한국지하수토양환경학회 춘계학술발표회 2013년 4월 11일-12일 한화리조트 제주
Oxidation Kinetics of BTEX in Soil Slurry using Persulfate/Fe
2+system
Ardie Septian · Jiyeon Choi · Sanghwa Oh · Won Sik Shin*
Department of Environmental Engineering, Kyungpook National University, Daegu, 702-701, Republic of Korea e-mail: [email protected]
Abstract
Potassium persulfate (PS) oxidation of BTEX in aqueous solution and soil slurry was investigated. PS was chemically activated by the addition of Fe2+ as transition metal activator to initiate sulfate radical (SO4-.) with initial PS/Fe2+ mass ratio 1:1. The obtained kinetic data was fitted to the first-order kinetic model. Results indicated that BTEX was effectively degraded by potassium persulfate oxidation at 30°C and equilibrium was reached within 24 h for both aqueous solution and soil slurry experiments. In order to accelerate PS performance, the effect of Fe2+ concentration variation on the activation of persulfate was determined. Among the various PS/Fe2+ mass ratios (1:10, 1:5, 1:1, 1:0.5, 1:0.1), the 1:5 ratio was more effective in oxidizing BTEX in both aqueous solution and soil slurry. Higher ferrous concentration achieved higher BTEX degradation as PS/Fe2+ mass ratio increased. However, BTEX concentration was ineffectively reduced by PS oxidation in aqueous solution and soil slurry for PS/Fe2+ mass ratio 1:10 as indicated by slight changes in BTEX concentration between PS/Fe2+ mass ratio variation 1:10 and 1:5. Results of this study indicate that PS oxidation is effective in oxidizing BTEX with Fe2+ as metal activator at PS/Fe2+ mass ratios up to 1:5.
key w o rds : B TE X , Fe2+, oxidation, potassium persulfate, sulfate radical.
1. Introduction
Aromatic hydrocarbon in petroleum fuel that mostly consists of Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) has been a serious problem by contaminating soil and aquatic ecosystem. In situ chemical oxidation (ISCO) has attracted a great attention as one of the method which widely being used in waste site remediation. Potassium persulfate (K2S2O8) is one of oxidator among all common ISCO oxidants. Persulfate anion with a high redox potential can be chemically activated to form sulfate radical by using metal activator.
2. Materials and Method
Aqueous solution of BTEX was prepared by individually or mixed by injecting directly BTEX into 40 mL Amber glass vial with Miniert cap. Initial concentration used for each B, T, E, X was 100 mg L-1 followed by addition of 100 mg L-1 Fe2+ solution and filling up the mixture with DI water without headspace. 2 g of uncontaminated soil (ɸ
= 0.2 mm) was transferred into 40 mL Amber glass vial with Miniert cap to prepare soil slurry before the addition of BTEX, Fe2+ solution, and DI water. The prepared samples were shaken at 30°C and 200 rpm for 48 h. The samples were injected with 100 mg L-1 of potassium persulfate (PS/Fe2+ mass ratio 1:1). The samples were shaken and sampled at several time variation up to 84 h reaction for kinetic oxidation investigation. For investigating PS/Fe2+ mass ratio, samples were prepared by PS/Fe2+ mass ratios 1:10, 1:5, 1:1, 1:0.5, and 1:0.1. During sampling, the samples were centrifuged at 1500 rpm for 20 min. Then, 10 mL of supernatant was taken, mixed with 1 mL of methanol to quench the oxidation, and added with 10 mL of hexane for extraction. The mixture was shaken at 200 rpm for at least 1 h. Finally, 1 mL of hexane layer extractant was taken and analyzed by using Agilent 6890N Gas Chromatograph with DB-5MS column (Agilent Technologies, 60m x 0.25 mm i.d., film thickness = 0.25 μm)
Oxidation Experiment k (hr-1) R2 SSE
Benzene individual 0.1361 ± 0.0083 0.9966 27.526
mixed 0.0166 ± 0.0024 0.8349 583.87
Toluene individual 0.0829 ± 0.0134 0.9607 414.53
mixed 0.0125 ± 0.0017 0.8931 372.59
Ethylbenzene individual 0.1036 ± 0.0355 0.7862 1188.2
mixed 0.0150 ± 0.0014 0.9319 194.27
Xylene individual 0.0584 ± 0.0105 0.9019 353.65
mixed 0.0105 ± 0.0008 0.9490 64.540
Oxidation Experiment k (hr-1) R2 SSE
Benzene individual 0.0588 ± 0.0186 0.8434 170.31
mixed 0.0176 ± 0.0014 0.9551 121.76
Toluene individual 0.0552 ± 0.0195 0.8099 168.14
mixed 0.0241 ± 0.0032 0.8936 351.70
Ethylbenzene individual 0.1213 ± 0.0232 0.9588 146.44
mixed 0.0284 ± 0.0046 0.8607 432.44
Xylene individual 0.0876 ± 0.0231 0.8481 404.69
mixed 0.0103 ± 0.0015 0.8746 198.79
3. Results and Discussions
Table 1. First order kinetic constant of BTEX oxidation by persulfate in individual and mixed BTEX aqueous solution.
Table 2. First order kinetic constant of BTEX oxidation by persulfate in individual and mixed BTEX slurry.
(a) benzene
Time (hour)
0 20 40 60 80 100 120
C(t)/Co
0 20 40 60 80 100 120
benzene alone w/ BTEX
(b) toluene
Time (hour)
0 20 40 60 80 100 120
C(t)/Co
0 20 40 60 80 100 120
toluene alone w/ BTEX
(c) ethylbenzene
Time (hour)
0 20 40 60 80 100 120
C(t)/Co
0 20 40 60 80 100 120
ethylbenzene alone w/ BTEX
(d) xylene
Time (hour)
0 20 40 60 80 100 120
C(t)/Co
0 20 40 60 80 100 120
xylene alone w/ BTEX
(e) benzene
Time (hour)
0 20 40 60 80 100 120
C(t)/Co
0 20 40 60 80 100
benzene alone w/ BTEX
(f) toluene
Time (hour)
0 20 40 60 80 100 120
C(t)/Co
0 20 40 60 80 100
toluene alone w/ BTEX
(g) ethylbenzene
Time (hour)
0 20 40 60 80 100 120
C(t)/Co
0 20 40 60 80 100
ethylbenzene alone w/ BTEX
(h) xylene
Time (hour)
0 20 40 60 80 100 120
C(t)/Co
0 20 40 60 80 100
xylene alone w/ BTEX
i) Aqueous Phase
Experimental PS/Fe (1:10) PS/Fe (1:5)PS/Fe (1:1) PS/Fe (1:0.5)PS/Fe (1:0.1)
BTEX Removed (mg/L)
0 20 40 60 80 100 120
benzene toluene ethylbenzene o-xylene
j) Slurry Phase
Experimental PS/Fe (1:10) PS/Fe (1:5)PS/Fe (1:1) PS/Fe (1:0.5)PS/Fe (1:0.1)
BTEX Removed (mg/L)
0 20 40 60 80 100 120
benzene toluene ethylbenzene o-xylene
Figure 1. Comparison of BTEX concentration remained between individual and mixed BTEX (a-d) aqueous phase (e-h) slurry phase and comparison of PS/Fe2+ mass ratio for BTEX oxidation (i) aqueous phase (j) slurry phase using potassium persulfate (PS) at 30°C and in shaker with 200 rpm. [B]0, [T]0, [E]0, [X]0
=100 mg L-1. [PS]0 =100 mg L-1. [Fe2+]0 =100 mg L-1 (ratio PS:Fe2+ 1:1). Uncontaminated soil 0.2 mm particle size = 2 g. No PS addition to control experiment. No pH adjustment. Each experiment point was conducted in duplicate.
First-order kinetic rates showed that the oxidation in individual BTEX oxidation was faster than that in mixed BTEX system. It was assumed that the oxidation among Benzene, Toluene, Ethylbenzene, and Xylene by PS was occurred competitively in mixed BTEX system, while the oxidation was occurred individually in individual BTEX system.
4. Conclusions
The results of this study indicated that PS oxidation with Fe2+ was effective in BTEX degradation in aqueous solution and soil slurry less than 24 h. Individual BTEX oxidation rate was higher than in mixed BTEX due to easier feasibility of potassium persulfate for oxidizing contaminant individual BTEX system. By increasing the PS/Fe2+ mass ratio, the BTEX contaminant to be oxidized also increases up to 1:5.
Acknowledgement
This research is financially supported by Republic of Korea Ministry of Environment as "Green Remediation Research Center for Organic-Inorganic Combined Contamination (The GAIA Project-2012000550004)".
References
1. Achugasim, D., Osuji, L.C., and Ojinnaka, C.M., (2011) Use of activated persulfate in the removal of petroleum hydrocarbons from crude oil polluted soils, Research Journal of Chemical Sciences, Vol.1(7), 57-67.
2. Rodriguez, S., Santos, A., Romero, A., and Vincente, F., (2012) Kinetic of oxidation and mineralization of priority and emerging pollutants by activated persulfate, Chem. Eng. J., 203, 225-234.
