A process for treating flue gas containing fly ash and carbon dioxide is disclosed. In the process, carbon dioxide and fly ash are contacted with an aqueous metal hydroxide solution to convert carbon dioxide into a metal carbonate, and wherein the metal carbonate and the metal hydroxide cause the fly ash to undergo a geopolymerization reaction and form a geopolymerized fly ash. The geopolymerized fly ash is recovered for disposal or for further use, such as a concrete additive.