Alkaline absorbent for simultaneously removing SO3 and mercury in coal-fired flue gas and preparation method thereof

The invention discloses a preparation method of an alkaline absorbent for simultaneously removing SO3 and mercury in coal-fired flue gas, which comprises the following steps: mixing alkaline residues, carbide slag and red mud, dipping in a halide salt solution, uniformly stirring and mixing, then drying and calcining, cooling to room temperature after the drying and calcining are finished to obtain a calcined product, and finally grinding to obtain the alkaline absorbent. Compared with the prior art, the alkaline absorbent is prepared from the alkaline waste residues such as waste alkali residues, carbide slag and red mud in the chemical industry as raw materials, the desulfurization wastewater concentrated solution is adopted as the halogenation modifier, comprehensive utilization of waste can be achieved, cooperative treatment of SO3 and mercury heavy metal can be achieved, the cost is low, the preparation process is simple and convenient, and industrial production is facilitated. And the energy-saving and