HYDROTHERMAL TECHNOLOGY OF ZEOLITE MATERIALS SYNTHESIS FROM FLY ASH

Transcription

1 International Journal of Arts & Sciences, CD-ROM. ISSN: :: 6(3): (2013) HYDROTHERMAL TECHNOLOGY OF ZEOLITE MATERIALS SYNTHESIS FROM FLY ASH Wojciech Franus and Ma gorzata Franus Lublin University of Technology, Poland Magdalena Wdowin Mineral and Energy Economy Research Institute of The Polish Academy of Sciences, Poland In this paper the conversion technology of F-class fly ashes into Na-P1 zeolite material has been presented. In the proposed solution four process stages can be distinguished: a stage of the reactor loading, a reaction stage, a stage for separation of reaction products, and a stage for final processing of the obtained material. The prototype line was the basis for obtaining a zeolite material, in which Na-P1 type was a dominant phase. For synthesis processes the following conditions were applied: 20 kg fly ash, 12 kg NaOH, 90 dm 3 water, a reaction temperature of 80 C and reaction duration of 36 hours. The content of pure zeolite phase in the reaction product was 81% with a BET surface area increasing from 15 to 75 m 2 g -1. A high conversion rate of the fly ash into the Na-P1 zeolite indicates the necessity of industrial research into the construction of a processing line capable of manufacturing zeolite material in industrial conditions. Keywords: Fly ash, Synthesis of zeolites, Technical line. Introduction Synthetic zeolite materials can be prepared with chemical reagents in the reaction of sodium silicate and sodium aluminate, minerals resources include: clay minerals, minerals from the silica group, and some Circumstantial Combustion Products CCP (such as fly ash) [1-4]. The paper presents a method for producing zeolite material on the basis of the hydrothermal reaction of Class F fly ash and NaOH aq at ¼ technical scale based on designed technical line [5-8]. The main component of the line is the reaction vessel about the total volume of 1.3 m 3. This vessel is equipped with a three heaters, the probe to control of reaction temperature, the sensor of reactor filling level, a mechanical stirrer and a membrane pump. Above the reservoir the weight tank is placed that is suspended on the tensometric weight where the synthesis reaction substrates (fly ash and NaOH) are weighted. Water required for the synthesis is dispensed through the flow meter. After loading the reactor is started heating system and control of process conditions. After completion of the reaction cycle, the conversion of fly ash products are directed to a hydraulic press in which the zeolite material is rinsed with excess NaOHaq and then subjected to a drying process in order to activate the surface properties of the obtained material. The proposed 391

2 392 Wojciech Franus et al. technical solution the fly ash conversion into the zeolite material is fully automated and controlled by both the PC as well as the touch screens from the various components of the line. Using the following conditions of the synthesis process: 20 kg fly ash, 12 kg NaOH, 90 dm3 water, temperature 80 C and the duration of the reaction 36 h, can be obtain Na-P1 zeolite type about total conversion level into the zeolite material up to 81%. The high degree of conversion and textual and ion-exchange properties point to a broad spectrum of applications of received zeolite materials in industrial and environmental engineering. Materials and Methods F-class fly ash used for synthesis was obtained by combustion of coal at the Kozienice power plant. The chemical composition of the fly ash is predominately SiO 2 (52%) and Al 2 O 3 (32%) with Fe 2 O 3 (5%) respectively. The rest of the chemical components occur in insignificant amounts [5, 9]. The mineral composition is dominated by spherical forms of aluminosilicate glass (68%) and mullite (22%). In addition quartz and iron oxides occur in the form of magnetite and hematite on the aluminosilicate spheres (Fig. 1). Figure 1. SEM images of fly ash used for the synthesis. 1) magnification 5000X, 2) magnification 10000X. Chemical and mineral composition of all substrates and products of the reaction were thoroughly characterized by X-ray diffraction and scanning electron microscopy. Textural properties were determined by low temperature N 2 isotherms. Mineral composition were characterized by using a Philips X pert APD diffractometer with PW 3020 goniometer, Cu lamp and graphite monochromator. Analysis was performed in an angular range of 5 65 (2 ) and the collected data was analyzed by X Pert Highscore softwere. Identified mineral phases were compared with the PDF-2 release 2010 data base formalized by ICDD. Morphology and chemical composition in the field of main mineral components of the investigated materials was examined by scanning electron microscope SEM FEI Quanta 250 FEG, equipped with EDS. The chemical composition of the fly ashes used for synthesis reactions was determined by XRF method. With a X-ray tube equipped with dual Cr-Au anode with a maximum power of 3kW was the excitation source.

3 Hydrothermal Technology of Zeolite Materials Synthesis Textural properties study of fly ash and zeolite material were investigated by using an ASAP 2020, Micromeritics. Parameters such as specific surface area, pore size distribution and pore volume were evaluated by analyzing the Nitrogen adsorption/desorption isotherm. Measurement was carried out at -194,85 ºC in liquid Nitrogen. Prior to analysis the sample was degassed under high vacuum at 250 ºC for 24 h (10-3 hpa). The specific surface area was estimated using BET theory and pore size distribution by BJH method. Technological Line for Conversion of Fly Ashes into Zeolites Figure 2 presents a photography of the device for producing zeolites for ½ technical scale. In this test arrangement 4 process stages can be distinguished: a stage of the reactor loading, a reaction stage, a stage for separation of reaction products, and a stage for final processing of the obtained material. Figure. 2. The prototype line for the synthesis of zeolites from fly ash. The stage for the reactor loading consists of two storage tanks, where granulated NaOH and fly ash are stored. These tanks are connected with two worm gears with a weight tank, the purpose of each worm gear is the transport of fly ash and sodium hydroxide granules from the storage tank to the weight tank. The tank is made of stainless steel with the symbol 316L. It has the shape of a converse cone head ended by a roller. In order to avoid an excessive dustiness of the room the tank is closed by cap. To provide suitable amount of substrates for the synthesis reaction, the tank is mounted on three weight stain gauges sensors. In order to improve the dump of substrates (NaOH, fly ash) to the synthesis reaction tank the worm gears and the weight tank are equipped with pneumatic piston vibrators. The main component of the described line is a reaction tank, where the conversion process of fly ash into zeolites is carried out. Total volume of the tank is 130 dm 3 (working volume is 100 dm 3 ). The tank is equipped with a system of three heaters (2 kw each), a probe for controlling the reaction temperature, and the level of tank filling probe, and a stirrer which is

4 394 Wojciech Franus et al. sequentially switched on and is responsible for the homogenization of the material and prevents the aggregation of the material during the reaction process. At the tank outlet a pneumatic membrane is installed that pumps the zeolitic material during and after reaction. The separation of the products block consist of a filter press, and two tanks in which the post-reaction aqueous solution of NaOH as well as materials rinsing solution are stored. The aqueous solution from the first rinsing of the reaction products is directed to the storage tank and then pumped back to the reactor for further synthesis. A solution from rinsing is returns to its original composition and is directed to the next reaction cycle. The volume of water during loading and the volume of solution after modification process and recycling are controlled by flowmeters. The final processing stage consists of a ribbon feeder and the rotary furnace. The drying step of the zeolitic material is obtained by filtration of the solution and calcination is using a rotary furnace. The whole process is fully automated and controlled by a computer or touch screens located in the cabinets of each technological blocks. Results A series of zeolite synthesis reactions were carried out thanks to the proposed technological solution. For obtaining a monomineral zeolite Na-P1 the following conditions of the conversion process were applied: 20 kg of fly ash, 12 kg NaOH, 90 dm 3 H 2 O, temprerature of the process 80 o C and duration 36 hours. Obtained zeolite materials were fully characterized by scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), powder X-ray diffraction and N 2 adsorption-desorption isotherm. Figure 3. XRD patterns of the studied materials. Diffractograms that show the mineral composition of the zeolite material are presented in figure 3. A presence of Na-P1 zeolite phase in the reaction products was determine based on the characteristic interplanar distances d hkl = 7,10; 5,01; 4,10; 3,18 Å. The content of the pure zeolite phase in the product obtained under given conditions was 81%.

5 Hydrothermal Technology of Zeolite Materials Synthesis Figure 4. SEM images of Na-P1 zeolite material 1) magnification 6000X, 2) magnification 30000X. The morphologies of the fly ash used for the synthesis reaction and the obtained zeolite Na- P1 are shown in figure 4. Chemical analysis in the microarea revealed that sodium is the main exchange cation in the zeolite structure, which balances the charge of aluminosilicate framework. Averaged ratios of individual cations obtained by EDS are as follows: Na+K+Ca+Mg/Si = 0,44; Si/Al = 1,42. Nitrogen adsorption-desorption isotherms and pore size distributions (PSD) obtained by BJH method are presented in figure 5. Fly ash has a low specific surface area (15 m 2 g -1 ), while zeolite obtained on the basis of fly ash, showed much better textural parameters, where a specific surface area is 75 m 2 g -1. Nitrogen adsorption-desorption isotherm for fly ash represents type II isotherm in IUPAC classification and is characteristic for meso- and macroporous materials with relatively small specific surface area. In addition, pore size distribution scheme indicates a low porosity of fly ash. Figure 5. Nitrogen adsorption-desorption isotherms (77 K) and pore size distribution of the studied materials, 1- fly ash, 2-Na-P1 zeolite material. Zeolite material Na-P1 obtained on a basis of fly ash has higher specific surface area. An isotherm shape can be classified as I type in IUPAC classification. It indicates presence of micropores (the Langmuir isotherm, monolayer adsorption by micropore filling) and also mesopores (a hysteresis loop in the range of p/p 0 = 0,4). The hysteresis loop is the most similar

6 396 Wojciech Franus et al. to the H4 type in IUPAC classification, that is characteristic for mesopores in the shape of narrow slits. The pore size distribution by BJH indicate an mesoporous structure of the material. Conclusions The proposed technological solution allows to achieve a high level of fly ash conversion into zeolite material, where the content of pure zeolite phase is 81%. The mineral composition is dominated by Na-P1 zeolite type. Porous structure of the obtained material as well as its textural properties indicates the possibility of using it as a sorbent for various types of environmental contamination, for example, petroleum substances, heavy metals, radionuclides from mine water and ammonium from wastewater. This researches are financed by NCBIR within Project no PSB1/A2/7/2012 and WND- POIG /09. References 1. Querol X., Plana F., Alastuey A., Lopez-Soler A., (1997), Synthesis of Na-zeolites from fly ash, Fuel, 76, Querol X., Moreno N., Umana J. C., Alastuey A., Hernandez E., Lopez-Soler A., Plana F., (2002), Synthesis of zeolites from coal fly ash: an overview, Internat. J. Coal Geol., 50, Tanaka H., Sakai Y., Hino R., (2002), Formation of Na-A and -X zeolites from waste solutions in conversion of coal fly ash to zeolites, Mater. Res. Bull., 37, Franus W., (2012), Characterization of X-type zeolite prepared from coal fly ash, Polish J. Environ. Studies, 21 (2), Derkowski A., Franus W., Beran E., Czímerová A., (2006), Properties and potential applications of zeolitic materials produced from fly ash using simple method of synthesis. Powder Technol., 166 (1), Kikuchi R., (1999), Application of coal ash to environmental improvement. Transformation into zeolite, potassium fertilizer, and FGD absorbent, Resources, Conservation and Recycling, 27, Hollman G. G., Steenbruggen G., Janssen-Jurkovicova M., (1999), A two-step process for the synthesis of zeolites from coal fly ash, Fuel, 78, Majchrzak-Kuc ba, I., (2011), Mikroporowate i mezoporowate materia y z popio ów lotnych. Monografie Politechniki Cz stochowskiej, 201, Derkowski A., Franus W., Waniak-Nowicka H., Czímerová A., (2007), Textural properties vs. CEC and EGME retention of Na-X zeolite prepared from fly ash at room temperature, Internat. J. Miner. Process., 82 (2),