Extradon of Metab from a Contaminated Sandy Soil Using Citric Acid Raman Bassi, Shiv 0. Prosher Department of Agricultural and Biosystems Engineering, Macdonald Campus, McGill University, Ste-Anne-de-Bellevue, Quebec, Canada H9X 3V9

B.K. Simpson Department of Food Science and Agricultural Chemistry, Macdonald Campus, McGill University, Ste-Anne-de-Bellevue, Quebec, Canada H9X 3V9

twenty four-hour washing of a contaminated soil with 0.5 M citric acid reduced the levels of Cd, Cu, Zn, and Pb from 0.01, 0.04, 0.42, and 41.52 mg g-1 to 0, 0.02, 0.18 and 5.21 mg g-1, respectively. Extending the washing period beyond 24 hours did not influence the results significantly. Metal ions present in higher amounts were removed more easily. A column study was also conducted to compare metal leaching with surface and subsurface application of 0.3 M citric acid to 60 cm long soil columns packed with metal-contaminated soil. Results indicated that the uniform distribution of citric acid, applied through the subirrigation system, resulted in a more eflcient extraction of metal ions. The extraction of Zn and Pb from the columns with subsurface application of citric acid was, respectively, 38 and 27 times higher than from the columns with surface application of citric acid. Afer washing the contaminated soil with various citric acid concentrations, the metal-rich wash solution was treated effectively using chitosan jlakes.

INTROWCTKN Soil washing, a water-based process that employs

chemical and physical extraction processes to remove contaminants from the soil, has recently become a common ex-situ technique for remediating sites conta- minated with organic and inorganic pollutants. This process has been proven successful in the remedia- tion of various heavy metal-contaminated sites includ- ing certain Superfund sites in the US ill.

Several studies have attempted to optimize the extraction of heavy metals from contaminated soils using various wash solutions, including strong mineral

acids, reducing agents, surfactants, and a number of chelating agents, such as nitriloacetic acid (NTA), eth- ylenediaminetetraacetic acid (EDTA), ethylene glycol- (-aminoethylethed-N,N,N,N- tetraacetic acid (EGTA), cyclodextrin derivatives, pyridine-2,6-dicarboxylic acid (PDA), and 1,2-diaminocyclohexane N,N,N’,N’- tetraacetic acid (DCyTA), etc. 12, 3, 4 , 5, 6, 71. Davis and Singh applied EDTA and DTPA, and chlorine, all at various concentrations, to zinc (11) contaminated (artificially) soil columns for the purpose of determin- ing their metal-extraction efficiency [21. Removal of zinc from the soil increased with increasing EDTA concentration. Total zinc removal efficiency increased to 79% with 1 mM EDTA extraction solution. The gen- eral trend of the washings with DTPA was the same as with EDTA.

A noticeable extraction of cadmium from spiked soils using the chelator PDA was observed [31 while measuring the extracted metal concentration in the aqueous phase under different pH, soil suspension, total ligand concentration, and total carbonate con- centration conditions. A comparison of the metal extraction capabilities of EDTA and NTA showed that EDTA released 10-30% more Pb than NTA from a metal-polluted soil that had 211,271, 665, 1,383, and 332 pg g” of Pb, Zn, Cu, and Cd, respectively [81. Recently, Hong and Pintauro tested four chelators, NTA, EDTA, EGTA, and DCyTA, for their abilities to remove cadmium from contaminated kaoline [91. EGTA and DCyTA removed 100% of the cadmium over a wide pH range (2.5-12.5). EDTA and NTA removed less of the adsorbed cadmium. All four chelators exhibited some desorption selectivity for Cd, Cu, and Pb adsorbed on kaoline. The observed metal

Environmental Progress (Vo1.19, No.4) Winter 2000 275

ordering for chelation and dissolution was Cd> Cu> Pb (for EGTA), Cd> Pb> Cu (for EDTA and DCyTA), and Cu> Cd> Pb (for NTA).

A number of studies have also been conducted to determine the metal extraction efficiency of strong mineral acids, including HNO, and HCl. In one such study, Mortazavi, et. al., found that HNO, was a more efficient extracting agent than HCl for the removal of Pb 1101. Approximately 66% of Pb in the soil was removed using 0.1 N HNO, compared to only 33% Pb removal using 0.1 N HCl. However, in case of Cd extraction, 0.1 N HCl was found to be more efficient than 0.1 N HNO,. These inorganic chemicals show a significant potential to extract metal ions from the soil. However, their use is associated with a number of dis- turbing physical, chemical, and biological properties.

Organic acids can also chelate the metal ions and thereby facilitate their transport in soils [11,12,131. In a comparative bench scale study of the ability of 12 chelating agents, including 10 different organic acids, and two common metal chelators, such as EDTA and DTPA, Wasay 1131 showed that citric acid was the most efficient, extracting 54%, 68%, 85% and 96% of Cr, Mn, Pb and Hg, respectively, from a contaminated clay loam soil.

Citric acid forms mononuclear, binuclear, o r polynuclear and bi-, tri-, and multidentate complexes, depending upon the type of metal ion. For example, metals, such as Fe and Ni, form bidentate, mononu- clear complexes with two carboxyl acid groups of the citric acid molecule. Copper, Cd, and Pb form triden- tate, mononuclear complexes with citric acid involv- ing two carboxyl acid groups and the hydroxyl group [141. Because citric acid is reasonably inexpensive, rel- atively easy to handle, and has a comparatively low affinity for alkaline earth metals (Ca, K, and Mg), it is a suitable candidate for soil washing.

The soil washing process results in a metal-rich solution that must also be decontaminated prior to disposal or reuse. Major methods to remove metal ions from wastewaters include filtration, ion exchange, precipitation, adsorption, or chelation by a variety of sorbents, electrodeposition, and membrane systems. All of these technologies have their inherent advantages and disadvantages.

The reclamation of wastewaters through a process known as chelation ion exchange seems to be a better alternative to existing remediation technologies. Some of the best chelation ion exchange materials are biopolymers, which are particularly efficient at adsorbing positively charged ions due to the presence of several functional groups (e.g., -OH, -COOH, etc.). One such biopolymer that has been studied for accu- mulating metal ions from single-solute pure metal solutions is chitosan, because its ability to form com- plexes with metal ions, particularly transition metal and post-transitional metal ions, is well documented [15,16,171. Chitosan is produced by deacetylation of chitin with sodium hydroxide at high temperature.

In this paper, we report the results of washing a heavy metal-contaminated soil from an abandoned lead battery plant near Montreal, Quebec, Canada, with different concentrations of citric acid. Cleanup of

the wash-solutions using chitosan flakes is also report- ed, as are the results of experiments to determine the shaking time requirements and the number of cycles required for complete remediation of the soil. A col- umn study was also conducted to compare the metal leaching with surface and subsurface application of citric acid to 60 cm long soil columns.

MATERIALS AND METHODS

Jbperimental Soil The samples were taken from the top layer (0-20

cm) of soil near an abandoned automobile lead bat- tery plant in St. Jean Sur Richelieu, Quebec, Canada. The soil was passed through a 0.2 cm sieve, air dried, and stored for further use.

Soil Characterization Soil was characterized in terms of texture, pH, electri-

cal conductivity (mS cm '1, effective cation exchange capacity (cmol [+I kg' soil), and elemental composition (mg element g ' dry soil) using standard methods of soil analysis. Due to high concentration of lead carbonate in the soil, its organic matter content was determined by the wet oxidation method 1181. The procedure outlined by Sims and Kline [19] was used to determine the exchangeable, soluble, organic-bound, carbonate- bound, and residual fractions of the metal ions.

Washing Procedure Mixtures containing 2 g of air-dried metal contami-

nated soil and 25 ml of different concentrations of cit- ric acid, adjusted to a pH of 5.5 with 0.1 N NaOH, were agitated at 200 rpm for 24 hours. This pH was chosen because Wasay [131 had reported that the metal removal efficiency of citric acid was highest at this pH. In another experiment, flasks containing 2 g of soil and 25 ml of 0.1 M citric acid (pH 5.5) were shaken for 120 hours, with samples taken at 24, 48, 72,96, and 120 hours.

To have some idea about the number of total wash- ings required for complete remediation of the metal contaminated soil, a 2 g sample of soil was shaken for 24 hours with 25 ml of 0.1 M citric acid at pH 5.5, and centrifuged at 3000 g for 20 minutes. The supernatant was kept for metal analyses, and the pellet was mixed with a fresh acid solution. This procedure was repeat- ed five times.

The final mixtures were centrifuged at 2500 g for 20 minutes. The supernatant and pellet were digested, separately with nitric acid alone (supernatant), and with a nitric and perchloric acid (3:l) mixture (pellet), in a microwave digestion system (Prolabo 3.6). An Atomic Absorption Spectrophotometer (AAS) (Perkin- Elmer 2380) was used to analyze metals in the digest- ed liquid and soil samples.

Treatment of the Wash-Solution Flasks containing 0.5 g of chitosan and 25 ml of the

metal-rich wash-solution were equilibrated for 1 2 hours. The mixture was centrifuged at 2500 g for 20 minutes and the supernatant was digested with 5 ml

276 Winter 2000 Environmental Progress (Vo1.19, No.4)

of nitric acid for 20 minutes in a microwave digestion system (Prolabo 3.6). Final volume was adjusted to 100 ml with distilled water and the amounts of metal ions present in the digest were estimated using AAS (Perkin-Elmer 2380).

columastudy Column study was conducted to compare the metal

leaching with surface and subsurface application of citric acid in 60 cm long soil columns packed with metal-contaminated soil. A flushing solution was pre- pared using citric acid (0.3 M) and its pH was adjusted to 5.5 with 0.1 N NaOH. Each of six soil columns, 10 cm in diameter and 60 cm in height, was packed with 6,270 g of the contaminated soil, producing a bulk density of 1.33 g cm3. Packed soil columns were divided into two sets, each having three columns. In one set, the flushing solution was applied at the sur- face of columns to saturate the soil. In the second set, an absolute saturation was achieved by introducing the flushing solution from the bottom of soil columns. After saturation, the flushing solution was allowed to remain in soil columns for 24 hours, and then drained and collected. Metals were analyzed with the AAS (Perkin-Elmer 2380). Soil samples were taken from the sampling ports present at the top (5 cm from the top), bottom (55 cm from the top), and middle (30 cm from the top) of each column. The oven-dried soil samples were analyzed for heavy metals using AAS (Perkin- Elmer 2380). Prior to metal analyses, both soil and liq- uid samples were digested by employing a microwave digestion system (Prolabo 3.6). The same procedure was repeated 19 more times.

The experiments were conducted in triplicate and the presented data are means of three values. The deviations from the central mean value are expressed as standard deviation.

RESULTS AND MSCUSSK)N

Soil characterlzatfon Table 1 shows the selected physico-chemical prop-

erties of the contaminated soil. The contaminated soil is sandy with 0.7% organic matter content. Despite the texture, higher values of CEC (17.06 cmol [+I kg' soil) could be attributed to high levels of easily exchange- able cations, such as Ca" and Na', present in the soil.

Various fractions of metal ions present in the contam- inated soil are shown in Table 2. Most of the metal ions are present as organically-bound, carbonate-bound, and residual forms. A small fraction is present in exchange- able and soluble form. Almost 60% of the Pb is present in carbonate form, whereas most of the Pb content of soils used by Wasay [131 was present as Fe-Mn oxides.

Soil Was- Scale Study In this experiment, metal-contaminated soil was

mixed with various concentrations of citric acid for 24 hours. The wash-solution was then treated with chi- tosan flakes to remove the metals.

It was found that although the citric acid removed significant quantities of metal ions from the contami-

Table 1. Initial Characterizaiion of the Contaminated Son

Soil Texture

Organic Matter (%I

PH In Water In CaCl,

Electric Conductivity (mS cm-1)

Effective CEC (cmol(+) Kg-1)

Elemental Composition (mg element g' dry soil) Zinc (Zn) Copper (Cu) Cadmium (Cd) Lead (Pb) Calcium (Ca) Magnesium (Mg) Sodium (Na) Potassium (K) Iron (Fe) Manganese (Mn) Aluminum (All

Sand Fine Gravel (7.6%) Coarse Sand (56.8%) Medium Sand (16.8%) Fine Sand (18.6%)

0.7

7.17k0.006 6.60k0.006

2.82*0.257

17.06

0.42k0.03 0.04kO.01 0.01k0.00 41.52k0.03 76.92k7.80 6.67k 1.44 28.75k9.44 2.50k0.66 2.40k0.84 0.19k0.04 3.8350.67

nated soil (Figure l), removal depended on the type of metal contaminant, the citric acid concentration, and the initial concentrations of the metal ions.

Removal of Pb and Zn, which were present at much higher concentrations than Cu and Cd, respond- ed to increased concentration of citric acid, whereas Cu and Cd did not. Neale, et. al., [201 also found an increased lead recovery with an increase in the con- centration of citric acid. A 24-hour mixing of the cont- aminated soil with 0.5 M citric acid removed 40, 50, 100, and 84% of Cu, Zn, Cd, and Pb, respectively, from the soil. Our results are in agreement with previ- ous studies [131, which reported a citrate (0.2 M) caused removal of 83% in Pb, 88% in Cu, 90% in Zn, and 100% in Cd, from sandy clay loam soil polluted with 0.794, 0.926, 1.029, and 1.036 mg g of Cd, Cu, Zn, and Pb, respectively. The smaller reduction in the levels of Zn and Cu in the present study might be due to their low initial concentrations compared to the ones in previous studies, since strength of metal reten- tion generally increases as the initial concentration of the contaminant decreases f211. However, an absolute reduction in the levels of Cd from the soil might have occurred due to their initially lower levels in the cont- aminated soil. Moreover, removal of cadmium using acids and chelating agents was already found easier

Environmental Progress (Vol. 19, No.4) Winter 2000 277

TABLE 2. Forms of Heavy Metals Present in the Contaminated Soil

Heavy mg metal g-l dry soil

Metal Exchangeable Soluble organic Carbonate Residual Total

Zn 0.00077 0.00074 0.019 0.057 0.378 0.455

c u 0.00083 0.00074 0.013 0.009 0.023 0.046

Cd 0.00050 0 0 0.003 0 0.0035

Pb 0.0049 0.021 9.080 24.621 6.685 40.41 1

0.15 I 3 0.12 } a 0.8 E E

22

v v

tS 0.6 z 0.09 3 8 0.4 s 0.06 N" B

c

0.2 0.03

0.0 0.00 0 0.1 0.2 0.3 0.4 0.5

Citric acid (M)

0.05 I

0 0.1 0.2 0.3 0.4 0.5

Cihic acid (M)

0 0.1 0.2 0.3 0.4 0.5

Citric acid (M)

- 80.0

- 60.0 v E" B 8 40.0 e

20.0

0.0 0 0.1 0.2 0.3 0.4 0.5

Citric acid (M)

Figure 1: Effects of citric acid concentration, n removing heavy metals from the metal contaminated soil (black barsoil; striped bakwash-solution not passed through chitosan; white bar=wash-solution passed through chitosan).

than removing lead and chromium [201. The efficient removal of Pb from the soil could be attributed to its higher initial concentrations. Greater metal removal efficiencies by mineral acids and chelating agents, like citrate, EDTA, DTPA, and NTA have already been reported from the soils contaminated with higher con- centrations of metals t201.

The remediation problem is not fully solved even when the metal ions have been mobilized by the use of organic acids. The metal-rich leachate produced through soil washings also needs to be treated before disposal or further use. Some physico-chemical and biological methods have been developed and

employed for reclamation of wastewaters. Chelation ion exchange has been gaining attention in removing only the toxic metal ions, while harmless ions move on into the environment. Some of the best chelation ion exchange materials consist of different biopoly- mers and their derivatives. Such materials include cel- lulosics, alginates, proteins, chitin, and chitosan. Chi- tosan, which is produced from the natural polymer chitin, has already been reported as a more efficient scavenger of metal ions than other biopolymers (16, 221. Therefore, our present study explores the possi- bility of using chitosan flakes to treat metal-rich leachate from soil washing with citric acid.

278 Winter 2000 Environmental Progress (Vo1.19, No.4)

1.0 I 0.12

- I

0 24 48 72 96 120

Time (Hour)

n E" 0.8 W p 0.6 8

0.4

0.2

0.0

N

0.05 I

- n E" 0.09

P g 0.06

W - -

u 5 0.03 -

I

^M 0.04 E 5 0.03 v

c C

-

-

8 0.02 -0

0.01

0.00

- 4 0 "

'M 30 M

3

5 20 f

u 10

1 0

0 24 48 72 96 120

Time (Hour)

100.0

G 80.0 E W - 5 60.0 co u 40.0

20.0

0.0

c

.n a

0 24 48 72 % 120

Ti (Hour)

r

0 24 48 72 % 120

Time (Hour)

Figure 2: Time-course study of heavy metal removal by 0.1 M citric acid (black baksoil; white bar=warh-tolution).

Wash-solution collected after washing the soil con- tained 0.01, 0.04, 0.37 and 60 mg of Cd, Cu, Zn, and Pb, respectively. On treating the wash-solution with chitosan flakes for 12 h at ambient temperature, levels of Cd, Cu, Zn, and Pb were reduced to 0, 0.02, 0, and 25 mg, respectively (Figure 1). Therefore, a single treatment of the wash-solution with chitosan flakes resulted in a reduction of 25, 50, 60, and 100% of Zn, Cu, Pb, and Cd, respectively. Capabilities of different forms of chitosan to adsorb metal ions from pure sin- gle-solute metal solutions have been fairly well docu- mented [16,171. However, use of chitosan flakes in treating leachate from soil washing with chelating agents has never been reported.

Various processes, such as adsorption, ion exchange, and chelation, are suggested to be respon- sible for complex formation between chitosan and metal ions. The evidence currently available supports the concept that chitosan-metal ion complex forma- tion occurs primarily through the amino groups func- tioning as ligands 123,241. Chitosan, produced by deacetylation of chitin, has many more reactive amino groups than the chitin and therefore has a higher affinity for metal ions. A significant uptake of Pb(I1) on both chitin and chitosan was observed [251. How- ever, the uptake of Pb(I1) on chitin was approximately 21% of that on chitosan.

Metal extracting capacity of 0.1 M citric acid from the contaminated soil as a function of washing time is rep- resented in Figure 2. Removal of metal ions from the soil did not increase with increasing the mixing time beyond 24 h. Kinetic experiments done by Wasay 1131

also indicated that in most cases equilibrium was attained within 24 h for maximum heavy metal removal.

A study involving renewal of washing solution, such as citric acid (0.1 M), after each washing proce- dure showed a consistent decrease in metal concen- trations with an increase in the number of washings (Figure 3). After five repeated washings with 0.1 M cit- ric acid, the Cu, Zn, and Pb contents of the contami- nated soils decreased from 0.05, 0.42, and 43.86 mg '-' soil to 0.01, 0.1, and 5.39 mg gl soil, respectively. In each of the washings, the contaminated soil was mixed with 0.1 M citric acid. An increase in citrate concentration might have reduced the number of washings required to extract metal ions, particularly those present in greater concentrations.

+Z" - cu 1

zoo :I1 100

+Cd +Pb

Figure 3: Remedialon of metal contaminated soil using citric acid (0.1 M).

Environmental Progress (Vol. 19, No.4) Winter 2000 279

Soil Washing-Column Study Six PVC columns, 10 cm in internal diameter and

60 cm in height, packed with 6,270 g of the metal- contaminated soil were used in this study. Each soil column contained 62.7 mg of Cd, 326.04 mg of cop- per, 2,691.1 mg of zinc, and 260,330.4 mg of lead. The leachate obtained from soil flushing, either with sur- face or subsurface application of the flushing solution, showed noticeable levels of the metal ions (Figure 4). However, there was a much higher extraction of Zn, Cd, and Pb from the soil columns with subsurface application of the flushing solution as compared to the ones with surface application. The Cu content in leachates did not vary much with the type of applica- tion. After 20 flushings with citric acid, the cumulative values of Cu, Cd, Zn, and Pb in the leachate from columns with subsurface application were 11.607 mg, 15.325 mg, 1,576 mg, and 73,480.7 mg, respectively, whereas, in case of columns with surface application, these values were 0 mg for Cd, 9.487 mg for Cu, 41 mg for Zn, and 2,679 mg for Pb (Figure 4). Extraction of Pb from columns with subsurface application of cit- ric acid was rapid initially and exhibited a consistent decline till 9 flushing cycles, after which it became constant. Likewise, initial rapid extraction was also observed in the case of Cu. The extraction of Zn and Cd, however, showed fluctuating patterns.

Residual levels of Zn, Cu, Cd, and Pb in soil columns were also estimated. Soil samples were taken from three different depths after 5, 10, 15, and 20 flushings. Values observed for sampling ports present

5 n

v 8 4 - Y

8 3 3 - Y 0 8 2 -

at the top, middle, and bottom of the column were calculated to represent the upper 17.5 cm, the middle 25 cm, and lower 17.5 cm of the column, respectively. Though a significant decrease was observed in Zn, Cu, and Pb contents of the contaminated soil (Table 31, a conclusive mass balance between the metal ions present in the leachate and the soil after flushings could not be derived. This lack in mass balance could be explained due to the fewer number of sampling ports in the soil columns.

Overall, the extraction of metal ions was higher in columns with subsurface application as compared to ones with surface application. Results suggest that the uniform distribution of citric acid', applied through the subirrigation system, resulted in a more efficient extraction of metal ions. On the other hand, flushing solution applied at the surface can flow rapidly through the preferential flow paths, bypassing most of the soil matrix.

Soil flushing as a remediation technology is in its infant stage. Very few reports are available detailing the capabilities of various flushing solutions to leach out metal ions from metal-contaminated soils. Reed, et. al. [261, investigated the capabilities of some chemi- cals, such as HC1, EDTA, CaCl,, as flushing solutions to extract Pb from columns packed with an artificially polluted sandy loam soil. Several flushing solutions including EDTA and DTPA were also applied to extract Zn from zinc-contaminated (artificially) soil columns [21. In the latter case, experiments were con- ducted using Plexiglas column with a 1.9 cm internal

15000 n

8 12000 W Y

8 9000 u G 0 0 6000

h n

W g 120 W iY4 Y 8 90 Y 8 3

e9 30 81

Y Y

c fi 8 60 8 2

0 0

1 3 5 7 9 11 13 15 17 19

Cycle

1 3 5 7 9 11 13 15 17 19 Cycle

U

1 3 5 7 9 11 13 15 17 19 1 3 5 7 9 11 13 15 17 19 Cycle Cycle

Figure 4: levels of Zn, Cu, Cd, and Pb in the leachate obtained from flushing soil columns with 0.3 M citric acid (white barsurface application; black bar=subsurface application).

280 Winter 2000 Environmental Progress (Vol. 19, No.4)

diameter and length of 5 cm, and washing solutions were injected from the base of the column. Effects of ionic strength, flow rate, and type of zinc contamina- tion were studied. Complete Zn removal was obtained with EDTA and DTPA. Recently, Wasay [131 used cer- tain organic acids as flushing agents to leach out heavy metal from contaminated soils, which were packed in soil columns having dimensions 2 cm in internal diameter and 4 cm in height. The flushing solutions were applied at the surface of soil columns.

Comparison of data obtained from soil washing and soil flushing studies indicated that bench-scale soil washing with citric acid removed more metal ions from the metal-contaminated soil (Figure 1) than soil flushing. This is attributed to relatively greater contact

between soil particles and the chelating molecules. Secondly, shaking of the metal-contaminated soil with the leachate, a process involved in soil washing, may have also positively influenced the attraction of metal ions towards chelating molecules. Despite this limita- tion, soil flushing, an in-situ remediation process, offers other advantages like no soil replacement or disposal costs, minimal disruption to the ecosystem, minimized worker exposure to contaminants, and cost advantages at greater depths. The estimated treatment price for soil washing, including disposal of sludges and all known cost components, is in the range of US$170-US$280/ton, whereas costs for soil flushing ranges between US$SO to US$lbO/ton [ll.

Table 3. Residual levels of Zn, Cu, Cd, and Pb in Soil Columns after Flushing with 0.3 M Citric Acid (pH 5.5)

Surface Application Cycle

0 TOP

Middle

Bottom

5 TOP

Middle

Bottom

10 TOP

Middle

Bottom

15 TOP

Middle

Bottom

20 TOP

Middle

Bottom

Zn cu Cd (mg) (mg) (mg)

768.0 50.0 1097.2 kO.0 768.0 kO.0

768.0 kO.0

1097.2 kO.0 768.0 kO.0

768.0 kO.0 1097.2 kO.0 768.0 kO.0

768.0 kO.0 1097.2 kO.0 768.0 kO.0

768.0 kO.0 1097.2 kO.0 768.0 kO.0

95.0 k9.1 135.8 k13.0 95.0 k9.1

93.8 k18.5

125.4 k5.2 103.0 k19.2

98.1 k9.0 130.6 k25.1 107.8 k15.6

89.6 k4.8 126.2 k9.1 99.3 k13.4

93.8 k2.1 121.9 k22.5 97.5 k7.6

18.2 kO.0 26.1 kO.0 18.2 kO.0

18.2 kO.0

26.1 kO.0 18.2 kO.0

18.2 kO.0 26.1 kO.0 18.2 kO.0

18.2 kO.0 26.1 kO.0 18.2 kO.0

18.2 kO.0 26.1 50.0 18.2 kO.0

Subsurface Application

81723.1 768.0 k6917.7 kO.0 116747.4 1097.2 k9882.5 kO.0 81723.1 768.0 k6917.7 kO.0

85601.9 768.8 k5233.4 k22.1

111919.5 950.9 k2328.2 k158.3 80993.5 844.8 k5242.2 k38.4

84385.8 716.8 k5567.9 k22.1 111956.1 914.3 k8515.5 k31.6 85537.9 768.0 k714.6 k38.4

81633.5 652.8 k4442.5 k175.9 113620.2 658.5 k4732.3 k219.0 83246.5 780.8 k3402.4 k22.17

84961.9 563.9 k3961.7 k96.6 112943.6 731.5 k2944.9 k247.3 81479.9 742.4 k3750.2 k181.4

cu ( m d

95.0 k9.1 135.8 k13.0 95.0 k9.1

93.8 k7.6

136.7 k10.5 99.9 k14.7

89.6 k11.1 132.3 k25.3 98.1 k5.8

88.3 k2.7 128.0 k11.9 101.1 k9.2

88.9

114.0 k23.7 101.1 k8.4

k5.8

Cd rn

18.2 k0.0 26.1 k0.0 18.2 k0.0

18.2 k0.0

26.1 k0.0 18.2 k0.0

18.2 k0.0 26.1 k0.0 18.2 k0.0

18.2 k0.0 26.1 k0.0 18.2 k0.0

18.2 k0.0 26.1 k0.0 18.2 k0.0

Pb (mg)

81723.1

116747.4 k9882.5 81723.1 k6917.7

k6917.7

76397.8 k4514.2

95405.8 k3571.9 81543.9 k42 15.5

67859.4 k 1396.8 92626.1 k5876.2 75412.1 k1682.9

63 186.9 k6893.6 99520.5 k11792.7 76833.1 k2423.4

72096.6 k1517.4 93119.9 k4828.0 74196.0 k2039.7

Winter 2000 281 Environmental Progress (Vo1.19, No.4)

CONCLUSIONS Citric acid was found to be very effective in extract-

ing metal ions from a metal contaminated soil having 0.01, 0.04, 0.42, 41.52 mg g of Cd, Cu, Zn, and Pb ions, respectively. Results indicate that the extraction of metal ions varies with the type and retention form of the ion, concentration of citric acid, and initial metal concentration in the soil. A 24 h washing of the contaminated soil with 0.5 M citric acid reduces the levels of Cd, Cu, Zn, and Pb from 0.01, 0.04, 0.42, 41.52 mg g ’ to 0, 0.02, 0.18, and 5.21 mg g ’ , respec- tively. Metal ion extraction through soil washing with citric acid did not increase with longer washing time. Wash-solution containing chronically higher levels of metal ions was effectively treated with chitosan flakes. Results from the column study indicate that extraction of metal ions from soil columns with subsurface appli- cation of citric acid was much more efficient than the ones with surface application of the flushing solution.

LITERATURE CITED 1. Anderson, W.C., “Innovative Site Remediation

Technology: Soil Washing and Flushing,” American Academy of Environmental Engineers, Annapolis, MD (1993).

2. Davis , A.P. and I. S i n g h , “Washing of Zinc(I1) from Contaminated Soil Column,” J. Environ. Eng.,

3. Hong, A.P.K. and T.C. Chen, “Chelating Extrac- tion and Recovery of Cadmium from Soil Using Pyridine-2,6-dicarboxylic acid,” Water Air Soil Pol-

4. Kari, F.G. and W. Giger, “Speciation and Fate of Ethylenediaminetetraacetic acid (EDTA) in Munici- pal Wastewater Treatment,” Water Res., 30, pp.

5. Legic, I.A., “Pb Mobility and Extractant Optimiza- tion for Contaminated Soils,” Environ. Prog., 16,

6. Doong, R., et. al., “Surfactant Enhanced Remedia- tion of Cadmium Contaminated Soils,” Water Sci. Technol., 37, pp. 65-71 (1998).

7. Garcia-Delgado, R.A., et. al., “Soil Flushing with EDTA Solutions: A Model for Changed Flow,” Sep. Sci. Technol., 33, pp. 867-886 (1998).

8. Elliot, H.A. and G.A. Brown, “Comparative Eval- uation of NTA and EDTA for Extractive Decontami- nation of Pb Polluted Soils,” Water Air Soil Pollut.,

9. Hong, A.P.K. and P.N. Pintauro, “Desorption- Complexation-Dissolution Characteristics of Adsorbed Cadmium from Kaoline by Chelators,” WaterAir Soil Pollut., 86, pp. 35-50 (1995).

10. Mortazavi, S., et. al., “Remediation of Soils Cont- aminated with Heavy Metals and PCBs,” Environ- ment Canada Chemical Spills, 9th Technical Semi- nar, Edmonton, AB (1992).

11. Abumaizar, R. and L.I. Khan, “Laboratory Inves- tigation of Heavy Metal Removal by Soil Wash- ing,’’ J. Air. Waste Manage. Assoc., 46, pp. 765-768 (1996).

12. Matsuyama, H., et. al., “Enhancement of Extrac-

121, pp. 174-185 (1995).

lut., 86, pp. 335-346 (1996).

122-134 (1996).

pp. 88-92 (1997).

45, pp. 361-369 (1989).

tion Rates by Addition of Organic Acids to Aque- ous Phase in Solvent Extraction of Rare Earth Met- als in Presence of Diethylenetriaminepentaacetic Acid (DTPA),” J . Chem. Eng. Japan, 29, pp. 126- 133 (1996).

13. Wasay, S.A., “Bioremediation of Soils Polluted by Heavy Metals Using Organic Acids,” Ph.D. Thesis, McGill University, Montreal, Canada (1998).

14. Francis, A.J., et. al., “Biodegradation of Metal Citrate Complexes and Interactions for Toxic Metal Mobility,” Nature, 356, pp. 140-142 (1992).

15. Peniche-Covas, C., et. al., “The Adsorption of Mercuric Ions by Chitosan,” J . Appl. Polym. Sci.,

16. Findon, A., et. al., “Transport Studies for Sorption of Copper Ions by Chitosan,” J . Environ. Sci. & Health, A28, pp. 173-175 (1993).

17. Ngah, W.S.W. and I.M. Isa, “Comparison Study of Copper Adsorption on Chitosan, Dowex A-1, and Zerolit,” J . Appl. Polym. Sci., 67, pp. 1067-1070 ( 1998).

18. Jackson, M.L., “Soil Chemical Analysis,” Prentice- Hall Inc., Englewood Cliffs, New Jersey (1958).

19. Sims, J.T. and J.S. Kline, “Chemical Fractionation and Plant Uptake of Heavy Metals in Soils Amend- ed with Co-composted Sewage Sludge,” J. Envi- ron. Qual., 20, pp. 387-395 (1991).

20. Neale, C.N., et. al., “Evaluating Acids and Chelat- ing Agents for Removing Heavy Metals from Cont- aminated Soils,” Environ. Prog., 16, pp. 274-279 (1997).

21. Cline, S.R. and B.E. Reed, “Lead Removal from Soils via Bench-scale Soil Washing Techniques,” J. Environ. Eng., 121, pp. 700-705 (1995).

22. Deans, J.R. and B.G. Dixon, “Uptake of Pb” and Cu” by Novel Biopolymers,” Water. Res., 26, pp. 469-472 (1992).

23. Udaybhaskar, P., et. al., “Hexavalent Chromium Interaction with Chitosan,” J. Appl. Polym. Sci., 39,

24. Guibal, E., et. al. , “Uranium Sorption by Gluta- mate Glucan: A Modified Chitosan-Part 11: Kinetic Study” WaterSA, 19, pp. 119-126 (1993).

25. Eiden, C. et. al., “Interaction of Lead and Chromi- um with Chitin and Chitosan,” J. App1. Polym. Sci.,

26. Reed, B.E., et. al., “Chemical Conditioning of Electrode Reservoirs during Electrokinetic Soil Flushing of Pb-contaminated Silt Loam,” J. Envi- ron. Eng., 121, pp. 805-815 (1996).

46, pp. 1147-1150 (1992).

pp. 739-747 (1990).

25, pp. 1587-1599 (1980).

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