biochar- and phosphate-induced immobilization of heavy metals in contaminated soil and water:...

RESEARCH ARTICLE

Biochar- and phosphate-induced immobilization of heavymetals in contaminated soil and water: implicationon simultaneous remediation of contaminated soiland groundwater

Yuan Liang & Xinde Cao & Ling Zhao & Eduardo Arellano

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

Abstract Long-term wastewater irrigation or solid waste dis-posal has resulted in the heavy metal contamination in bothsoil and groundwater. It is often separately implemented forremediation of contaminated soil or groundwater at a specificsite. The main objective of this study was to demonstrate thehypothesis of simultaneous remediation of both heavy metalcontaminated soil and groundwater by integrating the chem-ical immobilization and pump-and-treat methods. To accom-plish the objective, three experiments were conducted, i.e., anincubation experiment was first conducted to determine howdairy-manure-derived biochar and phosphate rock tailing in-duced immobilization of Cd in the Cd-contaminated soils;second, a batch sorption experiment was carried out to deter-mine whether the pre-amended contaminated soil still had theability to retain Pb, Zn and Cd from aqueous solution. BCRsequential extraction as well as XRD and SEM analysis wereconducted to explore the possible retention mechanism; andlast, a laboratory-scale model test was undertaken by leachingthe Pb, Zn, and Cd contaminated groundwater through thepre-amended contaminated soils to demonstrate how theheavy metals in both contaminated soil and groundwater weresimultaneously retained and immobilized. The incubation ex-periment showed that the phosphate biochar were effective in

immobilizing soil Cd with Cd concentration in TCLP (toxicitycharacteristics leaching procedure) extract reduced by 19.6 %and 13.7 %, respectively. The batch sorption experiment re-vealed that the pre-amended soil still had ability to retain Pb,Zn, and Cd from aqueous solution. The phosphate-inducedmetal retention was mainly due to the metal–phosphate pre-cipitation, while both sorption and precipitation were respon-sible for the metal stabilization in the biochar amendment. Thelaboratory-scale test demonstrated that the soil amended withphosphate removed groundwater Pb, Zn, and Cd by 96.4 %,44.6 %, and 49.2 %, respectively, and the soil amended withbiochar removed groundwater Pb, Zn, and Cd by 97.4 %,53.4 %, and 54.5 %, respectively. Meanwhile, the metals fromboth groundwater and soil itself were immobilized with theamendments, with the leachability of the three metals in theCaCl2 and TCLP extracts being reduced by up to 98.1 % and62.7 %, respectively. Our results indicate that the integratedchemical immobilization and pump-and-treat method devel-oped in this study provides a novel way for simultaneousremediation of bothmetal-contaminated soil and groundwater.

Keywords Biochar . Contaminated soil and groundwater .

Heavymetals . Integrated remediationmethod . Phosphorousamendments

Introduction

Many of the heavy metals (e.g., Pb, Cd, Zn) originated fromsolid waste disposal, wastewater irrigation, pesticide applica-tion, and atmospheric deposition can accumulate in surfacesoil and have a potential to leach into groundwater (Niu et al.2013). The studies showed that some certain soil in the North-east of China which received extensive wastewater irrigationcontains as high as 24.6 mg kg−1 As and 3.2 mg kg−1 Cd;

Responsible editor: Zhihong Xu

Y. Liang :X. Cao (*) : L. ZhaoSchool of Environmental Science and Engineering, Shanghai JiaoTong University, Shanghai 200240, Chinae-mail: [email protected]

Y. LiangSchool of Environmental Science and Engineering, SuzhouUniversity of Science and Technology, Suzhou 215009, China

E. ArellanoDepartment Ecosystems y Medio Ambiente, Pontificia UniversidadCatólica de Chile, Santiago, Chile

Environ Sci Pollut ResDOI 10.1007/s11356-013-2423-1

meanwhile, as much as 2.1 mg l−1 Cd and 15.2 mg l−1 Asaccumulates in groundwater, which poses an environmentalrisk for human health (Guo and Zhou 2006; Wu et al. 2011). Ithas been reported that rice grain grown in these areascontained 2.6 mg kg−1 Cd (Wu et al. 2011), much higher thanthe China Hygienic Standard for Food (GB2715-2005).

A variety of methods have been developed for remediationof contaminated soil and groundwater. Among the commonlyused soil remediation methods including chemical immobili-zation (Kumpiene et al. 2008), phytoremediation (Memon andSchroder 2009), and soil washing (Davezza et al. 2011),chemical immobilization is a cost-effective and promising soilremediation technique, and has been extensively used in im-mobilization of heavy metals in contaminated soils(Kumpiene et al. 2008). Chemical immobilization relies onaddition of the soil amendments to help retain metals in thestable solid phase by sorption, precipitation, complexation,ion exchange or redox process, thereby decreasing mobilityand bioavailability of metals (Kumpiene et al. 2008).

Phosphorus-bearing materials as conventional remediationamendments have been widely applied in immobilization ofPb, Cu, Zn, Cd, and As in contaminated soils (Miretzky andFernandez-Cirelli 2008). Fang et al. (2012) reported that thetriple superphosphate fertilizer and phosphate rock tailingcould significantly reduce phytoavailable Pb, Cu, and Zn ina multi-metal contaminated soil. Waterlot et al. (2011) indi-cated phosphorus fertilizer amendment reduced the mobilityand phytoavailability of Cd, Pb, and Zn in highly contaminat-ed kitchen garden soils. The phosphorus-induced metal im-mobilization is mainly due to formation of metal–phosphateprecipitates (Hashimoto et al. 2009), especially Pb–P mineralssuch as Pb5(PO4)3X (X=Cl, F, OH) which have been proventhe most stable form under a wide range of soil pH and Ehnatural conditions(Miretzky and Fernandez-Cirelli 2008).Biochar is the product of biomass pyrolysis under oxygen-limited condition which emerges as a potential effectiveamendment for retention of heavy metals and organic contam-inants in soils (Beesley and Marmiroli 2011; Beesley et al.2011). Beesley and Marmiroli (2011) indicated that incorpo-ration with hardwood-derived biochar could significantly de-crease Zn and Cd concentration in soil pore water and result inreduction in phytotoxicity. Uchimiya et al. (2011) showed thatcottonseed hull biochars had effect for Pb and Cu immobili-zation in soil. Biochar is generally characterized by micropo-rous structure, large specific surface, ample oxygen functionalgroups, high pH and CEC. These properties are proposed tohave a great contribution to heavy metals stabilization(Uchimiya et al. 2011). Abundant mineral substances alsoplays an important role in the biochar's sorption ability forthe heavy metals. Cao et al. (2011) reported that phosphorusoriginally contained in dairy manure biochar could react withsoi l Pb to form insoluble hydroxypyromorphitePb5(PO4)3(OH), resulting in soil Pb immobilization.

While for cleaning groundwater, the most commoncleaning methods include permeable reactive barrier, air strip-ping, activate carbon adsorption, ion exchange, and pump-and-treat (Caliman et al. 2011). The pump-and-treat method isimplemented by pumping the groundwater out, followed byremoving contaminants from the groundwater through sorp-tion, ion exchange, precipitation, etc. Pump-and-treat methodhas been proven a simple way for the remediation of contam-inated groundwater (Rivett et al. 2006; Diels andVanbroekhoven 2008), and has been widely applied in reme-diation of light nonaqueous phase liquid (LNAPL)-contami-nated aquifers (Forsyth and Sudicky 1998), chlorinated sol-vent contamination at a controlled field-experiment site(Rivett et al. 2006). Diels and Vanbroekhoven (2008) showedthat pump-and-treat was effective in removing Cd, Cr, and Znfrom a contaminated groundwater.

The soil and corresponding groundwater contamination isoften in a close relation at a specific site. The toxic metals(e.g., Cd, As, Cr) in the contaminated soils may seep throughthe fissured and faulted zones, leading to groundwater con-tamination (El Khalil et al. 2008; Zhao et al. 2009a). A soilcolumn leaching experiment showed that more than 58.3 % ofZn from composted red soil was transported into groundwaterwith simulated rainfall leaching (Chen et al. 2010). Converse-ly, the heavy metals in groundwater could accumulate in soilbecause of fluctuation of groundwater level. Therefore, it ishighly essential to remedy both contaminated soil and ground-water simultaneously. However, the contaminated soil andgroundwater are often remediated separately one from theother at a specific site. There are few studies concerned withthe remediation of organic contaminants in contaminated soiland groundwater (Reichenauer and Germida 2008; Yang et al.2005). Reichenauer and Germida (2008) reported polycyclicaromatic hydrocarbons, petroleum hydrocarbons, and volatilechlorinated solvents in soil and groundwater could be re-moved by phytodegradation and rhizodegradation. Yanget al. (2005) showed that pulsed air sparing could degradepetroleum hydrocarbon contaminated soil and groundwater.However, at present, to our knowledge, there are few studiesavailable directly concerning simultaneous remediation ofheavy metal contaminated soil and groundwater.

This study aimed to demonstrate the hypothesis of simul-taneous remediation of heavy metals contaminated soil andgroundwater by coupling the chemical immobilization withthe pump-and-treat method. The concept of this technology ispumping the contaminated groundwater out and spreading itthrough the pre-amended contaminated soil, allowing theheavy metals in soil and groundwater to be retained with theamendments by a variety of reactions, including acid/base,oxidation/reduction, and precipitation/dissolution, sorption, orion exchange. Therefore, the specific objectives were (1) todetermine immobilization of Cd in the Cd contaminated soilsamended by dairy-manure-derived biochar and phosphorus-

Environ Sci Pollut Res

bearing material, (2) to determine the retention ability of thepre-amended contaminated soil for Pb, Zn and Cd from aque-ous solution, and (3) to demonstrate simultaneous immobili-zation of heavy metals in both contaminated soil and ground-water in a laboratory-scale leaching test.

Materials and methods

Characterization of the soil, groundwater, and amendmentsmaterials

The original soil and groundwater were collected from afarmland located in the suburb of Shenyang city, Northeastof China. This farmland belongs to an area that has beenirrigated with industrial wastewater from electroplating andsmelting for at least 30 years between 1960s and 1990s (Zhaoet al. 2009b). The preliminary characterization shows that theconcentration of soil Pb, Cu, Zn, and Cd was 60.7, 32.6,136.6, and 1.84 mg kg−1, respectively. According to theChinese regulations, Cd concentration was above the LevelIII of China Environmental Quality Standard for Soil(GB15618-1995). The collected groundwater contained375 μg l−1 Pb, 559 μg l−1 Zn, and 0.48 μg l−1 Cd in whichPb and Zn exceed the Level II of China Environmental Qual-ity Standard for Groundwater (GB/T 14848–1993). To meetthe study objectives, the highly contaminated soil was artifi-cially prepared from the original collected soil by spiking Cd(NO3)2 at the concentration of 60 mg kg−1 Cd and the highlycontaminated groundwater was made from the original col-lected groundwater by spiking Pb (NO3)2, Zn (NO3)2, and Cd(NO3)2 at the concentration of 50mg l−1 Pb, 50mg l−1 Zn, and1.5 mg l−1 Cd, respectively.

The amendments for the heavy metals immobilizationincluded phosphorus-bearing material (PT), and dairymanure-derived biochar (DM). The P-bearing materialamendment was a mixture of phosphate mine tailing andtriple superphosphate fertilizer (molar ratio of P is 1:1)(Fang et al. 2012). The biochar was produced from dairymanure at 350 °C under O2-limited condition for 4 h (Caoand Harris 2010).

The pH was measured using the pH/Ion 510 BenchMeter (Eutech Instruments Pte Ltd/Oakon Instruments).Soil texture was analyzed following the method providedby American Society for Testing and Materials (ASTM2000). Soil and amendments was digested using HNO3/H2O2 hot block digestion procedure (USEPA 1986). Phos-phorus in the digest was determined using the colorimetrymethod (Olsen and Sommers 1982). Concentration of Pb,Cd, and Zn in the digest was determined using an atomicabsorption spectrometry (AAS) (Jena AAS novAA350).Elemental (C, H, N) analyses on biochar was conductedusing the CHNS/O Analyzer (Perkin Elmer, 2400 II).

Selected physical and chemical properties of contaminat-ed soil, groundwater, and amendments used in the exper-iment are presented in Table 1.

Soil pre-amendment

One kilogram of the prepared highly Cd-contaminatedsoil (Cd =60 mg kg−1) was homogeneously mixed with2 % (w/w) of PT, and 5 % (w/w) of DM. The applicationrates of the amendments have been proved to be the mosteffective in immobilizing heavy metals in soils (Cao et al.2011; Cao et al. 2013). The soil without amendment wasdesignated as control. All the control and treatments werecarried out in triplicates and incubated for 56 d withmoisture content of 60–70 % of maximum water holdingcapacity. At the end of the incubation period, the soil withor without treatment was divided into three parts: oneportion (approximately 100 g) was subjected to the toxicitycharacteristics leaching procedure (TCLP) test to determineimmobilization of metals (USEPA 1992), second portion (ap-proximately 100 g) was collected for later batch sorptionexperiment, and the last portion (approximately 700 g) wasfor the later demonstration test.

The heavy metal leachability (L , %) can be calculated asfollows:

L %ð Þ ¼ CTVT

Cm; ð1Þ

where CT is the heavy metal concentration in the extract (mgl−1), VT is the volume of the extract (ml), C is the concentra-tion of heavy metal in soil (mg kg−1), and m is the weight ofsoil.

Sorption of heavy metals by the amended contaminated soilfrom aqueous solution

The sorption experiment was conducted in 50-ml polypropyl-ene tubes. One gram of the unamended or amended soilcollected in Soil pre-amendment section was mixed with40 ml of 0.01 M NaNO3 containing a series concentrationsof 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 thenagitated on a reciprocating shaker at 200 rpm for 48 h at 25 °C.After equilibrium, solid and liquid phases were separated bycentrifugation at 4,000 rpm for 15 min and the solutions werefiltered through 0.45-μm Millipore filters. The filtrate wasimmediately acidified to pH<2 with concentrated HNO3 forPb, Zn, and Cd analysis using AAS.

The sorption isotherms of heavy metals by the soils werefitted using Langmuir and Freundlich models. Their equationsare expressed as follows:


Langmuir model qe ¼Qmax⋅b⋅Ce

1þ bCeð2Þ

Freundlich model qe ¼ −K fC1ne; ð3Þ

where qe is the amount of the metal adsorbed per unit weightof samples (mmol kg−1), Ce is the equilibrium concentrationof solution (mmol l−1), Qmax is the maximum adsorptioncapacity (mmol kg−1), and b is related to the affinity of thebinding sites. K f and n are indicators of adsorption capacityand intensity, respectively.

The solids remaining on the filter and in the tubes werecollected and air-dried for characterization using X-ray diffrac-tion (XRD), scanning electron microscopy-energy dispersivespectrometer (SEM-EDS), and sequential extraction experiment(BCR). XRD analysis can provide crystallographic composi-tion. The XRD patterns were obtained on a Rigaku D/Max-2550 PC (Rigaku Corporation, Japan) by scanning at a rangefrom 20° to 55° at 2°/min. For morphology, soils were gold-coated for SEM observation with qualitative EDS analysis andX-ray elemental dot mapping analysis (JEOL, JSM-7600F,Oxford Inca; Oxford Corporation, UK) at an acceleration volt-age of 20 kV. To determine the speciation of heavy metals, thesequential extraction experiment was conducted using the mod-ified BCR method described by Castillo et al. (2011). Forquality control, the total concentration of Pb, Zn, and Cd inthe collected soil was also determined by usingHNO3/H2O2 hotblock digestion (USEPA 1986) and compared with the sum ofthe concentration of each soil extraction. A good agreement was

observed with the standard errors for the three metals being4.10–11.2 %.

Laboratory-scale demonstration test

The laboratory-scale test was carried out to demonstrate thefeasibility of simultaneous remediation of heavy metals in soiland groundwater. Approximately 700 g of soils collected asdescribed in Soil pre-amendment section was packed into poly-propylene pots (10 cm in diameter and 20 cm in height) withsmall holes in the bottom of the pot. One 2-cm layer of quartz (2–4 mm diameter size) was added into the pot to filter the leachateand support the soil. A layer of filter paper was placed at the topof soil to facilitate the groundwater loading distribution andreduce evaporation loss. A total of 160 l of contaminated ground-water was loaded in every treatment and let the groundwater flowthrough the pot filled with the treated soils. The groundwater waspassed through the pots using a timer and a rotameter that keepeach treatment at the samewater level, and the effluent speedwasat 105–135 ml h−1 for all soils. The effluent was collected every1.0 l and analyzed for heavy metal concentrations.

The breakthrough curves were plotted using changes inheavy metal concentration of the effluent in relation to theoriginal groundwater concentration as a function of the load-ing volume. The maximum metal retention amount (Qmax,mmol kg−1) from groundwater was obtained when the satura-tion point was reached and can be calculated as follows:

Qmax mmol kg−1� � ¼

Xn

i¼1

− C0−Cið ÞV i½ �

m⋅M

; ð4Þ

Table 1 Selected physico-chemical properties of soils,groundwater, and amendments

a Not determinedb Below detection limit

Contaminated soil Contaminated groundwater Amendments

PT DM

pH 7.2 6.0 7.5 9.1

Sand+silt(2–2,000 μm)

90.2 % –a – –

Clay (<2 μm) 9.8 % – – –

P 60.0 mg kg−1 – 17.0 % 0.64 %

Pb 60.7 mg kg−1 50.0 mg l−1 2.80 mg kg−1 0.005 mg kg−1

Cd 60.0 mg kg−1 1.50 mg l−1 BDLb 0.001 mg kg−1

Zn 165 mg kg−1 50.0 mg l−1 228 mg kg−1 523 mg kg−1

Fe – – – 6,160 mg kg−1

Mn – – – 440 mg kg−1

C – – 44.7 mg kg−1

H – – – 2.20 %

O – – – 2.00 %


where Qmax is the maximum heavy metal retention amountfrom groundwater (mmol kg−1), C0 is the concentration ofheavy metal in groundwater (mg l−1), Ci is the heavy metalconcentration in effluent (mg l−1), Vi is the volume of collect-ed effluent, which was supposed to be equal to the volume ofinfluent (l),m is the weight of soil used in the laboratory-scaleexperiment,M is the atomic weight of heavy metal and i is thenumber of collected effluent samples.

To determine the retention and immobilization of theheavy metals in soil, the soil was collected from thepots at the end of the study and subjected to 0.01 MCaCl2, and TCLP extractions. The TCLP has been usedto determine the mobility of contaminants under simu-lated landfill condition (USEPA 1992), while CaCl2extraction is supposed to give the bioavailable fractionof metals (Horckmans et al. 2007). The potential forleaching of Pb, Zn, and Cd in each treatment wascalculated as described in Soil pre-amendment section.

Results and discussion

Effect of amendments on the immobilization of Cd

The PT and DM amendments reduced soil Cd leachability inthe TCLP extraction by 19.6 % and 13.7 %, respectively,compared to the control (Fig. 1). The similar result wasobtained in the study by Beesley et al. (2010) thathardwood-derived biochar decreased almost 10 % Cd in soilpore water after incubation for 60 days. The DM biochar usedin this study had a high concentration of extractable P(6,400 mg/kg, Table 1), so the precipitation of Cd–P mineralswas possible, which may be responsible for Cd stabilization.Our previous work indicated that more than 25 % of Cdretention by the dairy manure biochar is attributed to precip-itation of Cd3(PO4)2 (Xu et al. 2013). Biochar has micropo-rous structure and ample oxygen functional groups that couldalso contribute to its high sorption to the metals (Uchimiyaet al. 2011). In addition, the strong alkalinity of DM biochar(pH=9.5, Table 1) could increase its negative surface-chargeand hydrolysis of heavy metals, correspondingly, enhancingthe adsorption affinity to heavy metals (Jiang et al. 2012). ThePT treatment was more effective than DM treatment in Cdimmobilization, which may be attributed to higher concentra-tion of total soluble P in PT materials. Thawornchaist andPolprasert (2009) found that high soluble tripsuperphosphatereduced Cd lechability in soil from 306 to 34 mg kg−1 afterincubation for 60 days. Lots of work has demonstrated that P-induced metal immobilization was most likely due to precip-itation or coprecipitation of metal phosphate minerals(Miretzky and Fernandez-Cirelli 2008; Hashimoto et al.2009).

Sorption of Pb, Zn, and Cd by the treated soils from aqueoussolution

As shown in Fig. 2 and Table 2, the sorption isotherm of totalheavy metals (Pb+Zn+Cd) by soils from the Pb, Zn, and Cdternary solutions was more fitted to Freundlich model (R2=0.915–0.982) than Langmuir model (R2=0.741–0.870). Theparameter of K f related to adsorption capacity was improvedin the amended soils with the following order: DM>PT>CK.As a result, total heavy metals (Pb+Zn+Cd) adsorptionamount was improved by 19.5 % and 26.5 % with PT andDM treatment, respectively, compared to the control. Theobservations indicated that the treated contaminated soils stillhad high sorption ability for Pb, Zn, and Cd.

The BCR analysis showed that PT and DM amendmentsinduced transformation of all three metals from soluble formsto stable forms (Fig. 3). The PTand DM amendments reducedthe acid soluble fraction of Pb from 54.7 % to 27.5 % and42.2 %, respectively. Correspondingly, the oxidizable phaseand the residual fraction of Pb with PT treated soil increasedfrom 1.70 % to 16.2 %, and from 0.11 % to17.3 %, respec-tively. The increase in oxidizable fraction may result from thesorption of Pb by phosphate rock mineral surface in the PT

CK PT DM0

10

20

30

40

50

60

70

80

TC

LP

Cd

(%)

Treatments

Fig. 1 The leachability (%) of Cd in the TCLP extract from the contam-inated soil unamended (CK) and amended with phosphorus (PT) anddairy manure biochar (DM) treatments. Brackets means error bar

0 3 6 9 12 150

20

40

60

80

100

120

140

CK PT DMFreundlich model Langmuir model

qe (

mm

ol K

g-1)

Ce (mmol L-1)

Pb+Zn+Cd

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


amendment, whereas the remarkable increase in residual frac-tion may be attributed to the Pb–P precipitation (Miretzky andFernandez-Cirelli 2008). XRD patterns of the PT-treated soilsshowed appearance of peaks at 2θ =30–30.5 and 2θ =30.5–31, which represent Pb10 (PO4)6(OH)2 and Ca2Pb8(PO4)6(OH) 2, respectively (Fig. 4), again confirming theformation of Pb–P precipitation or coprecipitation. SEM ele-mental dot maps further evidenced the association of Pb withP and with other elements (e.g., Ca and Cl; Fig. 5a).

As shown in Fig. 3, retention of Pb in the DM-treated soilwas associated with transformation from acid soluble form toall three relatively stable forms, i.e., reducible, oxidizable andresidual forms. The DM biochar contained high Fe (6,160 mgkg−1, Table 1), rich Fe oxides may act as the adsorbents forspecific adsorption of Pb (Jiang et al. 2012), resulting in theincrease of Pb reducible form. Jiang et al. (2012) showed thatthe non-electrostatic adsorption to Pb in three soils incorpo-rated with rice-straw derived biochar was associated with freeFe oxides in these soils. Complexation of Pb with organicfunctional groups of DM such as carboxylic, phenolic, hy-droxyl, carbonyl, or/and quinones is also possible (Uchimiyaet al. 2011; Jiang et al. 2012). This could be responsible for theincreased percentage of oxidizable fraction. Xu et al. (2013)indicated that minerals in the dairy manure biochar, especiallyP plays an important role in the metal retention probablythrough formation of metal phosphate precipitates. This as-sumption was further confirmed by the XRD analysis show-ing precipitates of Pb10 (PO4)6(OH)2 in the DM-treated soil(Fig. 4). SEM elemental dot maps further evidenced theassociation of Pb with P in the DM-amended soil (Fig. 5b).As a result, the percentage of residual with DM treatmentincreased, about 1.78 times that of the control.

Incorporation of PT and DM into soils had also reducedacid soluble fraction of Zn and Cd although the decrease wasvery limited compared with Pb (Fig. 3). However, the increasein residual fraction of Zn and Cd was significant, especially inthe PT-treated soil, where the residual fractions of Zn and Cdwere elevated by 1.5 times and 5 times, respectively. AlthoughXRD analysis did not show any peaks related to the precipi-tates of Zn and Cd in both PT and DM treated soils (Fig. 4),SEM elemental dot mapping evidenced association of Zn andCd with Pb and P in the PT-treated soil (Fig. 5a), suggesting apossible coprecipitation. A previous study indicated that Cd

immobilization induced by phosphate may be attributed tosurface complexation, and coprecipitation (Raicevic et al.2005). However, there was no association of Zn or Cd withany other elements (e.g., P, Ca) in the DM-treated soil, indi-cating that Zn or Cd immobilization induced by DM biocharwas probably due to the its complexation with the functiongroups such as –COOH or OH of biochar (Xu et al. 2013).

Our results indicated that the phosphate- and biochar-treated contaminated soil still had the potential to retain theheavy metal pollutants from aqueous solution, especially forPb retention andmeanwhile the metals can be stabilized by theamendments. It also suggested the technical feasibility of thesimultaneous immobilization of heavy metals in contaminatedsoil and groundwater.

Laboratory-scale demonstration test

The relative concentrations (C /C0) of the three metals in thegroundwater treatment are shown in the form of breakthroughcurves (Fig. 6). After 160 l groundwater leaching, an apparentplateau in the breakthrough curves was observed for Cd andZn, indicating these two metals reached saturation sorption bythe soils. However, the Pb relative concentration (C /C0) withCK, PT, and DM was 0–0.18 (Fig. 6a), much lower than 1.0,which means that Pb remained unsaturated because of its largeadsorption capacity by soil. The retention amount of Pb in thePT- and DM-amended soils from groundwater was up to 9.92and 10.1 g kg−1, respectively. Correspondingly, the Pb in thegroundwater was removed by 96.4% and 97.4%, respectively(Table 3).

As shown in Fig. 6, the PT and DM amended soils delayedthe Cd breakthrough points which appeared at 30 l in bothsoils (Table 3) and increased by 50 %, compared with thecontrol. The saturation points of groundwater Cd in the PTandDM amended soils increased from 105 l in the control to 132and 128 l, increasing by 25.7 % and 21.9 %, respectively. Themaximum amounts of Cd retained in the PT- and DM-treatedsoil disposed from contaminated groundwater were 100 and109 mg kg−1, an increase of 15.2 % and 25.5 %, respectively,compared to the control (Table 3). Correspondingly, Cd in thegroundwater was removed by 49.2 % and 54.5 %,respectively.

Table 2 Fitting parameters ofLangmuir and Freundlich modelsfor multi-metals (Pb–Zn–Cd)sorption by unamended andamended soils

Langmuir model Freundlich model

b

(l mM−1)

Qmax

(mM kg−1)

R2 KF

(mM kg−1) mM1/n

n R2

CK 1.48 96.77 0.870 53.51 3.89 0.982

PT 1.21 115.59 0.860 58.81 3.34 0.945

DM 2.63 122.45 0.741 72.62 17.08 0.915


Similar to Cd, PT and DM treatments prolonged the break-through 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 DMamended soils increased from 110 l in the control to 165 and160 l, increasing by 50.0 % and 45.4 %, respectively. The

maximum amounts of Zn in the PT- and DM-treated soilsdisposed from contaminated groundwater were 4.06 and4.75 g kg−1, an increase of 15.2 % and 34.8 %, respectively,compared to the control (Table 3). Correspondingly, Zn in thegroundwater was removed by 44.6 % and 53.4 %,respectively.

At the same time, Pb, Zn, and Cd in the soil and fromgroundwater were stabilized by the PT and DM amendments.Among the three metals, Pb showed the highest tendency toimmobilization with the addition of PT and DM amendments(Fig. 7). The Pb leachability in TCLP extraction decreased by32.8 % and 57.1 %, respectively, compared to the control, andthose in CaCl2 extraction reduced by 60.6 % and 98.2 %,respectively (Fig. 7). Cd was also immobilized by PTand DMtreatments, with the leachability in CaCl2 extract reduced by12.3% and 67.8%, respectively. However, the Cd leachabilityin TCLP extract only was reduced by 5.13 % and 17.7 % withPT and DM treatment (Fig. 7b). The Zn leachability in PT andDM amended soils was also reduced with the Zn in CaCl2 andTCLP 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 bypumping with the contaminated groundwater not only re-moved Pb, Zn, and Cd from contaminated water, but alsostabilized the metals in the contaminated soil, showing aprospect of simultaneous remediation of both contaminatedsoil and groundwater.

Conclusions

The incorporation of phosphate rock tailing and dairy manurebiochar could immobilize Cd in contaminated soil. The pre-immobilized contaminated soil could further sorb Pb, Zn, andCd from aqueous solutions and change them from soluble-

CK PT DM0

20

40

60

80

100

Pb

frac

tion

(%)

Residual Oxidizable Reducible Acid Soluble

a

CK PT DM0

20

40

60

80

100

Cd

frac

tion

(%

)

b

CK PT DM0

20

40

60

80

100

Zn

frac

tion

(%)

c

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

25 26 27 28 29 30 31 32 33 34 35 36 37

2

CK

PT

DM

C

W

QZ

LHP CLPQZ

Fig. 4 XRD patterns of the remaining solids in the unamended andamended soils after 4 mM multi-metals sorption. QZ quartz; LHP leadphosphate hydroxide, Pb10(PO4)6 (OH)2; CLP calcium lead phosphatehydroxide, Ca2Pb8(PO4)6(OH)2; W whitlockite, (Ca, Mg)3(PO4)2; CCaCO3


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


associated forms to immobilized fractions. The BCR, XRD,and SEM-EDS analysis showed that the phosphorus-induced

metal retention was mainly due to the metal–phosphate pre-cipitation, while both adsorption and precipitation were re-sponsible for the metal stabilization in the biochar amend-ment. The laboratory-scale test showed that phosphate andbiochar could greatly retain Pb, Zn, and Cd from groundwater,and meanwhile significantly immobilize the metals, especiallyfor Pb, from both groundwater and soil itself in the soil,demonstrating the feasibility of simultaneous remediation ofcontaminated soil and groundwater. Therefore, the integratedchemical immobilization and pump-and-treat method devel-oped in this study may provide a new way for simultaneousremediation of bothmetal-contaminated soil and groundwater.A field demonstration is necessary and is part of our futurestudy.

Acknowledgments This work was supported in part by the NationalNatural Science Foundation of China (No. 21077072, 21107070,21377081), Shanghai Pujiang Talent Project (No. 11PJ1404600), andSuzhou Science and Technology Support Program (No. SS201230).

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

Table 3 The treatment parameters of soil and groundwater remediationin the laboratory-scale test

CK PT DM

Pb The volume of treated groundwater (l) 160 160 160

Treated amount retained from groundwater(g kg−1)

9.63 9.92 10.1

Removal rate heavy metal in groundwater (%) 93.5 96.4 97.4

Zn The volume of breakthrough points (l) 20 32 32

The volume of saturation points (l) 110 165 160

The max. amount retained from groundwater(g kg−1)

3.52 4.06 4.75


Cd The volume of breakthrough points (l) 20 30 30

The volume of saturation points (l) 105 132 128

The max amount retained from groundwater(mg kg−1)

87.0 100 109


CK PT DM0

20

40

60

80

100

Lea

chab

ilit

y (%

) of

met

als

conc

entr

atio

n in

CaC

l 2 ext

ra

Treatments

CdZnPb

a

CK PT DM0

20

40

60

80

100

Lea

chab

ility

(%

) of

met

als

in T

CL

P ex

tra

Treatments

CdZnPb

b

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


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