Characteristics of Heavy Metals Adsorption Cu, Pb and Cd Using Synthetics Zeolite Zsm-5

It is generally known that zeolite has potential for heavy metal adsorption. The objectives of this study were to synthesize and characterize zeolite ZSM-5 and to figure out the adsorption capacity of zeolite ZSM-5 for heavy metals of Cu2+, Pb2+ and Cd2+. Characterization of zeolite ZSM-5 included some variables i.e. crystal structure (XRD), morphology (SEM), specific surface area and total pore volume (N2 physisorption). Adsorption capacity of zeolite ZSM-5 was analysed using a batch system with heavy metals of Cu2+, Pb2+ and Cd2+ in various concentrations (50, 100, 150, 200 and 250 ppm) with contact times 30, 60, 90, 120 and 250 minutes. Adsorption data was calculated by Langmuir and Freundlich isotherm. The results showed that the maximum adsorption capacity of zeolite ZSM-5 against heavy metals of Pb2+, Cu2+, and Cd2+, were 74.07, 69.93 and 60.24 mg g-1, respectively. These indicated that synthetic zeolite ZSM-5 had potential to adsorb heavy metals. The results also suggested that the adsorption capacity was affected by the pore size of zeolite, negative charge of zeolite, diameter of hydrated and electronegative ion.


INTRODUCTION
Heavy metal pollution is a phenomenon that cannot be detached from daily life. The high level of metal pollution by heavy metal such as Cu, Pb, Cd, Hg, Zn, and Ni is a part of the most important global issue. These metals may become a problem if they get into ecological system and the human health. Therefore, we need to cope with heavy metal pollution into the environment system in order to prevent those heavy metals become pollutants.
There were several processes reported to reduce the heavy metals pollution, for instances, adsorption, precipitation, filtering, osmosis, and electrolysis (Buasri et al. 2008 andMinceva et al. 2007). Among the adsorption processes, adsorption using zeolite was an alternative method to be used. Zeolite is a silicate alumina crystal with three dimension framework structure formed by tetrahedral silicate [SiO 4 ] 4-and octahedral alumina [AlO4] 5-that bundled by oxygen atom. Silicon atom is surrounded by 4 oxygen atoms to construct networks with regular pattern. In some spots in these networks, silicon atom is substituted by aluminum, having acoordinatation number with only 3 oxygen atoms. The existence of aluminum atom causes zeolite to have a negative charge that can be used as an ion exchange site with heavy metals. In addition, zeolite is a porous material. Zeolite shows some important characteristics such as ion adsorption selectivity, molecule an sieve, and active catalyst.
The researches about heavy metal adsorption using zeolite have been already done, but most researches show the use of natural zeolite like clinoptilolite (Buasri et al. 2008;Erdem et al. 2004;Inglezakis et al. 2004;Cincotti et al. 2006;Sprynskyy et al. 2006), phillip site natural zeolite (Al-Haj-Ali et al. 2004) and scolecite natural zeolite (Bosso et al. 2002). Natural zeolite has often been used as a heavy metal absorbent. However, the ability of this substance was relatively low. At present, there is a new technology to produce synthetic zeolits with higher quality (better characteristic and ability) than natural zeolits. The structure of synthetic zeolite can be modified with the necessity and uniformity of the structure. Said and Widiastuti (2008) found that synthetic zeolits can adsorb 14.54 mg g -1 of Cu 2+ with concentration 50 mg L -1 at pH 8 for 360 minutes. Gaurav et al. (2013) explained that synthetic zeolite made from fly ash can absorb 13.35 mg g -1 of Cd using 2 g of zeolite in concentration 100 mg L -1 at pH 6 and temperature 40 o C. Alvarez-Ayuso et al. (2003) found metal adsorption using synthetic zeolite NaP1 with 100 mg L -1 metal concentration can adsorb 43.6 mg g -1 ºf Cr, 20.1 mg g -1 of Ni, 32.6 mg g -1 of Zn and 50.5 mg g -1 of Cu. The research of Silva et al. (2012) on synthetic ZSM-5 zeolite as heavy metal ion exchanger for Cr 6+ showed that the efficiency of the heavy metal ion decreases to 78.50% with 11.90 mg g -1 adsorption capacity. ZSM-5 zeolite modified with Na and H 3 PO 4 can also adsorb Ni 2+ as much as 28.09 mg g -1 and 39.96 mg g -1 , respectively (Panneerselvam et al. 2009).
ZSM-5 zeolite is one of the synthetic zeolite. ZSM-5 zeolite has one of MFI framework shape. It has 3 dimension channel and 5.1-5.5 Å of micro pore size. Nowadays, ZSM-5 is commonly used as a catalyst and also used in dewaxing reaction, methanol conversion to gasoline, methanol to olefin, hydrocracking, benzene alkylation, NOx reduction and methane partial oxidation (Cejka and van Bekkum 2005). ZSM-5 zeolite has much potential to be developed and used as the material in heavy metal adsorption. In addition, ZSM-5 zeolite has micro pore similar to the size of heavy metal ions Cu 2+ , Pb 2+ , and Cd 2+ . Only few information explained the use of ZSM-5 zeolite as heavy metal absorbent. The objectives of this study were to (1) synthetize and characterize ZSM-5 zeolite and (2) to study the adsorption and the selectivity of ZSM-5 synthetic zeolite to heavy metals of Cu 2+ , Pb 2+ , and Cd 2+ .

Synthesize of Zeolite ZSM-5
To synthesize zeolite ZSM-5 low temperature method was used. The synthesis was started by dissolving 2.289 g of TPABr in 6.405 g of distilled water as first solution. Then, it was proceed with the second solution that consisted of 1.697 g of NaOH 50% and 0.082 g of NaAlO 2 . Both solutions were mixed in a polypropylene bottle and shaked for about 2 hours (homogenous), by adding 19.50 g of colloidal silica 40%. After a homogenous solutions were produced, it was allowed to stand overnight for aging process at room temperature. After that, the solution was put into an oven at 90 o C for 96 hours. The precipitatote was filtered using Buchner and dried in an oven at 105 o C for about 24 hours.

Characteristics of Synthesized Zeolite ZSM-5
Characteristics of zeolite ZSM-5 were various i.e. crystal structure by XRD Philips PW1830, morphology using SEM Zeiss EVO50 and the zeolite ZSM-5 specific surface area and total pore volume, and it were measured using the multi-point-N2-BET method on the Quantachrome Nova 2200e.

Adsorption of Heavy Metals Using Zeolite ZSM-5
Adsorption experiments were carried out with a batch system using 0.015 g of zeolite ZSM-5 in a 20 ml of solution containing heavy metals. Variation in the concentration of heavy metals were 50-250 ppm and 30-150 minutes of contact time. The concentration of heavy metals in the solution was determined before and after contacting with zeolite ZSM-5 and measured using AAS models GBC Avanta. In order to obtain the adsorption capacity, the amount of ions adsorbed per unit mass of adsorbent (in milligrams of metal ions per gram of adsorbent) was evaluated as follows: Where Ci (ppm) = initial metal concentration, Cf (ppm) = final metal concentration, V (L) = volume of reacting solution, W (g) = amount of zeolite in solution.
Two of the most commonly used isotherm theories have been adopted for interpreting adsorption data, namely the Freundlich and Langmuir equilibrium isotherm theories.
Langmuir q = a.bC/1 + b.c Linier form where c (ppm) was the amount of a metal adsorbed per mass unit of sorbent at equilibrium, q (mg g -1 ) is the amount of adsorbate at complete monolayer and b (mg g -1) is slope and a (mg g -1 ) of adsorption capacity. Vol. 20, No. 2, 2015: 77-83 where c and q were as defined for Langmuir with k and n were adsorption constant.

Characteristics of ZSM-5 Zeolite
Synthetic zeolite was successfully made by non-hydrothermal method. Characterization to zeolite was conducted with XRD, SEM, and nitrogen physisorption method.

X-ray diffraction (XRD)
XRD is a qualitative analysis method that was functioned to analyze crystal structure of a solid substance. All of material having crystal will show peaks if it were analyzed by XRD. The result of XRD diffractogram can show the crystallinity level of the materials. The result of ZSM-5 zeolite diffractogram is shown in the Figure 1. Diffraction pattern that was resulted by ZSM-5 showed the resemblance with the simulated ZSM-5 standard diffractogram, but there were difference at the intensity. The peak of synthetic zeolite appeared at 2 è = 7.9364 o , 7.9569 o , 23.9541 o and 23.9746 o , where approached the top a typical ZSM-5. Therefore, materials produced in this research fulfill the requirement to be classified as ZSM-5.

Scanning Electron Microscope (SEM)
SEM is a characteristic method to identity the morphology of zeolite, at surface, shape, and crystal size. The result of SEM analysis showed that ZSM-  Intensity (a, u) 5 crystal had rather spherical crystal morphology ( Figure 2). The morphology in Figure 2 was the original shape of ZSM-5 because of low temperature. Low temperature influenced the stability of crystal structure, surface and composition composed of pore in zeolite. Mimura et al. (2001) proposed that synthetic zeolite made from hydrothermal method at 160 o C gave products with the best crystallinity.

Specific Surface Area and Total Pore Volume
Characterization of synthetic zeolite pore was done with nitrogen physisorption. This method was used to determine the distribution of pore, specific surface area and pore size. Bruenne Emmett Teller (BET) method was used to determine specific surface area at synthetic zeolite and Barret Joyner Halenda (BJH) to determine distribution of pore size. The result showed that ZSM-5 zeolite has 213.82 m 2 g -1 of specific surface area and 0.22 cc g -1 of total pore volume.

Heavy Metals Adsorption using ZSM-5 Zeolite
Experiments of heavy metal adsorption was conducted using Cu 2+ , Pb 2+ and Cd 2+ . Adsorption was done at various concentration between 50-250 ppm and contact time for 30-150 minutes. The result of heavy metal ion adsorption by ZSM-5 zeolite is shown in Figure 3.
The adsorption capacity of each heavy metals by ZSM-5 did not show significantly increase at 30 minutes through 150 minutes of contact time. It was due to ZSM-5 zeolite had reached a saturation level since first 30 minutes of contact time. Thereby nevertheless time passed, will not influence the capacity of heavy metal ion adsorption. It also showed that ZSM-5 zeolite had adsorption ability relatively fast to heavy metal ions.
The influence of concentration to the adsorption capacity showed that the higher concentration of heavy metal ion the higher adsorption capacity. The same idea with Tofighy and Mohammadi (2011), higher concentration, the strength of mass transfer that pushed will also be greater, so can increase the ability of adsorption. The research of Said and Widiastuti (2008) also obtained that the increase in metal ion will give greater puss capacity, so metal ion will move from outer surface into zeolite micropores. It explained that the ability of zeolite was not only related to the adsorption of ion, but was also influenced by zeolite pores. Besides, those  To compare the ability of ZSM-5 adsorption to each metals ion and to understand the characteristic that affects it, we did the fitting the adsorption capacity of each metal ion. Figure 4 shows that the capacity of ZSM-5 zeolite to adsorp Pb 2+ was higher than adsorp Cu 2+ or Cd 2+ . The amount of ions adsorbed by ZSM-5 zeolite were 30.56-58.70 mg g -1 of Pb 2+ , 27.24-55.06 mg g -1 of Cu 2+ and 24.40-46.47 mg g -1 of Cd 2+ . It is organized based on the ability of adsorption level which are Pb 2+ > Cu 2+ > Cd 2+ .
The difference of this adsorption ability is affected by some characteristics, not only from zeolite but also from the characteristic of those metal ions. Pores of a certain size allows metal ion to enter that pore. Metal ion with bigger size than the pore size would decrease the adsorption ability. Chang and Shih (2000) described that the adsorption ability of zeolite X synthetic to heavy metals was bigger than zeolite A synthetic, because zeolite X synthetic had bigger pore size than zeolite A synthetic. Danny et al (2004) explained that adsorption of Cu 2+ and Cd 2+ using apatite hydroxy nano-sized with ion hydrate diameter Cu 2+ (4.19 Å) were smaller than Cd 2+ (4.26 Å). It was seen from the amount of Cu adsorbed that was higher than Cd ion. Minceva et al. (2007); Zamzow and Murphy (1992) and Kesraoui-Ouki et al. (1993) revealed that bigger metal ions have lower capacity of solidity and electrostatic adsorptive power. These will limit metal interaction with certain size to the adsorption ability. However, smaller ion radius and bigger ion valence will be more densely and strongly adsorbed. In research of Lide (1998), diameter of ion hydrate were 4.01 Å for Pb, 4.19 Å for Cu 2+ and 4.26 Å for Cd 2+ . Other characteristic that was related to the ion metal adsorption is electronegativity value. Metals with high electronegativity value will be easier to be adsorbed than low negativity value (Minceva et al. 2007). The electronegativity values of each metal ion used were 2.33, 1.90 and 1.69 for Pb 2+ , Cu 2+ , and Cd 2+ , respectively. Zeolite also showed characteristic bond structure of SiO 2 and AlO 3 . Because of this bound, zeolite has excess negative ion capacity that is used to bind the metal ions with cation exchange mechanism.
Langmuir and Freundlich were used to interprete adsorption models of heavy metals by ZSM-5 through the linearity coefficient determination with R 2 approaching unit value ( Figure  4). Because the Langmuir and Freundlich constant calculation only involve one q value (adsorption ability) from one level concentration, the adsorption ability of zeolite at each concentration was obtained by counting the average adsorption at each concentration level. To find adsorption model from this test, the maximum capacity to each heavy metals adsorption can also be obtained. Both equations are also widely used to evaluate the equilibrium characteristics in adsorption process. Langmuir equation explains adsorption process at the homogeneous surface, while Freundlich explained adsorption at heterogeneous surface. Parameter values from the three kinds of metals are summarized in Table 1.
The result showed that the adsorption isotherm of metal Pb 2+ , Cu 2+ and Cd 2+ using ZSM-5 zeolite are more suitable with Langmuir isotherm that was shown with regression value near to 1 (Figure 4). Based on Table 1, the ability of maximum adsorption of zeolite were Pb 2+ , Cu 2+ and Cd 2+ adsorption Adsorbed substances from metal ion at every zeolite surface are calculated in mg ion per gram unit of zeolite weight. The results of maximum adsorption capacity ZSM-5 to each heavy metals were 74.07 mg g -1 for Pb 2+ , 69.93 mg g -1 for Cu 2+ , and 60.24 mg g -1 for Cd 2+ . The result showed that adsorption ability of ZSM-5 zeolite to the heavy metals were higher than adsorption by natural zeolite. It was because synthetic zeolite has better characteristic than natural zeolite. Adsorption ability of natural zeolite to the heavy metals is shown in Table 2. The adsorption of Pb studied by Buasri et al. (2008) showed that the maximum adsorption ability of synthetic zeolite used was higher than that of natural zeolite but not as high as ZSM-5. Adsorption to heavy metals increased because zeolite used had been activated through saturation using 0.5 M of NaCl for 24 hours.

CONCLUSIONS
As concise as possible ZSM-5 synthetic zeolite has been created with low temperature method and .82 m 2 g -1 of specific surface area and 0.22 cc g -1 of total pore volume. The ability of synthetic zeolite adsorption ZSM-5 against the metal ion Pb 2+ , Cu 2+ and Cd 2+ was influenced by the differences in zeolites pore size, the negative charge of zeolite, hydrate and electronegativity diameter of each metal ion. The results showed that the adsorption of heavy metal ions adsorption occurred at a relatively rapid contact with the maximum adsorption capacity of each of the metals Pb 2+ 74.07 mg g -1 , Cu 2+ 69.93 mg g -1 , and Cd 2+ 60.24 mg g -1 .