Solvent-extraction process in the

In 1942, the Mallinckrodt Chemical Company adapted a diethylether extraction process to purify tons of uranium for the U.S. Manhattan Project [2] later, after an explosion, the process was switched to less volatile extractants. For simultaneous large-scale recovery of the plutonium in the spent fuel elements from the production reactors at Hanford, United States, methyl isobutyl ketone (MIBK) was originally chosen as extractant/solvent in the so-called Redox solvent extraction process. In the British Windscale plant, now Sellafield, another extractant/solvent, dibutylcarbitol (DBC or Butex), was preferred for reprocessing spent nuclear reactor fuels. These early extractants have now been replaced by tributylphosphate [TBP], diluted in an aliphatic hydrocarbon or mixture of such hydrocarbons, following the discovery of Warf [9] in 1945 that TBP separates tetravalent cerium from... 

Development of solvent extraction processes in the petroleum industry and theoretical aspects of solvent extraction are reviewed. Six extraction processes which have received industrial acceptance are described and performance characteristics of furfural, phenol, and Duosol processes are compared. Data are presented to demonstrate the applicability of adsorption analyses for stock evaluation and prediction of commercial extraction yields. Correlations for predicting solvent requirements and layer compositions and process design and engineering considerations are included. The desirability of further fundamental work to facilitate design calculations from physical data is suggested. 

Four generic criteria must be addressed for development of any solvent-extraction process in the nuclear or hydrometallurgical industries. Namely, the solvent must maintain its integrity over time and use. The process must accept wide feed variation, and the solvent components cannot be lost at an appreciable rate. The solvent must possess a relatively high affinity and selectivity for the component that is to be recovered from the feed stream. Also, the opposing phases in the process must be immiscible or very nearly so in order to effect efficient phase separation. Finally, the... 

TBP is a well-known extractant on many solvent extraction processes in the nuclear fuel processing industry. TBP has been an excellent all-around solvent for the reprocessing of irradiated nuclear fuel. It possesses all major requirements that extractants must have to be successfully applied in an industrial solvent extraction separation process. These properties have been also transferred to the solid polymeric extractant TVEX-TBP. 

Choppin, G. R. 2005. Solvent extraction processes in the nuclear fuel cycle. Solvent Extraction Research and Development, Japan 12 1-10. 

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

The production of CPO is based on relatively inexpensive cycHc substances these must be derivatized, however, to meet the requirements of resistance to heat softening and suitabiUty for metallization. Metathesis polymerization is problem-prone, since relatively large amounts of catalyst (WCl, C2H AlCl2) must be removed by solvent extraction (216). In the process, the price of CPO, at small batches, is several times higher than that of BPA-PC. 

Solvent extraction is often applied to separate two chemically similar metals such as nickel/ cobalt, adjacent rare earths, niobium/tantalum, zirconium/hafnium, etc. For the purpose of elaboration, the example of the separation of two chemically similar elements such as zirconium and hafnium from their nitrate solution, using TBP as an extractant is considered. The solvent extraction process in this case is chemically constant (K) is given by ... 

As discussed already, crowns may be involved in solvent extraction processes in which an inorganic reagent is transferred (sometimes selectively) from one phase (often water) into an immiscible organic phase the extraction involves ion-pair formation between the cationic crown complex and the counter ion (Blasius Janzen, 1981). 

None of the authors of this book is an expert in all the aspects of solvent extraction, nor do we believe that any of our readers will try to become one. This book is, therefore, written by authors from various disciplines of chemistry and by chemical engineers. The scientific level of the text only requires basic chemistry training, but not on a Ph.D. level, though the text may be quite useful for extra reading even at that level. The text is divided in two parts. The first part covers the fundamental chemistry of the solvent extraction process and the second part the techniques for its use in industry with a large number of applications. In this introductory chapter we try to put solvent extraction in its chemical context, historical as well as modem. The last two chapters describe the most recent applications and theoretical developments. 

The initial requirement in the development of a solvent extraction process for the recovery or separation of metals from an aqueous solution is knowledge of the solution composition, pH, temperature, and flow rate. Both pH and temperature can be adjusted, within certain economic limits, before feeding to the solvent extraction circuit, but only in a few cases can the leaching or dissolution conditions be dictated by the extraction process. Consequently, no serious development work on the extraction process can be carried out before the leaching conditions or the type of feed solution are established. 

Any successful solvent extraction process depends upon the selection of inexpensive extractants that can operate at the natural condition of the solution, with minimum loss of the organic phase to the aqueous solution. Also, an inexpensive means of recovery of the metal from the organic phase is necessary. In some cases, the cost of neutralization of the feed solution before solvent extraction processing or the cost of maintaining a buffered pH during extraction may prove excessive when coupled with solvent losses. 

In the optimization of the solvent extraction process for the recovery of copper using LIX 64N, Robinson [77] described the eost funetion in terms of the sum of the operating and capital costs. The operating eosts were taken as resulting from losses of eopper and solvent ... 

Pure isomers are often used as starting products for fine chemicals (e.g., different drugs). The separation of isomers entails great difficulties because they often have boiling points differing by only a fraction of a degree and they have closely similar solubilities in many solvents. Solvent extraction processes for the separation of isomers, therefore, have to rely more on chemical reactions than on nonspecific physical interactions between the solute and the solvent. 

NN applications, perhaps more important, is process control. Processes that are poorly understood or ill defined can hardly be simulated by empirical methods. The problem of particular importance for this review is the use of NN in chemical engineering to model nonlinear steady-state solvent extraction processes in extraction columns [112] or in batteries of counter-current mixer-settlers [113]. It has been shown on the example of zirconium/ hafnium separation that the knowledge acquired by the network in the learning process may be used for accurate prediction of the response of dependent process variables to a change of the independent variables in the extraction plant. If implemented in the real process, the NN would alert the operator to deviations from the nominal values and would predict the expected value if no corrective action was taken. As a processing time of a trained NN is short, less than a second, the NN can be used as a real-time sensor [113]. 

Figure 3 also illustrates the rapid growth of lubricating oil solvent extraction processes. From the point of view of popularity, furfural, phenol, and the Duosol processes are outstanding. Most of the recent developments have been improvements in the solvent recovery systems to minimize solvent consumption, to reduce costs, and in the treater sections, to increase raffinate yield. 

The first is a high-temperature solvent extraction process in which no catalyst is added. The liquids produced are those that are dissolved in the solvent, or solvent mixture. The solvent usually is a hydroaromatic hydrogen donor, while molecular hydrogen is added as a secondary source of hydrogen. 

In the following sections, the most important commercial applications of solvent-extraction technology in the field of extractive metallurgy are discussed in terms of the coordination chemistry relevant to the extraction process. The sole criterion for the inclusion of a given process is that it should have been utilized on an industrial scale. It may be noted that several interesting extraction systems in the early stages of development have been excluded on this basis, despite the pertinence of the chemical principles involved. 

In a typical solvent-extraction process,211 the pH value of the sodium tungstate solution is adjusted to about 2.5 with sulfuric acid, and the tungsten is extracted into a 7% solution of the tertiary amine Alamine 336 plus 7% isodecanol in kerosene in two countercurrent stages at a temperature of 50 °C. Distribution data are consistent with the extraction of species such as H2W1204o6 and Wi2O408- in reactions of the type208-212... 

The complexity of the problem and the diversity of operating conditions in saline water conversion make it unlikely that any process based on one principle or phenomenon will provide the most efficient conversion in all operating situations encountered. The art of saline water conversion has now reached a level at which one can begin to take stock with respect to the particular advantages of the many different processes in any given situation. The final selection of a process will only be possible after careful consideration of process operation data as applied to the conversion problem at hand. Since such data are available on but very few processes at the present time, it is only possible to project on the basis of theory and experience those points which set apart one process from another. The purpose of this paper is to present information now available which may help to locate the solvent extraction process in its rightful position in the saline water conversion field. 

To develop a new liquid-liquid extraction process in the nuclear held, it is therefore imperative to consider the stability of the molecules proposed as a major criterion and to integrate systematic degradation studies in order to check the robustness of the solvent submitted to radiolysis, particularly in terms of efficiency and of selectivity. 

Figure 2.45). Bulk sorbent phases can also be purchased. Typical column housings are manufactured of polypropylene or glass, and the sorbent is contained in the column by using porous frits made of polyethylene, stainless steel, or Teflon. Pesek and Matyska [87] describe three types of disk construction (1) the sorbent is contained between porous disks, which are inert with respect to the solvent extraction process (2) the sorbent is en-... 

Liquid-liquid partition chromatography was invented by A. J. P. Martin and R. M. L. Synge in 1941. Martin had earlier devised a multistage solvent extraction process for the separation of vitamin E, although this work was not published. He and Synge then... 

Co-location of the TBP and DBBP extraction processes in the same facility led inevitably to cross contamination of extractants. This problem was of greater consequence to the PRF system where small concentrations of DBBP in the TBP extractant interfered with plutonium stripping. No specific system malfunctions directly attributable to the presence of TBP in the DBBP solvent were identified. However, dilution of the DBBP extractant with TBP reduces its efficiency as an americium extractant. 

The acid concentration of the feed solution is an important processing parameter. Acid concentrations in the range 0.01-0.70 M were investigated in the development tests. In each test, the curium sorbed on the resin was sufficient to produce acceptable oxide products. However, the acid concentration of the feed is maintained in the range 0.20 to 0.35 M in the production runs. In one of the earlier production runs at lower acidity, a precipitate formed in the feed solution. This was thought to be caused by an unknown contaminant, probably a phosphate species from an earlier solvent extraction step. In the production runs, the reduced actinide capacity of the resin is noticeable at the higher acidities. Convenient batch sizes and short loading times for the current scale of production are achieved with actinide concentrations of about 10 g/L, but actinide concentration is not considered an important variable. 

Freeze-thaw vacuum, inter leave-air, and solvent extraction processes offer the greatest potential in drying these types of coated- and uncoated-paper books after they have been wetted and frozen. The drained-air, vacuum-air cycle, vacuum, microwave, and dielectric drying processes work well on uncoated paper, but they fail to dry books containing this type of coated paper. Small and large units for freeze-thaw, vacuum drying have been used successfully to remove water from these frozen coated and uncoated books. 

Solvent extraction. The press cake emerging from a screw press still retains 3 to 15 percent of residual oil. More complete extraction is done by solvent extraction of the residues obtained from mechanical pressing. The greater efficiency obtained in the solvent extraction process encouraged the industry for direct application to oilseeds. In the United States and Europe, continuous extractor units are used in which fresh seed flakes are added continuously and are subjected to a counterflow of solvent by which intimate contact is achieved between the seeds and solvent. The common solvent for edible oil is commercial hexane or heptane, commonly known as petroleum ethers, boiling in the range of 146 to 156°F (63.3 to 68.9°C). After extraction, maximum solvent recovery is necessary for economical operation. The solvent is recovered by distillation and is reused. The extraction oil is mixed with prepress oil for refining. The extracted meals contain less than 1 percent of residual oil. 

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