The formation and emission of SO

3

in coal-fired flue gas not only pose significant threats to atmospheric environments and human health but

also negatively affect power plant operations. Injecting alkaline sorbents into flue gas has proven to be an effective method for SO3 removal. The removal efficiency of SO

3

by injecting Na

2

CO

3

and Ca(OH)

2

absorbents was investigated under different flue gas conditions

and the removal performance was compared with that of the blended absorbents. Moreover

the physicochemical properties of the alkaline absorbents before and after the reaction were characterized using SEM

XRD

FT-IR

and XPS techniques. Based on experimental data and characterization results

the gas-solid reaction model were proposed to elucidate the mechanisms of SO

3

removal by Na

2

CO

3

and Ca(OH)

2

. Furthermore

the adsorption process of Na

2

CO

3

on SO

3

was simulated

and the adsorption energy was calculated and compared with that of Ca(OH)

2

. The results showed that

Na

2

CO

3

demonstrated superior SO

3

removal efficiency compared with Ca(OH)

2

and the removal efficiency was enhanced by increasing the reaction temperature

SO

3

mass concentration

absorbent stoichiometric ratio and residence time. The blended absorbent with a molar ratio of Ca:2 Na:S=5.00:1.25:1.00 achieved an SO

3

removal efficiency of 86.07% under practical operating conditions at a low cost. The findings indicated that the gas-solid reaction between Na

2

CO

3

and SO

3

followed the shrinking core model

while the reaction between Ca(OH)

2

and SO

3

adhered to the grain model. The adsorption energy of SO

3

on Na

2

CO

3

was higher than that on Ca(OH)

2

. This study can provide theoretical insights and technical support for efficient and cost-effective removal of SO

3

from coal-fired flue gas.