Mercury removal from wastewater by steamed hoof powder

~

Pergamon

PU: S0273-1223(99)00589-2

Wal Sci Teeh, Vol. 40, No, 7, pp, 109-116, 1999 CI999IAWQ Published by Elsevier Science Ltd Prinled In Greal Brilain, All nghts reserved 0273-1223/99 S20,00 + 0,00

MERCURY REMOVAL FROM WASTEWATER BY STEAMED HOOF POWDER M, H. Ansari, A. M. Deshkar, P. S. Kelkar, D. M. Dhannadhikari, M. Z. Hasan and R. Paramasivam National Environmental Engineering Research Institute. Nagpur 440010, India

ABSTRACT Steamed Hoof Powder (SHP), size < 5311, was observed to have high adsorption capacity for Hg(II) with >95% removal from a solullon containing 100 mg/L ofHg(IJ) with only 0,1% (WN) concentration ofSHP, The SHP has good setthng properties and gives clear and odour free emuent. Studies indicate that pH values between 2 and 10 have no effect on the adsorption of Hg(II) on SHP, Light metal ions like N&', K+, Ca 2+ and Mg2+ up to concentrations of 500 mglL and heavy metals like Cu2+, Zn2+, Cd2+, COl', Pb" , Nil', Mnl ', cr', Cr"', Fel + and Fe)' up to concentrations of 100 mgIL do not mterfere with the adsorption process. Anions like sulphate, acetate and phosphate up to concentrallons of 200 mgIL do not meerfere. Chloride interferes in the adsorption process when Hg(IJ) concentration is above 9.7 mgIL. The adsorption equilibrium was established within two hours. Studies indicate that adsorption occurs on the surface sites of the adsorbent. 0 1999 IAWQ Published by Elsevter Science Ltd. All rights reserved

KEYWORDS Adsorption equilibrium; biomagnification; mercury-chloride complex; methylmercury; steamed hoof powder; sulfur-mercury bond. INTRODUCTION Methylmercury is the most toxic and most stable compound of mercury. Anthropogenic methylmercury was responsible for the Minamata disease in Japan (Forstner and Wittman, 1981). Bioaccumulation and biomagnification of methylmercury in the food chain is the specific property of mercury among metals (Eisler, 1981). Methylmercury can be synthesised in the natural eco-system through biological methylation ofmercury(lI) by aquatic organisms (Jansen and Jemelov, 1969), through chemical (Imura et al., 1971), or through photochemical (Hayashi et al., 1979) processes. Consequently, it is essential to remove mercury from wastewaters. The major industries which discharge mercury through their effluents are caustic soda & chlorine manufacturing, wiring devices & switchgear, dental equipments & supplies, chemicals & allied products, and paints (The U.S. Bureau of Mines, 1991). Specific treatment methods to reduce mercury concentrations in wastewater are reduction process, sulfide treatment, ferrous chloride treatment, magnetic ferrites treatment, ion exchange, and ion exchange followed by chelating resin (Minimal National Standards, 1981-82). Adsorption of Hg(lI) from aqueous environment on inexpensive natural products and earth materials has been investigated by many workers, (Randall and Hautala, 1975; Friedman and Waiss Jr., 1972; Kumar and Dara, 1980; Pande and Chaudhary, 1981). Deshkar (1990) studied various tree barks for the removal of Hg(lI) from water. 109

M. H. ANSARI et al.

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The present communication presents the findings of an investigation on the use of Steamed Hoof Powder (SHP) in the removal of Hg(II) from aqueous solution. MATERIALS AND METHODS Hoof is the hard and horny part on the bottom of the feet of certain animals e.g. buffaloes, cows, goats and is mainly used as fertilizer. Hoof is heaped in a cylindrical container which has a capacity of about I tonne. Steam is passed for six hours through two sides and the middle of the container. Condensed steam is discharged from the bottom (Source: Qureshi Bone Mills, Sarai Tarin, U.P. htdia). After steaming, the hoof becomes a brown brittle mass which can be ground to any size. This SHP was used for the study. Particle sizes ofSHP were evaluated by utilizing U.S. Standard Sieve Series, ASTM Specification, Fischer Scientific Company, U.S.A. Steamed hoofin the present set of experiments was ground to the size < 53 microns. Stock Hg(II) solution (25 gIL) was prepared by dissolving mercury metal (GR Merck, India) in nitric acid. Working solutions were standardised by titrimetric procedure using EDTA as titrant, Xylenol orange in solid KN0 3 (0.5%) as indicator, and hexamine (10 mL of 30% aqueous solution per test) as buffer to maintain a pH of6.0. Batch adsorption tests were performed at room temperature between 34°C and 36°C. The reaction mixture consisted of a final volume of 100 mL containing suitable concentration of Hg(II) solution and 0.1 % (WN) of SHP i.e. 1.0 g of SHP in one litre of working solution. The reaction mixture was placed in a stoppered glass bottle of 300 mL capacity and gently agitated in a rotary shaker for 2 hrs to ensure equilibrium conditions. The supernatant liquid was passed through glass wool and analysed for residual mercury. Hg(lI) was determined by titrimetric procedures when concentration was more than 10 mg/L. Concentration below 10 mgIL of Hg(lI) was determined by cold vapour AAS (Perkin Elmer, 50B, Mercury Analyser). A blank was also run through all the procedure to compensate for any loss of Hg(m due to extraneous reasons. RESULTS AND DISCUSSION Nitrate matrix does not interfere in the reaction of Hg(II) with other ligands, and therefore this matrix was utilised in all the experiments. Loss of Hg(lI) due to extraneous reasons were not observed. Effect of pH on the uptake ofHg(II) 100 ml portions of 10 mgIL Hg(ll) solution were agitated with 0.1 g ofSHP (size < 5311) at different pH by adjusting with NaOH or H2S04 till adsorption equilibrium was established. Adsorption was monitored at each pH. It was observed that pH values between 2 and 10 had no effect on the adsorption of Hg
100.,-------------------------,

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VB

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-+-_--+

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•

•

•

-0+_-_---+0----;-------1 8

8

to

pH Figure I. Effect of pH on the Adsorption ofHg (II) on Steamed Hoof Powder.

Mercury removal from wastewater

111

Adsorption equilibrium Several 100 ml portions of 1000 mg/L ofHg(II) solution were agitated with 0.1 g ofSHP (size < 53 Il) for different times. Adsorption was monitored for 120 minutes. It was observed that adsorption took place with relatively rapid initial rate which decreased markedly within half an hour and approached an equilibrium condition in two hours (Fig. 2). With this result in view, a contact time of2 hours was selected for all the subsequent experiments. 300 ~

250

~

200

El

:a

1 ......

150

~

100

~'-'

50

...

,Q~

~

E

~

o

t::~

=

0

20

40

100

10

10

120

140

Time, t, (minutes) Figure 2. Time required for establishment of adsorption.

Kinetics ofthe adsorotion process Figure 3 shows a plot of log(mg Hg(ll) adsorbed/g adsorbent) Vs log(time). A straight line is obtained, which can be expressed as: (1)

where 'x' is the amount of Hg(lI) in mg adsorbed and 'm' is the mass of the adsorbent in grams. 't' is the contact period in minutes, 'N' is the slope of the linear plot, and '1(' is a constant. The considerable deviation of the plot from the origin in Fig. 3 indicates that the adsorption is quick and takes place on the exterior surface sites ofthe adsorbent (Ajmal et al., 1998).

3

-

2.5

2

~l>Il

1.5

log xlm

=0.2577 log t + 1.9355

j

r = 0.9524

0.5 0 0

1.5

0.5

2

Logt Figure 3. Kinetics of adsorption process [1000 mgIL as Hg (II)]

25

112

M. H. ANSARI et ai.

Effect of particle size on the uptake ofHgOI) 100 ml portions of 1000 mgIL of Hg(In solution were agitated with 0.1 g of different particle sizes of SHP for two hours. Particle sizes of <53 11, 101 J.l, 179.5 f1, 282 J.l, 427 11 and 548 11 were selected. The particle diameters are averages of the mesh sizes for the sieves passing and retaining the particles (Weber and Morris, 1963) except <5311 size. Adsorption was monitored with each particle size ofSHP.1t was observed that there was an increase in the adsorption capacity ofSHP with decreasing particle size i.e. with increasing surface area (Fig. 4). The inverse variation of the adsorption capacity with particle size ofSHP indicates that SHP is a non-porous adsorbent and that the adsorption takes place on the external surface sites (Weber and Morris, 1963). 300

xlm = - 02799s + 176.03 r=0.9967

250

200

150 100 50

o +--_---+---+----+----~

o

100

200

300

!500

tlOO

Figure 4. Effect of Particle Size on the Adsorption ofHg (II) on Steamed Hoof Powder

Table I. Effect of concentration on adsorption of Hg(m with Steamed Hoof Powder Hg(II) pH Hg(II) adsorbed removed ........... _._--_ ...... _--- ......... mg/g (percent) Initial Final No. Initial Final 95.2 3.3 4.8 95.2 l. 5.00 100 49.0 3.3 96.0 2. 2.0 5.30 51 25.2 96.9 3.3 5.30 3. 0.8 26 9.8 3.3 98.0 4. 5.30 0.2 10 4.92 98.4 3.3 5.32 0.08 5. 5 2.465 3.3 98.6 5.34 6. 0.035 2.5 0.99 99.0 3.3 5.50 0.010 7. 1.0 0.495 99.0 3.3 5.60 8. 0.005 0.5 0.249 99.6 3.3 5.85 0.001 9. 0.25 Blank was used as 100 ml of distilled water containing 0.1 g of SHP. After two hours of al!itation its nH was 6.0. SJ.

Hg(In concentration (mgIL)

Effect of concentration 100 ml portions of Hg(m solutions in the concentration range of 100-0.25 mgIL were agitated with 0.1 g of SHP (size <53 11) for two hours. Adsorption was monitored at each selected concentration of Hg(m. From Table I and Fig. 5 it is observed that as the initial Hg(II) concentration is increased, the amount of Hg(II) adsorbed per g of SHP increases along with the increase in Hg(m concentration remaining unadsorbed in bulk solution. The Freundlich equation was found to provide a good fit for the experimental data. Freundlich showed that adsorption from solution could be expressed by the equation: (2)

where 'C.' is the concentration of solute remaining in bulk solution at equilibrium (mgIL), 'x'is the mass of the contaminant adsorbed in mg at the surface and 'In' is the mass of the adsorbent in grams, '1(' is the

Mercury removal from wastewater

113

Freundlich isothenn constant (mg/g) (when Co = 1.0 mgIL) and N is another Freundlich isotherm constant (N) 1). The values of the constants in the present set of experiments are depicted in equation 3. xlm = 29.688 CeO 7192

(3)

The Freundlich isotherm in the logarithmic or linear form is: log x/m = log K + lIN log Ce

(4)

The linear form of the Freunlich Isotherm for the present set of experiments is depicted in Fig. 6 and equation 5. A good fit is suggested by the correlation coefficient (r) of 0.9989. The K value is 29.688 mg/g at log Ce = 0 or (Ce=l). log(mg Hg(ll)ads.)/(g SHP) = 1.4726+0.7192 log Hg(II) soln (mgIL)

(5)

100...------------------.,......--, 90 80

70 60

50 40

30 20

10

o I--+----.--+---+---+---+----.---+--.......--+-~ o 05 15 2 25 35 4 4.5 55

Ce Figure 5. Adsorption isotherm [mercury adsorption on Steamed Hoof Powder (34-36°C»).

Friedman and Waiss, Jr. (1972) obtained Freundlich adsorption isotherm in the concentration range of 0.001 • 20 g Hg(II)/L on wool as: log (Hg(II) ads.)/(g wool) = 1.9 + 0.33 log Hg(II) soln

(6)

log x/m = 0.7192 log Ce + 1.4726 r = 0.9989

0.5 -1

-0.5 ~

I

LogCe Figure 6. Freundlich adsorption isotherm mercury adsorption on Steamed Hoof Powder (34-36°C).

Ion exchange adsorption From Table I it is observed that as Hg(II) is adsorbed and removed from solution there is a decrease in pH of the solution. This indicates that hydrogen ions are released to the solution with the removal of Hg(ll). It is also observed that the addition of hydrogen ions to the solution is proportional to the quantity of Hg(II)

114

M. H. ANSARI et al.

removed from solution. This phenomenon indicates that Hg(II) is removed by SHP by ion exchange adsorption process. Effect of light metal ions The effect ofNa+, K+, Ca2+ and Mi+ on the adsorption of Hg(II) was investigated in batch experiments with concentrations from 0 to 500 mg/L of each metal which, shows that none of the light metals interferes. The typical results at 500 mg/L concentration of the above metals are presented in Table 2. Effect of heavy metal ions The effect of heavy metals Cu2+, Zn 2+, Fe2+, Fe3+, Cd2+, CoH , Pb2+, Ne+, Mn2+, c,3+, and Cr6+ on the adsorption of Hg(II) was investigated in batch experiments with concentrations from 0 to 100 mg/L of each metal, which shows that none of the metals interferes. The typical results at 100 mg/L concentration of the above heavy metals are presented in Table 2. Effect of anions The effect of anions, viz. chloride, sulfate, acetate, phosphate was studied (Table 2). Apart from chloride none of the anions interferes up to the concentration of 200 mg/L. Chloride forms strong complexes with Hg(II) [Formation constants at 25°C and zero ionic strength: HgCl+ (log~1)7.2; HgClz° (log~2)14.0; HgCh• (log~3)15.l; and HgCLt·2 (lOgP4)15.4]. Ansari et al. (1998) while studying the adsorption of Hg(ll) on treated lemon peel powder and other vegetable products observed that adsorption of Hg(II) on vegetable products decreases as the chloride concentration increases in the solution, indicating that as the number of chloride atoms increases in Hg-CI complexes, the adsorption properties of the complexes decreases, in the following order. Hg(II) < HgCl(I) < HgClz° < HgCh' < HgCLt-2 SHP contains sulphur in the form of keratin. Keratin contains large amount of cystine, with - 16% nitrogen and - 3.3% sulfur. Cystine is the oxidation product of cysteine amino acid. The authors are of the view that the combined action of moisture and heat during steaming of hoof may be responsible for the rupture of some of the disulfide cross-links of cystine molecule in keratin. Mercury has a strong affmity for sulfide, sulfhydryl ligand and disulfide bond. Figure 7 and Table 2 show the effect of chloride concentration on the adsorption of Hg(IO on SHP. It is observed that the effect of chloride on adsorption of Hg (II) on SHP is very gradual and a stage is reached when chloride is ineffective on the adsorption of Hg(1I) on SHP i.e. 9.7 mg of Hg(II) with 1.0 g ofSHP. The authors feel that 9.7 mg of Hg(m binds irreversibly with disulfide and sulfhydryl ligands present in SHP. CONCLUSIONS Steamed hoof powder can be used in the removal of Hg(II) from wastewater. It is observed that the pH between 2 and 10 has no effect on the adsorption of Hg(II) on SHP. The adsorption equilibrium is established within 2 hours. Studies indicate that SHP is a non porous adsorbent and the adsorption takes place on the external surface sites. Adsorption data fit well with the Freundlich Isotherm equation. Studies also indicate that Hg(II) is adsorbed by ion exchange mechanism. Light metals (Na+, K+, Ca2+, Mil upo 500 mg/L, heavy metals (Cu2+, Zn2+, Fe2+, Fe3+, Cd2+, CoH , Ni 2+, MnH , Cr, C~+) up to 100 mg/L and anions (S04 2', CH 3COO-, pOl) upto 200 mg/L do not interfere in the adsorption process. Chloride at 200 mgIL interferes in the adsorption process when Hg(D) concentration is above 9.7 mg/L. Therefore when the concentration of Hg(II) is less than 9.7 mg/L in a waste, it can successfully be removed by SHP without any interference from cations or anions. Hoof is comprised of keratin which contains sulfur. Possibly steaming of hoof makes available sulfur containing ligands for bonding with Hg(II). Sulfur bonds with Hg(1I) are actually responsible for irreversible attachment of 9.7 mg of Hg(II) with 1.0 g of SHP, which accounts for the ineffectiveness ofchloride in the adsorption of Hg(II) on SHP.

Mercury removal from wastewater

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Table 2. Effect ofmetal ions and anions on Hg(ll) removal by Steamed Hoof Powder SI. No

Initial Hg(I1) Cone. (mgIL)

Ions Studied

Concentrations Studied (mgIL)

Quantity ofHg(I1) adsorbed (mglg)

Effect of Heavy Metals Cu2+ 100 95.0 Zn2+ 100 95.1 Fe2+ 94.0 100 Fe3+ 93.0 100 Cd2+ 95.2 100 C02+ 95.2 100 Pb2+ 95.1 100 Ni2+ 100 95.2 Mn2+ 100 95.1 95.1 100 Cr C~+ 100 95.2 Effect of Lilzht Metal Ions Na+ 12. 500 95.0 100 K+ 13. 100 500 95.1 Ca2+ 500 14. 100 95.1 M7+ 15. 100 500 94.0 Effect of Anions 200 16. sol95.2 100 200 17. 100 CH3COO· 95.1 pol18. 100 200 95.0 19. 100 200 cr 9.7 100 mL portions of 100 mgIL Hg(II) solution containing particular cation or anion in increasing concentrations with 0.1 g of SHP (size <53 Il) were agitated for 2 hours. Adsorption was monitored at each concentration of cation or anion used.

I. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

100 100 100 100 100 100 100 100 100 100 100

120 .......- - - - - - - - - - - - - - - - - - . . . . , 100 10 10 00

10

, 00

110

200

210

200

Chloride Concentration (mgIL as CI) Figure 7. Effect oC chloride concentration on adsorption oCHg (II) on Steamed HooCPowder.

ACKNOWLEDGEMENTS The authors express their sincere thanks to the Director, National Environmental Engineering Research Institute (NEERI), Nagpur. 440020 (INDIA) for according permission for publication.

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REFERENCES Ajmal M., Ali M., Rehana Y., and Ances A. (1998). Adsorption behavlOr ofCadmiwn, Zinc, Nickel. and Lead from Aqueous Solutions by Mangifera Indica Seed Shell. Indian Journal ofEnvironmental Health, 40 (I), pp 15-26 Ansari M.H., Deshkar A.M., Kelkar P.S., Dhannadhikari D.M., and Hasan M.Z (1998). MerClJry(/l) Removal Jrom Aqueous Medium by Chemically Treated Lemon (CItrus aurantifolia) Peel Powder, in "The Asian Conference on Water & Wastewater Management" held during March 2-4, 1998, in Tehran, Iran. Deshkar A.M. (1990). Studies on Bondrng ofMercury on Some Commonly Available Indian Tree Barlcr. Ph.D. Thesis, Department of Chemistry, Nagpur University, Nagpur, India. Eisler Ronald (1981). Trace Metal Concentration in Marine Organisms. Pergamon Press, New York, (U.S.A). Forstner U. and Wittman a.T.W. (1981). Metal PollutIon in the Aquatic Environment. Springer Verlag, New York, (U.S.A). Friedman M. and Waiss, A.C. Jr. (1972). Mercury Uptake by Selected Agricultural Products and By-products. Environmental Science & Technology (Washington D.C., U.S.A.), 6 (5), pp 457-458. Hahne H.C.H and Kroonge W. (1973). Significance of pH and Chloride Concentration on Behaviour of Heavy Metal Pollutants; Mercury (II), Cadnuum (II), Zinc (II), and Lead (II). J. Environmental Quality (Madison, WISCOnsin, U.S.A) II (4), pp 444-450. Hayashi K., Kawai S., Ohno T., and Maid Y. (1979). I - PhotoalkyIation of inorganic mercury in the presence of amino acids. II • PhotomethyIation of morganic mercury by aliphatic amino acids. Yakugaku Zasshi (Tokyo, Japan), 99, p 1250. Imura N., Sukegawa F., Pan S., Nagao K., Kim J., Kwan T., and Ukita T. (1971). Chemical Methylation of Inorganic Mercury WIth Methylcobalarmn, a VitalJlln B I2 Analog. Science (Washington D.C, U.S.A.) 172, pp 1248-1249. Jansen S. and Jemelov A. (1969). Biological Methylation of Mercury in Aquatic Organisms. Nature (London, U.K.), 223, pp. 753·754. Kumar P. and Dara S.S. (1980). Modified Barks for Scavenging Toxic Heavy Metal Ions. J. Envr. Health (Nagpur, India), 22 (3), pp 196-202. Minimal National Standards. Caustic Soda (Mercury Cell) Industry COINDS/6/1981-82. Central Board for the Prevention and Control of Water Pollution, New Delhi - 110019. India. Pande M.P. and Chaudhary M. (1981). Inorganic Mercury-Bituminous Coal Sorption Interaction in Water. Water Science & Technology (London, U.K.), 13 (I), pp 697-711. Randall J.M., and Hautala E., (1975). Removal of Heavy Metal Ions from Waste Solutions by Contact with Agricultural ByproduclS. Proceedings of the 30m Industrial Wastes Conference, Purdue University (Michigan, Indiana, U.S.A.), May 6-8, pp 412-422. The U.S. Bureau of Mines (1991). Mercury in 1990. Ministry oflndustrial Survey (Washington D.C. U.S.A). Weber W,lJr., and Morris J.C. (1963). Kinetics of Adsorption on Carbon From Solutions. J ofthe Sanitary Eng. Division. ASCE. 89, No. SA2, Proc. Paper 3483, pp 31-59.