**11. Experimental**

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 mm. They were used in the appropriate form.

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 converted to oxides.

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

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 were also studied.
