5th International Conference on Chemical Engineering and Applications (CCEA 2014) Oral Presentation Effects of Wetting Agents and Approaching Anode on Lead Migration in Electrokinetic Soil Remediation 26-27 th August 2014, RegaLees Hotel, Taipei, Taiwan Presented by : • Ng Yee Sern 1, *, Mohd Ali Hashim 1 , Bhaskar Sen Gupta 2 1 University of Malaya, Malaysia 2 Queen’s University Belfast, United Kingdom Available online at: http://dx.doi.org/10.6084/m9.figshare.1272952
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5th International Conference on Chemical Engineering and Applications (CCEA 2014) Oral Presentation Effects of Wetting Agents and Approaching Anode on.
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5th International Conference on Chemical Engineering and Applications (CCEA 2014)
Oral Presentation
Effects of Wetting Agents and Approaching Anode on Lead Migration in Electrokinetic Soil Remediation
26-27th August 2014, RegaLees Hotel, Taipei, Taiwan
Presented by:• Ng Yee Sern1,*, Mohd Ali Hashim1, Bhaskar Sen Gupta2
1 University of Malaya, Malaysia2 Queen’s University Belfast, United Kingdom
Available online at: http://dx.doi.org/10.6084/m9.figshare.1272952
• Lead• One of the top six toxic threats in the world [1]
– Powerful neurotoxin
• Cause acute and chronic illnesses [2-3]
– Central and peripheral nervous systems, – Cardiovascular systems – Reproductive systems– gastrointestinal and urinary tracts
4
Introduction
• Lead contaminated soil• One of the pathways for human exposure• Mining, lead-acid battery manufacturing, shooting range soil• Lead concentration as high as 751.98-138,000mg/kg [1,4-7]
5
Introduction
• Electrokinetic soil remediation• Utilize low magnitude direct current as driving force• Electromigration – For heavy metals transport• Electroosmosis – For organic compounds transport
• Advantages• No soil permeability limitation• Concentrate heavy metals into a smaller soil volume
CCEA 2014
CCEA 2014 6
Introduction
• Electrokinetic Transport for Heavy Metals
DC supply
+
++
+
+
-
-
-
-
-
-
Theory [8-9]
•Main mechanism for heavy metals transport = Electromigration
• Cations move to cathode• Anions move to anode
• Cations and anions will be concentrated in cathode region and anode region, respectively
• Removal achieved by concentrating metal ions in cathode chamber
Saturated soil
Anode region Cathode region
++
-
-
+++++
+++++
-----
-----
CCEA 2014 7
Introduction
• Electrokinetic Transport for Heavy Metals
DC supply
+
++
+
+
-
-
-
-
-
-
Drawback for electrokinetic soil remediation
• Electrolysis produces H+ and OH-
• Two sections are exerted • low pH (anode region) • high pH (cathode region)
• High pH section:• reduces metal migration due to metal
hydroxides precipitates• accumulate metals in the middle of the
soil [10-11]
Saturated soil
++
-
-
+++++
+++++
-----
-----
Cathode regionAnode region
CCEA 2014 8
Introduction
Reduce metal hydroxides precipitation/enhance metal
migration
Buffer solution for reducing pH in cathode region[10]
Homogenize overall pH by circulation electrolyte between
anode and cathode chambers [12]
Approaching anode configuration
CCEA 2014 9
Introduction
• Approaching anode [10,13-14]
– Install extra electrodes along the soil– Anode is switched towards cathode from time to time
• Induce progressive acidification for soil
Total experiment duration: 5t
CCEA 2014 10
Introduction
Normal electrokinetic processNormal electrokinetic process- Electrolysis produces H+ and OH-
-H+ and OH- migrate to their respective electrodes
-Low and high pH regions are generated
-High pH region favours for metal hydroxides precipitation
2. DC was supplied at 1V/cm for 24 hours for Pb migration
3. For approaching anode, anode was switched to the middle electrode after 12 hours experiment
CCEA 2014 16
• Pb migration
Results and Discussion
0 5 10 15 20 25
0
2
4
6
8
10
12
0.01M NaNO3 - FA 0.01M NaNO3 - AA0.1M Citric acid - FA 0.1M Citric acid - AA
Time, hr
Cu
rren
t, m
A
a
0.5 1 1.5 2 2.5 3 3.5 4 4.5
0
2
4
6
8
0.01M NaNO3 - FA0.01M NaNO3 - AA
Soil section
So
il p
H
b
0.5 1 1.5 2 2.5 3 3.5 4 4.5
0
400
800
1,200
1,600
0.01M NaNO3 - FA0.01M NaNO3 - AA
Soil section
Pb
co
nce
ntr
ati
on
, m
g/k
g
c
General trend - Pb concentration was lower in S1-S2 (anode region) and higher at S3-S4 (cathode region). - Different migration magnitude (especially S3-S4) :
- Citric acid > NaNO3 - higher current by citric acid
- lower soil pH/pH gradient for better Pb desorption [15]
CCEA 2014 17
Results and Discussion
0.5 1 1.5 2 2.5 3 3.5 4 4.50
2
4
6
8
0.01M NaNO3 - FA 0.01M NaNO3 - AA0.1M Citric acid - FA 0.1M Citric acid - AA
Soil section
Soil
pH
b
0.5 1 1.5 2 2.5 3 3.5 4 4.50
400
800
1,200
1,600
0.01M NaNO3 - FA 0.01M NaNO3 - AA0.1M Citric acid - FA 0.1M Citric acid - AA
Soil section
Pb
conc
entr
atio
n, m
g/kg
c
NaNO3 – Fixed electrode (FA) test-Pb accumulation in S3 section - high soil pH at S3-S4 region - reduce in Pb mobilitypH at S3 is 4.61 = favours Pb adsorption [16-17]. pH at S4 is 6.62 = favours Pb hydrolysis into Pb(OH)2 and Pb(OH)3
- [18]
CCEA 2014 18
Results and Discussion
0.5 1 1.5 2 2.5 3 3.5 4 4.50
2
4
6
8
0.01M NaNO3 - FA 0.01M NaNO3 - AA0.1M Citric acid - FA 0.1M Citric acid - AA
Soil section
Soil
pH
b
0.5 1 1.5 2 2.5 3 3.5 4 4.50
400
800
1,200
1,600
0.01M NaNO3 - FA 0.01M NaNO3 - AA0.1M Citric acid - FA 0.1M Citric acid - AA
Soil section
Pb
conc
entr
atio
n, m
g/kg
c
NaNO3 – Approaching anode (AA) test - Pb accumulation/focusing in S3 region is not observed - due to better soil acidification [10]
- Higher Pb concentration detected in S1-S2 regions - lack of electricity to maintain Pb electromigration after anode shifting
CCEA 2014 19
Results and Discussion
0.5 1 1.5 2 2.5 3 3.5 4 4.50
2
4
6
8
0.01M NaNO3 - FA 0.01M NaNO3 - AA0.1M Citric acid - FA 0.1M Citric acid - AA
Soil section
Soil
pH
b
0.5 1 1.5 2 2.5 3 3.5 4 4.50
400
800
1,200
1,600
0.01M NaNO3 - FA 0.01M NaNO3 - AA0.1M Citric acid - FA 0.1M Citric acid - AA
Soil section
Pb
conc
entr
atio
n, m
g/kg
c
Citric acid- No Pb accumulation in S3 region- Pb was distributed equally at cathode region (S3-S4)
-No significant difference between FA and AA tests - good soil acidification /acid front is already achieved by citric acid
CCEA 2014 20
Results and Discussion
• Power consumption
0.01M NaNO3 - FA 0.01M NaNO3 - AA 0.1M Citric acid - FA 0.1M Citric acid - AA0
0.000400000000000001
0.000800000000000003
0.0012
0.00160000000000001
Pow
er co
nsum
ption
(kW
h)
Approaching anode reduces ≈20% of power consumption
Citric acid testApproaching anode maintained Pb migration at a lower power consumption
CCEA 2014 21
Conclusion
• Pb migrated and concentrated to a smaller soil volume under electrokinetic process with the aid of wetting agent.
• Pb migration was highly dependent on the types of wetting agents used
– Citric acid showed better migration than NaNO3
– Pb accumulation was observed in NaNO3 tests due to higher soil pH.
• Approaching anode (AA) was useful to reduce metal hydroxide precipitation when non-acidic wetting agent was used
• AA reduced power consumption by 18.75% while maintaining efficient Pb migration when citric acid was used as wetting agent.
CCEA 2014 22
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