Certain of the Vitro concentrates have been found to contain from 1-2 per cent uranium that cannot be dissolved in nitric acid. The insoluble Uranium is not extracted by the TBP-hexane solvent and is therefore, lost from the process in the raffinate. It was noted that when certain Vitro concentrates are processed, the solvent changed color and the uranyl nitrate product from the extraction process became contaminated with iron. Research indicated that the form of iron in the concentrate could be, changed to eliminate the contamination of the uranyl nitrate and that the nitric -acid-insoluble -uranium content could be reduced to 0.1-0.2 per cent by reacting the concentrate with hydrogen or carbon monoxide at temperatures of 1240 to 1350°F.
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