Zirconium and hafnium separation in different inorganic and natural compounds
Loading...
Date
2018-09
Authors
Kankwanzi-Tuipende, Roy
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
Zirconium (Zr) and hafnium (Hf) co-exist in the mineral zircon ore and its treated
modified form, namely Plasma-Dissociated Zircon (PDZ), which always contain a
small amount of Hf ranging between 1-3 %. The physical and chemical properties of
Zr and Hf are almost identical and their separation is notoriously difficult, tedious and
involves expensive processes. The purpose of this study was to initially investigate
the possible separation of (Zr/Hf)O2 in inorganic salts and PDZ ((Zr/Hf)O2.SiO2) and
apply these optimum separation conditions to separate Zr and Hf from PDZ.
The dissolution of the inorganic salts were done using the flux fusion technique
during which a mixture of 90.9 % ZrO2 and 9.09 % HfO2 (try to replicate the natural
abundance in minerals) were fused with NH4F.HF as flux. The successful dissolution
of the metal oxides was confirmed by total and accurate recovery of 100.6(2) % for
ZrO2 while unexpectedly high HfO2 recovery was (121.2(9) %) was obtained.
Possible solution matrix effects such as high F- concentration, were suspected as
reasons for the high Hf recovery. H2SO4 was added to flux mixture and excess
fluoride was removed by the evaporation of HF. This variation led to excellent Hf
recoveries and quantitative results indicated the recovery of 100.1(2) % for Zr and
100(2) % for Hf. This method was subsequently used for the dissolution of PDZ and
the analytical results indicated the presence of 66.0(4) % for Zr and 1.43(1) % for Hf.
These fluoride solutions were subsequently investigated for the possible separation
of Zr and Hf using, ion exchange, solvent extraction and microwave assisted
dissolution.
The separation of Zr and Hf in the fluoride matrix was investigated with an ion
exchange process. Three different anion resins, namely Dowex Marathon wba,
Dowex 21k and Amberlite IRA-900 were investigated for elemental separation. The
strong anion exchanger resin, Amberlite IRA-900 was selected and different
experimental parameters such as flow rate, eluent and eluent concentrations were
investigated. Quantitative results indicated the preferential elution of Zr over Hf. At
0.05 M HCl only Zr was eluted while Hf was completely retained in the column and
the recovery of Zr was 86.44 % from the inorganic Zr/Hf mixture. The optimum
conditions, Amberlite IRA-900 resin, 0.05 M HCl and 20 cm column length, which are
developed for the inorganic Zr/Hf mixture, were applied on the PDZ material and the
recovery of Zr was 24(6) %.
The isolated of ZrO2 from this reaction mixture, was re-dissolved using NH4F.HF as
flux. The concentration of Zr was quantitatively determined using ICP-OES. The
obtained average metal recoveries were 77.8(7) and 0.11(0) % for Zr and Hf
respectively which are extremely promising, pointing to the separation of the two
elements and the removal of the Hf from the Zr. The drawback to this method is, the
low Zr recovery (compared to the amounts initially used in the separation process).
Solvent extraction was the next technique to be investigated for separation of Zr and
Hf as an alternative to ion exchange due to low Zr recoveries obtained in ion
exchange separation method. The results obtained using MIBK as an extractant from
H2SO4 solutions indicated a slight preferential extraction of Zr into the organic layer,
leaving Hf in the aqueous layer with recoveries of 65(1) % Zr and 4(1) % Hf.
Microwave assisted digestion in H2SO4 of both (Zr/Hf)O2 and PDZ were inconclusive.
Validation of the analytical results using ICP-OES was also performed. Most of the
results obtained for the Zr and Hf quantification in the inorganic salt ((Zr/Hf)O2), were
accepted at the 95% confidence interval. However, other results indicated poor
precision and accuracy of Hf hence the null hypothesis was rejected.
Description
Keywords
Zirconium, Hafnium, Plasma-dissociated zircon, Quantitative analysis, Dissolution, Separation, Isolation, Dissertation (M.Sc. (Chemistry))--University of the Free State, 2018