Fluoride complexation of rutherfordium (Rf, element 104)

Abstract

Zirconium / Hafnium / Thorium / Rutherfordium / Fluoride complexation / Anion and cation exchange chromatography Summary. The fluoride complexation of the group-4 elements Zr, Hf and Rf, and of the pseudo-homolog Th, has been investigated in mixed HNO 3 /HF solutions by studying K d values on both cation exchange resins (CIX) and anion exchange resins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the four elements are strongly retained as cations below 10 Ϫ3 M HF. For Zr and Hf, the decrease of the K d values due to the formation of fluoride complexes occurs between 10 Ϫ3 M HF and 10 Ϫ2 M HF. For Rf and Th, this decrease is observed at one order of magnitude higher HF concentrations. On the AIX, for Zr and Hf, a rise of the K d values due to the formation of anionic fluoride complexes is observed between 10 Ϫ3 M HF and 10 Ϫ2 M HF, i.e. in the same range of HF concentrations where the decrease of the K d values on the CIX is observed, yielding a consistent picture. For Rf and Th, on the AIX, no rise of the K d values is observed even if the HF concentration is increased up to 1 M. By varying the concentration of the counter ion NO 3 Ϫ which is competing for the binding sites on the AIX resin, it could be shown, nevertheless, that Rf does form anionic fluoride complexes. Apparently, there is a more specific competition of NO 3 Ϫ with respect to [RfF x ] (xϪ4)Ϫ than with [ZrF y ] (yϪ4)Ϫ and [HfF z ] (zϪ4)Ϫ .

Elution Curve of Rutherfordium (Rf) in Anion-Exchange Chromatography with Hydrofluoric Acid Solution

“…The Kd values of Rf in HFIHNO3 were also measured by the rapid ion-exchange separation method as a ratio of specific radioactivities of Rf in the solid and liquid phases, in which the significant differences in the Kd values between Rf and Hf were observed. 4 The measurement of the Kd values of Rf in the reversed-phase extraction chromatography from 8 M HCl into tributylphosphate (TBP) was carried out and the extraction sequence among Rf, Zr, and Hf was established through the Kd values.5 In our previous report,6 the anionexchange behavior of Rf was studied together with its lighter homologues, Zr and Hf, as a function of HF concentration in 1.9-13.9 M. The Kd values of Rf were deduced from the relationship between adsorption probability and the Kd values of Zr and Hf by assuming that the kinetics in the fluoride complexation and the ion-exchange processes of RI is the same as those of the homologues, Zr and Hf. However, no Kd values of Rf directly measured from elution curves in chromatographic experiments have not been reported yet.…”

Chemistry of the superheavy elements

“…Studies of anionic species in mixed HF/HNO 3 solutions, performed on an anion-exchange resin, yielded a surprise [54]: while from 10 −3 to 10 −1 M HF K d values for Zr and Hf increase from ≈10 to above 100 no significant rise was seen for Rf. However, follow-up experiments showed for Hf a significant and for Rf an even more pronounced dependence of the adsorption probability on NO 3 − and HF 2 − counter-ion concentrations [9,47,53].…”

Chemistry of superheavy elements

“…Experimental results about the Rf behavior in comparison with its lighter homologs and pseudo-homologs were obtained (i) from extracting neutral species into tributylphosphate (TBP) and trioctylphosphine oxide (TOPO) with HCl solutions [160][161][162][163][164][165], (ii) from extractions of anionic complexes with triisooctyl amine (TiOA) with HF and HCl solutions [166,167], (iii) from ion-exchange studies of predominantly cationic species with HF and HNO 3 solutions [168][169][170][171], (iv) from ion-exchange studies of predominantly anionic species with HF, HCl, and HNO 3 solutions [135,138,168,172,173], from ion-exchange studies of anionic and cationic species with H 2 SO 4 and mixed H 2 SO 4 /HCLO 4 solutions [174], and (v) from adsorption experiments on cobalt ferrocyanide [175]. After very briefly summarizing more recent results from experiments with HCl, HNO 3 , and H 2 SO 4 solution, experimental data obtained over a wide range of HF concentrations, and their interpretation, will be discussed.…”

“…This reflects the above mentioned decreasing trend Zr ≥ Hf > Rf in the formation of positively charged complexes. To investigate the successive F − complex formation of cationic species, the behavior of Zr, Hf, Th, and Rf in mixed 0.1 M HNO 3 /HF solutions was studied in cation-exchange chromatography experiments with ARCA [168]. For Zr and Hf, K d -values drop from 10 −4 M to 10 −2 M HF.…”