Metal concentrations in the aqueous

The equilibrium metal concentrations in the aqueous and organic phases and the equilibrium acidity of the aqueous phase are presented along with the calculated values for the distribution coefficient in Table IV. 

The practical significance of metal release from sulfide minerals has focussed attention on the mechanisms which operate under the conditions of the highest metal concentrations in the aqueous phase of field situations, and on the associated organisms. The most studied substrates have been iron and copper sulfide minerals and the unique position of T. ferrooxidans as the principal terminal member of the pH-dependent successions of both sulfur-oxidizing and iron-oxidizing bacteria has led to intensive investigation of this... 

The permeability tests for alkali metal ions in the aqueous solution were also conducted. When an aqueous salt solution moves to cell 2 through the membrane from cell 1, the apparent diffusion coefficient of the salt D can be deduced from a relationship among the cell volumes Vj and V2, the solution concentration cx and c2, the thickness of membrane, and time t6 . In Table 12, permeabilities of potassium chloride and sodium chloride through the 67 membrane prepared by the casting polymerization technique from the monomer solution in THF or DMSO are compared with each other and with that the permeability through Visking dialyzer tubing. The... 

The facilitated transfers of Na+ and K+ into the NB phase were observed by the current-scan polarography at an electrolyte-dropping electrode [12]. In the case of ion transfers into the DCE phase, cyclic voltammetry was measured at an aqueous gel electrode [9]. Both measurements were carried out under two distinctive experimental conditions. One is a N15C5 diffusion-control system where the concentration of N15C5 in the organic phase is much smaller than that of a metal ion in the aqueous phase. The other is a metal ion diffusion-control system where, conversely, the concentration of metal ion is much smaller than that of N15C5. Typical polarograms measured in the both experimental systems are shown in Fig. 2. 

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. 

The distribution of M depends on both the free amine salt in the organic phase and the concentration of free 17 in the aqueous phase until all metal in the aqueous phase is bound in the ML7 complex. At constant amine concentration, Eq. (4.64) indicates that a plot of Du vs. [L ] would have a linear slope p if the denominator of Eq. (4.64) is 1 i.e., the metal species in the aqueous phase are dominated by the uncomplexed metal ion At higher [L ] concentrations, where the ML7 complex begins to dominate in the aqneons phase, the >m valne becomes equal to [RNHL]. Equations (4.64) and (4.4) show that 5-shaped curves result for metals with large values. In a plot of Dm vs. [RNHL] ,j a straight line of slope p is obtained only at constant [L ]. From such measurements both p, and Pp can be evalnated. The following example illustrates this. 

Solvent extraction has become a common technique for the determination of formation constants, P , of aqneons hydrophilic metal complexes of type MX , particularly in the case when the metal is only available in trace concentrations, as the distribntion can easily be measnred with radioactive techniques (see also section 4.15). The method reqnires the formation of an extractable complex of the metal ion, which, in the simplest and most commonly used case, is an nn-charged lipophilic complex of type MA. The metal-organic complex MA serves as a probe for the concentration of metal ions in the aqueous phase through its equilibrium with the free section 4.8.2. This same principle is used in the design of metal selective electrodes (see Chapter 15). Extractants typically used for this purpose are P-diketones like acetylacetone (HAA) or thenoyltrifluoroacteone (TTA), and weak large organic acids like dinonyl naph-talene sulphonic acid (DNNA). 

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]. 

For most exploratory work, analysis of the organic phase is not necessary. If no volume change of the phases occurs and no third phase or crud is formed, the analysis of the aqueous raffinates is sufficient, since the metal concentration in the solvent can be readily calculated from the initial metal concentration of the feed solution and the phase ratio used. 

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. 

By increasing the ionic strength, that is, the acid or metallic salt concentration, in the aqueous phase, the concentration of the extracted acid or salt in the organic phase increases and induces an increase in the attractions between reverse micelles (see below). Numerically, all the terms can be evaluated (7, 37, 83). It can then clearly be concluded that this effect is the origin of the third-phase formation. 

The extraction kinetics of Ni(II) and Zn(II) with //-alkyl-substituted dithizone (HL) in chloroform has been studied by HSS method [7]. The observed extraction rate constants was linearly proportional to both metal ion concentration in the aqueous phase [M2+] and ligand concentration in the organic phase [HL]0, and inversely to the hydrogen ion concentration [H + ] in the aqueous phase. Thus, the rate law for the extraction was determined as... 

Two-phase electrolysis — Electrolysis of two-phase systems, esp. of two liquid phases. The usual case is that an organic compound is dissolved in a nonaqueous solvent and that solution, together with an aqueous electrolyte solution is forced to impinge on an electrode. The electrolysis reaction of the dissolved organic compound can proceed via a small equilibrium concentration in the aqueous phase, or it can proceed as a reaction at the three-phase boundary formed by the aqueous, the nonaqueous phase, and the electrode metal. A very effective way of delivering a two-phase mixture to an electrode is the use of a - bubble electrode. 

The observed extraction rate constants linearly depended on both the metal ion concentration [M +] and the hydrogen ion concentration in the aqueous phase. However, the observed extraction rate constant (k ) did not decrease with an increase in the distribution constant ( Tq) of the ligand as was expected from the mechanism in the aqueous phase. Furthermore, the HSS method revealed that the dissociated form of the n-alkyl-dithizone was adsorbed at the interface generated by vigorous stirring [5]. The following scheme was proposed based on the experimental results, considering both the aqueous... 

Where t is the regeneration time, in minutes, V is the volume of aqueous regeneration solution, y is the amount of resin, R is the radius of a spherical resin bead, B is the adsorption capacity of the resin, in g-mole-metal-ion/g-resin, D is the effective intraparticle diffusivity of the heavy metal ion through the resin, and is the concentration of metal ion in the aqueous regeneration solution. 

When the organic complexing agent in the solvent is nearly all combined as extracted complexes, further increase in concentration of the complex-forming metal ions in the aqueous phase will cause the distribution coefflcient for metal extraction to decrease. This phenomenon has been observed for uranyi nitrate [G3, Ml, M2] and for zirconium and hafnium nitrates [H4] when extracted by TBP in kerosene. 

The usual practice is to add the chelating agent, HR, to the organic phase. It distributes between the two phases, and in the aqueous phase it dissociates as a weak acid. The metal ion, M"+, reacts with nR to form the chelate MR , which then distributes into the organic phase. The distribution ratio is given by the ratio of the metal chelate concentration in the organic phase to the metal ion concentration in the aqueous phase. The following equation can be derived ... 

Some additional information can be derived from the spectra of other metals. It is postulated that a neutral salt, MX2, is being extracted, which can be demonstrated with the aid of the spectra of palladium chloride. The spectrum of the anionic palladium chloride, (NH4>2PdCU, has maximum absorption at 428 nm, whereas the maximum absorption of PdCb dissolved in toluene is at 338 nm. When (NH4)2PdCb is being extracted, the maximum absorption is very close to that of PdCb, at 344 nm. The extraction efficiency decreases with increasing chloride concentration in the aqueous phase [13]. 

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