Fly ash refers to the fine ash collected from the flue gas after coal combustion, which is the main solid waste 

discharged from coal-fired power plants. It resembles cement in appearance and varies in color from milky white 

to grayish-black. The color of fly ash is an important quality index, which can reflect the amount and difference 

of carbon content. To some extent, it can also reflect the fineness of fly ash. The darker the color, the finer the 

particle size of fly ash and the higher the carbon content. Fly ash can be divided into low calcium fly ash and high 

calcium fly ash. High-calcium fly ash is usually yellowish in color and low-calcium fly ash is grayish in color. Fly 

ash particles are multi-porous honeycomb structures with large specific surface area and high adsorption activity. 

The particle size ranges from 0.5 to 300μm. And the bead wall has a porous structure, the porosity is up to 50% - 80%, 

has a strong water absorption.