Environ Sci Pollut Res DOI 10.1007/s11356-014-3032-3
RESEARCH ARTICLE
Arsenic and copper stabilisation in a contaminated soil by coal fly ash and green waste compost Daniel C. W. Tsang & Alex C. K. Yip & William E. Olds & Paul A. Weber
Received: 19 December 2013 / Accepted: 12 May 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract In situ metal stabilisation by amendments has been demonstrated as an appealing low-cost remediation strategy for contaminated soil. This study investigated the short-term leaching behaviour and long-term stability of As and Cu in soil amended with coal fly ash and/or green waste compost. Locally abundant inorganic (limestone and bentonite) and carbonaceous (lignite) resources were also studied for comparison. Column leaching experiments revealed that coal fly ash outperformed limestone and bentonite amendments for As stabilisation. It also maintained the As stability under continuous leaching of acidic solution, which was potentially attributed to high-affinity adsorption, co-precipitation, and pozzolanic reaction of coal fly ash. However, Cu leaching in the column experiments could not be mitigated by any of these inorganic amendments, suggesting the need for co-addition of carbonaceous materials that provides strong chelation with oxygen-containing functional groups for Cu stabilisation.
Green waste compost suppressed the Cu leaching more effectively than lignite due to the difference in chemical composition and dissolved organic matter. After 9-month soil incubation, coal fly ash was able to minimise the concentrations of As and Cu in the soil solution without the addition of carbonaceous materials. Nevertheless, leachability tests suggested that the provision of green waste compost and lignite augmented the simultaneous reduction of As and Cu leachability in a fairly aggressive leaching environment. These results highlight the importance of assessing stability and remobilisation of sequestered metals under varying environmental conditions for ensuring a plausible and enduring soil stabilisation.
Responsible editor: Zhihong Xu
Introduction
Electronic supplementary material The online version of this article (doi:10.1007/s11356-014-3032-3) contains supplementary material, which is available to authorized users. D. C. W. Tsang : W. E. Olds Department of Civil and Natural Resources Engineering, University of Canterbury, Christchurch 8140, New Zealand D. C. W. Tsang (*) Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China e-mail: [email protected] A. C. K. Yip Department of Chemical and Process Engineering, University of Canterbury, Christchurch 8140, New Zealand W. E. Olds : P. A. Weber Solid Energy New Zealand, Private Bag 1303, Christchurch 8140, New Zealand
Keywords Contaminant sequestration . Industrial by-products . Metal mobility . Soil amendments . Site remediation
Arsenic (As) contamination, resulting from geogenic/ volcanogenic sources and anthropogenic activities (metal mining, coal/petroleum-related, agricultural uses of arsenical pesticides, and industrial uses of arsenical preservatives), has been identified in 105 countries and estimated to affect over 226 million people worldwide (Murcott 2012). High As mobility and plant uptake in agricultural soil are commonly observed in places where phosphate fertiliser is applied and As-rich groundwater is used for irrigation (Reedy et al. 2007; de la Fuente et al. 2010). On the other hand, extremely high concentrations of As are often associated with the mining and smelting of copper, lead, gold, and silver ores, as well as the wood industry that uses chromated copper arsenate as preservatives (Han et al. 2003; Tsang et al. 2013a). The co-presence of metalloids (e.g. As) and heavy metals (e.g. Cu) at high
Environ Sci Pollut Res
concentrations presents a major challenge to cost-effective remediation of these agricultural and industrial contaminated sites. In recent years, potential application of industrial byproducts as reactive stabilisers for in situ soil amendment (i.e. soil stabilisation) has captured extensive interests. This remediation strategy enables resource recycling and reduces environmental burden of waste management, while accomplishing metal sequestration in the contaminated soil at a low-to-moderate cost with a low carbon footprint, in view of minimal requirement for energy and chemical consumption (Tsang et al. 2013b; Tsang and Yip 2014). Coal fly ash is a readily available by-product from heat/energy generation processes such as boiler and gasification. In addition to its traditional use in glass, ceramics, and concrete production (Wang and Wu 2006; Blissett and Rowson 2012), coal fly ash is an effective stabiliser that offers less energy-intensive and more economically competitive metal removal process in mine tailings and wastewater treatment (Yeheyis et al. 2009; Wang et al. 2013). Recent studies have also explored the efficacy of using coal fly ash for restoration of contaminated sites and demonstrated significant decreases of metal uptake by plants, microbial/phyto-toxicity, exchangeable metal fraction in soil, and diffusion flux of free metals into solution (Kumpiene et al. 2007; Ruttens et al. 2010; Gu et al. 2011; Moon et al. 2013a). On the other hand, green waste compost also proves effective for revitalisation (e.g. nutrient replenishment, water retention, biomass production) of the contaminated soil (Alvarenga et al. 2009; Farrell et al. 2010; Padmavathiamma and Li 2010a). In addition to strong complexation with Cu, compost was shown to alleviate the As phytotoxicity in a recent study (Caporale et al. 2013). This was attributed to partial stabilisation of As via outer-sphere complexation with protonated amino groups and/or Fe-bridged ternary inner-sphere complexation with carboxylate/phenolate groups on the surface (Mikutta and Kretzschmar 2011). Moreover, improved plant yield was observed for combined application of compost and inorganic materials (Khan and Jones 2009; Padmavathiamma and Li 2010a; Qi et al. 2011). Commonly studied soil amendments also included biochar (Cao et al. 2011; Uchimiya et al. 2011; Moon et al. 2013b), lignite/ humus (Ok et al. 2011; Qi et al. 2011), lime/limestone (Hartley and Lepp 2008; Padmavathiamma and Li 2010b), lime-based waste materials (Moon et al. 2011; Ahmad et al. 2012), and bentonite (Ruttens et al. 2010; Yeheyis et al. 2010). Metal mobility and bioavailability can be significantly suppressed in the amended soil through adsorption, cation exchange, surface complexation, (co-)precipitation, surface precipitation, and transformation/incorporation on the stabiliser surface (Kumpiene et al. 2008; Miretzky and Cirelli 2010; Komarek et al. 2013). However, potential risks of increased migration and transience of heavy metals are still
present with the use of soil amendments (Farrell et al. 2010; Santos et al. 2010; Ahmad et al. 2012), which may be aggravated in an acidic environment as revealed by recent studies (Houben et al. 2013; Tsang et al. 2013b). Therefore, shortterm leaching and long-term stability of the soil stabilisation approach in such condition are important issues that should be fully understood upfront. This study assessed the effectiveness of coal fly ash and green waste compost for soil stabilisation, and the short-term remobilisation potential and long-term leachability under a moderately aggressive leaching condition. Locally abundant resources (lignite, limestone, and bentonite) were evaluated for comparison. Column leaching experiments and standard leachability test were performed on a soil contaminated by As, Cu, and Cr (due to past timber treatment activities) after incubation with individual or combined soil amendments.
Experimental methods Field-contaminated soil The contaminated soil was obtained from a former timber treatment facility in Tapanui, New Zealand, which was operational from the early 1940s until 1986. The total volume of contaminated soil was 1,634 m3 and the total concentrations of As, Cu, and Cr across the contaminated site were 570– 7,280, 498–4,540, and 426–3,460 mg kg−1, respectively (Tsang et al. 2013a; Hartley et al. 2014). The soil sample was collected from a contamination hot spot, air-dried, and passed through a 2-mm sieve. The concentrations of As, Cu, and Cr in the soil sample were 3,300, 2,100, and 2,800 mg kg −1 , respectively, as determined by nitric/ hydrochloric acid digestion followed by metal analysis (US EPA Method 200.2). The As concentration exceeded the soil guideline values in New Zealand (20 mg kg−1 for rural residential land use; 70 mg kg−1 for commercial/industrial land use; NZ MfE 2010) and required a 97.9–99.4 % extraction by soil washing if selected for remediation, which was practically unachievable (Tsang et al. 2013a; Hartley et al. 2014). The soil contained 5.7 % silt and clay content (measured by 63-μm sieving) and 0.43 % organic carbon content (measured by LECO combustion with acid pretreatment to remove carbonates), with a soil pH of 7.3 at a 1:2 soil to water ratio. The soil mineralogy consisted of quartz (38 %), calcic plagioclase feldspar (34 %), muscovite (15 %), and chlorite (13 %), as identified by using X-ray diffraction (XRD) plus Semiquant analysis (Philips PW1830) and SIROQUANT search/match programme. The relative mass percentages in the soil were 2.74 % Fe, 5.12 % Al, 1.58 % Ca, 0.06 % Mn, and 0.7 % Mg, as shown by borate fusion X-ray fluorescence (XRF) spectrometry (SpectraChem Analytical, ISO 17025).
Environ Sci Pollut Res
Stabiliser characteristics Coal fly ash was collected from a subbituminous coalcombustion plant in Southland, New Zealand, which had a pH 12 and acid neutralising capacity of 54.3 % CaCO3. There was negligible metal/metalloid leaching from coal fly ash (such as As, Cu, Cr, Cd, Se, Pb, and Zn, which were below 0.001 mg L−1) in Synthetic Precipitation Leaching Procedure. The coal fly ash contained 13.6 % Ca, 9.1 % Si, 6.2 % Fe, and 2.2 % Al (by weight) as determined by using XRF. Various crystalline-phase minerals were identified by XRD analysis: quartz (14 %, SiO2), merwinite (12 %, Ca3Mg(SiO4)2), calcite (4 %, CaCO3), and portlandite (2 %, Ca(OH)2). The amounts of poorly crystalline Fe and Al oxides were 5,700 and 6,760 mg kg−1, respectively, as determined by using oxalate extraction method (Shang and Zelazny 2008). The specific surface area was 211.6 m2 g−1, as calculated by using the BET analysis of nitrogen gas adsorption isotherm (TriStar 3000, Micromeritics) after sample degassing at 3,00 °C for a few hours. For comparison, ultra-fine limestone (90 wt% CaCO3 < 106 μm) and bentonite (Mintech NZ Ltd) were studied in parallel. The latter was locally prepared from calcium bentonite with soda ash and marketed as low-value soil enhancers for earthing purposes. The XRD and BET analyses revealed a mineralogical composition of kaolin (44 %, Al2(Si2O5)(OH)4), illite (29 %, K0.5(Al,Fe,Mg)3(Si,Al)4O10(OH)2), quartz (15 %, SiO2), calcic plagioclase feldspar (12 %, Ca(Al2Si2O8)), and a surface area of 42.9 m2 g−1, respectively. A summary was provided in the Supplementary Materials (Table SM-1). Green waste compost (Living Earth Ltd, New Zealand) was produced from garden and kitchen waste by indoor tunnel composting system at 55 °C or above for at least 3 days followed by curing for up to 120 days. The compost had a pH 7.5–8, moisture content of 45–55 %, and bulk density of approximately 0.6 kg L−1. Lignite (a low-rank coal accounting for 70 % of coal reserve in New Zealand) was obtained from 0.2–1.5 km below ground at the New Vale Mine in Southland, New Zealand. All materials were air-dried at 37 °C and passed through 2-mm sieve before use. Elemental analysis (wt%, Elementar Combustion Analyser, Hanau) indicated that compost contained 24.2 % C, 2.8 % H, 24.8 % O, 2.1 % N, and 46.1 % inorganic ash; lignite contained 57.7 % C, 5.1 % H, 31.1 % O, 0.7 % N, and 5.4 % inorganic ash (Table SM-2). After repeatedly washing with 1 M HCl for inorganic removal, the carbonaceous samples were analysed by nuclear magnetic resonance (NMR) spectroscopy (Bruker AMX 200 Mhz horizontal bore magnet) as described in the Supplementary Materials. The organic carbons (wt%) of green waste compost were composed of 10.6 % phenolic, 8.8 % carboxyl, 1.3 % carbonyl, 22.3 % aromatic, 25.3 % aliphatic, and 31.7 % carbohydrates, whereas those of lignite were 12.1 % phenolic, 4.9 % carboxyl, 2.0 % carbonyl, 30.2 % aromatic, 33.8 % aliphatic, and 17.0 % carbohydrates, respectively (Fig. SM-1
and Table SM-3). These characteristics reflected the food waste source of compost (more carboxylates and ash) and the long-term humification and diagenesis of lignite (more aromatic and aliphatic structures). Arsenic and copper stabilisation The short-term leaching potential of As, Cu, and Cr from the soil amended with the above reactive stabilisers was assessed in column experiments. The contaminated soil (100 g) was homogeneously blended with individual (5 and 10 wt%) or mixed (5 wt% each) waste materials at a bulk density of 1.3 kg L−1 and packed into PVC columns with an inner diameter of 52 mm and a length of 300 mm. Quartz sand layers (approximately 100 g, prewashed by diluted HCl and deionised water for five times) were placed at the bottom and top of the columns for evenly distributed flow. The columns were first slowly saturated with upward-flowing deionised water from the bottom to avoid air entrapment and then flushed with pH 4.93 acetate buffer at a flow rate of 0.9–1.0 mL min−1 using a peristaltic pump. This test can be applied as a risk assessment tool for measuring the ability of remediation technologies (e.g. stabilisation) in retarding the mobility of contaminants in a fairly aggressive leaching environment (Kimmell et al. 2001). Blank columns containing only contaminated soil were used as control. As the inflow and outflow volumes were equal after initial saturation, effluent samples were collected and weighed for calculation of total pore volume. After a 0.45-μm filtration, the concentrations of As, Cu, Cr, and mineral cations were periodically analysed by using inductively coupled plasma mass spectroscopy (Agilent 7500cx), of which the experimental detection limits (after sample dilution) of As, Cu, and Cr were 0.014, 0.02, and 0.005 mg L−1, respectively. Dissolved organic matter in the effluent was also quantified by measuring UV absorbance at a wavelength of 254 nm (Thermo Scientific GENESYS 10S UV-Vis Spectrophotometer). The effluent concentrations were plotted against pore volume to construct the breakthrough curves. For quality control, every tenth sample was duplicated and every 20th was spiked, after which blanks were run before further analysis. Moreover, one-third of the column experiments were run in duplicate to ensure data reliability and reproducibility. To investigate the effectiveness in the long term, the soil sample (20 g each) was initially mixed with the above materials (individual or in combination, 5 wt% each) and then incubated at saturated water content and room temperature. The containers were sealed with parafilm and stored in the dark. After 9-month static incubation, the soil solution was analysed for metal concentrations as previously described, and the soil mixtures (including the amendments) were analysed by using Toxicity Characteristic Leaching Procedure (TCLP; US EPA Method 1311) as a performance indicator. The supernatant was separated by centrifugation at 4,000 rpm for 15 min, filtered through 0.45-μm membrane filter, acidified
Environ Sci Pollut Res
with concentrated nitric acid, and stored in amber vials at 4 °C before analysis. All experiments were duplicated and average values were presented.
Results and discussion Short-term remobilisation risk—coal fly ash, limestone, and bentonite Coal fly ash and green waste compost can be deployed in field using soil augers or disc harrows after water spraying, but adequate measures should be in place to avoid erosion of these low-density materials during storm events, e.g. granulation with binding/foaming agents (Limbachiya et al. 2012). These engineering issues are assumed to be properly addressed in the following experiments. Figure 1 illustrates the breakthrough curves of As, Cu, and Cr from the untreated and
coal fly ash-stabilised soil columns under continuous acid leaching. The results show that As and Cu were the major risk drivers while Cr leaching was negligible despite its high concentration in the contaminated soil (Fig. 1). This was because As existed as partially soluble arsenic trioxide/pentoxide and copper-arsenate precipitates whereas Cr was present in the forms of insoluble trivalent chromium oxides and ironchromium co-precipitates (Tsang and Hartley 2014). With the addition of coal fly ash, the mobility of As was substantially inhibited at an amendment ratio of 5 wt% and was nearly eliminated at 10 wt%. The As stability was maintained throughout the 120 pore volumes of acid leaching, suggesting that As became more geochemically stable in the presence of coal fly ash. Due to the high surface area (211.6 m2 g−1) of coal fly ash and the presence of large amounts of poorly crystalline Fe and Al oxides (5,700 and 6,760 mg kg−1, respectively), As could be strongly adsorbed in the form of bidentate mononuclear inner-sphere complexes, which was
Fig. 1 Short-term remobilisation risk of untreated soil and coal fly ash-stabilised soil
Environ Sci Pollut Res
observed on co-precipitated Fe/Al hydroxides (Jing et al. 2005; Masue et al. 2007). On the other hand, significant amounts of relatively soluble Ca minerals (12 wt% merwinite (Ksp = 10−13.7), 4 wt% calcite (Ksp = 10−8.5), and 2 wt% portlandite (Ksp =10−5.3)) might result in precipitation of insoluble calcium-arsenate compounds (Ksp =10−21.1 to 10−40.1), based on speciation calculation and previous reports (Zhu et al. 2006; Moon et al. 2011; Oh et al. 2012; Wang and Tsang 2013). In addition, As might be entrapped into calcium-silicate-hydrate phases produced by the pozzolanic reaction of coal fly ash (13.6 wt% Ca and 9.1 wt% Si based on XRF analysis) (Chen et al. 2004; Moon et al. 2013a). The relative significance of these mechanisms, however, required further spectroscopic investigations. Although Cu could be stabilised via adsorption onto surface hydroxyl groups of Fe/Al oxides in coal fly ash, the results indicate that Cu mobility remained unchanged under acetic acid leaching (Fig. 1). This suggested that the binding strength of Cu sequestration should be tested against leaching of organic acids (acetic, oxalic, citric acids, etc) in plant root
exudates. Notable dissolution of Ca and Al in the first 20 pore volumes may deserve attention in field applications. It should be noted that a high dosage (e.g. 10 wt% or above) of coal fly ash would alter soil texture, increase water-holding capacity, and reduce hydraulic conductivity (Pathan et al. 2003; Yeheyis et al. 2010). As there was little difference in the effectiveness of 5 and 10 wt% amendments, a smaller amount of coal fly ash (if well mixed in the field) was recommended for practical deployment and minimal ecological impact. For comparison, Fig. 2 illustrates the leaching of As and Cu from limestone- and bentonite-stabilised soil columns. With the high alkalinity and Ca solubility of limestone, calcium arsenate precipitation contributes to the initial suppression of As leaching. However, the treatment with 5 or 10 wt% limestone was less effective compared with coal fly ash due to the absence of high-affinity adsorption on the Fe/Al coprecipitates or incorporation into calcium-silicate-hydrate phases. Under prolonged acid leaching, As started to leach out from the limestone-stabilised soil as the initial effluent pH gradually decreased from 6.5 to 5.0 within 15 pore volumes.
Fig. 2 Short-term remobilisation risk of limestone-stabilised soil and bentonite-stabilised soil
Environ Sci Pollut Res
Fig. 3 Short-term remobilisation risk of coal fly ash/green waste compost-stabilised soil and coal fly ash/lignite-stabilised soil
The results further indicate that limestone was unable to reduce the Cu leachability without a sustained alkaline environment. Similar results were reported in the literature where the metal stabilisation efficiency of limestone treatment was extremely low at the end of leaching period (Ruttens et al. 2010). Moreover, the release and accumulation of CO2 due to acid neutralisation of limestone resulted in column clogging after 30 pore volumes from which significant Ca dissolution was observed. On the other hand, Ca-rich bentonite (42.9 m2 g−1) initially reduced the leaching of As and Cu via As precipitation and Cu adsorption. However, their stability was not sustainable in an acidic and complexing condition. Short-term remobilisation risk—co-addition of green waste compost and lignite As coal fly ash had limited efficiency for Cu sequestration, green waste compost and lignite were added to achieve the
Fig. 4 Leaching of dissolved organic matter from green waste compost and lignite
Environ Sci Pollut Res
stabilisation (Fig. 3), based on the hypothesis that the oxygencontaining, proton-dissociating functional groups (primarily carboxylates at pH above 5 and phenolates at pH above 8) on carbonaceous materials may contribute to strong metal binding (Milne et al. 2003; Tsang et al. 2009; Uchimiya et al. 2011; Olds et al. 2013). Both green waste compost and lignite contain the aforementioned functional groups: 8.8 % carboxylate groups and 46.1 % inorganic ash (surface hydroxyl groups) in green waste compost; 4.9 % carboxylates and Fig. 5 Pore water concentrations after long-term soil stabilisation
5.4 % ash in lignite. The larger amount of functional groups present in the green waste compost resulted in better Cu sequestration compared with lignite, as shown in Fig. 3. Moreover, Fig. 4 shows that a larger amount of dissolved organic matter (or more aromatic moieties) was released from lignite, which comprised 30.2 % aromatic carbons based on NMR analysis. Since the aromatic components were found to solubilise Cu to a greater extent, especially at low Cu to dissolved organic matter ratios (Amery et al. 2010; Baken
Environ Sci Pollut Res
et al. 2011; Craven et al. 2012; Ahmed et al. 2013), the mobilisation of aromatic moieties from lignite may hinder its effectiveness for Cu sequestration under a dynamic leaching condition. Dissolution of organic matter continued for 60–80 pore volumes before reaching the background level (Fig. 4). Recent chromatographic and spectroscopic findings revealed that the mobilisation of As was facilitated by dissolved organic matter through formation of ternary arsenic-iron-organic matter complexes and nanosized colloids (Liu et al. 2011; Fig. 6 TCLP leachability after long-term soil stabilisation
Sharma et al. 2011; Neubauer et al. 2013). Nevertheless, the presence of green waste compost or lignite did not facilitate As leaching in this study (comparing Figs. 1 and 3). This was because at pH above 4.5, the As transport was mainly coupled with colloidal Fe oxides (Neubauer et al. 2013), while there was negligible Fe dissolution or Fecolloid mobilisation from the coal fly ash-stabilised soil (Fig. 3). On the other hand, attention may rather be paid to substantial Ca dissolution and moderate Al dissolution within the first 20 pore volumes.
Environ Sci Pollut Res
Long-term soil stabilisation After 9-month static incubation (Fig. 5), coal fly ash significantly reduced the As concentration in the soil solution although there was incomplete As sequestration. On the contrary, the addition of limestone and bentonite provided an alkaline environment (solution pH of 8–8.5) that induced greater solubilisation of As due to its oxyanion nature, resulting in higher environmental risks of bioavailable As. In addition, coal fly ash was able to remove Cu from the soil solution because of its high surface area and surface hydroxyl groups, corroborating the reported decrease in diffusion flux of free metals into solution (Gu et al. 2011). Therefore, the copresence of green waste compost and lignite did not manifest noticeable benefits in terms of the pore water concentrations. However, Fig. 6 illustrates that the As leachability was reduced by coal fly ash to a smaller extent in TCLP tests (from 7.65 mg L−1 to 4.45 and 2.68 mg L−1 at 5 and 10 wt%, respectively). Moreover, there was no reduction in the Cu leachability (26.4 mg L−1), which was much higher than As and Cr leachability. By contrast, limestone and bentonite increased the As leachability (11.3–17.5 mg L−1) while limestone reduced the Cu leachability to some extent (13.8– 18.5 mg L −1 ). These results implied that irreversible stabilisation of Cu could not be chiefly achieved by the inorganic amendments. Hence, Fig. 6 shows an advantage of simultaneous reduction of Cu leachability (9.9–18.9 mg L−1) accomplished by the combined applications of green waste compost or lignite together with inorganic amendments. In a closed system, green waste compost and lignite demonstrated similar efficacy for Cu sequestration through their strong complexation affinity (K Cu–DOM = 10 5.6 to 10 11.5 M −1 (Craven et al. 2012)). Yet, the residual Cu leachability remained at a rather high level. These results suggest that the soil simultaneously contaminated by As and Cu requires an integration of remediation strategies (e.g. prior extraction).
Conclusions In situ soil stabilisation with locally available industrial byproducts has gained increasing popularity as a low-cost remediation alternative. This study underlined the significance of assessing the short-term mobility and long-term stability of As (metalloid) and Cu (heavy metal) of the waste-stabilised soil. Coal fly ash outperformed commonly used amendments by limestone and bentonite for As and Cu sequestration from the soil solution. However, Cu leaching was not reduced under continuous acid flushing although As stability could be sustained. Therefore, combined application of coal fly ash together with carbonaceous materials was useful for mitigating the Cu leachability. Green waste compost proved to be
more effective than lignite, probably because of the difference in chemical composition and extent of dissolution. In order to minimise the residual metal leachability, soil stabilisation by the mixed amendments may be augmented by a preceding treatment process. Acknowledgements The authors appreciate the financial support from the Brian Mason Scientific & Technical Trust (New Zealand) and the provision of field soil sample from Golder Associates (New Zealand) Ltd for this study.
References Ahmad M, Moon DH, Lim KJ, Shope CL, Lee SS, Usman ARA, Kim KR, Park JH, Hur SO, Yang JE, Ok YS (2012) An assessment of the utilization of waste resources for the immobilization of Pb and Cu in the soil from a Korean military shooting range. Environ Earth Sci 67:1023–1031 Ahmed IAM, Hamilton-Taylor J, Lofts S, Meeussen JCL, Lin C, Zhang H, Davison W (2013) Testing copper-speciation predictions in freshwaters over a wide range of metal-organic matter ratios. Environ Sci Technol 47:1487–1495 Alvarenga P, Palma P, Goncalves AP, Fernandes RM, de Varennes A, Vallini G, Duarte E, Cunha-Queda AC (2009) Organic residues as immobilizing agents in aided phytostabilization: (II) effects on soil biochemical and ecotoxicological characteristics. Chemosphere 74: 1301–1308 Amery F, Degryse F, Van Moorleghem C, Duyck M, Smolders E (2010) The dissociation kinetics of Cu-dissolved organic matter complexes from soil and soil amendments. Anal Chim Acta 670:24–32 Baken S, Degryse F, Verheyen L, Merckx R, Smolders E (2011) Metal complexation properties of freshwater dissolved organic matter are explained by its aromaticity and by anthropogenic ligands. Environ Sci Technol 45:2584–2590 Blissett RS, Rowson NA (2012) A review of the multi-component utilisation of coal fly ash. Fuel 97:1–23 Cao X, Ma L, Liang Y, Gao B, Harris W (2011) Simultaneous immobilization of lead and atrazine in contaminated soils using dairymanure biochar. Environ Sci Technol 45:4884–4889 Caporale AG, Pigna M, Sommella A, Dynes JJ, Cozzolino V, Violante A (2013) Influence of compost on the mobility of arsenic in soil and its uptake by bean plants (Phaseolus vulgaris L.) irrigated with arsenite-contaminated water. J Environ Manag 128:837–843 Chen JJ, Thomas JJ, Taylor HFW, Jennings HM (2004) Solubility and structure of calcium silicate hydrate. Cem Concr Res 34:1499–1519 Craven AM, Aiken GR, Ryan JN (2012) Copper(II) binding by dissolved organic matter: importance of the copper-to-dissolved organic matter ratio and implications for the biotic ligand model. Environ Sci Technol 46:9948–9955 de la Fuente C, Clemente R, Alburquerque JA, Velez D, Bernal MP (2010) Implications of the use of As-rich groundwater for agricultural purposes and the effects of soil amendments on As solubility. Environ Sci Technol 44:9463–9469 Farrell M, Perkins WT, Hobbs PJ, Griffith GW, Jones DL (2010) Migration of heavy metals in soil as influenced by compost amendments. Environ Pollut 158:55–64 Gu HH, Qiu H, Tian T, Zhan SS, Deng THB, Chaney RL, Wang SZ, Tang YT, Morel JL, Qiu RL (2011) Mitigation effects of silicon rich amendments on heavy metal accumulation in rice (Oryza sativa L.) planted on multi-metal contaminated acidic soil. Chemosphere 83:1234–1240
Environ Sci Pollut Res Han FX, Su Y, Monts DL, Plodinec MJ, Banin A, Triplett GE (2003) Assessment of global industrial-age anthropogenic arsenic contamination. Naturwissenschaften 90:395–401 Hartley W, Lepp NW (2008) Effect of in situ soil amendments on arsenic uptake in successive harvests of ryegrass (Lolium perenne cv Elka) grown in amended As-polluted soils. Environ Pollut 156:1030– 1040 Hartley NR, Tsang DCW, Olds WE, Weber PA (2014) Soil washing enhanced by humic substances and biodegradable chelating agents. Soil Sed Contam 23:599–613 Houben D, Evrard L, Sonnet P (2013) Mobility, bioavailability and pHdependent leaching of cadmium, zinc and lead in a contaminated soil amended with biochar. Chemosphere 92:1450–1457 Jing C, Liu S, Patel M, Meng X (2005) Arsenic leachability in water treatment adsorbents. Environ Sci Technol 39:5481–5487 Khan MJ, Jones DL (2009) Effect of composts, lime and diammonium phosphate on the phytoavailability of heavy metals in a copper mine tailing soil. Pedosphere 19:631–641 Kimmell TA, Williams LR, Sorini SS (2001) The RCRA Toxicity Characteristic Leaching Procedure (TCLP): a concept for a new method. Federal Facilities Environmental Journal 12(3):7–24 Komarek M, Vanek A, Ettler V (2013) Chemical stabilisation of metals and arsenic in contaminated soils using oxides - A review. Environ Pollut 172:9–22 Kumpiene J, Lagerkvist A, Maurice C (2007) Stabilization of Pb- and Cucontaminated soil using coal fly ash and peat. Environ Pollut 145: 365–373 Kumpiene J, Lagerkvist A, Maurice C (2008) Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments—a review. Waste Manag 28: 215–225 Limbachiya M, Meddah MS, Fotiadou S (2012) Performance of granulated foam glass concrete. Constr Build Mater 28:759–768 Liu G, Fernandez A, Cai Y (2011) Complexation of arsenite with humic acid in the presence of ferric iron. Environ Sci Technol 45:3210– 3216 Masue Y, Loeppert RH, Kramer TA (2007) Arsenate and arsenite adsorption and desorption behavior on coprecipitated aluminum:iron hydroxides. Environ Sci Technol 41:937–842 Mikutta C, Kretzschmar R (2011) Spectroscopic evidence for ternary complex formation between arsenate and ferric iron complexes of humic substances. Environ Sci Technol 45:9550–9557 Milne CJ, Kinniburgh DG, Van Riemsdijk WH, Tipping E (2003) Generic NICA–Donnan model parameters for metal-ion binding by humic substances. Environ Sci Technol 37:958–971 Miretzky P, Cirelli AF (2010) Remediation of arsenic-contaminated soils by iron amendments: a review. Crit Rev Environ Sci Technol 40:93– 115 Moon DH, Kim KW, Yoon IH, Grubb DG, Shin DY, Cheong KH, Choi HI, Ok YS, Park JH (2011) Stabilization of arsenic-contaminated mine tailings using natural and calcined oyster shells. Environ Earth Sci 64:597–605 Moon DH, Park JW, Cheong KH, Hyun S, Koutsospyros A, Park JH, Ok YS (2013a) Stabilization of lead and copper contaminated firing range soil using calcined oyster shells and fly ash. Environ Geochem Health 35:705–714 Moon DH, Park JW, Chang YY, Ok YS, Lee SS, Ahmad M, Koutsospyros A, Park JH, Baek K (2013b) Immobilization of lead in contaminated firing range soil using biochar. Environ Sci Pollut Res 20:8464–8471 Murcott S (2012) Arsenic contamination in the world: an international sourcebook. IWA Publishing, London, ISBN 1780400381 Neubauer E, Kohler SJ, von der Kammer F, Laudon H, Hofmann T (2013) Effect of pH and stream order on iron and arsenic speciation in boreal catchments. Environ Sci Technol 47:7120–7128
NZ MfE (2010) Proposed national environmental standard for assessing and managing contaminants in soil: discussion document. Ministry for the Environment, Wellington, New Zealand, ISBN: 978-0-47833243-8 Oh C, Rhee S, Oh M, Park J (2012) Removal characteristics of As(III) and As(V) from acidic aqueous solution by steel making slag. J Hazard Mater 213:147–155 Ok YS, Kim SC, Kim DK, Skousen JG, Lee JS, Cheong YW, Kim SJ, Yang JE (2011) Ameliorants to immobilize Cd in rice paddy soils contaminated by abandoned metal mines in Korea. Environ Geochem Health 33:23–30 Olds WE, Tsang DCW, Weber PA (2013) Acid mine drainage treatment assisted by lignite-derived humic substances: metal removal and speciation modelling. Water Air Soil Pollut 224:1521 Padmavathiamma PK, Li LY (2010a) Phytoavailability and fractionation of lead and manganese in a contaminated soil after application of three amendments. Bioresour Technol 101:5667–5676 Padmavathiamma PK, Li LY (2010b) Effect of amendments on phytoavailability and fractionation of copper and zinc in a contaminated soil. Int J Phytoremediat 12:697–715 Pathan SM, Aylmore LAG, Colmer TD (2003) Properties of several fly ash materials in relation to use as soil amendments. J Environ Qual 32:687–693 Qi Y, Szendrak D, Yuen RTW, Hoadley AFA, Mudd G (2011) Application of sludge dewatered products to soil and its effects on the leaching behaviour of heavy metals. Chem Eng J 166:586–595 Reedy RC, Scanlon BR, Nicot JP, Tachovsky JA (2007) Unsaturated zone arsenic distribution and implications for groundwater contamination. Environ Sci Technol 41:6914–6919 Ruttens A, Adriaensen K, Meers E, De Vocht A, Geebelen W, Carleer R, Vangronsveld J (2010) Long-term sustainability of metal immobilization by soil amendments: cyclonic ashes versus lime addition. Environ Pollut 158:1428–1434 Santos S, Costa CAE, Duarte AC, Scherer HW, Scheider RJ, Esteves VI, Santos EBH (2010) Influence of different organic amendments on the potential availability of metals from soil: a study on metal fractionation and extraction kinetics by EDTA. Chemosphere 78: 389–396 Shang C, Zelazny LW (2008) Selective dissolution techniques for mineral analysis of soils and sediments, vol SSSA Book Series, no. 5, Part 5th edn, Methods of soil analysis. Part 5. Mineralogical methods. Soil Science Society of America, Inc, Madison, pp 33–80 Sharma P, Rolle M, Kocar B, Fendorf S, Kappler A (2011) Influence of natural organic matter on As transport and retention. Environ Sci Technol 45:546–553 Tsang DCW, Hartley NR (2014) Metal distribution and spectroscopic analysis after soil washing with chelating agents and humic substances. Environ Sci Pollut Res 21:3987–3995 Tsang DCW, Yip ACK (2014) Comparing chemical-enhanced washing and waste-based stabilisation approach for soil remediation. J Soils Sediments 14:936–947 Tsang DCW, Graham NJD, Lo IMC (2009) Humic acid aggregation in zero-valent iron systems and its effects on trichloroethylene removal. Chemosphere 75:1338–1343 Tsang DCW, Olds WE, Weber PA (2013a) Residual leachability of CCAcontaminated soil after treatment with biodegradable chelating agents and lignite-derived humic substances. J Soils Sediments 13: 895–905 Tsang DCW, Olds WE, Weber PA, Yip ACK (2013b) Soil stabilisation using AMD sludge, compost and lignite: TCLP leachability and continuous acid leaching. Chemosphere 93:2839–2847 Uchimiya M, Chang SC, Klasson KT (2011) Screening biochars for heavy metal retention in soil: role of oxygen functional groups. J Hazard Mater 190:432–441
Environ Sci Pollut Res US EPA (1992) Method 1311: Toxicity Characteristic Leaching Procedure. U.S. Environmental Protection Agency, Washington, DC US EPA (1994) Method 200.2: Sample preparation procedure for spectrochemical determination of total recoverable elements. Revision 2.8. U.S. Environmental Protection Agency, Washington, DC Wang YR, Tsang DCW (2013) Effects of solution chemistry on arsenic(V) removal by low-cost adsorbents. J Environ Sci 25: 2291–2298 Wang S, Wu H (2006) Environmental-benign utilisation of fly ash as lowcost adsorbents. J Hazard Mater B136:482–501
Wang YR, Tsang DCW, Olds WE, Weber PA (2013) Utilizing acid mine drainage sludge and coal fly ash for phosphate removal from dairy wastewater. Environ Technol 34:3177–3182 Yeheyis MB, Shang JQ, Yanful EK (2009) Long-term evaluation of coal fly ash and mine tailings co-placement: a site-specific study. J Environ Manag 91:237–244 Yeheyis MB, Shang JQ, Yanful EK (2010) Feasibility of using coal fly ash for mine waste containment. J Environ Eng 136:682–690 Zhu YN, Zhang XH, Xie QL, Wang Q, Cheng GW (2006) Solubility and stability of calcium arsenates at 25 °C. Water Air Soil Pollut 169: 221–238
RESEARCH ARTICLE
Arsenic and copper stabilisation in a contaminated soil by coal fly ash and green waste compost Daniel C. W. Tsang & Alex C. K. Yip & William E. Olds & Paul A. Weber
Received: 19 December 2013 / Accepted: 12 May 2014 # Springer-Verlag Berlin Heidelberg 2014
Abstract In situ metal stabilisation by amendments has been demonstrated as an appealing low-cost remediation strategy for contaminated soil. This study investigated the short-term leaching behaviour and long-term stability of As and Cu in soil amended with coal fly ash and/or green waste compost. Locally abundant inorganic (limestone and bentonite) and carbonaceous (lignite) resources were also studied for comparison. Column leaching experiments revealed that coal fly ash outperformed limestone and bentonite amendments for As stabilisation. It also maintained the As stability under continuous leaching of acidic solution, which was potentially attributed to high-affinity adsorption, co-precipitation, and pozzolanic reaction of coal fly ash. However, Cu leaching in the column experiments could not be mitigated by any of these inorganic amendments, suggesting the need for co-addition of carbonaceous materials that provides strong chelation with oxygen-containing functional groups for Cu stabilisation.
Green waste compost suppressed the Cu leaching more effectively than lignite due to the difference in chemical composition and dissolved organic matter. After 9-month soil incubation, coal fly ash was able to minimise the concentrations of As and Cu in the soil solution without the addition of carbonaceous materials. Nevertheless, leachability tests suggested that the provision of green waste compost and lignite augmented the simultaneous reduction of As and Cu leachability in a fairly aggressive leaching environment. These results highlight the importance of assessing stability and remobilisation of sequestered metals under varying environmental conditions for ensuring a plausible and enduring soil stabilisation.
Responsible editor: Zhihong Xu
Introduction
Electronic supplementary material The online version of this article (doi:10.1007/s11356-014-3032-3) contains supplementary material, which is available to authorized users. D. C. W. Tsang : W. E. Olds Department of Civil and Natural Resources Engineering, University of Canterbury, Christchurch 8140, New Zealand D. C. W. Tsang (*) Department of Civil and Environmental Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China e-mail: [email protected] A. C. K. Yip Department of Chemical and Process Engineering, University of Canterbury, Christchurch 8140, New Zealand W. E. Olds : P. A. Weber Solid Energy New Zealand, Private Bag 1303, Christchurch 8140, New Zealand
Keywords Contaminant sequestration . Industrial by-products . Metal mobility . Soil amendments . Site remediation
Arsenic (As) contamination, resulting from geogenic/ volcanogenic sources and anthropogenic activities (metal mining, coal/petroleum-related, agricultural uses of arsenical pesticides, and industrial uses of arsenical preservatives), has been identified in 105 countries and estimated to affect over 226 million people worldwide (Murcott 2012). High As mobility and plant uptake in agricultural soil are commonly observed in places where phosphate fertiliser is applied and As-rich groundwater is used for irrigation (Reedy et al. 2007; de la Fuente et al. 2010). On the other hand, extremely high concentrations of As are often associated with the mining and smelting of copper, lead, gold, and silver ores, as well as the wood industry that uses chromated copper arsenate as preservatives (Han et al. 2003; Tsang et al. 2013a). The co-presence of metalloids (e.g. As) and heavy metals (e.g. Cu) at high
Environ Sci Pollut Res
concentrations presents a major challenge to cost-effective remediation of these agricultural and industrial contaminated sites. In recent years, potential application of industrial byproducts as reactive stabilisers for in situ soil amendment (i.e. soil stabilisation) has captured extensive interests. This remediation strategy enables resource recycling and reduces environmental burden of waste management, while accomplishing metal sequestration in the contaminated soil at a low-to-moderate cost with a low carbon footprint, in view of minimal requirement for energy and chemical consumption (Tsang et al. 2013b; Tsang and Yip 2014). Coal fly ash is a readily available by-product from heat/energy generation processes such as boiler and gasification. In addition to its traditional use in glass, ceramics, and concrete production (Wang and Wu 2006; Blissett and Rowson 2012), coal fly ash is an effective stabiliser that offers less energy-intensive and more economically competitive metal removal process in mine tailings and wastewater treatment (Yeheyis et al. 2009; Wang et al. 2013). Recent studies have also explored the efficacy of using coal fly ash for restoration of contaminated sites and demonstrated significant decreases of metal uptake by plants, microbial/phyto-toxicity, exchangeable metal fraction in soil, and diffusion flux of free metals into solution (Kumpiene et al. 2007; Ruttens et al. 2010; Gu et al. 2011; Moon et al. 2013a). On the other hand, green waste compost also proves effective for revitalisation (e.g. nutrient replenishment, water retention, biomass production) of the contaminated soil (Alvarenga et al. 2009; Farrell et al. 2010; Padmavathiamma and Li 2010a). In addition to strong complexation with Cu, compost was shown to alleviate the As phytotoxicity in a recent study (Caporale et al. 2013). This was attributed to partial stabilisation of As via outer-sphere complexation with protonated amino groups and/or Fe-bridged ternary inner-sphere complexation with carboxylate/phenolate groups on the surface (Mikutta and Kretzschmar 2011). Moreover, improved plant yield was observed for combined application of compost and inorganic materials (Khan and Jones 2009; Padmavathiamma and Li 2010a; Qi et al. 2011). Commonly studied soil amendments also included biochar (Cao et al. 2011; Uchimiya et al. 2011; Moon et al. 2013b), lignite/ humus (Ok et al. 2011; Qi et al. 2011), lime/limestone (Hartley and Lepp 2008; Padmavathiamma and Li 2010b), lime-based waste materials (Moon et al. 2011; Ahmad et al. 2012), and bentonite (Ruttens et al. 2010; Yeheyis et al. 2010). Metal mobility and bioavailability can be significantly suppressed in the amended soil through adsorption, cation exchange, surface complexation, (co-)precipitation, surface precipitation, and transformation/incorporation on the stabiliser surface (Kumpiene et al. 2008; Miretzky and Cirelli 2010; Komarek et al. 2013). However, potential risks of increased migration and transience of heavy metals are still
present with the use of soil amendments (Farrell et al. 2010; Santos et al. 2010; Ahmad et al. 2012), which may be aggravated in an acidic environment as revealed by recent studies (Houben et al. 2013; Tsang et al. 2013b). Therefore, shortterm leaching and long-term stability of the soil stabilisation approach in such condition are important issues that should be fully understood upfront. This study assessed the effectiveness of coal fly ash and green waste compost for soil stabilisation, and the short-term remobilisation potential and long-term leachability under a moderately aggressive leaching condition. Locally abundant resources (lignite, limestone, and bentonite) were evaluated for comparison. Column leaching experiments and standard leachability test were performed on a soil contaminated by As, Cu, and Cr (due to past timber treatment activities) after incubation with individual or combined soil amendments.
Experimental methods Field-contaminated soil The contaminated soil was obtained from a former timber treatment facility in Tapanui, New Zealand, which was operational from the early 1940s until 1986. The total volume of contaminated soil was 1,634 m3 and the total concentrations of As, Cu, and Cr across the contaminated site were 570– 7,280, 498–4,540, and 426–3,460 mg kg−1, respectively (Tsang et al. 2013a; Hartley et al. 2014). The soil sample was collected from a contamination hot spot, air-dried, and passed through a 2-mm sieve. The concentrations of As, Cu, and Cr in the soil sample were 3,300, 2,100, and 2,800 mg kg −1 , respectively, as determined by nitric/ hydrochloric acid digestion followed by metal analysis (US EPA Method 200.2). The As concentration exceeded the soil guideline values in New Zealand (20 mg kg−1 for rural residential land use; 70 mg kg−1 for commercial/industrial land use; NZ MfE 2010) and required a 97.9–99.4 % extraction by soil washing if selected for remediation, which was practically unachievable (Tsang et al. 2013a; Hartley et al. 2014). The soil contained 5.7 % silt and clay content (measured by 63-μm sieving) and 0.43 % organic carbon content (measured by LECO combustion with acid pretreatment to remove carbonates), with a soil pH of 7.3 at a 1:2 soil to water ratio. The soil mineralogy consisted of quartz (38 %), calcic plagioclase feldspar (34 %), muscovite (15 %), and chlorite (13 %), as identified by using X-ray diffraction (XRD) plus Semiquant analysis (Philips PW1830) and SIROQUANT search/match programme. The relative mass percentages in the soil were 2.74 % Fe, 5.12 % Al, 1.58 % Ca, 0.06 % Mn, and 0.7 % Mg, as shown by borate fusion X-ray fluorescence (XRF) spectrometry (SpectraChem Analytical, ISO 17025).
Environ Sci Pollut Res
Stabiliser characteristics Coal fly ash was collected from a subbituminous coalcombustion plant in Southland, New Zealand, which had a pH 12 and acid neutralising capacity of 54.3 % CaCO3. There was negligible metal/metalloid leaching from coal fly ash (such as As, Cu, Cr, Cd, Se, Pb, and Zn, which were below 0.001 mg L−1) in Synthetic Precipitation Leaching Procedure. The coal fly ash contained 13.6 % Ca, 9.1 % Si, 6.2 % Fe, and 2.2 % Al (by weight) as determined by using XRF. Various crystalline-phase minerals were identified by XRD analysis: quartz (14 %, SiO2), merwinite (12 %, Ca3Mg(SiO4)2), calcite (4 %, CaCO3), and portlandite (2 %, Ca(OH)2). The amounts of poorly crystalline Fe and Al oxides were 5,700 and 6,760 mg kg−1, respectively, as determined by using oxalate extraction method (Shang and Zelazny 2008). The specific surface area was 211.6 m2 g−1, as calculated by using the BET analysis of nitrogen gas adsorption isotherm (TriStar 3000, Micromeritics) after sample degassing at 3,00 °C for a few hours. For comparison, ultra-fine limestone (90 wt% CaCO3 < 106 μm) and bentonite (Mintech NZ Ltd) were studied in parallel. The latter was locally prepared from calcium bentonite with soda ash and marketed as low-value soil enhancers for earthing purposes. The XRD and BET analyses revealed a mineralogical composition of kaolin (44 %, Al2(Si2O5)(OH)4), illite (29 %, K0.5(Al,Fe,Mg)3(Si,Al)4O10(OH)2), quartz (15 %, SiO2), calcic plagioclase feldspar (12 %, Ca(Al2Si2O8)), and a surface area of 42.9 m2 g−1, respectively. A summary was provided in the Supplementary Materials (Table SM-1). Green waste compost (Living Earth Ltd, New Zealand) was produced from garden and kitchen waste by indoor tunnel composting system at 55 °C or above for at least 3 days followed by curing for up to 120 days. The compost had a pH 7.5–8, moisture content of 45–55 %, and bulk density of approximately 0.6 kg L−1. Lignite (a low-rank coal accounting for 70 % of coal reserve in New Zealand) was obtained from 0.2–1.5 km below ground at the New Vale Mine in Southland, New Zealand. All materials were air-dried at 37 °C and passed through 2-mm sieve before use. Elemental analysis (wt%, Elementar Combustion Analyser, Hanau) indicated that compost contained 24.2 % C, 2.8 % H, 24.8 % O, 2.1 % N, and 46.1 % inorganic ash; lignite contained 57.7 % C, 5.1 % H, 31.1 % O, 0.7 % N, and 5.4 % inorganic ash (Table SM-2). After repeatedly washing with 1 M HCl for inorganic removal, the carbonaceous samples were analysed by nuclear magnetic resonance (NMR) spectroscopy (Bruker AMX 200 Mhz horizontal bore magnet) as described in the Supplementary Materials. The organic carbons (wt%) of green waste compost were composed of 10.6 % phenolic, 8.8 % carboxyl, 1.3 % carbonyl, 22.3 % aromatic, 25.3 % aliphatic, and 31.7 % carbohydrates, whereas those of lignite were 12.1 % phenolic, 4.9 % carboxyl, 2.0 % carbonyl, 30.2 % aromatic, 33.8 % aliphatic, and 17.0 % carbohydrates, respectively (Fig. SM-1
and Table SM-3). These characteristics reflected the food waste source of compost (more carboxylates and ash) and the long-term humification and diagenesis of lignite (more aromatic and aliphatic structures). Arsenic and copper stabilisation The short-term leaching potential of As, Cu, and Cr from the soil amended with the above reactive stabilisers was assessed in column experiments. The contaminated soil (100 g) was homogeneously blended with individual (5 and 10 wt%) or mixed (5 wt% each) waste materials at a bulk density of 1.3 kg L−1 and packed into PVC columns with an inner diameter of 52 mm and a length of 300 mm. Quartz sand layers (approximately 100 g, prewashed by diluted HCl and deionised water for five times) were placed at the bottom and top of the columns for evenly distributed flow. The columns were first slowly saturated with upward-flowing deionised water from the bottom to avoid air entrapment and then flushed with pH 4.93 acetate buffer at a flow rate of 0.9–1.0 mL min−1 using a peristaltic pump. This test can be applied as a risk assessment tool for measuring the ability of remediation technologies (e.g. stabilisation) in retarding the mobility of contaminants in a fairly aggressive leaching environment (Kimmell et al. 2001). Blank columns containing only contaminated soil were used as control. As the inflow and outflow volumes were equal after initial saturation, effluent samples were collected and weighed for calculation of total pore volume. After a 0.45-μm filtration, the concentrations of As, Cu, Cr, and mineral cations were periodically analysed by using inductively coupled plasma mass spectroscopy (Agilent 7500cx), of which the experimental detection limits (after sample dilution) of As, Cu, and Cr were 0.014, 0.02, and 0.005 mg L−1, respectively. Dissolved organic matter in the effluent was also quantified by measuring UV absorbance at a wavelength of 254 nm (Thermo Scientific GENESYS 10S UV-Vis Spectrophotometer). The effluent concentrations were plotted against pore volume to construct the breakthrough curves. For quality control, every tenth sample was duplicated and every 20th was spiked, after which blanks were run before further analysis. Moreover, one-third of the column experiments were run in duplicate to ensure data reliability and reproducibility. To investigate the effectiveness in the long term, the soil sample (20 g each) was initially mixed with the above materials (individual or in combination, 5 wt% each) and then incubated at saturated water content and room temperature. The containers were sealed with parafilm and stored in the dark. After 9-month static incubation, the soil solution was analysed for metal concentrations as previously described, and the soil mixtures (including the amendments) were analysed by using Toxicity Characteristic Leaching Procedure (TCLP; US EPA Method 1311) as a performance indicator. The supernatant was separated by centrifugation at 4,000 rpm for 15 min, filtered through 0.45-μm membrane filter, acidified
Environ Sci Pollut Res
with concentrated nitric acid, and stored in amber vials at 4 °C before analysis. All experiments were duplicated and average values were presented.
Results and discussion Short-term remobilisation risk—coal fly ash, limestone, and bentonite Coal fly ash and green waste compost can be deployed in field using soil augers or disc harrows after water spraying, but adequate measures should be in place to avoid erosion of these low-density materials during storm events, e.g. granulation with binding/foaming agents (Limbachiya et al. 2012). These engineering issues are assumed to be properly addressed in the following experiments. Figure 1 illustrates the breakthrough curves of As, Cu, and Cr from the untreated and
coal fly ash-stabilised soil columns under continuous acid leaching. The results show that As and Cu were the major risk drivers while Cr leaching was negligible despite its high concentration in the contaminated soil (Fig. 1). This was because As existed as partially soluble arsenic trioxide/pentoxide and copper-arsenate precipitates whereas Cr was present in the forms of insoluble trivalent chromium oxides and ironchromium co-precipitates (Tsang and Hartley 2014). With the addition of coal fly ash, the mobility of As was substantially inhibited at an amendment ratio of 5 wt% and was nearly eliminated at 10 wt%. The As stability was maintained throughout the 120 pore volumes of acid leaching, suggesting that As became more geochemically stable in the presence of coal fly ash. Due to the high surface area (211.6 m2 g−1) of coal fly ash and the presence of large amounts of poorly crystalline Fe and Al oxides (5,700 and 6,760 mg kg−1, respectively), As could be strongly adsorbed in the form of bidentate mononuclear inner-sphere complexes, which was
Fig. 1 Short-term remobilisation risk of untreated soil and coal fly ash-stabilised soil
Environ Sci Pollut Res
observed on co-precipitated Fe/Al hydroxides (Jing et al. 2005; Masue et al. 2007). On the other hand, significant amounts of relatively soluble Ca minerals (12 wt% merwinite (Ksp = 10−13.7), 4 wt% calcite (Ksp = 10−8.5), and 2 wt% portlandite (Ksp =10−5.3)) might result in precipitation of insoluble calcium-arsenate compounds (Ksp =10−21.1 to 10−40.1), based on speciation calculation and previous reports (Zhu et al. 2006; Moon et al. 2011; Oh et al. 2012; Wang and Tsang 2013). In addition, As might be entrapped into calcium-silicate-hydrate phases produced by the pozzolanic reaction of coal fly ash (13.6 wt% Ca and 9.1 wt% Si based on XRF analysis) (Chen et al. 2004; Moon et al. 2013a). The relative significance of these mechanisms, however, required further spectroscopic investigations. Although Cu could be stabilised via adsorption onto surface hydroxyl groups of Fe/Al oxides in coal fly ash, the results indicate that Cu mobility remained unchanged under acetic acid leaching (Fig. 1). This suggested that the binding strength of Cu sequestration should be tested against leaching of organic acids (acetic, oxalic, citric acids, etc) in plant root
exudates. Notable dissolution of Ca and Al in the first 20 pore volumes may deserve attention in field applications. It should be noted that a high dosage (e.g. 10 wt% or above) of coal fly ash would alter soil texture, increase water-holding capacity, and reduce hydraulic conductivity (Pathan et al. 2003; Yeheyis et al. 2010). As there was little difference in the effectiveness of 5 and 10 wt% amendments, a smaller amount of coal fly ash (if well mixed in the field) was recommended for practical deployment and minimal ecological impact. For comparison, Fig. 2 illustrates the leaching of As and Cu from limestone- and bentonite-stabilised soil columns. With the high alkalinity and Ca solubility of limestone, calcium arsenate precipitation contributes to the initial suppression of As leaching. However, the treatment with 5 or 10 wt% limestone was less effective compared with coal fly ash due to the absence of high-affinity adsorption on the Fe/Al coprecipitates or incorporation into calcium-silicate-hydrate phases. Under prolonged acid leaching, As started to leach out from the limestone-stabilised soil as the initial effluent pH gradually decreased from 6.5 to 5.0 within 15 pore volumes.
Fig. 2 Short-term remobilisation risk of limestone-stabilised soil and bentonite-stabilised soil
Environ Sci Pollut Res
Fig. 3 Short-term remobilisation risk of coal fly ash/green waste compost-stabilised soil and coal fly ash/lignite-stabilised soil
The results further indicate that limestone was unable to reduce the Cu leachability without a sustained alkaline environment. Similar results were reported in the literature where the metal stabilisation efficiency of limestone treatment was extremely low at the end of leaching period (Ruttens et al. 2010). Moreover, the release and accumulation of CO2 due to acid neutralisation of limestone resulted in column clogging after 30 pore volumes from which significant Ca dissolution was observed. On the other hand, Ca-rich bentonite (42.9 m2 g−1) initially reduced the leaching of As and Cu via As precipitation and Cu adsorption. However, their stability was not sustainable in an acidic and complexing condition. Short-term remobilisation risk—co-addition of green waste compost and lignite As coal fly ash had limited efficiency for Cu sequestration, green waste compost and lignite were added to achieve the
Fig. 4 Leaching of dissolved organic matter from green waste compost and lignite
Environ Sci Pollut Res
stabilisation (Fig. 3), based on the hypothesis that the oxygencontaining, proton-dissociating functional groups (primarily carboxylates at pH above 5 and phenolates at pH above 8) on carbonaceous materials may contribute to strong metal binding (Milne et al. 2003; Tsang et al. 2009; Uchimiya et al. 2011; Olds et al. 2013). Both green waste compost and lignite contain the aforementioned functional groups: 8.8 % carboxylate groups and 46.1 % inorganic ash (surface hydroxyl groups) in green waste compost; 4.9 % carboxylates and Fig. 5 Pore water concentrations after long-term soil stabilisation
5.4 % ash in lignite. The larger amount of functional groups present in the green waste compost resulted in better Cu sequestration compared with lignite, as shown in Fig. 3. Moreover, Fig. 4 shows that a larger amount of dissolved organic matter (or more aromatic moieties) was released from lignite, which comprised 30.2 % aromatic carbons based on NMR analysis. Since the aromatic components were found to solubilise Cu to a greater extent, especially at low Cu to dissolved organic matter ratios (Amery et al. 2010; Baken
Environ Sci Pollut Res
et al. 2011; Craven et al. 2012; Ahmed et al. 2013), the mobilisation of aromatic moieties from lignite may hinder its effectiveness for Cu sequestration under a dynamic leaching condition. Dissolution of organic matter continued for 60–80 pore volumes before reaching the background level (Fig. 4). Recent chromatographic and spectroscopic findings revealed that the mobilisation of As was facilitated by dissolved organic matter through formation of ternary arsenic-iron-organic matter complexes and nanosized colloids (Liu et al. 2011; Fig. 6 TCLP leachability after long-term soil stabilisation
Sharma et al. 2011; Neubauer et al. 2013). Nevertheless, the presence of green waste compost or lignite did not facilitate As leaching in this study (comparing Figs. 1 and 3). This was because at pH above 4.5, the As transport was mainly coupled with colloidal Fe oxides (Neubauer et al. 2013), while there was negligible Fe dissolution or Fecolloid mobilisation from the coal fly ash-stabilised soil (Fig. 3). On the other hand, attention may rather be paid to substantial Ca dissolution and moderate Al dissolution within the first 20 pore volumes.
Environ Sci Pollut Res
Long-term soil stabilisation After 9-month static incubation (Fig. 5), coal fly ash significantly reduced the As concentration in the soil solution although there was incomplete As sequestration. On the contrary, the addition of limestone and bentonite provided an alkaline environment (solution pH of 8–8.5) that induced greater solubilisation of As due to its oxyanion nature, resulting in higher environmental risks of bioavailable As. In addition, coal fly ash was able to remove Cu from the soil solution because of its high surface area and surface hydroxyl groups, corroborating the reported decrease in diffusion flux of free metals into solution (Gu et al. 2011). Therefore, the copresence of green waste compost and lignite did not manifest noticeable benefits in terms of the pore water concentrations. However, Fig. 6 illustrates that the As leachability was reduced by coal fly ash to a smaller extent in TCLP tests (from 7.65 mg L−1 to 4.45 and 2.68 mg L−1 at 5 and 10 wt%, respectively). Moreover, there was no reduction in the Cu leachability (26.4 mg L−1), which was much higher than As and Cr leachability. By contrast, limestone and bentonite increased the As leachability (11.3–17.5 mg L−1) while limestone reduced the Cu leachability to some extent (13.8– 18.5 mg L −1 ). These results implied that irreversible stabilisation of Cu could not be chiefly achieved by the inorganic amendments. Hence, Fig. 6 shows an advantage of simultaneous reduction of Cu leachability (9.9–18.9 mg L−1) accomplished by the combined applications of green waste compost or lignite together with inorganic amendments. In a closed system, green waste compost and lignite demonstrated similar efficacy for Cu sequestration through their strong complexation affinity (K Cu–DOM = 10 5.6 to 10 11.5 M −1 (Craven et al. 2012)). Yet, the residual Cu leachability remained at a rather high level. These results suggest that the soil simultaneously contaminated by As and Cu requires an integration of remediation strategies (e.g. prior extraction).
Conclusions In situ soil stabilisation with locally available industrial byproducts has gained increasing popularity as a low-cost remediation alternative. This study underlined the significance of assessing the short-term mobility and long-term stability of As (metalloid) and Cu (heavy metal) of the waste-stabilised soil. Coal fly ash outperformed commonly used amendments by limestone and bentonite for As and Cu sequestration from the soil solution. However, Cu leaching was not reduced under continuous acid flushing although As stability could be sustained. Therefore, combined application of coal fly ash together with carbonaceous materials was useful for mitigating the Cu leachability. Green waste compost proved to be
more effective than lignite, probably because of the difference in chemical composition and extent of dissolution. In order to minimise the residual metal leachability, soil stabilisation by the mixed amendments may be augmented by a preceding treatment process. Acknowledgements The authors appreciate the financial support from the Brian Mason Scientific & Technical Trust (New Zealand) and the provision of field soil sample from Golder Associates (New Zealand) Ltd for this study.
References Ahmad M, Moon DH, Lim KJ, Shope CL, Lee SS, Usman ARA, Kim KR, Park JH, Hur SO, Yang JE, Ok YS (2012) An assessment of the utilization of waste resources for the immobilization of Pb and Cu in the soil from a Korean military shooting range. Environ Earth Sci 67:1023–1031 Ahmed IAM, Hamilton-Taylor J, Lofts S, Meeussen JCL, Lin C, Zhang H, Davison W (2013) Testing copper-speciation predictions in freshwaters over a wide range of metal-organic matter ratios. Environ Sci Technol 47:1487–1495 Alvarenga P, Palma P, Goncalves AP, Fernandes RM, de Varennes A, Vallini G, Duarte E, Cunha-Queda AC (2009) Organic residues as immobilizing agents in aided phytostabilization: (II) effects on soil biochemical and ecotoxicological characteristics. Chemosphere 74: 1301–1308 Amery F, Degryse F, Van Moorleghem C, Duyck M, Smolders E (2010) The dissociation kinetics of Cu-dissolved organic matter complexes from soil and soil amendments. Anal Chim Acta 670:24–32 Baken S, Degryse F, Verheyen L, Merckx R, Smolders E (2011) Metal complexation properties of freshwater dissolved organic matter are explained by its aromaticity and by anthropogenic ligands. Environ Sci Technol 45:2584–2590 Blissett RS, Rowson NA (2012) A review of the multi-component utilisation of coal fly ash. Fuel 97:1–23 Cao X, Ma L, Liang Y, Gao B, Harris W (2011) Simultaneous immobilization of lead and atrazine in contaminated soils using dairymanure biochar. Environ Sci Technol 45:4884–4889 Caporale AG, Pigna M, Sommella A, Dynes JJ, Cozzolino V, Violante A (2013) Influence of compost on the mobility of arsenic in soil and its uptake by bean plants (Phaseolus vulgaris L.) irrigated with arsenite-contaminated water. J Environ Manag 128:837–843 Chen JJ, Thomas JJ, Taylor HFW, Jennings HM (2004) Solubility and structure of calcium silicate hydrate. Cem Concr Res 34:1499–1519 Craven AM, Aiken GR, Ryan JN (2012) Copper(II) binding by dissolved organic matter: importance of the copper-to-dissolved organic matter ratio and implications for the biotic ligand model. Environ Sci Technol 46:9948–9955 de la Fuente C, Clemente R, Alburquerque JA, Velez D, Bernal MP (2010) Implications of the use of As-rich groundwater for agricultural purposes and the effects of soil amendments on As solubility. Environ Sci Technol 44:9463–9469 Farrell M, Perkins WT, Hobbs PJ, Griffith GW, Jones DL (2010) Migration of heavy metals in soil as influenced by compost amendments. Environ Pollut 158:55–64 Gu HH, Qiu H, Tian T, Zhan SS, Deng THB, Chaney RL, Wang SZ, Tang YT, Morel JL, Qiu RL (2011) Mitigation effects of silicon rich amendments on heavy metal accumulation in rice (Oryza sativa L.) planted on multi-metal contaminated acidic soil. Chemosphere 83:1234–1240
Environ Sci Pollut Res Han FX, Su Y, Monts DL, Plodinec MJ, Banin A, Triplett GE (2003) Assessment of global industrial-age anthropogenic arsenic contamination. Naturwissenschaften 90:395–401 Hartley W, Lepp NW (2008) Effect of in situ soil amendments on arsenic uptake in successive harvests of ryegrass (Lolium perenne cv Elka) grown in amended As-polluted soils. Environ Pollut 156:1030– 1040 Hartley NR, Tsang DCW, Olds WE, Weber PA (2014) Soil washing enhanced by humic substances and biodegradable chelating agents. Soil Sed Contam 23:599–613 Houben D, Evrard L, Sonnet P (2013) Mobility, bioavailability and pHdependent leaching of cadmium, zinc and lead in a contaminated soil amended with biochar. Chemosphere 92:1450–1457 Jing C, Liu S, Patel M, Meng X (2005) Arsenic leachability in water treatment adsorbents. Environ Sci Technol 39:5481–5487 Khan MJ, Jones DL (2009) Effect of composts, lime and diammonium phosphate on the phytoavailability of heavy metals in a copper mine tailing soil. Pedosphere 19:631–641 Kimmell TA, Williams LR, Sorini SS (2001) The RCRA Toxicity Characteristic Leaching Procedure (TCLP): a concept for a new method. Federal Facilities Environmental Journal 12(3):7–24 Komarek M, Vanek A, Ettler V (2013) Chemical stabilisation of metals and arsenic in contaminated soils using oxides - A review. Environ Pollut 172:9–22 Kumpiene J, Lagerkvist A, Maurice C (2007) Stabilization of Pb- and Cucontaminated soil using coal fly ash and peat. Environ Pollut 145: 365–373 Kumpiene J, Lagerkvist A, Maurice C (2008) Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments—a review. Waste Manag 28: 215–225 Limbachiya M, Meddah MS, Fotiadou S (2012) Performance of granulated foam glass concrete. Constr Build Mater 28:759–768 Liu G, Fernandez A, Cai Y (2011) Complexation of arsenite with humic acid in the presence of ferric iron. Environ Sci Technol 45:3210– 3216 Masue Y, Loeppert RH, Kramer TA (2007) Arsenate and arsenite adsorption and desorption behavior on coprecipitated aluminum:iron hydroxides. Environ Sci Technol 41:937–842 Mikutta C, Kretzschmar R (2011) Spectroscopic evidence for ternary complex formation between arsenate and ferric iron complexes of humic substances. Environ Sci Technol 45:9550–9557 Milne CJ, Kinniburgh DG, Van Riemsdijk WH, Tipping E (2003) Generic NICA–Donnan model parameters for metal-ion binding by humic substances. Environ Sci Technol 37:958–971 Miretzky P, Cirelli AF (2010) Remediation of arsenic-contaminated soils by iron amendments: a review. Crit Rev Environ Sci Technol 40:93– 115 Moon DH, Kim KW, Yoon IH, Grubb DG, Shin DY, Cheong KH, Choi HI, Ok YS, Park JH (2011) Stabilization of arsenic-contaminated mine tailings using natural and calcined oyster shells. Environ Earth Sci 64:597–605 Moon DH, Park JW, Cheong KH, Hyun S, Koutsospyros A, Park JH, Ok YS (2013a) Stabilization of lead and copper contaminated firing range soil using calcined oyster shells and fly ash. Environ Geochem Health 35:705–714 Moon DH, Park JW, Chang YY, Ok YS, Lee SS, Ahmad M, Koutsospyros A, Park JH, Baek K (2013b) Immobilization of lead in contaminated firing range soil using biochar. Environ Sci Pollut Res 20:8464–8471 Murcott S (2012) Arsenic contamination in the world: an international sourcebook. IWA Publishing, London, ISBN 1780400381 Neubauer E, Kohler SJ, von der Kammer F, Laudon H, Hofmann T (2013) Effect of pH and stream order on iron and arsenic speciation in boreal catchments. Environ Sci Technol 47:7120–7128
NZ MfE (2010) Proposed national environmental standard for assessing and managing contaminants in soil: discussion document. Ministry for the Environment, Wellington, New Zealand, ISBN: 978-0-47833243-8 Oh C, Rhee S, Oh M, Park J (2012) Removal characteristics of As(III) and As(V) from acidic aqueous solution by steel making slag. J Hazard Mater 213:147–155 Ok YS, Kim SC, Kim DK, Skousen JG, Lee JS, Cheong YW, Kim SJ, Yang JE (2011) Ameliorants to immobilize Cd in rice paddy soils contaminated by abandoned metal mines in Korea. Environ Geochem Health 33:23–30 Olds WE, Tsang DCW, Weber PA (2013) Acid mine drainage treatment assisted by lignite-derived humic substances: metal removal and speciation modelling. Water Air Soil Pollut 224:1521 Padmavathiamma PK, Li LY (2010a) Phytoavailability and fractionation of lead and manganese in a contaminated soil after application of three amendments. Bioresour Technol 101:5667–5676 Padmavathiamma PK, Li LY (2010b) Effect of amendments on phytoavailability and fractionation of copper and zinc in a contaminated soil. Int J Phytoremediat 12:697–715 Pathan SM, Aylmore LAG, Colmer TD (2003) Properties of several fly ash materials in relation to use as soil amendments. J Environ Qual 32:687–693 Qi Y, Szendrak D, Yuen RTW, Hoadley AFA, Mudd G (2011) Application of sludge dewatered products to soil and its effects on the leaching behaviour of heavy metals. Chem Eng J 166:586–595 Reedy RC, Scanlon BR, Nicot JP, Tachovsky JA (2007) Unsaturated zone arsenic distribution and implications for groundwater contamination. Environ Sci Technol 41:6914–6919 Ruttens A, Adriaensen K, Meers E, De Vocht A, Geebelen W, Carleer R, Vangronsveld J (2010) Long-term sustainability of metal immobilization by soil amendments: cyclonic ashes versus lime addition. Environ Pollut 158:1428–1434 Santos S, Costa CAE, Duarte AC, Scherer HW, Scheider RJ, Esteves VI, Santos EBH (2010) Influence of different organic amendments on the potential availability of metals from soil: a study on metal fractionation and extraction kinetics by EDTA. Chemosphere 78: 389–396 Shang C, Zelazny LW (2008) Selective dissolution techniques for mineral analysis of soils and sediments, vol SSSA Book Series, no. 5, Part 5th edn, Methods of soil analysis. Part 5. Mineralogical methods. Soil Science Society of America, Inc, Madison, pp 33–80 Sharma P, Rolle M, Kocar B, Fendorf S, Kappler A (2011) Influence of natural organic matter on As transport and retention. Environ Sci Technol 45:546–553 Tsang DCW, Hartley NR (2014) Metal distribution and spectroscopic analysis after soil washing with chelating agents and humic substances. Environ Sci Pollut Res 21:3987–3995 Tsang DCW, Yip ACK (2014) Comparing chemical-enhanced washing and waste-based stabilisation approach for soil remediation. J Soils Sediments 14:936–947 Tsang DCW, Graham NJD, Lo IMC (2009) Humic acid aggregation in zero-valent iron systems and its effects on trichloroethylene removal. Chemosphere 75:1338–1343 Tsang DCW, Olds WE, Weber PA (2013a) Residual leachability of CCAcontaminated soil after treatment with biodegradable chelating agents and lignite-derived humic substances. J Soils Sediments 13: 895–905 Tsang DCW, Olds WE, Weber PA, Yip ACK (2013b) Soil stabilisation using AMD sludge, compost and lignite: TCLP leachability and continuous acid leaching. Chemosphere 93:2839–2847 Uchimiya M, Chang SC, Klasson KT (2011) Screening biochars for heavy metal retention in soil: role of oxygen functional groups. J Hazard Mater 190:432–441
Environ Sci Pollut Res US EPA (1992) Method 1311: Toxicity Characteristic Leaching Procedure. U.S. Environmental Protection Agency, Washington, DC US EPA (1994) Method 200.2: Sample preparation procedure for spectrochemical determination of total recoverable elements. Revision 2.8. U.S. Environmental Protection Agency, Washington, DC Wang YR, Tsang DCW (2013) Effects of solution chemistry on arsenic(V) removal by low-cost adsorbents. J Environ Sci 25: 2291–2298 Wang S, Wu H (2006) Environmental-benign utilisation of fly ash as lowcost adsorbents. J Hazard Mater B136:482–501
Wang YR, Tsang DCW, Olds WE, Weber PA (2013) Utilizing acid mine drainage sludge and coal fly ash for phosphate removal from dairy wastewater. Environ Technol 34:3177–3182 Yeheyis MB, Shang JQ, Yanful EK (2009) Long-term evaluation of coal fly ash and mine tailings co-placement: a site-specific study. J Environ Manag 91:237–244 Yeheyis MB, Shang JQ, Yanful EK (2010) Feasibility of using coal fly ash for mine waste containment. J Environ Eng 136:682–690 Zhu YN, Zhang XH, Xie QL, Wang Q, Cheng GW (2006) Solubility and stability of calcium arsenates at 25 °C. Water Air Soil Pollut 169: 221–238
