Affinity Series

Affinity series for various hydrous oxides are compiled in [3089]. The compilation of affinity series in [3168] also includes Agl and Hg. A review of affinity series of metal cations is presented in [2981]. Increasing affinity in a series from Li to Cs is reported for materials with PZCs at pH 4, and decreasing affinity in a series from Li to Cs is reported for materials with PZCs at pH 5. An analytical expression for stability constants of =SOMe and =SOH2X complexes (TLM) as a function of the dielectric constant of the solid and the ionic radii was proposed in [3169]. The results for common oxides and common anions and cations are tabulated. Examples of ion specihcity in different phenomena, not directly related to surface charging, are presented in [3170]. 

Specihc examples of afhnity series are presented in this section. The =, and symbols between the chemical symbols of elements denote the order in afhnity to a certain surface. A B means that the ion A has a higher affinity that is, the Gq and uptake of counterions are higher and the absolute value of the potential and the stability are lower in the presence of A than in the presence of B under conditions that are otherwise the same. The valency of the ions is not indicated (only monovalent anions and cations). The measured quantities, namely, 

C uptake of counterions, and critical coagulant concentration (CCC), are usually compared at constant concentration of ions (salts). In very concentrated solutions, the activities of different ions in salt solutions of equal concentrations can be very different (see Section 4.3). 

Electroacoustics, 0.01 M sodium salts BrO3 C1=NO3=C1O4. In 0.1 M sodium salts BrOj C1=NO3 CIO4 [509]. Ion specificity in yield stress was also observed. 

Titration, 0.1 M chlorides Li Na Cs [963], also in the presence of organic co-solvents. 

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This series has been well determined by experiment and shows an extension of our normal spectrochemical series. The surprise in this series is the position of H2S relative to the rest of the ligands and particularly the position of H2S relative to MeSMe. The MeSH compound was also examined (not reported in the affinity series) and was found to be a stronger ligand than H2S but weaker than MeSMe. The relative weakness of H2S was not explained, but theoretical calculations using density functional theory indicate that [ AuH2S]+ was not planar,... 

Ligand affinity series of more bare metal ions and one-coordinate ions are needed to understand the effect of the electronic structure of the ion on ligand strength. The study of catalytic cycles in the gas phase (especially where they relate to condensed phase catalysis) appears to be a growth area for the future. 

In coal, copper shows an organic affinity different from the Mellor and Maley (14) series, and zinc appears to be completely associated with the inorganic matter. Copper in the physicochemical environment of coal deposition can be reduced to the univalent state (5). Univalent copper cannot be expected to behave like the bivalent metals. The ionic potential of univalent copper fits reasonably well into the organic affinity series (Figure la). 

Analyses of float-sink separates of coal reveal a systematic variation of the minor elements with the organic matter which can be arranged into an organic affinity series. This series appears to be related to the chelating properties of the metals. Deviations in this series may be explained by the chemical nature of the depositional environment. 

The affinity series of the inorganic exchangers for alkali metal ions vary depending on both the crystalline form of the exchanger and the nature of the sorption media. Most of the hydrous oxides can be obtained as amorphous structures. At low loading the amorphous hydrous oxides of Al, Si, Ti, Zr, Ce(IV) and Sb(V) exhibit the usual selectivity sequence Li+ < Na < K < Rb < Cs+. This selectivity sequence is observed with the... 

One useful aspect of the ISE approach is the ease with which selectivity testing can be performed. Once the polymer is employed as the active ingredient in a polymer membrane electrode, the binding can be examined by measuring the potential of a cell as outlined below. We have seen that the selectivity obtained by batch extraction procedures gives the same affinity series as that measured by using the polymer in an electrode [11]. 

It was demonstrated in Sections A and B that in spite of a few discrepancies the macroscopic parameters characterizing the distribution of ions between solution and the surface (Kd, PH50) taken from different sources are rather consistent. These coefficients can be used to compare affinities between different ions and certain surface. For example silica has higher affinity to Zn (Fig. 4.58) than to Ni (Fig. 4.57), at least at pH >6.5, and iron III (hydr) oxides have higher affinity to Se IV (Fig. 4.60) than to Se VI (Fig, 4.62). Many affinity series have been established using experimental results obtained at certain experimental conditions, but apparently the relative affinity of a surface to different ions is rather insensitive to experimental... 

Experiments with various synthetic Fe, Al, and Mn oxides showed that the affinity of trace elements for Mn oxide was usually much greater than that for Fe or Al oxides. Pickering (1979) recorded the following affinity series for freshly precipitated Fe, Al, and Mn oxides. 

Inert electrolytes show ion specificity, as discussed in Chapter 2 and illustrated in Figures 2.4, 2.5, 2.9, and 2.10. The anions affect the positive branches of the charging and electrokinetic curves, and the cations affect the negative branches. The affinity to particular monovalent anions and cations depends on the character of the surface, and follows the hard- soft acid-base principle that is, hard surfaces prefer to adsorb hard ions, and soft surfaces prefer to adsorb soft ions. The effects of ion specihcity on the charging and electrokinetic curves are usually minor. The affinity series observed in coagulation behavior are termed Hoffmeister series. 

Coagulation Li > Na > K F > BrOj > Br > NO3 > CIO3 > Cl > CIO4 [2846]. Urea (up to 10 M) stabilized positively charged hematite (CCC increased), but destabilized negatively charged hematite (CCC decreased). The anion affinity series was preserved in the presence of urea, and cation affinity series was reversed at [urea] > 5 M. 

Titration, 0.001-1 M chlorides no clear affinity series of Group 1 cations... 

Titration, 0.01-4 M chlorides no clear affinity series of Group 1 cations [1891]. Apparently, Cs>Li at low salt concentration, but Li>Cs at higher salt concentrations. 

Titration, 0.001-1 M chlorides, pH 3.5-10, LiCl, KCl, KNO3, CsCl pH- and ionic strength-dependent affinity series, but the differences are rather insignificant [2613]. 

Electroacoustic studies of silica at high ionic strengths produced controversial results similar to those discussed in Section 4.3.2. Amorphous materials [1813,1870] showed a shift in the IEP to high pH at 1-1 electrolyte concentrations of 0.1 M or higher. The shift was more substantial in the presence of Cs than in the presence of other monovalent cations. This result is in line with the cation specificity series reported in Section 4.1.5. However, the IEP of quartz [1813] was not shifted in the presence of 1-1 electrolytes. Montmorillonite and kaolinite [2271] showed shifts in the IEP and similar cation affinity series as amorphous silica. Contradictory results are reported for goethite [76,1318]. 

The relative affinity series 24 was found for bare Au+ ions binding with various molecules M, to yield complex ions [AuM]+. This took place in the low-pressure regime of a Fourier transform ion cyclotron resonance MS. The absolute bond dissociation energies were evaluated by means of ab initio MO calculations at the MP2 level of theory255. 

Barrer and Munday [92] showed this synthetic species to have the following affinity series Cs>Rb>K>Na>Li Ba>Sr>Ca... 

Nilrosomonas eiiropaea, 727 Ammonium ions, alkyl-affinity series inorganic anions, 802 platinum group metal complexes affinity series, 808... 

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