Biochar- and phosphate-induced immobilization of ...

Environ Sci Pollut Res (2014) 21:4665–4674 DOI 10.1007/s11356-013-2423-1

RESEARCH ARTICLE

Biochar- and phosphate-induced immobilization of heavy metals in contaminated soil and water: implication on simultaneous remediation of contaminated soil and groundwater Yuan Liang & Xinde Cao & Ling Zhao & Eduardo Arellano

Received: 14 August 2013 / Accepted: 1 December 2013 / Published online: 19 December 2013 # Springer-Verlag Berlin Heidelberg 2013

Abstract Long-term wastewater irrigation or solid waste disposal has resulted in the heavy metal contamination in both soil and groundwater. It is often separately implemented for remediation of contaminated soil or groundwater at a specific site. The main objective of this study was to demonstrate the hypothesis of simultaneous remediation of both heavy metal contaminated soil and groundwater by integrating the chemical immobilization and pump-and-treat methods. To accomplish the objective, three experiments were conducted, i.e., an incubation experiment was first conducted to determine how dairy-manure-derived biochar and phosphate rock tailing induced immobilization of Cd in the Cd-contaminated soils; second, a batch sorption experiment was carried out to determine whether the pre-amended contaminated soil still had the ability to retain Pb, Zn and Cd from aqueous solution. BCR sequential extraction as well as XRD and SEM analysis were conducted to explore the possible retention mechanism; and last, a laboratory-scale model test was undertaken by leaching the Pb, Zn, and Cd contaminated groundwater through the pre-amended contaminated soils to demonstrate how the heavy metals in both contaminated soil and groundwater were simultaneously retained and immobilized. The incubation experiment showed that the phosphate biochar were effective in

immobilizing soil Cd with Cd concentration in TCLP (toxicity characteristics leaching procedure) extract reduced by 19.6 % and 13.7 %, respectively. The batch sorption experiment revealed that the pre-amended soil still had ability to retain Pb, Zn, and Cd from aqueous solution. The phosphate-induced metal retention was mainly due to the metal–phosphate precipitation, while both sorption and precipitation were responsible for the metal stabilization in the biochar amendment. The laboratory-scale test demonstrated that the soil amended with phosphate removed groundwater Pb, Zn, and Cd by 96.4 %, 44.6 %, and 49.2 %, respectively, and the soil amended with biochar removed groundwater Pb, Zn, and Cd by 97.4 %, 53.4 %, and 54.5 %, respectively. Meanwhile, the metals from both groundwater and soil itself were immobilized with the amendments, with the leachability of the three metals in the CaCl2 and TCLP extracts being reduced by up to 98.1 % and 62.7 %, respectively. Our results indicate that the integrated chemical immobilization and pump-and-treat method developed in this study provides a novel way for simultaneous remediation of both metal-contaminated soil and groundwater. Keywords Biochar . Contaminated soil and groundwater . Heavy metals . Integrated remediation method . Phosphorous amendments

Responsible editor: Zhihong Xu Y. Liang : X. Cao (*) : L. Zhao School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China e-mail: [email protected] Y. Liang School of Environmental Science and Engineering, Suzhou University of Science and Technology, Suzhou 215009, China E. Arellano Department Ecosystems y Medio Ambiente, Pontificia Universidad Católica de Chile, Santiago, Chile

Introduction Many of the heavy metals (e.g., Pb, Cd, Zn) originated from solid waste disposal, wastewater irrigation, pesticide application, and atmospheric deposition can accumulate in surface soil and have a potential to leach into groundwater (Niu et al. 2013). The studies showed that some certain soil in the Northeast of China which received extensive wastewater irrigation contains as high as 24.6 mg kg−1 As and 3.2 mg kg−1 Cd;

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meanwhile, as much as 2.1 mg l−1 Cd and 15.2 mg l−1 As accumulates in groundwater, which poses an environmental risk for human health (Guo and Zhou 2006; Wu et al. 2011). It has been reported that rice grain grown in these areas contained 2.6 mg kg−1 Cd (Wu et al. 2011), much higher than the China Hygienic Standard for Food (GB2715-2005). A variety of methods have been developed for remediation of contaminated soil and groundwater. Among the commonly used soil remediation methods including chemical immobilization (Kumpiene et al. 2008), phytoremediation (Memon and Schroder 2009), and soil washing (Davezza et al. 2011), chemical immobilization is a cost-effective and promising soil remediation technique, and has been extensively used in immobilization of heavy metals in contaminated soils (Kumpiene et al. 2008). Chemical immobilization relies on addition of the soil amendments to help retain metals in the stable solid phase by sorption, precipitation, complexation, ion exchange or redox process, thereby decreasing mobility and bioavailability of metals (Kumpiene et al. 2008). Phosphorus-bearing materials as conventional remediation amendments have been widely applied in immobilization of Pb, Cu, Zn, Cd, and As in contaminated soils (Miretzky and Fernandez-Cirelli 2008). Fang et al. (2012) reported that the triple superphosphate fertilizer and phosphate rock tailing could significantly reduce phytoavailable Pb, Cu, and Zn in a multi-metal contaminated soil. Waterlot et al. (2011) indicated phosphorus fertilizer amendment reduced the mobility and phytoavailability of Cd, Pb, and Zn in highly contaminated kitchen garden soils. The phosphorus-induced metal immobilization is mainly due to formation of metal–phosphate precipitates (Hashimoto et al. 2009), especially Pb–P minerals such as Pb5(PO4)3X (X=Cl, F, OH) which have been proven the most stable form under a wide range of soil pH and Eh natural conditions(Miretzky and Fernandez-Cirelli 2008). Biochar is the product of biomass pyrolysis under oxygenlimited condition which emerges as a potential effective amendment for retention of heavy metals and organic contaminants in soils (Beesley and Marmiroli 2011; Beesley et al. 2011). Beesley and Marmiroli (2011) indicated that incorporation with hardwood-derived biochar could significantly decrease Zn and Cd concentration in soil pore water and result in reduction in phytotoxicity. Uchimiya et al. (2011) showed that cottonseed hull biochars had effect for Pb and Cu immobilization in soil. Biochar is generally characterized by microporous structure, large specific surface, ample oxygen functional groups, high pH and CEC. These properties are proposed to have a great contribution to heavy metals stabilization (Uchimiya et al. 2011). Abundant mineral substances also plays an important role in the biochar's sorption ability for the heavy metals. Cao et al. (2011) reported that phosphorus originally contained in dairy manure biochar could react with soil Pb to form insoluble hydroxypyromorphite Pb5(PO4)3(OH), resulting in soil Pb immobilization.

Environ Sci Pollut Res (2014) 21:4665–4674

While for cleaning groundwater, the most common cleaning methods include permeable reactive barrier, air stripping, activate carbon adsorption, ion exchange, and pumpand-treat (Caliman et al. 2011). The pump-and-treat method is implemented by pumping the groundwater out, followed by removing contaminants from the groundwater through sorption, ion exchange, precipitation, etc. Pump-and-treat method has been proven a simple way for the remediation of contaminated groundwater (Rivett et al. 2006; Diels and Vanbroekhoven 2008), and has been widely applied in remediation of light nonaqueous phase liquid (LNAPL)-contaminated aquifers (Forsyth and Sudicky 1998), chlorinated solvent contamination at a controlled field-experiment site (Rivett et al. 2006). Diels and Vanbroekhoven (2008) showed that pump-and-treat was effective in removing Cd, Cr, and Zn from a contaminated groundwater. The soil and corresponding groundwater contamination is often in a close relation at a specific site. The toxic metals (e.g., Cd, As, Cr) in the contaminated soils may seep through the fissured and faulted zones, leading to groundwater contamination (El Khalil et al. 2008; Zhao et al. 2009a). A soil column leaching experiment showed that more than 58.3 % of Zn from composted red soil was transported into groundwater with simulated rainfall leaching (Chen et al. 2010). Conversely, the heavy metals in groundwater could accumulate in soil because of fluctuation of groundwater level. Therefore, it is highly essential to remedy both contaminated soil and groundwater simultaneously. However, the contaminated soil and groundwater are often remediated separately one from the other at a specific site. There are few studies concerned with the remediation of organic contaminants in contaminated soil and groundwater (Reichenauer and Germida 2008; Yang et al. 2005). Reichenauer and Germida (2008) reported polycyclic aromatic hydrocarbons, petroleum hydrocarbons, and volatile chlorinated solvents in soil and groundwater could be removed by phytodegradation and rhizodegradation. Yang et al. (2005) showed that pulsed air sparing could degrade petroleum hydrocarbon contaminated soil and groundwater. However, at present, to our knowledge, there are few studies available directly concerning simultaneous remediation of heavy metal contaminated soil and groundwater. This study aimed to demonstrate the hypothesis of simultaneous remediation of heavy metals contaminated soil and groundwater by coupling the chemical immobilization with the pump-and-treat method. The concept of this technology is pumping the contaminated groundwater out and spreading it through the pre-amended contaminated soil, allowing the heavy metals in soil and groundwater to be retained with the amendments by a variety of reactions, including acid/base, oxidation/reduction, and precipitation/dissolution, sorption, or ion exchange. Therefore, the specific objectives were (1) to determine immobilization of Cd in the Cd contaminated soils amended by dairy-manure-derived biochar and phosphorus-


bearing material, (2) to determine the retention ability of the pre-amended contaminated soil for Pb, Zn and Cd from aqueous solution, and (3) to demonstrate simultaneous immobilization of heavy metals in both contaminated soil and groundwater in a laboratory-scale leaching test.

Materials and methods Characterization of the soil, groundwater, and amendments materials The original soil and groundwater were collected from a farmland located in the suburb of Shenyang city, Northeast of China. This farmland belongs to an area that has been irrigated with industrial wastewater from electroplating and smelting for at least 30 years between 1960s and 1990s (Zhao et al. 2009b). The preliminary characterization shows that the concentration of soil Pb, Cu, Zn, and Cd was 60.7, 32.6, 136.6, and 1.84 mg kg−1, respectively. According to the Chinese regulations, Cd concentration was above the Level III of China Environmental Quality Standard for Soil (GB15618-1995). The collected groundwater contained 375 μg l−1 Pb, 559 μg l−1 Zn, and 0.48 μg l−1 Cd in which Pb and Zn exceed the Level II of China Environmental Quality Standard for Groundwater (GB/T 14848–1993). To meet the study objectives, the highly contaminated soil was artificially prepared from the original collected soil by spiking Cd (NO3)2 at the concentration of 60 mg kg−1 Cd and the highly contaminated groundwater was made from the original collected groundwater by spiking Pb (NO3)2, Zn (NO3)2, and Cd (NO3)2 at the concentration of 50 mg l−1 Pb, 50 mg l−1 Zn, and 1.5 mg l−1 Cd, respectively. The amendments for the heavy metals immobilization included phosphorus-bearing material (PT), and dairy manure-derived biochar (DM). The P-bearing material amendment was a mixture of phosphate mine tailing and triple superphosphate fertilizer (molar ratio of P is 1:1) (Fang et al. 2012). The biochar was produced from dairy manure at 350 °C under O2-limited condition for 4 h (Cao and Harris 2010). The pH was measured using the pH/Ion 510 Bench Meter (Eutech Instruments Pte Ltd/Oakon Instruments). Soil texture was analyzed following the method provided by American Society for Testing and Materials (ASTM 2000). Soil and amendments was digested using HNO3/ H2O2 hot block digestion procedure (USEPA 1986). Phosphorus in the digest was determined using the colorimetry method (Olsen and Sommers 1982). Concentration of Pb, Cd, and Zn in the digest was determined using an atomic absorption spectrometry (AAS) (Jena AAS novAA350). Elemental (C, H, N) analyses on biochar was conducted using the CHNS/O Analyzer (Perkin Elmer, 2400 II).

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Selected physical and chemical properties of contaminated soil, groundwater, and amendments used in the experiment are presented in Table 1. Soil pre-amendment One kilogram of the prepared highly Cd-contaminated soil (Cd =60 mg kg−1) was homogeneously mixed with 2 % (w/w) of PT, and 5 % (w/w) of DM. The application rates of the amendments have been proved to be the most effective in immobilizing heavy metals in soils (Cao et al. 2011; Cao et al. 2013). The soil without amendment was designated as control. All the control and treatments were carried out in triplicates and incubated for 56 d with moisture content of 60–70 % of maximum water holding capacity. At the end of the incubation period, the soil with or without treatment was divided into three parts: one portion (approximately 100 g) was subjected to the toxicity characteristics leaching procedure (TCLP) test to determine immobilization of metals (USEPA 1992), second portion (approximately 100 g) was collected for later batch sorption experiment, and the last portion (approximately 700 g) was for the later demonstration test. The heavy metal leachability (L, %) can be calculated as follows: L ð% Þ ¼

CTV T ; Cm

ð1Þ

where C T is the heavy metal concentration in the extract (mg l−1), V T is the volume of the extract (ml), C is the concentration of heavy metal in soil (mg kg−1), and m is the weight of soil. Sorption of heavy metals by the amended contaminated soil from aqueous solution The sorption experiment was conducted in 50-ml polypropylene tubes. One gram of the unamended or amended soil collected in Soil pre-amendment section was mixed with 40 ml of 0.01 M NaNO3 containing a series concentrations of Pb, Zn, and Cd in the ternary solutions (0, 0.1, 0.5, 1.0, 2.0, 3.0, 4.0 mM for each), respectively. The mixture was then agitated on a reciprocating shaker at 200 rpm for 48 h at 25 °C. After equilibrium, solid and liquid phases were separated by centrifugation at 4,000 rpm for 15 min and the solutions were filtered through 0.45-μm Millipore filters. The filtrate was immediately acidified to pHCK. As a result, total heavy metals (Pb+Zn+Cd) adsorption amount was improved by 19.5 % and 26.5 % with PT and DM treatment, respectively, compared to the control. The observations indicated that the treated contaminated soils still had high sorption ability for Pb, Zn, and Cd. The BCR analysis showed that PT and DM amendments induced transformation of all three metals from soluble forms to stable forms (Fig. 3). The PT and DM amendments reduced the acid soluble fraction of Pb from 54.7 % to 27.5 % and 42.2 %, respectively. Correspondingly, the oxidizable phase and the residual fraction of Pb with PT treated soil increased from 1.70 % to 16.2 %, and from 0.11 % to17.3 %, respectively. The increase in oxidizable fraction may result from the sorption of Pb by phosphate rock mineral surface in the PT 140

Pb+Zn+Cd 120 100 -1

Results and discussion

80

qe (mmol Kg )

where Q max is the maximum heavy metal retention amount from groundwater (mmol kg−1), C 0 is the concentration of heavy metal in groundwater (mg l−1), C i is the heavy metal concentration in effluent (mg l−1), V i is the volume of collected effluent, which was supposed to be equal to the volume of influent (l), m is the weight of soil used in the laboratory-scale experiment, M is the atomic weight of heavy metal and i is the number of collected effluent samples. To determine the retention and immobilization of the heavy metals in soil, the soil was collected from the pots at the end of the study and subjected to 0.01 M CaCl2, and TCLP extractions. The TCLP has been used to determine the mobility of contaminants under simulated landfill condition (USEPA 1992), while CaCl2 extraction is supposed to give the bioavailable fraction of metals (Horckmans et al. 2007). The potential for leaching of Pb, Zn, and Cd in each treatment was calculated as described in Soil pre-amendment section.

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80 CK PT DM Freundlich model Langmuir model

60 40 20 0

0

3

6

9

12

15

-1

Ce (mmol L )

Fig. 2 Isotherms of multi-metal sorption by the unamended (CK) and amended soils with phosphorus (PT) and dairy-manure-derived biochar (DM) treatments

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Table 2 Fitting parameters of Langmuir and Freundlich models for multi-metals (Pb–Zn–Cd) sorption by unamended and amended soils

Langmuir model b

Q max −1

CK PT DM

Freundlich model R2 −1

(l mM )

(mM kg )

1.48 1.21 2.63

96.77 115.59 122.45

amendment, whereas the remarkable increase in residual fraction may be attributed to the Pb–P precipitation (Miretzky and Fernandez-Cirelli 2008). XRD patterns of the PT-treated soils showed appearance of peaks at 2θ =30–30.5 and 2θ =30.5– 31, which represent Pb 10 (PO 4 ) 6 (OH) 2 and Ca 2 Pb 8 (PO4)6(OH) 2, respectively (Fig. 4), again confirming the formation of Pb–P precipitation or coprecipitation. SEM elemental dot maps further evidenced the association of Pb with P and with other elements (e.g., Ca and Cl; Fig. 5a). As shown in Fig. 3, retention of Pb in the DM-treated soil was associated with transformation from acid soluble form to all three relatively stable forms, i.e., reducible, oxidizable and residual forms. The DM biochar contained high Fe (6,160 mg kg−1, Table 1), rich Fe oxides may act as the adsorbents for specific adsorption of Pb (Jiang et al. 2012), resulting in the increase of Pb reducible form. Jiang et al. (2012) showed that the non-electrostatic adsorption to Pb in three soils incorporated with rice-straw derived biochar was associated with free Fe oxides in these soils. Complexation of Pb with organic functional groups of DM such as carboxylic, phenolic, hydroxyl, carbonyl, or/and quinones is also possible (Uchimiya et al. 2011; Jiang et al. 2012). This could be responsible for the increased percentage of oxidizable fraction. Xu et al. (2013) indicated that minerals in the dairy manure biochar, especially P plays an important role in the metal retention probably through formation of metal phosphate precipitates. This assumption was further confirmed by the XRD analysis showing precipitates of Pb10 (PO4)6(OH)2 in the DM-treated soil (Fig. 4). SEM elemental dot maps further evidenced the association of Pb with P in the DM-amended soil (Fig. 5b). As a result, the percentage of residual with DM treatment increased, about 1.78 times that of the control. Incorporation of PT and DM into soils had also reduced acid soluble fraction of Zn and Cd although the decrease was very limited compared with Pb (Fig. 3). However, the increase in residual fraction of Zn and Cd was significant, especially in the PT-treated soil, where the residual fractions of Zn and Cd were elevated by 1.5 times and 5 times, respectively. Although XRD analysis did not show any peaks related to the precipitates of Zn and Cd in both PT and DM treated soils (Fig. 4), SEM elemental dot mapping evidenced association of Zn and Cd with Pb and P in the PT-treated soil (Fig. 5a), suggesting a possible coprecipitation. A previous study indicated that Cd

KF −1

n

R2

3.89 3.34 17.08

0.982 0.945 0.915

1/n

(mM kg ) mM 0.870 0.860 0.741

53.51 58.81 72.62

immobilization induced by phosphate may be attributed to surface complexation, and coprecipitation (Raicevic et al. 2005). However, there was no association of Zn or Cd with any other elements (e.g., P, Ca) in the DM-treated soil, indicating that Zn or Cd immobilization induced by DM biochar was probably due to the its complexation with the function groups such as –COOH or OH of biochar (Xu et al. 2013). Our results indicated that the phosphate- and biochartreated contaminated soil still had the potential to retain the heavy metal pollutants from aqueous solution, especially for Pb retention and meanwhile the metals can be stabilized by the amendments. It also suggested the technical feasibility of the simultaneous immobilization of heavy metals in contaminated soil and groundwater.

Laboratory-scale demonstration test The relative concentrations (C/C 0) of the three metals in the groundwater treatment are shown in the form of breakthrough curves (Fig. 6). After 160 l groundwater leaching, an apparent plateau in the breakthrough curves was observed for Cd and Zn, indicating these two metals reached saturation sorption by the soils. However, the Pb relative concentration (C/C 0) with CK, PT, and DM was 0–0.18 (Fig. 6a), much lower than 1.0, which means that Pb remained unsaturated because of its large adsorption capacity by soil. The retention amount of Pb in the PT- and DM-amended soils from groundwater was up to 9.92 and 10.1 g kg−1, respectively. Correspondingly, the Pb in the groundwater was removed by 96.4 % and 97.4 %, respectively (Table 3). As shown in Fig. 6, the PT and DM amended soils delayed the Cd breakthrough points which appeared at 30 l in both soils (Table 3) and increased by 50 %, compared with the control. The saturation points of groundwater Cd in the PT and DM amended soils increased from 105 l in the control to 132 and 128 l, increasing by 25.7 % and 21.9 %, respectively. The maximum amounts of Cd retained in the PT- and DM-treated soil disposed from contaminated groundwater were 100 and 109 mg kg−1, an increase of 15.2 % and 25.5 %, respectively, compared to the control (Table 3). Correspondingly, Cd in the groundwater was removed by 49.2 % and 54.5 %, respectively.

Environ Sci Pollut Res (2014) 21:4665–4674 Residual Reducible 100

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Oxidizable Acid Soluble

a QZ QZ

80

LHP CLP W

Pb fraction (%)

DM C

60

PT

40 CK

20

25

0 CK

100

PT

DM

b

Cd fraction (%)

80

60

40

20

0 CK 100

PT

DM

c

Zn fraction (%)

80

60

40

20

0 CK

PT

DM

Fig. 3 The BCR-based fractionation of Pb (a), Cd (b), and Zn (c) in the unamended and amended soils after 4 mM multi-metal sorption

Similar to Cd, PT and DM treatments prolonged the breakthrough points of Zn, which appeared at 32 l in both soils (Table 3) and increased by 60 %, compared with the control. The saturation points of groundwater Zn in the PT and DM amended soils increased from 110 l in the control to 165 and 160 l, increasing by 50.0 % and 45.4 %, respectively. The

26

27

28

29

30

31 2

32

33

34

35

36

37

Fig. 4 XRD patterns of the remaining solids in the unamended and amended soils after 4 mM multi-metals sorption. QZ quartz; LHP lead phosphate hydroxide, Pb10(PO4)6 (OH)2; CLP calcium lead phosphate hydroxide, Ca2Pb8(PO4)6(OH)2; W whitlockite, (Ca, Mg)3(PO4)2; C CaCO3

maximum amounts of Zn in the PT- and DM-treated soils disposed from contaminated groundwater were 4.06 and 4.75 g kg−1, an increase of 15.2 % and 34.8 %, respectively, compared to the control (Table 3). Correspondingly, Zn in the groundwater was removed by 44.6 % and 53.4 %, respectively. At the same time, Pb, Zn, and Cd in the soil and from groundwater were stabilized by the PT and DM amendments. Among the three metals, Pb showed the highest tendency to immobilization with the addition of PT and DM amendments (Fig. 7). The Pb leachability in TCLP extraction decreased by 32.8 % and 57.1 %, respectively, compared to the control, and those in CaCl2 extraction reduced by 60.6 % and 98.2 %, respectively (Fig. 7). Cd was also immobilized by PT and DM treatments, with the leachability in CaCl2 extract reduced by 12.3 % and 67.8 %, respectively. However, the Cd leachability in TCLP extract only was reduced by 5.13 % and 17.7 % with PT and DM treatment (Fig. 7b). The Zn leachability in PT and DM amended soils was also reduced with the Zn in CaCl2 and TCLP extractions decreased by 9.39–72.6 % and 10.6– 16.8 %, respectively (Fig. 7). Overall, the use of PT- and DM-treated soils followed by pumping with the contaminated groundwater not only removed Pb, Zn, and Cd from contaminated water, but also stabilized the metals in the contaminated soil, showing a prospect of simultaneous remediation of both contaminated soil and groundwater.

Conclusions The incorporation of phosphate rock tailing and dairy manure biochar could immobilize Cd in contaminated soil. The preimmobilized contaminated soil could further sorb Pb, Zn, and Cd from aqueous solutions and change them from soluble-

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Fig. 5 SEM-EDS and elemental dot maps of remaining solids in the amended soils with PT (a) and DM (b) after 4 mM multi-metal sorption

4673 Leachability (%) of metals concentration in CaCl 2 extra

Environ Sci Pollut Res (2014) 21:4665–4674 100

a

Cd Zn Pb

80

60

40

20

0 CK

PT

DM

Treatments

Leachability (%) of metals in TCLP extra

100

Cd Zn Pb

b

80

60

40

20

0 CK

Fig. 6 Breakthrough curves of heavy metals with contaminated groundwater loading in the unamended and amended soils

associated forms to immobilized fractions. The BCR, XRD, and SEM-EDS analysis showed that the phosphorus-induced Table 3 The treatment parameters of soil and groundwater remediation in the laboratory-scale test CK Pb

The volume of treated groundwater (l) Treated amount retained from groundwater (g kg−1) Removal rate heavy metal in groundwater (%) Zn The volume of breakthrough points (l) The volume of saturation points (l) The max. amount retained from groundwater (g kg−1) Removal rate heavy metal in groundwater (%) Cd The volume of breakthrough points (l) The volume of saturation points (l) The max amount retained from groundwater (mg kg−1) Removal rate heavy metal in groundwater (%)

PT

DM

160 160 160 9.63 9.92 10.1 93.5 20 110 3.52

96.4 32 165 4.06

97.4 32 160 4.75

40.6 20 105 87.0

44.6 30 132 100

53.4 30 128 109

42.6 49.2 54.5

PT

DM

Treatments Fig. 7 Leachability (%) of Pb, Cd, and Zn in the CaCl2 extract (a) and TCLP extract (b) of unamended and amended soils after contaminated groundwater loading

metal retention was mainly due to the metal–phosphate precipitation, while both adsorption and precipitation were responsible for the metal stabilization in the biochar amendment. The laboratory-scale test showed that phosphate and biochar could greatly retain Pb, Zn, and Cd from groundwater, and meanwhile significantly immobilize the metals, especially for Pb, from both groundwater and soil itself in the soil, demonstrating the feasibility of simultaneous remediation of contaminated soil and groundwater. Therefore, the integrated chemical immobilization and pump-and-treat method developed in this study may provide a new way for simultaneous remediation of both metal-contaminated soil and groundwater. A field demonstration is necessary and is part of our future study. Acknowledgments This work was supported in part by the National Natural Science Foundation of China (No. 21077072, 21107070, 21377081), Shanghai Pujiang Talent Project (No. 11PJ1404600), and Suzhou Science and Technology Support Program (No. SS201230).

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