A process for removing sulfur dioxide from a flue gas, the process comprising: absorbing sulfur dioxide from a flue gas using an ammonia-containing solution to produce an ammonium sulfate solution that contains dissolved ammonium sulfate; heating and delivering at least a first portion of the ammonium sulfate solution to a vessel in which the ammonium sulfate solution dissolves potassium chloride and first potassium sulfate crystals precipitate to form a slurry that contains the first potassium sulfate crystals and an ammonium chloride solution, the ammonium chloride solution containing dissolved ammonium chloride and a first residual amount of the dissolved potassium sulfate; cooling the slurry to precipitate second potassium sulfate crystals from the first residual amount of the dissolved potassium sulfate in the ammonium chloride solution; removing the first and second potassium sulfate crystals from the ammonium chloride solution to yield a first residual ammonium chloride solution (38,48) that contains the dissolved ammonium chloride and a second residual amount of the dissolved potassium sulfate; absorbing ammonia into the first residual ammonium chloride solution to precipitate third potassium sulfate crystals from the second residual amount of the dissolved potassium sulfate in the first residual ammonium chloride solution; and removing the third potassium sulfate crystals from the first residual ammonium chloride solution (38,48,60) to yield a second residual ammonium chloride solution that contains free ammonia and the dissolved ammonium chloride and is substantially free of the dissolved potassium sulfate. absorbing sulfur dioxide from a flue gas using an ammonia-containing solution to produce an ammonium sulfate solution that contains dissolved ammonium sulfate; heating and delivering at least a first portion of the ammonium sulfate solution to a vessel in which the ammonium sulfate solution dissolves potassium chloride and first potassium sulfate crystals precipitate to form a slurry that contains the first potassium sulfate crystals and an ammonium chloride solution, the ammonium chloride solution containing dissolved ammonium chloride and a first residual amount of the dissolved potassium sulfate; cooling the slurry to precipitate second potassium sulfate crystals from the first residual amount of the dissolved potassium sulfate in the ammonium chloride solution; removing the first and second potassium sulfate crystals from the ammonium chloride solution to yield a first residual ammonium chloride solution (38,48) that contains the dissolved ammonium chloride and a second residual amount of the dissolved potassium sulfate; absorbing ammonia into the first residual ammonium chloride solution to precipitate third potassium sulfate crystals from the second residual amount of the dissolved potassium sulfate in the first residual ammonium chloride solution; and removing the third potassium sulfate crystals from the first residual ammonium chloride solution (38,48,60) to yield a second residual ammonium chloride solution that contains free ammonia and the dissolved ammonium chloride and is substantially free of the dissolved potassium sulfate.