Flue Gas Desulfurization Fly Ash Research Articles

Flue gas desulfurization (FGD) fly ash as a sustainable, safe alternative for cement-based materials

The reduction in fly ash production in coal-fired power plants has created an opportunity to explore alternative types of fly ashes previously deemed unfit for use in concrete. In plants using flue gas desulfurization (FGD) processes, fly ash could contain high amounts of sulfur oxides, making its use in concrete inadvisable. However, the type of sulfur compound present in a fly ash strongly impacts its performance in concrete. In this study, two types of fly ash were used to evaluate the effect of sulfur oxides on mortar mixtures incorporating fly ash as supplementary cementitious material (SCM); one from an FGD unit, with high sulfur oxide content (in the form of hannebachite), and the other generated in a system without FGD, with negligible sulfur oxide. Calorimetry results show that hannebachite can effectively control C3A hydration similar to gypsum; however, its presence in FGD fly ash does not induce deleterious expansion associated with internal sulfate attack in mortars. TGA and XRD analyses suggest that hannebachite has lower reactivity than sulfate. Hannebachite not only maintains the pozzolanic reactivity of the fly ash, but its fineness may promote OPC hydration, increasing compressive strength. The results of this study indicate that FGD fly ash can be used as an SCM, allowing more sustainable concrete production.

Durability and microstructure analysis of the road base material prepared from red mud and flue gas desulfurization fly ash

The present study aimed to investigate the durability and microstructure evolution of road base materials (RBM) prepared from red mud and flue gas desulfurization fly ash. The durability testing showed that the strength of RBM with the blast furnace slag addition of 1wt%, 3wt% and 5wt% reached 3.81, 4.87, and 5.84 MPa after 5 freezing–thawing (F–T) cycles and reached 5.21, 5.75, and 6.98 MPa after 20 weting–drying (W–D) cycles, respectively. The results also indicated that hydration products were continuously formed even during W–D and F–T exposures, resulting in an increase of the strength and durability of RBM. The observed increase of macropores (>1 μm) after F–T and W–D exposures suggested that the mechanism of RBM deterioration is pore enlargement due to cracks that develop inside their matrix. Moreover, the F–T exposure showed a greater negative effect on the durability of RBM compared to the W–D exposure. The leaching tests showed that sodium and heavy metals were solidified below the minimum requirement, which indicates that these wastes are suitable for use as a natural material replacement in road base construction.

Preparation and characterization of a red mud-based road base material: Strength formation mechanism and leaching characteristics

The present study was designed to prepare and characterize an eco-friendly road base material using mainly red mud in terms of mechanical properties, hydration and leaching characteristics. The microstructure was characterized by using scanning electron microscopy, X-ray diffractometer, Fourier transform infrared spectroscopy, electron probe microanalysis, Magnetic angle spinning Nuclear magnetic resonance and mercury intrusion porosimetry while inductively coupled plasma emission spectrometer was adopted to characterize the leaching behavior of hazardous compounds. The results showed that the strength of the optimum proportion reached 5.92 MPa and 6.66 MPa after curing for 7 and 28 days respectively and meet the highest strength requirement (class I) of 5–7 MPa for road base in Chinese standards. The results also showed that the strength increased with long term soaking which implies a good durability of RBM against water. The microstructure analysis indicated that predominant hydration products are C-S-H, C-A-S-H, N-A-S-H gels, ettringite and are responsible for strength development in the road base. The leaching results showed that all parameters in specimens cured for 7d and 28d are lower than drinking water GB 5749-2006 standard limits. Therefore, based on strength and environmental performance, red mud-flue gas desulfurization fly ash mix can be used as a road base material. This process is believed to reduce environmental pollution related to red mud and flue gas desulfurization fly ash, lower the road base cost and also save huge disposal fees that is used for safe disposal of these wastes.

NIKKISO PUMPS EXPANDS IN MIDDLE EAST

The reduction in fly ash production in coal-fired power plants has created an opportunity to explore alternative types of fly ashes previously deemed unfit for use in concrete. In plants using flue gas desulfurization (FGD) processes, fly ash could contain high amounts of sulfur oxides, making its use in concrete inadvisable. However, the type of sulfur compound present in a fly ash strongly impacts its performance in concrete. In this study, two types of fly ash were used to evaluate the effect of sulfur oxides on mortar mixtures incorporating fly ash as supplementary cementitious material (SCM); one from an FGD unit, with high sulfur oxide content (in the form of hannebachite), and the other generated in a system without FGD, with negligible sulfur oxide. Calorimetry results show that hannebachite can effectively control C3A hydration similar to gypsum; however, its presence in FGD fly ash does not induce deleterious expansion associated with internal sulfate attack in mortars. TGA and XRD analyses suggest that hannebachite has lower reactivity than sulfate. Hannebachite not only maintains the pozzolanic reactivity of the fly ash, but its fineness may promote OPC hydration, increasing compressive strength. The results of this study indicate that FGD fly ash can be used as an SCM, allowing more sustainable concrete production.