Effect of Clean Coal Combustion Products in ReducingSoluble Phosphorus in Soil I. Adsorption Study

Balaji Seshadri & Nanthi S. Bolan & Anitha Kunhikrishnan

Received: 16 November 2012 /Accepted: 4 March 2013 /Published online: 24 March 2013# Springer Science+Business Media Dordrecht 2013

Abstract The study examined the effectiveness of var-ious coal combustion products (CCPs) [fly ash (FA),fluidized bed combustion ash (FBC), and flue gas de-sulfurization gypsum (FGD)] on phosphorus (P) adsorp-tion in soils using batch sorption studies. The resultsindicated that P adsorption increased with increasingapplication rates of CCPs. The effect of CCPs in in-creasing P adsorption followed: FBC > FA > FGD.There was an inverse relationship between the CCP-induced increase in P adsorption and initial soil pH,demonstrating that acidic and neutral soils respondedmore effectively to CCP addition than alkaline soils.The increases in soil pH and calcium (Ca) concentrationin the soil solution resulting from CCP application en-hanced P retention through adsorption and precipitationreactions.

Keywords Phosphorus . Coal combustionproducts . Adsorption . Soil properties . Mobility

1 Introduction

Coal combustion products (CCPs) are generated inlarge quantities as a result of coal-fired power gener-ation worldwide and dumped in and/or around powerstations. The volume being generated is so enormousthat ash ponds and dump sites, which accumulatethese CCPs, are fast expanding. Coal still remains tobe the less expensive fuel and available in abundanceat least for the next 50 years. The International EnergyAgency or IEA (2010) reports that coal fuels 41 % ofglobal electricity and is also predicted to increase up to44 % by 2030. This means more CCPs will be pro-duced in impending years. Australia, being the largestcoal exporter, uses coal for 77 % of its electricitygeneration (IEA 2010). In Australia, the 30 coal-firedpower stations generate more than 12 Mt of CCPsevery year, posing threat to the environment due toincessant dumping and underutilization of CCPs(ADAA 2009). Twardowska and Stefaniak (2006)warned that the current rate of CCP production rendersits disposal unavailable and may cause detrimentaleffects on the environment owing to overall toxiceffect of ash materials.

Over the years, the CCPs are being used exten-sively in the construction industry, agriculture, andtowards environmental restoration. Agricultural ap-plications focused mainly on improving soil struc-tural attributes (Acton and Gregorich 1995; Fulekarand Dave 1986; Sahu 1999), liming value (Stout etal. 1998; Terman et al. 1978; Wang et al. 1994), andphosphorus (P) (im)mobilization capacity (Cheungand Venkitachalam 2000; McDowell 2004, 2005;

Water Air Soil Pollut (2013) 224:1524DOI 10.1007/s11270-013-1524-2

B. Seshadri (*) :N. S. BolanCentre for Environmental Risk Assessment andRemediation, Building-X, University of South Australia,Mawson Lakes, South Australia 5095, Australiae-mail: Balaji.Seshadri@unisa.edu.au

B. Seshadri :N. S. BolanCooperative Research Centre for ContaminationAssessment and Remediation of the Environment,PO Box 486, Salisbury, South Australia 5106, Australia

A. KunhikrishnanChemical Safety Division, Department of Agro-Food Safety,National Academy of Agricultural Science,Suwon-si, Gyeonggi-do 441-707, Republic of Korea

Stout et al. 2003) of the soil. With the above-mentionedcharacteristics related to agricultural uses, CCPs canalso be used for reclaiming degraded soils, therebyproviding an economical way of disposal. This studywill focus on the effect of CCPs on P adsorption in soil.

P has been one of the most limiting nutrients afternitrogen in most agricultural soils throughout the world.Australian soils are generally poor in retaining P andalso inherently low in P. Loss of P from soils throughrunoff and leaching poses environmental degradationnot only to land resources but also to surface water(eutrophication) and ground water (Pierzynski et al.2005). Generally, P is transported from soil in particu-late form and dissolved form (soluble inorganic P).Although the particulate P loss can be decreased throughmanagement practices such as riparian buffers, the sol-uble inorganic P loss had been an issue in soils havinglow P retention capacity (PRC) (McDowell andCondron 2004). An understanding of PRC of soils isvital for fertilizer management (Hedley andMcLaughlin2005) and safeguarding water quality (Sharpley et al.1994). Optimal pH and high concentration of P-sorptivecomponents such as calcium (Ca), iron (Fe), and alumi-num (Al) in soil solution are good prerequisites forenhancing the retention of P in soils (McDowell 2004;Stout et al. 1998). Generally, at alkaline pH, Ca formsprecipitates with P and in acidic conditions, P adsorbs tohydrated Al and Fe oxides. Traditionally, lime (CaCO3)has been widely used to overcome soil acidity by in-creasing the soil pH (Anderson et al. 1995; Sumner andYamadu 2002). Several studies have investigated thatliming can also enhance P adsorption in soils throughaddition of Ca+ to the soil solution (Barrow 1984; Bolanet al. 1988; Curtin and Smillie 1995; Murphy andStevens 2010).

Researchers have shown that some of the CCPs areeffective in decreasing soil solution P loss (Callahan etal. 2002; McDowell 2005; Stout et al. 2000) becauseof their high alkalinity and liming value. Some studieshave also shown the effectiveness of fly ash (FA) inmitigating particulate P loss through erosion or organ-ic P loss through mineralization (Stuczynski et al.1998a, b). The mechanisms by which the CCPs min-imize P loss mainly constitute their neutralizing ca-pacity in acidic soils and precipitation of P with Ca inalkaline soils. Various reasons have been attributed tothe beneficial effects of CCPs in reducing the loss of Pthrough leaching and erosion (Callahan et al. 2002;McDowell 2005; Pathan et al. 2002; Reichert and

Norton 1994; Stout et al. 2000), which include: (1)increase in soil pH resulting from the addition ofalkaline CCPs; (2) increases in surface area, anionexchange capacity (AEC), and water holding capacity(WHC); (3) increases in Ca, Fe, and Al concentration;and (4) increase in soil strength through slaking andsoil dispersion. These CCPs can be an effective re-placement for their natural counterparts if used judi-ciously. Hence, efforts have been taken globally on thepossible usage of CCPs for increasing P retention insoils that are naturally poor in P retention.

Development of strategies to minimize the loss of Pfrom soils requires a detailed understanding of P in-teractions and factors of immobilization. There has beenno comprehensive study comparing the effect of variousCCPs on P adsorption and their influencing chemicalcharacteristics such as pH, PRC, and concentration of P-sorptive components such as Fe, Al, and Ca. Therefore,the objective of this study was to examine the effect ofCCPs on P adsorption in soils by examining the effect ofpH and the role of cations such as Fe, Al, and Ca.

2 Materials and Methods

2.1 Soils and CCPs

The soils used for the study were collected from SouthAustralia (four soils): Adelaide hills (ADL), Kapunda(KPD), Kulpara (KUL), and Wallaro (WAL);Queensland (two soils): Birbie island (BIR) andPittsworth (PIT); and New South Wales (one soil):Drake (DRA). The soils selected varied in pH and Pretaining capacity. The CCPs used were FA (collectedfrom Port Augusta Power station, South Australia),fluidized bed combustion ash (FBC, Redbank PowerLimited, Queensland), and flue gas desulfurizationgypsum (FGD, Illinois, United States).

2.2 Characterization of Soil and CCP Samples

The soil samples were analyzed for pH, electricalconductivity (EC), soil texture, and total heavy metals.The soil pH and EC were determined by shaking thesoil samples with water at a ratio of 1:5 for 1 h usingan end-over-end shaker and measured the solutionwith a pH/conductivity meter. The soil texture wasestablished using a micropipette method (Miller andMiller 1987) and shown in Table 1. For the total metal

1524, Page 2 of 11 Water Air Soil Pollut (2013) 224:1524

analysis, the soils were digested using aqua regia andthe concentration of metals in the extract was deter-mined by inductively coupled plasma‐optical emissionspectrometry (ICP-OES) (McDowell 2005). The PRCof the soils was determined using the phosphate reten-tion test (Saunders 1965) and the CaCO3 equivalence(CCE) for CCPs was determined using the methoddescribed by Rayment and Higginson (1992).

The CCPs were analyzed for pH, EC, and elementalcomposition following the above-mentioned methods(Table 2). The Olsen P (Olsen et al. 1954) was mea-sured for all CCPs and soil samples.

2.3 Soil Preparation and Incubation with CCPs

The soils were air dried, sieved to <2 mm size, andincubated with 0 and 15 % (w/w) of CCPs in a plasticbag for 21 days at 80 % of the total WHC. After 21 daysof incubation, the pH and EC of the incubated samplesweremeasured. All the incubated sampleswere analyzedfor Fe and Al using ammonium oxalate solution foramorphous (Feox and Alox) fractions (McKeague andDay 1966) and dithionite–citrate solution for crystalline(Fecd and Alcd) fractions (USDA 1972). For the Feox andAlox, 1 g of <0.15 mm soil sample was weighed in a 50-mL centrifuge tube and 40 mL of acid ammonium oxa-late solution (pH=3.0) was added and stoppered the tubetightly. The tubes were shaken in an end-over-end shakerfor 4 h in the dark. The tubes were then centrifuged at4,000 rpm for 20 min and the clear supernatant wastransferred to glass containers and stored in the darkbefore analysis. For the Fecd and Alcd, 1 g of <0.15-mm soil sample was weighed in a 50-mL centrifuge tubeand 50 mL of sodium citrate solution was added alongwith 0.8 g of dithionate. The tubes were stoppered andshaken in an end-over-end shaker for 16 h. The tubeswere then centrifuged at 4,000 rpm for 20 min and theclear supernatant was transferred to glass containers andstored before analysis. The Ca concentration in the solu-tion was determined by extracting Ca with deionizedwater (1:2 sample to water ratio) in a 50-mL centrifugetube (Seoane and LeirÓs 2001). All the extracts wereanalyzed using inductively coupled plasma‐mass spec-trometry (ICP-MS).

2.4 Sorption Experiment

The effect of CCPs on P sorption was studied using batchsorption experiments and fitted to isotherm equations

(mentioned below). Three different soils (BIR-acidic,KPD-neutral, and KUL-alkaline) were incubated withCCPs (0 and 15 % w/w) for 21 days to study the effectof CCPs on P sorption and the influence of increase in pHtowards P sorption.

For the P sorption measurement, 1 g of CCP-amended soil sample was weighed into a 50-mLcentrifuge tube and then mixed with 20 mL ofwater containing graded concentrations of P (0, 5,10, 20, 50, and 150 mg P L−1) as KH2PO4

(McDowell 2004). Then, the tubes were equilibratedfor 16 h using an end-over-end shaker at roomtemperature (25±2 °C). The tubes were thencentrifuged for 20 min (4,000 rpm) and 1-mL ali-quots of the supernatant solution were transferred to50-mL centrifuge tubes. The phosphate concentra-tions of the solutions were measured using thephosphomolybdate method (Murphy and Riley1962). The amount of P sorbed was calculated fromthe difference between added and equilibrium con-centrations (Eq. 1):

S ¼ Ci � Ceð ÞV W= ð1Þ

where S is the adsorbed P amount per unit weight ofsolid (milligrams per kilogram), Ce is the equilibrium Pconcentration in the solution (milligrams per liter), Ci isthe initial P concentration in the solution (milligrams perliter), V is the volume of the solution (liters), andW is theweight of the air-dried soil (grams).

The sorption data were fitted to the two most com-mon equilibrium isotherms [Langmuir (Eq. 2) andFreundlich (Eq. 3)]:

S ¼ XmbC 1þ bCð Þ= ð2Þ

S ¼ KfCn ð3Þ

where S is the amount of P sorbed (milligrams perkilograms), C is equilibrium P concentration (milli-grams per liter), b is the constant related to the bindingstrength, Xm is the maximum adsorption amount de-termined by the specific surface area (milligrams pergram), Kf and n are constants. Kf (liters per kilogram)is the Freundlich distribution coefficient that describesthe equilibrium partitioning of P between solid andliquid phases and thus can be used as an index of Pmobility in the soil, and n is an empirical constantrelated to the intensity of the adsorption.

Water Air Soil Pollut (2013) 224:1524 Page 3 of 11, 1524

Tab

le1

Characteristicsof

thesoils

used

Soil,types,

andlocatio

nSand

Silt

Clay

Soiltype

pHPositive

charge

Negative

charge

Olsen

P(m

gkg

−1)

PRC

(%)

Total

elem

entalconcentration(m

gkg

−1)

PCa

Fe

Al

ADL

33.6±1.08

49.3±0.47

17.1±0.18

Loam

5.65

±0.29

2.24

5.64

3.82

±0.09

23.4

34.12±3.62

52.02±4.16

16,364

±45

.01

19,474

±49

.12

Kurosol

SA

BIR

94.1±1.73

2.92

±0.06

3.13

±0.09

Sand

3.42

±0.24

4.94

5.69

N.D.

4.62

N.D.

169.89

±6.14

502.64

±11.54

456.44

±10

.42

Pod

osol

Qld

DRA

39.1±0.65

47.6±1.56

13.1±0.79

Loam

5.17

±0.28

4.43

10.58

2.43

±0.06

19.6

26.32±3.17

47.82±3.92

16,019

±41

.23

10,418

±42

.19

Tenosol

NSW

KPD

53.2±0.45

29.2±0.19

15.5±0.11

Sandy

loam

7.14

±0.42

4.03

32.63

9.60

±0.34

7.43

348.4±9.89

5,99

6±29

.62

18,170

±35

.67

25,865

±51

.29

Calcarosol

SA

KUL

52.1±0.44

26.3±0.17

21.5±0.15

Sandy

clay

loam

9.12

±0.57

5.48

45.23

8.32

±0.31

11.5

74.26±1.81

6,56

6±33

.22

16,099

±75

.81

24,911

±49

.34

Calcarosol

SA

PIT

4.83

±0.14

47.8±1.29

47.2±0.64

Siltyclay

6.46

±0.39

3.16

11.59

2.96

±0.08

21.6

31.24±3.29

45.18±3.78

16,942

±47

.82

19,827

±52

.36

Vertosol

QLD

WAL

75.3±1.37

13.9±0.21

10.7±0.04

Sandy

loam

7.76

±0.45

3.90

36.58

7.71

±0.27

22.7

396.2±9.97

6,72

3±36

.14

16,421

±71

.86

22,948

±38

.72

Calcarosol

SA

N.D.no

tdetected

(detectio

nlim

it—

0.09

mgkg

−1)

1524, Page 4 of 11 Water Air Soil Pollut (2013) 224:1524

2.5 Effect of pH on CCP-induced Increasein P Retention

To study the effect of initial soil pH on CCP-inducedincrease in P retention, seven different soils (Table 1)with varying pH were used. The pH and the locationof soils are provided in Table 1. The soils were incu-bated with 0, 15, and 30 % (w/w) FBC for 21 days andthe pH and P retention were determined as mentionedabove.

2.6 Statistical Analysis

All statistical analyses were carried out using MicrosoftExcel 2010 software package. The effect of CCPs on thesorption of P in soils was examined by correlationanalysis. General curve fitting software was used toobtain the sorption isotherms for the soils and theircomponents. Sorption isotherm data were fitted to theFreundlich and Langmuir sorption models.

3 Results and Discussion

3.1 Properties of Soils and CCPs

The pH of the soils used ranged from 3.4 to 9.1 withKPD showing neutral pH (7.1) and PRC ranged fromabout 4.6 to 23.4 %. The elemental analysis results arelisted in Table 1. Among the soils, KPD and WALsoils showed high total P concentration; Ca contentswere high in KPD and KUL. Total Fe and Al concen-trations were high for all the soils except BIR, whichalso had low Ca concentration and total P was belowdetectable limits. The Olsen P values for the soilsranged from 3.82 to 9.6 mg kg−1.

In the case of CCPs, the pH were high (>10) forall CCPs and FBC had the highest pH (12.7). TheFBC had the highest CCE value (23.25 %),followed by FA (16.75 %). The Olsen P was highfor FA (260.4 mg kg−1), whereas FBC and FGDhad very low Olsen P values (Table 2). Pathan etal. (2002) observed 92.5 mg kg−1 extractable Pconcentration from a weathered FA in a WesternAustralia power station.

The total P concentration was highest for FA(1,522 mg kg−1), followed by FGD (623.85 mg kg−1)and FBC (154.35 mg kg−1). Aitken et al. (1984) ob-served 1,010 mg kg−1 total P concentration in FAT

able

2Chemical

prop

ertiesof

thestud

iedcoal

combu

stionprod

ucts

CCPs

pHEC(μScm

−1)

Olsen

P(m

gkg

−1)

CCE(%

)Total

elem

entalconcentration(m

gkg

−1)

PCa

Fe

Al

S

FA10

.2±0.17

1.34

±0.08

260.4±8.23

16.75

1,52

2±18

.38

18,035

.1±51

.62

121,30

0±18

5.97

25,170

±50

.21

N.D.

FBC

12.7±0.12

9.70

±0.17

11.52±1.62

23.25

154.3±3.75

149

,675

.2±76

.37

157,60

0±17

3.95

34,015

±57

.28

5,90

5.53

±32

.88

FGD

10.1±0.07

2.33

±0.11

2.25

2±0.93

11.25

623.8±12

.38

220,80

0±19

6.58

2,53

0.23

±23

.33

1,16

4.1±14

.14

156,25

0±17

2.53

N.D.no

tdetected

(detectio

nlim

it—

0.01

mgkg

−1),CCEcalcium

carbon

ateequivalence

Water Air Soil Pollut (2013) 224:1524 Page 5 of 11, 1524

collected from Port Augusta Power station, which isclose to the observed value of the FA used in thisexperiment. Contrastingly, FGD had the highest totalCa concentration at 220,800 mg kg−1 (Table 2), whichis attributed to the liming of coal before combustion.Killingley et al. (2000) studied FAs from various pow-er stations in Australia and found total P concentra-tions ranging from 648 to 7,360 mg kg−1 and total Caconcentration reached up to 27,400 mg kg−1. The highsulfur (S) contents in FBC and FGD are a result oflimestone scrubbing in the coal combustion units(Ritchey et al. 1995) to meet the emission standardsset by the global and local environment authorities.

3.2 Sorption Experiment

The effect of CCPs on P adsorption was measuredusing batch sorption isotherms. Overall, the additionof CCPs increased the sorption of P as measured bythe Kf value and the sorption of P increased in thefollowing order FBC > FA > FGD (Fig. 1). Initially,the KPD soil was used to study the effects of the threeCCPs at varying application rates (0, 15, and 30 %).The results showed that FBC was the most effectiveamendment in sorbing P, followed by FA. For both FAand FBC additions, the P sorption increased withincreasing application rates. The KPD soil amendedwith FGD showed the least response, although therewas over 50 % increase in P sorption at 15 %

application rate (Fig. 1). This can be attributed to pHand CCE values (Table 2). The Kf values for the CCP-amended soils were higher compared to the controlsoil (Table 3). The FBC-amended soils have thehighest sorption of P, followed by FA and FGD(Fig. 1).

The sorption isotherms are explained using thethree soils (BIR, KPD, and KUL) with variable pH,amended with 0, 15, and 30 % of FBC (Table 3). Thereason for using soils with variable pH is because thedifference in initial pH of the soil showed distinctchanges in P sorption on the application of CCPs tothe soil (Table 3), which will be discussed in detaillater. The results indicated that the addition of FBCaffected P sorption in all the three soils. The differencein Kf values between the soils at various applicationrates of CCPs was more pronounced in BIR soil,followed by KPD and KUL, which can be attributedto the initial pH of the soils and the change in pH afterthe application of FBC (Table 3). The sorption iso-therms fitted better to the Freundlich equation than tothe Langmuir equation, based on the R2 values (Zhouand Li 2001) that ranged from 0.991 to 0.999 for theFreundlich equation and 0.979 to 0.991 for theLangmuir equation (Table 3).

Several studies reported that the Freundlich equa-tion is effective in describing P sorption for soils(Barrow 1978, 2000; Cheung and Venkitachalam2000). It is an empirical equation and corresponds toa model of adsorption in which the affinity term de-creases exponentially as the amount of adsorption in-creases. Rushton et al. (2005) stated that an advantageof the Freundlich isotherm is that it assumes unlimitedsorption sites that correlated better with a heteroge-neous soil medium having different chemical/physicalproperties. Cheung and Venkitachalam (2000) arguedthat although Kf and Xm showed good correlation, theydo not reflect the same characteristics because Xm

represents the saturation level of sorbed P at highsolution concentrations.

Higher Kf values indicate greater retention of P insoils (Barrow 2000). Generally, a relatively largechange in sorbed P can be observed when the solutionconcentration deviates from unity and the sorptionintensity parameter (n) is higher. Hence, n measuresthe extent of impact on P sorption when a solutionconcentration changes from unity (Cheung andVenkitachalam 2000). The Kf is positively related toP sorption capacity of soils. The n values for P

0 4 8 12 16 20

P in solution (mg L-1)

0

2000

4000

6000

8000

10000

P ad

sorb

ed (

mg

kg-1

)

Fig. 1 Effect of CCPs (FA, FBC, and FGD) on P adsorption insoil at 15 % application rate

1524, Page 6 of 11 Water Air Soil Pollut (2013) 224:1524

adsorption decreased with increasing CCP applicationrates, but the differences were not as significant as theKf values (Table 3).

3.3 The Role of pH in the Sorption of P

The increase in P sorption (as measured by the Kf value)with the addition of CCPs to KPD soil is attributed to anincrease in soil pH (Fig. 2). The pH increased with increas-ing CCP application rate and the greatest pH increaseswere seen in FBC and FA. The decline in P sorption afteran initial increase at 15 % application rate of FGD isattributed to the decrease in soil pH. Barrow (1969) arguedthat while the adsorption of anions such as sulfate andmolybdate has often been shown to decrease with anincrease in pH, the opposite effect has been noticed inthe case of adsorption of P. Hence, pH is an importantfactor in anion adsorption, especially sorption of P. Forthis reason, seven different soils with varying pH werechosen to study the role of pH as affected by FBCapplication in the retention of P. The soils were mea-sured for the pH changes and PRC. The changes inPRC were expressed as delta P retention and weredetermined by calculating the difference between the Pretention values of amended soils and control soils.

A comparison between delta P retention and initial soilpH showed the decrease in delta P with an increase ininitial soil pH (Fig. 3). This indicates that the effect of

Table 3 Freundlich and Langmuir equations describing the adsorption of P in variable pH soils added with increasing application ratesof FBC

Soil samples Application rates Freundlich equation Langmuir equation

Kf n R2 Xm b R2

BIR 0 % FBC 649.07 0.737 0.991 5,913.12 0.133 0.979

pH—3.4

15 % FBC 935.65 0.625 0.999 6,104.71 0.123 0.983

ΔpH—3.04

30 % FBC 1,476.7 0.507 0.991 7,863.21 0.164 0.981

KPD 0 % FBC 881.34 0.627 0.998 2,606.32 0.166 0.987

pH—7.1

15 % FBC 1,175.3 0.552 0.992 2,986.41 0.172 0.984

ΔpH—1.7

30 % FBC 1,381.6 0.514 0.992 3,100.50 0.179 0.991

KUL 0 % FBC 777.67 0.686 0.998 3,128.48 0.128 0.985

pH—9.1

15 % FBC 927.16 0.675 0.998 3,463.82 0.156 0.981

ΔpH—0.43

30 % FBC 1,092.1 0.644 0.995 3,891.16 0.161 0.986

pH initial soil pH, ΔpH difference between initial soil pH and pH of amended soil

6 7 8 9 10pH

400

600

800

1000

1200

1400

Kf(L

kg-1)

FAFBCFGD

Y = 191.4 * X - 752.8R2 = 0.867

Fig. 2 The relationship between pH of Adelaide hills (ADL)soil and increase in P sorption as affected by CCPs at threeapplication rates (0, 15, and 30 % w/w). Error bars represent thestandard deviation between replicates

Water Air Soil Pollut (2013) 224:1524 Page 7 of 11, 1524

CCPs in increasing P sorption was less pronounced insoils with high initial pH. The delta pH values alsoinfluenced changes in the P adsorption (Table 3). Theacidic soil (BIR) with a delta pH of 3.04 showed higherincrease in P sorption at the highest application rate ofFBC compared to the alkaline soil (KUL) with a delta pHof 0.43. Curtin et al. (1992) saturated a soil with Ca andobserved that an increase in pH increased the retention ofP, which they attributed to the precipitation of Ca phos-phates. Chen et al. (2007) compared the P sorption capac-ities of 15 different FAs (with different pH) and concludedthat the highest P sorption occurred at alkaline pH.

3.4 The Role of P Sorptive Components Like Al, Fe,and Ca in Sorption of P

The influence of Al, Fe, and Ca in soil solution on Psorption was evaluated by relating various fractions ofthese cations with % P retention at varying rates of FBCapplication to seven different soils. Both crystalline andamorphous fractions of Al and Fe showed poor

R² = 0.1265

0

5

10

15

20

25

30

35

40

45

0 100 200 300 400

P r

eten

tio

n (

%)

Alcd(µg g-1)

a R² = 0.4435

0

5

10

15

20

25

30

35

40

45

0 200 400 600 800 1000 1200 1400 1600

P r

eten

tio

n (

%)

Alox (µg g-1)

b

R² = 0.1267

0

5

10

15

20

25

30

35

40

45

0 500 1000 1500 2000 2500 3000

P r

eten

tio

n (

%)

Fecd (µg g-1)

c R² = 0.2804

0

5

10

15

20

25

30

35

40

45

0 500 1000 1500

P r

eten

tio

n (

%)

Feox(µg g-1)

d

Fig. 4 Relationship between % P retention and a Alcd, b Alox, cFecd, and d Feox for seven soils [Adelaide hills (ADL), Kapunda(KPD), Kulpara (KUL), Wallaro (WAL), Birbie Island (BIR),

Pittsworth (PIT), and Drake (DRA)] at three different (0, 15, and30 % w/w) application rates of FBC. Error bars represent thestandard deviation between replicates

4 6 8 10pH of soil

16

18

20

22

24

26D

elta

P r

etai

ned

(%

)Y = -0.894 * X + 27.45R2 = 0.309

Fig. 3 Relationship between initial soil pH and increase in Pretention (delta P retention) resulting from FBC application at15 % (w/w) rate to seven soils [Adelaide hills (ADL), Kapunda(KPD), Kulpara (KUL), Wallaro (WAL), Birbie Island (BIR),Pittsworth (PIT), and Drake (DRA)]. Error bars represent thestandard deviation between replicates

1524, Page 8 of 11 Water Air Soil Pollut (2013) 224:1524

correlation (Fig. 4a, b, c, and d), in which the greatestrelation with % P retention was for Alox (R

2=0.4435).When the values of both Al and Fe were combined, thecorrelation between (Al + Fe)ox and % P retentionslightly increased (R2=0.4914) and was the highestamong the extractable Fe and Al values (Fig. 5a andb). Sakadevan and Bavor (1998) related P sorption withAlox, Feox and also combination of both Alox and Feoxfor soils treated with blast furnace slag and observed thatthe (Al + Fe)ox played a significant role in P sorption. Asignificant relation between the extractable Fe fractionsand % P retention was not found. Also, the regressionbetween (Al + Fe)cd and % P retention was also verylow. Stout et al. (1998) found that the increase in the

concentration of Al, Fe, and Ca in soil solution resultingfrom the application of CCPs decreased P loss in soils,which was due to the formation of insoluble Al-P, Fe-P,and Ca-P (McDowell 2005).

However, among the three cations, Ca in solutionwas best associated (R2=0.5137) with % P retention(Fig. 6). This suggests that Ca in solution may be theinfluencing factor for P retention, which can also bejustified by the increase in pH on the addition of CCPs(McDowell 2005). Chen et al. (2007) analyzed 15different FAs for P sorption maxima and found that Pimmobilization was governed by Ca (especially CaOand CaSO4) and Fe (especially Fecd) ingredients. Theyalso proposed that P immobilization by FA may be dueto the formation of Ca-P precipitate and sorptionthrough ligand exchange with Fe-related compounds.

4 Conclusions

The CCPs proved to increase the sorption of P in soilswhen applied at optimal rates. The sorption results indi-cate that CCPs are effective in enhancing the PRC of soilsby decreasing the soil solution P. Among the CCPs, FBCwas very effective in increasing P sorption, followed byFA and FGD. The pH played a major role in P sorption inall the soil samples. The addition of CCPs showed pos-itive results in acidic and neutral soils in terms of increasein P adsorption, whereas alkaline soils showed the leastresponse on the effect of CCPs. The Ca concentration inthe soil solution has been the major factor for P adsorp-tion compared to Al and Fe in the solution.

R² = 0.1408

0

5

10

15

20

25

30

35

40

45

0 1000 2000 3000 4000

P r

eten

tio

n (

%)

(Al+Fe)cd(µg g-1)

a R² = 0.4914

0

5

10

15

20

25

30

35

40

45

0 500 1000 1500 2000 2500

P r

eten

tio

n (

%)

(Al+Fe)ox(µg g-1)

b

Fig. 5 Relationship between % P retention and a (Al + Fe)cdand b (Al = Fe)ox for seven soils [Adelaide hills (ADL),Kapunda (KPD), Kulpara (KUL), Wallaro (WAL), Birbie Island

(BIR), Pittsworth (PIT), and Drake (DRA)] at three different (0,15, and 30 % w/w) application rates of FBC. Error bars repre-sent the standard deviation between replicates

R² = 0.5137

0

5

10

15

20

25

30

35

40

45

0 500 1000 1500 2000 2500 3000

P r

eten

tio

n (

%)

Ca in solution (µg g-1)

Fig. 6 Relationship between % P retention and Ca in solution. forseven soils [Adelaide hills (ADL), Kapunda (KPD), Kulpara(KUL), Wallaro (WAL), Birbie Island (BIR), Pittsworth (PIT),and Drake (DRA)] at three different (0, 15, and 30 % w/w)application rates of FBC. Error bars represent the standard devi-ation between replicates

Water Air Soil Pollut (2013) 224:1524 Page 9 of 11, 1524

Acknowledgments This study was sponsored by the Cooper-ative Research Centre for Contamination Assessment and Re-mediation of the Environment (CRC CARE), Australia incollaboration with the University of South Australia. The au-thors thank Dr. Mohammad Rahman for technical assistancewith the ICP analysis. The postdoctoral fellowship program(PJ008650042012) at the National Academy of AgriculturalScience, Rural Development Administration, Republic of Koreasupported Dr. Kunhikrishnan's contribution.

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