A scrubber for scrubbing at least one pollutant from flue gas includes a first stage configured to provide a chemical oxidant to a stream of flue gas, and a second stage configured to provide a chemical or chemicals to the stream of flue gas, a scrubbing medium recirculation feature configured to continuously recirculate a slurry used in the second stage, and a by-product processing portion configured to remove a by-product from a stream of slurry withdrawn from the scrubber. The by-product includes reaction products of at least one pollutant.