Unburned Carbon from Fly Ash for Mercury Adsorption: I. Separation and Characterization of Unburned Carbon

Abstract

In searching for a low cost adsorbent for mercury removal from flue gas, this study focuses on the utilization of unburned carbons from fly ash as the substitute material for the costly activated carbons. In this first paper of the series, various separation technologies are introduced for the extraction of unburned carbon from different sources of fly ash. The unburned carbons have been efficiently separated from clean ash, which is a value-added product for the concrete industry, with the separation technologies such as gravity separation, electrostatic separation, and froth flotation. Carbon concentrate with a LOI (Loss On Ignition) value of 67~80% has been generated from the processes. Characterization of the carbon products has been performed to determine the physical and chemical properties of the material. It has been found that the unburned carbon particles had a porous structure, which is similar to the activated carbon. The BET surface area of these materials was in a range of 25~58m 2 /g. The majority of the pores are in the range of macropore, and some parts of the surface were embedded with glass spheres. There is a linear relationship between the LOI value and the carbon and sulfur content in the carbon concentrate. Chemical analysis indicated that the mercury content in unburned carbon was much higher than the other separation products, which suggests that the carbon has certain ability to capture mercury from flue gas.

Toward an indexing approach to evaluate fly ashes for geopolymer manufacture

“…Unburnt coal particles have much higher SSA, usually between 20-60 m 2 /g [24], due to their internal porosity which is accessible to nitrogen in the BET method.…”

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

“…Rubel et al [137] also reported that carbon-rich products from combustion ash could decrease NOx emissions and Hg due to ion-pair interactions between NO + and O2 -at the surface of carbon, with subsequent condensation of NO2 in micropores. In addition, the pore size on the surface of the adsorbent can be changed after adsorption of a certain amount of Hg, producing the optimum pore size (micropores, < 2nm) for adsorbed NOx [138]. Rubel et al [137] also showed that the surface area of adsorbents increased due to adsorption of NOx, as shown in Figure 12.…”

The Character of Dual Site Adsorbent on Coal Fly Ash Toward Benzene Adsorption

“…One application of CFA is used as an adsorbent [2]. CFA is composed of some oxides including Al 2 O 3 , SiO 2 having active site and unburned carbon (C) as a mesopore material [3] that enables it to act as a dual site adsorbent. On the other side, benzene is one of the toxic pollutant and carcinogenic compound [4] used as a raw material in the petrochemical industry [5].…”