Fly ash zeolites for water treatment applications

Accepted Manuscript Title: Fly ash zeolites for water treatment applications Author: Nevin Koshy D.N. Singh PII: DOI: Reference:

S2213-3437(16)30046-X http://dx.doi.org/doi:10.1016/j.jece.2016.02.002 JECE 969

To appear in: Received date: Revised date: Accepted date:

8-11-2015 8-1-2016 1-2-2016

Please cite this article as: Nevin Koshy, D.N.Singh, Fly ash zeolites for water treatment applications, Journal of Environmental Chemical Engineering http://dx.doi.org/10.1016/j.jece.2016.02.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Fly ash zeolites for water treatment applications Nevin Koshya and D. N. Singhb* a Research Scholar, Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India, [email protected] b Professor, Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai-400076, India, [email protected] *Corresponding author. Tel.: +91-22-2576-7340; fax: +91-22-2576-7302

Highlights 1. 2. 3.

Conventional and novel applications of fly ash zeolites for water treatment. Fly ash zeolites have been used for removal of heavy metals and ionic species. Treatment of industrial sludges, acid mine drainage and domestic wastewater.

Abstract In the last few decades, fly ash, a coal combustion residue, has been used as a raw material for synthesis of microporous aluminosiliceous minerals known as zeolites. Due to their excellent ion exchange capacity, high surface area and unique pore characteristics, zeolites have been used for removal of heavy metals (viz., As, Cd, Cr, Cs, Cu, Fe, Hg, Mn, Ni, Pb, Sr, W and Zn) and ionic species (viz., ammonium, chloride, fluoride, nitrate, phosphate and sulphate) from industrial sludges, acid mine drainage and wastewater from domestic and industrial sources. In addition, fly ash zeolites find their application as sorbent medium in permeable reactive barriers and contaminant barrier liners for immobilizing the contaminant 1

plume in soil. This paper reviews the applications of fly ash zeolites in various water treatment studies and other related environmental cleanup projects, viz., depuration of wastewater containing industrial dyes and hazardous ions and leachate treatment. Furthermore, novel applications in the use of fly ash zeolites as permeable reactive barriers and contaminant barrier liners as well as the future scope of research for environmental cleanup are also discussed. Keywords: Fly ash zeolite, applications, water treatment; heavy metal removal, effluent treatment, permeable reactive barrier. Notation The following symbols are used in this paper: AMD

acid mine drainage

BOD

biological oxygen demand

CEC

cation exchange capacity (in meq/100g)

ce

equilibrium concentration (in mg/l)

ci

initial ion concentration (in mg/l)

COD

chemical oxygen demand

HTAB

hexadecyltrimethylammonium bromide

pHe

pH after interaction

PRB

permeable reactive barrier

PZC

point of zero charge

q

contaminant uptake (in mg/g)

SSA

specific surface area (in m2/g)

t

interaction time

T

temperature (in º C)

VOC

volatile organic compounds

η

contaminant removal efficiency (in %)

2

1. Introduction Fly ash is a coal combustion by-product generated in large quantities from coal thermal power plants around the globe (Blissett and Rowson 2012). Hence, its utilization has gained momentum in the past few decades and has been used as cement additive (due to its pozzolanic property), in brick manufacturing (Koukouzas et al. 2011b), as backfill material (Nhan et al. 1996; Shih and Chang 1996), for reinforcing filler in polymers (Kruger 1997; Garde et al. 1999) and as a soil ameliorant (Jala and Goyal 2006). Furthermore, due to its high silica and alumina content, fly ash has been perceived as an ideal precursor for synthesis of zeolites (Holler and Wirsching 1985) and geopolymers (Silverstrim et al. 1988; Davidovits 1991). Zeolites are three-dimensional tetrahedral aluminosilicate minerals, having their negative charge (generated by isomorphous substitution of Si4+ by Al3+) counterbalanced by native cations (Na+, K+, Ca2+ and Mg2+) and water molecules in their pores and channels. The general formula for a zeolite is M2/nO.Al2O3.xSiO2.yH2O where M is any alkali or alkaline earth element, n is the valence charge on that element, x varies from 2 to 10 and y varies from 2 to 7. The Al2O3 and SiO2 are the structural cations because they form the tetrahedral framework with oxygen (Mumpton, 1985). Some common zeolites synthesized from fly ash are presented in Table 1. Naturally occurring zeolites (natural zeolites) have restricted pore sizes and channels, whereas fly ash-based synthetic zeolites possess a variety of pore structures and are potential and probably economically viable sorbent minerals for trapping various contaminants from air and water (Hollman et al. 1999, Franus et al. 2014). Though raw fly ash has the potential for the removal of heavy metals, dyes and anions (Mohan et al. 2002; Weng and Huang 2004; Cho et al. 2005; Gitari et al. 2006; Alinnor 2007; Lu et al. 3

2009; Balsamo et al. 2011; Al-Khaldi et al. 2013), zeolites synthesized from it, augment its immobilization characteristics to several folds (Lin et al. 1998; Woolard et al. 2002; Li et al. 2006;). Incidentally, zeolitized fly ash has been reported to have higher lead sorption capacity than raw fly ash (6-7 times) and natural zeolites (3-5 times) (Lee et al. 2000; Itskos et al. 2010a). Utilization of fly ash for synthesizing zeolites and determination of their heavy metal uptake potential is important in consumption of ash currently dumped at disposal sites and also for creating water treatment solutions for regions/countries facing limited water resources. Based on the available literature, the locations of fly ashes, which have been zeolitized for applications in depuration of contaminated water and wastewater, have been illustrated in Fig. 1. In spite of India producing over 130 million tons/year and Russia having 1.5 billion tons of ash-slag waste stored in ash-disposal sites, very few studies have been conducted in these countries with regard to environmental cleanup using fly ash zeolites that would subsequently help in the bulk utilization of fly ash (Haque 2013; Kakaras et al. 2004; Mir and Sridharan 2013; http://ksfenix.org/en; Putilov and Putilova 2010).

1.1. Synthesis and pretreatment of zeolites before their applications Fly ash due to its activation using alkalis, such as NaOH, KOH, Ca(OH)2 and LiOH, undergoes dissolution and subsequently crystallizes into zeolitic minerals (Steenbruggen and Hollman 1998; Kolay et al. 2001; Moreno et al. 2001; Chen et al. 2006; Medina et al. 2010; Jha and Singh 2014; Koshy et al., 2015a; Koshy et al., 2015b). The synthesis methods include: (i) conventional hydrothermal treatment (Holler and Wirsching 1985; Murayama et al. 2002; Adamczyk and Bialecka, 2005; Cundy and Cox, 2005; Moriyama et al. 2005; 4

Derkowski et al., 2006; Fansuri et al., 2008; Wdowin et al. 2014), (ii) alkali fusion-assisted hydrothermal treatment (Shigemoto et al. 1993; Ojha et al., 2004; Terzano et al., 2005; Mishra and Tiwari 2006; Wu et al., 2008; Kazemian et al. 2010; Jha and Singh, 2013), (iii) microwave-assisted hydrothermal treatment (Inada et al. 2005; Querol et al. 1997; Tanaka et al., 2008), (iv) ultrasonication-assisted hydrothermal (Feng et al., 2004; Andaç et al., 2005; Kim et al., 2010; Belviso et al. 2011; 2013) and (v) molten salt method (Park et al., 2000; Choi et al., 2001). In addition, pure zeolites can be synthesized from silica and alumina extracts obtained by alkali leaching of fly ash (El-Naggar et al. 2008). Upon activation, the particle size range of the original fly ash (generally, 0.5 µm to 400 µm) decreases, due to the alkali etching on the surface of the fly ash particles and subsequent nucleation and crystallization of small zeolitic minerals (Fig. 2), finally resulting in an increase in specific surface area (Apiratikul and Pavasant 2008; Visa et al. 2012; Itskos et al. 2015). Consequently, this augmentation in surface area facilitates better sorption characteristics in the end product (read zeolites). The presence of significant amount of fly ash residues after synthesis of zeolites limits its contaminant sorption capacity (Zhang et al., 2011a). Hence, pretreatment of raw fly ash can be employed to obtain purer zeolites as well as for synthesizing application-specific end products. In larger particle size fractions of fly ash, i.e., >250 µm, unburnt carbon is also present (generally, less than 20% depending on type of coal and coal-firing system), which can be removed using sieves in order to increase its zeolitization potential, resulting in a larger surface area (Jha et al. 2009; Itskos et al. 2010b; Visa and Chelaru 2014; Cardoso et al., 2015a). Alternatively, calcination at elevated temperature (800 ºC) can remove unburned carbon and other volatile compounds (Prasad et al. 2011). Furthermore, the removal of Fe2O3 5

and TiO2 using magnetic separation also enhances the zeolitic end products in terms of its purity and structure (Lee et al. 2000; Cardoso et al., 2015a). A 6000 Gauss permanent magnet coated with a low-porosity paper can be used to manually separate the magnetic and nonmagnetic fractions (Cardoso et al., 2015a). Interestingly, surface loading on zeolites with species such as iron and titanium, has been reported to boost their cation exchange capacity (Doula and Dimirkou 2008; Doula 2009; Visa et al. 2015). Washing of fly ash with water reduces the concentration of soluble compounds such as Na2O, MgO, CaO and K2O (Wang et al., 2009a; Visa and Chelaru 2014) and lowers the pH (which is initially >10) (Murayama et al. 2003). In addition, acid treatment removes impurities, such as iron oxide, from raw fly ash, yielding a higher concentration of aluminosilicates (Wang et al., 2009a; 2009b; Zhou et al. 2014). Furthermore, the synthesized zeolites can be washed with NaCl solution to obtain mono-cation saturated zeolite (i.e., sodium zeolite), which offers better ion exchange capacity (Wei et al. 2013; Zhang et al., 2011b). In this context, although washing using distilled/deionized water lowers the pH, the pH of synthesized zeolite is generally not lowered below neutral (Jha et al. 2008). This is because drastic lowering of pH can cause collapse of the zeolitic crystals, which is initially indicated by exfoliation of top layers of crystals (at pH=4.2 for zeolite P), followed by entire breakdown of crystallinity (at pH=3.8 for zeolite P) and subsequent exposure of the underlying fly ash spherules (Murayama et al. 2003; Qiu and Zheng 2007). In addition, mild acid washing of the synthesized zeolite converts calcite present in the sorbent into soluble gypsum and anhydrite, which aid precipitation of calcium phosphate when utilized for phosphate removal (Zhang et al. 2007). In this context, to ascertain their sustainability in acidic environment, acid resistance of the zeolites is determined by mineralogical analysis of the acid-treated end product (Murayama et 6

al. 2003). Loading of alumina on zeolites through wet impregnation method using aluminium chloride hexahydrate improves the adsorption characteristics (Qiu and Zheng 2007).

2. Conventional applications of fly ash zeolites In order to reduce contaminant concentration in water to permissible limits, as demanded by environmental regulations, several methods have been used viz., adsorption, precipitation, coagulation, flocculation, ion exchange, reverse osmosis, biosorption and photocatalysis (Ali and Gupta 2006; Blais et al. 2008; Ali 2010; Ali 2012; Ali et al. 2012; Ali 2014; Visa and Chelaru 2014). Out of these, ion exchange is a popular technique, using sorbents such as activated carbon, polymeric resins and zeolites (Ali and El‐Bishtawi 1997). In this context, zeolites synthesized from fly ash appear to an economically viable and efficient choice as a potential ion-exchanger. Due to the presence of innocuous exchangeable ions, zeolites have been proven to be ideal for ion-exchange applications, such as removal of hazardous heavy metals and radioactive ions (Hafez et al. 1978; Dyer and Keir 1984; Mimura et al. 2001; Bosso and Enzweiler 2002; Borhade et al. 2012; Ogata et al. 2015). Furthermore, they are excellent sorbents, owing to their highly porous microstructure containing a large number of rigid cages and channels (Álvarez-Ayuso et al. 2003). Generally, zeolites can be applied in various forms, viz., powder (Moreno et al. 2001), slurry (García-Sánchez et al. 1999) and pellets (Ostroski et al. 2009) depending on the requirement and situation. For large flowing water bodies, zeolite powder is feasible while zeolite slurry is ideal for closed wastewater treatment system and for injection grouting for the soil remediation. Pelletized zeolite has been applied in soil remediation and is suitable for water treatment through a filter column and offers appropriate hydraulic conductivity along 7

with easy handling and replenishment in the reactor bed system (Gworek 1992).

2.1. Application for heavy metal removal Heavy metals pose environmental concern due to their non-biodegradability and bioaccumulation in humans, animals and plants, resulting in diseases and disorders (Shih and Chang 1996; Al-Anber and Al-Anber 2008; Visa et al. 2012). Furthermore, they can kill the bacteria responsible for decomposition of active sludge from secondary sewage treatment plants (Visa et al. 2012). If not treated properly before discharge, effluents containing ammonia and phosphorus can result in eutrophication of water bodies (Ji et al. 2015). Their main sources include industries manufacturing paints, pigments, petrochemicals and battery and effluents from metal extraction, fabrication and finishing (Ali and El‐Bishtawi 1997). Furthermore, water from acid mine drainage contains high concentration of heavy metals such as arsenic, chromium, copper, iron, lead, manganese, nickel and zinc in addition to sulphate, ammonium and high total hardness and total dissolved solids with pH as low as 2 (Moreno et al. 2001; Ríos et al. 2008; Prasad and Mortimer 2011; Prasad et al. 2011). These heavy metals reach water bodies through highway runoff (Laxen and Harrison 1977), industrial effluents, contaminant spills (Liu et al. 2005) and water percolation through contaminated soils (Mulligan et al. 2001) and consequently, they enter the food chain (Arora et al. 2008). Amongst the different sorbents, zeolites (fly ash-based zeolites, in particular) are gaining popularity amidst researchers for heavy metal removal due to the low-cost and bulk availability of raw material (i.e., fly ash) and also due to the presence of well-defined molecular and porous structure, high thermal stability, ion selectivity, ion exchange capacity 8

and surface area (Petrus and Warchoł 2005; Nascimento et al. 2009). The heavy metal removal efficiency of fly ash zeolites is much higher as compared to raw fly ash, which can mainly be attributed to their mineralogical alteration (Kolay and Singh 2000; Kolay et al. 2001). For example, while, raw fly ash removes <8% Pb2+, its zeolitized counterpart shows up to 98% removal (Lee et al. 2000). From Table 2, it can be inferred that the metal uptake depends on several parameters such as type and initial concentration of heavy metal, type of zeolite, dosage (liquid-to-solid ratio), interaction time, temperature and pH of the system (Wang et al. 2006; Wu et al. 2008). Different zeolites can selectively uptake heavy metals depending on their pore structures. For example, the smaller pore size of hydroxysodalite aids Cr3+ sorption better than NaP1 due to lack of competition from larger-sized innocuous cations such as Na+ and Ca2+ (Wu et al. 2008). Zeolites A and X, having high CEC and bigger pores (0.42 nm for A and 0.74 nm for X), can allow heavy metals with hydrated radii less than their effective pore sizes to pass through and can remove Cd2+, Co2+ and Zn2+ present in multi-contaminant systems (Chang and Shih 2000; Wang et al., 2009a; Izidoro et al. 2013). Incidentally, the removal efficiency is higher for ions with smaller hydrated radii (Visa et al., 2012). Zeolite W removes 99% of As5+ in 5 min from a 740 ppb contaminated solution at pH=7 (Medina et al. 2010). As observed from Table 2, the removal efficiency increases with increase in contact time due to greater interaction between contaminant and sorbent (Wang et al. 2006). It has been reported by few researchers that Pb2+ reached equilibrium in 25 min whereas Cr3+ required 4 h (Wu et al. 2008; Visa et al. 2012). Increase in the initial concentration of the contaminant has been observed to shift the equilibrium towards the higher sorption capacity region (Apiratikul and Pavasant 2008). However, the systems with lower concentrations reached equilibrium faster 9

(i.e., equilibrium time gets reduced) and showed higher metal uptake (Wang et al. 2006; Apiratikul and Pavasant 2008). This occurs due to the availability of more active exchange sites on the surface for ion exchange with less number of adsorbate ions (Wang et al. 2006). The increase in sorbent dosage decreases the equilibrium sorption capacities due to the availability of more substrate for the sorbate (contaminant) to adhere on, thereby, decreasing the sorbate population on it (Apiratikul and Pavasant 2008). Incidentally, the sorbent characteristics and the sorption mechanism can be understood using the kinetic models developed, which include pseudo-first order rate equation (Lagergren 1898) and pseudo-second order rate equation (Blanchard et al. 1984; Ho and McKay 1999; Rudzinski and Plazinski 2006). Generally, pseudo-second order kinetics is followed in the case of sorption of most heavy metals and dye-heavy metal mixed pollutants (Hui et al. 2005; Wang et al. 2006; El-Naggar et al. 2008; Fungaro et al. 2009; Visa and Chelaru 2014). The rate-controlling mechanisms, which are essential for the design and operation of full-scale batch processing plants, can be understood by analyzing the experimental sorption data using Lagergren (Lagergren 1898), Ho and Mckay (Ho and McKay 1999) and Morris-Weber (Weber and Morris 1962) models. For example, the rate limiting steps for Cd2+ and Pb2+ are external mass transfer and intraparticle diffusion while that of Cu2+ is governed by intraparticle diffusion (Apiratikul and Pavasant 2008). Furthermore, determination of the sorption capacity of a sorbent per unit time is useful for designing equipment and estimating the operating costs of effluent treatment facilities. In this context, column study throws light on the transport phenomena, which takes place under saturated conditions and is useful for determining optimum sorbent quantity and density of packing (Hong et al. 2009; Rahman et al. 2009). Furthermore, it shows a breakthrough (i.e., 10

excessive contaminant concentration beyond permissible limit after treatment through the column bed) of heavy metals in the reverse order of the selectivity series (Table 3) (Steenbruggen and Hollman 1998). However, when leachate containing suspended impurities is passed through columns, clogging of pores can occur, resulting in large head losses (Otal et al. 2005). Along with the other parameters, the pH of the system also affects the performance of contaminant-zeolite interaction and can be studied by considering a range of pH in the sorption experiments which is generally adjusted by addition of appropriate concentration and volume of acids (viz., HCl or HNO3) or alkalis (NaOH or Na-acetate) (Qiu and Zheng 2007; Apiratikul and Pavasant 2008). Some zeolites have negative surface charge at pH>3 (i.e., the point of zero charge (PZC) is less than 3), indicating its application as a potential sorbent of cations (like heavy metals) for pH>3 (Apiratikul and Pavasant 2008). At higher pH, lesser number of H+ ions competes for cation exchange sites thereby allowing cation exchange of other ions, viz., heavy metals and ammonium (Juan et al. 2009). Generally, at high pH (i.e., ~10), the uptake (immobilization) of heavy metals by zeolites is reported to be higher than its CEC (Steenbruggen and Hollman 1998). This is due to the precipitation of hydroxides from the solution in addition to the cation exchange taking place in zeolitic matrix (Steenbruggen and Hollman 1998; Ríos et al. 2008; Sui et al. 2008; Deng and Ge 2015). The preferential uptake (i.e., ion selectivity) of certain heavy metals, such as copper and iron, is due to their lower precipitation pH (Dean et al. 1972, Jha et al. 2008). At pH>7, zinc precipitates while it gets adsorbed on the zeolite at lower pH (Hong et al. 2009). Nevertheless, precipitation reaction is not preferred at times, due to sludge generation (i.e., the

undesirable

precipitate

formation),

which 11

further

demands

supplementary

treatment/removal (Visa et al. 2012). Generation of sludge with low settling and dewatering characteristics will hinder large-scale treatment process (Zhang et al., 2011c). In order to prevent precipitation, the pH of the solution can be lowered through acidification (Qiu and Zheng 2009). However, for large scale treatment of effluents, addition of acid is dangerous, difficult and costly and may even destroy the zeolite structure. 2.2. Application for textile effluent treatment (dye removal) The effluents discharged from textile industries include dyes, hazardous and toxic metals, suspended solids, pathogenic microorganisms and biodegradable organic compounds, which are capable of harmfully affecting the ecosystem of water bodies (Wang et al., 2009b). These colored textile effluents having varying pH, high chemical oxygen demand, temperature and suspended oils, reduce light permeability, thereby, affecting photosynthesis (Visa and Chelaru 2014). Table 4 shows the utilization of fly ash zeolites for dye removal. Fly ash treated with NaOH and the surfactant hexadecyltrimethylammonium bromide (HTAB), when interacted with bi-pollutant solutions having methylene blue along with either Cd2+ or Cu2+, exhibited dye removal capacity of 1.6 mg/g and 1.7 mg/g, respectively (Visa and Chelaru 2014). Incidentally, pseudo second-order kinetics best fits the experimental data in simultaneous sorption of dyes and heavy metals on surfactant modified zeolites (Wang et al., 2009b; Visa et al. 2015). Both Langmuir and Freundlich isotherms have been opined to describe methylene blue and on fly ash and its derived zeolites (Fungaro et al. 2009; Wang et al., 2009b; Sun et al. 2010; Atun et al. 2011) while Langmuir best described indigo carmine adsorption on hydroxysodalite (de Carvalho et al. 2011). The adsorption of methylene blue on fly ash based NaP1 zeolite is an exothermic reaction and spontaneous in nature. It attains a constant value for pH ranging from 5 to 10 due to ion exchange on pH independent sites and 12

reaches equilibrium in 10 min (Fungaro et al. 2009). The maximum adsorption of acid fuchsin dye, on fly ash based zeolite LTA-Z has been reported at pH=5 and is endothermic in nature (Xu et al. 2014). Interestingly, in dye sorption, there could be an initial competition in adsorption between water and dye molecules, resulting in a two-step isotherm showing two plateaus (Atun et al. 2011). In hydroxysodalite, methylene blue sorption takes place only on the surface since these large dye molecules are unable to enter the small channels, thus underutilizing the cation exchange capacity of the zeolite (Woolard et al. 2002). Similarly, safranine, possessing larger size as compared to thionine molecule, shows lower adsorption on the zeolitic porous surfaces (Atun et al. 2011). While it is evident that the metal uptake is relatively high for fly ash zeolites with higher surface area, large-sized dye molecules cannot enter the smaller pores of the zeolites, thus leaving the ion exchange sites underutilized.

2.3. Application for leachate and sewage effluent treatment Municipal solid waste (MSW) landfill leachate, domestic wastewater, swinewater, dairy soiled water and dairy cattle slurry have high biological and chemical oxygen demand (BOD and COD) along with a large amount of ammonium and suspended solids (Chen et al. 2012; Murnane et al. 2015). Ammonia remains as a long-term pollutant in the methanogenic phase of decomposition and hence, its concentration has to be lowered (Otal et al. 2005). Furthermore, due to unregulated disposal of hazardous and toxic waste, presence of heavy metals has also been reported (Mohan and Gandhimathi 2009). Zeolites NaP1, analcime and chabazite, synthesized from Spanish fly ash (60% zeolitic content, CEC=270 meq/100g), have been employed as a decantation-assisting reagent in landfill leachate treatment. When these are used along with a coagulant and a flocculant, reduction of 53% ammonium, 82% 13

suspended solids and 43% COD have been reported (Luna et al. 2007). Interestingly, when MSW leachate was water-diluted to 10% and filtered, a decline has been observed in BOD, COD and total kjeldahl nitrogen (TKN) by 18%, 12% and 38%, respectively. In some cases, compared to synthetic zeolites, zeolitized fly ash exhibit better treatment efficiencies for wastewater although insignificant reduction in COD has also been reported (Otal et al. 2005). Fly ash zeolites have also been used for removal of ionic species such as ammonium, phosphate and sulphates (Tables 5 and 6). In this context, in order to facilitate the removal of negatively charged species, the polarity of zeolites can be modified using surfactant compounds such as HTAB (Doula and Dimirkou 2008; Doula 2009; Visa et al. 2015; Visa and Chelaru 2014). Different anionic species are present in water depending on its source, i.e., acid mine drainage contains sulphate (Somerset et al. 2005) while sewage wastewater has high concentrations of ammonium and phosphate (Chen et al. 2006; Zhang et al. 2007; Cardoso et al., 2015b). Domestic wastewater contains almost several folds more ammonium content as compared to phosphate (N/P=5 in China) (Zhang et al. 2007). Ammonium is also present in acid mine drainage along with other heavy metals (Ríos et al. 2008). Its taste threshold in water is 35 mg/l while its odour limit is 1.5 mg/l (USEPA 2009). The presence of ammonia gas in water, which is toxic for aquatic life, depends on the pH and temperature conditions. A pH range of 5.5 to 10.5 has been reported to be optimum for ammonium removal (Zhang et al. 2007). However, at high pH (pH>8), the ammonium ions in the solution get volatilized to ammonia gas, resulting in possible overestimation of ammonium removal (Emerson et al. 2011; Zhang et al., 2011a; 2011b). Furthermore, the presence of other cations and anions interfere with ammonium removal due to competitive sorption, with the order of influence of 14

cations: K+>Ca2+>Na+>Mg2+ and that of anions: CO32ˉ>Clˉ>SO42ˉ (Zhang et al., 2011a; Cardoso et al., 2015b). Also, higher concentration and double charge of Ca2+, Mg2+ and Sr2+, if present in wastewater, can lead to their preferential sorption, hence, reducing NH4+ retention. However, this does not pose much concern in fly ash zeolites since they inherently contain oxides of Ca and Na, which tend to leach out (Juan et al. 2009; Cardoso et al., 2015b). In swine wastewater treatment, the ammonium removal efficiency and the final pH have been reported to decrease at higher concentrations due to the presence of multicontaminants in the system (Cardoso et al., 2015b). Incidentally, low-calcium fly ash based zeolites show better ammonium removal capacities since high-calcium fly ash based zeolites show Ca2+ leaching and have lower zeolitic content (Zhang et al., 2011a; 2011b). Incidentally, the lower sorption capacity can be addressed, to some extent, by suitable modification of the zeolite using mild acid (such as 0.01 mol/L H2SO4), which alters the sparingly soluble calcite into soluble gypsum and anhydrite, thus favoring precipitation of calcium phosphate (Chen et al. 2006). However, it should be noted that high concentration of acid destroys the zeolitic structure, removes Al3+, Ca2+, Fe2+ and Mg2+ and lowers CEC (Zhang et al. 2007). The adsorption kinetics has been reported to follow Langmuir, Freundlich and Ho’s pseudo second-order models. However, best fit has been obtained using Langmuir model for low-calcium fly ash zeolite and Freundlich for high-calcium fly ash zeolite (Zhang et al., 2011b). Phosphate immobilization capacity (PIC) of raw fly ash (around 52 mg/g) gets augmented several folds upon alkali activation (Zhang et al., 2011c) and by saturation of Nazeolite with Ca2+ (Chen et al. 2006). PIC has been observed to be higher for zeolites synthesized from high-calcium fly ashes where free CaO is the major contributor to 15

phosphate removal (Chen et al. 2006). Favorable pH for removal is 3.5 to 9 for zeolites from fly ash having high calcium and 3.5 to 5.5 for fly ashes with low calcium (Chen et al. 2006) and, in general, an optimum value of 7 is adopted (Zhang et al., 2011c; Ji et al. 2014). Incidentally, iron modified zeolite (whose synthesis does not generate waste alkaline solution) shows high PIC due to ligand exchange with Fe-based compounds (Chen et al. 2006; Xie et al. 2014). Ji et al. (2014) have used a 4:1 mixture of low- and high-calcium fly ash based zeolites for removal of over 40% of both ammonia and phosphate (dosage=4g/l, pH=7.5). The authors have opined that, in sewage treatment, these two types of fly ashes should be applied one after the other for better efficiency (Ji et al. 2014). A zeolite with CEC=279 meq/100g has shown PIC=12.98 mg/g while PIC=87.51 mg/g has been observed for zeolite with CEC=69 meq/100g (Ji et al. 2014). Due to the presence of bivalent cations, viz., Ca2+ and Mg2+, PIC is enhanced in seawater compared to pure water (Guan et al. 2009). Langmuir model best fits the phosphate adsorption kinetics (Zhang et al., 2011c).

2.4. Other applications Fly ash zeolites have been successfully used for treating lignite minewater (Itskos et al. 2015) and for reducing hardness wherein 72% reduction has been reported for minewater treated with 40 g/l (solid-to-liquid ratio) of fly ash zeolite (Prasad et al. 2011). In addition, soils with heavy metal spillage when treated with zeolite (viz., NaP1 with CEC=200 meq/100g), along with phytoremediation, have shown over 95% decrease in concentrations of Cd2+, Co2+, Cu2+, Ni2+ and Zn2+ (dosage = 250 ton/ha) (Querol et al. 2006). Radionuclide, viz., 133Cs+, has been immobilized by containment in a fly ash geopolymer through geopolymerization reactions, forming a solid block with compressive strength of 30 MPa (Li et al. 2013). The 16

sulphuric acid mist generated in lead-battery manufacturing plants has been removed using zeolites synthesized from fly ash activated using NaOH and CaO (Shu et al. 2015). Due to their thermal stability, non-flammability, non-degradability and sorption characteristics, zeolites can act as excellent sorbents of water in dehydration applications (Panitchakarn et al. 2014) and volatile organic compounds (VOCs) such as benzene, chlorofluorocarbons, formaldehyde and methylene chloride, which pose health risks and harm the environment (Rayalu et al. 2006; Zhou et al. 2014). Benzene vapor has been removed using NaP1 (69.2% zeolite with SSA=22.08 m2/g) and Na-A (66.5% zeolite with SSA=39.28 m2/g) (Wei et al. 2013; Zhou et al. 2014).

2.5. Recovery of immobilized heavy metals from the spent zeolites The recovery of contaminants and regeneration of spent sorbents (read zeolites) are useful to make the water treatment processes economically viable and sustainable (Wang et al., 2009a). NaCl solution can be used to recover heavy metals and ammonium adsorbed by zeolites, to an extent (Steenbruggen and Hollman 1998; Wang et al., 2009a; Zhang et al., 2011a). However, when leached with deionized or distilled water, fly ash zeolites have shown negligible desorption of both dyes and heavy metals (Querol et al., 2006; Visa and Chelaru 2014). Similarly, leaching of manganese-sorbed zeolites using ammonium acetate followed by acetic acid has shown negligible recovery of the heavy metal (Belviso et al. 2014). In this context, it has been shown that regenerated zeolites show a decrease in its sorption capacity due to the partial disintegration of its structure (Chunfeng et al., 2009).

3. Novel dimensions in zeolite applications 17

Apart from the conventional applications for water treatment, fly ash zeolites are now finding applications for remediation of contaminated soils in the form of permeable reactive barriers and liners and as backfill material in radioactive contaminant disposal sites (Ibrahim et al. 2008; Regmi et al. 2009; Indraratna et al. 2014; Du et al. 2015).

3.1. Application as permeable reactive barrier (PRB) Spills or discharges of contaminants (leachates and hazardous compounds) in soil migrate due to rainwater percolation, resulting in groundwater and surface water contamination (Erto et al. 2011). In this context, permeable reactive barriers (PRBs) offer in-situ remediation at low operating and maintenance costs (Regmi et al. 2009; Erto et al. 2011; Indraratna et al. 2014). Fig. 3 shows the conceptualization of PRB for treatment of a contaminant plume in the soil. In a PRB, the reactive media (such as activated charcoal, exchange resin and zeolite) should have hydraulic conductivity greater than the surrounding media, i.e., the soils, in order to allow the flow of the contaminant plume through the barrier under natural hydraulic gradient (Erto et al. 2011). Interestingly, a soil-natural zeolite layering technique has also been used for treatment of polluted river water (Boonsook et al. 2003; Masunaga et al. 2003) and this methodology has the potential to be augmented using fly ash based zeolites. Czurda and Haus (2002) have suggested that in a fly ash zeolite PRB with funnel and gate configuration (a system of walls which channelizes the contaminant plume towards the PRB), a secondary electrokinetic treatment, which is provided after the treatment through the PRB has been over, can be employed for ensuring complete contaminant removal.

3.2. Application as liner In contaminant barrier liner systems (viz., radioactive waste disposal site and 18

municipal and industrial landfills), coarser particles (commonly, sand) are mixed with bentonite in order to prevent desiccation cracking (Ruhl and Daniel 1997). However, such materials added to compacted clays should ensure geotechnical stability and low hydraulic conductivity (k≤10-9 m/s) (Hong et al. 2011). Hence, sorbents such as fly ash, natural zeolites and fly ash zeolites have been investigated for their potential as additives in bentonite (Kaya and Durukan 2004; Rahman et al. 2009; Çoruh and Ergun 2010; Ibrahim et al. 2008; Du et al. 2015). Practically, higher sorption capacity of the zeolites helps in reduction of liner thickness in addition to lesser contaminant migration (Kaya and Durukan 2004).

4. Limitations High pH (>10) in the zeolitic end product has to be lowered failing which the treated effluent will have high pH and subsequently precipitate (Prasad et al., 2011). After zeolite synthesis, removal of excess alkali (like NaOH or KOH) and lowering of pH, require huge amount of water, hence adding to the production cost along with generation of highly alkaline effluents (Moreno, 2001). Although deionized water can be used for removing excess alkali (thereby lowering the pH), pH below 4 can lead to drastic disintegration of the zeolitic crystals (Murayama et al., 2003). Furthermore, high pH and total dissolved solids and very large concentrations of sodium and calcium in the treated water are current shortcomings in using fly ash zeolites (Prasad et al., 2011). Incidentally, leaching of hazardous elements such as Cr, Hg, Se and V from raw fly ash has also been reported (Carlson and Adriano, 1993; Davidson and Bassett, 1993; Steenbruggen and Hollman, 1998; Koukouzas et al. 2011a; Georgakopoulos et al. 2012). While treating acid mine drainage water using zeolites synthesized from an Indian fly ash, 19

high leaching of chromium has been reported (Prasad and Mortimer, 2011). The type and amount of leaching depends on the parent coal and combustion technique employed. Hence, care should be taken to properly characterize the fly ash before applications in water treatment (Hong et al., 2009).

5. Conclusions and future outlook Fly ash based zeolites have been demonstrated extensively in literature to be an efficient scavenger of hazardous and toxic cations and anions in water. Furthermore, they have the potential in effluent treatment for removal of dyes and heavy metals and for applications such as permeable reactive barriers and contaminant barrier liners. The contaminant removal using zeolites takes place through sorption and/or precipitation and the removal efficiency depends upon the pH, initial contaminant concentration and the solid to liquid ratio of the system. Only few studies have been conducted on removal of arsenic and mercury using fly ash zeolites and further studies using different types of zeolites would prove to be useful in finding the ideal type of zeolite. Bacterial loading on fly ash based zeolites can be used for heavy metal and phosphate removal, thus offering, an economically viable alternative to existing methods. Although studies exist for landfill leachate treatment using raw fly ashes, utilization of fly ash based zeolites could yield better results as indicated by few initial studies. While a large number of studies have been conducted on heavy metal removal, very few studies exist on other crucial applications such as soil remediation using permeable reactive barriers (PRBs) and contaminant containment using zeolite-based liners. Despite studies on PRBs using natural and commercial zeolites, utilization of fly ash based zeolites has not been explored much. For containment of hazardous, toxic and radioactive waste, 20

feasibility of liner materials using bentonite-embedded fly ash zeolites can be investigated. In addition, in situ remediation studies would be quite useful to understand the effectiveness of this material in large-scale resource recovery technologies.

21

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doi:10.1016/j.desal.2011.03.085 Zhang, M., Zhang, H., Xu, D., Han, L., Zhang, J., Zhang, L., Wu W., and Tian, B. (2011c). “Removal of phosphate from aqueous solution using zeolite synthesized from fly ash by alkaline fusion followed by hydrothermal treatment.” Separ. Sci. Technol.,, 46(14), 22602274. doi:10.1080/01496395.2011.586664 Zhou, L., Chen, Y.L., Zhang, X.H., Tian, F.M., and Zu, Z.N. (2014). Zeolites developed from mixed alkali modified coal fly ash for adsorption of volatile organic compounds.” Mater. Lett., 119, 140-142. doi:10.1016/j.matlet.2013.12.097

45

List of Figures

Applications AMD Anions Dye Heavy metal PRB and Liners Wastewater VOC

Fig. 1. Locations of fly ashes that have been zeolitized and characterized for water treatment applications

46

Fig. 2. Scanning electron micrographs showing rod/needle shaped zeolites synthesized from fly ash

47

Fig. 3. Conceptualization of a permeable reactive barrier (PRB)

48

Table 1. Some common zeolites synthesized from fly ash Zeolite

Chemical formula

References

Analcime

NaAlSi2O6·H2O.

Remy and Ferrell (1989)

Cancrinite

Na6Ca2Al6Si6O24(CO3)2·2H2O

Qiu and Zheng, 2009

Chabazite

(Ca,Na2,K2,Mg)Al2Si4O12·6H2O

Dêdêcêk et al. (2009)

Clinoptilolite

(Na,K,Ca)2-3Al3(Al,Si)2Si13O36·12H2O Zabochnicka-Świątek and Malińska (2010)

Hydroxy-sodalite

Na1.08Al2Si1.68O7.44·1.8H2O

Ahmaruzzaman (2010)

Mordenite

(Ca, Na2, K2)Al2Si10O24·7H2O

Sasaki et al. (2003)

Na-A

Na12Al12Si12O48·24H2O

Qiu and Zheng, 2009

Na-P1

Na6Al4Si4O24·4H2O

Qiu and Zheng, 2009

Na-Y

Na58Al58Si134O384·260H2O

Qiu and Zheng, 2009

Scolecite

Ca2Al2Si3O10·3H2O

Qiu and Zheng, 2009

Phillipsite

(Ca,Na2,K2)3Al6Si10O32·12H2O

Hay (1966)

Zeolite A

NaAlSi1.1O4.2·2.25H2O

Ahmaruzzaman (2010)

Zeolite X

NaAlSi1.23O4.46·3.07H2O

Ahmaruzzaman (2010)

Zeolite Y

NaAlSi2.43O6.86·4.46H2O

Ahmaruzzaman (2010)

49

Table 2. Metal uptake characteristics of various fly ash based zeolites

Ionic species

Zeolite a

Fly ash source

Zeolite SiO2/ Al2O3

Operating conditions CEC

η

(meq/100g)

(%)

q t (min)

Brazil

290

100

Spain

270

99.16

T

Ci

Dosage

Reference

(mg/g) pH 3.3

(ºC) (mg/l)

30

(g/ml)

0.04

0.01

Cardoso et al. (2015a)

0.955

0.03

Querol et al. (2002)

0.74

0.01

Medina et al. (2010)

Na-P1 As5+ W

Mexico

A

South Africa

99 1.764

105

7

99.9

5

25

2h/24h

0.2 Koukouzas et al. (2010)

Erionite, Linde, ZSM-18

Poland

Na-al

Romania

2.146

120

0.2

60

156.2 10.2

120

515

0.002

60

87.7 10.2

120

515

0.003

3.3

30

0.22

0.01

Cardoso et al. (2015a)

0.186

0.03

Querol et al. (2002)

Brazil

290

94.09

Spain

270

100

South Korea

2h/24h

Visa and Chelaru (2014)

Cd2+

Na-P1

99.9

1.22

85

50

117.5

25

0.0001 Lee et al. (2000)

Na-P1, FAU, CHA

1.18

228.7

98.94

4.6

0.002

0.08

1.49

283.3

96.64

4.6

0.002

0.08

98

1.55

1000

0.02

Itskos et al. (2015)

0.013

Visa et al. (2012)

1000

0.02

Itskos et al. (2015)

1124.1

0.01

Izidoro et al. (2013)

UK

PHI

Greece

PHI, CLI

Romania

THO

Greece

Prasad and Mortimer (2011)

2.47

30.2 3.19

Brazil

79 310

X

60

20

90 1.55

92.4

60

20

24h

140

97.8

120

21

1

140

90.9

120

21

1

240

25

Thailand

32.75 4A Co

3

200

0.005

China

Hui et al. (2005)

2+

22.22 Na-P1

14.5

Apiratikul and Pavasant (2008)

Spain

270

China

1.2

560

South Africa

1.764

105

13.5

3

240

25

68.57 38

3

25

300

0.005

0.751

0.03

200

Querol et al. (2002) Wang et al. (2009a)

A 99.9

2h/24h

0.2

Koukouzas et al. (2010)

Cu2+ 4A

98.42

40.1

3

240

25

200

0.005

89.57

49.9

3

240

25

300

0.005

China

Hui et al. (2005)

51

Erionite, Linde, ZSM-18

Na-al

Poland

2.146

120

100

2h/24h

0.2

71

119.1 10.2

120

350

0.002

71

56.5 10.2

120

350

0.003

Romania

Visa and Chelaru (2014)

42

30

0.0005

64

40

0.0005

Australia

Wang et al. (2006) 80

Na-P1

Cr3+

3.4

240

20

9

3.4

240

20

Wu et al. (2008)

Spain

Na-P1, FAU, CHA

1.8 China

South Korea

Koukouzas et al. (2010)

270 1.22

9.44 89

36 73.5

25

0.03 0

1.18

228.7

84.24

4.6

0.053

0.08

1.49

283.3

84.95

4.6

0.053

0.08

UK

Querol et al. (2002) Lee et al. (2000)

Prasad and Mortimer (2011)

PHI

Greece

2.47

100

1.55

60

20

1000

0.02

Itskos et al. (2015)

THO

Greece

3.19

98

1.55

60

20

1000

0.02

Itskos et al. (2015)

X

China

1.31

500

25

200

A

South Africa

1.764

105

28.9 100

52

3 2h/24h

Wang et al. (2009a) 0.2

Koukouzas et al. (2010)

4A

87.33

35.6

3

240

25

200

0.005

73.52

41.6

3

240

25

300

0.005

China

Erionite, Linde, ZSM-18

Poland

HS, Na-P1

China

Na-P1, FAU, CHA

UK

Hui et al. (2005)

2.146

120

100

2h/24h 32.2 3.4

240

0.2 20

Wu et al. (2008)

1.18

228.7

82.8

4.6

2.152

0.08

1.49

283.3

90.38

4.6

2.151

0.08

Prasad and Mortimer (2011)

PHI

Greece

2.47

100

1.55

60

20

1000

0.02

Itskos et al. (2015)

THO

Greece

3.19

100

1.55

60

20

1000

0.02

Itskos et al. (2015)

97.47

3.3

30

5.62

0.01

290 Brazil 2+

Fe

Na-P1

Cardoso et al. (2015a) 290

99.87

Spain

270

99.25

FAU, SOD, A

South Africa

75.81

30

X, A, SOD

Italy

125

99.65

Na-P1

Australia

3.3

30

5 28

53

4.64

0.01

444

0.03

0.47 µg/kg

2.64

Hg2+

Mn2+

Koukouzas et al. (2010)

10 30

Querol et al. (2002) Somerset et al. (2008)

0.1

Belviso et al. (2014)

0.0005 Wang et al. (2006)

Na-P1, FAU, CHA

A

4A

Erionite, Linde, ZSM-18

Brazil

290

Spain

270

93.33

3.3

30

63.63

0.06

0.01

Cardoso et al. (2015a)

11

0.03

Querol et al. (2002)

1.18

228.7

86.76

4.6

19.544

0.08

1.49

283.3

74.75

4.6

19.544

0.08

1.764

105

99.9

UK

South Africa

Prasad and Mortimer (2011)

2h/24h

0.2

21.06

9.5

3

240

25

200

0.005

14.01

8.8

3

240

25

300

0.005

China

Poland

Koukouzas et al. (2010)

Hui et al. (2005)

2.146

120

100

Australia

2h/24h 65.8

0.2 40

Koukouzas et al. (2010)

0.0005 Wang et al. (2006)

Na-P1 Ni2+

Spain

Na-P1, FAU, CHA

270

40.5

0.316

0.03

1.18

228.7

48.28

4.6

0.52

0.08

1.49

283.3

25.59

4.6

0.52

0.08

48

1.55

1000

0.02

Itskos et al. (2015)

0.005

Visa et al. (2012)

0.02

Itskos et al. (2015)

UK

PHI

Greece

PHI, CLI

Romania

THO

Greece

Querol et al. (2002)

Prasad and Mortimer (2011)

2.47

2000 3.19

52

54

60

20

25 1.55

60

20

1000

A

South Africa

1.764

105

99.9

2h/24h

0.2

Erionite, Linde, ZSM-18

Poland

2.146

120

100

2h/24h

0.2

FAU, SOD, A

South Africa

75.81

95

Koukouzas et al. (2010)

South Korea

1.22

98

3.23 µg/kg

2.64 266.4

25

0.41

Somerset et al. (2008) 0.0001 Lee et al. (2000)

Na-P1 Spain

270

100

240

0.03

1.18

228.7

55.44

4.6

1.26

0.08

1.49

283.3

50.07

4.6

1.26

0.08

Querol et al. (2002)

Pb2+ Na-P1, FAU, CHA

UK

Prasad and Mortimer (2011)

PHI

Greece

2.47

100

1.55

60

20

1000

0.02

Itskos et al. (2015)

THO

Greece

3.19

100

1.55

60

20

1000

0.02

Itskos et al. (2015)

X

Thailand

120

21

Na-P1, FAU, CHA

UK

PHI, CLI

Romania

140 1.18

228.7

420.6 98.77

4.6

1 0.647

Apiratikul and Pavasant (2008)

0.08

Prasad and Mortimer (2011)

0.013

Visa et al. (2012)

Sr2+

Zn2+

18.9

China

1.2

560

South Africa

1.764

105

29.7

90 3

25

200

Wang et al. (2009a)

A 100

55

2h/24h

0.2

Koukouzas et al. (2010)

A, ANA, PHI, HC

4A

Erionite, Linde, ZSM-18

Na-P1

62.57

100

57.2

100

Brazil

Nascimento et al. (2009)

66.42

30.6

3

240

25

200

0.005

42.17

27

3

240

25

300

0.005

China

Poland

Hui et al. (2005)

2.146

120

100

Brazil

290

80.76

Spain

270

South Korea

1.22

Na-P1, FAU, CHA

UK

1.49

PHI

Greece

THO X

3.3

30

94.4 65

283.3

2h/24h

65.8 4.6

2.47

95

1.55

60

Greece

3.19

60

1.55

60

China

1.31

22.4

a

Koukouzas et al. (2010)

0.13

0.01

Cardoso et al. (2015a)

54

0.03

Querol et al. (2002)

25

98.02

500

0.2

3

0.0001 Lee et al. (2000) 0.646

0.08

Prasad and Mortimer (2011)

20

1000

0.02

Itskos et al. (2015)

20

1000

0.02

Itskos et al. (2015)

25

200

Wang et al. (2009a)

ANA - analcime, CHA - chabazite, CLI - clinoptilolite, FAU - faujasite, HC - hydroxycancrinite, Na-al - Na-aluminosilicate, PHI - phillipsite, THO thomsonite

56

Table 3. Heavy metal selectivity series of fly ash zeolites

Zeolite

Fly ash source

a

China Canada UK Brazil Spain

PHI, CLI SOD X

South Korea The Netherlands Romania India Thailand

X, FAU

Japan

Selectivity series Pb2+>Cu2+>Zn2+≥Mn2+

Brazil

A, ANA, PHI, HC 4A CAN FAU

Na-P1

CEC (meq/100 g)

290 270

240

140

Reference Nascimento et al. (2009)

Cu2+>Cr3+>Zn2+>Co2+>Ni2+ Hui et al. (2005) Pb2+>Cu2+>Ni2+> Qiu and Zheng (2009) 2+ 5+ 2+ 2+ 2+ 2+ Fe >As >Pb >Zn >Cu >Ni > Ríos et al. (2008) Cr2+ As5+>Mn2+>Fe2+>Cu2+>Ni2+>Zn2+ Cardoso et al. (2015a) Fe3+≥Cu2+≥Pb2+≥Cd2+>Zn2+>Mn2+ Moreno et al. (2001) >Sr2+ 2+ Pb >Cu2+>Cd2+>Zn2+ Lee et al. (2000) 2+ 2+ 2+ 2+ 2+ Ba >Cu >Cd ≈Zn >Co>Ni Steenbruggen and Hollman (1998) 2+ 2+ 2+ Pb >Zn ≥Cd Visa et al. (2012) Pb2+>Cd2+>Zn2+ Borhade et al. (2012) 2+ 2+ 2+ Pb >Cu >Cd Apiratikul and Pavasant (2008) 2+ 2+ 2+ 2+ Pb >Cu >Cd >Ni Jha et al. (2008)

a

ANA - analcime, CAN - cancrinite, CLI - clinoptilolite, FAU - faujasite, HC hydroxycancrinite, PHI - phillipsite, SOD - sodalite

57

Table 4. Dye removal using fly ash zeolites

Zeolite a

Dye

Alizarin sulfonate

Fly ash source

HS

South Africa

A

China

HS

South Africa

Methylene blue Na-P1

SSA

q

(m2/g)

(x10-5 mol/g)

7.4

0.713

X

China

Na-P1

Australia

SOD, ANA

Reference

4

0.01 30

7.4

3.383

4

24

4.46

3 d

5.32

3 d

Turkey

X, SOD

Woolard et al. (2002) Wang et al. (2009b)

0.01

Australia

Na-P1, Y, X, SOD, ANA Safranine

T Dosage

(h) (ºC) (g/ml)

25.98

Woolard et al. (2002)

Wang et al. (2006) 25.7

Rhodamine B

t pH

35.42

30

Wang et al. (2009b)

3 d

25.7

0.398

Wang et al. (2006)

27.4

3

6.34 1

45

0.01

29.4

1.5

6.34 1

25

0.01

28.5

1.8

6.34 1

45

0.01 Atun et al. (2011)

Na-P1, Y, X, SOD, ANA Thionine

SOD, ANA X, SOD a

Turkey

27.4

3

6.39 1

45

0.01

29.4

4.25

6.39 1

25

0.01

28.5

3.6

6.39 1

25

0.01

ANA - analcime, HS - hydroxysodalite, SOD - sodalite

58

Table 5. Removal of ammonium using fly ash zeolites Operating conditions t T Ci Dosage pHe (min) (ºC) (mg/l) (g/ml) 2.54 8 25 100 0.004 GIS China 2.62 45.511 69 4.8 8 25 7.3 0.004 8.5 25 10 0.004 137 76 2.52 7.7 30 25 52.2 0.02 9.2 K-F Spain 110 66 1.62 7.7 144 25 52.2 0.02 85 74 1.44 7.7 30 25 52.2 0.02 8.7 K-PHI, K-CHA Spain 115 71 1.8 7.7 144 25 52.2 0.02 290 28.1 3.3 30 9.6 0.010 52 31 5.7 30 25 1205 0.02 7.11 Brazil 59 17 30 25 578 0.02 8.05 280 81 14 30 25 340 0.02 9.3 70 4 30 25 125 0.02 10.7 Na-P1 131 76 2.34 7.7 30 25 52.2 0.02 8 Spain 99 71 1.8 7.7 144 25 52.2 0.02 1.82 213 24h 0.01 China 1.91 175 60 24h 10 0.01 10.08 1.56 161.5 154.3 70 4.5 7.5 25 25 0.005 Na-P1, ANA, CHA Spain 56.7 5.24 30 245 0.03 8.11 Na-P1, FAU, CHA India 1.49 283.3 19.57 1 485 0.01 47.7 17.77 8 75 25 152.6 0.004 48 23.89 8 75 25 50 0.004 Zeolite X with small 15.7 8 35 0.004 amounts of A, P and China 3.34 27.015 279 18.19 8 25 100 0.004 HS 51.1 8 25 7.3 0.004 74.6 25 10 0.004 a ANA - analcime, CHA - chabazite, FAU - faujasite, GIS – gismondine, HS - hydroxysodalite, PHI – phillipsite Zeolite a

Fly ash source

SiO2/ Al2O3

SSA (m2/g)

CEC η q (meq/100g) (%) (mg/g) pH

59

Reference

Zhang et al. (2011b) Juan et al. (2009) Juan et al. (2009) Cardoso et al. (2015a) Cardoso et al. (2015b)

Juan et al. (2009) Zhang et al. (2007) Xie et al. (2014) Otal et al. (2005) Prasad et al. (2011) Zhang et al. (2011a)

Zhang et al. (2011b)

Table 6. Removal of anions using fly ash zeolites Anion

Zeolite a

Fly ash source

Chloride Fluoride Nitrate

Na-P1 Na-P1 Na-P1

Brazil Brazil Brazil

GIS

China

HS

China

Phosphate Na-P1

China

SiO2/ Al2O3

2.62

SSA (m2/g)

CEC (meq/100g)

η (%)

290 290 290

48.38 75 52.63

45.511

69

91.49 90.84 1.82

103 101 213

1.91

175

1.56

161.5

57.68 Na-P1, ANA, CHA Spain Na-P1, SOD Thailand 3.57 35.38 Sulphate Na-P1 Brazil a ANA - analcime, CHA - chabazite, GIS - gismondine, SOD - sodalite

154.3 213 208.9 188 290

q (mg/g) pH 3.3 3.3 3.3

Operating conditions t T Ci Dosage (min) (ºC) (mg/l) (g/ml) 30 12.4 0.01 30 1.2 0.01 30 3.8 0.01 30 0.0125 28h 30 167.87 1 28h 40 1 28h 50 1 24h 1000 24h 1000 0.0187 24h 0.01 24h 0.01 24h 12 24h 25 0.005

102.9 94 7 156.36 7 184.17 7 42.2 47.17 38.26 62.77 5.31 95 5.52 18.2 34.68 40.85 24h 91 5.24 30 57.14 24h 84.97 3.3 30 56.28

60

1000 25000 15000 406

0.03 0.01 0.01

Reference Cardoso et al. (2015a) Cardoso et al. (2015a) Cardoso et al. (2015a) Zhang et al. (2011c) Chen et al. (2006)

Zhang et al. (2007) Xie et al. (2014) Wu et al. (2006) Chen et al. (2006) Otal et al. (2005) Pengthamkeerati et al. (2008) Cardoso et al. (2015a)