Process of solvent extraction for separation of rare earth elements (REEs) through partial reflux of rare earths in solvent based on separation factor

Abstract

A process of solvent extraction for separation of rare earth elements (REEs) based on separation factor is provided. The method includes repeatedly contacting the REEs containing aqueous solution with a suitable solvent containing a diluent and/or a modifier and an REE as a partial reflux.

Claims

1. A process of solvent extraction for separation of rare earth elements from an aqueous solution comprising the rare earth elements (REEs) based on a separation factor between each of the rare earth elements, the process comprising: repeatedly contacting the aqueous solution comprising the rare earth elements with a solvent containing a diluent and/or a modifier and a partial reflux of a rare earth element having a lower distribution coefficient in relation to a targeted rare earth element to eliminate the targeted rare earth element from a raffinate of the aqueous solution comprising the rare earth elements.

2. The process as claimed in claim 1, wherein the targeted rare earth element is praseodymium, and wherein the partial reflux of the rare earth element reduces a number of separation solvent extraction stages required and eliminates a need of chemical processing for cerium separation prior to the solvent extraction for separation of the rare earth elements.

3. The process as claimed in claim 1, wherein the solvent comprises neutral phosphorus, acidic phosphorus, carboxylic acids, amines, ionic liquids, or any mixture thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic drawing of a solvent extraction process;

(2) FIG. 2 is a schematic drawing of another solvent extraction process;

(3) FIG. 3A is a schematic drawing of a solvent extraction process for light rare earths according to an aspect of the disclosure;

(4) FIG. 3B is a schematic drawing of another solvent extraction process for light rare earths according to an aspect of the disclosure;

(5) FIG. 3C is a schematic drawing of another solvent extraction process for light rare earths according to an aspect of the disclosure;

(6) FIG. 4 is a schematic drawing of a process for fractionation of light rare earths according to an aspect of the disclosure; and

(7) FIG. 5 is a schematic drawing of another process for fractionation of light rare earths according to an aspect of the disclosure.

DESCRIPTION OF THE INVENTION

(8) Conventionally, separation factors of adjacent REEs are the basis for solvent extraction process and equipment design for achieving their partitioning. It is seen that several adjacent REEs have low separation factors requiring large number of stages to achieve the desired separation. The objective of the separation is to eliminate the targeted RE with higher distribution coefficient from the raffinate, so that the raffinate can be further processed to recover the remaining REEs. It has now been found that refluxing the solvent with an REE having a lower distribution factor in relation to the targeted RE in the aqueous feed will result in elimination of the targeted RE from the raffinate. For example, Pr/Ce separation requires about 100 stages due to a separation factor of 2.0. During the extraction of LREE feed, the raffinate contains majorly La and Ce; however it also contains some amount of Pr due to the low separation factor of Pr/Ce. Removal of Pr from this stream is difficult requiring additional solvent extraction stages or alternatively, the raffinate has to be subjected to chemical processes to convert Ce.sup.3+ to Ce.sup.4+ for its removal. Refluxing the solvent with La before introduction of the solvent into the extraction section eliminates Pr from the raffinate, thereby generating a raffinate containing only La and Ce with only traces of Pr. La from the solvent is exchanged with Pr from the aqueous stream before the raffinate is discharged from the extraction section. This is based on the higher separation factor of 8.0 of Pr/La. As shown in FIG. 3C, the raffinate from the NdPr separation section contains only LaCe, thus requiring only 176 stages totally to produce separated La, Ce, Pr and Nd.

EXAMPLES

Example 1

(9) The inland red sediment placer deposit in Ganjam District of Odisha State containing heavy minerals including the RE bearing mineral was subjected to water scrubbing, de-sliming and spiraling to recover heavy minerals. This heavy mineral concentrate was passed through a series of electrostatic separators namely, high tension roll separators and electrostatic plate separators and the resultant concentrate of non-conducting minerals was subjected to high intensity magnetic separation process to yield RE bearing mineral as the product. This was then reacted at high temperature (140 C.) with caustic lye for cracking the RE mineral, followed by water leaching and HCl acid dissolution to pH 3.0 to produce mixed rare earth chloride (MRECL) of the following RE composition: CeO.sub.2: 46.65%; La.sub.2O.sub.3: 22%; Pr.sub.6O.sub.11: 5.5%; Nd.sub.2O.sub.3: 20%; Sm.sub.2O.sub.3: 3.92%; Y.sub.2O.sub.3: 0.81%, Others: 1.12%.

(10) This MRECL was taken for solvent extraction using PC88A (1.5 M) with kerosene as the diluent and isodecanol as the modifier, wherein in the first SX cycle, MRECL was fractionated into LREE, SEG and HREE fractions. The LREE fraction was subjected to a second cycle of SX using PC88A as the solvent with the above mentioned composition. Apart from LREE feed, the aqueous inlet to NdPr extraction section also contains the scrub raffinate from Ce scrubbing section. The SX scheme for LREE fractionation is shown in FIG. 4.

(11) As shown in FIG. 4, saponified solvent extracts Ce and Pr from the raffinate from NdPr extraction section and is then fed countercurrent to the NdPr extraction section, wherein the Nd, Pr and Ce from the LREE are extracted before the Ce and Pr removal in the Ce-scrubbing and Pr-scrubbing sections. Nd is stripped from the solvent before it is recycled as the lean solvent (LS). The stage-wise analysis of the extract and the raffinate from the NdPr extraction section is listed in Table 3.

(12) TABLE-US-00003 TABLE 3 Nd.sub.2O.sub.3 Stage TREO (g/l) La.sub.2O.sub.3 (%) CeO.sub.2 (%) Pr.sub.6O.sub.11 (%) (%) O1 26.60 0.63 84.65 8.43 6.29 O2 26.70 1.29 73.41 12.82 12.48 O7 26.32 2.87 44.33 12.20 40.60 O12 27.53 2.80 38.59 8.78 49.83 (Ext) A1 211.94 20.61 55.94 5.60 17.85 A6 195.3 19.93 59.32 6.97 13.78 A11 199.16 20.57 71.63 5.60 2.20 A12 200.72 21.39 75.11 3.29 0.21 (Raff)

(13) The O & A stages listed in column 1 at Table 3 are organic and aqueous outlet streams from the respective stages. 1 is the entry stage, while 12 is the exit stage for the streams. A12 is the raffinate, while O12 is the extract. A12 contains a significant amount (3.29%) of Pr. It also contains 0.21% Nd. This means that after La extraction from the raffinate, CePrNd separation would require a separate solvent extraction cycle to produce Ce of >99% purity.

Example 2

(14) Keeping all the processes and parameters given in the example 1) unchanged, the LREE fraction (along with Ce scrub raffinate) was subjected to a second cycle of SX using PC88A as the solvent but the PC88A solvent to NdPr extraction section was preloaded with La. The scheme for the SX is shown in FIG. 5.

(15) As shown in FIG. 5, saponified solvent containing La from a suitable stage in the Ce extraction section is drawn and is then fed countercurrent to the NdPr extraction section, wherein the Nd, Pr and Ce from the LREE are extracted before Ce and Pr removal in the Ce scrubbing and Pr scrubbing sections. Nd is stripped from the solvent before it is recycled as the lean solvent (LS). The stage-wise analysis of the extract and the raffinate from the NdPr extraction section is shown in Table 4.

(16) TABLE-US-00004 TABLE 4 Nd.sub.2O.sub.3 Stage TREO (g/l) La.sub.2O.sub.3 (%) CeO.sub.2 (%) Pr.sub.6O.sub.11 (%) (%) O1 29.7 18.01 79.55 1.97 0.27 O2 30.22 15.51 80.93 2.95 0.41 O7 30.22 1.24 82.66 11.7 4.2 O12 30.38 3.19 46.21 14.3 36.1 (Ext) A1 209.3 16.36 61.34 8.63 13.47 A2 215.34 15.94 77.73 5.04 1.09 A7 207.62 42.57 56.4 0.81 0.02 A12 212.1 65.11 34.79 0.1 0 (Raff)

(17) The O & A stages listed in column 1 of Table 4 are organic and aqueous outlet streams from the respective stages. 1 is the entry stage, while 12 is the exit stage for the streams. A12 is the raffinate, while O12 is the extract. A12 contains only 0.1% Pr and nil Nd. This means that after La extraction from the raffinate, Ce product of >99% purity can be directly produced without any separate solvent extraction cycle for further cerium purification.