A rotating drum apparatus for the mixing and processing of materials, the rotating drum apparatus comprising: a rotating drum (12) arranged with the length of the drum and the axis of rotation of the drum extending along the horizontal; an inlet at a first point on the drum (12) for receiving materials prior to mixing and/or processing; a screw (14) within the drum (12) for mixing the materials whilst conveying them lengthwise along the drum (12), wherein the screw (14) includes a helical blade extending along the length of the drum (12) with the outer edge of the helical blade being fixed to the inner surface of the drum (12) such that material can be conveyed and mixed in separated volumes (16) between each turn of the screw blade (14); an outlet at a second point along the drum for discharge of materials after mixing and/or processing; and a plurality mixing devices (18) for promoting mixing of the material in each of the separated volumes (16) of material as the material is conveyed along the screw (14), wherein the plurality of mixing devices (18) are spaced apart along the blade of the screw (14), and wherein there is at least one mixing device (18) for each turn of the screw blade (14).