Study On Mechanism Of Arsenic Adsorption On Unburned Carbon And Calcium Oxide Surface In Fly Ash

With the increase of global industrialization and the burning of fossil fuels,the atmospheric environment has been gradually destroyed,and human health has been further threatened.The problem of pollutant emission from coal-fired power station has gained a lot of public concern.This paper aims to study the enrichment effect of arsenic elements in fly ash components in coal-fired power plants by using quantum chemical calculation methods.Based on the cluster model theory,the surface model of unburned carbon and calcium oxide in fly ash is established.On the basis of density functional theory,the adsorption configurations of AsO and As₂O₃ molecules on the surface of unburned carbon and calcium oxide were obtained.The adsorption process and adsorption mechanism were further understood by parameters such as adsorption energy,adsorption bond length and atomic charge transfer.This paper provides theoretical guidance for strengthening the enrichment of arsenic on fly ash and reducing arsenic pollution in coal-fired power stations.Quantitative calculation results showed that AsO and As₂O₃ molecules exist on the unburned carbon surface in the form of physical adsorption as well as chemical adsorption,in which the physical adsorption is weak and has a low stability.HCl and NO gas can affect the enrichment of arsenic on the unburned carbon surface.Both kinds of gases can increase the adsorption capacity of zigzag unburned carbon surface on AsO and As₂O₃ molecules,in which the effect of NO is more obvious.Meanwhile,the above two gases also improve the adsorption capacity of armchair unburned carbon on AsO,but inhibit the adsorption process of As₂O₃ molecules on it.The oxygen functional group also has a certain lifting effect on the surface activity and its adsorption capacityof unburned carbon for arsenic,and the degree of improvement is in the order of:phenolic hydroxyl>lactone>carbonyl>semi-quinone>carboxyl.The above oxygen functional groups increase the adsorption capacity of the carbonaceous surface by increasing the activity of neighboring carbon atoms,which by themselves do not bring any new active sites to the system.Finally,vacancy has an effect on the adsorption capacity of unburned carbon.The absence of the top carbon atom increases the adsorption capacity of the armchair unburned carbon surface on arsenic,but reduces the adsorption capacity of the arsenic on the surface of zigzag unburned carbon.At the same time,the lack of carbon atoms affects the stability of the unburned carbon structure,resulting in a large deformation of the adsorption structure.Based on the theory of shell-embedded cluster model,a scientific and rational surface model of calcium oxide can be established,and the size of the central cluster does not affect its adsorption capacity for arsenic under the premise of ensuring sufficient adsorption sites.Both AsO and As₂O₃ molecules exist on the surface of calcium oxide in the form of chemisorption,but the adsorption energy is high,and the chemical bond strength between the two is weak,and the adsorption stability is low.