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Accepted Manuscript Title: Immediate remediation of heavy metal (Cr(VI)) contaminated soil by high energy electron beam irradiation Author: Jing Zhang Guilong Zhang Dongqing Cai Zhengyan Wu PII: S0304-3894(14)00907-8 DOI: http://dx.doi.org/doi:10.1016/j.jhazmat.2014.11.007 Reference: HAZMAT 16379 To appear in: Journal of Hazardous Materials Received date: 29-6-2014 Revised date: 15-9-2014 Accepted date: 12-11-2014 Please cite this article as: Jing Zhang, Guilong Zhang, Dongqing Cai, Zhengyan Wu, Immediate remediation of heavy metal (Cr(VI)) contaminated soil by high energy electron beam irradiation, Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2014.11.007 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Page 1: Immediate remediation of heavy metal (Cr(VI)) contaminated soil by high energy electron beam irradiation

Accepted Manuscript

Title: Immediate remediation of heavy metal (Cr(VI))contaminated soil by high energy electron beam irradiation

Author: Jing Zhang Guilong Zhang Dongqing Cai ZhengyanWu

PII: S0304-3894(14)00907-8DOI: http://dx.doi.org/doi:10.1016/j.jhazmat.2014.11.007Reference: HAZMAT 16379

To appear in: Journal of Hazardous Materials

Received date: 29-6-2014Revised date: 15-9-2014Accepted date: 12-11-2014

Please cite this article as: Jing Zhang, Guilong Zhang, Dongqing Cai,Zhengyan Wu, Immediate remediation of heavy metal (Cr(VI)) contaminatedsoil by high energy electron beam irradiation, Journal of Hazardous Materialshttp://dx.doi.org/10.1016/j.jhazmat.2014.11.007

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

Page 2: Immediate remediation of heavy metal (Cr(VI)) contaminated soil by high energy electron beam irradiation

Immediate remediation of heavy metal (Cr(VI)) contaminated soil by high

energy electron beam irradiation

Jing Zhang,†,‡ Guilong Zhang,†,‡ Dongqing Cai,*,†,‡ and Zhengyan Wu*,†,‡

†Key Laboratory of Ion Beam Bioengineering, Hefei Institutes of Physical Science,

Chinese Academy of Sciences, Hefei 230031, People’s Republic of China

‡Bioenergy Forest Research Center of State Forestry Administration, Hefei 230031,

People’s Republic of China

*Corresponding authors. Tel.: +86-551-65595012; fax: +86-551-65591413.

E-mail addresses: [email protected] (D. Cai), [email protected] (Z. Wu).

Highlights

• An immediate remediation method for Cr(VI) contaminated soil (CCS) was

developed.

• High energy electron beam (HEEB) irradiation could reduce Cr(VI) in CCS to

Cr(III).

• This effect was attributed to electrons, hydrated electrons and reductive radicals.

• This remediation method was effective, environmentally friendly and low-cost.

Abstract

This work developed an immediate and high-performance remediation method for

Cr(VI) contaminated soil (CCS) using high energy electron beam (HEEB) irradiation.

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The result indicated that, compared with γ-ray irradiation, HEEB irradiation displayed

a significant reduction efficiency on Cr(VI) in CCS to Cr(III) with substantially lower

toxicity, which was mainly attributed to the reduction effects of electrons, hydrated

electrons and reductive radicals generated in the irradiation process of HEEB. This

work could provide a one-step and effective method for the remediation of heavy

metal contaminated soil (HMCS).

Keywords: High energy electron beam irradiation, Cr(VI) contaminated soil,

Reduction, Reductive radicals

1.

2.

3.

4. Introduction

Discharging industrial waste containing heavy metals into water and soil could

cause severe environment contamination. Moreover, heavy metals could enter the

dining tables of households and restaurants through the crops grown in contaminated

fields. Soil contamination by heavy metal has caused serious public concern and

anxiety on food safety [1-3]. Ensuring the soil security is of crucial importance for a

safe food supply. It is time to develop a high-performance remediation approach for

heavy metal contaminated soil (HMCS) to improve soil quality and maintain soil

health.

Until now, several remediation approaches for HMCS have been reported mainly

through physical (electrical enrichment and washing), chemical (reduction, adsorption

and inactivation) and biological (plant enrichment) methods [4-6]. Although these

methods could resolve the HMCS problem to various degrees, the procedure of the

physical method was usually relatively complex with high cost, the chemical methods

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could introduce secondary pollution, and the biological method needed rather long

time. Therefore, it was necessary to develop a low-cost, high-efficiency and

environmentally-friendly approach for the remediation of HMCS. In this case, a new

technology, high energy electron beam (HEEB) irradiation, was introduced to resolve

this problem.

Because of the high sterilization efficiency, low cost and facile operation, HEEB

irradiation has been applied widely in food fresh keeping [7]. In addition, HEEB

irradiation was also used in the remediation of heavy metal contaminated water [8].

However, HEEB was rarely applied to treat the heavy metals in soil. Hence, we

attempted herein to investigate the remediation performance of HEEB irradiation on

HMCS in consideration of its industrial scale treatment capacity and

environmentally-friendly property.

In this work, chromium was selected as the mode heavy metal contaminant of soil,

because chromium is one of the extremely toxic heavy metals in soil mainly attributed

to the discharge of chromium-containing waste and waste-water from ore refining,

steel and alloys production, metal plating, tannery, wood preservation, pigmentation

and so on [9]. The most stable states of chromium in soil were Cr(III) and Cr(VI),

wherein Cr(VI) displayed higher toxicity, carcinogenicity, solubility and mobility and

thus higher health risk for humans compared with Cr(III) [10-12]. Hence, the

reduction of Cr(VI) to Cr(III) using reduction agents, as a promising approach, is

attracting more and more attention for the remediation of Cr(VI) contaminated soil

(CCS) [13-15]. However, this method required quantities of chemical reagents, which

could probably result in secondary pollution, high cost and thus small application

prospect [13, 14]. Therefore, it is necessary to develop a new Cr (VI) reduction

approach with simple procedure, low cost, high efficiency, environmentally-friendly

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property and industrial-scale treatment capacity.

Here, HEEB irradiation was used as a facile approach for reduction of Cr(VI) to

Cr(III) in soil, and it was found that this method could effectively and immediately

reduce Cr(VI) to Cr(III) in soil. The mechanism was also investigated and the results

indicated that both electrons and radicals played key roles in the reduction process.

Additionally, the influences of the initial Cr(VI) concentration and the HEEB

irradiation fluency on the reduction performance were also studied. This work is

attempting to provide an immediate and promising approach for the reduction of

Cr(VI) in soil, which could be favorable for the treatment of the other heavy metal

contaminants in soil.

5. Materials and methods

5.1. Materials

K2Cr2O7 and other chemicals were of analytical reagent grade and purchased from

Sinopharm Chemical Reagent Company (Shanghai, China). Deionized water was used

throughout this work.

5.2. Cr(VI) contaminated soil sample preparation

Soil (0-20 cm depth) was collected from the Dongpu Island in Anhui province of

China. Then it was ground to 100-150 mesh after air drying. Cr(VI) (actually the

K2Cr2O7) aqueous solution (2 g) with a certain concentration (60, 80, 100 or 120 ppm)

was added to the resulting soil (2 g) in a centrifuge tube (10 mL) to obtain the CCS

sample with Cr(VI) initial concentration of 30, 40, 50, or 60 ppm.

5.3. HEEB or γ-ray irradiation

HEEB irradiation of Cr(VI) aqueous solution (100 ppm) or CCS samples in sealed

centrifuge tubes was carried out using the HEEB accelerator (10 MeV and 10 kW)

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(IHI10, IHI Co., Japan) with absorbed doses of 10, 20, 30 and 40 kGy detected by

dosimeter of silver dichromate at room temperature. Afterwards, the concentration of

Cr(VI) remained in the solution or soil was determined using a UV-Vis

spectrophotometer (UV 2550, Shimadzu Co., Japan) at a wavelength of 520 nm by

diphenylcarbazine (DPC) method [16]. All experiments were performed in triplicate.

In addition, γ-ray irradiation on the CCS sample with an initial concentration of

50 ppm in a sealed centrifuge tube (10 mL) was performed using a cobalt-60 radiation

source with absorbed doses of 10 and 20 kGy.

5.4. Preparation and addition of DMSO

In order to investigate the influence of reductive radicals on the reduction

performance of HEEB, 0.2 mL of dimethylsulfoxide (DMSO) aqueous solution with

concentration of 20, 40, 200, or 700 µL/L, as a reductive radical scavenger, was added

to the CCS samples respectively before HEEB irradiation. After that, their reduction

efficiencies were determined compared with the one without DMSO.

6. Results and discussion

6.1. Reduction performance investigation

To obtain the reduction performance of HEEB irradiation on Cr(VI) in soil, the

reduction performance in aqueous solution was investigated firstly, as Cr(VI) exists in

soil is mainly aqueous Cr(VI). As shown in Fig. 1, with the increasing absorbed dose

of HEEB, the reduction efficiency (RE) of HEEB irradiation on Cr(VI) in aqueous

solution increased initially (<30 kGy), reaching the maximum value (approximately

97%) at 30 kGy, and then decreased (>30 kGy). In other words, 30 kGy is the

optimum absorbed dose of HEEB for the reduction of Cr(VI) in aqueous solution.

This result indicated that HEEB possessed a high reduction ability on Cr(VI) in

aqueous solution, and is feasible to reduce the Cr(VI) in soil.

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The reduction performance of HEEB on Cr(VI) in CCS was further investigated. It

can be seen in Fig. 2, with the increase of absorbed dose of HEEB, the RE on Cr(VI)

in CCS increased initially (<30 kGy) and then decreased (>30 kGy), which was

similar to that in aqueous solution. It is worth noting that the maximum value of RC

(89%) in CCS (Fig. 2A) was lower than that (94%) in aqueous solution with Cr(VI)

initial concentration of 60 ppm (Fig. 2B), which was probably because of the

resistance effect of soil colloidal particles on the HEEB lowering the contact

probability between electrons and Cr(VI). Interestingly, the RE of HEEB generally

increased with the initial concentrations of Cr(VI) in CCS, which was probably

attributed to the cascade effect of HEEB or some secondary particles such as hydrated

electrons (eaq-) (e- + n H2O = eaq

-) [8], and reductive radicals such as hydroxyl radicals

generated from water radiolysis during the irradiation process. Thus higher initial

Cr(VI) concentration was favorable to the cascade effect and resulted in higher RE.

This result demonstrated that HEEB had a significant reduction capacity on the Cr(VI)

in CCS probably with the aid of the reduction effects of electrons and some secondary

particles.

6.2. Mechanism study for the reduction performance of the HEEB irradiation

To obtain the reduction mechanism of HEEB on Cr(VI) in CCS, the reduction

performance of HEEB on Cr(VI) in CCS was investigated compared with γ-ray. It

could be clearly seen in Fig. 3 that the RE of HEEB was rather high, while γ-ray

nearly had no reduction effect on Cr(VI), illustrating that electrons or some secondary

particles other than γ-ray played a key role in the reduction of Cr(VI).

Besides the electrons, reductive radicals (mainly H· and OH·) generated during

the irradiation process could also probably has reduction capacity on Cr(VI) in CCS

[8]. To evaluate the reduction effect of reductive radicals, DMSO as a radical

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scavenger was added to the CCS before irradiation. As shown in Fig. 4, the RE of

Cr(VI) decreased with the increasing DMSO concentration, proving that reductive

radicals could be generated in the irradiation process and possessed a reduction ability

on Cr(VI) to a certain degree.

Based on the preceding analysis, HEEB possessed an immediate and significant

reduction performance on Cr(VI) in CCS through the reduction effects of electrons,

hydrated electrons, and reductive radicals (Fig. 5). To remedy the Cr(VI)

contaminated soil, the soil could be placed on a conveyor and treated by a fixed

HEEB facility as shown in Fig. 5. Of course it is promising to treat a whole field of

Cr(VI) contaminated soil if a mobile HEEB facility is available.

7. Conclusions

In this article, HEEB irradiation, as a remediation approach for HMCS, was used to

treat the Cr(VI) contaminated soil and displayed an immediate and significant

reduction ability from Cr(VI) to Cr(III), so that the toxicity of chromium in soil was

substantially lowered. Electrons, hydrated electrons, and reductive radicals generated

in the irradiation process could probably play key roles in the reduction process. This

work could provide a one-step and effective method for the remediation of heavy

metal contaminated soil.

Acknowledgments

The authors acknowledge financial support from the Key Program of the Chinese

Academy of Sciences (No. KSZD-EW-Z-022-05) and the Scientific and

Technological Project of Anhui Province of China (No. 1206c0805014).

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Figure captions: Fig. 1. Reduction performance of HEEB irradiation on Cr(VI) in aqueous solution

with an initial concentration of 100 ppm.

Fig. 2. (A) Reduction performance of HEEB irradiation on Cr(VI) in CCS with

different initial concentrations; (B) Reduction performance of HEEB irradiation on

Cr(VI) in aqueous solution with an initial concentration of 60 ppm.

Fig. 3. Reduction performance of γ-ray and HEEB irradiation on Cr (VI) in CCS with

an initial concentration of 50 ppm.

Fig. 4. Reduction performance of HEEB irradiation on Cr(VI) in CCS (initial

concentration of 50 ppm) after addition of DMSO aqueous solutions (0.2 mL) with

different concentrations of 0 (a), 20 (b), 40 (c), 200 (d), and 700 µL/L (e).

Fig. 5. Schematic diagram showing the CCS placed on a conveyor system and treated

by a fixed HEEB facility.

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Figures:

Fig. 1

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Fig. 2

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Fig. 3

Fig. 4

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Fig. 5

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