SOLVENT EXTRACTION OF ZIRCONIUM AND HAFNIUM

Solvent extraction separation of zirconium and hafnium from nitric acid solutions using mixture of Cyanex-272 and TBP

A solvent extraction method has been employed to extract and separate zirconium and hafnium from the nitric acid medium using Cyanex-272 and its mixture with TBP in kerosene. The effects of the experimental parameters such as contact time between phases, aging time, nitric acid concentration, Cyanex-272 and TBP concentration on the metals separation, and various stripping agents on the metals back extraction from the loaded organic phase have been investigated. The maximum separation factor of 16 was obtained in the single extraction system with 1% (v/v) Cyanex-272 from 2.5 M HNO3 solution. The combination of Cyanex-272 with TBP exhibited a significant synergistic effect for Zr extraction and the antagonistic effect for Hf extraction. The proposed novel synergistic mixture consisting of 0.5% (v/v) Cyanex-272 and 20% (v/v) TBP in kerosene offered the maximum separation factor of 99.7 from 2.5 M HNO3 solution. By applying a slope method, the extracted zirconium species were proposed to be ZrO(NO3)2·2Cyanex272·2TBP in the organic phase. Among the investigated stripping agents, 4 M H2SO4 solution showed the best efficiency for the stripping of zirconium and hafnium from the loaded mixture of Cyanex-272 and TBP with separation factor of 10.1.

Liquid-liquid extraction of Hf(IV) from nitric acid with dibutylsulfoxide in cyclohexane

A liquid-liquid extraction method has been investigated for quantitative extraction of hafnium from 8 M HNO3using 50% di-n-butyl sulfoxide (DBSO) dissolved in cyclohexane. The extraction parameters such as nitric acid, DBSO and metal ion concentrations, equilibration time and temperature were optimized. The extraction was found to be independent of metal ion concentration in the range 4.5 × 10−4−4.5 × 10−2M and inversely dependent upon the temperature. Phosphate, fluoride and oxalate interfere seriously and have almost masked the extraction of Hf(IV) whereas, thiocyanate and bromide have greatly decreased (25–34%) the extraction. The stoichiometric composition of the extracted species was found to be Hf(NO3)4·2DBSO. Hafnium can be stripped from the organic phase by using 1 M HClO4. The proposed method allows the mutual separation of Hf(IV) and Zr(IV) using H2O2as masking agent for zirconium. The method has also been applied on synthetic mixtures of Hf and Zr for their separation and, the recovery was found to be quantitative.