Uranium recovery sulfuric acid leach liquors

Recovery of uranium from leach liquors. Uranium may be recovered from leach liquors by precipitation, ion exchange, or solvent extraction. Precipitation with sodium hydroxide was the recovery method used in the first uranium mills. When used on sodium carbonate leach liquors, the uranium precipitate is fairly free of other metallic contaminants, because sodium carbonate dissolves few other metals beside uranium. However, when used in sulfuric acid leach liquors, the uranium precipitate contains other metals, such as iron dissolved from the ore by the add, and is no longer commercially acceptable. Consequently, in the United States, uranium mills emfdoying add leaching now follow it with selective recovery by either solvent extraction or ion exchange. These processes are described in Secs. 8.5 and 8.6, respectively. 

TABLE 5.3. Chemical bases for the Ames (amine) and Dapex (HDEHP) processes for uranium recovery from sulfuric acid leach liquors. (From Musicas and Schulz.)... 

The recovery of uranium from ores uses SX to reject impurities and concentrate the uranium in solution so that it can be economically recovered (Gupta and Singh 2003 Lloyd 1983). The choice of extractant depends on the lixiviant used in the upstream leaching operation, which, in turn, depends on the type of ore in which the uranium is found. Most nranium-bearing ores are readily leached in sulfuric acid and the uraninm is recovered by SX using amines or dialkylorganophosphorus acids. Phosphate ores (snch as those in Florida) are leached in a mixture of sulfuric and phosphoric acids or in phosphoric acid alone. Hot nitric acid has also been used as a lixiviant for nraninm ores (as at Phalaborwa, South Africa). The two common extraction systems for the recovery of uranium(VI) from sulfate leach liquors are compared in Table 5.6. 

Organophosphorus acids were among the first extractants to be used in the commercial recovery of uranium from solutions obtained by the leaching of low-grade ores with sulfuric acid. In the so-called Dapex process,70 114 the leach liquor is extracted with a solution of about 0.1 M D2EHPA in kerosene, and the pH value of the aqueous phase is adjusted to close to 1.0 in order to prevent the coextraction of vanadium impurities. Since iron(III) also extracts under these conditions, the leach liquor is reduced with metallic iron prior to extraction to convert any iron(III) present to the iron(II) state. 

Uranium ores are leached with dilute sulfuric acid or an alkaline carbonate [3812-32-6] solution. Hexavalent uranium forms anionic complexes, such as uranyl sulfate [56959-61-6], U02(S04)"23, which are more selectively adsorbed by strong base anion exchangers than are other anions in the leach liquors. Sulfate complexes are eluted with an acidified NaCl or ammonium nitrate [6484-52-2], NH4N03, solution. Carbonate complexes are eluted with a neutral brine solution. Uranium is precipitated from the eluent and shipped to other locations for enrichment. Columnar recovery systems were popular in South Africa and Canada. Continuous resin-in-pulp (RIP) systems gained popularity in the United States since they eliminated a difficult and costly ore particle/leach liquor separation step. 

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