|Zirconium ores are concentrated by gravitational methods with magnet and electric separation refining. The metal is obtained from its compounds, the concentrate is first decomposed. For this purpose two methods are used:|
1. Chlorine treatment with coal at 900-1000°C. The main product, ZrCl4, is then sublimated and captured.
2. Fusing with caustic soda at 500-600°C or with soda (sodium carbonate) at 1100°C:
ZrSiO4 + 2Na2CO3 = Na2ZrO3 + Na2SiO3 + 2CO2;
3. Sintering with lime or calcium carbonate (adding CaCl2) at 1100-1200°C:
ZrSiO4 + 3CaO = CaZrO3 + Ca2SiO4;
4. Fusing with potassium fluosilicate at 900°C:
ZrSiO4 + K2SiF6 = K2ZrF6 + 2SiO2.
For cases (2, 3) all silica compounds are leached by water, the residue is decomposed by hydrochloric or sulphuric acid. The sintered fluorozirconate (4) is treated by acidified water, during which potassium fluorozirconate is dissolved; after cooling 75-90% is settled out.
Methods of Zirconium compounds separation from acidified solutions are as follows:
1. Zirconium oxychloride ZrOCl2×8H2O crystallization during hydrochloric solutions evaporation;
2. Hydrolytic sedimentation of the basic Zirconium sulphates XZrO2×YSO3×ZH2O from hydrochloric or sulphuric solutions;
3. Zirconium sulphate crystallization Zr(SO4)2 adding concentrated sulphuric acid or by sulphuric solutions evaporation. After sulphates or chlorides roasting ZrO2 appears.
Zr sponge or powder is produced by ZrCl4, K2ZrF6 or ZrO2 metallothermic reduction. Chloride is reduced by magnesium or sodium, potassium fluorozirconate is reduced by sodium and Zirconium dioxide - by calcium or its hydride. Electrolytic pulverous Zirconium is obtained by smelting the mixture of zirconium halogenides and alkali metals chlorides. Compact ductile Zirconium is manufactured from pressed sponge smelting in vacuum arc furnaces as a consumable electrode. The ingots or iodide refining bars electron-beam melting is a method of high-purity Zirconium production.
|Zirconia, derived from zircon, is the starting-point for the preparation of metallic zirconium and its compounds. The metal was first obtained by Berzelius, in 1824, by heating together potassium zirconifluoride and potassium. The reaction is analogous to that by which he had obtained silicon in the previous year, viz. |
K2ZrF6 + 4K = Zr + 6KF.
Later, the metal was prepared by Troost by passing zirconium tetrachloride vapour over heated sodium or magnesium. Weiss and Neumann obtained the powdered metal by mixing potassium zirconi-fluoride with purified sodium, covering the mixture with potassium chloride, compressing it into an iron vessel, and starting the reaction by means of a flame. The product was washed with alcohol and hydrochloric acid. By substituting aluminium for sodium a better product, containing 99.8 per cent, of the metal, was obtained. Lely and Hamburger have prepared the metal by reducing the anhydrous chloride with sodium in a vacuum.
An alternative method of preparing zirconium is to reduce its oxide by another metal or by carbon. Thus Phipson heated the dioxide with magnesium powder and obtained zirconium as a black, velvety powder; Winkler, however, on passing hydrogen over a heated mixture of zirconia and magnesium, obtained the solid hydride ZrH2, mixed with unchanged zirconia. Wedekind, on the other hand, obtained colloidal zirconium, which formed a dark blue suspension in water, together with the nitride Zr2N3, by the reaction between zirconia and magnesium in presence of air.
Moissan prepared zirconium by heating the oxide with excess of carbon in an electric furnace and fusing the resulting carbide with excess of zirconia. The temperature of reduction of zirconia by carbon is about 1400° C.
Lastly, Wedekind has obtained a metallic powder containing 99 per cent, of zirconium by reducing the dioxide with calcium in an evacuated iron vessel. The powder produced was washed successively with water, acetic acid, dilute hydrochloric acid and acetone in absence of air, dried in vacuo at 250°-300° C., and then heated to 800°-1000° C. The metal has been investigated analytically by Wedekind and Lewis.