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
12Figure 2. Scanning electron micrograph of the virgin GAC
RESULTS and DISCUSSION
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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