Utilization of Fly Ash as a Compost Amendment in Enhancing the Growth of Mustard Plants

2 - Carbon dioxide sequestration by direct mineralization of fly ash

As a natural source of carbon, coal has been extensively utilized in both industrial and domestic contexts. However, when coal-fired power is generated, it produces a large amount of solid waste. Among them, solid waste represented by fly ash is characterized by a large output and difficult treatment. Therefore, the comprehensive utilization of fly ash is becoming increasingly imperative. Fly ash contains abundant valuable components. Its distinctive physicochemical properties provide a solid foundation for its application. This paper reviews the current situation and research progress of fly ash utilization from two aspects: resource utilization and deep processing. Firstly, hazards and physicochemical properties of fly ash are summarized. Based on this, the development trends of fly ash in building materials and ecological restoration were discussed. Subsequently, the research progress of deep processing technologies on adsorbents and electrochemical energy storage materials is reviewed. The adsorption capacity of the modified fly ash material for Cd2 + reached 90.27 mg/g. The battery capacity of the fly ash-based electrode reaches 688 milliampere-hours per gram. This paper provides a reference for the dual utilization of fly ash resource recovery and deep processing, and is expected to become a key approach for the industrial utilization of fly ash.

Chapter Seven - Utilization of Fly Ash in Ceramic Brickmaking

In this study, the potential utilization of fly ash was investigated as an additive in solidification process of radioactive waste sludge from research reactor. Coal formations include various percentages of natural radioactive elements; therefore, coal fly ash includes various levels of radioactivity. For this reason, fly ashes have to be evaluated for potential environmental implications in case of further usage in any construction material. But for use in solidification of radioactive sludge, the radiological effects of fly ash are in the range of radioactive waste management limits. The results show that fly ash has a strong fixing capacity for radioactive isotopes. Specimens with addition of 5-15% fly ash to concrete was observed to be sufficient to achieve the target compressive strength of 20 MPa required for near-surface disposal. An optimum mixture comprising 15% fly ash, 35% cement, and 50% radioactive waste sludge could provide the solidification required for long-term storage and disposal. The codisposal of radioactive fly ash with radioactive sludge by solidification decreases the usage of cement in solidification process. By this method, radioactive fly ash can become a valuable additive instead of industrial waste. This study supports the utilization of fly ash in industry and the solidification of radioactive waste in the nuclear industry.

Utilization of mechanochemically pretreated municipal solid waste incineration fly ash for supplementary cementitious material

The rapidly increasing demand for energy in China leads to the construction of new power plants all over the country. Coal, as the main fuel resource of those power plants, results in increasing problems with the disposal of solid residues from combustion and off gas cleaning. This investigation describes chances for the utilization of fly ash from coal-fired power plants in China. After briefly comparing the situation in China and Germany, the status of aluminum recycling from fly ash and the advantages for using fly ash in concrete products are introduced. Chemical and physical analyses of Chinese fly ash samples, e.g., X-ray diffraction (XRD), ICP (Inductive Coupled Plasma) and particle size analysis, water requirement, etc. are presented. Reasonable amounts of aluminum were detected in the samples under investigation, but for recovery only sophisticated procedures are available up to now. Therefore, simpler techniques are suggested for the first steps in the utilization of Chinese fly ash.

Circulating fluidized bed combustion (CFBC) is a newer type of burner that employ a circulating process to burn fuel effectively. CFBC burning process is gaining more popularity due to its compact size, high efficiency and lower burning temperature compared to the pulverized coal combustion (PCC) burner. The CFBC burner produces fly ash with different physical properties compared to the PCC burner, i.e. the fly ash is not rounded, and required higher water content for comparable workability. The CFBC fly ash also has a high sulfur content that is detrimental for hardened concrete. Due to its drawbacks, the CFBC hardly used as cementitious material and geopolymer precursor. This study focuses on comparing variations in the concentration of NaOH solution and variations in the ratio of alkaline activators to the setting time and compressive strength of geopolymer mortars on a new class of CFBC fly ash, which have low sulfur content. The concentrations of NaOH solution were 6M, 8M, 10M, and 12M, while the alkaline activator ratios used were 3.0, 2.5, 2.0, 1.0, and 0.5. It was concluded that the low sulfur CFBC fly ash has a potential to be utilized as geopolymer precursor, however, with a shortcoming in its high water demand. The CFBC fly ash used in this study resulted in a geopolymer matrix with good compressive strength and stability. The water demand varies with the fly ash sampling time shows the challenges in the utilization of the fly ash. The highest mortar’s compressive strength, 33.4 MPa at 90 days was achieved at NaOH concentration of 8M and ratio of sodium silicate solution to sodium hydroxide solution of 2.5 with excellent stability.

In this study, utilization of coal fly ash with higher loss on ignition (LOI) for geopolymer mortar was investigated. The fly ash with approximately 9% of LOI was compared with Class F fly ash. Relationship between heat curing condition and strength was clarified. As the results, although compressive strength of geopolymer mortar with higher LOI was 30-50% smaller, it was available for geopolymer mortar as an alumina silicate material. The higher temperature and the longer period for initial curing, the higher strength was obtained. In order to decrease drying shrinkage, the higher temperature and the longer period for heat curing were required.

Utilization of fly ash as an alternative to silica sand for green sand mould casting process

Application of fly ash-amended composts as manure enhances the crop yield of certain plants like corn, sorghum, collard and mustard greens. Organic compost made out of grass and leaves (home-made) is better than the commercial composts for amendment with fly ash. A 20--40% fly ash in the amended compost and a soil to ash-amended compost ratio of 3:1 are recommended for making bed for plantation. Organic compost mixed with fly ash, due to reduced porosity, will help the bed to retain water and conserve water supply to plants. Organic compost will release to the manure additional quantities of N, P, and S that are not substantially available in fly ash. It appears that chemical reaction and/or mineralization occurs during composting of fly ash with organic manure to release more N, P, K and S to the system. Potassium is more elevated in all plants grown in potted soil treated with fly ash-amended compost than in those grown in soil or soil treated with organic manure. Contrary to expectation Ca in fly ash is not effectively used by plants as the latter treated with ash- amended compost is not rich in Ca. This suggests that Ca may be tied up as insoluble CaSO{sub 4} in the manure so that it may not be bioavailable to the plant. Uptake of boron by bean, bell pepper and egg plant is considerably higher than that absorbed by corn, sorghum and greens resulting in poor yield for the former.

Application of fly ash-amended composts as manure enhances the crop yield of certain plants like corn, sorghum, collard and mustard greens. Organic compost made out of grass and leaves (home-made) is better than the commercial composts for amendment with fly ash. A 20--40% fly ash in the amended compost and a soil to ash-amended compost ratio of 3:1 are recommended for making bed for plantation. Organic compost mixed with fly ash, due to reduced porosity, will help the bed to retain water and conserve water supply to plants. Organic compost will release to the manure additional quantities of N, P, and S that are not substantially available in fly ash. It appears that chemical reaction and/or mineralization occurs during composting of fly ash with organic manure to release more N, P, K and S to the system. Potassium is more elevated in all plants grown in potted soil treated with fly ash-amended compost than in those grown in soil or soil treated with organic manure. Contrary to expectation Ca in fly ash is not effectively used by plants as the latter treated with ash- amended compost is not rich in Ca. This suggests that Ca may be tied up as insoluble CaSO{sub 4} in the manure so that it may not be bioavailable to the plant. Uptake of boron by bean, bell pepper and egg plant is considerably higher than that absorbed by corn, sorghum and greens resulting in poor yield for the former.

The utilization of fly ash in construction and cement industry increases from last few decades. But the question on utilization of fly ash for construction purpose was raised by many investigators as it causes a source of radioactive gas radon and increase in the gamma dose. In order to optimize the utilization of fly ash in cement with additional benefit of reducing radon diffusion coefficient and exhalation rate were studied. The compressive strength of mortar is the key factor for cement industry, thus it should not be sacrificed for utilization of fly ash. Keeping this in mind, compressive strength, porosity, radon diffusion and exhalation rate study was carried out through the mortar reinforced with the blending of fly ash with cement. The results indicated decrease in effective radon diffusion coefficient from 0.363 × 10−7 to 0.013 × 10−7 m2/s for fly ash up to 50 % substitution. The addition of fly ash in cement first decreased the radon exhalation rates up to 25 % substitution then increases and similar trends were observed for compressive strength. Thus, the addition of fly ash exerts a positive effect up to a 20–25 % replacement beyond which it may introduce negative effect depending upon the level of substitution.

Does the utilization of coal fly ash in concrete construction present a radiation hazard?

The utilization of biomass fly ash and lime was investigated as cement replacements in blast furnace briquetting. Sample characterization included chemical (XRF) and mineralogical (XRD) analysis, particle size determination, and thermal behaviour (TGA/DSC-TGA). Additionally, the mechanical performance and fly ash, lime, and fly ash/lime mixtures as cement replacements were determined by incorporation in mortars tested by standardized methods (EN 196-1). Based on the results, detrimental alkali, sulphur, and chlorine contents of the biomass fly ashes do not seem to restrict use in briquetting. However, the utilization of fly ashes as cement replacements resulted in significant decline of 28 day compression strength values. The two different fly ash samples attested to 28 day compression strength of app. 72% and 55% of the respective control. Inferior mechanical performance was related to moisture absorption according to XRD and DSC-TGA and relatively larger particle size. Respectively, lime additions encouraged fly ash strength development only in the case of inferior fly ash performance related to the aforementioned effects. The results provide important information for the forth-coming manufacture of blast furnace test briquettes, which is to commence in the near future.

Traditionally fly ash is thought to be glassy, spherical particle originating from pulverized coal combustion (PCC) at temperature up to 1700 °C. However, nowadays fluidized bed combustion (FBC) technology is spreading quickly around the world as it is an efficient and environmentally friendly method. FBC is also able to utilize mixtures of low-grade solid fuels (e.g., coal, lignite, biomass, and waste) that have fluctuating quality, composition, and moisture contents. However, this leads to a high variation in the produced fly ash quality, unlike PCC fly ash, and hence challenges when attempting to utilize this fly ash. In this study, the utilization of fluidized bed combustion fly ash (FBCFA) was reviewed using the Scopus database. The most promising utilization target for FBCFA from biomass combustion is as a fertilizer and soil amendment. In construction, the FBCFA from various fuels is utilized as cement replacement material, in non-cement binders, as lightweight aggregates and cast-concrete products. Other types of construction applications include mine backfilling material, soil stabilizer, and road construction material. There are also other promising applications for FBCFA utilization, such as catalysts support material and utilization in waste stabilization.