Abstract: In an apparatus for treating aggressive, explosive, radioactive or toxic material or solid suspensions within a container and having a rotatable shaft supported in a housing and having one end projecting into the container and another end acted upon by a drive element, an arrangement for sealing the support and the drive element of the shaft includes a mechanical seal arranged between the shaft and the housing in the area of the container, and a static, hermetically closing sealing element arranged in the area of the drive element between the shaft and the drive element, on the one hand, and the housing, on the other hand. The interior space of the housing is filled with a lubricant which is maintained at a pressure corresponding or exceeding the pressure in the container.