Solvent Extraction: Classical and Novel Approaches Book, 2011, Elsevier (original) (raw)
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The Chemistry of Solvent Extraction
ing oxygen-bearing extractants of the classical type is decreasing, as one would expect, and not much substantially new addition to the field of chelating agent extraction systems has been made. From the fundamental side, inorganic solvent extraction chemistry is now very concerned with the study of species extracted into, or formed in, the organic phase. Problems of specific complex formation in the process of extractive transfer of metals are being explored. We would particularly draw attention to the ever-increasing interest in spectrometric and spectroscopic techniques aiding the interpretation of the nature of metal-extractant interaction. This is primarily reflected in a faster general progress on the structural side.
Solvent extraction (SX) or liquid-liquid distribution1 techniques have a broad field of applications in inorganic and organic chemistry and large-scale industrial separations, in analytical chemistry, in pharmaceutical and biochemical industries, and in waste treatment. In addition, SX is a good instrument for studying fundamental understanding of equilibrium and kinetics of complex formation processes. Extraction methods have now become a routine procedure in separation technologies. The literature volumes of publications on the subject, and the number of newly discovered extraction methods, increase every year. Many methods based on chelate extraction have been considered as routine practice. The hitherto unexplored potentialities are also very considerable. Extraction is a major tool in the study of the processes of complex formation and of the state of compounds in solution. This monograph differs in scope and approach from the recent books by Rydberg et al. and Ritcey (Rydberg ...
Solvent Extraction: Kinetic Study of Major and Minor Compounds
Journal of the American Oil Chemists' Society, 2010
The effects of temperature and contact time on lipid extraction from sunflower collets was investigated in a batch extractor with hexane as solvent. The total removed material varied in quantity and composition due to changes in temperature and contact time. Higher temperatures enhanced oil extraction as well as increased the tocopherol and phospholipid contents of the oil. The kinetic data for triglycerols, phospholipid and tocopherols extraction were interpreted by using an equation that considers extraction as the sum of two components: diffusion and washing. Effective diffusion coefficients for oil, tocopherols and phospholipid at different temperatures were determined. Control of temperature and contact time are essential to obtain good quality oil and reduce refining costs. Extraction at 60°C and short contact times (30 min) obtained high oil yield (98%) accompanied by significant tocopherol extraction ([99%) and reduced phospholipid extraction (66%).
DESALINATION AND WATER TREATMENT
Since its first practical application in the mid-forties of XX century on the separation and purification of metals, solvent extraction had matured in this issue, being its usefulness demonstrated by the miriade of works published along the years, and by the number of solvent extraction plants built and into production around the world. Now in the XXI century, its application is moving around a theme, in connection with the above, and related to the recovery-separation-purification of metals from raw materials, as urban mining and the treatment of metal-bearing secondary materials and wastes are. Entering the third decade of XXI century, this work reviews the most advanced contributions in the use of solvent extraction science on metals recovery from a variety of sources, as demanded by the social, environmental and profitability conditions in which the world is living nowadays.
EXTRACTION xtraction is a process whereby a mixture of several substances in the liquid phase is at least partially separated upon addition of a liquid solvent in which E the original substances have different solubilities. When some of the original substances are solids, the process is called leaching. In a sense, the role of solvent in extraction is analogous to the role of enthalpy in distillation. The solvent-rich phase is called the extract, and the solvent-poor phase is called the raffinate. A high degree of separation may be achieved with several extraction stages in series, particularly in countercurrent flow. crystallization, or adsorption sometimes are equally possible. Differences in solubility, and hence of separability by extraction, are associated with differences in chemical structure, whereas differences in vapor pressure are the basis of separation by distillation. Extraction often is effective at near-ambient temperatures, a valuable feature in the separation of thermally unstable natural mixtures or pharmaceutical substances such as penicillin. The simplest separation by extraction involves two substances and a solvent. Equilibria in such cases are represented conveniently on triangular diagrams, either equilateral or right-angled, as for example on Figures 14.1 and 14.2. Equivalent representations on rectangular coordinates also are shown. Equilibria between any number of substances are representable in terms of activity coefficient correlations such as the UNlQUAC or NRTL. In theory, these correlations involve only parameters that are derivable from measurements on binary mixtures, but in practice the resulting accuracy may be poor and some multicomponent equilibrium measurements also should be used to find the parameters. Finding the parameters of these equations is a complex enough operation to require the use of a computer. An extensive compilation of equilibrium diagrams and UNlQUAC and NRTL parameters is that of Sorensen and Ark (1979-1980). Extensive bibliographies have been compiled by Wisniak and Tamir (1 980-198 1). The highest degree of separation with a minimum of Processes of separation by extraction, distillation, On a ternary equilibrium diagram like that of Figure 14.1, the limits of mutual solubilities are marked by the binodal curve and the compositions of phases in equilibrium by tielines. The region within the dome is two-phase and that outside is one-phase. The most common systems are those with one pair (Type I, Fig. 14.1) and two pairs (Type 11, Fig. 14.4) of partially miscible substances. For instance, of the approximately lo00 sets of data collected and analyzed by Sorensen and Arlt (1979), 75% are Type I and 20% are Type 11. The remaining small percentage of systems exhibit a considerable variety of behaviors, a few of which appear in Figure 14.4. As some of these examples show, the effect of temperature on phase behavior of liquids often is very pronounced. Both equilateral and right triangular diagrams have the property that the compositions of mixtures of all proportions of two mixtures appear on the straight line connecting the original solvent is attained with a series of countercurrent stages. Such an assembly of mixing and separating equipment is represented in Figure 14.3(a). and more schematically in Figure 14.3(b). In the laboratory, the performance of a continuous countercurrent extractor can be simulated with a series of batch operations in separatov funnels, as in Figure 14.3(c). As the number of operations increases horizontally, the terminal concentrations E, and R3 approach asymptotically those obtained in continuous equipment. Various kinds of more sophisticated continuous equipment also are widely used in laboratories; some are described by Lo et a/. (1983, pp, 497-506). Laboratory work is of particular importance for complex mixtures whose equilibrium relations are not known and for which stage requirements cannot be calculated. In mixer-separators the contact times can be made long enough for any desired approach to equilibrium, but 80-90% efficiencies are economically justifiable. If five stages are required to duplicate the performance of four equilibrium stages, the stage efficiency is 80%. Since mixer-separator assemblies take much floor space, they usually are employed in batteries of at most four or five units. A large variety of more compact equipment is being used. The simplest in concept are various kinds of tower arrangements. The relations between their dimensions, the operating conditions, and the equivalent number of stages are the key information. Calculations of the relations between the input and output amounts and compositions and the number of extraction stages are based on material balances and equilibrium relations. Knowledge of efficiencies and capacities of the equipment then is applied to find its actual size and configuration. Since extraction processes usually are performed under adiabatic and isothermal conditions, in this respect the design problem is simpler than for thermal separations where enthalpy balances also are involved. On the other hand, the design is complicated by the fact that extraction is feasible only of nonideal liquid mixtures. Consequently, the activity coefficient behaviors of two liquid phases must be taken into account or direct equilibrium data must be available. mixtures. Moreover, the relative amounts of the original mixtures corresponding to an overall composition may be found from ratios of Line segments. Thus, on the figure of Example 14.2, the amounts of extract and raffinate corresponding to an overall composition M are in the ratio E , / R N = M R N / E , M. Experimental data on only 26 quaternary systems were found by Sorensen and Arlt (1979), and none of more complex systems, although a few scattered measurements do appear in the literature. Graphical representation of quaternary systems is possible but awkward, so that their behavior usually is analyzed with equations. To a limited degree of accuracy, the phase behavior of complex mixtures can be predicted from measurements on binary mixtures, and considerably better when some ternary measurements also are available. The data are correlated as activity coefficients by means of the UNIQUAC or NRTL equations. The basic principle of application is that at equilibrium the activity of each component is the same in both phases. In terms of activity coefficients this 459
A STUDY OF PARAMETERS AFFECTING THE
Lactic acid has recently been drawing much interest as a raw material for biodegradable polymer. One of the promising technologies for recovery of lactic acid from fermentation broth is reactive liquid-liquid extraction. Equilibrium studies on the reactive extraction of lactic acid with trioctylamine (TOA) in various organic phases and its re-extraction into aqueous solutions were carried out. In this study distribution coefficient, extractability, stripping efficiency of various active and inert diluents with TOA as extractant were investigated, which were higher for active diluents. The effects of operating temperature, speed of agitation, agitation time and diluent composition on extraction efficiency were also studied. Temperature and extraction efficiency were inversely proportional to each other, whereas extraction efficiency was little affected by speed of agitation and agitation time.
Solvent Extraction, 2012
separation of iron(III) and some other heavy metals. In common, selectivity of some heavy metals, extracted by acidic extractants may be considered from .1. Development of chelating extractants (see .2) led to the design of the commercial reagents specifically for copper extraction. These were an aliphatic α-hydroxyoxime (LIX 63, Henkel) and βhydroxyoxime based on benzophenone (LIX 64). LIX 63, with pH 50 values of. 3-4, was unable to extract copper from commercial leach liquors without alkali addition, also this reagent extracted iron(III) at lower pH values than copper. These disadvantages were largely overcome by LIX 64 that extracted copper selectively from iron in the pH range 1.5-2.5, but with slow kinetics of extraction.
Solvent extraction of metals with carboxylic acids — Theoretical analysis of extraction behaviour
Hydrometallurgy, 1988
This paper describes a new, theoretical method for analysing the behaviour of metals during solvent extraction with carboxylic acids. A general solvent extraction equation, which allows for extraction of partially hydrolyzed species, solvation of the metal within the carboxylate complex and polymerization of the organic species, is used: M(OH),~/'-~+ + (n-q+m)/p (HR)p =I/x(M(OH)qR,,_~.mHR)x + (n-q) H + and a general expression for the distribution coefficient is derived, taking into account eomplexation of the metal in the aqueous phase by inorganic ligands. This general expression is then used to generate sets of theoretical log D/pH curves for different parameters in the extraction equation. For a given set of experimental log D/pH data, the most probable values of the different parameters are deduced by curve-matching. The equilibrium constant for extraction is then found from the position of the experimental curve. This direct approach readily reveals uncertainties arising from the interactive effect of some of the experimental parameters; in these eases alternative experimental techniques can be used to characterize the organic species, thereby improving the accuracy of the derived equilibrium constant. Examples of the technique are given for Fe (III), Cu (II) and Zn(II).