Purification of SO2-containing exhaust air

摘要

Process for preparing a sodium dithionite solution as the end product from sodium borohydride, aqueous sodium hydroxide and sulphur dioxide, characterized in that sulphur dioxide contained in an exhaust gas is scrubbed out in at least a first scrubbing stage (I) with a scrubbing agent containing aqueous sodium hydroxide, exhaust gas is removed from this scrubbing stage, part of the scrubbing product from this scrubbing stage (I) is drawn off from this scrubbing stage (I) and is mixed with a sodium borohydride solution in aqueous sodium hydroxide, that the mixture is cooled and degassed and the cooled and degassed mixture is drawn off as the end product. <IMAGE>