**12. Results**

128 Ion Exchange Technologies

**11. Experimental** 

converted to oxides.

were also studied.

mm. They were used in the appropriate form.

The strongly basic anion exchangers Dowex 1x1, Dowex 1x2, Dowex 1x4, Dowex 1x8 (type 1), Dowex 1x16, Dowex 2x8 (type 2) and macroporous Dowex MSA-1 produced by the Dow Chemical Company (USA) as well as Lewatit MonoPlus M 500, Lewatit MonoPlus M 600, Lewatit MonoPlus MP 500, Lewatit MonoPlus MP 64 and Lewatit MP 62 produced by Lanxess (Germany) were used in the investigations. From the group of polyacrylate anion exchangers Amberlite IRA 458, Amberlite IRA 68 and Amberlite IRA 958 (Rohm and Haas, France) were selected. Additionally, in the case of separations of rare earth elements in the polar organic solvent systems there were used the following: Zerolite FF IP 2-3%, Zerolite FF IP 3-5%, Zerolite FF IP 7-9%, Lewatit MP 5080, Purolite A 850, Permutit SK, Wofatit SBWx2%, Wofatit SBWx4%, Wofatit SBWx6%, Wofatit SBWx8%, Wofatit SBWx12%, Wofatit SBWx16%, Wofatit SBKx7%. The bead size of these anion exchangers was 0.15-0.3

In the case of rare earth elements separation in the presence of complexing agents (L=IDA, HEDTA, CDTA or EDTA) 1.5 or 2.5 g of the oxides of rare earth elements with 2% excess of stoichiometric quantities of complexing agent solution (in the Ln(III):L=1:1 or Ln(III):L=1:2 systems) were mixed while heated. Moreover, in the case of the systems in the polar organic solvent the rare earth element solution of 2.5-100 g Ln2O3/dm3 for separation of Y(III) from Nd(III) and 1.5-5.3 g Ln2O3/dm3 for separation of Sm(III) from Y(III) were prepared by dissolving the appropriate rare earth element oxides in HNO3 and then the organic solvent was added. In order to measure affinity series the breakthrough curves were determined using the solutions of rare earth elements at a concentration 0.01 M or 0.004 M. These solutions were passed continuously through 2 cm i.d. glass columns packed with the suitable ion exchanger keeping the flow rate 0.2 cm3/cm2min. The breakthrough curves were normally obtained using 40-80 cm3 of the anion exchanger in the appropriate form. The effluent was collected as fractions of 15-10 cm3 from which oxalates were precipitated and

The percentage of micro component in macro component was determined by the spectrophotometric analysis using a SPECORD M 42 spectrophotometer (Zeiss, Germany). The determination was made by a direct method using the neodymium adsorption maximum =793.4 nm and the praseodymium adsorption =444 nm. Calculations were made by using the background adsorption elimination method. In some cases the

There were determined the affinity of rare earth element complexes and the effects of kind of functional groups (basicity), kind of skeleton, porosity of skeleton (microporous and macroporous), cross linking degree of anion exchanger skeleton as well as kind and concentration of complexing agent and polar organic solvent (methanol, ethanol, 1 propanol, 2-propanol, acetone, dimethylformamide, dimethylsulphoxide). The effect of the nitric acid concentration, the addition of another organic solvent and the concentration of rare earth elements(III) (up to 100 g Ln2O3) on effectiveness of their sorption and separation

determination was made using the XRF spectrometer (Canberra Packard).

As follows from the literature data little attention was paid to the purification of rare earth elements using complexing agents and separation of formed anionic complexes on strongly and weakly basic anion exchangers (Hubicka & Hubicki, 1992a; Hubicka & Hubicki, 1992b). For this aim such complexing agents as iminodiacetic acid (IDA), N' -(2 hydroxoethyl)ethylenediamine-N,N,N' -triacetic acid (HEDTA), *trans*-1,2-cyklohexanediaminetetraacetic acid (CDTA) and ethylenediaminetetraacetic acid (EDTA) can be proposed.

It was worth mentioning that iminodiacetic acid (IDA) as the eluent is not applied in the separation of rare earth elements(III) on cation exchangers. In the aqueous solution and the solid state the following complexes of [Ln(ida)]+, [Ln(ida)2]- , [Ln(ida)OH], [Ln(ida)2OH]2- and [Ln(ida)3]3- types with IDA are formed. Based on the breakthrough curves found the affinity series in the Ln(III):IDA=1:2 system and at pH 5.07-6.0 for most rare earth element complexes was found for the anion exchanger Dowex 1 in the acetate and IMDA forms to be as follows: **Ho(III) Dy(III) > Gd(III) > Eu(III) > Er(III) > Y(III) > Yb(III) > Sm(III) > Tm(III) > Nd(III) > Pr(III) >>La(III)** (Hubicka & Drobek, 1998)**.**

The affinity series for the anion exchanger in the acetate and IDA forms is the same, but for the acetate form greater differentiation in affinity of individual lanthanides was found. Additionally, it can be stated that the affinity of rare earth elements for the anion exchangers does not depend on the stability constants of Ln(III)-IDA complexes and the obtained series is different from that of rare earth element complexes with EDTA, CDTA and HEDTA. Taking into account the position of individual lanthanides in the above mentioned series the possibility of purification of La(III) from Nd(III) or Pr(III); Sm(III) from Ho(III); Nd(III) from Y(III); Y(III) from Dy(III), Ho(III) as well as Yb(III) from Ho(III) and Er(III) is possible.

As follows from the obtained data the most effective separations of La(III) from Nd(III) or Pr(III) were achieved on Dowex 2 (type 2) with 8% DVB. Using Dowex 2x8 in the acetate form with an anion exchanger bed of 1 dm3, over 1285 g La2O3 was obtained, in which the Nd2O3 content (0.52%) was reduced to below 0.005% and 1100 g La2O3 in which the Pr6O11 content (0.50%) was reduced to below 0.01% (Fig.10). It is also worth noting that the yield of obtained La2O3 is high about 96%. Comparing the earlier results of La(III) purification from Nd(III) on the anion exchanger of the same type with those obtained for EDTA, it follows that using IDA increases the amount of purified La2O3 by over 20 times. The analogous results were obtained on Dowex 1x8 (Hubicka & Drobek, 2000b).

Satisfactory results were also obtained on Dowex MSA-1. On 1 dm3 of this anion exchanger in the acetate form 1100 g of La2O3 was purified from Nd2O3 and 600 g La2O3 from Pr6O11. Despite slightly worse performance separation of those pairs on Dowex MSA-1, in comparison with the analogous results obtained for Dowex 1x8 and Dowex 2x8, due to their favourable physicochemical properties, such as large resistance to chemical agents, welldeveloped surface area and availability of all ion exchange groups, it can be recommended for the use on a macro scale (Hubicka & Kołodyńska, 2000).

**Figure 10.** Separation of La(III) from Nd(III) (0.52%) and La(III) from Pr(III) (0.50%) on Dowex 1x2, Dowex 1x4, Dowex 1x8 and Dowex 2x8 as well as Dowex MSA-1 in the acetate form (1 dm3 of anion exchanger in the Cl form, Ln(III):IDA=1:2, pH 6.0, 2.5g Ln2O3/dm3).

In next step the optimal conditions for sorption and separation processes of Sm(III)-Ho(III) on the polystyrene anion exchangers were studied. It was found that in the Sm(III) from Ho(III) separation the most effective was Dowex 2x8 (type 2). On 1dm3 of Dowex 2x8 about 221 g of Sm2O3 was purified from Ho2O3 (Fig.11).

**Figure 11.** Separation of Nd(III) from Y(III) (0.35%) and Sm(III) from Ho(III) (0.33%) on Dowex 1x2, Dowex 1x4, Dowex 1x8 and Dowex 2x8 as well as Dowex MSA-1 in the Ac form (1 dm3 of anion exchanger in the Cl form, Ln(III):IDA=1:2, pH 5.0, 1.5g Ln2O3/dm3).

It was found that for Dowex 1 the effectiveness of Sm(III)-Ho(III) pair separation (as pairs of LaIII)-Nd(III) and La (III)-Pr (III)) increases with the increasing degree of cross linking from 2 to 8% DVB. The Ho(III) complexes with IDA exhibit the greatest affinity for the anion exchanger Dowex 1 in the acetate form of cross linking 8 % DVB and the smallest for Dowex 1 in the acetate form of cross linking 2 % DVB.

As for the Nd(III) separation from Y(III) it should be emphasized that in the ion exchange processes of rare earth elements(III) separation on cation exchangers using such eluents as ammonium acetate or DTPA, the yttrium(III) elutes close to neodymium(III), and partially overlaps the neodymium(III) (Fig.11). The above method obtaining high purity neodymium(III) on Dowex 1x8 or Dowex 2x8 can be complementary to obtaining this element from the neodymium concentrates in the process of lanthanide(III) elution on the polystyrene-sulphone cation exchangers (Hubicka et al., 1998).

Due to the increasing demand for yttrium(III) in many branches of industry and technology, purification of yttrium(III) from heavy lanthanides(III) can be of significant applicative character. Its advantage is a simple method and low consumption of iminodiacetic acid. Based on the results of purification of the studied pairs of rare earth elemet(III) complexes on anion exchangers of polystyrene skeleton, it was proved that the anion exchangers Dowex 1 and Dowex 2 of the cross linking 8% DVB in the acetate form are the most effective. On 1 dm3 of strongly basic anion exchangers Dowex 1x8 and Dowex 2x8 it can be obtained more than:


The best results were obtained during purification of Y(III) from Ho(III) and Y(III) from Dy(III). However, the amount of Y(III) purified from Er(III) is smaller which is in accordance with the erbium position in the affinity series of rare earth element complexes with IDA compared to the strongly basic gel anion exchanger Dowex 1x4.

In the process of ion exchange separation of rare earth elements on cation exchangers, most eluents washe out ytterbium(III) in the first fractions. However, if the content of ytterbium(III) is small, it is eluted along with heavy lanthanides(III) and yttrium(III). Whereas separation of ytterbium(III) to ytterbium(II) using reduction with metallic limestone at elevated temperature in the argon atmosphere or using the reduction electrolytic method is a multi-stage expensive process (Hubicka & Drobek, 1999; Hubicka & Drobek, 2000a; Hubicka & Drobek, 2000b).

The affinity series of anionic complexes of rare earth elements(III) with IDA for the strongly basic gel anion exchanger Dowex 1 in both acetate and iminodiacetate forms indicates atypical position of ytterbium(III) in it, which creates possibility of Yb(III) purification from accompanying heavy lanthanides(III) such as e.g. Ho(III) or Er(III). The process of Yb(III) separation from Ho(III) and Yb(III) from Er(III) in the acetate form was studied using the anion exchangers Dowex 1x4 and Dowex 1x8 by means of the frontal analysis technique (Fig.12).

Assuming that 1:2 complexes are formed the sorption process of Ln(III)-IDA complexes can be written as:

$$\text{RCH:COO} + [\text{Ln(ida)}\text{z}]^\cdot = \text{R[Ln(ida)CH:COO]} + \text{Hidar}$$

and

130 Ion Exchange Technologies

exchanger in the Cl-

exchanger in the Cl-

**Figure 10.** Separation of La(III) from Nd(III) (0.52%) and La(III) from Pr(III) (0.50%) on Dowex 1x2, Dowex 1x4, Dowex 1x8 and Dowex 2x8 as well as Dowex MSA-1 in the acetate form (1 dm3 of anion

In next step the optimal conditions for sorption and separation processes of Sm(III)-Ho(III) on the polystyrene anion exchangers were studied. It was found that in the Sm(III) from Ho(III) separation the most effective was Dowex 2x8 (type 2). On 1dm3 of Dowex 2x8 about

La(III)-Pr(III)

Nd(III)-Y(III)

Sm(III)-Ho(III)

La(III)-Nd(III)

**Figure 11.** Separation of Nd(III) from Y(III) (0.35%) and Sm(III) from Ho(III) (0.33%) on Dowex 1x2, Dowex 1x4, Dowex 1x8 and Dowex 2x8 as well as Dowex MSA-1 in the Ac form (1 dm3 of anion

It was found that for Dowex 1 the effectiveness of Sm(III)-Ho(III) pair separation (as pairs of LaIII)-Nd(III) and La (III)-Pr (III)) increases with the increasing degree of cross linking from 2 to 8% DVB. The Ho(III) complexes with IDA exhibit the greatest affinity for the anion exchanger Dowex 1 in the acetate form of cross linking 8 % DVB and the smallest for Dowex

As for the Nd(III) separation from Y(III) it should be emphasized that in the ion exchange processes of rare earth elements(III) separation on cation exchangers using such eluents as ammonium acetate or DTPA, the yttrium(III) elutes close to neodymium(III), and partially overlaps the neodymium(III) (Fig.11). The above method obtaining high purity

form, Ln(III):IDA=1:2, pH 5.0, 1.5g Ln2O3/dm3).

1x2 1x4 1x8 2x8 MSA-1

form, Ln(III):IDA=1:2, pH 6.0, 2.5g Ln2O3/dm3).

1x2 1x4 1x8 2x8 MSA-1

221 g of Sm2O3 was purified from Ho2O3 (Fig.11).

0,0 0,5 1,0 1,5 2,0

[kg/dm<sup>3</sup> ]

1 in the acetate form of cross linking 2 % DVB.

0,0 0,1 0,2 0,3 0,4 [kg/dm<sup>3</sup> ]

$$\text{RCH:}\\\text{COO} + [\text{Ln(ida)z}]^\cdot \rightleftharpoons \text{R[Ln(ida)z]} + \text{CH:}\\\text{COO}^-$$

as well as for the IDA form

**Figure 12.** Separation of Yb(III) from Er(III) (0.36%) and Yb(III) from Ho(III) (0.35%) on Dowex 1x4 and Dowex 1x8 in the acetate form (1 dm3 of anion exchanger in the Cl form, Ln(III):IDA=1:2, pH 5.0, 1.5g Ln2O3/dm3).

The acetate form of the studied anion exchangers shows greater differentiation in the affinity of individual complexes than in the iminodiacetate form. Structure and porosity of the skeleton of the anion exchanger and cross linking degree play a significant role in the sorption process. Taking into consideration the kind of functional groups, it was shown that in the separation process the anion exchanger Dowex 2x8 proved to be a little more effective for the pair La(III)-Pr(III) whereas the results are similar for all other pairs.

HEDTA is more readily soluble in water than EDTA. It forms with rare earth element complex compounds in the ratio 1:1. For example, the following complexes are known: [Ln(hedta(OH)]- , [LnH(hedta)2]2- and [Ln(hedta)2]3-. The studies of sorption of the Ln(III) complexes with HEDTA on anion exchangers were begun by (Brücher et al. 1975). The affinity of the rare earth element complexes with HEDTA at pH 7.5 (Ln(III):HEDTA=1:1) for the anion exchanger Dowex 1x2 in the HEDTA form is: **Dy(III) > Ho(III) > Er(III) > Gd(III) > Y(III) > Tm(III) > Tb(III) > Eu(III) > Sm(III) > Yb(III) > Nd(III) > Pr(III) La(III)** (Hubicka & Drobek, 1997a) and differs from that of rare earth element complexes with EDTA and CDTA.

Based on the determined affinity the possibility of separation of Sm(III) from Ho(III) and Sm(III) from Y(III); Y(III) from Ho(III); Y(III) from Er(III); Y(III) from Dy(III); Nd(III) from Y(III) as well as Yb(III) from Ho(III) and Yb(III) from Er(III) complexes with HEDTA in the macro-micro component system by the frontal analysis technique is possible (Hubicka & Drobek, 1997b).

Separation of Sm(III) from Ho(III) (Ln(III):HEDTA=1:1, pH 4.0 and 7.5) in the HEDTA form was conducted on the strongly basic polystyrene anion exchangers Dowex 1 with cross linking 2, 4 and 8% DVB as well as Dowex MSA-1.

As follows from the comparison of the obtained data, the process of purification of Sm(III) from Ho(III) and Sm(III) from Y(III) is the most effective on the anion exchanger Dowex 1x4 in the HEDTA form at solution pH 7.5 (Fig. 13). On 1 dm3 of this anion exchanger it is possible to obtain about 48 g Sm2O3 in which Ho2O3 content can be reduced from 0.33% to the value below 0.05% and about 15 g Sm2O3 in which Y2O3 content can be reduced from 0.37% to the value below 0.03%. Using the macroporous Dowex MSA-1 gave less advantageous results of Sm(III) purification from Ho(III).

132 Ion Exchange Technologies

Ln2O3/dm3).

[Ln(hedta(OH)]-

Drobek, 1997b).

linking 2, 4 and 8% DVB as well as Dowex MSA-1.

CDTA.

RHida + [Ln(ida)2]- ⇄ R[Ln(ida)2] + Hida-

**Figure 12.** Separation of Yb(III) from Er(III) (0.36%) and Yb(III) from Ho(III) (0.35%) on Dowex 1x4 and

The acetate form of the studied anion exchangers shows greater differentiation in the affinity of individual complexes than in the iminodiacetate form. Structure and porosity of the skeleton of the anion exchanger and cross linking degree play a significant role in the sorption process. Taking into consideration the kind of functional groups, it was shown that in the separation process the anion exchanger Dowex 2x8 proved to be a little more effective

HEDTA is more readily soluble in water than EDTA. It forms with rare earth element complex compounds in the ratio 1:1. For example, the following complexes are known:

complexes with HEDTA on anion exchangers were begun by (Brücher et al. 1975). The affinity of the rare earth element complexes with HEDTA at pH 7.5 (Ln(III):HEDTA=1:1) for the anion exchanger Dowex 1x2 in the HEDTA form is: **Dy(III) > Ho(III) > Er(III) > Gd(III) > Y(III) > Tm(III) > Tb(III) > Eu(III) > Sm(III) > Yb(III) > Nd(III) > Pr(III) La(III)** (Hubicka & Drobek, 1997a) and differs from that of rare earth element complexes with EDTA and

Based on the determined affinity the possibility of separation of Sm(III) from Ho(III) and Sm(III) from Y(III); Y(III) from Ho(III); Y(III) from Er(III); Y(III) from Dy(III); Nd(III) from Y(III) as well as Yb(III) from Ho(III) and Yb(III) from Er(III) complexes with HEDTA in the macro-micro component system by the frontal analysis technique is possible (Hubicka &

Separation of Sm(III) from Ho(III) (Ln(III):HEDTA=1:1, pH 4.0 and 7.5) in the HEDTA form was conducted on the strongly basic polystyrene anion exchangers Dowex 1 with cross

As follows from the comparison of the obtained data, the process of purification of Sm(III) from Ho(III) and Sm(III) from Y(III) is the most effective on the anion exchanger Dowex 1x4 in the HEDTA form at solution pH 7.5 (Fig. 13). On 1 dm3 of this anion exchanger it is

, [LnH(hedta)2]2- and [Ln(hedta)2]3-. The studies of sorption of the Ln(III)

for the pair La(III)-Pr(III) whereas the results are similar for all other pairs.

1x4 1x8

form, Ln(III):IDA=1:2, pH 5.0, 1.5g

Yb(III)-Er(III)

Yb(III)-Ho(III)

Dowex 1x8 in the acetate form (1 dm3 of anion exchanger in the Cl-

0,0 0,1 0,2 0,3 0,4 [kg/dm<sup>3</sup> ]

**Figure 13.** Separation of Sm(III) from Ho(III) (0.33%) on Dowex 1x2, Dowex 1x4, Dowex 1x8 and Dowex MSA-1 in the HEDTA form (1 dm3 of anion exchanger in the Cl form, Ln(III):HEDTA=1:1, pH 4.0 and 7.5, 1.5g Ln2O3/dm3).

A smaller amount of Sm(III) purified from Y(III) compared with that of Sm(III) purified from Ho(III)confirms that the Ho(III) complexes exhibit greater affinity than that of Y(III) complexes which is in agreement with the determined affinity series of the rare earth elements(III) complexes with HEDTA.

As follows from the series of rare earth elements(III) complexes with HEDTA for the anion exchanger Dowex 1x2 in the HEDTA form, also the Y(III) complexes are characterized by greater affinity for this anion exchanger than corresponding Nd(III) complexes which indicates possibility of purification of Nd(III) from Y(III) in the macro-micro component system by the frontal analysis technique. In the process of Nd(III) purification from Y(III) the best separation results were obtained using the anion exchanger Dowex 1 of the 4% DVB cross linking. The amount of neodymium(III) purified from yttrium(III) (under the same conditions) obtained using the anion exchangers Dowex 1x2 and Dowex 1x8 is comparable and lower than using the anion exchanger Dowex 1x4. However, the anion exchanger Dowex 2x8proved to be useless in the process of Nd(III) purification from Y(III) (Fig. 14).

The affinity of the complexes of the [LnH(hedta)2]2- type is greater for heavy lanthanides(III) such as Dy(III), Ho(III) and Er(III) than for Y(III) which suggests possibility of purification of Y(III) macro quantities from Dy(III), Ho(III) and Er(III) micro quantities. As follows from the studies, similar to the pair Nd(III)-Y(III) the effectiveness of the pairs Y(III)-Ho(III) and Y(III)-Er(III) separation on strongly basic gel polystyrene anion exchangers is greater at solutions pH 7.5 than pH 4.0. Of all studied anion exchangers Dowex 1x4 gave the best results in purification of the above mentioned rare earth elements(III) complexes with HEDTA. The anion exchanger Dowex 1x4 was also used for separation of the pair Y(III)-

Dy(III). The obtained results show that on 1 dm3 of this anion exchanger in the HEDTA form it is possible to obtain 16 g of yttrium(III) (counted over Y2O3) in which the dysprosium(III) content can be reduced over 10 times i.e. from 0.365% Dy2O3 to the value below 0.035%.

**Figure 14.** Separation of Nd(III) from Y(III) (0.35%) on Dowex 1x2, Dowex 1x4, Dowex 1x8 and Dowex 2x8 in the HEDTA form (1 dm3 of anion exchanger in the Cl form, Ln(III):HEDTA=1:1, pH 4.0 and 7.5, 1.5g Ln2O3/dm3).

In the determined affinity series of rare earth elements(III) with HEDTA for strong basic anion exchangers of the polystyrene skeleton one can see atypical position of Yb(III). Using the strongly basic anion exchanger Dowex 1 with different DVB cross linking, it was proved that for Dowex 1x2 in the HEDTA form, in the affinity series position of Yb(III) is near light rare earth: **Yb(III) > Nd(III) > Pr(III) > La(III).** However, its position is different for Dowex 1x4 in the HEDTA form: **Ho(III) > Y(III) > Sm(III) > Nd(III) > Yb(III)** and Dowex 1x8 in the HEDTA form **Ho(III) > Y(III) > Yb(III) > Sm(III) > Nd(III)**, which indicates that the purification process of Yb(III) from Ho(III) should be more effective on Dowex 1x4.

Based on the results of Yb(III) separation from Ho(III), Yb(III) purification from Er(III) as a micro component was carried out at pH 7.5 using Dowex 1x2 and Dowex 1x4 in the HEDTA form. In this case the anion exchanger Dowex 1x4 also proved to be more effective than Dowex 1x2 (Fig.15).

The obtained results of separation of the pairs Yb(III)-Ho(III) and Yb(III)-Er(III) are in agreement with the breakthrough curves and calculated values of distribution coefficients of the Yb(III), Ho(III) and Er(III) with HEDTA on the anion exchanger Dowex 1x2 in the HEDTA form (Hubicka & Drobek, 1997c). The agreement of the results in Yb(III) purification from Ho(III) and Er(III) with the affinity series of rare earth complexes with HEDTA leads to the suggestion that it is also possible to purify Yb(III) macro quantities from Dy(III), Tm(III) and Y(III) (Hubicka & Drobek, 1997c).

Non-monotonic and atypical the affinity series of anion lanthanide complexes with CDTA was also obtained for isotopes of these elements on the strongly basic anion exchanger Dowex 1x4 in the H2cdta2- form by Wódkiewicz and Dybczyński (1968): **Pm(III) > Nd(III) > Sm(III) > Pr(III) > Ce(III) > Eu(III) > Gd(III) > La(III) > Sc(III) > Tb(III) > Dy(III) > Ho(III) >**  **Y(III) > Er(III) > Tm(III) > Yb(III) > Lu(III)**. Higher affinity of the Nd(cdta)- and Sm(cdta) complexes for the anion exchangers than that of [Y(cdta)]- complexes was used for yttrium purification in the macro-micro component system by the frontal analysis technique on the polystyrene anion exchangers Dowex 1x2 and Dowex 1x4 (Hubicka, 1989a). Based on the obtained results it was pointed out that the affinity depends not only on the type of complexes, their structure but also on physicochemical properties of anion exchangers such as their form. The most effective form in the separation of [Y(cdta)] from [Nd(cdta)]- , [Sm(cdta)] and [Eu(cdta)] complexes proved to be the acetate from rather than the H2cdta2 one but the chloride form of the anion exchangers was completely useless.

134 Ion Exchange Technologies

1.5g Ln2O3/dm3).

Dowex 1x2 (Fig.15).

Dy(III). The obtained results show that on 1 dm3 of this anion exchanger in the HEDTA form it is possible to obtain 16 g of yttrium(III) (counted over Y2O3) in which the dysprosium(III) content can be reduced over 10 times i.e. from 0.365% Dy2O3 to the value below 0.035%.

**Figure 14.** Separation of Nd(III) from Y(III) (0.35%) on Dowex 1x2, Dowex 1x4, Dowex 1x8 and Dowex

In the determined affinity series of rare earth elements(III) with HEDTA for strong basic anion exchangers of the polystyrene skeleton one can see atypical position of Yb(III). Using the strongly basic anion exchanger Dowex 1 with different DVB cross linking, it was proved that for Dowex 1x2 in the HEDTA form, in the affinity series position of Yb(III) is near light rare earth: **Yb(III) > Nd(III) > Pr(III) > La(III).** However, its position is different for Dowex 1x4 in the HEDTA form: **Ho(III) > Y(III) > Sm(III) > Nd(III) > Yb(III)** and Dowex 1x8 in the HEDTA form **Ho(III) > Y(III) > Yb(III) > Sm(III) > Nd(III)**, which indicates that the

Based on the results of Yb(III) separation from Ho(III), Yb(III) purification from Er(III) as a micro component was carried out at pH 7.5 using Dowex 1x2 and Dowex 1x4 in the HEDTA form. In this case the anion exchanger Dowex 1x4 also proved to be more effective than

The obtained results of separation of the pairs Yb(III)-Ho(III) and Yb(III)-Er(III) are in agreement with the breakthrough curves and calculated values of distribution coefficients of the Yb(III), Ho(III) and Er(III) with HEDTA on the anion exchanger Dowex 1x2 in the HEDTA form (Hubicka & Drobek, 1997c). The agreement of the results in Yb(III) purification from Ho(III) and Er(III) with the affinity series of rare earth complexes with HEDTA leads to the suggestion that it is also possible to purify Yb(III) macro quantities

Non-monotonic and atypical the affinity series of anion lanthanide complexes with CDTA was also obtained for isotopes of these elements on the strongly basic anion exchanger Dowex 1x4 in the H2cdta2- form by Wódkiewicz and Dybczyński (1968): **Pm(III) > Nd(III) > Sm(III) > Pr(III) > Ce(III) > Eu(III) > Gd(III) > La(III) > Sc(III) > Tb(III) > Dy(III) > Ho(III) >** 

purification process of Yb(III) from Ho(III) should be more effective on Dowex 1x4.

form, Ln(III):HEDTA=1:1, pH 4.0 and 7.5,

pH 4.0

pH 7.5

2x8 in the HEDTA form (1 dm3 of anion exchanger in the Cl-

0,0

0,1

0,2

0,3

0,4 [kg/dm<sup>3</sup> ]

1x2 1x4 1x8 2x8

from Dy(III), Tm(III) and Y(III) (Hubicka & Drobek, 1997c).

**Figure 15.** Separation of Yb(III) from Ho(III) (0.34%) on Dowex 1x2, Dowex 1x4 and Dowex 1x8 in the HEDTA form (1 dm3 of anion exchanger in the Cl form, Ln(III):HEDTA=1:1, pH 4.0 and 7.5, 1.5g Ln2O3/dm3).

Taking the above into consideration it was interesting to study applicability of the anion exchanger of the polyacrylate skeleton for separation of rare earth elements(III) complexes with CDTA (Hubicka & Kołodyńska, 2003). As follows from the breakthrough curves the Nd(III) and Sm(III) complexes with CDTA exhibit higher affinity for both strongly basic and weakly basic polyacrylate anion exchangers Amberlite IRA 458, Amberlite IRA 958 for the corresponding Y(III) complexes and their affinity is arranged in the same order as for strongly basic polystyrene anion exchangers.

Assuming that the complexes 1:1 are formed, the anion exchange reaction can be written as:

$$\text{RCH:}\\\text{cCOO} + \text{Ln(cdata)} \rightleftharpoons \text{RLn(cdata)} + \text{CH:}\\\text{cCOO} +$$

The obtained data indicate that the strongly basic, polyacrylate, gel anion exchanger Amberlite IRA 458 is more effective in purification of Y(III) from Nd(III) in comparison with the strongly basic, macroporous anion exchanger Amberlite IRA 958.

It was shown that the weakly basic polyacrylate gel anion exchanger Amberlite IRA 68 is more effective than the strongly basic, gel anion exchangers of polyacrylate and polystyrene types (Fig. 16). On 1 dm3 of this anion exchanger it is possible to obtain about 90 g Y2O3 in

which the Nd2O3 content was reduced from 0.35% to below 0.005% and about 81 g Y2O3 in which the Sm2O3 content was reduced from 0.36% to below 0.015%. Therefore, polyacrylate anion exchangers with respect to their applicability in purification of Y(III) from Nd(III) and Sm(III) complexes with CDTA can be arranged as follows: weakly basic, gel > strongly basic, gel > strongly basic, macroporous (Hubicka & Kołodyńska, 2003; Hubicka & Kołodyńska, 2004).

The analogous results were obtained using the monodisperse anion exchangers Lewatit MonoPlus M 500, Lewatit MonoPlus M 600, Lewatit MonoPlus MP 500, Lewatit MonoPlus MP 64 and the heterodisperse anion exchanger Lewatit MP 62 (Hubicka & Kołodyńska, 2008). The data indicate that Lewatit MonoPlus M 500 (type 1) in the acetate form is more effective in purification of Y(III) from Nd(III) and Y(III) from Sm(III) in comparison with Lewatit MonoPlus M 600 (type 2).

**Figure 16.** Separation of Y(III) from Sm(III) (0.36%) and Y(III) from Nd(III) (0.35%) on Amberlite IRA 458, Amberlite IRA 68, Amberlite IRA 958 and Dowex 2x8 in the CDTA form (1 dm3 of anion exchanger in the Cl form, Ln(III):CDTA=1:1, pH 4.8, 1.5g Ln2O3/dm3).

On 1 dm3 of this anion exchanger, it is possible to obtain approximately 79 g Y2O3 in which the Nd2O3 content was reduced from 0.35% to below 0.005% and approximately 70 g Y2O3 in which the Sm2O3 content was reduced from 0.35% to below 0.015% (data not presented). It was also shown that purification of Y(III) from Nd(III) in the system with CDTA on the polystyrene anion exchangers is less effective than in the system with EDTA (Hubicka & Kołodyńska, 2007). Smaller differentiation in affinity of the [Ln(cdta)] complexes than the [Ln(edta)]– complexes on anion exchangers can be justified by larger 'flexibility' of EDTA compared with the 'rigidity' structure of CDTA.

Ion exchange reactions proceed not only in the aqueous system but also in the non-aqueous solvents such as alcohols, ketones, glycols, etc. as well as in the mixed systems, e.g. wateralcohol, water-ketone, etc. Application of non-aqueous and mixed solvents in the anion exchange of metal complexes has increased considerably by a number of possible separations. In most cases the distribution coefficients of metal complexes in mixed media like water-alcohol, water-acetone etc. are larger than those in pure water solutions (Moody & Thomas, 1968; Marcus, 1983). Therefore, using an unusual order of affinity series of anion lanthanide complexes with EDTA of Ln(edta) type for the strongly basic anion exchanger in the H2edta2- form (Dybczyński, 1964; Dybczyński, 1970): **Sm(III) > Eu(III) > Gd(III) > Nd(III) > Pr(III) > Tb(III) > Ce(III) > Dy(III) > La(III) > Ho(III) > Y(III) > Er(III) > Sc(III) > Tm(III) > Yb(III) > Lu(III)** and higher affinity of the [Nd(edta)]- complexes than that of [Y(edta)] complexes the yttrium(III) purification as a macro component from neodymium(III) by the frontal analysis technique in the solvent organic system were also carried out. The results of separation of Y(III) from Nd(III) (Nd2O3 0.35%) in the presence of EDTA without and with 10%(v/v) and 20%(v/v) addition of methanol, 1-propanol, 2-propanol and acetone on Lewatit MonoPlus M 500, Lewatit MonoPlus M 600, Lewatit MonoPlus MP 500, Lewatit MonoPlus MP 64 and Lewatit MP 62 are presented in Fig. 17.

136 Ion Exchange Technologies

Lewatit MonoPlus M 600 (type 2).

0,0

0,1

0,2

0,3

0,4 [kg/dm<sup>3</sup> ]

2004).

in the Cl-

which the Nd2O3 content was reduced from 0.35% to below 0.005% and about 81 g Y2O3 in which the Sm2O3 content was reduced from 0.36% to below 0.015%. Therefore, polyacrylate anion exchangers with respect to their applicability in purification of Y(III) from Nd(III) and Sm(III) complexes with CDTA can be arranged as follows: weakly basic, gel > strongly basic, gel > strongly basic, macroporous (Hubicka & Kołodyńska, 2003; Hubicka & Kołodyńska,

The analogous results were obtained using the monodisperse anion exchangers Lewatit MonoPlus M 500, Lewatit MonoPlus M 600, Lewatit MonoPlus MP 500, Lewatit MonoPlus MP 64 and the heterodisperse anion exchanger Lewatit MP 62 (Hubicka & Kołodyńska, 2008). The data indicate that Lewatit MonoPlus M 500 (type 1) in the acetate form is more effective in purification of Y(III) from Nd(III) and Y(III) from Sm(III) in comparison with

**Figure 16.** Separation of Y(III) from Sm(III) (0.36%) and Y(III) from Nd(III) (0.35%) on Amberlite IRA 458, Amberlite IRA 68, Amberlite IRA 958 and Dowex 2x8 in the CDTA form (1 dm3 of anion exchanger

Y(III)-Sm(III)

Y(III)-Nd(III)

On 1 dm3 of this anion exchanger, it is possible to obtain approximately 79 g Y2O3 in which the Nd2O3 content was reduced from 0.35% to below 0.005% and approximately 70 g Y2O3 in which the Sm2O3 content was reduced from 0.35% to below 0.015% (data not presented). It was also shown that purification of Y(III) from Nd(III) in the system with CDTA on the polystyrene anion exchangers is less effective than in the system with EDTA (Hubicka &

[Ln(edta)]– complexes on anion exchangers can be justified by larger 'flexibility' of EDTA

Ion exchange reactions proceed not only in the aqueous system but also in the non-aqueous solvents such as alcohols, ketones, glycols, etc. as well as in the mixed systems, e.g. wateralcohol, water-ketone, etc. Application of non-aqueous and mixed solvents in the anion exchange of metal complexes has increased considerably by a number of possible separations. In most cases the distribution coefficients of metal complexes in mixed media

complexes than the

form, Ln(III):CDTA=1:1, pH 4.8, 1.5g Ln2O3/dm3).

compared with the 'rigidity' structure of CDTA.

Kołodyńska, 2007). Smaller differentiation in affinity of the [Ln(cdta)]-

<sup>458</sup> <sup>68</sup> <sup>958</sup> 2x8

**Figure 17.** Separation of Y(III) from Nd(III) (0.35%) on Lewatit MonoPlus M 500, Lewatit MonoPlus M 600, Lewatit MonoPlus MP 500, Lewatit MonoPlus MP 64 and Lewatit MP 62 in the H2O-20 % (v/v) polar organic solvent systems (1 dm3 of anion exchanger in the Cl form, Ln(III):EDTA=1:1, pH 4.8, 1.5g Ln2O3/dm3).

Taking into consideration the effect of the addition of polar organic solvent on the effectiveness of separation of rare earth element(III) complexes with EDTA on the above mentioned anion exchangers the best results of Y(III) from Nd(III) purification are obtained in 20% (v/v) methanol system on Lewatit MonoPlus M 500 and Lewatit MonoPlus MP 64. Taking 1 dm3 bed of Lewatit MonoPlus M 500 it is possible to obtain above 158 g Y2O3 in which the Nd2O3 content can be reduced from 0.35% to below 0.005%, whereas 182 g Y2O3 for Lewatit MonoPlus MP 64. The yield obtained in these processes is above 70-100% higher than that obtained in the aqueous solutions. However, the increase of methanol addition up to 20% (v/v) increases accordingly the yield of purified Y2O3 only by about 15%, but the increase of methanol addition up to 50% (v/v) already affects insignificantly the yield increase in this process (Hubicka & Kołodyńska, 2005; Hubicka & Kołodyńska, 2007).

Analogous studies on the separation of Y(III)-Nd(III) with EDTA were also carried out in the presence of ethanol, 1-propanol, 2-propanol and acetone. However, only 20% (v/v) addition of acetone to the system increases effectiveness of separation process compared to the aqueous solutions.

Moreover the analogous studies were carried out for the IDA complexing agent. The data obtained indicate that Lewatit MonoPlus M 500 and Lewatit MonoPlus M 600 in the acetate form in aqueous solutions are the most effective in separation of the [Sm(ida)2]—[Ho(ida)2] pair (Fig.18).

**Figure 18.** Fig. 18. Separation of Sm(III) from Ho(III) (0.35%), Y(III) from Ho(III) (0.36%) and Y(III) from Er(III) (0.35%) on Lewatit MonoPlus M 500 in the H2O-20 % (v/v) CH3OH (1 dm3 of anion exchanger in the Cl form, Ln(III):IDA=1:1, pH 5.0, 1.5g Ln2O3/dm3).

Taking into account the effect of types of functional groups -N+(CH3)3 (Lewatit MonoPlus M 500) and -N+(CH3)2C2H4OH (Lewatit MonoPlus M 600) on the results of separation of rare earth element(III) complexes with IDA both for the Sm(III)-Ho(III) and Y(III)-Ho(III) pairs, the anion exchanger Lewatit MonoPlus M 500 (type 1) of slightly larger basicity of the functional group compared with the anion exchanger Lewatit MonoPlus M 600 (type 2). However, the addition of 10% (v/v) or 20% (v/v) methanol proved to be disadvantageous both for Lewatit MonoPlus M 500 and Lewatit MonoPlus M 600.

Due to the fact that the addition of polar solvent improves the efficiency of the separation of rare earth elements(III) only for the selected complexing agents, the possibility of selective separation of nitrate complexes of rare earth elements(III) in a polar organic solvent-H2O-HNO3 by the frontal analysis was also examined in the case of the absence of complexing agents. In the studies the following parameters were taken into account: type of the functional groups, type of the anion exchanger skeleton, the degree of cross linking, porosity and grain size as well as the effect of type and concentration of polar organic solvent, the presence of another organic solvent and the concentration of nitric(V) acid as well as the concentration of rare earth elements(III) in solution (Hubicki & Olszak, 1994; Hubicki et al. 1995; Hubicki & Olszak, 1996a; Hubicki & Olszak, 1996b; Hubicki et al. 1996).

Taking into account the obtained affinity series for the anion exchangers Wofatit SBWx4%, Wofatit SBKx7% and Wofatit SBWx6%in the systems:

#### **90% v/v CH3OH-10% v/v 7M HNO3 – Wofatit SBWx4%**

138 Ion Exchange Technologies

aqueous solutions.

pair (Fig.18).

the Cl-

of acetone to the system increases effectiveness of separation process compared to the

Moreover the analogous studies were carried out for the IDA complexing agent. The data obtained indicate that Lewatit MonoPlus M 500 and Lewatit MonoPlus M 600 in the acetate form in aqueous solutions are the most effective in separation of the [Sm(ida)2]—[Ho(ida)2]-

**Figure 18.** Fig. 18. Separation of Sm(III) from Ho(III) (0.35%), Y(III) from Ho(III) (0.36%) and Y(III) from Er(III) (0.35%) on Lewatit MonoPlus M 500 in the H2O-20 % (v/v) CH3OH (1 dm3 of anion exchanger in

Sm(III)-Ho(III)

Y(III)-Ho(III)

Y(III)-Er(III)

Taking into account the effect of types of functional groups -N+(CH3)3 (Lewatit MonoPlus M 500) and -N+(CH3)2C2H4OH (Lewatit MonoPlus M 600) on the results of separation of rare earth element(III) complexes with IDA both for the Sm(III)-Ho(III) and Y(III)-Ho(III) pairs, the anion exchanger Lewatit MonoPlus M 500 (type 1) of slightly larger basicity of the functional group compared with the anion exchanger Lewatit MonoPlus M 600 (type 2). However, the addition of 10% (v/v) or 20% (v/v) methanol proved to be disadvantageous

Due to the fact that the addition of polar solvent improves the efficiency of the separation of rare earth elements(III) only for the selected complexing agents, the possibility of selective separation of nitrate complexes of rare earth elements(III) in a polar organic solvent-H2O-HNO3 by the frontal analysis was also examined in the case of the absence of complexing agents. In the studies the following parameters were taken into account: type of the functional groups, type of the anion exchanger skeleton, the degree of cross linking, porosity and grain size as well as the effect of type and concentration of polar organic solvent, the presence of another organic solvent and the concentration of nitric(V) acid as well as the concentration of rare earth elements(III) in solution (Hubicki & Olszak, 1994; Hubicki et al.

Taking into account the obtained affinity series for the anion exchangers Wofatit SBWx4%,

form, Ln(III):IDA=1:1, pH 5.0, 1.5g Ln2O3/dm3).

0,0 0,1

0,2

0,3

0,4

[kg/dm<sup>3</sup> ]

Wofatit SBKx7% and Wofatit SBWx6%in the systems:

both for Lewatit MonoPlus M 500 and Lewatit MonoPlus M 600.

without MeOH

with MeOH

1995; Hubicki & Olszak, 1996a; Hubicki & Olszak, 1996b; Hubicki et al. 1996).

**Nd(III)** > Pr(III) > **Sm(III)** > Ce(III) > La(III) > Eu(III) > Gd(III) > Tb(III) > **Y(III)** > Dy(III) > Tm(III) Ho(III) Er(III) > Yb(III),

### **90% v/v CH3OH-10% v/v 7M HNO3 – Wofatit SBKx7%**

Pr(III) **Nd(III)** > La(III) > **Sm(III)** > Eu(III) > Gd(III) > Tb(III) > Dy(III) Ho(III) = Er(IIII) = Tm(III) = Yb(III) > **Y(III),**

#### **90% v/v C2H5OH-10% v/v 7M HNO3 – Wofatit SBWx4%**

**Nd(III)** > La(III) Pr(III) > **Sm(III)** > Eu(III) > Gd(III) > Tb(III) > Dy(III) > Ho(III) Er(III) > Yb(III) **Y(III)** Tm(III),

### **90% v/v C2H5OH-10% v/v 7M HNO3 – Wofatit SBKx7%**

Yb(III) La(III) **Y(III)** = Pr(III) = **Nd(III)** = Tb(III) = Er(III) Eu(III) = Dy(III) = Ho(III) **Sm(III)** = Gd(III) = Tm(III),

### **90% v/v CH3COCH3-10% v/v 7M HNO3 – Wofatit SBWx4%**

**Nd(III)** > La(III) Pr(III) > **Sm(III)** > Eu(III) > Gd(III) > Tb(III) > Er(III) > Dy(III) > Ho(III) = **Y(III)** Tm(III) > Yb(III),

#### **90% v/v CH3COCH3-10% v/v 7M HNO3 – Wofatit SBKWx7%**

**Nd(III)** > La(III) Pr(III) > **Sm(III)** > Eu(III) > Gd(III) > Tb(III) > Dy(III) > Ho(III) Er(III) > Yb(III) **Y(III)** Tm(III),

it was found that the distribution coefficients have the largest values in the CH3OH system.

The differences in affinity of rare earth(III) elements nitrate complexes for anion exchangers in individual systems, for example Y(III)-Nd(III), Sm(III)-Nd(III), are probably due to a different structure of complexes (degree of their solvation) or different stability or kinetics of their formation in the anion exchanger phase. Probably in the resin phase the [Nd(NO3)5]2 complexes are formed, whereas Y(III) forms the complexes of [Y(NO3)4]- (Korkish, 1968). It was also found that macroporous anion exchangers give better separation results whereas using strongly basic anion exchangers with the pyridine functional group Permutit SK the obtained results were worse. The analogous situation was in the case of Amberlite IRA 938 and Wofatit SBWx2% (Hubicki et al. 1996; Hubicki and Olszak, 1998a; Hubicki and Olszak, 1998b; Hubicki and Olszak, 1998c; Hubicki and Olszak, 1998d; Hubicki and Olszak, 1998e).

Additionally, it should be emphasized that these non-typical affinity series give the opportunity to obtain ion exchange separation of rare earth elements. Very interesting is the position of Y(III) in the obtained affinity series on Wofatit SBKx7%in the 90% v/v CH3OH-10% v/v 7M HNO3 system (Hubicki and Olszak, 1994; Hubicki et al. 1995). As follows from the theory of yttrium(III) migration in the lanthanide series, it behaves like pseudolanthanide(III) when the central ion-ligand bonding in the complex is covalently shortened and behaves like heavy lanthanides(III) when this bonding is of ionic character. In the studied system yttrium(III) behaves like heavy lanthanide(III).

Noteworthy are also the results of treatment of macro quantities of yttrium(III) from neodymium(III) in the 90% v/v CH3OH–10% v/v 7 M HNO3 system on the strongly basic anion exchanger Wofatit SBW with the degree of cross linking 4 and 6% DVB. On this anion exchanger, the effect of nitric(V) acid concentration in the 90% v/v CH3OH–10% v/v 0.1-9 M HNO3 system as well as the effect of the addition of ammonium nitrate(V) in the 90% v/v CH3OH–10% v/v 0,1 M HNO3 –1-5 M NH4NO3 system were also studied (Fig.19).

**Figure 19.** Mass (Dg) and volume (Dv) distribution coefficients as well as the number of the theoretical plates (N) of Wofatit SBWx6% in the dependence of HNO3 concentration (0.1-9.0 M).

It was shown that with the increasing concentration of nitric(V) acid, the efficiency of sorption and separation of nitrate complexes of rare earth elements(III) initially increases in the systems 7-8 M HNO3–CH3OH, 3 M HNO3–C2H5OH and 7 M HNO3–CH3COCH3 and then decreases. The results of the effect of HNO3 concentration on the efficiency of the purification process of Y(III) from Nd (III) (<0.001%Nd2O3) on the anion exchanger Wofatit SBWx4 with a varyingdegree of the cross linking is shown in Fig.20a. The analogous results obtained for the Sm(III)-Nd(III) pair are shown in Fig. 20b.

The type of skeleton of the used ion exchanger is also an important parameter. For the polyacrylate anion exchangers Amberlite IRA 458, Amberlite IRA 958 and Purolite A 850 the efficiency of the sorption process is low. Mass of the purified yttrium oxide(III) (<0.001%Nd2O3) was equal to 0.18 kg/dm3 for Amberlite IRA 458; 0.26 kg/dm3 for Amberlite IRA 958 and 0.09 kg/dm3 for Purolite A 850. The anion exchanger Amberlite IRA 68 proved to be completely useless. However, the best results were obtained on the strongly basic anion exchangers of type 1. For example, using Lewatit MP 5080 with the macroporous 25 skeleton structure there was achieved 1.9 kg Y2O3/dm3 (<0.001%Nd2O3) in the methanol system while in the acetone system 2.3 kg Y2O3/dm3 (<0.001%Nd2O3) (Fig.21).

Noteworthy are also the results of treatment of macro quantities of yttrium(III) from neodymium(III) in the 90% v/v CH3OH–10% v/v 7 M HNO3 system on the strongly basic anion exchanger Wofatit SBW with the degree of cross linking 4 and 6% DVB. On this anion exchanger, the effect of nitric(V) acid concentration in the 90% v/v CH3OH–10% v/v 0.1-9 M HNO3 system as well as the effect of the addition of ammonium nitrate(V) in the 90% v/v

**Figure 19.** Mass (Dg) and volume (Dv) distribution coefficients as well as the number of the theoretical

Dv

M HNO3

Dg N

It was shown that with the increasing concentration of nitric(V) acid, the efficiency of sorption and separation of nitrate complexes of rare earth elements(III) initially increases in the systems 7-8 M HNO3–CH3OH, 3 M HNO3–C2H5OH and 7 M HNO3–CH3COCH3 and then decreases. The results of the effect of HNO3 concentration on the efficiency of the purification process of Y(III) from Nd (III) (<0.001%Nd2O3) on the anion exchanger Wofatit SBWx4 with a varyingdegree of the cross linking is shown in Fig.20a. The analogous results

The type of skeleton of the used ion exchanger is also an important parameter. For the polyacrylate anion exchangers Amberlite IRA 458, Amberlite IRA 958 and Purolite A 850 the efficiency of the sorption process is low. Mass of the purified yttrium oxide(III) (<0.001%Nd2O3) was equal to 0.18 kg/dm3 for Amberlite IRA 458; 0.26 kg/dm3 for Amberlite IRA 958 and 0.09 kg/dm3 for Purolite A 850. The anion exchanger Amberlite IRA 68 proved to be completely useless. However, the best results were obtained on the strongly basic anion exchangers of type 1. For example, using Lewatit MP 5080 with the macroporous 25 skeleton structure there was achieved 1.9 kg Y2O3/dm3 (<0.001%Nd2O3) in the methanol

plates (N) of Wofatit SBWx6% in the dependence of HNO3 concentration (0.1-9.0 M).

0,1 0,5 1,0 3,0 6,0 7,0 8,0 9,0

system while in the acetone system 2.3 kg Y2O3/dm3 (<0.001%Nd2O3) (Fig.21).

obtained for the Sm(III)-Nd(III) pair are shown in Fig. 20b.

0

200

400

600

800

CH3OH–10% v/v 0,1 M HNO3 –1-5 M NH4NO3 system were also studied (Fig.19).

**Figure 20.** a-b. Effect of the HNO3 concentration on the effectiveness of Y(III) from Nd(III) separation (<0.001%Nd2O3) on Wofatit SBWx4 (a) and Sm(III) from Nd(III) (<0.001%Nd2O3) on Wofatit SBWx6 (b) at different HNO3 concentrations in the methanol and acetone systems.

**Figure 21.** Separation of Y(III) fromNd(III) (<0.001%Nd2O3) on Lewatit MP 5080 in the 90% v/v CH3OH–10% v/v 7 M HNO3 and 90% v/v CH3COCH3–10% v/v 7 M HNO3 systems.

Good results were also obtained on Zerolit FF IP 2-3%, Zerolit 3-5% FF IP and Wofatit SBWx6%. In in the case of Zerolit FF IP 7-9% more than two fold decrease of the efficiency of purification process of Y(III) from Nd(III) was obtained (Hubicki et a. 1994).

The influence of cross linking degree on the effectiveness of separation of Y(III)-Nd (III) pair was also studied. For the ion exchanger Dowex it increases from 2% to 6% DVB and then decreases. For the systems with methanol this effect is observed at 4% DVB. For Zerolit FF IP the highest sorption capacities were obtained at the degree of cross linking equal to 2-3%, which may be associated with the sieve effect (Hubicki & Olszak, 1996; Hubicki, et al. 1996). In comparison with the separation of yttrium(III) from neodymium(III) the effects of the purification process of samarium(III) from neodymium(III) are much lower. This is due to a smaller difference between the distribution coefficients of Sm(III)-Nd(III) in comparison with the Y(III)-Nd(III) pair. Taking into account the effectiveness of this sorption process gel and macroporous anion exchangers can be arranged as follows: in the Ln(NO3)3–90% v/v CH3OH–10% 7 M HNO3 system: Lewatit MP 5080 (0.26 kg/dm3) > Wofatit SBWx6% (0.16 kg/dm3) > Dowex 1x4 (0.11 kg/dm3) > Wofatit SBKx7% (0.07 kg/dm3) > Wofatit SBWx7% (0.04 kg/dm3) > Dowex 1x8 (0.031 kg/dm3) > Dowex 1x2 (0.03 kg/dm3) > Wofatit SBWx4% (0.02 kg/dm3) > Dowex 1x10 (0.01 kg/dm3) > Dowex 1x1 (0.009 kg/dm3) (Hubicki & Olszak, 2000a; Hubicki & Olszak, 2001). The strongly basic anion exchanger Lewatit MP 5080 proved to be the most effective (Hubicki & Olszak, 2001). Depending on the separation system the obtained results are in the range from 0.26 to 0.24 kg of Sm2O3 (0.001 % Nd2O3) on 1 dm3 of the ion exchanger. The smaller results were obtained on Wofat SBWx6 - 0.18 kg Sm2O3 (0.001% Nd2O3)/dm3). Much smaller yield of Sm(III) from Nd(III) purification compared with that of Y(III) from Nd(III) is caused by a smaller difference between the distribution coefficients of Sm(III)-Nd(III) compared with Y(III)-Nd(III). Different affinities of neodymium(III) and samarium(III) nitrate complexes in the systems Ln(NO3)3–90% v/v CH3OH–10% 1 M or 7 M HNO3 as well as in Ln(NO3)3–90% v/v CH3COCH3–10% 1 M or 7 M HNO3 are probably caused by the formation of neodymium nitrate complexes with a higher negative charge, e.g. [Nd(NO3)5]2- than that of samarium(III) complexes , e.g. [Sm(NO3)4]- ) or by their different structures (possibly by the differences in the degree of solvation) and the kinetics of formation of neodymium(III) and samarium(III) anionic nitrate complexes (Hubicki, et al. 1996; Hubicki and Olszak, 2000a; Hubicki and Olszak, 2000b; Hubicki and Olszak, 2001; Hubicki and Olszak, 2002).

**Figure 22.** a-c. Separation of Y(III) from Nd(III) (<0.001%Nd2O3) on Dowex 1 (a), Zerolit FF IP (b) and Wofatit SBW (c) with different cross linking in the methanol and acetone systems.

Determination which of the used organic solvents possesses the best sorption properties is not possible.

However, it should be noted that using 1-propanol and 2-propanol the efficiency of the separation process is lower than for methanol and acetone (data not presented). It was also shown that for dimethylosulphoxide (DMF) in a 90% v/v DMF-10% v/v 7 M HNO3 system separation does not occur.

In industrial processes of ion exchange separation of rare earth elements(III) on cation exchangers using aminopolycarboxylic acids or hydroxyacids as eluents, the concentration of lanthanides(III) in the eluate rarely exceeds a few grams per liter. In the present study, the effect of concentration of rare earth elements(III) on the efficiency of Y(III)-Nd(III) pair separation in the macro-micro component was investigated. It was found that in the methanol and ethanol systems the increase in the concentration of purified yttrium(III) to 50 g Ln2O3/dm3 practically does not affect the efficiency of the process. However, further increase of Ln2O3 concentration decreases the efficiency of the ion exchange column. Very good results were obtained at a concentration of 50 g Ln2O3/dm3 in the acetone system.

The effect of the percentage concentration of Nd(III) on the effectiveness of the separation process was also examined. Both, in the case of yttrium(III) and samarium(III) separation at 0.1% of neodymium(III) content the effectiveness of the process is much better.

The sorption of nitrate(V) complexes of rare earth elements(III) is also dependent not only on the type of solvent used but also on its concentration in the mixture. This fact was confirmed by the results of the separation of yttrium(III) from neodymium(III). The addition of an organic solvent such as methanol or acetone (with a lower polarity and dielectric constant than water) generally reduces the degree of dissociation of rare earth elements(III) and increases their tendency to form ion complexes. At the same time the distribution coefficients of lanthanides(III) on anion exchangers are also changed.

It should be mentioned that the anion exchangers can be regenerated with water in the amount of 2–4 bed volumes after the purification process of rare earth elements. The relatively high yield of rare earth elements purification, the low costs and the simple and cheap regeneration of the anion exchanger bed when the purification process is over, as well as the possibility of methanol recovery from the eluate by using the distillation method suggest the possibility of using this process in technologies for high purity rare earth production.

### **13. Conclusions**

) or

142 Ion Exchange Technologies

Olszak, 2001; Hubicki and Olszak, 2002).

CH3OH–10% 7 M HNO3 system: Lewatit MP 5080 (0.26 kg/dm3) > Wofatit SBWx6% (0.16 kg/dm3) > Dowex 1x4 (0.11 kg/dm3) > Wofatit SBKx7% (0.07 kg/dm3) > Wofatit SBWx7% (0.04 kg/dm3) > Dowex 1x8 (0.031 kg/dm3) > Dowex 1x2 (0.03 kg/dm3) > Wofatit SBWx4% (0.02 kg/dm3) > Dowex 1x10 (0.01 kg/dm3) > Dowex 1x1 (0.009 kg/dm3) (Hubicki & Olszak, 2000a; Hubicki & Olszak, 2001). The strongly basic anion exchanger Lewatit MP 5080 proved to be the most effective (Hubicki & Olszak, 2001). Depending on the separation system the obtained results are in the range from 0.26 to 0.24 kg of Sm2O3 (0.001 % Nd2O3) on 1 dm3 of the ion exchanger. The smaller results were obtained on Wofat SBWx6 - 0.18 kg Sm2O3 (0.001% Nd2O3)/dm3). Much smaller yield of Sm(III) from Nd(III) purification compared with that of Y(III) from Nd(III) is caused by a smaller difference between the distribution coefficients of Sm(III)-Nd(III) compared with Y(III)-Nd(III). Different affinities of neodymium(III) and samarium(III) nitrate complexes in the systems Ln(NO3)3–90% v/v CH3OH–10% 1 M or 7 M HNO3 as well as in Ln(NO3)3–90% v/v CH3COCH3–10% 1 M or 7 M HNO3 are probably caused by the formation of neodymium nitrate complexes with a higher negative charge, e.g. [Nd(NO3)5]2- than that of samarium(III) complexes , e.g. [Sm(NO3)4]-

by their different structures (possibly by the differences in the degree of solvation) and the kinetics of formation of neodymium(III) and samarium(III) anionic nitrate complexes (Hubicki, et al. 1996; Hubicki and Olszak, 2000a; Hubicki and Olszak, 2000b; Hubicki and

**Figure 22.** a-c. Separation of Y(III) from Nd(III) (<0.001%Nd2O3) on Dowex 1 (a), Zerolit FF IP (b) and

Wofatit SBW (c) with different cross linking in the methanol and acetone systems.

Rare earth elements(III) are extremely important for the development of economy and technology. Among others, they are used for the production of electronic equipment, in automotive, aerospace, missile, military industries and even in medical diagnostics.

Atypical affinity series create new possibilities of ion exchange separation of rare earth elements(III) which is very significant from a practical point of view. The results of rare earth elements nitrate complexes separation in the micro-macro component system as well

as in the presence of aminopolycarboxylic acids and organic solvents can be successfully applied in production of rare earth elements(III), particularly yttrium(III), ytterbium(III), samarium(III) and lanthanum(III) of a large purity degree. It is worth mentioning that regeneration of anion exchangers in these systems is very economical using distilled water as a regenerating factor.

### **Author details**

Dorota Kołodyńska and Zbigniew Hubicki

*Maria Curie-Skłodowska University, Faculty of Chemistry, Department of Inorganic Chemistry, Lublin, Poland* 

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