Abstract: A process for removal of particulate material and sulfur dioxide from a gas stream by washing the gas stream in a treatment zone in a wet scrubber by injection of a reactant such as high calcium or magnesium lime to control pH in the range of 6.0 to 8.5. A resultant slurry containing calcium sulfate, calcium sulfite and solids is formed in the scrubber and a controlled quantity of the solids containing slurry is recycled to the scrubber washing zone as part of the washing fluid to aid in co-precipitation by providing nucleation sites for the calcium sulfate and sulfite crystals maintaining an unsaturated calcium sulfate level in the slurry.