The invention provides a new enclosure for slag pelletizers, and a new method of operating such an enclosure, that minimizes the noise and the escape into the ambient atmosphere of hydrogen sulfide and airborne particulate material produced by the pelletization. The enclosure consists of impereable walls and a roof, the pelletized material being removed through an openable door at one end that is closed during the process. The enclosure has three successive zones, in the first of which contains the pelletizer, this being supplied with only the amount of water needed for pelletization. In the second zone containing the slag pile a plurality of very fine mist producing nozzles supply water to the gases to cool them using its latent heat of evaporation, the amount of water supplied being such as to cool them as much as possible while being limited so that it all remains vaporized and cannot enter the slag pile to increase its moisture content. In the third zone the quantity of water supplied is sufficient to condense the water vapor, entraining the soluble hydrogen sulfide and the particulate matter. The condensed water and entrained material is removed and treated, preferably with waste alkaline water, to stabilize the hydrogen sulfide, remove the particulate material, and recycle the water. The non-condensible gases exiting from the top of the third zone can pass through a chimney to the atmosphere or to a gas scrubber for further scrubbing.