Uranyl Hydrogen Orthophosphate 4-Hydrate

The preparation of uranyl hydrogen orthophosphate 4-hydrate has been described,1 2 but a detailed procedure giving a pure product has not been recorded. The directions given here represent a modification of those mentioned in the earlier reports.3 

Two hundred fifty milliliters of 1.1 M orthophosphoric acid is added with vigorous stirring to 250 ml. of 1 M uranyl nitrate or perchlorate solution. The solution is seeded with a few crystals of the product to promote immediate precipitation. The suspension is then stirred for 12 hours and the mother liquor removed by centrifuging or filtering. The precipitate is slurried in 250 ml. of ca. 0.01 M perchloric acid for 12 hours, and the suspension is filtered. The solid is then slurried twice in 125-ml. portions of acetone to remove solution and sorbed perchlorate and separated from each wash solution by filtration. The sample is dried in a vacuum desiccator, using continuous 

Uranium. A sample containing ca. 2 millimols of uranium is fumed down with sulfuric acid in a 150-ml. beaker to remove nitrate. Then 20 ml. of 18 M sulfuric acid and 20 ml. of 85% phosphoric acid are added, and the solution is diluted with water to 75 to 80 ml. and cooled. This solution is passed over amalgamated zinc in a reductor at a rate of 30 ml./min. The reductor is washed successively with one 20-ml. portion of 3 Af sulfuric acid, three 40-ml. portions of 7.5% sulfuric acid, and one 40-ml. portion of water, the washings being added to the reduced solution. The resulting light bluish-green uranium (IV) solution is treated with 30 ml. of iron(III) chloride solution (100 g. of the 6-hydrate per liter) and allowed to stand for 5 to 10 min. or until it becomes distinctly yellow. Fifteen milliliters of 85% phosphoric acid and 8 drops of diphenyl-aminesulfonic acid indicator are added, and the solution is titrated immediately with 0.1 N potassium dichromate to a sharp purple end point. 

Phosphate. Because of interference by uranium in the usual magnesium ammonium orthophosphate procedure,5 uranium is first removed by a cation-exchange procedure. A column (2.5 by 36 cm.) of 50 to 75 cc. of Dowex-50 resin is washed with 200 ml. of Z N hydrochloric acid and then 200 ml. of water at flow rates of 2 to 3 ml./min. An acidic solution of the product, containing 100 to 150 mg. of orthophosphate, is passed through the column at a rate of 1 ml./min. The column is washed with water until the washings are neutral to litmus, and phosphate is determined in the combined eluate and washings by the usual gravimetric procedure.6 Uranium can be eluted from the 

Uranyl hydrogen orthophosphate 4-hydrate is a bright yellow compound, the crystals of which appear as tabular four-sided plates or truncated squares6 and belong to the tetragonal system.7 The calculated density is 3.417 and the observed density 3.399.6 The compound dissolves readily in dilute acids. At 110° it is converted to the 2-hydrate. 

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Uranium, determination of, in uranyl hydrogen orthophosphate 4-hydrate, 5 151... 

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