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(1)AGH UNIVERSITY OF SCIENCE AND TECHNOLOGY FACULTY OF ENERGY AND FUELS. PhD Thesis THE USE OF MODIFIED FLY ASH FOR CARBON DIOXIDE CAPTURE. ZASTOSOWANIE MODYFIKOWANYCH POPIOŁÓW LOTNYCH DO WYCHWYTYWANIA DITLENKU WĘGLA. Natalia Czuma Supervisor: Dr hab. Katarzyna Zarębska, prof. AGH Co-supervisor: Dr inż. Paweł Baran AGH University of Science and Technology in Krakow Faculty of Energy and Fuels Department of Coal Chemistry and Environmental Sciences Cracow, 2018.

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(3) Acknowledgements I would like to express my special appreciation and thanks to my supervisors Professor Katarzyna Zarębska and Dr Paweł Baran for their continuous help and support at every stage of writing this thesis. I would also like to thank to my family and everyone else who supported me throughout the duration of my PhD studies. Lastly, I would like to express special thanks to InnoEnergy PhD School for providing me with financial support..

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(5) Uprzedzony o odpowiedzialności karnej na podstawie art. 115 ust. 1 i 2 ustawy z dnia 4 lutego 1994 r. o prawie autorskim i prawach pokrewnych (t.j. Dz.U. z 2006 r. Nr 90, poz. 631 z późn. zm.): „ Kto przywłaszcza sobie autorstwo albo wprowadza w błąd co do autorstwa całości lub części cudzego utworu albo artystycznego wykonania, podlega grzywnie, karze ograniczenia wolności albo pozbawienia wolności do lat 3. Tej samej karze podlega, kto rozpowszechnia bez podania nazwiska lub pseudonimu twórcy cudzy utwór w wersji oryginalnej albo w postaci opracowania, artystyczne wykonanie albo publicznie zniekształca taki utwór, artystyczne wykonanie, fonogram, wideogram lub nadanie.”, a także uprzedzony o odpowiedzialności dyscyplinarnej na podstawie art. 211 ust. 1 ustawy z dnia 27 lipca 2005 r. Prawo o szkolnictwie wyższym (t.j. Dz. U. z 2012 r. poz. 572, z późn. zm.) „Za naruszenie przepisów obowiązujących w uczelni oraz za czyny uchybiające godności studenta student ponosi odpowiedzialność dyscyplinarną przed komisją dyscyplinarną albo przed sądem koleżeńskim samorządu studenckiego, zwanym dalej "sądem koleżeńskim"”, oświadczam, że niniejszą pracę dyplomową wykonałem(-am) osobiście i samodzielnie i że nie korzystałem(-am) ze źródeł innych niż wymienione w pracy.. ……………………………………………………. podpis autora pracy.

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(7) TABLE OF CONTENTS. Introduction ______________________________________________________________ 13 Aim of this PhD thesis___________________________________________________________ 14. Chapter 1 Zeolites – introductory information ___________________________________ 17 Chapter 2 Fly ashes _________________________________________________________ 29 Chapter 3 Zeolites synthesized out of fly ash ____________________________________ 41 3.1. Hydrothermal method of zeolite synthesis out of fly ashes _________________________ 41 3.2. Fusion method of zeolite synthesis out of fly ashes _______________________________ 41 3.3. Two-step method of zeolite synthesis out of fly ashes _____________________________ 42 3.4. Molten salt method of zeolite synthesis out of fly ashes ___________________________ 42 3.5. Alternative energy sources ___________________________________________________ 42 3.6. Seawater in the process of synthesis of zeolites from fly ash ________________________ 43 3.7. Waste mine water in the process of synthesis of zeolites from fly ash ________________ 44 3.8. An additional source of aluminum in the synthesis of zeolites from fly ash ____________ 44 3.9. Modification of fly ash for the synthesis of zeolites from fly ash _____________________ 45 3.10. Mechanism for synthesizing zeolites from fly ash ________________________________ 46 3.11. Methods for estimating the efficiency of synthesizing zeolites from fly ash ___________ 48 3.12. Properties of fly ash zeolites _________________________________________________ 49 3.13. Application of fly ash zeolites ________________________________________________ 50 3.14. Zeolites from fly ash production on a semi-technical scale _________________________ 52. Chapter 4 Carbon dioxide and sulPHur dioxide __________________________________ 55 4.1. Carbon dioxide _____________________________________________________________ 55 4.1.1. Reduction in carbon dioxide emissions ________________________________________________ 57 4.1.2. CO2 capture technologies ___________________________________________________________ 58. 4.2. Sulphur dioxide ____________________________________________________________ 60 4.2.1. Reduction in sulphur dioxide emissions _______________________________________________ 61. 7.

(8) Chapter 5 Fly ash for zeolite synthesis analysis___________________________________ 65 5.1 Fly ashes selected for the research _____________________________________________ 66. Chapter 6 Fly ash zeolite synthesis by the hydrothermal method ____________________ 81 6.1. Synthesis of zeolite materials – selection of synthesis parameters ___________________ 81 6.2. Method directed at Na-X zeolite synthesis ______________________________________ 81 6.3. Method directed at sodalite synthesis __________________________________________ 82 6.4. Method directed at Na-P1 zeolite synthesis______________________________________ 82 6.5. Method directed at Na-A zeolite synthesis ______________________________________ 83 6.6. Selection of own-model synthesis parameters ___________________________________ 87 6.7. Conclusions of results obtained as an effect of synthesis performed with the use of ownmodel parameters ____________________________________________________________ 101 6.8. Additives for the synthesis process ___________________________________________ 101 6.8.1. Experimentation – additives for the synthesis process __________________________________ 102 6.8.2. Results – additives for the synthesis process __________________________________________ 103 6.8.3. Analysis of results and conclusions __________________________________________________ 105. Chapter 7 Zeolite synthesis from fly ash by the fusion method _____________________ 107 7.1. Synthesis of zeolite materials – selecting the parameters of the synthesis reaction _____ 107 7.2. Analysis of results _________________________________________________________ 119 7.2.1. F500, 6-h hydrothermal process subsequent to the fusion reaction ________________________ 120 7.2.2. F550, 6-h hydrothermal process subsequent to the fusion reaction ________________________ 121 7.2.3. F600, 6-h hydrothermal process subsequent to the fusion reaction ________________________ 121 7.2.4. F650, 6-h hydrothermal treatment subsequent to the fusion reaction ______________________ 122 7.2.5. F700, 6-h hydrothermal treatment subsequent to the fusion reaction ______________________ 122. 7.3. Conclusion _______________________________________________________________ 123. Chapter 8 Synthesis of zeolites from fly ash using a modified two-step method _______ 125 8.1. Synthesis – introduction ____________________________________________________ 125 8.2. Experimental material ______________________________________________________ 126. 8.

(9) 8.3. Synthesis ________________________________________________________________ 128 8.4. Synthesis process results ____________________________________________________ 128 8.5. Data analysis _____________________________________________________________ 133 8.6. Analysis of the effect of the amount of ash added _______________________________ 133 8.7. Analysis of the impact of the type of ash used __________________________________ 134 8.8. Effect of the use of solutions after hydrothermal synthesis ________________________ 134 8.9. Impact of the use of solutions enriched in silicon and aluminum ____________________ 135 8.10. Conclusion ______________________________________________________________ 136. Chapter 9 Synthesis of zeolites from fly ash using microwave and ultrasonic energy ___ 139 9.1. Introduction ______________________________________________________________ 139 9.2. Apparatus________________________________________________________________ 139 9.3. Parameters – microwave reactor _____________________________________________ 141 9.4. Parameters – ultrasonic shredder _____________________________________________ 141 9.5. RESULTS _________________________________________________________________ 143 9.6. Analysis _________________________________________________________________ 144 9.7. Ultrasonic and microwave energy as an additional process step in the synthesis of zeolite materials ____________________________________________________________________ 145 9.8. Conclusions ______________________________________________________________ 146. Chapter 10 Specific surface area measurements of samples selected for sorption experiments _____________________________________________________________ 147 Chapter 11 Carbon dioxide sorption __________________________________________ 153 11.1. Samples selected for sorption experiments ____________________________________ 154 11.2. Determination of sorption capacity, porous texture parameters and estimation of regeneration properties of fly ash zeolites in relation to carbon dioxide _________________ 155 11.2.1. Sorption capacity measurements and determination of texture parameters ________________ 155 11.2.2. Procedure for THE estimation of sorption capacity and regeneration properties ____________ 157. 9.

(10) 11.2.3. Measurement procedure _________________________________________________________ 158 11.2.4. CO2 sorption results performed on materials synthesized with the use of the hydrothermal method _____________________________________________________________________________ 158 11.2.5. Analysis of CO2 sorption results performed on materials synthesized with the use of the hydrothermal method _________________________________________________________________ 161 11.2.6. CO2 sorption results performed on materials synthesized with the use of the fusion method __ 163 11.2.7. Analysis of CO2 sorption results performed on materials synthesized with the use of THE fusion method _____________________________________________________________________________ 166 11.2.8. CO2 sorption results performed on materials synthesized with the use of the modified two-step method _____________________________________________________________________________ 167 11.2.9. Analysis of CO2 sorption results performed on materials synthesized with the use of the modified two-step method _____________________________________________________________________ 170 11.2.10. CO2 sorption results performed on commercial zeolite A and X _________________________ 171 11.2.11. Analysis of CO2 sorption results performed on commercial zeolite A and X ________________ 173 11.2.12. CO2 sorption results performed on raw material for fly ash zeolite synthesis in this work ____ 174 11.2.13. Analysis of CO2 sorption results performed on raw material for fly ash zeolite synthesis in this work _______________________________________________________________________________ 175 11.2.14. Conclusions ___________________________________________________________________ 176. Chapter 12 sulphur dioxide sorption __________________________________________ 179 12.1. Samples selected for sorption tests __________________________________________ 180 12.2. sulphur dioxide sorption capacity of fly ash zeolites _____________________________ 180 12.2.1. Procedure _____________________________________________________________________ 180 12.2.2. SO2 sorption results performed on materials synthesized with the use of the hydrothermal method ____________________________________________________________________________________ 182 12.2.3. SO2 sorption results performed on materials synthesized with the use of the fusion method __ 184 12.2.4. SO2 sorption results performed on materials synthesized with the use of the modified two-step method _____________________________________________________________________________ 186 12.2.5. SO2 sorption results performed on commercial zeolite A and X __________________________ 188 12.2.6. SO2 sorption results performed on E and L fly ash _____________________________________ 190. 12.3. Results analysis __________________________________________________________ 191 12.4 Conclusions ______________________________________________________________ 194. General conclusions _______________________________________________________ 197 10.

(11) Academic achievements of the author ________________________________________ 201 References _______________________________________________________________ 207 Summary ________________________________________________________________ 221 Streszczenie ______________________________________________________________ 223 List of figures_____________________________________________________________ 225 List of tables _____________________________________________________________ 231 Appendix I. Apparatus used in the experimental part of the work __________________ 233. 11.

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(13) INTRODUCTION. INTRODUCTION Air quality has become one of the major concerns in today’s world. Carbon dioxide is considered as one of the gases responsible for global warming on earth. These greenhouse gases form a “mantle” around the planet, affecting the exchange of thermal energy. This phenomenon is called the greenhouse effect. It is believed that the increased emission of carbon dioxide is related to human activity, mainly in the form of the human impact on forest management, processes related to industrialization and the burning of large quantities of fossil fuels. It is generally accepted that increased greenhouse gas emissions increase the average temperature on earth. Additionally, industrialization and fossil fuel burning leads to increased emission of toxic gas – sulphur dioxide. In the areas where emissions of carbon dioxide or sulphur dioxide cannot be avoided, in order to reduce them, undesired components of flue gases can be captured. After capturing, they can be directed towards other uses (e.g., processed as substrates, stored, chemically utilized). At this moment, the process of capturing impurities still requires improvements. In the case of carbon dioxide, the most industrially used process is amine absorption process (applicable only in the case of major installations, due to high initial and operational costs), while, on a smaller scale, activated carbons can be applied. For sulphur dioxide, differentiated methods, mainly involving bounding with calcium, are used. Still, in all cases, the search for alternative methods is ongoing. The use of fly ash zeolite in the adsorption purification of flue gas has many advantages. First and foremost, the ecological effect should be underlined. The use of waste material from the energy sector as a raw material for production of sorbent is a highly efficient way of recycling. Not only is the amount of waste reduced, but the cost of substrates for synthesis is minimized. At the same time, the economy of the solution is satisfying. This work presents the results of the synthesis of fly ash zeolites with the use of the most well-known synthesis methods. For this purpose, a selection of fly ash and the analysis of raw material were performed. With the use of selected raw material, the synthesis with the use of hydrothermal, fusion and modified two-step method was performed in order to select the best synthesis parameters, based on the estimated efficiency of synthesis and the analysis of the obtained materials. In the case of the hydrothermal synthesis method, the additives for the synthesis process were tested. In the. 13.

(14) INTRODUCTION. fusion process, maximizing the estimated efficiency of synthesis was the aim. In the case of the twostep synthesis, modification was proposed, with the aim of minimalizing the post-synthesis waste. The second approach was focused on carbon dioxide sorption behaviours of samples synthesized with the use of selected synthesis methods. This step was directed at determining the behaviours of zeolites synthesized by the same/different methods. A preliminary attempt to check the regeneration possibilities was also tested. The results of carbon dioxide sorption incentivized us to perform additional experiments using a second gas as a sorbate – sulphur dioxide. The analysis of these gases’ sorption process should allow for common conclusions to be drawn, which could be generalized. Broadly speaking, as the experiments focused on determining the nature of the synthesis and its application in the sorption process of fly ash zeolites, this work should be of interest to scientists, given the relatively high volume of papers in this area. Nevertheless, there are still copious uncertainties and questions, which need to be addressed. In the opinion of the current author, the major deficiency is that there is no summary work comparing synthesis processes, the influences of changing synthesis parameters and the properties of materials synthesized by means of one of the synthesis methods in the case of material properties. Sorption properties presented in a comparative manner are of high scientific value. The main goal of this PhD thesis was to fill that gap knowledge by providing general conclusions based on experimental data. AIM OF THIS PHD THESIS The aims of this PhD thesis were to undertake the following: ». Experimental analysis of fly ash zeolite synthesis by different methods and estimation of process efficiency. ». Experimental analysis of synthesis enhancement by synthesis condition changes and additives for the synthesis process. ». Characterization of selected samples by various techniques in order to establish their physicochemical properties. ». Experimental analysis of the potential for using fly ash zeolites as SO2 and CO2 adsorbents, along with a preliminary check of regeneration possibilities 14.

(15) INTRODUCTION. The following aims of the work are directed at fulfilling the objective of this thesis: ». Fly ash is a raw material for the synthesis of different types of zeolites. ». It is possible to enhance the synthesis method by the selection of appropriate synthesis conditions or using additives for the synthesis process. ». Fly ash zeolites are appropriate to be used as carbon dioxide and sulphur dioxide adsorbents. 15.

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(17) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. CHAPTER 1 ZEOLITES – INTRODUCTORY INFORMATION The first reports on zeolites as a distinct group of minerals date back to 1756. The establishment of this distinct group is attributed to a Swedish mineralogist, Axel Frederick Cronstedt, and related to the discovery of stilbite. The term “zeolite” is derived from two Greek words, “zeo” (boiling) and “lithos” (stone), since water is released by these materials while being heated (Breck, 1973). Currently, 191 forms of zeolites are known, of which 40 occur in nature (http://asdn.net, 2017). Zeolites can be divided into natural and synthetic types. Their composition is based on silicate compounds (SiO4) and alumina compounds (AlO4), connected by shared ions to form polyhedra, which are the basic units of the spatial arrangement of zeolites. Differences in the chemical composition of zeolites occur due to the substitution of a cation in the tetrahedral position, e.g., in many silicates part of the silica cation is substituted by Al3+ ions, which leads to the occurrence of an additional negative charge compensated by cations. Differences between natural and synthetic zeolites, related to their chemical composition, can occur as a result of the presence of components other than a given zeolite in the deposits, from which zeolites are mined. Examples of such “contaminations” in natural zeolites include clay minerals, other minerals, quartz, metals or other zeolites. Another difference that can occur in synthetic zeolites is the possibility of the substitution of quartz atoms by germanium, whereas aluminium atoms can be substituted by gallium, chromium, iron, boron and, less frequently, other elements (Gołek, 2007). In the case of synthetic zeolites, there is much greater diversity in terms of the occurrence of different crystallographic structures conditioning the properties of zeolites. A considerable proportion of synthetic zeolites have natural counterparts. Zeolite deposits most frequently occur adjacent to rocks containing volcanic matter, which is extremely diverse in terms of its composition and age. Natural zeolites are mostly products of the modification of volcanic glass under different geological, geochemical and temperature conditions. Apart from volcanic glass, zeolites could also be formed on the basis of such precursors as smectites, feldspars, feldspathoids or biogenic silica. The most common mechanism of natural zeolites formation is based on a reaction of rocks and ash clouds with alkaline waters, often containing. 17.

(18) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. substantial amounts of minerals. The formation of zeolites in natural conditions is a long-term process taking place over thousands of years. The most commonly occurring zeolites are: •Clinoptilolite (Na6[(AlO2)6(SiO2)30]*24H2O) (Fig. 1) •Heulandite (Ca[Al2Si7O18]*6H2O) •Mordenite (Na8[(AlO2)8(SiO2)40]*24H2O) •Chabazite (Ca2[(AIO2)4(SiO2)8]*13H2O) (Fig. 2) •Analcime (Na16[(AlO2)16(SiO2)32]*16H2O) •Phillipsite ([Ca,Na2,K2]3Al6Si10O32*12H2O) •Erionite ([Na2,K2,Ca)2Al4Si14O36*15H2O), •Ferrierite ([Na,K]2Mg[OH/Al3Si15O36]*9H2O) (Fig. 3). Fig. 1. Clinoptilolite (zeolites.blog.onet.pl, 2016). 18.

(19) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. Fig. 2. Chabazite (http://www.redcrystal.pl, 2016). Fig. 3. Ferrierite (http://www.mindat.org, 2016). 19.

(20) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. Natural zeolites have wide applications in industry and medicine. Limitations related to the possibilities of using natural zeolites appear when the presence of identical and repeatable structures and a high purity of zeolite material are required. The available data concerning the deposits of naturally occurring zeolites have not been precisely assessed to date. An additional problem connected with the assessment of the deposits, as well as with the manufacturing of natural zeolites, refers to the inclusion of materials containing volcanic tufts, which have a lower zeolite content, into the group of the produced zeolites. The production scope of natural zeolites is presented in Fig. 4.. Fig. 4. The annual production of natural zeolites (U.S. Geological Survey, 2016). Synthetic zeolites are obtained as a result of a synthesis reaction carried out under hydrothermal conditions. It is possible to obtain high-purity zeolite material using aqueous aluminate and silicate solutions of alkali metals, or by means of the recrystallization of natural aluminosilicates. In general terms, the most extensively used method for hydrothermal synthesis from aqueous aluminate and silicate solutions consists of the following stages:. 20.

(21) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. a) Mixing amorphous sources of silicon and aluminium (most frequently in oxide forms) with cation sources in pH higher than 7 b) Heating the aqueous mixture of substrates in a digester (the temperature often amounting to over 100°C) c) Substrates remaining in the amorphous state while being heated d) Crystallization of zeolites after the induction period of the reaction, upon which the crystallization process substantially accelerates e) Substitution of the amorphous materials by zeolite crystals (followed by filtration, washing and drying of the obtained material) The above-presented process is schematically depicted in Fig. 5.. Fig. 5. Scheme of the hydrothermal synthesis of natural zeolite (the substrate Si-O and Al-O bonds are transformed, due to the presence of an aqueous mineralizing medium OH and/or F into crystalline products into Si-O-Al bonds; the crystalline structure defines microporosity) (Cundy and Cox, 2005). 21.

(22) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. The synthesis based on recrystallization of natural aluminosilicates consists of the use of cheaper substrates, most frequently from the kaolinite group, in which the existing crystalline structure is first destroyed, before the obtained amorphous material undergoes hydrothermal processing in an appropriate alkaline solution. It is also possible to obtain zeolites using waste materials, i.e., by means of synthesizing zeolites from fly ashes or by using rice husk ash (Thuadaij and Nuntiya, 2011). Zeolites are crystalline solids consisting of silicon, aluminium and oxygen, which are arranged in a three-dimensional lattice of tetrahedra of AlO4 and SiO4, bound with a single atom of oxygen and forming a repeatable pattern of pores and channels. In the pores and channels, particles of water and cations can nest, which compensate for the negative charge of the structure (http://asdn.net, 2017) (the substitution of an Si4+ or Al3+ ion generates an unbalanced negative charge). The cations present in the lattice are mobile and can be substituted by other cations (as schematically shown in Fig.6).. Fig. 6. Scheme of a fragment of the zeolite skeleton (Łukarska, 2015). The basic units forming the zeolite skeleton are the primary elements of the zeolite crystal structure, the so-called primary building units (PBUs) (zeolites.blog.onet.pl, 2016). These are SiO4 and AlO4 tetrahedra, connected with each other by shared oxygen atoms. Tetrahedra, in the centre of which a silicon and an aluminium atom, respectively, are linked with each other by an oxygen bridge in accordance with Löwenstein’s rule. This states that the formation of direct linkages between aluminate tetrahedra is forbidden – the Si/Al ratio has to be greater than 1. The spatial arrangement of tetrahedra is realized by forming larger and regularly repeatable 22.

(23) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. geometrical forms, which are secondary unit cells, i.e., the so-called secondary building units (SBUs). SBUs are presented in Fig. 7.. Fig. 7. SBUs in zeolites (http://www.ch.ic.ac.uk, 2017). Links between the SBUs form the three-dimensional zeolite structure (Łukarska, 2015). A schematic diagram of zeolite formation (from aluminosilicate to zeolite) is shown in Fig. 8.. 23.

(24) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. Fig. 8. The schematic diagram of the formation of selected zeolites (Daramola, Aransiola and Ojumu, 2012). The empirical formula of zeolites can be shown by Eq. 1:. (1) where: M – a cation of an alkali metal (most frequently Na+, K+, Mg2+, Ca2+, Sr2+, Ba2+), X – is equal to or greater than 2 (AlO4 tetrahedrons are bridged only with SiO4), x, y – integers, n – the valence of the cation. The Si/Al ratio is an extremely important parameter for characterizing zeolites. It provides information on the zeolite structure and the number of cations, determines surface properties (water repellence, acidity) and influences adsorption and ion exchange properties, as well as catalytic behaviour (Daramola, Aransiola and Ojumu, 2012). Zeolites can be classified with regard to numerous criteria. Table 1 presents one of the most commonly used classifications, as introduced by Breck (1973). This classification relies on the membership of a given structure in a particular group, based on the presence of a particular SBU. It. 24.

(25) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. should be noted that, if such a classification criterion is adopted, a given structure can belong to more than one group. Table 1. Breck’s classification of zeolites. Group. SBUs. 1. Single 4-ring (S4R). 2. Single 6-ring (S6R). 3. Double 4-ring (D4R). 4. Double 6-ring (D6R). 5. Complex 4-1, T5O10 unit. 6. Complex 5-1, T8O16 unit. 7. Complex 4-4-1, Y10O20 unit. Another classification approach can involve dividing zeolites with regard to the types of channels occurring in the structures (Breck, 1973). The following systems are distinguished: a) One-dimensional, non-intersecting channels (Fig. 9). Fig. 9. An example of non-intersecting zeolite channels (Breck, 1973). 25.

(26) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. b) Two-dimensional channels (Fig. 10). Fig. 10. Examples of two-dimensional zeolite channels (Breck, 1973). c) Three-dimensional channels (Fig. 11) . Channels with relatively stable parameters. . Channels whose parameters depend on the crystallographic direction. Fig. 11. An example three-dimensional zeolite channels (Breck, 1973). 26.

(27) CHAPTER 1. ZEOLITES – INTRODUCTORY INFORMATION. An additional criterion for classifying zeolites refers to differences in cavity (pore) widths: a) Narrow-porous: containing 8-rings, e.g., zeolite A, b) Medium-porous: containing 10-rings, e.g., ZSM-5, ZSM-11, c) Wide-porous: containing 12-rings, e.g., zeolites of the X and Y types. Zeolites are stable solids that are generally resistant to high temperatures and pressures, do not dissolve in water and are not oxidized in air. As they are non-reactive and composed of naturally occurring substances, they are regarded as non-harmful to the natural environment. The most interesting properties of zeolites are connected with their structure, based on an opencage framework of cavities and apertures. Their sizes and the negative charge on the framework mean that cations can be accommodated in the structure and ion exchange. The size of the cavities also enables molecules of the proper size to be trapped in the structure; therefore, zeolites are also called molecular sieves. An additional property of zeolites is that they are capable of reversible hydration. A characteristic feature of naturally occurring zeolites is the presence of different forms and sizes of cavities in a sample. Uniform and repeatable structures can be obtained in synthetic zeolites (http://www.explainthatstuff.com, 2016). The possible applications of zeolites, resulting from their properties, are wide-ranging. Zeolites are used both in industry and in everyday life. Their main applications are related to their unique ion sorption, catalytic, sorption and molecular sieve properties. Other areas where zeolites are used include agriculture, medicine, chemical technology (e.g., gas desulphurization, crude oil refining), environmental engineering (removing ammonia and heavy metals from water and sewage), gas separation/adsorption and removing radionuclides from sewage (Wdowin et al., 2014). Moreover, they are used in air dehumidification processes and in animal husbandry.. 27.

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(29) CHAPTER 2. FLY ASHES. CHAPTER 2 FLY ASHES In the Polish context, the consumption of hard and brown coal for the generation of electrical and thermal energy is conspicuous. According to 2015 data, 77% of energy in Poland is generated from hard and brown coal (http://gramwzielone.pl, 2017). The data presented in Fig. 12 and Fig. 13 illustrate the structure of the utilization of particular fuels for the generation of electrical energy and heat. In both these cases, the contribution of hard and brown coal is prevalent.. Fig. 12. The structure of the installed electrical capacity in 2012 (Departament Informacji Gospodarczej Polska Agencja Informacji i Inwestycji Zagranicznych S.A., 2012). Fig. 13. The structure of heat generation according to the fuels used (Departament Informacji Gospodarczej Polska Agencja Informacji i Inwestycji Zagranicznych S.A., 2012). 29.

(30) CHAPTER 2. FLY ASHES. Forecasts point to the further use of coal as the main energy carrier until at least the middle of this century (Pyssa, 2005). The combustion of fossil fuels, regardless of the applied technology, leads to significant amounts of wastes, which can negatively impact the environment. The main atmospheric contaminants include dusts, carbon oxides, sulphur oxides and nitrogen oxides. Solid combustion products, such as slag and ash (combustion wastes), and products of flue gas desulphurization are also classified as wastes (Pyssa, 2005). The most significant amounts of these types of wastes are generated in the field of professional and industrial power engineering. In Poland, in accordance with the Regulation by the Minister of the Environment of 9 December 2014 on the catalogue of wastes, these wastes are classified as “wastes from power stations and other combustion plants”, marked with the code 10 01 and not indicated as hazardous wastes. With reference to solid wastes (ashes, slags, ash-slag mixtures, combustion products from systems based on fluidized bed technology), the term “combustion by-products” (in Polish, UPS) is also used. It was coined in the 1990s by national power producers in order to change the perception of these wastes and emphasize their value as anthropogenic raw materials (http://www.surowce-naturalne.pl, 2017). Quantitatively, the largest proportion of UPS comprise fly ashes (Monzón et al., 2017), which represent some of the most important energy wastes (Galos and Uliasz-Bocheńczyk, 2005) and are examined in this thesis. Fly ash, according to the PN-EN 450-1:2009 norm, is defined as “fine-grain dust, mostly composed of spherical glassy grains, obtained while burning coal dust with or without the participation of coincinerated materials that exhibit pozzolanic properties, and containing mainly SiO2 and Al2O3, with the content of reactive SiO2, specified and described in EN 197-1, being no less than 25% of the total mass”. The mechanism by which fly ash is formed is schematically presented in Fig. 14.. 30.

(31) CHAPTER 2. FLY ASHES. Fig. 14. Fly ash formation mechanism (Seames, 2003). Fly ashes are captured from the combustion cycle by means of dedusting exhaust gases. The principal dedusting methods include electrostatic precipitators (ESPs), fabric filters and wet scrubbers. A classification of dedusting methods is shown in Fig. 15.. Fig. 15. Overview of methods for the removal of solid particulates from the combustion cycle (European Commission, 2006). 31.

(32) CHAPTER 2. FLY ASHES. In power plants, the most commonly used devices are ESPs. They operate on the principle of charging electrically neutral dust particles, which takes place due to the fact that electric charges leave the electrode upon a corona discharge, in a strong heterogeneous electrical field with the applied voltage in the range of 40-80 kV. Dust grains acquire an electric charge from gas molecules ionized by flow. Charged particulates are attracted by the oppositely charged electrode, where they are collected (the collecting electrode). On the electrode, they undergo a discharge and are cyclically removed from it. The schematic diagram of the operation of an ESP is shown in Fig. 16.. Fig. 16. Operating diagram of an ESP (https://www.oransi.com/, 2018). Due to the fact that the formation of fly ash depends on a number of factors, such as the kind of coal used, applied combustion technology, boiler type, distance travelled by dust particulates in the combustion cycle and the applied flue gas desulphurization process, on the basis of Szponder (2012), the following classification of fly ashes is proposed: a) By combustion chamber design: . Ashes from burning in conventional boilers;. . Ashes from burning in fluidized bed boilers;. b) By type of fuel used in power boilers:. 32. . Fly ashes from burning hard coal;. . Fly ashes from burning hard coal and biomass;. . Fly ashes from burning brown coal;.

(33) CHAPTER 2. FLY ASHES. . Fly ashes from burning brown coal and biomass;. c) By selective process of collecting ashes from different sections of electrical precipitators: . Fly ashes from Zone I;. . Fly ashes from Zone II;. . Fly ashes from Zone III;. d) By applied flue gas desulphurization technology: . Conventional fly ashes;. . Conventional fly ashes containing flue gas desulphurization products;. . Fluidized fly ashes.. The above-presented classification takes into account significant differences in the properties of fly ashes, which are related to their composition, mainly their mineral and chemical composition, as well as to the loss on ignition (LOI) value. It was assumed that the most significant classification refers to fuel combustion technologies and the type of burned coal. As far as boilers are concerned, the principal differences between burning fuels in pulverized and fluidized bed boilers are discussed below. Since the combustion temperature in a fluidized bed amounts to approximately 850°C, fly ashes that are formed due to the combustion of both brown and hard coal, compared to fly ashes from pulverized boilers, exhibit a low degree of sintering, as they are composed of irregularly shaped particles with a well-developed specific surface area – they have a considerable open porosity, which leads to increased water demand, and do not contain the glassy phase (Pyssa, 2005; ZapotocznaSytek et al., 2013). It should also be noted that the physico-chemical properties of fluidized ashes will still heavily depend on the kind of fuel, the sulphur content in a fuel, the type of the applied sorbent, the combustion method used in a particular boiler and the boiler design, and the oxidation state of flue gas desulphurization products (Pyssa, 2005). In the case of fluidized ashes, a decrease in the SiO2 content is observed with a simultaneous increase in the CaO and S content. In the phase composition of waste products from fluidized bed boilers, the prevailing components are semi-morphous products of dehydration and dihydroxylation of clay minerals as well as crystalline phases (anhydrite, calcite). The content of free active calcium oxide (CaO) ranges from 1% to 8%. β-quartz SiO2 is also present to a considerable extent. As fluidized ashes are characterized by a high content of. 33.

(34) CHAPTER 2. FLY ASHES. dehydrated clay minerals, mainly kaolinite, extremely pozzolanic-active metakaolinite is formed in this way (Zapotoczna-Sytek et al., 2013). In Table 2, the main characteristics of hard coal and lignite ashes burnt in fluidized bed boilers are presented. Table 2. Sample compositions of hard coal and lignite fly ashes burnt in fluidized bed boilers (ZapotocznaSytek et al., 2013). Content or particular characteristic Fluidized hard coal fly Fluidized brown coal ash fly ash. Properties. Units. SiO2 Al2O3 Fe2O3 CaO CaO (free) MgO SO3 LOI Water demand % through sieve no. 0.063 mm Activity coefficient after 28 days. % % % % % % % % %. 32.52-40.81 15.5-20.77 3.27-7.50 9.08-21.80 0.76-7.06 1.31-3.52 4.80-11.80 3.84-14.67 40.00-98.00. 36.50-42.20 26.70-30 2.85-6.35 11.50-16.20 2.83-5.91 1.17-2.50 2.26-3.85 1.82-3.58 63.00-800. %. 64.45-100. 68.30-80.50. %. 90.00-105.00. 90.00-100.00. Regarding pulverized boilers, the kind of fuel used is of major importance. In contrast to hard coal, brown coal is usually not enriched, which leads to the differentiation of fuels and, as a result, influences ash composition. In the case of hard coals, a higher content of the glassy phase and mullite is observed, whereas brown coals contain quartz, calcium oxide and anhydrite in higher quantities. Apart from spherical grains, brown coals also contain grains of irregular shapes (Gawlicki and Małolepszy, 2013).. 34.

(35) CHAPTER 2. FLY ASHES. Table 3 shows examples of compositions of hard and brown coal fly ashes burnt in pulverized boilers. Table 3. The average chemical composition of hard and brown coal fly ashes burnt in pulverized boilers (Zapotoczna-Sytek et al., 2013). Characteristic type of fly ash (mass percentage) From brown coal Component From hard coal (Aluminosilicate) (Aluminosilicate) Turów SiO2 52 48 Al2O3 20 31 Fe2O3 13 7 CaO 6 3 MgO 3 1.5 SO3 1 0.5 Na2O+K2O 1.8 1.5. (Calcium sulphate) Konin 45 8 5 32 3 1.7 0.2 (trace amounts). Table 4 presents the output of combustion by-products in selected countries or regions in 2010. The term “combustion by-products” is understood here as the total amount of fly ash and bottom ash and, for some installations, that of by-products of desulphurization processes. The table allows us to roughly illustrate the amounts of generated fly ashes, taking into account the fact that fly ashes represent 70% of all combustion by-products (Monzón et al., 2017). Table 4 also illustrates the level of the utilization of fly ashes worldwide, showing considerable differences between particular regions and countries in this regard. According to the data contained in Table 4, in 2010, 777 million tonnes of fly ash were produced worldwide; more current data presented in Yao et al. (2015) indicate fly ash generation at the level of 750 million tonnes. Table 4. Global production and utilization of fly ashes (Heidrich, Feuerborn and Weir, 2013). Country/region Australia Canada China Europe India Japan Middle East and Africa USA Other Asia Russian Federation Total. Coal combustion products production, Mt 13 6.8 395 52.6 105 11.1 32.2 118 16.7 26.6 777.1. Coal combustion products utilization, Mt 6 2.3 265 47.8 14.5 10.7 3.4 49.7 11.1 5 415.5. Utilization rate, % 45.8 33.8 67.1 90.9 13.8 96.4 10.6 42.1 66.5 18.8 53.5 35.

(36) CHAPTER 2. FLY ASHES. In Poland, in 2015, 3.3 million tonnes of fly ashes were generated. Selected data on the generation, utilization and storage of fly ashes in Poland in the period 2011-2015 are presented in Table 5. The data were prepared on the basis of the Polish Annual Statistical Report (published by the Central Statistical Office; GUS, in Polish) for the respective years. Table 5. The amounts of fly ashes generated, utilized and stored in Poland in the period 2011-2015. Fly ashes generated during the year, Mt Conditioned Year. 2011 2012 2013 2014 2015. Total. Utilized. 4.5 4.5 4.5 3.8 3.3. 4.3 3.9 3.9 0.1 0.1. Total. Stored. 0.2 0.7 0.5 0.1 0.2. 0 0 0 0 0. Transferred to other recipients. Temporarily stored. n/a n/a n/a 3.5 2.9. 0 0 0.1 0.1 0. Ashes stored so far (disposed of in landfills, as of the end of the year) 18.5 27.2 27.2 26.9 26.3. On the basis of the data presented in Table 5, it can be observed that the amount of generated fly ashes is decreasing. However, they are still produced in substantial quantities. It can also be seen that, over the last few years, the quantities of fly ashes transferred to other recipients have been significant. Due to their peculiar properties, fly ashes find applications in numerous fields. The quantities of the produced wastes from power stations and the possibilities of their utilization significantly vary across countries, as shown in Table 4. Both for Poland and for other EU member states, an increase in the level of utilization of fly ashes is observed. In Poland, this level is high (Galos and Uliasz-Bocheńczyk, 2005). In Fig. 17, there is a diagram showing some options for fly ash utilization.. 36.

(37) CHAPTER 2. FLY ASHES. Fig. 17. Applications of fly ashes (Heidrich, Feuerborn and Weir, 2013). In Poland, the main directions of fly ash management involve their utilization in the construction industry (the contribution of this sector to the utilization of ashes is estimated at 55-57%) (Galos and Uliasz-Bocheńczyk, 2005), in the mining industry, or as a raw material in road-building. Moreover, there is a range of options for using fly ashes in other fields, i.e., as fertilizers, catalytic agents, a potential source for the recovery of cenospheres, unburnt coal, magnetic particles and precious metals, such as germanium, gallium, vanadium, titanium and aluminium (Yao et al., 2015). Another important application is connected with their use as sorbents, from both the gaseous and the liquid phase (Ahmaruzzaman, 2010). Fly ashes can also be used as cheap material for manufacturing ceramics, glass ceramics and other glass products, as well as geopolymers, mesoporous material and zeolites (Blissett and Rowson, 2012).. 37.

(38) CHAPTER 2. FLY ASHES. In the construction industry, large quantities of fly ash from hard coal are used for the manufacturing of Portland cement clinker, both as a basic ingredient and as a corrective additive. Due to their pozzolanic properties, i.e., the ability to react with lime in an aqueous environment, forming highstrength plastic after hardening (Pytel and Małolepszy, 1999), fly ashes can be used for cement production. In Poland, qualitative and quantitative guidelines are described in the PN-EN 197-1:2002 norm “Cement. Part 1: Composition, specifications and conformity criteria for common cements”, which gives particular consideration to roasting losses of less than 5%, a reactive calcium oxide content of less than 10%, a free calcium oxide content of less than 1% by weight, and a reactive silicon dioxide content of more than 25%. The norm distinguishes four types of cements in which fly ash is used, with the quantitative content of ash ranging from 6% to 55%. The pozzolanic properties of ashes and the small particle size allow for the use of fly ash in the production of concrete. The addition of ash reduces the demand for water, improves workability, reduces the permeability of the grout and thus of concrete, as well as improves the resistance of concrete to aggressive factors. Guidelines for the application of ash additive to concrete are specified in the norm PN-EN 450:1998 “Fly ash for concrete – definitions, requirements and quality control” (Galos and Uliasz-Bocheńczyk, 2005). Fly ashes can also be involved in the production of lightweight aggregates used in road and other types of construction (drainage and filtration layers, speed reduction belts, road bases, as drainage and moisture accumulation substrates under green and sports areas), in horticulture (as substrates for hydroponic cultivation, and as heat-insulating and sound-absorbing layers), as components of light structural concretes, and in the production of building materials with good insulating properties (Sokołowski, 2005). Fly ashes can also be used in the building ceramics industry as a weakening additive or as a basic raw material. Underground mining uses fly ashes to eliminate and fill old goafs and goafs with active longwalls and unnecessary ventilation drifts, make explosionproof structures and explosion prevention devices, eliminate fire hazards, and separate methane fields to recover methane and prevent air from escaping through caving zones (Galos and UliaszBocheńczyk, 2005). In the road-building industry, fly ashes may be used in various ways at different stages of road construction (material for forming embankments, improvement, strengthening, soil stabilization, road base construction, use of lean cement and ash mixtures to form upper layers of road base) (Gawlicki and Małolepszy, 2013).. 38.

(39) CHAPTER 2. FLY ASHES. The properties of fly ashes make these materials a good raw material for a variety of processes. In particular, it is beneficial to process them into materials with often more prospective properties, which can be referred to as “upcycling”.. 39.

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(41) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. CHAPTER 3 ZEOLITES SYNTHESIZED OUT OF FLY ASH A similar composition of chemical components of fly ash and some volcanic rocks has led scientists to explore the possibility of converting fly ash into zeolite materials. Literature data indicate that it is possible to convert fly ash into zeolites using a variety of methods. Since the experiments by Höller and Wirsching in 1985 on the hydrothermal synthesis of zeolites from fly ash, many articles and patents have been published regarding the synthesis of zeolite materials using a variety of methods. However, it should be noted that the production of zeolites from fly ash results in a mixture of unreacted raw material and crystalline zeolites. The main methods of fly ash zeolite synthesis include (Majchrzak-Kucęba, 2011): . Hydrothermal method;. . Fusion method;. . Two-step method;. . Molten salt method.. 3.1. HYDROTHERMAL METHOD OF ZEOLITE SYNTHESIS OUT OF FLY ASHES The hydrothermal method is based on combinations in closed and open systems of various ratios of fly ash and activating factor with temperature, pressure and reaction time to obtain different types of zeolites. The idea of the process is based on the dissolution of silicon and aluminium sources from fly ash and the next stage of crystallization of dissolved components in the form of zeolites. In the process, KOH or NaOH solutions with different molarities are most commonly used. A significant amount of research has been carried out to determine possible synthesis parameters (Querol et al., 1997; Cundy and Cox, 2005; Majchrzak-Kucęba, 2011; Mainganye, Ojumu and Petrik, 2013; Franus, Wdowin and Franus, 2014). 3.2. FUSION METHOD OF ZEOLITE SYNTHESIS OUT OF FLY ASHES The fusion method proposed by Shigemoto and Hayashi (1993) consists of sintering a mixture of fly ash with the hydroxide, producing highly reactive aluminates and sodium silicates, which easily. 41.

(42) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. dissolve in water and enhance the formation of zeolites. Using the fusion method before the hydrothermal method, it is possible to obtain type X zeolites with high efficiency. 3.3. TWO-STEP METHOD OF ZEOLITE SYNTHESIS OUT OF FLY ASHES The two-step method consists of the synthesis of materials in a two-step process to produce highpurity zeolite material (> 99%) (Hollman, Steenbruggen and Janssen-Jurkovičová, 1999; Sommerville et al., 2013), which is not the same as in the case of other methods, where the ash mixture and zeolite are obtained. 3.4. MOLTEN SALT METHOD OF ZEOLITE SYNTHESIS OUT OF FLY ASHES The method of molten salts, as proposed by Park, Choi, Woo Taik Lim et al. (2000) and Park, Choi, Woo Talk Lim et al. (2000), is based on using a mixture of salts instead of liquid-activating solutions. This method allows us to limit the quantities of alkaline reaction waste water generated after the synthesis, which have been associated in the literature with the environmental problem linked to the synthesis of zeolites from fly ash (Behin et al., 2016). However, this method has disadvantages pertinent to the possibility of obtaining materials with low ion exchange properties. 3.5. ALTERNATIVE ENERGY SOURCES Literature data indicate the possibility of synthesizing zeolite materials using a variety of process modifications. The use of alternative energy sources is one of the possibilities. An example is the use of microwave energy and ultrasonic energy in the process of synthesizing zeolites from fly ash. Conventional methods of converting fly ash into zeolite material are based on the process of dissolving silicon and aluminium contained in the ash under the influence of the base, creating nucleation seeds and the crystal growth process itself. These processes are often time-consuming and energy-consuming as they occur at elevated temperatures. In addition, conventional heating is limited by the thermal conductivity of the reaction vessel and does not ensure uniform heat distribution (Pathak, Roy and Das, 2014). One of the possibilities to reduce energy consumption in the synthesis of zeolite materials is the use of microwave energy or ultrasonic energy.. 42.

(43) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. The American patent from 1988 can be considered pioneering work in the field of the microwave synthesis of fly ash zeolites (P. Chu, F.G. Dwyer, 1988). Meanwhile, although the first article describing the synthesis of zeolite Y and ZSM-5 appeared in 1993, a significant reduction in the reaction time and the lack of undesired phases in the sample were demonstrated in minutes (Arafat et al., 1993). The unique properties of microwave energy are used in the production process of zeolites from pure constituents (Li and Yang, 2008; Wu et al., 2013; Ansari et al., 2014), fly ashes (Tanaka et al., 2008; Bukhari et al., 2014, 2015) or, e.g., perlite (Azizi and Asemi, 2014). Research conducted by Wang et al. (2008), Purnama et al. (2014), Musyoka et al. (2011), Andaç et al. (2006), Wu et al. (2006) and Bukhari et al. (2015) indicate the possibility of using ultrasound energy in the synthesis of zeolite materials. The experiment carried out by Park et al. (2001) compared the hydrothermal synthesis of 4A zeolite from kaolin with results obtained at the same time and temperature, using ultrasonic energy. The experiment showed the possibility of obtaining a higher degree of crystallinity using ultrasonic energy. It has been shown that the use of ultrasound allows us to reduce the process temperature and the time of synthesis. Similar conclusions were obtained in other studies (e.g., Belviso et al., 2011), where ultrasonic energy was combined with the fusion process for the production of zeolites with fly ash, and where the synthesis of zeolites from fly ash took place when combining ultrasonic energy with the classic hydrothermal method. In addition, some authors have reported a decrease in the size of crystallites of zeolites generated using ultrasonic energy (Andaç et al., 2006; Musyoka, Petrik and Hums, 2011). According to data available in the literature, the use of these energies can significantly reduce the time needed to crystallize zeolite materials, when using alternative energy separately (Andrés et al., 1999; Pathak and Srivastava, 2012), and when including it as one of process steps, in relation to both the classic hydrothermal method (Tanaka et al., 2008; Wu et al., 2013), and the fusion method (Bukhari et al., 2014). Each of these possibilities was found to reduce the time needed for the synthesis process to occur. 3.6. SEAWATER IN THE PROCESS OF SYNTHESIS OF ZEOLITES FROM FLY ASH One of the proposed possibilities for the synthesis of zeolite materials, as presented in Lee, Matsue and Henmi (2001) and Belviso et al. (2009), involves the use of seawater in the process. Such a modification was recognized by authors as an opportunity to reduce process costs by replacing 43.

(44) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. distilled water, as well as due to testing the possibility of conducting synthesis at low temperatures (35-60°C), using hot sea waste water from turbine cooling (Belviso et al., 2009). In light of the reports on the possibility of using salt additives in the synthesis of zeolite materials (Franus, Wdowin and Franus, 2014), the use of seawater seems to be justified. 3.7. WASTE MINE WATER IN THE PROCESS OF SYNTHESIS OF ZEOLITES FROM FLY ASH Highly interesting studies were also presented by Musyoka, Petrik and Hums (2011) and Musyoka et al. (2013), showing the possibility of using mine waste water (both neutral and salt brines), instead of distilled water in the synthesis of zeolite materials, as well as the impact of ultrasonic energy in the process (Musyoka, Petrik and Hums, 2011). Research has shown the possibility of using solid and liquid industrial wastes generated during the production of energy from coal to produce zeolite materials. 3.8. AN ADDITIONAL SOURCE OF ALUMINUM IN THE SYNTHESIS OF ZEOLITES FROM FLY ASH Due to the presence of aluminium in forms that are more difficult to dissolve in an alkaline environment (e.g., mullite), it is possible that the introduction of additional aluminium may affect reactions (Bhagwanjee and Devendra Narain, 2016). Such an additive may be particularly useful when there is a desire to obtain a zeolitic material with a lower ratio of silicon to aluminium. Zeolites characterized by a lower Si/Al ratio show higher alkalinity (Lee and Jo, 2010), while obtaining them will be beneficial when considering the use of zeolites from fly ash for purposes in which a higher basicity of the material will be an advantage. An example is the treatment of waste water (Fotovat, Kazemian and Kazemeini, 2009) or the sorption of acidic gases from other gases (Lee and Jo, 2010). There are many reports confirming the possibility of using various sources of aluminium in the synthesis of zeolites from pure components (Suresh and Sundaramoorthy, 2014) and when used as an additive in the synthesis of zeolites from waste (Fotovat, Kazemian and Kazemeini, 2009). The most frequently mentioned are Al2O3, NaAlO2 and aluminium foil. There are also reports in the literature confirming the possibility of using waste aluminium as one of the components in the synthesis of zeolites (Czuma, Zarębska and Baran, 2016a; Sánchez-Hernández et al., 2016).. 44.

(45) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. 3.9. MODIFICATION OF FLY ASH FOR THE SYNTHESIS OF ZEOLITES FROM FLY ASH In addition, it is possible to carry out modifications on the raw material – fly ash. Each modification of fly ash is carried out to facilitate the crystallization process of zeolites. One possibility of modifying fly ash is to remove, with the use of acids, undesirable components that may hinder the desired zeolite effect in subsequent applications (such as iron or alkaline oxides). In addition, the acid reaction can remove part of Al2O3, which will be beneficial if there is a need to adjust the Si/Al ratio. A proposal for such a procedure has been presented by Ojha, Pradhan and Samanta (2004). Another possibility of removing undesirable components considered to be obstructing the synthesis of zeolite materials, is magnetic separation involving the removal of ferromagnetic components from fly ash in order to improve the efficiency of the process (Sommerville et al., 2013; Cardoso et al., 2015). The separation process can be carried out using various methods (Czuma et al., 2016). Removal of unburned coal from fly ash is also considered to be one of the possibilities to improve the properties of the starting material for the synthesis of zeolite materials. The presence of unburnt carbon can reduce the efficiency of zeolite synthesis due to the possibility of particle deposition on the ash surface, slowing down the process of glassy phase dissolution (Cardoso et al., 2015). In addition, the presence of unburned carbon in the ash may affect the subsequent deterioration of the properties of zeolites, for example, by reducing the cation exchange capacity (CEC) of the material. Conducting the fly ash fractioning process may also influence the result of the synthesis of zeolites from fly ash. It is logical to say that, in the case of using ash with granules of a smaller diameter, one can expect an increase in the speed of the dissolution process of silicon and aluminium sources, and thus a beneficial effect on the synthesis of zeolites from fly ash. In addition, due to the possibility of accumulating individual fly ash components in individual fractions, it should be expected that the size of granules will play a role and the presence of individual components in given fractions may positively or negatively influence the synthesis (Czuma et al., 2017).. 45.

(46) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. 3.10. MECHANISM FOR SYNTHESIZING ZEOLITES FROM FLY ASH The mechanism of forming zeolites from fly ash is not well recognized. This is certainly due to the fact that the formation of zeolite material is influenced by many factors, the analysis of which is hampered by the use of fly ash as raw material, as characterized by significant variability in composition. It should be noted that both fly ash and zeolites predominantly consist of silicon and aluminium, with a significant difference present in the form of these components – in zeolites they form a well-defined crystal structure. The process of forming zeolite material in the hydrothermal process is shown schematically in Fig. 18. The individual stages consist of dissolving the aluminosilicates present in the fly ash, before the process of the nucleation and crystallization of zeolites begins. Individual processes can be accelerated or delayed by various factors, i.e., the presence of building materials in various forms – aluminosilicate glass and crystalline quartz is much easier to digest than mullite, which often remains unchanged after the synthesis process (Zhao, Lu and Zhu, 1997), the presence of a significant amount of cations from fly ash, etc.. 46.

(47) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. Fig. 18. Diagram of the formation of zeolites from fly ash in a hydrothermal process (Bukhari et al., 2015). 47.

(48) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. 3.11. METHODS FOR ESTIMATING THE EFFICIENCY OF SYNTHESIZING ZEOLITES FROM FLY ASH In the synthesized material, there is a mixture of zeolites and remains of unreacted fly ash; at present, there is no method allowing the separation of components, especially given that zeolitic crystals often grow on ash grains. It is also problematic to determine the amount of zeolite material in the sample. The main indicator of the quality of fly ash-derived zeolite is the degree of fly ash conversion into zeolite material, which is also known by the term ‘‘zeolite purity’’ or degree of crystallinity. The literature provides information on the possibility of using a series of analyses to estimate the amount of zeolite material in the sample. They consist of the comparison of specific parameters of zeolites from fly ash with pure commercial zeolites. Methods for estimating the conversion rate of ash into zeolite are presented in Fig. 19 (MajchrzakKucȩba, 2013).. Fig. 19. Methods for the evaluation of fly ash conversion into zeolite material (CF: conversion factor). When calculating CFXRD, it is possible to use two approaches: the first is to calculate fields under XRD reflections, characteristic for a given zeolite phase, then compare values with the surface values of the analogous reflections of commercial zeolites (Mainganye, Ojumu and Petrik, 2013); the other approach is to compare the intensity of reflections (Subbulekshmi, 2016). CFCEC allows us to estimate the conversion rate by analysing the ion exchange capability compared to a commercial zeolite. The cation exchange parameter (CEC) itself is often described in the literature as the determination of zeolite quality, especially used for sorption from solutions. The problem 48.

(49) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. when comparing CFCEC and when examining the CEC parameter itself is the lack of an international standard, which allows for the comparison of the results obtained. Currently, various methods are used to determine the CEC, which creates difficulties in comparing the results of the studies (Munthali et al., 2014). When zeolites are used as adsorbents in an aqueous system, the cation exchange capacity (CEC) of zeolites is an important factor when estimating their working ability; however, no international standard method is available for the determination of the CEC of zeolites, which poses a challenge in the comparison of the results. CFBET+V is based on comparing the porosity values (specific area (SBET) and microporous volume (Vmicro)) of fly ash zeolites with pure commercial ones (Gross-Lorgouilloux et al., 2010). CFIR is ascertained by comparing the ratio of intensity of the peak at 560 cm–1 to that of the peak at 464 cm–1, along with the corresponding ratios for standard, commercial zeolites (Rayalu et al., 2005). Calculation of the thermogravimetric fly ash-to-zeolite conversion factor CFTGA is based on the comparison of the mass loss of the commercial zeolite (standard), which occurred during dehydration, with that of the fly ash-derived zeolite. This mass loss is characteristic of a specific zeolite type, and the corresponding zeolite water content in the sample of zeolites indicates their degree of crystallinity and zeolite phase content. In the case of the preparation of mixtures of various types of zeolites, some of the proposed methods cannot be used (CFCEC, CFBET+V, CFTGA). The existence of different types of zeolites makes it impossible to estimate the content of individual zeolites. The availability of some zeolitic forms in pure form (commercial) is also problematic (e.g., no commercial zeolite P1 is available). 3.12. PROPERTIES OF FLY ASH ZEOLITES Properties of zeolites from fly ash are similar to their synthetic and natural equivalents. Differences in the properties of zeolite material synthesized from fly ash will result from the presence of fly ash elements, which have not participated in the zeolite crystal formation process. At present, it is not possible to separate the zeolite in its pure form. In practice, this means that the material for further use in the case of fly ash zeolites will be a mixture of zeolite and fly ash (Shih and Chang, 1996). In addition, in comparison with commercial zeolites with strictly defined repetitive and uniform pore and channel sizes, as well as the size of crystals, in the case of fly ash zeolites, it is not possible to 49.

(50) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. control the synthesis process so closely due to the variable composition of the fly ash. Given the lower content of pure zeolite material in the unit weight of zeolite from fly ash, it should be taken into account that such properties as sorption capacity and ion exchange capacity may be lowered, compared to pure zeolites. The interaction of unreacted ash in processes using fly ash zeolites cannot be ruled out; however, due to the stability of the fly ash residue, it can be assumed that this phenomenon will be minimal. Natural zeolites may be contaminated with mineral deposits adjacent to them (Akimkhan, 2012), which is why a well-founded opinion on the closer relationship of zeolites from fly ash to natural zeolites than to the ones formed from pure chemical components may appear. Natural and commercial zeolites present no adverse health impacts on living organisms (Jacobs et al., 2001). For an example the use of them as additive to animal fodder, see Tzia and Zorpas (2012). The available literature data do not provide information on this use of fly ash zeolites, but it should be assumed that this will not be possible due to the possible presence of, e.g., heavy metals in the material produced from fly ash. The above-presented features of zeolites from fly ash indicate some limitations to be taken into account when using it. However, given the starting material from which they are produced, benefits prevail. Compared with fly ash, the use of the spectrum of fly ash zeolites is significantly higher due to the properties of zeolites (catalytic, ionic and adsorptive), as well as the reduction in material toxicity: the mobility of components, such as Cd, PB, Ni and Cr, is lower in the case of zeolite from fly ash than fly ash itself, as they are immobilized in a newly formed mineral (Belviso, 2017). In the author’s reasoning, when processing fly ash into zeolites, we deal with the processing of waste, which results in products of a value higher than processed raw materials. Such an effect causes a reduction in both the amount of waste and the amount of materials used in the primary production of sorbents. All this allows us to determine the production process of zeolite materials as “upcycling”. 3.13. APPLICATION OF FLY ASH ZEOLITES The above-mentioned properties allow for the use of fly ash zeolites in many areas, largely overlapping with natural and commercial zeolite applications. Fields in which applications for ash. 50.

(51) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. zeolites can be found include catalysis, drying, gas and liquid purification (through ion exchange or use of sorption properties), separation of gas mixtures (through the action of molecular sieves), and the processing of crude oil, or the regeneration of oils etc. (Franus, Wdowin and Franus, 2014). Due to the low cost, there is much interest in the possibility of utilizing zeolites in the process of the separation or purification of gas mixtures, mainly exhaust gases. The possibility of the sorption of carbon dioxide has been observed (Franus et al., 2015; Kalvachev et al., 2016; Majchrzak and Nowak, 2017; Zhang et al., 2017). The conducted research revealed different sorption capacities of zeolites, which depend on the type and amount present in zeolite material. In order to improve the sorption properties of zeolites from fly ash, the impregnation of zeolitic material with substances to increase the affinity of carbon dioxide to the sorbent has been proposed. An example is the use of polyethyleneimine PEI (Wdowin, Panek and Franus, 2014) or other amines (Ji et al., 2013). A less demanding modification of zeolite from fly ash was proposed by Lee and Jo (2010), who conducted an ion exchange for alkaline earth metal cations, resulting in a positive effect on the sorption of carbon dioxide. In the literature on fly ash zeolites, information on sulphur dioxide uptake is also available (Srinivasan and Grutzeck, 1999; Bopaiah and Grutzeck, 2000; Gupta, Gaur and Verma, 2004; Pedrolo et al., 2017). Information can also be found on nitrogen oxides sorption (Bopaiah and Grutzeck, 2000; Rezaei et al., 2015), ammonia (Querol, Moreno, Umaa, Juan et al., 2002) or mercury (Wdowin et al., 2015). Much attention has been paid to research on water and waste water treatment both from heavy metal ions (Querol, Moreno, Umaa, Juan et al., 2002; Koukouzas et al., 2010; Harja et al., 2012; Czarna et al., 2016; Koshy and Singh, 2016) and from dyes (Woolard, Strong and Erasmus, 2002) or ammonia (Wdowin et al., 2015). Additionally, in catalysis processes, fly ash zeolites have been used, for example, as a catalyst in methanol transformation into olefins (Missengue et al., 2017), a catalyst in the fast pyrolysis of jatropha (Vichaphund et al., 2014), a heterogeneous catalyst in biodiesel production (Babajide et al., 2012) or a potential catalyst for catalytic cracking (Ojha and Pradhan, 2001).. 51.

(52) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. Zeolites from fly ash have been successfully used as sorbents of petroleum derivatives (Bandura et al., 2015). One of the most interesting applications is the use of fly ash zeolites as a controlled release fertilizer (Elliot and Zhang, 2005; Flores et al., 2017). Research has also been carried out on the possibility of using these types of materials to remove benzene, toluene and isomers of xylene (Bandura et al., 2016). 3.14. ZEOLITES FROM FLY ASH PRODUCTION ON A SEMI-TECHNICAL SCALE The presented properties and possible applications of zeolites from fly ash indicate that their production may be beneficial. Initial laboratory tests have attempted to transfer the synthesis of zeolites from fly ash on a semi-technical scale. One of the proposals to transfer production to a larger scale was carried out in Spain (Querol et al., 2001, 2007), involving the construction of a 10 m3 reactor, allowing for the synthesis, filtration and rinsing of the material. In the process, according to Querol et al. (1999), 1,100 kg of fly ash and 352 kg of NaOH were used, resulting in 1,354 kg of material being obtained as a result of the synthesis. Illustrative photographs of the installation are shown in Fig. 20, Fig. 21 and Fig. 22.. 3. Fig. 20. Top of the R-410 10 m reactor used for the synthesis of zeolites from fly ashes on a pilot plant scale (Querol et al., 2007). 52.

(53) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. Fig. 21. Pneumatic press filters used for washing and drying the zeolite from fly ashes during a pilot plant experiment (Querol et al., 2007). Fig. 22. Packing of 2.7 tons of zeolite-rich product synthesized in a pilot-scale experiment (Querol et al., 2007). 53.

(54) CHAPTER 3. ZEOLITES SYNTHESIZED OUT OF FLY ASH. In Poland, another installation was built, the scheme of which is presented in Fig. 23.. Fig. 23. Technological scheme of the prototype line for the synthesis of zeolite (Wdowin et al., 2014). According to the data presented in Wdowin et al. (2014), it is possible to load 20 kg of fly ash and 12 kg of NaOH in order to produce material with a pure zeolite content in the sample of 81%. Both installations are based on the hydrothermal synthesis of fly ash zeolites.. 54.

(55) CHAPTER 4. CARBON DIOXIDE AND SULPHUR DIOXIDE. CHAPTER 4 CARBON DIOXIDE AND SULPHUR DIOXIDE Sustainable development can be defined as development that meet the needs of the present without compromising the ability of future generations. Growing awareness of environmental problems has led to concerns associated with global climate change. It is commonly believed that emissions of greenhouse gases (GHGs) are of the most concern and therefore, nowadays, much effort is dedicated to reduce such emissions. It should be noted, however, GHGs are not the only major concern in this context. An example of pollutant gas that also needs to be controlled is sulphur dioxide. 4.1. CARBON DIOXIDE Carbon dioxide, created as a result of fossil fuel burning, is believed to be the most significant GHG in terms of amount. GHGs form a “mantle” around the earth, affecting the exchange of thermal energy. This phenomenon is called the “greenhouse effect”. It is believed that the increased emissions of carbon dioxide are associated with human activity, mainly human impacts on forest management – the impact on natural absorbers of CO2, processes related to industrialization and the burning of large quantities of fossil fuels (https://www.epa.gov/, 2018). It is commonly believed that the increase in carbon dioxide emissions has led to an increase in the earth’s average temperature. From 1880 to 2012, the average global temperature increased by 0.85°C. In addition, a higher rate of temperature increase has been observed over the past 50 years, with the global temperature increasing by about 0.13°C per decade (in the previous 50-year period this increase was at the level of 0.07°C). It is estimated that in the next 20 years, the global average temperature will increase by about 0.2°C per decade (Dombrowicki, Gałan and Zborowska, 2012). It should be noted that even a small increase in average temperature will have a huge impact on the earth’s ecosystem. Differences in temperature are particularly visible in respect of weather and climate. An anomaly in rainfall is now observable: more floods and droughts and the effect on the warm air mass. In addition, melting glaciers, warming oceans, increased acidity in the oceans and increased water levels in the oceans are observed. It is estimated that these changes may be more and more noticeable, which will directly affect the environment and people’s lives. Therefore, a reduction in carbon dioxide emissions is one of the leading aims of environmental policies of EU countries as well as countries outside the EU. 55.

(56) CHAPTER 4. CARBON DIOXIDE AND SULPHUR DIOXIDE. World energy-related CO2 emissions will increase to 35.6 billion metric tons in 2020 from 32.2 billion metric tons in 2012, or even to 43.2 billion metric tons in 2040 (the reference scenario). In 1990, CO2 emissions associated with the consumption of liquid fuels accounted for the largest portion (43%) of global emissions. In 2012, CO2 emissions associated with the consumption of liquid fuels fell to 36% of total emissions and are projected to remain at that level until 2040. Coal, which is the most carbon-intensive fossil fuel, became the leading source of world energy-related CO2 emissions in 2006 and will remain one of the leading sources until 2040. However, although coal accounted for 39% of total emissions in 1990 and 43% in 2012, its share is projected to stabilize and then decline to 38% in 2040. The natural gas share of CO2 emissions, which was a relatively small 19% of total energy-related CO2 emissions in 1990 and 20% in 2012, will increase over the projection period to 26% of total fossil fuel emissions in 2040 (U.S. Energy Information Administration, 2016). World energy-related carbon dioxide emissions by fuel type and projections of emissions are shown in Fig. 24.. Fig. 24. World energy-related carbon dioxide emissions by fuel type, 1990-2040, billion metric tons (U.S. Energy Information Administration, 2016). 56.