Abstract: Off-gas produced by a blast furnace is treated by scrubbing and cooling the gas with water and then settling solids from the liquid effluent. The liquid effluent is cooled following settling, and a major portion of the cooled effluent is recirculated for another pass through the scrubbing and cooling steps. The remainder of the effluent is chemically treated, and heavy metals are precipitated and settled as sludge. The clarified effluent is filtered and then treated with a cation exchange resin in a sodium cycle. A substantial part of the ion-exchange-treated effluent is returned to the scrubbing and cooling steps, and another substantial part is discharged as blowdown. Return of water which is of adequate quality to prevent scaling significantly reduces the make-up requirements. By discharging the ion-exchange-treated effluent to blowdown while ammonium ions are being removed from solution by a given charge of ion-exchange resin, the standards for maximum blowdown discharge of ammonia are satisfied.