterpr~ted by the Langmuir and Freundlich isotherm equations. Langmuir and Freundlich constants h_ave been d~termme_d. Adsorpt1~n ex­periments were carried out to investigate the competitive effect o_n_ the_ uptake_ of metal wns from_ bmary mixtures. Shemdorf _ Rebhun - Sheintuch (SRS) model was used to study the competitive mteractwns for the adsorptiOn of Pb - Hg, Pb - Cd and Cd - Hg mixtures by the adsorbent.

The presence of heavy metals in the environment is of major concern because of their toxicity and threat to human life and the environment. Heavy metals such as Pb(IJ), Hg(II) and Cd(II) have been classified as priority pollutants by the U.S. Environmental Protection Agency 1• Heavy metals at low concentrations are difficult to remove from aqueous media. Treatment methods like chemical precipitation, reverse osmosis, solvent extraction etc., are inefficient when heavy metals are present at trace concentrations in a large volume of solution. Adsorption is one of few alternatives available in such a situation. Among the different types of adsorbents reported, active carbon, ion-exchange resins, chelating agent supported on variou

4s

substrates2•3 and waste meterials such as fly ash ,

peanut she115, sawdust6

, coconut husk7, and waste

Fe(III)/Cr(III) hydroxide8 have been applied for the removal of metal ions. A survey of the literature on water analysis shows that metal oxide can be used as a very successful adsorbing agent9

. Chelating agents supported on metal oxide gels as adsorbents are stable, easy to prepare and can be used selectively for the preconcentration of different metals 10

'11

• In the present investigation Pb(II), Hg(II) and Cd(II) ions were removed from the water using humic acid treated boehmite (AIOOH).

*For correspondence [E-mail: tsani @rediffmaiLcom}

Experimental Procedure

A boehmite (AlOOH) suspension was prepared by the same procedure as described elsewhere 12

• The suspension was heated at 170°C for 8 h, after which the translucent suspension was dried. The product was ground and sieved to -80 + 230 mesh size (0.096 mm dia.). Humic acid (HA) obtained from Fluka, Switzerland, was coated on AlOOH at pH 3.0 using batch adsorption technique as described in previous report13

• The quantity of HA in the supernatant solu­tion was determined using UV-visible spectropho­tometer. The HA coated AlOOH (HA-AlOOH) was washed with 0.01 M NaC104 followed by distilled water. The product was dried at 60°C for 24 h and sieved to -80 + 230 mesh size. The surface area measurement of AlOOH and HA-AIOOH was car­ried out by applying the BET equation to the ad­sorption isotherm of N2 at -190°C (Gemini -2360 Analyser). The surface area of AlOOH and HA­AlOOH was found to be 108.1 and 122.5 m2/g re­spectively. The cation exchange capacity determined by Na saturation method 14 was found to be 0.58 and 1.68 meq/g for AlOOH and HA-AlOOH respec­tively. A potentiometric titration method 15 was used to determine the zero point charge (pH,pc) of the sample, and was found to be 9.2 for AIOOH and 7.9 for HA-AlOOH. The porosity of the adsorbents was determined using mercury porosimeter and was found to be 0.41 for AlOOH and 0.59 for HA-

ABRAHAM & ANIRUDHAN : SORPTION RECOVERY OF METAL IONS USING HUMUS-BOEHMITE COMPLEX 287

30

25

20 ~ t>ll 15 e r::r 10

Adsorbent dose : 2 giL 5 pH :3.0

0 Temperature : 30°C

0 50 100 150 200 250 300

c., mg!L

Fig. l-Adsorption isotherm of HA on AIOOH.

! .. ~ ~

~ ~

- 0

~ : .. "' :i u z li II < ~

!:: ~ :>:

"' : ~ 0 0: .. ~

~

~

:: ~

A

_, WAVE NUH BER c m

Fig.2-FTIR spectra of (A) AIOOH and (B) HA-AIOOH.

AlOOH. The data clearly indicate that the surface of AlOOH was modified after HA treatment.

In adsorption experiments, a fixed amount of adsorbent (0.1g) and 50 mL of an aqueous phase were placed in 100 mL glass-stoppered flask and shaken at 200 rpm for 6 h using a thermostated shaker bath. Preliminary runs showed that the adsorption studied was completed after 5 h. After filtration, the aqueous pH was measured with a pH meter, and the concentration of Pb(II) and Cd(II) was analysed using a atomic absorption spectrophotometer (Perkin Elmer -2380) . A Perkin-Elmer-mercury analyser model MAS-50 A was used for the estimation of Hg(II). Each experiment was duplicated under identical conditions. The amount of metal adsorbed qe (mglg) is obtained as follows:

.. . (1)

where C0 and Ce are the initial and equilibrium solution concentration (mg/1), V is the volume of the solution and W is the amount of adsorbent used. The effect of different initial added concentrations of metal ions on single solute adsorption was studied using concentration range between 5 and 150 mg IL at 30°C . In order to determine the competition among various binary solution mixtures (Pb-Hg, Pb-Cd and and Cd-Hg) batch experiments were conducted using 50 mL combined solution containing varied concentration of metal ions with 0.1g of the adsorbent. After adsorption equilibrium was reached, the contents filtered and filtrate was analysed for metals.

Results and Discussion The adsorption isotherm of HA by AlOOH at 30°C

and pH 3.0 was determined (Fig.1). The isotherm corresponds to isotherm of the L-type in the classification of Giles 16

• The L-type nature of the curve indicates strong tendency with process for monolayer formation. With L-type isotherm, the adsorption sites in the AlOOH are gradually filled and subsequent adsorption became difficult so that adsorption tends to be limited. According to this adsorption isotherm it was possible to design an operational condition for preparing HA-AlOOH complex. The humic acid content coated on AlOOH was calculated and found to be 21.0 mg/g of AlOOH.

Infrared spectra of AlOOH and HA-AlOOH have been recorded on a Bruker IFS 66V FTIR spectrometer (Fig. 2). The asymmetric absorption peaks at 3292 cm-1 for AlOOH and 3426 cm-1 for HA-AlOOH indicate the presence of exchangeable -OH groups in the adsorbents. The band at 2924 cm-1

for HA-AlOOH corresponds to -C-H stretching from­CH2 group, while band at 1598 cm-1 may be due to the -N-H vibration. Also the bands at 789 and 464 cm-1 for AlOOH and 716 and 462 cm-1 for the HA­AlOOH confirm the presence of H-0-Al bonding in both adsorbents. The two bands at 1738 em -I ( vc =o)

and 1460 cm-1 (vc-o) in HA-AlOOH indicate the presence of -COOH groups 17

• It is therefore clear that the surface of the original AlOOH has been modified by treatment with HA.

Batch adsorption studies have been carried out to evaluate the efficiency of surface modification on the

288 INDIAN J. CHEM. TECHNOL., JULY 2001

OAI E ...; .. ..Q .. 0

"' "0 ., c :::1 0 E -<

0.6 r----------------.

0.5

0.3

0.2

0.1

0

0.6

0.5

0.4

0.3

0.2

0.1

0

0.6

0.5

0.4

0.3

0.2

0.1

0 0 5 10

Cd(ll)

Initial concn. : 10 mg!L +A100H .HA-AIOOH -~-._.,....._. __ ._

Hg(ll)

Initial concn. : I 0 mg/L +A100H • HA-A100H

Pb(II)

Initial concn. : I 0 mg!L +AIOOH .HA-AIOOH

15 20 25

Adsorbent dose Ws, giL

30

Fig.3- Effect of sorbent concentration on the adsorption of metal ions on AIOOH and HA-AIOOH.

removal of Pb(II), Hg(II) and Cd(II) using modified and non-modified AlOOH. Fig.3 shows the removal of metal ions as a function of sorbent dosage by AlOOH and HA-AlOOH . A minimum adsorbent dosage of 200 mg HA-AlOOH or 500 mg AlOOH for Pb(II), 500 mg HA-AlOOH or 1000 mg AlOOH for Hg(II) and 700 mg of HA-AlOOH or 1250 mg AlOOH for Cd (II) is required for the complete removal of metal from 10 mg/L in 50 mL. These data clearly show that HA-AlOOH is 2.5, 2.0 and 1.8 times more effective than AlOOH for the removal of Pb(II), Hg(II) and Cd(II) respectively. The functional groups of the adsorbed HA (here -COOH groups) provide new adsorption sites for metal ions at the surface.

100

90

80

70 <f?. 60 -; 50 . .... 0 40 E ..

30 0: 20 . Adsorbent dose : 2 giL

10 Initial concn. : IO mg!L

0 + Pb . _Hg .A Cd

0 2 4 6 8 10

pH

Fig.4-Effect of pH on the removal of metal ions by HA-AIOOH

6 Adsorbent dose Temperature

5 pH

..J ~

4

•• 3 ~ u 2

20 40

:2 giL : 30°C : 6.0

+ Pb • Hg .A Cd

60 80 100

c., mg!L 120

Fig.5-Plots of C./qe versus Ce for the adsorption of metal ions on HA-AIOOH.

High porosity and moderate ion exchange capacity of HA-AlOOH may also contribute for its high adsorption capacity compared to HA free AlOOH.

The adsorption behaviour of Pb(II) , Hg(II) and Cd (II) on the adsorbent at various pH values was investigated in the batch process (Fig.4). The adsorption of metal ions from solution by solid phase can occur with formation of surface complex between the adsorbed ligand and the metal. However, the sites responsible for the adsorption process are not exclusively due to adsorbed organic molecule . Other sites on oxide surface can also contribute to adsorption process. Hg(II) and Cd(II) showed nearly similar behaviour and were quantitatively retained at pH 6.0 by HA-AlOOH. The maximum adsorption capacities determined for each metal at pH 6.0 were 91.7% Hg(II) and 80.8 % Cd (II). Fig. 4 also shows that Pb(II) removal increased up to pH 5.5 and thereafter the percentage removal gradually decreased with the increase of pH. A maximum removal of

ABRAHAM & ANIRUDHAN: SORPTION RECOVERY OF METAL IONS USING HUMUS-BOEHMITE COMPLEX 289

Table !-Langmuir & Freundlich isotherm constants for the single-solute adsorption on HA-AlOOH

Metal Langmuir constants Qo(mg/g) b (Limg) r

Pb 38.08 0.099 0.988

Hg 34.65 0.049 0.978

Cd 29.14 0.051 0.982

3 + Cd. Hg • Pb

2.5 Adsorbent dose :2 giL

2 Temperature : 30°C pH :6.0

,: 1.5

1).0

.s 0.5

0

~.5~----~~----~------------~ 0 0.5 1

log c. 1.5 2

Fig.6--Plots of log qe versus log Ce for the adsorption of metal ions on HA-AlOOH.

96.7% for Pb (II) was observed at pH 5.5. The effect of pH on metal adsorption can be explained as due to the exchange behaviour of H+ from peripheral -COOH groups from adsorbed HA. It has been shown that final pH is always less than the initial pH. This indicates that as the metal ions M2+ and MOH+ are bound on the substrate, H+ ions are released into the solution.

Different isotherm models like Langmuir and Freundlich isotherms have been applied in order to interpret the adsorption data. The equilibrium data for the adsorption of metal ions onto HA-AlOOH were fitted in the linearised Langmuir equation

Ce 1 Ce -=-+­qe QDb QO

... (2)

where Ce is the equilibrium metal concentration (mg/L) and qe is the amount of metal onto sorbent (mg /g). Q0 and b are the Langmuir constants related to adsorption capacity and binding energy respectively. The applicability of Langmuir isotherm model has been tested by plotting C/qe versus Ce (Fig. 5) at 30°C. The basic assumption in the Langmuir isotherm is that sorption take place at specific sites on the adsorbent and once a site is occupied no further adsorption can take place at that

~ E

1 .. Q

"' ~ • ,-., -.._, Oil :c

Oil 'O:b E -a 1! .. Q .. ~ • :::::--~ Cl.

Freundlich constants KF lin

6.317 0.372

4.012 0.409

3.790 0.412

14

12

10

8

6

4

2

0 30 Temperature

pH 25 Adsorbent dose

20

15

10

5

0 20 40

r

0.985

0.988

0.991

Temperature : JO'C pH :6.0 Adsolbent dose : 2 g/1 Initial Hg(ll) concn : • 5 mg!L

60

4 IOmg!L X25mg!L •somg!L + 75 mg!L

(A)

80 100

Equilibrium Pb(ll) concentration, mg!L

Fig.7-(A) Adsorption isotherms of Pb(II) by HA-AlOOH with Hg(II) added and (B) the amount of Hg(II) adsorbed by HA-AIOOH in the presence of Pb(II).

site. This implies that at saturation the adsorbent is covered uniformly by a layer of molecules. The slope and intercept of the linear plots obtained by regression analysis of the data gives the values of Q0 and b (Table 1). The maximum adsorption capacities of HA-AlOOH were found to be 38.08, 34.65 and 29.14 mg/g for Pb (II), Hg(II) and Cd (II) respectively.

The adsorption data were also fitted to the rearranged Freundlich equation.

log qe = log KF + 1/n log Ce ... (3)

A linear relationship was observed among the plotted parameters (Fig.6) which indicates the applicability of Freundlich equation. Table 1 shows the values of Kp and lin obtained from the intercept and slope of the respective isotherm plots.

290 INDIAN J. CHEM. TECHNOL.. JULY 2001

~ 12 . .. E . " "tl .. .c ; 8 .

"' "tl

" ' ~ -..... "tl u

Temperature pH

u Adsorbent dose

Temperature pH Adsorbent dose Initial Cd(ll) concn

: 30"C :6.0 :2 gil : 85mg/L A IOmg/L x 25 mg!L • 50 mg!L

+ 75 mg!L

(B)

(A)

Initial Cd(II) concn : + 0 mg!L 8 5 mg/L A 10 mg/L x 25 mg!L • 50 mg/L + 75 mg!L

'~--------~--~--~~--~--~ ' Equilibrium Pb(IJ) concentration, mg/L

Fig.8-(A) Adsorption isotherms of Pb(Il) by HA·AIOOH with Cd(II) added and (B) the amount of Cd(II) adsorbed by HA-AIOOH in the presence of Pb(II).

Table 2-Competitive coefficients for binary - solute systems, derived by the application of SRS equation

Metal ions Competitive coefficients G;j Gji

Pb+ Hg 2.39 3.16

n 45 45

0.978 0.993

Hg+Cd 1.89 2.20

n 28 28

0.991 0.992

Pb+Cd 0.59 4.88

n 28 28

0.993 0.986

Competitive adsorption of Pb(Il), Hg(Il) and Cd(Il) ions were also studied. In order to determine the competition among various binary solute mixtures (Pb-Hg, Pb-Cd and Cd-Hg) batch experiments were conducted using 50 mL combined solution containing varied concent!Jltion of metal ions with 0.1 g of the adsorbent. Adsorption isotherms of Pb(Il) by HA­AlOOH with varied concentration of Hg(Il) are shown in Fig. 7 A. It is seen that the amount of Pb(Il) adsorption decreased with increasing concentration of Hg(Il). The presence of Pb(Il) tended to reduce Hg(Il) adsorption, but the degree of supression was less than

14

.. 12 til. 5 10

"tf .. .c 8 .. 0

"' "0 6 " g 4

"0 u 2

o . 25

~ 20 5 "tf 15 .. .Q .. 0

"' "0 10 " a-e .. 5 ::r:

0

(B)

(A)

Temperature : 30'C pH :6.0

Adsorbent dose : 2 gil

Initial Cd(ll) concn: 8 5 mg/L

.

A 10 mg/L x 25 mg/L esomg/L +75 mg!L

Iiiitia1 Cd(TI) c.>ncn : •· 0 mg/L 8 5 mg!L .6. 10 mg/L x 25 mg!L • 50 mg/L + 75 mg/L

Adsorbent dose

:30' C :6.0

:2 gil

0 20 40 60 80 100 120

Equilibrium Hg(II) concentration, mg!L

Fig.9-(A) Adsorption isotherms of Hg(II) by HA-AIOOH with Cd(II) added and (B) the amount of Cd(II) adsorbed by HA-AIOOH in the presence of Hg(II).

that of Hg(II) on Pb(II) adsorption (Fig.7B). The competitive interaction of Pb(II) on Hg(II) adsorption was greater than those of Hg(II) on Pb(II) adsorption .

Fig. 8A shows the adsorption isotherms of Pb(II) by HA-AlOOH in presence of Cd(II). It is clear from the figure that the amount of Pb(Il) adsorption is su­pressed by the addition of Cd(II). Similarly the pres­ence of Pb (II) tended to reduce the amount of Cd(ll) adsorbed by HA-AlOOH . Increasing the equilibrium Pb(II) concentration resulted in less Cd(ll) adsorption, although the effect appeared to be more pronounced at low equilibrium Pb(ll) concentration (Fig. 8B). The presence of Cd(II) had little effect on Pb(II) adsorp­tion by HA-AIOOH. Adsorption isotherms of Hg(ll) in presence of Cd(II) are shown in Fig. 9. The pres­ence of Cd(ll) tended to suppress Hg(Il) adsorption. Similarly the addition of Hg(Il) suppressed the amount of Cd(ll) adsorbed. The competitive effect of Cd(ll) on Hg(ll) adsorption was less than that of Hg(II) on Cd(II) adsorption.

Competitive coefficients for binary -solute mixtures on a concentration basis were calculated using Shein­dorf -Rebhun-Sheintuch (SRS) equation 18

. [_!_-1] J_ C)n;

(qe)i- KFiCei(Cei +aij ej 000 (4)

ABRAHAM & ANIRUDHAN: SORPTION RECOVERY OF METAL IONS USING HUMUS-BOEHMITE COMPLEX 291

100

90 (B) 80 • 70

60

.r:l 50 Q., ...... 40 "0 u 30 .

20

10

0 0 50 100 150 200 250

BCd/Pb

40 (A)

30

"0 25

~ 20 .r:l Q.,

15

10

5

0 0 20 40 60 80 100

BPb/Cd

Fig.IO-SRS competitive isotherm plots for (A) Pb(Il) adsorption in the presence of Cd(Il) and (B) Cd(Il) adsorption in the presence of Pb(Il)

where (qe);i is the amount of solute i adsorbed per unit weight of adsorbent at equilibrium in presence of competitive solute j, Kp; is the single component Freundlich constant for solute i, lin; is the Freundlich exponential for solute i , Ce; and Cei are the equilibrium concentration of solute i and j and a;i is the competitive coefficient. The linear forms of the SRS equation can be written as

Ce; /Cej =(B; fq )-a;j

Cei ICe; =(Bi /C;)-ai;

... (5)

... (6)

where B= Kp; (CeJqei rt<ni- Il and ai; is the coefficient having negative numerical value of the y-intercept. Competitive coefficient a;i was calculated by plotting Ce/Cei versus B/Cej between two metal ions. Similarly ai; was calculated by plotting Ce/Ce; vs B/Cei· The values of competitive coefficients are summarized in Table.2. The magnitude of Pb(II) competition on Cd (II) adsorption by HA-AlOOH was significant and this data get conformed to the linear SRS equations yielding a competitive coefficient of 0.59

(Fig. IO(A)). The perusal of data given in (Fig.IO(B)) indicaLes that the extent of Cd(Il) interaction with Pb(Il) adsorption was less than the other cases. In this case the competitive coefficient was found to be 4.f>8. The correlation coefficients were found to be in the range of 0.97-0.99, which indicate a good positive relationship with the data and suggests the applicability of the SRS equation in the present system.

Conclusions HA-AlOOH was found to be more effective than

AlOOH for the removal of Pb(II), Hg(II) and Cd(II). The carboxylate functional groups of the adsorbed HA on the surface provide new adsorption sites for metal ions. The maximum adsorption capacities determined for Hg(II) and Cd(Il) at pH 6.0 were found to be 91.7 and 80.8 % respectively; where as the maximum removal 96.7 % Pb(II) was observed at pH 5.5. The adsorption data were analysed using Langmuir and Freundlich isotherm models. The adsorptive behaviour of cationic mixtures by HA-AlOOH was investigated using SRS equation. Most of the isotherm data are found to conform to the linear SRS expression, making it possible to derive competitive coefficients for each solute combination of Pb, Hg and Cd. The adsorption of Hg(II) and Cd(Il) was significantly reduced by competitive interactions with Pb (II), while Pb(II) adsorption was not greatly supressed by either Hg(II) or Cd(II). Competitive coefficients appeared to be consistent with the experimental observations.

Acknowledgements The authors are grateful to Prof. P Indrasenan,

Head, Department of Chemistry, University of Kerala, Trivandrum for providing laboratory facilities.

References I Keith L H & Telliard W A, Environ Sci Techno[, 13 (1979)

416. 2 Harland C E, Ion Exchange: Theory and Practice (Royal

Society of Chemistry, U.K), 1994. 3 Dias Filho N L, Polito W L & Gushikam Y, Talanta , 42

(1995) 1031. 4 Sen A K & De A K,Indian J Techno[, 25 (1987) 259. 5 Azab M S & Petersan P J, Wat Sci Technol, 21 (1989) 1705. 6 Raji C & Anirudhan T S, Indian J Chern Technol, 3 (1996)

345. 7 Manju G N, Raji C & Anirudhan T S, Wat Res, 32 (1998)

3062 8 Namasivayam C & Ranganathan K, Wat Res, 29 (1995)

1737. 9 Vasely V & Pekarek V, Talanta, 19 (1972) 219.

292 JNDIAN J. CHEM. TECHNOL., JULY 2001

10 Koijan R, Analyst, 119 (1994) 1863. II Pyell V & Fresenius G S, J Anal Chern, 342 ( 1992) 281. 12 McBride M B & Wesselink L G, Environ Sci Techno!, 22

(1988) 702. 13 Beena T Abraham & Anirudhan T S, J Sci lnd Res., 58

(1949) 807 14 Black C A, Method of Soil Analysis (American Society of

Agronomy, Madison, W.l.),l979.

15 Schwarz J A, Driscoll C T & Bhanot A K, J Colloid Interface Sci, 97 (1984) 55

16 Giles C H, Smith D. & Huitson, J Colloid Interface Sci, 4 (1974) 755.

17 Nakanishi K & Solamon P H, Infrared Absorption Spectroscopy (Holden Day, Inc, San Francisco, USA), 1977.

18 Sheindorf C, Rebhun M & Sheintuch M, J Colloid Interface Sci, 79 (1981) 136.