Why Are Iron and Nickel the Only Heavy Metals in Earth's Core?

[gdp]

Sounds much like the separation of the slag on top of liquid iron in the iron and steel making process.

http://www.tfhrc.gov/hnr20/recycle/waste/ssa1.htm

Yes, exactly. There is no fundamental difference in the physical principles involved.

Indeed, one can view the mantle as the "slag" that "floated to the top" when the core material settled out, and the lithosphere or crust as the "slag" that likewise "floated to the top" of the mantle. In both cases, one had two mutually immiscible substances that separated due to differences in their specific gravities.