AU2019250770A2 - Amphiphilic asymmetrical diglycolamides and use thereof for extracting rare earth metals from acidic aqueous solutions - Google Patents

Abstract

The invention relates to new optimized amphiphilic asymmetrical diglycolamides suitable for use as rare earth metal extracting agents. Said diglycolamides have general formulae (I) and (II), where: R

Description

AMPHIPHILIC ASYMMETRICAL DIGLYCOLAMIDES AND USE THEREOF FOR EXTRACTING RARE EARTH METALS FROM ACIDIC AQUEOUS SOLUTIONS DESCRIPTION TECHNICAL FIELD

The invention relates to the field of extraction of rare earth metals contained in

acidic aqueous solutions derived from natural or urban ores. More specifically, the invention relates to novel asymmetrical diglycolamides of

optimised amphiphilic nature suitable for use as extractants of rare earth metals. It also relates to the use of thesediglycolamides to extract rare earth metals

from acidic aqueous solutions. The invention further finds applications in the production of rare earth metals

from concentrates derived from « urban ores », i.e. "mines" composed of industrial and domestic waste comprising rare earth metals, and in particular in the recycling of rare

earth metals contained in:

- waste electrical and electronic equipment (also called "WEEE" or "W3E")

and more specifically in spent or scrap permanent magnets of Neodymium-Iron-Boron type (or NdFeB) or Samarium-Cobalt type (or Sm-Co); and

- spent primary and secondary batteries of Nickel-Metal Hydride type (or Ni

MH).

However, it can also be applied to produce rare earth metals from concentrates derived from rare earth-containing natural ores such as monazite, bastnaesite, apatite or

xenotime, or from concentrates derived from residues of natural ores, e.g. tin slag.

STATE OF THE PRIOR ART

Rare earth metals (hereafter "REMs") group together metals characterized by similar properties, namely scandium (Sc), yttrium (Y) and all the lanthanides, the latter

corresponding to the 15 chemical elements listed in Mendeleev's periodic table of elements ranging from atomic number 57 for lanthanum (La) to atomic number 71 for lutecium (Lu). Within this group, a distinction is made between (( light REMs, i.e. having an atomic number of no more than 61 (scandium, yttrium, lanthanum, cerium, praseodymium and neodymium), and « heavy » REMs, i.e. having an atomic number of at least 62 (samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium and ytterbium).

The particular electronic configuration of REMs, and especially their unsaturated

4f electron sublayer, imparts unique chemical, structural and physical properties thereto. Advantage is taken of these properties in industrial applications as varied as they are

sophisticated: glass and ceramics, polishing, catalysis (particularly oil and automotive industries), production of high-tech alloys, permanent magnets, optical devices (in

particular photo cameras and video cameras), luminophores, rechargeable batteries for electrical or hybrid vehicles, alternators for wind turbines, etc.

REMs therefore belong to so-called "technological" metals for which supply is strategic.

World demand for rare earth metals is constantly on the increase (approximately

9 % to 15 % per year). However, since the number of countries producing rare earth metals remains limited - China alone currently supplying more than 90 % of world rare

earth production - there is a non-negligible, long-term risk of shortage in rare earth supplies, hence the need to optimise all channels allowing production thereof.

The recycling of REMs contained in post-consumption waste and manufacturing scrap, as yet in its infancy, represents one pathway for producing REMs.

One of the leading markets, in volume and potential market value, for the recycling of REMs concerns NdFeB permanent magnets included in electrical or hybrid

vehicles, wind turbines, hard disks, induction motors or other electrical equipment. This resource for the recovery and recycling of REMs is of particular interest since these

magnets contain a large amount of light REMs (about 30 weight % of neodymium

/praseodymium mixture) and a smaller amount of high-value heavy REMs (dysprosium and sometimes terbium). In addition to containing iron in large amount, NdFeB permanent magnets generally have an anticorrosion protective coating made of nickel and copper or other transition metals (cobalt, chromium, etc).

A further resource of interest for the recycling of REMs concerns Ni-MH batteries which are chiefly used in electrical or hybrid vehicles but also in various portable

appliances which contain a mixture of lanthanum, cerium, neodymium and praseodymium, as well as iron, nickel and cobalt.

Recycling REMs contained in post-consumption waste or manufacturing scrap

therefore implies the ability to obtain efficient separation thereof from other metal elements contained in these wastes and scrap, and in particular from iron.

Hydrometallurgy, based on liquid-liquid extraction, is widely considered to be one of the most suitable processes for extraction of REMs from the medium in which they

are contained and for separation thereof. The hydrometallurgical processes currently in industrial use for the retrieval of

REMs from an acidic aqueous phase preferably employ organophosphorus extractants such as phosphoric acids, phosphonic acids, phosphinic acids, carboxylic acids and alkyl

phosphates. For example, these are di-2-ethylhexylphosphoric acid (or HDEHP), 2-ethylhexyl-2-ethylhexylphosphonic acid (or HEH[EHP]), bis(trimethyl-2,4,4

pentyl)phosphinic acid (or CyanexT M 272), neodecanoic acid (or VersaticTM 10) and ti-n butylphosphate (or TBP).

However, the use of these extractants is not adapted to the recovery of REMs contained in an acidic aqueous phase derived from the treatment of post-consumption

waste or manufacturing scrap, since they all have the disadvantage of extracting

transition metals in high amount and iron in particular. The use thereof would therefore require the removal of these transition metals from the aqueous phase before REM

extraction, which would lead to a process that is cumbersome to implement and therefore of little industrial interest.

Diglycolamides (hereafter "DGAs") represent a family of extractants developed by a Japanese team as part of research into the reprocessing of spent nuclear fuel with a

view to co-extracting trivalent actinides and lanthanides from a raffinate of the PUREX process, but which recently gave rise to a certain number of studies into the use thereof for the recycling of REMs.

DGAs meet the general formula RR'NC(O)CH 20CH 2C(O)NR"R"' where R, R', R" and R"' represent hydrocarbon groups, typically alkyls.

They are said to be "symmetrical" when R, R', R" and R"' are each the same and "asymmetrical" when this is not the case.

Among asymmetrical DGAs, a distinction is made between two sub-types:

- Type 1 asymmetrical DGAs where R and R'are each the same, R" and R"' are

each the same but differ from R and R'; and

- Type 11 asymmetrical DGAs where R and R" are each the same, R'and R"' are

each the same but differ from R and R". With regard to the use of symmetrical DGAs as extractants for the recycling of

REMs, it was shown in International application PCT WO 2016/046179, hereafter reference [1], that lipophilic symmetrical DGAs having 24 or more carbon atoms , such as

NNN',N'-tetraoctyl-3-oxapentanediamide (or TODGA), allow recovery of dysprosium, praseodymium and neodymium from an acidic aqueous phase derived from the

treatment of NdFeB permanent magnets, not only quantitatively but also selectively in relation to the other metal elements contained in this phase, in particular in relation to

iron and boron. With regard to the use of asymmetrical DGAs as extractants for the recycling of

REMs, the data given in the literature are much less convincing.

For example, Mowafi and Mohamed (Sep. Sci. Technol. 2017, 52(6), 1006-1014, hereafter reference [2]) used NN-dihexyl-N',N'-didecyldiglycolamide (or (DH-DD)-DGA) to

recover several REMs from three acidic aqueous media: nitric, sulfuric and hydrochloric. Not only the evaluation of the selectivity of this DGA for REMs against iron, nickel, cobalt

and caesium has been solely conducted in a nitric aqueous medium, the concentrations of metal elements used in this study, namely 0.002 mol/L, are much lower than those

expected for an aqueous phase derived from treatment of waste or manufacturing scrap; this is particularly true with regard to iron, the concentrations thereof in waste and

manufacturing scrap being an essential issue when recycling REMs.

Narita and Tanaka (Solvent Extraction Research and Development, Japan, 2013, 20, 115-121, hereafter reference [3]) focused on the use of NN'-dimethyl-NN'-di-n-octyl

diglycolamide (or MODGA), as extractant with a view to recovering REMs from acidic aqueous media derived from the manufacture of NdFeB permanent magnets. These

authors show that it is possible with this DGA to separate neodymium and dysprosium from iron and nickel, and dysprosium from neodymium in a nitric or sulfuric aqueous

medium. However, their work is solely based on acidic aqueous phases containing only

0.001 mol/L of dysprosium, neodymium, iron and nickel, i.e. here again concentrations far removed from those expected in an acidic aqueous phase derived from treatment of

NdFeB permanent magnets. Therefore, no test has been conducted on acidic aqueous phases simulating those actually obtained from the treatment of permanent magnets. In

addition, the latter work does not specify the behaviour and impact of other metal elements also contained in an acidic aqueous phase derived from treatment of NdFeB

permanent magnets, such as praseodymium or cobalt. Finally, it is important to cite work by E Ravi et al. (Radiochim. Acta 2014, 102(7), 609-617, hereafter reference [4]) which, although unrelated to the field of REM recycling

from waste and manufacturing scrap but concerning the reprocessing of spent nuclear fuel, shows that the extraction of europium from a nitric aqueous phase having molarity

higher than 1 by asymmetrical DGAs of formula RR'NC(O)CH20CH 2C(O)N((CH 12 )1 CH 3) 2 where R and R' represent an n-butyl, n-hexyl, n-octyl or n-decyl group, does not vary

significantly when the number of carbon atoms, in the alkyl R and R' groups, decreases from 8 to 6, then from 6 to 4.

Faced with the major challenge of recycling REMs contained in post-consumption waste and manufacturing scrap, and in particular in spent or scrap NdFeB permanent

magnets and spent Ni-MH primary and secondary batteries, the inventors have considered that it is desirable to increase the panel of extractants able to be used for

recycling needs.

They therefore set themselves the objective of providing novel extractants allowing highly efficient extraction of REMs from acidic aqueous solutions derived from

the treatment of natural or urban ores, together with good selectivity in relation to other

U

metal elements also likely to be contained in these aqueous solutions and in particular iron, cobalt and nickel.

In the course of their work, the inventors ascertained that, contrary to the teaching of reference [4], the degree of amphiphilicity of an asymmetrical DGA

dependent upon the number of carbon atoms of the hydrocarbon groups carried by the two amide nitrogens - has an impact on the capacity thereof to extract REMs from acidic

aqueous solutions and on the selectivity of this extraction, and that therefore it is possible

to provide asymmetrical DGAs having extremely interesting properties both in terms of REM extraction capacity and extraction selectivity by optimising the amphiphilicity of

these DGAs. In particular, they have found that these properties are at least equivalent to and

even greater than those displayed by TODGA used in reference [1]. The invention is based on these findings.

DESCRIPTION OF THE INVENTION

These objectives are reached with the invention of which the first subject is a

diglycolamide meeting one of general formulae (1) and (II):

0 0 0 0 R11- O R2 R1 '- O ) ,R1

R12 0 R2 02

(1) (II) where:

R' is a linear or branched alkyl group having 2 to 24 carbon atoms; R 2 is a linear or branched alkyl group having 9 to 14 carbon atoms;

with the exception however of the diglycolamide of general formula (1) where R1 is an n-butyl group and R 2 is an n-dodecyl group, and of thediglycolamide of general formula

(II) where R1 is an ethyl group and R 2 is an n-dodecyl group. Therefore, whether meeting general formula (1) or general formula (II), the DGA

of the invention has the characteristics of comprising:

- first, two same hydrophilic groups each having 2 to 4 carbon atoms and

corresponding to the radicals R'; and

- secondly, two same lipophilic groups each having 9 to 14 carbon atoms and

corresponding to the radicals R2

. In the foregoing and in the remainder hereof, it is meant by: - "linear or branched alkyl group having 2 to 4 carbon atoms", any group

selected from among ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl

groups; - "linear or branched alkyl group having 9 to 14 carbon atoms", any linear or

branched chain alkyl group having 9, 10, 11, 12, 13 or 14 carbon atoms such as the groups

n-nonyl, isononyl, n-decyl, isodecyl, n-undecyl, isoundecyl, n-dodecyl, isododecyl, n-tridecyl, isotridecyl, n-tetradecyl, isotetradecyl, 2-methyloctyl, 2-methylnonyl, 2-methyldecyl, 2-methylundecyl, 2-methyldodecyl, 2-methyltridecyl, 2-ethylheptyl, 2-ethyloctyl, 2-ethylnonyl, 2-ethyldecyl, 2-ethylundecyl, 2-ethyldodecyl, 2-propylhexyl,

2-propylheptyl, 2-propyloctyl, 2-propylnonyl, 2-propyldecyl, 2-propylundecyl, 2-butylhexyl, 2-butylheptyl, 2-butyloctyl, 2-butyldecyl, 2-hexyloctyl, 3,7-dimethyloctyl,

2,4,6-trimethylheptyl group, etc. Also, the terms "aqueous medium", "aqueous solution" and "aqueous phase"

are equivalent and interchangeable, and the terms "organic solution" and "organic phase" are equivalent and interchangeable.

In addition, the expressions "from .... to .... " and "between .... and .... " are

equivalent and are meant to include the limits. According to the invention, R1 is advantageously an ethyl, n-propyl, isopropyl,

n-butyl or isobutyl group, whilst R 2 is advantageously a linear alkyl group. In addition, it is preferred that R 2 has from 10 to 14 carbon atoms, or in other

words that R 2 is selected from among n-decyl, n-undecyl, n-dodecyl, n-tridecyl and n-tetradecyl groups, preference among these being given to the n-dodecyl group.

Therefore, as examples of preferred DGAs, mention can be made of:

- the DGA of general formula (1) where R1 is an ethyl group and R 2 is an

n-dodecyl group, hereafter called (DE-DDd)-DGA;

- the DGA of general formula (1) where R1 is an n-propyl group and R 2 is an

n-dodecyl group, hereafter called (DP-DDd)-DGA;

- the DGA of general formula (1) where R1 is an isopropyl group and R 2 is an

n-dodecyl group, hereafter called (DiP-DDd)-DGA;

- the DGA of general formula (II) where R1 is an n-propyl group and R 2 is an n-dodecyl group, hereafter called DPDDdDGA;

- the DGA of general formula (II) where R1 is an n-butyl group and R 2 is an n-dodecyl group, hereafter called DBDDdDGA; and

- the DGA of general formula (II) where R1 is an isobutyl group and R 2 is an

n-dodecyl group, hereafter called DiBDDdDGA. Among these DGAs, best preference is given to:

- (DE-DDd)-DGA for particularly high performance in extracting all REMs from a nitric aqueous medium, with REM distribution coefficients depending on the extracted

REM that are 8 to 15 times higher than those obtained with TODGA under the same operating conditions;

- DPDDdDGA for particularly high performance in extracting dysprosium from a sulfuric aqueous medium, with a dysprosium distribution coefficient that is 110 times

higher than that obtained with TODGA under the same operating conditions; and

- DBDDdDGA for particularly high performance in extracting all REMs from a hydrochloric aqueous medium with distribution coefficients, depending on the extracted

REM, that are 2 to 4 times higher than those obtained with TODGA under the same

operating conditions. A further subject of the invention is the use of a DGA such as afore-defined to

extract at least one rare earth metal from an acidic aqueous solution. In the invention, said at least one rare earth metal is preferably extracted from

the acidic aqueous solution via liquid-liquid extraction, in which case this aqueous solution is contacted with a water-immiscible organic solution comprising the DGA in an

organic diluent, then separated from the organic solution. The concentration of the DGA in the organic solution is advantageously between

0.05 mol/L and 0.5 mol/L and is preferably 0.1 mol/L

The organic solution may additionally comprise a phase modifier able to increase the load capacity of the DGA, i.e. the maximum concentration of metal elements that may

be contained in the organic solution without the occurrence of the formation of a third phase through de-mixing when this organic solution is contacted with an aqueous

solution containing metal elements. The phase modifier can particularly be selected from among trialkyl phosphates

such as tri-n-butylphosphate (or TBP) or tri-n-hexylphosphate (or THP), alcohols such as

n-octanol, n-decanol or isodecanol, and monoamides such as NN-dihexyloctanamide (or DHOA), NN-dibutyldecanamide (or DBDA), NN-di(2-ethylhexyl)acetamide (or D2EHAA),

NN-di(2-ethylhexyl)propionamide (or D2EHPA), NN-di(2-ethylhexyl)isobutyramide (or D2EHiBA) or NN-dihexyldecanamide (or DHDA).

Also, this phase modifier preferably does not represent more than 15 volume

% of the organic solution, even no more than 10 volume %of the volume of this solution if it

is an alcohol such as n-octanol. With regard to the organic diluent, this can be any non-polar organic diluent

proposed for use for liquid-liquid extraction, such as a hydrocarbon or mixture of

hydrocarbons e.g. n-dodecane, hydrogenated tetrapropylene (TPH), kerosene, IsaneTM IP_

185T or IsaneTM IP-175T, preference being given to n-dodecane.

In the invention, the acidic aqueous solution from which at least one said rare

earth metal is extracted, preferably comprises a mineral acid which is advantageously nitric acid, sulfuric acid, hydrochloric acid or a mixture thereof.

Evidently however, said acidic aqueous solution may comprise a mineral acid other than HNO 3, H 2 SO4 and HCI, or a mixture of mineral acids other than a mixture of

these acids. At all events, the concentration of the mineral acid or mixture of mineral acids in

the acidic aqueous solution is preferably between 0.1 mol/L and 5 mol/L

This acidic aqueous solution can firstly be a solution derived from dissolution in an acid medium of a concentrate of urban ore and in particular a concentrate ofW3E

waste.

-LU

In this respect, it can particularly be a solution derived from the dissolution in an acid medium of a material in divided form (powder, fragments, etc.) and resulting from

treatment (e.g. demagnetisation + grinding) of spent or scrap NdFeB or Sm-Co permanent magnets.

As a variant, it can also be a solution derived from dissolution in an acid medium of a material in divided form (powder, fragments, etc.) and resulting from treatment (e.g.

heat treatment + grinding) of spent Ni-MH primary or secondary batteries.

As a further variant, it can also be a solution derived from the dissolution in an acid medium of a natural ore comprising rare earths such as monazite, bastnaesite,

apatite or xenotime, or from dissolution in an acid medium of a residue of a natural ore such as tin slag.

Whichever the case, the rare earth is preferably selected from among lanthanum, praseodymium, neodymium, dysprosium and mixtures thereof.

Other characteristics and advantages of the invention will become apparent from the following additional description. This additional description is evidently given solely to

illustrate the object of the invention and is not in any manner to be construed as a

limitation thereof.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS I - SYNTHESIS OF THE DIGLYCOLAMIDES OF THE INVENTION:

1.1- DGA of general formula (I):

DGAs of general formula (1) can be obtained with the synthesis method represented below:

0 0O + (R2O)2-NH O NOH R2 + (R 1 )2-NH O O 0 2 R2 4 3 1 COMU DIPEA

0 0

R1 R2

(1)

In this synthesis method, a solution comprising 0.2 mol/L (1eq.) ofdiglycolic

anhydride, denoted 1, and 0.2 mol/L (1 eq.) of an amine denoted 2 of formula (R 2 ) 2 -NH where R 2 is such as defined in general formula (1), in an apolar aprotic solvent such as

2-methyltetrahydrofurane (or 2-MeTHF), is left under agitation for 6 hours leading to

dialkyldiglycolamic acid denoted 3. A coupling reagent such as 1-cyano-2-ethoxy-2-oxoethylidenaminooxy)

dimethylamino-morpholino-carbenium hexafluorophosphate (or COMU - 1.2 eq.) and a tertiary amine such as NN-diisopropylethylamine (or DIPEA - 2 eq.) are added to the

medium and left under agitation for 5 minutes before adding an amine (1.1 eq.) denoted 4 of formula (R') 2 -NH where R1 is such as defined in general formula (1). The medium is

left under agitation overnight at ambient temperature. The reaction is halted with the addition of water, the medium filtered and the

filtrate washed with saturated Na 2 CO 3 solution and 10 % HCI solution. The organic phase

obtained is dried over MgSO4 , filtered and concentrated, and the residue obtained is purified by flash chromatography on silica gel using a gradient of heptane/ethyl acetate

mixture. The fractions containing the pure product are combined and concentrated. A pure DGA is obtained of general formula (1) in the form of a colourless-to-yellow oil with a

yield of 37 %to 71 %.

The following were thus synthesized:

1) (DE-DDd)-DGA, meeting the following particular formula:

0 0

N N

1H NMR (CDCI,3 400 MHz): (ppm):4.30 (se, 4H), 3.24 (m, 8H); 1.49 (m, 4H), 1.25 (m, 36H), 1.15 (t, J = 7.1 Hz, 31H), 1.08 (m, 31H), 0.86 (t, J = 7.1 Hz, 6H) 13 C NMR (CDCI,3 101 MHz): 5 (ppm): 168.44, 168.10, 68.68, 48.80, 45.87, 40.98, 40.21, 31.90, 26.66, 29.60, 29.56, 29.51, 29.44, 29.37, 29.32, 28.82, 27.51, 27.07, 26.75, 22.65, 14.06,12.81

HRMS (ES/ positive mode): m/z calculated for {MH}*: 525.4995; found: 525.4996

2) (DP-DDd)-DGA, meeting the following particular formula:

o o

N 0 N

1H NMR (CDCI ,3400 MHz): & (ppm): 4.26 (s, 2 H), 4.28 (s, 2 H), 3.24 (m, 4 H), 3.14 (t, 3JH,H

= 8 Hz, 4 H), 1.51 (m, 8 H), 1.22 (m, 36 H), 0.85 (m, 12 H) 13 C NMR (CDCI,3 101 MHz): 5 (ppm): 168.55, 168.42, 69.10, 69.04, 48.47, 47.32, 46.90, 45.73, 31.89, 29.63, 29.60, 29.56, 29.52, 29.40, 29.34, 29.32, 28.94, 27.58, 27.01, 26.81,

22.66, 22.06, 20.75, 14.09, 11.35, 11.13 HRMS (ES/ positive mode): m/z calculated for {MH}*: 553.5308; found: 553.5310

3) (DiP-DDd)-DGA, meeting the following particular formula:

0 0

N 0 N

-L _3

'H NMR (CDCI,3 400 MHz): (ppm): 4.27 (s, 2 H), 4.23 (s, 2 H), 3.93 (s, 1H), 3.43 (s, 1H), 3.28 (t, J = 7.6 Hz, 2H), 3.16 (t, J = 7.6 Hz, 2H), 1.51 (m, 4H), 1.40 (d, J = 5.7 Hz, 6H), 1.25

(m, 37H), 1.17 (d, J = 6.4 Hz, 6H), 0.87 (t, J = 6.7 Hz, 6H) 13 C NMR (CDCI,3 101 MHz): 6(ppm): 168.56, 167.80, 70.96, 69.17, 48.05, 47.07, 46.01, 45.90, 32.04, 29.78, 29.75, 29.74, 29.67, 29.55, 29.48, 29.08, 27.73, 27.17, 26.95, 22.81, 20.93, 20.57, 14.25

HRMS (ES/ positive mode): m/z calculated for{MH}*: 553.5308; found: 553.5305

1.2 - DGA of general formula (II): DGAs of general formula (II) can be obtained with the synthesis method

represented below: 0 0 R 1-CHO + R2-NH 2 NaBH4 R1 R 2-NH + HO OH

1' 2' 3' 4'

DIPEA

0 0 R o R1 R2 R2 (II) In this synthesis method, a solution comprising 2 mol/L (1eq.) of an aldehyde denoted 1' of formula R-CHO where R1 has the same meaning as in general formula (II),

and 2 mol/L (1 eq.) of an amine denoted 2' of formula R 2-NH 2 where R 2 has the same meaning as in general formula (II), in a polar protic solvent such as ethanol, is left under

agitation for 30 minutes at 40 °C. After cooling the medium to 0 °C, ethanol is added (2 mL per mmole). A reducing agent such as sodium borohydride (NaBH 4 - 2.5 eq.) is then

slowly added to the medium which is left under agitation overnight at ambient temperature.

A saturated aqueous solution of NH 4 CI and water is added and the aqueous phase is extracted twice with ethyl acetate. The organic phases are combined, dried over

MgSO4 , filtered and concentrated. The residue is purified by flash chromatography on silica gel using a gradient of dichloromethane + 5 % NH3/isopropanol mixture. The fractions containing the pure product are combined and concentrated.

An amine is obtained denoted 3' of formula RR 2-NH where R1 and R 2 have the same meaning as in general formula (II), in the form of a white solid or colourless oil with

a yield of 46 %to 61 %. A solution comprising diglycolic acid (1 eq.), a coupling reagent such as COMU

(2.2 eq.) and a tertiary amine such as DIPEA (4 eq.) in an apolar aprotic solvent such as 2

MeTHF is left under agitation for 15 minutes at ambient temperature. The addition is made of amine 3' (2.2 eq.) to the medium which is left under agitation overnight at

ambient temperature. The reaction is halted with the addition of water and the organic phase is washed

with saturated Na 2 CO 3 solution and 10 % HCI solution. The organic phase obtained is dried over MgSO4 , filtered and concentrated, and the residue is purified by flash

chromatography on silica gel using a gradient ofdichloromethane/ethyl acetate mixture. The fractions containing the pure product are combined and concentrated. A pure DGA is

obtained of general formula (II) in the form of a colourless-to-yellow oil with a yield of

46 %to 57 %.

The following were thus synthesized: 10) DPDDdDGA, meeting the following particular formula: 0 0

N O ,- N

1H NMR (CDCI ,3 400 MHz): & (ppm): 4.31 (s, 4H), 3.26 (q, J = 7.5 Hz, 4H), 3.10 (q, J = 7.6 Hz, 4H), 1.54 (m, 8H), 1.25 (m, 38H), 0.88 (m, 12H) 13 C NMR (CDCI,3 101 MHz): & (ppm): 168.64, 168.60, 68.52, 68.45, 48.31, 47.55, 46.85, 45.94, 32.05, 29.81, 29.78, 29.72, 29.69, 29.61, 29.53, 29.49, 28.92, 27.64, 27.20, 26.95,

26.92, 22.82, 22.01, 20.81,14.25,11.48,11.22,11.19 HRMS (ES/ positive mode): m/z calculated for{MH}*: 553.5308; found: 553.5309

_L _j

20) DBDDdDGA, meeting the following particular formula: 0 0

N N

1H NMR (CDCI,3400 MHz): (ppm): 4.38 (se, 4 H), 3.22 (m, 4 H), 3.09 (m, 4 H), 1.45 (m, 8

H), 1.25 (m, 42 H), 0.93 (t, J = 7.4 Hz, 3 H), 0.88 (t, J = 6.8 Hz, 9 H) 13 C NMR (CDCI,3 101 MHz): 6 (ppm): 169.10, 68.53, 46.94, 46.84, 46.28, 45.77, 32.06, 30.83, 29.93, 29.90, 29.88, 29.83, 29.81, 29.77, 29.75, 29.69, 28.83, 27.57, 27.38, 26.82, 22.82, 20.25, 19.99, 19.96, 14.27, 13.98, 13.92 HRMS (ES/ positive mode: m/z calculated for {MH}*: 581.5621; found: 581.5616

30) DiBDDdDGA, meeting the following particular formula:

0 0 N N

1H NMR (CDCI,3400 MHz): (ppm): 4.32 (m, 4 H), 3.29 (t, J = 7.5 Hz, 2 H), 3.17 (m, 4 H), 3.01 (d, J = 7.5 Hz, 2 H), 1.93 (m, 2 H), 1.51 (m, 4 H), 1.25 (m, 36 H), 0.88 (m, 18 H) 13 C NMR (CDCI,3 101 MHz): 6 (ppm): 169.00, 69.97, 53.85, 52.44, 47.19, 45.97, 31.92,

29.63, 29.61, 29.56, 29.43, 29.38, 29.35, 28.77, 27.49, 27.26, 27.10, 26.88, 26.69, 22.69, 20.15, 19.90,14.12

HRMS (ES/ positive mode): m/z calculated for {MH}*: 581.5621; found: 581.5620

II -EXTRACTANT PROPERTIES OF THE DIGLYCOLAMIDES OF THE INVENTION:

In the following examples, concentrations were measured by inductively coupled

plasma atomic emission spectroscopy (or ICP-AES) or by inductively coupled plasma mass spectrometry (or ICP-MS).

Also, the distribution coefficients and separation factors were determined in accordance with general practice in the field of liquid-liquid extractions, namely that:

.LU

- the distribution (or partition) coefficient of a metal element M, denoted DM,

between two phases, respectively organic and aqueous, is equal to:

Dm = [M]org.

[M]aq.

where:

[M]org. = concentration of the metal element in the organic phase at extraction

equilibrium (in mg/L); and

[M]aq. = concentration of the metal element in the aqueous phase at extraction equilibrium (in mg/L);

- the separation factor between two metal elements M1 and M2, denoted

SFM1/M2, is equal to: DM1 SFM1/M2 =Dm DM2

where: DM1= distribution coefficient of metal element M1; and

DM2 = distribution coefficient of metal element M2.

11.1- In nitric aqueous medium: Extractions were performed using:

- as organic phases: solutions comprising either 0.1 mol/L of a DGA of the invention, or 0.1 mol/L of a DGA of the state of the art, namely TODGA, in a TPH/n

octanol mixture (90:10, v/v); and

- as aqueous phases: aliquots of an aqueous solution representing a true

lixiviate called "solution A", comprising 3 mol/L of nitric acid (to simulate the likely acidity of an aqueous solution derived from dissolution of REM-rich fractions in nitric acid), and

representative light and heavy REMs (La', Pr', Nd' and Dy"') as well as representative metal impurities (Fe"', Co", Ni"). The concentrations of these elements in solution A are

specified in Table 1 below.

-L

/ Table 1

Metal elements Concentrations (mg/L)

La 955 Pr 977 Nd 972 Dy 963 Fe 9420 Co 970 Ni 937

Each of these extractions was conducted, in a tube and under agitation, by contacting an organic phase with an aliquot of solution A for 30 minutes at 25 °C. The O/A

volume ratio was 1. No third phase was observed during the extraction phases. After centrifugation and separation of the phases, each organic phase containing

REMs was subjected to stripping for analytical purposes via contacting, in a tube and under agitation, with an aqueous solution comprising 1 mol/L of nitric acid, 0.2 mol/L of

N,N',N,N'-tetraethyldiglycolamide (or TEDGA) and 0.5 mol/L of oxalic acid for 15 minutes at 25 °C, with an O/A volume ratio of 0.2. The mixture was centrifuged and the phases

separated.

The concentrations of the different metal elements were measured in solution A before extraction, in the aqueous phases obtained after extraction, and in the organic

phases after stripping. The distribution coefficients and REM/impurity separation factors obtained from

these measurements are respectively given in Tables 2 and 3 below and compared with those obtained under the same operating conditions with a prior art diglycolamide

namelyTODGA. Tables 2 and 3 below respectively give the distribution coefficients and

REM/impurity separation factors such as obtained for three DGAs of general formula (1), namely (DE-DDd)-DGA, (DP-DDd)-DGA and (DiP-DDd)-DGA, for a DGA of general formula (II), namely DiBDDdDGA, and for TODGA.

-LO

Table 2

(DE-DDd)-DGA (DP-DDd)-DGA (DiP-DDd)-DGA DiBDDdDGA TODGA

DLa 15.1 2.4 3.0 2.2 1.9 DPr 206 25.5 31.5 16.7 15.3 DNd 618 65.6 149 42.8 41.8 DDy >960 >960 >960 >960 >960 DFe 0.01 < 0.01 < 0.01 < 0.01 < 0.01

Dc. <0.03 <0.03 <0.03 <0.03 <0.03 DNi < 0.03 < 0.03 < 0.03 < 0.03 < 0.03

Table 3

(DE-DDd)-DGA (DP-DDd)-DGA (DiP-DDd)-DGA DiBDDdDGA TODGA

SFLa/Fe 1510 > 190 > 300 > 220 > 190

SFPr/Fe 20600 > 1500 > 3 200 > 1700 > 1500

SFNd/Fe 61800 >4200 >14900 >4300 >4200

SFDy/Fe > 100 000 > 100 000 > 100 000 > 100 000 > 100 000

SFLa/Co, Ni > 500 > 65 > 100 > 75 > 65

SFPr/Co, Ni > 6 900 > 500 > 1100 > 560 > 500

SFNd/Co, Ni > 20 600 > 1400 > 5 000 > 1400 > 1400

SFDy/Co, Ni > 333 00 > 333 00 > 333 00 > 333 00 > 3300

These results show that the DGAs of the invention have higher REM extractant

properties than those of TODGA in a nitric aqueous medium. They also show that these DGAs have particularly high affinity for heavy REMs

such as dysprosium.

(DE-DDd)-DGA, which comprises two ethyl groups carried by the same amide nitrogen, exhibits the best performance probably due to the structure thereof which

through reduced steric hindrance allows better REM accessibility to this DGA and hence better coordination of REMs by this DGA. This DGA therefore leads to REM distribution coefficients 8 to 15 times higher than those obtained with TODGA.

Comparison between the respective performance levels of (DE-DDd)-DGA and the other DGAs of the invention shows that an increase in length of the hydrophilic alkyl

chains substantially reduces the affinity of these DGAs for REMs, whether the asymmetrical DGAs are of type I or type 11.

Conversely, the presence of branching in the hydrophilic alkyl chains appears to

increase affinity. Yet, this goes against work reported in the literature for example by Sasaki et al., Solvent Extr. Ion Exch. 2015, 33(7), 625-641, hereafter reference [5], for

symmetrical DGAs in which the presence of branching reduces affinity for REMs, in particular by comparing the performance levels of TODGA and NNN',N'-tetra(2

ethylhexyl)diglycolamide (or TEHDGA). Regarding the extraction of iron, nickel and cobalt impurities, the results for each

of the assayed DGAs of the invention indicate distribution coefficients for iron of 0.01 or lower, and distribution coefficients for nickel and cobalt lower than 0.03. These values

correspond to the quantification limits of analytical equipment (ICP-AESandICP-MS) used

for analyses.

11.2 - In sulfuric aqueous medium:

Extractions/strippings were performed following the same operating protocol as described under item 11.1 above with the exception that for extractions, as aqueous

phases, aliquots of an aqueous solution were used called "solution B", which also simulates a true lixiviate but comprising 2 mol/L of sulfuric acid (instead of 3 mol/L of

nitric acid as in solution A). The concentrations of the metal elements in solution B are specified in Table 4

below.

LU

Table 4

Metal elements Concentrations (mg/L)

La 914 Pr 966 Nd 957 Dy 962 Fe 10150 Co 981 Ni 967

The concentrations of the different metal elements were measured in solution B before extraction, in the aqueous phases obtained after extraction and in the organic

phases obtained after stripping. Tables 5 and 6 below respectively give the distribution coefficients and

REM/impurity separation factors such as obtained for the three DGAs of general formula

(II), namely DPDDdDGA, DBDDdDGA and DiBDDdDGA, and for TODGA.

Table 5

DPDDdDGA DBDDdDGA DiBDDdDGA TODGA

DLa < 0.005 < 0.005 < 0.005 < 0.005 Dpr 0.07 0.02 < 0.005 < 0.005 DNd 0.27 0.06 0.01 < 0.005 DDy 25.14 4.02 0.55 0.23 DFe < 0.01 < 0.01 < 0.01 < 0.01 Dco < 0.03 < 0.03 < 0.03 < 0.03 DNi < 0.03 < 0.03 < 0.03 < 0.03

L_

Table 6

DPDDdDGA DBDDdDGA DiBDDdDGA TODGA

SFPr/Fe >7 >2 N.Q. N.Q.

SFNd/Fe > 27 >6 >1 N.Q.

SFDy/Fe >2500 >400 >55 >23

SFPr/Co, Ni >2 > 0.7 N.Q. N.Q.

SFNd/Co, Ni >9 >3 > 0.3 N.Q.

SFDy/Co, Ni > 840 > 130 >18 >8

N.Q.: non-quantifiable

These results show that the DGAs of the invention also have REM extraction properties that are higher than those of TODGA in a sulfuric aqueous medium.

It is known that, in general, the affinity of DGAs for REMs in a sulfuric medium is much lower than in a nitric medium. This is due to the fact that S0 4 2 - ions are much more

complexifying for REMs than NO3 -ions in solution. Therefore, in a sulfuric acid medium,

only heavy REMs such as dysprosium are extracted by TODGA but only very partially (DDy = 0.2). The very low extraction of heavy REMs by TODGA and the lack of affinity of TODGA

for light REMs in sulfuric medium have already been reported in the literature. Among the DGAs of the invention, DPDDdDGA leads to a distribution coefficient

of dysprosium that is 110 times higher than that obtained with TODGA, and to excellent separation factors in relation to other REMs (SFDy/La > 5 000, SFDy/Pr = 350 and SFDy/Nd =93).

This means that it is a candidate of choice for performing both efficient and selective extraction of dysprosium in a sulfuric aqueous medium, bearing in mind that dysprosium

is one of the REMs with the highest application potential.

As above, the distribution coefficients of impurities are lower than 0.01 for iron and lower than 0.03 for nickel and cobalt.

11.3 - In hydrochloric aqueous medium: Extractions/strippings were performed following the same operating protocol as

described under item 11.1 above with the exception that for extractions, as aqueous phases, aliquots of an aqueous solution called "solution C" were used, which also simulates a true lixiviate but comprising 2 mol/L of hydrochloric acid (instead of 3 mol/L of nitric acid in solution A).

The concentrations of the metal elements in solution C are specified in Table 7 below.

Table 7

Metal elements Concentrations (mg/L)

La 940 Pr 1071 Nd 859 Dy 1073 Fe 9488 Co 1015 Ni 937

The concentrations of the different metal elements were measured in solution C before extraction, in the aqueous phases after extraction and in the organic phases after

stripping.

Tables 8 and 9 below respectively give the distribution coefficients and REM/impurity separation factors such as obtained for a DGA of general formula (II),

namely DBDDdDGA, and for TODGA. Table 8

DBDDdDGA TODGA

DLa 2.9 1.0 Dpr 132.9 31.1 DNd > 215 92.2 DDy >265 >265 DFe 0.81 0.73 Dco < 0.03 < 0.03 DNi < 0.03 < 0.03

L_

Table 9

DBDDdDGA TODGA

SFLa/Fe 3.6 1.4

SFPr/Fe 164.1 42.6

SFNd/Fe > 265 126.3 SFDy/Fe > 327 > 363

SFLa/Co, Ni > 725 > 250

SFPr/Co, Ni > 4 430 > 1037 SFNd/Co, Ni 3.6 1.4

SFDy/Co, Ni 164.1 42.6

These results show that DBDDdDGA leads to distribution coefficients for lanthanum, praseodymium and neodymium which are 2 to 4 times higher than those

obtained with TODGA. DBDDdDGA has excellent affinity for praseodymium, neodymium and dysprosium, and lesser but nevertheless satisfactory affinity for lanthanum.

Nickel and cobalt impurities are not extracted by this DGA (DM < 0.03).

On the other hand, iron is slightly extracted, as it is by TODGA. However, the better affinity of DBDDdDGA for REMs allows selectivity in relation

to iron to be increased significantly, compared with that obtained with TODGA.

CITED REFERENCES

[1] International application PCTWO2016/046179

[2] Mowafi and Mohamed, Sep. Sci. Technol. 2017,52(6),1006-1014

[3] Narita and Tanaka, Solvent Extraction Research and Development, Japan, 2013, 20, 115-121

[4] Ravi etal., Radiochim.Acta2014,102(7), 609-617

[5] Sasaki et al., Solvent Extr.Ion Exch. 2015, 33(7), 625-641

It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the

common general knowledge in the art, in Australia or any other country. In the claims which follow and in the preceding description of the invention, except

where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an

inclusive sense, i.e. to specify the presence of the stated features but not to preclude the

presence or addition of further features in various embodiments of the invention.

Claims (16)

1. Diglycolamide, meeting one of general formulae (1) and (II):

0 0 0 0 R" O R2 R" - O R1

RI R2 R2 R2 (1) (II) where:

R1 is a linear or branched alkyl group having 2 to 4 carbon atoms; and

R 2 is a linear or branched alkyl group having 9 to 14 carbon atoms; with the exception however of the diglycolamide of general formula (1) where R1 is an

n-butyl group and R 2 is an n-dodecyl group, and of thediglycolamide of general formula (II) where R1 is an ethyl group and R 2 is an n-dodecyl group.

2. Diglycolamide according to claim 1, wherein R 2 is a linear alkyl group.

3. Diglycolamide according to claim 2, wherein R 2 is selected from among n

decyl, n-undecyl, n-dodecyl, n-tridecyl and n-tetradecyl groups.

4. Diglycolamide according to claim 3, wherein R 2 is an n-dodecyl group.

5. Diglycolamide according to any one of claims 1 to 4, which is selected from

among:

- the diglycolamide of general formula (1) where R1 is an ethyl group and R 2 is an n-dodecyl group;

- the diglycolamide of general formula (1) wherein R1 is an n-propyl group and R2 is an n-dodecyl group;

- the diglycolamide of general formula (1) where R1 is an isopropyl group and R 2 is an n-dodecyl group;

- the diglycolamide of general formula (II) where R' is an n-propyl group and

R 2 is an n-dodecyl group;

- the diglycolamide of general formula (II) where RI is an n-butyl group and R2

is an n-dodecylgroup;and

- the diglycolamide of general formula (II) where RI is an isobutyl group and R2 is an n-dodecyl group.

6. Diglycolamide according to claim 5, which is selected from among:

- the diglycolamide of general formula (1) where R'is an ethyl group and R2 is an n-dodecylgroup;

- the diglycolamide of general formula (II) where R' is an n-propyl group and R 2 is an n-dodecyl group; and

- the diglycolamide of general formula (II) where RI is an n-butyl group and R2

is an n-dodecyl group.

7. Use of a diglycolamide according to any one of claims 1 to 6 to extract at least one rare earth metal from an acidic aqueous solution.

8. Use according to claim 7, which comprises contacting the acidic aqueous solution with a water-immiscible organic solution comprising the diglycolamide in an

organic diluent, followed by separating the aqueous and organic solutions.

9. Use according to claim 8, wherein the concentration of thediglycolamide in the organic solution is between 0.05 mol/L and 0.5 mol/L

10. Use according to any one of claims 7 to 9, wherein the acidic aqueous

solution comprises a mineral acid or a mixture of mineral acids.

11. Use according to claim 10, wherein the mineral acid is nitric acid, sulphuric

acid or hydrochloric acid.

12. Use according to claim 10, wherein the concentration of the mineral acid or

mixture of mineral acids in the acidic aqueous solution is between 0.1 mol/L and 5 mol/L

13. Use according to any one of claims 7 to 12, wherein the rare earth metal is selected from among lanthanum, praseodymium, neodymium, dysprosium and mixtures

thereof.

14. Use according to any one of claims 7 to 13, wherein the acidic aqueous

solution is produced from dissolution of a concentrate of urban ore in an acid medium.

15. Use according to any one of claims 7 to 13, wherein the acidic aqueous solution is produced from dissolution in an acid medium of material in divided form and

resulting from the treatment of spent or scrap Neodymium-Iron-Boron or Samarium Cobalt permanent magnets, or from treatment of spent electrochemical Nickel-Metal

Hydride primary or secondary batteries.

16. Use according to any one of claims 7 to 13, wherein the acidic aqueous

solution is produced from dissolution of a natural ore or residue of a natural ore in an acid medium.