SYNTHESIS AND CHARACTERIZATION OF NA-P ZEOLITE FROM COAL FLY ASH

Transcription

1 SYNTHESIS AND CHARACTERIZATION OF NA-P ZEOLITE FROM COAL FLY ASH M.K.Dwivedi 1, Payal Jain 2, Chanchala Alawa 3 1,2,3 Dept.of Chemistry, Govt. Holkar Autonomous, Science College Indore, MP (India) ABSTRACT Zeolite was synthesized by direct hydrothermal treatment with sodium hydroxide at different concentration ratios at varying temperatures of 350,450 and 550 C and activation time of 12 h was applied. Characterization of coal fly ash and synthesized zeolite was done using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and BET surface area. The zeolite material formed was zeolite NaP.The yield of zeolite formed depends on the concentration of sodium hydroxide used. Keywords: Hydrothermal treatment, Fly ash, NaP zeolite I. INTRODUCTION Coal fly ash is a waste material from thermal power plants that is found in abundance in the world. Since wide scale coal firing for power generation began in the 1920s, many millions of tons of ash and related by-products have been created. In India about 160 MT of fly ash is generated from burning of coal in power plants. As a matter of fact, the disposal of fly ash will soon be too costly if not forbidden. Throughout the world, much research is being conducted on the use of waste materials in order to either avert an increasing toxic threat to the environment or to streamline present waste disposal techniques by making them more affordable. It, therefore, follows logically that an economically viable solution to this problem should include utilization of waste materials in new products for other applications rather than disposal in a landfill. One of the promising areas in this context is synthesis of zeolites from the coal flyash. The aluminosilicate glass in coal fly ash is a readily available source of Si and Al for zeolite synthesis so as to obtain high value industrial products with environmental utilization [1,2]. Several approaches have been done for proper utilization of fly ash either for lowering the cost of disposal or for minimising environmental impact. Another approach is to convert coal fly ash into zeolites which have wider applications in ion exchange, catalysts, molecular sieves, and adsorbents [3,4]. Zeolites are natural or synthetic aluminosilicates comprising of orderly arrangement of silicate and alumina tetrahedra. The substitution of Si by Al ions create an overall negative charge that is compensated by cations such as Na +, Ca 2+ and Mg 2+, providing zeolites with cation exchange ability [5]. The high percentage of aluminosilicate in fly ash (60-80%) makes them a cheap and readily available source of Si and Al for zeolite synthesis. Low cost fly ash based zeolites can be used for environmental mitigation where the use of commercial zeolites is restricted due to procurement and prohibitive costs [6]. Several studies have been performed on the conversion of Coal Fly Ash into zeolite by hydrothermal treatment but these have not exhausted all the types of CFA in different parts of the world [7-19].It is therefore important to study synthesis of zeolite from coal fly ash from Mandeedeep,India to determine 326 P a g e

2 the utilization of various types of coal fly ash. Various conditions such as temperature, incubation time and concentration of alkaline produce different types of zeolites worth studying in that particular respect. The purpose of this study is to investigate the hydrothermal synthesis of zeolite from coal fly ash, which has many advantages compared with the other methods, in order to establish a more effective and environmentally friendly method for the treatment of coal fly ash. II. MATERIALS AND METHODS 2.1 Sampling and Sample Pretreatment. Coal fly ash was collected from H.E.G. Thermal Power Station, Mandideep (Bhopal)India.The sample was sealed and transported in polythene bag and then air dried for 24 h. Before use, they were screened by 100micron sieve followed by removal of magnetic materials mainly iron fillings using a magnet which interfere with zeolite formation. 2.2 Zeolite Synthesis The direct hydrothermal method was used for the synthesis of zeolites since it is fast, economic and less involving than the other fusion and the microwave methods [11, 18]. NaOH is added with coal fly ash in different ratios of1:2, 1:1.5 and 1:1.2 and kept for fusion at varying temperatures of 350,450 and 550 o C for 12 hours. After this fusion mixtures were washed with double distilled water and agitated for 24 hours on magnetic stirrer to wash off excess of alkali, filtered on whatmann filter paper and dried in oven for 12 hours at 110 o C and stored in desiccator before use. 2.3 Characterization of Coal Fly Ash and Zeolite The chemical constituents of fly ash were analyzed using Bruker S-8 Tiger WDXRF. The surface area was measured with a model QS-7 Quantasorb surface area analyzer. The specific gravity was determined using specific gravity bottles. The Scanning Electron Microscopy (SEM) was carried out using model LEO 438 VP, UK to study micro structure and qualitative characteristics of the ash of the fly ash. The identification of the mineralogical constituents and phase properties of fly ash was examined by Bruker D-8 advance X-ray diffractometer with a Cu-anode. The diffractometer was operated at 40 kv and 40 ma for 1 h over the range of 2θ from 0 to 80. The infrared spectrum of the adsorbent was recorded in potassium bromide and Nujol mull in the range of cm using a Perkin Elmer spectrophotometer. III. RESULTS AND DISCUSSION 3.1 X Ray Fluorescence The chemical composition of Coal Fly Ashis shown in Table 1. The type of CFA used in this study can be classified as class F since it contains a total percentage of SiO 2, Al 2 O 3 and Fe 2 O 3 of more than 80% and CaO of less than 20%. The Coal Fly Ash contains mainly SiO 2, Al 2 O 3 ratio of 2.43:1. The fly ash predominantly consists of trace metals with the chief constituents being oxides, silicates and aluminosilicates of calcium, iron and other bases. These oxides have a tendency to form metal hydroxide complexes in the solution and the subsequent acidic or basic dissociation of these complexes at the solid-solution interface leads to the development of a positive or negative charge on the surface. 327 P a g e

3 Table 1: Chemical constituents of the fly ash Constituents Weight % SiO Al 2 O Fe 2 O CaO 4.10 TiO K 2 O 2.14 P 2 O SO Na 2 O 1.23 MgO 0.63 LOI XRD X-ray Diffraction revealed the occurrence of the characteristic reflection peaks of CFA and the generated zeolite material (Figs.1&2). As shown in Fig. 1 the XRD pattern of CFA mainly shows the presence of crystalline quartz and mullite phases. Besides some crystalline phases (quartz, mullite, hematite etc), ash is primarily composed of amorphous material. The intensity of quartz is very strong with mullite forming a chemically stable and dense glassy surface layer. The low calcium oxide intensity is characteristic of low-ca Class-F fly ash.after CFA treatment several sharp diffraction peaks of great intensity emerge confirming formation of zeolites (Fig.2). Data obtained from XRD shows that the quartz and mullite have changed their mineral phases which is reflected by their intensity count/seconds. Zeolite from alkali activated fly ash (1:1.5) was identified as Na-P type as confirmed by software, JCPDF (1998)[20] corresponding to maximum peak intensity of 390 counts per second and diffraction angle (2 theta) equal to 28 o.it is observed that there is reduction in the silica and alumina contents associated with the crystalline particles of the fly ash due to its alkali activation. This can be attributed to the dissolution of the metal oxides and release of corresponding soluble ions Na+. The Si/Al ratio of the zeolite crystals present in alkali activated fly ash is around one, which corresponds to a tetrahedral framework structure of the zeolite Na-P where there is presence of the Al3+ which have replaced equal number of Si4+. Hence, it can be opined that such replacement of ions results in development of negative charge in the tetrahedral framework from (SiO4)-4 to (AlO4)-5. This can be attributed to development of negative charge on the pores and channels of zeolite structure and external linkages of Na+ to neutralize it in the tetrahedral framework consisting of Al 3+ions. The mullite phase did not change much, indicating that it was a relatively stable phase during the hydrothermal reaction. 328 P a g e

4 Intensity (Arb. Unit) Fig. 1: X-ray diffraction pattern of CFA : FTIR Fig. 2: X-ray diffraction pattern of Zeolite The infrared spectrum of fly ash (Fig. 3) shows broad and weak peaks in the region of cm-1 associated with the functional groups that are on the surface of coal fly ash. The band appearing at 560 cm-1 is associated with octahedral aluminium present in mullite. In addition, bands appearing between cm-1 are associated with tetrahedral vibrations formed which are known as secondary building units and fragments of alumino-silicate system. Band appearing at 2360 cm-1 could be attributed due to alkyl groups that are present in clay material of coal fly ash. Bands appearing at cm-1 and cm-1 assign to asymmetric stretching mode and bending mode of T-O bond respectively. These bands are more or less dependent on the crystal structure. The mid infrared region of the spectrum contains the fundamental framework vibrations of Si(Al)O4 groupings. Although some interference can be made about surface functional groups from IR spectra, the weak and broad bands do not provide any definitive information about the nature of the surface oxides. The data, however, indicate the presence of some surface groups on the CFA. It is observed that there are significant changes in the intensities and the width of various bands due to interaction of fly ash with alkali (fig 4)..It can be noticed that there is an increase in intensity and broadness of the stretching frequency OH band at 3452 cm -1 after the treatment. This can be attributed to an increase in P a g e

5 hydrated products due to the reaction between amorphous silicate and the alkali. Further the shift in the frequency to lower values indicates change in acidic character of the terminal Si-OH group. Moreover, asymmetrical stretching of TO 4 (SiO 4 and AlO 4 ) band corresponding to the variation in frequency from 1076 to 1000 cm -1 and the increase in its sharpness confirms synthesis of silicates and change in its acidic characteristics. This can be attributed to substitution of Si +4 by Al +3 in some of the tetrahedral framework of the primary building units of the aluminosilicates and their external linkage with the Na + ions due to their interaction with the alkali.the band at 434 cm -1 indicates the increased crystallization of product CFA Transmittance Wave Number (cm-1) Fig 3:FTIR spectra of coal fly ash Fig 4:FTIR spectra of alkali activated coal flyash 3.4 SEM Analysis The results of SEM investigation of coal fly ash and zeolite are shown in Fig. 5&6. Fig 5 reveals typical fly ash morphology and surface texture. Most of the particles present in the fly ash are sub-angular and spherical in shape. The image also reveals that the particles present in the fly ash are covered with relatively smooth grains of quartz, clusters of iron (Fe-oxide). Irregular surface of glass matrix is observed which may be responsible for an increase in adsorbent pore volume. Fig 6 shows a significant transition in morphology from lumps to crystalline form which is attributed to chemical reaction between Si4+, Al3+, and Na+ ions and their nucleation and precipitation of zeolite Na-P crystals. Fig 5:SEM of coal flyash Fig 6:SEM of Zeolite 3.5 BET Surface area for the prepared zeolite material was found to be 60.36m2/g whereas the surface area of fly ash was only 2.89 m2/g. The increase in surface area could be attributed to the formation of zeolite structure. 330 P a g e

6 IV. CONCLUSION The study has shown that coal fly ash is a potential silica source for the synthesis of zeolite. NaP type zeolite has been successfully synthesized from coal fly ash.zeolite formed can be used for water and soil improvement agent in the field of environmental protection. V. ACKNOWLEDGEMENT Authors are thankful to Madhya Pradesh Council of Science & Technology (MPCOST) Bhopal (India) for financial support. REFERENCES [1] Ojha, K., Pradhan, N. C. and Samanta, A. N., Zeolite from fly ash synthesis and characterization, Bull.Mater. Sci., 27(6),2004, [2] V. K. Jha, M. Nagae, M. Matsuda, and M. Miyake, Zeolite From CoalFly Ash and Heavy metal ion removal characteristics of thus obtainedzeolite X in multi-metal systems, J. Environ.Management, 90, 2009, [3] P. Solanki, V. Gupta, and R. Kulshrestha, Synthesis of zeolite from flyash and removal of heavy metals ions newly synthesisedzeolite, Environ. J. Chemistry, 7 (4), 2010, [4]. J. F Bogomolov,V.P PetranovskyandD.W Breck,1974,Zeolite molecular sieves (New York: John Wiley and ons) [5] P. Kumar, N. Mal, Y. Oumi and K. Yamana, T. Sano, Mesoporous Materials prepared using Coal Fly Ash as the Silicon and Aluminium Source, Journal of Materials Chemistry, 11,200, [6] X.Querol, X.Moreno, J.C Uman a, A. Alastuey, Herna ndez, Lo peze.a Soler, and P. Plana, Synthesis of zeolites from coal fly ash: anoverview, International J. of Coal Geology, 50,2002, [7] F.Mostafa Bakr and H. Mohamed Fodial. O.Ibraheem Al1, M. Said-Sheikh and M.Tarek Salama. Controllable synthesis of NaP zeolite and its application in calcium adsorption*, Science China Materials,, 58,2015, [8] Chang HL, Shih WH. Synthesis of zeolites A and X from fly ashes and their ion exchange behavior with cobalt ions, Ind. Eng. Chem. Res.;39,2000, [9] S.S. Rayalu, A.K. Bansiwal, S.U. Mesharan, S. Labhsetwar and S.Devotta, Fly ash based zeolite analysis: Versatile material for energyand environmental conservation, Catalysis survey from Asia,: 10(2),2006, [10] Hui KS, Chao CYH. Effects of step-change of synthesis temperature on synthesis of zeolite 4A from coal fly ash. Microporous Mesoporous Mat.;88,2006, [11] K. Ojha, M.C. Pradhan, and A. Samanta, Zeolite from fly ash: synthesis and characterization Bulletin of Material. Science,: 27(60), 2004, [12] Breck DW. (1974) Zeolite molecular sieves, John Wiley and Sons, New York [13] Z. Adamaczk, and B. Biacka, Hydrothermal Synthesis of zeolite from Polish coal fly ash, Polish J. Environ. Studies,: 14 (4),2005, P a g e

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