Phosphoric acid solvent extraction, uranium

Solvent Extraction. Liquid—hquid extractioa, well known ia the chemical iadustry, was first used ia extractive metallurgy for the processiag of uranium. When a dilute solution of uranium is contacted with an extractant such as di(2-ethylhexyl) phosphoric acid (D2EHPA) or R2HPO4, dissolved ia... 

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. 

DEPA-TOPO [di (2-ethylhexyl) phosphoric acid and trioctylphosphine oxide] A process for recovering uranium from wet-process phosphoric acid, by solvent extraction with a mixture of the two named reagents. Developed at Oak Ridge National Laboratory and first commercialized in 1978 by Freeport Minerals Corporation and Wyoming Mineral Corporation. 

Hurst, F. J. Recovery of uranium from wet-process phosphoric acid by solvent extraction, presented at Annual AIME Meeting, Las Vegas, February 1976. Young, W. Davy Power-Gas, Paper at AIME Annal Meeting, New Orleans, February 1979, p. 59. 

The primary separation of plutonium and uranium from the fission products involves a solvent extraction with 30 vol % TBP at room temperature. The activity levels in this separation are quite high ( 1700 Ci/L for the fission products) and the aqueous waste, which contains 99+% of the fission products, is a high-level waste. Am and Cm are not extracted and Np is partially extracted. Because of the high radiation levels, there are radiolysis problems with TPB, leading to solvent degradation. Primary products of the radiolysis of TBP are the dibutyl- and monobutylphosphoric acids along with phosphoric acid. These degradation products are removed in the solvent purification steps. 

It is used in the mining industry to recover metals such as copper and nickel. Parasite plants, based on solvent extraction, are used in the phosphate industry to recover by-product uranium from crude phosphoric acid. The uranium concentration in phosphoric acid is very low but, because of the high volume of phosphoric acid that is produced to meet agricultural needs, considerable uranium can be recovered using solvent extraction. In the nuclear industry [5], solvent extraction is used to purify uranium and plutonium [using the plutonium and uranium recovery by extraction (PUREX) process], zirconium from hafnium, and for many other applications. It is also used in environmental applications to clean soil, say, to remove polychlorinated biphenyls (PCBs), dioxins, pesticides, and other hazardous pollutants. 

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. 

Williams [W3] reported that from 1959 to 1968 thorium was recovered as a by-product of Rio Algom s uranium mill at Elliot Lake, Ontario. Thorium-bearing uraninite ore was dissolved in sulfuric acid. Uranium was first recovered by anion exchange. Then thorium was recovered from the acid solution by solvent extraction with alkyl phosphoric acid, probably di(2-ethyl-hexyl)phosphoric acid. 

Uranium is found in phosphate ores which are mined and processed to produce a fertilizer product of high phosphate content. The first step in the recovery of phosphate from ore consists of digestion with sulfuric acid followed by uranium removal. To date, the process is economical only if uranium is recovered as a by-product. Three solvent extraction processes are in commercial operation using the following extractants a mixture of di(2-ethylhexyl)phosphoric acid (DEHPA) and trioctylphosphine oxide... 

The ORNL research program resulted in the development of two basic processes. These processes are similar as far as equipment is concerned, and they differ only in the solvent used [36]. Uranium extraction is achieved in a process that comprises two cycles (Figure 11.28). In the first cycle, uranium is extracted from phosphoric acid with an organic solvent in five stages and then stripped from this solvent with fresh phosphoric acid,... 

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