in the alpha versions you could place a medium storage on the same platform full of a smelt-able material (clay for example) and if the smelter was on it would automatically pull the ores and smelt them then return them to an open location. Apparently this is broken in the last few versions I've seen.
to recreate: build an extra large platform c, place a soil extractor on one side of the center, and a smelter on the other side so their backs are together (this is my current set up). place any form of empty storage on the smelter end (couple of medium storage units for example) and some full soil containers on the other end. select clay or quartz and activate the soil extractor. once done I would expect the output to go to the next available storage spot then for the smelter to pull it for processing.