Zirconium and hafnium separation in different inorganic and natural compounds

[摘要] Zirconium (Zr) and hafnium (Hf) co-exist in the mineral zircon ore and its treatedmodified form, namely Plasma-Dissociated Zircon (PDZ), which always contain asmall amount of Hf ranging between 1-3 %. The physical and chemical properties ofZr and Hf are almost identical and their separation is notoriously difficult, tedious andinvolves expensive processes. The purpose of this study was to initially investigatethe possible separation of (Zr/Hf)O2 in inorganic salts and PDZ ((Zr/Hf)O2.SiO2) andapply these optimum separation conditions to separate Zr and Hf from PDZ.The dissolution of the inorganic salts were done using the flux fusion techniqueduring which a mixture of 90.9 % ZrO2 and 9.09 % HfO2 (try to replicate the naturalabundance in minerals) were fused with NH4F.HF as flux. The successful dissolutionof the metal oxides was confirmed by total and accurate recovery of 100.6(2) % forZrO2 while unexpectedly high HfO2 recovery was (121.2(9) %) was obtained.Possible solution matrix effects such as high F- concentration, were suspected asreasons for the high Hf recovery. H2SO4 was added to flux mixture and excessfluoride was removed by the evaporation of HF. This variation led to excellent Hfrecoveries and quantitative results indicated the recovery of 100.1(2) % for Zr and100(2) % for Hf. This method was subsequently used for the dissolution of PDZ andthe 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 separationof Zr and Hf using, ion exchange, solvent extraction and microwave assisteddissolution.The separation of Zr and Hf in the fluoride matrix was investigated with an ionexchange process. Three different anion resins, namely Dowex Marathon wba,Dowex 21k and Amberlite IRA-900 were investigated for elemental separation. Thestrong anion exchanger resin, Amberlite IRA-900 was selected and differentexperimental parameters such as flow rate, eluent and eluent concentrations wereinvestigated. Quantitative results indicated the preferential elution of Zr over Hf. At0.05 M HCl only Zr was eluted while Hf was completely retained in the column andthe recovery of Zr was 86.44 % from the inorganic Zr/Hf mixture. The optimumconditions, Amberlite IRA-900 resin, 0.05 M HCl and 20 cm column length, which aredeveloped for the inorganic Zr/Hf mixture, were applied on the PDZ material and therecovery of Zr was 24(6) %.The isolated of ZrO2 from this reaction mixture, was re-dissolved using NH4F.HF asflux. The concentration of Zr was quantitatively determined using ICP-OES. Theobtained average metal recoveries were 77.8(7) and 0.11(0) % for Zr and Hfrespectively which are extremely promising, pointing to the separation of the twoelements and the removal of the Hf from the Zr. The drawback to this method is, thelow 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 andHf as an alternative to ion exchange due to low Zr recoveries obtained in ionexchange separation method. The results obtained using MIBK as an extractant fromH2SO4 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 theresults obtained for the Zr and Hf quantification in the inorganic salt ((Zr/Hf)O2), wereaccepted at the 95% confidence interval. However, other results indicated poorprecision and accuracy of Hf hence the null hypothesis was rejected.

[发布机构] University of the Free State