Industrial by-product gypsum, also known as flue gas desulfurization (FGD) gypsum, refers to gypsum produced when calcium oxide reacts with desulfurization and denitrification agents during flue gas desulfurization and denitrification processes. Currently, industrial by-product gypsum mainly originates from flue gas desulfurization and denitrification, as well as waste generated by industries such as steel and copper metallurgy, phosphate chemical processing, and fertilizer production.