Metallurgical assemblies and systems according to the present technology may include a refractory vessel including sides and a base. The base may define a plurality of apertures centrally located within the base. The sides and the base may at least partially define an interior volume of the refractory vessel. The assemblies may include a lid removably coupled with the refractory vessel and configured to form a seal with the refractory vessel. The lid may define a plurality of apertures through the lid. The assemblies may also include a current collector proximate the base of the refractory vessel. The current collector may include conductive extensions positioned within the plurality of apertures centrally located within the base.