Method and apparatus for preparing fumed silica from coal gangue

The invention discloses a method and an apparatus for preparing fumed silica from coal gangue. The method comprises: performing pressurized reaction, in microwave fields, on activated coal gangue powder and hydrofluoric acid, converging the generated silicon tetrafluoride gas with water vapor to obtain a mixture and introducing the mixture into a micorwave-absorbing agent packed column under microwave irradiation, and performing high-temperature pyrohydrolysis reaction on the mixture to generate gas silicon dioxide and hydrogen fluoride; performing shock chilling, gathering, separating, acid-removing and purging on the generated gas silicon dioxide and hydrogen fluoride as well as unreacted water vapor to prepare a fumed silica product; separating the hydrogen fluoride gas and the water vapor from a cyclone separator and the top of an acid removing furnace, and adding the water to prepare hydrofluoric acid for recycling, wherein the fumed silica product can be used as a thickening agent, a rubber reinforcing agent and a washing assistant agent, and the like; by-products are aluminum fluoride, iron fluoride and magnesium fluoride and the like; the microwave-absorbing agent in the present invention can significantly improve the direct hydrolysis efficiency of silicon tetrafluoride; the pressurized microwave reaction can significantly increase the reaction rate and conversion rate of silicon dioxide and hydrofluoric acid; and the microwave-absorbing agent is recycled and easy to regenerate, and has a high utilization rate, a simple process and low preparation cost.