Stabilization of lead and copper contaminated firing range soil using calcined oyster shells and fly ash
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- Moon, D.H., Park, J., Cheong, K.H. et al. Environ Geochem Health (2013) 35: 705. doi:10.1007/s10653-013-9528-9
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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.
KeywordsLeadCopperStabilizationOyster shellFly ash
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.
Military firing range soil
Physicochemical and mineralogical properties and total concentrations of heavy metals in the soil
Korean warning standardsa
Organic matter content (%)b
Sand and silt
Heavy metals (mg/kg)
Physicochemical properties of firing range soil, COS, and FA
Firing range soil
Major chemical properties
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.
Test matrix for untreated and treated samples
Firing range soil (wt%)
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
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
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).
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.
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)”.