Extraction cycles

Nuclear Waste. NRC defines high level radioactive waste to include (/) irradiated (spent) reactor fuel (2) Hquid waste resulting from the operation of the first cycle solvent extraction system, and the concentrated wastes from subsequent extraction cycles, in a faciHty for reprocessing irradiated reactor fuel and (3) soHds into which such Hquid wastes have been converted. Approximately 23,000 metric tons of spent nuclear fuel has been stored at commercial nuclear reactors as of 1991. This amount is expected to double by the year 2001. 

In addition to fuel and targets(15J6) from SRP reactors, SRP also reprocesses a wide variety of fuels from offsite research reactors and a wide range of unirradiated plutonium scrap materials.(17) Following customary Savannah River practice, initial processing of each offsite material is designed to transform the actinides to a solution that is compatible with one of the solvent extraction cycles in either of the separations areas. A major advantage of this practice is that the... 

Route all neptunium as Np(V) to the high-level waste in the first extraction cycle... 

Successfully examples of applications have been reported for the analysis of pesticides in food using PLE during the extraction step [138-147]. Research had been conducted to optimize the effects of extraction temperature, number of extraction cycles, and various extraction solvent mixture compositions on the extraction effectiveness and recoveries of pesticides fi om food. Besides, cleanup sorbent material(s) can also be imbedded in the extraction cells so that cleanup can also be processed simultaneously with extraction. Although it has the advantages of low solvent consumption and short extraction period, the initial cost is high, large amount of unwanted matrix substances are co-extracted and some unstable compounds, such as endrin yielded low recoveries. 

Hitherto we have dealt with model FICs that are mostly useful as solid electrolytes. The other class of compounds of importance as electrode materials in solid state batteries is mixed electronic-ionic conductors (with high ionic conductivity). The conduction arises from reversible electrochemical insertion of the conducting species. In order for such a material to be useful in high-energy batteries, the extent of insertion must be large and the material must sustain repeated insertion-extraction cycles. A number of transition-metal oxide and sulphide systems have been investigated as solid electrodes (Murphy Christian, 1979). 

As a case-study, the decaffeination process for tea will be considered, where in every case the extraction parameters (pressure, temperature and extraction cycle) are maintained. In the... 

In the case of the Canadian yttrium-heavy rare earth concentrate, this is leached with HN03, causing all rare earths to go into solution. Solvent extraction separates yttrium from the other heavy rare earths, each of which can eventually be separated by further solvent extraction. In the case of xenotime, this is leached with hot H2S04 and separation of yttrium and the heavy rare earths completed in ion-exchange columns. The liquid-liquid organic solvent extraction cycle is complete within 5-10 days and is a continuous process. The resin ion-exchange cycle requires 60—90 days and is a batch process. Both processes result in pure rare earth oxides and chemicals. 

Uranium is back-extracted (and thus removed from the organic phase) with 0.01 M HNO3. It is purified by a series of solvent extraction cycles until the Pu/U ratio is < 10-8 and the total (3y activity is less than twice that of aged natural uranium. 

Secondary amine extractants are used for the recovery of zinc from liquors obtained by the leaching of pyrite cinders at the Metalquimica del Nervion plant in Bilbao, Spain,69 and at the Quimigal plant near Lisbon, Portugal.91 Traces of other metals that also form chloro anions, such as copper, cadmium and iron(III), are also extracted, and both plants use a second extraction cycle with D2EHPA to further purify the zinc solution prior to electrowinning. 

Many variants of the Purex (Plutonium Uranium Reduction Extraction) process23S based on TBP extraction have been developed but a basic outline flowsheet is illustrated in Figure 38. This shows the so-called early split flowsheet most commonly used in existing plants. It involves the separation of the uranium and plutonium using two different back-extractant streams during the first solvent extraction cycle. Additional solvent extraction cycles are then carried out independently on the uranium and plutonium streams to effect further purification. An alternative arrangement is the iate split flowsheet used at the Cap La Hague plant in France, and the... 

Bretault, R, Houdin, P., Emin, J.L., Baron, P. 2005. The reprocessing plant of the future A single extraction cycle. Proc. WM 05 Conference, February 27 to March 3, 2005, Tucson, AZ. 

FIGURE 2.5 (a) Stage-analysis data of DHOA and TBP in uranium extraction cycle, (b)... 

Note Number in bracket refers to overall DF of U over Th Strippant distilled water. a After extraction cycle. 

The flowsheet of the UREX process, developed in the United States, includes the following extraction cycles (1) separation of uranium and technetium, (2) separation of plutonium, (3) separation of cesium and strontium, (4) separation of MAs and Rare Earth Elements (REE), and (5) group separation of MA from REE metals.9,10 Flowsheet development in Europe11 includes a modified PUREX process and, after that, the DIAMEX process for separation of MAs and lanthanides, the SANEX process for separation of MAs from lanthanides, and a special cycle for Am/Cm separation. Cesium and strontium will be in the raffinate of the DIAMEX process, and this raffinate will be vitrified, or cesium can be preliminarily extracted.12... 

FIGURE 6.3 DIAMEX-SANEX flowsheet with organophosphorus acid regeneration in extraction cycle. (From Heres, X., Ameil, E., Martinez, I., Baron, P., Hill, C., Extractant separation in Diamex Sanex Process. Presentation on Global 07 conference. With permission.)... 

---