The ashes from lignite combustion are characterized by high CaO and free CaO contents and are a potentially interesting material for CO2 bonding, more particularly as theirs economical use is limited. The findings of CO2 absorption by suspensions prepared on the basis of ash from lignite combustion are presented in the paper. On these grounds CO2 sequestration potential via mineral carbonation in ash aqueous suspensions in Poland will be estimated

The production of electricity and heat in Poland is the reason why the commercial power industry is the largest emitter of CO₂. At the same time, significant amounts of solid by-products of combustion, which can be used to bind CO₂ by mineral carbonation, are generated during the production processes. The article presents the results of research on mineral sequestration of CO₂ (suspension-CO₂) using fluidized bed combustion (FBC) fly ashes from hard coal combustion. The analyzed fluidized bed combustion (FBC) fly ashes were characterized by a significant free CaO content (1.7–6.8%) and a high CO₂ binding potential ranging from 9.7 to 15.7%. In the case of fluidized bed combustion (FBC) fly ashes suspensions, the basic product of the carbonation process is calcium carbonate, which is clearly indicated by the results of the phase composition determination of solidified suspensions of fluidized bed combustion (FBC) fly ashes. The degree of carbonation, i.e. the degree of CO₂ binding, calculated on the basis of the calcium carbonate content, in the analyzed suspensions was up to 1.1%. Mineral carbonation also reduces the leachability of pollutants such as: Zn, Cu, Pb, Ni, As, Hg, Cd, Cr, Cl, and SO₄^2-. The pH is also reduced from about 12 to about 9. Aqueous suspensions of fluidized bed combustion (FBC) fly ashes with introduced CO₂ can potentially be used in underground mining. These activities are in line with the concepts of Carbon Capture and Utilization and the idea of circular economy.

Limited use of biomass has been observed in recent years. The processes of electricity and heat production in conventional boilers and fluidized bed boilers generate waste – mainly fly ash. This waste is traditionally used in many industries. The most important are: mining, production of building materials (including cement) and road construction. The use of fly ash in underground mining (suspension technology) is a method of fly ash recovery, which is typical for the Polish industry. The amount of fly ash (10 01 02) and waste (10 01 82) including ashes from fluidized bed boilers in the year 2012 amounted to 1,490.7 thousand tons. For many years, fly ashes from hard coal combustion in conventional boilers has also been used in various production technologies of building materials, such as: cement, concrete, building ceramics and lightweight aggregates. The ashes from hard coal combustion in fluidized bed boilers are also used in the production of cement and autoclaved aerated concrete. Due to extensive economic use, commercial power plants started to reclassify fly ash from hard coal combustion, turning waste into a by-product after meeting the requirements of the Act on waste of 14 December 2012. The ashes from the co-combustion of biomass are also used. The utilization of fly ash from lignite combustion, both from conventional boilers and fluidized bed boilers, is a cause of concern, while the total recovery of fly ash from the combustion of hard coal and lignite has decreased in recent years. For this reason, studies on the use of traditional fly ash technologies such as the production of building materials and new fly ash technologies such as the use as sorbents in power generation and wastewater treatment, as well as on binding CO₂ through mineral sequestration in the Carbon Capture and Utilization, are being carried out.