Assessment of Heavy Metals Immobilization in Artificially Contaminated Soils Using Some Local Amendments

doi:10.4236/ojmetal.2013.32A1009

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Open Journal of Metal, 2013, 3, 68-76

http://dx.doi.org/10.4236/ojmetal.2013.32A1009 Published Online July 2013 (http://www.scirp.org/journal/ojmetal)

Assessment of Heavy Metals Immobilization in Artificially

Contaminated Soils Using Some Local Amendments

Noha H. Abdel-Kader, Reda R. Shahin*, Hasan A. Khater

Soils Department, Faculty of Agriculture, Cairo University, Giza, Egypt

Email: *dredashahin@gmail.com

Received May 17, 2013; revised June 23, 2013; accepted July 2, 2013

License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Three alluvial soil samples with different textures were artificially polluted with chloride solutions of Cd, Pb, Co and

chromate solution for Cr. The aqua-regia extracted concentration ranges in the artificially polluted soils were 1134 -

1489 mg·kg−1 for Pb, 854 - 938 mg·kg−1 for Cr, 166 - 346 mg·kg−1 for Co and 44 - 54 mg·kg−1 for Cd. The aqua-regia

extracted metals were the highest in the spiked clay soil due to its high adsorption capacity. Rock phosphate (PR), lime-

stone (LS) and Portland-cement (Cem) were mixed with the spiked soils at 1% and 2% rates (w/w) and incubated at 30

C for 2, 7, 14, 30, 60, 150 and 360 days. The extracted DTPA metals significantly decreased with different magnitudes

with increasing the incubation period accompanied by increases in both pH and EC. The data showed that cement (Cem)

treatment dropped the DTPA-Pb from @ 1000 to @ 400 mg·kg−1 in all the studied soils (60% decrease) in the first 2

months while it gradually decreased from 400 to 200 mg·kg−1 (20% decrease) in the next 10 months. Limestone (LS)

and rock phosphate (PR) materials were relatively less effective in lowering DTPA-Pb after 12 months of incubation.

The data showed also that cement (Cem) treatment was the most effective one in lowering DTPA-Cd by @ 60% as

compared to the un-amended soils after 12 months of soil incubation. Extractable DTPA-Co and Cr showed consistent

decreases with time down to nearly 50% of un-amended soils due to the effect of the added amendments after 12

months of incubation with superior reductions for the cement treatment in all the investigated soils. The statistical

analysis confirmed that in all the studied metals and treatment, cement treatment (Cem) was significantly the most ef-

fective in lowering the DTPA extracted metals as indicated from LSD test. It was found that up to 73% and 57% of the

applied Pb and Cd, respectively, were fixed by only 1% cement. However, the present study showed that from the prac-

tical and economic points of view, that 1% Cement was the best treatment to immobilize Pb and Cd from all the artifi-

cially polluted soils.

Keywords: Heavy Metals; Immobilization Efficiency; Rock Phosphate; Portland Cement; Lime-Stone

1. Introduction

The contamination of soils with heavy metals is now

worldwide concerned due to its hazard to ecosystem in-

cluding soil, water, plant, animal and human life. The

common international technologies of the remediation of

the heavy metals contaminated sites are physical, chemi-

cal and biological techniques. The immobilization tech-

nique is commonly recognized for the in-situ remediation

of heavy metals contaminated soils (Unite State Envi-

ronmental Protection Agency (EPA), [1]. Immobiliza-

tion is the reduction of the solubility of heavy metals

through chemical reactions (ion-exchange, adsorption,

precipitation and complexation processes) making them

less harmful or less mobile (Hashimoto et al. [2] and

Wang et al. [3]). The mostly applied amendments in-

clude clay material, cement, zeolites, phosphates, and

organic composts GWRTAC [4] and Finžgar et al. [5].

Zhang and Pu [6] used limestone (AL), rock phosphate

(RP), palygorskite (PG), and calcium magnesium phos-

phate (CMP) to stabilize heavy metals in two urban soils

(calcareous soil and acidic soil) polluted with cadmium,

copper, zinc and lead for 12 months. The results showed

that application of those materials reduced exchangeable

forms in the order of Pb > Cd > Cu > Zn. Phosphate and

and palygorskite treatments were more efficient than

limestone and rock phosphate in stabilizing heavy metals.

Padmavathiamma and Li [7] found that lime application

to H.M. polluted soil lowered plant available Pb and Mn,

while rock phosphate decreased plant available Pb and

increased plant Mn. Houben et al. [8] found that the ad-

*Corresponding author.

N. H. ABDEL-KADER ET AL. 69

dition of CaCO3 to heavy metals contaminated soils sig-

nificantly reduced both the leaching and the availability

of Cd, Zn and Pb metals. Chen et al. [9] applied rock

phosphate with a rate of 2500 mg P2O5 kg−1 soil and

found that it could successfully reduce the bioavailability

and increase the geochemical stability of Pb, Zn and Cd

in soil. In addition, Chen et al. [10] showed that rock

phosphate of the smallest grain size (<35 microns) was

superior to all of other grain sizes more than 35 microns

for reducing uptake in plant (Brassica oleracea L.) shoots

for Cd (19.6% - 50.0%), Pb (21.9% - 51.4%) and Zn

(22.4% - 34.6%), respectively, as compared with the soil

without application of rock phosphate. Cao et al. [11]

stated that rock phosphate amendment significantly re-

duced Pb water solubility, phyto-availability, and bio-

accessibility by 72% - 100%, 15% - 86%, and 28% -

92%, respectively due to the formation of insoluble Pb-

phosphate minerals and reduced water soluble Cu and Zn

by 31% - 80% and 40% - 69%, respectively. Al-Oud and

Hilal [12] found that the admixing 0.5% of cement could

reduce the 0.5 N HNO3 extracted Pb by values up to 65%

in the polluted sandy soils in Saudi Arabia. Alpaslan and

Yukselen [13] conducted several leaching experiments

for mixtures of different additives (lime, activated carbon,

clay, zeolite, sand and cement) with artificially Pb con-

taminated (spiked) soil samples. They stated that lime

and cement were significantly effective in Pb immobili-

zation with 88% efficiency at 1:21 lime:soil ratio and

99% efficiency at 1:15 cement:soil ratio, respectively.

The objective of the present work is to evaluate the ef-

ficiency of different local amendments to stabilize or

immobilize heavy metals in different soil types artifi-

cially spiked with Pb, Cd, Cr and Co heavy metals.

2. Materials and Methods

Three soil samples with different textures were taken

from the most common polluted spots at Bahr el Bakar

and Helwan. The collected samples were subjected to the

physical and chemical analyses according to Sparks et al.

[14] and their characteristics are presented in Table 1.

Solutions of different concentrations of cadmium (Cd),

lead (Pb), and cobalt (Co) were prepared using metal

chlorides and Cr as chromate, then sprayed onto the soil

samples with continuous mixing to homogenize the dis-

tribution of the applied heavy metals. The spiked soils

were allowed to be air-dried after each portion of sprayed

metals solution. The total amounts of the metals were

applied to exceed their maximum concentrations in soils

as reported by EPA [15]. After spiking, the soil was su-

persaturated with deionized water and then mixed peri-

odically for two weeks. The wetting and air dry cycle

procedure was repeated five times to allow sufficient

mixing of the applied metals and soil to imitate field

conditions (Shanbleh and Kharabsheh, [16]; Lin et al.,

[17]). The aqua regia extraction was conducted and based

on the procedure recommended by Cottenie et al. [18]

which standardized by the International Organization for

Standardisation (ISO 11466, [19]). In this procedure the

soil sample intake was of 1 g, which were placed in 100

ml Pyrex digestion tubes, then 3 ml distilled water was

added to obtain slurry. Thereafter, 7.5 ml of 37% HCl

and 2.5 ml of 70% HNO3 (3:1) mixture were added to the

tube which was covered and left overnight. Then, the

suspension was digested at 130˚C for 2 h, in a reﬂux

condenser. The obtained suspension was then ﬁltered

through an ashless Whatman 41 ﬁlter, diluted to 25 ml

with 0.5 mol·L−1 HNO3, and stored in polyethylene bot-

tles at 4˚C for analyses.

The available metal contents of soils were extracted in

DTPA (diethylene-triamine-penta-acetic acid) according

to Lindsay and Norwell [20] as modified by ISO 14870

[21]. The DTPA-TEA solution was prepared by mixing

of 0.005 mol·L−1 DTPA, 0.01 mol·L−1 CaCl2, 0.1 mol·L−1

tri-ethanolamine (TEA) with pH adjusted to 7.3 with 1

mol·L −1 HCl solution. An amount of 5 g of soil sample

(<2 mm) was weighted into a 125 mL Erlenmeyer flask,

then 20 ml of DTPA-TEA extracting solution was added

and shaken for 2 h at room temperature using a platform

shaker. The soil suspension was centrifuged at 2000 rpm

for 15 min. and the clear supernatant was diluted to 50

mL with re-distilled water. Both aqua-regia and DTPA-

extractable contents were determined by a Perkin-Elmer

model 1100B ﬂame atomic absorption spectrometer (AAS).

Analysis of variance and LSD were used to compare

treatment means. All the statistical analyses were carried

out using Costat software [22].

The chemical and physical properties of the artificially

contaminated soils are presented in Table 2.

Three local amendments were chosen, i.e. Phosphate

rock (PR), Limestone (LS), and Portland cement (Cem).

Portions of 100 g from the artificially contaminated soils

were mixed with 1 g and 2 g of each amendment. A con-

trol treatment (C0) for each soil with no amendment ad-

dition was also prepared. Each treatment was carried out

in triplicates. Replications of the homogeneous soil mix-

tures were watered to saturation level and placed in

sealed small polyethylene bags in order to maintain the

moisture level. The sealed soil mixture bags were incu-

bated for 2, 7, 14, 30, 60, 150 and 360 days at 31˚C ±

2˚C. The soil bags were thoroughly mixed during the in-

cubation process. At each period, a replicate from each

treatment was removed from the incubator and the

DTPA-TEA extractable fractions of the studied metals in

soils were determined after incubation. The difference in

initial concentration and final concentration, knowing dry

mass of soil, allowed for the calculation of the exact

amount of heavy metals adsorbed per gram of soil. A

tandard solution was run with each batch to justify the s

N. H. ABDEL-KADER ET AL.

Table 1. Some physical and chemical characteristics of the initial soil samples.

Soil texture Particle size fraction (g/kg)

Sand Silt Clay

(1:2.5) EC dS/m OM

(g/kg)

CaCO3

(g/kg)

CEC

Cmol/kg

Sandy L. 748 144 108 7.79 1.14 1.5 11.6 9.4

Loamy 460 378 162 7.83 1.94 11.3 22 33.6

Clay 424 90 486 7.55 3.66 26.6 3.26 48.1

Cd (mg/kg) Pb (mg/kg) Co (mg/kg) Cr (mg/kg)

Aqua-Regia DTPA Aqua-Regia DTPA Aqua-Regia DTPA Aqua-Regia DTPA

Sandy L. 1.02 0.08 20.3 0.3 3.2 0.53 16.3 7.37

Loamy 2.01 0.14 46 1.3 5.5 0.67 11.12 4.13

Clay 3.03 0.03 10.5 0.1 5.68 0.45 9.32 2.5

Table 2. The chemical characteristics of the spiked soil samples and the different amendments used in the incubation experi-

ment.

Pb (mg/kg) Cd (mg/kg) Co (mg/kg) Cr (mg/kg)

1:2.5

dS/m Aqua-Regia DTPAAqua-Regia DTPAAqua-RegiaDTPA Aqua-RegiaDTPA

Sandy loam 8.8510.4 1134.2 1027.244.53 34.65165.70 23.97 854.4 189.10

Loamy 8.585.0 1421.1 1008.352.71 31.65229.30 18.62 878.2 153.80

Spiked soils

Clay 8.4426.4 1488.9 988.454.09 23.13346.10 7.70 938.0 67.20

P-Rock 2.1 0.0044.80 0.11 1.26 ND 3.5 0.03

Limestone 3.0 0.0170.16 0.02 0.08 ND 7.1 0.08

Amendment

Cement 9.3 0.2300.10 0.0084.78 0.007 18.1 0.12

ND = Not detected.

data. The efficiency (E) of different amendments for im-

mobilization heavy metals can be evaluated using the

expression:



0120

% 100ECCC



 



where E = immobilization efficiency %; C12 = equilib-

rium extractable concentration (mg·kg−1) of single metal

in the amended soil at the end of incubation experiment

(12 months); C0 = initial extractable concentration

(mg·kg−1) of single metal in the amended soil at zero

time.

3. Results and Discussion

The data of the spiked soil samples, showed tremendous

increases in the Aqua-regia extracted Pb, Cd, Co and Cr

proportional to their applied amounts. Table 2 showed

that the aqua-regia extracted metal concentrations were

the highest in the clay soil due to its high adsorption ca-

pacity for all the tested heavy metals and the vice versa

for the sandy soil. The highest concentration was re-

corded for Pb and the least for Cd in the different soils in

the order: Pb >Cr > Co > Cd. This is due to the high

geochemical affinity of Pb to react with soil constituents

forming inner-sphere complexes and even precipitate in

different forms. In contrast to Pb, Cd tend to be less and

weakly adsorbed by different soils which facilitate its

leaching (Irha et al. [23]). Table 2 indicated that the

concentrations of the labile heavy metal forms (i.e.

DTPA-extracted) were higher in the spiked sandy soil

compared to clay one due to the lack of adsorping/active

surfaces in sandy soil. Li-Yi et al. [24], Mbarki et al. [25]

and Selim [26] concluded that the free heavy metal ion

concentrations in sandy soils were higher than in clay

one receiving the same pollutants. Figure 1 showed the

initially adsorbed concentrations in the spiked soils for

the investigated metals. These values were obtained by

subtracting The DTPA from Aqua-regia extracted heavy

metal concentrations. It was clearly noticed the clay soil

initially adsorbed the highest concentrations of all the

investigated heavy metals while sandy one adsorbed the

lowest values. Again, chromium (Cr) and lead (Pb)

showed the highest concentrations initially adsorbed in

all the investigated soils which may rendered to their

high adsorption affinity and the formation of inner-

sphere complexes with the active surfaces of soil con-

stituents. This is in agreement with Gomes et al. [13]

whom observed that in a competitive situation Cr and Pb

were the heavy-metal cations most strongly adsorbed by

seven Brazilian soils, whereas Cd, Ni, and Zn were the

least adsorbed.

The obtained data showed that the application of the

N. H. ABDEL-KADER ET AL. 71

different amendments had a significant effect on pH

value of all the studied soils (Figure 2). Generally, in all

treatments, the pH significantly increased within 2 days

f incubation showing the highest jump between 60 and o

10 0

200

300

400

500

600

700

800

900

1000

Co PbC

Initially Fixed (mg/kg)

Sa ndy loamLoamy Clay

Sand y loamLoamyClay

Initially Fixed (mg/kg)

Figure 1. Initially fixed heavy metal concentrations in the artificially contaminated soils.

Figure 2. Changes of pH and EC of the polluted soils throughout the incubation periods as affected by the applied rates of the

local amendments.

N. H. ABDEL-KADER ET AL.

150 days followed by steady increases upto 360 days.

Soil pH value increased with increasing application rates

of amendments. When the same rates of amendments

were applied, the pH values increased in the sequence of

Cem > LS > PR. With respect to pH changes in the in-

vestigated soils, significantly the highest pH values were

recoded in the sandy soil as compared to the same treat-

ments in the clay one. This could be rendered to the low

buffering capacity of sandy soils and the lack of reserve

acidity that can alleviate the alkalinity effect of the ap-

plied amendments. In addition, the initial pH values of

the artificially polluted soil were more than 8.44 and 8.85,

which may limit the buffering action to the bases pro-

duced from the hydrolysis of the highly alkaline compo-

nents of Portland cement. Tylor [27] stated that there are

four chief minerals present in a Portland cement grain:

tricalcium silicate (Ca3SiO5), dicalcium silicate

(Ca2SiO4), tricalcium aluminate (Ca3Al2O5) and calcium

aluminoferrite (Ca4AlnFe2−nO7). The initial increase of

pH is typical of cementitious systems because the cement

produces high amount of Ca(OH)2; and high concentra-

tion of hydroxyl ions (Brown [28] and Tylor [27]) as in

the following reactions:

Tricalcium silicate

 

 

2CaOSiO7HO

CaOSiO4H O+3CaOH



 2

Dicalcium silicate

 



2CaO SiO5HO

CaOSiO4H O+CaOH





Tricalcium aluminate









 

2CaOSiO7HO

CaOSiO4H O+3CaOH







The incubation of the amended soils also caused gen-

eral increases in EC values with time in most of the in-

vestigated amendments (Figure 2). Limestons (LS) treat-

ments showed the highest EC values followed by Cement

(Cem.) as shown in loamy and clay soils and EC values

increased by increasing the percent of application. It is

clearly noticed that the majority of EC increases were

recorded between 150 and 360 days of incubation period

which could be rendered to the hydrolysis and solubility

of Ca-compounds that may take longer time. The pres-

ence of siliceous-aluminous materials in cement compo-

sition creates some kind of high adsorption sites for met-

als found in soils. Moreover, the production of calcium

hydroxide during cement hydrolysis, increase pH of the

treated soils and subsequently decreasing the bioavail-

ability of heavy metals in soils. Figure 3 Showed that

cement (Cem) treatment dropped the DTPA-Pb from @

1000 to @ 400 mg/kg in all the studied soils (60% de-

crease) in the first 2 months while it gradually decreased

from 400 to 200 mg/kg (20% decrease) in the next 10

months. Limestone (LS) and rock phosphate (PR) mate-

rials were relatively less effective in lowering DTPA-Pb

after 12 months of incubation. The data showed also that

cement (Cem) treatment was the most effective one in

lowering DTPA-Cd by @ 60% as compared to the un-

amended soils after 12 months of soil incubation.

Extractable DTPA-Co and Cr (Figure 4) showed con-

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

050100 150 200250 300 350 40

Time (Days)

DTPA-Pb (mg/kg)

Control PR 1%PR 2%LS 1%

LS 2%Cem. 1%Cem. 2%

Sandy

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

050100 150 200 250 300 350 40

Time (Days)

DTPA-Pb (mg/kg)

Loamy

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

050100 150200250 30035040

Time (Da ys)

DTPA-Pb (mg/ kg)

Clay

050100 150 200 250300 350 40

Time (Days)

DTPA-Cd (mg/kg)

050100 150 200 250300 350 400

Time (Days)

DTPA -Cd (mg/kg)

050100 150 200 250300 350 400

Time (Days)

DTPA -Cd (mg/kg)

Control PR 1%PR 2%LS 1%

LS 2%Cem. 1%Cem. 2%

Figure 3. Changes of pH and EC of the polluted soils throughout the incubation periods as affected by the applied rates of the

local amendments.

N. H. ABDEL-KADER ET AL. 73

050100 150 200 250300350 400

Time (Days)

DTPA-C o (m g /kg )

Sandy

050100150200 250 300 350400

Time (Days)

DTPA-Co (mg/kg)

Loamy

050100 150200 250 300 350 400

Time (Days)

DTPA-Co (mg/kg)

Control PR 1%PR 2%LS 1%

LS 2%Cem. 1%Cem. 2%

Clay

100

110

120

130

140

150

160

170

180

190

200

050100150 200250300350 400

Time (Days)

DTPA-Cr (mg/kg)

100

110

120

130

140

150

160

050100150200 250 300350400

Time (Days)

DTPA-Cr (mg/kg)

050100 150 200 250300 350 400

Time (D ays)

DTPA-Cr (mg/kg )

Control PR 1%PR 2%LS 1%

LS 2%Cem. 1%Cem. 2%

Figure 4. Extractable DTPA-Co and Cr from the polluted soils throughout the incubation periods as affected by the applied

rates of the local amendments.

sistent decreases with time down to nearly 50% of un-

amended soils due to the effect of the added amendments

after 12 months of incubation with superior reductions

for the cement treatment in all the investigated soils. The

statistical analysis (Table 3) confirmed that in all the

studied metals and treatment, cement treatment (Cem)

was significantly the most effective in lowering the

DTPA extracted metals as indicated from LSD test.

In addition, LSD test showed that cement treatment

was significantly decreased all the DTPA extractable

metals, and the increased of the applied cement from 1 to

2% didn’t show any significant differences, which indi-

cated that only 1% of cement was enough to get the low-

est DTPA extracted metals in all the investigated soils.

Table 4 showed the heavy metals concentrations that

immobilized by the effect of the different local amend-

ments, it was obtained by subtracting concentration at the

end of the incubation experiment i.e. 12 months (C12)

from the relevant concentration in the polluted soil at

zero time (C0), so amendment immobilized metal = (C0)-

(C12). The obtained data showed that the immobilized

concentrations by the different amendments could be in

the order: Pb > Cr > Cd > Co in all the studied treatments.

gain, it could be concluded that cement (Cem) had the A

N. H. ABDEL-KADER ET AL.

Table 3. LSD analysis of the mean concentrations of different metals in the different treatments and soils at the end of the

incubation experiment.

Concentration (mg/kg soil)

Soil

type

Treatment

symbol Pb Cd Co Cr

Sandy Control 990.6 a 34.67 a 23.960 a 153.1 a

PR 1% 795.9 b 30.97 b 21.159 b 140.1 b

PR 2% 787.2 b 30.91 b 20.939 b 139.0 b

LS 1% 763.8 b 30.59 b 20.730 b 130.6 c

LS 2% 738.4 b 30.35 b 20.677 b 125.2 c

Cem 1% 563.8 c 28.19 bc 20.121 b 117.4 d

Cem 2% 538.0 c 26.81 c 19.870 b 115.8 d

LSD 0.05 99.1 2.29 0.913 7.4

Loamy Control 1026.6 a 31.587 a 18.64 a 188.9 a

PR 1% 821.2 b 28.899 b 17.71 ab 175.9 b

PR 2% 812.2 b 28.640 b 17.05 b 174.0 b

LS 1% 715.9 bc 28.154 bc 16.89 b 173.7 b

LS 2% 677.7 c 27.650 bc 16.69 b 165.9 b

Cem 1% 570.0 d 26.401 cd 15.61 c 146.9 c

Cem 2% 543.7 d 25.171 cd 14.85 c 142.5 c

LSD 0.05 104.5 1.532 0.98 9.8

Clay Control 1012.6 a 23.064 a 7.689 a 67.16 a

PR 1% 770.1 b 20.221 b 7.039 b 63.83 b

PR 2% 760.6 b 19.901 b 6.949 b 62.42 b

LS 1% 736.2 b 19.760 b 6.847 b 59.31 c

LS 2% 722.1 b 19.654 b 6.737 b 57.39 cd

Cem 1% 687.8 b 18.961 bc 6.016 c 55.98 cd

Cem 2% 572.2 c 18.406 c 5.890 c 54.61 d

LSD 0.05 88.7 0.943 0.354 2.85

*Means within a column followed by the same letter are not significantly different; according to Fisher’s protected LSD test at p ≤ 0.05.

Table 4. Immobilized concentrations of heavy metals in different polluted soils amended with local materials (C0-C12)

mg·kg−1.

PR 1% PR 2% LS 1% LS 2% Cem 1% Cem 2% Initial-DTPA

Clay Co 2.23 2.90 2.40 3.16 3.97 4.04 7.70

(C0-C12) Cd 7.42 9.18 7.63 8.71 9.70 10.33 23.13

Cr 13.21 18.77 13.09 20.29 23.22 27.74 67.20

Pb 568.04 598.55 565.29 594.16 658.17 682.94 988.4

loam Co 5.05 5.47 5.30 6.62 7.66 8.21 18.62

(C0-C12) Cd 7.39 8.67 9.08 9.71 9.87 12.31 34.65

Cr 41.82 47.96 46.55 51.25 57.51 62.77 153.80

Pb 604.71 649.80 594.35 660.28 740.60 768.4 1008.3

Sand Co 3.81 4.16 3.86 4.38 7.22 7.88 23.97

(C0-C12) Cd 9.64 12.40 10.42 12.85 18.06 19.53 31.65

Cr 55.07 56.70 59.50 64.39 73.39 81.85 189.10

Pb 494.02 517.69 498.23 526.02 753.36 762.99 1027.2

N. H. ABDEL-KADER ET AL. 75

most effective immobilization in all the investigated

heavy metals polluted soils. Cobalt (Co) and chromium

(Cr) showed the lowest response to the added amend-

ments as their immobilized concentrations were 2.23 to

8.21 and 13.2 to 81.85 mg·kg−1, respectively, as com-

pared to that of immobilized Pb-concentrations (494.02

to 762.99 mg·kg−1).

Figure 5 showed that the immobilization efficiency



0120

% ECCC



 



100 of lead (Pb) was the

highest (67% - 73%) among the other heavy metals in all

the investigated soils especially those treated with ce-

ment. The immobilization efficiency for Cd was 28.48%

- 57.06%, for Cr it was 34.55% - 38.81% and for Co it

ranged between 30.12% - 51.56% of the initial DTPA

concentrations were fixed by only 1% cement. However,

the present study showed that from the paractical and

economic points of view, that 1% Cement was the best

treatment to immobilize Pb and Cd from all the artifi-

cially polluted soils.

According to Ganjidoust et al. [29], it is found that the

hydrating cement product enhances the heavy metals

precipitation on the surfaces of their particles as shown in

Figure 6. Lead (Pb) and Cd were found in stabilized

forms of Ca2Pb2O5(OH)2, and CaCd(OH)4, respectively.

Co CdCrPb CoCdCrPb Co Cd CrPb

Clayloam Sand

I mmobilizati on E f ficiency

PR 1%PR 2%LS 1%LS 2%Cem. 1%Cem. 2%

Figure 5. The efficiency of the heavy metals immobilization

for different types and rates of local amendments.

Cement particle

Pb-Precipitate

CaZn

(OH)

·2H

CaCd(OH)

Particle’s

Surface

Cr-incorpor ation

HgO

BaSO

-BaCO

Calcium silicate

hydrate

Figure 6. Immobilization of heavy metals by hydrated par-

ticle of Portland cement as suggested by Ganjidoust et al.

(2009).

In addition, Komisarek and Wiatrowska [30] stated

that cementitious material has the potential ability to

immobilize heavy metals by adsorption, precipitation sur-

face complexation and isomorphous substitution.

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