Apparatus for heat treatment of raw materials for production of a melt includes a first chamber having a first chamber crucible, a first chamber inlet for a raw material leading to the first chamber crucible, at least one first chamber microwave generator, and a first chamber outlet for a melt formed from the raw material, at least a second chamber having a second chamber crucible, a second chamber inlet for receiving the melt leading to the second chamber crucible, at least one second chamber microwave generator, and a second chamber outlet, and one or more baffles or cascades arranged within the apparatus so that the melt flows over, under, or through an opening in at least one of the baffles or cascades. A preheating chamber and/or a storage chamber can also be included. A method of producing a homogeneous melt from raw materials by volume microwave heating is also provided.