Abstract: The invention apparatus comprises a mixing vessel closure having rotating mixing blades secured thereto. The mixing blades are driven through an axially engaged and disengaged direct coupling. The closure is mounted on a power base structure for rotation about an axis that is substantially transverse of the mixing blade axis. Additionally, the closure mounting includes a translational drive for linearly raising and lowering the closure at each of two positions about the transverse axis. A portable mixing vessel including a material charge is placed under the vessel closure. The closure is translated down to a sealed cover position over a vessel opening and secured to the vessel. The unitized assembly of the closure and vessel is translated away from a vessel supporting transport base and rotated to a inverted position. The unitized assembly is then translated down to engage a rotatory power transmission coupling.