In this work, the textural properties of a series of whole anthracitic-derived fly ashes sampled in eight hoppers from the electrostatic precipitators and their sized fractions (from >150 to <25 μm) are investigated. Data from N2 adsorption isotherms at 77 K, helium density, and mercury porosimetry have contributed to establish a relationship between the Brunauer−Emmett−Teller (BET) surface areas, V TOT, porosity, carbon content (the type of fly ash carbons), and Hg retention in these fly ashes. The unburned carbons in these ashes are macroporous materials, and they are different from the carbons in fly ashes from classes C and F (the latter derived from the combustion of bituminous coals) and show different textural properties. These ashes represent the end member of the fly ash classes C and F with respect to certain textural properties. Although the BET surface area and V TOT values for the studied samples are the lowest reported, they increase with the increase in carbon content, anisotropic carbon content, and particle size of the ashes. Thus, a positive relationship between all these parameters and Hg capture by the coarser ash fractions was found. The finest fraction of carbons (<25 μm) represented an exception. Although it makes a significant contribution to the total carbon of the whole fly ashes and shows relatively higher surface areas and V TOT values, its Hg concentration was found to be the lowest. This suggests that the type of unburned carbons in the finest fraction and/or other adsorption mechanisms may play a role in Hg concentration. Because the textural properties of anisotropic carbons depend on their subtype and on their origin, the need for its differentiation has been evidenced.

The graphitization process of two different carbonized anthracites in the temperature interval of 2000−2800 °C was studied by using the optical properties of the materials prepared. These optical properties are defined by the main axes ( , , and ) and parameters (R ev, R st, and R am) of the reflectance-indicating surface (RIS) and the anisotropy indexes (B W and oil bireflectance ratio). Two temperature segments, with the second one being a plateau, were found to occur in the evolution of the structural organization (textural anisotropy) of the materials. The variation with the temperature of the structural order of the materials as determined from X-ray diffraction and Raman crystalline parameters followed a similar tendency, thus confirming the validity of the optical properties as another indicator of the textural and structural changes occurring during anthracite high-temperature treatment. Moreover, as shown by the optical microscopic observation of the materials, crystalline aggregates, microspheres, and flake microstructures, which were previously detected in natural graphites, were developed from the dense and massive particles, with their proportion being higher in those materials with a larger degree of textural anisotropy and/or structural order.