, the organic phase suction line 32 and the mixture feed line 41 may be suitably arranged so long as the aqueous phase A and the organic phase O stored in the feed compartment 3 can be conveyed to the reaction compartment 4 while being mixed.

It is desirable to provide a spray nozzle or a full cone nozzle at the distal end of the mixture feed line 41. A plurality of orifices are formed on the circumferential surface at the distal end of the spray nozzle or full cone nozzle. The mixture (emulsion) issuing from the spray nozzle or full cone nozzle is discharged into the reaction compartment 4 as an even finer emulsion, enabling the extractive reaction to be carried out more efficiently. The spray nozzle or full cone nozzle is not limited to a conical shape. For example, a trumpet-shaped nozzle may be used when the intention is to broadly discharge the mixture of aqueous phase A and organic phase O. The diameter of the plurality of orifices formed on the circumferential surface of the spray nozzle or full cone nozzle may be suitably selected without particular limitation, although the diameter is preferably between 30 μm and 20 mm, more preferably between 30 μm and 10 mm, and even more preferably between 100 μm and 6 mm. Within this range in diameter, the extractive reaction can be fully carried out while maintaining good phase separation of the aqueous phase A and the organic phase O.

Next, the operation of this liquid-liquid extraction unit 1 is described.

When the liquid-liquid extraction unit 1 is used to extract and separate rare-earth elements, for instance, a rare-earth element-containing aqueous phase A and an organic phase O to which an extractant has been added are introduced to the feed compartment 3 from, respectively, the aqueous phase inlet and the organic phase inlet. There is no particular need at this point to use a means for mixing together both phases A and O; rather, the two phases A and O are stored within the feed compartment 3 in a vertically phase-separated state owing to a difference in their specific gravities. The stored aqueous phase A and organic phase O are drawn to, typically, a pump P serving as the mixing feeder from, respectively, the aqueous phase suction line 31 and the organic phase suction line 32, and are agitated within the pump (mixing feeder) P, thereby forming an emulsion-state mixture M of the aqueous phase A and the organic phase O. This mixture M is then expelled into the reaction compartment 4 through the mixture feed line 41. The expelled emulsion-state mixture M gradually phase-separates in the reaction compartment 4, at which time the desired rare-earth element contained in the aqueous phase A is extracted to the organic phase O. The partially phase-separated aqueous phase A and organic phase O then move to the standing compartment 5 in fluid communication therewith above and below the second partition 2b, and fully phase-separate in the standing compartment 5. The fully phase-separated aqueous phase A and organic phase O are discharged from, respectively, the aqueous phase outlet and the organic phase outlet and recovered outside of the liquid-liquid extraction unit 1. In cases where a plurality of rare-earth elements are contained in the aqueous phase A and where some portion of the rare-earth elements cannot be extracted by the organic phase O, the unextracted rare-earth element is discharged from the aqueous phase outlet while remaining in the aqueous phase.

A multistage liquid-liquid extraction apparatus that carries out a multistage extraction operation can be constructed from a plurality of the liquid-liquid extraction units 1 of the invention by, as illustrated by the four-stage liquid-liquid extraction apparatus shown in FIG. 2, connecting the aqueous phase outlet of one unit to the aqueous phase inlet of another unit, connecting the organic phase outlet of the one unit to the aqueous phase inlet of the other unit, and similarly coupling together all of the units in this fashion. Moreover, as shown in the examples described below, when consecutively carrying out an extraction step that extracts a rare-earth element from an aqueous phase A into an organic phase O, a scrubbing step that scrubs the organic phase O and a back-extraction step that recovers the rare-earth element from the organic phase O, some or all of these extraction, scrubbing and back-extraction sections may be built as multistage liquid-liquid extraction apparatuses using the liquid-liquid extraction unit 1 of the invention.

As explained above, the liquid-liquid extraction unit of the invention makes it possible, without the use of an agitator as in prior-art extraction units, to agitate and mix together an aqueous phase A and an organic phase O with only, for example, a single pump (mixing feeder) P to rapidly form an emulsion, carry an extractive reaction and effect phase separation. Accordingly, solvent extraction can be carried out under easier operation and control than in the prior art, which has required close control of the liquid levels using separate pumps for feeding the aqueous phase A, feeding the organic phase O, discharging the aqueous phase A and discharging the organic phase O. Moreover, with the liquid-liquid extraction unit of the invention, phase separation is rapid and operation at a large flow rate comparable to that of prior-art mixer-settlers is possible while maintaining a good efficiency. At the same time, because the liquid-liquid extraction unit of the invention is much smaller than prior-art mixer-settlers, when used to build a multistage liquid-liquid extraction apparatus that extracts and separates a plurality of elements existing in admixture within an aqueous phase A or a multistage continuous extraction system arrived at by coupling together a plurality of such multistage liquid-liquid extraction apparatuses, the footprint occupied by the resulting equipment can be greatly reduced and the volume of liquid required for solvent extraction can be substantially decreased, contributing to significant cost reductions.

EXAMPLES

Experimental Examples are given below to more concretely illustrate the advantageous effects of the liquid-liquid extraction unit of the invention, although it should be noted that the invention and the extraction process used therein are not limited by the following Examples.

Experimental Example 1

A multistage liquid-liquid extraction apparatus (FIG. 2) was constructed by coupling together four liquid-liquid extraction units 1 like that shown in FIG. 1. The dimensions of the liquid-liquid extraction units 1 used were 120 mm (W)×200 mm (D)×200 mm (H). A first partition 2a measuring 2 mm×120 mm×140 mm (H) was positioned 60 mm from one end of the unit in the horizontal direction, and a second partition 2b measuring 2 mm×120 mm×120 mm (H) was positioned 140 mm from the same end. The main body 11 of the unit was divided into three compartments: a feed compartment 3, a reaction compartment 4 and a standing compartment 5. The first partition 2a positioned between the feed compartment 3 and the reaction compartment 4 was disposed so as to form a 3 mm gap with the base of the unit, and the second partition 2b positioned between the reaction compartment 4 and the standing compartment 5 was disposed so as to form a 5 mm gap with the base. A spray nozzle having a plurality of 4 mm diameter orifices formed in a circumferential surface of a conical line closed at the distal end was mounted on a distal end of the mixture feed line