Uranium recovery with amine extractants

The alkyl amines offer greater selectivity than organophosphorus compounds in many applications, particularly in uranium hydrometallurgy. Amine extraction is typified by the Amex process, which uses a tertiary or branched secondary amine to extract uranium from sulfate leach liquors (11). A similar process based on the use of a primary or straight-chain secondary amine (sometimes modified with an organic-soluble alcohol) has given good results in thorium recovery (12). 

Babcock ( ) also reported pilot plant uranium and chromium recovery projects using ILMs. Membrane modules were constructed with hollow fiber polysulfone supports containing kerosene solutions of commercially available hydrometallurgical complexatlon agents such as tertiary amines. Operating coats for the extraction step calculated from uranium recovery data were 0.8/kg Ur for a 3.8 x 10 ra /day plant which were superior to costs associated with solvent extraction and ion-exchange. 

Thus there is considerable incentive to find extractants that could tolerate higher quantities of solids in H2SO4 leach liquors. Stripping of uranium from the Amex process extractant and subsequent regeneration of the amine solvent also consume considerable quantities of acid and base. Recovery of uranium from H2SO4 solutions would be simplified if a convenient neutral extractant could be found. An extractant with better selectivity for vanadium and molybdenum than HDEHP and long-chain amines is also desirable. 

Leaching operations in the Kerr-McGee mill are described in this section, with reference to Fig. 5.6. Recovery of uranium from leach liquor by solvent extraction with organic amines in the Amex process is to be described in Sec. 8.6. 

Thoriuin recovery processes. Because of the many elements in the solution, their chemical similarity, and the presence of phosphoric acid, separation of thorium from this acid solution has proved to be difficult. Wylie [WS] has reviewed the numerous separatirm processes that have been developed. Figure 6.5 shows the principal steps in seven of these processes and gives references for more details. Processes 4 and 6 appear to be the most economic when thorium, rare earths, and uranium all are to be recovered. Process 4, involving separation of thorium and rare earths from phosphate and uranium by precipitation with oxalic acid, is described next. Process 6, involving separation by solvent extraction with organic amines, is described in Sec. 8.6. 

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. 

Another important technology for the concentration and winning of minerals and metals is solvent extraction. Up to the time of writing there is only one area where RR-based chemicals are used commercially. Tertiary amines (- fatty amines) with short- to medium-length alkyl chains and their - quatenary derivatives form ion pair complexes with certain metals that are dissolved in an aqueous medium. These reagents are widely used for the recovery of uranium, vanadium, nickel and, to a lesser extent, molybdenum. 

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