Concentrations in the Aqueous Phase

The distribution of highly extractable solutes such as and Pu between the aqueous and organic phases is strongly dependent upon the nitrate anion concentration in the aqueous phase. This salting effect permits extraction or reextraction (stripping) of the solute by controlling the nitric acid concentration in the aqueous phase. The distribution coefficient, D, of the solute is expressed as... 

Figure 3. Bromine concentration in the aqueous phase in equilibrium with complexes of different MEP MEM ratios 1 1 3 1, 9 1. Taken from Ref. [66]...

Tests were performed at 75°C using a University of Texas Model 500 spinning drop tensiometer. Active surfactant concentration in the aqueous phase prior to oil addition was 0.50% wt. The Kem River crude oil was from the Patricia Lease. The pH of the deionized water surfactant solutions was 8. The pH of the aqueous NaCl surfactant solutions was 9.5 unless otherwise noted. values represent the average deviation of two or three measurements at different times (0.75-1 h apart). D.I., deionized. 

Tests were performed at 75°C using a University of Texas Model 500 spinning drop tensiometer. Active surfactant concentration in the aqueous phase prior to addition of the oil phase was 0.5% wt. Interfacial tension values are the average of duplicate or triplicate determinations. 

Aqueous-organic two-phase reaction has been widely performed [18]. One of the purposes of using two-phase reaction system is to control the substrate concentration in aqueous phase where the biocatalysts exist. Hydrophobic substrate and products dissolve easily in the organic phase, so that the concentration in the aqueous phase decreases. The merits of controlling and decreasing the substrate concentration in the aqueous phase are as follows ... 

After only a small percentage of the monomer has been converted to polymer (in the presence of emulsifier), the initially low surface tension of the aqueous emulsion rises rather abruptly, indicating a decrease in the soap concentration in the aqueous phase of the emulsion. The soap concentration is then too low to maintain micelles, which may therefore be abandoned as a locus for further polymerization beyond this point. As additional evidence of the depletion of soap in the aqueous phase, monomer droplets are no longer stable, and upon discontinuing agitation a supernatant monomer layer is readily formed. 

Toxicity as a result of the surfactant-enhanced PAH concentration in the aqueous phase... 

FIG. 19 Dependence of the half-wave potentials for Fc (curve 1) and ZnPor (curve 2) oxidation in benzene on CIO7 concentration in the aqueous phase. In these measurements, half-wave potentials were extracted from reversible steady-state voltammograms obtained at a 25 pm diameter Pt UME. The benzene phase contained 0.25 M tetra-w-hexylammonium perchlorate (THAP) and either 5 mM Fc or 1 mM ZnPor. All potentials were measured with respect to an Ag/AgCl reference electrode in the aqueous phase. (Reprinted from Ref. 48. Copyright 1996 American Chemical Society.)... 

The ET reaction between aqueous oxidants and decamethylferrocene (DMFc), in both DCE and NB, has been studied over a wide range of conditions and shown to be a complex process [86]. The apparent potential-dependence of the ET rate constant was contrary to Butler-Volmer theory, when the interfacial potential drop at the ITIES was adjusted via the CIO4 concentration in the aqueous phase. The highest reaction rate was observed with the smallest concentration of CIO4 in the aqueous phase, which corresponded to the lowest driving force for the oxidation process. In contrast, the ET rate increased with driving force when this was adjusted via the redox potential of the aqueous oxidant. Moreover, a Butler-Volmer trend was found when TBA was used as the potential-determining ion, with an a value of 0.38 [86]. 

FIG. 22 Dependence of ET rates on CIO4 concentration in the aqueous phase for the reduction of TCNQ in DCE by aqueous Fe(CN)6. The aqueous phase contained 0.1 M Li2S04 with various concentrations of NaC104, while the DCE phase contained 0.1 M TEIAP. The SECM approach curves for the generation of Fe(CN)6 by the reduction of Fe(CN)g present in the bulk aqueous phase, were obtained with a 25 pm diameter Pt UME. From top to bottom, the first four solid experimental curves are shown for [CIO4 ] = 0.01, 0.025, 0.1, and 0.25 M. For the bottom solid line, there was no TCNQ in the DCE phase. The dashed lines are the corresponding theoretical curves for ki2 = 0.3, 0.2, 0.04, 0.015, and 0 cm s ... 

The demetalation kinetics of ZnTTP by an acidic aqueous phase have also been reported [61]. In this study, ZnTTP was considered to adsorb at the interface producing Zn and free base porphyrin by proton attack. The demetalation kinetics of ZnTTP were analyzed as a pseudo-first-order reaction, because the proton concentration in the aqueous phase was in large excess. The rate law was found to be described by... 

Figure 11 analyzes the effect of the electrolyte concentration in the aqueous phase, for fixed electrolyte concentrations in the organic phase c" = 10 mM and 50 mM, and a Galvani potential difference/= 5. These theoretical results are in agreement with the observations in Ref. 13. Moreover, it is shown that a deerease in the eleetrolyte eoneen-tration in the organic phase has a similar effeet to a deerease in the eleetrolyte eoneentra-tion in the aqueous phase. 

Both substrate and product have suface-active properties and favor mass transfer across the liquid-liquid interface. Their physicochemical properties modulate the behavior of the reaction in the heterogeneous system. Saturating substrate concentration in the aqueous phase (L aq) was not constant. It increased when using a high initial concentration of LA LA and when the HP concentration increased. The percentage of transferred LA T = LA qlLAf) depended on LA, and HP concentrations ... 

The different chemical-physical characteristics of the dyes molecules, as well as of their intermediates, can differently influence the bioavailability through the actual concentration in the aqueous phase, where microorganisms or enzymes are active,... 

Tests are made on the extraction of acetic acid from a dilute aqueous solution by means of a ketone in a small spray tower of diameter 46 mm and effective height of 1090 mm with the aqueous phase run into the top of the tower. The ketone enters free from acid at the rate of 0.0014 m3/sm2, and leaves with an acid concentration of 0.38 kmol/m3. The concentration in the aqueous phase falls from 1.19 to 0.82 kmol/m3. 

A suspension process using redox initiation in a water medium was developed. The redox system is a combination of persulfatesulfite. Often ferrous or cupric salts were added as a catalyst for the redox reaction. Polymerizations were run in water at low temperature (20-25°C) and low pressure (65-85 psi). Monomer to monomer-plus-water weight ratios of 0.20 to 0.25 were used. Good agitation was required to keep an adequate monomer concentration in the aqueous phase. Yields ofup to 100% were obtained with polymer inherent viscosities of0.4 to 1.5 dl/g in C6F5C1. Reactions were run on both a 1-gal and a 100-gal scale. 

An ion exchanger (0.04 g) and a metal ion solution (10 4 M, 25 ml) were taken into 50 ml Erlenmeyer flasks. Then, the flasks were shaken with a mechanical shaker at 30 °C for 24 h. The metal ion concentration in the aqueous phase was determined by means of ICP-AES. From a decrease of the metal ion concentration in the aqueous phase, uptake of metal ion in mmol/g was calculated. Here, only nitric acid was used in the pH adjustment. 

Into a three-necked flask (200 ml) equipped with a mechanical stirrer, an ion exchanger (0.3 g) and water (135 mL) were taken. The resulting mixture was allowed to stand overnight for swelling of the ion exchanger. Then, a lead nitrate solution (0.05 M, 15 ml) was added to the flask, and immediately the resulting solution was stirred at 400 rpm for the first 2 min, and then at 170 rpm. At pertinent intervals, an aliquot of the aqueous phase was sampled, and the concentration of Pb(II) in the sample was measured. From a decrease in the Pb(II) concentration in the aqueous phase, the uptake of Pb(II) at the sampled time was calculated. 

An increase has also been observed in the LAS concentration in the aqueous phase during the cold season, due to reduced microbial activity [3,18,23]. Therefore the flow of LAS towards the coastal zone will be strongly influenced by the seasonal variable as confirmed by the values obtained by Takada et al. [3], who found that for the Tamagawa estuary the flow of LAS was five times higher in winter than in summer. However, in long-term monitoring [6,31,32], the variations detected are principally a function of tidal influence and of the time of day, or the day of the week, when the LAS is introduced into the system [6,33],... 

The preservative must be sufficiently soluble in water to achieve adequate concentrations in the aqueous phase of a two or more phase system. The proportion of preservative remaining undissociated at the pH of the preparation must be capable of penetrating the microorganisms and destroying its integrity. 

Solvent extraction results are presented typically in the form of diagrams. This is schematically illustrated in Fig. 4. la for three hypothetical substances. A, B, and C. The distribution ratio is investigated as a function of the concentration of some reactant Z, which may be pH, concentration of extractant in the organic phase (e.g., an organic acid HA, [HA]o,j), the extractant anion concentration in the aqueous phase (e.g., [CT]), salt concentration in the aqueous phase, etc. The... 

Fig. 4.1 Liquid-liquid distribution plots, (a) The distribution ratios D for three different substances A, B, and C, plotted against the variahle Z of the aqueous phase. Z may represent pH, concentration of extractant in organic phase ([HA]org), free ligand ion concentration in the aqueous phase ([A ]), aqueous salt concentration, etc. (b) Same systems showing percentage extraction %E as a function of Z. D and Z are usually plotted on logarithmic scale. 

Fig. 4.8 Distribution ratios (from bottom to top) of acetic (Cj ), propionic (Cj O), butyric (C4 A), and valeric (C5 A) acids (carbon chain length Co) between carbon tetrachloride and water as a function of the acid concentration in the aqueous phase, [HA]aq. (From Ref. 1 la.)...

Subscript 0 indicates initial concentrations in the aqueous phase. 

A distribution isotherm is then constructed by plotting the metal concentration in the organic phase against the concentration in the aqueous phase, as a function of the phase ratio. An example of such an isotherm is shown in Fig. 7.1, for the extraction of nickel by DEHPA(Na) at pH 6, showing three different concentrations of extractant [1]. 

Soluble loss of a reagent (extractant, modifier, or diluent) from the solvent phase is an inherent part of the solvent extraction process, since all organic compounds are soluble, to some extent, in water. The conditions prevailing in the system can also promote solubility, which can be a particular problem if the composition and properties of the aqueous phase are inflexible. For example, the solubility of alkylphosphoric acid and carboxylic acid extractants is dependent on temperature, pH, and salt concentration in the aqueous phase. 

Three causes of extractant solubility in the aqueous phase may be distinguished solubility of un-ionized and ionized extractant and metal-extractant species. For extractants such as acids, amines, and chelating reagents, their polar character will always result in some solubility in the aqueous phase over the pH range in which they are useful for metal extraction. Solubility depends on many factors including temperature, pH, and salt concentration in the aqueous phase, as discussed in Chapter 2. 

Increasing the temperature of a system can be expected to increase the solubility of all the components of a solvent. Variation of pH is likely to affect only the polar components of the solvent. By increasing the salt concentration in the aqueous phase, most solvent components are expected to exhibit decreased solubility because of salting out. The solubility of a solvent component in the aqueous phase is also likely to increase with increase in the concentration of the component in the solvent. 

---