Journal of Environmental Management 137 (2014) 16e22
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Removal of Mn from aqueous solution using fly ash and its hydrothermal synthetic zeolite Claudia Belviso a, *, Francesco Cavalcante a, Spartaco Di Gennaro b, Antonio Lettino a, Achille Palma b, Pietro Ragone a, Saverio Fiore a a b
Institute of Methodologies for Environmental Analysis e National Research Council of Italy (IMAA e CNR), Tito Scalo, Potenza, Italy Metapontum Agrobios, Metaponto, Matera, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 19 November 2013 Received in revised form 27 January 2014 Accepted 31 January 2014 Available online
A number of water purification processes have been developed in recent years based on the utilisation of low-cost materials with high pollutant removal efficiency. Among these materials, fly ash and zeolite synthesised from fly ash are two examples of high-efficiency adsorbents. Column absorption tests were performed in order to compare the manganese sorption behaviour of an Italian coal fly ash and zeolite synthesised from it. Different masses of both materials (10e60 g) were exposed to solutions containing a total metal concentration of 10 mg/L. Batch adsorption studies were also conducted to determine the effect of time on the removal on Mn sequestration. The results indicate that both materials are effective for the removal of Mn from aqueous solution by precipitation due to the high pH of the solid/liquid mixtures. However, the leaching tests reveal that the amount of Mn removed from the fly ash was greater than that leached from the zeolite, thereby indicating that the metal is partially sequestrated by zeolite. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Mn Water Zeolite Fly ash Sorption
1. Introduction A number of water purification processes are based on the utilisation of low-cost materials with high pollutant removal efficiency. Two materials that have seen wide application are fly ash (e.g., Vadapalli et al., 2011; Ozturk and Kavak, 2005; Rios et al., 2008; Itskos et al., 2010; Prasad and Mortimer, 2011; Visa et al., 2012) and natural zeolite (e.g., Kocaoba et al., 2007; Baker et al., 2009; Lee et al., 2010; Wang and Peng, 2010; Can et al., 2010; Karatas, 2012). Fly ash is a waste by-product of thermal power plants that has found use in concrete and cement manufacturing. However, more than half of the fly ash that is produced is disposed of in landfills due to a lack of applications for the material. Coal fly ash is mainly comprised of amorphous aluminosilicate and a small amount of quartz and mullite; hematite, magnetite and carbon can also be observed. Zeolites are microporous crystalline hydrated aluminosilicates characterised by a three-dimensional network of tetrahedral (Si, Al)O4 units that form a system of interconnected pores. The aluminium ion produces a net negative charge, which is balanced by the presence of an extra cation in the framework. One important
* Corresponding author. Tel.: þ39 (0)971427224; fax: þ39 (0)971427222. E-mail address: [email protected] (C. Belviso). http://dx.doi.org/10.1016/j.jenvman.2014.01.040 0301-4797/Ó 2014 Elsevier Ltd. All rights reserved.
property of zeolite is its ability to exchange cations. Due to their similar structure and physicochemical properties, synthetic zeolites have replaced natural zeolites in a variety of applications. Synthetic zeolites can be produced from a number of source materials, and fly ash is one of the most frequently used materials in experiments at low temperature (Belviso et al., 2011, 2012a; 2013). Zeolites synthesised from fly ash have been used for the removal of ammonium from contaminated solutions (e.g., Zhang et al., 2007, 2011), the treatment of acid mine drainage and mine water remediation (Rios et al., 2008; Somerset et al., 2008; Prasad and Mortimer, 2011) and the removal of heavy metals from soil and contaminated aqueous solutions (Moreno et al., 2001; Scott et al., 2001; Alvarez-Ayuso et al., 2003; Lee et al., 2003; Querol et al., 2006; Belviso et al., 2010a; Medina et al., 2010; Koukouzas et al., 2010; Solanki et al., 2010; Visa et al., 2012; Belviso et al., 2012b). An example of an environmental problem related to high environmental metal concentrations can be found in a recent geochemical investigation carried out in the Basilicata region (Italy). We documented a high concentration of Mn in some aquifers in the region in the absence of industrial Mn sources, indicating that the metal was leached from soil and sediment (Fiore, 2010). It is well known that high Mn concentrations in water and food can induce serious health problems in humans and animals (Aschner et al., 2005). The application of fly ash (Sharma et al., 2007; Mohan and Gandhimathi, 2009; Gupta and Bhattacharyya, 2011)
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
or natural zeolite (Taffarel and Rubio, 2009, 2010; Rajica et al., 2009; Shavandi et al., 2012) for the removal of manganese from aqueous solutions has been investigated by a number of researchers, whereas few articles have investigated the action of zeolite synthesised from fly ash (Nascimento et al., 2009). In this study, column and batch experiments were performed to compare the performance of fly ash and zeolite synthesised from fly ash for the removal of Mn from water. In addition, leaching tests were performed to investigate the speciation of Mn following sequestration. 2. Materials and methods The experiments were performed using a sample of coal combustion fly ash obtained from the ENEL thermoelectric power plants of Cerano (Brindisi, Italy) and a sample of zeolite synthesised from the fly ash sample following a previously described method (Belviso et al., 2010b; c). The mineralogical characterisations of fly ash and zeolite were performed by powder X-ray diffraction (XRD; Rigaku RINT-2200) using Cu-Ka radiation and a graphite monochromator. Morphological observations were performed using scanning electron microscopy (SEM, Zeiss Supra 40), and the major chemical constituents of the samples were determined by X-ray fluorescence spectroscopy (XRF; Philips, PW 1480). The cation exchange capacity (CEC) of both the fly ash and synthetic products
17
was determined using the cross-exchange method (Pansini et al., 1996; Cerri et al., 2002) with Naþ as the exchangeable cation. The pH at which the sorbent surface charge is zero (pHPZC) was determined for both fly ash and zeolite using the solid addition method (Mohan and Gandhimathi, 2009; Oladoja and Aliu, 2009). The background electrolyte was 0.1 M KNO3 (Aldrich). The pH of the solutions was adjusted from approximately 2e12 by adding 0.1 N HNO3 or NaOH. The total volume was then adjusted to 50 mL by adding the KNO3 solution. Fly ash and synthetic zeolite (1.0 g) were added (in separate experiments) to each flask, shaken for 24 h at room temperature and then centrifuged at 4500 rpm for 15 min. The difference between the initial pH (pH0) and final pH (pHf) (DpH ¼ pH0 pHf) was plotted against pH0. The point of intersection of the resulting curve for each material with pH0 gave the pHPZC for fly ash and synthetic zeolite. After the characterisation of the source materials, a series of batch adsorption experiments was conducted at room temperature to evaluate the Mn sorption capacity of the fly ash and synthetic zeolite samples. Batch adsorption tests were performed by shaking a series of bottles of fly ash and zeolitic material, in separate experiments. The procedure involved mixing 10 g of each sample with 100 mL of contaminated solution and stirring the mixture for 5, 15, 30, 45, 60, 120, 180 or 240 min. The contaminated solution (10 mg/ L) was prepared by dissolving MnCl2$4H2O (Sigma-Aldrich) in Milli-Q water. The resulting suspension was filtered, stored in a
Fig. 1. XRD pattern and SEM image of [a] fly ash; [b] zeolites synthesized from fly ashX ¼ zeolite X; S ¼ sodalite; A ¼ zeolite A; Mul ¼ mullite; Qtz ¼ quartz.
18
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
Table 1 Chemical composition of surnatant solutions after batch tests. Contact time (m)
Fly ash
Zeolites
Elements concentration (mg/L)
5 15 30 45 60 120 180 240 5 15 30 45 60 120 180 240
Removed Mn (%)
Mn
Ca
K
Mg
Na
0.02 0.01 0.02 0.01 0.01 0.04 0.00 0.01 0.04 0.03 0.02 0.04 0.31 0.02 0.02 0.09
264.8 296.3 308.4 320.8 319.5 331.4 340.3 330.0 3.96 3.91 3.91 5.45 21.94 5.80 6.88 8.53
8.29 14.42 5.76 5.71 5.82 6.51 5.71 5.73 115.2 114.3 116.4 206.6 107.5 110.8 107.4 89.22
0.31 0.17 0.24 0.19 0.14 0.51 0.07 0.15 0.03 0.03 0.04 0.53 2.68 0.08 0.23 0.96
14.42 14.60 14.48 14.62 14.79 15.17 15.02 14.48 5531 5701 5688 8386 5361 5706 5459 4379
99.76 99.87 99.82 99.86 99.89 99.56 99.96 99.90 99.65 99.76 99.84 99.61 97.12 99.84 99.77 99.13
polyethylene bottle and acidified to pH 2e3 with nitric acid prior to chemical analysis. The pH of the suspension was measured after each trial. To complement the batch experiments, column sorption tests were conducted using a glass column (7 cm diameter) to determine the heavy metal sorption ability of the fly ash and zeolite samples under more realistic flow-through conditions. The column used was filled with 10, 20, 30 or 60 g of each sample, and 100, 250, 500 or 1000 mL of Mn-contaminated solution was passed through the column for each trial mass (flow 15 ml/min).
The concentration of Mn in the resulting supernatant solution was determined using inductively coupled plasma mass spectrometry (ICP-MS; Perkin Elmer ELAN 6100). The concentrations of Ca, K, Mg and Na in the supernatant solution were also determined. Mineralogical and morphological analyses of the fly ash and synthetic zeolite samples following both batch and column tests were performed by XRD and SEM to identify the formation of new phases in the samples during sorption. To estimate the mobility of adsorbed Mn, leaching tests were performed on the samples used in the batch and column experiments. An initial extraction was performed using 1 M NH4CH3COOH (ammonium acetate) at pH 7.25. The suspension was shaken for 2 h at room temperature and then centrifuged at 4500 rpm for 30 min to recover the solid residue. The residues were washed with Milli-Q distilled water, dried overnight and leached with an acetic acid solution buffered at pH 2.88. The suspension was shaken for 16 h at room temperature and centrifuged at 4500 rpm for 30 min. The supernatant solutions of each step were analysed for Mn content by ICP-MS. The solid residues were analysed by XRD and SEM to determine the effect of the leaching procedure on the mineral phases.
3. Results and discussion 3.1. Fly ash and zeolites As expected, the fly ash sample was primarily composed of amorphous aluminosilicates, and low levels of mullite and quartz
Table 2 Chemical composition of surnatant solutions after column tests. Amount Elements concentration (mg/L) (g) Mn Ca K Mg Na Fly ash 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 Zeolites 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 n.d. not detected.
0.11 0.00 0.00 0.00 0.12 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.02 0.01 0.00 0.00
431.4 435.6 492.2 784.4 215.5 181.5 355.1 526.2 147.5 200.1 259.4 376.6 80.40 127.5 159.7 257.1
6.73 9.80 12.68 25.88 2.89 4.19 6.56 13.25 1.52 2.24 3.40 6.45 0.82 1.08 1.53 3.09
1.58 18.74 14.12 35.21 0.14 6.74 6.47 8.94 0.11 2.11 2.51 3.43 0.22 1.10 0.95 1.52
0.23 0.03 0.01 0.02 0.39 0.06 n.d n.d 0.40 0.18 0.03 0.20 0.27 0.23 0.19 0.23
n.d 2.88 2.38 4.01 n.d n.d n.d 3.89 2.36 n.d n.d n.d 3.95 n.d 3.07 2.30
132.6 242.8 332.1 476.5 50.27 82.01 142.01 255.2 21.64 41.61 52.13 107.2 5.85 12.42 12.28 15.14
0.21 0.12 0.02 0.05 0.36 n.d 0.03 0.03 0.53 0.04 0.09 0.03 0.97 0.18 0.77 0.55
Removed Mn (%)
21.49 32.48 41.27 94.78 8.25 11.60 18.90 38.42 3.90 6.00 8.91 18.04 2.05 2.56 3.68 8.35 7439.7 13 369 20 217 36 452 2596 4825 7934 14 803 1138 2055 2139 6498 335.7 667.2 562.8 658.7
98.96 99.97 99.98 100.0 98.92 100.0 100.0 100.0 99.90 100.0 100.0 100.0 99.85 99.94 100.0 100.0 97.90 99.60 99.91 99.85 96.36 99.40 100.0 100.0 96.31 98.35 99.69 98.18 97.48 97.82 98.20 97.85
Fig. 2. Effect of: [a] fly ash and [b] zeolite X mass on the removal of Mn using 100 ml (rhombic symbol), 250 ml (square symbol), 500 ml (triangular symbol) and 1000 ml (spherical symbol) of contaminated solution.
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
were also observed. SEM observations revealed that the fly ash sample was primarily composed of cenospheres and plenospheres, with particle sizes ranging from tens of nanometres to approximately 100 mm. These spherical particles featured a coarse surface and were frequently found in clusters (Fig. 1a). A high proportion of the grains exhibited a compact texture, but shards, highly vesiculated glassy fragments, carbon blocks and small spongious grains were also observed. The chemical composition is as follows (mass %): SiO2 ¼ 46.80, TiO2 ¼ 1.49, Al2O3 ¼ 28.21, Fe2O3 ¼ 5.23, MnO ¼ 0.06, MgO ¼ 1.46, CaO ¼ 5.57, K2O ¼ 1.26, Na2O ¼ 0.54, P2O5 ¼ 0.76 and LOI ¼ 8.66. The XRD pattern of the zeolitic material synthesised from fly ash features lines that can be attributed to X-type zeolite, sodalite, Atype zeolite and a geopolymeric phase (Fig. 1b). A small amount of Na carbonate was also observed. The cation exchange capacity (CEC) of the fly ash sample and the zeolitic material were found to be 0.04 meq/g and 1.25 meq/g, respectively. The ability of the fly ash and zeolite samples to reduce the solution Mn concentration was determined by calculating the relative amount of metal removed using the following equation:
%Metal removal ¼ ½ðCi CxÞ=Ci 100 where Ci is the initial metal concentration and Cx is the metal concentration after exposure to the sample material. The values
19
determined from the batch and column experiments are reported in Tables 1 and 2, respectively. 3.2. Batch tests The results of the batch tests are reported in Table 1. The solutions filtered through fly ash exhibited higher Ca and Mg concentrations than those filtered through the synthetic zeolite. Ca was found to be in the range of 264e340 mg/L in the fly ash experiments and 4e22 mg/L in the zeolite experiments. The changes in the K and Na concentrations were also determined for the fly ash and zeolite experiments. The measured K concentration ranged from 4.76e14.42 mg/L in the fly ash experiments and from 89.22e 206.6 mg/L in the zeolite experiments. The measured Na concentration ranged from 14.42e15.17 mg/L in fly ash experiments and from 4379e8386 mg/L in zeolite experiments. The results indicate that passing the solution through fly ash removes almost all of the contaminant (w99%) after only a few minutes (Table 1). The rapid removal of the contaminant from the solution was also observed in the zeolite experiments. After 5 min, the amount of Mn removed was very high, remaining constant through t ¼ 60 min, at which time the capacity of the zeolite to remove Mn decreased. Over longer exposure times, the Mn concentration reached an equilibrium through t ¼ 240 min, when a new species was observed at low concentrations (Table 1). The XRD patterns of the solid residues obtained from the batch tests
Fig. 3. XRD patterns of [a] fly ash and [b] zeolites after column tests (20 ge100 ml) and following leaching tests. The profiles of the starting samples are also shown. The circle indicates a diffraction line of a probably Mn compound not identified. X ¼ zeolite X; S ¼ sodalite; A ¼ zeolite A; Mul ¼ mullite.
20
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
demonstrated the presence of a secondary phase in the fly ash samples. This phase was not detected in the zeolite samples. 3.3. Column tests The solutions obtained from the column tests with fly ash generally exhibited high Ca and Mg concentration ranges 784.4e 80.40 mg/L and 0.11e35.21 mg/L, respectively and low K and Na concentration ranges 0.82e25.88 mg/L and 2.05e94.78 mg/L, respectively (Table 2). However, the observed concentrations of all of the elements decreased after filtering 1000 mL of the solution. Furthermore, the Mn level in the supernatant solutions was found to be very low. Even at the lowest fly ash mass, a drastic reduction of the Mn concentration was obtained (w99%). The trend was also observed in experiments featuring higher masses of the waste material (Fig. 2a) and experiments using the synthetic zeolite instead of fly ash (Fig. 2b). The results revealed that 10 g of the zeolite sample was sufficient to remove w97% of the Mn from solution, and a sample mass of 30 g was required to sequester approximately 100% of the Mn from solution. The opposite behaviour was observed for Ca and Mg concentrations in the experiments using zeolite. In fact, the Ca and Mg concentrations were lower than those observed in the presence of fly ash (from below the limit of detection to 4.01 mg/L and to 0.97 mg/L, respectively). In contrast, the K and Na concentration ranges 5.85e476.5 mg/L and 335.7e36452 mg/L, respectively were higher than those observed after exposure to fly ash (Table 2). These opposing trends reflect the role of Ca and Mg in the crystal structure of zeolite. Na is a primary building block of the synthetic zeolite, and its concentration in the filtered solution was further increased by the fusion of the fly ash with NaOH prior to incubation. As previously observed in the column tests, the XRD pattern of the solid residues obtained after column sorption tests featuring fly ash exhibits a new diffraction line at approximately 3.04 A (Fig. 3a). No other novel peaks were identified, most likely because they were masked by the signals corresponding to other minerals. Although this new mineral phase cannot be unequivocally identified, it is ascribed to a Mn compound. Such a phase was not detected in the residue of the synthetic zeolite column test (Fig. 3b). 3.4. Mn sequestration mechanism
Fig. 4. Point of zero charge (PZC) of: [a] synthetic zeolite, [b] fly ash.
Table 3 Mn concentration (mg/L) in solutions after leaching tests. Fly ash
Precipitation and adsorption mechanisms have been proposed to explain Mn sequestration using fly ash and zeolite because of the high pH of these materials (Lee et al., 2009, 2010; Sharma et al., 2007). pH is very important for cation sorption because it affects the chemical speciation of the metal in solution. It also influences the ionisation of chemically active sites on the sorbent (e.g., Mohan and Gandhimathi, 2009; Fiol and Villaescusa, 2009; Kragovic et al., 2012). In other words, pHpzc gives an indication of the ionisation of functional groups and their potential interaction with metal species in solution. At pHs higher than pHpzc, the sorbent surface is negatively charged and can interact with positive metal species, while at pHs lower than pHpzc, the sorbent surface is positively charged and can interact with negative metal species. Based on this information, the surface of the investigated zeolite is negatively charged near pHs ¼ 12.3, as the pHpzc value is 12 (Fig. 4a), thus inducing electrostatic attraction between the negatively charged zeolite and Mn ions. In fact, at pH > 5.0, Mn is in a cationic form (Mn2þ or MnOHþ) (Lee et al., 2010 and references therein). This phenomenon is responsible for high metal sorption on zeolite and its removal from solution. Distinct mechanisms hold for fly ash. The fly ash pHpzc (12.20) and the average pHs (11.90) (Fig. 4b) indicate that the sorption of Mn on the fly ash surface is
1 step Batch tests 5 Contact time (min) 15 45 60 120 Column tests 10 100 ml solution 20 30 60 10 250 ml solution 20 30 60 10 500 ml solution 20 30 60 10 1000 ml solution 20 30 60
Zeolites 2 step
Sum
1 step
2 step
Sum
1.13 1.13 1.12 1.10 1.10
6.28 6.85 6.33 7.05 6.95
7.41 7.98 7.44 8.15 8.05
0.011 0.005 0.005 0.007 0.006
0.124 0.151 0.099 0.122 0.119
0.135 0.156 0.104 0.128 0.124
0.56 1.01 0.75 0.57 0.78 1.55 1.12 0.92 1.00 1.99 1.65 0.85 1.19 2.74 2.02 1.62
4.15 4.55 4.24 3.28 7.07 5.33 4.90 4.39 17.45 12.90 7.08 4.69 35.10 20.81 8.63 7.76
4.72 5.57 5.00 3.95 7.85 6.88 6.03 5.32 18.46 14.90 8.73 5.55 36.30 23.56 10.66 9.39
0.006 0.004 0.004 0.003 0.007 0.005 0.003 0.003 0.014 0.009 0.003 0.019 0.029 0.011 0.004 0.004
0.161 0.083 0.064 0.055 0.338 0.137 0.092 0.061 0.907 0.164 0.172 0.074 1.550 0.409 0.409 0.171
0.166 0.086 0.068 0.058 0.344 0.142 0.095 0.063 0.921 0.173 0.175 0.093 1.579 0.420 0.413 0.174
1 step: NHy-CH3COOH e 2 step: acetic acid e Amount fly ash and zeolites (g).
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
21
Fig. 5. Mn leachability of residual samples of fly ash and synthetic zeolites following [a] column tests and [b] batch tests. 100 ml (rhombic symbol), 250 ml (square symbol), 500 ml (triangular symbol) and 1000 ml (spherical symbol).
inhibited, as both the solid surface and the adsorbing specie have net positive charges. These charges induce electrostatic repulsion and greatly decrease the metal sorption. 3.5. Leaching tests The described mechanism was confirmed by leaching tests performed on the solid residues of both materials (Table 3). The results suggest that even after the first leaching step, the amount of Mn recovered from the fly ash was higher than that leached from the zeolite. Analogous behaviour was recorded after the second extraction step at a lower pH (z3). These findings are graphically depicted in Fig. 5, which shows the Mn leachability of residual samples after column and batch tests. It is clear that synthetic zeolite is a more suitable material for Mn removal from polluted water than is fly ash. 4. Conclusions Coal fly ash and its hydrothermal synthetic zeolite were investigated for their ability to remove Mn from aqueous solution. The results indicated that both materials were able to remove Mn from aqueous solution. Batch tests revealed that short contact times were sufficient to reduce the amount of Mn in the contaminated solutions whereas column tests indicated that both materials exhibited high removal efficiency for Mn. The data also showed that the precipitation process determined the Mn reduction in polluted solution and that pH differences led to a higher Mn surface adsorption on the zeolite than on the fly ash. Finally, sequential leaching tests determined that Mn leachability is higher in fly ash samples than zeolite samples. This study represents a starting point for developing filtration systems at real scale using zeolite synthesised by a waste material. Acknowledgements The authors wish to express their gratitude to Prof. Maurizio De’ Gennaro and to Prof. Piergiulio Cappelletti (University of Naples, Italy) for suggestions and CEC analyses. This study was financially supported by Basilicata Innovazione (Potenza, Italy).
References Alvarez-Ayuso, E., Garcia-Sanchez, A., Querol, X., 2003. Purification of metal electroplating waste waters using zeolites. Water. Res. 37, 4855e4862. Aschner, M., Erikson, K.M., Dorman, D.C., 2005. Manganese dosimetry: species differences and implications for neurotoxicity. Crit. Rev. Toxicol. 35, 1e32. Baker, H.M., Massadeh, A.M., Younes, H.A., 2009. Natural Jordanian zeolite: removal of heavy metal ions from water samples using column and batch methods. Environ. Monit. Assess. 157, 319e330. Belviso, C., Cavalcante, C., Ragone, P., Fiore, S., 2010a. Immobilization of Ni by synthesising zeolite at low temperatures in a polluted soil. Chemosphere 78, 1172e1176. Belviso, C., Cavalcante, F., Fiore, S., 2010b. Synthesis of zeolite from Italian coal fly ash. Differences in crystallization temperature using seawater instead of distilled water. Waste Manage. 30, 839e847. Belviso, C., Cavalcante, F., Lettino, A., Fiore, S., 2010c. Zeolite synthesised from fused coal fly ash at low temperature using seawater for crystallization. Coal Comb. Gas. Prod. 2, 1e13. Belviso, C., Cavalcante, F., Lettino, A., Fiore, S., 2011. Effects of ultrasonic treatment on zeolite synthesized from coal fly ash. Ultrason. Sonochem. 18, 661e668. Belviso, C., Cavalcante, F., Huertas, F.J., Lettino, A., Ragone, P., Fiore, S., 2012a. The crystallisation of zeolite (X and A-type) from fly ash at 25 C in artificial sea water. Micropor. Mesopor. Mat. 162, 115e121. Belviso, C., Cavalcante, F., Ragone, P., Fiore, S., 2012b. Immobilization of Zn and Pb in polluted soil by in Situ crystallization zeolites from fly ash. Water Air Soil. Pollut. 223, 5357e5364. Belviso, C., Cavalcante, F., Fiore, S., 2013. Ultrasonic waves induce rapid zeolite synthesis in a seawater solution. Ultrason. Sonochem. 20, 32e36. Can, Ö., Balköse, D., Ülkü, S., 2010. Batch and column studies on heavy metal removal using a local zeolitic tuff. Desalination 259, 17e21. Cerri, G., Langella, A., Pansini, M., Cappelletti, P., 2002. Methods of determining cation exchange capacities for clinoptilolite-rich rocks of the Logudoro region in Northern Sardinia, Italy. Clays Clay Min. 50, 127e135. Fiol, N., Villaescusa, I., 2009. Determination of sorbent point zero charge: usefulness in sorption studies. Environ. Chem. Lett. 7, 79e84. Fiore, S., 2010. Valori di fondo di manganese, ferro e solfati nelle acque di falda del sito di interesse nazionale della Val Basento. Istituto di Metodologie per l’Analisi Ambientale, p. 50. Internal Report. Gupta, S.S., Bhattacharyya, K.G., 2011. Kinetics of adsorption of metal ions on inorganic materials: a review. Adv. Colloid. Interfac. 162, 39e58. Itskos, G., Koukouzas, N., Vasilatos, C., Megremi, I., Moutsatsou, A., 2010. Comparative uptakes study of toxic elements from aqueous media by the different particle-size-fractions of fly ash. J. Hazard. Mater. 183, 787e792. Karatas, M., 2012. Removal of Pb(II) from water by natural zeolitic tuff: kinetics and thermodynamics. J. Hazard. Mater. 199e200, 383e389. Kocaoba, S., Orhan, Y., Akyuz, T., 2007. Kinetics and equilibrium studies of heavy metal ions removal by use of natural zeolite. Desalination 214, 1e10. Koukouzas, N., Vasilatos, C., Itskos, G., Mitsis, I., Moutsatsou, A., 2010. Removal of heavy metals from wastewater using CFB-coal fly ash zeolitic materials. J. Hazard. Mater. 173, 581e588. Kragovic, M., Dakovic, A., Sekulic, Z., Trgo, M., Ugrina, M., Peric, J., Gatta, G.D., 2012. Removal of lead from aqueous solutions by using the natural and Fe(III)modified zeolite. Appl. Surf. Sci. 258, 3667e3673.
22
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
Lee, M.G., Cheon, J.K., Kam, S.K., 2003. Heavy metal adsorption characteristics of zeolite synthesized from fly ash. J. Ind. Eng. Chem. 9, 174e180. Lee, S.-M., Tiwari, D., Choi, K.-M., Yang, J.-K., Chang, Y.-Y., Lee, H.-D., 2009. Removal of Mn(II) from aqueous solutions using manganese-coated sand samples. J. Chem. Eng. Data 54, 1823e1828. Lee, S.-M., Kim, W.-G., Yang, J.-K., Tiwari, D., 2010. Sorption behaviour of manganese-coated calcined-starfish and manganese-coated sand for Mn(II). Environ. Technol. 31, 445e453. Lee, S.H., Jo, H.Y., Yun, S.T., Lee, Y.J., 2010. Evaluation of factors affecting performance of a zeolitic rock barrier to remove zinc from water. J. Hazard. Mater. 175, 224e234. Medina, A., Gamero, P., Almanza, J.M., Vargas, A., Montoya, A., Vargas, G., Izquierdo, M., 2010. Fly ash from a Mexican mineral coal. II. Source of W zeolite and its effectiveness in arsenic (V) adsorption. J. Hazard. Mater. 181, 91e104. Mohan, S., Gandhimathi, R., 2009. Removal of heavy metal ions from municipal solid waste leachate using coal fly ash as an adsorbent. J. Hazard. Mater. 169, 351e359. Moreno, N., Querol, X., Ayora, C., Alastuey, A., Fernandez-Pereira, C., JanssenJurkovicova, M., 2001. Potential environmental applications of pure zeolitic material synthesized from fly ash. J. Environ. Eng., 994e1002. Nascimento, M., Moreira, S.P.S., de Souza Vicente, P., 2009. Adsorption of heavy metal cations using coal fly ash modified by hydrothermal method. Fuel 88, 1714e1719. Oladoja, N.A., Aliu, Y.D., 2009. Removal of heavy metal ions from municipal solid waste leachate using coal fly ash as an adsorbent. J. Hazard. Mater. 164, 1496e 1502. Ozturk, N., Kavak, D., 2005. Adsorption of boron from aqueous solutions using fly ash: batch and column studies. J. Hazard. Mater. 12, 81e88. Pansini, M., Colella, C., Caputo, D., de Gennaro, M., Langella, A., 1996. Evaluation of phillipsite as cation exchanger in lead removal from water. Micropor. Mater. 5, 357e364. Prasad, B., Mortimer, R.J.G., 2011. Treatment of acid mine drainage using fly ash zeolite. Water Air Soil. Pollut. 218, 667e679. Querol, X., Alastuey, A., Moreno, N., Alvarez-Ayuo, E., García-Sánchez, A., Cama, J., Ayora, C., Simón, M., 2006. Immobilization of heavy metals in polluted soils by the addition of zeolitic materials synthesized from coal fly ash. Chemosphere 62, 171e180.
Rajica, N., Stojakovica, D., Jevtica, S., Logarb, N.Z., Kovacc, J., Kaucicb, V., 2009. Removal of aqueous manganese using the natural zeolitic tuff from the Vranjska Banja deposit in Serbia. J. Hazard. Mater. 172, 1450e1457. Rios, C.A., Williams, C.D., Roberts, C.L., 2008. Removal of heavy metals from acid mine drainage (AMD) using coal fly ash, natural clinker and synthetic zeolites. J. Hazard. Mater. 156, 23e35. Scott, J., Guang, D., Naeramitmarnsuk, K., Thabuot, M., Amal, R., 2001. Zeolite synthesis from coal fly ash for the removal of lead ions from aqueous solution. J. Chem. Technol. Biotechnol. 77, 63e69. Sharma, Y.C., Uma, Singh, S.N., Paras, Goded, F., 2007. Fly ash for the removal of Mn(II) from aqueous solutions and wastewaters. Chem. Eng. J. 132, 319e323. Shavandi, M.A., Haddadian, Z., Ismail, M.H.S., Abdullah, N., Abidin, Z.Z., 2012. Removal of Fe(II), Mn(II) and Zn(II) from palm oil effluent (POME) by natural zeolite. J. Taiwan Institute Chem. Eng. 43, 750e759. Somerset, V., Petrik, L., Iwuoha, E., 2008. Alkaline hydrothermal conversion of fly ash precipitates into zeolites. 3 the removal of mercury and lead ions from wastewater. J. Environ. Manage. 87, 125e131. Solanki, P., Gupta, V., Kulshrestha, R., 2010. Synthesis of zeolite from fly ash and removal of heavy metal ions from newly synthesized zeolite. J. Chem. 7, 1200e 1205. Taffarel, S.R., Rubio, J., 2009. On the removal of Mn2þ ions by adsorption onto natural and activated Chilean zeolites. Min. Eng. 22, 336e343. Taffarel, S.R., Rubio, J., 2010. Removal of Mn2þ from aqueous solution by manganese oxide coated zeolite. Miner. Eng. 23, 1131e1138. Vadapalli, V.R.K., Gitari, W.M., Ellendt, A., Petrik, L.F., Blfour, G., 2011. Synthesis of zeolite-P from coal fly ash derivative and its utilisation in mine-water remediation. S. Afr. J. Sci. 106, 1e7. Visa, M., Isac, L., Duta, A., 2012. Fly ash adsorbents for multi-cation wastewater treatment. Appl. Surf. Sci. 258, 6345e6352. Wang, S., Peng, Y., 2010. Natural zeolites as effective adsorbents in water and wastewater treatment. Chem. Eng. J. 156, 11e24. Zhang, B., Wu, D., Wang, C., He, S., Zhang, Z., Kong, H., 2007. Simultaneous removal of ammonium and phosphate by zeolite synthesized from coal fly ash as influenced by treatment. J. Environ. Sci. 19, 540e545. Zhang, M., Zhang, H., Xu, D., Han, L., Niu, D., Tian, B., Zhang, J., Zhang, L., Wu, W., 2011. Removal of ammonium from aqueous solutions using zeolite synthesized from fly ash by a fusion method. Desalination 271, 111e121.
Contents lists available at ScienceDirect
Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Removal of Mn from aqueous solution using fly ash and its hydrothermal synthetic zeolite Claudia Belviso a, *, Francesco Cavalcante a, Spartaco Di Gennaro b, Antonio Lettino a, Achille Palma b, Pietro Ragone a, Saverio Fiore a a b
Institute of Methodologies for Environmental Analysis e National Research Council of Italy (IMAA e CNR), Tito Scalo, Potenza, Italy Metapontum Agrobios, Metaponto, Matera, Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 19 November 2013 Received in revised form 27 January 2014 Accepted 31 January 2014 Available online
A number of water purification processes have been developed in recent years based on the utilisation of low-cost materials with high pollutant removal efficiency. Among these materials, fly ash and zeolite synthesised from fly ash are two examples of high-efficiency adsorbents. Column absorption tests were performed in order to compare the manganese sorption behaviour of an Italian coal fly ash and zeolite synthesised from it. Different masses of both materials (10e60 g) were exposed to solutions containing a total metal concentration of 10 mg/L. Batch adsorption studies were also conducted to determine the effect of time on the removal on Mn sequestration. The results indicate that both materials are effective for the removal of Mn from aqueous solution by precipitation due to the high pH of the solid/liquid mixtures. However, the leaching tests reveal that the amount of Mn removed from the fly ash was greater than that leached from the zeolite, thereby indicating that the metal is partially sequestrated by zeolite. Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Mn Water Zeolite Fly ash Sorption
1. Introduction A number of water purification processes are based on the utilisation of low-cost materials with high pollutant removal efficiency. Two materials that have seen wide application are fly ash (e.g., Vadapalli et al., 2011; Ozturk and Kavak, 2005; Rios et al., 2008; Itskos et al., 2010; Prasad and Mortimer, 2011; Visa et al., 2012) and natural zeolite (e.g., Kocaoba et al., 2007; Baker et al., 2009; Lee et al., 2010; Wang and Peng, 2010; Can et al., 2010; Karatas, 2012). Fly ash is a waste by-product of thermal power plants that has found use in concrete and cement manufacturing. However, more than half of the fly ash that is produced is disposed of in landfills due to a lack of applications for the material. Coal fly ash is mainly comprised of amorphous aluminosilicate and a small amount of quartz and mullite; hematite, magnetite and carbon can also be observed. Zeolites are microporous crystalline hydrated aluminosilicates characterised by a three-dimensional network of tetrahedral (Si, Al)O4 units that form a system of interconnected pores. The aluminium ion produces a net negative charge, which is balanced by the presence of an extra cation in the framework. One important
* Corresponding author. Tel.: þ39 (0)971427224; fax: þ39 (0)971427222. E-mail address: [email protected] (C. Belviso). http://dx.doi.org/10.1016/j.jenvman.2014.01.040 0301-4797/Ó 2014 Elsevier Ltd. All rights reserved.
property of zeolite is its ability to exchange cations. Due to their similar structure and physicochemical properties, synthetic zeolites have replaced natural zeolites in a variety of applications. Synthetic zeolites can be produced from a number of source materials, and fly ash is one of the most frequently used materials in experiments at low temperature (Belviso et al., 2011, 2012a; 2013). Zeolites synthesised from fly ash have been used for the removal of ammonium from contaminated solutions (e.g., Zhang et al., 2007, 2011), the treatment of acid mine drainage and mine water remediation (Rios et al., 2008; Somerset et al., 2008; Prasad and Mortimer, 2011) and the removal of heavy metals from soil and contaminated aqueous solutions (Moreno et al., 2001; Scott et al., 2001; Alvarez-Ayuso et al., 2003; Lee et al., 2003; Querol et al., 2006; Belviso et al., 2010a; Medina et al., 2010; Koukouzas et al., 2010; Solanki et al., 2010; Visa et al., 2012; Belviso et al., 2012b). An example of an environmental problem related to high environmental metal concentrations can be found in a recent geochemical investigation carried out in the Basilicata region (Italy). We documented a high concentration of Mn in some aquifers in the region in the absence of industrial Mn sources, indicating that the metal was leached from soil and sediment (Fiore, 2010). It is well known that high Mn concentrations in water and food can induce serious health problems in humans and animals (Aschner et al., 2005). The application of fly ash (Sharma et al., 2007; Mohan and Gandhimathi, 2009; Gupta and Bhattacharyya, 2011)
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
or natural zeolite (Taffarel and Rubio, 2009, 2010; Rajica et al., 2009; Shavandi et al., 2012) for the removal of manganese from aqueous solutions has been investigated by a number of researchers, whereas few articles have investigated the action of zeolite synthesised from fly ash (Nascimento et al., 2009). In this study, column and batch experiments were performed to compare the performance of fly ash and zeolite synthesised from fly ash for the removal of Mn from water. In addition, leaching tests were performed to investigate the speciation of Mn following sequestration. 2. Materials and methods The experiments were performed using a sample of coal combustion fly ash obtained from the ENEL thermoelectric power plants of Cerano (Brindisi, Italy) and a sample of zeolite synthesised from the fly ash sample following a previously described method (Belviso et al., 2010b; c). The mineralogical characterisations of fly ash and zeolite were performed by powder X-ray diffraction (XRD; Rigaku RINT-2200) using Cu-Ka radiation and a graphite monochromator. Morphological observations were performed using scanning electron microscopy (SEM, Zeiss Supra 40), and the major chemical constituents of the samples were determined by X-ray fluorescence spectroscopy (XRF; Philips, PW 1480). The cation exchange capacity (CEC) of both the fly ash and synthetic products
17
was determined using the cross-exchange method (Pansini et al., 1996; Cerri et al., 2002) with Naþ as the exchangeable cation. The pH at which the sorbent surface charge is zero (pHPZC) was determined for both fly ash and zeolite using the solid addition method (Mohan and Gandhimathi, 2009; Oladoja and Aliu, 2009). The background electrolyte was 0.1 M KNO3 (Aldrich). The pH of the solutions was adjusted from approximately 2e12 by adding 0.1 N HNO3 or NaOH. The total volume was then adjusted to 50 mL by adding the KNO3 solution. Fly ash and synthetic zeolite (1.0 g) were added (in separate experiments) to each flask, shaken for 24 h at room temperature and then centrifuged at 4500 rpm for 15 min. The difference between the initial pH (pH0) and final pH (pHf) (DpH ¼ pH0 pHf) was plotted against pH0. The point of intersection of the resulting curve for each material with pH0 gave the pHPZC for fly ash and synthetic zeolite. After the characterisation of the source materials, a series of batch adsorption experiments was conducted at room temperature to evaluate the Mn sorption capacity of the fly ash and synthetic zeolite samples. Batch adsorption tests were performed by shaking a series of bottles of fly ash and zeolitic material, in separate experiments. The procedure involved mixing 10 g of each sample with 100 mL of contaminated solution and stirring the mixture for 5, 15, 30, 45, 60, 120, 180 or 240 min. The contaminated solution (10 mg/ L) was prepared by dissolving MnCl2$4H2O (Sigma-Aldrich) in Milli-Q water. The resulting suspension was filtered, stored in a
Fig. 1. XRD pattern and SEM image of [a] fly ash; [b] zeolites synthesized from fly ashX ¼ zeolite X; S ¼ sodalite; A ¼ zeolite A; Mul ¼ mullite; Qtz ¼ quartz.
18
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
Table 1 Chemical composition of surnatant solutions after batch tests. Contact time (m)
Fly ash
Zeolites
Elements concentration (mg/L)
5 15 30 45 60 120 180 240 5 15 30 45 60 120 180 240
Removed Mn (%)
Mn
Ca
K
Mg
Na
0.02 0.01 0.02 0.01 0.01 0.04 0.00 0.01 0.04 0.03 0.02 0.04 0.31 0.02 0.02 0.09
264.8 296.3 308.4 320.8 319.5 331.4 340.3 330.0 3.96 3.91 3.91 5.45 21.94 5.80 6.88 8.53
8.29 14.42 5.76 5.71 5.82 6.51 5.71 5.73 115.2 114.3 116.4 206.6 107.5 110.8 107.4 89.22
0.31 0.17 0.24 0.19 0.14 0.51 0.07 0.15 0.03 0.03 0.04 0.53 2.68 0.08 0.23 0.96
14.42 14.60 14.48 14.62 14.79 15.17 15.02 14.48 5531 5701 5688 8386 5361 5706 5459 4379
99.76 99.87 99.82 99.86 99.89 99.56 99.96 99.90 99.65 99.76 99.84 99.61 97.12 99.84 99.77 99.13
polyethylene bottle and acidified to pH 2e3 with nitric acid prior to chemical analysis. The pH of the suspension was measured after each trial. To complement the batch experiments, column sorption tests were conducted using a glass column (7 cm diameter) to determine the heavy metal sorption ability of the fly ash and zeolite samples under more realistic flow-through conditions. The column used was filled with 10, 20, 30 or 60 g of each sample, and 100, 250, 500 or 1000 mL of Mn-contaminated solution was passed through the column for each trial mass (flow 15 ml/min).
The concentration of Mn in the resulting supernatant solution was determined using inductively coupled plasma mass spectrometry (ICP-MS; Perkin Elmer ELAN 6100). The concentrations of Ca, K, Mg and Na in the supernatant solution were also determined. Mineralogical and morphological analyses of the fly ash and synthetic zeolite samples following both batch and column tests were performed by XRD and SEM to identify the formation of new phases in the samples during sorption. To estimate the mobility of adsorbed Mn, leaching tests were performed on the samples used in the batch and column experiments. An initial extraction was performed using 1 M NH4CH3COOH (ammonium acetate) at pH 7.25. The suspension was shaken for 2 h at room temperature and then centrifuged at 4500 rpm for 30 min to recover the solid residue. The residues were washed with Milli-Q distilled water, dried overnight and leached with an acetic acid solution buffered at pH 2.88. The suspension was shaken for 16 h at room temperature and centrifuged at 4500 rpm for 30 min. The supernatant solutions of each step were analysed for Mn content by ICP-MS. The solid residues were analysed by XRD and SEM to determine the effect of the leaching procedure on the mineral phases.
3. Results and discussion 3.1. Fly ash and zeolites As expected, the fly ash sample was primarily composed of amorphous aluminosilicates, and low levels of mullite and quartz
Table 2 Chemical composition of surnatant solutions after column tests. Amount Elements concentration (mg/L) (g) Mn Ca K Mg Na Fly ash 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 Zeolites 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 100 ml polluted 10 solution 20 30 60 n.d. not detected.
0.11 0.00 0.00 0.00 0.12 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.02 0.01 0.00 0.00
431.4 435.6 492.2 784.4 215.5 181.5 355.1 526.2 147.5 200.1 259.4 376.6 80.40 127.5 159.7 257.1
6.73 9.80 12.68 25.88 2.89 4.19 6.56 13.25 1.52 2.24 3.40 6.45 0.82 1.08 1.53 3.09
1.58 18.74 14.12 35.21 0.14 6.74 6.47 8.94 0.11 2.11 2.51 3.43 0.22 1.10 0.95 1.52
0.23 0.03 0.01 0.02 0.39 0.06 n.d n.d 0.40 0.18 0.03 0.20 0.27 0.23 0.19 0.23
n.d 2.88 2.38 4.01 n.d n.d n.d 3.89 2.36 n.d n.d n.d 3.95 n.d 3.07 2.30
132.6 242.8 332.1 476.5 50.27 82.01 142.01 255.2 21.64 41.61 52.13 107.2 5.85 12.42 12.28 15.14
0.21 0.12 0.02 0.05 0.36 n.d 0.03 0.03 0.53 0.04 0.09 0.03 0.97 0.18 0.77 0.55
Removed Mn (%)
21.49 32.48 41.27 94.78 8.25 11.60 18.90 38.42 3.90 6.00 8.91 18.04 2.05 2.56 3.68 8.35 7439.7 13 369 20 217 36 452 2596 4825 7934 14 803 1138 2055 2139 6498 335.7 667.2 562.8 658.7
98.96 99.97 99.98 100.0 98.92 100.0 100.0 100.0 99.90 100.0 100.0 100.0 99.85 99.94 100.0 100.0 97.90 99.60 99.91 99.85 96.36 99.40 100.0 100.0 96.31 98.35 99.69 98.18 97.48 97.82 98.20 97.85
Fig. 2. Effect of: [a] fly ash and [b] zeolite X mass on the removal of Mn using 100 ml (rhombic symbol), 250 ml (square symbol), 500 ml (triangular symbol) and 1000 ml (spherical symbol) of contaminated solution.
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
were also observed. SEM observations revealed that the fly ash sample was primarily composed of cenospheres and plenospheres, with particle sizes ranging from tens of nanometres to approximately 100 mm. These spherical particles featured a coarse surface and were frequently found in clusters (Fig. 1a). A high proportion of the grains exhibited a compact texture, but shards, highly vesiculated glassy fragments, carbon blocks and small spongious grains were also observed. The chemical composition is as follows (mass %): SiO2 ¼ 46.80, TiO2 ¼ 1.49, Al2O3 ¼ 28.21, Fe2O3 ¼ 5.23, MnO ¼ 0.06, MgO ¼ 1.46, CaO ¼ 5.57, K2O ¼ 1.26, Na2O ¼ 0.54, P2O5 ¼ 0.76 and LOI ¼ 8.66. The XRD pattern of the zeolitic material synthesised from fly ash features lines that can be attributed to X-type zeolite, sodalite, Atype zeolite and a geopolymeric phase (Fig. 1b). A small amount of Na carbonate was also observed. The cation exchange capacity (CEC) of the fly ash sample and the zeolitic material were found to be 0.04 meq/g and 1.25 meq/g, respectively. The ability of the fly ash and zeolite samples to reduce the solution Mn concentration was determined by calculating the relative amount of metal removed using the following equation:
%Metal removal ¼ ½ðCi CxÞ=Ci 100 where Ci is the initial metal concentration and Cx is the metal concentration after exposure to the sample material. The values
19
determined from the batch and column experiments are reported in Tables 1 and 2, respectively. 3.2. Batch tests The results of the batch tests are reported in Table 1. The solutions filtered through fly ash exhibited higher Ca and Mg concentrations than those filtered through the synthetic zeolite. Ca was found to be in the range of 264e340 mg/L in the fly ash experiments and 4e22 mg/L in the zeolite experiments. The changes in the K and Na concentrations were also determined for the fly ash and zeolite experiments. The measured K concentration ranged from 4.76e14.42 mg/L in the fly ash experiments and from 89.22e 206.6 mg/L in the zeolite experiments. The measured Na concentration ranged from 14.42e15.17 mg/L in fly ash experiments and from 4379e8386 mg/L in zeolite experiments. The results indicate that passing the solution through fly ash removes almost all of the contaminant (w99%) after only a few minutes (Table 1). The rapid removal of the contaminant from the solution was also observed in the zeolite experiments. After 5 min, the amount of Mn removed was very high, remaining constant through t ¼ 60 min, at which time the capacity of the zeolite to remove Mn decreased. Over longer exposure times, the Mn concentration reached an equilibrium through t ¼ 240 min, when a new species was observed at low concentrations (Table 1). The XRD patterns of the solid residues obtained from the batch tests
Fig. 3. XRD patterns of [a] fly ash and [b] zeolites after column tests (20 ge100 ml) and following leaching tests. The profiles of the starting samples are also shown. The circle indicates a diffraction line of a probably Mn compound not identified. X ¼ zeolite X; S ¼ sodalite; A ¼ zeolite A; Mul ¼ mullite.
20
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
demonstrated the presence of a secondary phase in the fly ash samples. This phase was not detected in the zeolite samples. 3.3. Column tests The solutions obtained from the column tests with fly ash generally exhibited high Ca and Mg concentration ranges 784.4e 80.40 mg/L and 0.11e35.21 mg/L, respectively and low K and Na concentration ranges 0.82e25.88 mg/L and 2.05e94.78 mg/L, respectively (Table 2). However, the observed concentrations of all of the elements decreased after filtering 1000 mL of the solution. Furthermore, the Mn level in the supernatant solutions was found to be very low. Even at the lowest fly ash mass, a drastic reduction of the Mn concentration was obtained (w99%). The trend was also observed in experiments featuring higher masses of the waste material (Fig. 2a) and experiments using the synthetic zeolite instead of fly ash (Fig. 2b). The results revealed that 10 g of the zeolite sample was sufficient to remove w97% of the Mn from solution, and a sample mass of 30 g was required to sequester approximately 100% of the Mn from solution. The opposite behaviour was observed for Ca and Mg concentrations in the experiments using zeolite. In fact, the Ca and Mg concentrations were lower than those observed in the presence of fly ash (from below the limit of detection to 4.01 mg/L and to 0.97 mg/L, respectively). In contrast, the K and Na concentration ranges 5.85e476.5 mg/L and 335.7e36452 mg/L, respectively were higher than those observed after exposure to fly ash (Table 2). These opposing trends reflect the role of Ca and Mg in the crystal structure of zeolite. Na is a primary building block of the synthetic zeolite, and its concentration in the filtered solution was further increased by the fusion of the fly ash with NaOH prior to incubation. As previously observed in the column tests, the XRD pattern of the solid residues obtained after column sorption tests featuring fly ash exhibits a new diffraction line at approximately 3.04 A (Fig. 3a). No other novel peaks were identified, most likely because they were masked by the signals corresponding to other minerals. Although this new mineral phase cannot be unequivocally identified, it is ascribed to a Mn compound. Such a phase was not detected in the residue of the synthetic zeolite column test (Fig. 3b). 3.4. Mn sequestration mechanism
Fig. 4. Point of zero charge (PZC) of: [a] synthetic zeolite, [b] fly ash.
Table 3 Mn concentration (mg/L) in solutions after leaching tests. Fly ash
Precipitation and adsorption mechanisms have been proposed to explain Mn sequestration using fly ash and zeolite because of the high pH of these materials (Lee et al., 2009, 2010; Sharma et al., 2007). pH is very important for cation sorption because it affects the chemical speciation of the metal in solution. It also influences the ionisation of chemically active sites on the sorbent (e.g., Mohan and Gandhimathi, 2009; Fiol and Villaescusa, 2009; Kragovic et al., 2012). In other words, pHpzc gives an indication of the ionisation of functional groups and their potential interaction with metal species in solution. At pHs higher than pHpzc, the sorbent surface is negatively charged and can interact with positive metal species, while at pHs lower than pHpzc, the sorbent surface is positively charged and can interact with negative metal species. Based on this information, the surface of the investigated zeolite is negatively charged near pHs ¼ 12.3, as the pHpzc value is 12 (Fig. 4a), thus inducing electrostatic attraction between the negatively charged zeolite and Mn ions. In fact, at pH > 5.0, Mn is in a cationic form (Mn2þ or MnOHþ) (Lee et al., 2010 and references therein). This phenomenon is responsible for high metal sorption on zeolite and its removal from solution. Distinct mechanisms hold for fly ash. The fly ash pHpzc (12.20) and the average pHs (11.90) (Fig. 4b) indicate that the sorption of Mn on the fly ash surface is
1 step Batch tests 5 Contact time (min) 15 45 60 120 Column tests 10 100 ml solution 20 30 60 10 250 ml solution 20 30 60 10 500 ml solution 20 30 60 10 1000 ml solution 20 30 60
Zeolites 2 step
Sum
1 step
2 step
Sum
1.13 1.13 1.12 1.10 1.10
6.28 6.85 6.33 7.05 6.95
7.41 7.98 7.44 8.15 8.05
0.011 0.005 0.005 0.007 0.006
0.124 0.151 0.099 0.122 0.119
0.135 0.156 0.104 0.128 0.124
0.56 1.01 0.75 0.57 0.78 1.55 1.12 0.92 1.00 1.99 1.65 0.85 1.19 2.74 2.02 1.62
4.15 4.55 4.24 3.28 7.07 5.33 4.90 4.39 17.45 12.90 7.08 4.69 35.10 20.81 8.63 7.76
4.72 5.57 5.00 3.95 7.85 6.88 6.03 5.32 18.46 14.90 8.73 5.55 36.30 23.56 10.66 9.39
0.006 0.004 0.004 0.003 0.007 0.005 0.003 0.003 0.014 0.009 0.003 0.019 0.029 0.011 0.004 0.004
0.161 0.083 0.064 0.055 0.338 0.137 0.092 0.061 0.907 0.164 0.172 0.074 1.550 0.409 0.409 0.171
0.166 0.086 0.068 0.058 0.344 0.142 0.095 0.063 0.921 0.173 0.175 0.093 1.579 0.420 0.413 0.174
1 step: NHy-CH3COOH e 2 step: acetic acid e Amount fly ash and zeolites (g).
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
21
Fig. 5. Mn leachability of residual samples of fly ash and synthetic zeolites following [a] column tests and [b] batch tests. 100 ml (rhombic symbol), 250 ml (square symbol), 500 ml (triangular symbol) and 1000 ml (spherical symbol).
inhibited, as both the solid surface and the adsorbing specie have net positive charges. These charges induce electrostatic repulsion and greatly decrease the metal sorption. 3.5. Leaching tests The described mechanism was confirmed by leaching tests performed on the solid residues of both materials (Table 3). The results suggest that even after the first leaching step, the amount of Mn recovered from the fly ash was higher than that leached from the zeolite. Analogous behaviour was recorded after the second extraction step at a lower pH (z3). These findings are graphically depicted in Fig. 5, which shows the Mn leachability of residual samples after column and batch tests. It is clear that synthetic zeolite is a more suitable material for Mn removal from polluted water than is fly ash. 4. Conclusions Coal fly ash and its hydrothermal synthetic zeolite were investigated for their ability to remove Mn from aqueous solution. The results indicated that both materials were able to remove Mn from aqueous solution. Batch tests revealed that short contact times were sufficient to reduce the amount of Mn in the contaminated solutions whereas column tests indicated that both materials exhibited high removal efficiency for Mn. The data also showed that the precipitation process determined the Mn reduction in polluted solution and that pH differences led to a higher Mn surface adsorption on the zeolite than on the fly ash. Finally, sequential leaching tests determined that Mn leachability is higher in fly ash samples than zeolite samples. This study represents a starting point for developing filtration systems at real scale using zeolite synthesised by a waste material. Acknowledgements The authors wish to express their gratitude to Prof. Maurizio De’ Gennaro and to Prof. Piergiulio Cappelletti (University of Naples, Italy) for suggestions and CEC analyses. This study was financially supported by Basilicata Innovazione (Potenza, Italy).
References Alvarez-Ayuso, E., Garcia-Sanchez, A., Querol, X., 2003. Purification of metal electroplating waste waters using zeolites. Water. Res. 37, 4855e4862. Aschner, M., Erikson, K.M., Dorman, D.C., 2005. Manganese dosimetry: species differences and implications for neurotoxicity. Crit. Rev. Toxicol. 35, 1e32. Baker, H.M., Massadeh, A.M., Younes, H.A., 2009. Natural Jordanian zeolite: removal of heavy metal ions from water samples using column and batch methods. Environ. Monit. Assess. 157, 319e330. Belviso, C., Cavalcante, C., Ragone, P., Fiore, S., 2010a. Immobilization of Ni by synthesising zeolite at low temperatures in a polluted soil. Chemosphere 78, 1172e1176. Belviso, C., Cavalcante, F., Fiore, S., 2010b. Synthesis of zeolite from Italian coal fly ash. Differences in crystallization temperature using seawater instead of distilled water. Waste Manage. 30, 839e847. Belviso, C., Cavalcante, F., Lettino, A., Fiore, S., 2010c. Zeolite synthesised from fused coal fly ash at low temperature using seawater for crystallization. Coal Comb. Gas. Prod. 2, 1e13. Belviso, C., Cavalcante, F., Lettino, A., Fiore, S., 2011. Effects of ultrasonic treatment on zeolite synthesized from coal fly ash. Ultrason. Sonochem. 18, 661e668. Belviso, C., Cavalcante, F., Huertas, F.J., Lettino, A., Ragone, P., Fiore, S., 2012a. The crystallisation of zeolite (X and A-type) from fly ash at 25 C in artificial sea water. Micropor. Mesopor. Mat. 162, 115e121. Belviso, C., Cavalcante, F., Ragone, P., Fiore, S., 2012b. Immobilization of Zn and Pb in polluted soil by in Situ crystallization zeolites from fly ash. Water Air Soil. Pollut. 223, 5357e5364. Belviso, C., Cavalcante, F., Fiore, S., 2013. Ultrasonic waves induce rapid zeolite synthesis in a seawater solution. Ultrason. Sonochem. 20, 32e36. Can, Ö., Balköse, D., Ülkü, S., 2010. Batch and column studies on heavy metal removal using a local zeolitic tuff. Desalination 259, 17e21. Cerri, G., Langella, A., Pansini, M., Cappelletti, P., 2002. Methods of determining cation exchange capacities for clinoptilolite-rich rocks of the Logudoro region in Northern Sardinia, Italy. Clays Clay Min. 50, 127e135. Fiol, N., Villaescusa, I., 2009. Determination of sorbent point zero charge: usefulness in sorption studies. Environ. Chem. Lett. 7, 79e84. Fiore, S., 2010. Valori di fondo di manganese, ferro e solfati nelle acque di falda del sito di interesse nazionale della Val Basento. Istituto di Metodologie per l’Analisi Ambientale, p. 50. Internal Report. Gupta, S.S., Bhattacharyya, K.G., 2011. Kinetics of adsorption of metal ions on inorganic materials: a review. Adv. Colloid. Interfac. 162, 39e58. Itskos, G., Koukouzas, N., Vasilatos, C., Megremi, I., Moutsatsou, A., 2010. Comparative uptakes study of toxic elements from aqueous media by the different particle-size-fractions of fly ash. J. Hazard. Mater. 183, 787e792. Karatas, M., 2012. Removal of Pb(II) from water by natural zeolitic tuff: kinetics and thermodynamics. J. Hazard. Mater. 199e200, 383e389. Kocaoba, S., Orhan, Y., Akyuz, T., 2007. Kinetics and equilibrium studies of heavy metal ions removal by use of natural zeolite. Desalination 214, 1e10. Koukouzas, N., Vasilatos, C., Itskos, G., Mitsis, I., Moutsatsou, A., 2010. Removal of heavy metals from wastewater using CFB-coal fly ash zeolitic materials. J. Hazard. Mater. 173, 581e588. Kragovic, M., Dakovic, A., Sekulic, Z., Trgo, M., Ugrina, M., Peric, J., Gatta, G.D., 2012. Removal of lead from aqueous solutions by using the natural and Fe(III)modified zeolite. Appl. Surf. Sci. 258, 3667e3673.
22
C. Belviso et al. / Journal of Environmental Management 137 (2014) 16e22
Lee, M.G., Cheon, J.K., Kam, S.K., 2003. Heavy metal adsorption characteristics of zeolite synthesized from fly ash. J. Ind. Eng. Chem. 9, 174e180. Lee, S.-M., Tiwari, D., Choi, K.-M., Yang, J.-K., Chang, Y.-Y., Lee, H.-D., 2009. Removal of Mn(II) from aqueous solutions using manganese-coated sand samples. J. Chem. Eng. Data 54, 1823e1828. Lee, S.-M., Kim, W.-G., Yang, J.-K., Tiwari, D., 2010. Sorption behaviour of manganese-coated calcined-starfish and manganese-coated sand for Mn(II). Environ. Technol. 31, 445e453. Lee, S.H., Jo, H.Y., Yun, S.T., Lee, Y.J., 2010. Evaluation of factors affecting performance of a zeolitic rock barrier to remove zinc from water. J. Hazard. Mater. 175, 224e234. Medina, A., Gamero, P., Almanza, J.M., Vargas, A., Montoya, A., Vargas, G., Izquierdo, M., 2010. Fly ash from a Mexican mineral coal. II. Source of W zeolite and its effectiveness in arsenic (V) adsorption. J. Hazard. Mater. 181, 91e104. Mohan, S., Gandhimathi, R., 2009. Removal of heavy metal ions from municipal solid waste leachate using coal fly ash as an adsorbent. J. Hazard. Mater. 169, 351e359. Moreno, N., Querol, X., Ayora, C., Alastuey, A., Fernandez-Pereira, C., JanssenJurkovicova, M., 2001. Potential environmental applications of pure zeolitic material synthesized from fly ash. J. Environ. Eng., 994e1002. Nascimento, M., Moreira, S.P.S., de Souza Vicente, P., 2009. Adsorption of heavy metal cations using coal fly ash modified by hydrothermal method. Fuel 88, 1714e1719. Oladoja, N.A., Aliu, Y.D., 2009. Removal of heavy metal ions from municipal solid waste leachate using coal fly ash as an adsorbent. J. Hazard. Mater. 164, 1496e 1502. Ozturk, N., Kavak, D., 2005. Adsorption of boron from aqueous solutions using fly ash: batch and column studies. J. Hazard. Mater. 12, 81e88. Pansini, M., Colella, C., Caputo, D., de Gennaro, M., Langella, A., 1996. Evaluation of phillipsite as cation exchanger in lead removal from water. Micropor. Mater. 5, 357e364. Prasad, B., Mortimer, R.J.G., 2011. Treatment of acid mine drainage using fly ash zeolite. Water Air Soil. Pollut. 218, 667e679. Querol, X., Alastuey, A., Moreno, N., Alvarez-Ayuo, E., García-Sánchez, A., Cama, J., Ayora, C., Simón, M., 2006. Immobilization of heavy metals in polluted soils by the addition of zeolitic materials synthesized from coal fly ash. Chemosphere 62, 171e180.
Rajica, N., Stojakovica, D., Jevtica, S., Logarb, N.Z., Kovacc, J., Kaucicb, V., 2009. Removal of aqueous manganese using the natural zeolitic tuff from the Vranjska Banja deposit in Serbia. J. Hazard. Mater. 172, 1450e1457. Rios, C.A., Williams, C.D., Roberts, C.L., 2008. Removal of heavy metals from acid mine drainage (AMD) using coal fly ash, natural clinker and synthetic zeolites. J. Hazard. Mater. 156, 23e35. Scott, J., Guang, D., Naeramitmarnsuk, K., Thabuot, M., Amal, R., 2001. Zeolite synthesis from coal fly ash for the removal of lead ions from aqueous solution. J. Chem. Technol. Biotechnol. 77, 63e69. Sharma, Y.C., Uma, Singh, S.N., Paras, Goded, F., 2007. Fly ash for the removal of Mn(II) from aqueous solutions and wastewaters. Chem. Eng. J. 132, 319e323. Shavandi, M.A., Haddadian, Z., Ismail, M.H.S., Abdullah, N., Abidin, Z.Z., 2012. Removal of Fe(II), Mn(II) and Zn(II) from palm oil effluent (POME) by natural zeolite. J. Taiwan Institute Chem. Eng. 43, 750e759. Somerset, V., Petrik, L., Iwuoha, E., 2008. Alkaline hydrothermal conversion of fly ash precipitates into zeolites. 3 the removal of mercury and lead ions from wastewater. J. Environ. Manage. 87, 125e131. Solanki, P., Gupta, V., Kulshrestha, R., 2010. Synthesis of zeolite from fly ash and removal of heavy metal ions from newly synthesized zeolite. J. Chem. 7, 1200e 1205. Taffarel, S.R., Rubio, J., 2009. On the removal of Mn2þ ions by adsorption onto natural and activated Chilean zeolites. Min. Eng. 22, 336e343. Taffarel, S.R., Rubio, J., 2010. Removal of Mn2þ from aqueous solution by manganese oxide coated zeolite. Miner. Eng. 23, 1131e1138. Vadapalli, V.R.K., Gitari, W.M., Ellendt, A., Petrik, L.F., Blfour, G., 2011. Synthesis of zeolite-P from coal fly ash derivative and its utilisation in mine-water remediation. S. Afr. J. Sci. 106, 1e7. Visa, M., Isac, L., Duta, A., 2012. Fly ash adsorbents for multi-cation wastewater treatment. Appl. Surf. Sci. 258, 6345e6352. Wang, S., Peng, Y., 2010. Natural zeolites as effective adsorbents in water and wastewater treatment. Chem. Eng. J. 156, 11e24. Zhang, B., Wu, D., Wang, C., He, S., Zhang, Z., Kong, H., 2007. Simultaneous removal of ammonium and phosphate by zeolite synthesized from coal fly ash as influenced by treatment. J. Environ. Sci. 19, 540e545. Zhang, M., Zhang, H., Xu, D., Han, L., Niu, D., Tian, B., Zhang, J., Zhang, L., Wu, W., 2011. Removal of ammonium from aqueous solutions using zeolite synthesized from fly ash by a fusion method. Desalination 271, 111e121.
