PhD Paper-1

The research article is originally published at Water, Air, & Soil Pollution A Springer Journal http://www.springer.com/environment/journal/11270 The original publication is available at: http://dx.doi.org/10.1007/s11270-015-2312-y

Chelant-Assisted Depollution of Metal-Contaminated Fe-Coated Sands and Subsequent Recovery of the Chemicals Using Solid-Phase Extraction Systems

Ismail M. M. Rahman, 1, 2, * Zinnat A. Begum, 3, * Hikaru Sawai, 2 Masashi Ogino, 2 Yoshiaki Furusho, 4 Satoshi Mizutani, 5 Hiroshi Hasegawa 6, * 1

Department of Applied and Environmental Chemistry, Faculty of Science, University of Chittagong, Chittagong 4331, Bangladesh

2

Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan

3

Department of Civil Engineering, Southern University, 739/A Mehedibag Road, Chittagong 4000, Bangladesh 4

5

GL Sciences Inc., Nishishinjuku 6-22-1, Shinjuku, Tokyo 163-1130, Japan

Graduate School of Engineering, Osaka City University, Sugimoto 3-3-138, Sumiyoshi-Ku, Osaka 558-8585, Japan

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Institute of Science and Engineering, Kanazawa University, Kakuma, Kanazawa 920-1192, Japan

*Author(s) for correspondence E-mail: [email protected], [email protected] (I.M.M. Rahman); [email protected] (Z.A. Begum); [email protected] (H. Hasegawa). TEL/Fax: +81-76-234-4792 Please Cite the article as: I.M.M. Rahman, Z.A. Begum, H. Sawai, M. Ogino, Y. Furusho, S. Mizutani and H. Hasegawa, Chelant-assisted depollution of metal-contaminated Fe-coated sands and subsequent recovery of the chemicals using solid-phase extraction systems, Water Air and Soil Pollution, 226(3): 37, 2015.

Water, Air, & Soil Pollution, 226(3): 37, 2015 The original publication is available at: http://dx.doi.org/10.1007/s11270-015-2312-y

Abstract The disposal of potentially toxic element (PTE)-loaded sludge that is produced during industrial or commercial wastewater treatments evoke concerns because of the probability of hazardous environmental consequences. In the current work, we proposed a chelant-assisted decontamination technique of the laboratory-produced PTE-loaded (As, Cd, Pb) polymericFe-coated sludge and subsequent recovery of the chelants and PTEs. The chelant options include both biodegradable (EDDS, GLDA and HIDS) and non-biodegradable (EDTA) alternatives. The washing performance was compared and discussed in terms of the solution pH and relative stabilities of the complexes of PTEs and chelants in solution. The changes in solution pH or chelants have no significant effect on the chelant-induced removal efficiency of Cd, and the same result was observed for Pb at extreme and moderate acidic pH. The Asextraction rate is also improved with chelant in the solution despite a limited interaction between the chelant and the arsenic species in the solution. The column-packed solid-phase extraction (SPE) system, which was equipped with macrocycle, chelating resin, or ionexchange resin, was used to explore the corresponding separation performance of the PTEs and chelant. The macrocycle-equipped SPE system shows better selectivity than other SPEs in terms of extraction and recovery performance of the PTEs regardless of the chelants. Some unique points of the proposed process are minimum environmental burden due to the use of biodegradable materials in the washing solution and cost minimization by recycling the ingredients.

Keywords Polymeric Fe-modified sand; Potentially toxic element (PTE); Wastewater treatment; Sludge decontamination; Chelant-induced washing; Solid-Phase Extraction (SPE)

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1.0 Introduction Elements with possible harmful properties, which have been meaninglessly termed as “heavy metal” (Duffus 2002) and suggested to be renamed as “potentially toxic element” PTE (Capra et al. 2014), have been consumed in different areas for thousands of years. The intrusion of PTEs into the atmospheric systems via mining residues, sewage sludge, wastewaters, etc. induces risks to humans, which range from chronic disorders to ecological catastrophes (Järup 2003; Mohammed et al. 2011). However, the exposure to PTEs continues and is even increasing in some areas despite authoritarian monitoring. The foremost health risks for human because of PTEs are associated with the exposure to lead, cadmium, mercury and arsenic (Järup 2003). The priority pollutant list of the Environmental Protection Agency (EPA) includes the aforementioned PTEs to establish the ambient water quality criteria and effluent limitations. Furthermore, according to the relative toxicity of various metals, lead, cadmium, mercury and arsenic are not required even in small amounts by any organism (U.S. EPA 2012). Various treatment technologies have been developed to remove the above-listed PTEs from water, such as ion exchange, electrodialysis, reverse osmosis, membrane filtration, electro-winning, solvent stripping, precipitation, adsorption, and so forth (LaGrega et al. 1994; Rahman et al. 2013a). The implications of stringent water quality standards constrain the conventional water treatment options, such as coagulation, sedimentation, and filtration, in removing trace amounts of PTEs. The classical applications of Al- and/ Fe-salt as the coagulant is gradually replaced by metal-oxide/hydroxide-coated sands to either overcome the limitations with the reactor design or minimize the sludge disposal cost (Kuan et al. 1998). The precipitation and adsorption methods are typically used to synthesize Fe- or Al-coated sand (Scheidegger et al. 1993; Ying and Axe 2005). The abundance of iron oxides in natural environments and the corresponding adsorption-favorable properties, such as relatively high surface area and variable surface charge, inspired researchers to develop innovative Fecoating techniques for sand to remove PTEs (Cundy et al. 2008; Giles et al. 2011; Rahman et al. 2013b). Among the proposed options to produce Fe-coating solid materials, the 3


modification of a solid surface with polymeric Fe species produces innovative and promising classes of sorbent materials (Cooper et al. 2002), and the corresponding superior efficiency in coagulating or adsorbing undesirable components from waste waters was reported (Jiang and Graham 1996; 1998; Cooper et al. 2002; Jiang et al. 2002; Jiang and Zeng 2003). Despite increasing recommendations for the use of Fe-coated sands for liquid-waste decontamination, the stability of the retained PTEs and safe management of the sludge become issues of concern (Ford 2002; Badruzzaman 2003; Rahman et al. 2013b). Various methods to securely dispose PTE-loaded Fe-coated solid sludge have been recommended: solidification/stabilization, vitrification, sub-aqueous disposal by burying in mud or mixed with organic matters, disposal to brick-lined pits, etc. (Dutré and Vandecasteele 1995; Jing et al. 2003; Kumpiene et al. 2007; van Herwijnen et al. 2007; Kumpiene et al. 2008). However, long-term effects of landfill leachates and the inadequate justification of waste classification in terms of the corresponding hazardous nature according to the toxicity characteristic leaching procedure have increasingly raised public concerns and even been challenged through legal proceedings (Badruzzaman 2003; Halim et al. 2004; Leupin et al. 2005). In the current work, a method to decontaminate PTE-loaded polymeric-Fe-coated sands and subsequent recovery of chemicals are discussed. The two-step technique consists of chelant-assisted washing remediation of the laboratory-produced PTE-contaminated sand sludge and subsequent selective recovery of the PTEs and chelants from the washing solution using solid-phase extraction (SPE) systems. Furthermore, the comparative efficiency of different chelants was evaluated to find a suitable eco-friendly alternative of the nonbiodegradable chelants for solid-waste management.

2.0 Experimental 2.1 Materials Silica sand samples of various properties, which were marked with distinctive codes (SS5, SS-6, SS-7, and SS-8), were procured from Tokai Recycle Technique Co., Ltd (Gifu, Japan) (Table 1: sand sample characteristics; Fig. 1: comparative particle size distribution).

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Ethylenediaminetetraacetic acid (Kanto Chemical, Tokyo, Japan; EDTA), [S,S]ethylenediaminedisuccinic acid (Chelest, Osaka, Japan; EDDS), DL-2-(2-carboxymethyl) nitrilotriacetic acid (AkzoNobel, Amsterdam, Netherlands; GLDA) and 3-hydroxy-2,2'iminodisuccinic acid (Nippon Shukubai, Tokyo, Japan; HIDS) are the chelants, which were used as extractants (Table 2: data related to the metal-chelant interaction). Sodium chloride, sodium bicarbonate, sodium arsenate dibasic heptahydrate (Wako Pure Chemical, Osaka, Japan), ferric chloride, cadmium diacetate and lead diacetate (Kanto Chemical, Tokyo, Japan) were used to prepare the polymeric Fe-modified sand samples and the source of PTEs in the simulated wastewaters. Acetic acid/sodium acetate (Kanto Chemical, Tokyo, Japan; HOAc/NaOAc), N-2hydroxyethylpiperazine-N´-2-ethanesulfonic acid (Nacalai Tesque, Kyoto, Japan; HEPES) and 3-(cyclohexylamino)-1-propanesulfonic acid (MP Biomedicals, Solon, OH; CAPS) were used as the buffer reagents for pH 3 or 5, 7 and 10, respectively. The pH was adjusted using HCl or NaOH (Kanto Chemical, Tokyo, Japan; 1 mol L–1). The PlasmaCAL multi-element solution with 5% HNO3 (SCP Science, Québec, Canada) and arsenic standard solution (Kanto Chemical, Tokyo, Japan) were used as the standards during the instrumental analysis of the PTE in the solution. The stock concentrates of the standards and solutions were diluted with ultrapure water based on weight to prepare the working standards and solutions. All chemicals or reagents were of analytical grade and used without further purification. AnaLig TE 01 (GL Sciences, Tokyo, Japan; TE-01), Chelex 100 (Bio-Rad Laboratories, Hercules, CA; C-100) and NOBIAS Ion SC 1 (Hitachi High-Technologies, Tokyo, Japan; SC-1) are the column-packed SPE systems that were used for the separation study. The SPE systems were equipped, respectively, with the macrocycle (base support: silica gel, functional group: crown ether), chelating resin (base support: styrene divinylbenzene, functional group: iminodiacetic acid) and ion-exchange resin (base support: hydrophilic methacrylate, functional group: sulfonic acid).

The laboratory wares were: low-density polyethylene (PE) containers (Nalgene Nunc, Rochester, NY), screw-capped PE tubes (AS ONE, Osaka, Japan), polypropylene (PP) Jar 5


(Tomiki Medical Instrument, Kanazawa, Japan), conical PP centrifuge tubes (Biologix Research, Lenexa, KS), and micropipette tips (Nichiryo, Tokyo, Japan). The pre-cleaning procedure involved sequential overnight soaking in the Scat 20X-PF alkaline detergent (Nacalai Tesque, Kyoto, Japan) and HCl (Kanto Chemical, Tokyo, Japan; 4 mol L–1) and rinsing with ultrapure water after each step. 2.2 Instruments The metal concentrations were analyzed using an inductively coupled plasma optical emission spectrometer (Thermo Fisher Scientific, Waltham, MA; Model: iCAP 6300; ICPOES). The chelant concentration was verified using a high-performance liquid chromatography system (Tosoh, Tokyo, Japan; Model: TOSOH 8020; HPLC). The metalcontent in the polymeric Fe-modified sand before and after PTE loading was determined using the microwave-powered digestion assembly (Anton Paar GmbH, Graz, Austria; Model: Multiwave 3000). A digital pH-meter (Horiba Instruments, Kyoto, Japan; Model: Navi F-52) was used to measure the solution pH. The SPE was separated using a combination of a vacuum manifold kit (GL Sciences, Tokyo, Japan; Model: GL-SPE) and an air pump (AS ONE, Osaka, Japan; Model: CAS-1). The homogeneous interaction between the solid and solution phases was ensured using an end-over-end shaker (Iwaki, Tokyo, Japan; Model: SHK-U4). The filtration assembly was equipped with a suction pump (AS ONE, Osaka, Japan; Model: MAS-1) and cellulose membrane filters of 0.45 µm pore size (Advantec, Tokyo, Japan). The ultrapure water of resistivity > 18.2 MΩ·cm–1 was obtained from an automated water purification system (Sartorius Stedim Biotech GmbH, Göttingen, Germany; Model: Arium Pro). 2.3 Methods 2.3.1

Preparation of polymeric Fe-modified sand

The silica sand samples (SS-5, SS-6, SS-7, and SS-8; 50 g) were washed with NaCl solution (1 mol L–1) and subsequently modified with the Fe-coating treatment. The Fecoating solution, which contained Fe-polymeric species, was prepared at a concentration of 40 g L–1 Fe by slowly adding NaHCO3 (0.5 mol L–1) to the FeCl3 solution to obtain a final 6


OH–-to-Fe3+ molar ratio of 0.1, and the mixture was aged at 40 °C for 1.5 h. After the aging period, the NaCl-washed silica sand was added to the Fe-coating solution while maintaining a solid-solution ratio of 1:10. Then, the mixture was shaken in the end-over-end shaker at 150 rpm for 24 h at room temperature (25 ± 1 °C). The supernatant was removed after the designated shaking period using centrifugation and filtration and subsequently discarded. The product was washed with ultrapure water for several times until the chloride content completely diminished. Then, the polymeric Fe-coated sand was dried at 100 °C for 48 h. The two-step method to prepare Fe-coated sand was similar to that of Jiang and Graham (1998) and Cooper et al. (2002). The term “polymeric Fe-modified sand” is used throughout the manuscript according to Cooper et al. (2002) to define the distinctive technique of Fe coating on the solid surface. 2.3.2

Sorption of heavy metals to the polymeric Fe-modified sands

The mixed-metal solution, which contained arsenic, cadmium or lead (50 mg L–1), was prepared by adding the corresponding concentrations of Na2HAsO4·7H2O, Cd(OAc)2 and Pb(OAc)2 in ultrapure water, and the solution pH was adjusted to 6.5. Then, 50 g of the polymeric Fe-coated sand was added to 200 mL of the mixed-metal solution and subjected to overnight shaking at 150 rpm in an end-over-end shaker at room temperature (25 ± 1 °C). The solid fraction was later separated using sequential centrifugation and filtration treatment and subsequently dried for 48 h at 100 °C. 2.3.3

Determination of adsorbed heavy-metal content in the polymeric Fe-modified sands

The metal-loading extent in the polymeric Fe-coated sand sample was determined using microwave-assisted digestion with a mixture of 60% HNO3 (3 mL) and 36% HCl (9 mL) according to the EPA method 3052 (U.S. EPA 1996). Then, the digested sample was filtered and heated on a hot plate at 60 °C to concentrate to a minimum volume. The concentrate was subsequently diluted to 100 mL with ultrapure water and analyzed.

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2.3.4

Washing treatment of the metal-laden polymeric Fe-modified sand

The metal-laden polymeric Fe-modified sand (0.5 g) was added to the chelants (EDTA, EDDS, GLDA or HIDS; 0.01 mol L–1) of different pH values (3, 5, 7 and 10). The solution pH was selected to represent extreme-acidic, moderate-acidic, neutral and basic environments. The subsequent processes were: shaking at 200 rpm (duration: 6 h), incubation (duration: 20 min), separation via centrifugation at 3000 rpm (duration: 15 min) and filtration to separate the supernatant and the solid residue. The supernatant was subjected to the metal analysis using ICP-OES. 2.3.5

SPE-treatment of the washing solution to separate the chelant and metals

The solutions of chelants (EDTA, EDDS, GLDA or HIDS) that were obtained after washing the metal-laden polymeric Fe-modified sands were treated using the SPE systems with various components (e.g., macrocycle, chelating resin, or ion-exchange resin; column volume: 5 mL). The SPE process involved the following steps: conditioning, loading, washing and elution. The method to optimize the performance of each step was described in detail elsewhere (Hasegawa et al. 2011; Rahman et al. 2011a; 2011b). The SPE-system conditioning included sequential rinsing with HNO3 (8 mL; 1 mol L–1), ultrapure water (6 mL) and HEPES buffer solution (~40 mL; 0.1 mol L–1). The feed rate of the washing solution (4 mL; pH 7) to the SPE systems was maintained at 0.2 mL min–1, and the effluent was collected to quantify the retained metal content in the SPE. The SPE systems were washed with ultrapure water (4 mL) to isolate the weakly bound fraction of the metals to the SPE. Then, the regenerative back-washing of the SPE systems with HNO3 (1 and 6 mol L–1) was performed to ensure the elution of the “captured” metal-species. 2.4 Statistical analyses All statistical analyses were performed using SPSS Statistics 17.0 (SPSS, Inc., Chicago, IL). For the data comparison, one-way ANOVA was performed using the General Linear Model, where either the solution pH conditions or the chelants were fixed, and the PTEextraction rate (%) was the dependent variable. The means were compared using Duncan’s

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multiple range test (DMRT) at p = 0.05. Correlation analyses were performed to measure the strength of the relationships among the variables.

3.0 Results and Discussion 3.1 Polymeric Fe coating and metal-sorption characteristics of the sand samples The Fe solution that was prepared for the coating application on the sands was expected to contain 55% Fe as small-sized species and 37% Fe as medium-sized polymers (Jiang and Graham 1996; 1998). The comparative extent of Fe coating on the SS-5, SS-6, SS-7, and SS8 silica sands was checked (Fig. 2a), and the highest Fe-coating amount (mg kg–1) was observed for the sample code SS-8. SS-8 has lower %SiO2 content and higher %Al2O3 content than the other sand types (Table 1). Moreover, the comparison of particle size distribution for different sand-types (Fig. 1) indicate that approximately 73.1% of the particles in SS-8 belong to the lowest size fractions, whereas it is less than 11% in other types. The mineral sorption property of the geological material is generally related to the surface area, and an inverse proportionality between the surface area and particle size was assumed (Horowitz and Elrick 1987; Dubois et al. 2011). Hence, the higher rate of Fe coating to SS-8 can be correlated to its increased net surface area compared with the other sand sample variants. The comparative rate of metal assimilation in the polymeric Fe-coated sands (SS-7 and SS-8) is shown in Fig. 2b, and the data pattern (mean ± SD) indicates the quantitative loading of Pb, whereas the incorporation rate of As or Cd occurs at approximately 50% of the total dosed amount. However, there is no significant difference in the Cd- or Pb-loading rate with the Fe-coating extent, whereas the As-loading rate is significantly higher (p ≤ 0.001) in SS-7 than in SS-8 (Fig. 2b). 3.2 Effect of the solution pH on the washing efficiency of the chelants The solution pH affects the interaction efficiency of the chelants with the metals retained in the solid phases by controlling several factors, such as the sorption or desorption behavior of the metals, solubility ratio of the metal species and chelants in the aqueous medium, etc. (Kim and Ong 1999; Peters 1999; Lim et al. 2004; Polettini et al. 2007; Zou et al. 2009).

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Consequently, a varying pattern of metal mobilization is observed when the solution pH varies (Table 3). The control experiments with ultrapure water confirm a below 1% release of As and Pb at neutral pH. Cd and Pb are released at a significantly higher rate (> 80%) at acidic pH conditions than neutral or basic pH, whereas the As release rate is higher (> 55%) in the basic pH region. There is no significant difference in Cd leaching at pH values 3 and 5. The observed trends for Cd and Pb indicate the leaching possibility of the corresponding PTEs from the metal-laden Fe-coated sand sludge under the effect of acidic aqueous deposition. Overall, the Cd and Pb extraction rates (%) are negatively correlated to the increase in solution pH, and the correlation is stronger for Cd (r = –0.921, p < 0.01) than for Pb (r = – 0.828, p < 0.01). The comparative Fe release from the coated sand surface was less than 1% at pH 7 without chelant in the solution, whereas the chelant-addition enhances it by up to 16%. Furthermore, the overall Fe leaching remains below 30% with or without chelant at pH 3, 5 and 10. The pattern indicates strong attachments of the Fe coating in the sand structures. The Fe leaching amounts at pH 3 and 10 during the EDDS-assisted treatment are not significantly different, and the same result was observed for pH 5 and 7 with HIDS in the solution. The Fe extraction rates were negatively correlated to the pH change with EDTA (r = –0.783, p < 0.01) and GLDA (r = –0.756, p < 0.01) in the solution. The basic pH region (pH 10) with EDTA or EDDS in the solution has the highest arsenic release rates, whereas the solution pH of 3 for GLDA- or HIDS-assisted treatments has the highest arsenic release rates. In addition, the As release with GLDA does not significantly change at pH 5 and 10. There is no significant difference in the Cd release rate with the change in pH (3, 5, 7 or 10) and chelant (EDTA, EDDS, GLDA or HIDS) in the solution. A similar behavior was observed for the EDTA-assisted Pb extraction. The extraction rates of Cd and Pb are approximately 90% in all cases. The Pb extraction significantly decreases (p < 0.05) at pH 10 with EDDS, but the difference is not significant for pH 3, 5 and 7. The difference is also not significant for the Pb extraction rates at pH 7 and 10 with GLDA in the

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solution. The solution pH is negatively correlated to the EDDS (r = –0.780, p < 0.01), GLDA (r = –0.759, p < 0.01) and HIDS (r = –0.900, p < 0.01) -assisted extractions of Pb. The chelant-assisted Cd or Pb extraction rates are not significantly different from that of the controls at pH 5. The same result was observed for Cd at pH 3 regardless of the chelant variants, and the EDDS-induced Pb extractions. However, the As extraction rates significantly increases (p < 0.001) with EDTA, EDDS, GLDA and HIDS in the solution compared with that of the controls. The simultaneous release of the retained PTEs and the H+ exchange from the solid surface functional groups may increase the solubility of the bound PTEs at acidic pH (Vandevivere et al. 2001; Lim et al. 2004). A lower chelant-induced PTE-extraction rate can be assumed in the neutral pH domain compared with the acidic pH domain because of the reduced solubility of oxides and other solid phases when metal hydroxy complexes form in the neutral pH environment (Elliott and Brown 1989; Begum et al. 2012a). The rate of PTE release significantly increases (p < 0.001) with the chelants in the solution in the neutral pH domain compared with the controlled conditions. However, different chelants (EDTA, EDDS, GLDA or HIDS) do not have significantly different effects on the Cd-extraction rates at pH 7. The differences among the Pb extraction rates with EDTA, EDDS and HIDS are not significant, and the GLDA-assisted extraction rates are approximately 15% lower than those with the other chelants. The chelantinduced As-release rates with EDTA, EDDS and GLDA are also not significantly different, whereas the HIDS-assisted leaching rate increases by approximately 7% compared with those with the other chelants. The increased leaching of PTEs in alkaline conditions compared with the neutral pH environment is generally expected because the number of reactive species Ln– in the solution increases (Fischer and Bipp 2002). However, the assumption is somewhat altered in the present study for Pb extraction. In addition, EDDS, GLDA and HIDS do not have significantly different efficiency in extracting As, Cd or Pb in the alkaline pH region. 3.3 Effect of metal-chelant stability constants on the washing with chelants The chelants can form soluble complexes with PTEs to detach the species from their corresponding bound states, and the stability of the metal-chelant (ML) complexes in the 11


solution can be presumed from the stability constant value (logKML) (Martell and Hancock 1996; Nowack 2002). Among the PTEs included in this study, As has no known affinity or possibility of interaction with the chelants (Hasegawa et al. 2011), whereas Cd and Pb form stable ML complexes in the solution. Moreover, the Fe polymeric coating on sand can interact with the used chelants (Begum et al. 2012c; 2012b). The comparative logKML values of the ML complexes (M = Cd2+, Pb2+, Fe3+; L = EDTA, EDDS, GLDA, HIDS) confirms the following stability sequence: logKFeL > logKPbL > logKCdL (Table 2). The formation pattern of ML complexes indicates that Fe should be released at a higher rate than the other PTEs in this study with chelant in the solution, whereas the absorbed arsenic content in the Fe-coated sands should hypothetically remain intact with the introduction of chelants. However, the release patterns of Fe and As with chelant in the solution contradict the assumption, as shown in Table 3. Jessen et al. (2005) estimated that 37-40% of the retained arsenic in the Fe-coated solids was located in the surface structural layer and remained mobile. Therefore, the higher chelant-induced rate of As leaching can be attributed to the desorption of the Fe-bound As fractions (Rahman et al. 2013b). The relative stability of the ML complexes may be varied because of different equilibrium conditions, which are attributed to the H+ ion activity in the solution (Davidge et al. 2001), and was calculated (Table 2). It should be noted that the solution pH-dependent stability of the ML complexes (logK′ML) should be greater than 6 to be considered in practical applications (Orama et al. 2002). Accordingly, the Cd-, Pb-EDDS, -GLDA, and -HIDS complexes are unsuitable in terms of stability in acidic pH domains, except Pb-GLDA at pH 5 and Cd-HIDS at pH 7. Hence, the superior PTE extraction efficiency in the acidic pH domain cannot be associated with the ML complex stability characteristics in the solution (M = Cd2+, Pb2+; L = EDDS, GLDA, HIDS) (Table 3). The other regulating factors are related to the interaction between the chelant solution and the PTE species, which were mentioned in the previous section, and can be considered to explain the PTE extraction behavior at acidic pH. Furthermore, the order of the logK′ML values and the corresponding PTE-extraction patterns indicate a non-complaint correlation between the ML complex stability and the PTEdissolution rate (Tables 2 and 3). The attributable factors can be any or a combination of the 12


following factors, which may take priority over the general dissolution preferences: (a) the lower formation rate of the dominant species of the chelant at specific solution pH (Hong and Pintauro 1996; Vandevivere et al. 2001); (b) the generation of a persistent condition that is more favorable to the PTE solubility over a wide concentration range (Begum et al. 2013); (c) the likely occurrence of kinetic hindrance during the coordination interactions between the metal ions and the multidentate chelants (Nowack 2002). 3.4 Separation of chelant and metals using SPE-systems The chelants and PTE in the solution were separated using TE-01, C-100, and SC-1 SPE systems packed with macrocycle, chelating resin, and ion-exchange resins, respectively, at pH 7 under pre-optimized conditions (Fig. 5). The comparative PTE extraction ability of the SPEs indicates a significant change of the corresponding retention capacity (%) of C-100 and SC-1 in the presence of a chelant in the solution. The SC-1 SPE cannot retain all PTEs (As(V), Cd(II) and Pb(II)), whereas C-100 cannot retain only As(V) regardless of the chelant types. However, the retention rates for PTEs in the TE-01 assembly are quantitative with each chelant. Although the retention rates of Cd are quantitative in C-100 SPE with EDDS, GLDA or HIDS chelants in the solution, the Pb rates are varied possibly because the Pb-L complexes have better thermodynamic stability than Cd-L at pH 7 (calculated as logK′ML, see Table 2). The inability of C-100 to retain Cd or Pb with EDTA in the solution also indicates the limited effectivity of the SPE for logK′ML > 13.1 (logK′Cd-L: 13.1, logK′Pb-L: 14.6; pH 7). There is no known evidence of the interaction between the As species and the chelants. Both C-100 and SC-1 fail to retain As(V) from the chelant-spiked solution. Hence, with a chelant in the solution, the PTE retention mechanism of C-100 or SC-1 is presumably the successive “capture” of the ML complexes or free chelants and free PTE ions (if any). On the contrary, the mechanism of the macrocycle-equipped TE-01 is the host-guest format of selectivity towards the target PTE species based on specific electronic and spatial features of the guest (Izatt et al. 1995; Rahman et al. 2011a; 2011c; 2013a). A schematic illustration of the comparative metal-capture mechanisms of conventional SPEs and macrocycle-equipped SPEs is shown in Fig. 4. 13


4.0 Conclusion The chelant-assisted depollution of PTE-loaded (As, Cd and Pb) polymeric Fe-coated sand and the selective separation of the PTE and the chelants were studied. The restricted consumption of EDTA for the chelant-assisted solid-waste treatment was recommended because of its prolonged environmental persistence and related negative consequences. Therefore, the washing reagents include biodegradable (EDDS, GLDA and HIDS) and nonbiodegradable (EDTA) chelants. The eco-friendly alternatives that were verified in the current work can replace EDTA for the chelant-assisted washing removal of Cd or Pb from polymeric Fe-coated waste solids. The effect of pH is not evident for the Cd extraction regardless of the chelants, and the chelant-assisted Pb-removal was also not significantly different, except the decreased rates of GLDA and EDDS at pH 7 and 10, respectively. However, the chelant-assisted dissolution rate of the PTEs was not consistent with the corresponding stabilities of PTE-chelant complexes in the solution. The As removal rate cannot be correlated with the chelant, but the washing rate improves when there is chelant in the solution. The chelant-rich washing solution was further processed to separate the chelant and the PTEs to provide an option to reuse the washing liquid in the process flow and ensure recovery of the PTEs before the waste sludge disposal. Three different SPE options, which were equipped with macrocycle (TE-01), chelating resin (C-100), and ion-exchange resin (SC-1) were evaluated. TE-01 shows better retaining selectivity and separation ability than C100 and SC-1. Hence, the macrocycle-equipped SPE option is recommended for the design of an eco-friendly and cost-effective scheme to recover chelant and PTEs.

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Acknowledgment The study was partially supported by the Grants-in-Aid for Scientific Research (24310056) from the Japan Society for the Promotion of Science. One of the authors, Ismail M. M. Rahman, acknowledges the financial grant from The Public Foundation of Chubu Science and Technology Center, Japan to support his research at Kanazawa University, Japan. The authors also acknowledge the kind support from Dr. Md. Alamgir (Department of Soil Science, University of Chittagong, Chittagong 4331, Bangladesh) for the statistical analysis of the data.

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Water, Air, & Soil Pollution, 226(3): 37, 2015 The original publication is available at: http://dx.doi.org/10.1007/s11270-015-2312-y Jiang, J.-Q., Cooper, C. & Ouki, S. (2002). Comparison of modified montmorillonite adsorbents: Part I: Preparation, characterization and phenol adsorption. Chemosphere, 47, 711–716. Jiang, J.-Q. & Graham, N. J. D. (1998). Preparation and characterisation of an optimal polyferric sulphate (PFS) as a coagulant for water treatment. Journal of Chemical Technology & Biotechnology, 73, 351–358. Jiang, J. Q. & Graham, N. J. D. (1996). Enhanced coagulation using Al/Fe(III) coagulants: Effect of coagulant chemistry on the removal of colour-causing NOM. Environmental Technology, 17, 937–950. Jing, C., Korfiatis, G. P. & Meng, X. (2003). Immobilization Mechanisms of Arsenate in Iron Hydroxide Sludge Stabilized with Cement. Environmental Science & Technology, 37, 5050– 5056. Kim, C. & Ong, S.-K. (1999). Recycling of lead-contaminated EDTA wastewater. Journal of Hazardous Materials, 69, 273–286. Kuan, W. H., Lo, S. L., Wang, M. K. & Lin, C. F. (1998). Removal of Se(IV) and Se(VI) from water by aluminum-oxide-coated sand. Water Research, 32, 915–923. Kumpiene, J., Lagerkvist, A. & Maurice, C. (2008). Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments – A review. Waste Management, 28, 215–225. Kumpiene, J., Lagerkvist, A. & Maurice, C. (2007). Stabilization of Pb- and Cu-contaminated soil using coal fly ash and peat. Environmental Pollution, 145, 365–373. LaGrega, M. D., Buckingham, P. L. & Evans, J. C. (1994). Hazardous waste management. New York: McGraw-Hill. Leupin, O. X., Hug, S. J. & Badruzzaman, A. B. M. (2005). Arsenic removal from Bangladesh tube well water with filter columns containing zerovalent iron filings and sand. Environmental Science & Technology, 39, 8032–8037. Lim, T. T., Tay, J. H. & Wang, J. Y. (2004). Chelating-agent-enhanced heavy metal extraction from a contaminated acidic soil. Journal of Environmental Engineering-Asce, 130, 59–66. Martell, A. E., Smith, R. M. & Motekaitis, R. J. (2004). NIST Standard Reference Database 46: NIST Critically Selected Stability Constants of Metal Complexes Database (Version 8.0 For Windows). Texas A&M University, College Station, TX. Martell, A. E. & Hancock, R. D. (1996). Metal Complexes in Aqueous Solutions. New York: Plenum Press. Mohammed, A. S., Kapri, A. & Goel, R. (2011). Heavy Metal Pollution: Source, Impact, and Remedies. In M. S. Khan, A. Zaidi, R. Goel & J. Musarrat (eds.), Biomanagement of MetalContaminated Soils. Dordrecht, Netherlands: Springer. Nowack, B. (2002). Environmental chemistry of aminopolycarboxylate chelating agents. Environmental Science & Technology, 36, 4009–4016.

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Water, Air, & Soil Pollution, 226(3): 37, 2015 The original publication is available at: http://dx.doi.org/10.1007/s11270-015-2312-y Orama, M., Hyvonen, H., Saarinen, H. & Aksela, R. (2002). Complexation of [S,S] and mixed stereoisomers of N,N'-ethylenediaminedisuccinic acid (EDDS) with Fe(III), Cu(II), Zn(II) and Mn(II) ions in aqueous solution. Journal of the Chemical Society, Dalton Transactions, 4644– 4648. Peters, R. W. (1999). Chelant extraction of heavy metals from contaminated soils. Journal of Hazardous Materials, 66, 151–210. Polettini, A., Pomi, R. & Rolle, E. (2007). The effect of operating variables on chelant-assisted remediation of contaminated dredged sediment. Chemosphere, 66, 866–877. Rahman, I. M. M., Begum, Z. A. & Hasegawa, H. (2013a). Selective separation of elements from complex solution matrix with molecular recognition plus macrocycles attached to a solid-phase: A review. Microchemical Journal, 110, 485–493. Rahman, I. M. M., Begum, Z. A., Sawai, H., Maki, T. & Hasegawa, H. (2013b). Decontamination of spent iron-oxide coated sand from filters used in arsenic removal. Chemosphere, 92, 196–200. Rahman, I. M. M., Begum, Z. A. & Hasegawa, H. (2011a). Application of Molecular Recognition Technology: For Selective Solid Phase Extraction of Ions. Saarbrücken, Germany: Lambert Academic Publishing. Rahman, I. M. M., Begum, Z. A., Nakano, M., Furusho, Y., Maki, T. & Hasegawa, H. (2011b). Selective separation of arsenic species from aqueous solutions with immobilized macrocyclic material containing solid phase extraction columns. Chemosphere, 82, 549–556. Rahman, I. M. M., Furusho, Y., Begum, Z. A., Izatt, N., Bruening, R., Sabarudin, A. & Hasegawa, H. (2011c). Separation of lead from high matrix electroless nickel plating waste solution using an ion-selective immobilized macrocycle system. Microchemical Journal, 98, 103–108. Scheidegger, A., Borkovec, M. & Sticher, H. (1993). Coating of silica sand with goethite Preparation and analytical identification. Geoderma, 58, 43–65. U.S. EPA (2012). The Clean Water Act (Priority Pollutants: Appendix A to 40 CFR Part 423). Washington, D.C.: Environmental Protection Agency (EPA). U.S. EPA (1996). Test Methods for Evaluating Solid Waste, Physical/Chemical Methods (EPA Method 3052: Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices) (SW-846). Washington, D.C.: Environmental Protection Agency (EPA). van Herwijnen, R., Hutchings, T. R., Al-Tabbaa, A., Moffat, A. J., Johns, M. L. & Ouki, S. K. (2007). Remediation of metal contaminated soil with mineral-amended composts. Environmental Pollution, 150, 347–354. Vandevivere, P., Hammes, F., Verstraete, W., Feijtel, T. & Schowanek, D. (2001). Metal decontamination of soil, sediment, and sewage sludge by means of transition metal chelant [S,S]-EDDS. Journal of Environmental Engineering-Asce, 127, 802–811.

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Water, Air, & Soil Pollution, 226(3): 37, 2015 The original publication is available at: http://dx.doi.org/10.1007/s11270-015-2312-y Table 1: Physical properties and chemical composition of the sand samples

Code No.

SiO2 (%)

Al2O3 (%)

Fe2O3 (%)

CaO (%)

MgO (%)

Undefined (%)

SS-5

95.50

2.24

0.18

0.02

0.08

1.98

SS-6

95.00

2.80

0.19

0.03

0.08

1.90

SS-7

93.30

3.42

0.30

0.04

0.08

2.86

SS-8

87.90

6.23

0.45

0.45

0.12

4.85

21


Table 2: Acid dissociation constants (pKa) of the chelants, the stability constants (logKML) and conditional stability constants (logK´ML) (at different pH) of metal-chelant complexes Chelant

pKa

logKML

EDTAa

pKa1 2.00

pKa2 2.69

pKa3 6.13

pKa4 10.37

Cd 16.5

Pb 18

Fe 25.1

EDDSb

2.95

3.86

6.84

10.01

10.9

12.7

22.0

c

GLDA

2.56

3.49

5.01

9.39

10.31

11.6

15.27

HIDSc

2.14

3.08

4.07

9.61

7.58

10.21

14.96

logK´ML at different pH d Chelant a

EDTA EDDS

b

GLDAc HIDSc a

Cd 3

10

Pb 3

5

7

5

7

6.1

10.0

13.1

15.5

10.0

12.6

–

3.8

7.5

10.2

0.5

3.5

5.8

7.8

10.0

2.5

3.4

5.0

6.9

10

Fe 3

5

7

10

14.6

14.6

13.8

14.7

13.2

9.0

5.6

9.2

9.4

9.1

11.1

10.0

3.4

4.2

7.1

9.1

8.7

5.5

5.1

5.1

3.9

3.4

5.6

7.5

7.9

6.8

5.7

5.3

3.2

At 25 °C (µ = 0.1 M), (Martell et al. 2004). b At 20 °C (µ = 0.1 M), (Martell et al. 2004). c At 25 °C (µ = 0.1 M), (Begum et al. 2012c; 2012b). d The change in conditional stability constants of various metal-chelant complexes in terms of the solution pH is calculated with the aid of the computer program HySS2009 (Alderighi et al. 1999).

22


Table 3: Effect of the solution pH on the chelant-assisted extraction (%) of PTEs from the metal-laden polymeric Fe-modified sands (SS-8). Temperature: 25 ± 1 °C; n = 3. The values in the same column for the data-subsets of each PTE with identical letters are not significantly different at P ≤ 5%. PTEs Fe

As

Cd

Pb

pH

Control

EDTA

EDDS

GLDA

HIDS

Mean

SD

Mean

SD

Mean

SD

Mean

SD

Mean

SD

3

17.80c

1.44

23.90c

1.93

16.40c

1.32

29.10d

2.35

25.20c

2.03

5

9.20b

0.74

19.00b

1.53

12.90b

1.04

17.70c

1.43

13.80a

1.11

7

0.01a

–

13.70a

1.10

9.50a

0.77

11.40a

0.92

15.90a

1.28

10

10.10b

0.81

15.50a

1.25

15.10c

1.22

14.70b

1.19

21.10b

1.70

3

32.80b

2.65

65.60c

3.57

54.40c

2.96

75.20c

4.09

76.70d

4.17

5

31.70b

2.56

58.80b

3.20

47.80b

2.60

59.90b

3.26

55.40b

3.01

7

0.01a

–

39.70a

2.16

35.90a

1.95

39.10a

2.13

46.60a

2.53

10

55.70c

4.49

73.30d

3.98

65.20d

3.54

60.90b

3.31

68.20c

3.71

3

97.90c

3.71

99.00a

3.75

98.10a

3.45

98.90a

3.25

98.70a

4.05

5

99.20c

3.76

99.20a

3.76

99.20a

3.49

99.10a

3.26

99.20a

4.07

7

29.40b

1.11

98.80a

3.74

98.50a

3.47

99.00a

3.26

98.20a

4.02

10

10.80a

0.41

96.80a

3.67

95.80a

3.37

96.90a

3.19

94.80a

3.89

3

83.60c

3.17

90.50a

3.43

85.90b

3.25

90.00b

3.41

92.30c

3.50

5

90.70d

3.44

90.70a

3.44

89.40b

3.39

92.80b

3.52

91.00c

3.45

7

0.70a

0.03

89.90a

3.41

85.60b

3.24

69.40a

2.63

83.90b

3.18

10

7.10b

0.27

88.40a

3.35

70.60a

2.67

73.00a

2.77

76.70a

2.91

23


60

SS-5

SS-7

SS-6

SS-8

Content (%)

50 40 30 20 10 0 53 75 06 .15 12 0.3 .425 0.6 0.85 1.18 0.0 0.0 0.1 0 0.2 0

Particle size (mm)

Figure 1: Distribution of particle sizes in different silica sand samples, which were marked with distinctive codes (SS-5, SS-6, SS-7, and SS-8).

24

Water, Air, & Soil Pollution, 226(3): 37, 2015 The original publication is available at: http://dx.doi.org/10.1007/s11270-015-2312-y (a)

750 600 450 300 150 0

120 Metal-loading rate (%)

-1

Fe-coating extent (mg kg )

900

SS-5

SS-6

SS-7

(b)

SS-8

100 80 60 40 20 0

SS-8

SS-7

As

Cd

Pb

Figure 2: (a) Comparative extent of Fe-coating in different silica sand samples that were marked with distinctive codes (SS-5, SS-6, SS-7, and SS-8); (b) The rate of metal assimilation in the polymeric Fe-modified sands (SS-7 and SS-8). Temperature: 25 ± 1 °C; n = 3.

25

Water, Air, & Soil Pollution, 226(3): 37, 2015 The original publication is available at: http://dx.doi.org/10.1007/s11270-015-2312-y Extraction

SPE-activity (%)

125

(a)

As(V)

Recovery

Cd(II)

Pb(II)

100 75 50 25 0

SPE-activity (%)

125

(b)

100 75 50 25 0

SPE-activity (%)

125

(c)

100 75 50 25 0

SPE-activity (%)

125

(d)

100 75 50 25 0

SPE-activity (%)

125

(e)

100 75 50 25 0 TE-01 C-100

SC-1

TE-01 C-100

SC-1

TE-01 C-100

SC-1

Figure 3: Comparative activity of different SPE systems (TE-01: AnaLig TE 01, C-100: Chelex 100, SC-1: NOBIAS Ion SC 1) for the separation of chelant (a. Control, b. EDTA, c. EDDS, d. GLDA, e. HIDS) and metals from the metal-laden polymeric Fe-modified sands, which were treated with washing solutions. Temperature: 25 ± 1 °C; pH: 7; n = 3. 26


Figure 4: Schematic illustration of the comparative metal and chelant separation mechanism of different SPE systems: (a) macrocycle-equipped SPEs (e.g., AnaLig TE 01); (b) conventional SPEs (Chelex 100 and NOBIAS Ion SC 1).

27