IEG 환경지질연구정보센터

(1)

한국지하수토양환경학회 춘계학술발표회 2013년 4월 11일-12일 한화리조트 제주

Effect of Metal Activators (Fe

²⁺

, Co

²⁺

, Cu

²⁺

and Zn

²⁺

) on the Persulfate Oxidation of BTEX in Contaminated Soils

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

Effect of various transition metals for the activation of potassium persulfate (PS) in BTEX oxidation was investigated. Recent study showed that heavy metals with low valence have ability to activate oxidant by donating electron and stimulating the production of sulfate radical (SO4-.

). Prior to PS oxidation, sorption experiment in slurry phase showed that BTEX sorbed in uncontaminated natural soil slurry reached equilibrium condition after 48 h. The BTEX oxidation experiment was conducted at PS/metal activator mass ratio 1:1. Among the tested transition metals (Fe²⁺, Co²⁺, Cu²⁺ and Zn²⁺) as PS activator, Fe²⁺ showed the highest BTEX removal in aqueous system followed by Co²⁺, Cu²⁺

and Zn²⁺. Fe²⁺ showed similar result of BTEX removal with Co²⁺ in soil slurry. However, there was no difference in BTEX removal between Cu²⁺ and Zn²⁺ in soil slurry. Experiment without the addition of metal activator was also investigated. The results indicated that combination between PS and Fe²⁺removed higher BTEX concentration than single PS in slurry phase while in aqueous phase the combination between PS and Fe²⁺ showed slight difference in oxidizing BTEX compared with single PS.

key w o rds : B TE X , C o²⁺, C u²⁺, Fe²⁺, m etal activator, potassium persulfate, Z n²⁺.

1. Introduction

For decades, Benzene, Toluene, Ethylbenzene, and Xylene (BTEX) has contaminated soil and aquatic ecosystem.

Oxidation was applied to remove BTEX contamination from aqueous and slurry phase using potassium persulfate.

Although persulfate without additional activation will not appreciably oxidize most organic contaminants including BTEX, persulfate may oxidize BTEX over longer period of time at ambient temperatures. Thus, it’s necessary to investigate the effect of metal activator type and to design eco-friendly method for removing BTEX contaminant in the real environment.

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^-1followed by addition of 100 mg L^-1Fe²⁺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. 100 mg L^-1 of Co²⁺, Cu²⁺, and Zn²⁺ solutions were also utilized as metal activator for investigating the effect of metal activator type to persulfate oxidation. The experiment without metal activator addition was also investigated. 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/metal activator mass 1:1). The samples were shaken and sampled after 84 h. 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. After that, 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).

(2)

3. Results and Discussions

Figure 1. Determination of BTEX sorption equilibrium in slurry phase (a-b) uncontaminated soil (c-f) natural soil at 30°C and in shaker with 200 rpm. [B], [T], [E], [X]=100 mg L^-1. soil 0.2 mm particle size = 2 g. No pH adjustment. Each experiment point was conducted in duplicate.

a) Aqueous Phase

Experimental PS+Fe Fe PS+Co Co PS+Cu Cu PS+Zn Zn

Concentration Removed (mg/L)

0 20 40 60 80 100 120

140 benzene

toluene ethylbenzene o-xylene

b) Slurry Phase

Experimental PS+Fe Fe PS+Co Co PS+Cu Cu PS+Zn Zn

Concentration Removed (mg/L)

0 20 40 60 80 100 120 140 160 180

benzene toluene ethylbenzene o-xylene

c) Aqueous Phase

Experimental

w/o (PS+Fe) PS PS+Fe

C(t) (mg/L)

0 20 40 60 80 100 120

d) Slurry Phase

Experimental

w/o (PS+Fe) PS PS+Fe

C(t) (mg/L)

0 20 40 60 80 100 120

Figure 2. BTEX amount removed using potassium persulfate (PS) as effect of metal activator (Fe²⁺, Co²⁺, Cu²⁺, Zn²⁺) in (a) aqueous phase (b) slurry phase and comparison of BTEX oxidation with and without metal activator addition in (c) aqueous phase and (d) slurry phase at 30°C and in shaker with 200 rpm.

[B], [T], [E], [X]=100 mg L^-1. [PS]=100 mg L^-1. [Fe²⁺]=[Co²⁺]=[Cu²⁺]=[Zn²⁺]=100 mg L^-1. Ratio PS:metal activator (1:1). Uncontaminated soil 0.2 mm particle size = 2 g. No pH adjustment. Reaction period was fulfilled within 84 h. Each experiment point was conducted in duplicate.

Experiment results showed that PS activated by Fe²⁺ was better in removing BTEX contaminant comparing with Co²⁺, Cu²⁺, and Zn²⁺ as metal activators both in aqueous phase and soil slurry phase. It’s necessary to utilize heavy metal which has ability to donate free electron to activate persulfate.

4. Conclusions

The results of this study indicate that Fe²⁺ showed the best result compared with Co²⁺, Cu²⁺, and Zn²⁺ in activating persulfate both in aqueous phase and soil slurry phase, showed by the BTEX concentration removal after oxidation. The combination between PS and Fe²⁺ was better than single PS for oxidizing BTEX in slurry sample.

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. Liang, C., Huang, C.F.., and Chen, Y.J., (2008) Potential for activated persulfate degradation of BTEX contamination, Water Resarch, 42, 4091-4100.

2. Liang, C., Bruell, C.J., Marley, M.C., and Sperry, K.L., (2004) Persulfate oxidation for in situ remediation of TCE. I. Activated by ferrous by ferrous ion with and without a persulfate-thiosulfate redox couple, Chemosphere, 55, 1213-1223.

(c) Benzene

Time (day)

0 1 2 3 4 5 6

C(t) (mg/L)

0 10 20 30 40 50 60 70

equilibrium point

(d) Toluene

Time (day)

0 1 2 3 4 5 6

C(t) (mg/L)

0 10 20 30 40 50 60 70

equilibrium point

(e) Ethylbenzene

Time (day)

0 1 2 3 4 5 6

C(t) (mg/L)

0 20 40 60

equilibrium point

(f) o-Xylene

Time (day)

0 1 2 3 4 5 6

C(t) (mg/L)

0 20 40 60

equilibrium point (a) Ethylbenzene

Time (day)

0 1 2 3 4 5 6

C(t) (mg/L)

0 5 10 15 20 25

equilibrium time

(b) o-Xylene

Time (day)

0 1 2 3 4 5 6

C(t) (mg/L)

0 5 10 15 20 25 30 35

equilibrium point