Chemical Properties of Zirconium
Compounds of Zirconium
|With the exception of the dihydride and sesquioxide, zirconium is quadrivalent in all its known compounds. In this respect it resembles thorium rather than titanium. The characteristic zirconifluorides connect zirconium with silicon, titanium, and tin; the existence of a stable nitrate shows the superior metallic properties of this metal.|
Zirconium and the Halogens
|In accordance with the almost unexceptional quadrivalency of zirconium, only the tetrahalides ZrF4, ZrCl4, ZrBr4, ZrI4 are known, together with some oxyhalides, double or complex halides, and addition compounds.|
Detection of Zirconium
|Sodium and potassium hydroxides, ammonia, and ammonium sulphide solutions precipitate zirconium hydroxide, which is insoluble in excess of alkali hydroxide and is thus distinguished from the hydroxides of aluminium and glucinum. Ammonium carbonate solution produces a flocculent precipitate of basic carbonate, which is soluble in excess of the reagent, but is reprecipitated on boiling. |
There are three reactions by which zirconium is distinguished from thorium.
Hydrogen peroxide precipitates zirconium peroxide from neutral or slightly acid solutions of zirconium salts; in presence of alkali there is no precipitation since the alkali per zirconates are soluble in water, and by this means iron can be separated from zirconium.
- Solution of oxalic acid or of an oxalate precipitates white zirconium oxalate, which is soluble in excess of either reagent. In the case of thorium it is the neutral oxalate alone, and not also free oxalic acid solution which dissolves the precipitated oxalate.
- Hydrofluoric acid precipitates thorium, but not zirconium; for zirconium fluoride, unlike thorium fluoride, forms a double or complex fluoride with a soluble fluoride added in excess.
- From a cold solution of a zirconium salt potassium sulphate gradually precipitates potassium zirconyl sulphate, but from a boiling solution a basic zirconium sulphate insoluble in dilute hydrochloric acid is precipitated. Thorium does not form such an insoluble basic sulphate.
Sodium thiosulphate precipitates zirconium hydroxide mixed with sulphur. Turmeric paper is coloured reddish brown when moistened with a hydrochloric acid solution of a zirconium salt and then dried.
Zirconia is-distinguished from other earths by its infusibility in the oxyhydrogen flame, in which it glows brightly.
Estimation of Zirconium
|Zirconium is invariably estimated by being converted into the dioxide ZrO2, which is ignited and weighed as such. Compounds of iron and titanium, however, frequently occur together with zirconium, and various methods have been devised to separate the latter metal from the two former metals. |
Separation of Zirconium and Iron Since zirconium is not precipitated by sodium hydroxide in presence of hydrogen peroxide, iron may be quantitatively separated as ferric hydroxide by adding to the mixed solution sodium peroxide dissolved in ice-water; the zirconium can then be estimated in the filtrate.
On the other hand, concentrated hydrogen peroxide precipitates zirconium peroxide from acid solution, and according to Bailey this reaction suffices to separate zirconium from iron and titanium.
Iron can also be quantitatively separated from zirconium and other metals by the use of nitroso-β-naphthol. According to Rivot iron may be estimated when obtained as ferric oxide mixed with unreducible oxides by determining the loss of weight which is caused by reduction in hydrogen; and Gutbier and Huller have applied this method to the estimation of iron and zirconium. According to Daniel and Leberle, however, the method gives variable results according to the proportion of iron present, and the question has been the subject of considerable controversy.
Titanium and zirconium can be separated from iron by passing hydrogen sulphide through a solution of the mixed sulphates to reduce the iron, displacing hydrogen sulphide by sulphur dioxide to prevent oxidation, and adding sodium acetate, ammonium sulphate, sulphurous acid or sodium thiosulphate, all of which precipitate titanium and zirconium, leaving iron in solution.
Separation of Zirconium and Titanium The following method of estimating zirconium and titanium, when they occur together - as, for example, in rocks - is recommended by Dittrich and Pohl. The precipitated oxides are fused with potassium hydrogen sulphate, and the solution of sulphates thus obtained is reduced with hydrogen sulphide. Tartaric acid is then added, followed by ammonia and ammonium sulphide; thus the iron alone is precipitated. The tartaric acid is removed from the filtrate, and the titanium and zirconium are then precipitated and weighed together. The mixture is subsequently dissolved in potassium persulphate solution, sulphuric acid and hydrogen peroxide are added, and the titanium is then estimated colorimetrically.
An alternative method for separating titanium and zirconium consists in adding a solution containing their nitrates, neutralised with sodium carbonate, to a boiling concentrated solution of ammonium salicylate. The zirconium is precipitated, and all the titanium is in the filtrate.