Preparation of Potassium Fluorozirconate from Hydrochloric Acid Liquors
Abstract Generated abstract
This paper addresses the preparation of potassium fluorozirconate and fluorohafnate from hydrochloric acid liquors obtained after lime decomposition and leaching of zirconium concentrate, with attention to simplifying the conversion of zirconium and hafnium compounds into double fluoride salts. The authors propose direct treatment of hydrofluoric acid acidified zirconium oxychloride solutions with potassium fluoride, replacing a three step sequence involving oxychloride crystallization, hydroxide precipitation, and dissolution in hydrofluoric acid. Experimental preparation at room temperature followed by recrystallization produced potassium fluorozirconate with analytical composition close to calculated values and a yield of 85 to 90 percent of theoretical. The results indicate the practical feasibility of a one stage route, with possible yield improvement through recycling of mother liquor.
Full Text
OBTAINING POTASSIUM FLUOROZIRCONATE FROM HYDROCHLORIC-ACID LIQUORS
V. M. VITYUGIN, N. Ya. NEGODINA, I. P. ONUFRIENOK
(Presented by Prof. A. G. Stromberg, Doctor of Chemical Sciences)
For the use of zirconium as a structural material for nuclear reactors, its purification from hafnium is mandatory. Of the known methods for purifying zirconium from hafnium, the method of separating these metals by crystallization from solutions of double fluoride salts [1] has found the widest application in the Soviet Union. However, the fluorozirconate method has substantial disadvantages. Decomposition of zirconium concentrate is carried out with the aid of rather expensive reagents (potassium fluorosilicate and potassium chloride). Sintering of the charge during decomposition of zirconium concentrate is accompanied by such undesirable phenomena as excessive melting and the evolution of hydrogen fluoride. This makes it difficult to carry out the sintering process in continuous rotary furnaces and creates unsanitary working conditions.
At the same time, in the Soviet Union the lime method for decomposing zirconium concentrate is being successfully used [2]. In the lime method of decomposition, relatively inexpensive chalk and recycled calcium chloride are used as reagents. Sintering is readily carried out in continuous rotary furnaces. After hydrochloric-acid leaching of the zirconium-chalk sinter, solutions saturated with zirconium oxychloride are obtained.
Taking into account the relative low cost of decomposing zirconium concentrate by the lime method, it would be rational to obtain solutions of double fluoride salts of zirconium and hafnium from hydrochloric-acid liquors according to the following scheme [2].
From hydrochloric-acid liquors, zirconium and hafnium oxychlorides are crystallized, dissolved in water, and zirconium and hafnium hydroxides are precipitated with ammonia. The hydroxides are then dissolved in hydrofluoric acid and, finally, by adding potassium fluoride, potassium fluorozirconate and fluorohafniate are obtained:
\[ \mathrm{ZrOCl_2 + 2NH_4OH + H_2O = Zr(OH)_4 + 2NH_4Cl;} \]
\[ \mathrm{Zr(OH)_4 + 4HF = ZrF_4 + 4H_2O;} \]
\[ \mathrm{ZrF_4 + 2KF = K_2ZrF_6.} \]
Thus, for converting zirconium and hafnium oxychlorides into double fluoride salts, three reagents are required, and the process is carried out in three operations.
In the present work, a method is proposed for obtaining potassium fluorozirconate and fluorohafnate directly from hydrochloric-acid solutions acidified with hydrofluoric acid, by treating them with potassium fluoride. In this case the reactions proceed according to the equations:
\[ \mathrm{ZrOCl_2 + 2HF + 4KF = K_2ZrF_6 + 2KCl + H_2O,} \]
\[ \mathrm{HfOCl_2 + 2HF + 4KF = K_2HfF_6 + 2KCl + H_2O.} \]
For an experimental verification of this method, purified zirconium oxychloride, potassium fluoride of the “chda” grade, and 40% hydrofluoric acid were used as starting reagents.
Zirconium oxychloride and potassium fluoride were dissolved in distilled water at an S:L ratio of \(1:1.5\). To the zirconium oxychloride solution was added a 40% hydrofluoric-acid solution in an amount 1.5 times greater than the calculated amount, and then, with stirring, the potassium fluoride solution was added in small portions in an amount 6% greater than the theoretical amount. All operations were carried out at room temperature. The crystals obtained were washed once with water (by decantation) and, with heating to about \(90^\circ\), dissolved in distilled water. The solution was evaporated to \(1/2\) of its volume and cooled. The crystals were filtered off, dried in a drying cabinet at \(t = 105^\circ\), and analyzed.
The results of the analysis are given in Table 1.
Table 1
| Composition, % | Zr | K | F | Cl |
|---|---|---|---|---|
| Experimental data | 31.85 | 27.03 | 40.06 | 1.06 |
| Calculated data | 32.10 | 27.59 | 40.23 | — |
The yield of fluorozirconate in our experiments was 85–90% of the theoretical value, but if the mother liquor is recycled, the yield can be increased.
The experiments demonstrated the fundamental possibility of obtaining potassium fluorozirconate and fluorohafnate from an aqueous solution of zirconium oxychloride, in one stage, using potassium fluoride and hydrofluoric acid.
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