extractionoftervalentlanthanideswith acidic organophosphorus compounds

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EXTRACTIONOFTERVALENTLANTHANIDESWITH ACIDICORGANOPHOSPHORUS COMPOUNDSShoji Motomizu a & Henry Freiser aa Department of Chemistry, Strategic Metals Recovery Research Facility, University ofArizona, Tucson, AZ, 85721Version of record first published: 27 Sep 2010.

To cite this article: Shoji Motomizu & Henry Freiser (1985): EXTRACTIONOFTERVALENTLANTHANIDESWITH ACIDICORGANOPHOSPHORUS COMPOUNDS, Solvent Extraction and Ion Exchange, 3:5, 637-665

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SOLVENT EXTRACTION AND ION EXCHANGE, 3(5), 637-665 (1985)

EXTRACTION OF TERVALENT LANTHANIDES WITHACIDIC ORGANOPHOSPHORUS COHPOUNDS

Shoji Motomizu 1 and Henry Freiser

Strategic Metals Recovery Research FacilityDepartment of ChemistryUniversity of Arizona

Tucson, AZ 85721

ABSTRACT

The equilibrium 3excraction behavior for a series of tervalentlanthanide ions (Ln +) using a chloroform solution containingdi(2-ethyl-hexyl)phosphoric acid (HDEHP), diphenylphosphinic acid(HDPP) , dibutylphosphorothioic acid (HOBPT) , di-n-octylphosphorodithoic acid (HDOPDT), or di(2-ethylhexyl)phosphorodithioic acid(HDEHPDT), either alone or combined with adduct forming agentsis studied. The extracted species are Ln(DEHP)3(HDEHP)3'Ln(Dpp)3(HOPP)3' Ln(DBPT)3' and are Ln(DBPT)3(HDEHP)B in thepresence of o-phen and its analogs (B). Extraction constants forthe lanthanides follow the order HDPP > HDEHP > HOBPT » HDOPDT.HDP? was the most selective of all the extractants examined.HDOPDT and HDEHPDT were found to be ineffective lanthanide extractants.

INTRODUCTION

As a part of a systematic evaluation of the use of chelating

ex.tractants in extracting and separating tervalent lanthanides,

the equilibrium extraction behavior of a series of representative

lanthanide ions with chloroform containing one of several kinds of

ligands alone) or combined with adduct fonning agents was studied

In detail 0-6). From the results obtained in the previous

1On study leave from Faculty of Science) Okayama UniversitYJ

Okayama 703, JAPAN.

637

Copyright © 1985 by Marcel Dekker,Inc. 0736·6299/85/0305.Q637$3.50/0

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638 MOTOMIZU AND FREISER

studies, it was observed that extractants of greater acidity

exhibited both higher extraction constants and selectivity, as

seen from the results obtained with 8-quinolinol (pKa

= 10.9) (J)

and 5,7-dibromo-8-quinolinol (pKa

= 7.3) (3), and with benzoyl

phenylhydroxylamine (pKa

= 8.2) and N-(m-trifluoromethylbenzoyl)

phenylhydroxylamine (pKa

= 8.0) (6). Hence, a comparative study

was conducted using strong acids such as the acidic organo

phosphorus extractants.

Hany acidic organophosphorus compounds have been studied for

the extraction of lanthanide metals (7-10). One of the most

important acidic organophosphorus compounds is di(2-ethylhexyl)

phosphoric acid (HDEHP), whose extraction behavior has been

compiled by Marcus et a l , (JO). HDEHP and its analogs, in organic

solvents of low polarity, are present as dimers (JO, 11). A

dialkylphosphinic acid such as di-t-butylphosphinic acid (J2) or

di-t-pentylphosphinic acid (13) is dimeric both in the solid state

and in many organic solvents. Peppard et a1. reported the ex

traction behavior of lanthanides(III), actinides(III) and ura

rri umf VL) into benzene with di-n-octylphosphinic acid (HL). The

extraction mechanism reported is as follows:

M3+

+ 2.s(HL)z<O)::;;=:::=:: ML(HL2)2(0) + 3H+

2+ +U0

2+ 2(HL)z<0)~ U02(HL2)z<0) + 2H

Handley (J4, 15) and his coworkers Cl6) examined the 0,0 '

dialkylphosphorothioic and 0,0 '-dialkylphosphorodithioic acids as

metal ext rae tant s. According to their results, lanthanum (III)

could be extracted into carbon tetrachloride with di-n-buty lphos

phorothioic acid, but was only poorly extracted with di-n-

butylphosphorodithioic acid. Recently, }lusikas et aI . examined

the extraction of americium (III) and europium (III). with di-(2

ethylhexyl)phosphorodithioic acid (HDEHPDT) (J6). In contrast to

the results obtained by Handley (JS, 17), americium and europium

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TERVALENT LANTHANIDES 639

could be extracted into dodecane fairly well with HDEHPDT. That a

'hard' metal such as Eu3+ can be extracted with a 'soft' ligand

such as (DEHPDT)-, was reminiscent of our findings that a nitrogen

ligand such as phen seemed to bond with lanthanide chelates at

least as readily as with the hydrated lanthanide ions (3).

In this work the extraction behavior of lanthanides with

acidic organophosphorus compounds such as di-( 2-ethylhexyl)phos

phoric acid, diphenylphosphinic acid, di-n-butylphosphorothioic

acid, di-n-octylphosphorodithioic acid and di-(2- ethylhexyl)phos

pho r od i t h i.o i.c acid was examined to compare lanthanide e x t r a c t a-:

bility and selectivity. The adduct formation reaction with neu-

tral auxiliary ligands was also studied.

EXPERIMENTAL

Reagents

Diphenylphosphinic acid, HOPP (Aldrich Chem. Co ; , 99%), and

di-(2-ethylhexyl)phosphoric acid, HDERP (Aldrich Chem. Co , , 9S%)

were used without further purification. The ammonium salt of di-

n-butylphosphorothioic acid, HDBPT, was prepared by reacting

equimolar quantities of di-n-butylhydrogen phosphite and sulfur in

dry IJ2-dichloroethane with vigorous stirring and simultaneous

passage of dry ammonia gas (1S). The solid product obtained was

recrystalized twice from a mixture of dry acetone and n-rhe xa ne ,

mv p , 14S-150 0C (Lit: 147-150 0 C [lS]). Di-n-octylphosphorodi

thioie acid) HDOPDT J and its potassium sal t were prepared by

reacting 0.64 moles of n-octanol (Alfa Product: above 99%) and

0.16 moles of phosphorus pentasulfide until the pentasulfide

disappeared. The product was dissolved in. benzene and converted

to its potassium salt by neutralizing with potassium carbonate

(19) . The potassium salts obtained were recrystallized thrice

from a mixture of dry acetone and benzene; m.p. 156-1570 C (Lit:

153.5 - 154.5 0 C [20]). In similar fashion. other 0,0 "e-di a Lky Ie-

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pho s pho r o r d i t h i o i c . acids (RO)2PSSH (R n-C4Hg-, n-C

5Hll,n-C

6H13-, n-CgH1 9-, n-C l OH2l-, 2-ethylhexyl and p-methylphenyl

groups) and their potassium salts were prepared.

The other materials such as lanthanides (99.9%) J Arsenazo

(Ill) and 1,10-phenanthroline, phen, used here have been described

previously (1). 4,7-Dimethyl-l,10-phenanthroline, 4,7-DHP (Alfa

Products) and trioctylphosphine oxide, TOPO (Eastman Organic

Chemicals) were used without further purification.

All the other chemicals were analytical reagent grade, used

without further purification.

Extractant Solutions

HDPP and HDEIIP were dissolved in chloroform, which had been

washed with distilled water beforehand. HOOPDT and HDEHPDT, which

were liquid at room temperature, were also dissolved in chloro

form, and their concentrations were determined by two phase

acid-base titrations. Chloroform solutions of HDBDT and HDOPDT

were prepared as follows:

Transfer an adequate amount of salt into a separatory funnel.

To it add about 10-fold molar excess of 2M sulfuric acid (the

volume of the aqueous phase is below one-tenth of the organic

phase). Shake with a given volume of chloroform for 3-5 minutes.

After phase separation, use the organic phase as the extractant

solution.

Apparatus

A Gilford spectrophotometer, Model 2400, and a Cary recording

spectrophotometer, Hodel 219 (Varian) were used for measuring

absorbances, and an Orion Research Hodel 70lA Digital Ionalyzer

was used for pH measurements. An Eberbach 6015 shaker was used to

equilibrate the solutions.

Procedures

Spectrophotometric method for the determinatiqn of 0,0'-

dialkylphosphorodithioic acid and O,O'-dialkylphosphorothioic

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acid: Transfer up to 5 mL of sample solution into a glass vial,

neutralize with sodium hydroxide, adjust the concentration of

sodium sulfate to 0.2 M, and dilute the mixture to 10 mL with

distilled water. To it add 1 mL of phosphate buffer solution (1 M,

pH = 6.3) and 0.5 mL of methylene blue solution 00-3 M) added.

Shake the mixture with 5 mL of l,2-dichloroethane for 30 minutes.

After phase separation, measure the absorbance of the organic

phase at 658 nm. The calibration curve is prepared by using 10 mL

of an aqueous solution containing the same amounts of sodium

sulfate and 5 mL of HDOPDT or HDBPT l,2-dichloroethane solutions.

The molar absorptivities calculated from the slopes of calibration

curves for HDOPDT and HDBPT are 1.10 x 105 and 5.00 x 10 4 M -1-1

cm respectively. In general, the molar absorptivity of

ion-pairs involving methylene blue extracted into an organic phase

is about 1 x 105 M -1 cm- l (20). Hence, either about half of the

HDBPT is extracted as the ion-pair, or the stoichiometry of the

extracted complex is unusual.

Determination of the distribution and acid dissociation

constants of diphenylphosphinic acid and di-n-butylphosphorothioic

acid: Equilibrate a 10 mL portion of an aqueous solution at the

desired pH and an equal volume of the chloroform solut ion of the

reagent (HDPP or HDBPT) in a vial by vigorous shaking for 30

minutes. After phase separation, measure the pH of the aqueous

phase and determine the tot al concentra t i o n of the reagent in the

aqueous or

concentra eion

organic

of HDPP

phase spectrophotometrically. The

of chloroform phase is determined

spectrophotometrically at 265.5 nm (A ), and the concentrationmax

of HDPP of the aqueous phase is determined spectrophotometrically

at 264.8 nm, after acidifying the aqueous phase to 1M with

perchloric acid. The concentration of HDBPT in the aqueous phase

is determined spectrophotometrically by the methylene blue method

described above.

Determination of the distribution ratio of lanthanide metals:

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The pH value of the aqueous phase

the equil ibrium pH value. After

aqueous phase is transferred into a

A 10-mL portion of lanthanide metal solution in which pH and ionic

strength (u = 0.1) are adjusted with sodium perchlorate and

perchloric acid, and an equal volume of the extrac tant solution

are equil i br a t e d in a vial by vigorous shaking for 15 minutes at

(20 .! llo C, a time period which was found suf f icient for

attainment of equilibrium.

after extraction is taken as

phase separation,S mL of the

10-mL volumetric flask, and the concentration of lanthanide metal

is determined spectrophotometrically by the Arsenazo III method

(ll after adjusting the pH to 2.6 z, 0.1 with sodium formate and

formic acid. Among the anions tested, perchlorate affects the

L03+ -Arsenaz.o III reaction the least. Nevertheless, the

calibration curve was prepared using solutions containing similar

amounts of perchlorate ion. lIDBPT up to 0.015 M, lIDPP up to 0.001-4M and HDOPDT up to 10 H did not interfere with the Arsenazo III

lanthanide reaction.

RESULTS A~~ DISCUSSION

Distribution behavior of HDPP and HDBIT between chloroform

and aqueous medium: The distribution ratio (DL) and the

distribution constant (KD

) of HL between the aqueous and organic

phases, the aggregation constant in the organic phase (K ) andagg

the acid dissociation constant in the aqueous phase (KA)

refer to

CL(o) / CL[HL]o / [HL]

[(HL)m1o / [HL]~

[H+j [L-j / [HL]

where CL is the stoichiometric concentration of ffi.. J the subscript

o refers to the organic phase, and absence of a subscript

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TERVALENT LANTHANIDES

indicates the aqueous phase. From equations (1)

643

(4), the

following equation can be derived:

D = L~ -1 + m Km K -m Cm-1L -D L D a gg c'L L ( 5)

where ~L = 1 + (KAf(H+l), and it

the organic phase is only (HL)m'

to [(HL)m]o' and D is much larger

is assumed that the aggregate in

When [HIlo is neglected compared

than 1, equation (6) is derived.

(6)

Twhere CL CL(o) + CL.

TIn Figure 1, the plots of log DL against log CL and log CLfor HDPP are shown. The slope of the plot of log DL against log

C~ is 0.5, and the slope of the plot of log DL against log CL is

1.0, which signifies that in the organic phase, HL is present as a

dimer in the concentration range of 10- 4 to 2 x 10-2 M. By using

equation (5), the value of log (K~D ) was calculated to be 4.36agg

~ 0.05 (10 data points).TIn Figure' 2, the plot of log DL against log CL for HIlBPT is

shown. The slope of the plot is 0 at the concentration of HL

below 2 x 10-2 M. From these results, HOBPT is seen to be present

in chloroform entirely as a monomer.

In Figure 3, the plot of log DL against pH for HDPP is shown.

By using equation (5), the value of pK a was calculated to be 1.52

~ 0.07 (6 data points). In Figure 3, the plot of log DL against

pH for diphenylphosphoric acid is also shown for comparison. The

extractability of the reagent is lower than that of HOPP, probably

because of the hydrophilicity associated with its oxygen atom.

In Figure 4, the plot of log DL against pH for HDBPT is

shown. As expected from the results of Figure 2, the slope of the

plot at high pH region is 1.0. By using equation (5), in which HL

is assumed to be present as a monomer in the organic phase, the

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1.61 2

a.,..,.

,..,A00a,..,

1.2

0.8

0.4

-4.4 -4.0 -3.6 -3.2

1.0

~ope

-2.8

0.5

-2.4 -2.0 -1.6

:za'"'a3...NC

TLog CL

or Log CL

TFigure 1. The plots of log D

Lvs. log CL and log CL for HDPP. (1) Log DL

Tvs. Log C

L;(2) Log DL vs. Log C

L,pH = O.07~O.01; 1 M (HCL0

4+ NaC10

4).

""Q.

...,"'"...'"'""

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values of log KD and pKa were calculated to be Z.13 ~ 0.04 and

0.93 ~ 0.06 (7 data points), respectively.

Extraction of lanthanide ions (Ln3+ ) with di-<2-ethylhexyl)

phosphoric acid: The extraction behavior of lanthanide with HDEHP

into chloroform was studied both in the absence and presence of

adduct forming agents. The plots of log D against variables such

as pH of the aqueous phase and the logarithm of concentration of

HDEHP and of adduct forming agent in the organic phase were

obtained to determine the stoichiometry and equilibrium constants

of the extraction. In Table 11 which summarizes the results of

analysis of the extraction data, the slopes of all the log 0 vs.

Slope = 0.5

2.5

Z.O

-3 -Z -1

Figure Z. The plots

pH = 0.44~0.01;

Tof log DL vs. log CL for HDBDT.

0.5 M (HZS04 + NaZS04).

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'"o...,o'"HNc::>z"..,'"'"H'Jl

~

o~

'"

2.0

2.62.4

••,•o

pH

2.0

,,,•,

\

•,,o •,

o

o

1.6

oo

1.20.8

Ys. pH for HOPP and Oiphenylphosphoric acid.T -3

C = 1 x 10 M; 1 M (HCID + NaCID ).L 4 4

~'L'

0.4

- - 0

o-0.4

-log [HC104]

Figure 3. The plots of log DL

(1) HDPP; (2) Diphenylphosphoric Acid.

0.8

0.4

-0.8

-0.4

0' 0eoo.....

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o 0.5 1.0 1.5

pH

2.0 2.5 3.0

Figure 4. The plots of log D1 vs. pH for HDBPT.

0.5 M (H2S0 4 + NaS04).

0.01 H;

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TABLE 1. SU~~~RY OF RESULTS ON HDEHP EXTRACTION

Log 0 vs m(X - Xl/2 ) Log KexSlope (m+s· ) Xl/ 2

No. of- m Points

X = pH; [(HDEHP)2]o 2 -3x 10 N

Lu 2.70±0.03 2.03 9 2.00::0.07

Yb 2.76::0.05 2.14 6 1. 68::0.08

Ho 2.75::0.03 2.61 8 0.24::0.09

Eu 2.76::0.05 3.16 7 -1.36::0.04

Pr 2.53::0.05 3.59 7 -2.65::0.12

Ce 2.80::0.03 3.67 7 -2.95::0.05

La 2.43±0.04 3.84 7 -3.39::0.17

X = Log [(HDEHP)2]o

Lu (pH=2. 36±0. 01) 3.04±0.04 -3.02 10 1.95±0.05

Yb (pH=2.52::0.01) 3.02::0.03 -3.05 9 1. 58±0. 03

Ho (pH=2.99±0.01) 2.84±0.03 -3.03 11 0.16±0.06

Eu (pH=3.62±0.01) 2.77±0.04 -3.12 9 -1.50±0.07

Pr (pH=4.03±0.01) 2.55±0.03 -3.15 7 -2.68±0.03

Ce (pH=4.05±0.02) 2.74±0.05 -3.10 8 -2.87±0.05

La (pH=4.19::0.01) 2.60::0.03 -3.05 11 -3.44±0.11

X = Log [(HDEHP)2]o , [Phen] = 0.02 M0

Yb (pH=3.67±0.Ol) 1. 82::0 .10 -4.53 8

Ho (pH=3.65::0.01) 2.21±0.03 -4.15 11 -0.91±0.05

Eu (pH=3.67±0.01) 2.13±0.03 -4.04 10 -1.18::0.04

Pr (pH=3.62±0.02) 2.19±0.03 -3.70 10 -1. 89±0. 06

Ce (pH=3.65::0.02) 2.00±0.04 -3.58 9 -2.10±0.03

La (pH=3. 53±0. 01) 2.35±0.02 -3.10 11 -2.69±0.05

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TABLE I (CO}lTl~lJED )

Log D vs m(X - Xl/ Z) Log KexSlope (m±sm) Xl/Z

No. ofPoints

X = Log [Phen]0

Lu (pH=3.Z0, [(HL)Z]o=1xl 0-4 M) l.l9±0.O3 -Z.66 7 0.74±0.05

Yb (pH=3.Z0, [CHL)?] =_ 0

1.Z5xlO-4tO 0.82~0.01 -1.80 8 0.38±0.08

Ho (pH=3.71, [CHL)2]o=

2xlO-4t1.) 1. 72~0.01 -Z.67 6 -0.85±0.10

Eu (pH=3.65, [(HL)Z] =-4 0

1. 05±0. OZ -Z.50 -1.l9±0.04Z.5xlO tI) 8

Pr (pH=3.64, [(HL)Z]o=-45xlO tI) 1. 07±0. 01 -2.92 8 -1. 73±0.05

Ce (pH=3.65, [(HL)Z]o=lxlO- 3tI) 1. OZ±O. 01 -Z.92 8 -1. 95~0. 03

La (pH=3.70, [(HL)Z]o=

lxlO-3t1) 1. 07±0. 01 -Z.65 9 -Z. 61±0. 05

(Table I Continued)

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650

TABLE I (CONTI~uED)

MOTOMIZU AND FREISER

Log D vs m(X - X1/ 2)Slope (m±sm) Xl / 2

x = Log [4,7-DPP]o

Lu (pH=2.98, [(HL)2Jo=

I x 10-4M) O.23±O.02

No. ofPoints

5 0.6 ±O.l

Yb (pll=3.06, [(HL)Z] =-4 0

1.25x10 M) 0.50±0.02

Ho (pH=3.4S, [(HL)Z]o·

I x 10-4~l) O.49±0. 03

Eu (pH=3.6Z, [(HL)2] •-4 0

Z.5x10 M) 0.S4±0.01

Pr (pH=3.64, [(HL)Z] =-4 0

2.5x10 M) 0.S8±0.01

Ce (pH=3.62, [(HL)ZJ o=IxI0-3M) 0.97±0.01

La (pH=3.4S, [(HL)2Jo=-3lxlO H) 0.S7±0.01

X· Log [4,7-D~WJo

La (pH=4.os, [(HL)ZJo=lxI0- 3M) 0.S6±0.OZ

-1.2

-2.0

-Z.80

-2.66

-2.96

-2.20

-4.90

7

7

10

9

S

7

5

0.5 ±O.l

-0.5 ±O.l

-0. 97±0. 06

-1.69±0.05

-1. SO±O. 02

-2.22±0.05

-2.24±0.04

Aqueous Phase: 0.1 M ([HCI04] + [~aCI04])

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pH plots are seen to substantially three, indicating that the

extracted species contains three ligand anions. From Table 1, the

slopes of log D vs. log [HL] are °also seen to be close to three.o

Since HDEHP is present as d ime r in the organic phase (10), the

extraction reaction can be written as

Kex---'"~

(7) .

Values of about Z.5 for the slope of log D v s . pH plots for

praseodynium and lanthanum may be attributed to the presence of

intermediate water-soluble complexes.

In Table 2, the results of the examination of the auxiliary

ligands, or adduct fonning

examined, only phen and

agents, are shown. Of the reagents

its derivatives are effective in

increasing lanthanide extractability. The behavior of adduct

forming agents (B) such as phen, 4,7-DPP or 4,7-DMP, as indicated

from the data in Table 1, is similar, yielding a complex

containing only one B molecule. The plots of the values of (log D

-Zlog[(HL)Z]o- 3pH) against log [Bl o for phen and 4,7-DPP are

shown in Figures 5 and 6. In case of 4,7-DPP, as this reagent is

very bulky, it is very difficult to fonn

ho

0 11 0 3+ Yb3+ 3+c i ome t r r ca Y with Lu I or HD .

adduct complexes

The slopes for

stoi-

these

metals are smaller than one. In the presence of B, the slopes of

the plots of log D v s , log [HL] are close to two. Thus, the0

extraction can be written as follows:

Kex(B)Ln 3+ + Z(HL)Z(o) + B(0)

..,LnL3(HL)B(0)

+ 3H+ ( 8),

where B represents phen and its derivatives.

From the equations (7) and (8), equation (9) is derived.

KAD( B)

(9 )

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TABLE 2. ADDUCT-FORHING AGENT

Chelating agent: HDEHP ([(HL)2 Jo = 6 x 10-5 M)

Metal: La3+ (2 x 10-5 M)

Reagent

None

phen

4,7-DPP

4,7-DMP

2,9-DMP

Bipyridine

Triphenylphosphine oxide

(BuO)3 P = 0

(Oety1-0)3 P 0

Pyridine

TOPO

Cone. M

0.01

0.010.02

0.01

0.020.10

0.020.10

0.020.10

0.020.10

0.020.10

0.020.10

0.020.10

0.020.10

0.020.10

0.010.02

pH

4.043.96

4.07

4.01

4.044.25

4.05

4.074.14

4.064.07

4.044.04

4.024.01

4.044.07

7.057.98

4.735.42

4.935.74

4.605.36

4.124.12

Log D

-0.93-0.91

0.21

0.96

0.711. 61

-1.03

-0.82-1.08

-1.00-1.17

-0.910.95

-0.85-1. 26

-0.83-0.41

0.020.28

-0.75-1.00

-1. 79-1.38

-1. 79-1.54

-1. 79-1. 79

Log D-3pH

-13.05-12.79

-12.01

-11.08

-11. 41-11.14

-13 .18

-12.94-13.50

-13 .18-13.38

-13.03-13.07

-12.91-13.29

-12.95-12.62

-21.13-23.66

-14.94-17.26

-16.58-18.60

-15.59-17.62

-14.15-14.15

4-CH3

-py = 4-methylpyridine; 3-CH3-py

- 3-methylpyridine.

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-1-2-3-4

o 0 0

-5

o

-6

-5

-1

-2

3

:c 4Co

'"'-3

0~ 5N

:::>~ 6~

000...

N

I-4

Q

00 7s

Log [Phen]a

Figure 5. The plots of (log D - 2 log [(HL)2]0 - 3 pH) vs.

log [Phen]o' (1) Lu; (2) Yb; (3) Ho; (4) Eu; (5) Pr;

(6) Ce; (7) La. IlL: HDEHP.

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(,54

-1

-2'"""'"

0,....,N~

-''"~ -3......000-'N

Q

000-'

-4

-5


12

-3 -2

Log [Batho-phen]o

-1

Figure 6. The plots of

log [Batho-phen]o.

(6) Ce; (7) La.

(log D - 2 log [(HL)2]0 - 3 pH) vs.

(1) Lu; (2) Yb; (3) Ho; (4) Eu; (5) Pr;

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TABLE 3. EQUILIBRIill! CONSTANTS

HL: Di(2-ethylhexyl)phosphoric acid

Lu3+ Yb 3+ H0 3+ Eu3+ Pr 3+ Ce3+ La3+

Log K 1. 97 1.63 0.20 -1.47 -2.66 -2.91 -3.42ex

Log Kex(phen) 0.74 0.38 -0.88 -1.19 -1.81 -2.02 -2.55

Log Kex(DPP) 0.6 0.5 -0.5 -0.97 -1. 69 -1.80 -2.22

Log Kex(4, 7-D~1P) -2.24

Log KAD(phen) -1. 23 -1. 25 -1.08 0.28 0.85 0.89 0.87

Log KAD(DPP) -1. 3 -1.1 -0.7 0.46 0.97 1.11 1.20

Log K 1.18AD(4,7-DMP)

K[LnL

3(HL)3]0[H+]3 K[LnL

3(HL)(AD)]0[H+J 3

ex [Ln3+J[(HL)2]~ ex (AD) [Ln3+J[(HL)2]~[AD]0

Kex(AD)KAD Kex

phen: D-phen; B-phen: Bathophen; CH3-phen: 4,7-Dinethylphen.

In Table 3, the equilibrium constants obtained for HDEHP are

summarized. From Table 3, it is found that log Kex increases

while log KAD(B) decreases with the atomic number of the

lanthanide. This signifies that, although the Lewis acidity of

the metal can be expectd to increase with increasing atomic

number, a greater fraction of this acidity is neutralizd by the

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4


Atomic Number of Lanthanides

Figure 7. The plots of log Ke x

vs. atomic number of lanthanides.

HL: (1) HDEHP; (2) HOEHP; 0) di-n-octylphosphinic acid;

(4) HOPP; (5) HOBDT. Extracting Solvent: (1) tolnene;

(2) CHC13;

0) benzene; (4) CHC13;

(5) CHC13•

Aqueous

Phase: (1) 0.5 M (HCl); (2) 0.1 N (HCI04

+ NaCI04);

(3) 1.0 M (HCl + NaCl); (4) 0.1 M (HCI04

+ NaCI04);(5) 0.1 M (HCI0

4+ NaCI0

4)•

.(2). (4) and (5): this work; (1): Ref. 22; 3: Ref. 13.

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TERVAlENT lANTHANIDES 657

primary ligand, leaving less for bonding with the auxiliary

ligand.

In Figure 7, the values of log Ke x are plotted against the

atomic number. The plot is almost linear and its slope is the

same as that obtained with toluene (Z2, 23). The values of log

and this probably reflects the greater HDEHP extract-

K withex

toluene,

chloroform are unfortunately smaller than those with

ability into chloroform than into toluene.

Extraction of lanthanide ions with diphenylphosphinic acid:

In Table 4, the results for the plots of log D v s pH and log D

The slopes of the plots of

three. The plots of log D

inHLofconcentrationinitial

against log [(HL)ZJ o are summarized.

log D against pH are very close toT T

against log (l/Z Cl)o (Cl:chloroform) all indicate a slope very close to three.

From these results, the extraction stoichiometry can be

expressed as

(0)

On the basis of the equation (10), the extraction constants and

apparent extraction

differences between

In Figure 7 J

lanthanide metal is

constant (Kex(app)) were calculated. The

log K and log K ( ) are O.Z to 0.3.ex ex appthe plot of log Ke x against atomic number of

shown. For comparison, the plot 5 for d i-o-

octylphosphinic acid are shown (13). It is very interesting that

the values of log Ke x

with HDPP are very large compared to those

with di-n-octylphosphinic acid. This ~s because the sterie

hindrance of HOP? is less and the distribution ratio of HDPP

it self is lower than d i-n-octylphos phinic acid. The auxiliary

ligands shown in Table 2, except those agents containing nitrogen

atoms, were examined and found not to be effective in increasing

the distribution ratio of lanthanide metals. Phen and its deriv

atives could not be examined because the pH used for extraction of

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TABLE 4. SUClliARY OF RESULTS ON HOPP EXTRACTION

Log D vs m(X - X~)

Slope (m:tSm) X~ II of Points

(These are calculated according to:

X = pH

Lu (C T= 5 x 10-4 tI)LT -4

Yb (C = 5 x 10 tI)LT 3

He (CL

= 1 x 10- tI)

.Eu (CL

T= 5 x 10-3 tI)

Pr (C T= 2 x 10-2 tI)L

Ce (C T= 2 x 10-2N)

LLa (C T= 2 x 10- 2 N)

L

X ';' Log(CLT / 2)

Lu (pH = 1.06 :t 0.01)

Yb (pH = 1.07 :t 0.01)

Ho (pH = 1.35 :t 0.01)

Eu (pH = 1.74.:t 0.01)

Pr (pH = 1.75 :t 0.01)

Ce (pH = 1.93 :t 0.01)

La (pH = 2.25 :t 0.02)

2.72 + 0.08

3.02 + 0.02

3.09 + 0.06

3.04 + 0.07

3.13 + 0.06

2.99 + 0.04

3.04 + 0.04

3.06 + 0.02

2.99 + 0.04

2.92 + 0.02

3.10 + 0.03

3.00 + 0.03

2.98 + 0.02

2.97 + 0.01

1. 35

1.43

1. 57

1.39

1.41

1. 51

1. 89

-3.34

-3.27

-3.13

-3.24

-2.36

-2.43

-2.33

9

6

7

8

8

9

8

9

9

9

9

13

10

6.67 + 0.04

6.50 + 0.04

5.24 + 0.03

3.65 + 0.07

1. 77 + 0.06

1.49 + 0.04

0.31 + 0.03

6.84 + 0.04

6.60 + 0.04

5.30 + 0.04

3.66 + 0.04

1.84 + 0.03

1.50 + 0.02

0.23 + 0.02

2.02 + 0.07

7.10 + 0.04

1. 74 + 0.07

0.64 + 0.11

6.85 + 0.07

5.51 + 0.07

4.03' + 0.05

7

7

9

8

9

9

11-2.52

-2.42

-3.08

-2.42

-3.21

-3.43

-3.35

2.91 + 0.04

2.60 + 0.04

2.79 + 0.03

2.79 + 0.03

2.73 + 0.02

2.80 + 0.03

2.68 + 0.04

(These values are calculated according to: Kex = O[H+J3 / [(HL)2J~)

X = Log[(HL)2]0

Lu (pH = 1.06)

Yb (pH = 1. 07)

He (pH = 1. 35)

Eu (pH = 1. 74)

Pr (pH = 1. 75)

Ce (pH = 1. 93)

La (pH = 2.25)

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lanthanide metal was near or below 2, where these 1 igands are in

their protonated forms.

Extraction of lanthanide ions with di-n-butylphosphorothioic

acid: Table 5, the results for the plots of log D v s log C~ and

log [HL] are summarized. The slopes of their plots are veryaclose to three. Thus, the extraction stoichiometry can be

expressed as follows:

Ln3 + + 3HL(0)

(11 )

On the basis of the equilibrium (10), the values of log Ke x were

calculated. In Figure 7. the plots of log Ke x

against atomic

number of lanthanides are shown. Decrease in the value of log Ke x

as the atomic number decreases is very small from Lu to SID, com

pared to HDEHP and HOPF. Though in lanthanides from Sm to Ce the

slope of the plot of log Kex against atomic number is steeper than

that in metals from Lu to Sm, it is not so steep as the slopes of

the plots for HDEHP and HDPP, emphasizing that reagent selectivity

(the slope) depends on the particular metal pair under consider-

The values of (log D-3 pli ) decrease at

b about 10- 2 M f bia eve ,except or ytter aum•

a t i on, In Figure 8. the

log [TOPOl o are shown.

concentrations of TOPO

plots of the value of (log 0-3 pH) vs

This decrease may be due to stronger interaction between HDBPT and

TOPO than that between HDBPT and the lanthanide metal ion in the

organic phase. In the case of Yb, however, the interaction

between HDBPT and Yb is stronger than that between HOBPT and TOPO.

Thus, the slope of the plots of (log D-3pH) against log [TOPO) is

positive but is still smaller than one.

Extraction of lanthanide ions with di-n-occylphosphordithioic

acid and di-2-ethylhexylphosphorodithioic acid: As showe 1n

Figure 9, ytterbium and europium were quite well extracted with

HDOPDT and HOEHPDT, used as received, but with the reagents

purified as the potassium salts extractability was very bad. If

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TABLE 5. Su}fr~Y OF RESULTS ON HDBDT EXTRACTION

(Log D - 3 pH) vs m(X - Xl )~

Slope (m::J::Sm) Corr. /I of Points

[ +]3 T 3(These are calculated according to: Kex(app) = D H / (CL ) .)

TX = Log CL

(These are calculated according to:

Lu

Yb

Ho

Tb

Eu

Sm

Nd

Pr

Ce

La

X = Log

3.05 + 0.03

3.07 + 0.02

3.28 + 0.03

2.98 + 0.02

2.91 + 0.05

2.83 + 0.02

3.04 + 0.03

3.06 + 0.04

3.22 + 0.03

3.12 + 0.09

2.95 + 0.05

[HL]o

0.9995

0.9997

0.9995

0.9997

0.9986

0.9996

0.9994

0.9992

0.9996

0.9979

0.9992

Kex

11 -1.86 :!:. 0.04

8 -1.88 + 0.03

9 -2.18 + 0.05

9 -2.12 + 0.02

10 -2.05 + 0.05

9 -2.07 + 0.06

9 -2.12 + 0.02

8 -2.44 + 0.05

8 -2.55 + 0.07

6 -2.68 + 0.05

7 -2.99 + 0.04

D[H+]3 / [HL]3.)o

Lu

Yb

Ho

Tb

Eu

Sm

~d

Pr

Ce

La

3.01 + 0.03

3.04 + 0.02

3.23 + 0.03

2.94 + 0.02

2.87 + 0.05

2.80 + 0.02

3.00 + 0.03

3.01 + 0.04

3.18 :!:. 0.03

3.09 + 0.10

2.90 + 0.05

0.9995

0.9997

0.9996

0.9997

0.9986

0.9996

0.9995

0.9992

0.9996

0.9978

0.9992

11

8

9

9

10

9

9

8

8

6

7

-1.77 + 0.03

-1.80 + 0.02

-2.01 + 0.06

-2.03 + 0.03

-1.96 + 0.07

-1.99 + 0.06

-2.03 + 0.03

-2.36 + 0.03

-2.46 + 0.06

-2.59 + 0.05

-2.90 + 0.03

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fERVALENT LANTHANIDES 661

-4.5

-5.0

'" -5.5c,

M 1

Q

000

-x-x~,..,-6.0 2 --

3

4

-6.5 5

6 ... f)U ~

-7.0

-3.0 -2.5 -2.0 -1.5

Log [TOPO]O

Figure 8. The plots of (log D - 3pH) v s . log [TOPO]o'

(1) Yb (~); (2) Eu (X); (3) Sm (0); (4) Pr (e);

(5) Ce (0); (6) La (~). HL: HOBPT (0.1 M);

pH = 1.83 ~ 1.95. The horizontal lines are the value of

log D of each metal in the absence of TOPO.

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0.8

0.6

0.4

0.2

o

-0.2

-0.4

-0.6

-0.8

Figure 9. The plots of log D vs. pH for HDOPDT and HDEHPDT.

(1) and (2) HDOPDT, 5 x 10-3 M; (3) HDOPDT 0.2 M;

(4) HDEHPDT, 5 x 10-3 M. (1), (2), and (4) Raw Product;

(3) HDOPDT was purified as salt. (1), (3) and (4) Yb;

(2) Eu.

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the behavior of the unpurified HDEHPDT is attributed to HDEHP as a

likely hydrolysis product, we can estimate from the appropriate

extraction constant that the content of HOEHP in HDEHPDT is about

25%. The other O,O'-dialkylphosphorodithioic acids (as potassium

salts) were also found not to be very good lanthanide e~tractants.

CONCLUSIONS

In this work, extraction behavior of lanthanide metals with

organophosphorus compounds was investigated. From the results

obtained, the order of the extractability of lanthanide metal ions

by organophosphorus compounds is expected to be:

though we could only examine the extractants in ....hich R was not

always the same. As far as selectivity towards lanthanides is

concerned, HDPP and HDEHP are similar, but the former is better

for Ce, (probably) Pr, and La separations.

In the case of HDEHP, the extractability of lanthanide was

improved in the presence of phen and its derivatives. The

selectivity towards lanthanides, however, was not improved by this

means.

In the case of HDBPT, the selectivity to....ard lanthanides was

not good, but the bonding of the extracted lanthanide complex is

very interesting. Further work .... ith HDBPT and its family will be

done from the standpoint of the bonding of the complex.

This research was funded by a grant from the United States

Department of Energy.

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664

REFERENCES


M. Kawashima and H. Freiser, Anal. Chern. , 21., 284 (981) .

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E. Yarnada and H. Freiser, Anal. Chem • J 21.. 2115 (981) .

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4.

5. o. Tochiyama and H. Freiser, Anal. Chim. Acta, lll. 233

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Received by Editor

June 14, 1985

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extractionoftervalentlanthanideswith acidic organophosphorus compounds

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