If you're thinking of a centrifuge as a machine:
* Decanter: This word refers to a device that separates liquids from solids by gravity, essentially the opposite of a centrifuge that uses centrifugal force.
* Filter: This word applies to a device that separates particles based on size or properties, but it doesn't necessarily involve the same forces as a centrifuge.
If you're thinking of the action of centrifuging:
* Decanting: This word describes the process of carefully pouring a liquid from a container, leaving behind sediment.
* Sedimentation: This refers to the process of settling heavier particles to the bottom of a liquid, again using gravity instead of centrifugal force.
Ultimately, the best antonym for "centrifuge" depends on the specific context.