Environmental Geochemistry and Health

, Volume 35, Issue 6, pp 705–714

Stabilization of lead and copper contaminated firing range soil using calcined oyster shells and fly ash

Authors

    • Department of Environmental EngineeringChosun University
  • Jae-Woo Park
    • Department of Civil and Environmental EngineeringHanyang University
  • Kyung Hoon Cheong
    • Department of Environmental EngineeringChosun University
  • Seunghun Hyun
    • Division of Environmental Science and Ecological EngineeringKorea University
  • Agamemnon Koutsospyros
    • Mechanical, Civil and Environmental EngineeringUniversity of New Haven
  • Jeong-Hun Park
    • Department of Environmental EngineeringChonnam National University
  • Yong Sik Ok
    • Department of Biological EnvironmentKangwon National University
Original paper

DOI: 10.1007/s10653-013-9528-9

Cite this article as:
Moon, D.H., Park, J., Cheong, K.H. et al. Environ Geochem Health (2013) 35: 705. doi:10.1007/s10653-013-9528-9

Abstract

A stabilization/solidification treatment scheme was devised to stabilize Pb and Cu contaminated soil from a firing range using renewable waste resources as additives, namely waste oyster shells (WOS) and fly ash (FA). The WOS, serving as the primary stabilizing agent, was pre-treated at a high temperature to activate quicklime from calcite. Class C FA was used as a secondary additive along with the calcined oyster shells (COS). The effectiveness of the treatment was evaluated by means of the toxicity characteristic leaching procedure (TCLP) and the 0.1 M HCl extraction tests following a curing period of 28 days. The combined treatment with 10 wt% COS and 5 wt% FA cause a significant reduction in Pb (>98 %) and Cu (>96 %) leachability which was indicated by the results from both extraction tests (TCLP and 0.1 M HCl). Scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDX) analyses are used to investigate the mechanism responsible for Pb and Cu stabilization. SEM–EDX results indicate that effective Pb and Cu immobilization using the combined COS–FA treatment is most probably associated with ettringite and pozzolanic reaction products. The treatment results suggest that the combined COS–FA treatment is a cost effective method for the stabilization of firing range soil.

Keywords

LeadCopperStabilizationOyster shellFly ash

Introduction

Lead (Pb) and copper (Cu) contamination of firing range soil is a serious problem due to the toxicity associated with heavy metals. Lead is known as one of the most toxic elements to living organisms (Kelly 1999; Prathumratana et al. 2010). Lead can cause harm to the brain, red blood cells, blood vessels, kidneys and the nervous system (Lin et al. 1996; Long and Zhang 1998). On the other hand, Cu is an essential element which forms organic complexes and incorporated in metalloproteins, especially in hemoglobin (Kos and Lesˇtan 2004). However, high concentrations of Cu accumulated in soil can have negative effects on microbial mediated soil processes caused by its antifungal and algicidal properties (Wright and Welbourn 2002). Moreover, Cu has been verified to be an aquatic toxin (USEPA 1988).

Used bullets are considered to be an important source of Pb and Cu contamination in military and civilian firing ranges. A bullet pellet normally consists of Pb (>90 %), antimony (Sb; 2–7 %), arsenic (As; 0.5–2 %), nickel (Ni; <0.5 %) and traces of bismuth (Bi) and silver (Ag) (Chrastný et al. 2010; Dermatas et al. 2006; Robinson et al. 2008; Sorvari et al. 2006). Moreover, a bullet shell is mainly composed of Cu (89–95 %) and zinc (Zn; 5–10 %) (Robinson et al. 2008; USEPA 2003). Evidently, Pb and Cu are major elements of concern that cause serious heavy metal contamination in firing range soils. Lead and Cu concentrations in firing range soils can reach 20,000 mg/kg (Lin 1996; Stansley and Roscoe 1996; Dermatas et al. 2006) and 2,000 mg/kg, respectively (Vantelon et al. 2005) depending on length of range operations. There are more than 3,000 active small arms firing ranges in the USA (USEPA 2005) and approximately 1,400 active small arms firing ranges in Korea (MOE 2005). The down range backstop is the area behind the target into which the bullets are discharged into. Bullet fragments and Pb and Cu particulates can significantly accumulate in firing range soils from impacts with the surface of the down range backstop during range operations. Remedial action is required to prevent Pb and Cu contamination and minimize serious environmental risks to groundwater and surface water (Craig et al. 1999; Knechtenhofer et al. 2003) and contamination of plants and vegetation in the vicinity of firing ranges (Cao et al. 2003; Robinson et al. 2008).

Stabilization/solidification (S/S) processes has been widely and successfully used to treat heavy metal contaminated soils. Various S/S agents such as Portland cement, quicklime, hydrated lime, fly ash (FA), cement kiln duct, etc. have been used to immobilize heavy metals in contaminated soil (Pereira et al. 2001; Dermatas and Meng 2003; Moon and Dermatas 2006, 2007; Yin et al. 2006; Moon et al. 2008, 2010; Israel et al. 2012). In this study, a novel combination of additives derived from renewable waste materials (oyster shells and FA) were used as stabilizing agents to immobilize Pb and Cu in contaminated firing range soil. The use of renewable waste materials (i.e. oyster shells and FA) over conventional stabilizing agents (i.e. Portland cement, lime, cement kiln dust, etc.) offers multiple benefits: (1) it lowers the risk of adverse environmental effects caused by uncontrolled or controlled disposal of natural/industrial waste materials, (2) it reduces the material and energy requirements for non-renewable natural resources needed for the production of conventional stabilizing agents, (3) it provides soil conditioning comparable to that of conventional stabilizing agents, (4) it is cost effective. Therefore, oyster shell based S/S agents represent an environment friendly green technology that is more attractive from a sustainability perspective than conventional agents. From a materials flow analysis standpoint, waste oyster shells (WOS) are generated at a rate of 250,000 tons per year in Korea and about 60 % of the WOS stream generated each year is used to seed oyster beds and as a fertilizer (Lee et al. 2005). The balance (40 %) of the WOS is dumped in coastal areas causing serious odor problems and potential degradation to the surrounding environment. Use of WOS and FA for soil stabilization, provides a unique opportunity of incorporating industrial ecology practices in environmental control technologies leading to a sustainable, cost-effective option for a S/S agent that addresses effectively several environmental problems (odor nuisance, potential environmental degradation, heavy metal remediation, FA disposal) simultaneously.

FA can be categorized into two groups: Class C with high CaO content (>20 %) and Class F with low CaO content (<10 %) (ACAA 1999). The total production of FA in 2008 in the USA was 72.5 million short tons and the utilization rates of FA were 41.6 %. Approximately 40 million short tons were landfilled which cost approximately 1.2 billion dollars per year (ACAA 2008). Similarly, in 2008, the total production of coal combustion by-products (CCBs) in Korea was 7.6 million tons and approximately 67 % of them are recycled with the remaining 33 % landfilled (Moon et al. 2009b). CCBs are generally composed of 84 % of FA and 16 % of bottom ash. Therefore, the disposal of huge amounts of unused FA can cause major problems for land use and potential environmental pollution (Misra et al. 2005). The problems may be averted by beneficial use of FA (e.g. soil stabilization, civil construction applications).

In previous studies, effective Pb immobilization was attained in contaminated mine tailings by application of WOS in natural and calcined states (Moon et al. 2009b). Also, effective Cu immobilization was obtained with WOS and calcined oyster shells (COS) (Moon et al. 2011). Moreover, FA based S/S treatment for contaminated soil and tailings was effective in reducing Pb release. In this study, COS was used as the main stabilizing agent. COS was obtained from the high temperature calcination process (900 °C for 2 h). The main phase in WOS is calcite (CaCO3) which was transformed into quicklime (CaO) during the calcination process. It is hypothesized that a novel mixture of COS and FA may be more effective on Pb and Cu immobilization due to the concurrent formation of insoluble Pb and Cu phases.

The objective of this study was to evaluate the effectiveness of Pb and Cu immobilization upon COS and FA treatment. The effectiveness of the treatment was evaluated using both the toxicity characteristic leaching procedure (TCLP) and the 0.1 M HCl extraction tests following the stabilization treatment. The mechanism responsible for effective Pb and Cu immobilization was investigated using scanning electron microscopy (SEM)–energy dispersive X-ray (EDX) analyses.

Experimental methodology

Military firing range soil

Heavy metal contaminated soil from a military firing range was collected from the Busan Metropolitan City in Korea at a depth of 0–30 cm below the ground surface. The total Pb and Cu concentrations based on extraction by aqua regia [1 mL of HNO3 (65 %, Merck) and 3 mL of HCl (37 %, J.T. Baker)] were approximately 7,996 and 540 mg/kg, respectively. The pH value of the contaminated soil was 6.90. The collected firing range soil was sieved through a #10 mesh (2 mm) to remove coarse particles and to provide homogeneous fractions of the soil. Physicochemical and mineralogical characterization information for the contaminated military firing range soil is presented in Table 1. The bulk chemistry of the contaminated military firing range soil was determined using X-ray fluorescence (XRF) is presented in Table 2.
Table 1

Physicochemical and mineralogical properties and total concentrations of heavy metals in the soil

Soil properties

Contaminated soil

Korean warning standardsa

Soil pH

6.9

 

Organic matter content (%)b

4.66

 

Composition (%)c

 Sand and silt

85

 

 Clay

15

 

 Textured

Loamy sand

 

Heavy metals (mg/kg)

  

 Cu

540

150

 Pb

7,996

200

 

Quartz

 
 

Orthoclase

 

Mineral compositions

Calcite

 
 

Albite

 
 

Muscovite

 

aKorean warning standards for soils in residential areas

bOrganic matter content (%) was calculated from measured loss-on-ignition (LOI) (Ball 1964; FitzPatrick 1983)

cSoil classification was conducted using a particle size analyzer (PSA); sand, 20–2,000 μm; silt, 2–20 μm; clay, <2 μm

dSoil texture as suggested by United States Department of Agriculture (USDA)

Table 2

Physicochemical properties of firing range soil, COS, and FA

 

Firing range soil

COS

FA

Major chemical properties

SiO2

62.4

2.59

38.2

Al2O3

18.7

0.96

19.8

Na2O

0.69

0.73

2.04

MgO

0.55

0.86

3.86

K2O

6.73

0.14

0.65

CaO

0.45

87.69

21.4

Fe2O3

3.87

0.40

5.11

LOI

4.66

5.10

2.2

pH (1:5)

6.89

12.5

11.9

Stabilization agents

WOS were obtained from a waste dump site in Tong-Young, Korea and pulverized to pass through a #20 sieve (0.853 mm). In order to activate quicklime from the calcite in the WOS, the WOS roasting process was conducted at 900 °C for 2 h to produce COS. The Class C FA was obtained from the American Fly Ash Company (Naperville, IL, USA). The bulk chemistry of the COS and FA are listed in Table 2.

Treatment conditions

The contaminated military firing range soil was stabilized with COS and FA with a liquid to solid (L:S) ratio of 0.2. All the treated samples were prepared in duplicate and cured for 7 days. The specific treatment conditions are presented in Table 3.
Table 3

Test matrix for untreated and treated samples

Sample ID

Firing range soil (wt%)

COS (wt%)

FA (wt%)

Control

100

0

0

FA10

100

10

COS10-FA5

100

10

5

COS10-FA10

100

10

10

COS15-FA5

100

15

5

COS15-FA10

100

15

10

L:S ratio = 0.2

Physicochemical analyses

Soil pH values were obtained in accordance with the Korean Standard Test (KST) method (MOE 2002) with a liquid to solid ratio of 5:1. In order to analyze the total Pb and Cu concentrations, soil samples (0.25 g) were mixed with aqua regia [1 mL of HNO3 (65 %, Merck) and 3 mL of HCl (37 %, J.T. Baker)] (Ure 1995). The mixture was then heated to 70 °C, shaken for 1 h, and diluted with 6 mL of distilled water to obtain a final L:S ratio of 20:1 (Ure 1995). The TCLP, in accordance with the U.S. EPA protocol (EPA 1992), and 0.1 M HCl extraction tests were used to evaluate the effectiveness of the stabilization treatment for the contaminated military firing range soil. The details of 0.1 M HCl extraction procedure have been explained in a previous publication (Moon et al. 2011). Subsequently, the extraction solution was filtered through a 0.45-μm membrane filter (Advantec MFS), and the filtrate was analyzed for soluble Pb and Cu by inductively coupled plasma mass spectrometry (ICP-MS; Agilent 7500ce, USA). All sample analyses were performed in triplicate and averaged values were reported only if the individual measurements were within an error of 10 %. Recovery spikes of two different quality control standards of lead nitrate and copper nitrate were used to monitor the accuracy and performance of the equipment.

X-ray powder diffraction (XRPD) analyses

In order to investigate the mineral composition of the contaminated soil, X-ray powder diffraction (XRPD) analyses were conducted (Moon et al. 2009a). The XRPD samples were air-dried and pulverized so that they could pass through a #400 sieve (38 μm). Step-scanned X-ray diffraction patterns were then collected using a PANalytical XRD instrument (X’Pert PRO MPD, Japan). XRPD analyses were performed at 40 kV and 30 mA using a diffracted beam graphite-monochromator with Cu radiation. The XRPD patterns were collected at 2θ values in the range of 5°–65°, with a 2θ step size of 0.03° and a count time of 3 s per step. The qualitative analyses of the XRPD patterns were conducted using the Jade software version 7.1 (MDI 2005) with reference to the patterns present in the International Centre for Diffraction Data database (ICDD 2002).

Scanning electron microscopy (SEM)–energy dispersive X-ray (EDX) analyses

The SEM analyses were performed to investigate the morphology of the treated sample (Moon et al. 2008). The SEM sample was prepared using a double-sided carbon tape coated with platinum (Pt). SEM analyses were performed using a Hitachi S-4800 SEM instrument equipped with an EDX spectroscopy, ISIS 310 system (Hitachi, Japan).

Results and discussion

Characteristics of military firing range soil

The military firing range soil composed of approximately 85 % sand and 15 % clay was classified as loamy sand according to the United States Department of Agriculture (USDA) (Table 1). XRD results showed that the main phases in the military firing range soil were quartz, orthoclase, calcite, albite, muscovite (Table 1). The military firing range soil is mainly composed of 62.4 wt% SiO2, 18.7 wt% Al2O3 and 6.74 wt% K2O. The COS consists of 87.7 wt% CaO, whereas the FA is composed of 38.2 wt% SiO2 and 19.8 wt% Al2O3 (Table 2).

Toxicity characteristic leaching procedure (TCLP) results

The TCLP Pb and Cu concentrations obtained from the samples treated with COS and FA are presented in Fig. 1. In the case of Pb, the TCLP Pb concentration of the control sample is approximately 21 mg/L, which is higher than the TCLP regulatory limit of 5 mg/L. Upon treatment with 10 wt% FA, the TCLP Pb concentration is reduced to 18.4 mg/L. This indicates that no significant Pb reduction (12 %) is attained upon treatment with FA as the sole additive. A significant Pb reduction of 0.42 mg/L (98 %) was obtained upon treatment with a combination of 10 wt% COS and 5 wt% FA and as a result the treated sample passed the TCLP regulatory limit of 5 mg/L. Other combination treatments of COS and FA showed a further reduction of Pb leachability (>99 %). This indicated that treatment with a combination of 10 wt% COS and 5 wt% FA was sufficient to pass the TCLP regulatory limit of 5 mg/L.
https://static-content.springer.com/image/art%3A10.1007%2Fs10653-013-9528-9/MediaObjects/10653_2013_9528_Fig1_HTML.gif
Fig. 1

TCLP Pb concentration (a) and TCLP Cu concentrations (b) of untreated (control), FA and COS–FA treated samples

In the case of Cu, the TCLP Cu concentration of the control sample is 0.47 mg/L, which is very low, indicating that leachable Cu is very limited in the TCLP extraction fluid. Since no TCLP regulatory limit has been established for Cu, a comparison of the TCLP Cu concentration in the control and the treated samples served as the basis for evaluating the effectiveness of treatment. A moderate reduction in TCLP Cu concentration of approximately 29 % (0.34 mg/L) is attained upon treatment with 10 wt% FA. Drastic TCLP Cu reductions are obtained upon treatment with all the combinations of COS and FA (<0.02 mg/L).

For both Pb and Cu extractions using the TCLP test, the pH value of the control sample is 4.04 (treatment pH 7.8). A similar TCLP pH value of 4.47 (treatment pH 9.47) is observed upon treatment with 10 wt% FA. This indicates that the CaO present in the FA may not be sufficient to consume the buffering capacity of the liquid, which is indicative of high TCLP Pb and Cu leachability. However, upon the combination treatment of COS and FA, the TCLP pH value is increased to 6.48 (treatment pH >12) and the buffering capacity of the liquid is probably consumed, leading to very low TCLP Pb and Cu leachability. Moon and Dermatas (2007) have showed that the buffering capacity of a liquid with an initial pH value similar to the pH value of the TCLP extraction fluid (3.25) was consumed at the pH region between 5.5 and 6.5 upon contaminated soil treatment with 20 wt% FA. Therefore, it is expected that the formation of pozzolanic reaction products such as calcium aluminum hydrate (CAH) and calcium silicate hydrate (CSH) take place at this TCLP pH region and that effective Pb immobilization occurs. Since the treatment pHs are higher than 12 for the COS and FA combination treatments, the solubilization of Al and Si from clay is expected (Keller 1964). At this pH range, Al and Si are available to form cementious hydrates (pozzolanic reaction products) such as CAH and CSH (Gougar et al. 1996). Moreover, Al and Si may be available from the FA itself. Therefore, the formation of CSH/CAH at high pH conditions induced by the high content of CaO from both COS and FA may play an important role in immobilizing Pb and Cu in contaminated firing range soil.

0.1 M HCl extraction results

The results of the 0.1 M HCl extraction tests for Pb and Cu concentrations obtained from the various treatment with COS and FA are presented in Fig. 2. The Pb concentration of the control sample is 3,660 mg/kg after 28 days of curing. The Pb concentration in the leachate is reduced by approximately 70 % upon treatment with 10 wt% FA. Moreover, a significant reduction in Pb release is attained upon the combination treatment of COS and FA, while the treatment pH value is close to 12. This indicates that Pb immobilization is effective even though strong acidic-leaching conditions are applied. This may be due to the buffering capacity of the liquid being consumed and the prevailing alkaline conditions. Therefore, pozzolanic reaction products at high pH conditions may be the key compounds responsible for Pb immobilization.
https://static-content.springer.com/image/art%3A10.1007%2Fs10653-013-9528-9/MediaObjects/10653_2013_9528_Fig2_HTML.gif
Fig. 2

Pb concentration (a) and Cu concentration (b) based on 0.1 M HCl extraction

Similarly, the Cu concentration of the control sample is 240 mg/kg after 28 days of curing and this Cu concentration is reduced to 82 mg/kg (about 66 % reduction) upon treatment with 10 wt% FA. No significant Cu concentrations are observed upon the combination treatment of COS and FA. This shows that Cu immobilization is successful under strong acidic leaching conditions. It is expected that effective Cu immobilization is strongly associated with pozzolanic reaction products. Reportedly, effective Cu immobilization at high pH conditions is achieved by the formation of CSH/CAH and ettringite (Moon et al. 2011).

SEM–EDX analyses

SEM–EDX results for the sample treated with 10 wt% COS and 5 wt% FA are presented in Fig. 3a. Ettringite [Ca6Al2(SO4)3(OH)12·26H2O] has needle morphology with a diversity of divalent cations such as Cu2+, Pb2+, Cd2+, Zn2+ potentially replacing Ca2+ in the ettringite minerals (Gougar et al. 1996). This indicates that Pb and Cu can be incorporated into the ettringite crystal structure. The elemental dot maps for the sample treated with 10 wt% COS and 5 wt% FA are presented in Fig. 3b, c. This shows that Pb and Cu immobilization is strongly associated with Al and Si. Therefore, pozzolanic reaction products including CSH/CAH may be the key compounds responsible for effective Pb and Cu immobilization. Overall, ettringite and pozzolanic reaction products may simultaneously contribute to the immobilization of Pb and Cu in the sample treated with 10 wt% COS and 5 wt% FA where a significant reduction in Pb leachability is obtained, based on both the TCLP test and 0.1 N HCl extraction.
https://static-content.springer.com/image/art%3A10.1007%2Fs10653-013-9528-9/MediaObjects/10653_2013_9528_Fig3_HTML.gif
Fig. 3

SEM-EDX results for the 10 wt% COS and 5 wt% fly ash treated samples (a), SEM elemental dot maps for the 10 wt% COS and 5 wt% FA treated samples, which show that Pb is associated with Al, Si and O (b) and SEM elemental dot maps for the 10 wt% COS and 5 wt% FA treated samples, which show that Cu is associated with Al, Si and O (c)

Conclusions

In this study, Pb and Cu contaminated firing range soil was stabilized using a combination of COS and FA. The effectiveness of the stabilization process was evaluated using the TCLP and 0.1 N HCl extraction tests. Moreover, the stabilization mechanism was investigated using SEM–EDX analyses. The combination treatment of 10 wt% COS and 5 wt% FA caused a drastic reduction in Pb (>98 %) and Cu (>96 %) leachability based on TCLP and 0.1 M HCl extraction tests. The sole addition of FA was not effective in reducing Pb and Cu leachability (higher than the TCLP regulatory limit of 5 mg/L for Pb). The SEM–EDX results showed that Pb and Cu immobilization was strongly associated with both ettringite and pozzolanic reaction products. Use of WOS and FA for soil stabilization, provides a unique opportunity of incorporating industrial ecology practices in environmental control technologies leading to a sustainable, cost-effective option for a S/S agent that addresses effectively several environmental problems (odor nuisance, potential environmental degradation, heavy metal remediation, FA disposal) simultaneously.

Acknowledgments

This research is financially supported by Republic of Korea Ministry of Environment as “Green Remediation Research Center for Organic–Inorganic Combined Contamination (The GAIA Project-2012000550001)”.

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© Springer Science+Business Media Dordrecht 2013