Uranium from sulfuric acid solution

AMEX [Amine extraction] A process for the solvent extraction of uranium from sulfuric acid solutions using an amine extractant ... 

Dapex [Di-alkylphosphoric acid extraction] A process for the solvent extraction of uranium from sulfuric acid solutions using di-(2-ethylhexyl) phosphoric acid (HDEHP). The HDEHP is dissolved in kerosene containing 4 percent of tributyl phosphate. The uranium is stripped from the organic phase by aqueous sodium carbonate and precipitated as uranyl peroxide (yellow cake). The process was no longer in use in 1988. See also Amex. 

Attempts to separate thorium and uranium from sulfuric acid solution of monazite by solvent extraction with TBP were unsuccessful because distribution coefficients of uranium and thorium from monazite solutions were too low, as these elements are complexed by phosphate ion. Development of extractants with higher distribution coefficients for these metals has made solvent extraction a practical process for recovering uranium and thorium from monazite sulfate solutions and from sulfuric acid solutions of other thorium ores. This section describes processes tested on a pilot-plant scale by Oak Ridge National Laboratory [C5]. 

A flow sheet similar to Fig. 4.3 could be used to extract uranium from sulfuric acid-leach solutions with organic amines, as illustrated in Fig. 5.9. 

There are also thorium recovery processes based on extraction from sulfuric acid solutions, e.g., with primary, secondary, or tertiary amines or alkyl phosphorous acids such as bis-2-ethylhexyl phosphoric acid (HDEHP) or dibutylbutyl phosphonate (DBBP). Thorium is then stripped into a nitric add solution. The alkyl phosphorous acid processes are often employed when recovering thorium as a by-product in uranium production. 

Sulfate ion is normally considered an interfering Ion in the extraction of uranium from aqueous solution by TBP. Veereswararao,i2it however, found that significant amounts of uranium may be extracted from sulfuric acid solution and that the extraction Is increased as the acid concentration is increased (figure 45). 

Electrochemical methods. Hie electrolysis of dilute sulfuric acid solutions with a mercury cathode results In the quantitative deposition of Cr, Fe, Co, Nl, Cu, Zn, Qa, Oe, Mo, Rh, Pd, Ag, Cd, In, Sn, Re, Ir, Pt, Au, Hg, and T1 In the cathode. i Arsenic, selenium, tellurium, osmium, and lead are quantitatively separated from the electrolyte, but are not quantitatively deposited In the cathode. Manganese, ruthenium, and antimony are Incompletely separated. Uranium and the remaining actinide elements, rare earth elements, the alkali and alkaline eeu th metals, aluminum, vanadium, zirconium, niobium, etc. remain In solution.Casto and Rodden and Warf— have reviewed the effects of many variables In the electrolytic separation of the above-named elements from uranium. According to Rodden and Warf optimum conditions for the purification of uranium In sulfuric acid solutions with a mercury cathode are electrolyte volume,... 

For vanadium solvent extraction, Hon powder can be added to reduce pentavalent vanadium to quadrivalent and trivalent Hon to divalent at a redox potential of —150 mV. The pH is adjusted to 2 by addition of NH, and an oxyvanadium cation is extracted in four countercurrent stages of mixer—settlers by a diesel oil solution of EHPA. Vanadium is stripped from the organic solvent with a 15 wt % sulfuric acid solution in four countercurrent stages. Addition of NH, steam, and sodium chlorate to the strip Hquor results in the precipitation of vanadium oxides, which are filtered, dried, fused, and flaked (22). Vanadium can also be extracted from oxidized uranium raffinate by solvent extraction with a tertiary amine, and ammonium metavanadate is produced from the soda-ash strip Hquor. Fused and flaked pentoxide is made from the ammonium metavanadate (23). 

Assay of beryUium metal and beryUium compounds is usuaUy accompHshed by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryUium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryUium content of the sample is calculated from the titration volume. Standards containing known beryUium concentrations must be analyzed along with the samples, as complexation of beryUium by fluoride is not quantitative. Titration rate and hold times ate critical therefore use of an automatic titrator is recommended. Other fluotide-complexing elements such as aluminum, sUicon, zirconium, hafnium, uranium, thorium, and rate earth elements must be absent, or must be corrected for if present in smaU amounts. Copper-beryUium and nickel—beryUium aUoys can be analyzed by titration if the beryUium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

In most uranium ores the element is present in several, usually many diverse minerals. Some of these dissolve in sulfuric acid solutions under mild conditions, while others may require more aggressive conditions. Thus, while it may be comfortable to recover 90-95% of the uranium present, it may be tough or impractical to win the balance amount of a few percent economically. Some of the most difficult uranium minerals to leach are those of the multiple oxide variety, most commonly brannerite and davidite. These usually have U(IV) as well as U(VI), together with a number of other elements such as titanium, iron, vanadium, thorium, and rare earths. To extract uranium from these sources is not as easy as other relatively simpler commonly occurring sources. 

In some scrub and strip circuits, the crud is mainly composed of silica, as well as inorganic sulfates. Also, if poor pH control is used in the uranium stripping circuits with ammonium sulfate, then uranium is a major constituent [33,46]. Such crud may be treated with dilute sulfuric acid, and recirculation through a pump results in the crud breaking down. There is evidence, in at least a few uranium circuits, that the presence of humic acids may be a possible cause of the crud problem [34,47]. Lignin appears to be another cause of crud formation [33,46]. Humic acids contained in the feed solution have also been implicated in the formation of waxy cruds in plants extracting uranium from phosphoric acid. 

Large-scale winning of copper by acidic leaching of copper ores sometimes results in waste solutions containing appreciable amounts of uranium. The uranium bearing aqueous raffinate from copper extraction is usually a dilute sulfuric acid solution. Uranium can be recovered using the same technique as described in section 12.3.1. A typical example is uranium production at the Olympic Dam mine in Australia, where the copper ore bodies are estimated to contain a total of over a million metric tons of uranium. 

Uranium U(VI) (also Fe, Co, Cu, Zn, and Cd) in 10 M HC1 solution is present in the form of the complex uranyl anion U02CI42, which is adsorbed on an anion exchange resin.43 44 Separation and purification of uranium from other elements is possible in sulfuric acid solution. When the H2S04 (aq) concentration is >0.01 M, uranium exists in the anionic forms U02(S04)22- and U02(S04)34. In contrast to uranium, other elements (Fe, Co, Cu, Zn, and Cd) do not form anionic complexes in sulfuric acid solution.34... 

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