Recovery potentials of cenospheres from bituminous coal fly ashes

Cenospheres are defined as hollow spherical particles with density less than water. This definition is based on natural concentration of cenospheres from fly ashes in wet disposal sites, i.e. ponds or lagoons. On the other hand, the lowest-density oxide in fly ashes, crystalline silica, has a density of 2.6 g/cm3. Therefore, hollow particles with densities of up to 2.6 g/cm3 are also present in fly ashes depending on the wall thickness and the ratio of the hollow part. These heavier cenospheres could also have high-value applications in construction industry as fillers and reinforcements. In this study, recovery potentials of cenospheres from two bituminous coal fly ashes were examined as a function of density and size. Fly ash samples from Çatalağzı (CFA) and Sugözü (SFA) thermal power plants were first subjected to float-sink, wet sieving and air classification tests to separate them into various products. These products were then analyzed under optical microscope for their cenosphere contents on the basis of point counting and area estimations. Separation efficiency was evaluated in terms of yield, cenosphere content and recovery of the products. Overall results showed that CFA has much more cenospheres than SFA, and cenosphere contents decreased with decreasing size and increasing density for both samples. Despite similar variations in cenosphere contents through density and size, CFA exhibited much higher yields and recoveries compared to SFA for the respective product.