Selective Porous Materials from Recycling of Industrial Waste Coal Fly Ash for Environmental Protection

1. OBTAINING OF SELECTIVE POROUS MATERIALS FROM RECYCLING OF INDUSTRIAL WASTE COAL FLY ASH FOR APPLICATIONS IN ENVIRONMENTAL PROTECTION E. David1, J. Kopac2, C. Sandru1, A. Armeanu1 1 Department of Carbon and Composite Materials, National Research Institute of Cryogenics & Isotope Technologies, Rm. Vâlcea , Romania 2Chair of Mechining Technology Management, Faculty of Mechanical Engineering Ljubljana, Slovenia 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

2. Outlook • Introduction • Generation, characteristics, hazards • Application examples • Experimental part • Raw material; • Acid washing pretreatment procedure; • Selective porous material synthesis • CO2 adsorption testing • Results and discussion • Conclusions 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

3. Introduction 3 • Waste is lost if we waste it, otherwise it is a resource. Resource is wasted if is ignored and does not conserve it with best practices and reduce cost • Resources are for the transformation of people and society • Focus on turning gray and brown fields into green fields for future • The earth, the water and the air are the concern of every nation • Clean air, clean water and resource conservation being vital • Billion tones of by-product materials are produced each year in the world. At an average cost of 30 € per tone, it would cost 125-130 € per tone if is discarded • These by-products come from industrial sources, agricultural sources, domestic/post-consumer sources and materials processing sources 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

4. Introduction 4 • One of industrial sources is fossil fuel power plants • Coal combustion products(CCPs) are produced by coal burning power plants to generate energy (electricity and heat) • These by-products generally can be used as a partial substitution of cement and many other everyday construction needs • Must be develop recycling technologies for high-volume applications of coal combustion products generated by using both conventional and clean coal technologies Schematic representation of a fossil fuel power plant 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

5. Caracterization 5 • Coal combustion by-products • Fly ash • Class C • Class F • Bottom ash • Micromorphology - fly ash particles predominantly spherical in shape and consist in solid spheres, cenospheres, irregular-shaped debris and porous unburnt carbon. The cenospheres are often porous and light in density • Hard and round , small with different sizes(0.074-0.005 mm); low to medium bulk density(0.54-086 g/cm3); surface area (300-500m2/kg) and light texture; The pH values vary from 1.2 to 12.5, with most ashes tending toward alkalinity. • The iron and unburnt carbon contents present influence the apparent color, which varies from yellow, brown, dark gray ;Fly ash also commonly contains shards of minerals like feldspars, unburned C, and other fine sized particles 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

6. Characterization 6 • Coal fly ash -one of the most complex materials that can be described and characterized • Approximately 315 individual minerals & 180 mineral groups have been identified in different ash samples • Metallic oxides are the major components, with varying contents of unburnt carbon determined by a loss on ignition (LOI) test • The contents of principal oxides are in a decreasing order SiO2 > Al2O3 > Fe2O3 > CaO >MgO >K2O • Fly ash contains many trace elements such as: Ti, Cr, Pb, Ni, Ba, Sr, V, Zn, Hg, Se, As, etc., • Because of this, mobility and leaching processes must be known to asses the probability of these elements migrating to the environment 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

7. Characterization 7 +100 -100 +140 -140+200 -200+270 -270+325 -325+400 Photographs of different fractions • Specific gravity :2.30 • The visual colour changes :the fraction of largest diameter contains more black particles (unburned carbon), while the smallest fractions are almost entirely grey (metal oxides) 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

8. Hazards 8 • The environmental impact of coal fly ash has been fully accepted • Most ash disposal methods finally lead to the dumping of fly ash on open land • Its disposal over large land areas leads to soil degradation and becomes danger to both human health and the environment • Fly ash has particles small enough , they escape emission control devices and are easily suspended in air and become a major source of pollution • Repeated exposure to fine particles of fly ash can cause irritation of the eyes, skin, nose, throat and respiratory tract and can even result in arsenic poisoning • Fly ash can stop natural drainage systems and contaminates the ground water with heavy metals • If the coal contain radioactive elements , these can remain after combustion in fly ash as polluting elements (i.e U and Th series).It is very important if this exist to monitor and regulate their release to the environment (air, water, soil) 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

9. Comprehensive applications 9 • Drawing direct comparisons between results presented in various studies is a challenging because of material properties, sample sizes, varying methodologies and experimentas goals • Recycling coal fly ash can be a good alternative to disposal and could achieve significant economic and environmental benefits as well • The global average utilization rate of fly ash is estimated to be nearly 25%. • It is considered that the recycling of such solid wastes makes it possible to save mineral resources and realize environmentally – friendly utilization of energy Different applications of coal fly ash 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

10. Comprehensive applications 10 • Construction industry • The ash separated in the combustion process can be used for conventional purposes, namely, mixed with cement and concrete • Construction work that demands coal ash as a raw material and the amount of coal ash emissions at thermal power stations depend on the season • Fly ash is emitted in the winter months while thermal power stations are operating at full capacity; On the other hand, the construction industry needs most of the coal ash during the building season in the summer Monthly amount of solid waste resulted from coal-fired power station having a capacity of 400MW 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

11. Comprehensive applications 11 • The precise properties of power plant ash are dependent upon the kind of coal each utility burns • Of all the uses for fly ash , the best known are as an additive in portland cement concrete and as a supplementary cementitious material • About 6 million BTUs are needed to produce one tone of cement . Use of fly ash saves that energy and conserves the resources • In both of these applications, fly ash increases strength and durability, increasing the lifetime of the product Composition of the fly ash 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

12. Comprehensive applications 12 • Soil amelioration • The physico-chemical properties of coal fly ash including silt and clay-sized particles , low bulk density, higher water –holding capacity , favorable pH and source of essential plant nutrients, etc., make it a potential amendament for soils • In addition , use of fly ash instead of lime can reduce CO2 emission (during calcite calcination to produce lime) and thus reduce global warming • Coal fly ash , being mostly alkaline(depending on the coal source and operating conditions of the plant) can be used for buffering the soil pH • Class C more indicate than class F due to higher content of CaO • Fly ash also contains some useful nutrients, such as P,K,S,Ca,Mg,Cu, Zn, which are beneficial for the plant growth 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

13. Comprehensive applications 13 • Other beneficial effects: • Improving the soil texture • Aeration and percolation • Water retention in the treated zone • Reducing soil bulk density and the consumption of other soil amelioration agents • Serving as an insecticide owing to the presence of abrasive silica in fly ash • Decreasing the mobility and availability of metals in the soil due to alkaline nature of the fly ash • Fly ash application improves the physical, chemical and biological qualities of soils to which it is applied 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

14. Comprehensive applications 14 • Ceramic industry • Coal fly ash contains appreciable amounts of SiO2,Al2O3, CaO, Fe2O3 among other oxides. These oxides have often been considered a low-cost material for ceramic industry • Catalysis • Metal and metal oxides are widely used as catalysts in various industrial applications • Fly ash mainly consists of various metal oxides with higher content of iron oxides and possesses higher thermal stability; • Utilization of fly ash in heterogeneous catalysis could provide a cost-effective and environmentally friendly method for recycling this industrial waste 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

15. Comprehensive applications 15 • Environmental protection • Most fly ash is alkaline and its surface is negatively charged at high pH • It can be expected to remove metal ions from solutions by electrostatic adsorption or precipitation • It contains a certain quantity of unburnt carbon, which has a high adsorption capacity • Fly ash could be used as an adsorbent in both gaseous and liquid applications to remove toxic gases or different heavy metal ions • Fly ash can be used for the removal of organic pollutants, capture CO2,SOx, and NOx from flue gases, the condition being to obtain suitable selective materials(carbon materials, zeolites, catalysts, etc) • A comparison of material cost and adsorption capacity showed that they are cheap and efficient in such applications 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

16. Experimental part 16 • The appearance of low-NOx control systems is increasing the ammonia and unburned C content of fly ash. Both have undetermined effects on the use of fly ash as soil amendaments and in cement and concrete applications. • Because the global disposal amount of coal ash will increase with the increase in energy demand, it is now necessary to consider coal ash applications other than the present ones; therefore a new applications is introduced in this paper. • The principale elements of coal ash are:SiO2 (40-65%) and Al2O3 (25-40%) with the proportion of such contents depending on the properties of the coal • In natural or sinthetic zeolites the ratio Si2O2 :Al2O3 → 1.5 to 2 or even 3 • After composition , coal fly ash is suitable raw material to obtain zeolites 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

17. Fraction composition 17 Certain fly ash/carbon mixture are characterized by a bi-modal particle size distribution in which the particle size of the carbon component is biased toward the coarse size fraction of the mixture, while the particle size of the fly ash component is biased toward the fine size fraction of the mixture 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

18. Experimental part 18 • Depth separation(Fly ash separation in component fractions) • Oxidic fraction • Unburnt carbon fraction • Magnetic fraction • Recovery of this fractions is one of the coal fly ash beneficiations, providing economic as well as environmental benefits A plot of the effect of screening fly ash compositions on the proportions of the fly ash components separated A plot of the particle size distribution of the fly ash composition-exp. text 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

19. Experimental part 19 • Characterization of fly ash samples • Samples with high unburned carbon content, titled FA01 and FA02 were provided from CET Govora, Valcea, Romania and characterized to determine their physical and chemical properties. • FA01 sample was generated from the combustion of pit coal in a pulverized boiler equipped with a low-NOx burner. • The FA02 sample was taken from a gasifier that uses a lower coal as fuel such as peat. These samples were chosen because they contain a big amount of unburned carbon, so high loss- on- ignition (LOI) value • FA01 and FA02 samples represent the average of 12 samples for each, collected during six months ( january - june 2015). • The fly ash samples were sieved into (+140) mesh and (–325) mesh fractions. (-140 to -325) mesh fractions was used for zeolite preparation 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

20. Experimental part 20 Characteristics of the studied fly ash samples • Fly ash composition (oxides) was determined by X-ray fluorescence (XRF) spectrometry using a spectrometer Philips PW1606. • The proximate and ultimate analysis was made using a FLASH-2000 Elemental Analyzer. • The morphology of samples was examined by scanning electronic microscopy (SEM) using Jeol JSM-7000 microscope equipped with an energy dispersive detector (EDS). • Loss-on- ignition (LOI) value of the samples was determined according to the ASTM C311 standard . 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

21. Experimental part 21 FA02 FA01 Oxide fraction Oxide fraction Unburned carbon fraction Unburned carbon fraction SEM images of coal fly ash 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

22. Experimental part 22 • Acid-Washing Pretreatment Procedure • Theacid-washing pretreatment of CFA was carried out under various pretreatment conditions(i.e. different acid type, acid concentration, acid/CFA ratio, pretreatment temperature and time). • CFA was initially added toHCl, H2SO4 and HNO3solutions (with10%, 25% and 30%acid concentrations)with the acid/CFA ratios of : 15mlHCl/1gCFA ; 20 mlHCl/1 gCFA ; 30 mlHCl/1gCFA. • The mixture wasstirred constantly at a rate of 300rpm at three different temperatures (75°C, 80°C and 90°C) for 2 h, 3 h, and 4 h. • Next, the solid sample was filtered off from the solution and washed repeatedly with distilled water until the solution reached pH 7 before being dried overnight at 105°C. 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

23. Experimental part 23 • Zeolite Synthesis • Zeolite was prepared by : • Fusion method • Hydrothermal method • In the fusion method → CFA (both pretreated and non-pretreated samples) was mixed with NaOH pellets (reagent grade) to obtain the NaOH/CFA mass ratios of 1.5 and 2.0 • In hydrothemal method was used 5M NaOH solution ( NaOH/CFA mass ratios of 1.5 and 2.0 ) 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

24. Experimental part 24 • CO2 Sorption-Desorption Measurement • Several physical characterizations of the solid products from the above preparation were observed to determine the phase formation, the degree of crystalline, the material specific surface area and the pore size distribution • A sample weight of ca. 10mg was loaded into an alumina sample pan in a TG unit and tested for CO2 sorption-desorption performances. The initial activation of the samples was carried out at 100OC for 1 h in nitrogen environment (ultra high purity) • The sorption run was carried out using both high purity (99.999%) and 15% CO2 (N2 as balance) gas, while the desorption run was conducted in N2 flow • The feed flow rate was controlled to 30mL/min by a mass flow controller (MFC) to the sample chamber. The sorption and desorption were both conducted at 75OC under atmospheric condition. 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

25. Results and discussion 25 • Acid-washing treatment with HCl, H2SO4, and HNO3 (at the acid concentrations of 10%, 25% and 30%) removed the impurities (i.e., Fe2O3, TiO2, MgO, CaO, K2O and SO3) from CFA resulting in the presence of higher SiO2 and Al2O3 percentages in the product • Among these three acids, the treatment with HCl provides the highest purity raw material (78-85% of SiO2 and Al2O3 depending on the acid concentration), whereas treatment with HNO3 achieves the lowest purity (60-70%). • Treatment with H2SO4 and HNO3 effectively remove CaO from CFA but are ineffective for Fe2O3 removal • On the other hand, the treatment with HCl efficiently removes both CaO and Fe2O3 from CFA. From the results, there were no significant changes in the percent yield of CFA after treatment with three acids (HCl, H2SO4, HNO3), they were all in a range of 54-57%wt. 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

26. Results and discussion 26 • Effect of acid concentration: the product purity strongly increases with increasing acid concentration from 10% to 25%; It is observed that HCl with a 25% concentration is the most suitable for CFA pretreatment. • The acid/CFA ratio shows insignificant impact on the product purity, whereas the increasing treatment temperature from 60 to 75 and 80ºC show a slightly positive effect on the product purity, but this positive impact became an inhibitory impact at 90ºC • The Fe2O3 content in CFA reduces from 17.3% to 16.4% and 13.2% when the treatment temperature increases from 60ºC to 75ºC and 80ºC, which could be due to the increase of reaction rate between HCl and Fe2O3 with increasing temperature; • The effect of pretreatment time on the product purity was carried out by varying the pretreatment time from 2 h to 3 h and 4 h. The product purity increased with an increasing pretreatment time from 2 h to 3 h and continues to increase slightly at 4 h. • Based on these results, the optimum conditions for acid-washing pretreatment are a 20%HCl with HCl/CFA ratio of 25 at 80ºC for 4 h. 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

27. Results and discussion 27 • Zeolite Synthesis from Treated and Untreated CFA • The fusion method was carried out on pretreated and non-pretreated CFA samples using the fusion temperature of 450°C ; 550ºC ; 600ºC,with NaOH/CFA ratio of 2 for 12 h followed by crystallization at 85ºC for 4 h. • BET results demonstrated that the pretreated sample has higher specific surface area and total pore volume with smaller pore size diameter. • It was determined that the fusion temperature provides insignificant impact on the material phase formation but strongly affects the material specific surface area and pore diameter, particularly for the pretreated samples. • The specific surface area of pretreated CFA increases from 151.7 to 229 m2/g as the fusion temperature increases from 450°C to 550ºC; nevertheless, at the fusion temperature of 600ºC, the specific surface area remains constant (or slightly decreases) at 224.2 m2/g. 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

28. Results and discussion 28 Phase formations without and with washing after fusion process Phase formations after fusion at different temperatures 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

29. Results and discussion 29 Material balance 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

30. Results and discussion 30 • For practical implementation , a sorbent should display good sorption capacityunder a more realistic CO2 concentration and gas temperature in a power plant • Hence , it was measured CO2 sorption capacities of the sorbents using 15% CO2 (balance N2) and 75 OC • CO2Sorption capacity very close to comercial zeolite 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

31. Results and discussion 31 • Unburned carbon in fly ash varies with combustion efficiency and its content range between 1% and 12%. • Fly ashes from burning coal, due to their significant unburned carbon content , are suitable raw materials for obtaining carbon amorphous porous materials, selective towards CO2 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

32. Conclusions 32 • The generation of coal fly ash is anticipated to increase for many years, as a result of the world's increasing reliance on coal-fired power generation. • Understanding the generation, characterizations and hazards provides both a background and a basis for the alternative uses of fly ash. • This review has attempted to investigate the production of fly ash at the global level and covers a wide range of applications to understand the status of fly ash utilization and thus develop alternative recycling technologies. • The knowledge of the various ways to use fly ash, such as in soil amelioration, the construction industry, the ceramic industry , catalysis, selective material synthesis, is essential for better management of fly ash and the reduction of environmental pollution. 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

33. Results and discussion 33 • Recycling of fly ash into zeolite is considered a new and good option. • The acid-washing pretreatment with 25%HCl using HCl/CFA ratio of 20.0 mlHCl/gCFA at 75ºC for 4 h could efficiently remove most impurities from CFA to trace levels (i.e., CaO and MgO) and up to 80-90% purity of the product (SiO2 and Al2O3) could be achieved. • However, Fe2O3 was reduced from 25.19% to 6.14%. By further fusion at 550ºC with NaOH/CFA ratio of 2.0 for 12 h following with crystallization at 85ºC for 4 h, zeolite with the main phases of sodium aluminum silicate hydrate and faujasite-Na can be achieved. • It was found that this synthesized material enhances good CO2 adsorption performance comparable to commercial grade molecular sieve (zeolite). • Fly ashes from burning coal, due to their significant unburned carbon content , are suitable raw materials for obtaining carbon amorphous porous materials, selective towards CO2 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany

34. E. David1, J. Kopac2, C.Sandru1, A.Armeanu1 1Department of Carbon &Composite Materials , National Research Institute of Cryogenics & Isotope Technologies, Rm. Vâlcea , Romania 2Chair of Mechining Technology Management, Faculty of Mechanical Engineering Ljubljana, Slovenia THANK YOU FOR LISTENING ! 2nd WORLD CONGRESS AND EXPO on RECYCLING July, 25-27, 2016 , Berlin, Germany