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Study on the Factors Affecting the Extraction and Separation of Zirconium and Hafnium by MIBK-HSCN-System
Zirconium and hafnium have opposite nuclear properties, but their chemical properties are very similar. The content of antimony in natural zirconium is generally 2% to 3%. For atomic energy grade sponge zirconium in nuclear power, the zirconium content in zirconium is less than 0.01%, so zirconium used in nuclear power plants must be separated by zirconium and hafnium.
Zr, Hf wet separation method used industrially mainly MIBK Extraction separation, N235 (trialkyl (mixed) tertiary) extraction separation and TBP (tributyl phosphate) Extraction method and the like. The advantage of MIBK extraction separation method is high extraction efficiency, and the disadvantage is serious environmental pollution. It is suitable for establishing a production line with an annual output of more than 1000t. The advantage of N235 extraction separation method is that the environmental pollution is small, and the disadvantage is that the extraction efficiency is low, and it is suitable for establishing an annual output of 500t. The following production lines; the advantages of the TBP extraction separation method are high extraction efficiency, the disadvantage is that the equipment is seriously corroded, there is emulsification in continuous production, and there is no scale production.
As a MIBK extraction agent obtained in the separation and purification of rare metals in a wide range of use, application MIBK extraction agent in the separation of zirconium, hafnium, there are many foreign patents and a small amount of research reports, few domestic research reports. Lin Zhenhan reviewed the basic principle, separation process conditions and extraction equipment for MIBK extraction and separation of zirconium and hafnium. Was added to the concentration of H + and SO 4 2 herein - Extraction hafnium zirconium ion impact on MIBK-HCNS system was studied, and the extraction and separation of zirconium, hafnium and superior aqueous phase acidity SO 4 2 - ion concentration.
 First, the experiment
(1) Reagents and instruments
MIBK (industrial grade) is supplied by Tianjin Jiashun Chemical Co., Ltd.; zirconium oxychloride (industrial grade) is produced by Sublimation Baker Group, the composition is shown in Table 1; other chemical reagents are of analytical grade.
Table 1 Main components of zirconium oxychloride
Component
ZrO 2 +HfO 2
HfO 2 /(ZrO 2 +HfO 2 )
Fe 2 O 3
SiO 2
TiO 2
Na 2 O
Ω/(%,mass fraction)
36.22
2 to 3
0.0007
0.0023
0.0005
0.001
DH-101 electric heating constant temperature air drying box, Tianjin Zhonghuan Experimental Electric Furnace Co., Ltd.; RJX-8-13 position electric furnace, Beijing Electric Furnace Factory.
(two) method
A quantitative volume of the organic phase and the aqueous phase were placed in a beaker and stirred for 10 min, and allowed to stand for stratification. The total metal concentration of zirconium and hafnium in the raffinate aqueous phase, the concentration of niobium and the acidity were analyzed. The total metal concentration of zirconium and hafnium and the concentration of niobium were calculated by subtraction method, and the distribution ratio and separation coefficient were calculated in turn. The raffinate aqueous phase, the organic opposite raffinate may be precipitated and calcined to obtain zirconia (yttrium), and the zirconium and hafnium concentrations may be analyzed.
(3) Analytical methods
The concentration and acidity of metal ions in the solution were analyzed by EDTA and NaOH standard solution titration; the content of cerium in zirconium was determined by ICP-AES (MS) method.
   Second, the results and discussion
(1) Effect of H + concentration in MIBK-HSCN system on extraction and separation of zirconium and hafnium
First, with different concentrations of HSCN 8mol·L - 1 MIBK extraction test for the saturated MIBK HSCN, wherein the concentration of MIBK in HSCN c HSCN (0), respectively 1.18,2.09,3.51,4.95,5.70 and 6.48 mol·L - 1, then MIBK zirconium saturated feed solution after extraction test carried out, wherein the feed solution, Zr, Hf a total concentration of 1.31 mol·L - 1, the mass percentage of 2% hafnium, an acidity of 15 mol·L - 1 ammonium thiocyanate at a concentration of 3.00 mol·L - 1. The distribution of HSCN in the two phases is shown in Figure 1. The concentration, partition coefficient and separation coefficient of zirconium in the organic phase vary with the acidity of the aqueous phase as shown in Figures 1-3.
Fig.1 Effect of c H + ( a ) on c HSCN ( 0 ) , c Zr + Hf ( 0 )
Figure 2 Effect of c H + ( a ) on D Zr , D Hf , D HSCN
Fig. 3 Effect of c H + ( a ) on the separation coefficient β of zirconium and hafnium
As shown in Fig. 1, when there is no zirconium in the aqueous phase solution, HSCN is linear in the equilibrium organic phase c HSCN ( 0 ) and the equilibrium aqueous phase c H + ( a ) ; when there is zirconium lanthanum, HSCN in the distribution of the two phases changes, with c H + (a) an increase in c H + (a) <1.5mol·L - 1 when, c HSCN (0) (Zr + Hf) remains substantially unchanged ; in c H + (a) ≥1.5 mol·L - 1 when, c HSCN (0) (Zr + Hf) rapidly increasing; in c H + (a)> 2.5 mol·L - 1 when, c HSCN (0 ) is basically consistent with the value of c HSCN ( 0 ) ( Zr + Hf ) . The results showed: The reaction MIBK Extraction HSCN, Zr, Hf and MIBK present in the extraction process, c H + (a) <1.5 mol·L - 1 , the reaction was extracted with zirconium to hafnium-based; c H + (a .) in 1.5 ~ 2 5 mol·L - 1 range, Zr, Hf has both extraction extracted HSCN react; on c H + (a)> 2.5 mol·L - 1 , the reaction mainly to extract HSCN. The distribution coefficient of the thiocyanate D HSCN in Fig. 2, the partition coefficient of the enthalpy of D Hf , and the variation of the partition coefficient D Zr of zirconium also illustrate the above reaction process. Thus, the c H + (a) <1.5 mol·L - at a low acid circumstances, facilitate the extraction of zirconium and hafnium; in c H + (a)> 2.5 mol·L - 1 under high acid conditions, more Conducive to the anti-extraction of zirconium.
As can be seen from FIGS. 1 to 3, as c H + ( a ) increases, c ( Zr + Hf )( 0 ) , D Hf , D Zr decreases, and the separation coefficient increases. When H H + ( a ) ≤ 2 mol · L - 1 , D Hf ≥ 1; when c H + ( a ) > 2 mol · L - 1 , D Hf < 1, and within this acidity range, due to The decomposition of HSCN causes precipitation of the solution. When c H + (a) <1.5 mol·L - 1 , the test is not precipitated during the phenomenon.
The above-described c H + (a) test results and discussion, Zr, Hf separated and extracted can be concluded that in order to efficiently extracted achieve separation of hafnium and zirconium, hafnium, acidity of the aqueous phase must be selected c H + (a) <1.5 mol·L - 1, this time D Hf> 1, the separation factor of 3-4, optimal c H + (a) should be 1 ~ 1.5 mol·L - 1.
(II) Effect of addition of (NH 4 ) 2 SO 4 on the extraction and separation of zirconium and hafnium
Is added to the zirconium in the feed solution (NH 4) 2 SO 4, the feed liquid C (NH4) 2SO4 (a) of 0.1,0.5,1.2 and 3 mol·L - 1, respectively extraction test. The result is shown in Figure 4.
Fig. 4 Effect of C ( NH4 ) 2SO4 ( a ) on the separation of zirconium and hafnium
It can be seen from Fig. 4 that (NH 4 ) 2 SO 4 is added to the feed liquid, and as the C ( NH4 ) 2SO4 ( a ) increases, the D Hf and the separation number increase rapidly, and the C ( NH4 ) 2SO4 ( a ) increases to 1 mol·L - 1 when, D Hf significantly increased to 2.5, D Zr decreased slightly to 0.2; in C (NH4) 2SO4 (a) ≥1 mol·L - 1 when, D Hf remained at 2.5, D Zr is maintained at 0.2; the separation factor is increased from 2 to 14. It is indicated that the addition of (NH 4 ) 2 SO 4 is beneficial to the extraction of cerium into the organic phase and significantly improves the separation ability of zirconium and hafnium. The authors concluded that there SCN - aqueous phase was added SO 4 2 - after, of ZrO 2 + and SO 4 2 - + 2 generated complex than SO 4 2 and HfO - generating a stable complex, and at the same time of HfO 2 + The SCN - generated complex is more stable than the complex formed by ZrO 2 + and SCN - , so that the ability of MIBK to extract HfO(SCN) 2 is enhanced, and the ability to extract ZrO(SCN) 2 is weakened. Found experimentally, the C (NH4) 2SO4 (a) > 1.0 mol·L - 1, aqueous solutions a white precipitate appeared, mainly produce basic zirconium sulfate precipitation, and therefore choose to add (NH 4) 2 SO 4 in best C (NH4) 2SO4 (a) is 0.8 ~ 1 mol·L - 1.
   Third, the conclusion
(1) The increase of the acidity of the equilibrium water phase reduces D Hf , D Zr and increases the separation factor. MIBK extracts zirconium lanthanum at low acid and HSCN extracts at high acid. Considering the factors such as the decomposition of D Hf and HSCN, the optimum extraction and separation of zirconium lanthanum aqueous phase acidity is 1 ~ 1.5 mol · L - 1 , D Hf > 1, the separation coefficient is 3 ~ 4, and the solution does not precipitate .
(2) Adding (NH 4 ) 2 SO 4 to the feed liquid significantly increases the separation factor of D Hf and zirconium. The best extraction separation of zirconium lanthanum. C (NH4) 2SO4 (a) is 0.8 ~ 1 mol·L - 1, the concentration in the selection of (NH 4) 2 SO 4 for 1 mol·L - 1 when D Hf is 2.5 at this time, the separation factor of 10 to 14, and the solution does not precipitate with basic zirconium sulfate.