Polyvalent ions

In addition to the collector, polyvalent ions may show sufficiently strong adsorption on oxide, sulfide, and other minerals to act as potential-determining ions (see Ref. 98). Judicious addition of various salts, then, as well as pH control, can permit a considerable amount of selectivity. 

To accomplish any separation of two cations (or two anions) of the same net charge, the stationary phase must show a preference for one more than the other. No variation in the eluant concentration will improve the separation. However, if the exchange involves ions of different net charges, the separation factor does depend on the eluant concentration. The more dilute the counterion concentration in the eluant, the more selective the exchange becomes for polyvalent ions. 

Whey concentration, both of whole whey and ultrafiltration permeate, is practiced successfully, but the solubility of lactose hmits the practical concentration of whey to about 20 percent total sohds, about a 4x concentration fac tor. (Membranes do not tolerate sohds forming on their surface.) Nanofiltration is used to soften water and clean up streams where complete removal of monovalent ions is either unnecessary or undesirable. Because of the ionic character of most NF membranes, they reject polyvalent ions much more readily than monovalent ions. NF is used to treat salt whey, the whey expressed after NaCl is added to curd. Nanofiltration permits the NaCl to permeate while retaining the other whey components, which may then be blended with ordinaiy whey. NF is also used to deacidify whey produced by the addition of HCl to milk in the production of casein. 

With strong cation-exchangers (e.g. with SO3H groups), the usual sequence is that polyvalent ions bind more firmly than mono- or di- valent ones, a typical series being as follows ... 

When there is a limitation of the phosphorus content in detergents of 1%, then addition of phosphonates can act as an alternative solution in combination with other polyvalent ion-binding substances. Especially when magnesium is a cause of water hardness the zeoliths can form precipitations. But phosphonates, like hydroxyethanephosphonic acid (HEDP) and ethylenediaminetetra-methylenephosphonic acid (EDTMP), are able to sequester magnesium ions as well. 

Amatucci GG, Badway E, Singhal A, Beaudoin B, Skandan G, Bowmer T, PUtz 1, Pereira N, Chapman T, Jaworski R (2001) Investigation of Yttrium and polyvalent ion intercalation into nanocrystaUine Vanadium Oxide. J Hectrochem Soc 4148 A940-A950 Tributsch H (1980) Photo-intercalation Possible apphcation in solar energy devices. Appl Phys 23 61-71... 

The shape of polarization curves for metals with low polarizability depends primarily on concentration polarization. In the case of highly polarizable metals, where activation polarization can be measured sufficiently accurately, the polarization curve can usually be described by an equation of the type (6.3) (i.e., by a Tafel equation). For metals forming polyvalent ions, slope b in this equation often has values between 30 and 60 mV. 

At high electrolyte concentrations of the soil solution, the double layer is compressed so that clay remains flocculated. A decrease in ion concentration, e.g. as a result of dilution by percolating rain water, can result in dispersion of clay and collapse of aggregates. If the exchange complex is dominated by polyvalent ions, the double layer may remain narrow even at low electrolyte concentrations and consequently aggregates remain intact (FAO, 2001). 

A number of studies have reported the abilities of different eluting salts to produce both different resolution and different selectivities.17 23 As expected, polyvalent ions are stronger eluters than monovalent ions. Some studies have suggested a correlation between eluting ability and ranking in the Hofmeister series. Others fail to observe this correlation, but nevertheless note differences in elution behavior. Overall, it is impossible to predict which eluting ions, if any, may produce a... 

There are two general types of liquid-membrane ISEs, namely one which involves liquid-phase ion exchange, with the response being selective to the anion or cation under scrutiny (generally polyvalent ions), while the other type involves... 

As both K" and can be calculated from experimental data, log K" can be determined. A plot of log K " against I gives a curve with small slope, such as illustrated in Figure 20.4. The determination of the intercept in this graph is easier than it is in Figure 20.3 for uni-univalent electrolytes, and the improvement is greater when the dissociation process involves polyvalent ions. 

The effect of valency on precipitatory power is most marked, the polyvalent ions being much more effective than the monovalent ions. As a rough approximation the liminal concentrations, i.e. the concentrations in milligram ions, per litre necessary to cause coagulation vary with the valency in the proportion valency 1 2 3,... 

The diminution of charge and eventual reversal of sign produced by the addition of electrolytes is more marked in the case of the polyvalent ions, and has been carefully investigated by Burton The Physical Properties of Colloidal Solutions, pp. 164-169) who in the case of a colloidal solution of copper obtained the following results ... 

Numerous experimental and theoretical studies of problems in this field have appeared and these have been reviewed under the title Metal Com-plexing by Polyphosphates by van Wazer (342). The phenomena which have been mentioned may be considered in general as due to complex formation. However, a simple qualitative and quantitative description of the facts may also be obtained if solutions of high-molecular polyphosphates arc considered as micro-heterogeneous systems and if the bonding of polyvalent ions is interpreted as involving ion exchange phenomena on the polyphosphate chains (77, 313, 319, 324). 

Partly demineralized whey is produced by subjecting whey to electrodialysis or ion exchange processing treatments to prederen-tlally remove polyvalent ions, vacuum concentrated and spray dryed. 

The following factors appear to control the emulsification properties of milk proteins in food product applications 1) the physico-chemical state of the proteins as influenced by pH, Ca and other polyvalent ions, denaturation, aggregation, enzyme modification, and conditions used to produce the emulsion 2) composition and processing conditions with respect to lipid-protein ratio, chemical emulsifiers, physical state of the fat phase, ionic activities, pH, and viscosity of the dispersion phase surrounding the fat globules and 3) the sequence and process for incorporating the respective components of the emulsion and for forming the emulsion. 

Lasalocid is the more disruptive polyether antibiotic to biological systems. This is due to its high tendency to dimerize and form complexes with biologically important divalent ions such as ("a and Mg ". Lasalocid exhibits a wide range of complexation affinities and transport capabilities, encompassing not only inorganic polyvalent ions but also primary amines and catecholamines (22). 

Traces of polyvalent ions—Ca2+ or Mg2+, for example—affect the results drastically. 

In pectic acids, all carboxyl groups are free, or at least not present as the methyl ester. Under suitable conditions, pectins will form jellies with sugar and acid, whereas the low-ester pectins will form gels with traces of polyvalent ions. The general structure of pectin is ... 

ZETA POTENTIAL. The potential across the interface of all solids and liquids. Specifically, the potential across the diffuse layer of ions surrounding a charged colloidal particle, which is largely responsible for colloidal stability. Discharge of the zeta potential, accompanied by precipitation of the colloid, occurs by addition of polyvalent ions of sign opposite to that of the colloidal particles. Zeta potentials can be calculated from electrophoretic mobilities, i.e., the rates at which colloidal particles travel between charged electrodes placed in the solution. 

A large body of information has been published on polyvalent ion exchange in zeolites. Examples of alkaline earth ion exchange in zeolites include studies on ion exchange of Na-A (5),... 

Figure 7.13 Electrophoretic mobility and zeta potential for spherical colloidal particles in electrolyte solutions containing polyvalent ions (A+lz+ = A /z = 70 ft cm2 mol -1). Electrolyte type is numbered with counter-ion charge number first ...

Hardness of a water sample is a measure of its capacity to precipitate soap. The presence of calcium and magnesium ions in water essentially contributes to its hardness. Other polyvalent ions, such as aluminum, also cause hardness. Their effect, however, is minimal, because these polyvalent ions occur in water often in complex forms and not as free ions. As a result, they cannot precipitate soap. Although calcium is not the only cation causing hardness, for the sake of convenience, hardness is expressed as mg CaC03/L. Similarly, anions other than carbonate, such as bicarbonate, also cause hardness in water. To distinguish the contributions of such anions from carbonates, hardness is sometimes termed as carbonate hardness and noncarbonate hardness. This can be determined from alkalinity. The relationship is as follows ... 

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