The present invention discloses an apparatus for slag treatment. A dual-cavity drum apparatus for treating slag supported by a mandrel comprises: left and right drums, a distribution disc, a mandrel and a feed hopper. In the apparatus, the distribution disc is placed between the left and right drums, the feed hopper is installed above the distribution disc, and a fixing ring below the distribution disc, and the mandrel joints the left and right drums and the distribution disc. The present apparatus is characterized in that supporting bearings are installed at the outboard of the left and right drums and the two ends of the mandrel, the left and right drums have inner and outer layer, the inner drum is composed of grates, one end of the grates are fixed on the end cover of the outer drum through socket formed by supporting ring, another end of the grates joint the supporting ring fixed at the outer drum, the mandrel joints the outer drum, a ring gear for transferring toque is installed at one side of the outboard of the outer drum, and the ring gear joints one side of the outer drum. The apparatus of the present invention cools slag fully, improves the properties of product slag, reduces weight of the apparatus and cost, and simultaneously increases space underneath for repair and maintenance.