The Refinatrix is found in the center of The Empty Throne Room, powered by six Manual Auto-cycles. Impure Senntisten crystals can be deposited in it for 20 Mining experience per crystal, converting them into Senntisten crystals.
The Refinatrix has a capacity that can be checked by right-clicking it. Its maximum capacity is 500, at which point one cannot deposit more crystals. More people need to power the Manual Auto-cycles to transport crystals away, or one can just hop to another world.