Recovery of Cenospheres and Fine Fraction from Coal Fly Ash by a Novel Dry Separation Method

Abstract

Aluminosilicate microspheres are a valuable fraction of coal fly ash with diverse applications due to their low density. Currently, there is no efficient and ecologically rational method of cenosphere recovery from fly ash. A combination of dry methods for the recovery of both fine ash particles and aluminosilicate microspheres from coal fly ash is presented. It is comprised of fluidised bed separation followed by screening and pneumatic separation in a free-fall air chamber. Fluidised bed separation was assisted by a mechanical activator to prevent agglomeration. This step reduced the portion of material that required further treatment by 52–55 wt.%, with the recovery of microspheres exceeding 97%. Then, the concentrates were individually subjected to pneumatic separation. The final separation product for the fly ash containing 0.64 wt.% cenospheres was a cenosphere concentrate that constituted about 17 wt.% of the initial fly ash. The recovery of cenospheres was around 81%. Usage of a combination of dry methods allowed for maintaining almost 83 wt.% of the raw material in its dry form. Furthermore, the produced fly ash grain fractions could be used for different industrial purposes.

Recent Advances in Methods for the Recovery of Carbon Nanominerals and Polyaromatic Hydrocarbons from Coal Fly Ash and Their Emerging Applications

“…This method of dry separation for carbon recovery or separation methods does not need any liquid media, and moreover, the particles stay undamaged in the dry phase. Therefore, such methods have advantages over the wet-based processes for the extraction of carbon particles from CFA or from other carbon sources [66]. There are different methods for the dry separation of carbon from CFA, but some of the most important methods are separation by size classification [82], incipient fluidization, electrostatic separation, and tribo-electrostatic separation (TES) [83,84].…”

“…The extraction of UC from CFA by FF applies a sequential separation step which has to be further separated. In FF, the efficiency of UC separation from CFA depends on the granulator separation of UC [66]. It is based on the separation of hydrophobic materials from hydrophilic materials [67].…”

“…Size-based classification techniques do not involve any liquid medium for the separation of UC and CFA particles [15]. Therefore, here, the separation takes place based on their size and density, generally by screening [66]. One most common method is separation of particles based on dry screening, which will separate the fine UC particles from coarse or irregular UC particles.…”

“…Another method is cyclone classifier, which is a cylinder with an airstream at the bottom [61,66]. Due to the air stream, there will be centrifugal forces on the larger or irregular particles, which will leave the cylinder from the bottom, while the finer UC particles will join the air stream in the center, will be vortexed, and will exit from the cyclone classifier from the inner core.…”

Analysis of the Possibility of Using Cenospheres in the Production of Cement Mortars for Use in an Elevated Temperature Environment

“…for the production of light, high strength concrete [ 14 , 15 , 16 ]. The important features of cenospheres are low bulk density of about 400 kg/m 3 [ 17 , 18 ], real density of about 2.3 kg/m 3 [ 19 ], low thermal conductivity at room temperature of 0.60 (W/(mK)), and a high melting point of 1200 °C [ 20 , 21 , 22 ]. The outer diameter of the CS can vary from 1 to 500 µm, with the majority of particles having a size of 60–200 μm, while their total fraction mass in CFA is about 1–2% [ 23 ].…”