hexavalent chromium removal by quaternized poly(4 ...1 hexavalent chromium removal by quaternized...
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Hexavalent Chromium Removal by Quaternized Poly(4-Vinylpyridine)
Coated Activated Carbon From Aqueous Solution
Ravi Kumar Kadari1, Baolin Deng2
Dianchen Gang1
1West Virginia University Institute of Technology2University of Missouri-Columbia
2005 CAST Annual Workshop at Virginia Tech, July 26 to July 28th
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OBJCETIVE
The objective of this study is to develop a novel method to remove and recover hexavalent chromium from aqueous solutions including Acid Mine Drainage (AMD).
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One of the major challenges facing coal and metal mining industries today is to address environmental damage associated with the mining activities.
INTRODUCTION
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Acid Mine Drainage may contain high concentrations of many toxic elements including divalent heavy metals and oxyanions of chromium (Cr) and arsenic (As).
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The Cr(VI) is morehazardous and it causesliver damage, pulmonarycongestions, vomiting,diarrhea, and potentiallycarcinogenic due to itshigher solubility.
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USEPA has set the maximum contaminant level (MCL) of Cr(VI) at 0.05 mg/L.Traditional methods for removing of Cr(VI) are reduction, precipitation, and filtration.
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The other possible treatment methods include membrane separation, extraction, and sorption based processes.
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Sorption based processes have been regarded as one of the most promising techniques due to the low Cr(VI) concentration and handling of large volume of aqueous solution.
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EXPERIMENTAL SECTION
The concentration of Cr(VI) was determined by the colorimetric method using Cary 50 Probe UV-Visible Spectrophotometer at wavelength of 540 nm.
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Figure 1. Cary 50 Probe UV-Visible Spectrophotometer
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4-vinylpyridine
Vacuum distillation
Cumene hydroperoxide [0.5% (w/v)
Poly (4-vinylpyridine) in CHCl3
GAC
Br(CH2)4Br in CH3OH
CH3(CH2)15Br in CH3OH
GAC-QPVP
Preparation of GAC -QPVP
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12Figure 2. Scanning electron micrograph of the virgin GAC
RESULTS and DISCUSSION
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13Figure 3. Scanning electron micrograph of the quaternized PVP coated GAC
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After coating (Figure 3)and quaternization process,fine particles and polymerchain have been depositedon the carbon surface, forma system of complicated pore network.
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Effect of pH on hexavalentchromium removal wasinvestigated in the pH range of 1-12 at an initial Cr(VI)concentration of 5 mg/L at25 °C.
Effect of pH
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pH0 2 4 6 8 10 12 14
Ads
orpt
ion
Cap
acity
(mg/
g)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0C
hrom
ium
Rem
oval
Eff
icie
ncy
(%)
0
20
40
60
80
100
120
Adsorption capacityRemoval Efficiency
Figure 4. Effect of pH on Cr(VI) removal , T = 25 °C
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It was noticed that the maximum removal efficiency observed at pH = 2.0 and it decreases as the solution becomes basic.
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The possible reactions in the anion-exchange can be expected as
−+− +⇔+ 422
72 2 HCrOHOHOCr−−−+−−+ +−⇔+− BrHCrOBrQPyGACHCrOBrQPyGAC 44 ...)()(
Where, −+− BrQPyGAC )( is theQPVP coated GAC.
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The flask with a desired quantity of QPVP coated GAC and Cr(VI) solution was placed on a shaker for 20 hr.Then the mixture was filtered and aqueous phase Cr(VI) was analyzed.
Adsorption Isotherms
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Figure 6. Adsorption isothermsE q u ilib r iu m C o n c e n tra tio n (m g /L )
0 5 1 0 1 5 2 0 2 5 3 0
Ads
orpt
ion
Cap
acity
(mg/
g)
0
1 0
2 0
3 0
4 0
5 0
C i = 1 0 m g /L , p H = 2C i = 2 6 m g /L , p H = 2 .5F re u n d lic h m o d e lL a n g m iu r m o d e l
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Adsorption capacities for the 10 and 26 mg/L Cr(VI) solutions were 12.6 and 38.9 mg/g, respectively.The adsorption data were better fitted to the Freundlichmodel than the Langmiurmodel.
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Effect of Anions
Due to the high concentrations of sulfate, chloride and heavy metals in AMD, it is important to evaluate roles of ions on Cr(VI) removal.
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C o n cen tra tio n o f A n io n (M )0 .2 0 .4 0 .6 0 .8 1 .0 1 .2
Ads
orpt
ion
Cap
acity
(mg/
g)
0
1
2
3
S O 4-2
C l-
H C O 3-
C H 3C O O -
Figure 7. Effect of anions on Cr(VI) (0.098 mM) removal, pH = 2
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GAC-QPVP had high affinity for Cr(VI). When the concentration of sulfate ion was greater than 500 times that of Cr(VI), it influenced the adsorption capacity slightly.
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Desorption of Cr(VI) was evaluated with NaOH andNH4OH at various concentrations and different time periods.
Desorption Study
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Concentration of Base (M)0.0 0.2 0.4 0.6 0.8 1.0 1.2
Rec
over
y Ef
ficie
ncy
(%)
0
10
20
30
40
50
60
70
80
90
100
desorption with NH4OH for 5 min.desorption with NH4OH for 30 min.desorption with NaOH for 5 min.desorption with NaOH for 30 min.
Figure 8. Desorption of Cr(VI)
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Maximum desorptionefficiencies for NaOH and NH4OH were 80% and 55%, respectively. Desorption efficiency increased with increasing base concentration.
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The adsorbed GAC-QPVP was treated with 0.2 M NaOH for 30 minutes to desorb Cr(VI), then the absorbent was washed and dried to regenerate GAC-QPVP .
Regeneration of GAC-QPVP
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Equlibrium Concentration (mg/L)0 10 20 30 40 50 60 70
Ads
orpt
ion
Cap
acity
(mg/
g)
0
10
20
30
40
50
60
70
80
Ci = 26 mg/L, pH = 2.5 with orignal GAC-QPVP
Ci = 65 mg/L, pH = 4.5 with Original GAC-QPVP
Ci = 26 mg/L, pH = 2.5 with regenerated GAC-QPVP
Ci = 65 mg/L, pH = 4.5 with regenerated GAC-QPVP
Figure 9. Adsorption isotherms of QPVP coated Original GAC and regenerated GAC
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Adsorption capacities of regenerated GAC-QPVP were decreased from 35% for concentration of 65 mg/L to 45% for 26 mg/L.
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CONCLUSIONSGAC-QPVP is a good adsorbent of hexavalentchromium in the acid medium.The adsorbent had good selectivity of Cr(VI) over other anions.
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QPVP coated GAC is easy to recover.The GAC-QPVP could be reused with a 35%-45% loss of adsorption capacity.
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Dianchen Gang (Faculty, WVU Tech)Baolin Deng (Faculty, UMC)Ravi Kumar Kadari (GA, WVU Tech)Jun Fang (GA, UMC)Kent Abe (UGA, WVU Tech)Billy Manual (UGA, WVU Tech)Derek Spurlock (UGA, WVU Tech)
Research Team
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Acknowledgement
The authors are grateful for the financial support from the U.S. Department of Energy (Grant No.: DE-FC26-02NT41607 CFDA No: 81.089).
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REFERENCESCosta, M. Potential hazards of hexavalent chromate in our drinking water. Reg. Toxicol. Pharmacol. 2003, 188, 1.Rajesh, N.; Yogesh K. Surfactant Enhanced Chromium Removal Using a Silica Gel Column. Universitas Scientiarum. 2001, 6, 55.Jakobsen, K.; Laska, R. Advanced treatment methods for electroplating wasters, Pollution Engineering, 1977, 8, 42.Besselievre, E.B. The treatment of industrial wastes, MeGraw-Hill, NY, 1980.Chanda, M.; Rempel, G.L. Quaternized poly(4-vinylpyridine) Gel-Coated on Silica. Fast Kinetics of Diffusion-Controlled Sorption of Organic Sulfonates. Ind. Eng. Chem. Res. 1994, 33, 623. Gang, D.; Benaerji, S.K.; Clevenger, T.E. Factors affecting chromium(VI) removal by modified poly(4-vinylpyridine) coated silicagel. Practice periodical of Hazardous, Toxic, and Radioactive Waste Management, 2001, 5, 58.Leyva R. R.; Juarex M.A.; Gurerrero Coronado R.M. Adsorption of Chromium(VI) from aqueous solutions on Activated Carbon. Wat. Sci. Tech. 1994, 30, 191.APHA, AWWA, WPCF Stand Methods for the Examination of Water and Wastewater, 1985. Octave Levenspiel, Chemical Reaction Engineering, Second Edition, 1995.