Ashes from co-combustion of coal and biomass: New industrial wastes

► Ashes from co-combustion of coal and biomass (10 types) subject to critical review. ► Ashes constitutes the potential source of pollution at nonadditive properties. ► Reported physicochemical properties, chemical composition, leachability of metals. ► Ashes nature depends on type and portion of biomass and conditions of combustion.