Preparation and characterization of sorbents prepared from ash (waste material) for sulfur dioxide (SO2) removal

Abstract

Sorbents synthesized from various types of ash (coal fly ash, coal bottom ash, oil palm ash, and incinerator ash) for flue gas desulfurization were investigated. The sorbents were prepared by mixing the ashes with calcium oxide and calcium sulfate using the water hydration method. The effects of various sorbent preparation variables, such as the hydration period, the ratio of calcium oxide to ash, and the amount of calcium sulfate, on the Brunauer-EmmettTeller (BET)-specific surface area of the resulting sorbent were studied using a two-level full factorial design. The surface area of the sorbents obtained range from 15.4 to 122.1 m 2 /g. Regression models were developed to correlate the significant variables to the surface area of the sorbents. An analysis of variance (ANOVA) showed that the model was significant at a confidence level of 95%. It was found that apart from all the individual variables studied, interactions between variables also exerted a significant influence on the surface area of the sorbent. From the activity test results, it was found that sorbents prepared from coal fly ash and oil palm ash have the highest SO 2 absorption capacity. Scanning electron microscope (SEM) analysis showed that the sorbent was composed of a compound with a high structural porosity, while an X-ray diffraction spectrum showed that calcium aluminum silicate hydrate compounds are the main products of the hydration reaction.

Influence of hydration variables on the properties of South African calcium/siliceous-based material

“…The mesopore is believed to responsible for the increased surface area. All the pore radii were within the range of 2-100 nm which as reported in literature [11,14] has been found to be the effective zone for sulphation reaction of SO 2 and Ca(OH) 2 /fly ash sorbents. Higher hydration period and low CaO/fly ash ratio sorbents showed higher BJH volume.…”

“…In the presence of water during the hydration process, the active silica and alumina in the siliceous material (in this case fly ash) reacts with hydrated lime to form complex compounds of calcium silicate/ alluminate hydrate [5,9,15,16]. It is believed that it is the complex compounds which are responsible for increased surface area in the sorbent [11]. The high specific surface area is important for the accessibility of Ca 2+ ions by SO 2 in the flue gas.…”

“…However, there were a few particles with smooth surfaces which may have been fly ash that did not take place in the reaction. The observed high porous structure in the prepared sorbent indicates that the fly ash reacted extensively with the calcium oxide, so that not only the surface layers of the spherical particles, but also the inside of the particles could not retain their original shape [11].…”

“…A rough 60.00 3.00 [11] quantitative approximation of the amount of the function groups in the samples was also done. The samples were micronized using ethanol and ground for 3 minutes, then dried for 24 h at room temperature.…”

Fabrication of Multifunctional Hybrid Composites Using Fly Ash to Control Environmental Pollutants: A Review

“…From the above results, it can be concluded that the ability of FA to capture SO2 is mainly related to its surface area, pore structures and calcium ion content. Specific surface area is increased after the FA is hydrated, leading to more calcium ions that can react with SO2 to produce CaSO4 [149,150].…”