Abstract: A mixer-settler apparatus is disclosed. The outlet tubes from the settler section are made positively adjustable in height so that proper phase separation can be obtained under varying conditions.

Abstract: An improved liquid-liquid extraction process for the separation of the elements of the lanthanide series is disclosed. The process involves dissolving the lanthanides in a sulfuric acid solution to form rare earth sulfates whereafter the solution is contacted with an organic solvent immiscible with water and containing di (2-ethylhexyl) phosphoric acid whereby the lanthanides are separated from impurities and at least some of the lanthanides are extracted into the organic phase. Thereafter, the organic and aqueous phases are separated and the organic phase containing the impurities-separated lanthanides is subjected to a back extraction with an aqueous phase comprising an aqueous solution with sulfuric acid. The contact time between the aqueous and organic phases in the back extraction is regulated so that a desired or desired elements of the lanthanides are back extracted into the aqueous phase. The contact time is controlled and is less than the total extraction equilibrium time between the phases.

Abstract: An apparatus for countercurrent extraction of a dissolved material from a first liquid phase to a second liquid phase is disclosed. The apparatus comprises overflow provision for each of the liquid phases with preferably adjustable overflow for the lower liquid phase whereby desired control of interface level can be obtained.