Review of the Natural,Modified,and Synthetic Zeolites for Heavy Metals Removal from Wastewater

Abstract

Low-cost zeolite sorbents, which have unique ion exchange and sorption properties, have been investigated as candidates for cost-effective removal of heavy metals from waste solution. Waste products from various industries are employed to prepare or modify zeolite for the improvement of adsorption capacity. In this review, the applications of natural, modified, and synthetic zeolite in removal of heavy metals from waste water solutions are summarized, and the removal efficiency on the same individual heavy metal is compared. It is unique in comparison with the existing literature reviews that three kinds of zeolites, including natural, modified, and synthetic zeolite, are used to remove the same heavy metal for comparative analysis, so a suitable adsorbent could be selected according to the properties of the wastewater in applications. Compared to natural zeolite, modified and synthetic zeolites have higher cation exchange capacities and sorption performance. Sorption process of three kinds of zeolites was generally spontaneous and endothermic, and removal mechanism of heavy metal ions was by adsorption and ion exchange processes. In summary, zeolites are effective adsorbent materials with great potential applications to remove heavy metals from waste water.

Introduction

The heavy metal contamination of wastewater, including ions of Cu, Cd, Pb, Zn, Ni, Cr, and Co, can be generated by some industries such as mineral processing, metal plating facilities, and tanneries, causing serious soil and water pollution (Lin and Juang, 2002). Especially metal ions Pb⁺², Cu⁺², Fe⁺³, and Cr⁺³ are not biodegraded and tend to accumulate in living organisms, which lead to numerous diseases and disorders (Moore and Ramamoorthy, 1984; Clement et al., 1995; Inglezakis et al., 2003). If the wastewater is discharged directly and not effectively treated for removal of heavy metal ions, the soils, groundwater, and surface water surrounding the industries would be at risk of serious contamination, resulting in great damage of ecological balance and aquatic ecosystem.

In recent years, various treatment technologies, including chemical precipitation, membrane filtration, phytoextraction, ion exchange, reverse osmosis, carbon adsorption, electrodialysis, coprecipitation, and adsorption are adopted to remove heavy metals from wastewater (Applegate, 1984; Huang and Blankenship, 1984; Sengupta and Clifford, 1986; Geselbarcht, 1996; Schnoor, 1997). The treatment processes of chemical precipitation, ion exchange, adsorption, and reverse osmosis are considered to be competitive and effective for the removal of heavy metals, but some disadvantages such as high operational costs, regeneration, and problem of posttreatment restrict them from the large-scale industrial applications. The technologies of ion exchange and adsorption are feasible and effective to remove heavy metals using an exchanger/sorbent with high selectivity for the target metal. Therefore, the use of alternative low-cost materials with high selectivity as potential sorbents has been emphasized recently. Zeolites as candidate materials are very attractive due to cost-effectiveness and good selectivity for heavy metals since it was the first attempt to purify water in the 19th century (Breck, 1974). Natural zeolites have been widely used in adsorption, catalysis, building industry, agriculture, soil remediation, and energy (Tsitsishvili et al., 1992; Bish and Ming, 2001), and the world natural zeolite consumption has reached 5.5 Mt in 2010 (Ozaydin et al., 2006). Most common natural zeolites are formed by alteration of glass-rich volcanic rocks (tuff) with freshwater in playa lakes or seawater (Badillo-Almaraz et al., 2003) and are cage-like structures consisting of three-dimensional frameworks of SiO₄ and AlO₄ tetrahedra. Its internal and external surface area is up to several 100 m²/g and cation-exchange capacities up to several miliequivalents per gram (Ming and Mumpton, 1989). The aluminum ion is small enough to occupy the position in the center of the tetrahedron of four oxygen atoms, and the isomorphous replacement of Si⁴⁺ by Al³⁺ produces a negative charge in the lattice. The net negative charge is balanced by the exchangeable cation (sodium, potassium, or calcium) and these cations can be exchangeable with certain cations in solutions such as lead, cadmium, zinc, and manganese (Breck, 1964; Barer, 1987). The natural zeolite is over 40 types and the synthetic or modified zeolite is over one hundred types. The most abundant natural clinoptilolite has two-dimensional 8-ring and 10-ring channel structure with the largest cavity dimension measuring 4.4 × 7.2 (Newsom, 1986). To improve the performance of natural zeolite, various synthetic and modified zeolites can be produced for more applications. Acid/base treatment and surfactant impregnation by ion exchange are commonly employed to change the hydrophilic/hydrophobic properties for adsorption of various ions or organics (Haggerty and Bowman, 1994; Sullivan et al., 1998; Bouffard and Duff, 2000; Bowman, 2003; Christidis et al., 2003; Dakovic et al., 2003, 2007a, 2007b; Cortes-Martinez et al., 2004, 2007; Ghiaci et al., 2004a, 2004b; Benkli et al., 2005; Cheng et al., 2005; Karadag et al., 2007a, 2007b, 2007c; Kuleyin, 2007; Lemic et al., 2006, 2007; Hernandez-Beltran et al., 2008; Misaelides et al., 2008; Noroozifar et al., 2008). Acid washing of natural zeolite may remove impurities that block the pores, and cations can be changed into H-form and finally dealuminate the structure. To change the surface properties of natural zeolites for higher adsorption/exchange efficiency, modification method using organic surfactants is widely employed. These organic surfactants include hexadecyltrimethylammonium (HDTMA), cetyltrimethylammonium bromide (CTMA), octadecyldimethylbenzyl ammonium (ODMBA), benzyltetradecyl ammonium (BDTDA), N-cetylpyridinium (CPD), and stearyldimethylbenzyl ammonium chloride (SDBAC). Surfactant-modified zeolite with complex functional groups can form positively charged exchange sites by the positive groups: NR+ of the surfactant, resulting in higher affinity for ions and adsorption for organics in aqueous solution.

Considerable research has been conducted to remove heavy metals from wastewater. Zamzow et al. (1990) studied the selectivity series of clinoptilolite in the sodium form for heavy metal: Pb²⁺ > Cd²⁺ > Cs⁺ > Cu²⁺ > Co²⁺ > Cr³⁺ > Zn²⁺ > Ni²⁺ > Hg²⁺. The interactions of Pb²⁺, Cd²⁺, and Cr³⁺ competing for ion-exchange sites in natural clinoptilolite was demonstrated by Mier et al. (2001). Inglezakis et al. (2002) studied the ion exchange of Pb²⁺, Cu²⁺, Fe³⁺, and Cr³⁺ on natural clinoptilolite and showed that equilibrium is favorable for Pb, unfavorable for Cu, and sigmoid for Cr³⁺ and Fe³⁺. Erdem et al. (2004) have studied the adsorption behavior of natural (clinoptilolite) zeolites with heavy metals and found that adsorption phenomena depend on charge density and hydrated ion diameter. The selectivity sequence can be given as Co²⁺ > Cu²⁺ > Zn²⁺ > Mn²⁺ (Erdem et al., 2004). Hui et al. (2005) investigated the removal performance and selectivity sequence of mixed heavy metal ions in aqueous solution by adsorption process on pure and chamfered-edge zeolite 4A, and the affinity order is as follows: Cu²⁺ > Cr³⁺ > Zn²⁺ > Co²⁺ > Ni²⁺. On the base of the reviewed publications, zeolites have been used in a large number of water treatment processes such as water softening and purification from ammonia, heavy metals, radioactive species, dissolved or emulsified organic substances, toxic anions, odor, and solids. Thousands of scientific articles, books, and patents, dealing with different aspects of zeolite utilization in wastewater treatment processes, were published in the last few decades. The general objective of this article is to overview the state-of-the-art knowledge concerning the use of different kinds of zeolites in wastewater treatment processes and summarize the most important properties of zeolites. The researchers usually focus on the applications and adsorption properties of zeolite on certain ions or organic removal from wastewater and the selectivity sequence of mixed metal ions in aqueous solution to facilitate their comparison and give an outstanding point that could assist the right choice of materials for practical purposes. In this review, the removal efficiency of the same heavy metal ion is compared by using different adsorbents of natural, modified, and synthesized zeolites. The optimal experimental conditions, including initial concentration of the heavy metal ions, contact time, initial pH of the solution, and the adsorbent dosage, are summarized in Table 5 –11, and the adsorption kinetics, thermodynamics, and adsorption isotherms are compared to determine the removal efficiency of the same individual heavy metal.

This review is unique in comparison with the existing literature reviews. We comprehensively discussed three kinds of zeolites: natural, modified, and synthetic zeolites, and their removal efficiency in the same heavy metal are summarized for comparative analysis. It is significant to guide in selecting a suitable adsorbent based on the properties of the wastewater.

Properties and Character of Natural Zeolite and Modified Zeolite

Natural zeolite

Natural zeolite identified is over 40 types in the world. The common forms are clinoptilolite, mordenite, phillipsite, chabazite, stilbite, analcime, and laumontite, and others are rare such as offretite, paulingite, barrerite, and mazzite. Among these zeolites, clinoptilolite is the most abundant natural zeolite and is widely used in the world. Zeolites are of three-dimensional structure constituted by (Si, Al)O₄ tetrahedra connected by all their oxygen vertices forming channels where H₂O molecules and exchangeable cations counterbalance the negative charge generated from the isomorphous substitution. The aluminum ion is small enough to occupy the position in the center of the tetrahedron of four oxygen atoms, and the replacement of Si⁴⁺ by Al³⁺ results in a negative charge in the lattice, balanced by the exchangeable cation (sodium, potassium, or calcium) and then replaced with heavy metals. The general chemical formula of zeolites is Mx/n[AlxSiyO₂(x + y)].pH₂O where M is (Na, K, Li) and/or (Ca, Mg, Ba, Sr), n is cation charge; y/x = 1–6, p/x = 1–4. Chemical formula and structure of some important natural zeolites are shown in Table 1 (Wang and Peng, 2010).

Table 1.

Structural Property of Some Natural Zeolites

Zeolite	Chemical formula	Structure	Symmetry, space group
Clinoptilolite	(K₂, Na₂, Ca)₃Al₆Si₃₀O₇₂.21H₂O	HEU	Monoclinic, C2/m
Mordenite	(Na₂, Ca)₄Al₆Si₃₀O₇₂.21H₂O	MOR	Orthorhombic, Cmcm
Chabazite	(Ca, Na₂, K₂,)₂Al₄Si₈O₂₄.12H₂O	CHA	Rhombohedral or triclinic P1
Phillipsite	K₂ (Ca, Na₂)₂Al₈Si₁₀O₃₂.12H₂O	PHI	Monoclinic, P2₁/m
Scolecite	Ca₄Al₈Si₁₂O₄₀.12H₂O	NAT	Monoclinic, Cc
Stilbite	Na₂, Ca₄Al₁₀Si₂₆O₇₂.30H₂O	STI	Monoclinic, C2/m
Analcime	Na₁₆, Al₁₆Si₃₂O₄₈.16H₂O	ANA	Cubic la3d
Laumontite	Ca₄Al₈Si₁₆O₄₈.16H₂O	LAU	Monoclinic, C2/m
Erionite	(Na₂K₂MgCa_1.5)₄Al₈Si₂₈O₇₂.28H₂O	ERI	Hexagonal P6₃/mmc
Ferrierite	(Na₂, K₂, Ca, Mg)₃Al₆Si₃₀O₇₂.20H₂O	FER	Orthorhombic, Immm

The zeolites' high performance of ion exchange and adsorption due to its special structure and ion exchange capacity is related to several factors, including the framework structure, ion size and shape, charge density of the anionic framework, ionic charge, and concentration of the external electrolyte solution (Bish and Ming, 2001; Kallo, 2001; Alpat et al., 2008; Ashrafizadeh et al., 2008). Table 2 shows that chemical composition and cation exchange capacity of various natural zeolites from the world.

Table 2.

Chemical Composition and CEC of Natural Zeolites

	Chemical composition (%)
Zeolite	SiO₂	Al₂O₃	Fe₂O₃	CaO	MgO	Na₂O	K₂O	TiO₂	CEC (meq/g)	Refs.
Turkish clinoptilolite	70.90	12.4	1.21	2.54	0.83	0.28	4.46	0.089	1.6–1.8	Kallo (2001)
Iranian clinoptilolite	70.00	10.46	0.46	0.20	—	2.86	4.92	0.02	1.2	Alpat et al. (2008)
Cuban clinoptilolite	62.36	13.14	1.63	2.72	1.22	3.99	1.20	—	—	Ashrafizadeh (2008)
Brazilian clinoptilolite	67.82	14.96	0.42	1.87	0.18	0.32	4.47	0.07	2.29	Cabrera et al. (2005)
Italian phillipsite chabazite	56.42	15.80	4.08	2.42	0.86	2.35	8.14	0.004	2.12	Campos et al. (2007)
Turkish clinoptilolite	69.72	11.74	1.21	2.30	0.31	0.76	4.14	—	1.84	Capasso et al. (2005)
Chinese clinoptilolite	65.52	9.89	1.04	3.17	0.61	2.31	0.88	0.21	1.03	Capasso et al. (2007)
Chilean clinoptilolite + mordenite	67.00	13.00	2.00	3.20	0.69	2.60	0.45	0.20	2.05	Du et al. (2005)
Croatian clinoptilolite	64.93	13.39	2.07	2.00	1.08	2.40	1.30	—	1.45	Erdem et al. (2004)
Iranian clinoptilolite + mordenite	66.50	11.81	1.30	3.11	0.72	2.01	3.12	0.21	1.20	Farkas et al. (2005)
Turkish clinoptilolite	64.99	9.99	3.99	3.51	1.01	0.18	1.95	—	1.84	Ghiaci et al. (2004a,b)
Chinese clinoptilolite	68.27	7.48	1.95	2.61	1.87	0.68	1.69	—	−1.2	Gunay (2007)
Turkish clinoptilolite	70.00	14.00	0.75	2.50	1.15	0.20	2.30	0.05	1.65	Ji et al. (2007)
Chinese clinoptilolite	69.50	11.05	0.08	2.95	0.13	2.95	1.13	0.14	1.03	Karadag et al. (2007a,b,c)
Ukrainian clinoptilolite	67.29	12.32	1.26	3.01	0.29	0.66	2.76	0.26	0.64	Lei et al. (2008)
Ukrainian clinoptilolite	64.56	12.02	0.95	3.58	0.68	0.94	2.03	0.23	1.63	Korkuna et al. (2006)
Slovakian clinoptilolite	67.16	12.30	2.30	2.91	1.10	0.66	2.28	0.17	1.17	Pilchowski and Chmielewská (2003)
Croatian clinoptilolite	55.80	13.32	1.30	5.75	0.70	3.90	2.35	—	1.45	Rozic et al. (2000)
Ukrainian clinoptilolite	66.70	12.30	1.05	2.10	1.07	2.06	2.96	—	0.64	Sprynskyy et al. (2005)
Australian clinoptilolite	68.26	12.99	1.37	2.09	0.83	0.64	4.11	0.23	1.20	Wang and Zhu (2006)

CEC, cation exchange capacity.

Modified zeolite

Natural zeolite is very attractive for wide applications due to its low cost and availability. Good performance of adsorption and cation exchange capacity depend on chemical/structural makeup of the zeolite, including Si/Al ratio, cation type, number, and location, which can be changed by several chemical treatments to improve the property of hydrophilicity/hydrophobicity for various ion or organic adsorption. The modification of zeolite was mainly carried out by the methods of simple acid/base treatment and surfactant modification. Simple acid washing can remove the impurity that blocks the pores, thus the removal rate of cations in wastewater is increased because the increased size of pore results in the bigger and more cations entering the pore. Some researchers investigated natural zeolite origin from different regions treated with HCl solution and found that ion exchange with H⁺ had an important effect on the microporosity and specific surface area of zeolites. The H-form zeolite possesses high ion-exchange capacity of metal ions. Another zeolite modification method is to use organic surfactants to change its surface property, which can extend the application of zeolites in wastewater treatment. The most frequently used modifying agents are quaternary amines such as HDTMA, CTMA, ODMBA, CPD, BDTDA, and SDBAC, forming a bilayer-like structure on the zeolite surface (Misaelides, 2011), which can sorb anionic species and nonpolar organics. The cation size of modifying agents is too large to enter the inner channel so it will not influence the chemical structure of zeolite, therefore surfactant modification zeolite can not only sorb anionic species but also exchange with metal cations. The cation exchange capacity (CEC) and effective cation exchange capacity (ECEC) of some modified zeolites are listed in Table 3.

Table 3.

CEC and ECEC of Selected Modified Zeolites

Zeolite	Modified method	CEC (meq/100 g)	ECEC (meq/100 g)	Refs.
Clinoptilolite zeolite	HDTMA		15	Haggerty and Bowman (1994)
Natural zeolites	HDTMA		7–9	Wingenfelder and Furrer (2006)
Clinoptilolite zeolite	HTDMA		11.45	Szala et al. (2015)
Na-P1 zeolite	HTDMA		24.4	Szala et al. (2015)
Chilean natural zeolite	CTAB	1.28	0.11	Taffarel and Rubio (2010)
Alumina	Sodium dodecyl benzenesulfonate	19.8		Fu et al. (1996)
Granite sand	SDS	1.3		Khan and Zareen (2006
Montmorillonite	SDS	48.3		Sánchez-Martín et al. (2008)
Illite	SDS	90.1		Sánchez-Martín et al. (2008)
Muscovite	SDS	24.8		Sánchez-Martín et al. (2008
Kaolinite	SDS	87		Sánchez-Martín et al. (2008)
Sepiolite	SDS	66.2		Sánchez-Martín et al. (2008)
Palygorskite	SDS	44.2		Sánchez-Martín et al. (2008)

ECEC, effective cation exchange capacity.

Synthetic zeolite

Principal raw materials with silica and alumina used to manufacture zeolites are the most abundant natural mineral components on earth. Clay minerals with their high contents of silicon and aluminum can easily dissolve and form zeolites under alkaline conditions and have been used frequently for zeolite synthesis. A variety of zeolites (A, X, N, P, etc.) has been synthesized using kaolin as an aluminosilicate source. Another source for synthesizing zeolite is from waste materials. Coal fly ash (CFA) containing significant amount of crystalline and amorphous aluminosilicate is another important raw material that could be utilized for zeolite production. More than 15 types of zeolites (NaA, NaX, NaY, NaP1, Kchabazite, Linde F, etc.) could be synthesized from CFA, and the type of zeolite depends on chemical and mineralogical composition of the CFA used. Some wastes, including rice husk ash, oil shale ash, and municipal solid waste incineration ash, are used to prepare zeolites (NaX, NaP1, ZSM-5, ZSM-48, etc.). Several other industrial wastes such as cupola slag and exhausted fluid cracking catalysts used for the synthesis of valuable zeolites (ZSM-5, NaA, NaX) have been also considered to be technically feasible and an environmentally appropriate alternative disposal. In addition, some municipal solid wastes such as nonrecyclable glass and thin-walled aluminum scrap (i.e. Al-foils and cans) also could be utilized as Si- and Al-sources in zeolite synthesis. The CEC of some synthetic zeolites are listed in Table 4.

Table 4.

CEC of Selected Synthetic Zeolites

Zeolite	Synthesized method	CEC (meq/g)	Refs.
NaP1	Obtained from CFA	4.5	Panayotova (2000)
NaA	Obtained from CFA	4.4	Panayotova (2000)
NaP1	Direct HT treatment of CFA	2.4	Chandra Rao et al. (2006)
NaX	Obtained from CFA	≈5	Erdem et al. (2004)
NaA + NaX	Obtained from Si-Al extracts from fused CFA	4.6	Koukouzas et al. (2010)
NaX	Room temperature synthesis	2.5	Derkowski et al. (2007)
NaA/NaP	Obtained from MSWIA	1.09	Sallam (2006)
Blend of NaA and K-A	Direct HT treatment of MSWIA	1.1	Bekta and Kara (2004)
NaP1	HT treatment of OSA	1.66	Shawabkeh et al. (2004)
NaA	Obtained from RHA	5.72	Foletto et al. (2009)
NaX	Obtained from RHA	4.61	Katsuki and Komarneni (2009
ZSM-5	From industrial wastes	2.07	Anuwattana and Khummongkol (2009)

CFA, coal fly ash; HT, hydrothermal treatment; MSWIA, Municipal Solid Waste Incineration Ash; RHA, rice husk ash.

Application for Heavy Metals Removal

Generally, the metals with density of over 5 g/cm³ are defined as heavy metals. A large number of elements fall into this category, but the ones of relevance in the environmental context are Cd, Cr, Cu, Ni, Zn, Pb, and Hg (Barakat, 2011). Heavy metals are dangerous and hazardous to human health, including reduced growth and development, cancer, organ damage, nervous system damage, and in extreme cases, death. Industrial wastewater streams containing heavy metals are produced from different industries. The conventional processes for removing heavy metals include chemical precipitation, flotation, adsorption, ion exchange, and electrochemical deposition. Natural zeolites as adsorbent of heavy metals gain great interest due to their valuable ion-exchange capability.

Heavy metal removal comparison by zeolites

Immobilization of heavy metals is quite a complicated process, and its removal efficiency is related to the types of adsorbent. Many scientific articles have been devoted on the removal of heavy metals from natural or industrial water in the past 20 years using natural and synthetic zeolites as adsorbent. Metal sorption ration depends on the ratio of zeolite and wastewater (S/L), temperature, contact time, initial concentration of metal ions, and solution pH. The optimal adsorption test conditions of main mental ions, including Cr³⁺, Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, and Co²⁺, are summarized using different zeolites as adsorbents.

Removal of Cr³⁺ by different adsorbents

For the heavy metal ion Cr³⁺, the maximum adsorption can reach 83.2 mg/g using modified zeolite, as shown in Table 5. Covarrubias et al. investigated Cr³⁺ removal using the zeolites from kaolin and natural mordenite. The sorption is only 3.5 mg/g using natural mordenite as an adsorbent and is 83.2 mg/g using the blend of NaY and NaP at the same experimental conditions (Covarrubias et al., 2006). Bosco et al. (2005) and Alvarez-Ayuso et al. (2003) used Brazilian and Greece natural zeolite adsorbents to study the removal of Cr³⁺ ion and reported that the adsorption ability of Brazilian natural zeolite is relatively low (about 3–14.5 mg/g), while Greece clinoptilolite is only 4.1 mg/g. Hui et al. (2005) and Alvarez-Ayuso et al. (2003) prepared zeolite 4A and NaP1 from coal fly ash to research heavy metal removal and stated that Cr³⁺ ion sorption is significantly improved to be 56.4 mg/g, so adsorption efficiency of the modified or synthesized zeolites are increased greatly.

Table 5.

Comparison for Cr ²⁺ Removal by Different Zeolites

Metal ion	Zeolite	Zeolite origin	T (°C)	Time (h)	Metal concentration (mg/L)	S/L ratios (g/mL)	pH	Metal sorption (mg/g)
Cr³⁺	Natural mordenite	From kaolin	25	24	500	1/200		3.5
Cr³⁺	Blend of NaX and NaA	From mordenite	25	24	500	1/200		71.1
Cr³⁺	Blend of NaY and NaP	From mordenite	25	24	500	1/200		83.2
Cr³⁺	NaP	From mordenite	25	24	500	1/200		52
Cr³⁺	Hydroxysodalite	From kaolin	25	24	500	1/200		34.7
Cr³⁺	Zeolite 4A	from CFA	25	1	50–100	1/1000	3–4	38.7–56.4
Cr³⁺	Natural scolecite	Brazil	55	1	50–250	1/60	6	3.0–14.5
Cr³⁺	Clinoptilolite	Greece	22	6	100	1/100	4	4.1
Cr³⁺	NaP1	From CFA	22	6	100	1/100	4	43.6

The missing pH value in Table 5 is not mentioned in reference.

Removal of Cd²⁺ by different adsorbents

In Table 6, the sorption of the heavy metal ion Cd²⁺ by natural and modified zeolites was investigated (Curkovi et al., 1997; Purna et al., 2006; Vinay et al., 2008; Ibrahim et al., 2010). Cd²⁺ adsorption quantity is 13.5 mg/g using Croatian natural clinoptilolite as adsorbent, when the Cd²⁺ ion concentration in waste water is 1,024 mg/L. If the metal ion content is lower than 100 mg/L in solution, the adsorption efficiency would be decreased using unmodified natural zeolite (Panayotova, 2000; Alvarez-Ayuso et al., 2003; Bosco et al., 2005). Jha et al. reported that the uptake capacity for Cd²⁺ ion of synthetic zeolites from CFA is higher to be 129.3 mg/g when initial content of Cd²⁺ ion is 500 mg/L. Zeolite NaP1 obtained from CFA showed the high sorption capacity values of 50.8 mg/g when Cd²⁺ ion content in wastewater is 100 mg/L. It was found that synthetic zeolite exhibited about 10 times greater sorption capacity for Cd²⁺ ion than natural zeolite, and while the Cd²⁺ metal sorption on natural zeolite increased with time, the effect of sorption temperature and solution pH on Cd²⁺ removal could be ignored.

Table 6.

Comparison for Cd ²⁺ Removal by Different Zeolites

Metal ion	Zeolite	Zeolite origin	T (°C)	Time (h)	Metal conc. (mg/L)	S/L ratios (g/mL)	pH	Metal sorption (mg/g)
Cd²⁺	Natural scolecite	Brazil	55	1	50–250	1/60	6	2.9–6.0
Cd²⁺	Clinoptilolite	Croatia	70	24	1024	1/100	4.5	13.5
Cd²⁺	Clinoptilolite	Greece	22	1	100	1/100	6	4.1
Cd²⁺	bentonite	Commercial	30	1.5	25	1/40	6	≈9.44
Cd²⁺	Zeolite X	From kaolin	25	0.5	20	1/125	7.5	92
Cd²⁺	Zeolite A	From kaolin	25	0.5	20	1/125	7.5	71
Cd²⁺	Na-clinoptilolite	Croatia	70	24	1024	1/100	4.5	23.6
Cd²⁺	NaP1	From CFA	22	1	100	1/100	6	50.8
Cd²⁺	NaX + activated carbon	From CFA	25	24	500	1/500		129.3

The missing pH value in Table 6 is not mentioned in reference.

Removal of Cu²⁺ by different adsorbents

From Table 7, the heavy metal ion Cu²⁺ can be adsorbed and removed by natural clinoptilolite from Greece and Bulgaria (Alvarez-Ayuso et al., 2003), but the adsorption quantity of Cu²⁺ is very low, below 5.3 mg/g (Panayotova, 2001; Erdem, 2004). Comparing to natural zeolite, modified or synthetic zeolite can improve significantly the adsorption rate of copper ion, the maximum can reach 101.7 mg/g using the blend of NaX⁺-activated carbon as adsorbent when Cu²⁺ ion concentration in solution is 500 mg/L (Jha et al., 2008). The Bulgaria natural zeolite (Panayotova, 2001) treated with NaOH, NaCl, and CH₃COONa is of relatively high sorption ratio and can be utilized for the removal of metal copper from low content waste water with 50 mg/L Cu²⁺ ion. The sorption value for Cu ion by the treated Bulgaria zeolite is about 4.8–4.9 mg/g, obviously higher compared with natural zeolite with 2.9 mg/g adsorption when the sorption conditions are the same.

Table 7.

Comparison for Cu ²⁺ Removal by Different Zeolites

Metal ion	Zeolite	Zeolite origin	T (°C)	Time (h)	Metal concentration (mg/L)	S/L ratios (g/mL)	pH	Metal sorption (mg/g)
Cu²⁺	Clinoptilolite	Greece	22	6	100	1/100	5	5.3
Cu²⁺	Clinoptilolite	Bulgaria	45	5	50	1/100	5.5–7.5	2.9
Cu²⁺	Zeolite A	From kaolin	25	0.5	20	1/125	7.5	41.6
Cu²⁺	Zeolite X	From kaolin	25	0.5	20	1/125	7.5	44.16
Cu²⁺	Zeolite 4A	From CFA	25	1	50–100	1/1000	3–4	39.8–72.0
Cu²⁺	NaP1	From CFA	22	6	100	1/100	5	50.5
Cu²⁺	NaX +-activated carbon	From CFA	25	24	500	1/500	7	101.7
Cu²⁺	NaOH modified	Bulgaria	45	5	50	1/100	5.5–7.5	4.8
Cu²⁺	CH₃COONa modified	Bulgaria	45	5	50	1/100	5.5–7.5	4.7
Cu²⁺	Na-clinoptilolite	Bulgaria	45	5	50	1/100	5.5–7.5	4.8

Removal of Pb²⁺ by different adsorbents

From Table 8, the intake capacity of natural zeolite from Croatia for the metal Pb is about 78.7 mg/g at the conditions of sorption temperature of 70°C, pH 4.5, and sorption time of 24 h, obviously higher than 10 mg/g intake capacity of Turkey zeolite (Curkovi et al., 1997; Bekta and Kara, 2004), so the structural diversity of natural zeolite is very significant for the adsorption of the metal Pb in the wastewater. After Croatia natural zeolite was treated with 2 M NaCl solution at 70°C for 24 h, the Pb sorption quantity was increased to 91.2 mg/g at the same experiment conditions. Jha et al. studied that when Pb²⁺ uptake experiments were carried out at the Pb²⁺ content range from 100 to 2,000 mg/L at 25°C for 24 h using composites of activated carbon/zeolite prepared from coal fly ash as adsorbent, its uptake capacity for Pb can reach to be 228 mg/g (Jha et al., 2008). The modified natural zeolite is favorable for Pb removal.

Table 8.

Comparison for Pb ²⁺ Removal by Different Zeolites

Metal ion	Zeolite	Zeolite origin	T (°C)	Time (h)	Metal conc. (mg/L)	S/L ratios (g/mL)	pH	Metal Sorption(mg/g)
Pb²⁺	Clinoptilolite	Croatia	70	24	100	1/100	4.5	78.7
Pb²⁺	Clinoptilolite	Turkey	25	2	10–100	1/100	2–7	10
Pb²⁺	Na-clinoptilolite	Croatia	70	24	100	1/100	4.5	91.2
Pb²⁺	NaX +-activated carbon	From CFA	25	24	1000	1/500		228
Pb²⁺	Zeolite A	From kaolin	25	0.5	20	1/250	7.5	213
Pb²⁺	Zeolite X	From kaolin	25	0.5	20	1/125	7.5	187

The missing pH value in Table 8 is not mentioned in reference.

Removal of Zn²⁺ by different adsorbents

The natural, modified, and synthesized zeolites can be utilized to remove metal Zn ion, as shown in Table 9. The sorption capacity for Zn ion of natural clinoptilolite in Greece is only 3.1 mg/g, but the synthetic zeolite from CFA is of excellent adsorption characteristic, and the Zn sorption value can reach to be 40.4 mg/g when Zn initial concentration is 100 mg/L and sorption time is 2 h (Alvarez-Ayuso et al., 2003; Hui et al., 2005).

Table 9.

Comparison for Zn ²⁺ Removal by Different Zeolites

Metal ion	Zeolite	Zeolite origin	T (°C)	Time (h)	Metal conc. (mg/L)	S/L ratios (g/mL)	pH	Metal sorption (mg/g)
Zn²⁺	Zeolite A	From kaolin	25	0.5	20	1/125	7.5	28.6
Zn²⁺	Zeolite X	From kaolin	25	0.5	20	1/125	7.5	41
Zn²⁺	Zeolite 4A	from CFA	25	2	50–100	1/1000	3–4	19.6–40.4
Zn²⁺	Clinoptilolite	Greece	22	1	100	1/100	6	3.1
Zn²⁺	NaP1	From CFA	22	1	100	1/100	6	32.6
Zn²⁺	Clinoptilolite	Turkey	25	5.5	50	1/50	6–7	22

Removal of Ni²⁺ by different adsorbents

Bosco et al. (2005) and Alvarez-Ayuso et al. (2003) investigated the natural zeolite from Brail and Greece as adsorbent used to remove metal nickel. They found that the Ni sorption capacity range is from 2.0 to 8.9 mg/g at optimal experiment conditions. Alvarez-Ayuso et al. compared metal sorption ability for nickel ions with two types of zeolite, natural clinoptilolite from Greece and NaP1 zeolite from CFA, and the results showed that synthetic NaP1 zeolite exhibited about 10 times greater sorption capacities compared with natural clinoptilolite when used in the purification of real metal electroplating wastewaters. Jha et al. (2008) also studied that the blend of NaX and activated carbon from CFA adsorbed metal Ni ion with Ni²⁺ initial content of 500 mg/L at room temperature for 24 h and found that the equilibrium intake capacity can reach to 132.1 mg/g, as shown in Table 10.

Table 10.

Comparison for Ni ²⁺ Removal by Different Zeolites

Metal ion	Zeolite	Zeolite origin	T (°C)	Time (h)	Metal concentration. (mg/L)	S/L ratios (g/mL)	pH	Metal sorption (mg/g)
Ni²⁺	Zeolite A	From kaolin	25	1	20	1/125	7.5	24.65
Ni²⁺	Zeolite X	From kaolin	25	1	20	1/125	7.5	24.89
Ni²⁺	Natural scolecite	Brazil	55	1	50–250	1/60	6	2.5–8.9
Ni²⁺	Clinoptilolite	Greece	22	1	100	1/100	6	2.0
Ni²⁺	NaP1	From CFA	22	1	100	1/100	6	20.1
Ni²⁺	Zeolite 4A	from CFA	25	1	50–100	1/1000	3–4	11.5–6.1
Ni²⁺	NaX +-activated carbon	From CFA	25	24	500	1/500		132.1

The missing pH value in Table 10 is not mentioned in reference.

Removal of Co²⁺ by different adsorbents

Comparison for Co²⁺ removal by different zeolites is shown in Table 11. The natural clinoptilolite from Turkey was used for the metal cobalt sorption (Panayotova, 2001), and the adsorption experiments can be carried out at room temperature for 5.5 h when initial Co ion concentration is 50 mg/L and solution pH is 6–7. Hui et al. discussed the influential parameters such as initial metal ions concentration, adsorbent dose, contact time, and initial pH of the solution on the adsorption process using zeolite 4A from coal fly ash as adsorbent. The Co metal sorption ranges from 5.5 to 16.8 mg/g under the optimal experiment conditions (Hui et al., 2005). Borandegi and Ejhieh (2015) got a result that the modified zeolite by glutamic acid showed good selectivity for cobalt in the presence of different multivalent cations.

Table 11.

Comparison for Co ²⁺ Removal by Different Zeolites

Metal ion	Zeolite	Zeolite origin	T (°C)	Time (h)	Metal concentration (mg/L)	S/L ratios (g/mL)	pH	Metal sorption (mg/g)
Co²⁺	Zeolite 4A	from coal flash	25	1	50–100	1/1000	3–4	5.5–16.8
Co²⁺	Natural zeolite (MCP)	From Iran	25	6	600	1/100	6	14.56
Co²⁺	Modified zeolite (MCP-GLU)	From Iran	25	6	600	1/100	6	29.38
Co²⁺	Modified zeolite (NCP)	From Iran	25	6	600	1/100	6	19.05
Co²⁺	Modified zeolite (NCP-GLU)	From Iran	25	6	600	1/100	6	41.47

Adsorption kinetics and thermodynamics

As seen from the literature review, natural, modified, and synthetic zeolites can be used for the removal of some heavy metals from wastewater. The zeolite samples from different regions show different sorption behavior in ion-exchange processes. Therefore kinetics and thermodynamics of heavy metal sorption are investigated by some researchers to determine the sorption characteristics of natural and synthetic zeolites with respect to heavy metals for exploring the applicability of these zeolites to purify real metal wastewaters. There are essentially three stages in the adsorption process by porous adsorbents: (1) solute transfer from the bulk solution to the external surface of the sorbent through a liquid boundary layer (film resistance); (2) solute transfer from the sorbent surface to the intraparticle active sites (intraparticle resistance); and (3) interactions of the solute with the available sites on both the external and internal surfaces of the sorbent (reaction resistance). One or more of the above-mentioned stages may control the rate at which the solute is adsorbed and the amount of solute that is adsorbed onto the sorbent. A pseudo-first-order equation for the sorption of liquid/solid system is based on solid capacity. It assumes that the rate of change of sorbate uptake with time is directly proportional to the difference in the saturation concentration and the amount of solid uptake with time. The Lagergren equation is the most widely used rate equation in liquid phase sorption. A pseudo-second-order equation is based on the amount of sorbed sorbate on the sorbent.

Some results are listed in Table 12. Bosco et al. (2005) show that the Lagergren pseudo-second order was the model that best described the sorption mechanism when natural scolecite from Brail was used as the adsorbent for Cr ion, and thermodynamic data indicate the spontaneity of the endothermic cation-exchange process. There was a significant enhancement in the sorption of metals at high temperature for the metals tested. The intake behavior was studied by Hui et al. (2005) and Alvarez-Ayuso et al. (2003) when Cr ion was sorbed by zeolite 4A prepared from coal fly ash. The experimental data were well fit by the pseudo-second-order kinetics model. The sorption process appeared to be practically instantaneous, and the metal amounts sorbed in the first half an hour corresponded to 100% of equilibrium sorbed amounts (Alvarez-Ayuso et al., 2003).

Table 12.

Kinetics and Thermodynamics of Zeolite Sorption

Metal ion	Zeolite	Zeolite origin	Kinetics	Thermodynamics
Cr³⁺	Natural scolecite	Brazil	Lagergren pseudo-second order	Spontaneous, endothermic, cation-exchange process
Cr³⁺	Clinoptilolite	Greece		Hydroxide precipitation
Cr³⁺	NaA	From CFA	pseudo-second order
Cr³⁺	NaP1	From CFA		Instantaneous, Hydroxide precipitation
Cd²⁺	Clinoptilolite	Greece		cation exchange
Cd²⁺	Natural scolecite	Brazil	Lagergren pseudo-second order	Spontaneous, endothermic, cation-exchange process
Cd²⁺	Natural zeolite	Kardjali	second-order kinetic
Cd²⁺	NaP1	From CFA		Instantaneous, cation exchange
Cd²⁺	Bentonite	Commercial	pseudo-second order
Cd²⁺	NaA	From kaolin	pseudo-second order
Cd²⁺	NaX +-activated carbon	From CFA	pseudo-second order
Cu²⁺	NaA	From CFA	pseudo-second order
Cu²⁺	Clinoptilolite	Greece		Hydroxide precipitation
Cu²⁺	NaP1	From CFA		Instantaneous, Hydroxide precipitation
Cu²⁺	NaX +-activated carbon	From CFA	pseudo-second order
Cu²⁺	Clinoptilolite	Bulgaria		Spontaneous, endothermic
Cu²⁺	NaOH modified	Bulgaria		Spontaneous, endothermic
Cu²⁺	CH₃COONa	Bulgaria		Spontaneous, endothermic
Cu²⁺	Na-clinoptilolite	Bulgaria		Spontaneous, endothermic
Pb²⁺	NaX +-activated carbon	From CFA	pseudo-second order
Pb²⁺	Clinoptilolite	Turkey	pseudo-second order
Zn²⁺	NaA	From CFA	pseudo-second order
Zn²⁺	NaP1	From CFA		Instantaneous, cation exchange
Zn²⁺	Bentonite	Commercial	pseudo-second order
Ni²⁺	Zeolite 4A	From CFA	pseudo-first order
Ni²⁺	Natural scolecite	Brazil	Lagergren pseudo-second order	Spontaneous, endothermic, cation-exchange process
Ni²⁺	NaP1	From CFA		Instantaneous, cation exchange
Ni²⁺	NaX +-activated carbon	From CFA	pseudo-second order
Co²⁺	NaA	From CFA	pseudo-second order

The heavy metal cadmium in solution was adsorbed by Brazilian natural scolecite (Bosco et al., 2005). Batch data were well fit with Lagergren pseudo-second order, and the sorption process was a spontaneous, endothermic cation-exchange process. Panayotova (2000) shows that kinetics data of Cd²⁺ uptake by Kardjali natural zeolite are best described by the kinetic equation for the second-order irreversible reactions. Some modified or synthetic zeolite as adsorbent was used to remove metal cadmium; the results showed that kinetics data obeyed the pseudo-second-order kinetic equation (Alvarez-Ayuso et al., 2003; Purna et al., 2006; Ibrahim et al., 2010).

From the article reviews (Panayotova, 2001; Alvarez-Ayuso et al., 2003; Hui et al., 2005; Purna et al., 2006), the batch experiments data can be depicted by the pseudo-second-order equation using natural and modified zeolites as adsorbents, and the metal copper sorption process mainly is spontaneous and endothermic.

Clinoptilolite from Turkey (Purna et al., 2006) and the composite of NaX⁺-activated carbon from CFA (Bekta and Kara, 2004) was used to sorb the metal Pb ion, the result showed that the experimental data were best fit with the pseudo-second-order model.

Hui et al. (2005) and Purna et al. (2006) studied the sorption behaviors of NaA from CFA and bentonite, and the sorption kinetics data for Zn can be described by the pseudo-second-order model.

For the metal Ni²⁺ ion sorption, some researchers found that the natural zeolite from Brail and modified zeolite from CFA can be used as adsorbents. The removal mechanism of Ni²⁺ ions using the adsorbents prepared from CFA as an adsorbent was by adsorption and ion-exchange processes, and kinetics data were fit with the pseudo-first-order kinetic model (Hui et al., 2005). Other studies about sorption kinetics of modified zeolites were given (Alvarez-Ayuso et al., 2003; Purna et al., 2006), and batch experiment data were described by the pseudo-second-order model. The sorption mechanism of Brazilian natural scolecite for nickel sorption complied with the Lagergren pseudo-second-order model, and thermodynamic data indicated the spontaneity of the endothermic cation-exchange process (Bosco et al., 2005).

Adsorption isotherms

Analysis of the isotherm data is important to develop an equation that accurately represents the results and could be used for design purposes. To investigate the sorption isotherm, equilibrium models of Dubinin–Kaganerp–Radushkevich (DKR), Langmuir, and Freundlich isotherm equations were analyzed. For the same metal sorption by the same zeolite, the adsorption data can fit with three equilibrium models. Table 13 lists the sorption isotherm of natural and modified zeolites.

Table 13.

Adsorption Isotherms

Metal ion	Zeolite	Zeolite origin	Metal removal (%)	Adsorption isotherms
Cr³⁺	Natural scolecite	Brazil	100–96	Freundlich isotherm
Cr³⁺	Clinoptilolite	Greece	>90	Langmuir model
Cr³⁺	NaA	From CFA		Langmuir model
Cr³⁺	NaP1	From CFA	>90	Langmuir model
Cd²⁺	Zeolite A	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Cd²⁺	Zeolite X	From kaolin	>99	Langmuir, Freundlich, Dubinin–Kaganerp–Radushkevich
Cd²⁺	Natural scolecite	Brazil	84–59	Freundlich isotherm
Cd²⁺	Natural zeolite	Kardjali	75–90	Freundlich model
Cd²⁺	Clinoptilolite	Greece	>90	Langmuir model
Cd²⁺	NaP1	From CFA	>90	Langmuir model
Cd²⁺	Bentonite		>70	Langmuir model
Cd²⁺	NaX +-activated carbon	From CFA		Langmuir model
Cu²⁺	Zeolite A	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Cu²⁺	Zeolite X	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Cu²⁺	Clinoptilolite	Turkey	77.96	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Cu²⁺	NaA	From CFA		Langmuir model
Cu²⁺	Clinoptilolite	Greece	>90	Langmuir model
Cu²⁺	NaP1	From CFA	>90	Langmuir model
Cu²⁺	NaX +-activated carbon	From CFA		Langmuir model
Cu²⁺	Clinoptilolite	Bulgaria	57	Langmuir model
Cu²⁺	NaOH-modified clinoptilolite	Bulgaria	95	Langmuir model
Cu²⁺	CH₃COONa-modified clinoptilolite	Bulgaria	93	Langmuir model
Cu²⁺	Na-clinoptilolite	Bulgaria	95	Langmuir model
Pb²⁺	Zeolite X	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Pb²⁺	Zeolite A	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Pb²⁺	NaX +-activated carbon	From CFA		Langmuir model
Pb²⁺	Clinoptilolite	Turkey		Langmuir model
Zn²⁺	Clinoptilolite	Turkey	45.96	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Zn²⁺	Zeolite A	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Zn²⁺	Zeolite X	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Zn²⁺	NaA	From CFA		Langmuir model
Zn²⁺	Clinoptilolite	Greece	>90	Langmuir model
Zn²⁺	NaP1	From CFA	>90	Langmuir model
Zn²⁺	Bentonite		>70	Langmuir model
Ni²⁺	Zeolite A	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer, Radushkevich
Ni²⁺	Zeolite X	From kaolin	>99	Langmuir, Freundlich, Dubinin Kaganer Radushkevich
Ni²⁺	NaA	From CFA		Langmuir model
Ni²⁺	Natural scolecite	Brazil	96–40	Freundlich isotherm
Ni²⁺	Clinoptilolite	Greece	>90	Langmuir model
Ni²⁺	NaP1	From CFA	>90	Langmuir model
Ni²⁺	NaX +-activated carbon	From CFA		Langmuir model
Co²⁺	NaA	From CFA		Langmuir model
Co²⁺	Clinoptilolite	Turkey	66.10	Langmuir, Freundlich, Dubinin Kaganer Radushkevich

Removal of Cr³⁺ by Brazilian natural zeolite, identified as scolecite, from the specific metal solutions was about 96–100%, and the adsorption isotherms fit with Freundlich models (Bosco et al., 2005). Alvarez-Ayuso et al. (2003) studied the sorption behavior of natural (clinoptilolite) and synthetic (NaP1) zeolites with respect to Cr(III) to consider its application to purify metal finishing wastewater; the removal of Cr³⁺ ion can reach over 90%. The Langmuir model was found to describe well Cr (III) sorption processes for two types of zeolites. Adsorption isotherms of metal ions for the synthetic zeolite NaA from CFA could be best modeled by the Langmuir equation (Hui et al., 2005).

In the uptake evaluation part of the study, adsorption ratios of Cd metal cations on zeolites A and X match Langmuir, Freundlich, and DKR adsorption isotherm data (Ibrahim et al., 2010). The sorption behaviors of natural zeolite from Brazilian and Kardjali can be described by Freundlich isotherm model (Panayotova, 2000; Bosco et al., 2005). The natural clinoptilolite from Greece and the synthetic zeolite from CFA were applied to remove Cr³⁺ ion from wastewater, and the obtained sorption data accorded with the Langmuir sorption model (Alvarez-Ayuso et al., 2003; Purna et al., 2006; Jha et al., 2008).

Modified zeolite from kaolin and natural zeolite from Turkey as adsorbents can remove effectively metal Cu²⁺ ion from the specified concentration solution, and adsorption equilibrium data are formulated into Langmuir, Freundlich, and Dubinin–Kaganer–Radushkevich models (Erdem et al., 2004; Ibrahim et al., 2010). Other researches about the adsorption for copper ion by natural, modified, and synthetic zeolites are also reported (Panayotova, 2001; Alvarez-Ayuso et al., 2003; Hui et al., 2005; Jha et al., 2008), and the sorption data for these zeolites well fitted with the Langmuir model.

Adsorption equilibrium measurements for Pb ion show that modified zeolites from Kaolin as adsorbent can be depicted by Langmuir, Freundlich, and Dubinin–Kaganer–Radushkevich models (Ibrahim et al., 2010). The sorption experiment data fit well with the Langmuir model when natural and synthetic zeolites are used to adsorb Pb²⁺ ion from the wastewater (Bekta and Kara, 2004; Jha et al., 2008).

45.96% heavy metal Zn ion can be removed by natural zeolite (Erdem et al., 2004), but over 90% Zinc can be adsorbed by modified or synthetic zeolite (Alvarez-Ayuso et al., 2003; Purna et al., 2006; Ibrahim et al., 2010). The adsorption equilibrium data of natural zeolite from Turkey and zeolite 4A from Kaolin can well fit with Langmuir, Freundlich, and Dubinin–Kaganer–Radushkevich (Erdem et al., 2004; Ibrahim et al., 2010), and the data of natural zeolite from Greece and zeolite 4A from CFA can be illustrated by the Langmuir model.

For the metal nickel removal, batch experimental data with zeolite A and X from Kaolin as adsorbents can be explained by three adsorption isotherm models of Langmuir, Freundlich, and Dubinin–Kaganer– Radushkevich (Ibrahim et al., 2010), and the isotherm data obtained from synthetic zeolite from CFA entirely fit with the Langmuir model. The adsorption isotherm data can be separately demonstrated by Freundlich isotherm and the Langmuir model with natural zeolite from Brazil and Greece for nickel sorption.

The clinoptilolite from Turkey was applied for sorption of cobalt ion, and the adsorption data conformed with Langmuir, Freundlich, and Dubinin–Kaganer–Radushkevich models (Erdem et al., 2004), but adsorption isotherm data can be explained with the Langmuir model with the synthetic zeolite NaA from CFA (Hui et al., 2005).

Conclusions

In this review, the character and property of some natural, modified, and synthetic zeolites are summarized. The sorption of the same heavy metal removal by different zeolites is compared. Modified and synthetic zeolites obtained from industrial or agricultural waste materials, such as CFA, have higher cation-exchange capability, which can greatly improve the sorption performance for heavy metals. According to optimal sorption conditions, the appropriate zeolite can effectively adsorb heavy metals from waste water with different initial concentrations. From the literature reviewed, the sorption kinetics of the vast majority of the zeolite can be described by the pseudo-second-order model, and that of others fit with the pseudo-first-order or second-order model. The sorption process of natural, modified, or synthetic zeolite was generally spontaneous and endothermic, and the removal mechanism of heavy metal ions was by adsorption and ion-exchange processes. Adsorption isotherms of different metal ions could be best modeled by Langmuir, Freundlich, or DKR equation. Zeolites as cost-effective adsorbent materials have great potential applications to remove heavy metals from waste water.

Footnotes

Acknowledgments

The author thanks National Natural Science Foundation (Grant No. 51504141) and Changjiang Scholars and Innovative Research Team in University (IRT13026) for providing the research grant.

Author Disclosure Statement

No competing financial interests exist.

References

Alpat

S.K.

, Ozbayrak

, Alpat

, and Akcay

(2008). The adsorption kinetics and removal of cationic dye, Toluidine Blue O, from aqueous solution with Turkish zeolite. J. Hazard. Mater., 151, 213.

Alvarez-Ayuso

, Garcia-Sanchez

, and Querol

(2003). Purification of metal electroplating waste waters using zeolites. Water Res., 37, 4855.

Anuwattana

, and Khummongkol

(2009). Conventional hydrothermal synthesis of Na-A zeolite from cupola slag and aluminum sludge. Hazard. Mater., 166, 227.

Applegate

L.E.

(1984). Membrane separation progresses. Chem. Eng., 91, 64.

Ashrafizadeh

S.N.

, Khorasani

, and Gorjiara

(2008). Ammonia removal from aqueous solutions by Iranian natural zeolite. Sep. Sci. Technol., 43, 960.

Badillo-Almaraz

, Trocellier

, and Davila-Rangel

(2003). The removal of heavy metal cations by natural zeolites. Nucl. Instrum. Methods Phys. Res. B., 210, 424.

Barakat

M.A.

(2011). New trends in removing heavy metals from industrial wastewater. Arab. J. Chem., 4, 361.

Barer

R.M.

(1987). Zeolites and Clay Minerals as Sorbent and Molecular Sieves. New York: Academic Press.

Bekta

, and Kara

(2004). Removal of lead from aqueous solutions by natural clinoptilolite: Equilibrium and kinetic studies. Sep. Purif. Technol., 39, 189.

10.

Benkli

Y.E.

, Can

M.F.

, Turan

, and Celik

M.S.

(2005). Modification of organo-zeolite surface for the removal of reactive azo dyes in fixed-bed reactors. Water Res., 39, 487.

11.

Bish

D.L.

, and Ming

D.W.

(2001). Applications of natural zeolites in water and wastewater treatment, natural zeolites: Occurrence, properties, applications. Rev. Mineral. Geochem., 45, 521.

12.

Borandegi

, and Ejhieh

A.N.

(2015). Enhanced removal efficiency of clinoptilolite nano-particles toward Co(II) from aqueous solution by modification with glutamic acid, Colloids Surf. A., 479, 35.

13.

Bosco

S.M.D.

, Jimenez

R.S.

, and Carvalh

W.A.

(2005). Removal of toxic metals from wastewater by Brazilian natural scolecite. J. Colloid Interf. Sci., 281, 424.

14.

Bouffard

S.C.

, and Duff

S.J.B.

(2000). Uptake of dehydroabietic acid using organically-tailored zeolites. Water Res., 34, 2469.

15.

Bowman

R.S.

(2003). Applications of surfactant-modified zeolites to environmental remediation. Micropor. Mesopor. Mater., 61, 43.

16.

Breck

D.W.

(1964). Crystalline molecular sieves. J. Chem. Edu., 41, 678.

17.

Breck

D.W.

(1974). Zeolite Molecular Sieves. New York: Wiley.

18.

Cabrera

, Gabaldon

, and Marzal

(2005). Sorption characteristics of heavy metal ions by a natural zeolite. J. Chem. Technol. Biotechnol., 80, 477.

19.

Campos

, Morais

L.C.

, and Buchler

P.M.

(2007). Removal of chromate from aqueous solution using treated natural zeolite. Environ. Geol., 52, 1521.

20.

Capasso

, Coppola

, Iovino

, Salvestrini

, and Colella

(2007). Sorption of humic acids on zeolitic tuffs. Micropor. Mesopor. Mater., 105, 324.

21.

Capasso

, Salvestrini

, Coppola

, Buondonno

, and Colella

(2005). Sorption of humic acid on zeolitic tuff: A preliminary investigation. Appl. Clay Sci., 28, 159.

22.

Chandra Rao

P.G.

, Satyaveni

, Ramesh

, Seshaiah

, Murthyb

K.S.N.

, and Choudary

N.V.

(2006). Sorption of cadmium and zinc from aqueous solutions by zeolite 4A, zeolite 13X and bentonite. J. Environ. Manage., 81, 265.

23.

Cheng

X.W.

, Zhong

, Wang

, Guo

, Huang

, and Long

Y.C.

(2005). Studies on modification and structural ultra-stabilization of natural STI zeolite. Micropor. Mesopor. Mater., 83, 233.

24.

Christidis

G.E.

, Moraetis

, Keheyan

, Akhalbedashvili

, Kekelidze

, Gevorkyan

, Yeritsyan

, and Sargsyan

(2003). Chemical and thermal modification of natural HEU-type zeolitic materials from Armenia, Georgia and Greece. Appl. Clay Sci., 24, 79.

25.

Clement

R.E.

, Eiceman

G.A.

, and Koester

C.J.

(1995). Environmental-analysis. Anal. Chem., 67, R221.

26.

Cortes-Martinez

, Martinez-Miranda

, Solache-Rios

, and Garcia-Sosa

(2004). Evaluation of natural and surfactant-modified zeolites in the removal of cadmium from aqueous solutions. Sep. Sci. Technol., 39, 2711.

27.

Cortes-Martinez

, Solache-Rios

, Martinez-Miranda

, and Alfaro-Cuevas

(2007). Sorption behavior of 4-chlorophenol from aqueous solutions by a surfactant-modified Mexican zeolitic rock in batch and fixed bed systems. Water Air Soil Pollut., 183, 85.

28.

Covarrubias

, Garcıa

, Arriagada

, Yánez

, and Garland

M.T.

(2006). Cr(III) exchange on zeolites obtained from kaolin and natural mordenite. Micropor Mesopor Mater., 88, 220.

29.

Curkovi

, Cerjan-stefanovic

, and Filipan

(1997). Metal ion exchange by natural and modified zeolites. Water Res., 31, 1379.

30.

Dakovic

, Matijasevic

, Rottinghaus

G.E.

, Dondur

, Pietrass

, and Clewett

C.F.M.

(2007a). Adsorption of zearalenone by organomodified natural zeolitic tuff. J. Colloid Interf. Sci., 311, 8.

31.

Dakovic

, Tomasevic-Canovic

, Rottinghaus

, Dondur

, and Masic

(2003). Adsorption of ochratoxin on octadecyldimethyl benzyl ammonium mexchanged-clinoptilolite-heulandite tuff. Colloids Surf. B., 30, 157.

32.

Dakovic

, Tomasevic-Canovic

, Rottinghaus

G.E.

, Matijasevic

, and Sekulic

(2007b). Fumonisin B-1 adsorption to octadecyldimethylbenzyl ammonium-modified clinoptilolite-rich zeolitic tuff. Micropor. Mesopor. Mater., 105, 285.

33.

Derkowski

, Franus

, Nowicka

, and Czímerová

(2007). Textural properties vs. CEC and EGME retention of Na-X zeolite prepared from fly ash at room temperature. Int. J. Miner. Process., 82, 57.

34.

, Liu

, Cao

, and Wang

(2005). Ammonia removal from aqueous solution using natural Chinese clinoptilolite. Sep. Purif. Technol., 44, 229.

35.

Erdem

, Karapinar

, and Donat

(2004). The removal of heavy metal cations by natural zeolites. J. Colloid Interf. Sci., 280, 309.

36.

Farkas

, Rozic

, and Barbaric-Mikocevic

(2005). Ammonium exchange in leakage waters of waste dumps using natural zeolite from the Krapina region, Croatia. J Hazard. Mater., 117, 25.

37.

Foletto

E.L.

, Castoldi

M.M.

, Oliveira

L.H.

, Hoffmann

, and Jahn

S.L.

(2009). Conversion of rice husk ash into zeolitic materials. Lat. Am. Appl. Res., 39, 75.

38.

, Somasundaran

, and Maltesh

(1996). Hydrocarbon and alcohol effects on sulfonate adsorption on alumina. Colloids Surf. A., 112, 55.

39.

Geselbarcht

(1996). Micro filtration/reverse osmosis pilot trials for livermore, California, advanced water reclamation. Water Reuse Conference Proceedings. American Water Works Association (AWWA), p. 187.

40.

Ghiaci

, Abbaspur

, Kia

, and Seyedeyn-Azad

(2004a). Equilibrium isotherm studies for the sorption of benzene, toluene, and phenol onto organo-zeolites and as-synthesized MCM-41. Sep. Purif. Technol., 40, 217.

41.

Ghiaci

, Kia

, Abbaspur

, and Seyedeyn-Azad

(2004b). Adsorption of chromate by surfactant-modified zeolites and MCM-41 molecular sieve. Sep. Purif. Technol., 40, 285.

42.

Gunay

(2007). Application of nonlinear regression analysis for ammonium exchange by natural (Bigadic) clinoptilolite. J. Hazard. Mater., 148, 708.

43.

Haggerty

G.M.

, and Bowman

R.S.

(1994). Sorption of chromate and other inorganic anions by organo-zeolite. Environ. Sci. Technol., 28, 452.

44.

Hernandez-Beltran

N.A.

, Olguin

M.T.

, and Rosas-Aburto

(2008). Effect of acid phosphate media on the stability of clinoptilolite-rich tuff. J. Incl. Phenomena Macrocyclic Chem., 61, 93.

45.

Huang

C.P.

, and Blankenship

D.W.

(1984). The removal of mercury(II) from dilute aqueous solution by activated carbon. Water Res., 18, 37.

46.

Hui

K.S.

, Chao

C.Y.H.

, and Kot

S.C.

(2005). Removal of mixed heavy metal ions in wastewater by zeolite 4A and residual products from recycled coal fly ash. J. Hazard. Mater. B., 127, 89.

47.

Ibrahim

H.S.

, Jamil

T.S.

, and Hegazy

E.Z.

(2010). Application of zeolite prepared from Egyptian kaolin for the removal of heavy metals: II. Isotherm models. J. Hazard. Mater., 182, 842.

48.

Inglezakis

V.J.

, Loizidou

M.D.

, and Grigoropoulou

H.P.

(2002). Equilibrium and kinetic ions exchange studies of Pb²⁺, Cd²⁺, Fe³⁺ and Cu²⁺ on natural clinoptilolite. Water Res., 36, 2784.

49.

Inglezakis

V.J.

, Loizidou

M.D.

, and Grigoropoulou

H.P.

(2003). Ion exchange of Pb²⁺, Cu²⁺, Fe³⁺, and Cr³⁺ on natural clinoptilolite: Selectivity determination and influence of acidity on metal uptake. J. Colloid Interf. Sci., 26, 49.

50.

Jha

V.K.

, Matsuda

, and Miyake

(2008). Sorption properties of the activated carbon-zeolite composite prepared from coal fly ash for Ni²⁺, Cu²⁺, Cd²⁺ and Pb²⁺. J. Hazard. Mater., 160, 148.

51.

Z.Y.

, Yuan

J.S.

, and Li

X.G.

(2007). Removal of ammonium from wastewater using calcium form clinoptilolite. J. Hazard. Mater., 141, 483.

52.

Kallo

(2001). Applications of natural zeolites in water and wastewater treatment. Rev. Mineral. Geochem., 45, 519.

53.

Karadag

, Akgul

, Tok

, Erturk

, Kaya

M.A.

, and Turan

(2007a). Basic and reactive dye removal using natural and modified zeolites. J. Chem. Eng. Data., 52, 2436.

54.

Karadag

, Koc

, Turan

, and Ozturk

(2007b). A comparative study of linear and non-linear regression analysis for ammonium exchange by clinoptilolite zeolite. J. Hazard. Mater., 144, 432.

55.

Karadag

, Turan

, Akgul

, Tok

, and Faki

(2007c). Adsorption equilibrium and kinetics of reactive black 5 and reactive red 239 in aqueous solution onto surfactant-modified zeolite. J. Chem. Eng. Data., 52, 1615.

56.

Katsuki

, and Komarneni

(2009). Synthesis of Na-A and/or Na-X zeolite/porous carbon composites from carbonized rice husk. J. Solid State Chem., 182, 1749.

57.

Khan

M.N.

, and Zareen

(2006). Sand sorption process for the removal of sodium dodecyl sulfate (anionic surfactant) from water. J. Hazard. Mater., 133, 269.

58.

Korkuna

, Leboda

, Skubiszewska-Zieba

, Vrublevs'ka

, Gun'ko

V.M.

, and Ryczkovski

(2006). Structural and physicochemical properties of natural zeolites: Clinoptilolite and mordenite. Micropor. Mesopor. Mater., 87, 243.

59.

Koukouzas

, Vasilatos

, Itskos

, Mitsis

, and Moutsatsou

(2010). Removal of heavy metals from wastewater using CFB-coal fly ash zeolitic materials. J. Hazard. Mater., 173, 581.

60.

Kuleyin

(2007). Removal of phenol and 4-chlorophenol by surfactant-modified natural zeolite. J. Hazard. Mater., 144, 307.

61.

Lei

L.C.

, Li

X.J.

, and Zhang

X.W.

(2008). Ammonium removal from aqueous solutions using microwave-treated natural Chinese zeolite. Sep. Purif. Technol., 58, 359.

62.

Lemic

, Kovacevic

, Tomasevic-Canovic

, Kovacevic

, Stanic

, and Pfend

(2006). Removal of atrazine, lindane and diazinone from water by organo-zeolites. Water Res., 40, 1079.

63.

Lemic

, Tomasevic-Canovic

, Adamovic

, Kovacevic

, and Milicevic

(2007). Competitive adsorption of polycyclic aromatic hydrocarbons on organo-zeolites. Micropor. Mesopor. Mater., 105, 317.

64.

Lin

S.H.

, and Juang

R.S.

(2002). Heavy metal removal from water by sorption using surfactant-modifed montmorillonite. J. Hazard. Mater., 92, 315.

65.

Mier

M.V.

, Callejas

R.L.

, Gehr

, Cisneros

B.E.J.

, and Alvarez

P.J.J.

(2001). Heavy metal removal with Mexican clinoptilolite: Multi-component ionic exchange. Water Res., 35, 373.

66.

Ming

D.W.

, and Mumpton

F.A.

(1989). Zeolites in soil. In Dixon

J.B.

and Weed

S.B.

, Eds., Minerals in Soil Environments, 2nd ed. Madison, WI: Soil Science Society of America, p. 873.

67.

Misaelides

(2011). Application of natural zeolites in environmental remediation: A short review. Microporous and Mesoporous Materials. 144, 15.

68.

Misaelides

, Zamboulis

, Sarridis

, Warchol

, and Godelitsas

(2008). Chromium(VI) uptake by polyhexamethylene-guanidine-modified natural zeolitic materials. Micropor. Mesopor. Mater., 108, 162.

69.

Moore

J.W.

, and Ramamoorthy

(1984) Heavy Metals in Natural Waters: Applied Monitoring and Impact Assessment. New York: Springer-Verlag.

70.

Newsom

J.M.

(1986). The zeolite cage structure. Science. 231, 1093.

71.

Noroozifar

, Khorasani-Motlagh

, Gorgij

M.N.

, and Naderpour

H.R.

(2008). Adsorption behavior of Cr(VI) on modified natural zeolite by a new bolaform N,N,N,N,N,N-hexamethyl-1,9-nonanediammonium dibromide reagent. J. Hazard. Mater., 155, 566.

72.

Ozaydin

, Kocar

, and Hepbasli

(2006). Natural zeolites in energy applications. Energ. Source. Part A., 28, 1425.

73.

Panayotova

M.I.

(2000). Use of zeolite for cadmium removal from wastewater. J. Environ. Sci.Health., A35, 1591.

74.

Panayotova

M.I.

(2001). Kinetics and thermodynamics of coppers ions removal from wastewater by use of zeolite, Waste Manage., 21, 671.

75.

Pilchowski

, and Chmielewská

(2003). Adsorptive separation of 1,2-dichloroethane from model wastewater by natural clinoptilolite. Acta Hydrochim. Hydrobiol., 3, 249.

76.

Rozic

, Cerjan-Stefanovic

, Kurajica

, Vancina

, and Hodzic

(2000). Ammoniacal nitrogen removal from water by treatment with clays and zeolites. Water Res., 34, 3675.

77.

Sallam

(2006). Zeolite synthesis from municipal solid waste ash using fusion and hydrothermal treatment. PhD Thesis, University of South Florida. Available at http://scholarcommons.usf.edu/etd/2688 (accessed February 19, 2016).

78.

Sánchez-Martín

M.J.

, Dorado

M.C.

, del Hoyo

, and Rodríguez-Cruz

M.S.

(2008). Influence of clay mineral structure and surfactant nature on the adsorption capacity of surfactants by clays. J. Hazard Mater., 150, 115.

79.

Schnoor

J.L.

(1997). Phytoremediation, TE-97-01, Ground-Water Remediation. Pittsburgh: Technologies Analysis Center, p. 43.

80.

Sengupta

A.K.

, and Clifford

(1986). Important process variables in chromate ion-exchange. Environ. Sci. Technol., 20, 149.

81.

Shawabkeh

, Al-Harahsheh

, Hami

, and Khlaifat

(2004) Conversion of oil shale ash into zeolite for cadmium and lead removal from wastewater. Fuel. 83, 98.

82.

Sprynskyy

, Lebedynets

, Terzyk

A.P.

, Kowalczyk

, Namiesnik

, and Buszewski

(2005). Ammonium sorption from aqueous solutions by the natural zeolite Transcarpathian clinoptilolite studied under dynamic conditions. J. Colloid Interf. Sci., 284, 408.

83.

Sullivan

E.J.

, Carey

J.W.

, and Bowman

R.S.

(1998). Thermodynamics of cationic surfactant sorption onto natural clinoptilolite. J. Colloid Interf. Sci., 206, 369.

84.

Szala

, Bajda

, and Jelen

(2015). Removal of chromium(VI) from aqueous solutions using zeolites modified with HDTMA and ODTMA surfactants. Clay Miner. 50, 103.

85.

Taffarel

S.R.

, and Rubio

(2010). Adsorption of sodium dodecyl benzene sulfonate from aqueous solution using a modified natural zeolite with CTAB. Miner. Eng., 23, 771.

86.

Tsitsishvili

G.V.

, Andronikashvili

T.G.

, Kirov

G.N.

, and Filizova

L.D.

(1992). Natural Zeolites. New York: E. Horwood.

87.

Wang

S.B.

, and Peng

Y.L.

(2010). Natural zeolites as effective adsorbents in water and wastewater treatment. Chem. Eng. J., 156, 11.

88.

Wang

S.B.

, and Zhu

Z.H.

(2006). Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution. J. Hazard. Mater., 136, 946.

89.

Wingenfelder

, and Furrer

(2006). Rainer Schulin sorption of antimonate by HDTMA-modified zeolite. Micropor. Mesopor. Mater., 95, 265.

90.

Zamzow

M.J.

, Eichbaum

B.R.

, Sandgren

K.R.

, and Shanks

D.E.

(1990). Removal of heavy metal and other cations from wastewater using zeolites. Sep. Sci. Technol., 25, 1555.

Review of the Natural,Modified,and Synthetic Zeolites for Heavy Metals Removal from Wastewater

Abstract

Abstract

Introduction

Properties and Character of Natural Zeolite and Modified Zeolite

Natural zeolite

Modified zeolite

Synthetic zeolite

Application for Heavy Metals Removal

Heavy metal removal comparison by zeolites

Removal of Cr3+ by different adsorbents

Removal of Cd2+ by different adsorbents

Removal of Cu2+ by different adsorbents

Removal of Pb2+ by different adsorbents

Removal of Zn2+ by different adsorbents

Removal of Ni2+ by different adsorbents

Removal of Co2+ by different adsorbents

Adsorption kinetics and thermodynamics

Adsorption isotherms

Conclusions

Footnotes

Acknowledgments

Author Disclosure Statement

References

Removal of Cr³⁺ by different adsorbents

Removal of Cd²⁺ by different adsorbents

Removal of Cu²⁺ by different adsorbents

Removal of Pb²⁺ by different adsorbents

Removal of Zn²⁺ by different adsorbents

Removal of Ni²⁺ by different adsorbents

Removal of Co²⁺ by different adsorbents