Kinetics of fly ash geopolymerization

Based on the wet chemical analysis, we measured and modeled the kinetics of reactions between fly ash and KOH at various temperatures and water-to-solid mass ratios (W/S). We find that three consecutive rate-limiting processes control reaction progress: (1) dissolution or alteration of the glass phase in the fly ash, (2) classical Fick diffusion through a surface layer, and (3) diffusive transport through a more complex gel structure (interstitial gel). This sequence of processes is independent of W/S (0.35–40), temperature (22–75 °C), and KOH concentration (5–10 M). The relative contribution of each process to the overall reaction progress changes with experimental conditions. Only if and when the third process is rate limiting, a fly ash geopolymer forms and develops mechanical strength (sufficiently low W/S ratio provided). The rate of reaction progress decreases significantly, due to slow transport of reacting species to the surface of the glass particles.     

Dissolution and geopolymerization of synthetic fly ash glass

Journal of Materials Science - Two fly ash glasses were synthesized and dissolved in KOH at a water/solid ratio of?≤?0.3. We measured reaction kinetics, gel formation, and...     

Biotoxicity evaluation of fly ash and bottom ash from different municipal solid waste incinerators

Different types of municipal solid waste incinerator (MSWI) fly and bottom ash were extracted by TCLP and PBET procedures. The biotoxicity of the leachate of fly ash and bottom ash was evaluated by Vibrio fischeri light inhibition test. The results indicate the following: (1) The optimal solid/liquid ratio was 1:100 for PBET extraction because it had the highest Pb and Cu extractable mass from MSWI fly ash. (2) The extractable metal mass from both fly ash and bottom ash by PBET procedure was significantly higher than that by TCLP procedure. (3) The metal concentrations of fly ash leachate from a fluidized bed incinerator was lower than that from mass-burning and mass-burning combined with rotary kiln incinerator. (4) The TCLP and PBET leachate from all MSWI fly ash samples showed biotoxicity. Even though bottom ash is regarded as a non-hazardous material, its TCLP and PBET leachate also showed biotoxicity. The pH significantly influenced the biotoxicity of leachate.     

Reaction kinetics of fly ash geopolymerization: Role of particle size controlled by using ball mill

Fly ash is milled for 0, 30 and 90?min and used to study the role of particle size on the kinetics of geopolymer formation. The increase in particle fineness is very prominent in the initial milling stage, and then slows down due to agglomeration effect of finer fraction. The fly ash geopolymerization kinetics and its mechanism is determined using heat of reaction data measured by isothermal conduction calorimeter. The improvement in reaction rate with milling is correlated with the median particle size of the fly ash. The apparent activation energy decreases with size reduction because finer fractions are more prone to alkali activation. Although the kinetics changes with particle fineness, but no alternation is detected in the reaction mechanism, governed by nucleation and growth. The apparent activation energy evaluated by rate method is showing three major steps of geopolymerization such as dissolution, gel formation and restructuring.     

Fixation of alkyl phosphate using waste incineration fly ash

Waste incineration fly ash (Fa), pretreated by washing with distilled water and heating at 1000°C in air, was treated with various concentrations of octyl phosphate [C₈H₁₇OPO₃H₂(OP)] aqueous solution by stirring at 25°C for 3 h and aging at 85°C for 24 h. X-ray fluorescence and X-ray diffraction measurements indicated that the major element of Fa is Ca which exists as CaO and gehlenite (2CaO · Al₂O₃ · SiO₂). Treating Fa in OP solutions dissolved the CaO and gehlenite to form calcium octyl phosphate (C₈H₁₇OPO₃Ca.nH₂O), which is composed of a multilayer alternating dicalcium phosphate dihydrate (CaHPO₄ · 2H₂O)-like phase and a bimolecular layer of octyl groups of the phosphates. Increasing the OP concentration increased the fixed amount of OP and amount of recovery after the treatment. The fixed amount and amount of recovery steeply increased during stirring at 25°C, and were almost unchanged by aging. These facts allow us to infer that Fa is available to fix alkyl phosphate ions such as OP.     

Assessment of Pb-slag, MSWI bottom ash and boiler and fly ash for using as a fine aggregate in cement mortar

Three types of wastes, metallurgical slag from Pb production (SLG), the sand-sized (0.1-2 mm) fraction of MSWI bottom ash from a grate furnace (SF), and boiler and fly ash from a fluidised bed incinerator (BFA), were characterized and used to replace the fine aggregate during preparation of cement mortar. The chemical and mineralogical behaviour of these wastes along with the reactivities of the wastes with lime and the hydration behaviour of ordinary Portland cement paste with and without these wastes added were evaluated by various chemical and instrumental techniques. The compressive strengths of the cement mortars containing waste as a partial substitution of fine aggregates were also assessed. Finally, leaching studies of the wastes and waste containing cement mortars were conducted. SLG addition does not show any adverse affect during the hydration of cement, or on the compressive strengths behaviours of mortars. Formation of expansive products like ettringite, aluminium hydroxide and H2 gas due to the reaction of some constituents of BFA and SF with alkali creates some cracks in the paste as well as in the cement mortars, which lower the compressive strength of the cement mortars. However, utilization of all materials in cement-based application significantly improves the leaching behaviour of the majority of the toxic elements compared to the waste as such.     

Behaviour of concrete-filled steel tubular columns incorporating fly ash

The subject of this work is to investigate the effect of fly ash on the strength of concrete filled steel tubular columns from 28 to 365 days. A contrast study was carried out on concrete filled steel tubular columns incorporating 10–40 wt% fly ash, and for control Portland cement concrete filled steel tubular columns. The effect of pre-coating the inner surface of steel tubes with a thin layer of fly ash was also studied. Assessments of the concrete mixes were based on the compressive strength and the bond strength. The results show that a lower replacement with fly ash can improve both bond strength and compressive strength, while a higher replacement with fly ash requires a relatively longer time to achieve similar beneficial effects. Pre-coating the inner surface of steel tubes with a thin layer of fly ash can notably improve the bond strength. The microstructure of the interface between concrete and steel tube was also studied by using scanning electron microscopy analyzer.     

Properties of concrete incorporating fly ash and ground granulated blast-furnace slag

This paper presents a laboratory study on the influence of combination of fly ash (FA) and ground granulated blast-furnace slag (GGBS) on the properties of high-strength concrete. A contrast study was carried out for the concrete (GGFAC) incorporating FA and GGBS, control Portland cement concrete and high-volume FA high-strength concrete (HFAC). Assessments of the concrete mixes were based on short- and long-term performance of concrete. These included compressive strength and resistance to H₂SO₄ attack. The microstructure of the concretes at the age of 7 days and 360 days was also studied by using scanning electron microscope. The results show that the combination of FA and GGBS can improve both short- and long-term properties of concrete, while HFAC requires a relatively longer time to get its beneficial effect.     

Emission of Pb and PAHs from thermally co-treated MSWI fly ash and bottom ash process

Municipal solid waste incinerator (MSWI) fly ash was regarded as a hazardous material because concentrations of TCLP leaching solution exceeded regulations. Previous studies have investigated the characteristics of thermally treated slag. However, the emissions of pollutant during the thermal treatment of MSWI fly ash have seldom been addressed. The main objective of this study was to evaluate the emission of Pb and PAHs from thermally co-treated MSWI fly and bottom ash process. The experimental parameters included the form of pretreatment, the proportion of bottom ash (bottom ash/fly ash, B/F=0, 0.1 and 1) and the retention time. The toxicity of thermally treated slag was also analyzed. The results indicated that (1) Pb emission occurred only in the solid phase and that PAHs were emitted from both solid and gas phases during thermal treatment process. (2) Washing pretreatment reduced not only the TCLP leaching concentration of Pb (from 15.75 to 1.67 mg/L), but also the emission of PAHs from the solid phase during thermal treatment process. (3) Adding bottom ash reduced the TCLP leaching concentration of thermally treated slag. (4) The concentration of Pb emission increased with retention time. (5) The thermal treatment reduced the toxicity of raw fly ash effectively, the inhibition ratio of raw fly ash and thermal treated slag were 98.71 and 18.35%, respectively.     

Utilization of ceramic waste as fine aggregate within Portland cement and fly ash concretes

The aim of this research work was to investigate the feasibility of using ceramic waste and fly ash to produce mortar and concrete. Ceramic waste fragments obtained from local industry were crushed and sieved to produce fine aggregates. The measured concrete properties demonstrate that while workability was reduced with increasing ceramic waste content for Portland cement concrete and fly ash concrete, the workability of the fly ash concrete with 100% ceramic waste as fine aggregate remained sufficient, in contrast to the Portland cement control concrete with 100% ceramic waste where close to zero slump was measured. The compressive strength of ceramic waste concrete was found to increase with ceramic waste content and was optimum at 50% for the control concrete, dropping when the ceramic waste content was increased beyond 50%. This was a direct consequence of having a less workable concrete. However, the compressive strength in the fly ash concrete increased with increasing ceramic waste content up to 100%. The benefits of using ceramic waste as fine aggregate in concrete containing fly ash were therefore verified.     

微波消解-AAS测定垃圾焚烧飞灰中重金属

采用微波消解法对城市生活垃圾焚烧飞灰样品进行预处理,在此基础上优化了城市生活垃圾焚烧飞灰的微波消解酸体系及消解程序.优化后的微波消解酸体系及用量比例为HNO3:HF:HClO4=3:4:1;消解程序的四个工步分别为:3min(5×101 kPa),3min(10×101 kPa),4min(15×101 kPa),6min(20×101 kPa).该方法的相对标准偏差为1.2%～4.5%,加标回收率为95.9%～103.7%,应用于实际的城市生活垃圾焚烧飞灰样品取得了良好的效果.     

Properties of controlled low-strength material made using industrial waste incineration bottom ash and quarry dust

Industrial waste incineration bottom ash and quarry dust are waste materials which, if reused, will contribute to sustainability. One of the potential uses of these materials in bulk quantities is in controlled low-strength material (CLSM). This paper evaluates the properties of controlled low-strength material (CLSM) made using industrial waste incineration bottom ash and quarry dust. Various mix proportions of CLSM containing bottom ash and quarry dust were developed and the properties evaluated. Tests were performed on the CLSM in fresh and hardened states involving flowability, stability, setting time, segregation resistance, California bearing ratio (CBR), and corrosivity and the results discussed. Results indicated that the setting time of the CLSM mixtures tested ranged from 3.7 to 8 h, the fresh density from 1539 to 2100 kg/m³, strength values from 0.22 to 11.42 MPa, mixtures were stable and no corrosivity. It is shown that addition of quarry dust enhanced the performance of CLSM made using bottom ash with regard to stability, strength, and CBR and hence both the industrial waste incineration bottom ash and quarry dust are potential materials for use in CLSM.     

Electrodialytic removal of heavy metals from municipal solid waste incineration fly ash using ammonium citrate as assisting agent

Electrodialytic remediation, an electrochemically assisted separation method, has previously shown potential for removal of heavy metals from municipal solid waste incineration (MSWI) fly ashes. In this work electrodialytic remediation of MSWI fly ash using ammonium citrate as assisting agent was studied, and the results were compared with traditional batch extraction experiments. The application of electric current was found to increase the heavy metal release significantly compared to batch extraction experiments at comparable conditions (same liquid-to-solid ratio, same assisting agent, and same extraction time). Up to 86% Cd, 20% Pb, 62% Zn, 81% Cu and 44% Cr was removed from 75 g of MSWI fly ash in electrodialytic remediation experiments using ammonium citrate as assisting agent. The time range for the experiments varied between 5 and 70 days.     

Melting of municipal solid waste incinerator fly ash by waste-derived thermite reaction

This work describes a novel approach for melting municipal solid waste incinerator (MSWI) fly ash, based on self-propagating reactions, by using energy-efficient simulated waste-derived thermite. The self-propagating characteristics, the properties of the recycled alloy and slag and the partitioning of heavy metals during the process are also studied. Experimental results demonstrate that the mix ratio of fly ash to the starting mixture of less than 30% supports the development of the self-propagating reaction with a melting temperature of 1350-2200 degrees C. Furthermore, metallic iron (or alloy) and the slag were retrieved after activation of the thermite reactions among the starting mixtures. It was noted that more than 91wt.% of iron was retrieved as alloy and the rest of non-reductive oxides as slag. During the thermite reactions, the partition of heavy metals to the SFA and flue gas varied with the characteristics of the target metals: Cd was mainly partitioned to flue gas (75-82%), and partition slightly increased with the increasing fly ash ratio; Pb and Zn, were mainly partitioned to the SFA, and the partition increased with increasing fly ash ratio; Cu was partitioned to the SFA (18-31%) and was not found in the flue gas; and moreover stable Cr and Ni were not identified in both the SFA and flue gas. On the other hand, the determined TCLP leaching concentrations were all well within the current regulatory thresholds, despite the various FA ratios. This suggests that the vitrified fly ash samples were environmental safe in heavy metal leaching. The results of this study suggested that melting of municipal solid waste incinerator fly ash by waste-derived thermite reactions was a feasible approach not only energy-beneficial but also environmental-safe.     

Vitrification of fly ash from municipal solid waste incinerator

Fly ash from municipal solid wastes (MSW) incinerators in Korea contains a large amount of toxic materials and requires pertinent treatments. However, since fly ash in Korea has a high chlorine concentration, it is difficult to apply cementation and chemical treatment techniques. In this study, we report the vitrification of fly ash along with the properties of the glasses and leaching characteristics of heavy metal ions.Fly ash can be vitrified by melting at 1500 degrees C for 30 min with the addition of >5 wt.% of SiO2. Glasses showed Vickers hardness of 4000-5000 MPa, bending strength of 60-90 MPa and indentation fracture toughness of approximately 0.9 MPa m(1/2). Glasses also showed the excellent resistance against leaching of heavy metal ions with Cd2+ <0.04 ppm, Cr3+ <0.02 ppm, Cu2+ <0.04 ppm and Pb2+ <0.2 ppm. These results indicate that the vitrification technique is effective for the stabilization and recycling of toxic incinerator fly ash.     

Feasibility study of using brick made from municipal solid waste incinerator fly ash slag

This study deals with the effect of MSWI slag on fired clay bricks. Brick samples were heated to temperatures which varied from 800 to 1,000 degrees C for 6h, with a heating rate of 10 degrees C/min. The material properties of the resultant material then determined, including speciation variation, loss on ignition, shrinkage, bulk density, 24-h absorption rate and compressive strength. Toxicity Characteristic Leaching Procedure tests were also conducted. The results indicate that the heavy metal concentrations in the leachates met the current regulatory thresholds. Increasing the amount of MSWI slag resulted in a decrease in the water absorption rate and an increase in the compressive strength of the MSWI-slag bricks. The 24-h absorption rate and compressive strength of the MSWI-slag brick made from samples containing slag sintered at 1,000 degrees C all met the Chinese National Standard (CNS) building requirements for second-class brick. The addition of MSWI slag to the mixture reduced the degree of firing shrinkage. This indicates that MSWI slag is indeed suitable for the partial replacement of clay in bricks.     

Properties of fresh concrete incorporating a high volume of fly ash as partial fine sand replacement

The use of fly ash in concrete is very common nowadays, mainly as a partial replacement for cement. However, the amount actually used in many countries is only between 15 to 25 percent. Disposal of unusable fly ash raises severe ecological problems and is quite expensive, not to mention the difficulty of finding dumping sites. Increased utilization of fly ash is thus, in many countries, in the national interest. A research program was initiated on the utilization of large quantities of fly ash Class F of marginal-quality in concrete as partial fine-sand replacement. The present paper studies the effect of such replacement on the properties of fresh concrete. The mechanical properties of the hardened concrete will be presented in another paper. The workability of most fly-ash mixtures was better than that of the reference mix (without fly ash). The water requirement of the fly-ash mixtures was either the same, or higher by about 9 percent, as compared with the reference mix. The rate and volume of bleeding were rather similar for the fly ash and the reference mixes. However, a significant reduction in bleeding by the fly-ash was found in the concrete mixtures with the chemical admixtures water reducer and retarder and high-range water reducer. Setting was delayed by the fly-ash, but the additional delay, that beyond the effect of the chemical admixture proper, was much less in the mixtures with the water reducer and retarder and negligible in the mixtures with the high-range water reducer.     

Removal of methylene blue from wastewater using fly ash as an adsorbent by hydrocyclone

The excessive release of color into the environment is a major concern worldwide. Adsorption process is among the most effective techniques for color removal from wastewater and fly ash has been widely used as an adsorbent. Therefore, this study was carried out to understand the adsorption behavior of methylene blue from aqueous systems onto fly ash using the continuous mode. Continuous mode sorption experiments were carried out to remove methylene blue from its aqueous solutions in hydrocyclone equipment. The experiments were performed at constant temperature and dimensions of hydrocyclone with variation of flows through the equipment, concentrations of methylene blue solutions and fly ash concentration, respectively. A maximum removal of 58.24% was observed at adsorbent dosage of 900mg/l at pH 6.75 for an initial methylene blue concentration of 65mg/l.     

Extraction of metals from municipal solid waste incinerator fly ash by hydrothermal process

This work examined the extraction properties of metallic elements from municipal incinerator fly ash under hydrothermal conditions. The ash was firstly pre-washed by distilled water, then subjected to hydrothermal treatments. The pre-washing process was effective for Na, K, Ca extraction with extraction percentages of 67%, 76% and 48%, respectively. The optimum contact time was 30 min for the pre-washing process. Five types of acids were tested for the extraction experiments and hydrochloric acid was found to be most effective for metal extraction from the ash. Compared to room condition, hydrothermal treatment accelerated the dissolution of the ash, thus promoted the reaction of acid with hazardous metals such as Cr, Cd, Pb, and furthermore, the consumption speed of acid was slowed down under hydrothermal condition. The acid simultaneously reacted with all the metal in the ash under hydrothermal condition but preferentially reacted with Ca at room condition. The optimum hydrothermal treatment temperature, time and liquid/solid ratio were 150 degrees C, 5h and 10:1 (ml:g), respectively.     

Mechanical and durability characteristics of gypsum-free blended cements incorporating sulphate-rich reject fly ash

To accommodate the wide variations among the different types of fly ash and the growing need for its greater utilization in the construction sector, relevant standards have been established that differentiate the appropriate qualities from the unacceptable ones. Unfortunately, potentially reject fly ashes (rFA), which do not comply with standard requirements, comprise a significant part of the total amount produced in coal or lignite burning stations. High-sulphate fly ash (HSFA) is a typical example of reject material, since all relevant standards (both European and ASTM) clearly define that sulphur trioxide should be kept under a certain low limit (approximately 3–5% depending on the standard) or else concrete’s durability may be threatened. The aim of this work was to design, produce and monitor the properties of a series of blended cements prepared by mixing clinker with a fly ash of high-sulphate content. No gypsum was added in the mixtures, since it is believed that sulphate ions necessary for the prolongation of the setting process (commonly provided by gypsum) could be provided by fly ash enriched in sulphates. All samples tested exhibited satisfactory initial and final setting times as well as decent compressive strength values when compared to the reference specimen containing only gypsum and no fly ash. Additionally, this paper reports on the performance aspects of blended pastes exposed to chloride binding tests and aggressive (a) 2% H₂SO₄ and (b) simulated marine environment solutions. Results revealed that waste materials not up to relevant standards could still contribute to the production of quality products of energy and economical efficiency.