zone refining

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zone refining
1. In metallurgy, the smallscale production of high-purity metals using the principle that an impure melt will deposit pure crystals on solidifying. A rod of the specimen is melted over a very narrow region at one end, and then the molten region is transferred along the rod by means of a moving furnace. Impurities collect in the molten zone and are swept to one end of the metal.

2. In geology, the same mechanism has been invoked whereby incompatible trace elements are partitioned into an advancing partial melt.