Global Journal of Engineering Sciences (GJES)
Remediation
Experimental of Chromium- Contaminated Soft Soil by Temperature-Controlled
Electric Combined Leaching
Authored by Qian Baoyuan
. Abstract
It is
often inefficient and difficult to achieve the ideal remediation effect using a
single remediation technology to repair contaminated soil, so the combined
remediation technology of temperature-controlled electric combined leaching has
aroused people’s interest. At present, it is widely used in
chromium-contaminated soft soil.
Keywords: Chromium-contaminated soft soil;
Electrokinetic remediation; Temperature-controlled
Introduction
Chromium
has a series of reactions with soil, such as adsorption, complexation,
reduction, oxidation and so on, which makes its existing form in soil different
from its input form [1]. According to the continuous extraction method proposed
by Tessier et al. [2], the forms of chromium in soil can be divided into the
following five forms: exchangeable, carbonate-bound, iron- manganese
oxidebound, organic-bound and residual. The remediation methods of chromium
contaminated soil are roughly divided into physical remediation, chemical
remediation, bioremediation and combined remediation, among which
electrokinetic remediation is a clean and efficient remediation method of
contaminated soil, which belongs to the physical and chemical remediation
method. The Lasagna technology, which was first used in Kentucky in 1995, and
the combined repair technology of Electro-KleanTM and electric adsorption used
in Louisiana in the future, the electrochemical oxidation technology used in
Germany, and the compound repair technology of EK-solar field used in a site in
South Korea [3].
Scholars
from all over the world have also carried out extensive experimental studies on
the electrokinetic remediation of chromium-contaminated soil. In the 1990s,
Ryan et al. [4] put forward the electrokinetic restoration method earlier, and
Reddy et al. [5] studied the difference of electrokinetic remediation effect of
different types of chromium contaminated soil. Kim et al. [6] conducted an
experimental study on the electro remediation of muddy soil polluted by
chromium, copper and lead. The results showed that the removal rate of heavy
metals depended on their forms in the soil, and the removal rate of
exchangeable and carbonate bound chromium reached 70%. Reddy et al. [7] studied
the effect of the initial form of chromium in soil on the effect of
electrokinetic remediation test.
Al-Hamdan
et al. [8] presented a systematic bench-scale laboratory study performed to
assess the transient behavior of chromium, nickel, and cadmium in different
soils during electrokinetic remediation. It is showed that in kaolin, the extent
of Ni (II) and Cd (II) migration towards the cathode increased as the treatment
time increased. Peng et al. [9] studied the effect of different electrolytes on
electrokinetic remediation of muddy soil polluted by chromium and zinc.
Distilled water, SDS solution and citric acid solution were used as
electrolytes. After 5 days of electrokinetic remediation, the total removal
rates of heavy metals were 20-51%, 26-65% and 34-69%, respectively, and the
removal rate of chromium was the highest when citric acid solution was used as
electrolyte. Li et al. [10] proposed to use the method close to the anode to
enhance the effect of electro remediation of chromium contaminated soil, that
is, the anode moves 7cm to the cathode every three days, which is beneficial to
the desorption and dissolution of chromium, promote the dissociation of
chromium from the soil, strengthen the migration ability of chromium in soil,
and improve the removal efficiency of chromium in soil. The effects of
acidification time, concentrations of acetic acid and citric acid on removal of
chromium from soils were studied by changing the acidification pretreatment
conditions, and then speciation analysis of the chromium was conducted to study
the regularity of Cr in different speciation’s [11]. The total chromium(Cr(T))
and hexavalent chromium(Cr(Ⅵ))
removal rates of the group acidized by citric acid(0.9 mol/L) for five days
were up to26.97% and 77.66%, respectively, while the Cr(T) and Cr(Ⅵ) removal rates of the group without acidification were 6.23%
and19.01%, respectively. The experiments of Meng et al. [12] proved that
acidification pretreatment can significantly improve the removal efficiency of
chromium in soil in electrokinetic remediation experiments.
In
addition, the citric acid fermentation broth was used to leach and repair the
Cr-Cu-Pb contaminated soil, and the chromium removal rate was 43.7%, which was
higher than that obtained by using citric acid leaching solution [13].
Accordingly, the authors of this paper improved the temperature-controlled
electric combined leaching remediation device based on the development of
temperature-controlled electric remediation device. Then, the effects of the
concentration of Cr (Ⅵ) and Cr (total),
voltage, temperature and the type of leaching solution on the remediation of
chromium-contaminated soil are considered and the remediation experiments of
chromium-contaminated soil by soil electrokinetic, leaching and electrokinetic
leaching were systematically carried out.
The
temperature-controlled electric remediation device was used to carry out the
remediation experiment on chromiumcontaminated soft soil. The factor that had
the greatest influence on the removal rate of Cr (VI) in the contaminated soil
was voltage, followed by temperature and the initial concentration of Cr (VI)
in the soil. Under the applied voltage of 36V, the removal rate of Cr (VI) in
each group was more than 96%, and the highest removal rate of Cr (total) in the
soil was 76%.
After
adopting the improvement measure of increasing the cross-sectional area of the
conductive part of the bottom surface of the soil column, the electric combined
leaching remediation experiment was carried out on the self-made chromium
contaminated soft soil. The study shows that after the experiment, the removal
rates of Cr (Ⅵ) and Cr (total) in the
soil column are improved correspondingly: the removal rate of Cr (VI) in the
soil column of each test group is more than 97%.At low voltage and 15V, the
removal rates of Cr (Ⅵ) and Cr (total) in the
test group containing oxalic acid, sodium dodecylbenzene sulfonate and citric
acid reached 99.6% and 89.4%, 99.2% and 89.6%, 98.1% and 80%, respectively.
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