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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