fluorine is recovered as calcium fluoride from a fluoroetchant solution composed mainly of hydrogen fluoride and ammonium fluoride using a sealed reaction tank equipped with a supply port for adding the fluoroetchant solution to the tank , a supply port for adding calcium carbonate to the tank , a vapor supply port for adding steam to heat the solution in the tank , an air supply port for providing air to aerate the contents of the tank , a stirrer for stirring the contents of the tank , an ejector for removing vapors from the tank connected to the tank via a mist separator for separating mist from the vapors being removed from the tank , and an exhaust port for removing calcium fluoride from the tank .