Separação de zircônio e háfnio por extração cromatográfica em (TBP-Si02)/HCI e determinação espectrofotométrica com arsenazo III

摘要

A separation method for zirconium and hafnium by extraction chromatography into TBP/SiC>2-HCl and further spectrophotometry determination of these elements using Arsenazo III in HC1 medium was developed. The methodology studied allows the determination of zirconium and hafnium in purification process samples and pure oxides used in the nuclear industries, providing the possibility of a cheaper analysis. A molar ratio of 1:4 for the Zr/Az and Hf/Az complexes in 6M HC1 was determinated by the Job and Molar - Ratio Methods. The photometric error was determinated as a function of the absorbance for the both elements. The minimum error found for the zirconium was of 0,76% at an absorbance of 0,57 and that for hafnium was of 3,2% at an absorbance of 0 , 214. The molar absorptivities obtained in 6M HC1 and 10~4 M H 2 S 0 4 for the Zr/Az and Hf/Az complexes were of 1, 2 .10^1/mole . cm and 8 .10^1/mole . cm, respectively. The purification of the Arsenazo III was developed by chromatography into cellulose. The standardize of this solution was made by photometric titration with U 0 g 2 + at pH about 2,2. The spectrophotometry method, using purified Arsenazo III solution in high acidity medium is simplified avoiding double wavelength measurements and increasing sensitivity and precision. The reproductiveness was perceptibly increased when the hidrolysis of the standard solutions was controled by adding concentrated HgSO^ for eliminating fluoride after the dissolution of the calcinated oxides and primary standards by fusion with NH^HF2- In the stock standard solutions, containig lmg/ml of the zirconium or hafnium, the final concentrations of the H2SO4 and HC1 were 0,1M and 6M, respectively. The distribuition coefficients (D's) of zirconium and hafnium for the systems, tri-n-butilphosphate (TBP) and tri-n-octilphosphine oxide (T0P0) in HC1 were studied to verify the better separation factor O). The separation factors stood betweem 6-9 withoutudappreciable difference betweem the systems. For the 5% TOPO/ciclohexano, the D's for the zirconium to HC1 1, 2, 3, 4 and 5M were 86 } 4, 87 } 3, 230 } 20, 2800 } 600 and 22000 + 5000, respectively; while for the hafnium to HC1 1, 2, 3 and 4M were 12 } 1, 13 } 1, 64 } 1 and 1150 } 40, respectively. For the 10% TBP/ciclohexano, the D's for the zirconium to HC1 6, 7, 8 and 9M were 1,08 } 0,06, 54 } 7, 914 } 66 and 7500 } 740, respectively; while for the hafnium to HC1 6, 7, 8 and 9M were 0,12 } 0,01, 8,1 } 0,7, 170 } 17 and 1760 } 126, respectively. The choice of the extraction chromatography using the TBP/Si0￡- HC1 system was for the slow kinetic of back - extraction of the T0P0 system. The separation of the zirconium and hafnium was studied for the 33% TBP/Si02-HCl 7M in a glass column with a height of 21cm and 0,4cm diameter. The elution rate was held at 0,1ml/ min. The spectrophotometry determination of zirconium and hafnium in the eluate were made with Arsenazo III in 6,5M HC1 medium at e60nm.