RU2538890C1 - Method of separating zirconium and hafnium tetrachlorides by extractive rectification - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of separating zirconium and hafnium tetrachlorides by extractive rectification includes blending carrier-extractant with mixture ZrCl₄+HfCl₄, fusion of charge with obtaining homogenous melt, evaporation of zirconium and hafnium tetrachlorides from melt, condensation of hafnium-enriched steam in form of sublimate. As carrier-extractant applied is LiCl-AlCl₃, and evaporation of zirconium and hafnium tetrachlorides from melt is realised at temperature 320°C or 450°C.

EFFECT: increase of comparative volatility of zirconium and hafnium chlorides in separation of zirconium and hafnium tetrachlorides from mixture of their chlorides by extractive rectification.

2 tbl, 3 ex

Description

The invention relates to chemical technology for the production of high-purity compounds of zirconium and hafnium, and in particular to methods for the separation of zirconium and hafnium from a mixture of their tetrachlorides by extractive distillation. The invention can be used in the production of nuclear zirconium and hafnium for the needs of nuclear energy.

Separation of zirconium and hafnium tetrachlorides from a mixture of their tetrachlorides is carried out by extractive distillation at almost normal (atmospheric) pressure. In this case, the separation of chlorides occurs against the background of a low-melting and low-volatile carrier extractant. When choosing carrier extractants, preference is given to that which is characterized by a low melting point, low corrosivity, the highest relative volatility of hafnium and zirconium chlorides over it, the greatest homogeneity of the melt in a wide range of concentrations of Zr (Hf) Cl ₄ dissolved in it. The separation of chlorides is estimated by the relative volatility coefficient of hafnium and zirconium tetrachlorides (separation coefficient) upon their single evaporation from a Zr (Hf) Cl ₄ carrier extractant melt.

A known method of separation of zirconium and hafnium chlorides in a melt of alkali metal chloroferrates [French patent No. 2250707, 1975]. A significant drawback of these extractant carriers is their extremely high corrosion activity and the inability to choose structural materials that are sufficiently stable in this environment.

A known method for the separation of zirconium and hafnium chlorides in a melt K ₂ ZrCl ₆ -Na ₂ ZrCl ₆ with a molar ratio of Na: K = 8: 29 [Kim JD, Spink DR "J. Chem. Eng. Data", 1975, v.19, No 1, p. 36-42.]. The separation coefficient of zirconium and hafnium chlorides is quite high and amounts to 1.7. The disadvantage of this extractant carrier is a narrow region of homogeneity of the melt K (Na) ZrCl ₆ -Zr (Hf) Cl ₄ . The melt is homogeneous with a Zr (Hf) Cl ₄ content of 60-70%. It is difficult to maintain such an exact concentration of zirconium (hafnium) tetrachlorides in the melt, its deviations are possible, leading to the formation of precipitation and worsening of the chloride separation process.

The most popular among carrier extractants for the distillation separation of zirconium and hafnium tetrachlorides is complex potassium chloraluminate. In practice, it is usually not a pure compound that is used, but its eutectic mixture with KCl (molar ratio of components AlCl ₃ : KCl = 1: 1.04), located quite close to the compound itself.

Known work [RP Tangri, DK Bose, S.K. Gupta Vapor Pressure of ZrCl ₄ and HfCl ₄ over Melt Systems KCl-AlCl ₃ (1: 1.04 mol) + ZrCl ₄ and KCl + Al ₃ (1: 1.04 mol) + HfCl ₄ / J. Chem. Eng. Data, 1995, No. 40, pp. 23-827], in which KCl-AlCl ₃ melt (1: 1.04 mol) is used as the carrier extractant. In this work, the vapor pressure of hafnium tetrachloride over a melt of HfCl ₄ -Cl-AlCl ₃ and the vapor of zirconium tetrachloride over a melt of ZrCl ₄ -Cl-AlCl _{3 was} studied. It was shown that the vapor pressure of HfCl ₄ is 1.5 times higher than the vapor of ZrCl ₄ in the molar concentration range of zirconium tetrachloride and hafnium tetrachloride (16.5-30 wt.%) In the melt, in the temperature range 212-354 ° С. However, the separation of zirconium and hafnium tetrachlorides from a mixture of their chlorides was not studied in this work.

In the work chosen for the prototype [LA Niselson, AA Egorov, EL Chuvilina, OA Arzhatkina / Solid-Liquid and Liquid-Vapor Equilibria in the Zr (Hf) Cl ₄ -KAlCl ₄ Systems: A Basis for the Extractive Distillation Separation of Zirconium and Hafnium Tetrachlorides /; J. Chem. Eng. Data, 2009, 54 (3), pp. 26-729], the separation of zirconium and hafnium tetrachlorides from a mixture of their chlorides over a KCl-AlCl ₃ melt (1: 1.04 mol) was studied. In this work, a eutectic mixture KCl-AlCl ₃ (1: 1.04 mol) with 36 wt. % mixture of ZrCl ₄ + 1.4% HfCl ₄ at ~ 450 ° C.

The relative volatility of the vapor of hafnium and zirconium tetrachloride was _{shown to} be α _{HfCl4 / ZrCl4} = 1.29 ± 0.04 over the KCl-AlCl ₃ melt (1: 1.04 mol). The disadvantage is the low relative volatility of zirconium and hafnium chlorides over the KCl-AlCl ₃ melt (1: 1.04 mol) during the separation of zirconium and hafnium tetrachlorides from a mixture of their chlorides.

The technical result of the claimed invention is to increase the relative volatility of zirconium and hafnium chlorides upon separation of zirconium and hafnium tetrachlorides from a mixture of their chlorides by extractive distillation.

The technical result is achieved by the fact that in the method for separating hafnium and zirconium chlorides by extractive distillation, which includes charging the extractant carrier with a mixture of ZrCl ₄ + HfCl ₄ , fusing the mixture to obtain a uniform melt, evaporating zirconium and hafnium tetrachlorides at a temperature of 320 ° C or 450 ° C and condensation of vapors enriched with hafnium in the form of a sublimate, LiCl-AlCl _{3 is} used as the carrier extractant.

The essence of the invention lies in the fact that found the influence of the type of extractant carrier on the relative volatility of zirconium and hafnium chlorides when they are separated by extractive distillation at 320 ° C or 450 ° C. The content of a mixture of zirconium and hafnium tetrachlorides in the Zr (Hf) Cl ₄ -LiCl-AlCl ₃ melt and the process temperature at which the relative volatility of hafnium and zirconium chlorides is 1.5 or more are experimentally determined.

The claimed invention is illustrated by examples.

Example 1 (prototype)

100-120 g of a mixture containing KCl-AlCl ₃ and a mixture of ZrCl ₄ + 1.4 mass were placed in a quartz ampoule. % HfCl ₄ taken in the amount of 36 wt. % of the weight of the obtained mixture. Next, the ampoule was sealed under vacuum and placed in a tube furnace. The mixture was fused to obtain a uniform melt.

Next, 5-6 g of the obtained melt was placed in a quartz ampoule, which was sealed under vacuum and placed vertically in a tube furnace. The melt was melted in an ampoule at 450 ° C. At this temperature, the vapor pressure of zirconium tetrachloride reaches atmospheric. In the lower part of the ampoule was a melt of Zr (Hf) Cl ₄ -CL-AlCl ₃ . In the upper part are saturated pairs of zirconium tetrachlorides (hafnium). Then the ampoule was moved up in the furnace so that the upper head of the ampoule was in the cold zone. The condensation time of the vapors of zirconium tetrachloride (hafnium) in the head of the ampoule was 20-30 minutes. After the end of the experiment, the head of the ampoule containing sublimate in the amount of 0.15-0.4 g was disconnected from the main part of the ampoule. The sublimate tetrachlorides and the melt from the lower part of the ampoule were subjected to chemical analysis for the content of hafnium and zirconium. For this purpose, weighed samples were dissolved in hydrochloric acid (1-2% Hcl), and the Hf / Zr ratio was determined in them. The analysis was performed by the method of atomic electron spectroscopy of inductively coupled plasma (AESIS) on a VISTA PRO instrument from VARION. The relative volatility of zirconium and hafnium chlorides calculated by the formula α = (Hf _subl / Zr _subl) / (Hf _melting / Zr _melting), where

Hf _subl - concentration of hafnium in sublimate (evaporated tetrachloride), mass. %;

Zr _subl - concentration of zirconium in sublimate (evaporated tetrachloride), mass. %;

Hf _rasp - concentration of hafnium in the melt, mass. %;

Zr _rasp - concentration of zirconium in the melt, mass. %

From the results of six independent determinations, the value α _{HfCl4 / ZrCl4} = 1.29 ± 0.04 was obtained.

Example 2

The experimental conditions are similar to those described in example 1, only LiCl-AlCl ₃ (1: 1 mol) was used as the carrier extractant. The results of the experiments are presented in table 1.

Table 1 The content of zirconium and hafnium in sublimate and melt and the calculated value of the coefficient of relative volatility of zirconium and hafnium tetrachlorides Experience Number The content of zirconium and hafnium in the final products, wt.% Relative volatility coefficient (α _{HfCl4 / ZrCl4} ) of zirconium and hafnium tetrachlorides sublimate melt Zr Hf Zr Hf one 37,141 0.815 12,600 0.182 1,52 2 37,807 0.843 12,563 0.182 1,54 3 36,998 0.807 12,569 0.183 1,50 four 37,096 0.816 12,555 0.183 1.51 5 37,190 0.852 12,224 0.182 1,54 6 37,005 0.799 12,570 0.181 1,50 α _{HfCl4 / ZrCl4} = 1.52 ± 0.02

From the results of six independent determinations, the value α _{HfCl4 / ZrCl4} = 1.52 ± 0.02, that is, more than in example 1, was obtained.

Example 3

The experimental conditions are similar to the conditions described in example 2, only evaporation from the melt of zirconium and hafnium tetrachlorides was carried out at a temperature of 320 ° C.

The results of the experiments are presented in table 2.

table 2 The content of zirconium and hafnium in sublimate and melt and the calculated value of the coefficient of relative volatility of zirconium and hafnium tetrachlorides Experience Number The content of zirconium and hafnium in the final products, wt.% Relative volatility coefficient (α _{HfCl4 / ZrCl4} ) of zirconium and hafnium tetrachlorides sublimate melt Zr Hf Zr Hf one 36,189 1,048 11,379 0.164 2.01 2 37,002 1,097 11,370 0.163 2.07 3 36,850 1.096 11,369 0.165 2.05 four 36,931 1,080 11.375 0.164 2.03 5 36,240 1,059 11.371 0.163 2.04 6 36,305 1.055 11,380 0.163 2.03 α _{HfCl4 / ZrCl4} = 2.04 ± 0.03

From the results of six independent determinations, the value α _{HfCl4 / ZrCl4} = 2.04 ± 0.03, that is, more than in Example 2, was obtained.

Claims (1)

1. The method of separation of zirconium and hafnium tetrachlorides by extractive distillation, including batching the extractant carrier with a mixture of ZrCl ₄ + HfCl ₄ , fusing the mixture to obtain a homogeneous melt, evaporation of zirconium and hafnium tetrachlorides from the melt, condensation of vapor enriched in hafnium, in the form of sublimate, in that LiCl-AlCl _{3 is} used as the carrier extractant, and the evaporation of zirconium and hafnium tetrachlorides from the melt is carried out at a temperature of 320 ° C or 450 ° C.