Remediation of Cr(VI)-Contaminated Acid Soil Using a

Research Article pubs.acs.org/journal/ascecg

Remediation of Cr(VI)-Contaminated Acid Soil Using a Nanocomposite Dongfang Wang,∥,†,§ Wei Guo,∥,†,§ Guilong Zhang,†,§,‡ Linglin Zhou,†,§ Min Wang,†,§ Yujuan Lu,*,⊥ Dongqing Cai,*,†,§,‡ and Zhengyan Wu*,†,§,‡

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Key Laboratory of Ion Beam Bioengineering, Hefei Institutes of Physical Science, Chinese Academy of Sciences, 350 Shushanhu Road, Hefei, Anhui 230031, People’s Republic of China § University of Science and Technology of China, No. 96 Jinzhai Road, Hefei, Anhui 230026, People’s Republic of China ⊥ College of Chemistry and Environmental Engineering, Shenzhen University, 3688 Nanhai Ave, Shenzhen,Guangdong 518060, People’s Republic of China ‡ Key Laboratory of Environmental Toxicology and Pollution Control Technology of Anhui Province, Hefei Institutes of Physical Science, Chinese Academy of Sciences, 350 Shushanhu Road, Hefei, Anhui 230031, People’s Republic of China S Supporting Information *

ABSTRACT: In this work, an acid soil remediation agent (ASRA) was developed based on a nano composite composed of anhydrous sodium carbonate (ASC), attapulgite (ATP), and straw ash-based biochar and biosilica (BCS), wherein ASC was supported by ATP, and the resulting ASC-ATP was loaded into the micro/nano pores of BCS. ASRA with a porous nanonetworks structure could efficiently inhibit the loss of Ca2+ and increase the pH of the acid soil. Meanwhile, it was shown that the ASRA was effective on acid soil in both lateral and vertical directions. Additionally, because of the pH improvement and the adsorption capacity, ASRA could significantly decrease the migration and contamination of hexavalent chromium (Cr(VI)). Additionally, the pot experiment proved that ASRA could effectively reduce the uptake of Cr(VI) by corn, and exhibit a positive effect on the height, chlorophyll content in the leaves and the root length of corn. Therefore, this work may provide a fundamental and facile method on the remediation of Cr(VI)-contaminated acid soil. KEYWORDS: Acid soil, Remediation, Cr(VI), Attapulgite, Biochar, Biosilica

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INTRODUCTION Acid soil (AS) occupies approximately 30% of the world’s icefree land and has become a major agricultural problem all over the world.1 AS can commonly lead to phosphorus deficiency, reduced productivity, and ionization of heavy metals which can be absorbed by crops and then human beings, causing a series of diseases.1−6 Generally speaking, the reasons of soil acidification (SA) mainly include acid rain, overuse of fertilizer, loss of cations, and so on, wherein the loss of cations is supposed to be the dominant one.1 Therefore, controlling the loss of cations in soil is a promising method for the remediation of SA. Until now, several approaches including physical (soil replacement), biological (plant remediation), and chemical (biochar, lime) methods have been developed to remediate SA.7−9 Therein, the former two methods were difficult to be applied because of their high cost and long duration. On the contrary, chemical methods especially those of lime (CaCO3) were widely used attributing to the relatively low cost and simple procedure. Although the application of lime could increase the soil pH to a certain extent, it was not able to © 2017 American Chemical Society

control the loss of cations and thus could not remediate SA completely.1 Therefore, it is important to develop a new kind of remediation agent which can not only improve the pH of soil but also reduce the loss of cations. In this study, an acid soil remediation agent (ASRA) was developed using a nanocomposite made up of anhydrous sodium carbonate (ASC), attapulgite (ATP), and straw ashbased biochar and biosilica (BCS). Herein, Ca2+ was chosen as the representative cation because of its high content and migration behavior in soil.10 Meanwhile, hexavalent chromium (Cr(VI)) was used as the target heavy metal herein because it is a typical heavy metal in acid soil and has been classified as one of the most toxic heavy metals because of its acute toxicity and potential carcinogenicity for living organisms.11−13 ATP, an environment-friendly natural clay material consisting of plenty of nanorods, could act as a nanocarrier for ASC due to its high Received: October 25, 2016 Revised: December 27, 2016 Published: January 12, 2017 2246

DOI: 10.1021/acssuschemeng.6b02569 ACS Sustainable Chem. Eng. 2017, 5, 2246−2254

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. (A) Schematic diagram of the leaching system. (B) Influence of ASRA (0.3 g) with different WBCS:WATP:WASC of (a) 0:0:0, (b) 3:3:3, (c) 1:2:3, (d) 2:1:3, and (e) 0:3:3 on the leaching loss of Ca2+ from soil with an initial CaCl2 concentration of 0.037 mg/g. (C) Influence of OASRA amount on the leaching loss of Ca2+ from soil with an initial CaCl2 concentration of 0.037 mg/g. (D) Influence of initial CaCl2 concentration on the leaching loss of Ca2+ from soil with OASRA amount of 0.3 g. (E) pH of the top soil: (a and b) before and after leaching without OASRA; (c) after leaching with OASRA (0.3 g). (F) Digital photographs illustrating the leaching loss of Ca2+ in perlite column without (a) or with (b) OASRA (0.1 g), wherein the brown color reflects the Ca2+ concentration.

specific surface area and nanonetworks structure. 14−18 Furthermore, BCS was used here as a microcarrier for ATPASC due to its huge amount (at least 500 thousand ton/y in China), renewable property, and micro/nanoporous structure.19−22 The fabricated ASRA could effectively decrease the Ca2+ loss in soil, increase the soil pH, inhibit the acidification rate of soil, and, thus, reduce the leaching loss of Cr(VI). Therefore, this work provides a low cost (∼100 dollar/ton), high efficiency, environmentally friendly, and facile approach to remediate Cr(VI)-contaminated AS.

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Preparation of ASRA. ASRA composites with different weight ratios (WBCS:WATP:WASC) were fabricated by mixing BCS, ATP, and ASC powders. The optimal ASRA composite with WBCS:WATP:WASC = 1:2:3 was obtained through Ca2+ leaching experiment and designated as OASRA (pH 10.5). Leaching Behavior Investigation of Ca2+ and CaCrO4 in AS. First of all, 100 mL of HCl (0.03 mol/L) was added to 200 g of dry sand (50−100 mesh), and the resulting sand was dried at 50 °C overnight to obtain acid sand. Then, the dry acid sand (50−100 mesh) was mixed with soil (50−100 mesh) at a certain weight ratio (Wsand/ Wsoil = 7:3), and the resulting sand−soil mixture (20 g, pH 5) was put into a centrifuge tube (60 mL) with a hole (diameter of 2 mm) at the bottom. Therein, a filter paper was placed on the bottom of the centrifuge tube to hold the sand−soil mixture. ASRAs were evenly spread on the surface of the sand−soil mixture with different weight ratios and added amounts. After that, to investigate the leaching performance of Ca2+, a different amount of CaCl2 was mixed with 10 g of the sand−soil respectively, and then the CaCl2−sand−soil mixture was placed on the top of the system. Meanwhile, to investigate the leaching performance of Cr(VI), 1.5 mg of CaCrO4 was added to the CaCl2−sand−soil mixture, and then the CaCrO4−CaCl2−sand−soil mixture was placed on the top of the system. The leachate was collected after being sprayed with 40 mL of deionized water on the top of the system, and then centrifuged for 5 min (4500 rpm). Finally, the

MATERIALS AND METHODS

Materials. ATP powder (100−200 mesh) was purchased from Mingmei Co, Ltd. (Anhui, China). BCS (approximately 35% SiO2 and 60% carbon, average particle size of 10 μm) was purchased from Kaidi Electric Power Co., Ltd. (Wuhan, China). CaCrO4 and other chemicals of analytical reagent grade were provided by Sinopharm Chemical Reagent Company (Shanghai, China). Deionized water was used in all the experiments except the pot experiments. Corn seeds were purchased from DuPont Pioneer Co. (Liaoning, China). Soil used in the pot experiments was taken from Dongpu Island (Hefei, China). 2247


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Figure 2. (A and C) Schematic diagrams of the systems to investigate the remediation effects of OASRA (7.0 g) on AS in lateral and vertical directions. (B and D) Effect of OASRA on soil pH in lateral and vertical directions.

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concentrations of Ca2+ and Cr(VI) in the leachate were measured.23,24 All experiments were performed in quintuplicate. Measurement of the pH of the Top Soil. After leaching, 5 g of sand-soil mixture was put in 25 mL of deionized water, and then the resulting system was shaken for 24 h. After centrifuging (4500 rpm) for 5 min, the pH of the supernatant was measured. This experiment was performed in quintuplicate. Visual Investigation of Ca2+ Leaching. First, 0.8 g of perlite and 0.1 g of OASRA were mixed evenly and then the mixture was added to a colorimetric tube (25 mL). Then 6 mL of NaOH (0.01 mol/L) aqueous solution and 4 mL of calconcarboxylic acid (W/W, 0.05%) were added to the tube. After that, 1 mL of CaCl2 (100 μg/mL) aqueous solution was added to the tube from the top of the system. Finally, the leaching behavior of Ca2+ could be investigated through the color of the solution in the bottom, wherein the darker brown color means higher Ca2+ leaching amount.23 Pot Experiments. AS (pH 4.75; 130 g) was placed in a pot (trapezoidal shape, height of 7 cm, and diameter of 10 cm (top) and 7 cm (bottom)) and then OASRAs with different amounts (0.00, 0.10, 0.50, and 1.00 g) were spread on the surface of AS. After that, 40 g of AS was placed on OASRA and two corn seeds were planted in the AS. Finally, 100 g of AS was mixed with 7.9 mg of CaCrO4 and the resulting mixture was put on the top of the system. The system was placed in a greenhouse at 20 °C, and water (50 mL) was sprayed evenly to the system every 3 days. All experiments were performed in quintuplicate. Characterizations. The morphology was measured using a scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (Sirion 200, FEI Co., USA). The structure and compositions analyses were conducted on a TTR-III X-ray diffractometer (XRD) (Rigaku Co., Japan) and a Fourier transform infrared (FTIR) spectrometer (iS10, Nicolet Co., USA). The thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) were carried out by a thermogravimetric analyzer (Q5000IR, TA Co., USA). The concentrations of Ca2+ and Cr(VI) were detected on a UV−vis spectrophotometer (UV 2550, Shimadzu Co., Japan) at 612 and 540 nm, respectively. The chromium content in corn was measured by an inductively coupled plasma-optical emission spectrometer (ICP-OES) (Optima 7300 DV, PerkinElmer Co., USA). The chlorophyll contents in corn leaves were determined by a chlorophyll meter (Konica Minolta Investment Ltd., Japan).

RESULTS AND DISCUSION Effects of ASRA on Ca2+ Loss and Soil pH. The influence of ASRA with different weight ratios on the leaching loss of Ca2+ in AS (pH 5) was investigated to obtain the optimal ASRA (Figure 1A). As shown in Figure 1B, all the ASRA samples could effectively immobilize Ca2+ and thus decreased the loss of Ca 2 + through leaching. Therein, the ASRA with WBCS:WATP:WASC of 1:2:3 displayed the highest capacity to control the leaching loss of Ca2+, indicating that the optimal weight ratio (WBCS:WATP:WASC) for ASRA was 1:2:3. The controlling performance of OASRA on the leaching loss of Ca2+ could be directly seen in the perlite column shown in Figure 1F. The effect of added amount of OASRA on the Ca2+ migration performance was also investigated. As shown in Figure 1C, Ca2+ concentration in the leachate decreased significantly with the increasing OASRA amount at first (0.3 g), illustrating that the optimal added amount of OASRA was 0.3 g. Additionally, Ca2+ leaching loss increased obviously with the increasing initial Ca2+ concentration in the AS especially in the range of 40−50 mg/L (Figure 1D), which was probably because the initial Ca2+ concentrations (>40 mg/ L) in AS were beyond the controlling ability of OASRA. Besides, the effect of OASRA on the pH of the top soil was investigated (Figure 1E), and the result indicated that OASRA could effectively increase the pH (from 4.93 to 7.11) of the top soil after leaching compared with water alone (from 4.93 to 5.41). This was probably because the high immobilization effect of OASRA on Ca2+ could facilitate the reduction of H+ amount in the top soil.1 The influence of OASRA on pH of soil in different distance from OASRA layer was also investigated. As shown in Figure 2, in both lateral (Figure 2A and B) and vertical (Figure 2C and D) directions, the soil pH decreased gradually from approximately 8.5 (in distance of 0 cm) to 6.0 (in distance of 12 cm) with the increasing distances from the OASRA layer. This result indicated that, under the condition in this work, the effective distances of OASRA on AS pH in lateral (both 2248


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Figure 3. SEM images of (a) ATP, (b) ASC, (c) BCS, (d) ASC−BCS (WASC:WBC = 3:1), (e) BCS−ATP (WBCS:WATP = 1:2), (f) ATP−ASC (WATP:WASC = 2:3), and (g) OASRA. (h) SEM image of OASRA with a higher magnification. (I−III) Arrows note ATP, BCS, and ASC.

leftwards and rightwards) and vertical (downward) directions were both approximately 12 cm. Mechanism Investigation of OASRA on the Immobilization of Ca2+. Naturally, ATP consisted of plenty of nanorods which tended to aggregate to form numerous bunches because of the nanoscale effect (Figure 3a).14 These ATP rods and the bunches cross-linked with each other to form a great many of micronano pores, which was favorable for the adsorption of ASC (noted by arrow III) in the pores. Meanwhile, the adsorbed ASC could probably increase the zeta potential (absolute value) and thus enhance the dispersion of ATP, and then the isolated ATP rods (noted by arrow I) could cross-link with each other to form nanonetworks structure (Figure 3f). Furthermore, the ATP, ASC (Figure 3b), and ATP−ASC could be loaded in the micro pores of BCS (Figure 3c) to form the ATP−BCS (Figure 3e), ASC−BCS (Figure 3d), and ATP−ASC−BCS (Figure 3g and h) complexes. Because of the porous nanonetworks structure,

the ATP−ASC−BCS complex possessed a high porosity and BET specific surface area (Figure 4A). Consequently, after being added to AS, the ATP−ASC−BCS complex could probably immobilize the Ca2+ in soil through the adsorption effect of ATP−BCS with porous nanonetworks structure. Figure 4A illustrated the pore size distribution curve and nitrogen adsorption−desorption isotherms of OASRA. The results indicated that OASRA possessed plenty of pores with a size distribution of 5−75 nm (inset of Figure 4A, BJH method) and a high BET specific surface area of 43.28 m2/g. Such porous structure and high specific surface area played key roles in the adsorption of Ca2+ and Cr(VI) by OASRA. FTIR measurements were carried out to further analyze the interactions in OASRA system. As shown in Figure 4Ba, b, and f, ATP−ASC possessed the characteristic peaks (1100 cm−1 for stretching vibration of Si−O−Si, 467 cm−1 for translational vibration of −OH, and 1440 cm−1 for stretching vibration of CO32−), displaying that ATP successfully combined with ASC.5 2249


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Figure 4. (A) N2 adsorption−desorption isotherms of OASRA. (inset) Pore size distribution of OASRA. (B) FTIR spectra of (a) ATP, (b) ASC, (c) BCS, (d) ASC−BCS (WASC:WBCS = 3:1), (e) BCS−ATP (WBCS:WATP = 1:2), (f) ATP−ASC (WATP:WASC = 2:3), and (g) OASRA. (C) XRD patterns of OASRA before (a) and after (b) leaching. (D) TGA (black) and DTA (blue) curves of OASRA.

Figure 5. (A) Schematic diagram of the leaching system. (B) Influence of leaching times on the leaching loss of Cr(VI) with OASRA (0.3 g) and CaCl2 (27.8 mg/g). (C and D) Influence of OASRA amount on the leaching loss of Cr(VI) and the top soil pH after leaching with and without CaCl2 (27.8 mg/g) in the top soil.

Furthermore, the comparative strength of the peaks of ATP− ASC (1440 cm−1 for CO32− stretching vibration) become

weakened compared with ASC. The peak of ATP−ASC (1100 cm−1 for stretching vibration of Si−O−Si) blue-shifted and the 2250


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Figure 6. (A−C) SEM images of CaCrO4, OASRA, and OASRA after leaching (designated as OASRA−Cr(VI)): (I) ATP, (II) BCS, (III) ASC, (IV) Cr(VI). (D) Schematic diagram of the structure of OASRA−Cr(VI). (E) SEM-EDX spectrum of OASRA−Cr(VI). (F) FTIR spectra of (a) CaCrO4, (b) OASRA, and (c) OASRA−Cr(VI).

peak (467 cm−1 for translational vibration of −OH) red-shifted compared with ATP. These were probably because hydrogen bonds formed between ATP (−OH) and ASC (CO32−). As shown in Figure 3Ba, c, and e, BCS-ATP possessed the characteristic peaks (467 cm−1 for translational vibration of −OH and 1030 cm−1 for stretching vibration of Si−O).21 The peaks (467 cm−1 for translational vibration of −OH, 1030 cm−1 for stretching vibration of Si−O) blue-shifted compared with ATP and BCS. This was probably because hydrogen bonds formed between ATP (−OH) and BCS (Si−O). Figure 4Bb−d displayed that the strength of peak of ASC-BCS (1030 cm−1 for stretching vibration of Si−O) weakened and the peak (1440 cm−1 for stretching vibration of CO32−) intensified compared with ASC. As shown in Figure 4Bg, new peaks were not observed in OASRA, suggesting that chemical reaction did not occur obviously during the preparation process of ATP−ASC− BCS, and the interaction among ATP, ASC, and BCS was mainly a physical process. XRD measurement was carried out to analyze the crystal structure of OASRA. As shown in Figure 4Ca, the characteristic peaks of ATP, ASC, and BCS were found in the spectrum of OASRA, indicating that they combined with each other successfully. The left shift of the characteristic peaks of ATP in OASRA after leaching did not occur compared with OASRA before leaching, indicating that no intercalation occurred between ASC and ATP.25 In other words, ASC was mainly loaded in the nanonetworks of ATP, which was in accordance

with the SEM image in Figure 3h. Additionally, after leaching in soil, the relative strength of the characteristic peaks of ATP and ASC in OASRA became weakened compared with the initial OASRA, and meanwhile, the characteristic peaks of CaCO3 were found in the XRD spectrum (Figure 4Ca and Cb), proving the production of CaCO3 through precipitation reaction 1 between CaCl2 and ASC. That was to say, the Ca2+ could also be immobilized in soil through the precipitation effect of OASRA. Ca 2 + + CO32 − = CaCO3

(1)

Besides, TG-DTA analysis was conducted to evaluate the actual weight ratio and the thermal stability of OASRA. As shown in Figure 4D, three distinct regions of weight loss were observed in the TG-DTA curve. The initial two weight loss regions (36.14−140.31 and 140.31−261.61 °C) were probably corresponding to water. The third weight loss region (261.61− 586.61 °C) was probably because of the degradation of organic matter in ATP.25 The result suggested that OASRA possessed a relatively high thermal stability. Influence of OASRA on Cr(VI) in AS. Besides, the influence of OASRA on the leaching loss of Cr(VI) from the soil upon OASRA layer was investigated (Figure 5A). It could be clearly seen in Figure 5B that OASRA could efficiently decrease the leaching loss of Cr(VI) from the top soil, and the leaching loss amount decreased dramatically with leaching times. Additionally, Figure 5C displayed that the leaching loss 2251


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Figure 7. (A) Schematic diagram of the pot experiment system. (B) Heights of corns treated with different samples. (C) Chlorophyll content in the leaves of corn treated with different samples. (D) Length of corns root treated with different samples. (E) Digital photographs (black rectangles note the yellow parts of corn leaves): (a) normal soil (pH = 5.35), (b) acid soil (pH = 4.64), (c, f, and g) acid soil + CaCrO4 (7.9 mg), (d) acid soil + CaCrO4 (7.9 mg) + OASRA (0.2 g), (e) acid soil + CaCrO4 (7.9 mg) + OASRA (0.5 g).

CaCl2 was not added to the sand. As shown in Figure 6, Cr(VI) (Figure 6A) was adsorbed in the ATP−ASC nanonetworks and meanwhile the resulting ATP−ASC−Cr(VI) (noted by arrows I, III, and IV, respectively in Figure 6C) complex was loaded in the micropores of BC (noted by arrow II in Figure 6B and C) to obtain OASRA−Cr(VI). The OASRA−Cr(VI) possessed a nanonetworks structure (Figure 6D) and a high spatial scale, resulting in a low migration behavior through the soil. As such, the OASRA could efficiently control the migration of Cr(VI) in soil and thus lower the environment risk. To further investigate the interactions of OASRA with Cr(VI), SEM-EDX, and FTIR measurements were performed. As shown in Figure 6E, the characteristic peaks of Cr(VI) appeared in the EDX spectrum of the OASRA−Cr(VI), suggesting that Cr(VI) was adsorbed by OASRA successfully. As shown in Figure 6F, the characteristic peaks of CaCrO4 (888 cm−1 for Cr−O vibration) (Figure 6Fa) and ATP (3470 cm−1 for stretching vibration of O−H) (Figure 6Fb) became weakened in OASRA−Cr(VI) (Figure 6Fc),27 which was probably because hydrogen bonds formed between CaCrO4 (Cr−O) and ATP (−OH). No new peaks were observed in OASRA−Cr(VI), indicating that chemical reaction did not

amount of Cr(VI) significantly decreased with the increase of OASRA amount. Moreover, in the presence of CaCl2, the leaching loss amount of Cr(VI) was significantly lower compared with the absence of CaCl2, which was probably attributed to the higher soil pH in the presence of CaCl2 (Figure 5D). Actually, soil pH had a great effect on the solubility of Cr(VI). At soil pH of 1.92−4.07, Cr(VI) displayed a high solubility due to reaction 2.26 At soil pH of 5.48 to 8.5, the Cr(VI) displayed a lower solubility attributing to reaction 3.26 As shown in Figure 5D, the pH of the top soil increased with the increasing OASRA amount, and the pH at the presence of CaCl2 was higher than that without CaCl2, which was probably because of the immobilization effect of OASRA on Ca2+. 2CaCrO4 + 2H+ = 2Ca 2 + + Cr2O7 2 − + H 2O

(2)

2Ca 2 + + Cr2O7 2 − + 2OH− = 2CaCrO4 + H 2O

(3)

Mechanism Investigation of OASRA on the Remediation of Cr(VI). To reveal the mechanism of OASRA on the migration of Cr(VI), the morphologies of OASRA before and after leaching were observed, wherein, to make a simple system, 2252


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technology may efficiently reduce the Cr(VI) amount in the soil around crops roots and thus the absorption amount of Cr(VI) by crops. Therefore, this technology may have a promising application prospect.

occur obviously in this system and the main interaction was a physical process. In a word, Cr(VI) was adsorbed in the porous nanonetworks structure of OASRA mainly through hydrogen bonds. Effects of OASRA on Corn. Cr(VI) in soil could influence the growth of crops because they tended to be accumulated in plants and induced crops to generate toxic substances harmful to metabolism.28 Herein, pot experiments were performed to obtain the remediation effect of OASRA on Cr(VI) in AS using corn as the model crop (Figure 7A). As shown in Figure 7B−D, both AS alone and AS added with Cr(VI) showed harmful effects on the corn growth within the seedling stage (21 days after seeding), causing lower height, chlorophyll content in the leaves and roots length compared with corns in normal soil, and the negative effects of AS with Cr(VI) were much higher than those of AS alone. It was noteworthy that, as shown in Figure 7E, several yellow spots appeared on the leaves of corn in AS added with Cr(VI), which was probably because of the harmful effect of Cr(VI). However, OASRA could significantly increase the heights, chlorophyll content, and roots length and also decrease the yellow spots on the leaves, wherein this effect became higher with the increase of OASRA amount. These results suggested that OASRA possessed a high ability to remediate AS and Cr(VI) and thus could greatly facilitate the growth of corns in AS. To further investigate the influence of OASRA on corn, on the 21st day after seeding, the total Cr amount in the corn was measured. As shown in Figure S1, the amount of Cr in the stems, leaves, and roots obviously decreased with the increasing OASRA amount, indicating that OASRA could efficiently decrease the uptake of Cr by corn, which was probably attributed to the high controlling ability of OASRA on the move and activity of Cr in AS. Therefore, OASRA could be used as a promising agent to remediate Cr in AS to decrease contamination risk in crops. As for the practical application of this technology, the OASRA can be evenly added onto the surface of a Cr(VI)contaminated AS field. Then the soil is ploughed using a rotary tiller to make the OASRA locate in the soil as a layer about 20 cm deep from the soil surface (Figure 8). The OASRA layer can act as a filter to control the leaching of Ca2+ and Cr(VI), and reduce the solubility and migration of Cr(VI). As a result, this

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CONCLUSIONS This work describes a fundamental and facile approach of remediating the Cr(VI) contamination in AS using a remediation agent named ASRA which was consisted of ATP, BCS, and ASC. The ASRA possessed a porous nanonetworks structure and could efficiently control the leaching loss of Ca2+, improve the soil pH, and thus reduce the move and activity of Cr(VI) in AS through hydrogen bonds. The pot experiment suggested that this approach could significantly inhibit the negative effects of Cr(VI) on the growth of corn in AS.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b02569. Total amounts of Cr in corn roots, stems, and leaves (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*Tel.: +86-551-65595012. Fax: +86-551-65595012. E-mail: [email protected] (Y.L.). *Tel.: +86-551-65595143. Fax: +86-551-65595012. E-mail: [email protected] (D.C.). *Tel.: +86-551-65595012. Fax: +86-551-65595012. E-mail: [email protected] (Z.W.). ORCID

Zhengyan Wu: 0000-0002-8142-1848 Author Contributions ∥

D.W. and W.G. are cofirst authors.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge financial support from the National Natural Science Foundation of China (No. 21407151), the Key Program of Chinese Academy of Sciences (No. KSZD-EW-Z022-05), the Youth Innovation Promotion Association of Chinese Academy of Sciences (No. 2015385), the Grant of the President Foundation of Hefei Institutes of Physical Science of Chinese Academy of Sciences (No. YZJJ201502), and the Science and Technology Service Programs of Chinese Academy of Sciences (Nos. KFJ-SW-STS-143-4, KFJ-EW-STS-083, and KFJ-EW-STS-067).

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REFERENCES

(1) Guo, J. H.; Liu, X. J.; Zhang, Y.; Shen, J. L.; Han, W. X.; Zhang, W. F.; Christie, P.; Goulding, K. W. T.; Vitousek, P. M.; Zhang, F. S. Significant acidification in major Chinese croplands. Science 2010, 327 (5968), 1008−1010. (2) Delhaize, E.; Ryan, P. R. Aluminum toxicity and tolerance in plants. Plant Physiol. 1995, 107 (2), 315−321. (3) Von Uexküll, H. R.; Mutert, E. Global extent, development and economic impact of acid soils. Plant Soil 1995, 171 (1), 1−15. (4) Matsuyama, N.; Saigusa, M.; Sakaiya, E.; Tamakawa, K.; Oyamada, Z.; Kudo, K. Acidification and soil productivity of allophanic

Figure 8. Practical application of OASRA in a field. 2253


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Remediation of Cr(VI)-Contaminated Acid Soil Using a

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