Hexavalent Chromium Removal by Quaternized Poly(4-Vinylpyridine) Coated Activated Carbon From Aqueous Solution Ravi Kumar Kadari 1, Baolin Deng 2 Dianchen Gang 1 1 West Virginia University Institute of Technology 2 University of Missouri-Columbia 2005 CAST Annual Workshop at Virginia Tech, July 26 to July 28th 1
2 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).
3 INTRODUCTION One of the major challenges facing coal and metal mining industries today is to address environmental damage associated with the mining activities.
Acid Mine Drainage may contain high concentrations of many toxic elements including divalent heavy metals and oxyanions of chromium (Cr) and arsenic (As). 4
The Cr(VI) is more hazardous and it causes liver damage, pulmonary congestions, vomiting, diarrhea, and potentially carcinogenic due to its higher solubility. 5
6 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.
The other possible treatment methods include membrane separation, extraction, and sorption based processes. 7
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. 8
9 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.
Figure 1. Cary 50 Probe UV-Visible Spectrophotometer 10
Preparation of GAC - QPVP 4-vinylpyridine Vacuum distillation Cumene hydroperoxide [0.5% (w/v) Poly (4-vinylpyridine) in CHCl 3 GAC Br(CH 2 ) 4 Br in CH 3 OH CH 3 (CH 2 ) 15 Br in CH 3 OH GAC-QPVP 11
RESULTS and DISCUSSION Figure 2. Scanning electron micrograph of the virgin GAC 12
Figure 3. Scanning electron micrograph of the quaternized PVP coated GAC 13
After coating (Figure 3) and quaternization process, fine particles and polymer chain have been deposited on the carbon surface, form a system of complicated pore network. 14
15 Effect of ph Effect of ph on hexavalent chromium removal was investigated in the ph range of 1-12 at an initial Cr(VI) concentration of 5 mg/l at 25 C.
Chromium Removal Efficiency (%) 120 100 80 60 40 20 0 0 2 4 6 8 10 12 14 ph 16 Adsorption capacity Removal Efficiency 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 Adsorption Capacity (mg/g) Figure 4. Effect of ph on Cr(VI) removal, T = 25 C
It was noticed that the maximum removal efficiency observed at ph = 2.0 and it decreases as the solution becomes basic. 17
18 The possible reactions in the anion-exchange can be expected as Cr 2 7 + + 2 + 4 2O H O 2H HCrO + GAC ( QPy ) Br + HCrO 4 GAC ( QPy ) Br... HCrO 4 + + Br Where, GAC ) + ( QPy Br is the QPVP coated GAC.
19 Adsorption Isotherms 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.
50 Adsorption Capacity (mg/g) 40 30 20 10 C i = 10 mg/l, ph = 2 C i = 26 m g/l, ph = 2.5 Freundlich model Langmiur model 0 0 5 10 15 20 25 30 Equilibrium C oncentration (m g/l) Figure 6. Adsorption isotherms 20
21 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 Freundlich model than the Langmiur model.
22 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.
3 Adsorption Capacity (mg/g) 2 1 SO 4-2 Cl - HCO 3 - CH 3 COO - 0 0.2 0.4 0.6 0.8 1.0 1.2 Concentration of Anion (M) Figure 7. Effect of anions on Cr(VI) (0.098 mm) removal, ph = 2 23
24 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.
25 Desorption Study Desorption of Cr(VI) was evaluated with NaOH and NH OH at various 4 concentrations and different time periods.
100 90 Recovery Efficiency (%) 80 70 60 50 40 30 20 10 desorption with NH 4 OH for 5 min. desorption with NH 4 OH for 30 min. desorption with NaOH for 5 min. desorption with NaOH for 30 min. 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 Concentration of Base (M) Figure 8. Desorption of Cr(VI) 26
27 Maximum desorption efficiencies for NaOH and NH 4 OH were 80% and 55%, respectively. Desorption efficiency increased with increasing base concentration.
Regeneration of GAC-QPVP 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. 28
80 Adsorption Capacity (mg/g) 70 60 50 40 30 20 10 C = 26 mg/l, ph = 2.5 with orignal GAC-QPVP i C i = 65 mg/l, ph = 4.5 with Original GAC-QPVP C i = 26 mg/l, ph = 2.5 with regenerated GAC-QPVP C i = 65 mg/l, ph = 4.5 with regenerated GAC-QPVP 0 0 10 20 30 40 50 60 70 Equlibrium Concentration (mg/l) Figure 9. Adsorption isotherms of QPVP coated Original GAC and regenerated GAC 29
30 Adsorption capacities of regenerated GAC-QPVP were decreased from 35% for concentration of 65 mg/l to 45% for 26 mg/l.
31 CONCLUSIONS GAC-QPVP is a good adsorbent of hexavalent chromium in the acid medium. The adsorbent had good selectivity of Cr(VI) over other anions.
32 QPVP coated GAC is easy to recover. The GAC-QPVP could be reused with a 35%- 45% loss of adsorption capacity.
33 Research Team 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)
34 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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