PRECIPITATION AND HYDROLYSIS OF URANIUM(VI) IN AQUEOUS SYSTEMS. VIII. A STUDY OF THE PRECIPITATES FORMED IN THE SYSTEMS URANYL NITRATE--SODIUM CARBONATE--ALKALINE EARTH CHLORIDES.

Abstract Uranium bearing precipitates which formed in the precipitation systems uranyl nitrate (2 × 10 −3 N)-sodium carbonate-barium, strontium, calcium and/or magnesium chloride when alkaline earth chloride was in excess of sodium carbonate have been investigated by means of light and electron microscopy, chemical and TGA analyses, i.r. and X-ray spectroscopy. The precipitate composition was found to be dependent on the initial molar ratio of sodium carbonate and uranyl nitrate. 1. 1. At [ Na 2 CO 3 ] [ UO 2 ( NO 3 ) 2 ] = 1·5 (final pH 6–7) slightly soluble polynuclear complexes containing uranyl-carbonato- and hydroxyl groups as well as the respective Me II ions have been obtained. Me II : U: CO 2 molar ratios were 1:5 (6): 1·5 (2) for Me II = Sr, Ca and Mg and 2:5:1·5 for Me II Ba. 2. 2. Crystals of Ba 2 UO 2 (CO 3 ) 3 × 6 H 2 O were isolated from the system with barium at initial molar concentration ratios of sodium carbonate and uranyl nitrate between 3 and 30 (final pH ∼ 7). 3. 3. At relatively high initial molar ratios of sodium carbonate and uranyl nitrate (increasing in the order Sr, (Ba), Ca, Mg (3); final pH ∼ 7) uranium was co-precipitated with the respective alkaline earth carbonate as a carrier. Under the given conditions strontium carbonate coprecipitated up to 6 M%, calcium carbonate only about 0·6 mol% of uranium. The co-precipitation mechanism is discussed.